JPH1131322A - Production of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a medium which has excellent electromagnetic conversion characteristics and is capable of attaining a high recording density without causing the degradation in a product yield by executing a calender treatment of a magnetic layer after the formation of a back-coating layer. SOLUTION: The magnetic recording medium 1 includes a nonmagnetic base 2, the magnetic layer 3 which is disposed on one surface side of this base and contains magnetic material powder and binder and a back-coating layer 4 which is disposed on the other surface side of the base 2. The thickness of the base 2 is specified to <=5.5 μm. The back-coating layer 4 is formed by applying a back-coating material on the opposite surface of the base 2 and drying this coating film prior to the calender treatment of the magnetic layer 3. The calender treatment of the magnetic layer 3 is executed after the formation of the back-coating layer 4. As a result, the generation of wrinkles and the flawing of calender rolls are effectively prevented at the treatment of the calender. Consequently, the magnetic recording medium having the good surface property and high output is obtd.

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 having excellent electromagnetic conversion characteristics, and more particularly to a method for manufacturing a magnetic recording medium which is thin and can achieve a high recording capacity.

[0002]

2. Description of the Related Art In recent years,
The demand for higher recording capacity for magnetic recording media for data storage for computers is rapidly increasing. Methods for increasing the recording capacity include a method of increasing the recording density of the magnetic recording medium and a method of increasing the recording capacity by increasing the area of the recording layer of the magnetic recording medium. As the former method, a method of using a ferromagnetic powder having a high coercive force and a small particle size in a coating type magnetic recording medium, or a method of increasing the density of the ferromagnetic powder by reducing the amount of a binder in the magnetic paint. And so on. In the latter method, for example, in the case of a type in which a tape-shaped medium is stored in a cassette like a magnetic tape, the recording capacity is increased by increasing the amount of tape that can be stored by reducing the thickness of the tape. A method is conceivable.

However, if the method of reducing the particle size of the ferromagnetic powder is used to increase the recording density, it is difficult to satisfactorily disperse the ferromagnetic powder in the magnetic paint. There is currently a limit to making it smaller. In addition, the method of relatively increasing the amount of ferromagnetic powder by reducing the amount of binder has a high possibility of causing a problem in terms of durability since it affects the strength of the magnetic layer.

[0004] Further, when the method of reducing the thickness of the medium is used to increase the recording capacity, it is necessary to reduce the thickness of the base film. In this case, since a coating film of an appropriate thickness is provided on a thin base film,
An appropriate strength is required for the base film. Therefore, the present inventors have provided a thin film of a metal or semi-metal on one or both sides of a thin base film of a specific thickness by vacuum film formation, and applied a magnetic paint thereon. High coating type magnetic recording media have been proposed (Japanese Patent Application Nos. 9-78624, 9-78625 and 9-142706).

The present inventors have conducted detailed studies on a method of manufacturing a coating type magnetic recording medium using a thin base film provided with the above thin film in order to further enhance the performance and product yield.

[0006] Japanese Patent Application Laid-Open Nos. 3-19609 and 4-49169 have different purposes from the proposals of the present inventors. However, a vacuum evaporation film is provided on a base film, and a coating mold is formed thereon. A magnetic recording medium provided with a magnetic layer is disclosed. However, in these publications, there is no specific description of a manufacturing process other than providing a magnetic layer by applying a magnetic paint after providing a vacuum deposited film on a base film.

In general, a coating type magnetic recording medium is manufactured by applying a magnetic paint on a base film, drying and calendering in this order, and thereafter providing a back coat layer. Using the thin base film provided with the above thin film and according to this general manufacturing method, the above publications (JP-A-3-19609, JP-A-4-49169)
In the case of manufacturing the magnetic recording medium described in Japanese Patent Application Laid-Open No. H11-209, wrinkles may occur on a guide roll at the exit of a drying furnace during coating of a magnetic layer, a thin film may be peeled off during a calendar process, and the resin roll may be damaged. is there. As a result, the output tends to deteriorate due to the lowering of the surface properties of the magnetic recording medium, and eventually, the product yield decreases.

