JPH11203676A - Production of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the output in a short wavelength region without the impairment of durability and magnetic characteristics by applying a magnetic coating material contg. ferromagnetic powder on a base at a shearing rate of a specific value or above at the time of producing a coating type magnetic recording medium. SOLUTION: The magnetic coating material contg. the ferromagnetic powder is extruded from an extrusion nozzle and is applied on the transported substrate by an extrusion nozzle coating application method which executes coating application of thin films and is excellent in control of the coating film thickness. The ferromagnetic powder is formed of fine powder of a metal alloy or hexagonal planar fine powder. Shearing force is applied on the coating at the time of coating in order to suppress the degradation in coating surface roughness by the leveling defect in the constitutive property development of the coating material. The constitutive property development of the coating material is drastically suppressed by specifying the shearing rate to >=150000 sec<-1> and, in addition, the leveling after the coating is improved by loosening the condensation of the coating material occurring during the time just before the coating and lowering the viscosity of the coating material, by which the uniformly coated surface is obtd. As a result, the roughness of the magnetic layer is improved and the surface characteristic is improved without changing the other surface processing conditions. The improvement in electromagnetic conversion characteristics is thus made possible without the impairment of the durability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a magnetic recording medium such as a magnetic tape, and more particularly to a method for manufacturing a magnetic recording medium having good surface properties and excellent output in a short wavelength region.

[0002]

2. Description of the Related Art Conventionally, a magnetic recording medium in which a magnetic layer in which a ferromagnetic powder is dispersed in a binder is provided on a non-magnetic support has been widely used. In order to respond to demands such as miniaturization of equipment, improvement of image quality, long-time recording, etc.
It has been desired to further improve the recording density of a magnetic recording medium. For applications such as audio and video, a digital recording system has been put to practical use in order to improve sound quality and image quality, and an output in a short wavelength region has been required as compared with a conventional analog recording system. . For example,
The shortest recording wavelength of “DDS-3” is about 0.3 μm. In order to enable high-density recording on coating type magnetic recording media and improve electromagnetic conversion characteristics at short wavelengths, magnetic properties have been improved by reducing the size of ferromagnetic powder, thinning the magnetic layer, increasing the orientation, and improving fillability. Methods such as improving characteristics and increasing surface properties to reduce spacing loss with the head have been taken.

[0003] However, there is a limit to the surface treatment using a calender as a means for improving the surface properties. If the magnetic layer surface is calendered under excessively high temperature and high pressure conditions, the magnetic layer is damaged or abrasives on the magnetic layer surface enter the magnetic layer and become ineffective, resulting in poor running and durability. However, there is a problem in reliability such as remarkably deteriorating the magnetic field. If a non-magnetic inorganic compound such as an abrasive is increased as a countermeasure, the magnetic properties are deteriorated, which is not preferable.

On the other hand, a method for manufacturing a thin film magnetic layer is disclosed in
No. 8471 describes that “a plurality of non-Newtonian organic solvent-based coating liquids are extruded from a plurality of slits of an extrusion-type coating head and immediately coated on a continuously running non-magnetic support. A method for manufacturing a recording medium, wherein a viscosity difference in the slit between adjacent coating liquids in the plurality of coating liquids is set to 50 cp or less. It is stated that a magnetic recording medium free from color unevenness, vertical stripes and the like during simultaneous coating can be obtained. Japanese Patent Application Laid-Open No. 4-271016 discloses a method of manufacturing a magnetic recording medium in which a plurality of organic solvent-based dispersion liquids are simultaneously coated in a multi-layer manner by using an extrusion-type coating head so as to overlap each other. And by defining the yield stress of the liquid in the uppermost layer,
It shows a method of applying a magnetic recording medium without color unevenness or vertical stripes. However, since the dispersion must be prepared so that the Reynolds number and the viscosity difference fall within a limited range,
There is a drawback that the amount of the material and the solvent that can be used in the dispersion is greatly restricted, and the range of choice of the material type and the amount of the compound is small. In addition, there is a problem that the obtained magnetic recording medium after coating has insufficient surface smoothness, and even if calendering is performed on the magnetic surface, the flatness is not improved, so that the electromagnetic conversion characteristics are poor.

Japanese Patent Application Laid-Open No. Hei 9-81935 discloses a magnetic tape in which a magnetic paint is extruded from an extrusion die arranged opposite to a film base material to be conveyed and the magnetic paint is applied to the film base material. In the manufacturing method, a flat surface parallel to the film substrate is formed on the surface of the extrusion die opposite to the film substrate, and the magnetic paint applied to the film substrate is brought into contact with the flat surface to form a flat surface. film has been shown to magnetic tape manufacturing method for "characterized in that so as to impart a shearing force to the magnetic coating with the base material, by a shear rate of 5 sec ^-1 or more, the film substrate It is shown that the adhesion between the magnetic layer and the film substrate can be improved without applying an adhesive primer coat to the magnetic layer. However, the shear rate studied here is extremely low at 6 sec ^-1 or less, which is not practical.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium having good surface properties and excellent output in a short wavelength region without impairing durability and magnetic characteristics as described above. It is in.

