JPH11110745A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tape-like magnetic recording medium whose travel stability and travel durability improve. SOLUTION: Bend rigidity DL in the longitudinal direction of the magnetic recording medium and bend rigidity DW in a width direction satisfy a formula (I) and a formula (II). The amount of fatty acid ester lubricant extracted by immersing the magnetic recording medium in n-hexane at 25 deg.C for one minute is set to be 5-550 mg/m<2> . The surface electric resistance of a magnetic layer-side in the recording medium is set to be 10<6> -10<10> Ω/(square).

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 tape-shaped magnetic recording medium having improved running stability and running durability.

[0002]

2. Description of the Related Art Effective means for improving running stability of a magnetic tape and ensuring running durability is, for example, a magnetic recording medium from the standpoint of magnetic recording medium design. Means for reducing the coefficient of friction of the magnetic tape by controlling the amount of carbon black and the particle size of the carbon black to be contained in the layer constituting the layer within a predetermined range, or controlling the amount of the lubricant.

[0003] As this kind of prior art, Japanese Patent Laid-Open No. 1-2
No. 48317 is known. This publication describes a magnetic recording medium in which two types of carbon black having specific particle diameters and oil absorption amounts are blended in a magnetic layer to reduce the friction coefficient, the rotational torque, and the starting torque.

However, the technology described in the above publication is
The focus is on studying the coefficient of friction, rotational torque, and starting torque for magnetic disks such as floppy disks.For a detailed study on improving the running stability and running durability of magnetic tapes whose running system is completely different from magnetic disks, see Nothing has been done. In recent years, the recording density has been increasing, and the development of multi-layer type media has been active. However, the above publication only describes a single-layer type medium, and is applicable to multi-layer media. Is not mentioned. In addition, since the magnetic disk has an overall thickness greater than that of the magnetic tape, the running torque is hardly affected by the bending stiffness, so that the magnetic disk technology cannot be directly applied to the magnetic tape. Further, in the above publication, the amount of the lubricant present on the surface of the magnetic layer and the surface electrical resistance were not sufficiently examined, and the performance was insufficient when only the specific carbon black was used.

Accordingly, it is an object of the present invention to provide a tape-shaped magnetic recording medium having improved running stability and running durability, particularly a multilayer magnetic recording medium.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on factors controlling the running stability and running durability of a tape-shaped magnetic recording medium, and have found that the bending stiffness of the magnetic recording medium and the presence of the magnetic recording medium on the surface of the magnetic layer are high. It has been found that the three physical properties of the amount of lubricant and the surface electrical resistance of the magnetic recording medium are the controlling factors, and further studies have been carried out. The above-mentioned object has been achieved by setting these three physical properties to specific ranges. It has been found that a magnetic recording medium can be obtained.

[0007] The present invention has been made based on the above findings, and includes a method of forming a ferromagnetic powder, carbon black,
In a tape-shaped magnetic recording medium having a magnetic layer containing a fatty acid ester-based lubricant and a binder and having a thickness of 5 to 10 μm, the bending rigidity DL in the longitudinal direction and the bending rigidity in the width direction of the magnetic recording medium DW satisfies the following formulas (1) and (2), respectively,
The amount of the fatty acid ester-based lubricant extracted by being immersed in n-hexane for 1 minute is 5 to 550 mg / m ² , and the surface electric resistance of the magnetic layer side of the magnetic recording medium is 10 ⁶ to 10 ¹⁰ Ω. The above object has been achieved by providing a magnetic recording medium characterized by // □.

[0008]

(Equation 3)

[0009]

(Equation 4)

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The most characteristic feature of the magnetic recording medium of the present invention is that the following physical properties (a) to (c) are in specific ranges, respectively, and are combined. (A) The bending stiffness DL in the longitudinal direction and the bending stiffness DW in the width direction of the magnetic recording medium are expressed by the above equations (1) and (2), respectively.
Meet. (B) the amount of the fatty acid ester-based lubricant extracted by immersing the magnetic recording medium in n-hexane at 25 ° C. for 1 minute is 5 to 5;
It is 550 mg / m ² . (C) The surface electrical resistance on the magnetic layer side of the magnetic recording medium is 10 ⁶ to 10 ¹⁰ Ω / □. Then, by combining these three physical properties having values in a specific range, it is possible to obtain a magnetic recording medium having an effect of improving running stability and running durability, as is clear from the examples described later. Such an effect cannot be obtained even if any one of these combinations is missing.

The physical properties (a) relate to the bending stiffness of the tape-shaped magnetic recording medium, and are defined in the longitudinal direction and the width direction of the magnetic recording medium. According to the present inventors' detailed studies, as shown in FIGS. 1A and 1B, the bending rigidity of the magnetic recording medium and the running torque (ie, tension) in the drive are positive. It turns out that there is a correlation. The smaller the value of the running torque, the better the running stability of the magnetic recording medium. Therefore, from this point, it is preferable that the bending rigidity of the magnetic recording medium is smaller. However, if the flexural rigidity is too small, the magnetic recording medium is likely to be scratched by contact between the magnetic head and the magnetic recording medium, and the head becomes dirty and the running durability is reduced. Furthermore,
If the stiffness is too low, the contact with the magnetic head is deteriorated, and the envelope characteristics are degraded. On the other hand, from the viewpoint of preventing head contamination (that is, improving running durability), it is preferable that the bending rigidity of the magnetic recording medium is large, but if the bending rigidity is too large, the head pressing pressure for obtaining high output, That is, it is necessary to increase the tension, and as a result,
The stable running property of the magnetic recording medium is impaired. Therefore, in the present invention, the value of the bending stiffness of the magnetic recording medium is defined as the above formulas (1) and (2) from the balance between running stability and running durability. Since the magnetic recording medium of the present invention is tape-shaped and has anisotropy in the running direction of the medium and in the direction perpendicular thereto, these studies were performed in both the longitudinal direction and the width direction of the medium.