Accordingly, it is an object of the present invention to provide a method of manufacturing a magnetic recording medium which is excellent in electromagnetic conversion characteristics and can achieve a high recording capacity while being thin without causing a reduction in product yield. .

[0009]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a method of manufacturing a coating type magnetic recording medium using a thin support having a thin film formed by vacuum film formation has not been known. It has been found that it is effective to perform the calendering step performed before the formation of the backcoat layer after the formation of the backcoat layer.

[0010] The present invention has been made based on the above-mentioned findings, and a magnetic substance powder is bonded to one surface of a support having a thickness of 5.5 μm or less and having a thin film formed by vacuum film formation on at least one surface. A magnetic recording medium having a magnetic layer containing an agent and a back coat layer on the opposite side, wherein the calendering of the magnetic layer is performed after the formation of the back coat layer. The object has been achieved by providing a method for manufacturing a magnetic recording medium characterized by the above-mentioned.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of a method of manufacturing a magnetic recording medium according to the present invention will be described with reference to an example of manufacturing a magnetic recording medium shown in FIG.

First, the structure of a magnetic recording medium obtained by the method of manufacturing a magnetic recording medium according to the present invention will be described with reference to FIG. 1. A magnetic recording medium 1 shown in FIG. A magnetic layer 3 is provided on one surface of the support 2 and contains a magnetic substance powder and a binder, and a back coat layer 4 is provided on the other surface of the support 2.
Further, a thin film 5 formed by vacuum film formation is provided between the support 2 and the magnetic layer 3.

The materials constituting the support 2 include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate, and polyethylene bisphenoxycarboxylate; polyolefins such as polyethylene and polypropylene; Non-magnetic materials such as cellulose derivatives such as cellulose acetate butyrate and cellulose acetate propionate; vinyl resins such as polyvinyl chloride and polyvinylidene chloride; and plastic materials such as polyamide and polycarbonate. Polyester (PE
T, PEN, etc.). You. The support composed of these materials may be subjected to a uniaxial or biaxial stretching treatment, a corona discharge treatment, or the like, as necessary.

The thickness of the support 2 is 5.5 μm or less, preferably 5.3 μm or less, from the viewpoint of obtaining a thin magnetic recording medium. When such a thin support is used, wrinkles are likely to occur during the manufacturing process of the magnetic recording medium. However, according to the manufacturing method of the present invention, such a problem is effectively prevented. The lower limit of the thickness is preferably 1.5 μm, more preferably 3.0 μm, as a practical value of the magnetic recording medium from the viewpoint of film strength. When such a thin support is used, its center line average roughness Ra is 1.5 to 7.0 nm (particularly 2.0 to 5.0 nm).
nm, especially 2.5 to 4.0 nm) is preferable in terms of the surface properties and running properties of the magnetic recording medium.

The magnetic layer 3 contains a magnetic powder and a binder as described above. As the magnetic powder,
What is usually used for magnetic recording media, for example, ferromagnetic metal oxide powder, ferromagnetic metal powder, ferromagnetic hexagonal ferrite powder and the like can be used without any particular limitation. To obtain high-density recording, a needle-like ferromagnetic metal powder or a plate-like ferromagnetic hexagonal ferrite powder is preferable.

