JPH09180169A - Magnetic recording media - Google Patents

Abstract

(57) [PROBLEMS] To reduce the thickness and surface roughness of a magnetic layer to a level comparable to that of a ME type magnetic recording medium, and to have excellent mechanical properties such as running property and durability. An MP type magnetic recording medium having a two-layer structure is provided. SOLUTION: A mixed solvent of methyl ethyl ketone, toluene, and cyclohexanone, a polyvinyl chloride resin, a polyurethane resin, and acicular goethite powder (long axis length: 0.10 μm, acicular ratio: 15) are formed on a PET film. , A granular iron oxide (axial ratio: 1.5), carbon black, stearic acid, n-butyl stearate, and polyisocyanate are blended to form a coating film of a non-magnetic coating material. A mixed solvent of methyl ethyl ketone, toluene, and cyclohexanone, polyvinyl chloride resin, polyurethane resin, and ferromagnetic metal powder (long axis length: 0.08 μm,
Needle ratio: 10, coercive force: 180 kA / m, saturation magnetic charge 0.18
T) is mixed to form a coating film of the magnetic paint obtained, and magnetic field orientation, coating film drying and calendering are performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium, and more particularly to a coating type magnetic recording medium in which a non-magnetic layer and a magnetic layer are laminated.

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium such as a video tape, a vapor deposition type (in general, ME (Metal Eva
It is called the poration) type, and is simply referred to as the ME type. ) And a coating film of a coating material in which magnetic powder is dispersed on a support, and drying the coating film (this is generally called MP (Metal Particle) type, hereinafter, simply referred to as MP. Type is known). In the ME type magnetic recording medium, since the magnetic metal powder is present in the magnetic layer at a high density and the thickness of the magnetic layer can be made thin, high density recording can be performed, and further, the high frequency characteristic is deteriorated. It has the advantage that it is small and high output characteristics can be obtained. However, the ME type magnetic recording medium has low productivity because it is manufactured through a complicated process of vapor deposition of magnetic metal powder.
Further, since the magnetic layer is a metal film, it is easily oxidized and has a drawback of being inferior in long-term storage stability. On the other hand, the MP type magnetic recording medium is superior in productivity and long-term storability to the ME type magnetic recording medium because the magnetic layer is obtained by drying a paint coating film in which magnetic powder is dispersed. Have advantages. However, in such an MP type magnetic recording medium, if the magnetic layer, that is, the coating film is formed to have a small thickness for high output, the following problems occur. That is, in order to form a thin coating film, it is conceivable to reduce the coating amount or to use a paint with a low concentration, but in the former case, the coating film is not leveled sufficiently and Since the drying starts, streaks and defects occur in the coating film, resulting in a problem that the yield is significantly reduced.In the latter case, the packing density of the magnetic powder in the coating film is significantly reduced, and the drying As a result, voids are generated in the film, which causes problems such as a decrease in recording density and a marked decrease in film strength, resulting in a decrease in the strength of the recording medium itself.

Therefore, in order to solve such a problem, a first paint coating film is formed on the surface of a support with a non-magnetic paint, and a second paint coating film is formed on this paint coating film with a magnetic paint. A two-layered MP type magnetic recording medium in which the first and second paint films are simultaneously dried, that is, a two-layered MP type magnetic recording layer in which a magnetic layer is laminated on a non-magnetic layer formed on the surface of a support. A magnetic recording medium has been proposed (for example, Japanese Patent Laid-Open No. 63-191315). Such a two-layered M
In a P-type magnetic recording medium, a magnetic coating film is formed on a non-magnetic coating film. Therefore, by using a high-concentration magnetic coating film, a thin coating film can be formed without extremely reducing the coating amount. It can be formed, and it is possible to solve the problem that voids and streaks are generated in the magnetic layer that occurs in the MP type magnetic recording medium including only the single magnetic layer. Further, since the magnetic layer is laminated on the non-magnetic layer, by increasing the thickness of the non-magnetic layer, the surface of the magnetic layer is hardly affected by the surface roughness of the support surface, and S / The N characteristic can be improved, and the strength of the recording medium can be kept high by forming the non-magnetic layer with a large thickness even if the magnetic layer is formed thin for high output. I also have.

[0004]

In recent years, there has been a demand for higher performance of magnetic recording media. Even in the MP type magnetic recording medium having the above-mentioned two-layer structure, the magnetic layer is further thinned and The surface is smoothed. However, in the case of the MP type magnetic recording medium having a two-layer structure, the coating film for the magnetic layer is formed on the coating film for the non-magnetic layer, and these are simultaneously dried. And the interfacial properties between the coating film for magnetic layer and the coating film for non-magnetic layer are the controllability of the thickness of the coating film for magnetic layer and the surface property (thickness of the magnetic layer obtained by drying and Surface roughness), and by simply examining the constituent materials and physical properties of the coating film for the magnetic layer, the thickness and surface roughness of the magnetic layer can reach levels comparable to those of ME-type magnetic recording media. It cannot be made smaller. Further, the MP-type magnetic recording medium having a two-layer structure has a higher recording medium strength, superior running property and durability than the ME-type magnetic recording medium, but the magnetic layer is further thinned. In this case, since the role of the non-magnetic layer for compensating the strength of the recording medium becomes larger, it is necessary to increase the strength of the non-magnetic layer more than ever. As described above, it is no exaggeration to say that the further improvement in performance of the MP type magnetic recording medium depends on the improvement in the physical properties of the non-magnetic layer (coating for non-magnetic layer). The level required for the physical properties of) is becoming more severe than ever.

