JP2001084584A - Production of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To embody a process for producing a magnetic recording medium which has magnetic layers excellent in the degree of orientation of magnetic powder and has excellent electromagnetic transducing characteristics even when the magnetic layers are formed as thin films of <=0.3 μm. SOLUTION: A coating material containing a radiation curing type binder resin for forming a lower layer nonmagnetic layer is applied on one surface of a nonmagnetic base and is subjected to drying, smoothing treatment and radiation curing. Next, a stage for applying the magnetic coating material for forming the upper layer magnetic layer on the formed lower layer nonmagnetic layer and a stage for applying the coating material for a back- coating layer on the other surface of the nonmagnetic base are successively executed. The process for producing the magnetic recording medium includes execution of a magnetic field orientation treatment on the previously applied magnetic coating material which is in a wet state by acting a magnetic field thereon while the magnetic coating material is undried yet at the time of application of the coating material for forming the back-coating layer.

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 used for recording and reproducing video, audio, data, and the like. More specifically, the present invention relates to a method for producing a magnetic recording medium having a magnetic layer having an excellent degree of orientation of magnetic powder and having excellent electromagnetic conversion characteristics even when the magnetic layer is thinned.

[0002]

2. Description of the Related Art Conventionally, in a magnetic recording medium having a magnetic layer on a non-magnetic support, a back coat layer is formed on the non-magnetic support surface opposite to the magnetic layer in order to improve the running property of the medium itself. Provision is being made. Although this back coat layer contributes to the improvement of running characteristics, it must be applied and dried separately from the magnetic layer to provide the back coat layer, which complicates the manufacturing process and directly affects the manufacturing cost. Exert. For this reason, the use of the back coat layer has been limited to high-grade products. Further, the back coat layer conventionally used has a main purpose of improving the runnability by including a pigment having a large particle size therein.

On the other hand, in response to recent demands for higher recording density of magnetic recording media, the magnetic layer is becoming more and more thinner, more filled, and more durable. Is becoming more advanced (high level).

In order to realize such a magnetic layer, proposals have conventionally been made such as forming the magnetic layer into a two-layer structure or providing an undercoat layer below the magnetic layer. Further, in these manufacturing methods, a lower-side layer is dried once, and then an upper magnetic layer is provided by a wet-on-dry coating method, or a lower layer and an upper magnetic layer are dried. Studies have also been made on a wet-on-wet coating method in which both are simultaneously provided in a wet state.

As a related prior art, for example, JP-A-53-92110 discloses a manufacturing method in which a magnetic field is applied to a two-layer coating film. JP-A-62-21
No. 2933 discloses a method for producing a magnetic recording medium in which at least two magnetic layers are simultaneously coated in a multi-layer manner, and a magnetic field is applied while the both layers are not dried to align the magnetic powder in the magnetic layers. I have. JP-B 5-59490 discloses that a magnetic layer is provided together with a non-magnetic undercoat layer by a simultaneous multilayer coating method.
There has been proposed a method for manufacturing a magnetic recording medium in which a magnetic field is applied while both layers are not dried to orient magnetic powder in the magnetic layer. Japanese Patent Application Laid-Open No. Hei 5-81667 discloses a nozzle for pre-coating so that a pre-coated magnetic paint and a post-coated magnetic paint in which pure iron or metal alloy magnetic particles are dispersed can be provided separately or integrally in a wet state. In addition, a method for manufacturing a magnetic recording medium is disclosed in which each paint is applied in a multi-layered manner using a post-coating nozzle and then subjected to a surface smoothing treatment. Further, Japanese Patent Application Laid-Open No. 7-176047 discloses a method comprising simultaneously applying a magnetic layer on both surfaces of a support, or applying a magnetic layer on the remaining surface after being coated on one side and not yet dried. A method for manufacturing a recording medium has been proposed. The purpose of this is to make the properties of the double-sided magnetic layers uniform.

[0006] Regarding the radiation-curable lower non-magnetic layer, Japanese Patent Publication No. 30221/1990 discloses that in a magnetic recording medium in which a non-magnetic undercoat layer is applied to a support and then a magnetic layer is formed, The layer is (A) a compound having a molecular weight of 5,000 or more, preferably 8000 or more, having two or more unsaturated double bonds curable by radiation, and (B) one unsaturated double bond curable by radiation. Having a molecular weight of 400 or more and less than 5000, preferably 600
(C) a compound having at least one unsaturated double bond curable by radiation and having a molecular weight of less than 400, and at least two or more selected from the above (A), (B) and (C). A magnetic recording medium formed by radiation irradiation using a radiation-curable paint contained therein. Is disclosed. However, there is almost no description about the magnetic layer in this publication, and it is difficult to obtain a magnetic recording medium having sufficient coating film properties.

Japanese Patent Application Laid-Open No. 9-185822 discloses that a non-ferromagnetic undercoat layer formed on one surface of a non-magnetic support and an upper magnetic layer formed on the non-ferromagnetic undercoat layer. A method for producing a magnetic recording medium comprising a layer and a backcoat layer on the other side of the non-magnetic support, the method comprising forming a non-ferromagnetic undercoat layer on one side of the non-magnetic support. Applying a magnetic paint for forming an upper magnetic layer on a paint for forming a non-ferromagnetic undercoat layer applied on the non-magnetic support; and Applying a coating for forming a back coat layer on the other surface of the non-ferromagnetic undercoat layer, a coating for forming the upper magnetic layer, and a magnetic coating for forming the upper magnetic layer. After the paint is applied, the magnetic paint for forming the upper magnetic layer is not Applying a magnetic field during drying, and performing a magnetic field orientation treatment, wherein the magnetic paint for forming the upper magnetic layer and the paint for forming the back coat layer are both applied when both paints are applied. A method for producing a magnetic recording medium, which is kept in an undried state. " However, the description regarding the hardening of the non-ferromagnetic layer coating film is insufficient. In this case, the interface between the upper magnetic layer and the lower non-magnetic layer becomes non-uniform, causing output fluctuation.

[0008]

When a magnetic layer is coated on the lower non-magnetic layer, the thickness of the magnetic layer must be reduced even if the above-mentioned proposed coating methods are used. Because of the thinness of the magnetic layer, the drying speed of the magnetic layer coating increases (the solvent evaporates easily), and the coating dries immediately. There was a tendency that the degree of orientation of the magnetic powder did not increase.
Also, when the drying speed of the magnetic layer coating film is extremely fast, solvent traces that have flown off the coating film remain as porous on the coating film surface,
In some cases, there is a disadvantage that the desired filling and high durability of the magnetic layer cannot be achieved. In addition, the above-described manufacturing method has a problem that the interface between the upper magnetic layer and the lower non-magnetic layer becomes non-uniform. Further, there remains a problem of how to efficiently provide a back coat layer.

The present invention has been made in view of such circumstances. An object of the present invention is to obtain a magnetic layer having an excellent degree of orientation even if the thickness of the magnetic layer is reduced, and to further increase the filling of the thinned magnetic layer and to form a uniform upper magnetic layer. The present invention provides a method for manufacturing a magnetic recording medium capable of providing an interface with a lower / non-magnetic layer.

[0010]

Means for Solving the Problems In order to solve such problems, the present inventors have intensively studied. In a method for manufacturing a magnetic recording medium including an upper magnetic layer / a lower nonmagnetic layer,
If the thickness of the upper magnetic layer is 0.3 μm or less, the drying speed of the coating film increases, especially as the film thickness decreases, and the magnetic field orientation of the magnetic powder in the coating film does not work well. The phenomenon that the surface property of the film deteriorated was observed.

Therefore, when providing a thin upper magnetic coating film having a thickness of 0.3 μm or less, the magnetic coating film must be in an undried state (especially a wet state) while the magnetic coating is in a wet state. The orientation of the magnetic powder can be greatly improved by applying a magnetic field while the magnetic coating film is not dried while maintaining the wet state of the magnetic coating film so that the coating layer is present. Furthermore, the present inventors have found that the magnetic layer can be highly filled and have high durability, and have reached the present invention.

Further, a thin film magnetic layer having a thickness of 0.3 μm or less is easily affected by the surface of the lower non-magnetic layer. We have:
By subjecting the lower non-magnetic layer to radiation curing treatment, it is possible to prevent deformation of the non-magnetic layer coating film generated by the conventional heat curing treatment and to improve the uniformity of the interface between the upper magnetic layer and the lower non-magnetic layer. We have now found the present invention.