The following are specific examples of the magnetic substance powder. As the ferromagnetic metal powder, an alloy or a simple metal powder having a shape such as a needle shape, a spindle shape, a plate shape or a spherical shape, for example, a metal content of 50% by weight is used.
At least 60% by weight of the metal content is at least 1%.
Types of ferromagnetic metals or alloys (eg, Fe, Co, N
i, Fe-Co, Fe-Ni, Co-Ni, Co-Ni
-Fe, Co-Ni-P, Co-Ni-Fe-B, Fe
-Ni-Zn, Fe-Co-Cr). In this case, other components (eg, Al, Si, S, Sc, Ti, V, C
r, Mn, Cu, Zn, Y, Mo, Rh, Pd, Ag,
Sn, Sb, Te, Ba, Ta, W, Re, Au, H
g, Pb, Bi, La, Ce, Pr, Nd, Sm, E
u, Gd, Tb, Dy, Ho, Yb, Lu, B, P). Further, a powder of iron nitride or an alloy containing hydroxide or oxide, or a mixture of these materials may be used. The other components may be contained in an alloy state, or may be localized in the form of an oxide or a hydroxide in the vicinity of the surface of the core metal component. As the ferromagnetic hexagonal ferrite powder, barium ferrite and strontium ferrite in the form of a small flat plate, and a part of their Fe atoms are Ti, Co, N
Examples include magnetic powders substituted with atoms such as i, Zn, and V. The ferromagnetic hexagonal ferrite powder may contain a rare earth element or a transition metal element as necessary.

The binder contained in the magnetic layer 3 can be used without limitation as long as it is a known binder used for a magnetic recording medium. For example, a thermoplastic resin, a thermosetting resin, a reactive resin, a mixture thereof and the like can be mentioned. Specifically, a copolymer of vinyl chloride and its modified product, a copolymer of acrylic acid, methacrylic acid and its ester, a copolymer of acrylonitrile (rubber-based resin),
Polyester resin, polyurethane resin, epoxy resin,
A fibrous resin, a polyamide resin, or the like can be used. The number average molecular weight of the binder is 2,000 to 200,
000 is preferred. In order to improve dispersibility, the above-mentioned binders may have a hydroxyl group, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a nitro group or a nitrate ester group, an acetyl group, a sulfate ester group or a salt thereof. And a polarizable functional group (a so-called polar group) such as an epoxy group, a nitrile group, a carbonyl group, an amino group, an alkylamino group, an alkylammonium group, a betaine structure such as sulfobetaine and carbobetaine.

The magnetic layer 3 is formed by applying a magnetic paint obtained by dispersing and dissolving the magnetic powder, the binder, and various additives used as necessary in a solvent. As the solvent, a ketone solvent, an ester solvent, an ether solvent, an aromatic hydrocarbon solvent, a chlorinated hydrocarbon solvent, or the like can be appropriately selected and used. Also, various solvents described in JP-A-57-162128 can be used. As the additive, an antistatic agent, a lubricant, an abrasive, a curing agent, and the like can be appropriately selected and used. Also, Japanese Patent Application Laid-Open No. 57-162128
Various additives described in Japanese Patent Application Laid-Open (JP-A) No. 6-208 can also be used.

The thickness of the magnetic layer 3 is set to 0.04 to 2.5 μm in order to increase the capacity by accommodating as many magnetic tapes as possible in a unit volume while maintaining the smoothness of the surface.
Is preferably, and more preferably, 0.07 to 1.8 μm.

The back coat layer 4 is formed by applying a commonly known back coat paint containing an inorganic powder and a binder. The components contained in the backcoat paint include, in addition to the inorganic powder and the binder, an antistatic agent, a lubricant, an abrasive, an organic powder, a curing agent, and the like. As these components, the same components as those contained in the magnetic paint are used. The thickness of the back coat layer 4 is well-balanced with the thickness of the magnetic layer 3 and is preferably a thickness that does not cause curling or cupping. Specifically, the thickness is preferably 0.05 to 2.5 μm, ~
1.8 μm is more preferable, and 0.2 to 1.5 μm is most preferable.

Between the support 2 and the magnetic layer 3,
A thin film 5 formed by a vacuum film forming method is provided. By providing the thin film 5, even when the thickness of the support 2 is reduced, the rigidity of the magnetic recording medium can be prevented from lowering. As a result, although the magnetic recording medium is thin, Instead, a high output can be obtained in a wide range from a low band to a high band.

The material for forming the thin film 5 is not particularly limited as long as it can optimize the rigidity of the magnetic recording medium. From the point of view, it is preferable to be formed from a metal or metalloid, an alloy thereof, or a composite thereof. The term "composite" as used herein refers to a mixture of a metal, a metalloid, an alloy thereof, and an oxide, nitride, carbide, or the like thereof.

