JP2647822B2 - Manufacturing method of magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a high density coated magnetic recording medium.

[0002]

2. Description of the Related Art Magnetic recording media are widely used as recording tapes, video tapes, computer tapes, disks, and the like. The density of magnetic recording media is increasing year by year,
Recording methods from analog to digital are also being studied. To meet this demand for higher density, a magnetic recording medium using a metal thin film for the magnetic layer has been proposed.However, in terms of practical reliability such as productivity and corrosion, magnetic powder is dispersed in a binder. A so-called coating type magnetic recording medium coated on a support is excellent. However, since the coating medium has a low degree of filling of the magnetic substance with respect to the metal thin film, the electromagnetic conversion characteristics are inferior.

Various methods have been proposed to improve the electromagnetic conversion characteristics of a coating type medium, such as improvement of the magnetic characteristics of a magnetic material and smoothing of the surface, but various methods have been proposed. is not.

[0004] To improve the performance of digital media, it is known to reduce the thickness of a magnetic layer. However, although effective in principle, there is a production problem in making the coating-type medium thinner. This is because coating defects such as pinholes and streaks tend to occur due to thinning of the magnetic layer, and a sufficient yield cannot be obtained. In addition, since the molding effect by the calender is reduced, the surface properties are poor and the electromagnetic conversion characteristics are not good.

In order to solve such a problem, it is conceivable to perform a calendering process after simultaneously forming a thin magnetic layer of 1 μm or less on a nonmagnetic layer having a certain thickness. As means that can be used for such purpose, it has been proposed to include a non-magnetic granular abrasive or filler in the undercoat layer. (Japanese Patent Laid-Open No. 62-222427)
However, the problem of these techniques is that when the magnetic layer and the non-magnetic layer are simultaneously coated and the upper magnetic body is oriented, the upper and lower layers are rotated by the magnetic field due to the magnetic field. Mixing at the interface of not only does not provide sufficient surface properties,
Since the orientation was not sufficiently performed, sufficient electromagnetic conversion characteristics could not be obtained.

Accordingly, the present applicant has attempted to improve the orientation of the magnetic particles in the upper layer by forming the non-magnetic lower layer with non-magnetic scaly particles. Regarding the provision of a nonmagnetic scale-like particle layer, a conductive intermediate layer using graphite has been proposed. (JP-A-55-55438)
However, such a substance improves the orientation, but is insufficient in durability because graphite itself has no effect of reinforcing the film. To solve this problem, a proposal has been made to mix an inorganic powder having a Mohs hardness of 5 or more. (JP 6
Further, the present applicant has attempted to improve the orientation of the magnetic particles in the upper layer by forming the nonmagnetic lower layer with nonmagnetic needle-like particles. Regarding providing a nonmagnetic needle-like particle layer, a reinforcing layer using needle-like oxalate has been proposed.
(Japanese Patent Publication No. 58-51327).

[0007] Although these proposals improve the orientation and ensure durability, the scale-like particles are liable to stacking during the actual production of the medium, and substances such as oxalate are difficult to disperse in the binder. Was found to impair the smoothness of the magnetic surface.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a magnetic recording medium having excellent electromagnetic conversion characteristics, particularly high RF output.

[0009]

That is, the above object of the present invention is to provide a method in which a lower layer containing at least a non-magnetic powder and a binder is coated on a support, and after the lower layer is dried, a ferromagnetic powder and a binder are contained. This can be achieved by providing a method for manufacturing a magnetic recording medium, characterized in that the upper magnetic layer is applied so that the dry thickness is 1 μm or less. Therefore, the present invention has invented the following manufacturing method. (1) A coating solution for an upper magnetic layer containing a ferromagnetic powder and a binder, and a coating solution for a lower layer containing a nonmagnetic powder and a binder are respectively prepared, and the coating solution for a lower layer is coated on a support, thereby obtaining The method of manufacturing a magnetic recording medium, wherein the coating solution for the upper magnetic layer is applied on the formed lower layer.
The conductive powder contains Fe as a main component and further contains at least Ni or
Needle-like ferromagnetic alloy powder containing Co and the longest axis
The average diameter of the length is 0.3 μm or less, and the lower layer coating solution has a ratio r ₁ / r of the longest axial length r ₁ and the shortest axial length r _2.
2 contains a non-magnetic powder of not less than 2.5 and less than 20, and the lower layer coating solution is applied on the support, and after the obtained lower layer is dried, the upper layer is dried so as to have a dry thickness of 1 μm or less. A method for producing a magnetic recording medium, comprising applying a coating solution for a magnetic layer. ( 2 ) The nonmagnetic powder of the lower layer coating solution has a needle ratio of 2.5.
2. The method for producing a magnetic recording medium according to claim 1, wherein the magnetic recording medium is a needle-shaped nonmagnetic powder having a particle size of not less than 20. ( 3 ) The method for producing a magnetic recording medium according to claim 1, wherein the nonmagnetic powder of the lower layer coating solution has an average diameter of the longest axial length of 3 µm or less. ( 4 ) The non-magnetic powder of the lower layer coating solution is Al ₂ O
₃ (α, γ), Cr ₂ O ₃ , α-Fe ₂ O ₃ , goethite (α-FeOOH), SiO ₂ , ZrO ₂ , Ce
_{2. The} method for producing a magnetic recording medium according to claim 1, comprising at least one of non-magnetic powders of O ₂ and TiO ₂ (rutile, anatase). ( 5 ) The support is made of polyethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide,
Polyaramid, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid,
The method for producing a magnetic recording medium according to claim 1, wherein the method is at least one selected from aromatic polyamides. ( 7 ) The method of manufacturing a magnetic recording medium according to claim 1, wherein there is substantially no mixed region between the lower layer and the upper magnetic layer. ( 7 ) The magnetic recording medium is a recording tape or a video tape.
2. The method for manufacturing a magnetic recording medium according to claim 1, wherein the method is for digital use such as for a tape, a computer tape, and a disk. ( 8) The binder preferably contains a polar group containing S.
The method for manufacturing a magnetic recording medium according to claim 1, wherein:

That is, the present invention is to improve the method of manufacturing a magnetic recording medium having a plurality of layers by applying an upper magnetic layer after the lower layer is dried. In other words, in wet-on-wet coating, the interface is soft and easily affected by other layers. For example, when the layer is oriented after coating, the ferromagnetic powder in the upper magnetic layer rotates, and the lower layer exerts the influence due to the rotation. And mixing occurs at the interface. In the present invention, a magnetic recording medium having a high output is obtained by applying an upper magnetic layer after the lower layer is dried and applying a device to the lower layer. In order to obtain this high output, the present invention uses acicular non-magnetic powder for the lower layer. Compared with the conventional granular non-magnetic powder, if the needle-shaped non-magnetic powder is present in alignment, a strong coating film is formed, and a high output can be obtained even when the ferromagnetic powder in the upper magnetic layer rotates.
That is, the present invention uses a nonmagnetic powder having a characteristic shape in the lower layer, and by providing the upper magnetic layer after the lower layer is dried, an extremely thin and smooth magnetic layer is obtained. is there.

As described above, the basic idea of the present invention is to use, as a lower layer coating solution, a dispersion in which nonmagnetic powder is dispersed in a binder and a magnetic paint for an upper magnetic layer in which ferromagnetic powder is dispersed in a binder, This is that it can be produced by applying the lower layer coating solution on a support, drying it, and then coating the upper layer magnetic layer with a magnetic paint. For example, it can be adjusted to 1 μm or less.

A feature of the present invention is that a nonmagnetic powder having a dry thickness of the upper magnetic layer of 1 μm or less and r ₁ / r ₂ (that is, an axial ratio) of 2.5 or more and less than 20 is provided in the lower layer. It contains. By defining the shape in this way, the non-magnetic powder is oriented in the longitudinal direction by the flow orientation at the time of coating, so that the rotational motion due to the magnetic field orientation of the upper magnetic layer to the ferromagnetic powder can be suppressed, and as a result, In addition, disturbance at the interface between the lower and upper magnetic layers can be suppressed, and the orientation of the ferromagnetic powder can be improved. Here, r ₁ is the longest axis length and r ₂ is the shortest axis length, but the specific shape of the nonmagnetic powder is basically arbitrary, and may be needle-like or plate-like, such as an electron microscope. Is actually measured by In addition, the axis does not mean a symmetric axis in a strict sense. In the case of a needle, r ₁ is usually, that is, what is called a major axis length, and is in a range of 3 μm or less, preferably 1.5 μm or less (ie, r ₂ is a minor axis length or a thickness), and a preferable axial ratio Is 5 to 20.
In the case of a scaly or plate-like shape, r ₁ usually refers to a plate diameter, and the value is in the range of 0.01 to 3 μm, preferably 0.05 to 1.5 μm (ie, r ₂
Is a plate thickness), and a preferable plate ratio is 5 to 20. The ferromagnetic powder of the upper magnetic layer mainly contains Fe,
Contains at least Ni or Co and has the longest axial length
Is an acicular ferromagnetic powder having an average diameter of 0.3 μm or less. Ingredient
As a body example, the acicular ferromagnetic powder is Co-γ-Fe ₂ O ₃ ,
Alloy ferromagnetism such as Fe-Ni alloy and Fe-Ni-Co alloy
Powder.

As the acicular nonmagnetic powder, nonmagnetic metals (Cu, Cr, Ag, Al, Ti, W, etc.) or oxides are preferable. For example, Al ₂ O ₃ (α, γ), Cr ₂
O ₃ , α ferrite, goethite (αFeOOH), S
iO ₂ (including glass), ZrO ₂ , CeO ₂ , TiO
₂ (rutile, anatase) and the like. Further, the thickness of the lower layer is preferably 0.5 μm or more, particularly preferably 0.5 to 5.0 μm. If the lower layer is thinner than 0.5 μm, productivity is reduced and calender moldability is deteriorated, so that it is difficult to obtain sufficient electromagnetic conversion characteristics. The shape of the ferromagnetic powder is acicular, the
In this case, the average particle diameter is also defined as the axial ratio of the nonmagnetic powder: r ₁ /
true that was defined in the r _2, r ₁ except for the difference of things
Has the same meaning as Hereinafter, ferromagnetic following r ₁ / r ₂
The axial ratio of the powder referred to as φ ₁ / φ _2. Φ ₁ of ferromagnetic powder is
0.3 μm or less, preferably 0.25 μm or less
And φ ₁ / φ ₂ is in the range of 2.5 or more.