That is, the present invention provides a lower nonmagnetic layer containing a radiation-curable binder resin formed on one surface of a nonmagnetic support, and a film thickness formed on the lower nonmagnetic layer. A method for producing a magnetic recording medium having an upper magnetic layer of 0.3 μm or less and a back coat layer formed on the other surface of the non-magnetic support, comprising: Applying a coating containing a radiation-curable binder resin for forming the lower non-magnetic layer, performing drying, smoothing and radiation-curing steps, and then on the formed lower non-magnetic layer,
A step of applying a magnetic paint for forming the upper magnetic layer and a step of applying a paint for forming the backcoat layer on the other surface of the nonmagnetic support in order, and a step of applying the paint for forming the backcoat layer. In some cases, the magnetic paint for forming the upper magnetic layer, which has been previously applied, is in a wet state, and then the magnetic paint for forming the upper magnetic layer is subjected to a magnetic field while it is not dried to perform a magnetic field orientation treatment. A method for manufacturing a magnetic recording medium, which includes performing a step.

Further, the present invention provides a lower non-magnetic layer containing a radiation-curable binder resin formed on one surface of a non-magnetic support, and a film thickness formed on the lower non-magnetic layer. A method for producing a magnetic recording medium having an upper magnetic layer of 0.3 μm or less and a back coat layer formed on the other surface of the non-magnetic support, comprising:
A step of applying a coating containing a radiation-curable binder resin for forming a lower non-magnetic layer, drying, smoothing and radiation curing is performed, and then a back coat layer is formed on the other surface of the non-magnetic support. A step of applying a coating material for forming and a step of applying a magnetic coating material for forming an upper magnetic layer on the formed lower non-magnetic layer are sequentially performed, and the step of applying the magnetic coating material for forming the upper magnetic layer is performed. In the step of performing the magnetic field orientation treatment by applying a magnetic field while the magnetic paint for forming the upper magnetic layer is wet while the paint for forming the back coat layer that has been previously applied is in a wet state. And a method for manufacturing a magnetic recording medium.

Further, the present invention relates to a lower non-magnetic layer containing a radiation-curable binder resin formed on one surface of a non-magnetic support, and a film thickness formed on the lower non-magnetic layer. A method for producing a magnetic recording medium having an upper magnetic layer of 0.3 μm or less and a back coat layer formed on the other surface of the non-magnetic support, comprising:
A step of applying a coating containing a radiation-curable binder resin for forming a lower non-magnetic layer, drying, smoothing and radiation curing is performed, and then, on the formed lower non-magnetic layer, an upper magnetic layer The step of applying a magnetic paint for formation and the step of applying a paint for forming a backcoat layer on the other surface of the nonmagnetic support are performed simultaneously, and thereafter, the magnetic paint for forming the upper magnetic layer is not yet coated. This is a method for manufacturing a magnetic recording medium, which includes performing a magnetic field orientation process by applying a magnetic field during drying.

The solid content in the coating for forming the back coat layer is preferably 8 to 30% by weight.

As described above, in the present invention, while the magnetic coating film is in the undried state (particularly wet state), the backcoat layer in the undried state (particularly wet state) always exists, and Since the magnetic field is applied by applying a magnetic field while the magnetic coating film is not dried while maintaining the wet state, the degree of orientation of the magnetic powder can be significantly improved. High filling can be achieved. In addition, by curing the lower non-magnetic layer coating film by radiation, deformation of the lower non-magnetic layer coating film caused by tightening of the winding caused by the conventionally generally performed thermosetting treatment can be eliminated, and a uniform upper magnetic layer can be eliminated. / Lower non-magnetic layer interface can be created.

[0018]

Embodiments of the present invention will be described.
The magnetic recording medium that is the object of the present invention was formed on one surface of a nonmagnetic support, a lower nonmagnetic layer containing a radiation-curable binder resin, and formed on this lower nonmagnetic layer. It has an upper magnetic layer having a thickness of 0.3 μm or less, and a back coat layer formed on the other surface of the nonmagnetic support. When manufacturing such a magnetic recording medium, the main part of the present invention is to apply a lower non-magnetic layer forming paint, drying, surface smoothing treatment and radiation curing treatment, on this lower non-magnetic layer, Apply the upper magnetic layer forming paint, and make sure that the backcoat layer in the undried state (particularly wet state) is always present while the coating is in the undried state (particularly wet state). While maintaining the wet state of the magnetic film while applying a magnetic field while the magnetic coating film is not dried.

First, a coating material for forming a lower non-magnetic layer is applied on one surface of a non-magnetic support, dried, surface smoothed, and radiation-cured. The paint for forming the lower non-magnetic layer will be described later.

A non-magnetic support having a lower non-magnetic layer coated on one side is continuously conveyed to apply a magnetic coating for forming an upper magnetic layer and a coating for forming a back coat layer. . As an application pattern, (1) After applying a magnetic paint for forming an upper magnetic layer on the lower nonmagnetic layer, applying a paint for forming a backcoat layer on the other surface of the nonmagnetic support, (2) After applying a coating material for forming a backcoat layer on the other surface of the nonmagnetic support, applying a magnetic coating material for forming an upper magnetic layer on the lower nonmagnetic layer. (3) Lower magnetic layer In which the application of the magnetic paint for forming the upper magnetic layer on the substrate and the application of the paint for forming the backcoat layer on the other surface of the non-magnetic support are performed at the same time. After performing any of these application patterns, a magnetic field orientation treatment, a drying treatment, and a surface smoothing treatment are performed.

In any of the above-mentioned coating patterns (1) to (3), while the magnetic coating film of the upper magnetic layer is in an undried state (particularly in a wet state), it must be in an undried state (particularly in a wet state). Of the back coat layer.

In order to carry out the above-mentioned coating patterns (1) to (3), it is preferable to use a device constituted by combining known devices. For example, the following apparatus configuration example may be used to implement the application pattern (1). A feeding device provided with a feeding roll in which a lower nonmagnetic layer is formed on a nonmagnetic support is located on the most upstream side. From the unwinding roll toward the downstream side, as main devices, a coating device for magnetic paint (for example, an extrusion nozzle), a coating device for coating for forming a back coat layer (for example, an extrusion nozzle), a magnetic field orientation device, A drying device, a surface smoothing device (for example, a calendering device), and a winding device are sequentially provided.

In order to implement the application pattern (2), in the case of the above (1), it is preferable that the coating device for the coating material for forming the back coat layer is disposed upstream of the coating device for the magnetic coating material. In the case of the application pattern (3), in the case of the above (1), the application device of the magnetic paint and the application device of the paint for forming the back coat layer are disposed at the same position in the non-magnetic support conveyance direction. good.

In the coating method according to the present invention, it is a preferable embodiment that the coating material for the upper magnetic layer and the coating material for the back coat layer are applied almost simultaneously on the front and back of the support and dried by the same drying means. Therefore, as the coating device, the coating device located on the most upstream side may be any device such as a gravure coat, a reverse roll coat, and an extrusion nozzle. However, the coating device on the downstream side needs to use an extrusion nozzle. There is. In the case where the front and back surfaces of the non-magnetic support are applied at the same time (3), it is necessary to use an extrusion nozzle for both. Regarding such a double-side coating method, the present applicant has already proposed the best coating method (Japanese Patent Laid-Open No. Hei 7-185449).
No., JP-A-7-184537).

In the case of the above-mentioned coating pattern (1), a coating device (for example, an extrusion nozzle) is used to coat the lower non-magnetic layer on the non-magnetic support coated with the lower non-magnetic layer, which runs continuously, using a coating device (eg, an extrusion nozzle). A magnetic paint for forming a layer is applied. After the application of the magnetic paint, various treatments such as smoothing of the wet film surface of the magnetic paint provided on the non-magnetic support and regulation of the coating film may be performed as the next step. As a smoothing means, a resin, a metal, a film or a bar of ceramics, or a permanent magnet,
Known methods such as a non-contact method such as a magnetic field by an electromagnet or vibration by an ultrasonic wave can be used. These can be used alone or in combination depending on the required characteristics. Immediately after the application of the magnetic paint, the paint for forming the back coat layer is applied to the other surface of the continuously running nonmagnetic support using an application device (for example, an extrusion nozzle).

After the magnetic coating material for forming the upper magnetic layer and the coating material for forming the back coat layer are applied on both surfaces of the non-magnetic support in this manner, the magnetic coating material for forming the upper magnetic layer is During the drying, a magnetic field is applied by applying a magnetic field by an alignment magnet of a magnetic field alignment apparatus (magnetic field alignment processing step).

