JPH1027330A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium having better surface smoothness and electromagnetic conversion characteristics by specifying a difference between the pH of ferromagnetic powder incorporated into a magnetic film and the pH of the magnetic powder or non-magnetic powder incorporated in an intermediate layer to a prescribed value or below. SOLUTION: The magnetic recording medium 1 includes a base 2, the intermediate layer 3 disposed thereon, the magnetic layer 4 disposed on the layer 3 and a back coating layer 5 disposed on the rear surface of the base 2. The difference from the pH of the magnetic powder incorporated into the magnetic layer 4 of this magnetic recording medium is <=2, more preferably <=1. When the difference of the pH exceeds 2, a difference in thixotropy between the magnetic film 4 and the intermediate layer 3 increases and unequal coating and coating film defects are liable to arise. The magnetic powder having pH4 to 12 is usually used as the magnetic powder to be incorporated into the magnetic film 4 and the powder having pH of >=7 is preferable and the powder having 8 to 11 is more preferable in terms of the improvement of the corrosion resistance and oxidation resistance of the coating film. The same holds true of the magnetic or non-magnetic powder to be incorporated into the intermediate layer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium, and more particularly, to a magnetic recording medium having excellent surface smoothness and electromagnetic conversion characteristics.

[0002]

2. Description of the Related Art Due to the demand for higher-density recording such as high-quality video tapes and large-capacity floppy disks, multilayer coated magnetic recording media have been used today. Such a multilayer coating type magnetic recording medium is usually manufactured by applying a magnetic paint obtained by dispersing a magnetic powder and a binder in an organic solvent on a non-magnetic support such as a polyester film, and drying. ing.

[0003] As a method of applying a magnetic paint on a support, there are a sequential coating method and a simultaneous coating method. Among the above methods, the simultaneous coating method has the advantages that the surface smoothness of the obtained magnetic recording medium is improved and that the coating process can be performed only once.

[0004] However, the simultaneous coating method is a method in which a coating material for forming a plurality of layers is simultaneously applied, that is, another coating material is placed on the lower coating material before the coating material is not dried. Care must be taken to control the physical properties of the paints used so that the paints to be mixed do not mix or repel each other. Viscosity is important as such a physical property that affects the applicability of a paint.
If the viscosities of the paints forming each layer are low, the paints will be mixed.On the other hand, if the viscosities of the paints are too high, the pressure will be too high when applying by the extrusion extrusion die head, and the paint will flow. There is a problem that it cannot be put out. The paint that solves this problem has a viscosity characteristic that the viscosity is sufficiently low until it is discharged from the lip of the die head due to the shear stress with the flow path, and the viscosity rises quickly when it comes out of the lip and is released from the stress. It is desirable to have one.

[0005] Factors governing the above viscosity characteristics include:
The shape and surface composition of the powder contained in the paint, the molecular weight and structure of the binder contained in the paint, the type and number of polar groups possessed by the binder, the amount and proportion of the powder and binder contained in the paint, etc. Additives and the like added to the paint are conceivable.

To cope with the improvement of the viscosity characteristics, for example, Japanese Patent Application Laid-Open No. 4-325917 discloses a magnetic recording medium coated with a plurality of paints having the same or similar thixotropic properties. Also,
Japanese Patent Application Laid-Open No. 5-128496 discloses a magnetic recording medium coated with a plurality of paints having a fixed relationship with respect to a flow curve.

The magnetic recording media disclosed in JP-A-4-325917 and JP-A-5-128496 have improved surface smoothness and electromagnetic conversion characteristics to some extent, but have high quality video tapes and large-capacity floppy disks. With the demand for higher density recording such as described above, a magnetic recording medium having more excellent surface smoothness and electromagnetic conversion characteristics is required.

Accordingly, it is an object of the present invention to provide a magnetic recording medium having further excellent surface smoothness and electromagnetic conversion characteristics.

[0009]

Means for Solving the Problems As a result of intensive studies, the present inventors have determined that the pH of the magnetic powder contained in the magnetic layer in the magnetic recording medium and the pH of the powder as the main component of the intermediate layer are specified. By making the relationship, the thixotropic properties of the intermediate layer and the magnetic layer are approximated, and it has been found that the above object can be achieved.

[0010] The present invention has been made based on the above findings, and comprises a support, an intermediate layer provided on the support, and a magnetic layer provided on the intermediate layer. A magnetic recording medium characterized in that the difference between the pH of the magnetic powder contained in the magnetic layer and the pH of the magnetic powder or the non-magnetic powder contained in the intermediate layer is 2 or less.

Hereinafter, the magnetic recording medium of the present invention will be described in detail with reference to the drawings. Here, FIG. 1 is an enlarged schematic view showing a cross section of a main part of a preferred embodiment of the magnetic recording medium of the present invention.

As shown in FIG. 1, a magnetic recording medium 1 according to the present embodiment has a support 2, an intermediate layer 3 provided on the support 2, and an intermediate layer 3 provided on the intermediate layer 3. It has a magnetic layer 4 and a back coat layer 5 provided on the back surface of the support 2.