The present invention has been made in view of the above problems, and the thickness and surface roughness of the magnetic layer are reduced to a level comparable to those of the ME type magnetic recording medium, and the running property is excellent. And an MP type magnetic recording medium having a two-layer structure having mechanical properties such as durability.

[0006]

In order to achieve the above-mentioned object, a magnetic recording medium according to the present invention has a first binder resin dissolved on a non-magnetic support and at least acicular goethite powder. Forming a first coating film of a non-magnetic coating material in which a non-magnetic powder composed of granular iron oxide powder having a particle diameter of 0.01 to 0.1 μm and carbon black is dispersed, and forming a first coating film on the first coating film. A second binder resin is dissolved to form a second coating film of a magnetic coating in which ferromagnetic powder having a major axis length of 0.3 μm or less is dispersed, and these first and second coating films are simultaneously dried. Thereby, the nonmagnetic layer having a thickness of 1 to 3 μm, in which the nonmagnetic powder is dispersed in the first binder resin, and the ferromagnetic powder are dispersed in the second binder resin, on the nonmagnetic support. A magnetic layer having a thickness of 0.5 μm or less is formed in this order. As a result, the non-magnetic coating material acts synergistically with the action of increasing the viscosity of the network structure formed by needle-shaped goethite and the chain structure of carbon black and the action of reducing the viscosity of the granular iron oxide powder. ,
The first coating film formed by this non-magnetic coating material is kept in a state of having a cohesive force that does not cause waviness between the first coating film and the second coating film applied thereon, and Since the granular iron oxide powder having a small particle size is uniformly present on the surface, the interface between the first coating film and the second coating film is flattened. And, the flattening of the interface between the first coating film and the second coating film,
Due to the dispersion of finely divided ferromagnetic powder having a major axis length of 0.3 μm or less in the magnetic paint, the second coating film has a thickness of 1 μm.
Even if it is applied to the following extremely thin thickness, the thickness of the coating film becomes uniform and the surface thereof is also flattened. As a result, in the recording medium obtained after drying, the non-magnetic layer has high strength due to the aligned arrangement of needle-like goethite and the chain structure of carbon black, and the magnetic layer is atomized with the major axis length of 0.3 μm or less. The ferromagnetic powder is evenly present, and the surface roughness (Ra) becomes an ultrathin layer (thickness of 0.5 μm or less) having a flat surface in the range of 0.003 to 0.015 μm. Therefore, the obtained recording medium has output characteristics and S / N characteristics comparable to those of the ME type magnetic recording medium, and the mechanical time characteristics such as running property and durability are greatly improved. In addition, the interface between the non-magnetic layer and the magnetic layer has a surface roughness (Ra).
Is 0.01 μm or less, so that an output signal with less noise can be obtained. Moreover, since the needle-shaped goethite can be obtained at low cost, the magnetic recording medium can be manufactured at low cost.

In the above, the surface roughness (Ra) is a non-contact surface roughness measuring device (TOPO-3D: manufactured by WYKO).
The square root mean square.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The acicular goethite powder is a hydrous iron oxide in the previous stage before becoming iron oxide, and generally has a needle-like ratio (major axis length / minor axis length) and a ratio to iron oxide. Has a large surface area,
It is also available at a low cost. The acicular goethite used as the nonmagnetic powder of the nonmagnetic coating material in the present invention has a major axis length (particle diameter) of 0.05 to 0.3 μm and an acicular ratio of 10 to 30. Those in are preferred. By having such a preferable major axis length and the acicular ratio, the acicular goethite is well dispersed in the paint, and is easily aligned in the paint film, which further flattens the paint film surface. Will be improved. If the major axis length of the acicular goethite powder is smaller than the above range, the still life tends to decrease, and if it exceeds the range, the surface smoothness of the surface of the non-magnetic layer tends to deteriorate and the electromagnetic conversion characteristics tend to deteriorate. Further, if the acicular ratio is smaller than the above range, it tends to be difficult to align and arrange, and the surface smoothness of the surface of the non-magnetic layer tends to decrease. If the acicular ratio is large, the particles are easily broken during preparation of the paint, and if broken, the particle diameter is small. The non-uniformity makes it difficult to flatten the coating surface.

Further, the granular iron oxide powder having a particle size of 0.01 to 0.1 μm used in the non-magnetic coating material in the present invention is a fine powder close to single crystal particles and has an axial ratio (optionally selected). It is a granular powder composed of spherical powder or polyhedral powder having no sharply protruding shape portion having an axial ratio of two axes of 1.5 or less. This granular iron oxide powder has a very good dispersibility in paints compared with titanium oxide, tin oxide, zinc oxide, etc., which have been generally used as non-magnetic inorganic powders in non-magnetic paints of this type. Then, by dispersing this in the paint, the viscosity of the paint can be reduced. Further, by being present on the coating film surface, unevenness on the coating film surface is reduced and the coating film surface is flattened.

The carbon black used in the non-magnetic paint is a known carbon black that has been generally used as a non-magnetic powder in this kind of non-magnetic paint, and is referred to as "Carbon Black Handbook". Used by referring to (Carbon Black Association). Here, the average particle diameter of the primary particles of carbon black is 0.01
5 to 0.06 μm, preferably 0.02 to 0.03 μm
m, specific surface area 20 to 300 m ² / g, preferably 15
0~250m ² / g, DBP oil absorption 25~300ml
/ 100g, preferably 150-250ml / 100g
It is. Specific examples of carbon black include SAF
(Super Ablation Furnace),
ISAF (Intermediate SAF), HA
F (High Absorption Furnace), F
F (Fine Furnace), FEF (Fast
Extruding Furnace), GPE (Ge
general Purpose Furnace), FT
(Fine Thermal), SRF (Semi R
einforcing Furnace), HCC (H
high Color Channel), HCF (Hi
gh Color Furnace) and the like. In the present invention, carbon black has a function of controlling the porosity of the film (non-magnetic layer), the powder volume ratio, and the conductivity in addition to the function of strengthening the film strength (strength of the non-magnetic layer) as described above.

