JPH09161260A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium having excellent electromagnetic conversion characteristics and high S/N by specifying each of the major axial diameter of magnetic powder particles which constitute a magnetic layer, the surface roughness of the magnetic layer and the squareness ratio of the magnetic recording medium. SOLUTION: This magnetic recording medium 1 consists of a base body 2 and a magnetic layer 3 formed on the base body 2. If necessary, an intermediate layer 4 is formed between the base body 2 and the magnetic layer 3, and moreover, a back coating layer 5 is formed if necessary on the back surface of the base body 2. The magnetic layer 3 of this magnetic recording medium contains magnetic powder particles having <=0.1μm major axial diameter. The surface roughness of the magnetic layer 3 is specified to <=5nm and the squareness ratio of the medium 1 is specified to >=0.87. Further, the aspect ratio (major axial diameter to minor axial diameter) of the magnetic powder particle is 1 to 5. The average pore diameter of the magnetic layer 3 is preferably <10nm.

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 which is excellent in electromagnetic conversion characteristics and has a high S / N ratio.

[0002]

2. Description of the Related Art Conventionally, magnetic recording media have been widely used in the form of tapes, disks, drums or sheets. Such a magnetic recording medium is usually manufactured by coating a nonmagnetic support such as polyester flume with a magnetic coating material containing magnetic powder and a binder as main components. In recent years, in particular, there has been a demand for miniaturization and high density of recording for magnetic recording media, and it is necessary to increase the S / N ratio in order to achieve such requirements. However, the magnetic recording media proposed hitherto have not been able to achieve a high S / N ratio that can satisfy recent requirements.

Therefore, it is an object of the present invention to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and a high S / N ratio.

[0004]

The present invention provides a magnetic recording medium comprising a support and a magnetic layer provided on the support, wherein the magnetic layer has a major axis diameter of 0.1 μm or less. It contains magnetic powder, the surface roughness Ra of the surface of the magnetic layer is 5 nm or less, and the squareness ratio of the magnetic recording medium is 0.8.
The above object is achieved by providing a magnetic recording medium characterized in that the number is 7 or more. Further, the present invention provides the above magnetic recording medium, wherein the magnetic powder has an axial ratio (major axis diameter / minor axis diameter) of a major axis diameter and a minor axis diameter of 1 to 5. The present invention also provides the above magnetic recording medium, wherein the average pore diameter of the magnetic layer is smaller than 10 nm.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic recording medium of the present invention will be described below in detail. First, a preferred configuration of the magnetic recording medium of the present invention will be described with reference to FIG.

The magnetic recording medium 1 of the present invention shown in FIG. 1 comprises a support 2 and a magnetic layer 3 provided on the support 2, and the support 2 and the magnetic layer 3 are provided. In between, an intermediate layer 4 is provided if necessary, and a back coat layer 5 is provided on the back surface of the support 2 as needed.

In the magnetic recording medium of the present invention, in addition to the support, the magnetic layer, the nonmagnetic layer and the backcoat layer, further, between the support and the nonmagnetic layer or the backcoat layer. Other layers such as a primer layer provided and another magnetic layer provided for recording a servo signal or the like corresponding to a hard system using a long wavelength signal may be provided.

As the above-mentioned support 1 used in the magnetic recording medium of the present invention, any known support can be used without any particular limitation. Specifically, a flexible film made of a polymer resin or Discs: Films, discs, cards and the like made of non-magnetic metals such as Cu, Al and Zn, glass, ceramics such as porcelain and ceramics can be used.

Examples of the polymer resin forming the flexible film or the disc include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate, polyethylene bisphenoxycarboxylate, polyethylene and the like. , Polyolefins such as polypropylene, cellulose acetate butyrate,
Cellulose derivatives such as cellulose acetate propionate, polyvinyl chloride, vinyl resins such as polyvinylidene chloride, or polyamide, polyimide, polycarbonate, polysulfone, polyetheretherketone, polyurethane, etc. Two or more can be used in combination.

Further, in the magnetic recording medium of the present invention, the back coat layer, which is optionally provided on the back surface of the support, can be formed by using a known back coat paint without particular limitation.

