JP2002063715A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having <=8 μm total thickness, excellent in electromagnetic transducing characteristics, repetitive durability and dimensional stability. SOLUTION: The magnetic recording medium having <=8 μm total thickness has a lower layer containing an inorganic powder and a bonding agent and an upper magnetic layer formed by dispersing a ferromagnetic powder in a bonding agent in this order on one surface of a non-magnetic substrate and has a back coating layer on the other surface of the substrate. The magnetic recording medium has curled amount d of 6.35 mm width in the width direction and >=0.4 mm and <=1.0 mm height in the projected direction of the magnetic layer. The non-magnetic substrate includes inorganic powder particles having 10-200 nm mean primary particle diameter and the number of the inorganic powder particles in the sectional face of the non-magnetic substrate is in the range of 10-200 particles/100 μm2.

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 in which a magnetic layer in which a ferromagnetic powder and a binder are dispersed is provided on a non-magnetic support. The present invention relates to a magnetic recording medium having degree stability.

[0002]

2. Description of the Related Art Magnetic recording media are widely used such as recording tapes, video tapes and floppy (registered trademark) disks. The magnetic recording medium has a non-magnetic support in which a magnetic layer is laminated on one surface, and a tape-like medium has a back coat layer laminated on the other surface as necessary. The disk-shaped medium is obtained by laminating magnetic layers on both sides of a nonmagnetic layer support. Generally, the coating type magnetic recording layer is
The ferromagnetic powder is dispersed in a binder, a lubricant,
It is obtained by applying and laminating a coating material containing an abrasive and, if necessary, carbon, on a nonmagnetic support. In recent years, thinning of the magnetic layer has been proposed to increase the output of the magnetic layer, and for that purpose, a magnetic recording medium in which an intermediate layer is laminated between a nonmagnetic support and a magnetic layer has been proposed. An evaporation type magnetic recording medium is obtained by forming a magnetic film on a non-magnetic support by a vacuum evaporation method. A magnetic material composed of a metal or alloy mainly composed of cobalt is deposited in an oxygen atmosphere, and a protective film and a lubricant film are formed on the deposited magnetic film as needed. With respect to the magnetic recording medium obtained in this way, audio tapes for recording and reproducing music are required to have higher original sound reproduction ability, and video tapes are required to have superior original sound reproduction ability. Backup tapes / disks are required to have excellent storability, high durability and no data loss.

[0003] In order to have such excellent electromagnetic conversion characteristics and to ensure durability, the magnetic material must have a high Hc, a high orientation, a thin coating, a protective layer for the magnetic layer, and a magnetic layer. / Development of lubricants for reducing the friction coefficient of the backing layer.

On the other hand, on the recording / reproducing apparatus side, as means for increasing the recording capacity per unit area, the recording frequency is shortened,
The use of narrow tracks in magnetic recording heads has been promoted. For example, in the case of a cartridge type recording medium, the length of the tape is reduced, the tape thickness is reduced, and more tape is wound around while keeping the capacity of the cartridge as it is. A typical example is the backup tape DD for computers.
This is an increase in capacity from the S-2 system to the DDS-3 system ("Report of Production and Demand Trends and Technical Trends of Recording Media in the World P97" issued by the Recording Media Association of Japan). Further, the recording density of the recording / reproducing head has been improved year by year by improving the surface recording density. Specifically, Long-Play mode and IOMEG in an 8 mm video system
Company A's Zip disk system is a representative. In such a system, it is important to control the position of the recording / reproducing head and the magnetic recording medium, and a tape-shaped medium requires more stable traveling when traveling through the recording / reproducing apparatus. Various guides have been proposed to be attached to a recording / reproducing device in order to realize stable running (No. 2976685). A flange is attached to the rotation guide and the fixed guide in order to make the magnetic recording medium run stably, and is generally a fixed flange. The tape running position is regulated by adjusting the height of the flange, and the accuracy of the flange position is important. However, if the tape running position is restricted to a position where the tape edge is strongly rubbed against the tape edge, the contact pressure between the tape edge and the guide flange during running increases, and running scratches occur on the guide flange surface due to repeated running. As a result, the end face of the tape is damaged by the scratch, and the magnetic layer, the intermediate layer, and the back layer applied on the non-magnetic support are dropped off.

[0005] In recent years, regarding the durability of the magnetic layer surface, as described above, the development of a highly durable binder and a lubricant for reducing the coefficient of friction has been advanced, and the relative speed of the head tape such as a D3 system is 10 m / s or more. Has been commercialized without failure. However, attempts have been made to increase the recording density of the magnetic recording media contained in the cassette case while reducing the capacity of the cassette case. Have been.

As the thickness of the tape has been reduced, non-magnetic supports made of polyethylene terephthalate, polyethylene naphthalate, and polyamide have been adopted. However, the bending stiffness of the tape decreases in proportion to the cube of the thickness, and it is inevitable that the tape strength decreases. At the same time, the narrowing of the track of the recording head is performed so that when the tape travels through the recording / reproducing device, the tape meanders during traveling during recording / reproducing, and the linearity of the recording / reproducing head on the tape is not hindered. It is necessary to regulate the traveling position more accurately than in the past by using a guide flange. In such a system where the tape thickness is thin and the tape running position is more strict than before,
The durability of the tape edge is important in addition to the durability of the magnetic layer surface. Japanese Patent Application Laid-Open No. Hei 9-180173 proposes coating a protective film on the end face of a slit to improve durability. However, coating a protective layer on the end face after slitting has the drawbacks that the protective liquid may bleed into the magnetic layer at the time of coating, and that the coating cost is high and an inexpensive tape cannot be supplied.