In the present invention, since the coating material for forming the backcoat layer in the undried state is present on the back surface of the non-magnetic support, even if the coating film for forming the upper magnetic layer is thin, "the upper magnetic layer forming The wet state of the magnetic paint for use "can be easily maintained. That is, the essential part of the production method of the present invention is to ensure that the backcoat layer in the undried state (particularly the wet state) always exists while the magnetic coating film is in the undried state (particularly the wet state) (another expression). When both coatings have been applied, each other's paint is still undried when the application of both paints is completed), while keeping the magnetic coating wet, apply a magnetic field while the magnetic coating is undried. Magnetic field orientation treatment. Therefore, as long as the main part of the present invention is satisfied, the application pattern (2) or the application pattern (3) may be performed as a modification of the application pattern (1). The point is that the upper magnetic coating film may be kept in an undried state before the magnetic field orientation treatment due to the presence of the undried backcoat layer forming paint.

In the magnetic field orientation treatment, the coating film may be pre-dried with a hot air blowing nozzle before the orientation magnet in a drying furnace, and then subjected to a magnetic field orientation treatment with an orientation magnet. Further, the orientation magnets may be arranged in multiple stages in a drying oven. Also,
The same effect can be obtained by installing the former-stage oriented magnet between the extrusion nozzle and the entrance of the drying furnace, and further installing the latter-stage oriented magnet in the drying furnace. Furthermore, regarding the magnetic field orientation treatment, this treatment is performed to orient the magnetic powder in the magnetic layer, and the orientation direction is parallel to the running direction of the medium, but is perpendicular to the running direction of the medium. Or in an oblique direction. In addition, permanent magnets such as ferrite magnets and rare earth magnets,
A magnetic field generating means such as an electromagnet or a solenoid is used. A plurality of these magnetic field generating means may be used in combination, and further, an appropriate drying step may be provided in advance before the orientation, or drying may be performed at the same time as the orientation so that the orientation after the drying is the highest. .

After the magnetic field orientation treatment is performed, each coating film is dried in a drying device (drying oven). The coating film may be dried by hot air blown from a hot air blowing nozzle,
In addition, drying and fixing may be performed by a known drying and evaporating means such as a far infrared ray, an electric heater, and a vacuum device, or by a known curing device such as an ultraviolet lamp or a radiation irradiation device. The drying temperature may be appropriately selected from the range of room temperature to about 300 ° C. depending on the heat resistance of the nonmagnetic support, the kind of the solvent, the concentration, and the like, or a temperature gradient may be provided in the drying furnace. As the gas atmosphere in the drying furnace, general air or an inert gas may be used. When drying is performed by an ultraviolet lamp or a radiation irradiation device, a curing reaction occurs. Therefore, when post-processing is considered, it is better to use other drying means as much as possible. Irradiation with ultraviolet rays or radiation while containing a solvent may involve ignition or smoking. In this case, it is preferable to use other drying means as much as possible.

It is preferable that the coating film (magnetic layer and back coat layer) subjected to the magnetic field orientation treatment and the drying treatment is calendered in-line by the following calendering device. By performing calendering in-line and in a state where the magnetic layer and the back coat layer are provided, the surface workability of the magnetic layer is significantly improved, and as a result, characteristics such as electromagnetic conversion characteristics are improved. In addition, by performing the in-line continuous processing, it is possible to reduce the loss of the coated raw material that has conventionally occurred due to the separate application line and calendering line.

After such a calendering treatment, to accelerate the curing of the magnetic layer, the back coat layer, etc.
It is preferable to perform a heat curing treatment at -80 ° C and / or an electron beam irradiation treatment.

Next, the magnetic recording medium is manufactured by processing into a predetermined tape shape or the like with a slitter, and further performing secondary processing such as polishing and cleaning on the magnetic surface and / or the back coat surface.

[Lower Non-Magnetic Layer] The lower non-magnetic layer contains at least carbon black and a radiation-curable binder resin. By including carbon black in the lower non-magnetic layer, the lubricant can be retained, so that the amount of the lubricant on the surface of the upper magnetic layer can be easily adjusted to a desired range. In the present invention, the thickness of the upper magnetic layer is as thin as 0.3 μm or less, and it is difficult for the upper magnetic layer alone to contain a sufficient amount of lubricant, and the lower carbon black is an important component. The carbon black of the lower non-magnetic layer is
It also has the effect of lowering the surface electrical resistance of the upper magnetic layer and the effect of reducing the light transmittance.

As the carbon black contained in the nonmagnetic layer, furnace black for rubber, thermal black for rubber, black for color, acetylene black and the like can be used. Specific surface area is 5 to 600 m ² / g, DB
P oil absorption is 30-400ml / 100g, particle size is 10
~ 100 nm is preferred. The carbon black that can be used can be specifically referred to “Carbon Black Handbook” edited by Carbon Black Association.

For the non-magnetic layer, various inorganic powders other than carbon black can be used. For example, acicular non-magnetic iron oxide (α-Fe ₂ O ₃ ) can be used.
However, high dispersibility can be obtained by using spherical ultrafine iron oxide particles, and the packing ratio of particles in the nonmagnetic layer can be increased. Therefore, the surface properties of the non-magnetic layer itself are improved, and the surface properties of the magnetic layer are improved, and the electromagnetic conversion characteristics are improved. Besides, various non-magnetic powders such as CaCO ₃ , titanium oxide, barium sulfate, α-Al ₂ O _{3 and the} like may be used.

The mixing ratio of carbon black and inorganic powder is preferably 100/0 to 75/25 by weight. If the mixing ratio of the inorganic powder exceeds 25 parts by weight, a problem occurs in the surface electric resistance.

The compounding amount of carbon black is 35 to 90% by weight, preferably 40 to 85% by weight in the lower nonmagnetic layer. If it is less than 35% by weight, the desired amount of lubricant cannot be held. On the other hand, if 90% by weight is used, a sufficient amount of the lubricant can be held. If the amount exceeds 90% by weight, the ratio of the binder resin in the lower non-magnetic layer decreases, and sufficient coating film strength cannot be obtained.

As the binder resin for the nonmagnetic layer, a radiation-curable binder resin is used. With a conventionally used thermoplastic resin or thermosetting resin, in order to obtain sufficient coating film properties, a non-magnetic layer coated raw roll is placed in an oven for a long time (for example, 70 ° C., 2 to 48 hours). It needs to be put in and cured. This poses a problem in that the coating of the non-magnetic layer is deformed due to the tightening of the winding and the smoothness of the surface of the non-magnetic layer is reduced, while the manufacturing process is troublesome.

In the production method disclosed in Japanese Patent No. 25666085, in which the upper magnetic layer is coated while the lower non-magnetic layer is in a wet state, the interface between the upper magnetic layer and the lower non-magnetic layer becomes non-uniform and output fluctuations occur. Wake up.

In order to eliminate such drawbacks, in the present invention, a radiation curable binder resin is used as a binder resin for the lower non-magnetic layer, a lower non-magnetic layer coating material is applied, dried, smoothed, and dried. Irradiation, three-dimensional cross-linking by radiation, and then application of the upper magnetic layer coating thereon resulted in favorable results. According to this method, the lower nonmagnetic layer is not swelled by the organic solvent because the three-dimensional crosslink has already been formed at the time when the upper magnetic layer is provided. Therefore, the magnetic paint can be applied onto the lower non-magnetic layer immediately after the formation of the lower non-magnetic layer, so that the process can be continued and simplified.

The radiation-curable binder resin used in the present invention is a resin containing one or more unsaturated double bonds in a molecular chain, which generates a radical by radiation and cures by crosslinking or polymerization. Say.

Examples of the radiation-curable binder resin include a large number of resins such as vinyl chloride resins, polyurethane resins, polyester resins, epoxy resins, phenoxy resins, fiber resins, polyether resins, and polyvinyl alcohol resins. Can be Among them, vinyl chloride resin,
Polyurethane resins are typical, and it is preferable to use a mixture of both.

The radiation-curable vinyl chloride resin is synthesized by modifying a vinyl chloride resin as a raw material with radiation. The raw material vinyl chloride resin has a vinyl chloride content of 60
-100% by weight, particularly preferably 60-95% by weight. Such vinyl chloride resins include vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate copolymer,
Vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl alcohol-maleic acid copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate-maleic acid copolymer, vinyl chloride-vinyl acetate-vinyl Alcohol-glycidyl (meth) acrylate copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate-glycidyl (meth) acrylate copolymer, vinyl chloride-hydroxyalkyl (meth) acrylate-allyl glycidyl ether copolymer, vinyl chloride Examples include a vinyl acetate-vinyl alcohol-allyl glycidyl ether copolymer, and a copolymer of vinyl chloride and a monomer containing an epoxy (glycidyl) group is particularly preferable. And the average degree of polymerization is 100-900
Is more preferable, and more preferably 100 to 600.