In the magnetic recording medium of the present invention, the difference between the pH of the magnetic powder contained in the magnetic layer 4 and the pH of the magnetic powder or non-magnetic powder contained in the intermediate layer 3 is 2 or less; Preferably it is 1 or less. When the pH difference exceeds 2, the difference in thixotropic property between the magnetic layer and the intermediate layer becomes large, and coating unevenness and coating film defects are likely to occur. Further, the magnetic powder contained in the magnetic layer 4 usually has a pH
The pH is preferably from 7 to 8 from the viewpoint of improving the contact resistance and oxidation resistance of the coating film.
To 11 are more preferred. Further, as the magnetic powder or non-magnetic powder contained in the intermediate layer 3, usually, pH
The pH is preferably from 7 to 8 from the viewpoint of improving the contact resistance and oxidation resistance of the coating film.
To 11 are more preferred. The pH of the magnetic powder or non-magnetic powder is determined according to JIS K 5101-1991.
Is a value measured by the normal temperature method described in.

The binder contained in the magnetic layer 4 and the intermediate layer 3 may be a binder having a basic polar group when the pH of the magnetic powder or non-magnetic powder contained in each layer is less than 7. When the pH is 7 or more, a binder having an acidic polar group is preferable. The dispersibility of the magnetic powder or non-magnetic powder contained in each of the layers is adjusted by combining the pH of the magnetic powder or non-magnetic powder contained in each of the layers with the binder contained in each of the layers as described above. Further, the surface smoothness of the obtained magnetic recording medium is improved.

Hereinafter, each layer constituting the magnetic recording medium 1 of the present embodiment will be described in detail. First, the support 2 will be described. As the support 2, any known support can be used without any particular limitation. Specifically, a flexible film or disk made of a synthetic polymer resin; Non-magnetic metals such as Cu, Al, Zn, glass, porcelain,
Films, disks, cards and the like made of ceramics such as ceramics can be used.

Examples of the high-molecular synthetic resin forming the flexible film or the disk include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate, and polyethylene bisphenoxycarboxylate; Polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose acetate butyrate and cellulose acetate propionate; vinyl resins such as polyvinyl chloride and polyvinylidene chloride; or polyamides, polyimides, polycarbonates, polysulfones, polyether ethers Ketones, polyurethanes and the like can be mentioned, and when used, they can be used alone or in combination of two or more.

Next, the magnetic layer 4 provided on the intermediate layer 3 in the magnetic recording medium 1 of the present invention will be described.
The magnetic layer 4 is an uppermost layer of the magnetic recording medium 1, that is, a layer provided as a layer located on the surface of the magnetic recording medium 1, and is formed by using a magnetic paint mainly composed of a magnetic powder, a binder and a solvent. Is done.

Examples of the magnetic powder contained in the magnetic paint include iron oxide-based magnetic powders such as γ-Fe ₂ O ₃ and Co-γ-Fe ₂ O ₃ , ferromagnetic metal powder mainly composed of iron, and the like. Hexagonal ferrite powder and the like.

The ferromagnetic metal powder has a metal content of 7
0% by weight or more, and a ferromagnetic metal powder in which 60% by weight or more of the metal component is iron. Specific examples of the ferromagnetic metal powder include, for example, Fe—Co, Fe—Ni, F
e-Al, Fe-Ni-Al, Fe-Co-Ni, Fe
-Ni-Al-Zn, Fe-Al-Si and the like. In the ferromagnetic metal powder mainly composed of iron oxide and iron, the shape is needle-like or spindle-like, and the major axis length is preferably 0.05 to 0.25 μm, more preferably 0.0 to 0.25 μm.
The preferred acicular ratio is 3 to 20, the preferred X-ray particle size is 130 to 250 °, and the preferred specific surface area is 30 to 60 m ² / g.

The hexagonal ferrite powder includes barium ferrite and strontium ferrite in the form of fine flat plates, and a part of their Fe atoms is composed of Ti, C
magnetic powders substituted with atoms such as o, Ni, Zn, V, and the like. In addition, the hexagonal ferrite powder has a preferable plate diameter of 0.02 to 0.09 μm, a preferable plate ratio of 2 to 7, and a preferable specific surface area of 30 to
60 m ² / g.

The coercive force of the iron oxide-based magnetic powder or ferromagnetic metal powder is preferably from 1500 to 2500 Oe, more preferably from 1600 to 2400 Oe. The coercive force of the hexagonal ferrite powder is 1
It is preferably 500 to 2500 Oe,
More preferably, it is 2400 Oe. If the coercive force is less than the above lower limit, the short-wavelength RF output is reduced due to easy demagnetization, and if the coercive force exceeds the above upper limit, the head magnetic field is insufficient and the write capability is insufficient, Further, since the overwrite characteristics are deteriorated, it is preferable to be within the above range. The saturation magnetization of the iron oxide-based magnetic powder or the ferromagnetic metal powder is 100 to 180.
It is preferably emu / g, more preferably 110-160 emu / g. The saturation magnetization of the hexagonal ferrite powder is preferably 30 to 70 emu / g, and more preferably 45 to 70 emu / g. If the above-mentioned saturation magnetization is less than the above lower limit, respectively, the filling rate of the magnetic powder becomes low and the output decreases, and if it exceeds the above upper limit, it becomes necessary to reduce the binder, and The interaction between the powders increases, and as a result, the magnetic powders are in an agglomerated state, making it difficult to obtain a desired output.