Hereinafter, general items that can be selected according to the present invention will be listed. In the present invention, each of the upper magnetic layer and the lower layer is usually composed of a single layer. However, a single-layer constitution or a multi-layer constitution may be employed as long as the above-mentioned composition and the prescribed conditions are satisfied. Hereinafter, the upper magnetic layer and the lower layer may be simply referred to as an upper layer and a lower layer. Preferably, the lower layer is substantially non-magnetic. The above non-magnetic powder does not necessarily have to be 100% pure, and the surface may be treated with another compound depending on the purpose.
At this time, if the purity is 70% or more, the effect is not reduced. For example, when using titanium oxide, it is generally used to treat the surface with alumina. The ignition loss is preferably 20% or less. The upper layer preferably has a ferromagnetic powder content of 70% or more. If the ferromagnetic powder content is less than 70%, the degree of filling is reduced, and the electromagnetic conversion characteristics are degraded. The ferromagnetic powder content here represents (% by weight) of (ferromagnetic powder) / (contained in the magnetic layer such as ferromagnetic powder + binder + additive). The magnetic properties of the magnetic recording medium of the present invention, when measured at a magnetic field of 5 KOe, have a squareness ratio of 0.7 or more, preferably 0.8 or more, and more preferably 0.9 or more for each layer. Sigma _S of the ferromagnetic powder used in the present invention is 50 emu / g or more, preferably 70
emu / g or more, and 100 em in the case of fine metal powder.
u / g or more is preferable. The water content is 0.01 to 2%.
It is preferred that It is preferable to optimize the water content of the ferromagnetic powder depending on the type of the binder. When cobalt-modified iron oxide is used as the ferromagnetic powder of the present invention, the ratio of divalent iron to trivalent iron is preferably 0 to 33.3%, and more preferably 5 to 10%. The amount of cobalt atoms relative to iron atoms is 0 to 15%, preferably 3 to
8%. Preferably, the pH of the ferromagnetic powder is optimized by the combination with the binder used. The range is 4-1
2. The ferromagnetic powder may be subjected to surface treatment with Al, Si, P, or an oxide thereof. The amount is 0.1 to 10% based on the ferromagnetic powder. The upper ferromagnetic powder may contain inorganic ions such as soluble Na, Ca, Fe, Ni, and Sr, but has no particular effect if it is 500 ppm or less. The ferromagnetic powder, Al in addition to Jo Tokoro atoms, Si, S, Sc, Ti , V, Cr, Cu, Y,
Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, T
a, W, Re, Au, Hg, Pb, Bi, La, Ce,
It may contain atoms such as Pr, Nd, P, Co, Mn, Zn, Ni, Sr, and B. These ferromagnetic fine powders may be preliminarily treated with a dispersant, a lubricant, a surfactant, an antistatic agent, and the like before dispersion before dispersion. Among the ferromagnetic powders, the ferromagnetic alloy fine powder may contain a small amount of hydroxide or oxide. A ferromagnetic alloy fine powder obtained by a known production method can be used, and the following method can be used. A method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen, a method of reducing iron oxide with a reducing gas such as hydrogen to obtain Fe or Fe—Co particles, Thermal decomposition method, reduction method by adding reducing agent such as sodium borohydride, hypophosphite or hydrazine to aqueous solution of ferromagnetic metal, reduction of fine powder by evaporating metal in low pressure inert gas And how to get it. The ferromagnetic alloy powder thus obtained is subjected to a known slow oxidation treatment, that is, a method of immersing in an organic solvent and then drying, and immersing in an organic solvent and then feeding an oxygen-containing gas to form an oxide film on the surface and drying. How to make
Any of the methods of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent can be used. The ferromagnetic powder used in the present invention preferably has a small number of vacancies, and the value is preferably 20% by volume or less, more preferably 5% by volume or less. The ferromagnetic powder used in the present invention can be produced according to a known method.

