JPH09128749A - Production of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic coating film having excellent durability by applying a magnetic coating material mixed with magnetic metallic powder, binder and hardener and an org. solvent of the prescribed values or above in prescribed compsn. rations on a nonmagnetic base consisting of a high- polymer material having a glass transition point of a prescribed temp. or above, thereby forming a magnetic coating film. SOLUTION: The magnetic film is formed by applying the magnetic coating material prepd. by mixing the magnetic metallic powder of >=10atom.% in Co/(Co+Fe) ratio, the binder, the hardener and the org. solvent on the nonmagnetic base consisting of the high-polymer material having the glass transition point Tg of >=120 deg.C. Thereafter, the magnetic film is cured by heating at temp. of >=75 deg.C. The magnetic coating film having the excellent durability is thereby formed without the occurrence of the deterioration in the characteristics of the rigid powder and the thermal deformation of the nonmagnetic powder. The magnetic recording medium which has the excellent electromagnetic conversion characteristics and substantially prevents the occurrence of drop-out is thus formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a coating type magnetic recording medium, and more particularly to improving the durability of a magnetic coating film.

[0002]

2. Description of the Related Art As a magnetic recording medium, a magnetic coating material prepared by dispersing a ferromagnetic powder, a binder, a curing agent, and various additives together with an organic solvent is coated and dried on a non-magnetic support, A magnetic layer is formed by heat curing,
A so-called coating type magnetic recording medium is known. In this coating type magnetic recording medium, metal fine particles have been used as ferromagnetic powder for the purpose of high density recording.

A coating type magnetic recording medium using such metal fine particles is used as a recording medium for computers such as a magnetic tape for audio or video, a high density floppy disk, a data cartridge for backup, etc. At the same time as becoming the mainstream of magnetic recording media, there are also remarkable improvements in characteristics.

In order to realize high density recording of this coating type magnetic recording medium, metal fine particles are used as the ferromagnetic powder, and the medium surface is super smoothed to minimize the spacing loss and at the same time. It is also important to reduce output loss due to recording demagnetization.

As a method for achieving these purposes, (1)
Increase of coercive force and saturation magnetization of ferromagnetic powder, (2) homogenization of coercive force distribution of ferromagnetic powder, (3) imparting perpendicular anisotropy,
(4) Examples include thinning of the magnetic coating film.

Of these, (1) and (2) are techniques for directly improving the output. In order to improve the coercive force and the saturation magnetization, the elemental composition of the ferromagnetic powder has been studied, and the metal fine particles having a coercive force of more than 160 kA / m and the saturation magnetization of more than 140 Am ³ / kg. Is also being developed. Also, the coercive force distribution reflects the particle size distribution of the ferromagnetic powder,
By making the particle sizes uniform, the coercive force distribution is also significantly improved.

The imparting of perpendicular anisotropy (3) is a method for increasing the density by perpendicular magnetic recording. In the case of a coating type magnetic recording medium, this is largely due to the control of the magnetic orientation of the ferromagnetic powder. For example, when acicular particles are used, it has been attempted to subject the coating film to vertical alignment treatment or oblique alignment treatment. However, these alignment treatments have not been put to practical use due to problems such as difficulty in alignment control and disturbance of the coating film surface due to alignment.

Next, the thinning of the magnetic coating film (4) is considered to be very effective as a method for reducing self-demagnetization loss.

However, the film thickness of the magnetic coating film is, for example, 1 μm.
If the film is simply thinned below, the surface shape of the non-magnetic support is likely to appear on the surface of the magnetic coating film, making it difficult to smooth the surface of the magnetic coating film. For this reason, when the magnetic coating film is made thin, a multilayer coating type configuration in which a nonmagnetic coating layer is interposed between the nonmagnetic support and the magnetic coating film is often adopted. By thus interposing the non-magnetic coating film, the thickness is increased between the surface of the non-magnetic support and the surface of the magnetic coating film, and the surface shape of the non-magnetic support is less likely to appear on the surface of the magnetic coating film. Therefore, a thin magnetic coating film is formed with a smooth surface shape.

[0010]

By the way, in order to perform recording in a high-density area, it is necessary to improve the electromagnetic conversion characteristics by the above-mentioned method and to take measures to suppress the dropout as much as possible. . This is because the higher the recording density, the greater the influence of the dropout on the reproduced signal.

For example, in an analog-recorded image signal, if dropout occurs, the image quality deteriorates. Further, in the data signal from the computer, the data may be lost due to the occurrence of dropout, which may cause a fatal defect.