[0007] Edge damage caused by continuous repetition running in a magnetic recording / reproducing apparatus can be prevented if there is sufficient support by a non-magnetic support. In a magnetic recording medium having a total thickness of more than 8 μm, a non-magnetic support having a thickness of 6 μm or more is usually used, and stable repetitive running with little edge damage has been achieved. However, in a recording medium having a total thickness of 8 μm or less, it is necessary to reduce the thickness of the non-magnetic support. For the purpose of preventing edge damage even if the thickness is reduced, polyethylene terephthalate (PET), which has been conventionally used, and Instead of polyethylene naphthalate (PEN) and the like, an aromatic polyamide (aramid) base has been used (Japanese Patent No. 2745881). However, in order to ensure stable playback output and compatibility between a plurality of playback devices, if the tape running position is restricted by restricting the guide flange, even if an aramid base is used, the edge deformation due to the VTR repetitive running will occur. Inevitably, powder fell onto the running path and tape edge deformation occurred.

Further, in a system that places importance on storage such as business use or data storage, it is necessary to ensure dimensional stability by long-term storage even when the tape thickness is reduced. Therefore, the non-magnetic support is required to be not only resistant to edge damage but also excellent in dimensional stability in long-term storage.

[0009]

Accordingly, an object of the present invention is to provide a magnetic recording medium having a total thickness of 8 μm or less, which has excellent electromagnetic conversion characteristics, excellent repetition durability, and excellent dimensional stability. To provide a magnetic recording medium.

[0010]

According to the present invention, a lower layer containing an inorganic powder and a binder and an upper magnetic layer formed by dispersing a ferromagnetic powder in a binder are provided in this order on one surface of a nonmagnetic support. A magnetic recording medium having a back coat layer on the other surface and having a total thickness of 8 μm or less, wherein the magnetic recording medium has a curl amount d in the width direction of 6.35 mm width and 0.4 mm in the convex direction of the magnetic layer.
As described above, the non-magnetic support contains inorganic powder particles, and the average primary particle size of the inorganic powder particles is 1 mm or less.
0 to 200 nm, and the number of the inorganic powder particles in the cross section of the nonmagnetic support is 10 to 200/100.
The present invention relates to a magnetic recording medium characterized by being in the range of μm ² .

In particular, in the magnetic recording medium of the present invention, the total thickness is 8
Despite being less than μm, the average primary particle size in the non-magnetic support is 10
200 nm inorganic powder particles (hereinafter also referred to as filler)
And the number of inorganic powder particles (fillers) measured by an electron microscope on the support surface of the cross section of the magnetic recording medium (tape) is 10
And 200 pieces / 100 [mu] m ^2, 0.4 mm or more curl amount d in the width direction in the magnetic layer protruding inward at 6.35mm Width 1.0
mm or less.

As a result of the inventors' detailed observation of the phenomenon when the tape-shaped magnetic recording medium is repeatedly run by the magnetic recording / reproducing apparatus, the deformation of the tape edge causes the tape guide flange to come into contact with the tape edge during repeated running. It was found that the end faces of the magnetic layer, the support, and the back layer were somewhat tanned and caused plastic deformation. In particular, the plastic deformation of the support depends on the number of added particles, and due to the sliding contact with the guide, the filler particles receive a force in the running direction from the minute projections on the surface of the guide flange and deform the support on the support. It is considered that plastic deformation is promoted by causing the movement. In addition, the detachment of the filler causes an abrasive wear effect between the tape guide flange and the tape guide flange, thereby promoting the deformation of the nonmagnetic support. That is, it has been found that the smaller the number of particles added to the nonmagnetic support, the more the deformation of the end face of the nonmagnetic support due to repeated sliding can be prevented. However, if the amount of the filler is too small, the suitability for production of the non-magnetic support and the suitability for production of the magnetic recording medium deteriorate, so that optimization is required. The present inventors have found that the average primary particle size of the filler dispersed in the support is 10 to 200.
nm, preferably 40 to 200 nm, more preferably 40 to 120 nm, and the number of filler particles on the support surface in the cross section of the tape is 10 to 200/10.
0 μm ² range, preferably 20-200 / 100 μm
m ² , more preferably 30 to 180 pieces / 100
It has been found that there is an optimum range in the range of μm ² . Here, the above “number of filler particles” means an average value of the number of particles of the inorganic powder over the entire thickness direction of the cross section in the thickness direction of the support, and the average value is 10 particles / 100 μm ² to 2
00/100 μm ² . Therefore, for example, in the case of a so-called dual base having a two-layer structure, one of the layers has 200/10
Even in a mode in which more than 0 μm ^{2 of the} filler is present and the other layer has less than 10 particles / 100 μm ^{2 of the} filler, the average value of the number of particles over the entire thickness direction of the nonmagnetic support is 10 pieces / 100 μm ² to 200
The number may be in the range of pcs / 100 μm ² .

Further, the nonmagnetic support has a convex portion so that the central portion on the magnetic layer side in the width direction of the tape swells, and the height (hereinafter, also referred to as the amount of cupping) with respect to the width of 6.35 mm is set at 0. When the thickness is in the range of 4 to 1.0 mm, friction of the tape edge during tape running due to contact between the edge of the tape, the flange of the tape guide of the tape running system, the flange of the tape reel, and the like is reduced. This reduces powder drop due to scraping of the tape edge, especially during fast-forward and rewind at high speeds, improves dirt on the running system, and also shows the appearance of the tape wound on the tape reel at the tape edge. It is possible to keep it in a neat and clean state. Also, even if there is a protrusion, there is little physical deformation of the protruding tape edge. As the above-mentioned cupping amount becomes smaller than 0.4 mm, the powder drop due to the drop of the magnetic layer at the tape edge increases, and as the above-mentioned cupping amount becomes larger than 1.0 mm, the powder drop due to the drop of the back layer at the tape edge increases. And both are not preferred.