The preferred ranges of the bending stiffness DL in the longitudinal direction and the bending stiffness DW in the width direction of the magnetic recording medium of the present invention are given by the following equations (1 ′) and (1 ″) and (2 ′) and (2 ″), respectively. It is the range which satisfies.

[0013]

(Equation 5)

[0014]

(Equation 6)

A specific method for measuring the bending stiffness of a magnetic recording medium is as follows. The measurement is performed using the device 10 shown in FIG. The apparatus 10 shown in FIG.
1 and 12, a micrometer 13 connected to the upper sample fixing unit 11, and a balance 14 connected to the lower sample fixing unit 12. Further, the upper sample fixing unit 11 is configured to be movable in a vertical direction,
The moving distance is measured by the micrometer 13. A 1/2 inch (12.65 mm) square sample 15 is cut out from a tape-shaped magnetic recording medium. At this time, the sample is cut out such that two opposite sides of the square are parallel to the longitudinal direction and the width direction of the tape-shaped magnetic recording medium. Next, both ends of the sample corresponding to the longitudinal direction of the tape-shaped magnetic recording medium are fixed to the upper and lower sample fixing portions 11 and 12 by the adhesive tape 16 in an extended state (ie, the distance between the sample fixing portions is 12.65 mm). I do.
From this state, the upper sample fixing part 11 is lowered to
5 and the distance between the upper and lower sample fixing portions 11 and 12 is 5
mm, the load displayed on the balance 14 is read in this state, and the value is divided by 12.65 mm to obtain the bending stress in the longitudinal direction. The bending stress in the width direction is measured in the same manner. In addition, bending
The bending is performed so that the magnetic layer is bent inward and outward, respectively, and the average value is defined as bending stress.

The physical properties (b) define the amount of the fatty acid ester-based lubricant present on the surface of the magnetic layer of the magnetic recording medium. According to the inventors' detailed examination, FIG.
As shown in (a) and (b), in magnetic recording media having the same value of flexural rigidity, it was found that the larger the amount of the fatty acid ester lubricant, the larger the running torque in the drive. It is considered that the reason is that if the amount of the fatty acid ester-based lubricant present on the surface of the magnetic layer is too large, sticking occurs between the magnetic recording medium and the magnetic head, causing a stick-slip phenomenon. As described above, since an increase in the running torque impairs the running stability of the magnetic recording medium, in the present invention, the upper limit of the amount of the fatty acid ester-based lubricant was set to 550 mg / m ² . On the other hand, if the amount of the fatty acid ester-based lubricant is too small, the lubricating effect of the lubricant is not sufficiently exhibited, so that the friction coefficient of the magnetic recording medium increases and the running torque also increases. Therefore, in the present invention, the lower limit of the amount of the fatty acid ester-based lubricant is set to 5 mg / m ² . A preferred range of the amount of the fatty acid ester-based lubricant is 100 to 500 mg /
m ^2, and more preferably 250 to 500 mg / m ²
It is.

A specific method for measuring the amount of the fatty acid ester-based lubricant is as follows. That is, from the magnetic recording medium,
A sample having a length of 2 m and an arbitrary width (generally, the width of a medium) was cut out, and the back coat layer was removed with a solvent such as methyl ethyl ketone.
The fatty acid ester is extracted by dipping in hexane. One minute after the immersion, the sample is taken out. The fatty acid ester in the n-hexane from which the fatty acid ester has been extracted is quantified using gas chromatography. By dividing the determined amount (mg) of the fatty acid ester by the area (m ² ) of the sample, the amount of the fatty acid ester-based lubricant is calculated.

The physical properties (c) define the surface electrical resistance on the magnetic layer side of the magnetic recording medium. According to a detailed study by the present inventors, there is a positive correlation between the surface electric resistance and the running torque (ie, tension) in the drive as shown in FIG. There was found. As described above, the running torque is a factor that affects the running stability of the magnetic recording medium. The surface electric resistance is a factor that affects the occurrence of dropout due to the attachment of dust and dust, and the higher the surface electric resistance, the more the dropout is likely to occur. Therefore, from the viewpoint of improving the running stability of the magnetic recording medium and reducing the dropout, it is desirable that the surface electric resistance is low. However, if a large amount of carbon black as an antistatic agent is added to the magnetic recording medium to reduce the surface electric resistance, the dispersibility and filling property of the magnetic powder are reduced, and the reproduction output is reduced. Inconvenience occurs. That is, from the viewpoint of improving the reproduction output, it is desirable to reduce the amount of carbon black. Therefore, in the present invention, the lower limit of the surface electric resistance is set to 10 ⁶ Ω / □ and the upper limit is set to 10 ¹⁰ Ω / □ from the balance between the improvement of the running stability and the reduction of the dropout and the improvement of the reproduction output. It is what it was. The preferable range of the value of the surface electric resistance is 10 ⁶ to 10 ⁹ Ω / □, and more preferably 10 ⁶ to 10 ⁸ Ω / □.

A specific method for measuring the surface electric resistance is as follows. That is, 24 carat gold plating is applied,
Two electrodes having a radius of 10 mm and having a roughness of N4 (see ISO 1302) are used, and these electrodes are used as a magnetic layer in a tape-shaped magnetic recording medium having a width of 1/2 inch (12.7 mm). Above, center-to-center distance d = 3.8
Place horizontally and parallel so as to be 1 mm. A 0.25N force is applied to both ends of the magnetic recording medium, and 100V is applied to the electrodes.
A DC voltage of ± 10 V is applied and the current between the electrodes is measured. The surface electric resistance is determined from this value.

