JPH09171617A - Production of magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium which has an excellent traveling property and durability and is adequate for high-density recording by using a magnetic coating material of which the distortion at the time of attaining the equal values in the modulus of storage elasticity and the modulus of loss elasticity attains a specific % or above within a range of specific strain % as a magnetic coating material. SOLUTION: The characteristic that the modulus G' of storage elasticity and the moulus G'' of loss elasticity decrease according to an increase in a strain γ is obtd. when the modulus G' of storage elasticity and the modulus G'' of loss elasticity when the magnitude of the strain γ is changed in a range of 0.1 to 1000% are examined with the magnetic coating material. The modulus G' of storage elasticity attain the value larger than the modulus G'' of loss elasticity within the range where the strain γ is small but when the distortion exceeds γc, the modulus G' of storage elasticity and the mobulus G'' of loss elasticity are inverted and the modulus G'' of loss elasticity attains the value larger than the modulus G' of storage elasticity. When the distortion γc at the time the curves of the moduli G' and G'' of elasticity intersect is regulated to >=50%, the tension in the process of the formation of the coating film and the oscillation of the coating film according to shrinkage are suppressed. Consequently, the surface roughness of the coating film is suppressed and the magnetic recording medium of a double layer constituting type having excellent traveling durability is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium, and more particularly to controlling dynamic viscoelasticity of magnetic paint.

[0002]

2. Description of the Related Art Conventionally, in video tapes, audio tapes, magnetic disks, etc., ferromagnetic powders such as ferromagnetic iron oxide, Co-modified iron oxide, CrO ₂ and ferromagnetic alloy powder are dispersed in a binder. A so-called coating type magnetic recording medium in which a magnetic coating film is formed by coating the prepared magnetic coating material on a non-magnetic support is widely used.

In recent years, in the field of magnetic recording, recording density and wavelength shortening are progressing, and even in the above-mentioned coating type magnetic recording medium, such recording density and wavelength shortening can be achieved. There is a growing demand to have corresponding properties.

Here, in the coating type magnetic recording medium,
As a method for improving the electromagnetic conversion characteristics in the high density recording area, thinning of the magnetic coating film can be mentioned. When the magnetic coating film is made thin, self-demagnetization loss during recording and thickness loss during reproduction are reduced, and electromagnetic conversion characteristics are effectively improved.

However, in this case, when the thickness of the magnetic coating film is reduced to, for example, 2 μm or less, the surface shape of the non-magnetic support is likely to be raised on the surface of the magnetic coating film, and the surface of the magnetic coating film is rough. become. If so, the electromagnetic conversion characteristics are deteriorated due to spacing loss, and dropouts frequently occur.

Therefore, in the coating type magnetic recording medium, a non-magnetic coating having a relatively large thickness is interposed between the magnetic coating and the non-magnetic support, whereby the surface shape of the non-magnetic support is changed to the magnetic coating. A multilayer coating type structure is adopted, which is difficult to appear on the film surface. In this multi-layer coating type magnetic recording medium, since a thin magnetic coating film can be formed on a smooth surface, excellent electromagnetic conversion characteristics can be obtained in the short wavelength region.

By the way, as a method for producing such a multilayer coating type magnetic recording medium, until now, a non-magnetic coating material was applied on a non-magnetic support, dried, and then calendered if necessary, A so-called dry-on-wet coating method is used in which a magnetic paint is applied onto the dried lower layer coating film.

However, in this coating method, since the lower coating film and the upper coating film are formed on separate lines, the manufacturing process is complicated, and the thin layer of the upper coating film is formed for the following reasons. There is a limit to conversion.

That is, to form a thin upper coating film,
A method of reducing the coating amount itself of the upper layer coating or adding a large amount of a solvent to the coating to dilute the concentration is adopted.

However, when the coating amount of the coating material is reduced, the drying starts before the coating film is sufficiently leveled, and coating defects such as streaks and marking patterns (in the case of the grab-aroll coating method) remain and the yield is increased. Becomes very bad.

On the other hand, when the concentration of the coating is diluted,
Many voids are formed in the coating film, the filling degree of the ferromagnetic powder becomes low, and the coating film strength becomes insufficient.

Therefore, as described in Japanese Patent Laid-Open No. 63-191315, the wet coating is applied to the lower coating film while the lower coating film is in a wet state. A method (wet-on-wet coating method) has been proposed.

In this wet-on-wet coating method, a lower layer coating material is applied to form a lower layer coating film, and then an upper layer coating material is applied onto the lower layer coating film. Wet coating method in which the coating material for the lower layer is sequentially coated, and an extrusion coater in which two slits for pushing the coating material for the lower layer and the coating material for the upper layer are formed in close proximity are used. A simultaneous multi-layer coating system is known in which paints are simultaneously coated.

In such a wet-on-wet coating method, even if the coating amount of the upper layer coating material is reduced, it is dried at the same time as the lower layer coating material, so that the coating film should be dried before being sufficiently leveled. There is no such thing as
The upper coating film is formed with good surface properties. Further, the adhesion between the lower layer and the upper layer is good, and good running durability can be obtained.

[0015]

However, this wet-on-wet coating method is
Various studies have been made in the case where the upper layer paints are all magnetic paints, but there is insufficient knowledge about the case of applying non-magnetic paints and magnetic paints. When applying the non-magnetic paint and the magnetic paint, if the conditions for the lower layer paint and the upper layer paint are both magnetic paints are applied as they are, disorder will occur at the lower layer upper layer interface and pinholes may occur in the coating film. In some cases, a phenomenon such as repelling may occur in the upper coating film. Also, depending on the physical properties of the paint,
Surface roughness occurs in the upper coating film, and the surface roughness causes spacing loss, RF envelope defect, deterioration of running property and durability, increase of dropout, and the like.