In the magnetic recording medium of the present invention, the magnetic layer provided on the support is the uppermost layer of the magnetic recording medium,
That is, it is a layer provided as a layer located on the surface of the magnetic recording medium, and is formed by applying a magnetic coating material on the support or the non-magnetic layer. As the above-mentioned magnetic paint, a paint containing magnetic powder having a specific major axis diameter, a binder and a solvent as main components is preferably used.

Examples of the magnetic powder include ferromagnetic metal powders containing iron as a main component. The coercive force of the ferromagnetic metal powder is preferably 1600 to 3000 Oe,
More preferably, it is from 00 to 3000 Oe. When the coercive force of each of the ferromagnetic metal powders is less than the above lower limit, demagnetization is likely to occur, and thus the short-wave RF output decreases,
On the other hand, if the upper limit is exceeded, the head magnetic field becomes insufficient and the write performance becomes insufficient, and further the overwrite characteristics are deteriorated. Also,
The saturation magnetization of the ferromagnetic metal powder is 100 to 180 emu /
It is preferably g, and more preferably 110 to 160 emu / g. If the saturation magnetization of the ferromagnetic metal powder is less than the above lower limit, the output decreases, and if it exceeds the above upper limit, the interaction between the magnetic powders increases, and the magnetic powders aggregate. Since it becomes a state and the dispersibility deteriorates and it becomes difficult to obtain a desired output, it is preferably within the above range. Therefore, the coercive force of the upper magnetic layer is
Preferably 1800 to 2400 Oe, more preferably 1
It is 800-2300 Oe. The saturation magnetic flux density of the magnetic layer containing the ferromagnetic metal powder is preferably 30.
00-4500 gauss, more preferably 3200-40
It is 00 gauss.

The ferromagnetic metal powder has a metal content of 7
0% by weight or more, and 60% by weight or more of the metal component is Fe.
The ferromagnetic metal powder which is Specific examples of the ferromagnetic metal powder include, for example, Fe-Co, Fe-Ni,
Fe-Co-Ni, Fe-Ni-Zn, etc. are mentioned.
The shape of the ferromagnetic metal powder is spherical, needle-like or spindle-like.

If desired, the magnetic powder may contain a rare earth element or a transition metal element.
In the present invention, the magnetic powder may be surface-treated in order to improve the dispersibility of the magnetic powder. The above surface treatment is "Characterization of Powder Surface
s "; can be carried out by a method similar to the method described in Academic Press, for example, a method of coating the surface of the above magnetic powder with an inorganic oxide. At this time, the inorganic oxide that can be used is Al ₂ O.
₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂
Examples thereof include O ₃ and ZnO, which may be used alone or in combination of two or more. The surface treatment can be performed by an organic treatment such as a silane coupling treatment, a titanium coupling treatment, and an alumina coupling treatment, in addition to the above method.

The specific surface area of the magnetic powder is 45-6.
It is preferably 5 m ² / g, more preferably 50 to 58. Further, the pH value of the water when the magnetic powder is dispersed in water is preferably 9.0 to 10.0, and particularly preferably about 9.5.

The binder may be a thermoplastic resin, a thermosetting resin, a reactive resin, or the like, which may be used alone or as a mixture.
Specific examples of the binder include vinyl chloride resins,
Polyester, polyurethane, nitrocellulose, epoxy resin, etc .;
No. 2128, page 2, upper right column, line 19 to page 2, lower right column 1
Resins and the like described in line 9 are exemplified. further,
The binder may contain a polar group for improving dispersibility and the like. The amount of the binder used is 100
It is preferably about 5 to 100 parts by weight, more preferably 5 to 70 parts by weight, based on parts by weight.

Examples of the above solvent include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents, chlorinated hydrocarbon solvents, and the like. The solvents described in JP-A-57-162128, page 3, lower right column, line 17 to page 4, lower left column, line 10 and the like can be used. The amount of the solvent used is preferably 80 to 500 parts by weight, more preferably 100 to 350 parts by weight, based on 100 parts by weight of the magnetic powder.

In addition, the above-mentioned magnetic paint contains additives usually used in magnetic recording media, such as a dispersant, a lubricant, an abrasive, an antistatic agent, a rust preventive, a fungicide, and a curing agent. , Can be added if necessary. As the above additives,
Specifically, it is described in page 2, upper left column, line 6 to page 2, upper right column, line 10 and page 3, upper left column, line 6 to page 3, upper right column, line 18 of JP-A-57-162128. And various additives.