Further, in order to enhance the dispersibility, -SO ₄ Y, -SO ₃ Y, -POY, -PO ₂ Y,-
PO ₃ Y, —COOY (Y is hydrogen or an alkali metal),
_{-SR, -NR 2, -NR 3 Cl} (R is a hydrogen or a hydrocarbon group), phosphobetaine, sulfobetaine, phosphamine, it is also preferable that the polar group of sulphamic etc. introduced in any manner. In order to enhance thermal stability, it is also preferable to introduce an epoxy group.

As a method of radiation-modifying the above vinyl chloride resin, a resin having a hydroxyl group or a carboxylic acid group is modified by reacting a (meth) acrylic group with a compound having a carboxylic anhydride or a dicarboxylic acid. A method of reacting and reacting a reactant (adduct) of tolylene diisocyanate with 2-hydroxyethyl methacrylate to modify at least one ethylenically unsaturated double bond and one isocyanate group in one molecule. A typical method is to react a monomer having a urethane bond and having no urethane bond in the molecule. Of these, the third method is excellent in the easiness of modification and the dispersibility and physical properties after the modification, and it is preferable that the modification is performed by the third method. Examples of such a monomer include 2-isocyanatoethyl (meth) acrylate. It is preferable that an average of 1 to 20, more preferably 2 to 15 acryl groups or methacryl groups exist in the molecule of the binder.

The radiation-curable polyurethane resin is a urethane resin having at least one acrylic bond in the molecule, and is a polyurethane acrylate compound bonded to an acrylic double bond-containing compound via a urethane bond.

The term "acrylic double bond" as used herein means a residue (acryloyl group or methacryloyl group) such as acrylic acid, acrylic ester, acrylamide, methacrylic acid, methacrylic ester, methacrylamide, and the like.

Examples of the acrylic double bond-containing compound (A) include mono- (meth) glycols such as ethylene glycol, diethylene glycol, and hexamethylene glycol.
Acrylate, trimethylolpropane, glycerin,
Mono (meth) acrylates of triol compounds such as trimethylolethane and mono (meth) acrylates of divalent or higher polyols such as di (meth) acrylate, pentaerythritol and dipentaerythritol mono (meth) acrylate and di (meth) acrylate
Hydroxy group-containing acrylic compounds such as acrylate and tri (meth) acrylate, glycerin monoallyl ether, and glycerin diallyl ether are preferable. These acrylic double bonds must be present in the binder molecule in at least one or more, preferably 2 to 20.

The polyurethane acrylate resin is generally obtained by reacting a hydroxyl group-containing resin (B '), a hydroxyl group-containing acrylic compound (A') and a polyisocyanate-containing compound (C '). Examples of the hydroxy group-containing resin include polyalkylene glycols such as polyethylene glycol, polybutylene glycol, and polypropylene glycol, and bisphenol A.
Alkylene oxide adducts, various glycols, and polyester polyols (B ') having a hydroxyl group at the terminal of the molecular chain. Among these, a polyurethane acrylate resin obtained by using the polyester polyol (B ′) as one component is preferable.

The carboxylic acid component of the polyester polyol (B ') includes aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, orthophthalic acid and 1,5-naphthalic acid, p-oxybenzoic acid, and p- (hydroxyethoxy). Aromatic oxycarboxylic acids such as benzoic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, aliphatic dicarboxylic acids such as dodecanedicarboxylic acid, fumaric acid, maleic acid, itaconic acid, tetrahydrophthalic acid, hexahydrophthalic acid, etc. And tri- or tetracarboxylic acids such as alicyclic dicarboxylic acid, trimellitic acid, trimesic acid and pyromellitic acid.

The glycol components of the polyester polyol (B ') include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, Ethylene oxide adducts and propylene oxide adducts such as pentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, bisphenol A, and hydrogenated bisphenol A Ethylene oxide and propylene oxide adducts, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like. Further, tri- or tetraol such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol may be used in combination. In addition to the above, examples of the polyester polyol include a lactone-based polyester diol chain obtained by ring-opening polymerization of a lactone such as caprolactone.

As the polyisocyanate (C ') used, 2,4-tolylene diisocyanate, 2,6-
Tolylene diisocyanate, p-phenylene diisocyanate, biphenylmethane diisocyanate, m-phenylene diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, 3,3′-dimethoxy 4,4′-biphenylene diisocyanate,
2,4-naphthalenediisocyanate, 3,3′-dimethyl-4,4′-biphenylenediisocyanate, 4,
4'-diphenylene diisocyanate, 4,4'-diisocyanate-diphenyl ether, 1,5-naphthalene diisocyanate, p-xylylene diisocyanate, m-xylylene diisocyanate, 1,3-diisocyanatomethylcyclohexane, 1,4-isocyanatomethylcyclohexane Diisocyanate compounds such as 4,4'-diisocyanate dicyclohexane, 4,4'-diisocyanate cyclohexylmethane, isophorone diisocyanate, or a trimer of 2,4-tolylene diisocyanate of 7 mol% or less of all isocyanate groups; A triisocyanate compound such as a trimer of methylene diisocyanate is exemplified.

Further, in order to enhance the dispersibility, -SO ₄ Y, -SO ₃ Y, -POY, -PO ₂ Y,-
PO ₃ Y, —COOY (Y is hydrogen or an alkali metal),
_{-SR, -NR 2, -NR 3 Cl} (R is a hydrogen or a hydrocarbon group), phosphobetaine, sulfobetaine, phosphamine, it is also preferable that the polar group of sulphamic etc. introduced in any manner. In order to enhance thermal stability, it is also preferable to introduce an epoxy group.

On the other hand, apart from the above-mentioned radiation-curable urethane synthesis method, the radiation-sensitive modification may be carried out using a thermosetting polyurethane resin as a raw material in the same manner as the vinyl chloride resin.

If necessary, a radiation-curable monomer or oligomer may be used, and the use thereof can increase the degree of crosslinking of the coating film. The amount added is preferably not more than 30 parts by weight, more preferably not more than 20 parts by weight, based on the resin contained in the coating material for the lower non-magnetic layer. If the amount is more than 30 parts by weight, the shock applied to the paint is large, and conversely, the gloss is reduced. The radiation-curable monomer or oligomer may be added at any time after the preparation of the paint and at the time of dispersion.

The content of the radiation-curable binder in the lower non-magnetic layer is a total of 1 for carbon black and inorganic powder.
For 100 parts by weight, 10 to 100 parts by weight is preferable,
12.5 to 70 parts by weight is more preferred. If the content of the binder is too small, the ratio of the binder resin in the lower non-magnetic layer decreases, and sufficient coating film strength cannot be obtained. If the content of the binder is too large, poor dispersion occurs during the preparation of the coating material for the lower non-magnetic layer, making it impossible to form a smooth lower non-magnetic layer surface.

The radiation used in the present invention is an electron beam, γ-ray, β-ray, ultraviolet ray, etc., preferably an electron beam. The dose is preferably 1 to 10 Mrad.
~ 7 Mrad is more preferred. The irradiation energy (acceleration voltage) is preferably 100 Kv or more. Irradiation with radiation is preferably performed before winding after coating and drying, but may be performed after winding.

The lower non-magnetic layer of the present invention preferably contains a lubricant as required. Lubricant is saturated,
Regardless of unsaturation, known fatty acids, esters, and saccharides may be used alone or as a mixture of two or more, and it is preferable to use a mixture of two or more fatty acids and esters having different melting points. This is because it is necessary to continuously supply a lubricant corresponding to any temperature environment used for the magnetic recording medium to the medium surface.

Specific examples of the fatty acid include saturated linear fatty acids such as stearic acid, palmitic acid, myristic acid, lauric acid, and erucic acid; saturated fatty acids having side chains such as isosetyl acid and isostearic acid; and oleic acid. ,
Unsaturated fatty acids such as linoleic acid and linolenic acid can be used as appropriate. As esters, butyl stearate, linear saturated fatty acid esters such as butyl palmitate, isocetyl stearate, saturated fatty acid esters having side chains such as isostearyl stearate, unsaturated fatty acid esters such as isostearyl oleate,
Fatty acid esters of unsaturated alcohols such as oleyl stearate, esters of unsaturated fatty acids and unsaturated alcohols such as oleyl oleate, esters of dihydric alcohols such as ethylene glycol distearate, ethylene glycol monooleate, ethylene glycol dioleate Ester, esters of dihydric alcohols such as neopentyl glycol dioleate and unsaturated fatty acids, and saccharides such as sorbitan monostearate, sorbitan tristearate, sorbitan monooleate and sorbitan trioleate with saturated or unsaturated fatty acids Esters and the like. The content of the lubricant in the lower non-magnetic layer may be appropriately adjusted according to the purpose, but is preferably 1 to 20% by weight based on the total weight of the carbon black and the inorganic powder.