In the present invention, specific means for satisfying the above physical properties (a) to (c) include: i) an intermediate layer containing carbon black and a binder on a nonmagnetic support; A magnetic layer containing carbon black, ferromagnetic powder, a binder and a fatty acid ester-based lubricant is provided in this order, and a carbon black having an oil absorption of 5 to 200 ml / 100 g is contained in the magnetic layer. Oil absorption 250 ~
Use 600ml / 100g. ii) An intermediate layer containing carbon black and a binder and a magnetic layer containing carbon black, ferromagnetic powder, a binder and a fatty acid ester-based lubricant are provided in this order on a nonmagnetic support, and the intermediate layer contains The ratio of the oil absorption of carbon black to the oil absorption of carbon black contained in the magnetic layer (former / latter) is controlled to 2 to 5. And the like. The above-mentioned means i) and ii) may be used in combination. Further, the present invention is not limited to these means. For example, the type of the fatty acid ester as the lubricant and the amount thereof may be appropriately selected, and the type and the amount of the binder or carbon black may be appropriately selected. There are also methods such as appropriately selecting the coating conditions and calendering conditions (especially calender temperature) of the layer to be formed, and appropriately adjusting the thickness of each layer constituting the magnetic recording medium.

Next, a magnetic recording medium according to a preferred embodiment which satisfies the physical properties (a) to (c) will be described with reference to the drawings. Here, FIG. 3 is a schematic diagram showing the structure of one embodiment of the magnetic recording medium of the present invention.

The magnetic recording medium 1 shown in FIG. 3 is in the form of a tape, and an intermediate layer 3 is provided on one surface of a support 2 adjacent to the support 2. A magnetic layer 4 is provided as the uppermost layer. Further, the back coat layer 5 is provided on the other surface of the support 2.

The intermediate layer 3 may be a magnetic layer or a non-magnetic layer. When the intermediate layer 3 is a layer having magnetism, the intermediate layer 3 is a magnetic layer containing a magnetic powder, and includes a magnetic powder, a non-magnetic powder, a fatty acid ester-based lubricant, carbon black, a binder and a solvent. It is formed using a magnetic paint mainly composed of. On the other hand, when the intermediate layer 3 is a non-magnetic layer, the intermediate layer 3 is made of a non-magnetic paint containing non-magnetic powder, a fatty acid ester-based lubricant, carbon black, a binder and a solvent as main components. Formed (hereinafter referred to as “intermediate layer paint”
).

As the magnetic powder, a ferromagnetic powder is preferably used, and as the ferromagnetic powder, both a soft magnetic powder and a hard magnetic powder are preferably used.

Examples of the hard magnetic powder include a ferromagnetic hexagonal ferrite powder, a ferromagnetic metal powder mainly composed of iron, γ-Fe ₂ O ₃ , γ-Fe ₂ O ₃ ,
Ferromagnetic iron oxide based powders such as adhered FeOx (4/3 ≦ x <1.5). Among these, it is particularly preferable to use ferromagnetic hexagonal ferrite powder.

As the above ferromagnetic hexagonal ferrite powder, barium ferrite and strontium ferrite in the form of fine flat plate, and part of their Fe atoms are Ti, C
Magnetic powders substituted with atoms such as o, Ni, Zn, V, and the like. The ferromagnetic hexagonal ferrite powder,
The preferred plate diameter is 0.02 to 0.09 μm, the preferred plate ratio is 2 to 7, and the preferred BET specific surface area is 30 to 60 m ² / g.

The ferromagnetic metal powder includes a ferromagnetic metal powder in which the metal content is 70% by weight or more and 60% or more of the metal content is iron. Specific examples of the ferromagnetic metal powder include Fe-Co, Fe-Ni, Fe-
Al, Fe-Ni-Al, Fe-Co-Ni, Fe-N
i-Al-Zn, Fe-Al-Si, and the like.

The ferromagnetic metal powder mainly composed of iron and the ferromagnetic iron oxide-based powder preferably have a needle-like or spindle-like shape. The major axis length is preferably 0.05 to 0.25 μm, more preferably 0.05 to 0.2 μm.
0.2 μm. When high density recording is required,
It is preferable that the major axis length is short, and those having a length of about 0.05 to 0.12 μm can also be used. The preferred needle ratio is 3
20, preferred X Sentsubu径is 13～25Nm, preferably has a BET specific surface area is 30 to 60 m ² / g.

The coercive force of the above hard magnetic powder is 1.2 × 10 ⁵
To 2.2 × 10 ⁵ A / m, particularly preferably 1.3 × 10 ^{5 to} 2.0 × 10 ⁵ A / m. Within the above range, the RF output in all wavelength regions can be obtained without excess and deficiency, and the overwrite characteristics are also good.

The saturation magnetization of the ferromagnetic metal powder and the ferromagnetic iron oxide-based powder is 6.2 × 10 ^{-6 to} 2.4 × 1.
Is preferably 0 ^-5 Wb / g, especially 8.8 × 10
^{-6 to} 2.0 × 10 ^-5 Wb / g is preferred. The saturation magnetization of the ferromagnetic hexagonal ferrite powder is 3.
It is preferably from 5 × 10 ^{−6 to} 9.0 × 10 ⁻⁶ Wb / g, and particularly preferably from 6.2 × 10 ^{−6 to} 8.8 × 10 ⁻⁶ Wb / g. Within the above range, a sufficient reproduction output can be obtained.

On the other hand, the soft magnetic powder is not particularly limited, but is preferably used for a so-called weak electric device such as a magnetic head and an electronic circuit. Magnetic Properties and Applications ”(Shokabo, 1984), pp. 368-376, specifically, oxide soft magnetic powders and metallic soft magnetic powders can be used. can do.