To prepare the above magnetic paint, for example,
The magnetic powder and the binder are charged together with a part of the solvent into a Nauter mixer or the like to be premixed to obtain a mixture, and the obtained mixture is kneaded with a continuous pressure kneader or the like, and then diluted with a part of the solvent. Then, after dispersion treatment using a sand mill or the like, a method of mixing additives such as a lubricant, filtering, and further mixing a curing agent such as polyisocyanate and the remaining solvent can be mentioned.

The thickness of the above magnetic layer is 0.05 to 1.0.
The thickness is preferably μm, more preferably 0.05 to 0.8 μm. If it is less than 0.05 μm, uniform coating becomes difficult and durability may be deteriorated, resulting in insufficient output in the low range. If it exceeds 1.0 μm, the thickness loss increases, and the overwrite characteristics may be significantly reduced.

The intermediate layer which is optionally provided on the magnetic support includes a non-magnetic layer and the like.
The non-magnetic layer is a layer formed by applying a non-magnetic paint on the magnetic support. The non-magnetic coating material used when forming the non-magnetic layer is preferably a coating material composed of non-magnetic powder, a binder and a solvent, or a coating material composed of the binder and the solvent. The non-magnetic powder is not particularly limited as long as it is non-magnetic, but carbon black, graphite, titanium oxide, barium sulfate, zinc sulfide, magnesium carbonate, calcium carbonate, zinc oxide,
Calcium oxide, magnesium oxide, tungsten disulfide, molybdenum disulfide, boron nitride, tin dioxide, silicon dioxide, nonmagnetic chromium oxide, alumina, silicon carbide, cerium oxide, corundum, artificial diamond, nonmagnetic iron oxide, garnet , Garnet, silica, silicon nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, diatomaceous earth, dolomite, resinous powders, among others, carbon black, titanium oxide, barium sulfate, calcium carbonate, alumina And non-magnetic iron oxide are preferably used. The non-magnetic powder may be subjected to the surface treatment described above in order to improve the dispersibility of the non-magnetic powder.

When the non-magnetic layer contains non-magnetic powder, the particle size of the non-magnetic powder is preferably 0.001.
˜3 μm, more preferably 0.005 to 1 μm, and most preferably 0.005 to 0.5 μm. The non-magnetic powder is preferably contained in the non-magnetic layer formed by applying the non-magnetic coating material in an amount of 5 to 99% by weight, more preferably 30 to 95% by weight, and most preferably 50 to 95% by weight. It is desirable to incorporate it in the above non-magnetic paint so that it is contained by weight.

The binder may be a thermoplastic resin, a thermosetting resin, a reactive resin, or the like, which may be used alone or as a mixture.
As the binder, specifically, vinyl chloride resin, polyester, polyurethane, nitrocellulose,
Epoxy resin and the like can be mentioned.
Resins and the like described in JP-A No. 162128, page 2, upper right column, line 19 to page 2, lower right column, line 19 and the like can be mentioned. Further, the binder may contain a polar group for improving dispersibility and the like. The amount of the binder used is preferably about 5 to 50 parts by weight, and particularly preferably 5 to 22 parts by weight, based on 100 parts by weight of the non-magnetic powder.

Examples of the solvent include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents, chlorinated hydrocarbon solvents, and the like. The solvents described in JP-A-57-162128, page 3, lower right column, line 17 to page 4, lower left column, line 10 and the like can be used.

In addition, the non-magnetic coating material contains additives usually used in magnetic recording media such as a dispersant, a lubricant, an abrasive, an antistatic agent, a rust preventive, a fungicide, and a curing agent. , Can be added if necessary. As the above additives,
Specifically, it is described in page 2, upper left column, line 6 to page 2, upper right column, line 10 and page 3, upper left column, line 6 to page 3, upper right column, line 18 of JP-A-57-162128. And various additives.

To prepare the above non-magnetic paint, for example,
The non-magnetic powder and the binder are charged together with a part of the solvent into a Nauter mixer or the like to be premixed to obtain a mixture, and the obtained mixture is kneaded by a continuous pressure kneader or the like, and then it is mixed with the solvent. Examples include a method of diluting a part of the mixture, carrying out a dispersion treatment using a sand mill or the like, mixing an additive such as a lubricant, filtering, and further mixing the remaining solvent and a curing agent.