Most of such dropouts are adhered matter (dust, dust, etc.) on the tape, missing coating film,
Although it is caused by scratches on the coating film, the cause of the dropout is due to the durability of the coating film, except for the deposits on the tape. Therefore, the dropout can be suppressed to a considerably low level by improving the durability of the coating film, and the reliability in the high density recording area is improved.

Here, as a method for improving the durability of the coating film, it is effective to increase the degree of crosslinking of the binder used in the coating film. In order to increase the degree of crosslinking of the binder, it is possible to improve the molecular design of the binder and the curing agent, but raising the curing temperature is a general measure.

However, when the curing temperature is raised, the influence of heat on various materials constituting the medium poses a problem. For example, the magnetic metal powder contained in the magnetic coating film is apt to generate rust under high temperature conditions, resulting in impaired magnetic properties. Also,
A polyethylene terephthalate film or a polyethylene-2,6-naphthalate film, which is widely used as a non-magnetic support, has deteriorated physical properties at high temperatures.

For this reason, it is necessary to be very careful in raising the curing temperature, and the durability of the coating film cannot be improved sufficiently.

Therefore, the present invention has been proposed in view of such conventional circumstances, and a magnetic coating film having excellent durability without deterioration of characteristics of the magnetic powder or thermal deformation of the non-magnetic support is provided. An object of the present invention is to provide a method of manufacturing a magnetic recording medium that can be formed, has excellent electromagnetic conversion characteristics, and can obtain a magnetic recording medium with suppressed dropout.

[0017]

To achieve the above object, the magnetic recording medium of the present invention has a glass transition point Tg of 1 or less.
Co / (Co + Fe) on a non-magnetic support above 20 ℃
After coating a magnetic coating material prepared by mixing a magnetic metal powder having a ratio of 10 atomic% or more, a binder, a curing agent and an organic solvent to form a magnetic coating film, heat curing at a temperature of 75 ° C or higher. It is a feature.

Further, a non-magnetic coating material prepared by mixing at least a non-magnetic powder, a binder and an organic solvent is applied onto a non-magnetic support having a glass transition point Tg of 120 ° C. or more to form a non-magnetic coating film. After formation, Co /
A magnetic coating material prepared by mixing a metal magnetic powder having a (Co + Fe) ratio of 10 atomic% or more, a binder, a curing agent and an organic solvent is applied to form a magnetic coating film, which is heated and cured at a temperature of 75 ° C. or higher. It is characterized by that.

Thus, a non-magnetic support having a glass transition point Tg of 120 ° C. or higher is used, and the ferromagnetic powder mixed in the magnetic coating has a Co / (Co + Fe) ratio of 10
When the metal powder of atomic% or more is used and the heat curing temperature is set to 75 ° C. or more, the cross-linking reaction proceeds without causing thermal deterioration of the non-magnetic support or the metal magnetic powder, and a high strength magnetic coating film is obtained. Can be formed. Therefore, it is possible to manufacture a magnetic recording medium having good magnetic characteristics and electromagnetic conversion characteristics, suppressing dropout, and exhibiting good recording and reproducing characteristics.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described.

In order to manufacture a coating type magnetic recording medium, ferromagnetic powder, a binder and a curing agent are kneaded together with an organic solvent,
Disperse to prepare a magnetic paint. Then, this magnetic paint is applied on a non-magnetic support and dried to form a magnetic coating film,
Further heat treatment cures the magnetic coating film.

In the present invention, in the manufacturing process of such a medium, in order to form a magnetic coating film having excellent durability, the heat curing temperature is set to 75 ° C. or higher. And, in order to withstand heat curing at such a relatively high temperature,
Glass transition point Tg of 120 ° C as material for non-magnetic support
The above-mentioned materials are used, and as the ferromagnetic powder to be mixed with the magnetic coating material, a metal magnetic powder having a Co / (Co + Fe) ratio of 10 atomic% or more is used. Hereinafter, this design condition will be described in detail.

First, in the present invention, as the ferromagnetic powder to be mixed with the magnetic paint, a Co--Fe based metal magnetic powder having a Co / (Co + Fe) ratio of 10 atomic% or more is used. This Co /
The (Co + Fe) ratio is set in terms of heat resistance and magnetic properties. When the Co / (Co + Fe) ratio is less than 10 atomic%, the magnetic properties are remarkably deteriorated by the heat curing at a temperature of 75 ° C. or higher performed in the subsequent step. Note that Co
The more preferable range of the / (Co + Fe) ratio is 20 to 40.
Atomic%. When the Co / (Co + Fe) ratio is 20 atomic% or more, the initial saturation magnetization amount becomes large, and the characteristic deterioration during heat curing can be suppressed to a very small level. However, if this ratio exceeds 40 atom%, it is advantageous in suppressing deterioration at the time of high temperature curing, but since the ratio of Co becomes large, the cost becomes high and it is not practical.