Therefore, the coercive force of the magnetic layer 4 containing the iron oxide-based magnetic powder or the ferromagnetic metal powder is preferably from 1500 to 2500 Oe, more preferably from 1600 to 2500 Oe.
2400 Oe, and the coercive force of the magnetic layer 4 containing the hexagonal ferrite powder is preferably 1500 to 25
00 Oe. The saturation magnetic flux density of the magnetic layer 4 containing the iron oxide-based magnetic powder or the ferromagnetic metal powder is:
It is preferably 3000-4500 gauss, more preferably 3200-4000 gauss, and the saturation magnetic flux density of the magnetic layer 4 containing the above hexagonal ferrite powder is preferably 1500-2500 gauss, more preferably 160 gauss.
0-2500 gauss.

The magnetic powder contained in the magnetic paint used for forming the magnetic layer 4 may contain a rare earth element or a transition metal element, if necessary. In the present invention, the magnetic powder may be subjected to a surface treatment in order to improve the dispersibility and the like of the magnetic powder.
The above-mentioned surface treatment is described in “Characterization of Powder Surfa
ces "; a method similar to the method described in Academic Press and the like, for example, a method of coating the surface of the ferromagnetic powder with an inorganic oxide. At this time, the inorganic oxide that can be used is Al ₂
O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb
Examples thereof include ₂ O ₃ , ZnO, and the like. These may be used alone or in combination of two or more. The surface treatment can be performed by an organic treatment such as a silane coupling treatment, a titanium coupling treatment, and an aluminum coupling treatment, in addition to the above method.

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

The magnetic coating material used for forming the magnetic layer 4 includes a usual magnetic recording medium such as a dispersant, a lubricant, an abrasive, an antistatic agent, a rust inhibitor, a fungicide, and a curing agent. The additives used can be added as needed. As the above additives, specifically, JP-A-57-1
No. 62128, page 2, upper left column, line 6 to page 2, upper right column 1,
Various additives described in line 0, page 3, upper left column, line 6 to page 3, upper right column, line 18 can be mentioned.

The thickness of the magnetic layer 4 is 0.05 to 1 μm.
Is preferably, and more preferably 0.01 to 0.5 μm. When the thickness of the magnetic layer 4 is less than 0.05 μm, dropout increases, durability deteriorates,
If it exceeds 1 μm, the electromagnetic conversion characteristics (output) deteriorate, so that it is preferable to be within the above range.

Next, the intermediate layer 3 provided on the support 2 will be described. The intermediate layer 3 may be a layer having magnetism or a layer having no magnetism. When the intermediate layer 3 is a layer having magnetism, the intermediate layer 3 is a magnetic layer containing a magnetic powder (hereinafter, referred to as “magnetic intermediate layer”), and mainly includes a magnetic powder, a binder, and a solvent. It is formed using a magnetic paint as a component. When the intermediate layer 3 is a layer having no magnetism, the intermediate layer 3 is a nonmagnetic layer containing a nonmagnetic powder (hereinafter, referred to as a “nonmagnetic intermediate layer”). It is formed by using a magnetic paint mainly composed of a powder, a binder and a solvent.

As the magnetic powder contained in the magnetic paint used for forming the magnetic intermediate layer, a ferromagnetic powder is preferably used. As the ferromagnetic powder, both a soft magnetic powder and a hard magnetic powder are preferable. Used. The type of the soft magnetic powder is not particularly limited, but is preferably used for so-called weak electric devices such as a magnetic head and an electronic circuit. For example, "Physical (lower) magnetic properties of a ferromagnetic material and Application ”(Shokabo, 1984) 368
To 376 pages can be used, and specific examples thereof include oxide soft magnetic powder. As the oxide soft magnetic powder, spinel-type ferrite powder is preferably used. As the spinel-type ferrite powder, MnFe ₂ O ₄ , Fe ₃ O ₄ , CoFe ₂ O ₄ ,
NiFe ₂ O ₄ , MgFe ₂ O ₄ , Li _0.5 Fe _2.5 O
₄ , Mn-Zn ferrite, Ni-Zn ferrite, Ni-Cu ferrite, Cu-Zn ferrite, Mg-Zn ferrite, Li-Zn ferrite, Zn ferrite, Mn ferrite, etc. Can be. These oxide soft magnetic powders may be used alone or in combination of two or more.