As the binder used in the lower and upper magnetic layers of the present invention, conventionally known thermoplastic resins, thermosetting resins,
Reactive resins and mixtures thereof are used. In the present invention, these can be used in combination with the epoxy group-containing resin. As the thermoplastic resin, the glass transition temperature is −100 to 150 ° C., and the number average molecular weight is 1000 to 200.
000, preferably 10,000 to 100,000, and a degree of polymerization of about 50 to 1,000. Such examples include vinyl chloride, vinyl acetate, vinyl alcohol,
Polymer or copolymer containing maleic acid, acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, vinyl ether, etc. as constituent units, polyurethane There are resins and various rubber-based resins. As the thermosetting resin or the reactive resin, phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, acrylic-based reactive resin, formaldehyde resin, silicone resin, epoxy-polyamide resin, polyester resin And a mixture of a polyester polyol and a polyisocyanate, a mixture of a polyurethane and a polyisocyanate, and the like. These resins are described in detail in "Plastic Handbook" published by Asakura Shoten. It is also possible to use a known electron beam-curable resin. These examples and the method for producing them are described in detail in JP-A-62-256219. The above resins can be used alone or in combination, but preferred are at least one selected from vinyl chloride resin, vinyl chloride vinyl acetate resin, vinyl chloride vinyl acetate vinyl alcohol resin, vinyl chloride vinyl acetate maleic anhydride copolymer. Examples include a combination of a seed and a polyurethane resin, or a combination of these with a polyisocyanate.
The structure of the polyurethane resin is polyester polyurethane,
Known materials such as polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, polyester polycarbonate polyurethane, and polycaprolactone polyurethane can be used. For all the binders shown here, COOM, SO ₃ M,
OSO ₃ M, P = O (OM) ₂ , OP = O (OM)
₂ , (where M is a hydrogen atom or an alkali metal base), OH, NR ² , N ⁺ R ³ , R is a hydrocarbon group,
It is preferable to use one obtained by introducing at least one or more polar groups selected from H, CN, and the like by copolymerization or addition reaction. The amount of such a polar group is 10 ^-1 to 10 ^-8 mol / g, preferably 10 ^-2 to 10 ^-6 mol / g. As the vinyl chloride-based copolymer, preferably, an epoxy group-containing vinyl chloride-based copolymer is mentioned, and a vinyl chloride repeating unit, a repeating unit having an epoxy group, and, if desired, —SO ₃ M and —OSO ₃ M , -COOM and -PO (OM) ₂ (wherein M is a hydrogen atom or an alkali metal base) and a repeating unit having a polar group. In combination with the repeating unit having an epoxy group, an epoxy group-containing vinyl chloride copolymer preferably contains a repeating unit having an -SO ₃ Na. The content of the repeating unit having a polar group in the copolymer is usually in the range of 0.01 to 5.0 mol% (preferably, 0.5 to 3.0 mol%). The content of the repeating unit having an epoxy group in the copolymer,
Usually 1.0 to 30 mol% (preferably 1 to 20 mol%)
Within the range. The vinyl chloride polymer is usually used in an amount of 0.01 to 0.5 with respect to 1 mol of the vinyl chloride repeating unit.
It contains a repeating unit having a mole (preferably 0.01 to 0.3 mole) of an epoxy group. If the content of the repeating unit having an epoxy group is less than 1 mol%, or if the amount of the repeating unit having an epoxy group is less than 0.01 mol per 1 mol of the vinyl chloride repeating unit, hydrochloric acid from the vinyl chloride copolymer may be used. On the other hand, it may not be possible to effectively prevent the release of gas. On the other hand, if the amount of the repeating unit having an epoxy group is higher than 30 mol% or the amount of the repeating unit having an epoxy group per 1 mol of the vinyl chloride repeating unit is more than 0.5 mol, vinyl chloride may be prevented. In some cases, the hardness of the system copolymer is reduced, and when this is used, the running durability of the magnetic layer may be reduced. When the content of the repeating unit having a specific polar group is less than 0.01 mol%, the dispersibility of the ferromagnetic powder may be insufficient. When the content is more than 5.0 mol%, the copolymer may absorb moisture. And may have poor weather resistance. Usually, the number average molecular weight of such a vinyl chloride copolymer is in the range of 15,000 to 60,000. Such a vinyl chloride copolymer having an epoxy group and a specific polar group can be produced, for example, as follows. For example, an epoxy group and —SO ₃ N as a polar group
When a vinyl chloride copolymer into which a is introduced is produced, a reactive double bond and -SO ₃ N as a polar group are used.
a) and a mixture of sodium 2- (meth) acrylamido-2-methylpropanesulfonate (a monomer having a reactive double bond and a polar group) and diglycidyl acrylate. 10 under pressure
It can be produced by polymerizing at a temperature of 0 ° C. or lower. Examples of the monomer having a reactive double bond and a polar group used for introducing a polar group by the above method,
In addition to the above sodium 2- (meth) acrylamide-2-methylpropanesulfonate, 2- (meth) acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid and its sodium or potassium salt, (meth)
Ethyl acrylate-2-ethyl sulfonate and sodium or potassium salt, (anhydride) maleic acid and (meth)
Acrylic acid and (meth) acrylic acid-2-phosphate can be exemplified. Also, for the introduction of epoxy groups,
Glycidyl (meth) acrylate is generally used as a monomer having a reactive double bond and an epoxy group. In addition,
In addition to the above-described production methods, for example, a vinyl chloride copolymer having polyfunctional -OH is produced by a polymerization reaction of vinyl chloride and vinyl alcohol, and the copolymer and a polar group described below. A method of reacting with a compound containing a chlorine atom (dehydrochlorination reaction) to introduce a polar group into the copolymer can be used.

