JPH08273158A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE: To improve the dispersibility of magnetic powder in a magnetic layer and to produce a magnetic recording medium excellent in output characteristics. CONSTITUTION: A mixture contg. magnetic powder, a binder having epoxy groups and a solvent is kneaded under pressure, the resultant kneaded material is diluted with a solvent to prepare a magnetic coating material and a magnetic layer is formed on a substrate by coating with the coating material. When a magnetic recording medium is produced through the processes, an acidic sulfite is added to the mixture immediately before kneading under pressure.

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 magnetic recording medium, and more particularly to a method for manufacturing a magnetic recording medium having improved dispersibility of magnetic powder and excellent output characteristics.

[0002]

2. Description of the Related Art Magnetic recording media are widely used in the form of tapes, disks, drums or sheets. Such a magnetic recording medium is
Usually, it is produced by applying a magnetic powder containing a magnetic powder and a binder as a main component on a support such as a polyester film. In recent years, there has been a demand for miniaturization of magnetic recording media as well as for higher recording density. In order to meet such demands, for example, coercive force and saturation magnetization of magnetic powder are improved, Proposals have been made to reduce the thickness. In addition to these requirements, high-quality magnetic recording media have come to be demanded, and in order to meet such demands, magnetic recording media having excellent output characteristics have been proposed.

In order to increase the density and output of the magnetic recording medium, it has been proposed to make the magnetic powder into fine particles. Usually, the magnetic powder is dispersed and fixed in the magnetic layer by using a polar binder having a molecular weight of 20,000, but when such a binder is used for dispersing and fixing the fine magnetic powder. , Its dispersion is becoming difficult.

Therefore, at present, Japanese Patent Laid-Open No. 60-2358.
Self-dispersion using a binder in which a polar group such as a sulfonic acid group, a hydroxyl group or a carboxyl group is contained in a vinyl chloride resin as described in JP-A-14 is mainly used. However, as a result of further atomization of the magnetic powder, the number of polar groups in the binder has become insufficient, and dispersion is limited.

Therefore, attempts have been made to introduce a larger amount of polar groups into the binder, but a binder having a large amount of polar groups, particularly an epoxy group-containing binder having a large amount of sulfonic acid groups, is If the amount of sulfonic acid groups introduced is too large, on the contrary, there arises a problem that the dispersibility decreases.

Accordingly, it is an object of the present invention to provide a method of manufacturing a magnetic recording medium which has improved dispersibility of magnetic powder in a magnetic layer and excellent output characteristics.

[0007]

In order to achieve the above object,
As a result of earnest studies by the present inventors, the introduction of the polar group into the binder was carried out during the preparation of the magnetic paint, so that the polar group was introduced into the binder without lowering the dispersibility of the magnetic powder. I found that I would get it.

The present invention has been made on the basis of the above findings. A mixture containing magnetic powder, an epoxy group-containing binder and a solvent is kneaded under pressure to form a kneaded product, and the kneaded product is diluted with a solvent. In a method for producing a magnetic recording medium, which comprises a step of preparing a magnetic coating material and applying the magnetic coating material onto a support to form a magnetic layer, an acidic sulfite is added to the mixture immediately before kneading the mixture under pressure. The above object is achieved by providing a method for producing a magnetic recording medium, which is characterized by adding.

The magnetic recording medium produced by the method of the present invention is used, for example, in the form of a magnetic disk, a magnetic drum, etc., and particularly preferably in the form of a magnetic tape such as 8 mm video tape or DAT tape. used.

The method of manufacturing the magnetic recording medium of the present invention will be described in detail below.

In the method for producing a magnetic recording medium of the present invention, first, a mixture containing magnetic powder, an epoxy group-containing binder and a solvent is kneaded under pressure to form a kneaded product. Each of the magnetic powder, the binder and the solvent constituting the mixture will be described below.

As the magnetic powder, conventionally known magnetic materials can be used without particular limitation. Examples of such magnetic materials include ferromagnetic iron oxide, ferromagnetic chromium dioxide and ferromagnetic metal powder. . A particularly preferred magnetic powder is
The BET surface area is 40 m ² / g or more. It is preferable to use a magnetic powder having such a surface area because high density recording can be further achieved. The BET surface area of the magnetic powder is more preferably 40 to 65.