Furthermore, in the magnetic recording medium of the present invention, in order to secure excellent dimensional stability, the heat shrinkage in the MD direction when stored for 1 week under a load of 0.1 N in an environment of 60 ° C. and 90% is 0.1%. 3
% Is preferable. This makes it possible to suppress the deterioration of the Z error rate (BER) due to the tape deformation on the reel core side due to long-term storage in the cassette. Further, in the magnetic recording medium of the present invention, the coercive force of the magnetic layer is set to 159 KA / m in order to achieve high density recording / high output.
As mentioned above, it is preferable to be 237 KA / m or less. The coercive force Hc of the magnetic material used for the magnetic layer is 79 KA / m or more,
16 KA / m or less, preferably 158 KA / m or more, 2
37 KA / m or less. The magnetic layer provided on the lower layer in order to obtain higher output has a thickness of 0.05 μm or more and 1.0 μm or more.
It is preferable that the magnetic layer be a thin magnetic layer having a thickness of 0.5 μm or less and a lower layer thickness be 0.5 μm or more and 2.0 μm or less. The magnetic material having Hc is mixed and dispersed with a binder to prepare and disperse a magnetic liquid.
By coating a thin magnetic layer having a thickness of 0.1 μm or less, a highly durable magnetic recording medium that maintains high output can be provided.

Further, in the magnetic recording medium of the present invention, the non-magnetic support is made of an aromatic polyamide resin, particularly, it has a breaking strength of 10%.
Preferably, it consists of ~ 20% of aramid.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Non-magnetic support] The non-magnetic support used in the present invention is made of, for example, an aromatic polyamide resin and has, for example, the general formula -NHCO-Ar1-CONH-Ar2 (where Ar1, Ar2 is a divalent organic group containing at least one aromatic ring, and preferably has a carbon number in the range of 6 to 25) or -CO-Ar3-NH- (where Ar3 is at least one A divalent organic group containing an aromatic ring, preferably having a carbon number in the range of 6 to 25). For example, those composed of paraphenylene terephthalamide, paraphenylene isophthalamide, metaphenylene terephthalamide, metaphenyl isophthalamide and the like can be mentioned. Further, those having a substituent such as a nitro group, an alkyl group, or an alkoxy group on the phenyl nucleus are also included. Among these aromatic polyamides, those mainly composed of paraphenylene terephthalamide are more preferable, and have high mechanical strength, high elastic modulus, low moisture absorption, excellent heat resistance, mechanical and thermal dimensional stability. Because it is good, it is suitable as a good material for high-density recording media. Examples of the monomer constituting the aromatic polyamide having the structure described above include acid chlorides such as terephthalic acid chloride and diamines such as paraphenylenediamine and metaphenylenediamine.

The above-mentioned aromatic polyamide is described, for example, in US Pat.
2628898. Further, the aromatic polyamide is also available as a commercial product, and examples thereof include Aramica (manufactured by Asahi Kasei Kogyo Co., Ltd.) and MICRON (manufactured by Toray Industries, Inc.). The thickness of the aromatic polyamide film used in the present invention is generally 1.0 to 6.5 μm, preferably 2.0 to 6.0 μm, more preferably 3.0 to 6.0 μm.
It is in the range of 5.0 μm. Further, the magnetic recording medium of the present invention has a total layer thickness of 2 μm or more and less than 8 μm, preferably 2 μm or more and less than 6.8 μm, from the viewpoint of achieving high density and thinness using an aramid film. Appropriate. The inorganic powder (filler) particles contained in the nonmagnetic support are selected from spherical silica, colloidal silica, titanium oxide and the like. The average primary particle size is 10 to 200 nm,
More preferably, it is 40 to 200 nm. It is preferable that the fillers contained in the support have the same particle diameter as much as possible. It is preferable that the cumulative number up to twice the particle size with respect to the average primary particle size is 90% or more of the total number.
In addition, in order to control the surface properties of the magnetic layer side and the back layer side, two types of dopes with different amounts of filler particles were prepared. Multilayer films having different properties can be obtained. It is also possible to provide cupping on the film itself depending on the drying conditions of the film. It is preferable that the filler contained in the support is uniformly dispersed in the state of primary particles as much as possible.

[Magnetic Layer] The magnetic layer of the magnetic recording medium of the present invention is obtained by dispersing ferromagnetic powder in a binder.
The ferromagnetic powder used is ferromagnetic iron oxide, cobalt-containing ferromagnetic iron oxide, barium ferrite powder or ferromagnetic metal powder. Ferromagnetic powder SBET (BET specific surface area) of 40 to 80 m ² / g, preferably 50 to 70 m ² /
g. The crystallite size is 12 to 25 nm, preferably 13 to 22 nm, particularly preferably 14 to 20 nm.
It is. The major axis length is 0.05 to 0.25 μm, preferably 0.07 to 0.2 μm, and particularly preferably 0.08 to 0.15 μm. PH of ferromagnetic powder is 7
The above is preferred. Fe, Ni,
Fe-Co, Fe-Ni, Co-Ni, Co-Ni-F
e or the like, or an alloy, and 20% by weight of the metal component.
Within the following ranges, aluminum, silicon, sulfur, scandium, titanium, vanadium, chromium, manganese, copper,
Can contain zinc, yttrium, molybdenum, rhodium, palladium, gold, tin, antimony, boron, barium, tantalum, tungsten, rhenium, silver, lead, phosphorus, lanthanum, cerium, praseodymium, neodymium, tellurium, bismuth, etc. .