[0007]

According to the present invention, there is provided a method for producing a coating type magnetic recording medium wherein the thickness of a magnetic layer containing a ferromagnetic powder is 0.05 to 1.0 μm. The magnetic paint is applied on the support at 150,000 sec ^-1.
It is characterized by being applied at the above shear rate. The present inventors have found that the present invention is a method for producing a magnetic recording medium having good electromagnetic conversion characteristics. That is, by setting the shear rate at the time of coating the magnetic layer to 150,000 sec ^-1 or more, the surface roughness of the magnetic layer after coating can be significantly improved. When calender surface treatment is performed after coating and drying the magnetic layer, the roughness of the magnetic layer after coating and the roughness of the magnetic layer after calender surface processing are almost in a proportional relationship, and the coating roughness of the magnetic layer should be improved. Thereby, the surface properties of the magnetic layer are improved without changing other surface processing conditions. Since the amount of deformation of the surface of the magnetic layer was small, it was possible to improve the electromagnetic conversion characteristics without impairing the durability, and the above-mentioned object was achieved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The coating method of the present invention can be used for an extrusion nozzle coating method, a reverse roll coating method, a gravure roll coating method, and the like. In particular, an extrusion nozzle coating method which is excellent in controlling the thickness of a thin film when coated is preferred. . In the extrusion nozzle coating method, as shown in FIG. 1, a magnetic paint is extruded from an extrusion nozzle arranged opposite to a conveyed support and applied to the support.

The materials of the magnetic coating material for the magnetic recording medium, the coating material for the intermediate layer, the non-magnetic support, and the back coating material used in the practice of the present invention and the method for producing the same are described below. As the ferromagnetic powder used in the present invention, a metal alloy fine powder or a hexagonal plate-like fine powder is preferably used. As the metal alloy fine powder, Hc is 1500 to 3000 Oe and σs is 120
~ 160 emu / g, average major axis diameter is 0.05 ~ 0.2μ
m, average minor axis diameter is 10 to 20 nm, and aspect ratio is 1.
It is preferably from 2 to 20. The Hc of the produced medium is preferably from 1500 to 3000 Oe. Ni, Zn, Co, Al, Si,
Y and other rare earth elements may be added. As the hexagonal plate-like fine powder, Hc is 1000 to 2000 Oe, σs
Is 50-70 emu / g and the average plate grain size is 30-80 n
m, the plate ratio is preferably 3 to 7. Further, Hc of the produced medium is preferably 1200 to 2200 Oe. Ni, Co, Ti, Z
n, Sn, and other rare earth elements may be added.

[0010] Further, these ferromagnetic alloy fine powders may be ferromagnetic alloy fine powders having an oxide film or a partially carbonized or nitrided particle surface or a ferromagnetic alloy fine powder having a carbonaceous film formed on the surface. Good. The ferromagnetic alloy fine powder may contain a small amount of hydroxide or oxide. The specific surface area of these ferromagnetic alloy fine powders by the BET method is 40 to 80 m ² / g, preferably 45 to 65 m ² / g.
m ² / g, and if it is less than 40 m ² / g, the noise becomes high, and if it exceeds 80 m ² / g, it is difficult to obtain surface properties, which is not preferable. Such a ferromagnetic powder is usually used in a binder 100
% of the ferromagnetic powder in the magnetic layer, and the content of the ferromagnetic powder in the magnetic layer is 50 to 95 wt.
%, Preferably 55 to 90 wt%. If the content of the ferromagnetic powder is too large, the amount of additives such as resin in the magnetic layer is relatively reduced, so that the durability of the magnetic layer is reduced. However, if the amount is too small, a high reproduction output cannot be obtained. The inorganic fine powder to be added to the magnetic layer is preferably used in a weight ratio of 0.1 to 20 wt% with respect to the ferromagnetic powder. These may be appropriately selected as needed according to the balance between the durability and head wear required for the medium and the output at the shortest recording wavelength,
A single system or a mixed system may be used, and the particle size distribution or the like can be selected alone. Further, similarly to the intermediate layer described below, conventionally known materials such as a lubricant and an antistatic agent can be used.