The ferromagnetic iron oxide used as the magnetic powder is FeOx (1.33≤x≤1.5).
Alternatively, FeOx to which a metal such as Cr, Mn, Co, or Ni is added can be used. Further, as the above-mentioned ferromagnetic chromium dioxide, CrO ₂ or CrO ₂ can be used as Na, K, F
Metals such as e and Mn, oxides of these metals, or P
It is possible to use a material to which a non-metal element such as
Further, the ferromagnetic metal powder has a metal content of 70% by weight or more and 80% by weight or more of at least one ferromagnetic metal (for example, Fe, Co, Ni, etc.). Can be used. Specific examples of the ferromagnetic metal powder include Fe-Co, Fe-Ni, Fe-
Al, Fe-Ni-Al, Co-Ni, Fe-Co-N
i, Fe-Ni-Al-Zn, Fe-Al-Si, etc. are mentioned.

The magnetic powder may contain, if necessary,
A rare earth element or a transition metal element can be contained. Further, as the magnetic powder, a micro-plate-like hexagonal barium ferrite and a part of its Fe atoms are Ti,
Magnetic powders substituted with atoms such as Co, Zn, and V can also be used.

The magnetic powder may be surface-treated in order to improve its dispersibility and the like. The above surface treatment is "Characterization of Powder Surfaces"; Acad
It can be carried out by a method similar to the method described in emicPress, and examples thereof include a method of coating the surface of the magnetic powder with an inorganic oxide. The surface treatment may be performed by an organic treatment such as a silane coupling treatment, a titanium coupling treatment and an alumina coupling treatment other than the above method.

Next, the epoxy group-containing binder will be described. As the epoxy-containing binder, polymers and copolymers containing an epoxy group can be used without particular limitation. In particular, it is preferable to use a vinyl chloride-modified resin or a polyurethane resin as the epoxy-containing binder because the affinity with the magnetic powder is good and the dispersibility of the magnetic powder is further improved. The epoxy group-containing binder,
It is preferable that the epoxy group content is 0.1 meq / g or more. When the content of the epoxy group is less than 0.1 meq / g, for example, the durability of the magnetic layer is reduced, the magnetic head is clogged, the output is reduced, and the abrasion resistance is deteriorated. Therefore, it is preferable to contain 0.1 meq / g or more. More preferably, the epoxy group-containing binder contains an epoxy group in an amount of 0.2 to 1 meq / g.

Further, as the above epoxy group-containing binder,
A commercially available product can also be used. Examples of such commercially available products include MR110 series manufactured by Nippon Zeon Co., Ltd.

The above binder is preferably added in an amount of 5 to 40 parts by weight, based on 100 parts by weight of the magnetic powder, and 5 to 2 parts by weight.
It is more preferable to add 0 part by weight.

The above binder is preferably dissolved in a solvent described below and dispersed and mixed as a solution.

Next, the solvent will be described. As the solvent, a solvent suitable for dissolving the binder can be used without particular limitation. Examples of such solvents include ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, ester solvents such as ethyl acetate, ether solvents such as tetrahydrofuran and dioxane, benzene, toluene and xylene. Examples thereof include aromatic hydrocarbon-based solvents, chlorinated hydrocarbon-based solvents, and the like. Specifically, page 3, lower right column 1 of JP-A-57-162128
The solvent described in lines 7 to 10 in the lower left column of page 4 can be used. Such a solvent can use 1 type (s) or 2 or more types.

It is preferable to add 100 to 400 parts by weight of the above solvent to 100 parts by weight of the magnetic powder.
It is more preferable to add 50 to 300 parts by weight.

When the mixture containing the above magnetic powder, the above binder and the above solvent is kneaded under pressure, components other than these, which are usually used in the preparation of magnetic paints, such as various additives, are added to the above mixture. You can also do it. Examples of such additives include a dispersant, a lubricant, an abrasive, an antistatic agent, a rust preventive and a fungicide.
Specifically, an abrasive such as carbon powder for reducing the surface resistance of the magnetic layer or alumina powder for enhancing the durability of the magnetic layer; JP-A-57-162128, page 2, upper left column, line 6 Examples include various additives described in page 10, upper right column, line 10 and page 3, upper left column, line 6 to page 3, upper right column, line 18. The carbon powder and the abrasive are preferably added in an amount of 5 to 50 parts by weight, more preferably 5 to 40 parts by weight, based on 100 parts by weight of the magnetic powder.