Therefore, the present invention has been proposed in view of such conventional circumstances, and it is possible to form the interface between the lower layer and the upper layer to be smooth and to form the magnetic coating film with a good surface property, and to obtain the electromagnetic conversion characteristics. It is an object of the present invention to provide a method of manufacturing a magnetic recording medium, which is excellent in shape, has a good shape of the RF envelope, can suppress dropout, and can also be manufactured with a high yield.

[0017]

In order to achieve the above object, the inventors of the present invention have conducted extensive studies and, as a result, have found that the state of the coating film shows that the coating film is oscillated by tension and contraction during the coating film formation process. Therefore, it has been found that it is important to control the coating material from the dynamic viscoelastic physical properties in order to form a magnetic coating film having a good surface property.

The method for producing a magnetic recording medium of the present invention has been completed based on such findings, and is prepared by dispersing a magnetic powder and a binder together with a solvent on a non-magnetic support. When a magnetic coating film is formed by applying a magnetic coating material, the storage elastic modulus G ′ and loss elastic modulus G ″ measured by the strain control type viscometer of the magnetic coating material at an angular frequency of 1 Hz are It is characterized in that the strain γc is set to 50% or more when the storage elastic modulus G ′ and the loss elastic modulus G ″ are equal in the range of 0.1 to 1000%.

By using the magnetic coating material satisfying such conditions, the oscillation of the coating film due to the tension and shrinkage during the coating film formation process can be suppressed, and the magnetic coating film can be formed with a good surface property. Become so.

In the present invention, the magnetic coating film may be formed on the non-magnetic support through the non-magnetic coating film.
In this case, after the nonmagnetic coating material prepared by dispersing the nonmagnetic powder and the binder together with the solvent on the nonmagnetic support to form the nonmagnetic coating film, the strain γc has a magnetic property satisfying the above conditions. A magnetic coating film is formed by applying a paint.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described.

In order to prepare a coating type magnetic recording medium, a magnetic coating prepared by dispersing a magnetic powder and a binder together with a solvent is sequentially coated on a continuously running non-magnetic support to form a magnetic coating. Form a film.

In the formation of such a magnetic coating film, the surface of the magnetic coating film is roughened due to the oscillation of the coating film.
This causes deterioration of electromagnetic conversion characteristics of the medium, defective RF envelope, deterioration of running property and durability, increase of dropout, and the like.

Therefore, in the present invention, in order to suppress the oscillation of such a coating film and make the surface of the magnetic coating film in a good state, the magnetic coating material is subjected to a strain control viscometer under the condition of an angular frequency of 1 Hz. The measured storage elastic modulus G ′ and loss elastic modulus G ″ have a strain γc of 50% when the storage elastic modulus G ′ and the loss elastic modulus G ″ are equal in a strain range of 0.1 to 1000%. The above settings are made.

The storage elastic modulus G'and the loss elastic modulus G "will be described in detail below.

In the field of rheology, deformation when a force is applied to a substance is roughly classified into elastic deformation and flow, and flow is further classified into viscous flow and plastic flow. Here, a dispersion liquid in which a solid powder is dispersed in a solvent, which is used for forming a magnetic coating film, shows a physical property (viscoelasticity) that is a combination of elasticity and viscosity in terms of rheology.

Such a viscoelastic body generally exhibits a peculiar behavior (dynamic property) when a stress or a strain which periodically changes with time is applied.

For example, in the case of a completely elastic body, the strain γ
Is given while changing sinusoidally with time,
As shown in, the strain γ and the stress σ are observed as a sine wave of the same frequency with no phase difference. In a completely viscous body, as shown in FIG. 2, the strain γ is observed with a phase difference δ of 90 ° behind the stress σ.

On the other hand, in the viscoelastic body, as shown in FIG.
The strain γ is observed later than the stress σ with a phase difference δ of 0 ° <δ <90 °. That is, the stress σ in the viscoelastic body
Is a complex number composed of a real part (elastic component) having the same phase as the distortion γ and an imaginary part (viscous component) having a phase advanced by 90 °, and the phase advances by δ from the distortion γ as a whole.

If the elastic modulus G ^* is defined as the ratio between the stress σ and the strain γ, the elastic modulus G ^* in this case is a complex number. This G ^* is called a complex elastic modulus, the real part G ′ is called a storage elastic modulus (elastic element), and the imaginary part G ″ is called a loss elastic modulus (viscous element). The phase difference between stress σ and strain γ is When δ, G ^* , G ′, G ″ are represented as follows.

Complex elastic modulus G ^* = σ / γ Storage elastic modulus G ′ = G ^* cosδ Loss elastic modulus G ″ = G ^* sinδ In order to control the oscillation of the magnetic coating film during the coating film formation process, this storage is controlled. It is important to regulate the elastic modulus G ′ and the loss elastic modulus G ″.

That is, in the commonly used magnetic paint, the storage elastic modulus G ′ and loss elastic modulus G ″ when the magnitude of the strain γ is changed in the range of 0.1 to 1000% are shown in FIG. As shown in (1), a curve in which the storage elastic modulus G ′ and the loss elastic modulus G ″ decrease as the strain γ increases is obtained. The range of the strain γ from 0.1 to 1000% is based on the magnitude of the strain of the coating film which is considered to occur during the film formation process. The measuring device and the measuring conditions used for the measurement in FIG. 4 are as follows.

Apparatus: Strain control type viscometer (Rheometrics, trade name RFS-II type) Measurement mode: Strain insertion (angular frequency fixed at 1 Hz) Geometry: Titanium, 50 mm diameter parallel plate Such as shown in FIG. Such a curve is obtained due to the non-linear viscoelasticity of the paint.

Here, the storage elastic modulus G'has a larger value than the loss elastic modulus G "in the range where the strain γ is small, but when the strain exceeds γc, the storage elastic modulus G'and the loss elastic modulus G" are obtained.
Is reversed, and the loss elastic modulus G ″ becomes a value larger than the storage elastic modulus G ′.