A commonly known intermediate magnetic layer can be used as the intermediate layer.

In the magnetic recording medium of the present invention, therefore, the magnetic layer has a major axis diameter of the magnetic powder of 0.1 μm or less, preferably 0.9 to 0.5, and the surface of the magnetic layer. Has a surface roughness Ra of 5 nm or less, preferably 3 nm to 1.5 nm, and the magnetic recording medium has a squareness ratio of 0.87 or more, preferably 0.88 to 0.92. If the major axis diameter exceeds 0.1 μm, the number of particles of the magnetic powder per unit volume of the magnetic layer increases, so noise increases and the surface roughness Ra becomes 5 or less.
When it exceeds nm, it causes surface noise and leads to a decrease in output at high frequencies. If the squareness ratio is less than 0.87, SFD (Switchin
g Field Distribution) becomes large, and interference between adjacent waveforms becomes large.

The magnetic powder preferably has an axial ratio (major axis diameter / minor axis diameter) of the major axis diameter to the minor axis diameter of 6 or less, more preferably 1 to 5. . The minor axis diameter of the magnetic powder is preferably 0.01 to 0.02 μm. If the axial ratio exceeds 6, it is difficult to achieve high density packing even if it is sufficiently dispersed, and the perpendicular magnetization component of the coating film becomes small, which is not preferable. Furthermore,
The average pore diameter of the magnetic layer is preferably smaller than 10 nm, more preferably 5 to 10 nm. Further, the half-value width of the pore diameter (the width of the distribution when the half of the height at the peak value of the void amount in the pore distribution chart is taken) is preferably less than 10 nm, and 6
More preferably, it is not more than nm. The average pore size is
When it is 10 nm or more, the amount of lubricant leached out is large and the running durability for a long time is deteriorated, which is not preferable.
When the half-width is 10 nm or more, the dispersibility is poor, the filling degree of the magnetic powder is low, and the noise of the obtained magnetic recording medium is high, which is not preferable.

The pore diameter is determined as follows. That is, the formed coating film (coating of the magnetic layer) is peeled off, the obtained coating film is immersed in dodecane, and then the temperature is raised with a measuring instrument (DSC2000, manufactured by Seiko Denshi), Lower the temperature at a high speed (-0.3 ° C / min),
Utilizing the freezing point depression phenomenon of dodecane existing in the micropores in the coating film, a pore diameter distribution map was obtained from the calorific value and freezing point depression temperature difference, and the average pore diameter was obtained based on the obtained distribution map. And the half width were calculated.

The magnetic recording medium of the present invention is manufactured through a magnetic field orientation treatment and a drying treatment, and the solvent content of the magnetic layer before the magnetic field orientation treatment is preferably 100 parts by weight of the magnetic powder. Is 40 parts by weight or more, and more preferably 4
0 to 120 parts by weight, so that the solvent content of the magnetic layer after the magnetic field orientation treatment is preferably 40 parts by weight or less, more preferably 20 parts by weight or less with respect to 100 parts by weight of the magnetic powder, It is desirable that it is manufactured by performing the drying treatment. The magnetic field orientation treatment and the drying treatment will be described later.

The magnetic recording medium of the present invention is suitable as a magnetic tape such as an 8 mm video tape or a DAT tape, but can also be applied as another magnetic recording medium such as a floppy disk.

Next, an example of a method for producing the magnetic recording medium of the present invention (the magnetic recording medium having a non-magnetic layer and a back coat layer shown in FIG. 1) will be outlined. First, the magnetic coating material and the non-magnetic coating material on the support are subjected to simultaneous multi-layer coating by a wet-on-wet method so that the dry thicknesses of the magnetic layer and the non-magnetic layer are the thicknesses, respectively, A coating film for the magnetic layer and the non-magnetic layer is formed. That is, it is preferable that the magnetic layer is coated and formed when the non-magnetic layer is wet. Next, the coating film is subjected to a magnetic field orientation process, a drying process and a winding process. After that, calendering is performed if necessary, and then a back coat layer is further formed if necessary. Next, if necessary, for example, when obtaining a magnetic tape, the magnetic tape is subjected to aging treatment at 40 to 70 ° C. for 6 to 72 hours, and slit into a desired width.