As the soft magnetic powder, a metal soft magnetic powder or the like can be used. Examples of the metal soft magnetic powder include Fe-Si alloy and Fe-Al alloy (Alperm, Alf
enol, Alfer), permalloy (Ni-Fe-based binary alloy and multi-component alloy to which Mo, Cu, Cr, etc. are added), sendust (Fe-Si-Al [9.6% by weight of Si, 5. 4% by weight of Al and the balance being Fe]), Fe—Co alloys and the like. These metal soft magnetic powders may be used alone or in combination of two or more.

The coercive force of the above oxide soft magnetic powder is usually 0.1 to 150 Oe, and the saturation magnetization thereof is usually 30 to 9 Oe.
0 emu / g. The coercive force of the metal soft magnetic powder is usually 0.02 to 100 Oe, and the saturation magnetization is usually 50 to 100 Oe.
~ 500 emu / g.

The above soft magnetic powder can be produced, for example, as follows. That is, the metal soft magnetic powder can be obtained by a gas phase method. The oxide soft magnetic powder can be produced by a glass crystallization method, a coprecipitation firing method, a calcining method, a hydrothermal synthesis method, a sol-gel method, or the like.

The shape of the soft magnetic powder is not particularly limited, and specific examples include a sphere, a plate, and a needle. Further, the size is preferably from 5 to 800 nm.

Examples of the hard magnetic powder include iron oxide magnetic powder, ferromagnetic metal powder mainly composed of iron, and hexagonal ferrite powder. The iron oxide-based magnetic powder, the ferromagnetic metal powder mainly composed of iron, and the hexagonal ferrite powder include the iron oxide-based magnetic powder, ferromagnetic powder contained in the magnetic paint used for forming the magnetic layer 4. The same thing as a metal powder and a hexagonal ferrite powder is used. The physical properties such as the coercive force, saturation magnetization, shape, and specific surface area of the iron oxide-based magnetic powder, the ferromagnetic metal powder, and the hexagonal ferrite powder are also different from those of the ferromagnetic metal powder and the hexagonal crystal used for forming the magnetic layer 4. The properties are the same as those of the ferrite powder.

The magnetic powder contained in the magnetic coating material used for forming the magnetic intermediate layer may contain a rare earth element or a transition metal element, if necessary. In the present invention, in order to improve the dispersibility and the like of the ferromagnetic powder, the same as the surface treatment performed on the magnetic powder contained in the coating material used for forming the magnetic layer 4 is used. Surface treatment can be performed.

As the solvent, the same solvent as that contained in the magnetic paint used for forming the magnetic layer 4 is used. The amount of the solvent used is preferably 80 to 500 parts by weight, more preferably 100 to 350 parts by weight, based on 100 parts by weight of the magnetic powder.

The magnetic paint used for forming the magnetic intermediate layer may optionally contain additives which are added to the magnetic paint used for forming the magnetic layer 4. Further, a non-magnetic powder contained in a non-magnetic coating used for forming a non-magnetic intermediate layer described later can be added to the magnetic coating used for forming the magnetic intermediate layer.

The thickness of the magnetic intermediate layer is 0.2 to 5 μm.
Is preferably 0.5 to 4 μm, and most preferably 0.5 to 3.5 μm. When the thickness of the magnetic intermediate layer is less than 0.2 μm, the bending rigidity of the obtained magnetic recording medium becomes weak, and
If it exceeds m, the bending stiffness of the obtained magnetic recording medium may become too strong, or cupping or curling may occur to reduce head contact.

The non-magnetic powder contained in the non-magnetic paint used for forming the above-mentioned non-magnetic intermediate layer is not particularly limited. For example, carbon black, graphite, titanium oxide, barium sulfate, zinc sulfide, magnesium carbonate, Calcium carbonate, zinc oxide, calcium oxide, magnesium oxide, tungsten disulfide, molybdenum disulfide, boron nitride, tin dioxide, silicon dioxide, nonmagnetic chromium oxide, alumina, silicon carbide, cerium oxide, corundum, artificial diamond, nonmagnetic Iron oxide, garnet, garnet, silica, silicon nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, diatomaceous earth, dolomite, resinous powder, etc., among which non-magnetic iron oxide, oxide Titanium, carbon black, alumina,
Silicon oxide, boron nitride and the like are preferably used. These nonmagnetic powders may be used alone or as a mixture of two or more. The shape of the nonmagnetic powder is spherical, plate-like,
Needle-like or amorphous may be used, and its size is
5 to 200 nm for spherical, plate, and amorphous
It is preferable that the long axis length is 20 to 300 nm and the axial ratio is 3 to 20 in the needle-shaped one.

In the present invention, in order to improve the dispersibility and the like of the non-magnetic powder, the same non-magnetic powder as the magnetic powder contained in the magnetic paint used for forming the magnetic layer 4 is added to the non-magnetic powder. Surface treatment can be applied.