The paint for forming the lower non-magnetic layer is prepared by adding an organic solvent to the above components. The organic solvent used is not particularly limited, and one or two or more of various solvents such as ketone solvents such as methyl ethyl ketone (MEK), methyl isobutyl ketone and cyclohexanone, and aromatic solvents such as toluene are appropriately selected. It may be used. The amount of the organic solvent to be added may be about 100 to 900 parts by weight based on 100 parts by weight of the total of the solid content (carbon black, various inorganic particles, etc.) and the binder.

The solid content in the coating material for forming the lower non-magnetic layer is preferably 5 to 45% by weight, more preferably 10 to 45% by weight.
40% by weight. If the value is too low or too high, it is difficult to obtain a uniform coating film.

The surface roughness of the lower non-magnetic layer (the surface roughness is represented by center line average roughness (JIS-B-0601) Ra) needs to be good. Ra of the lower nonmagnetic layer after the smoothing treatment is preferably 8.0 nm or less, and is 6.0 or less.
nm or less, more preferably 5.0 nm or less. If it exceeds 8.0 nm, the interface between the upper magnetic layer and the lower non-magnetic layer becomes non-uniform, and the output tends to fluctuate.

The thickness of the lower non-magnetic layer is usually from 0.1 to
It is 2.5 μm, preferably 0.3 to 2.3 μm. When the non-magnetic layer is too thin, the surface properties of the non-magnetic support are easily affected, and as a result, the surface properties of the non-magnetic layer are deteriorated, and the surface properties of the magnetic layer are also likely to deteriorate. It tends to decrease. In addition, since the light transmittance increases, there is a problem in detecting the tape end based on a change in the light transmittance. On the other hand, even if the nonmagnetic layer is made thicker than a certain degree, the performance is not improved.

[Upper Magnetic Layer] The upper magnetic layer contains at least a ferromagnetic powder, a binder resin and an abrasive.

In the present invention, it is preferable to use a metal alloy fine powder or a hexagonal plate-like fine powder as the ferromagnetic powder. As the metal alloy fine powder, the holding force Hc is 150
0-3000 Oe, saturation magnetization s is 120-160 em
u / g, the average major axis diameter is preferably 0.05 to 0.2 μm, the average minor axis diameter is 10 to 20 nm, and the aspect ratio is preferably 1.2 to 20. The Hc of the prepared medium is 150
0 to 3000 Oe is preferred. As an additive element, Ni, Zn, Co, Al, Si, Y, and other rare earth elements may be added according to the purpose. The hexagonal plate-like fine powder has a coercive force Hc of 1000 to 2000 Oe, a saturation magnetization s of 50 to 70 emu / g, and an average plate grain size of 30 to 80.
nm and the plate ratio are preferably 3 to 7. Further, Hc of the produced medium is preferably 1200 to 2200 Oe.
As the additional element, Ni, Co, Ti,
Zn, Sn, and other rare earth elements may be added. In addition, known materials can be used according to the purpose without any particular limitation.

Such a ferromagnetic powder may be contained in an amount of about 70 to 90 parts by weight in the composition of the magnetic layer. If the content of the ferromagnetic powder is too large, the content of the binder is reduced, so that the surface smoothness due to calendar processing is liable to deteriorate. On the other hand, if the content is too small, a high reproduction output cannot be obtained.

The binder resin is not particularly limited as long as it is generally used, and any of a thermoplastic resin, a thermosetting or reactive resin, and a radiation-curable binder resin can be used.

For example, polyester polyurethane resin,
Vinyl chloride copolymer, vinyl chloride-acrylate copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate -Acrylonitrile copolymer, acrylate-vinylidene chloride copolymer, methacrylate-vinylidene chloride copolymer, methacrylate-ethylene copolymer, polyvinyl fluoride-vinylidene chloride-acrylonitrile copolymer Polymer, acrylonitrile-butadiene copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate,
Cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin-chlorovinyl ether acrylate copolymer, amino resin, and synthetic rubber thermoplastic resin.

The content of these binders used in the magnetic layer is preferably 5 to 40 parts by weight, particularly preferably 10 to 30 parts by weight, per 100 parts by weight of the ferromagnetic powder. If the content of the binder is too small, the strength of the magnetic layer decreases, so that the running durability tends to deteriorate. On the other hand, if the content is too large, the content of the ferromagnetic powder decreases, so that the electromagnetic conversion characteristics decrease.

As a crosslinking agent for curing these binders, various polyisocyanates, particularly diisocyanates, can be used. In particular, tolylene diisocyanate,
It is preferable to use at least one of hexamethylene diisocyanate and methylene diisocyanate. These crosslinking agents include a crosslinking agent modified to one having a plurality of hydroxyl groups such as trimethylolpropane or a diisocyanate compound 3
It is particularly preferable to use the compound as an isocyanurate-type cross-linking agent to which molecules are bonded. The content of the crosslinking agent is preferably 10 to 30 parts by weight based on 100 parts by weight of the binder. In order to cure such a thermosetting resin, it may be generally heated in a heating oven at 50 to 70 ° C. for 12 to 48 hours.

Further, in order to increase the mechanical strength of the magnetic layer and to prevent clogging of the magnetic head,
Contains abrasives. Examples of the abrasive include α-alumina (Mohs hardness 9), chromium oxide (Mohs hardness 9),
Polishing of silicon carbide (Mohs hardness 9.5), silicon oxide (Mohs hardness 7), aluminum nitride (Mohs hardness 9), boron nitride (Mohs hardness 9.5), etc., with a Mohs hardness of 6 or more, preferably a Mohs hardness of 9 or more. It is preferable to include at least one material. These are usually indeterminate shapes, prevent clogging of the magnetic head, and improve the strength of the coating.

The average particle size of the abrasive is, for example, 0.01 to
0.2 μm, preferably 0.05 to 0.2 μm. If the average particle size is too large, the amount of protrusion from the surface of the magnetic layer increases, which causes a decrease in electromagnetic conversion characteristics, an increase in dropout, an increase in head wear, and the like. If the average particle size is too small, the amount of protrusion from the surface of the magnetic layer becomes small, and the effect of preventing head clogging becomes insufficient. The average particle size is usually measured by a transmission electron microscope. The content of the abrasive is 3 to 25 parts per 100 parts by weight of the ferromagnetic powder.
It may be contained by weight, preferably 5 to 20 parts by weight.

Further, a dispersant such as a surfactant, a lubricant such as a higher fatty acid, a fatty acid ester, and silicone oil, and other various additives may be added to the magnetic layer as needed.

The coating material for forming the magnetic layer is prepared by adding an organic solvent to each of the above components. The organic solvent used is not particularly limited, and the same organic solvents as those used for the lower non-magnetic layer can be used.

The solid content concentration in the coating material for forming a magnetic layer is preferably 5 to 45% by weight, more preferably 10 to 40% by weight. If this value is less than 5% by weight, it is difficult to obtain a uniform coating film. When this value exceeds 45% by weight,
Since the drying speed of the coating of the magnetic layer is increased, and the solvent in the coating of the magnetic layer is transferred to the coating of the undercoat, it is difficult to improve the orientation of the magnetic layer, which is an effect of the present invention. .

The thickness of the upper magnetic layer is 0.30 μm or less,
Preferably it is 0.05 to 0.30 μm, more preferably 0.10 to 0.25 μm. A thickness of less than 0.20 μm, such as 0.15 μm, is also suitable. If the magnetic layer is too thick, self-demagnetization loss and thickness loss increase.

The center line average roughness (Ra) of the magnetic layer surface is:
Preferably 1.0 to 8.0 nm, more preferably 2.0
７7.0 nm. When Ra is less than 1.0 nm, the surface is too smooth, running stability is deteriorated, and trouble during running is likely to occur. On the other hand, if the thickness exceeds 8.0 nm, the surface of the magnetic layer becomes rough, and the electromagnetic conversion characteristics such as reproduction output tend to deteriorate.

[Backcoat layer] The backcoat layer is provided for improving running stability, preventing the magnetic layer from being charged, and the like. The back coat layer preferably contains 30 to 80% by weight of carbon black. If the content of carbon black is too small, the antistatic effect tends to decrease, and the running stability tends to decrease. Also, since the light transmittance is likely to be high, there is a problem in a method of detecting the end of the tape by a change in the light transmittance. On the other hand, if the content of carbon black is too large, the strength of the back coat layer is reduced, and running durability is likely to be deteriorated. Any carbon black may be used as long as it is commonly used, and the average particle size is preferably about 5 to 500 nm. The average particle size is usually measured by a transmission electron microscope.