The above-mentioned simultaneous multilayer coating method is disclosed in JP-A-5-73.
No. 42, line 31 to column 43, line 31, etc. of Japanese Patent No. 883, the above-mentioned magnetic coating material for forming the magnetic layer is dried before the non-magnetic coating material for forming the non-magnetic layer is dried. It is a coating method, and the interface between the above magnetic layer and the above non-magnetic layer is smooth and the surface properties of the above magnetic layer are good, so there are few dropouts and high density recording is possible. Moreover, a magnetic recording medium having excellent durability of the coating film (magnetic layer and non-magnetic layer) can be obtained.

Further, it is preferable that the magnetic field orientation treatment and the drying treatment are continuously performed by using an apparatus as shown in FIG. The apparatus 1 shown in FIG. 2 includes an orienting machine 10 and a dryer 20.
The orienting machine 10 includes a ventilation nozzle 11a, 11b, 11c, 11 for forming a coating film of the magnetic coating material and a coating film of the non-magnetic coating material and blowing air toward the support 2 '.
d, 11e, 11f and magnets 12a, 12b, 12c, 12d for orienting the magnetic powder in the magnetic paint. Further, the dryer 20 has a plurality of ventilation nozzles 21 and 2.
A nozzle aggregate 22 having 1, 21, ... Is provided. Further, the orienting machine 10 and the dryer 20 include
.. and conveyors 23, 23 .. for transferring the above-mentioned support 2'in the directions of the arrows in the figure, respectively.
・ Is provided. And, for example, when the magnetic recording medium of the present invention is a magnetic tape, it is about 500 Oe or more, preferably about 1 or more in the direction parallel to the coated surface of the magnetic paint.
000 to 10000 Oe magnetic field is applied, or the magnetic coating material and the non-magnetic coating material are in a wet state of 1000 to 1000 Oe.
The magnetic field orientation treatment can be performed by a method of passing through a solenoid of 10000 Oe or the like, and at the same time, the drying treatment is performed by the air from the ventilation nozzles 11a to 11f and the treatment by the dryer 20. . At this time, the temperature of the air blown to the coating film of the magnetic paint in the ventilation nozzles 11a to 11f is 30 to 50 ° C.
Although the amount of air is not particularly limited, it is desirable that the amount of solvent in the magnetic layer after the magnetic field orientation treatment is within the above range.

The above-mentioned drying treatment is, for example, 30 to 1
It can be performed by blowing the gas heated to 20 ° C. from the ventilation nozzle, and at this time, the degree of drying of the coating film can be controlled by controlling the temperature of the gas and the supply amount thereof.

Further, in the present invention, the aligning machine 10 described above is used.
The amount of the solvent of the coating film of the magnetic coating material when it is supplied to the magnetic powder is preferably 40 parts by weight or more, and more preferably 40 to 120 parts by weight, when the weight of the magnetic powder is 100 parts by weight. The amount of the solvent in the coating film of the magnetic paint at the time of supplying is preferably 40 parts by weight or less, preferably 20 parts by weight or less, when the weight of the magnetic powder is 100 parts by weight. By carrying out the orientation treatment and the drying treatment in this manner, the magnetic recording medium of the present invention having the above surface roughness and squareness ratio can be obtained.

The calendering treatment can be carried out by a super calendering method in which two rolls such as a metal roll and a cotton roll or a synthetic resin roll, a metal roll and a metal roll are passed. Also,
The conditions for the calendar treatment are 60 to 140 ° C. and 100
It can be up to 500 kg / cm.

The backcoat layer, which is provided as necessary, is provided on the back surface of the support (the surface on which the magnetic layer and the nonmagnetic layer are not provided), and is usually the backcoat layer. It is obtained by coating the above-mentioned support with the back coat paint used for formation.

When manufacturing the magnetic recording medium of the present invention, finishing steps such as polishing and cleaning of the surface of the magnetic layer may be carried out, if necessary. The above-mentioned magnetic paint and non-magnetic paint can also be applied by a generally known sequential multilayer coating method.