As the oxide soft magnetic powder, a spinel type ferrite powder is preferably used. As the spinel type ferrite powder, MnFe ₂ O ₄ , Fe ₃ O ₄ ,
CoFe ₂ O ₄ , NiFe ₂ O ₄ , MgFe ₂ O ₄ , L
i _0.5 Fe _2.5 O ₄ , Mn-Zn ferrite, Ni
-Zn ferrite, Ni-Cu ferrite, Cu-
Zn-based ferrite, Mg-Zn-based ferrite, Li-Z
Examples thereof include n-based ferrite, Zn-based ferrite, and Mn-based ferrite. These oxide soft magnetic powders may be used alone or in combination of two or more. Examples of the metal soft magnetic powder include Fe-Si alloys, Fe-Al alloys (Alperm, Alfenol, Alfer), and permalloy (Ni-
Fe-based binary alloys and multi-component alloys to which Mo, Cu, Cr, etc. are added), sendust (Fe-9.6 wt%)
Si-5.4 wt% Al), an Fe-Co alloy, and the like. These metal soft magnetic powders may be used alone or in combination of two or more.

The coercive force of the above oxide soft magnetic powder is usually 8 to
12000 A / m, and the saturation magnetization is usually 3.5 × 10
^{−5 to} 1.2 × 10 ⁻⁴ Wb / g. The coercive force of the metal soft magnetic powder is usually 1.6 to 8000 A / m, and the saturation magnetization is usually 6 × 10 ^{−5 to} 6 × 10 ⁻⁴ Wb / g.

The shape of the soft magnetic powder is not particularly limited, but may be spherical, plate-like, needle-like or the like.
It is preferably from 800 nm.

The above various magnetic powders may contain a rare earth element or a transition metal element as required.

Further, the above magnetic powder has a dispersibility and the like.
May be applied to improve the surface treatment. This surface
Processing is "Characterization of Powder Surfaces" (T.
J. Wiseman et al., Academic Press, 1976)
Can be performed in the same way as
If the method of coating the surface of the magnetic powder with an inorganic oxide
Are listed. Inorganic oxidation that can be used in this case
The object is Al_TwoO _Three, SiO_Two, TiO_Two, ZrO
_Two, SnO_Two, Sb_TwoO_Three, ZnO, etc.
When using them alone or in combination of two or more
May be used. In addition, the above-mentioned surface treatment is other than the above method.
Silane coupling treatment, titanium coupling treatment
And organic processing such as aluminum coupling
Can also be done.

Next, the non-magnetic powder will be described. As the non-magnetic powder, for example, non-magnetic iron oxide (Bengara), barium sulfate, zinc sulfide, magnesium carbonate, calcium carbonate, calcium oxide, zinc oxide, zinc oxide Examples include magnesium, magnesium dioxide, boron nitride, tin dioxide, silicon carbide, cerium oxide, corundum, garnet, silica stone, boron carbide, diatomaceous earth, and resinous powder. Among these, nonmagnetic iron oxide (borax), boron nitride, and the like are preferably used. These nonmagnetic powders may be used alone or in combination of two or more. The shape of the nonmagnetic powder may be spherical, plate-like, needle-like, or amorphous. Its size is preferably 5 to 200 nm in spherical, plate-like and amorphous ones,
In the case of a needle-like material, the major axis length is preferably 20 to 300 nm, and the needle-like ratio is preferably 3 to 20. When the nonmagnetic powder is used in combination with the magnetic powder (that is, when the intermediate layer 3 is a magnetic layer), preferably 0.1 to 1000 parts by weight with respect to 100 parts by weight of the magnetic powder, More preferably, it is used in an amount of 1 to 500 parts by weight. On the other hand, when the magnetic powder is not used (that is, when the intermediate layer 3 is a non-magnetic layer), the amount of other components is determined based on 100 parts by weight of the non-magnetic powder. The various non-magnetic powders described above may be subjected to the same treatment as the surface treatment applied to the magnetic powders, if necessary.

As described above, the fatty acid ester is used as a lubricant, and migrates (bleeds out) from the inside of the magnetic recording medium to the surface to exhibit a lubricating effect. Examples of the fatty acid ester include caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, linolenic acid, oleic acid, elaidic acid, behenic acid, malonic acid, succinic acid, Maleic acid, glutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid,
Examples thereof include alkyl esters such as 1,12-dodecanedicarboxylic acid and octanedicarboxylic acid.
From the viewpoint that the physical properties of (c) can be easily satisfied, those having a total carbon number of 12 to 36 are preferable. Particularly preferred as the fatty acid ester are an alkyl ester of stearic acid (particularly, an alkyl group having 3 to 8 carbon atoms) and a fatty acid ester having a branched structure or an unsaturated bond. When the intermediate layer 3 is a magnetic layer, the fatty acid ester is based on 100 parts by weight of the total amount of the magnetic powder and the nonmagnetic powder, and when the intermediate layer 3 is a nonmagnetic layer, The amount of 1 to 10 parts by weight, particularly 2 to 5 parts by weight based on 100 parts by weight of the non-magnetic powder, may be as described in (a) to
It is preferable because the physical properties of (c) can be easily satisfied. One or two or more of these fatty acid esters can be used.

The carbon black has the function of absorbing and retaining the fatty acid ester and controlling the degree to which the fatty acid ester moves from the inside of the magnetic recording medium to the surface. The use of the carbon black is preferable because the physical properties (a) to (c) can be easily satisfied. In particular, as described above, JIS K-6221-1982 A as carbon black is used.
Oil absorption measured according to the method is 250-600 ml / 1
It is preferable to use the one having a weight of 00 g, especially 350 to 600 ml / 100 g, since the physical properties (a) to (c) can be more easily satisfied.

In addition to the above-mentioned carbon black, the above-mentioned carbon black preferably has an average particle diameter of primary particles of 10 to 60 nm, particularly 20 to 40 nm, in addition to the above-mentioned oil absorption. If the average particle diameter exceeds 60 nm, the surface electric resistance may increase, and if the average particle diameter is less than 10 nm, the paint may thicken. Therefore, it is preferable that the average particle diameter be within the above range in order to balance these.