The back coat layer may contain, in addition to the carbon black, non-magnetic inorganic powders such as various abrasives mentioned in the description of the magnetic layer in order to increase the mechanical strength. The content of the nonmagnetic inorganic powder is preferably 0.1 to 5 parts by weight, based on 100 parts by weight of carbon black,
More preferably, it is 0.5 to 2 parts by weight. The average particle size of the non-magnetic inorganic powder is preferably 0.1 to 0.5 μm. If the content of such a nonmagnetic inorganic powder is too small, the mechanical strength of the back coat layer tends to be insufficient, and if it is too large, the amount of abrasion of the guide in the tape sliding path tends to increase.

In addition, if necessary, a dispersant such as a surfactant, a lubricant such as a higher fatty acid, a fatty acid ester, or silicone oil, and other various additives may be added.

A binder, a crosslinking agent,
The solvent and the like may be the same as those used in the above-mentioned coating for the magnetic layer. The content of the binder is preferably 15 to 200 parts by weight, more preferably 50 to 180 parts by weight, based on 100 parts by weight of the total of the solid content. If the content of the binder is too large, the friction with the medium sliding contact path becomes too large, the running stability is reduced, and a running accident is likely to occur.
In addition, problems such as blocking with the magnetic layer occur. When the content of the binder is too small, the strength of the back coat layer is reduced, and the running durability is easily reduced.

The solid content concentration in the coating material for forming the backcoat layer is preferably 8 to 30% by weight, more preferably 10 to 30% by weight.
25% by weight. If this value is less than 8% by weight, it is difficult to obtain a uniform coating film. When this value exceeds 30% by weight, the drying speed of the coating film of the back coat layer increases,
It is difficult to improve the degree of orientation of the magnetic layer, which is an effect of the present invention.

The thickness (after calendering) of the back coat layer is 1.0 μm or less, preferably 0.1 to 1.0 μm.
m, more preferably 0.2 to 0.8 μm. If the back coat layer is too thick, the friction between the back coat layer and the medium sliding contact path becomes too large, and the running stability tends to decrease. On the other hand, if it is too thin, the surface properties of the backcoat layer will decrease due to the influence of the surface properties of the nonmagnetic support. For this reason, when the back coat is thermally cured, the roughness of the back coat layer surface is transferred to the magnetic layer surface, resulting in a decrease in high-frequency output, S / N, and C / N. On the other hand, if the back coat layer is too thin, the back coat layer will be shaved during running of the medium.

[Non-Magnetic Support] The material used as the non-magnetic support is not particularly limited, and may be selected from various flexible materials and various rigid materials according to the purpose, and may be tape-shaped or the like according to various standards. The shape and the size may be set. For example, as a flexible material, polyethylene terephthalate, polyesters such as polyethylene naphthalate, polyolefins such as polypropylene, polyamide, polyimide,
Various resins such as polycarbonate are exemplified.

The thickness of these nonmagnetic supports is 3.0 to 1
It is preferably 5.0 μm. The form of the nonmagnetic support is not particularly limited, and may be any of a tape form, a sheet form, a card form, a disk form, and the like, and various materials are selected according to the form and as necessary. Can be used.

The surface roughness of the non-magnetic support used in the present invention is not more than 20 nm, preferably not more than 15 nm, as a center line average surface roughness Ra. The surface roughness of the non-magnetic support is
It can be freely controlled by the size and amount of the filler added to the non-magnetic support as needed. Examples of these fillers include, in addition to oxides and carbonates such as Ca, Si, Ti, and Al, organic resin fine powders such as an acrylic resin. Preferably, a combination of Al ₂ O ₃ and an organic resin fine powder is used. It is.

[Coating Manufacturing Method] Each of the coatings for the lower non-magnetic layer and the upper magnetic layer is mixed at least in the kneading step, the dispersing step, and before or after these steps, if necessary. It is manufactured by performing a filtration step. Each step may be divided into two or more steps. All materials such as ferromagnetic powder, non-magnetic inorganic powder, binder, abrasive, carbon black, lubricant, and solvent used in the present invention may be added at the beginning or during any step. Further, individual materials may be added in two or more steps in a divided manner.

For kneading and dispersing the paint, it is a matter of course that a conventionally known manufacturing technique can be used for some or all of the processes. However, in the kneading process, a material having a strong kneading force such as a continuous kneader or a pressure kneader is used. It is preferred to use
In the case of using a continuous kneader or a pressure kneader, kneading treatment is performed with all or a part of the ferromagnetic powder or nonmagnetic inorganic powder and the binder (however, preferably 10% by weight or more of the total binder). The slurry temperature during kneading is 50 ° C to 110 ° C.
C is preferred.

For dispersion of the paint, it is desirable to use a dispersion medium having a high specific gravity, and ceramic media such as zirconia and titania are suitable. Conventionally used glass beads, metal beads, alumina beads and the like can be selectively used depending on the composition.

[0090]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. [Preparation of paint for upper magnetic layer] (Preparation of binder solution) 10 parts by weight of vinyl chloride resin (manufactured by Zeon Corporation: MR-110) 7 parts by weight of polyester polyurethane resin (UR-8300 manufactured by Toyobo Co., Ltd.) 21 parts by weight of MEK Part Toluene 21 parts by weight Cyclohexanone 21 parts by weight The above composition was charged into a hypermixer, mixed and stirred to obtain a binder solution.

(Kneading) The following composition was charged into a pressure kneader and kneaded for 2 hours. α-Fe magnetic powder 100 parts by weight (Hc = 1650 Oe, σs = 128 emu / g, BET = 57 m ² / g, major axis length = 0.10 μm) α-Al ₂ O ₃ 12 parts by weight (Sumitomo Chemical Co., Ltd .: HIT -82, average particle size = 0.13 μm) 40 parts by weight of binder solution The following composition was added to the kneaded slurry to adjust the viscosity to an optimum for dispersion treatment. Binder solution 40 parts by weight MEK 15 parts by weight Toluene 15 parts by weight Cyclohexanone 15 parts by weight

(Dispersion) The above slurry was subjected to dispersion treatment in a sand mill.

(Viscosity Adjusting Liquid) The following composition was charged into a hypermixer and mixed and stirred for 1 hour to obtain a viscosity adjusting liquid. 95% cut filtration accuracy of the viscosity adjusting liquid = 1.2μ
Circulation filtration was performed using a depth filter of m. 0.5 parts by weight of stearic acid 0.5 parts by weight of myristic acid 0.5 parts by weight of butyl stearate 210 parts by weight of MEK 210 parts by weight of toluene 210 parts by weight of cyclohexanone

(Viscosity Adjustment) After the above-mentioned solution was mixed and stirred with the slurry after dispersion, dispersion treatment was performed again with a sand mill to obtain a coating material. 95% cut filtration accuracy of the above paint =
Circulation filtration was performed using a 1.2 μm depth filter.

(Final paint) 0.8 parts by weight of an isocyanate compound (manufactured by Nippon Polyurethane Co., Ltd., Coronate L) was added to 100 parts by weight of the filtered paint, followed by stirring and mixing, and a depth filter having a 95% cut filtration accuracy of 1.2 μm was used. And the resulting mixture was subjected to circulation filtration to obtain a final coating material for the magnetic layer.

[Preparation of lower non-magnetic layer coating material (a)] (Preparation of binder solution) Electron beam-curable vinyl chloride resin 10 parts by weight (vinyl chloride-epoxy containing monomer copolymer, average degree of polymerization = 310, epoxy Content = 3 wt%, S content = 0.6 wt%, Acrylic content = 6 / molecule, Tg = 60 ° C.) Electron beam-curable polyester polyurethane resin 7 parts by weight (phosphorus compound-hydroxy-containing polyester polyurethane, number average) (Molecular weight = 13000, acryl content = 6 / molecule, Tg = 10 ° C.) MEK 21 parts by weight Toluene 21 parts by weight Cyclohexanone 21 parts by weight The above composition was charged into a hyper mixer and stirred to obtain a binder solution.

(Kneading) The following composition was charged into a pressure kneader and kneaded for 2 hours. Acicular α-Fe ₂ O ₃ 10 parts by weight (manufactured by Toda Kogyo: DPN-250BW, major axis length = 0.15 μm, specific surface area = 53 m ² / g) 90 parts by weight of carbon black (manufactured by Columbia Carbon: Raven760B, average) Particle size = 30 nm, specific surface area = 70 m ² / g, DPB oil absorption = 48 ml / 100 g) Binder solution 40 parts by weight The following composition was added to the slurry after kneading to adjust the viscosity to be optimal for dispersion treatment. Binder solution 40 parts by weight MEK 15 parts by weight Toluene 15 parts by weight Cyclohexanone 15 parts by weight

(Dispersion) The above slurry was subjected to a dispersion treatment in a sand mill.