As the solvent contained in the non-magnetic paint used for forming the non-magnetic intermediate layer, the same solvent as the solvent contained in the magnetic paint used for forming the magnetic layer 4 is used. The amount of the solvent used is 10
It is preferably from 80 to 500 parts by weight, more preferably from 100 to 350 parts by weight, based on 0 parts by weight.

The magnetic paint used for forming the non-magnetic intermediate layer may optionally contain additives which are added to the magnetic paint used for forming the magnetic layer 4.

The thickness of the non-magnetic intermediate layer is 0.2 to 5 μm.
m, more preferably 0.5 to 4 μm, and most preferably 0.5 to 3.5 μm. If the thickness of the non-magnetic intermediate layer is less than 0.2 μm, the bending rigidity of the obtained magnetic recording medium 1 becomes weak, and
If it exceeds μm, the bending rigidity of the obtained magnetic recording medium may become too strong, or cupping or curling may occur, resulting in a decrease in head contact.

In a preferred embodiment of the present invention, the binder contained in the magnetic paint or the non-magnetic paint used for forming the magnetic layer and the intermediate layer is, as described above, the magnetic powder contained in each of the layers. Or p of nonmagnetic powder
When H is less than 7, the binder has a basic polar group, and when the pH is 7 or more, the binder has an acidic polar group. Hereinafter, the binder contained in the magnetic paint or the non-magnetic paint will be described. Examples of the binder include a thermoplastic resin, a thermosetting resin, and a reactive resin. Can be. Specific examples of the binder include vinyl chloride resin, polyester, polyurethane, nitrocellulose, epoxy resin, and the like.
Resins and the like described in page 7, upper right column, line 19 to page 2, lower right column, line 19 of JP-A-7-162128 are exemplified.
Examples of the acidic polar group that the binder has, for example,
Phosphoric acid and its salts, sulfonic acid and its salts, carboxylic acid and its salts, and the like. Further, as the basic polar group of the binder, for example, a primary amine,
Secondary amines, tertiary amines, quaternary ammonium salts and the like can be mentioned. The acidic or basic polar group is preferably contained in an amount of 10 ⁻² to 10 ⁻⁶ equivalent / g in one molecule of the binder. As the binder, a binder having one kind of the polar group in the molecule or a binder having two or more kinds of the polar groups may be used.

The polymerization degree of the binder is from 120 to
It is preferable that the number average molecular weight of the binder is 6,000 to 60,000,
The weight average molecular weight is preferably from 10,000 to 140,000.

As the binder having an acidic polar group and the binder having a basic polar group, commercially available products can also be used. The binder having an acidic polar group is manufactured by Union Carbide (VAGH, VY
HH, VMCH, VAGF), manufactured by Zeon Corporation (MR-
105, MR-110, MR-100), manufactured by Toyobo Co., Ltd. (Vylon UR8200, UR8300), and the like. As the binder having a basic polar group, Nissin Chemical Industry Co., Ltd. (MPR-TAO), Sekisui Chemical Industrial company (S-LEC E.C110, C130) and the like can be used. [However, the name in parentheses is the product name. In the present invention,
In use, the above binders may be used alone or in combination of two or more. The amount of the binder used is preferably about 5 to 200 parts by weight, more preferably 5 to 70 parts by weight, based on 100 parts by weight of the magnetic powder or the nonmagnetic powder.

In order to prepare the magnetic paint used for forming the magnetic layer 4 and the (non) magnetic paint used for forming the intermediate layer 3, for example, the (non) magnetic powder and the binder are mixed with a solvent. A part of the mixture is put into a Nauta mixer or the like and preliminarily mixed to obtain a mixture, and the obtained mixture is kneaded by a continuous pressure kneader or the like, and then diluted with a part of a solvent and dispersed using a sand mill or the like. After that, a method of mixing an additive such as a lubricant, filtering, and further mixing the remaining solvent, a curing agent, and the like can be given.

The magnetic layer 4 is preferably applied and formed when the intermediate layer 3 is wet.

In the magnetic recording medium 1 of the present embodiment, the back coat layer 5 provided on the back surface of the support 2 as necessary can be formed using a known back coat paint without any particular limitation. .

Although the embodiments of the magnetic recording medium of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are possible. For example, a primer layer may be formed between the support and the intermediate layer or the back coat layer, or another layer provided for recording a servo signal or the like corresponding to a hard system using a long wavelength signal. Other layers may be interposed as appropriate as long as the magnetic layer and the purpose of the present invention are not impaired.

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

Next, an outline of an example of a method for producing a magnetic recording medium of the present invention (a magnetic recording medium comprising a support, an intermediate layer, a magnetic layer and a back coat layer shown in FIG. 1) will be outlined. State. First, a magnetic or non-magnetic coating material for forming the intermediate layer and a magnetic coating material for forming the magnetic layer are wetted on the support so that the dry thickness of the intermediate layer and the magnetic layer is the above-mentioned thickness.・ Simultaneous multilayer coating is performed by an on-wet method to form a coating film of the intermediate layer and the magnetic layer. That is, the magnetic layer is applied when the intermediate layer is wet.
It is preferably formed. Next, the coating film is subjected to a magnetic field orientation treatment, dried, subjected to a calendering treatment, and further coated with the back coat paint on the back surface of the support to form a back coat layer, Perform a drying process. Next, if necessary, for example, when obtaining a magnetic tape, the magnetic tape is subjected to aging treatment at 40 to 70 ° C. for 6 to 72 hours, and slit into a desired width.