In the present invention, the strain γc when the curves of the storage elastic modulus G ′ and the loss elastic modulus G ″ intersect is regulated to 50% or more. When the strain γc of the magnetic paint is regulated in this way, a coating film is formed. Oscillation of the coating film due to tension and shrinkage during the process can be suppressed.As a result, the surface roughness of the magnetic coating film due to the oscillation of the coating film is suppressed, the yield of the medium is improved, and the electromagnetic conversion characteristics are improved. Thus, a multilayer coating type magnetic recording medium excellent in running durability will be manufactured.

The strain γc of the magnetic paint is adjusted by controlling the kind and molecular weight of the binder used in the paint, the contents of magnetic powder and other solid powder components, the kind of solvent and the degree of dispersion.

Here, specific materials for the magnetic coating material include those shown below.

First, as the ferromagnetic powder, γ-Fe is used.
₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Co-coated γ-Fe ₂ O ₃ ,
CrO ₂ and ferrites represented by magnetite, that is, Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , and Co-deposited F
e ₃ O ₄ and the like.

Further, a hexagonal ferrite having a plate shape and having an easy magnetization axis in a direction perpendicular to the plate surface is also suitable as the ferromagnetic powder. Hexagonal ferrite includes barium ferrite, strontium ferrite, and the like, and a part of iron element is another element (for example, Ti, Co, Zn,
In, Mn, Ge, Nb, etc.). Among hexagonal ferrites, barium ferrite is particularly preferable, and barium ferrite in which a part of Fe is substituted with at least Co and Zn has an average particle diameter (diagonal length of plate surface of hexagonal ferrite). Is 300 to 900 angstroms, the plate ratio (value obtained by dividing the length of the diagonal of the plate surface of the hexagonal ferrite by the plate thickness) is 2.0 to 10.0, and the coercive force is 450 to 150.
0 Oe is preferred.

Alternatively, a metallic magnetic powder may be used as the ferromagnetic powder. As the metal magnetic powder, F
e, Co, etc., as well as Fe-Al based, Fe-Al
-Ni-based, Fe-Al-Zn-based, Fe-Al-Co-based,
Fe-Al-Ca system, Fe-Ni system, Fe-Ni-Al
System, Fe-Ni-Co system, Fe-Ni-Si-Al-M
n-based, Fe-Ni-Si-Al-Zn-based, Fe-Al-
Si-based, Fe-Ni-Zn-based, Fe-Ni-Mn-based, F
e-Ni-Si system, Fe-Mn-Zn system, Fe-Co-
Examples of the alloy powder include Ni—P-based and Ni—Co-based alloy powders containing Fe, Ni, Co, and the like as main components.

Of these, the Fe-based magnetic powder has excellent electrical characteristics. Further, in terms of corrosion resistance and dispersibility, Fe
-Al system, Fe-Al-Ca system, Fe-Al-Ni system,
Fe-Al-Zn system, Fe-Al-Co system, Fe-Ni
-Si-Al-Zn system, Fe-Ni-Si-Al-Mn
Fe-Al-based alloy powders such as iron-based alloys are preferred.

The shape of these metal magnetic powders has an average major axis length of 0.5 μm or less, preferably 0.01 to 0.4 μm.
It is more preferably 0.01 to 0.3 μm and have an axial ratio (average major axis length / average minor axis length) of 12 or less, preferably 10 or less. For example, Fe—Al based ferromagnetic metal powder (Fe: Al weight ratio = 100: 5) having an average major axis length of 0.16 μm and a coercive force Hc of 1580 Oe.
A material having a saturation magnetization amount σs of 120 emu / g exhibits extremely excellent characteristics. The average major axis length and average minor axis length can be determined by observation with a transmission electron microscope.

As described above, as the ferromagnetic powder, oxide magnetic powder or metal magnetic powder can be used, but in any case, the saturation magnetization amount (σs) is preferably 70 emu / g or more. If the saturation magnetization is less than 70 emu / g, sufficient electromagnetic conversion characteristics may not be obtained. Further, from the viewpoint of enabling recording / reproducing in the high density recording area, the specific surface area by the BET method is preferably 45 m ² / g or more.

Typical binders are polyurethane resins, polyester resins, vinyl chloride resins such as vinyl chloride copolymers, and the like.

These resins are --SO ₃ M, --OSO ₃ M,
-COOM, -PO (OM ') ₂ (where M represents a hydrogen atom or an alkali metal such as Na, K, Li, and M'
Preferably represents a hydrogen atom or an alkali atom such as Na, K or Li, an alkyl group) and a repeating unit having at least a polar group selected from sulfobetaine groups. These polar groups have the effect of improving the dispersibility of the ferromagnetic powder, and the content is 0.1 to 8.0.
It is preferably mol%, more preferably 0.2 to 6.0 mol%. When the content of the polar group is less than 0.1 mol%, the dispersibility of the magnetic powder is reduced. Conversely, the content rate is 8.0 mol%
If it exceeds, the magnetic coating material tends to gel. Also,
The weight average molecular weight of the resin is 15,000 to 50,000.
Is preferably within the range.

The vinyl chloride copolymer containing a polar group can be obtained by an addition reaction of a copolymer having a hydroxyl group such as a vinyl chloride-vinyl alcohol copolymer with a compound having a polar group and a chlorine atom. Can be synthesized.

The polyester is synthesized by reacting a polyol with a polybasic acid. Incidentally, other polar group-introduced polyesters can also be synthesized by a known method.

Polyurethane is synthesized by the reaction of polyol and polyisocyanate. As this polyol, a polyester polyol obtained by reacting a polyol with a polybasic acid is generally used. In addition,
When a polyester polyol having a polar group is used as a raw material, a polyurethane having a polar group can be synthesized.