The intermediate layer used in the present invention comprises a binder and a nonmagnetic inorganic pigment. The content, shape, size, material, surface treatment, and the like of the inorganic pigment can be selected from known ones as necessary, but an inorganic fine powder is particularly preferable. In the intermediate layer of the present invention, the content of the inorganic fine powder can be selected without particular limitation. The shape can be selected without particular limitation, such as a granular shape, a needle shape, a spindle shape, and a plate shape, but a granular shape or a needle shape is preferable. As the size of the inorganic fine powder, if it is granular, the average particle size is preferably from 0.01 to 0.05 μm, and from 0.02 to 0.05 μm.
0.04 μm is more preferred. If it is acicular, the average major axis length is preferably 0.05 to 0.30 μm, and 0.10 to 0.30 μm.
0.20 μm is more preferred. If the particle size is less than 0.01 μm and the needle shape is smaller than 0.05 μm, the specific surface area increases and the amount of resin used increases, so that dispersion tends to be difficult. On the other hand, if the particle size is larger than 0.05 μm and the needle shape is larger than 0.30 μm, the surface smoothness of the intermediate layer tends to deteriorate. The aspect ratio of the granular shape is preferably 1.5 or less, and the aspect ratio of the acicular shape is preferably 2.4 to 10.

Specifically, α iron oxide, titanium oxide, calcium carbonate, α alumina, chromium oxide, silicon carbide, silicon oxide, carbon black and the like can be mentioned. These inorganic fine powders can be used in an appropriate combination according to the required performance of the magnetic layer and the back coat layer in addition to the intermediate layer.
In addition, the inorganic fine powder is preferably a compound having a uniform particle size distribution. When used for the intermediate layer,
It is preferably α-iron oxide or titanium oxide, and more preferably α-iron oxide. The surface treatment can be carried out irrespective of inorganic or organic as required, for example, by adjusting the amount of acid or base adsorbed or making the secondary particles easier to loosen.

The intermediate layer of the present invention preferably contains a lubricant as required. Lubricants may be used singly or as a mixture of two or more known fatty acids, esters, or saccharides, regardless of whether they are saturated or unsaturated.
It is preferable to use a mixture of two or more fatty acids and esters having different melting points. It is used for magnetic recording media,
This is because it is necessary to continuously supply a lubricant corresponding to any temperature environment to the medium surface. Specifically, fatty acids such as stearic acid, palmitic acid, myristic acid, lauric acid, saturated straight-chains such as erucic acid, and isocetyl acid,
Saturated ones having side chains such as isostearic acid and unsaturated fatty acids such as oleic acid, linoleic acid and linolenic acid can be used as appropriate. Esters include linear saturated fatty acid esters such as butyl stearate and butyl palmitate, saturated fatty acid esters having side chains such as isocetyl stearate and isostearyl stearate, unsaturated fatty acid esters such as isostearyl oleate, and oleyl Saturated fatty acid esters of unsaturated alcohols such as stearate, esters of unsaturated fatty acids and unsaturated alcohols such as oleyl oleate, esters of dihydric alcohols such as ethylene glycol distearate, ethylene glycol monooleate, ethylene glycol dioleate Ester, esters of dihydric alcohols such as neopentyl glycol dioleate and unsaturated fatty acids, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, sorbitan trio And the like esters of sugars such as benzoate and saturated and unsaturated fatty acids.
The content of the lubricant in the intermediate layer may be appropriately adjusted according to the purpose, but is preferably 1 to 20% by weight based on the total weight of the inorganic fine powder and carbon black. The surface roughness of the intermediate layer needs to be good. Immediately after providing the intermediate layer (without processing), Ra is preferably 15 nm or less,
11 nm or less is more preferable, and 10 nm or less is most preferable. Ra after processing the intermediate layer by a calendar or the like is preferably 6 nm or less, more preferably 5 nm or less,
Most preferably 4.5 nm or less.

As the binder used in the magnetic layer, intermediate layer and back coat layer of the present invention, a thermoplastic resin, a thermosetting or reactive resin, an electron beam sensitive modified resin, etc. are used. It is appropriately selected and used in accordance with the characteristics of the medium and the process conditions. Examples of the thermoplastic resin include, in addition to a vinyl chloride copolymer and a polyurethane resin, for example, a (meth) acrylic resin, a polyester resin, an acrylonitrile-butadiene-based copolymer, a polyamide resin, polyvinyl butyral, nitrocellulose, and a styrene-butadiene-based resin. Copolymer, polyvinyl alcohol resin, acetal resin, epoxy resin, phenoxy resin, polyether resin, polyfunctional polyether such as polycaprolactone, polyamide resin, polyimide resin, phenol resin, polybutadiene elastomer, chlorinated rubber, acrylic Rubber, isoprene rubber, epoxy-modified rubber and the like. Examples of the thermosetting resin include a phenol resin, an epoxy resin, a polyurethane curable resin, a urea resin, a butyral resin, a polymer resin, a melanin resin, which undergo polycondensation.
Examples include alkyd resins, silicone resins, acrylic reaction resins, polyamide resins, epoxy-polyamide resins, saturated polyester resins, and urea-formaldehyde resins.