The magnetic powder, the binder, the solvent and the additives as optional components are mixed and kneaded under pressure to form a kneaded product. In this case, there is no particular limitation on the time from the preparation of the above mixture to the kneading under pressure, and no particular problem has been observed even if the kneading under pressure is carried out after storage for about 7 days. However, from the viewpoint of dispersibility, it is preferable to knead under pressure within about 5 hours after the addition of the acidic sulfite.
For example, a Nauta mixer or the like can be used to mix the above components.

A major feature of the present invention is that an acidic sulfite is added to the mixture just before the mixture is kneaded under pressure. As a result, a part of the epoxy groups in the binder reacts with the acidic sulfite to introduce an appropriate amount of sulfonic acid group into the binder. As a result, the dispersibility of the magnetic powder is improved. In the conventional epoxy group-containing binder containing a large amount of sulfonic acid group, since the sulfonic acid group is introduced into the molecule at the time of its synthesis, the binder in the above-mentioned binder may be affected by moisture in the air during storage. Part of the epoxy group reacts, as a result of increasing the molecular weight, it is considered that the dispersibility is reduced, in the present invention, since the decrease in dispersibility due to such an increase in the molecular weight does not occur, A large amount of sulfonic acid groups can be introduced into the binder without reducing the dispersibility.

It is important that the acidic sulfite is added immediately before the mixture is kneaded under pressure. Here, "immediately before" means that the acidic sulfite is added to the mixture and immediately kneaded under pressure. Not only in the case but also in the case where a time difference inevitably occurs in the process from the addition of the acidic sulfite to the mixture to the kneading under pressure.

The amount of the acidic sulfite added can be appropriately adjusted depending on the amount of sulfonic acid groups to be introduced into the binder, but as a general range, it is 0. It is preferable to add 01 to 1.0 part by weight. If the addition amount is less than 0.01 parts by weight, the dispersion effect may not be exhibited, and if it exceeds 1.0 parts by weight,
Rather, the aggregation action is manifested and the dispersion is deteriorated, so it is preferably within the above range. More preferably, the amount of the acidic sulfite added is 0.02 to 0.9 part by weight.

The acidic sulfite is represented by MHSO ₃ (M is a monovalent cation). The cation is
It is preferably a metal ion, more preferably an alkali metal ion.

The order of mixing the mixture is not particularly limited, but it is preferable to add the solvent in two or more portions because the dispersibility of the magnetic powder is extremely improved. For example, the magnetic powder, the binder, the carbon powder, the alumina powder, and part of the solvent are mixed and stirred, and then the acidic sulfite is added and immediately kneaded under pressure. And, the balance of the above solvent is preferably added in the dilution step described later.

The conditions of the pressure kneading are not particularly limited and can be appropriately adjusted depending on the kind of the binder used, the solid content of the mixture, etc., but the pressure is generally in the range of 0.5 to It is preferably 10 kg / cm ² , the kneading time is preferably 5 to 120 minutes, and the kneading temperature is preferably 20 to 80 ° C. As a means for pressure kneading, conventionally known means such as a pressure kneader and an extruder can be used without particular limitation.

The solid content of the kneaded product thus obtained is not particularly limited, but is preferably 70% or more as a general range from the viewpoint that shear stress is easily applied during dispersion.

After a kneaded product is obtained by pressure kneading, the kneaded product is diluted with a solvent to prepare a magnetic coating material. In this case, it is preferable to add and dissolve and dilute the rest of the binder and the rest of the solvent that were not used during the pressure kneading, and mix and disperse. More specifically, to the kneaded product, a part of the solvent is added and dissolved, mixed and dispersed using, for example, a ball mill or a sand mill, and then the rest of the binder and the rest of the solvent are added. Dilute, mix and disperse. As described above, the dispersibility of the magnetic powder is remarkably improved by adding the binder and the solvent in plural times.