The metallic magnetic powder may contain a trace amount of other metal elements as long as Fe and Co are the main components. For example, Fe-Co-Al based alloy,
Fe-Ni-Al-based alloy, Fe-Co-Al-P-based alloy, Fe-Co-Si-Al-Mn-based alloy, Fe-Co
-Mn-Zn alloy, Fe-Co-Zn alloy, Fe-
Co-Ni based alloy, Fe-Co-Ni-Cr based alloy, F
e-Co-Ni-P alloy, Fe-Co-B alloy, F
It may be an alloy powder such as an e-Co-Cr-B type alloy or an Fe-Co-V type alloy. Further, an appropriate amount of a light metal element such as Al, Si, P and B may be added for the purpose of preventing sintering during reduction or maintaining the shape.

The shape of these metallic magnetic powders is preferably as follows.

First, the specific surface area is 20 to 90 m ² / g,
It is preferably 25 to 70 m ² / g. This is because when the specific surface area is in this range, the ferromagnetic powder is often relatively fine particles, the noise characteristics are improved, and high density recording becomes possible.

However, in the case of metal powder, it cannot be said that the specific surface area directly reflects the particle size.

That is, assuming that the fine structure of the metal powder is cylindrical, it has a three-layer structure of a cylinder made of pure metal, a shell made of iron oxide, and a shell made of light metal from the inside. In the metal powder, the overall density (average density) easily changes even if the ratio of these three layers changes slightly.
Therefore, the specific surface area represented by the surface area per unit weight also changes depending on the ratio of these three layers regardless of the actual surface area.

Further, the metal particles have irregularities formed on the surface in the gradual oxidation process. Therefore, the size of the irregularities increases the surface area regardless of the size of the particles themselves. Due to the influence of such density and the influence of surface irregularities, it cannot be said that the fine metal particles have a large specific surface area.

Therefore, when evaluating the particle size of metal particles, it is more practical to directly measure the major axis length and minor axis length of the particles.

The major axis length and the minor axis length of the metal particles can be measured from a transmission electron microscope photograph. The major axis length of the metal magnetic particles measured in this manner is less than 0.3 μm,
Further, it is preferably less than 0.15 μm. Also,
The acicular ratio (major axis length / minor axis length) is preferably as small as possible within the range in which shape anisotropy is maintained. Usually, a needle-like ratio of 2 or more and 15 or less is selected, and a needle-like ratio of 3 or more and less than 10 is desirable. If the acicular ratio is less than 2, the orientation of the ferromagnetic powder is reduced and the output is reduced. Also, the acicular ratio is 1
If it exceeds 5, there is a possibility that the output of the short wavelength signal will decrease.

In the present invention, a metallic magnetic powder having a Co / (Co + Fe) atomic ratio of 10 atomic% or more is used as the ferromagnetic powder, but other magnetic coating materials are coated magnetic recording media. Any of the commonly used ones can be used.

For example, as the binder, a thermoplastic resin, a thermosetting resin, a reactive resin or the like known as a binder for a medium is used, and particularly, the number average molecular weight thereof is 5,000 to 10,000.
0 is preferable.

As the thermoplastic resin, vinyl chloride, vinyl acetate, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, Acrylic ester-vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer,
Acrylic ester-vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-vinyl chloride copolymer, methacrylic acid ester-ethylene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer Coal, 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 resins, synthetic rubbers and the like.

As the thermosetting resin, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin,
Polyamine resin, urea formaldehyde resin and the like can also be used.

All of the above-mentioned binders contain -SO ₃ M, -OSO ₃ M, -C for the purpose of improving the dispersibility of the pigment.
OOM, P = O (OM) 2 ( where formula, M is a hydrogen atom or a lithium, potassium, an alkali metal such as sodium) _{or, -NR 1 R 2, -NR 1} R 2 R 3 + X - in Side chain type amine represented,> NR ₁ R ₂ ⁺ main chain type amine represented by X ⁻ (wherein R ₁ , R ₂ and R ₃ represent a hydrogen atom or a hydrocarbon group, and X ⁻ is A halogen element ion such as fluorine, chlorine, bromine or iodine, or an inorganic ion or an organic ion), or a polar functional group such as -OH, -SH, -CN or an epoxy group may be introduced. The amount of these polar functional groups introduced into the binder is preferably 10 ^-1 to 10 ^-8 mol / g, more preferably 10 ^-2 to 10 ^-6 mol / g.