The magnetic powder is described, for example, in JP-A-8-2553.
As described in No. 34, Co is 10
It is preferable that the composition contains 4040 at%, Al 2220 at%, and Y 1115 at% from the viewpoint that sintering is reduced and the dispersibility is excellent. Further, the ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide. Further, the ferromagnetic powder used for the magnetic layer of the magnetic recording medium of the present invention has Fe as a main component, the major axis length is 0.05 to 0.19 μm,
Further, it is preferable that the crystallite size be 100 to 230 A from the viewpoint of reducing the noise while highly filling the magnetic powder. Further, the ferromagnetic powder used in the magnetic layer of the magnetic recording medium of the present invention has a coercive force of 79 to 316 KA / m and a s of 1.26 to 2.26 × 10 ^-4 Wb · m / kg.
It is preferable from the viewpoint of reducing the recording demagnetization loss and preventing a reduction in the amount of magnetization due to thermal fluctuation. Further, the SSA of the ferromagnetic powder is preferably from 35 to 60 m ² / g from the viewpoint of appropriate dispersion viscosity and affinity with the binder. The method for producing these ferromagnetic powders is already known, and the ferromagnetic powder used in the present invention can also be produced according to a known method.

The shape of the ferromagnetic powder is not particularly limited, but usually needle-like, granular, dice-like, rice-granular (also called spindle-like), plate-like, and the like are used. In particular, it is preferable to use needle-shaped or spindle-shaped ferromagnetic powder. In the present invention, a binder, a curing agent and a ferromagnetic powder are generally used.
The mixture is kneaded and dispersed together with a solvent such as methyl ethyl ketone, dioxane, cyclohexanone, and ethyl acetate used in the preparation of the magnetic paint to obtain a paint for forming a magnetic layer. The kneading and dispersion can be performed according to a usual method.

[Binder] As the binder used in the magnetic layer of the magnetic recording medium of the present invention, conventionally known thermoplastic resins, thermosetting resins, reactive resins and the like can be used. Preferred binders are vinyl chloride resins, vinyl chloride-vinyl acetate resins, cellulose resins such as nitrocellulose, phenoxy resins, and polyurethane resins.
Among them, it is more preferable to use a vinyl chloride resin, a vinyl chloride-vinyl acetate resin, or a polyurethane resin because the hardness of the back coat layer is close to the hardness of the magnetic layer and the back image can be reduced. Further, it is preferable that a part of the binder contains a polyurethane resin having a cyclic structure and an ether group from the viewpoint of improving dispersibility.

A particularly preferred binder is a polyurethane resin obtained by reacting a diol with an organic diisocyanate, wherein the diol is a short-chain diol having a cyclic structure and a long-chain diol having an ether bond, based on the polyurethane resin. , Each 17 ~
It contains 40% by weight and 10% by weight to 50% by weight, and contains 1.0 to 5.0 mol / g of the ether bond in the long-chain diol with respect to the polyurethane resin. Tg is -20 to 150 ° C, preferably 2
The temperature is 0 to 120 ° C, more preferably 50 to 100 ° C.

Regardless of whether the cyclic portion of the long-chain diol is aliphatic or aromatic, the coating Tg is 50 to 150 ° C., preferably 70 to 100 ° C., and the calendering temperature is ± 30 ° C.
It is preferable to optimize the coating film Tg so as to obtain the coating film Tg, and to adjust the binder composition so as to achieve both the calender moldability and the coating film strength.

The binder is usually cured with a polyisocyanate curing agent. Polyurethane resin 100
The amount of the curing agent to be used is 0 to 150 parts by weight, preferably 0 to 100 parts by weight, more preferably 0 to 50 parts by weight.

The content of the hydroxyl group in the polyurethane resin is as follows:
The number is preferably 3 to 20 per molecule, and more preferably 4 to 5 per molecule. If the number is less than 3 per molecule, the reactivity with the polyisocyanate curing agent decreases, so that the coating film strength and durability tend to decrease.
On the other hand, if the number is more than 20, the solubility and dispersibility in a solvent are likely to be reduced.

In order to adjust the content of the hydroxyl group in the polyurethane resin, a compound having three or more hydroxyl groups can be used. Specifically, trimethylolethane, trimethylolpropane, trimellitic anhydride, glycerin, pentaerythritol, hexanetriol, a dibasic acid made from a polyester polyol described in JP-B-6-64726, and the above compound as glycol Examples include branched polyesters and polyetheresters having three or more hydroxyl groups obtained as components. Preferred are trifunctional ones, and if they have more than four functionalities, they tend to gel during the reaction process.

The polyurethane resin has —SO in the molecule.
_ThreeM, -OSO_ThreeM, -COOM, -PO _ThreeMM ', -O
PO_ThreeMM ', -NRR', -N⁺RR'R "COO
^-(Where M and M ′ each independently represent a hydrogen atom,
Potassium metal, alkaline earth metal or ammonium salt
R, R 'and R "each independently represent an atom having 1 to 12 carbon atoms.
At least one polar group selected from
And particularly preferably -SO
_ThreeM, -OSO_ThreeM. The amounts of these polar groups are preferred
H, 1 × 10^-Five~ 2 × 10^-Foureq / g, particularly good
Preferably 5 × 10^-Five~ 1 × 10^-Foureq / g. 1x
10^-FiveIf less than eq / g, the adsorption to the powder becomes insufficient.
Therefore, dispersibility is reduced, and 2 × 10^-Fourmore than eq / g
If so, dispersibility decreases because solubility in the solvent decreases
Tend.

Number average molecular weight (Mn) of polyurethane resin
Is preferably from 5,000 to 100,000, more preferably from 10,000 to 50,000, particularly preferably from 20,000 to 40,000. If it is less than 5,000, the strength and durability of the coating film will be low, and if it is more than 100,000, the solubility and dispersibility in a solvent tend to be low.

The cyclic structure of the polyurethane resin affects rigidity, and the ether group contributes to flexibility. The above-mentioned polyurethane resin has high solubility and radius of inertia (expansion of molecule)
And the dispersibility of the powder is good. In addition, the polyurethane resin has two characteristics of hardness (high Tg, high Young's modulus) and toughness (elongation) of the polyurethane resin itself.