These resins may be used alone or in combination of two or more. For example,
When the polyurethane and / or polyester and the vinyl chloride resin are mixed and used, the weight ratio is 90:10.
It may be in the range of 10:90, preferably 70:30 to 30:70.

Further, the following resins may be used together in an amount of 50% by weight or less based on the total binder.

That is, as the resin to be used in combination, a vinyl chloride-vinyl acetate copolymer having a weight average molecular weight of 10,000 to 200,000, a vinyl chloride-vinylidene chloride copolymer, a vinyl chloride-acrylonitrile copolymer,
Butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (nitrocellulose etc.), styrene-butadiene copolymer, phenol resin, epoxy resin, urea resin, melamine resin,
Examples thereof include phenoxy resin, silicone resin, acrylic resin, urea formamide resin, and various synthetic rubber resins.

As the binder, the above resins are used, and the amount of the binder to be mixed in the upper magnetic layer is preferably 8 to 25 parts by weight with respect to 100 parts by weight of the ferromagnetic powder. It is preferably 10 to 20 parts by weight.

In addition, the magnetic coating material usually contains abrasives, lubricants, durability improvers, dispersants, antistatic agents used in magnetic recording media of this type for the purpose of improving running durability of the media. Also, additives such as conductive fine powder may be added.

As a polishing agent, Japanese Patent Laid-Open No. 4-214218 is used.
Solid powders as described in the publication can be used. The average particle size of this abrasive is 0.05 μm to 0.6 μm, preferably 0.05 μm to 0.5 μm, and more preferably 0.05 μm to 0.3 μm. The amount of the abrasive added is 3 to 100 parts by weight of the magnetic powder.
The amount is 20 parts by weight, preferably 5 to 15 parts by weight, more preferably 5 to 10 parts by weight.

As the lubricant, fatty acids, fatty acid esters, etc. may be used alone or in combination. The fatty acid may be a monobasic acid or a dibasic acid and has 6 to 6 carbon atoms.
30 is preferable, and 12 to 22 is more preferable.

The amount of the fatty acid or fatty acid ester added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the magnetic powder. When the amount of the fatty acid is less than 0.2% by weight, the running property of the medium is not sufficiently improved. When the amount exceeds 10% by weight, the fatty acid exudes on the surface of the magnetic layer,
The output tends to decrease. On the other hand, if the amount of the fatty acid ester added is less than 0.2% by weight, still durability is particularly insufficient. If it exceeds 10% by weight, the fatty acid ester is likely to seep out to the surface of the magnetic layer and the output tends to be reduced. When using a fatty acid and a fatty acid ester together,
The ratio of fatty acid to fatty acid ester is 10:90 by weight.
90:10 is preferred.

A known lubricant may be used in combination with the above fatty acids and fatty acid esters. Examples of the lubricant used in combination include silicone oil, carbon fluoride, fatty acid amide, and α-olefin oxide.

Polyisocyanate or the like is used as the curing agent. Examples of polyisocyanates include aromatic polyisocyanates such as adducts of tolylene diisocyanate (TDI) and active hydrogen compounds, and aliphatic polyisocyanates such as adducts of hexamethylene diisocyanate (HMDI) and active hydrogen compounds. is there. The weight average molecular weight of these polyisocyanates is 100 to 3,000.
A range of 0 is desirable.

As a dispersant, JP-A-4-214218 is available.
Compounds such as those described in the publication can be used. These dispersants are suitably used in the range of 0.5 to 5% by weight with respect to the magnetic powder.

As the antistatic agent, Japanese Patent Laid-Open No. 4-2142 is known.
Surfactants such as those described in JP 18 can be used. The addition amount of these antistatic agents is preferably in the range of 0.01 to 40% by weight with respect to the binder. In addition,
Conductive fine powder may be added as an antistatic agent. As the conductive fine powder, for example, carbon black, graphite, tin oxide, silver powder, silver oxide, silver nitrate, silver organic compounds, metal particles such as copper powder, zinc oxide, barium sulfate,
Examples include pigments such as metal oxides such as titanium oxide that have been coated with a conductive substance such as a tin oxide coating or an antimony solid solution tin oxide coating. The average particle size of these conductive fine powders is 5 to 700 nm, preferably 5 to 2 nm.
It is good that it is 00 nm. The amount of the conductive fine powder added is appropriately 1 to 20 parts by weight, preferably 2 to 7 parts by weight, based on 100 parts by weight of the magnetic powder.

The magnetic coating material is prepared by mixing various additives such as the ferromagnetic powder, binder and dispersant, lubricant, abrasive, antistatic agent and the like with a solvent to prepare a high concentration magnetic coating material.
It is prepared by diluting and dispersing this high-concentration magnetic paint.

As a solvent for forming the coating material, a solvent usually used in this type of magnetic recording medium, for example, JP-A-4-
What is described in 214218 gazette is used. This solvent may be used alone or in combination of two or more kinds.

As the kneading disperser, for example, any of those described in JP-A-4-214218 can be used. In particular, since a power consumption load of 0.05 to 0.5 kW (per kg of magnetic powder) can be provided,
A pressure kneader, open kneader, continuous kneader, two-roll mill, and three-roll mill are suitable.

However, the kind and molecular weight of the binder used in the magnetic paint, the content of the solid powder component, the kind of solvent and the degree of dispersion are set so that the distortion γc of the paint satisfies a predetermined condition.

The magnetic coating film is formed by successively coating the thus prepared magnetic coating material on a continuously running strip-shaped non-magnetic support.

Examples of the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, polyamides, aramid resins and polycarbonates. And the like. These non-magnetic supports may have a single-layer structure or a multi-layer structure. Further, for example, surface treatment such as corona discharge treatment may be applied.