The simultaneous multi-layer coating method is described in Japanese Patent Application Laid-Open No. 5-73.
No. 883, column 42, line 31 to column 43, line 31, etc., wherein the magnetic paint which forms the magnetic layer before the magnetic or non-magnetic paint which forms the intermediate layer dries A method of coating, wherein the interface between the intermediate layer and the magnetic layer is smooth and the surface properties of the magnetic layer are also good, so that the dropout is small, the high density recording can be supported, and the coating film can be formed. A magnetic recording medium having excellent durability of the (intermediate layer and the magnetic layer) can be obtained.

The magnetic field orientation treatment is performed before the magnetic or non-magnetic paint for forming the intermediate layer and the magnetic paint for forming the magnetic layer are dried.
When the magnetic recording medium of the present invention is a magnetic tape, it is at least about 500 Oe, preferably about 1,000 to 10,000 Oe, in a direction parallel to the surface of the magnetic paint forming the magnetic layer.
The method can be performed by a method of applying a magnetic field of e, a method of passing the magnetic or non-magnetic coating material for forming the intermediate layer and the magnetic coating material through a solenoid of 1000 to 10000 Oe in a wet state, or the like.

The above calendering treatment can be performed by a super calendering method or the like in which two rolls such as a metal roll and a cotton roll or a synthetic resin roll, a metal roll and a metal roll are passed. Also,
The conditions of the calender treatment are as follows: the roll surface temperature is 60 to 1;
At 40 ° C., the roll linear pressure can be 100 to 500 kg / cm.

The drying treatment is carried out, for example, at 30 to 120 ° C.
In this case, the degree of drying of the coating film can be controlled by controlling the temperature of the gas and the supply amount of the gas.

The back coat layer provided as needed is provided on the back side of the support (the surface on which the intermediate layer and the magnetic layer are not provided).
It is obtained by applying a back coat paint, which is usually used for forming a back coat layer, on the support.

In the production of the magnetic recording medium of the present invention, a finishing step such as a polishing or cleaning step for the surface of the magnetic layer can be performed if necessary. The application of the magnetic or non-magnetic coating material for forming the intermediate layer and the magnetic coating material for forming the magnetic layer can also be performed by a generally known sequential coating method.

[0058]

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

Example 1 Using a non-magnetic paint (A) for forming an intermediate layer having the following composition, a magnetic paint (a) for forming a magnetic layer having the following composition, and a backcoat paint having the following composition, the following [magnetic recording Method of Manufacturing Medium] A magnetic tape was manufactured.

Nonmagnetic paint (A) for forming an intermediate layer, nonmagnetic inorganic powder α-Fe ₂ O ₃ (Bengara) 100 parts by weight (major axis length: 0.15 μm) pH: 9.6 Alumina 5 parts by weight Central particle size: pH when 5.0 μg of 0.1 μm is dispersed in 100 ml of water; 7.0 ・ 2 parts by weight of carbon black Central particle size: 0.02 μm pH; 9.0 ・ 10 parts by weight of “MR110” [ Trade name, manufactured by Nippon Zeon Co., Ltd., vinyl chloride copolymer] Hydroxyl group content: 3 × 10 ⁻⁴ equivalent / g Sulfonate group content: 1 × 10 ⁻⁴ equivalent / g Average polymerization degree: 300 Number average Molecular weight; 12000 Weight average molecular weight: 28000 ・ 10 parts by weight of “UR8300” [trade name, urethane resin manufactured by Toyobo Co., Ltd.] Hydroxyl content: 7 × 10 ⁻⁵ equivalent / g Sulfonate content: 3 × ^10-5 equivalents / g number average 28,000 parts by weight of myristic acid 1 part by weight of butyl stearate 5 parts by weight of "Coronate L" [trade name, manufactured by Nippon Polyurethane Co., Ltd., polyisocyanate compound] Methyl ethyl ketone, toluene, cyclohexanone (1: 1) 250 parts by weight)