Polyisocyanate is used as a curing agent for forming a crosslinked structure in these binders. As the polyisocyanate, toluene diisocyanate and adducts thereof, alkylene diisocyanate and adducts thereof can be used. The amount of the polyisocyanate to be added is 5 to 80 parts by weight, preferably 10 to 50 parts by weight, based on 100 parts by weight of the binder.

A lubricant, a surface active agent, non-magnetic reinforcing particles and the like may be added to the magnetic paint, if necessary.

Examples of the lubricant include solid lubricants such as graphite, molybdenum disulfide, and tungsten disulfide, silicone oil, fatty acids having 10 to 22 carbon atoms, and 10 to 22 carbon atoms.
And fatty acid esters synthesized from the above fatty acids and alcohols having 2 to 26 carbon atoms, terpene-based compounds and oligomers thereof, and fluorine-based lubricants.

As the surfactant, any of nonionic, anionic, cationic and amphoteric surfactants can be used.

As the non-magnetic reinforcing particles, aluminum oxide (α, β, γ), chromium oxide, silicon carbide, diamond, garnet, emery, boron nitride, titanium carbide, titanium carbide (rutile type, anatase type), etc. is there. These particles have a Mohs hardness of 4 or more, preferably 5 or more, more preferably 6 or more, and a specific gravity of 2 to
6, preferably in the range of 3 to 5, and the average primary particle size is 1.0 μm or less, preferably 0.5 μm or less, more preferably 0.3 μm or less. Further, the addition amount of these particles is 20 with respect to 100 parts by weight of the ferromagnetic powder.
It is suitable that the amount is not more than 10 parts by weight, preferably not more than 10 parts by weight, more preferably not more than 5 parts by weight.

As the organic solvent for forming a coating material, a ketone solvent such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, an alcohol solvent such as methanol, ethanol and propanol, methyl acetate, ethyl acetate, butyl acetate and propyl acetate. , Ethyl lactate, ester solvents such as ethylene glycol acetate, diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, ether solvents such as dioxane, benzene, toluene, aromatic hydrocarbon solvents such as xylene, methylene chloride, ethylene chloride, Examples thereof include halogenated hydrocarbon solvents such as carbon tetrachloride, chloroform, chlorobenzene and the like, and these are appropriately mixed and used.

As a kneading device for kneading these materials, a continuous biaxial kneader, a continuous biaxial kneader capable of diluting in multiple stages, a kneader, a pressure kneader, a roll kneader, or the like, which has been conventionally known, is used. The machine can be used and is not limited in any way.

As the dispersing device, a roll mill, a ball mill, a horizontal sand mill, a vertical sand mill, a spike mill, a pin mill, a tower mill, a DCP, an agitator, a homogenizer, an ultrasonic disperser or the like can be used.

The magnetic coating film is formed by coating the magnetic coating material prepared under the above conditions on a non-magnetic support and drying.

As the non-magnetic support for forming the magnetic coating film, one having a glass transition point Tg of 120 ° C. or higher is used in the present invention so as to withstand the heat curing treatment carried out in the next step. . Specific examples of the non-magnetic support having a glass transition point Tg of 120 ° C. or higher include aromatic polyamide (glass transition point Tg: 150 ° C. or higher).
Alternatively, polyimide may be used. In addition,
Currently used non-magnetic supports such as polyethylene terephthalate (PET) and polyethylene-2,6-naphthalate (PEN) have a glass transition point Tg of 6 for PET.
It is unsuitable since it is 9 ° C and 113 ° C in PEN.

As a coating method for coating the magnetic coating on these non-magnetic supports, a gravure coater,
A knife coater, a wire bar coater, a doctor blade coater, a reverse roll coater, a dipping coater, an air knife coater, a die coater and the like are used.

After the magnetic coating film is formed in this manner, the magnetic coating film is heat-cured. In the present invention, the heat-curing temperature is regulated to 75 ° C. or higher.

When heat-cured at a temperature of 75 ° C. or higher, the crosslinking reaction of the binder with the curing agent is promoted, and a highly crosslinked structure is formed in the binder. Therefore, a magnetic coating film having excellent durability is formed. In addition, at this time, in the conventional material design of the medium, when a temperature of 75 ° C. or higher was applied, there was a concern that the magnetic properties of the ferromagnetic powder would be deteriorated and the non-magnetic support would be thermally deformed. Co / (Co + F
e) Since the ratio and the glass transition point Tg of the non-magnetic support are regulated, the ferromagnetic powder and the non-magnetic support are prevented from being thermally deteriorated.