The thickness of the non-magnetic support is not particularly limited. For example, when the medium is a film or sheet,
It is suitable to be 2 to 100 μm, preferably 3 to 50 μm. In the case of a disc or card, 30
In the case of a drum shape, it is appropriately selected depending on the design of the recorder or the like.

As a coating device for coating the magnetic coating material on the non-magnetic support, in addition to an extrusion coater, a reverse roll, a gravure roll, an air doctor coater, a blade coater, an air knife coater, a squeeze coater, an impregnation coater, a transfer roll coater. Any coating device usually used for coating magnetic paints such as a kiss coater, a cast coater, and a spray coater can be used.

After forming the magnetic coating film, a magnetic field orientation treatment, a drying treatment, a surface smoothing treatment, a burnishing treatment, a blade treatment, etc. are performed, and then a desired medium shape is obtained. The magnetic recording medium is manufactured by cutting. As the medium shape, any shape commonly used in magnetic recording media such as a tape shape, a film shape, a sheet shape, a card shape, a disk shape and a drum shape can be adopted.

Since the magnetic recording medium manufactured in this manner uses a magnetic coating material having a strain γc satisfying a predetermined condition, oscillation of the coating film is suppressed,
The magnetic coating film is formed with good surface properties. Therefore, the electromagnetic conversion characteristics are excellent, the shape of the RF envelope is also good, dropout is suppressed, and excellent running property and durability are obtained.

The above is an example in which the present invention is applied to the production of a magnetic recording medium having a single-layer structure. In the present invention, a magnetic coating film is formed on a non-magnetic support through a non-magnetic coating film. It may be applied to the production of a multi-layer coating type structure.

In this case, a lower layer non-magnetic coating material prepared by dispersing a non-magnetic powder and a binder together with a solvent is applied on a non-magnetic support to form a lower layer coating film. An upper layer coating film is formed by applying an upper layer magnetic coating material having a strain γc satisfying a predetermined condition.

Here, as the non-magnetic powder contained in the non-magnetic coating material, carbon black, graphite, TiO.
₂ , barium sulfate, ZnS, MgCO ₃ , CaCO ₃ , Z
nO, CaO, tungsten disulfide, molybdenum disulfide, boron nitride, MgO, SnO ₂ , SiO ₂ , Cr ₂ O ₃ ,
α-Al ₂ O ₃ , α-Fe ₂ O ₃ , α-FeOOH, Si
C, cerium oxide, corundum, artificial diamond, α
-Iron oxide, garnet, garnet, silica stone, silicon nitride, silicon carbide, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, tribolite, diatomaceous earth, dolomite and the like. Of these, carbon black and C
aCO ₃ , TiO ₂ , barium sulfate, α-Al ₂ O ₃ , α-
Inorganic powders such as Fe ₂ O ₃ , α-FeOOH and Cr ₂ O ₃ are preferable. In addition, these non-magnetic powders are Si compounds and /
Alternatively, it may be surface-treated with an Al compound. By using the surface-treated non-magnetic powder, the surface property of the upper magnetic coating film is improved. The surface treatment is Si,
The content of Al is 0.1 to 10% by weight with respect to the non-magnetic powder.
It is preferable to carry out so that

The shape of the non-magnetic powder is preferably needle-like. By using the acicular non-magnetic powder, the smoothness of the lower coating film surface is improved, and as a result, the surface of the upper coating film laminated thereon is also smooth. The major axis length, minor axis diameter and axial ratio (major axis diameter / minor axis diameter) of the non-magnetic powder are preferably in the following ranges. That is, the major axis diameter of the non-magnetic powder is 0.50 μm or less, preferably 0.40 μm or less, and more preferably 0.30 μm or less. The minor axis diameter is 0.10 μm or less, preferably 0.08 μm or less, and more preferably 0.06 μm or less. The axial ratio (major axis diameter / minor axis diameter) is 2
-20, preferably 5-15, more preferably 5-1
0 is appropriate. Specific surface area is 10 to 250 m ² / g,
It is preferably 20 to 150 m ² / g, more preferably 30 to 100 m ² / g. When the non-magnetic powder having the major axis diameter, the minor axis diameter, the axial ratio and the specific surface area as described above is used, the surface property of the lower layer coating film becomes good, and the surface property of the upper layer coating film laminated thereon is also improved. It will be in good condition.

The mixing amount of the non-magnetic powder in the lower coating film is 50 to 9 with respect to the total amount of all components constituting the lower coating film.
It is suitable to be 9% by weight, preferably 60 to 95% by weight, more preferably 70 to 95% by weight. By setting the mixing amount of the non-magnetic powder within this range, the surface properties of the lower layer coating film and thus the upper layer coating film are improved.

As the binder, the solvent for forming the paint, and various additives, any of those exemplified above for the magnetic coating film can be used. In addition, the mixing amount of the binder is 1
5 to 150 parts by weight, preferably 10 to 100 parts by weight
It is preferable to set the amount to 120 parts by weight.

In order to form the lower layer coating film and the upper layer coating film with such a lower layer non-magnetic coating material and the upper layer magnetic coating material, for example, a coating film forming system as shown in FIG. 5 is used.

That is, in this coating film forming system, the non-magnetic support 11 on which a coating film is formed is conveyed from the supply roll 13 toward the winding roll 12, and along this conveying direction. Coating device 14, orientation magnet 1
5, the dryer 16, and the calendar device 17 are arranged in this order.

In such a coating film forming system, the upper layer magnetic coating material and the lower layer non-magnetic coating material are first coated in multiple layers on the non-magnetic support 11 by the coating device 14.

This coating device 14 is, as shown in FIG.
Lower layer extrusion coater 1 for applying lower layer coating material
8 and the upper layer extrusion coater 19 for applying the upper layer coating so that the lower layer extrusion coater 18 is the introduction side of the non-magnetic support 11 and the upper layer extrusion coater 19 is the delivery side of the non-magnetic support 11. It is located and configured.