ClCH ₂ CH ₂ SO ₃ M, ClCH ₂ CH ₂ OSO ₃ M, ClCH ₂ COOM, ClCH ₂ PO (OM) _{2 In} the polar groups mentioned in the above description, S is
Most preferred are polar groups containing. In addition, epichlorohydrin is usually used to introduce an epoxy group using this dehydrochlorination reaction. The vinyl chloride copolymer may contain another monomer. Examples of other monomers include vinyl ether (eg, methyl vinyl ether, isobutyl vinyl ether, lauryl vinyl ether), α
Monoolefins (eg, ethylene, propylene), acrylates (eg, (meth) acrylates containing a functional group such as methyl (meth) acrylate, hydroxyethyl (meth) acrylate), unsaturated nitriles (eg, , (Meth) acrylonitrile), aromatic vinyl (eg, styrene, α-methylstyrene), and vinyl ester (eg, vinyl acetate, vinyl propionate, etc.). Specific examples of these binders used in the present invention include VAGH and VYH manufactured by Union Carbide.
H, VMCH, VAGF, VAGD, VROH, VYE
S, VYNC, VMCC, XYHL, XYSG, PKH
H, PKHJ, PKHC, PKFE, manufactured by Nissin Chemical Industries: MPR-TA, MPR-TA5, MPR-TAL,
MPR-TSN, MPR-TMF, MPR-TS, MP
R-TM, manufactured by Denki Kagaku: 1000 W, DX80, DX
81, DX82, DX83, manufactured by Zeon Corporation: MR11
0, MR100, 400X110A, manufactured by Nippon Polyurethane: Nipporan N2301, N2302, N230
4. Dainippon Ink Co., Ltd .: Pandex T-5105, T
-R3080, T-5201, Barnock D-400,
D-210-80, Chris Bon 6109, 7209, manufactured by Toyobo: Byron UR8200, UR8300, RV
530, RV280, manufactured by Dainichi Seika Co., Ltd .: Daifu eramine 4
020, 5020, 5100, 5300, 9020, 9
No. 022, 7020; MX5004, manufactured by Mitsubishi Kasei Co., Ltd .; Samprene SP-150, manufactured by Sanyo Chemical Co., Ltd .; Saran F310, F210, manufactured by Asahi Kasei Corporation. The binder used in the present invention is 5
It is used in the range of 50 to 50% by weight, preferably in the range of 10 to 35% by weight. When a vinyl chloride resin is used, 5 to 30% by weight, when a polyurethane resin is used, 2 to 20% by weight, and when polyisocyanate is 2 to 20% by weight.
It is preferable to use these in combination within the range described above. In the lower layer, the binder used in the present invention is in a total range of 5 to 50% by weight, preferably 10 to 3% by weight, based on the nonmagnetic powder.
It is used in the range of 5% by weight. When a vinyl chloride resin is used, 3 to 30% by weight is used. When a polyurethane resin is used, 3 to 30% by weight.
It is preferable to use these in combination in the range of ２０20% by weight. Further, in the present invention, an epoxy group-containing resin having a molecular weight of 30,000 or more can be used in an amount of 3 to 30% by weight based on the nonmagnetic powder, and a resin other than the epoxy group-containing resin can be used in an amount of 3 to 30% based on the nonmagnetic powder. % By weight, 3 to 30% by weight when a polyurethane resin is used, and 0% by weight of a polyisocyanate.
Although the epoxy group can be used in an amount of 4 × 10 ^{−5 to} 16 × 10 ^{−4 based on the} total weight of the binder (including the curing agent).
It is preferable to be contained in the range of eq / g. In the present invention, when a polyurethane resin is used, the glass transition temperature is −50 to 100 ° C., the elongation at break is 100 to 2000%,
The breaking stress is 0.05 to 10 kg / cm ² , and the yield point is 0.1 kg / cm ² .
It is preferably from 0.05 to 10 Kg / cm ² . Examples of the polyisocyanate used in the present invention include tolylene diisocyanate, 4-4'-diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-
Isocyanates such as toluidiisocyanate, isophorone diisocyanate, and triphenylmethane triisocyanate, products of these isocyanates and polyalcohol, and polyisocyanates formed by condensation of isocyanates can be used. Commercially available trade names of these isocyanates include Nippon Polyurethane Co .: Coronate L,
Coronate HL, Coronate 2030, Coronate 20
31, Millionate MR, Millionate MTL, manufactured by Takeda Pharmaceutical Co., Ltd .: Takenate D-102, Takenate D-110
N, Takenate D-200, Takenate D-202, manufactured by Sumitomo Bayer: Desmodur L, Desmodur I
L, death module N, death module HL, etc.
These can be used singly or in combination of two or more by using the difference in curing reactivity for both the lower layer and the upper layer.

In the present invention, optional additives such as an antistatic agent such as carbon black, an abrasive, a coloring agent, a lubricant and a dispersant can be used in the upper layer and / or the lower layer as required. As carbon black, furnace for rubber, thermal for rubber, black for color, acetylene black, and the like can be used. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be one obtained by graphitizing a part of the surface. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. These carbon blacks can be used alone or in combination. Carbon black has functions such as preventing the upper magnetic layer from being charged, reducing the coefficient of friction, imparting light-shielding properties, and improving the film strength, and differs depending on the carbon black used. Therefore, these carbon blacks used in the present invention vary in type, amount, and combination, and have a particle size,
Of course, it is possible to use differently according to the purpose based on the above-mentioned various characteristics such as oil absorption, conductivity, pH and the like. The carbon black that can be used in the present invention can be referred to, for example, “Carbon Black Handbook” (edited by Carbon Black Association).