The coating material for forming a magnetic layer contains α α
-Includes commonly used additives or fillers such as abrasives such as Al ₂ O ₃ and Cr ₂ O ₃ , antistatic agents such as carbon black, lubricants such as fatty acids, fatty acid esters, silicone oils, and dispersants. You may go out. The magnetic layer of the magnetic recording medium of the present invention preferably has a Tg of 30 ° C. or more and 150 ° C. or less from the viewpoint of improving running durability.
Further, the thickness of the magnetic layer is from 0.03 to 1.0 μm, preferably from 0.05 to 0.5 μm, more preferably from 0.05 to 0.3 μm from the viewpoint of sharpness of magnetization reversal for enhancing digital recording performance.
It is. Further, the magnetic recording medium of the present invention has a squareness ratio of 0.82
Above, and SFD of 0.5 or less, high output,
It is preferable from the viewpoint of high erasing characteristics.

[Lower Layer (Nonmagnetic Layer)] The lower layer of the magnetic recording medium of the present invention is a nonmagnetic layer containing an inorganic powder and a binder. The inorganic powder is preferably substantially non-magnetic. The nonmagnetic inorganic powder can be selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and nonmagnetic metals. As the inorganic compound, for example, titanium oxide (Ti
O ₂ , TiO), α-alumina, β-alumina, γ-alumina, α-iron oxide, chromium oxide, zinc oxide, tin oxide, tungsten oxide, vanadium oxide, silicon carbide, oxide having an α conversion rate of 90 to 100% Use cerium, corundum, silicon nitride, titanium carbide, silicon dioxide, magnesium oxide, zirconium oxide, boron nitride, calcium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, goethite, aluminum hydroxide, etc. alone or in combination. be able to. Particularly preferred are titanium dioxide, zinc oxide, iron oxide and barium sulfate, and more preferred are titanium dioxide and iron oxide. Examples of the non-magnetic metal include Cu, Ti, Zn, and Al.
The average particle size of these non-magnetic powders is preferably 0.005 to 2 μm, but if necessary, non-magnetic powders having different average particle sizes may be combined, or even a single non-magnetic powder may have a broad particle size distribution. A similar effect can be provided. Particularly preferably, the average particle size is 0.01 μm to 0.2 μm.
m of non-magnetic powder. The pH of the non-magnetic powder is particularly preferably from 6 to 9. The specific surface area of the nonmagnetic powder is 1 to 10
0 m ² / g, preferably from 5 to 50 m ² / g, more preferably 7~40m ² / g. The nonmagnetic powder preferably has a crystallite size of 0.01 μm to 2 μm. The oil absorption using DBP is 5 to 100 ml / 100 g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 60 ml / 100 g.
ml / 100 g. Specific gravity is 1 to 12, preferably 3
~ 6. The shape may be any of a needle shape, a spindle shape, a spherical shape, a polyhedral shape, and a plate shape.

The binder, lubricant, dispersant, additive, solvent, dispersing method, etc. of the non-magnetic layer can be appropriately applied to those of the above-described magnetic layer. In particular, with respect to the amount and type of the binder, the amount of the additive and the type of the dispersant, and the like, the known technology for the magnetic layer can be applied.

The thickness of the layer is set, for example, in the range of 0.03-1.
μm, preferably 0.05 to 0.5 μm, more preferably 0.05 to 0.3 μm, and the lower layer (nonmagnetic layer)
33 μm, preferably 0.5-2 μm, more preferably 0.8-1.5 μm. The thickness of the non-magnetic layer is preferably larger than the thickness of the magnetic layer. A magnetic recording medium having two magnetic layers is also preferable. In this case, for example, the upper layer is 0.2 to 2 μm, preferably 0.2 to 1.5 μm.
m, and the lower layer can have a thickness of 0.5 to 1.5 μm. By reducing the thickness of the lower layer, the amount of cupping of the protrusion of the magnetic layer can be set within the range of the present invention.

[Backcoat layer] The thickness of the backcoat layer formed on the magnetic recording medium of the present invention is 0.05 to 1.0.
It is preferable to set within the range of μm. 0.2-0.8
It is preferably set within the range of μm, 0.3 to 0.8
More preferably, it is set within the range of μm. It is also possible to form the magnetic layer convex cupping with the thickness of the back, and for that purpose, the thicker is preferable.

It is preferable to use a particulate oxide for the back coat layer. As the particulate oxide, titanium oxide, α
-It is preferred to use either iron oxide or mixtures thereof. Conventionally used titanium oxide and α-iron oxide can be used. The shape of the particles is not particularly limited. In the case of a sphere, the particle size is 0.01 to 0.1 μm
In the case of a needle shape, the needle ratio is 2 to 20.
Is appropriate, and the major axis length is 0.05 to 0.3 μm.
m is preferred. At least a part of the surface of the granular oxide may be modified with another compound or coated with another compound, for example, Al ₂ O ₃ , SiO ₂ , or ZrO ₂ .

It is preferable to use carbon black for the back coat layer in order to prevent electric resistance. As the carbon black used for the back coat layer, those commonly used for magnetic recording tapes can be widely used. For example, furnace black for rubber, thermal black for rubber, carbon black for color, acetylene black and the like can be used. In order to prevent the unevenness of the back coat layer from being reflected on the magnetic layer, the particle size of the carbon black is preferably set to 0.3 μm or less. A particularly preferred particle size is 0.01 to 0.1 μm. The amount of carbon black used in the back coat layer is preferably in a range where the optical transmission density (transmission value of TR-927 manufactured by Macbeth) is 2.0 or less.

In order to improve running durability, it is advantageous to use two types of carbon black having different average particle sizes in the back coat layer. In this case, the first carbon black having an average particle size in the range of 0.01 to 0.04 μm and the average particle size of 0.05 to 0.5 μm.
Combinations with a second carbon black in the range of 3 μm are preferred. The content of the second carbon black is
The total amount of the particulate oxide and the first carbon black is 10
As 0 parts by weight, 0.1 to 10 parts by weight is suitable,
0.3 to 3 parts by weight is preferred.