Therefore, it is possible to obtain a magnetic recording medium which has excellent magnetic characteristics and electromagnetic conversion characteristics, and in which the coating film does not drop off or become scratched when repeatedly run, and in which dropout is suppressed.

The magnetic recording medium manufactured by the present invention is
It may be a multi-layer coating type magnetic recording medium in which a non-magnetic coating film is formed under the magnetic coating film.

To manufacture this multi-layer coating type magnetic recording medium, a non-magnetic coating material prepared by mixing a non-magnetic powder, a binder and a curing agent together with an organic solvent is coated on a non-magnetic support. After forming the magnetic coating film, on this non-magnetic coating film,
A magnetic coating material prepared by mixing magnetic powder, a binder and a curing agent together with an organic solvent is applied to form a magnetic coating film, which is then cured by heating.

In such a manufacturing process, a non-magnetic support having a glass transition point Tg of 120 ° C. or higher is used, and a ferromagnetic powder mixed with a magnetic coating material is Co /
Using a metal powder having a (Co + Fe) ratio of 10 atomic% or more,
Further, when the temperature for heat curing is set to 75 ° C. or higher, the crosslinking reaction proceeds without causing thermal deterioration of the non-magnetic support or the metallic magnetic powder, and a strong magnetic coating film can be formed. Therefore, it is possible to manufacture a magnetic recording medium having good magnetic characteristics and electromagnetic conversion characteristics, suppressing dropout, and exhibiting good recording and reproducing characteristics.

As the non-magnetic powder to be mixed with the non-magnetic paint, acicular hematite, goethite, rutile type titanium oxide, anatase type titanium oxide, carbon black, 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, barium carbonate, strontium carbonate, barium titanate and the like. To be These nonmagnetic powders may be doped with an appropriate amount of impurities according to the purpose.

The specific surface area of these non-magnetic powders is 5
It is desirable to be ˜100 m ² / g, preferably 20-70 m ² / g. The fact that the specific surface area is in such a relatively large range means that the powder is fine particles, and the surface of the non-magnetic coating film is smoothed. Therefore, the surface of the magnetic coating film formed thereon is also smoothed, and a magnetic recording medium having excellent modulation noise characteristics and less affected by spacing loss can be obtained. However,
If the specific surface area is too large, it will be difficult to disperse it in the paint.
This results in impairing the smoothness of the coating film.

As the binder, the curing agent and the organic solvent to be mixed with the non-magnetic paint, any of those exemplified above for the magnetic paint can be used.

As a method for applying these two types of paints, the non-magnetic paint and the magnetic paint, a die head having two slits through which the paint is extruded is used, and the non-magnetic paint and the magnetic paint are applied on the non-magnetic support by the die head. Simultaneous multi-layer coating method (wet on.
Wet coating method) is preferable. According to this simultaneous multi-layer coating method, a uniform coating film can be formed and good adhesiveness can be obtained at the upper and lower interfaces. The die coater used in this simultaneous multi-layer coating method includes a 2-lip method, a 3-lip method, a 4-lip method, and the like.

The multi-layer coating type structure is not limited to the two-layer structure, but may be a multi-layer structure in which the number of laminated non-magnetic coating films or magnetic coating films is increased.

Further, in both of the single-layer coating type and the multi-layer coating type, it is possible to have an additional structure as in a normal coating type magnetic recording medium.

For example, a back coat layer may be provided on the surface of the non-magnetic support opposite to the side on which the magnetic layer is formed for the purpose of improving the running property of the medium, preventing electrification and preventing transfer. An undercoat layer may be provided on the non-magnetic support for the purpose of enhancing the adhesion to the coating film. These backcoat layer and undercoat layer can be formed according to a conventional method.

[0061]

EXAMPLES Examples of the present invention will be described below based on experimental results.

Example 1 An upper layer magnetic coating material was prepared based on the following composition. The coating was carried out by mixing a magnetic metal powder, a binder, an additive and a solvent, kneading with a continuous kneader, and then dispersing with a sand mill for 4 hours according to a conventional method.