As the metal or metalloid forming the thin film layer 5 or an alloy thereof, Fe, Ni, Co, T
i, W, Mo, Al, Mn, Cr, Cu, Zn, Zr,
It is preferable to use at least one kind of metal or metalloid selected from the group consisting of Sn, B, Si, Ge and Sb, or an alloy or a composite thereof, and particularly preferably used are Co, Cu, Al, A simple metal such as Ti and Ni, a simple metal such as Si and Ge, or an alloy thereof, and particularly preferably used are a simple metal such as Co, Ti, Ni and Cu, and a semi-metal such as Si and Ge. It is a simple substance of a metal or an alloy thereof. Forming the thin film 5 from these materials has the advantage that the rigidity, strength and hardness of the magnetic recording medium can be further optimized.

The thickness of the thin film 5 is related to the overall thickness of the magnetic recording medium and the thickness of the magnetic layer 3, and is preferably 0.05 to 1 μm from the viewpoint that appropriate rigidity can be imparted to the magnetic recording medium.
m, more preferably 0.08 to 0.3 μm.

Although the overall thickness of the magnetic recording medium 1 shown in FIG. 1 is generally 3 to 15 μm, as will be described later, the manufacturing method of the present invention tends to cause wrinkles during the manufacturing process. It is particularly effective for producing a thin magnetic recording medium having a thickness of 3 to 7 μm (especially 4.2 to 6.8 μm, especially 4.5 to 6.5 μm).

Next, a method of manufacturing the magnetic recording medium 1 shown in FIG. 1 will be described. First, a thin film 5 having a predetermined thickness is formed on one surface of the support 2 by a vacuum film forming method. By using the vacuum film formation method, the corrosion resistance of the formed thin film 5 is extremely improved, and a magnetic recording medium having excellent storage durability can be obtained. Examples of such a vacuum film forming method include vacuum deposition, sputtering, and ion plating.
Is appropriately selected and used in accordance with the material for forming

Next, using a coater head, the thin film 5
A magnetic paint is applied on the substrate to form a coating film of the magnetic paint. Then, a magnetic field orientation treatment is performed while the coating film is in an undried state to orient the magnetic substance powder in the coating film. When the magnetic recording medium 1 is a magnetic tape, for example, the magnetic field orientation processing is performed in a direction parallel to the coating surface of the magnetic paint by about 50%.
0 Oe or more, preferably about 1,000 to 10,000 O
e, a method of applying a magnetic field of 1,000 to 10,000 to 10,000.
It can be performed by a method of passing through an Oe solenoid or the like.

Next, the above-mentioned coating film is dried, and the magnetic layer 3 is dried.
To form This drying can be performed, for example, by using a drying furnace and supplying a heated gas. 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.

Thus, in the present invention, prior to the calendar treatment of the magnetic layer 3, a back coat paint is applied to the surface on the opposite side of the support 2 to form a coating film of the back coat paint. The back coat layer 4 is formed by drying the coating film. Then, after the formation of the back coat layer 4,
The calendar processing of the magnetic layer 3 is performed. As described above, by performing the calendering process on the magnetic layer 3 after the formation of the back coat layer 4, wrinkles are generated during the calendering process, and the calendar roll is effectively prevented from being damaged. As a result, a magnetic recording medium having good surface properties and high output can be obtained, as is clear from the examples described later. In particular, the occurrence of the wrinkles and the damage of the calendar roll are remarkable when the thickness of the support or the total thickness of the magnetic recording medium is small. However, according to the manufacturing method of the present invention, such a case is not observed. However, it is possible to effectively prevent wrinkles and calendar rolls from being damaged. That is, the production method of the present invention provides a thin support, for example, 5.5 μm or less (in particular,
5.3 μm or less) or a thin magnetic recording medium, for example, having a total thickness of 3 to 7 μm.
m (especially 4.2 to 6.8 μm, especially 4.5 to 6.5
μm) is very effective when manufacturing a magnetic recording medium.