The mixing ratio (weight ratio) of these acicular goethite powder, granular iron oxide powder and carbon black is 50.
To 95 (acicular goethite powder): 1 to 40 (granular iron oxide powder): 4 to 30 (carbon black), preferably 60 to 80 (acicular goethite powder): 10 to 20
(Granular iron oxide powder): 10 to 15 (carbon black)
Is particularly preferable. If the blending amount of the acicular goethite powder is less than this range, the coating film strength tends to decrease, and if the blending amount is large, the unevenness of the coating film tends to increase. Also, if the blending amount of the granular iron oxide powder is less than this range, the unevenness of the coating film tends to increase, and if it is increased, the viscosity of the coating material decreases and the coating film of the magnetic coating material is formed on the non-magnetic coating material. Disturbances tend to occur at these interfaces during the operation. When the amount of carbon black is less than this range, the viscosity of the coating composition is reduced, and when the coating film of the magnetic coating composition is formed on the non-magnetic coating composition, the interface tends to be disturbed. If so, the viscosity of the coating material increases and coating streaks tend to occur.

As the binder resin (binder) of the non-magnetic coating material, conventionally known thermoplastic resins, thermosetting resins or reactive resins, and mixtures thereof are used. For example, vinyl chloride copolymers (copolymerizable monomers include vinyl acetate, vinyl propionate and other fatty acid vinyl esters, methyl acrylate, ethyl acrylate, propyl acrylate, lauryl acrylate, stearyl acrylate, methyl methacrylate) , Alkyl (meth) acrylates such as ethyl methacrylate, vinylidene chloride, etc. are preferable because they have the effect of increasing the solvent solubility.Vinyl alcohol, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) as an OH group-containing copolymerization monomer. Acrylate, hydroxybutyl (meth) acrylate, hydroxylauryl (meth) acrylate, hydroxystearyl (meth) acrylate, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate Relate, hydroxyethyl allyl ether,
Hydroxypropyl allyl ether, hydroxybutyl allyl ether and the like are preferable because they combine with a polyisocyanate compound or an epoxy compound to improve the mechanical strength. Others maleic acid, (meth) acrylic acid, acrylonitrile,
If necessary, ethylene, styrene, etc. can be copolymerized. Acrylic resins represented by polymethyl methacrylate (copolymer monomers include those similar to those used in the above vinyl chloride copolymer); nitrocellulose, cellulose acetate propionate, cellulose acetate Cellulose resins such as butyrate; polyvinyl acetal resin, polyvinyl butyral resin, epoxy resin, phenoxy resin, polyester polyurethane resin, polyether polyurethane resin, polyether ester polyurethane resin, polycarbonate polyurethane resin, polyester resin, polyether resin, various types Rubber-based resins and the like can be mentioned.
Of these, vinyl chloride resins, acrylic resins, fibrin resins, polyurethane resins, polyester resins and polyether resins are preferred. These various resins are used alone or in combination of two or more. In order to improve the dispersibility of the non-magnetic powder in the paint and the durability of the non-magnetic layer after drying, it is preferable to introduce a polar group as exemplified below into the molecule of the binder resin. For example, -COOM,
_{-SO 3 M, -SO 4 M,} -PO 3 M 2, -OPO 2 M
₂ , amino group, ammonium base, -OH, -SH, epoxy group and the like. Here, M represents a hydrogen atom, an alkali metal or ammonium, and a plurality of Ms in one group.
, They may be the same as or different from each other.

As the organic solvent for the non-magnetic paint, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone and other ketones; methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate monoethyl ether, etc., ester solvents; ethers, Glycol ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane; benzene, toluene,
Tar-based substances (aromatic hydrocarbons) such as xylene; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform, ethylene chlorohydrin, dichlorobenzene and the like can be used. These solvents are used alone or in combination of two or more.

If necessary, a substance having a lubricating effect, an antistatic effect, a dispersing effect and a plasticizing effect, which has been conventionally used in this field (MP type magnetic recording medium), is added to the non-magnetic coating material. These substances include substances that dissolve in the paint (eg, surfactants, fatty acids, fatty acid esters, etc.),
And a substance (for example, a metal oxide, a metal nitride, a metal sulfide, etc.) that disperses in a paint while maintaining its particulate form.

The production of the non-magnetic paint basically comprises a step of mixing the above-mentioned various materials by stirring and a kneading step. As the stirrer, a stirrer known per se such as a planetary mixer, a double planetary mixer, a chemical mixer and the like can be used. As the kneader, a kneader, a Banbury mixer, a single screw extruder,
A known stirrer such as a twin-screw kneader can be used.