The weight ratio of the particulate oxide to carbon black is from 60/40 to 90/10, more preferably from 70/30 to
A ratio of 80/20 is appropriate. As described above, by including the particulate oxide in a larger amount than the carbon black, a back coat layer having good powder dispersibility and a smooth surface can be formed. The paint for forming a back coat layer having such a composition has higher thixotropy than a conventional paint for forming a back coat mainly composed of carbon black. For this reason, it is possible to perform the application by the extrusion method or the gravure method at a high concentration. By applying such a high concentration paint,
Despite its thin film thickness, a back coat layer having high adhesive strength to the support and high mechanical strength can be formed.

The amount of the binder used is 10 to 4 with respect to the total weight of the particulate oxide and carbon black as 100 parts by weight.
0 parts by weight, more preferably from 20 to 32 parts by weight.
Parts by weight. The film strength of the back coat layer thus formed is high, and the surface electric resistance is low.

As the binder for the back coat layer, conventionally known thermoplastic resins, thermosetting resins, reactive resins and the like can be used.

The magnetic recording medium of the present invention has a soft magnetic layer containing a soft magnetic powder, a second magnetic layer, a cushion layer, an overcoat layer, an adhesive layer, in addition to a magnetic layer, a nonmagnetic layer and / or a backcoat layer. It may have a layer and a protective layer. These layers can be provided at appropriate positions so that the function can be effectively exhibited.

The magnetic recording medium of the present invention is produced, for example, by applying a paint to the surface of the running non-magnetic support so that the layer thickness after drying is within the above-mentioned predetermined range. Can be. Multiple magnetic and non-magnetic paints
The layers may be applied sequentially or simultaneously. Air doctor coat, as a coating machine for applying magnetic paint,
Blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, spray coat,
Spin coating or the like can be used. These can be referred to, for example, "Latest Coating Technology" (May 31, 1983) issued by Sogo Gijutsu Center.

In the present invention, when producing a magnetic recording tape having a magnetic layer and a lower layer (non-magnetic layer) on one surface of a support, for example, the following method can be used. (1) Gravure generally applied in the application of magnetic paint,
The lower layer is first applied by a coating device such as a roll, a blade, an extrusion, etc.
No. 46186, JP-A-60-238179, JP-A-2-265672, etc., using a support pressurized extrusion coating apparatus and the like disclosed in
A method of applying the upper layer. (2) JP-A-63-88080, JP-A-2-17
No. 971, JP-A-2-265672, and a method for applying upper and lower layers almost simultaneously using a single coating head having two paint passage slits. (3) A method in which the upper and lower layers are coated almost simultaneously using an extrusion coating device with a backup roll disclosed in JP-A-2-174965.

The back coat layer can be prepared by applying a coating material for forming a back coat layer in which a particulate component such as an abrasive and an antistatic agent and a binder are dispersed in an organic solvent, on the surface opposite to the magnetic layer. it can. As in the above preferred embodiment, if the amount of the particulate oxide used is larger than the carbon black, sufficient dispersibility can be ensured, so that the back coat layer is formed without performing the roll kneading conventionally required. Paint can be prepared. If the carbon black content ratio is low, the amount of residual cyclohexane after drying can be reduced even if cyclohexanone is used as a solvent.

The applied magnetic layer is dried after subjecting the ferromagnetic powder contained in the magnetic layer to a magnetic field orientation treatment. The magnetic field alignment treatment can be appropriately performed by a method known to those skilled in the art. Increasing the drying temperature of the magnetic layer can also increase the cupping of the magnetic layer protrusion.

After drying, the magnetic layer is subjected to a surface smoothing treatment using a super calender roll or the like. By performing the surface smoothing treatment, pores generated by removing the solvent during drying disappear, and the filling rate of the ferromagnetic powder in the magnetic layer is improved. Therefore, a magnetic recording tape having high electromagnetic conversion characteristics can be obtained.

Epoxy as a calendering roll,
Use a heat-resistant plastic roll such as polyimide, polyamide, or polyamide-imide. Moreover, it can also process with a metal roll.

The magnetic recording medium of the present invention preferably has a surface with good smoothness. In order to improve the smoothness, it is effective to subject the magnetic layer formed by selecting a specific binder as described above to the above-described calendering treatment. In the calendering, the temperature of the calender roll is set to 60 to 100 ° C, preferably 70 to 100 ° C, particularly preferably 80 to 100 ° C, and the pressure is set to 100 to 500 kg.
/ Cm, preferably 200 to 450 kg / cm, particularly preferably 300 to 400 kg / cm. The obtained magnetic recording tape can be cut into a desired size using a cutting machine or the like and used. The magnetic recording tape that has been subjected to the calendering treatment is subjected to a heat treatment to reduce the heat shrinkage.

[0049]

The present invention will be further described below with reference to examples. <Magnetic tape preparation method> Magnetic layer Example 1 Ferromagnetic metal fine powder Composition Fe / Co = 100/30 (atomic ratio) 100 parts Al / Fe = 13/100 atomic ratio, Y / Fe = 7/100 atomic ratio Hc 187kA / m BET specific surface area 49m ² / g Crystallite size 160Å Particle size (major axis diameter) 0.09μm Needle ratio 7 σs: 1.82 × 10 ^-4 Wb · kg Vinyl chloride copolymer 10 parts Nippon Zeon MR-110 polyurethane resin 6 parts Hydrogenated phenol A molar ratio 0.6 phenol peroxy oxy adduct of bisphenol A molar ratio 0.3 sulfoisophthalic acid ethylene oxyto adduct molar ratio 0.05 diphenyl methane isocyanate molar ratio 1.0 trimethylol fluorene molar ratio 0.05 urethane group concentration 4.0 meq / g ether group concentration 5.0 meq / g molecular weight (number average) 25,000 α-Al ₂ O ₃ (average particle diameter 0.15 [mu] m) 5 parts mosquitoes - carbon black (average particle size 0.08μ ) 0.5 parts Butyl stearate 1 part 5 parts Methyl ethyl ketone 90 parts Cyclohexanone 30 parts 60 parts Toluene stearate