Among the above resins, those having a hydroxyl group at the terminal and / or the side chain are preferred because they can be easily used as a reactive resin, such as cross-linking using polyisocyanate or electron beam cross-linking modification. Further terminus or -COOH in the side chain as a polar _{group, -SO 3 M, -OSO 3 M} , -OP
_{O 3 X, -PO 3 X,} -PO 2 X, -N + R 3 Cl-,
It may contain an acidic polar group such as —NR _2, etc., a basic polar group, and the like, and the inclusion thereof is suitable for improving dispersibility. These may be used alone or in combination of two or more. Of these, those preferably used are a combination of a vinyl chloride copolymer and a polyurethane resin as shown below. Examples of the resin used in the present invention include vinyl chloride copolymers. More specifically, those having a vinyl chloride content of 60 to 95 wt%, particularly preferably 60 to 90 wt%, have an average degree of polymerization of 100%. It is preferably about 500. The polyurethane resin used in combination with such a vinyl chloride resin is particularly effective in that it has good wear resistance and good adhesion to a support. In addition, in addition to these resins, various known resins may be contained.

Further, it is also possible to use a resin obtained by introducing a (meth) acrylic double bond into the above-mentioned resin and subjecting it to electron beam-sensitive modification. The content of the electron beam functional group is 1 to 40% by mole, preferably 10 to 30% by mole in the hydroxyl group component in view of stability at the time of production, electron beam curability, etc., especially in the case of a vinyl chloride copolymer. When a monomer is reacted so as to have 1 to 20, preferably 2 to 10 functional groups per molecule, an electron beam curable resin excellent in both dispersibility and curability can be obtained. The support used in the present invention is polyethylene terephthalate (P
Known films such as polyesters such as ET) and polyethylene naphthalate (PEN), polyolefins, polyamide, polyimide, polyamide imide, polysulfone cellulose triacetate, and polycarbonate can be used. It is necessary to use a support having a center line surface roughness of 0.03 μm or less, preferably 0.02 μm or less, more preferably 0.01 μm or less. It is preferable that not only is small, but there is no coarse protrusion of 0.5 μm or more. In particular, when a magnetic layer is applied without providing an intermediate layer on a support, it is preferable to use a support having as good a surface property as possible. Further, a known back coat layer may be appropriately provided on the surface of the non-magnetic support on which the magnetic layer is not provided (the back surface) for the purpose of improving the running property of the magnetic recording medium, preventing charge and preventing transfer, and the like. preferable.

Next, the manufacturing process of the magnetic recording medium of the present invention will be described. First, the step of producing the magnetic paint of the magnetic recording medium of the present invention is at least a kneading step, a dispersion step,
And a mixing step provided as necessary before and after these steps. Each of the steps may be divided into two or more stages, or the raw materials may be divided and added in two or more steps. In kneading the magnetic paint, various kneaders can be used. As this kneading machine,
Examples include a two-roll mill, a three-roll mill, an open kneader, a continuous twin-screw kneader, a continuous single-screw kneader, a pressure kneader, a planetary mixer, and the like; high-speed stirrers include a high-speed impeller disperser and a high-speed stone mill. , Disperser, high-speed mixer, homogenizer and the like, and examples of the media stirring type mill include a ball mill, a pepper mill, a cobol mill, a sand grinder, a pin type mill, an ultra fine mill, an attritor, a basket mill and the like.

When a continuous kneader or a pressure kneader is used, all or a part of the ferromagnetic powder and the binder (preferably 30% by weight or more of the total binder) is used as the ferromagnetic powder.
The binder is blended in a range of 15 to 500 wt% with respect to 00 wt% and kneaded. Further, in dispersing the paint that can be used in each step, it is desirable to use a dispersion medium having a high specific gravity, and a ceramic medium such as zirconia is preferable. The application of the intermediate layer is not particularly limited, such as a roll coater such as a gravure roll and a reverse roll, and an extrusion nozzle coater such as an extrusion type. The coating of the magnetic layer is preferably performed by an extrusion nozzle coater of an extrusion type or the like. This is indispensable especially when applying simultaneously or sequentially in a wet state. The method of applying the intermediate layer and the magnetic layer is a method of applying and drying the intermediate layer, processing if necessary, and applying the magnetic layer one after another (sequential application), or applying the intermediate layer and then applying the magnetic layer while still wet. There is a method in which the magnetic layer is applied by wet coating (wet sequential application), and a method in which the intermediate layer and the magnetic layer are simultaneously overlapped and applied (wet simultaneous application), but any method can be used according to the purpose without any particular limitation. Sequential coating is preferred, in which the compatibility of the binder between the intermediate layer paint and the magnetic paint, the type and amount of the solvent used, and the viscosity of the paint need not be adjusted, and the surface roughness can be adjusted.