Magnetic coating composition for upper layer Fe—Co based metal magnetic powder 100 parts by weight [Co / (Co + Fe) ratio = 20 atomic%, major axis length 0.86 μm, acicular ratio 4] 14 parts by weight polyvinyl chloride resin ( Polymerization degree 150, sulfonic acid sodium salt as polar functional group containing 5 × 10 ⁻⁵ mol / g) Polyester polyurethane resin 6 parts by weight (sodium sulfonic acid salt as polar functional group containing 1 × 10 ⁻⁴ mol / g) Additives: carbon 2 parts by weight Al ₂ O ₃ 5 parts by weight Stearic acid 1 part by weight Heptyl stearate 1 part by weight Methyl ethyl ketone 150 parts by weight Cyclohexanone 150 parts by weight 4 parts by weight of the magnetic paint prepared in this manner and polyisocyanate After the addition, a nonmagnetic support made of aromatic polyamide having a thickness of 4.5 μm (surface roughness; good roughness surface = 5.5 n
m, rough surface = 7.0 nm) so that the dry coating thickness was 3 μm to form a magnetic coating film. Then, the magnetic coating film was subjected to a solenoid coil orientation treatment, drying, and calendar treatment in this order, and then the temperature was adjusted to 7
Curing treatment was performed at 5 ° C. for 20 hours.

Next, a back coat paint was prepared based on the following composition, and applied to the surface of the non-magnetic support opposite to the side on which the magnetic coating was formed in a thickness of 0.5 μm and dried. A back coat layer was formed.

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 raw tape prepared as described above is cut into 8 mm width. A magnetic tape was produced by cutting into pieces.

Example 2 and Example 3 Magnetic tapes were produced in the same manner as in Example 1 except that the temperature for curing the magnetic coating film was 90 ° C or 120 ° C.

Examples 4 to 6 Magnetic properties were the same as in Example 1 except that the Co / (Co + Fe) ratio of the magnetic coating material was 10 at%, 30 at% or 50 at%. A tape was made.

Comparative Examples 1 and 2 As Example 1 except that a 7.0 μm thick polyethylene terephthalate (PET) film or a 4.5 μm thick polyethylene naphthalate (PEN) film was used as the non-magnetic support. A magnetic tape was produced in the same manner.

Comparative Example 3 A magnetic tape was produced in the same manner as in Example 1 except that Co / (Co + Fe) ratio was 0 atom%, that is, pure iron powder was used as the metal magnetic powder of the magnetic coating material.

Comparative Example 4 A magnetic tape was produced in the same manner as in Example 1 except that the temperature for curing the magnetic coating film was 60 ° C.

With respect to the magnetic tape manufactured as described above, the magnetic characteristics, the electromagnetic conversion characteristics, the C / N ratio, the number of dropouts, and the heat shrinkage rate by the curing treatment were examined.

The magnetic characteristics were measured by a vibrating sample magnetometer (manufactured by Toei Industry Co., Ltd.) to obtain an external magnetic field of 0.8 MA / m (10
It was measured under the condition of kOe). The measured characteristics are saturation magnetic flux density Bm, coercive force Hc, and squareness ratio Rs.

The electromagnetic conversion characteristics were evaluated by measuring the output at the wavelength λ = 0.5 μm with a measuring device obtained by modifying a Hi-8 deck (manufactured by Sony Corporation) for electromagnetic conversion characteristic measurement. The C / N ratio was obtained by measuring the noise level 1 MHz away from the center frequency. The electromagnetic conversion characteristics and C / N were recorded as relative values when the value on the standard tape was 0 dB.

The heat shrinkage was measured according to JIS-C-2318.

The number of dropouts was 3μ generated in 3 minutes.
It was evaluated by measuring the number of occurrences of output decrease of 10 dB or more per sec.

The results of these measurements are shown in Table 1.

[0077]

[Table 1]

As can be seen from Table 1, an aromatic polyamide film is used as the non-magnetic support, a Co / (Co + Fe) ratio of 10 atomic% or more is used as the ferromagnetic powder, and the curing temperature is 75 ° C. or more. The magnetic tapes of Examples 1 to 6 produced by setting are all excellent in magnetic characteristics, have good electromagnetic conversion characteristics, and have a high C / N ratio. Moreover, there is no heat shrinkage, and the dropout is suppressed within the allowable range.

On the other hand, the glass transition point Tg is 120.
The magnetic tapes of Comparative Example 1 and Comparative Example 2 using PET or PEN having a temperature lower than ° C as a non-magnetic support have large thermal shrinkage and increase in dropout. It is considered that this increase in dropout is due to a change in the contact of the tape with the head due to heat shrinkage.

Further, the magnetic tape of Comparative Example 3 using the metal magnetic powder containing no Co has inferior magnetic characteristics to the magnetic tape of Example 1, and the electromagnetic conversion characteristics are low by that much. It has become. As for the magnetic characteristics, a change was observed before and after the curing treatment, which suggests that the curing treatment causes the characteristic deterioration.
However, when observing the magnetic powder in an arbitrary region of the magnetic tape after the curing treatment, no clear rust was observed. It is considered that there is a portion where oxidation is locally advanced.