When the intermediate layer 3 is a magnetic layer, the amount of the carbon black is based on 100 parts by weight of the total amount of the magnetic powder and the nonmagnetic powder. In the case of (2), the amount is preferably 2 to 15 parts by weight, particularly 5 to 10 parts by weight with respect to 100 parts by weight of the nonmagnetic powder, because the physical properties (a) to (c) can be easily satisfied. preferable.

The binder contained in the intermediate layer 3 can be used without limitation as long as it is used for a magnetic recording medium. For example, a thermoplastic resin, a thermosetting resin, a reactive resin, a mixture thereof, and the like can be given. Specifically, a copolymer of vinyl chloride and a modified product thereof, a copolymer of acrylic acid, methacrylic acid and its ester, a copolymer of acrylonitrile (rubber-based resin),
Polyester resin, polyurethane resin, epoxy resin,
Cellulosic resins, polyamide resins and the like can be used. The binder preferably has a number average molecular weight of 2,000 to 200,000. Further, in order to improve the dispersibility of magnetic powder and the like, a hydroxyl group, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a nitro group or a nitrate ester group, an acetyl group,
Contains polarizable functional groups (so-called polar groups) such as sulfate groups or their salts, epoxy groups, nitrile groups, carbonyl groups, amino groups, alkylamino groups, alkylammonium bases, betaine structures such as sulfobetaine and carbobetaine. May be. The amount of the binder is such that the physical properties (a) to (c) can be easily satisfied.
When the intermediate layer 3 is a magnetic layer, the total amount of the magnetic powder and the non-magnetic powder is 100 parts by weight. When the intermediate layer 3 is a non-magnetic layer, the non-magnetic powder 100 is used.
The amount is preferably 10 to 30 parts by weight, particularly preferably 12 to 25 parts by weight with respect to parts by weight.

It is also preferable that the intermediate layer 3 contains an abrasive for the purpose of improving the running durability of the magnetic recording medium. As the abrasive, for example, a substance having a Mohs hardness of 7 or more such as alumina, silica, titanium oxide, ZrO ₂ , and Cr ₂ O ₃ is used. The average particle size (primary particles) of the abrasive is preferably from 0.03 to 0.40 μm, and more preferably from 0.05 to 0.30 μm, from the viewpoints of reduction in friction coefficient during running and improvement in running durability. It is even more preferred. The abrasive, when the intermediate layer 3 is a magnetic layer,
When the intermediate layer 3 is a non-magnetic layer, the total amount of the magnetic powder and the non-magnetic powder is 100 parts by weight. Preferably, 10 parts by weight are blended. Note that the abrasives according to the present invention are not included in the above-mentioned nonmagnetic powder.

Further, the intermediate layer 3 may contain a lubricant other than the fatty acid ester. As such a lubricant,
For example, fatty acids can be used. As the fatty acid, the same fatty acids as those described above as the fatty acid constituting the fatty acid ester can be used. The fatty acid is used in an amount of 100 parts by weight in total when the intermediate layer 3 is a magnetic layer and when the intermediate layer 3 is a non-magnetic layer. It is preferable to mix 1 to 10 parts by weight, particularly 2 to 5 parts by weight, with respect to 100 parts by weight of the magnetic powder.

Further, it is preferable that a curing agent is added to the intermediate layer 3 for the purpose of increasing its rigidity. As the curing agent, an isocyanate-based curing agent or an amine-based curing agent represented by Coronate L (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd. is generally used. When the intermediate layer 3 is a magnetic layer, the hardening agent is used based on 100 parts by weight of the total amount of the magnetic powder and the nonmagnetic powder, and when the intermediate layer 3 is a nonmagnetic layer, It is preferable to mix 1 to 7 parts by weight, especially 2 to 5 parts by weight, with respect to 100 parts by weight of the nonmagnetic powder.

The intermediate layer 3 is formed by applying an intermediate layer paint containing the various components and the solvent described above on the non-magnetic support 2. Examples of the solvent include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents, and chlorinated hydrocarbon solvents. The compounding amount of the solvent in the intermediate layer paint is 80 to 200 parts by weight based on 100 parts by weight of the total amount of the magnetic powder and the nonmagnetic powder contained in the intermediate layer paint, or 100 parts by weight of the nonmagnetic powder. And particularly preferably 100 to 130 parts by weight.

To prepare the above intermediate layer paint, for example,
The magnetic powder, the non-magnetic powder, the binder, and the like are put into a Nauta mixer or the like together with a part of the solvent and preliminarily mixed to obtain a mixture, and the mixture is kneaded by a continuous pressure kneader or the like,
Next, a method of diluting with a part of the solvent, performing a dispersion treatment using a sand mill or the like, mixing an additive such as a fatty acid ester, filtering, and further mixing a curing agent and the rest of the solvent is mentioned. be able to.

The thickness of the intermediate layer 3 formed by applying the above-mentioned intermediate layer coating material is 0.5 to 3.0 μm, irrespective of whether the intermediate layer 3 is magnetic or non-magnetic. 5-2.5μ
m is preferable. It is preferable that the thickness of the intermediate layer 3 be within the above range because the physical properties (a) to (c) can be easily satisfied.

When the intermediate layer 3 is a magnetic layer containing a hard magnetic powder, the coercive force (Hc) of the intermediate layer 3 is 120 to 2
It is preferably 50 kA / m, particularly preferably 130 to 220 kA / m. The saturation magnetic flux density (Bs) is 0.02
０．１0.13T, particularly preferably 0.05０．０0.09T. It is preferable that the coercive force and the saturation magnetic flux density of the intermediate layer 3 are within the above ranges, since the electromagnetic conversion characteristics are particularly excellent in the output characteristics in the low range and the high range. On the other hand, when the intermediate layer 3 is a magnetic layer containing a soft magnetic powder, Hc is 1 to 15
000 kA / m and Bs are preferably 0.3 to 0.6T.