In the dilution step, other components may be added, if necessary, in addition to the balance of the binder and the balance of the solvent. Examples of such components include lubricants such as oleyl oleate, tridecyl stearate (TDS), n-butyl stearate, myristic acid, oleic acid and stearic acid for enhancing the lubricity of the magnetic layer. The lubricant is preferably added in an amount of 0.5 to 20 parts by weight, more preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the magnetic powder.

In the diluting step, it is possible to add a curing agent for forming cross-linkage between the binders. By using such a curing agent,
It is preferable because the mechanical strength (coating strength) of the magnetic layer can be improved. As the curing agent, for example, acid anhydride, polyamine and polyisocyanate type curing agents can be used. As the polyisocyanate-based curing agent, Coronate L, Coronate HL, Coronate HX, Coronate N and the like manufactured by Nippon Polyurethane Industry Co., Ltd. can be preferably used. Such curing agent is
It is preferable to add 0.5 to 20 parts by weight, and more preferably 2 to 10 parts by weight to 100 parts by weight of the magnetic powder.

The solid content in the above magnetic paint is 30 to 5
It is preferably 0% by weight, more preferably 35 to 45% by weight. If the solid content is less than 30% by weight, the output of the obtained magnetic recording medium may be reduced, and if it exceeds 50% by weight, the coating property of the magnetic coating material may be reduced. Preferably.

A surfactant may be added to the magnetic coating material in order to enhance the dispersibility of the magnetic powder.

The magnetic coating material thus obtained is coated on a support to form a magnetic layer. The method for applying the magnetic paint is not particularly limited, and for example, die coating or roll coating can be used.

As the above support, a known magnetic or non-magnetic support can be used without particular limitation. Specifically, known resins such as polyethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, and aromatic polyamide; metals such as aluminum and copper; and paper are used. be able to. The form may be a film, a tape, a sheet, a disc, a drum, or the like. Before the magnetic layer is provided on the support, the surface thereof may be previously subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, and the like. The preferable thickness of the support is 1 to 300 μm.
m.

After applying the above-mentioned magnetic paint, magnetic field orientation treatment of the magnetic powder in the coating film and subsequent drying treatment may be performed.

The above-mentioned drying can be carried out, for example, by supplying a gas heated to 30 to 120 ° C. At this time, the degree of drying of the coating film is controlled by controlling the temperature of the gas and the supply amount thereof. be able to. After the above drying is completed,
You may perform a calendar process as needed. After this,
If necessary, for example, when obtaining a magnetic tape, 4
After aging treatment at 0 to 70 ° C., slit to a desired width.

The dry thickness of the magnetic layer thus formed is preferably 0.05 to 10 μm,
More preferably, it is from 05 to 5 μm.

In the method of manufacturing a magnetic recording medium of the present invention, the magnetic layer is formed so as to be composed of a plurality of two or more layers, and all or at least one of the magnetic layers is formed. The formation can also be performed by the method described above. In this case, each magnetic layer can be formed by a known sequential multilayer coating method or simultaneous multilayer coating.

Further, a non-magnetic layer may be formed between the magnetic layer and the support, and the non-magnetic layer may be formed by the method described above (however, in this case, the magnetic powder is used instead of the magnetic powder). And use non-magnetic powder).

[0043]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but it goes without saying that the present invention is not limited to these examples. In the following description, “part” means part by weight unless otherwise specified.

Example 1 A magnetic coating material was prepared from the following composition. That is, magnetic powder, carbon black, alumina, MR110 (binder) and UR8200 (binder)
Was charged into a mixer, and a part of the mixed solvent was added. Immediately before pressure-kneading this mixture with a pressure kneader (manufactured by Moriyama Seisakusho), the amount of acidic sodium sulfite shown in Table 1 was added to the mixture. Kneaded product obtained after pressure kneading (solid content 80
%), A part of the mixed solvent was added to dilute, and the mixture was dispersed using a sand mill to obtain a dispersion liquid. The solid content of this dispersion was 40%. To this dispersion liquid, myristic acid (lubricant) and n-butyl stearate (lubricant) were added together with the rest of the mixed solvent and diluted to obtain a mixed dispersion liquid. This mixed dispersion is a filter (HT20L manufactured by Nippon Roki Co., Ltd.)
After filtering with, Coronate L (curing agent) was added and mixed to obtain a magnetic paint.