The abrasive used in the present invention includes α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond, silicon nitride, carbonized carbon having an α conversion of 90% or more. Known materials mainly having a Mohs hardness of 6 or more such as silicon titanium carbide, titanium oxide, silicon dioxide, and boron nitride are used alone or in combination. Further, a composite of these abrasives (abrasive whose surface is treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the effect remains unchanged if the main component is 90% or more. The particle size of these abrasives is preferably from 0.01 to 2 μm. However, if necessary, abrasives having different particle sizes can be combined, or even a single abrasive can have the same effect by widening the particle size distribution. . The shape of the abrasive used in the present invention may be any of a needle shape, a spherical shape, and a dice shape, but a shape having a part of a corner is preferable because of high abrasiveness. Specific examples of the abrasive used in the present invention include AKP-20, A manufactured by Sumitomo Chemical Co., Ltd.
KP-30, AKP-50, HIT-50, manufactured by Nippon Chemical Industry: G5, G7, S-1, manufactured by Toda Kogyo: 100E
D, 140ED, and the like. These abrasives may be added to the magnetic paint after being subjected to dispersion treatment with a binder in advance. The amount of the abrasive used is 20% by weight or less of the ferromagnetic powder in the upper magnetic layer and 20% by weight or less of the nonmagnetic powder in the lower layer.

The following are listed as additives having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, and the like. Solid lubricants such as molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, and carbon black. Silicone oils, silicones having polar groups, fatty acid-modified silicones, fluorine-containing silicones, fluorine-containing alcohols, fluorine-containing esters, polyolefins, polyglycols, alkyl phosphates and their alkali metal salts, alkyl sulfates and their alkali metal salts, polyphenyl Ether, fluorine-containing alkyl sulfate and its alkali metal salt, carbon number 1
0 to 24 monobasic fatty acids (which may contain an unsaturated bond or may be branched), and their metal salts (Li, Na, K, Cu, etc.) or 12 to 24 carbon atoms
22 mono-, di-, tri-, tetra-, penta-, hexa-hydric alcohols (which may contain unsaturated bonds or may be branched), alkoxy alcohols having 12 to 22 carbon atoms, 10 carbon atoms ~ 24 monobasic fatty acids (which may contain unsaturated bonds or may be branched) and have 2 to 12 carbon atoms
Mono-fatty acid esters or di-fatty acids comprising any one of monohydric, divalent, trivalent, tetravalent, pentavalent, and hexavalent alcohols (which may contain an unsaturated bond or may be branched) Organic lubricants such as esters or trifatty acid esters, fatty acid esters of monoalkyl ethers of alkylene oxide polymers, fatty acid amides having 8 to 22 carbon atoms, and aliphatic amines having 8 to 22 carbon atoms can be used. Specific examples of these include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, isooctyl stearate, myristin Octyl acid, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol, lauryl alcohol. Also, nonionic surfactants such as alkylene oxides, glycerin, glycidol, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives, heterocycles, phosphoniums or sulfoniums, Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate group, phosphate group, etc., amino acids, aminosulfonic acids, sulfuric acid or phosphates of amino alcohol And alkylbedine-type amphoteric surfactants and the like can also be used. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents and the like are not necessarily 100% pure, and may contain impurities such as isomers, unreacted materials, by-products, decomposition products, oxides, etc. in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. These lubricants and surfactants used in the present invention can be selectively used in the lower layer and the upper magnetic layer according to their types and amounts as needed. For example, by controlling the bleeding to the surface using fatty acids having different melting points in the lower layer and the upper magnetic layer, controlling bleeding to the surface using esters having different boiling points and polarities, and adjusting the amount of the surfactant. It is possible to improve the stability of coating and to improve the lubricating effect by increasing the amount of the lubricant added in the intermediate layer. Of course, the present invention is not limited to the examples shown here. Further, all or a part of the additives used in the present invention may be added in any step of the lower layer paint, the upper layer magnetic paint production, for example, when mixed with the ferromagnetic powder before the kneading step,
When added in a kneading step with a ferromagnetic powder, a binder and a solvent, when added in a dispersion step, when added after dispersion,
There are cases where it is added immediately before application.

The organic solvent used in the present invention may be any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone, tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol. Alcohols such as methylcyclohexanol, esters such as methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, and glycol acetate; glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, and dioxane; benzene; Aromatic hydrocarbons such as toluene, xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, Chloroform, ethylene chlorohydrin, dichlorobenzene, chlorinated hydrocarbons and the like, N,
N-dimethylformamide, hexane and the like can be used.

The thickness of the magnetic recording medium of the present invention is 1 to 100 μm, preferably 6 to 20 μm for the support, 1 μm or less, preferably 1 to 0.2 μm for the upper magnetic layer, and 0.5 μm or more for the lower layer. It is 0.5 to 5 μm. When the thickness of the upper magnetic layer exceeds 1 μm, the effect of thinning the electromagnetic conversion characteristics is lost. When the thickness of the lower layer is less than 0.5 μm, the productivity is reduced, and the calender moldability is deteriorated, so that sufficient electromagnetic conversion characteristics cannot be obtained. Further, an undercoat layer for improving adhesion may be provided between the support and the lower layer. Their thickness is 0.01 to 2 μm, preferably 0.05 to 0.5
μm. Further, a back coat layer may be provided on the side of the support opposite to the magnetic layer side. This thickness is 0.1-2
μm, preferably 0.3 to 1.0 μm. Known undercoating layers and backcoat layers can be used.