Magnetic coating material for forming magnetic layer (a) 100 parts by weight of “ferromagnetic metal fine powder” [needle-shaped ferromagnetic metal powder mainly composed of iron] Coercive force: 1800 Oe Saturation magnetization: 120 emu / g Long axis Length: 1.0 μm Needle ratio: 8 Specific surface area: 45 m ² / g pH: 9.5 ・ Alumina 12 parts by weight Central particle diameter 0.1 μm pH; 7.0 ・ Carbon black 1 part by weight Central particle diameter 0.05 μm pH; 9.0 ・ 11 parts by weight “MR110” [trade name, manufactured by Nippon Zeon Co., Ltd., vinyl chloride copolymer] Hydroxyl content: 3 × 10 ⁻⁴ equivalent / g Sulfonate group content: 1 × 10 ^-4 equivalents / g Average degree of polymerization; 300 Number average molecular weight; 12000 Weight average molecular weight; 28000 ・ 7 parts by weight of “UR8300” [trade name, urethane resin manufactured by Toyobo Co., Ltd.] 2 parts by weight of myristic acid Butyl 2 parts by weight of stearate ・ 2 parts by weight of 2-ethylhexyl stearate ・ 4 parts by weight of “Coronate L” [Polyisocyanate compound manufactured by Nippon Polyurethane Co., Ltd.] ・ Methyl ethyl ketone, toluene, cyclohexanone (1: 1: 1 200 parts by weight)

Backcoat paint 32 parts by weight of carbon black (average primary particle size 0.028 μm) 8 parts by weight of carbon black (average primary particle size 0.062 μm) “Nipporan 2301” [trade name, Nippon Polyurethane Industry Co., Ltd. Polyurethane manufactured by Takeda Pharmaceutical Co., Ltd., 50 parts by weight) Nitrocellulose (having a viscosity of 1/2 second manufactured by Hercules Powder Co.) 20 parts by weight 4 parts by weight-Copper phthalocyanine 5 parts by weight-Stearic acid 1 part by weight-Methyl ethyl ketone 120 parts by weight-Toluene 120 parts by weight-Cyclohexanone 120 parts by weight

[Method of Manufacturing Magnetic Recording Medium] The non-magnetic paint (A) (excluding myristic acid, butyl stearate, polyisocyanate and a part of the solvent) for forming the above-mentioned intermediate layer was prepared using methyl ethyl ketone, toluene and cyclohexanone. And the mixture was adjusted so that the solid content concentration became 80%, and kneaded with a planetary mixer. Next, the mixture was diluted with the above solvent so that the solid content concentration became 40%, and dispersion treatment was performed with a vertical sand mill. Furthermore, after diluting with the solvent so that the solid content concentration becomes 35%, myristic acid and butyl stearate are added, the mixture is filtered through a filter having an absolute filtration accuracy of 1 μm, and polyisocyanate is added. The non-magnetic paint to be formed was used.
Further, the magnetic paint (a) for forming the magnetic layer (however,
Myristic acid, butyl stearate, 2-ethylhexyl stearate, polyisocyanate and a part of the solvent are excluded) in a mixed solvent of methyl ethyl ketone, toluene and cyclohexanone so as to have a solid concentration of 80%. And kneaded. Next, the mixture was diluted with the above solvent so that the solid content concentration became 40%, and dispersion treatment was performed with a vertical sand mill. Further, after diluting with the above-mentioned solvent so that the solid content concentration becomes 35%, myristic acid, butyl stearate and 2-ethylhexyl stearate are added, and the mixture is filtered through a filter having an absolute filtration accuracy of 1 μm to remove polyisocyanate. It was added to obtain a magnetic paint for forming a magnetic layer. Then, the thickness of 10 μm
On the surface of a polyethylene terephthalate (PET) film, a nonmagnetic paint for forming the intermediate layer formed as described above and a magnetic paint for forming the magnetic layer are dried by drying the nonmagnetic intermediate layer with a dry thickness of 2 μm and the magnetic layer. Was 0.5 μm to form a coating film of the intermediate layer and the magnetic layer.
Next, while the coating film was passed through a 5000 Oe solenoid magnet while the coating film was wet, a magnetic field orientation treatment was performed, and 8
After drying at 0 ° C., the film was wound. Next, after performing a surface smoothing treatment with a calender under the conditions of a surface temperature of 85 ° C. and a linear pressure of 350 kg / cm to form an intermediate layer and a magnetic layer, the back coat paint is dried on the back surface of the support at a dry thickness of 0.1 mm. It was applied to a thickness of 5 μm, dried at 90 ° C., and wound up. Then, after aging treatment at 50 ° C. for 16 hours, the tape was cut into a tape having a width of イ ン チ inch to obtain a magnetic tape.
Loaded in inch type data backup device.

The obtained magnetic tape as a magnetic recording medium was evaluated according to the following [Evaluation criteria for magnetic recording medium]. The results are shown in [Table 1].

[Evaluation Criteria of Magnetic Recording Medium] (1) Center Line Surface Roughness of Magnetic Recording Medium The obtained magnetic recording medium was measured by using a surface roughness shape measuring device “Surfcom 553A” manufactured by Tokyo Seimitsu Co., Ltd. use,
The center line surface roughness Ra was measured under the conditions of a needle radius of 2 μm, a load of 30 mg, a magnification of 200,000, and a cutoff of 0.08 mm. The center line surface roughness Ra is obtained by extracting a portion of the measurement length L from the roughness curve in the direction of the center line, setting the center line of the extracted portion as the X axis, and the direction of the vertical magnification as the Y axis,
When the roughness curve is represented by y = f (x), the value obtained by the following equation is represented by [nm].