Strong magnetism with the major axis length of the magnetic paint being 0.3 μm or less
As the powder, ferromagnetic iron oxide, ferromagnetic chromium dioxide, strong
Magnetic alloy powder or the like is used. Ferromagnetic iron oxide has the general formula F
x value in the case of eOx is 1.33 ≦ x ≦ 1.50
Ferromagnetic iron oxide in the range, namely maghemite (γ
-Fe_TwoO_Three, X = 1.50), magnetite (Fe _Three
O_Four, X = 1.33) and their beltride compounds
(FeOx, 1.33 <x <1.50). these
Ferromagnetic iron oxide may be added with divalent metal
Yes. Cr, Mn, Co, Ni, C as the divalent metal
u, Zn, etc., and 0 to 10 at for the above iron oxide.
Omic% is added. Ferromagnetic chrome dioxide
CrO_TwoAnd Na, K, Ti, V, Mn, F
e, Co, Ni, Tc, Ru, Sn, Ce, Pb, etc.
Metals, semiconductors such as P, Sb and Te, or their gold
CrO added with 0 to 20 wt% oxide of the genus_TwoUsed by
It is. Ferromagnetic alloy powder has a metal content of 75% by weight or more,
80% by weight or more of the genus is at least one kind of ferromagnetic metal (eg
For example, Fe, Co, Ni, Fe-Co, Fe-Ni)
20% by weight or less of metal content, preferably
0.5 to 5 wt% is Al, Si, S, Sc, Ti, V,
Cr, Mn, Cu, Zn, Y, Mo, Rh, Pd, A
g, Sn, Sb, Te, Ba, Ta, W, Re, Au,
Hy, Pb, Bi, La, Ce, Pr, Nd, B, P
Which composition has a small amount of water, hydroxide, acid
Compounds may be included. Ferromagnetism of these ferromagnetic powders
Alloy powder is preferably used. Needle ratio of ferromagnetic powder (long
It is preferable that the acicular powder has an axial length / minor axis length of 5 or more,
It is particularly preferable that the acicular ratio is in the range of 5 to 20. Heel
By having a needle-shaped ratio of
The surface property and squareness of the magnetic layer are improved. Also strong
The coercive force (Hc) of magnetic powder is 120-280 kA / m
170-210 kA / m is more preferable.

The same binder resin and organic solvent as those used in the magnetic paint are used in the magnetic paint. Here, the introduction of the polar group into the binder resin serves to improve the dispersibility of the ferromagnetic powder and the durability of the magnetic layer after drying. Also, various substances having a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect, an anticorrosive effect, a polishing effect, etc. can be blended in the same manner as the non-magnetic paint. These substances include substances that dissolve in the paint (for example, surfactants, fatty acids, fatty acid esters, etc.) and substances that disperse in the paint while maintaining the particulate form of the substance (for example, metal oxides, Metal nitride, metal sulfide, etc.) are also included.

The production of the magnetic paint comprises a step of mixing various materials by stirring and a kneading step, as in the case of the non-magnetic paint.

In the present invention, the weight average molecular weight of the binder resin is 10,000 to 100 for both the non-magnetic paint and the magnetic paint.
It is preferably 000, particularly preferably 20,000 to 50,000. Further, the difference in solubility parameter between the binder resin and the organic solvent is preferably 5 or less. This is because the resin is dissolved in the solvent without phase separation in the paint, and a uniform paint film with no unevenness is formed. Further, the glass transition temperature (Tg) of the binder resin is 30 to 6 for both the non-magnetic paint and the magnetic paint.
It is preferably in the range of 0 ° C., and the Tg of the binder resin of the magnetic paint is 5 to 10 ° C. higher than the Tg of the binder resin of the non-magnetic paint. This is because calendering works effectively in the calendering process after drying the coating film, which will be described later. Thereby, the thickness of the medium becomes more uniform and the surface (the surface of the magnetic layer) becomes smoother. The weight ratio of the binder resin to the whole non-magnetic powder in the non-magnetic paint is 1: 1.
It is preferably in the range of 0 to 1:20. Within this range, the non-magnetic powder and the resin are mixed in the paint without being unevenly distributed, and the strength and surface property of the dried non-magnetic layer are reduced. The weight ratio of the ferromagnetic powder to the binder resin in the magnetic paint is 100: 5 to 100 :.
A range of 15 is preferable. Within this range, the magnetic powder is well dispersed in the paint and the flatness of the magnetic layer surface is further improved. Further, the non-magnetic powder (acicular goethite powder,
Granular iron oxide powder and the total content of the filler containing carbon black, that is, the content of the substance existing in the non-magnetic layer while maintaining its particle shape is preferably 60 to 80% by weight. The content rate of the entire filler including the ferromagnetic powder, that is, the content rate of the substance existing in the magnetic layer while maintaining its particle shape is 80 to 9
It is preferably 0% by weight. This is because when the content of the entire filler in the non-magnetic layer is less than the above range, the film strength tends to decrease and the still life tends to decrease. This is because the still life and the like tend to be shortened. Further, when the content of the entire filler in the magnetic layer is smaller than the above range, the ratio of the ferromagnetic powder in the magnetic layer tends to be small, and the electromagnetic conversion characteristics tend to deteriorate.
This is because if it exceeds the above range, the proportion of the binder resin in the magnetic layer becomes small and the flatness of the surface tends to decrease.

In the present invention, the ratio of the intrinsic viscosity of the non-magnetic coating material to the intrinsic viscosity of the magnetic coating material is set in the range of 1: 0.2 to 1: 0.8 so that the coating of the non-magnetic coating material at the time of coating layer superposition It gives favorable results in reducing the waviness between the film and the coating of the magnetic paint. Especially, the intrinsic viscosity of non-magnetic paint is 5-20cp
More favorable results are obtained when the range is set to oise.
The weight average molecular weight of the binder resin is a value measured by a gel permeation chromatography (GPC) measuring device (manufactured by Shimadzu Corporation), and the intrinsic viscosity is a value measured by a B-type viscometer (manufactured by Tokimec Co., Ltd.). .