Further, in the magnetic tape of Comparative Example 4 in which the curing temperature was set as low as 60 ° C., the durability of the coating film was poor, probably because the curing reaction did not proceed, and the number of dropouts was remarkably increased as compared with the other cases. There is.

From the above results, in order to form a magnetic coating film having excellent durability while suppressing deterioration of magnetic characteristics and thermal deformation,
It was found that it is necessary to satisfy all the conditions that the non-magnetic support is an aromatic polyamide film, the Co / (Co + Fe) ratio of the ferromagnetic powder is 10 atomic% or more, and the curing temperature is 75 ° C or more. It was

The characteristics of the magnetic tapes of Examples 1 to 6 will be examined in more detail. First, Example 1 will be described.
On the other hand, looking at Examples 2 and 3 in which the curing temperature was set higher, the crosslinking reaction was accelerated and the durability of the coating film was improved as the curing temperature was increased. as a result,
The number of dropouts has been greatly reduced.

The magnetic properties were slightly deteriorated as the curing temperature was raised, but no oxidization of the metal powder was observed. Further, as the curing temperature increased, the shape of the backcoat layer surface was transferred to the magnetic layer relatively strongly, the surface property of the magnetic layer deteriorated, and the electromagnetic conversion characteristics were slightly deteriorated. Regarding the heat shrinkage, the curing temperature is 90 ° C.
If it is around, it can be suppressed to 0, but the curing temperature is 120 ° C.
When it goes up, some heat shrinkage will be recognized. However, this heat shrinkage is at a level where there is no problem.

Next, as compared with Example 1, C of metal magnetic powder was used.
Examples 4 to 6 in which the o / (Co + Fe) ratio was changed.
In comparison, in Example 5 in which the Co / (Co + Fe) ratio is increased to 20 atom%, the magnetic characteristics and electromagnetic conversion characteristics are improved as compared with Example 1. However, Co / (Co + F
e) In Example 6 in which the ratio was increased to 50%, the squareness ratio Rs was lowered probably because the acicularity of the particles was low, and the electromagnetic conversion characteristics were sufficiently practical values. It is a little lower than 1.

Example 7 A nonmagnetic coating material for the lower layer was prepared based on the following composition. The coating was performed by mixing a non-magnetic powder, a binder, an additive and a solvent according to a conventional method, kneading with a continuous kneader, and then dispersing with a sand mill for 4 hours.

Nonmagnetic coating composition for lower layer α-Fe ₂ O ₃ 100 parts by weight (specific surface area = 40 m ² / g, acicular ratio = 8) Polyvinyl chloride resin 14 parts by weight (polymerization degree 150, sulfone as polar functional group) Acid sodium salt 5 × 10 ⁻⁵ mol / g) Polyester polyurethane resin 6 parts by weight (sulfonic acid sodium salt 1 × 10 ⁻⁴ mol / g as a polar functional group) stearic acid 1 part by weight heptyl stearate 1 Parts by weight methyl ethyl ketone 105 parts by weight cyclohexanone 105 parts by weight 2 parts by weight of polyisocyanate was added to the thus prepared non-magnetic coating material. And this non-magnetic paint,
An aromatic polyamide film having a thickness of 4.5 μm (surface roughness; good roughness surface = 5.5 n) was formed by a 4-lip type die coater together with the same magnetic coating material as that prepared in Example 1.
m, bad roughness surface = 7.0 nm) to form a lower non-magnetic coating film and an upper magnetic coating film by simultaneous multilayer coating.

Then, in the same manner as in Example 1, orientation treatment, drying, calendering treatment, curing treatment (temperature 75 ° C., curing time 20 hours), formation of a back coat layer and cutting were performed to form a multilayer coating type magnetic layer. A tape was made. However, the film thickness constitution is such that after the curing treatment, the upper layer is 0.3 μm and the lower layer is 2.
4 μm.

Example 8 Example 7 was repeated except that acicular TiO ₂ (specific surface area 60 m ² / g, acicular ratio 5) was used as the non-magnetic powder of the non-magnetic coating material.
A magnetic tape was produced in the same manner as.

Comparative Examples 5 and 6 As Example 7 except that a 7.0 μm thick polyethylene terephthalate (PET) film or a 4.5 μm thick polyethylene naphthalate (PEN) film was used as the non-magnetic support. A magnetic tape was produced in the same manner.