The magnetic paint which has been subjected to the post-coating treatment as described above is usually subjected to known drying and evaporating means such as hot air, far-infrared rays, an electric heater, and a vacuum device provided inside a drying furnace or the like. Alternatively, it is dried and fixed by a known curing device such as an ultraviolet lamp or a radiation irradiation device. The drying temperature may be appropriately selected from the range of room temperature to about 300 ° C. depending on the heat resistance of the non-magnetic support, the kind of the solvent, the concentration, etc., and a temperature gradient may be provided in the drying furnace. As the gas atmosphere, general air or an inert gas may be used. When drying is performed by an ultraviolet lamp or a radiation irradiation device, a curing reaction occurs. Therefore, when post-processing is considered, it is better to use other drying means as much as possible.
Irradiation with ultraviolet rays or radiation while containing a solvent may involve ignition or smoking. In this case, it is preferable to use other drying means as much as possible. After drying the magnetic layer in this way, if necessary, a calendering treatment is performed as a surface smoothing treatment, and heat-resistant plastics such as epoxy, polyester, nylon, polyimide, polyamide, and polyimide amide are used as the calendering roll. It can be treated with a combination of a roll (which may be kneaded with carbon, metal or other inorganic compound) and a metal roll (combination of 3 to 7 stages), or a combination of metal rolls. Is preferably 70 ° C. or more, more preferably 80 ° C. or more, and the linear pressure is preferably 200 kg / cm, more preferably 300 kg / cm or more, and the speed is 20 m / m.
/ Min to 700 m / min. After calendar processing,
In order to accelerate the curing of the magnetic layer, the back coat layer, and the intermediate layer, a heat curing treatment at 40 ° C. to 80 ° C. and / or an electron beam irradiation treatment may be performed. Next, the magnetic recording medium is formed into a predetermined shape, and after that, a burnishing process or a blade process is performed as necessary, and then slitting is performed to produce a magnetic recording medium.

The shear rate of the present invention is calculated by the following equation (FIG. 1). Shearing speed τ = V / 2hw (sec ⁻¹ ) Here, V represents the coating speed (ie, the running speed of the support), and hw represents the wet film thickness. The gap between the nozzle lip and the support due to the magnetic paint is approximated by 2 hw. The wet film thickness can be calculated by the following equation. hw = Q / (dxWxV) Here, Q represents a liquid sending amount (paint weight) per unit time, d represents a specific gravity of the paint, and W represents an application width.
The shear rate depends on the wet film thickness and the application speed, and the wet film thickness is determined by the applied paint volume. In the case where a plurality of magnetic layers and intermediate layers are provided by a wet-on-wet method, the wet thickness here means the total wet thickness of these multiple layers. The solid content volume in the paint volume determines the film thickness after drying. The magnetic layer thickness used herein refers to the magnetic layer thickness of the tape after surface processing (calender).

According to the present invention, a shearing force is applied at the time of the most effective application in order to suppress the deterioration of the applied surface roughness due to poor leveling due to the appearance of the structural properties of the paint. The shear rate is 150,000 sec ^-1
If less than the effect is small, but at a higher shear rate not only the structural expression of the paint is notably suppressed,
The structural properties of the paint (i.e., the so-called condensation of the paint) generated immediately before the application are loosened, and the viscosity of the paint is reduced, so that the leveling after the application is good and a very uniform applied surface is obtained. Further, it is more effective to combine a means for suppressing the development of the structural properties of the paint not only at the time of application but also immediately before the application, for example, a method of irradiating the paint with ultrasonic waves. The coating speed is 30 to 600 m / min, preferably 80 to 400 m / min. If this value is less than 30 m / min, it becomes difficult to obtain a desired shear rate, and if it exceeds 600 m / min, it becomes difficult to apply the magnetic paint uniformly.

The wet film thickness is 1.0 to 12.0
μm is preferable, and 2.0 to 10.0 μm is more preferable. If the wet film thickness exceeds 12.0 μm, the velocity distribution in the coating solution becomes extremely non-uniform even with shearing within the range of the present invention, and the effect of shearing near the surface of the magnetic layer is unlikely to be obtained. On the other hand, if the thickness is less than 1.0 μm, it becomes difficult to apply a uniform wet thickness. After being applied, a magnetic layer is formed through a drying and calendering process. The thickness of the magnetic layer is 0.05 to 1.00 μm, preferably 0.10 to 1.00 μm.
0.75 μm, more preferably 0.10 to 0.30 μm
It is said. Assuming a high-density digital medium, such a magnetic layer has a high frequency (short wavelength) required for the medium.
It is set in consideration of the electromagnetic conversion characteristics at. The optimal film thickness required for recording on digital media is usually 1.0 μm or less,
If the thickness is larger than this, the effect of the demagnetizing field increases, and the output slightly decreases. On the other hand, if the thickness is less than 0.05 μm, the coating film thickness is not sufficient for the recording wavelength used. 0.2μ magnetic layer
When the film thickness is less than m, the size of the pigment in the paint (particularly the size of the abrasive) affects the magnetic layer. To reduce the influence, a magnetic layer may be provided on the intermediate layer by a wet-on-dry method. Further, the present invention is not limited to the magnetic layer single layer coating and the wet-on-dry coating, but depends on the total wet film thickness and the coating speed.
If the shear rate is 000 (sec-1) or more, for example, a wet-on-wet method of a magnetic layer having a thickness of 1.0 μm or less and an intermediate layer having an arbitrary thickness may be used.