[0066]

(Equation 1)

(2) Electromagnetic conversion characteristics (C / N characteristics) A 4.7 MHz single wave was recorded on the obtained magnetic tape using a DDS-1 drive, and the reproduction output (C) was observed with a spectrum analyzer. , And the noise level was expressed as C / N as a noise level (N) of 3.7 MHz.

Example 2 The same as Example 1 except that the vinyl chloride copolymer used in the coating material for forming the intermediate layer and the magnetic layer was changed to one having a polar group shown in Table 1. To obtain a magnetic tape as a magnetic recording medium. The obtained magnetic tape was evaluated in the same manner as in Example 1. The results are shown in [Table 1].

[Example 3] The non-magnetic powder and the magnetic powder used in the coating material for forming the intermediate layer and the magnetic layer were changed to those having the pH values shown in Table 1, and the vinyl chloride copolymer was obtained as shown in Table 1. ]
The operation was carried out in the same manner as in Example 1 except that the magnetic tape was changed to one having a polar group as shown in FIG. . The obtained magnetic tape was evaluated in the same manner as in Example 1. The results are shown in [Table 1].

Example 4 Non-magnetic paint for forming an intermediate layer
Non-magnetic inorganic powder α-Fe used for_TwoO_Three(Bengara) 1
Instead of 00 parts by weight, the average particle diameter of the soft magnetic powder is 0.1.
025 μm Fe _ThreeO_Four(Magnetite) 100 parts by weight
The operation was performed in the same manner as in Example 1 except that
A magnetic tape was obtained as an air recording medium. The magnetic tape obtained
The evaluation of the loop was performed in the same manner as in Example 1. The results are shown in the table
1].

Comparative Example 1 An operation was performed in the same manner as in Example 1 except that the non-magnetic powder used in the non-magnetic paint for forming the intermediate layer was changed to the one having the pH shown in Table 1. A magnetic tape as a magnetic recording medium was obtained. The obtained magnetic tape was evaluated in the same manner as in Example 1. The results are shown in [Table 1].

Comparative Example 2 The non-magnetic powder used for the non-magnetic coating for forming the intermediate layer was changed to the one shown in Table 1 and the vinyl chloride copolymer was changed to the following. Was performed in the same manner as in Example 1 to obtain a magnetic tape as a magnetic recording medium. -Vinyl chloride copolymer "ESREC E-C110" (trade name, manufactured by Sekisui Chemical Co., Ltd.) Hydroxyl content: 1.3 × 10 ^-3 equivalent / g Quaternary ammonium base content: 2.0 × ^10-5 equivalents / g Average degree of polymerization; 320 Number average molecular weight; 25,000 Weight average molecular weight; 50,000 The obtained magnetic tape was evaluated in the same manner as in Example 1.
The results are shown in [Table 1].

Comparative Example 3 The same as Example 1 except that the non-magnetic powder and the magnetic powder used in the coating material for forming the intermediate layer and the magnetic layer were changed to those having polar groups shown in Table 1. To obtain a magnetic tape as a magnetic recording medium. The obtained magnetic tape was evaluated in the same manner as in Example 1. The results are shown in [Table 1].

[0074]

[Table 1]

As is clear from the results shown in Table 1,
The magnetic tape (Examples 1 to 4) of the present invention in which the difference between the pH of the magnetic powder contained in the magnetic layer and the pH of the magnetic powder or the non-magnetic powder contained in the intermediate layer is 2 or less, has a smooth surface. It can be seen that they have excellent properties and electromagnetic conversion characteristics.

[0076]

As described in detail above, the magnetic recording medium of the present invention has a difference between the pH of the magnetic powder contained in the magnetic layer and the pH of the magnetic powder or the non-magnetic powder contained in the intermediate layer by two. By making the following, the surface smoothness and the electromagnetic conversion characteristics are excellent.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an enlarged cross section of a main part of a preferred embodiment of a magnetic recording medium of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic recording medium 2 Support 3 Intermediate layer 4 Magnetic layer 5 Back coat layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tadashi Yasuoka 2606 Akabane, Kakaicho, Haga-gun, Tochigi Pref.

Claims (3)

[Claims] 1. A magnetic recording medium comprising a support, an intermediate layer provided on the support, and a magnetic layer provided on the intermediate layer, wherein a magnetic powder contained in the magnetic layer The difference between the pH and the pH of the magnetic or non-magnetic powder contained in the intermediate layer is 2
A magnetic recording medium characterized by the following. 2. The binder contained in the magnetic layer and the intermediate layer has a basic polar group when the pH of the magnetic powder or the nonmagnetic powder contained in each of the layers is less than 7,
The magnetic recording medium according to claim 1, wherein the magnetic recording medium has an acidic polar group when the pH is 7 or more. 3. The pH of the magnetic powder contained in the magnetic layer
The magnetic recording medium according to claim 1, wherein the number is 8 to 11.