As materials for the non-magnetic support, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate; polyolefins such as polyethylene and polypropylene; cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propio Cellulose derivatives such as nates; vinyl-based resins such as polyvinyl chloride and polyvinylidene chloride; plastics such as polycarbonate, polyimide, polyamide-imide, etc., as well as aluminum, copper, tin, zinc or non-magnetic alloys containing these depending on the application. Non-magnetic metals; ceramics such as glass, pottery and porcelain; paper, baryta or C2-C10 alpha-polyolefins such as polyethylene, polypropylene and ethylene-butene copolymers Paper such as paper coated or laminated with kind can also be used. These non-magnetic supports may be transparent or opaque depending on the purpose of use. Also,
The form of the non-magnetic support may be any of film, tape, sheet, disk, card, drum and the like, and various materials are selected as necessary according to the form. The thickness of these non-magnetic supports is about 1 to 50 μm, preferably 1 to 30 μm in the case of a film, tape or sheet. In the case of a disk or a card, the length is about 0.5 to 10 mm, and in the case of a drum, the shape is cylindrical, and its type is determined according to the recorder to be used. The surface roughness (Ra) of the non-magnetic support is preferably 0.025 μm or less so that the medium surface (the surface of the magnetic layer) has the above-mentioned surface roughness (0.003 to 0.015 μm). , 0.02
More preferably, it is less than or equal to μm.

In the present invention, first, a coating film of a non-magnetic paint is formed on a support, and while this coating film is in a wet state, a coating film of a magnetic paint is continuously formed. For the formation of this coating film, a coating method known per se can be used. For example, air doctor coat, blade coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat,
Examples thereof include spin coating. A concrete description of these is given in "Coating Engineering", pages 253 to 277 (published by 4.3.20 of Showa), published by Asakura Shoten.

After forming the coating film of the non-magnetic paint and the coating film of the magnetic paint, magnetic field orientation, drying of the coating film and calendering are carried out to obtain a final magnetic recording medium. The calendering treatment is preferably performed by a super calendering method in which two rolls such as a metal roll and a cotton roll, a synthetic resin roll, a metal roll and a metal roll, or a synthetic resin roll and a synthetic resin roll are passed. As the resin for the synthetic resin roll, heat resistant resin such as epoxy or polyimide is used. Super calendar condition is about 30
Approximately 50 to 10 at pressure between rolls of 0 to 600 kg / cm
It is preferable to perform the treatment at a temperature of 0 ° C. and a treatment speed of 50 to 120 m / min. If the temperature and pressure exceed these upper limits, the magnetic layer, the nonmagnetic layer, and the nonmagnetic support are adversely affected. On the other hand, if the processing speed is lower than the lower limit, the processing operation takes time, and if it is higher than the upper limit, it becomes difficult to obtain the effect of surface smoothing.

The thickness of the magnetic layer in the magnetic recording medium after the calendering process is set to 0.05 to 0.5 μm. As a result, output characteristics comparable to those of the ME type magnetic recording medium can be obtained. When the thickness of the magnetic layer is less than 0.05 μm, the uniformity of the film is impaired, which is not preferable. The thickness of the entire magnetic recording medium after the calendering process is 6 to 9 μm.
The Young's modulus (Young's modulus in the running direction of the tape when the medium is a tape) is 50
It is preferably in the range of 0 to 1200 kg / mm ² .
As a result, the medium has high strength, and the running property and durability of the medium during the recording operation are improved. Young's modulus is 5
If it is less than 00 kg / mm ^2, the contact property between the head and the tape is deteriorated, and the electromagnetic conversion characteristics, the still life and the like tend to be deteriorated. The content of the whole filler (the non-magnetic powder and other additives) in the non-magnetic layer after the coating film is dried is preferably 60 to 80% by weight, and the whole filler (the ferromagnetic powder and other additives) in the magnetic layer is preferably contained. Content of additive) is 80-
90% by weight is preferred. If the content of the filler in the non-magnetic layer is less than the lower limit of the above range, sufficient strength cannot be obtained in the non-magnetic layer, and the running property and durability of the medium tend to deteriorate, and if it exceeds the upper limit, calendering The calendar during processing tends to not work sufficiently. If the filler content in the magnetic layer is below the lower limit of the above range, it tends to be difficult to obtain a sufficient recording density, and if it exceeds the upper limit, the durability of the magnetic layer tends to be reduced. In addition, the squareness ratio (measurement value at a magnetic field of 796 kA / m) in the medium scanning direction (the tape running direction when the medium is a tape) obtained by the calendering process is 0.8. The above is preferable, and 0.9 or more is more preferable. The electric resistance of the magnetic layer is preferably in the range of 10 ⁻⁶ to 10 ⁻¹² Ω / sq, more preferably in the range of 10 ⁻⁸ to 10 ⁻¹⁰ Ω / sq.

[0025]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

(Example 1) Preparation of magnetic paint for magnetic layer 100 parts by weight of ferromagnetic metal powder (major axis length: 0.08 μm) (acicular ratio: 10) (coercive force: 180 kA / m) (saturated magnetic charge) Amount: 0.18T) Polyvinyl chloride resin 10.0 parts by weight (Tg = 70 ° C.) Polyurethane resin 5.0 parts by weight (Tg = 30 ° C.) * Tg of the entire binder resin is 57 ° C. (calculated as a harmonic average) Methyl ethyl ketone (MEK) 12 parts by weight Toluene 12 parts by weight Cyclohexanone 4 parts by weight The above materials were kneaded for a certain period of time using a biaxial continuous kneader. Materials having the following composition were further added to the obtained kneaded product, diluted with a dissolver, and then dispersed with a sand mill to obtain a magnetic coating material.