Lower coating layer (non-magnetic) Non-magnetic powder αFe ₂ O ₃ Hematite 80 parts P / Fe = 1.3 / 100, Al / Fe = 6.0 / 100 atomic ratio, Si / Fe = 7.0 / 100 atomic ratio Long axis Length 0.15 μm Specific surface area by BET method 52 m ² / g pH 8 Tap density 0.8 DBP oil absorption 27-38 g / 100 g, carbon black 20 parts Average primary particle diameter 16 mμ DBP oil absorption 80 ml / 100 g pH 8.0 BET method Specific surface area of 250 m ² / g Volatile content 1.5% Vinyl chloride copolymer 12 parts MR-110 polyurethane resin 5 parts manufactured by Nippon Zeon 5 parts Hydrogenated bisphenol A molar ratio 0.6 Polyphenol oxyoxide adduct of bisphenol A Molar ratio 0.3 Sulfoisophthal Acid ethylene oxytoxide molar ratio 0.05 diphenylmethane isocyanate molar ratio 1.0 trimethylol perfluorocarbon molar ratio 0.05 urethane group concentration 4.0meq / g ether group concentration 5.0 meq / g Molecular weight (number average) 25,000 α-Al ₂ O ₃ (average particle size 0.3 μm) 1 part Butyl stearate 1 part Stearic acid 1 part Methyl ethyl ketone 100 parts Cyclohexanone 50 parts Toluene 50 parts

Each of the above-mentioned paints was kneaded with an open kneader, and then dispersed using a sand mill.
To the resulting lower dispersion, 5 parts of polyisocyanate (Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) was added to the coating liquid for the lower coating layer, and 40 parts of a mixed solvent of methyl ethyl ketone and cyclohexanone was added to each, and the average pore diameter was 1 μm. The solution was filtered using a filter having the following to prepare a coating solution for forming a lower coating layer and a magnetic layer. The obtained lower layer coating liquid is coated with a thickness of 4.5 μm so that the thickness after drying is 1.3 μm and immediately thereafter, the thickness of the magnetic layer is 0.25 μm thereon. Coating is performed simultaneously on a polyamide resin support having a center line surface roughness of 0.001 μm on the magnetic layer coating surface, and while both layers are still in a wet state, a rare earth magnet having a magnetic force of 500 mT (5000 G) and 4
After being oriented and dried by a solenoid having a magnetic force of 00 mT (4000 G), a 7-stage calendar composed of a metal roll and an epoxy resin roll is used at a temperature of 100 ° C. and a speed of 20 min.
The treatment was performed at 0 m / min., And then a back layer having a thickness of 0.5 μm was applied. Slit to 6.35mm width, DV
A tape 123 fraction for CPRO was prepared.

Aramid was prepared as a non-magnetic support by the following known method. PPTA polymer having an ηinh (logarithmic viscosity) of 5.5 is obtained by adding colloidal silica having an average particle size of 80 nm to 0.005.
The polymer solution was dissolved in concentrated sulfuric acid containing 1% by weight so as to have a polymer concentration of 11.5%. The dope was degassed under vacuum while keeping the dope at about 70 ° C. 3.5m / from die with 0.15mm x 300mm slit
At a discharge linear velocity of 1 minute, cast on a mirror-polished tantalum belt (moving at 12 m / min), and a relative humidity of about 85%, about 90%
The casting dope was optically isotropic by blowing air at a temperature of 5 ° C., and was introduced together with a belt into a 15% by weight aqueous sulfuric acid solution at −5 ° C. for coagulation. At this time, the film itself can be provided with cupping. Next, the coagulated film was peeled off from the belt, and washed by running in warm water of about 40 ° C., in a 1% aqueous solution of sodium carbonate, and then in 25 ° C. water. After washing, the film with a moisture content of about 280% is uniaxially stretched in the machine direction (MD) 1.2 times in the machine direction (MD) at room temperature using the difference in peripheral speed of the rolls. (TD) stretched 1.2 times, the center of the tenter was heated to a constant length of 150 ° C and dried, and an infrared lamp was installed near the exit of the tenter and heat-treated at 400 ° C, and then a long film was wound up. Was. The obtained PPTA film was excellent in transparency and had a thickness of 4.0 μm.

The properties of the obtained magnetic recording tape were measured by the following methods. <Magnetic characteristics> Magnetic characteristics are a vibration sample type magnetometer manufactured by Toei Industry.
Using VSM-P7 and DATA processing equipment manufactured by the company, measurement was performed with an applied magnetic field of 10 Koe. <Cupping> The tape was cut out by 10 cm, and the distance from the disk surface to the upper end of the tape was d when the magnetic layer was placed upward on the flat disk in a free state. <Heat Shrinkage> A sample of about 10 cm length was applied with a load of 0.1 N for one week at 60 ° C. and 90% for storage. The length before and after storage was measured at room temperature with a converter to determine the rate of change. <Preservability: Core DO> Digital VTR for business use (DVCP
RO) (25 MBPS-183 minutes long), and after recording, store at 60 ° C and 90% thermo for 1 week and reproduce. On the cassette reel core side, the time during which DO (1 μs-8 dB) exceeded 300 / min was measured. <Magnetic Layer and Lower Layer Thickness> The thickness of the magnetic layer was determined by observing and photographing an ultrathin section with a transmission electron microscope and correcting the photographic magnification. <Total Tape Thickness> Using a micrometer with an accuracy of 1 μm, ten tapes were superposed and measured, and the value was reduced to 1/10 to be the thickness per sheet. <Reproduction output> Using AJ-D750 (manufactured by Matsushita Electric Industrial) of a digital VTR for business use (DVCPRO), 25 ° C.
The data output waveform was observed at 0% RH. The output with the lowest output compared to the reference tape (DP121-66M) manufactured by Fuji Film Co., Ltd. was used as the reproduction output. The target was -0.5 dB or more.