[0041]

Next, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Example] A magnetic coating composition having the following composition and a non-magnetic coating composition having the following composition were used, and a back coating composition having the following composition was used as the back coating composition, according to the following [Method for producing magnetic recording medium]. A magnetic tape was manufactured to obtain a magnetic tape as a magnetic recording medium. When the coercive force and the saturation magnetic flux density of the magnetic layer formed by using the magnetic coating material were measured according to the [Measurement method] described later, the coercive force of the magnetic layer was 2240 Oe and the saturation magnetic flux density was 4300 gauss. Met.

Magnetic paint , acicular ferromagnetic metal powder mainly composed of iron 100 parts by weight, manufactured by Dowa Mining Co., Ltd., trade name "HL-56" Coercive force; 2120 Oe, saturation magnetization; 135 emu / g average major axis diameter; 0 0.065 μm Axial ratio: 4.2 ・ Sumitomo Chemical Co., Ltd., trade name "AKP-50" 5 parts by weight ・ Carbon black (average primary particle diameter 53 nm) 2 parts by weight ・ Sulfonic acid group-containing vinyl chloride polymer 10 Parts by weight-sulphonic acid group-containing polyurethane resin 5 parts by weight-butyl stearate 1 part by weight-myristic acid 2 parts by weight-brand name "Coronate L", manufactured by Nippon Polyurethane Industry Co., Ltd. 3 parts by weight [polyisocyanate compound] -methyl Ethyl titone 60 parts by weight Toluene 60 parts by weight Cyclohexanone 60 parts by weight

Non-magnetic paint -Bengala 100 parts by weight, Toda Kogyo Co., Ltd., trade name "DPN-250BX" -Carbon black (average primary particle diameter 53 nm) 2 parts by weight-Sulfonic acid group-containing vinyl chloride polymer 10 parts by weight- Sulfonic acid group-containing polyurethane resin 5 parts by weight-Butyl stearate 2 parts by weight-Myristic acid 2 parts by weight-Brand name "Coronate L", manufactured by Nippon Polyurethane Industry Co., Ltd. 5 parts by weight [polyisocyanate compound] -Methyl ethyl ketone 60 parts by weight -Toluene 60 parts by weight-Cyclohexanone 60 parts by weight

( Blending of back coat paint ) 100 parts by weight of trade name "TB5024" manufactured by Toyo Ink Co., Ltd. 2 parts by weight of trade name "Coronate L" manufactured by Nippon Polyurethane Industry Co., Ltd. [polyisocyanate compound]

[Production of Magnetic Recording Medium] The above magnetic paint and non-magnetic paint were each dried to a thickness of 0.2 on the surface of a polyethylene terephthalate film having a thickness of 4.5 μm.
It was applied so as to have a thickness of μm and 1.5 μm to form coating films of magnetic paint and non-magnetic paint. Then, while the coating film was in a wet state, the coating film was passed through a solenoid of 5000 Oe for magnetic field orientation treatment, dried at 80 ° C., and then wound. The solvent content of the magnetic layer before the magnetic field orientation treatment is 80 parts by weight with respect to 100 parts by weight of the magnetic powder, and the solvent content after the magnetic field orientation treatment is 100 parts by weight of the magnetic powder. The drying condition (wind velocity of hot air) was adjusted to 10 parts by weight, and the drying treatment in the magnetic field orientation treatment was performed. Next, roll surface temperature 100 ° C, roll linear pressure 3
After calendering under the conditions of 00 kg / cm to form the first and non-magnetic layers, a back coat paint was applied on the back surface of the support so that the dry thickness was 0.5 μm.
After being dried at 0 ° C., it was wound up. Then 6
After aging treatment at 0 ° C. for 24 hours, 3.8 m
The tape was cut into m-width tapes to obtain a magnetic tape, and the obtained magnetic tape was loaded into a 3.8 mm cassette case and then DDS.
A cassette was made.

The surface roughness and the squareness ratio of the obtained magnetic tape as a magnetic recording medium were measured as follows. The surface roughness was 2.5 nm and the squareness ratio was 0.88. Further, when the average pore diameter and its half-value width were determined according to the above measuring method, the average pore diameter was 7 nm and the half-value width was 5
mm.