Kneaded product 143 parts by weight MEK 93 parts by weight Toluene 93 parts by weight Cyclohexanone 31 parts by weight The solubility parameter (SP value) of MEK is 9.27, the SP value of toluene is 8.91, and the SP value of cyclohexanone is 9.88. And the SP value of the entire solvent calculated by the harmonic average is 9.20.

Preparation of non-magnetic paint for non-magnetic layer Needle-like goethite 98 parts by weight (long axis length: 0.10 μm, needle-like ratio: 15) Granular iron oxide 1 part by weight (axial ratio: 1.5) Carbon black 1 part by weight Polyvinyl chloride resin 10 parts by weight (Tg = 70 ° C.) Polyurethane 10 parts by weight (Tg = 30 ° C.) * Tg of the entire binder resin is 50 ° C. MEK 15 parts by weight Toluene 15 parts by weight Cyclohexanone 5 parts by weight Above materials Was kneaded for a certain period of time using a pressure kneader. A material having the composition shown below was further added to the obtained kneaded product, which was diluted with a dissolver and dispersed with a sand mill to obtain a non-magnetic coating material.

Kneaded material 155 parts by weight MEK 123 parts by weight Toluene 123 parts by weight Cyclohexanone 41 parts by weight To the whole non-magnetic coating material thus obtained, materials having the following composition were further added and stirred with a dissolver. ,
The final non-magnetic paint was prepared.

Stearic acid 1 part by weight n-butyl stearate 2 parts by weight Polyisocyanate 6 parts by weight A 6 μm thick polyethylene terephthalate film as a non-magnetic support is coated with a non-magnetic paint film and a magnetic paint film on one side. The coating was sequentially formed, and in a non-dried state, a solenoid magnetic field treatment was performed to perform an orientation treatment so as to have an axis of easy magnetization in the film running direction, and subsequently a calendar treatment by a super calender method and a heat curing treatment were performed. The conditions for calendering were a roll pressure of 450 kg / cm and a temperature of 80 ° C. The surface roughness of the magnetic layer after calendering was 0.0045 μm, and the surface roughness of the interface between the non-magnetic layer and the magnetic layer was 0.009 μm. The nonmagnetic layer thickness after curing was 2.0 μm, and the magnetic layer thickness was 0.2 μm.
The Young's modulus was 1000 kg / mm ² . Then, the magnetic tape was cut into a width of 6.35 mm to obtain a final magnetic tape.

Example 2 A magnetic tape was prepared in the same manner as in Example 1 except that acicular goethite powder having a major axis length (particle diameter) of 0.01 μm was used as the acicular goethite powder used in the non-magnetic paint. Created.

Example 3 A magnetic tape was prepared in the same manner as in Example 1 except that needle-like goethite powder having a major axis length (particle diameter) of 1.0 μm was used as the needle-like goethite powder used in the non-magnetic coating material. Created.

(Example 4) Needle-shaped goethite powder used in a non-magnetic paint has a needle-shaped ratio of 5 (long axis length: 0.10 μm).
A magnetic tape was prepared in the same manner as in Example 1 except that the needle-shaped goethite powder of No. 1 was used.

(Example 5) The needle-shaped goethite powder used for the non-magnetic coating material has a needle-shaped ratio of 50 (major axis length: 0.10μ).
A magnetic tape was prepared in the same manner as in Example 1 except that the acicular goethite powder of m) was used.

Example 6 As Example 1 except that the amounts of acicular goethite powder, granular iron oxide powder and carbon black in the non-magnetic paint were 30 parts by weight, 40 parts by weight and 30 parts by weight, respectively. A magnetic tape was prepared in the same manner.

(Embodiment 7) Granular iron oxide powder and carbon black were added to the non-magnetic coating material in an amount of 0.
A magnetic tape was prepared in the same manner as in Example 1 except that 1 part by weight and the amount of acicular goethite powder were 99.8 parts by weight.

(Example 8) 0.1 parts by weight of granular iron oxide, 69.9 parts by weight of acicular goethite powder, and 30 parts of carbon black in a non-magnetic coating material were used.
A magnetic tape was prepared in the same manner as in Example 1 except that the weight part was used.

(Example 9) The content of carbon black in the non-magnetic paint was 0.1 part by weight, the content of acicular goethite powder was 69.9 parts by weight, and the content of granular iron oxide was 30.
A magnetic tape was prepared in the same manner as in Example 1 except that the weight part was used.

(Example 10) A magnetic tape was prepared in the same manner as in Example 1 except that the total amount of the non-magnetic powder in the non-magnetic paint was 100 parts by weight and the amount of the binder resin was 5 parts by weight. .

Example 11 A magnetic tape was prepared in the same manner as in Example 1 except that the total amount of the nonmagnetic powder in the nonmagnetic coating material was 100 parts by weight and the amount of the binder resin was 30 parts by weight. .

Example 12 A magnetic tape was prepared in the same manner as in Example 1 except that a ferromagnetic powder having a needle-shaped ratio of 4 was used as the ferromagnetic powder of the magnetic paint.

(Embodiment 13) Calendar conditions of 100k
A magnetic tape was prepared in the same manner as in Example 1 except that the pressure between rolls was set to g / cm and the processing temperature was set to 50 ° C.

(Example 14) A magnetic tape was prepared in the same manner as in Example 1 except that a ferromagnetic powder having a needle-shaped ratio of 4 was used as the ferromagnetic powder of the magnetic paint.

(Example 15) The thickness of the non-magnetic layer was 0.5 μm.
A magnetic tape was prepared in the same manner as in Example 1 except that m was set.