Next, the magnetic layer 4 will be described. The magnetic layer 4 contains ferromagnetic powder, carbon black, a fatty acid ester-based lubricant, and a binder. As the fatty acid ester, the same fatty acid ester as described above as the fatty acid ester contained in the intermediate layer 3 can be used. In this case, the fatty acid ester contained in the magnetic layer 4 and the fatty acid ester contained in the intermediate layer 3 may be the same or different. The magnetic layer 4
May be two or more fatty acid esters.

The fatty acid ester is used in an amount of 1 to 6 parts by weight based on 100 parts by weight of the ferromagnetic powder contained in the magnetic layer 4.
In particular, the content of 1 to 2 parts by weight is as described in (a) to above.
It is preferable because the physical properties of (c) can be easily satisfied.

Examples of the ferromagnetic powder include ferromagnetic metal powder mainly composed of iron, oxide magnetic powder, hexagonal ferrite powder and the like exemplified as hard magnetic powder among the magnetic powders contained in the intermediate layer 3. It can be preferably used. Although the details of these magnetic powders are not particularly described, the detailed description of the intermediate layer 3 is appropriately applied. Among these magnetic powders, it is preferable to use a ferromagnetic metal powder mainly composed of iron and an oxide-based magnetic powder, and it is particularly preferable to use a ferromagnetic metal powder mainly composed of iron.

The same treatment as the surface treatment applied to the magnetic powder contained in the intermediate layer 3 can be applied to the ferromagnetic powder. In addition, the ferromagnetic powder may contain a rare earth element or a transition metal element as necessary.

As the carbon black, the intermediate layer 3
Can be used, but in particular, as described above, JIS K-622 because the physical properties (a) to (c) can be easily satisfied.
1-182 Oil absorption measured according to Method A is 50 to
200 ml / 100 g, especially 100-200 ml /
It is preferable to use 100 g. In this case, the ratio of the oil absorption of the carbon black contained in the intermediate layer 3 to the oil absorption of the carbon black contained in the magnetic layer 4 (former / latter) may be 2 to 5 as described above. It is preferable because the physical properties (a) to (c) can be more easily satisfied, and particularly preferably 2 to 4. The compounding amount of carbon black is preferably 0.1 to 5 parts by weight, particularly preferably 1 to 3 parts by weight, based on 100 parts by weight of the ferromagnetic powder.

As the above-mentioned binder, the same binder as described above as the binder contained in the intermediate layer 3 can be used. The binder is blended in an amount of 10 to 30 parts by weight, particularly 12 to 25 parts by weight, based on 100 parts by weight of the ferromagnetic powder, since the physical properties (a) to (c) can be easily satisfied. Is preferred.

The magnetic layer 4 has the same components as those described above as the components contained in the intermediate layer 3 in addition to the components described above.
For example, it is preferable to contain an abrasive, a fatty acid, a curing agent, and the like. Although the details of these components are not particularly described, the detailed description of the intermediate layer 3 is appropriately applied.
Preferred amounts of these components in the magnetic layer 4 are as follows with respect to 100 parts by weight of the ferromagnetic powder. Abrasive: 5 to 15 parts by weight, especially 6 to 12 parts by weight Fatty acid: 0.5 to 5 parts by weight, especially 1 to 3 parts by weight Hardener: 1 to 6 parts by weight, especially 3 to 5 parts by weight

The magnetic layer 4 is formed by applying a magnetic paint containing the various components and the solvent described above on the intermediate layer 3. As the solvent, those similar to those used for the above-mentioned intermediate layer paint can be used. The compounding amount of the solvent in the magnetic paint is preferably 200 to 400 parts by weight, particularly preferably 250 to 300 parts by weight based on 100 parts by weight of the ferromagnetic powder contained in the magnetic paint.

The thickness of the magnetic layer 4 formed by applying the above magnetic paint is 0.1 to 0.5 μm, especially 0.2 to 0.4 μm.
μm is preferred. It is preferable that the thickness of the magnetic layer 4 be within the above range because the physical properties (a) to (c) can be easily satisfied.

The coercive force (Hc) of the magnetic layer 4 is 130 to 26.
It is preferably 0 kA / m, particularly preferably 150 to 260 kA / m. The saturation magnetic flux density (Bs) is 0.3 to
It is preferably 0.5T, particularly preferably 0.4 to 0.45T. It is preferable that the coercive force and the saturation magnetic flux density of the magnetic layer 4 be within the above ranges, since C / N characteristics required for high-density recording can be obtained.

Incidentally, as for the points which are not particularly described with respect to the magnetic layer 4, the detailed description regarding the intermediate layer 3 is appropriately applied.

The material constituting the non-magnetic support 2 includes
Polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate and polyethylene bisphenoxycarboxylate; polyolefins such as polyethylene and polypropylene; cellulose derivatives such as cellulose acetate butyrate and cellulose acetate propionate Vinyl resins such as polyvinyl chloride and polyvinylidene chloride; polyamides;
Polyimide; polycarbonate; polysulfone; polyether / ether ketone, and a polymer resin such as polyurethane. These can be used alone or in combination of two or more. The support composed of these materials may be subjected to a uniaxial or biaxial stretching treatment, a corona discharge treatment, or the like, as necessary. Further, a thin adhesive layer (easily adhesive layer) may be provided on the surface of these plastic materials. Among these materials, the use of polyethylene terephthalate, polyethylene naphthalate, polyamide, or the like is described in the above (a) to
It is preferable because the physical properties of (c) can be easily satisfied.