The solvent content of the magnetic layer before the magnetic field orientation treatment is 200 parts by weight with respect to 100 parts by weight of the magnetic powder,
Furthermore, the solvent content after the magnetic field orientation treatment is 100
A magnetic tape (hereinafter referred to as "comparative product") was prepared as described above, except that the drying condition (hot air velocity) was adjusted to 100 parts by weight with respect to 100 parts by weight and the drying treatment in the magnetic field orientation treatment was performed. ) Got. The S / N ratio of the obtained comparative product and the magnetic tape as the magnetic recording medium of the present invention was measured as follows. The magnetic tape of the present invention was +0.5 dB higher than that of the comparative product. Met.
The surface roughness of the comparative product was 2.5 nm and the squareness ratio was 0.82.

[Measurement Method] ◎ Coercive Force and Saturation Magnetic Flux Density With respect to the magnetic layer coated on the support and the nonmagnetic layer, an adhesive tape is used to remove only the magnetic layer from the support and the nonmagnetic layer. The magnetic layer was peeled off, the magnetic layer was punched out into a predetermined size and shape, and a coercive force and a saturation magnetic flux density were measured with an applied magnetic field of 10 kOe for a loop time of 10 minutes using a vibrating magnetometer. ◎ Surface roughness of magnetic recording medium Surface roughness Ra The obtained magnetic recording medium was manufactured by Tokyo Seimitsu Co., Ltd.
Using a surface roughness profile measuring instrument, trade name "SurfM553A", the measurement was performed under the conditions of a needle radius of 2 µm, a load of 30 mg, a magnification of 200,000 and a cutoff of 0.08 mm. still,
Ra (center line average roughness) is obtained by extracting a portion of the measurement length L from the roughness curve in the direction of the center line, the center line of the extracted portion as the X axis, and the vertical magnification direction as the Y axis. Y
= F (x), the value obtained by the following equation is expressed in [nm].

[0050]

[Equation 1]

Squareness Ratio The ratio (Br / Bs) between the saturation magnetic flux density Bs and the residual magnetic flux density Br among the results obtained using the above vibrating magnetometer was defined as the squareness ratio of the coating film.

S / N ratio The obtained magnetic tape was wound around a drum having a diameter of 150 mmφ, and the (tangential velocity) peripheral speed of the drum was set to 6 m / sec and the recording frequency was set to 9 MHz to perform recording and reproduction on the magnetic tape. At this time, 8 MHz together with the reproduction signal (S) of 9 MHz
Output (measured as noise (N)) of 9 MH
Calculate the ratio between the output of z and the output of 8MHz, and use this as the S / N ratio.
Ratio. The output at each frequency was measured using a spectrum analyzer.

[0053]

The magnetic recording medium of the present invention has excellent electromagnetic conversion characteristics and a high S / N ratio.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a magnetic recording medium of the present invention.

FIG. 2 is a schematic view showing a main part of a manufacturing process of a magnetic recording medium of the present invention.

[Explanation of symbols]

 1 Magnetic Recording Medium 2 Support 3 Magnetic Layer 4 Intermediate Layer 5 Backcoat Layer 10 Orientation Machine 20 Dryer

Claims (4)

[Claims] 1. A magnetic recording medium comprising a support and a magnetic layer provided on the support, wherein the magnetic layer contains magnetic powder having a major axis diameter of 0.1 μm or less, The surface roughness Ra of the surface of the magnetic layer is 5 nm or less, and the squareness ratio of the magnetic recording medium is 0.87 or more. 2. The magnetic recording medium according to claim 1, wherein the magnetic powder has an axial ratio (major axis diameter / minor axis diameter) of a major axis diameter and a minor axis diameter of 6 or less. . 3. The magnetic layer has an average pore diameter of 10
The magnetic recording medium according to claim 1, which is smaller than nm. 4. The magnetic recording medium is manufactured through a magnetic field orientation treatment and a drying treatment, and the solvent content of the magnetic layer before the magnetic field orientation treatment is 40 parts by weight based on 100 parts by weight of magnetic powder. The above is characterized by being manufactured by performing the drying treatment so that the solvent content of the magnetic layer after the magnetic field orientation treatment is 40 parts by weight or less with respect to 100 parts by weight of the magnetic powder. Magnetic recording medium.