As the support used in the present invention, known films such as polyethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, polyaramid, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, and aromatic polyamide can be used. The support is preferably non-magnetic. These supports may be subjected to corona discharge treatment, plasma treatment, easy adhesion treatment, heat treatment, dust removal treatment, or the like in advance. The center line average surface roughness of the support is 0.1 μm or less, preferably 0.05 μm or less. Further, it is preferable that these supports not only have a small center line average surface roughness but also have no coarse protrusions of 1 μm or more. The surface roughness shape can be freely controlled by the size and amount of the filler added to the support as needed. Examples of these fillers include oxides and carbonates such as Ca, Si and Ti, and organic fine powders such as acryl. The F-5 value of the support used in the present invention in the tape running direction is preferably 5 to 50 kg / mm ² , and the F-5 value in the tape width direction is preferably 3 to 30 kg / mm ² . Generally, the F-5 value is higher than the F-5 value in the width direction of the tape, but this is not particularly necessary when it is necessary to increase the strength in the width direction.

The heat shrinkage of the support in the tape running direction and the width direction at 100 ° C. for 30 minutes is preferably 3% or less, more preferably 1.5% or less, and the heat shrinkage at 80 ° C. for 30 minutes is 30%. Preferably it is 1% or less, more preferably 0.1%.
5% or less. Breaking strength is 5-100kg in both directions
/ Mm ² , and the elastic modulus is preferably 100 to 2000 kg / mm ² .

The step of producing the magnetic paint and the non-magnetic paint of the magnetic recording medium of the present invention comprises at least a kneading step, a dispersing step, and a mixing step provided before and after these steps as necessary. Each step may be divided into two or more steps. Ferromagnetic powder used in the present invention, non-magnetic powder, binder, carbon black, abrasive,
All raw materials such as an antistatic agent, a lubricant, and a solvent may be added at the beginning or during any step. Further, individual raw materials may be added in two or more steps in a divided manner. For example, polyurethane may be divided and supplied in a kneading step, a dispersing step, and a mixing step for adjusting the viscosity after dispersion.

In order to achieve the object of the present invention, it is a matter of course that a conventional known manufacturing technique can be used as a part of the process. However, in the kneading step, a strong kneading force such as a continuous kneader or a pressure kneader is used. You can use what you have. When a continuous kneader or a pressure kneader is used, all or a part of each powder and the binder (however, 30% or more of the whole binder is preferable) and the kneading treatment is performed in the range of 15 to 500 parts with respect to 100 parts of the powder. . Details of these kneading processes are described in JP-A-1-106338 and JP-A-64-792.
No. 74.

In order to obtain the medium of the present invention, it is necessary to perform strong orientation. 1000G or more solenoid and 200
It is preferable to use a cobalt magnet of 0 G or more in combination, and it is preferable to provide an appropriate drying step before orientation so that the orientation after drying is the highest.

Furthermore, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyimide amide is used as the calendering roll. Further, the treatment can be performed between metal rolls. The processing temperature is preferably 70 ° C. or higher, more preferably 80 ° C. or higher. The linear pressure is preferably 200 kg / cm, more preferably 300 kg / cm or more.

SUS420J on the upper magnetic layer surface of the magnetic recording medium obtained by the manufacturing method of the present invention and the opposite surface thereof
Is preferably 0.5 or less, more preferably 0.5 or less.
3 or less, the surface resistivity is preferably 10 ^-5 to 10 ^-12 ohm / sq, and the elastic modulus at 0.5% elongation of the magnetic layer is preferably 100 to 2000 kg / mm in both the running direction and the width direction.
^{2. The} breaking strength is preferably 1 to 30 kg / cm ² , the elastic modulus of the magnetic recording medium is preferably 100 to 1500 kg / mm ^{2 in} both the running direction and the longitudinal direction, and the residual elongation is preferably 0.5% or less, 100 ° C. or less. Is preferably 1% or less, more preferably 0.5% or less, and most preferably 0.1% or less.

The residual solvent contained in the upper magnetic layer is preferably 100 mg / m ² or less, more preferably 10 mg / m ² or less.
/ M ² or less, and it is preferable that the residual solvent contained in the upper magnetic layer be smaller than the residual solvent contained in the lower layer.

The porosity of the upper magnetic layer is preferably 3
0 vol% or less, more preferably 10 vol% or less. When the magnetic properties of the magnetic recording medium obtained by the production method of the present invention are measured at a magnetic field of 5 KOe, the squareness ratio in the tape running direction is 0.70 or more, preferably 0.80 or more, more preferably 0.90 or more. is there. The squareness ratio in two directions perpendicular to the tape running direction is 8 which is the squareness ratio in the running direction.
It is preferably 0% or less. The SFD of the upper magnetic layer is preferably 0.6 or less.

[0031]

Next, the present invention will be described more specifically with reference to examples and comparative examples. In each example, “parts” means “parts by weight” unless otherwise specified.

A magnetic coating solution and a non-magnetic coating solution were prepared according to the following formulations. Example 1 upper magnetic layer for magnetic coating liquid formulation ferromagnetic powder: Fe alloy powder (Fe-Ni-Co) 100 parts Composition; Fe: Ni: Co = 92 : 6: 2 Hc1600Oe, σ S 135emu / g long axis length 0.18 μm, needle ratio 9 Vinyl chloride copolymer —SO ₃ Na, epoxy group-containing polyurethane resin 5 parts —SO ₃ Na content, molecular weight 45,000 α-alumina (average particle size 0.2 μm) 5 parts Cyclohexanone 150 parts Methyl ethyl ketone 150 Part After mixing and dispersing the above composition in a sand mill for 6 hours,
Polyisocyanate (Coronate L), 5 parts of stearic acid, and 10 parts of butyl stearate were added to obtain a magnetic coating solution.