The back coat layer 5 provided on the back surface of the nonmagnetic support 2 as necessary contains carbon black and a binder. As the carbon black and the binder, those similar to those used in the intermediate layer 3 and the magnetic layer 4 can be used. The compounding amount of the carbon black is 5 to 100 parts by weight, especially 10 to 70 parts by weight, based on 100 parts by weight of the binder contained in the back coat layer 5, so that the back coat layer has a suitable conductivity. Is preferred in that it can provide

The back coat layer 5 preferably has a surface electric resistance of 10 ⁹ Ω / □ or less from the viewpoints of antistatic properties and running stability. The value of the surface electrical resistance is 10 ⁹ Ω
In order to make it less than / □, for example, the compounding amount of the carbon black to be used may be within the above range. The lower the value of the surface electric resistance is, the more effective it is to prevent adhesion of dust and dust.

The back coat layer 5 is formed by applying a back coat paint containing the above-mentioned components, a solvent and the like on the non-magnetic support 2. The back coat formed by applying the back coat paint is formed. The thickness of the coat layer 5 is preferably 0.05 to 1.0 μm, particularly preferably 0.1 to 0.7 μm.

The thickness (total thickness) of the magnetic recording medium 1 composed of the support and the layers described above is 5 to 10 μm. That is, the magnetic recording medium of the present invention is thin.

Next, an outline of a preferred method of manufacturing the magnetic recording medium 1 shown in FIG. 3 will be described. First, the intermediate layer coating material for forming the intermediate layer 3 and the magnetic coating material for forming the magnetic layer 4 on the support 2 are mixed so that the thickness of the intermediate layer 3 and the thickness of the magnetic layer 4 become predetermined values, respectively. Is applied simultaneously by a wet-on-wet method to form a magnetic layer and an intermediate layer. That is, the magnetic layer is preferably applied and formed when the intermediate layer is wet. Next, these coating films are subjected to a magnetic field orientation treatment, and then subjected to a drying treatment and wound up. Thereafter, a calendering process is performed to further form the back coat layer 5. Alternatively, the magnetic layer 4 and the intermediate layer 3 may be formed after forming the back coat layer 5. Next, aging treatment is performed at 40 to 80 ° C. for 6 to 100 hours, and slit into a desired width.

The above simultaneous multi-layer coating method is described in JP-A-5-73.
No. 883, column 42, line 31 to column 43, line 31, etc., which is a method of applying a magnetic paint before the intermediate layer paint dries, wherein a boundary between the intermediate layer 3 and the magnetic layer 4 is provided. Since the surface becomes smooth and the surface property of the magnetic layer 4 becomes good, a magnetic recording medium which has a small dropout, can cope with high-density recording, and has excellent coating film (magnetic layer and intermediate layer) durability can be obtained. can get.

The magnetic field orientation treatment is performed before each paint is dried, and is about 40 kA / m or more, preferably about 80 to 800 kA / m, in a direction parallel to the coating surface of the paint.
Or a method in which the paint passes through a solenoid of 80 to 800 kA / m or the like in a wet state.

The drying treatment can be performed, for example, by supplying a heated gas. At this time, the degree of drying of the coating film can be controlled by controlling the temperature of the gas and the amount of the supplied gas.

Further, the calendering treatment is performed by a super calendering method in which a metal roll and a cotton roll or a synthetic resin roll are passed between two rolls and a metal roll and a metal roll are passed between two rolls. Can be. The conditions for the calendar processing are as described in the above (a) to (c).
From the point that the physical properties of
And a linear pressure of 250 to 350 kg / cm.

In the manufacture of the magnetic recording medium of the present invention, a finishing step such as a polishing or cleaning step for the surface of the magnetic layer can be performed, if necessary. Even with these steps, the physical properties (a) to (c) can be easily satisfied. The application of the magnetic paint and the intermediate layer paint can also be carried out by a generally known sequential multilayer coating method.

Although the magnetic recording medium of the present invention has been described based on the preferred embodiments, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention. . For example, in the above embodiment,
This is only a preferable example in which the physical properties of the above (a) to (c) can be easily satisfied, and the above (a) to (c) are obtained by other means.
The magnetic recording medium may satisfy such physical properties. The above embodiment relates to a magnetic recording medium having a magnetic / magnetic or magnetic / non-magnetic multilayer structure.
The present invention can be applied to a magnetic recording medium having a single magnetic layer structure. The magnetic recording medium 1 of the embodiment shown in FIG.
Further, a primer layer may be provided between the support 2 and the intermediate layer 3 or the back coat layer 5, or another magnetic layer for recording a servo signal or the like corresponding to a hard system using a long wavelength signal; Other layers may be provided. Further, the magnetic recording medium of the present invention can be applied to various kinds of magnetic recording media in the form of a tape, such as a magnetic tape such as an 8 mm video tape, a DAT tape, a DDS tape, a DVC tape, and a DLT tape.

[0073]

The present invention will be described in more detail with reference to the following examples and the effectiveness thereof will be illustrated. However, the scope of the present invention is not limited to such an embodiment.
In the following examples, “parts” are “parts by weight” unless otherwise specified.
Means

Example 1 The following components were kneaded in a kneader, dispersed by a stirrer, finely dispersed by a sand mill, and filtered by a 1 μm filter.
The hardener was added last to prepare the magnetic paint, the interlayer paint and the backcoat paint respectively.