The above-mentioned calendering treatment can be performed by a super calender method or the like in which a metal roll is passed between a cotton roll or a synthetic resin roll, or between two metal rolls. As the conditions for the calendering treatment, the linear pressure is preferably 100 to 350 kg / cm, particularly preferably 20 to 350 kg / cm.
0 to 300 kg / cm, and the temperature is preferably 70 to 300 kg / cm.
120 ° C, particularly preferably 85 to 110 ° C.

By the above-described calendering process, the center line average roughness Ra of the magnetic layer 3 becomes preferably 3.0 to 6.0 nm, particularly 3.5 to 4.8 nm, thereby increasing the output of the magnetic recording medium. . The center line average roughness Ra of the back coat layer is preferably 5 to 12 nm, particularly 6 to 9 n.
m.

After calendering, for example, at 40 to 80 ° C.
Aging is performed under the condition for 6 to 100 hours to complete the curing of the magnetic layer 3, the back coat layer 4, and the like. Next, for example, when a magnetic tape is obtained, it is cut into a predetermined width, burnished with a polishing tape, and subsequently cleaned with a nonwoven fabric or the like.

The method of manufacturing a magnetic recording medium according to the present invention has been described based on the preferred embodiment. However, the present invention is not limited to the above embodiment, and various methods can be used without departing from the spirit of the present invention. Changes are possible. For example, in the above embodiment, the magnetic layer is formed before the formation of the back coat layer. Alternatively, the magnetic layer may be formed after the formation of the back coat layer, or the back coat layer and the magnetic layer may be formed. May be formed simultaneously. Further, as the magnetic recording medium manufactured by the manufacturing method of the present invention,
1, the thin film 5 is formed on the back coat layer 4 side as shown in FIG. 2, or the thin film 5 is formed on both the magnetic layer 3 side and the back coat layer 4 side as shown in FIG. And the like are also included. Also, FIG.
In the magnetic recording medium having the configuration shown in FIG. 3, a non-magnetic or magnetic intermediate layer may be formed between the magnetic layer 3 and the thin film 5. The intermediate layer preferably has a thickness of 0.5 to 2.0 μm, particularly preferably 0.7 to 1.8 μm. When the intermediate layer is magnetic, Fe or an alloy mainly containing Fe, hexagonal Ba ferrite, or the like can be used as the magnetic powder. As the intermediate layer, the same non-magnetic powder, binder, solvent, and the like as those used in the above-described magnetic layer 3 can be used. Further, in the magnetic recording medium having the configuration shown in FIGS. 1 to 3, even if a layer mainly composed of carbon is formed on the surface of the thin film 5 (in FIG. 3, at least the surface of any one of the thin films 5). Good. In addition, the manufacturing method of the present invention provides a magnetic recording medium having a small overall thickness, such as 8
mm video tape, DDS tape, DVC tape, DL
It is particularly suitable for the production of magnetic tapes such as T tapes.

[0034]

The following examples illustrate the effectiveness of the present invention. However, the scope of the present invention is not limited to such an embodiment.

Example 1 A magnetic paint and a backcoat paint having the following composition were prepared by the following method.

Magnetic paint , 100 parts by weight of ferromagnetic powder mainly composed of iron [Coercive force: 1750 Oe, saturation magnetization: 125 emu / g, average major axis length: 0.16 μm] ・ Binder (MR-110) 11 weight Part [trade name of vinyl chloride copolymer resin manufactured by Zeon Corporation] 9 parts by weight of binder (UR8300) [trade name of sulfonic acid group-containing polyurethane resin manufactured by Toyobo Co., Ltd.]-Polishing 8 parts by weight [α-alumina, average primary particle size: 0.10 μm, Mohs hardness: 9] ・ Antistatic agent 1 part by weight [carbon black, average primary particle size: 0.02 μm] ・ Lubricant (myristic acid) 4 parts by weight (butyl stearate) 2 parts by weight Curing agent (Coronate L) 4 parts by weight [Product name of isocyanate-based curing agent manufactured by Nippon Polyurethane Industry Co., Ltd.] Solvent (methyl ethyl ketone / 300 parts by weight (toluene / cyclohexanone) (mixing weight ratio 1: 1: 1)