(Viscosity adjusting liquid) The following composition was charged into a hypermixer and stirred to obtain a viscosity adjusting liquid. 0.5 parts by weight of stearic acid 0.5 parts by weight of myristic acid 0.5 parts by weight of butyl stearate 100 parts by weight of MEK 100 parts by weight of toluene 100 parts by weight of cyclohexanone

(Viscosity Adjustment and Final Coating) After the above-mentioned solution was mixed and stirred with the dispersed slurry, the mixture was again subjected to a dispersion treatment with a sand mill to obtain a coating. The paint was circulated and filtered using a depth filter having a 95% cut filtration accuracy of 1.2 μm to obtain a final paint (a) for the lower nonmagnetic layer.

[Preparation of Coating (b) for Lower Nonmagnetic Layer] (Preparation of Binder Solution) 10 parts by weight of vinyl chloride resin (manufactured by Zeon Corporation: MR-110) Polyester polyurethane resin (manufactured by Toyobo Co., Ltd .: UR-8300) 7 parts by weight MEK 21 parts by weight Toluene 21 parts by weight Cyclohexanone 21 parts by weight The above composition was charged into a hypermixer and stirred to obtain a binder solution.

(Kneading) The following composition was charged into a pressure kneader and kneaded for 2 hours. Acicular α-Fe ₂ O ₃ 10 parts by weight (manufactured by Toda Kogyo: DPN-250BW, major axis length = 0.15 μm, specific surface area = 53 m ² / g) 90 parts by weight of carbon black (manufactured by Columbia Carbon: Raven760B, average) Particle size = 30 nm, specific surface area = 70 m ² / g, DPB oil absorption = 48 ml / 100 g) Binder solution 40 parts by weight The following composition was added to the slurry after kneading to adjust the viscosity to be optimal for dispersion treatment. Binder solution 40 parts by weight MEK 15 parts by weight Toluene 15 parts by weight Cyclohexanone 15 parts by weight

(Dispersion) The above slurry was subjected to dispersion treatment in a sand mill.

(Viscosity Adjusting Liquid) The following composition was charged into a hypermixer and stirred to obtain a viscosity adjusting liquid. 0.5 parts by weight of stearic acid 0.5 parts by weight of myristic acid 0.5 parts by weight of butyl stearate 100 parts by weight of MEK 100 parts by weight of toluene 100 parts by weight of cyclohexanone

(Viscosity adjustment) After the above-mentioned solution was mixed and stirred with the slurry after dispersion, dispersion treatment was performed again with a sand mill to obtain a paint. 95% cut filtration accuracy of the above paint =
Circulation filtration was performed using a 1.2 μm depth filter.

(Final paint) 0.8 parts by weight of an isocyanate compound (manufactured by Nippon Polyurethane, Coronate L) was added to 100 parts by weight of the filtered paint, and the mixture was stirred and mixed. A depth filter having a 95% cut filtration accuracy of 1.2 μm was used. And circulation filtration was performed to obtain a final coating material (b) for the lower nonmagnetic layer.

[Preparation of paint for back coat layer] (Preparation of binder solution) 65 parts by weight of vinyl chloride-vinyl acetate-vinyl alcohol copolymer (monomer weight ratio = 92: 3: 5, average polymerization degree = 420) Polyester polyurethane Resin (manufactured by Toyobo Co., Ltd .: UR-8300) 35 parts by weight MEK 260 parts by weight Toluene 260 parts by weight Cyclohexanone 260 parts by weight The above composition was charged into a hyper mixer and stirred to obtain a binder solution.

(Dispersion) The following composition was charged into a ball mill and dispersed for 24 hours. 80 parts by weight of carbon black (Columbia Carbon: Conductex SC, average particle size = 20 nm, BET = 220 m ² / g) 1 part by weight of carbon black (Colombia Carbon: Sevacarb MT, average particle size = 350 nm, BET = 8 m) ² / g) α-Fe ₂ O ₃ (manufactured by Toda Kogyo Co., Ltd .: TF100, average particle size = 0.1 μm) 1 part by weight Binder solution 880 parts by weight

(Viscosity Adjusting Liquid) The following composition was charged into a hypermixer and stirred to obtain a viscosity adjusting liquid. 1 part by weight of stearic acid 1 part by weight of myristic acid 2 parts by weight of butyl stearate 210 parts by weight of MEK 210 parts by weight of toluene 210 parts by weight of cyclohexanone

(Viscosity Adjustment) After the above-mentioned solution was mixed and stirred with the slurry after dispersion, dispersion treatment was again performed for 3 hours by a ball mill. 95% cut filtration accuracy of the above paint = 1.2μ
Circulation filtration was performed using a depth filter of m.

(Final paint) 1 part by weight of an isocyanate compound (manufactured by Nippon Polyurethane Co., Coronate-L) was added to 100 parts by weight of the filtered paint, stirred and mixed, and a 95% cut filter having a filtration accuracy of 1.2 μm was used as a depth filter. Was used to carry out circulation filtration to obtain a back coat paint.

[Preparation of Magnetic Tape] (Examples 1, 3, and 4) A lower non-magnetic layer coating material (a) is applied to the surface of a non-magnetic support (a polyethylene terephthalate film having a thickness of 8.3 μm), dried, and calendered. Processing,
The film was cured by irradiation with an electron beam in a nitrogen gas atmosphere. The upper magnetic layer coating is applied to the lower nonmagnetic layer, and the backcoat layer coating is applied to the back surface of the nonmagnetic support while the upper magnetic layer coating is wet, oriented, dried and calendered. Was given. Table 1 shows the thickness of the upper magnetic layer / lower non-magnetic layer after calendering. The thickness of the back coat layer after calendering was 0.5 μm for all samples. The roll was left at room temperature for 24 hours, cured in a heating oven at 60 ° C. for 24 hours, cut into a width of 8 mm, incorporated into a cassette, and used as a magnetic tape sample.

Example 2 Non-magnetic support (thickness: 8.3 μm)
m polyethylene terephthalate film), a coating for a lower non-magnetic layer (a) was applied to the surface, dried, calendered, and cured by irradiation with an electron beam in a nitrogen gas atmosphere. Apply the coating for the back coat layer on the back surface of the non-magnetic support, apply the coating for the upper magnetic layer on the lower non-magnetic layer while the coating for the back coat layer is wet, and perform orientation, drying, and calendering. gave. Table 1 shows the thickness of the upper magnetic layer / lower non-magnetic layer after calendering. The thickness of the back coat layer after calendering was 0.5 μm. The roll was left at room temperature for 24 hours, cured in a heating oven at 60 ° C. for 24 hours, cut into a width of 8 mm, incorporated into a cassette, and used as a magnetic tape sample.

(Comparative Example 1: Coating of upper magnetic layer, drying and coating of backcoat layer) Coating (a) for lower nonmagnetic layer is applied to the surface of nonmagnetic support (polyethylene terephthalate film having a thickness of 8.3 μm) and dried. Then, it was calendered and irradiated with an electron beam in a nitrogen gas atmosphere to be cured. A coating for the upper magnetic layer was applied on the lower nonmagnetic layer, and orientation, drying and calendering were performed. Thereafter, a back coat layer paint was applied to the back surface of the non-magnetic support, dried and calendered. Table 1 shows the thickness of the upper magnetic layer / lower non-magnetic layer after calendering. The thickness of the back coat layer after calendering was 0.5 μm. Roll this roll 24
After standing at room temperature for 24 hours, 24 hours in a heating oven at 60 ° C.
After curing for a time, it was cut into a width of 8 mm and assembled into a cassette to obtain a magnetic tape sample.

(Comparative Example 2: lower non-magnetic layer was not irradiated with an electron beam) Coating (a) for lower non-magnetic layer was applied to the surface of a non-magnetic support (polyethylene terephthalate film having a thickness of 8.3 μm), dried and calendered Processing was performed. The upper magnetic layer coating is applied to the lower nonmagnetic layer, and the backcoat layer coating is applied to the back surface of the nonmagnetic support while the upper magnetic layer coating is wet, oriented, dried and calendered. Was given. Table 1 shows the thickness of the upper magnetic layer / lower non-magnetic layer after calendering. The thickness of the back coat layer after calendering was 0.5 μm. The roll was left at room temperature for 24 hours, cured in a heating oven at 60 ° C. for 24 hours, cut into a width of 8 mm, incorporated into a cassette, and used as a magnetic tape sample.