Lower layer coating liquid formulation Acicular α-Fe ₂ O ₃ 100 parts Long axis length 0.5 μm Acicular ratio 10 Carbon black 5 parts Average particle diameter 20 mμ Vinyl chloride copolymer 8 parts —SO ₃ Na, epoxy group Content Molecular weight 45000 Polyurethane resin 5 parts -SO ₃ Na content, molecular weight 45000 Cyclohexane 100 parts Methyl ethyl ketone 100 parts After mixing and dispersing the above composition in a sand mill for 4 hours,
Polyisocyanate (Coronate L), 5 parts of stearic acid and 10 parts of butyl stearate were added to obtain a lower layer coating solution.

The lower non-magnetic layer was coated on a 5.5 μm thick polyethylene terephthalate, dried, coated with an upper magnetic layer, oriented with a permanent magnet, and dried.
Thereafter, a super calendar process was performed. The coating thickness was 0.3 μm for the magnetic layer and 3.0 μm for the non-magnetic layer. The raw material thus obtained was cut into a 3.81 mm width to produce a digital audio tape (DAT).

In Comparative Example, a tape was prepared by changing the factors shown in Table 1 with respect to Example 1. In addition, the simultaneous coating means that the above coating liquid is applied using two doctors having different gaps.
It refers to application in a wet state on polyethylene terephthalate. These tapes were evaluated by the following methods, and the results are shown in Table 1.

Used deck: SONY DTC-1000

Reproduction output: A signal having a single frequency of 4.7 MHz was input, the reproduction signal was output to a spectrum analyzer, and the peak value of the signal was read. The spectrum analyzer is HP-
3585A OdB is a single-layer magnetic layer tape of Comparative Example 1.

[0038]

[Table 1]

As is clear from the results shown in Table 1, it was found that Example 1 using the acicular nonmagnetic powder of the present invention can improve the RF output. Comparative Examples 1 and 2 not falling within the scope of the present invention
In No. 3, no good result of RF output was obtained. In addition, RF
The target output level is 3.0 dB or more.

[0040]

As described above, according to the present invention,
By coating the upper magnetic layer after the lower layer is dried and using a needle-shaped nonmagnetic powder for the lower layer, a magnetic recording medium having good electromagnetic conversion characteristics, specifically, high RF output can be obtained.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-188017 (JP, A) JP-A-63-157313 (JP, A) JP-A-1-300419 (JP, A) JP-A-2- 15415 (JP, A) JP-A-4-238111 (JP, A) JP-A-4-283416 (JP, A) JP-A-4-321924 (JP, A) JP-A-4-325917 (JP, A)

Claims (8)

(57) [Claims] 1. A coating solution for an upper magnetic layer containing a ferromagnetic powder and a binder, and a coating solution for a lower layer containing a nonmagnetic powder and a binder are prepared, and the coating solution for a lower layer is coated on a support. ,
The method of manufacturing a magnetic recording medium characterized by applying the resulting the upper magnetic layer coating liquid on the lower, front
The ferromagnetic powder contains Fe as a main component and at least Ni.
Or an acicular ferromagnetic alloy powder containing Co, and
The average diameter of the long shaft length is 0.3 μm or less, and the lower layer coating solution has a ratio r between the longest shaft length r ₁ and the shortest shaft length r _2.
1 / r ₂ comprises a non-magnetic powder is less than 2.5 more than 20, and the lower layer coating solution was coated on the support, and the obtained lower layer has dried, a dry thickness becomes 1μm or less A method for producing a magnetic recording medium, comprising applying a coating solution for an upper magnetic layer as described above. 2. The magnetic recording medium according to claim 1, wherein the non-magnetic powder of the lower layer coating liquid is a needle-shaped non-magnetic powder having a needle ratio of 2.5 or more and less than 20. Method. 3. The method for producing a magnetic recording medium according to claim 1, wherein the nonmagnetic powder of the lower layer coating solution has an average diameter of the longest axial length of 3 μm or less. 4. The non-magnetic powder of the lower layer coating solution is Al ₂
O ₃ (α, γ), Cr ₂ O ₃ , α-Fe ₂ O ₃ , goethite (α-FeOOH), SiO ₂ , ZrO ₂ , CeO
_2, TiO ₂ (rutile, anatase) The method of manufacturing a magnetic recording medium according to claim 1, characterized in that it comprises at least one of the non-magnetic powder. 5. The support is made of polyethylene terephthalate.
, Polyethylene naphthalate, polyphenylene sulfide, polyaramid, polycarbonate, polyamide, polyimide, polyamide imide, polysulfone,
At least one selected from aramid and aromatic polyamide
The method according to claim 1, wherein the magnetic recording medium is a seed. 6. The method according to claim 1, wherein there is substantially no mixed region between the lower magnetic layer and the upper magnetic layer. 7. The magnetic recording medium according to claim 1, wherein said magnetic recording medium is for digital recording such as a recording tape, a video tape, a computer tape, and a disk. Manufacturing method. 8. The binder comprises an S-containing polar group.
2. A method for manufacturing a magnetic recording medium according to claim 1, wherein:
Method.