Magnetic powder (BET surface area: 45 m ² / g) 100 parts Alumina (particle size 100 to 300 nm) 10 parts Carbon black (average primary particle size 50 nm) 1 part MR110 10 parts (binder: Nippon ZEON Corporation) Co., Ltd. epoxy group-containing vinyl chloride copolymer, epoxy group content 0.7 meq / g) UR8200 (binder: polyurethane manufactured by Toyobo, molecular weight 25000) 10 parts myristic acid (lubricant) 1 part n-Butyl stearate (lubricant) 1 part ・ Coronate L (curing agent, made by Nippon Polyurethane) 4 parts ・ Methyl ethyl ketone (solvent) 126 parts ・ Toluene (solvent) 126 parts ・ Cyclohexanone (solvent) 190 parts

The magnetic coating material thus obtained was applied by gravure coating to a dry thickness of 3 μm on the surface of a PET support having a thickness of 10 μm. The magnetic powder was subjected to a magnetic field orientation treatment by passing through a solenoid of 4000 Oe while the coating film was wet, and then the coating film was dried at 80 ° C., and then the support was wound. Then 9
The support was calendered under conditions of 0 ° C. and 300 kg / cm to form a magnetic layer. Then, a back coat layer was coated on the back surface of the PET support, and the obtained film was cut into a 3.8 mm width to obtain a magnetic recording medium.

Example 2 The amount of acidic sodium sulfite is shown in Table 1.
A magnetic recording medium was obtained by performing the same operation as in Example 1 except that the amount was changed to the amount shown in.

Comparative Example 1 A magnetic recording medium was obtained by the same procedure as in Example 1 except that unmodified MR110 (epoxy group-containing vinyl chloride copolymer) was used without adding any acidic sodium sulfite. .

Comparative Example 2 100 g of MR100 (epoxy group-containing vinyl chloride copolymer) was dispersed in water,
To this, 1.2 g of acidic sodium sulfite was added at 80 ° C. with stirring and reacted for 1 hour to introduce a sulfonic acid group,
A magnetic recording medium was obtained by the same operation as in Example 1 using the one washed with water and dried.

<Performance Evaluation> In order to examine the performance of the magnetic recording media obtained in the examples and comparative examples, coating gloss and output characteristics were measured. Output characteristics (dB)
Is a value obtained by recording a signal of 4.7 MHz on the magnetic recording medium, measuring the reproduction output, and setting the magnetic recording medium of Comparative Example 1 to 0.0 dB. Table 1 shows the results.

[0051]

[Table 1]

[0052]

As described above in detail, in the method for producing a magnetic recording medium of the present invention in which the introduction of a sulfonic acid group into an epoxy group-containing binder is carried out when preparing a magnetic coating material, the dispersibility of magnetic powder is improved. Will be improved. Therefore, the magnetic recording medium manufactured by the method of the present invention has excellent output characteristics.

Claims (5)

[Claims] 1. A mixture containing magnetic powder, an epoxy group-containing binder and a solvent is kneaded under pressure to form a kneaded product, and the kneaded product is diluted with a solvent to prepare a magnetic paint, and the magnetic paint is used as a support. In a method for producing a magnetic recording medium, which comprises a step of forming a magnetic layer by coating on the magnetic recording medium, an acidic sulfite is added to the mixture immediately before the mixture is kneaded under pressure. Production method. 2. The binder has an epoxy group of 0.1 me.
The method for producing a magnetic recording medium according to claim 1, which is a vinyl chloride-modified resin or a polyurethane resin containing q / g or more. 3. The magnetic powder 10 containing the acidic sulfite.
The method for producing a magnetic recording medium according to claim 1, wherein 0.01 to 1.0 part by weight is added to 0 part by weight. 4. The method for producing a magnetic recording medium according to claim 1, wherein the kneaded material has a solid content of 70% or more. 5. The BET surface area of the magnetic powder is 40 m ^2.
/ G or more, The manufacturing method of the magnetic recording medium in any one of Claims 1-4.