Comparative Example 7 A magnetic tape was produced in the same manner as in Example 7 except that Co / (Co + Fe) ratio was 0 atom%, that is, pure iron powder was used as the metal magnetic powder of the magnetic coating material.

Comparative Example 8 A magnetic tape was produced in the same manner as in Example 7 except that the temperature at which the magnetic coating film was cured was 60 ° C.

With respect to the magnetic tape manufactured as described above, the magnetic characteristics, the electromagnetic conversion characteristics, the C / N ratio, the number of dropouts, and the heat shrinkage ratio by the curing treatment were examined. Table 2 shows the results.

[0094]

[Table 2]

As shown in Table 2, in the case of the multi-layer coating type magnetic tape, the same tendency as in the case of the single-layer coating type magnetic tape is obtained.

That is, an aromatic polyamide film is used as the non-magnetic support and Co is used as the ferromagnetic powder.
The magnetic tapes of Example 7 and Example 8 which were manufactured by using a material having a // (Co + Fe) ratio of 10 atomic% or more and a curing temperature of 75 ° C. or more were excellent in magnetic properties and excellent. It has electromagnetic conversion characteristics and a high C / N ratio. Also, the heat shrinkage rate is small and dropout is suppressed.

On the other hand, the glass transition point Tg is 120
The magnetic tapes of Comparative Examples 5 and 6 using PET or PEN having a temperature lower than ° C as a non-magnetic support have large thermal shrinkage and increase in dropout.

Looking at the magnetic tape of Comparative Example 7 using the magnetic metal powder containing no Co, the magnetic characteristics were inferior to those of the magnetic tape of Example 7, and the electromagnetic conversion characteristics were low by that amount. It has become. Also in this case, the magnetic characteristics show a change before and after the curing treatment, which suggests that the curing treatment causes the characteristic deterioration. Further, when the magnetic powder was observed in an arbitrary region after the curing treatment, no clear rust was observed, but it is considered that there is a portion where oxidation is locally advanced.

Further, in the magnetic tape of Comparative Example 8 in which the curing temperature was set as low as 60 ° C., the durability of the coating film was poor, so that the coating film had defects and the number of dropouts was remarkably large as compared with the other cases. There is.

From the above results, even in the case of the multi-layer coating type constitution, in order to form a magnetic coating film excellent in durability while suppressing deterioration of magnetic properties and thermal deformation, the non-magnetic support is an aromatic polyamide film. And the ferromagnetic powder Co / (Co + F
e) The ratio is 10 atomic% or more, and the curing temperature is 75.
It was found that it was necessary to satisfy all the conditions such that the temperature was above ℃.

Regarding the magnetic tape of Example 8 in which the nonmagnetic powder of the nonmagnetic coating was changed from that of Example 7, the same characteristics as those of Example 7 were obtained.

[0102]

As is apparent from the above description, in the manufacturing method of the present invention, Co / (Co +) is provided on the non-magnetic support made of a polymer material having a glass transition point Tg of 120 ° C. or higher.
(Fe) ratio of 10 atomic% or more of metal magnetic powder, a binder, a curing agent, and a magnetic coating material prepared by mixing an organic solvent are applied to form a magnetic coating film, followed by heat curing at a temperature of 75 ° C. or higher. Therefore, it is possible to form a magnetic coating film having excellent durability without deteriorating the characteristics of the magnetic powder or thermally deforming the non-magnetic support,
It is possible to manufacture a magnetic recording medium that has excellent electromagnetic conversion characteristics and that is unlikely to cause dropout.

Claims (3)

[Claims] 1. A metal magnetic powder having a Co / (Co + Fe) ratio of 10 atomic% or more, a binder, a curing agent and an organic solvent are mixed on a non-magnetic support having a glass transition point Tg of 120 ° C. or more. The method for producing a magnetic recording medium, which comprises applying the magnetic coating composition described above to form a magnetic coating film, followed by heating and curing at a temperature of 75 ° C. or higher. 2. The method for producing a magnetic recording medium according to claim 2, wherein the non-magnetic support is made of aromatic polyamide. 3. A non-magnetic coating film is obtained by applying a non-magnetic coating material prepared by mixing at least a non-magnetic powder, a binder and an organic solvent onto a non-magnetic support having a glass transition point Tg of 120 ° C. or higher. After the formation, Co / (Co
+ Fe) ratio of 10 atomic% or more of metallic magnetic powder, binder,
The method for producing a magnetic recording medium according to claim 1, wherein a magnetic coating material prepared by mixing a curing agent and an organic solvent is applied to form a magnetic coating film, and the coating is heated and cured at a temperature of 75 ° C. or higher.