The lower layer extruding coater 18 and the upper layer extruding coater 19 are provided with slit portions 20 and 22 through which the coating material is extruded, and the coating material is supplied to the back side of the slit portions 20 and 22. Paint reservoirs 21 and 23 are provided. In such extrusion coaters 18 and 19, the coating material supplied to the coating material reservoirs 21 and 23 is extruded to the tip end portions of the coater through the slit portions 20 and 22.

On the other hand, the support 11 to which the coating material is applied has the lower layer extrusion coater 1 along the tip surfaces of the lower layer extrusion coater 18 and the upper layer extrusion coater 10.
8 is conveyed in the direction of arrow D in the drawing toward the upper layer extrusion coater 19.

The non-magnetic support 1 thus conveyed.
First, when passing through the lower layer extrusion coater 18, first, the slit portion 20 of the lower layer extrusion coater 18 is provided.
The lower layer coating material extruded from is applied to the surface to form the lower layer coating film 24. And, the upper layer extrusion coater 1
When passing through 9, the upper layer coating material extruded from the slit portion 22 of the upper layer extrusion coater 19 is applied onto the lower layer coating film 24 in a wet state, and two layers of coating films 24 and 25 are sequentially formed. .

Incidentally, these extrusion coaters 18, 19
The paint may be supplied to the via an in-line mixer.

Lower layer coating film 24 formed as described above
The upper coating film 25 is sequentially conveyed to the orienting magnet 15, the dryer 16 and the calender device 17.

In the orientation magnet 15, the upper coating film is subjected to magnetic field orientation treatment. As the orientation magnet 15, a longitudinal orientation magnet or a vertical orientation magnet is appropriately selected according to the type of magnetic powder contained in the upper coating film. The magnetic field of these orientation magnets is preferably about 20 to 10,000 Gauss.

In the dryer 16, the lower layer coating film and the upper layer coating film are dried by hot air from the nozzles arranged above and below the dryer 16. At this time, the drying condition is that the temperature is about 30.
It is preferable to set the temperature to 120 ° C and the drying time to about 0.1 to 10 minutes.

Then, the lower layer coating film and the upper layer coating film that have passed through the dryer 16 are further guided to the calender device 17 and subjected to surface smoothing treatment. Under the conditions of the surface smoothing treatment by the calendar device 17, temperature, linear pressure, conveyance speed, etc. are important. That is, the temperature is 50 to 140 ° C., the linear pressure is 50 to 1000 kg / cm, and the conveying speed is 20 to 10
It is preferably 00 m / min. If these conditions are not satisfied, the surface properties of the upper layer may be impaired.

The lower non-magnetic layer and the upper magnetic layer are formed as described above. In this coating film forming process, a magnetic paint having a strain γc satisfying a predetermined condition is used. Oscillation can be suppressed. Therefore,
The lower layer upper layer interface is formed smoothly, and the upper magnetic layer is formed with good surface properties. Further, the adhesion between the lower and upper layers is also good.

In this coating system, the non-magnetic coating material for the lower layer and the magnetic coating material for the upper layer are coated by separate coaters. As shown in FIG. 7, the lower layer extrusion coater and the upper layer extrusion coater are used. The extruding coater 26 in an integrated form may be used.

In addition to the extrusion coater, a reverse roll, a gravure roll, an air doctor coater, a blade coater, an air knife coater, a squeeze coater,
An impregnation coater, a transfer roll coater, a kiss coater, a cast coater, a spray coater or the like may be used. At this time, the coating methods of the lower layer non-magnetic coating material and the upper layer magnetic coating material may be the same or different. Therefore, for example, it is possible to combine a reverse roll and an extrusion coater, or combine a gravure roll and an extrusion coater to apply a non-magnetic paint or a magnetic paint.

In the above construction, the non-magnetic coating material for the lower layer and the magnetic coating material for the upper layer are sequentially applied, but an extrusion coater having two slits formed in close proximity is used, and the non-magnetic coating material is applied by the extrusion coater. The paint and the magnetic paint may be applied at the same time.

That is, as shown in FIG. 8, the extrusion coater 27 used in the simultaneous multi-layer coating method has two slit portions (the lower layer slit portion 2) through which the paint is extruded at the tip portion.
8. The upper layer slit portion 30) is formed in close proximity, and the lower layer coating material and the lower layer coating material reservoir 29, to which the lower layer coating material and the upper layer coating material are respectively supplied, are provided on the back sides of the two slit portions 28, 30.
An upper layer paint reservoir 31 is provided. In the extrusion coater 27, the lower layer coating material and the upper layer coating material supplied to the coating material reservoirs 29 and 31 are extruded to the tip of the coater through the slits 28 and 30. On the other hand, the support 11 to which the coating material is applied is conveyed in the direction D in the figure from the lower layer slit portion 28 toward the upper layer slit portion 30 along the tip surface of the extrusion coater.

The non-magnetic support 1 thus transported.
1 includes a lower layer slit portion 28 and an upper layer slit portion 3
When passing 0, the lower layer coating material extruded from the lower layer slit portion 28 is applied, and the upper layer coating material extruded from the upper layer slit 30 is applied onto the lower layer coating material to form two layers. The coating films 24 and 25 are simultaneously formed.

Then, the magnetic film on which the lower non-magnetic layer and the upper magnetic layer are thus formed is then subjected to varnishing treatment or blade treatment, etc., if necessary, to obtain a desired medium shape. As a result, it becomes a magnetic recording medium.

In the magnetic recording medium thus manufactured, the interface between the lower layer and the upper layer is smooth, and the surface property of the upper layer is good. Therefore, the electromagnetic recording characteristics are excellent and the shape of the RF envelope is also good. Dropout is suppressed. Further, since the lower layer and the upper layer have high adhesiveness, peeling of the film is unlikely to occur, high film strength is obtained, and excellent running durability is obtained.