The center line average surface roughness Ra is Taylor
JI using a Hobson Tallystep meter
The measurement was performed according to the SB-0601 method. The smaller the surface roughness Ra is both after coating and after processing, the better. The output of the short wavelength region is output from a Panasonic AJ-D750 deck.
And Panasonic's reference tape AJ-P
Measured using 63MP. The measurement frequency is 21 MH
z, the recording wavelength is 0.5 μm. As the tape output, a single waveform of the above-described measurement frequency and recording wavelength was recorded, and the reproduced output was compared with a reference tape and expressed in dB. A positive value is preferable as compared with each reference tape.

[0024]

EXAMPLE 1 The following magnetic coating composition was prepared to prepare a magnetic recording medium. Ferromagnetic metal fine powder (30% Co, Y-containing spindle-shaped Fe / Co alloy manufactured by Dowa Mining Co., Ltd., major axis length 0.10 μm, σs140 / emugHc, 2400 Oe) 100 parts by weight Vinyl chloride copolymer (Nihon Zeon) : MR110) 7.5 parts by weight Sulfonate-containing polyester polyurethane (Toyobo: UR8200) 5 parts by weight Phosphate ester compound (Toho Kagaku phosphanol RE610) 3 parts by weight α-alumina (Sumitomo Chemical HIT82) 3 parts by weight Stearic acid 1.2 parts by weight Parts butyl stearate 1 part by weight methyl ethyl ketone 94 parts by weight toluene 94 parts by weight cyclohexanone 94 parts by weight

The above composition for a magnetic layer was kneaded with a kneader and then dispersed in a sand grinder mill filled with ceramic beads. To the obtained magnetic paint, 3 parts by weight of a curing agent (Nippon Polyurethane: Coronate L) was added, and filtered using a filter (ROKITECHNO: HT10) to obtain a magnetic paint. The viscosity of this magnetic paint is a B-type viscometer V20.
Was 3000 cp. Immediately before the application, the magnetic layer paint was redispersed in a state of being uniformly dispersed by an ultrasonic disperser, filtered (ROKITECHNO: HT10), and applied to a support having a surface roughness of 4 nm (Teijin base 7AJ6).
96 (6.5 μm mirror surface PET) was applied by an extrusion die nozzle at an application speed of 150 m / min so that the tape had a magnetic layer thickness of 1.0 μm. In application,
While the magnetic layer is in a wet state, the oriented magnet (magnetic flux density 6
000 gauss) and oriented in the longitudinal direction (running direction) and dried. Thereafter, surface treatment is performed at a temperature of 90 ° C., a linear pressure of 350 kg / cm, and a speed of 100 m / min using a four-stage nip calender comprising a metal roll and an elastic roll.
Further, a back coat layer having the following composition is applied to the opposite side of the magnetic layer so that the dry thickness becomes 0.5 μm, and dried. 250 kg / cm, speed 1
The surface was treated at 00 m / min to obtain a web-shaped magnetic recording medium. This magnetic recording medium was slit to a width of 6.35 mm, and the surface was treated with a polishing tape.

Table 1 shows the shear rate during coating, the surface properties of the magnetic layer, the output in the short wavelength region of the magnetic recording medium, and the like in this example. The back coat has the following composition. 80.0 parts by weight of carbon black-1 (Sc Ultra: manufactured by Colombian Carbon Co., Ltd.) (average particle size: 21 nm, BET220 m ² / g) (containing 17 ppm of soluble sodium ion) (containing 9 ppm of soluble potassium ion) Carbon black-2 0 parts by weight (MT-CI: manufactured by Colombian Carbon Co., Ltd.) (Average particle size: 350 nm, BET: 8 m ² / g) (containing 46 ppm of soluble sodium ion) (containing 27 ppm of soluble potassium ion) α-iron oxide (100ED manufactured by Toda Kogyo Co., Ltd.) 1.0 part by weight (average particle size 0.1 μm) Vinyl chloride copolymer A 40.0 parts by weight (manufactured by Nissin Chemical Industry Co., Ltd., MPR-TA) (vinyl chloride-vinyl acetate-vinyl alcohol copolymer) Coalescence, average degree of polymerization 420) 25.0 parts by weight of vinyl chloride copolymer B (manufactured by Nissin Chemical Industry Co., Ltd., MP -Ano (L)) (PVC - vinyl acetate - vinyl alcohol copolymer, a nitrogen atom 390ppm containing, average polymerization degree 340) Polyester polyurethane 35.0 parts by weight (TS9555: Toyobo Co., Ltd.) (-SO ₃ Na Content, number average molecular weight 40000) methyl ethyl ketone 700.0 parts by weight toluene 400.0 parts by weight cyclohexanone 300.0 parts by weight

[0027]

[Table 1]