<Full Length Running> Digital VTR (DV
Using AJ-D750 (CPRO) (manufactured by Matsushita Electric Industrial Co., Ltd.), reproduction and rewinding were repeated 100 times at 5 ° C. and 80% RH. The amount of winding thickening was evaluated along with the full length running. Before starting the full length running, 380 m was wound on the supply reel, and the diameter of the winding was measured. After that, record the full length,
After 100 times of running (play & rewind),
After winding on a supply reel, the winding diameter was measured again.
The amount of increase in the winding diameter before and after running was evaluated as the amount of winding thickening.
0.4 mm or less is practically preferable. <Number of fillers> A small piece of magnetic tape is spun with an epoxy resin adhesive, and the tip of the embedded block is shaped appropriately.
After molding to the size, the cross section was cut out with a microtome to prepare observation data. The prepared cross-sectional sample was photographed at a magnification of 20,000 times using a scanning electron microscope FE-SEM S-800 manufactured by Hitachi, and the number of filler particles in the nonmagnetic support was measured.

In Comparative Example 1, Examples 2 and 4, the cupping of the support was made by film formation, and in Example 5, the amount of cupping was adjusted by changing the thickness of the lower layer and the backing. Example 3 relaxed the heat treatment, and Example 4 did not perform the heat treatment.

[0056]

[Table 1]

When Examples 1 to 5 and Comparative Example 1 are compared, when the cupping (convex of the magnetic layer) is in the range of 0.5 to 1.0 mm, the running system stain is small, but when the cupping is 0.2 mm, the running system stain becomes worse. You can see that Further, it is preferable to set the heat shrinkage to a small range of 0.3% or less, because the core-side DO can be kept low.

Examples 6 and 7 and Comparative Examples 2 and 3 were prepared by changing the concentration of the filler. The magnetic liquid, lower layer liquid, and back liquid were the same as in Example 1. Each was sectioned after embedding, and the average number of fillers on the aramid surface was determined.

[0059]

[Table 2]

When Examples 6 and 7 are compared with Comparative Examples 2 and 3, when the number of fillers in the cross section of the support is in the range of 16 to 190/100 μm ² , there is no winding thickening and there is little running system dirt. It can be seen that when the number exceeds 200/100 μm ² , the winding becomes thicker and the running system dirt gets worse.

In Examples 8, 9 and Comparative Example 4, aramid was formed into a multilayer structure by a co-casting method. The thickness of the layer on the magnetic layer side and the thickness of the layer on the back layer side were changed, and the filler concentration was changed. The back layer side was the belt surface side during casting, and the magnetic layer was the opposite side. The magnetic liquid, lower layer liquid, and back liquid were the same as in Example 1. After each embedding, the section is cut,
The average number of fillers on the aramid surface was determined.

[0062]

[Table 3]

When Examples 8 and 9 and Comparative Example 4 are compared,
(Because dual-based, average of each layer) support the average number of filler number of the cross section of the support even when the dual base without thickening wound in the range of 10 to 200 pieces / 100 [mu] m ^2, although running system dirt less , The average number of fillers is 20
It can be seen that if the number exceeds 0/100 μm ² , the winding becomes thick and the running system dirt decreases.

In Examples 10 and 11, and Comparative Example 5, the filler particle size was changed. Other conditions were the same as in Example 1.

[0065]

[Table 4]

Comparing Examples 10 and 11 with Comparative Example 5, it can be seen that when the filler particle diameter is 250 nm, the surface properties are rough and the output is low.

In Examples 12 and 13, the thickness of the magnetic layer was changed. However, the thickness of the lower layer and the thickness of the back were changed to match the total thickness. Other conditions were the same as in Example 1.

[0068]

[Table 5]

Examples 12 and 13 show that the effect of the present invention can be obtained even if the thickness of the magnetic layer changes. However, in Example 13 in which the thickness of the magnetic layer was as thick as 0.9 μm, the output was slightly lower.

[0070]

According to the present invention, the electromagnetic conversion characteristics are excellent,
It is possible to provide a magnetic recording medium having excellent running durability and good dimensional stability during storage with good mass productivity.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshihiko Miura 2-12-1, Ogimachi, Odawara City, Kanagawa Prefecture Inside the Fuji Photo Film Co., Ltd. Odawara Plant (72) Inventor Masatoshi Takahashi 2-12-12 Ogimachi, Odawara City, Kanagawa Prefecture No. 1 Fuji Photo Film Co., Ltd. Odawara Plant F-term (reference) 5D006 CB03 CB06 DA00 FA02 FA05 FA09

Claims (1)

[Claims] 1. A non-magnetic support having, on one surface, a lower layer containing an inorganic powder and a binder and an upper magnetic layer in which a ferromagnetic powder is dispersed in a binder in this order, and a back layer on the other surface. A magnetic recording medium having a total thickness of 8 μm or less having a coat layer, wherein the magnetic recording medium has a curl amount d in the width direction of 6.35 mm width and 0.4 mm or more and 1.0 mm or less in the convex direction of the magnetic layer, The non-magnetic support includes inorganic powder particles, the average primary particle size of the inorganic powder particles is in the range of 10 to 200 nm,
The number of the inorganic powder particles in the non-magnetic support cross section,
A magnetic recording medium characterized by being in the range of 10 to 200 pieces / 100 μm ² .