(Example 16) 10 parts by weight of polyvinyl chloride having a Tg of 70 ° C. and 5 parts by weight of a polyurethane resin having a Tg of 70 ° C. as a binder resin of a magnetic coating material (Tg of the entire binder resin is 70 ° C.) A magnetic tape was prepared in the same manner as in Example 1 except that it was used.

(Example 17) 10 parts by weight of polyvinyl chloride having a Tg of 50 ° C. and 5 parts by weight of a polyurethane resin having a Tg of −40 ° C. as a binder resin of a magnetic paint (Tg of the entire binder resin is 20 ° C.) A magnetic tape was prepared in the same manner as in Example 1 except that (1) was used.

(Example 18) 20 parts by weight of butyl rubber alone (SP value 7.8) was used as a binder resin for magnetic paint and non-magnetic paint, and methanol alone (SP) was used as an organic solvent.
A value of 14.5) was used to prepare a magnetic tape in the same manner as in Example 1.

(Comparative Example 1) Example 1 was repeated except that the particulate iron oxide was not added in the non-magnetic coating material, but the amount of carbon black was 10 parts by weight and the amount of acicular goethite powder was 90 parts by weight. A magnetic tape was prepared in the same manner as in.

Comparative Example 2 Example 1 was repeated except that carbon black was not added in the non-magnetic coating material, but the amount of granular iron oxide was 10 parts by weight and the amount of acicular goethite powder was 90 parts by weight. A magnetic tape was prepared in the same manner as in.

In the above Examples and Comparative Examples, the viscosity of the coating composition was measured by the Tokimec B type viscometer (No. 4 rotor, 60r).
pm).

The surface roughness of the magnetic layer and the surface roughness of the interface between the magnetic layer and the non-magnetic layer of the magnetic tapes of Examples and Comparative Examples thus prepared were measured, and the electromagnetic conversion characteristics (output, error) were measured. Rate) and still life were evaluated. The electromagnetic conversion characteristics and the evaluation of the still life are performed by the DVC-Pro video tape recorder (AG-D
750: manufactured by Matsushita Electric Industrial Co., Ltd.) and recorded at a wavelength of 0.
It was performed at 48 μm. The still life was measured in the pause mode when the detection output was decreased by -6 dB from the initial value. The results are shown in Table 1 below.

[0052]

[Table 1]

In the table, the output is shown by the amount of decrease from the output of the magnetic tape of Example 1 as a reference. The surface roughness is the value on the surface of the magnetic layer.

The magnetic recording tape of Example 1 has extremely good surface smoothness at the surface of the magnetic layer and at the interface between the magnetic layer and the non-magnetic layer, is excellent in both electromagnetic conversion characteristics and still life, and is also excellent in durability. It was a thing.

The magnetic recording tape of Example 2 has good surface smoothness and electromagnetic conversion characteristics, but the particle size of the needle-shaped goethite powder is extremely small. The still life was short.

Although the magnetic recording tape of Example 3 had a long still life, it had poor surface smoothness and deteriorated electromagnetic conversion characteristics as compared with the magnetic recording tape of Example 1.

Although the magnetic recording tape of Example 4 had a long still life, it had poor surface smoothness and deteriorated electromagnetic conversion characteristics as compared with the magnetic recording tape of Example 1. Also, the still life was slightly shortened.

In the magnetic recording tape of Example 5, the needle-shaped goethite powder was broken during the preparation of the magnetic paint and the particle diameter became non-uniform, so that the surface of the magnetic recording tape was smoother than that of the magnetic recording tape of Example 1. Deteriorated, resulting in deterioration of electromagnetic conversion characteristics and shortened still life.

In the magnetic recording tape of Example 6, the strength of the non-magnetic layer in the coating direction was lowered, and the still life was shorter than that of the magnetic recording tape of Example 1.

In the magnetic recording tape of Example 7, the viscosity of the non-magnetic coating material was reduced, and when the coating film of the upper layer coating material was formed on the coating film of the non-magnetic coating material, there was some disturbance at the interface between the coating films. As a result, the surface smoothness deteriorated and the electromagnetic conversion characteristics deteriorated as compared with the magnetic recording tape of Example 1. Also, the still life was slightly shortened.

In the magnetic recording tape of Example 8, the coating viscosity of the non-magnetic coating was increased, and some coating streaks were formed on the coating film of the non-magnetic coating. Therefore, the surface smoothness was higher than that of the magnetic recording tape of Example 1. And the electromagnetic conversion characteristics deteriorated. Also, the still life was slightly shortened.

In the magnetic recording tape of Example 9, the viscosity of the non-magnetic coating material became too small, and when the coating film of the upper layer coating material was formed on the coating film of the non-magnetic coating material, the interface between the coating films was slightly disturbed. Occurs, the surface smoothness was deteriorated and the electromagnetic conversion characteristics were deteriorated as compared with the magnetic recording tape of Example 1. Also, the still life was slightly shortened.

The magnetic recording tape of Example 10 had a lower surface smoothness than the magnetic recording tape of Example 1 because the dispersibility of the non-magnetic coating material was lowered and some coating streaks were formed on the coating film. As a result, the electromagnetic conversion characteristics were deteriorated and the still life was shortened.

In the magnetic recording tape of Example 11, since a non-adsorbed binder resin was generated in the non-magnetic coating material, some binder resin floated on the surface of the non-magnetic layer when calendered. As a result, the spacing loss between the magnetic layer and the head increased, and the electromagnetic conversion characteristics deteriorated.

In the magnetic recording tape of Example 12, the easy axis of magnetization of the ferromagnetic powder in the magnetic layer was easily reversed, and
The electromagnetic conversion characteristics were worse and the still life was shorter than that of the magnetic recording tape of No.