Example 2 In the same manner as in Example 1, coating was performed at a coating speed of 400 m / min so that the thickness of the magnetic layer of the tape became 1.0 μm. Table 1 shows the shear rate during coating, the surface properties of the magnetic layer, the output in the short wavelength region of the magnetic recording medium, and the like in this example. Example 3 As in Example 1, coating was performed at a coating speed of 100 m / min so that the thickness of the magnetic layer of the tape became 0.5 μm. Table 1 shows the shear rate during coating, the surface properties of the magnetic layer, the output in the short wavelength region of the magnetic recording medium, and the like in this example. Example 4 As in Example 1, coating was performed at a coating speed of 100 m / min so that the thickness of the magnetic layer of the tape became 0.3 μm. Table 1 shows the shear rate during coating, the surface properties of the magnetic layer, the output in the short wavelength region of the magnetic recording medium, and the like in this example.

Example 5 The following intermediate layer composition was prepared to prepare a magnetic recording medium having a multilayer structure. α Iron oxide (Toda Kogyo: DPN250BW) 100 parts by weight Vinyl chloride copolymer (Toyobo: TBO246) 9 parts by weight Electron beam-curable vinyl chloride resin Vinyl chloride-epoxy-containing monomer copolymer Average polymerization degree 310 Epoxy content 3% by weight S content 0.6% by weight Acrylic content 6 / molecule Tg 60 ° C Polyester polyurethane (Toyobo: TBO242) 9 parts by weight Electron beam-curable polyurethane resin Phosphorus compound-hydroxy-containing polyester polyurethane GPC Mn 26000 Acrylic content Amount 6 / molecule Tg-20 ° C Phosphate ester compound (Toho Kagaku Phosphanol RE610) 3 parts by weight α-alumina (Sumitomo Chemical HIT60A) 5 parts by weight Stearic acid 2 parts by weight Butyl stearate 1 part by weight Methyl ethyl ketone 80 parts by weight Tolue 80 parts by weight of cyclohexanone, 80 parts by weight

After kneading the above composition for an intermediate layer with a kneader, the composition was dispersed in a sand grinder mill filled with ceramic beads. The obtained intermediate layer paint was filtered using a filter (ROKITECHNO: HT40). Immediately before the application, the intermediate layer paint was redispersed with an ultrasonic disperser, filtered (ROKI TECHNO: HT20), extruded onto a support having a surface roughness of 4 nm, and coated with a die nozzle at a coating speed of 100 nm.
The coating was performed so that the thickness of the intermediate layer of the tape was 1.0 μm at m / min. After coating and drying, a four-stage nip calender consisting of a metal roll and an elastic roll is used at a temperature of 100 ° C. and a linear pressure of 350.
After performing surface treatment at a rate of 100 m / min at a rate of 100 kg / cm, an electron beam of 4.5 Mrad was irradiated and cured to obtain an intermediate layer raw material.
The surface roughness of the intermediate layer was 3.8 nm. A magnetic paint in which the solvent (methyl ethyl ketone, toluene, cyclohexanone) of Example 1 was changed to 161 parts by weight was applied on the intermediate layer prepared above at a coating speed of 100 m / min so that the magnetic layer thickness of the tape became 0.2 μm. Was applied. Except for this, a magnetic recording medium was prepared in the same manner as in Example 1. Table 1 shows the shear rate during coating, the surface properties of the magnetic layer, the output in the short wavelength region of the magnetic recording medium, and the like in this example.

Example 6 In the same manner as in Example 5, except that the solvent for the magnetic coating material was changed to 228 parts by weight, the coating was applied at a coating speed of 100 m / min so that the magnetic layer thickness of the tape became 0.2 μm. Table 1 shows the shear rate during coating, the surface properties of the magnetic layer, the output in the short wavelength region of the magnetic recording medium, and the like in this example. Example 7 In the same manner as in Example 6, coating was performed at a coating speed of 100 m / min so that the magnetic layer thickness of the tape became 0.15 μm. Table 1 shows the shear rate during coating, the surface properties of the magnetic layer, the output in the short wavelength region of the magnetic recording medium, and the like in this example. Example 8 In the same manner as in Example 5, except that the solvent for the magnetic paint was changed to 363 parts by weight, the coating was applied at a coating speed of 100 m / min so that the magnetic layer thickness of the tape became 0.15 μm. Table 1 shows the shear rate during coating, the surface properties of the magnetic layer, the output in the short wavelength region of the magnetic recording medium, and the like in this example.