(Comparative Example 3: W / W coating) A coating for lower non-magnetic layer (a) was applied to the surface of a non-magnetic support (polyethylene terephthalate film having a thickness of 8.3 μm), and a coating for lower non-magnetic layer was coated. a) The coating for the upper magnetic layer was applied in a wet state, and orientation, drying and calendering were performed, and the lower non-magnetic layer was cured by irradiating with an electron beam in a nitrogen gas atmosphere. Thereafter, a back coat layer paint was applied to the back surface of the non-magnetic support, dried and calendered. Table 1 shows the thickness of the upper magnetic layer / lower non-magnetic layer after calendering. The backcoat layer after calendering has a thickness of 0.1 mm.
It was 5 μm. After leaving this roll at room temperature for 24 hours, after curing in a heating oven at 60 ° C. for 24 hours,
It was cut into 8 mm width and assembled into a cassette to obtain a magnetic tape sample.

(Comparative Example 4: W / W coating) A coating for a lower non-magnetic layer (b) was applied to the surface of a non-magnetic support (a polyethylene terephthalate film having a thickness of 8.3 μm), and a coating for a lower non-magnetic layer was applied. b) The coating for the upper magnetic layer was applied in a wet state, and orientation, drying and calendering were performed. Thereafter, a back coat layer paint was applied to the back surface of the non-magnetic support, dried and calendered. Table 1 shows the thickness of the upper magnetic layer / lower non-magnetic layer after calendering. The thickness of the back coat layer after calendering was 0.5 μm. After leaving this roll at room temperature for 24 hours,
After curing in a heating oven for 24 hours, it was cut into a width of 8 mm and assembled into a cassette to obtain a magnetic tape sample.

(Comparative Example 5: W / D coating, lower layer thermosetting) On the surface of a non-magnetic support (a polyethylene terephthalate film having a thickness of 8.3 μm), a lower layer non-magnetic layer coating material (b) was applied.
It was dried, calendered, and wound up. After leaving the roll at room temperature for 24 hours, it was cured in a heating oven at 60 ° C. for 24 hours. On this lower non-magnetic layer, a paint for an upper magnetic layer was applied, oriented, dried and calendered. Table 1 shows the thickness of the upper magnetic layer / lower non-magnetic layer after calendering. Further, a paint for a back coat layer was applied to the back surface of the nonmagnetic support. After drying, calendering was performed. The thickness of the back coat layer after calendering was 0.5 μm. The roll was left at room temperature for 24 hours, cured in a heating oven at 60 ° C. for 24 hours, cut into a width of 8 mm, incorporated into a cassette, and used as a magnetic tape sample.

The following evaluation was performed for each of the obtained magnetic tape samples. <Output Fluctuation> The RF output when a sine wave signal having a frequency of 750 kHz was recorded and reproduced at an optimum recording current was measured by a spectrum analyzer (Advantest: TR4171). For the setting of the spectrum analyzer, the center frequency was set to 750 kHz, the frequency span was set to 0 Hz, and the sweep time was set to the optimum value, and the output fluctuation: Vp-p (dB) was confirmed.

<Degree of orientation and residual magnetic flux density Br> The magnetic properties of the tape sample were measured using a vibrating sample magnetometer (V
(SM-V type), and the maximum external magnetic field was set to 10 kOe. The degree of orientation is (Br / Bm)
_MD / (Br / Bm) _TD , where Bm is the saturation magnetic flux density, MD is the tape longitudinal direction, and TD is the tape width direction.

[0121]

[Table 1]

In the coating methods in the table, W / D indicates a wet-on-dry method, and W / W indicates a wet-on-wet method. From Table 1, Examples 1-4
In all of the tape samples, the degree of orientation was high and excellent without causing output fluctuation.

On the other hand, in Comparative Example 1, the orientation of the magnetic powder was not sufficient because the orientation treatment of the paint for the upper magnetic layer was performed in the absence of the paint for the backcoat layer. Comparative Example 2 is an example in which the lower non-magnetic layer was not irradiated with the electron beam. When the coating of the upper magnetic layer was applied, the lower non-magnetic layer swelled, and the interface between the upper magnetic layer and the lower non-magnetic layer was not good. It became uniform and caused output fluctuation. Comparative Examples 3 and 4 are examples in which the upper magnetic layer is applied while the lower nonmagnetic layer is in a wet state,
The interface between the upper magnetic layer and the lower nonmagnetic layer became non-uniform, causing output fluctuation. Comparative Example 5 is an example in which the upper magnetic layer is applied after heat-curing the lower non-magnetic layer coating film, and the lower winding tightness occurs, and the upper magnetic layer coating becomes non-uniform,
Caused output fluctuation.

[0124]

According to the present invention, even when the magnetic layer is thinned, it is possible to manufacture a magnetic recording medium having a magnetic layer having an excellent degree of magnetic powder orientation and having excellent electromagnetic conversion characteristics.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 5/70 G11B 5/70 5/735 5/735 5/738 5/738 // C08L 23:00 101 : 00 (72) Inventor Yamazaki Saki Katsuhiko 1-13-1 Nihonbashi, Chuo-ku, Tokyo FDC term in TDK Corporation 4F006 AA12 AA35 AA36 AA38 AA39 AB18 AB37 AB72 BA06 BA07 BA09 CA02 DA04 EA03 EA05 4J011 QB01 QB24 UA01 UA03 UA04 VA01 WA02 4J027 AA08 AG03 AG04 AJ08 CC03 CC05 CD08 5D006 BA04 BA05 BA06 CA01 CA04 CC02 EA01 EA05 FA09 5D112 AA03 AA05 AA08 AA22 BB01 BD01 BD08 CC01 CC17 CC19

Claims (4)

[Claims] 1. A lower nonmagnetic layer containing a radiation-curable binder resin formed on one surface of a nonmagnetic support, and a film thickness of 0.3 μm or less formed on the lower nonmagnetic layer. A magnetic recording medium comprising: an upper magnetic layer; and a backcoat layer formed on the other surface of the nonmagnetic support, comprising: a lower nonmagnetic layer on one surface of the nonmagnetic support. Apply a paint containing a radiation-curable binder resin for forming, dry,
Performing a smoothing process and a radiation curing process, and then applying a magnetic paint for forming an upper magnetic layer on the formed lower nonmagnetic layer, and a back coating on the other surface of the nonmagnetic support. The step of applying a coating for forming a layer is sequentially performed, and in the step of applying the coating for forming a back coat layer, the magnetic coating for forming an upper magnetic layer, which has been previously applied, is in a wet state. A method for producing a magnetic recording medium, comprising: performing a magnetic field orientation treatment by applying a magnetic field while the magnetic paint for forming the upper magnetic layer is not dried. 2. A lower non-magnetic layer containing a radiation-curable binder resin formed on one surface of a non-magnetic support, and a film thickness of 0.3 μm or less formed on the lower non-magnetic layer. A magnetic recording medium comprising: an upper magnetic layer; and a backcoat layer formed on the other surface of the nonmagnetic support, comprising: a lower nonmagnetic layer on one surface of the nonmagnetic support. Apply a paint containing a radiation-curable binder resin for forming, dry,
Performing a smoothing process and a radiation curing process, and then applying a coating for forming a back coat layer on the other surface of the nonmagnetic support; and forming an upper magnetic layer on the formed lower nonmagnetic layer. The step of applying a magnetic paint for forming is sequentially performed, and at the time of the applying step of the magnetic paint for forming the upper magnetic layer, the paint for forming the back coat layer previously applied is in a wet state. And performing a magnetic field orientation treatment by applying a magnetic field while the magnetic paint for forming the upper magnetic layer is not dried. 3. A lower nonmagnetic layer containing a radiation-curable binder resin formed on one surface of a nonmagnetic support, and a film thickness of 0.3 μm or less formed on the lower nonmagnetic layer. A magnetic recording medium having an upper magnetic layer and a backcoat layer formed on the other surface of the nonmagnetic support, comprising: a lower nonmagnetic layer on one surface of the nonmagnetic support. Apply a paint containing a radiation-curable binder resin for formation, dry,
Performing a smoothing treatment and a radiation curing step, and then applying a magnetic paint for forming an upper magnetic layer on the formed lower nonmagnetic layer, and a back coating on the other surface of the nonmagnetic support. A step of applying a coating for layer formation and simultaneously performing a magnetic field orientation process by applying a magnetic field while the magnetic coating for forming the upper magnetic layer is not dried. Manufacturing method. 4. The method for producing a magnetic recording medium according to claim 1, wherein the solid content concentration in the paint for forming the back coat layer is 8 to 30% by weight.