In order to improve the electromagnetic conversion characteristics in the high density recording area, it is desirable that the film thickness of the upper magnetic layer is 0.3 μm or less, preferably 0.1 to 0.3 μm. When the thickness of the upper magnetic layer exceeds 0.3 μm, the electrical characteristics are deteriorated and it becomes insufficient as a medium applied to, for example, a digital recording system.

The manufacturing process has been described above for the single-layer structure and the multi-layer coating type structure. Further, for the purpose of improving running property, preventing electrostatic charge and preventing transfer on the surface of the non-magnetic support on which the lower upper layer is not provided. A back coat layer may be provided, or an undercoat layer may be provided between the lower layer and the nonmagnetic support. These back coat layer and undercoat layer are formed according to a usual method.

[0099]

EXAMPLES Examples of the present invention will be described below based on experimental results. The present embodiment is an example in which the present invention is applied to the manufacture of a multilayer coating type magnetic recording medium.

Example 1 First, according to the following composition, each component of an upper layer magnetic coating material and a lower layer non-magnetic coating material was weighed out and kneaded and dispersed using a kneader and a sand mill, respectively.
A non-magnetic coating material for the lower layer was prepared.

<Magnetic coating for upper layer> 100 parts by weight of ferromagnetic iron powder (coercive force Hc: 1600 Oe, specific surface area by BET method: 55 m ² / g, major axis diameter: 0.25 μm, acicular ratio: 10, saturated Amount of magnetization σs: 120 emu / g) Binder: Potassium sulfonate group-containing vinyl chloride resin 14 parts by weight (average degree of polymerization 300) Sodium sulfonate group-containing polyurethane resin 6 parts by weight (Toyobo Co., Ltd. product name UR-8700) α-alumina 5 parts by weight Myristic acid 1 part by weight Butyl stearate 1 part by weight Solvent 226 parts by weight (Methyl ethyl ketone: toluene: cyclohexanone (weight ratio) = 1: 1: 1 mixed solvent) <Non-magnetic coating material for lower layer> α-Fe ₂ O ₃ 100 weight parts (specific surface area by BET method: 52m ² / g, major axis length: 0.15 [mu] m, acicular ratio: 6) forming Agent: Potassium sulfonate group-containing vinyl chloride resin 10 parts by weight (Nippon Zeon Co., Ltd., trade name MR-110) Sodium sulfonate group-containing polyurethane resin 8 parts by weight (Toyobo Co., Ltd. trade name UR-8700) Butyl stearate 1 Parts by weight mixed solvent 220 parts by weight (mixed solvent having a composition of methyl ethyl ketone: toluene: cyclohexanone (weight ratio) = 1: 1: 1) For each of the magnetic coating material for the upper layer and the non-magnetic coating material for the lower layer thus prepared, 5 parts by weight of a polyisocyanate compound (trade name Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.) was added. Here, the strain γc of the upper layer magnetic coating is
64.8% when measured with a strain control type viscometer
Met.

Then, the magnetic coating material for the upper layer and the non-magnetic coating material for the lower layer were multi-layer coated on a polyethylene terephthalate support having a thickness of 7.5 μm by a wet-on-wet coating method, and the coating film was undried. A magnetic field orientation treatment was performed for a certain period of time, followed by drying and surface smoothing treatment with a calendar to form a lower non-magnetic layer and an upper magnetic layer. The thickness (dry film thickness) of the lower non-magnetic layer was 1.5 μm and that of the upper magnetic layer was 0.15 μm.

Further, on the surface of the polyethylene terephthalate support opposite to the side on which the lower non-magnetic layer and the upper magnetic layer are formed, a back coating composition having the following composition is applied, dried, and surface smoothed by a calendar. By performing the treatment, a back coat layer having a thickness of 0.8 μm was formed, and a wide original anti-magnetic tape was obtained.

<Backcoat paint> Carbon black 40 parts by weight (average particle size 26 nm) Barium sulfate 10 parts by weight (average particle size 300 nm) Nitrocellulose 25 parts by weight Polyurethane resin 25 parts by weight (Nippon Polyurethane Industry Co., Ltd., trade name N -2301) Polyisocyanate compound 10 parts by weight (Nippon Polyurethane Industry Co., Ltd., trade name Coronate L) Mixed solvent 900 parts by weight (Methyl ethyl ketone: toluene: cyclohexanone (weight ratio) = 1: 1: 1 mixed solvent) The obtained original anti-magnetic tape was cut into a tape width of 8 mm to produce a magnetic tape.

Examples 2 to 5 In the same manner as in Example 1, except that the type of the ferromagnetic powder, the composition of the binder component, and the amount of the solvent mixed in the magnetic coating material for the upper layer were changed as shown in Table 1. To produce a magnetic tape.
The measurement results of the strain γc of the magnetic coating material for the upper layer are also shown in Table 1.

Comparative Examples 1 to 6 In the same manner as in Example 1, except that the type of the ferromagnetic powder, the composition of the binder component, and the mixed amount of the solvent in the magnetic coating material for the upper layer were changed as shown in Table 1. To produce a magnetic tape.
The measurement results of the strain γc of the magnetic coating material for the upper layer are also shown in Table 1. Thus, the strain γc used here is less than 50% (outside the predetermined range).

[0107]

[Table 1]

However, in the table, magnetic powder A, magnetic powder B, vinyl chloride resin A, vinyl chloride resin B, polyurethane resin and solvent are as follows.