Example 9 In the same manner as in Example 8, coating was performed at a coating speed of 100 m / min so that the magnetic layer thickness of the tape became 0.075 μm. Table 1 shows the shear rate during coating, the surface properties of the magnetic layer, the output in the short wavelength region of the magnetic recording medium, and the like in this example. Example 10 The same intermediate layer paint and magnetic paint as in Example 5 were simultaneously coated on the intermediate layer paint at a coating speed of 150 m / min with a two-slit extrusion die nozzle while the magnetic paint was wet (wet-on-wet method). ), And applied such that the thickness of the magnetic layer of the tape was 0.2 μm and the thickness of the intermediate layer was 1.0 μm. At this time, the hw (wet film thickness) of the intermediate layer is calculated based on the paint application volume.
13 μm. 7.70 μm in total with the hw of the magnetic layer
m. Table 1 shows the shear rate during coating, the surface properties of the magnetic layer, the output in the short wavelength region of the magnetic recording medium, and the like in this example. Comparative Example 1 In the same manner as in Example 1, coating was performed at a coating speed of 100 m / min so that the magnetic layer thickness of the tape became 1.5 μm. Table 2 shows the shear rate during coating, the surface properties of the magnetic layer, the output in the short wavelength region of the magnetic recording medium, and the like in this comparative example.

[0033]

[Table 2]

Comparative Example 2 In the same manner as in Example 1, coating was performed at a coating speed of 400 m / min so that the magnetic layer thickness of the tape became 1.5 μm. Table 2 shows the shear rate during coating, the surface properties of the magnetic layer, the output in the short wavelength region of the magnetic recording medium, and the like in this comparative example. Comparative Example 3 As in Example 1, coating was performed at a coating speed of 100 m / min so that the thickness of the magnetic layer of the tape became 1.0 μm. Table 2 shows the shear rate during coating, the surface properties of the magnetic layer, the output in the short wavelength region of the magnetic recording medium, and the like in this comparative example. Comparative Example 4 In the same manner as in Example 8, coating was performed at a coating speed of 100 m / min so that the magnetic layer thickness of the tape became 0.25 μm. Table 2 shows the shear rate during coating, the surface properties of the magnetic layer, the output in the short wavelength region of the magnetic recording medium, and the like in this comparative example. Comparative Example 5 Example 1 was repeated except that the thickness of the intermediate layer was set to 2.0 μm.
0 was applied. At this time, the hw (wet film thickness) of the intermediate layer was 10.26 μm from the applied volume of the paint.
The total value was 12.83 μm with the hw of the magnetic layer. Table 2 shows the shear rate during coating, the surface properties of the magnetic layer, the output in the short wavelength region of the magnetic recording medium, and the like in this comparative example.

[0035]

As shown in Tables 1 and 2, the effects of the present invention are clear. That is, when compared with Examples 1-4 and Comparative Example 3 in which the magnetic layer was directly coated on the support with a wet film thickness of 10 μm or less, the shear rate was 150,000 sec.
^{At -1} or more, the surface roughness after coating is clearly improved. In comparison with Examples 5 to 9 and Comparative Example 4 in which the intermediate layer was provided between the support and the magnetic layer, the shear rate was 1
It is clear that the present invention is extremely effective even in a medium suitable for short-wavelength recording, in which the surface after coating becomes extremely smooth and the magnetic layer is thin at around 50,000 sec ^-1 . Further, within the range of the wet film thickness and the shear rate of the present invention, as seen in Example 10 and Comparative Example 5, even in the multilayer coating by the wet-on-wet method, a smooth layer which could not be obtained conventionally was obtained. A coated surface is obtained. That is, the thickness of the magnetic layer containing the ferromagnetic powder is 0.05 to 1.0 μm.
m, a magnetic paint containing a ferromagnetic powder is coated on a support or an intermediate layer by 15
By applying at a shear rate of not less than 000 sec ^-1, a magnetic recording medium having good surface properties and excellent short-wavelength output can be manufactured, thereby achieving the object of the present invention.

[Brief description of the drawings]

FIG. 1 shows a gap between a nozzle lip and a support made of a magnetic paint, which is larger than a wet film thickness (hw) and is approximated by a value twice as large. This is because, since the support is moving at the speed V, the shearing speed τ of the magnetic paint in the sandwiched portion becomes larger as it is closer to the support, so that the shearing force is applied to the magnetic paint in the sandwiched portion, This is because a deviation occurs in the magnetic paint. The shear rate τ is represented by τ = V / 2hw (sec ⁻¹ ). The length of the flat surface of the nozzle lip is not limited.
It may be about 0 mm. After passing through the nozzle lip, the applied magnetic paint has a shear rate of 0, and is transported at the support speed V.

Claims (3)

[Claims] 1. A method for producing a coating type magnetic recording medium wherein the thickness of a magnetic layer containing a ferromagnetic powder is 0.05 to 1.0 μm, wherein a magnetic paint containing a ferromagnetic powder is coated on a support. A method for producing a magnetic recording medium, wherein the magnetic coating material is applied at a shear rate of 150,000 sec ^-1 or more, and the wet thickness of the magnetic paint is 10.0 μm or less. 2. The method according to claim 1, wherein an intermediate layer is pre-coated and dried on the support. 3. The method according to claim 1, wherein the magnetic paint contains the ferromagnetic powder in a uniformly dispersed state.