Preparation of Magnetic Paint A ferromagnetic powder, an abrasive, an antistatic agent, and a binder were adjusted with a solvent so that the solid content concentration became 83% by weight, and mixed with a powder mixer to form a mixture. Next, the mixture is
After dispersing with a solidifier (extrusion device for continuous twin-screw kneading) to which strong shearing can be added, the solid content concentration is reduced to 35 by the solvent.
%, And further dispersed by a milling device (vertical sand mill) equipped with titania beads having a particle size of 0.8 mm to obtain a kneaded product. Then, after adding a lubricant to the kneaded material, the solid content concentration is adjusted with a solvent so as to be 30% by weight, which is a concentration necessary for applying the paint, and the mixture is stirred for 1 hour with a stirrer. Filtration was performed using a filtration filter having a filtration accuracy of 1 μm. Thereafter, the filtered kneaded material was previously stirred with a stirrer, and a hardening agent was added to prepare a magnetic paint.

(B) Backcoat paint 40 parts by weight of carbon black (average primary particle diameter: 17 nm) 50 parts by weight of polyurethane resin [Nipporan 2301 (trade name)] [Nippon Polyurethane Industry Co., Ltd.] Nitrocellulose 20 Parts by weight Curing agent (Coronate L) 2 parts by weight [Product name of isocyanate-based curing agent manufactured by Nippon Polyurethane Industry Co., Ltd.] Solvent (methyl ethyl ketone / toluene / cyclohexanone) 420 parts by weight (mixing weight ratio 1: 1: 1) )

Preparation of backcoat paint A predetermined amount of a binder and a solvent are added to carbon black,
This is kneaded in a kneader, a pressure kneader, or the like, diluted with an appropriate amount of a solvent, dispersed by a sand mill or the like, and then the solvent is added so that the solid content concentration becomes 16% by weight.
After stirring for a minute, filtration was performed using a filtration filter having an absolute filtration accuracy of 1 micron. Thereafter, a curing agent was added to the filtered kneaded material to prepare a back coat paint.

Next, a magnetic tape as a magnetic recording medium was manufactured by performing the following steps (1) to (4).

(1) Formation of thin film and back coat layer Non-magnetic support (5.2 μm thick, center line average roughness Ra
A 0.1 μm thick Co thin film was formed on both sides of a (4.1 nm PET film) by a vacuum evaporation method.
Coating speed of 100 m / min on the surface of one Co thin film
Then, the back coat paint prepared as described above was applied so as to have a dry film thickness of 0.5 μm, dried at 30 to 120 ° C. to form a back coat layer, and then wound up.

(2) Formation of Magnetic Layer The magnetic coating material prepared as described above is stored in a coating material supply device, and is quantitatively supplied from the coating material supply device using a high-performance gear pump. (Die). Then, the magnetic coating material is sent from the coating device, and filtered using a filtering device having an absolute filtration accuracy of 1 micron installed in the coating solution sending line immediately before coating,
The coating is sent at a coating speed of 100 m / min to the surface on the opposite side of the web on which the back coat layer has been formed in the step (1). Then, a magnetic paint is applied so that the dry film thickness becomes 0.6 μm, and while the coating film is in a wet state, orientation treatment is performed using a permanent magnet having a magnetic flux density of 5000 Gauss, and further a magnetic flux density of 5000 Gauss. The orientation fixing process was performed using a solenoid electromagnet and a dryer in a coating line in which the temperature of hot air was adjusted to 30 ° C. Thereafter, in order to reduce the residual solvent in the magnetic recording medium to a specified value (weight of the magnetic layer: 2000 ppm or less),
After performing a drying treatment with a dryer in a coating line in which the hot air temperature was adjusted to 30 to 120 ° C., the film was wound up.