In the magnetic recording tape of Example 13, the surface roughness of the magnetic layer was 15.3 nm (0.153 μm), and the electromagnetic conversion characteristics were worse than those of the magnetic recording tape of Example 1. Also, the still life was slightly shortened.

In the magnetic recording tape of Example 14, the calender did not act effectively on the magnetic layer during the calendering process, and as a result, the surface smoothness was worse than that of the magnetic recording tape of Example 1 and the electromagnetic conversion characteristics were improved. It got worse. Also, the still life was slightly shortened.

In the magnetic recording tape of Example 15, the non-magnetic layer was not crushed during the calendering process, and its streak had an effect,
As compared with the magnetic recording tape of Example 1, the surface smoothness was poor and the electromagnetic conversion characteristics were poor. Also, the still life was slightly shortened.

The magnetic recording tape of Example 16 is the same as that of Example 1.
In comparison with the magnetic recording tape of No. 1, the tape has a lower rigidity, the contact between the head and the tape has deteriorated, and as a result, the electromagnetic conversion characteristics have deteriorated and the still life has become shorter.

In the magnetic recording tape of Example 17, the binder resin aggregated in the magnetic paint and the non-magnetic paint, and the surface smoothness was worse than that of the magnetic recording tape of Example 1,
As a result, the electromagnetic conversion characteristics were deteriorated and the still life was shortened.

In the magnetic recording tape of Comparative Example 1, the coating viscosity of the non-magnetic coating material increased, coating streaks were formed on the coating film, and the smoothness of the coating surface deteriorated. The surface smoothness of the magnetic layer and the non-magnetic layer was greatly deteriorated as compared with the recording tape, and as a result, the electromagnetic conversion characteristics were deteriorated and the still life was shortened.

In the magnetic recording tape of Comparative Example 2, the viscosity of the non-magnetic coating material was reduced, and when the coating film of the upper layer coating material was formed on the coating film of the non-magnetic coating material, a large disturbance was generated at the interface between the coating films. Therefore, as compared with the magnetic recording tape of Example 1, the surface smoothness of the magnetic layer and the non-magnetic layer was significantly deteriorated, the electromagnetic conversion characteristics were deteriorated, and the still life was shortened.

From the above results, it was confirmed that the magnetic recording tape according to the present invention has excellent performance, and particularly the magnetic recording tape prepared in Example 1 has extremely excellent performance.

[0074]

As described above, according to the present invention,
The non-magnetic layer has high strength due to the aligned arrangement of needle-shaped goethite and the chain structure of carbon black, and the magnetic layer has uniformly present finely divided ferromagnetic powder with a major axis length of 0.3 μm or less. Roughness (Ra) of 0.003 to
The output characteristics, the S / N characteristics, and the recording density of the ultrathin layer (thickness of 0.5 μm or less) having a flat surface in the range of 0.015 μm are comparable to those of the ME type magnetic recording medium, and the running is achieved. It is possible to obtain a high-performance MP type magnetic recording medium having excellent mechanical properties such as durability and durability.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukihiro Shimazaki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (11)

[Claims] 1. A non-magnetic support on which a first binder resin is dissolved, at least acicular goethite powder, and a particle size of 0.0.
A first coating film of a non-magnetic coating material in which a granular iron oxide powder of 1 to 0.1 μm and a non-magnetic powder composed of carbon black are dispersed is formed, and a second binder resin is formed on the first coating film. Melts and forms a second coating film of a magnetic paint in which a ferromagnetic powder having a major axis length of 0.3 μm or less is dispersed.
By simultaneously drying the coating film of 1., a nonmagnetic layer having a thickness of 1 to 3 μm in which the nonmagnetic powder is dispersed in the first binder resin on the nonmagnetic support, and the ferromagnetic powder is added to the second nonmagnetic layer.
A magnetic recording medium in which a magnetic layer having a thickness of 0.5 μm or less dispersed in the binder resin of 1 is formed in this order. 2. The acicular goethite powder has a major axis length of 0.05.
~ 0.3μm, needle ratio (major axis length / minor axis length) 10 ~ 30
The magnetic recording medium according to claim 1, which is a needle-shaped goethite. 3. An acicular goethite powder, granular iron oxide powder,
And the blending ratio (weight ratio) of carbon black is 50 to 9
The magnetic recording medium according to claim 1, which is 5: 4 to 40: 1 to 30. 4. The magnetic recording medium according to claim 1, wherein the granular iron oxide powder has an axial ratio of 1.5 or less. 5. The compounding ratio (weight ratio) of the first binder resin and the whole non-magnetic powder in the non-magnetic paint is 1:10.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a ratio of 1:50. 6. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder has an acicular ratio of 5 or more. 7. The surface roughness (Ra) of the magnetic layer is 0.003.
The magnetic recording medium according to claim 1, wherein the surface roughness (Ra) at the interface between the non-magnetic layer and the magnetic layer is 0.01 μm or less. 8. The glass transition point (T) of the second binder resin.
The magnetic recording medium according to claim 1, wherein g) is 5 to 10 ° C. higher than that of the first binder resin. 9. The magnetic recording medium according to claim 1, wherein the difference in solubility parameter (SP value) between the binder resin and the solvent in the non-magnetic paint and the magnetic paint is 5 or less. 10. The content of the whole filler containing the non-magnetic powder in the non-magnetic layer is 60 to 80% by weight, and the content of the whole filler containing the magnetic powder in the magnetic layer is 80 to 90% by weight. The magnetic recording medium according to claim 1. 11. The magnetic recording medium according to claim 1, wherein the total thickness of the recording medium is 6 to 9 μm, and the Young's modulus is 500 to 1200 kg / mm ² .