Magnetic powder A: coercive force Hc is 1600 Oe, B
Specific surface area by ET method is 55 m ² / g, major axis length is 0.2
Ferromagnetic iron fine powder having 5 μm, acicular ratio of 10 and σs of 120 emu / g Magnetic powder B: coercive force Hc of 2100 Oe, specific surface area by BET method of 50 m ² / g, major axis length of 0.08 μm, acicular Ferromagnetic iron fine powder having a ratio of 3 and σs of 145 emu / g Vinyl chloride resin A: Vinyl chloride resin containing potassium sulfonate group having an average degree of polymerization of 300 Vinyl chloride resin B: Potassium sulfonate group having an average degree of polymerization of 150 Containing vinyl chloride resin Polyurethane resin: Sodium sulfonate group-containing polyurethane resin (product name UR-8700, manufactured by Toyobo Co., Ltd.) Solvent: Mixed solvent in which methyl ethyl ketone, toluene, and cyclohexanone are mixed in equal weights. Condition, surface roughness R
a, electromagnetic conversion characteristics, RF envelope and the number of dropouts were measured. The measuring method is as follows.

Surface roughness: The tape surface was observed using a differential interference microscope. At this time, when the surface was judged to be considerably smooth, it was recorded as ◯, when it was judged to be slightly rough, it was marked as Δ, and when it was judged to be considerably rough, it was recorded as x.

Surface roughness Ra (nm): JIS B 06
It is the center line average roughness Ra defined by 01. The surface roughness Ra was measured using a tally step roughness meter manufactured by Taylor Hopson. Stylus is 2.5
× 0.1 μm, needle pressure 2 mg, cut-off filter 0.33 Hz, measurement speed 2.5 μm / s, reference length 0.5 mm. In the roughness curve,
The unevenness of 0.01 μm or more was cut.

Electromagnetic conversion characteristics: Chroma S / N (C-S /
N) and Lumi S / N (LS-N) were measured and evaluated. Note that the chroma S / N was measured by using a noise meter (manufactured by Shibasoku) to determine the difference between the S / N of the reference tape (manufactured by Sony Corporation) and the sample tape in the 100% white signal. The Lumi S / N was measured by using a noise meter (manufactured by Shibasoku) to find the difference in S / N between the reference tape (manufactured by Sony) and the sample tape in the chroma signal. These measurement data were recorded as total values when the value on the reference tape (manufactured by Sony Corporation) was 1 dB.

RF envelope: 8 sample tapes
It was run on a millideck (product name S-550 manufactured by Sony Corporation), the RF envelope at that time was displayed on an oscilloscope, and the ratio between the maximum value and the minimum value of the envelope was obtained and evaluated.

Number of Dropouts: The number of dropouts (the number of dropouts) of −12 dB / 5 μs detected per minute was measured by a measuring instrument manufactured by Shibasoku Co., Ltd. under the trade name of VHO1BZ.

The measurement results are shown in Table 2 together with the types of the lower layer non-magnetic coating material and the upper layer magnetic coating material used in each Example and Comparative Example.

[0116]

[Table 2]

As shown in Table 2, the magnetic tapes of Examples 1 to 5 using the magnetic coating material for the upper layer having the strain γc satisfying the predetermined condition have good surface properties and have good electromagnetic properties. The conversion characteristics and the RF envelope are also good, and the dropout is sufficiently suppressed.

On the other hand, the distortion γc of the magnetic coating material for the upper layer
In the magnetic tapes of Comparative Examples 1 to 6 which do not satisfy the predetermined condition, the surface of the upper magnetic layer is rough, so that the electromagnetic conversion characteristics are insufficient and dropouts frequently occur. In addition, the shape of the RF envelope is also poor.

From this, it was found that controlling the strain γc of the magnetic coating is effective in manufacturing a magnetic recording medium having good characteristics.

[0120]

As is apparent from the above description, according to the present invention, when the coating type magnetic recording medium is manufactured, the magnetic coating material has a storage elastic modulus G'with a strain of 0.1 to 1000%. Since the one having a strain γc of 50% or more when the loss elastic modulus G ″ becomes the same value is used, the magnetic coating film is formed with a good surface property. Therefore, the surface of the lower magnetic layer is not disturbed, and the surface of the upper magnetic layer is formed with good surface property.
The shape of the F envelope is also good, dropout is suppressed, running property and durability are excellent, and a magnetic recording medium suitable for high-density recording can be manufactured with a high yield.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing an oscillation waveform of a completely elastic body.

FIG. 2 is a characteristic diagram showing an oscillation waveform of a completely viscous body.

FIG. 3 is a characteristic diagram showing an oscillation waveform of a viscoelastic body.

FIG. 4 Angular frequency 1H measured by a strain control type viscometer
FIG. 3 is a characteristic diagram showing the relationship between strain and storage elastic modulus G ′ at z and the relationship between strain and loss elastic modulus G ″.

FIG. 5 is a schematic view showing a coating film forming system for forming a lower non-magnetic layer and an upper magnetic layer by a wet-on-wet coating method.

FIG. 6 is a schematic diagram illustrating an example of a coating apparatus of the coating film forming system.

FIG. 7 is a schematic view showing another example of a coating device.

FIG. 8 is a schematic view showing still another example of the coating apparatus.

Claims (2)

[Claims] 1. When forming a magnetic coating film by applying a magnetic coating material prepared by dispersing a magnetic powder and a binder together with a solvent onto a non-magnetic support, a strain control type viscosity of the magnetic coating material is provided. Angular frequency 1H depending on the meter
Storage modulus G'and loss modulus G "measured under the condition of z
Is the strain γc when the storage elastic modulus G ′ and the loss elastic modulus G ″ have the same value in the strain range of 0.1 to 1000%.
Is set to be 50% or more. 2. A non-magnetic coating material is prepared by dispersing a non-magnetic powder and a binder together with a solvent on a non-magnetic support to form a non-magnetic coating film. 2. The method for producing a magnetic recording medium according to claim 1, wherein a magnetic coating film is formed by applying a magnetic coating material prepared by dispersing magnetic powder and a binder together with a solvent onto the magnetic coating material.