(3) Calendering After the dustproofing and antistatic treatments, the surface properties of the magnetic recording medium are adjusted to a specified value (center line roughness Ra is preferably 4n).
m or less), a calendar process (mirror finishing process) was performed. The calendering was performed using a 7-stage super calender at a line speed of 100 m / min, a roll linear pressure of 300 kg / cm, and a roll surface temperature of 100 ° C. The dust removal treatment and the antistatic treatment were performed immediately before the calendar treatment.

(4) Slit and assembly process The obtained raw material was aged under predetermined conditions, and then slit to 3.8 mm according to the drive to obtain a pancake. Using this pancake, a magnetic tape as a magnetic recording medium having a total length of 120 m was obtained. This magnetic tape was loaded into a tape cassette to obtain a DAT tape cassette.

Example 2 Example 1 was the same as Example 1 except that a PET film having a thickness of 5.1 μm and a center line average roughness Ra of 4.1 nm was used as the support, and a Co thin film was formed only on the magnetic layer side. In the same manner as in Example 1, a magnetic tape was obtained.

Example 3 A magnetic tape was obtained in the same manner as in Example 1, except that the back coat layer was formed after the formation of the magnetic layer, and then the calendar treatment was performed.

Example 4 A magnetic coating material for an intermediate layer having the following composition was prepared, and an intermediate layer was placed between the magnetic layer and the thin film in Example 1 by a wet-on-wet simultaneous multilayer method (for the magnetic layer and the intermediate layer). A magnetic tape was obtained in the same manner as in Example 1 except that a PET film having a thickness of 5.0 μm was used as a support. The thickness of the magnetic layer in this magnetic tape was 0.1 μm, and the thickness of the intermediate layer was 1.2 μm.

100 parts by weight of magnetic paint / non-magnetic powder (α-iron oxide: needle-like, average major axis length 0.18 μm) for the intermediate layer 12 parts by weight of abrasive [α-alumina, average primary particle diameter: 0.1 10 μm, Mohs hardness: 9] 2 parts by weight of antistatic agent (carbon black: average primary particle size: 0.02 μm) 11 parts by weight of binder (MR-110) [vinyl chloride resin manufactured by Zeon Corporation] Brand name of polymer resin] 9 parts by weight of binder (UR8300) [brand name of sulfonic acid group-containing polyurethane resin manufactured by Toyobo Co., Ltd.] 2 parts by weight of lubricant (myristic acid) (butyl stearate) 2 parts by weight Curing agent (Coronate L) 4 parts by weight [Trade name of isocyanate-based curing agent manufactured by Nippon Polyurethane Industry Co., Ltd.] Solvent (methyl ethyl ketone / toluene / cyclohexanone) 300 weight Parts (weight ratio 1: 1: 1)

Example 5 A magnetic tape was obtained in the same manner as in Example 1 except that the back coat layer and the magnetic layer were simultaneously formed.

Comparative Example 1 A magnetic tape was obtained in the same manner as in Example 1, except that a calender treatment was performed after the formation of the magnetic layer, and then a back coat layer was formed.

Comparative Example 2 A magnetic tape was obtained in the same manner as in Example 2, except that the calender treatment was performed after the formation of the magnetic layer, and then the back coat layer was formed.

[Comparative Example 3] In Example 1, P having a thickness of 5.1 μm and a center line average roughness Ra of 10 nm was used as the support.
A magnetic tape was obtained in the same manner as in Example 1 except that the ET film was used, a calendar process was performed after the formation of the magnetic layer, and then a back coat layer was formed.

REFERENCE EXAMPLE In Example 1, PET having a thickness of 9 μm and a center line average roughness Ra of 4.1 nm was used as the support.
A magnetic tape was obtained in the same manner as in Example 1 except that a film was used, a calendar process was performed after the formation of the magnetic layer, and then a back coat layer was formed.

[Evaluation of Performance] With respect to the magnetic tapes obtained in Examples and Comparative Examples, the center line average roughness Ra of the magnetic layer and the back coat layer and the output of the magnetic tape were measured, and wrinkles occurred during the manufacturing process. Was observed.
Table 1 shows the results.

<Center Line Average Roughness Ra (nm)> Using Surfcom 553A (manufactured by Tokyo Seimitsu Co., Ltd.), a needle diameter of 2 μm was used.
Load 70mg, magnification 200,000, cutoff 0.08
mm, and the center line average roughness Ra (nm) was determined from the following equation (i).

[0056]

(Equation 1)

<Output of Magnetic Tape> The obtained magnetic tape was loaded into a DAT tape cassette, and this was inserted into Media.
Logic "Tape Evaluator Mo"
del 4500 "(trade name). Then, a 4.7 MHz signal is recorded on the magnetic tape,
The output (reproduction output) when this was reproduced was measured, and the output was obtained based on the reference example. The recording wavelength at 4.7 MHz was 0.07 μm.

<Presence or absence of wrinkles> Observation was visually made at the final exit of the calendar nip. If wrinkles were observed even for a moment, it was determined that "wrinkles were present". No occurrence ".

[0059]

[Table 1]

As is evident from the results shown in Table 1, the magnetic tape of the example manufactured using a thin support and calendering the magnetic layer after the formation of the back coat layer is a thick support. Like the magnetic tape of the reference example in which the back coat layer was formed after the magnetic layer was calendered, wrinkles did not occur in the manufacturing process, so a thin support was used and the back coat layer was formed after calendering. It can be seen that the surface properties are better and the output is higher than the magnetic tape of the comparative example manufactured by the above method.

[0061]

As described above, according to the method for manufacturing a magnetic recording medium of the present invention, wrinkles are generated and the roll is damaged in the manufacturing process even when a thin support is used. Is prevented. Therefore, a decrease in the surface properties of the magnetic recording medium is prevented, and a magnetic recording medium having excellent electromagnetic conversion characteristics can be manufactured without causing a decrease in product yield. Further, according to the method for manufacturing a magnetic recording medium of the present invention, a magnetic recording medium that can achieve a high recording capacity while being thin can be manufactured without lowering the product yield.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a structure of an example of a magnetic recording medium manufactured by a method for manufacturing a magnetic recording medium according to the present invention.

FIG. 2 is a schematic view showing the structure of another example of a magnetic recording medium manufactured by the method for manufacturing a magnetic recording medium of the present invention.

FIG. 3 is a schematic view showing the structure of another example of the magnetic recording medium manufactured by the method for manufacturing a magnetic recording medium of the present invention.

[Explanation of symbols]

 Reference Signs List 1 magnetic recording medium 2 support 3 magnetic layer 4 back coat layer 5 thin film

Continued on the front page (72) Inventor Akira Ishikawa 2606 Akabane, Kaimachi, Haga-gun, Tochigi Pref.

Claims (7)

[Claims] 1. A support having a thickness of 5.5 μm or less having a thin film formed by vacuum film formation on at least one surface and having, on one surface, a magnetic layer containing a magnetic powder and a binder, and A method for manufacturing a magnetic recording medium having a back coat layer on the opposite surface, wherein the magnetic layer is calendered after the formation of the back coat layer. 2. The method according to claim 1, wherein the magnetic layer is formed before the formation of the back coat layer. 3. The method for manufacturing a magnetic recording medium according to claim 1, wherein the magnetic layer is formed after the formation of the back coat layer. 4. The method according to claim 1, wherein said back coat layer and said magnetic layer are formed simultaneously. 5. The total thickness of the magnetic recording medium is 3-7.
The method for producing a magnetic recording medium according to claim 1, wherein the thickness is μm. 6. The method according to claim 1, wherein the thin film is formed on both surfaces of the support. 7. The method for manufacturing a magnetic recording medium according to claim 1, wherein the thin film is formed between the support and the magnetic layer.