<Magnetic paint> 100 parts of acicular ferromagnetic powder mainly composed of iron (coercive force: 145 kA / m, saturation magnetization: 1.65 × 10 ⁻⁵ Wb / g, average major axis length: 0. 11 μm, needle ratio; 8) Binder A 11 parts [vinyl chloride binder, MR104 (trade name) manufactured by Zeon Corporation] Binder 8 parts [Polyurethane binder, UR-8300 (trade name) of Toyobo Co., Ltd.] Abrasive (α-alumina, average particle size of primary particles; 0.3 μm) 12 parts Carbon black (see Table 1 for type and number of parts) Lubricant A (stearic acid) 1 part Lubricant B (butyl) 2 parts Curing agent [Coronate L (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd.] 4 parts Solvent A (methyl ethyl ketone) 100 parts Solvent B (toluene) 50 parts Solvent C (cyclohexanone) 100 copies

<Intermediate layer coating> 50 parts of plate-shaped ferromagnetic hexagonal barium ferrite powder (coercive force: 135 kA / m, saturation magnetization: 7.5 × 10 ⁻⁶ Wb / g, plate diameter: 30 nm,・ Acicular α-Fe ₂ O ₃ (non-magnetic powder, major axis length: 0.2 μm) 50 parts ・ Binder A (see Table 1 for the number of parts) [Vinyl chloride binder, manufactured by Zeon Corporation MR104 (trade name)] Binder B (see Table 1 for the number of parts) [Polyurethane binder, UR-8300 (trade name) of Toyobo] Abrasive (α-alumina, average particle diameter of primary particles; 0.3 μm) 12 parts ・ Carbon black (see Table 1 for type and number of parts) ・ 1 part of lubricant A (stearic acid) ・ 2 parts of lubricant B (butyl stearate) ・ 100 parts of solvent A (methyl ethyl ketone) ・ 100 parts of solvent B (toluene) 50 parts ・ Solvent C (Cyclohexanone) 100 parts

<Backcoat paint> 38.5 parts of carbon black (average particle diameter of primary particles; 18 nm) 1.5 parts of carbon black (average particle diameter of primary particles; 75 nm) 50 parts of polyurethane binder [Nippon Polyurethane Nipporan 2301 (trade name, manufactured by Kogyo Co., Ltd.) 28.6 parts of nitrocellulose binder [Celnova BTH1 / 2 (trade name), manufactured by Asahi Kasei Kogyo Co., Ltd.] 4 parts of hardener [Takeda Pharmaceutical Co., Ltd. -Polyisocyanate, D-250N (trade name)]-Copper phthalocyanine 5 parts-Lubricant (stearic acid) 1 part-Solvent A (methyl ethyl ketone) 140 parts-Solvent B (toluene) 140 parts-Solvent C (cyclohexanone) 140 Department

On a polyethylene terephthalate support having a thickness of 7 μm, a magnetic coating material and an intermediate coating material were coated with a magnetic layer and an intermediate layer having a dry thickness of 0.2 μm and 2.5 μm, respectively.
m, simultaneous multi-layer coating was performed with a die coater to form respective coating films. Next, while these coating films were changed from a wet state to a dry state, a magnetic field orientation treatment was performed using a 400 kA / m solenoid. Further, the coating film was dried by blowing hot air at 80 ° C. at a speed of 10 m / min in a drying furnace. After drying, the coating film was heated at a temperature of 100 ° C and a linear pressure of 30 ° C.
A calender treatment was performed under the condition of 0 kg / cm to form a magnetic layer and an intermediate layer. Subsequently, a backcoat paint was applied on the surface on the opposite side of the support so that the dry thickness became 0.5 μm, and dried at 90 ° C. to form a backcoat layer. Finally, the magnetic tape was slit to a width of 1/2 inch (12.7 mm) to produce a magnetic tape having the structure shown in FIG.

[Examples 2 to 4 and Comparative Examples 1 to 4] Table 1 shows the types and parts of carbon black compounded in the magnetic layer, the types and parts of carbon black compounded in the intermediate layer, and the number of binders. A magnetic tape was manufactured in the same manner as in Example 1 except for the following.

With respect to the magnetic tapes obtained in the examples and comparative examples, the flexural rigidity (longitudinal and width directions), the amount of fatty acid ester-based lubricant, and the surface electric resistance on the magnetic layer side and the back coat layer side were measured by the above-described methods. did. Table 2 shows the measurement results.
Shown in Table 2 also shows the total thickness and width of the magnetic tape.

[Evaluation of Performance] In order to evaluate the performance of the magnetic tapes obtained in the examples and comparative examples, the torque ratio and head contamination of the drive were measured by the following methods. Table 2 shows the results.

<Torque Ratio> A magnetic tape was assembled in a tape cassette, the tape cassette was loaded on a digital beta cam deck, and the magnetic tape was run. The current value of the capstan roll during running was measured, and this current value was used as a measure of torque. A relative value was calculated based on the current value of Example 1, and this relative value was used as a torque ratio. The torque ratio is a measure of the running stability of the magnetic tape,
The smaller the value, the higher the running stability.

<Dirt of Head> A magnetic tape was set in a tape cassette, and the tape cassette was loaded on a digital beta cam deck, and the magnetic tape was continuously run at 25 ° C. and 50% RH for 24 hours. Head dirt after continuous running was visually observed, and the degree was evaluated. The evaluation criteria are as follows. Small: No foreign matter adhered around the head gap or one foreign matter mass adhered. Average: 2 to 4 foreign matter blocks are attached. Many: Five or more foreign substance clusters are attached.

[0084]

[Table 1]

[0085]

[Table 2]

As is clear from the results shown in Tables 1 and 2, the magnetic tape of the embodiment (the product of the present invention) satisfying the above physical properties (a) to (c) was used as a magnetic tape of the comparative example to obtain a torque ratio. It can be seen that the head was small and the head dirt was small.

[0087]

As described in detail above, according to the tape-shaped magnetic recording medium of the present invention, running stability is improved, and running durability and electromagnetic conversion characteristics are improved.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between bending stiffness, torque ratio, and surface electrical resistance.

FIG. 2 is a diagram showing an apparatus for measuring bending stress.

FIG. 3 is a schematic diagram showing a configuration of an embodiment of a magnetic recording medium according to the present invention.

[Explanation of symbols]

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

Claims (5)

[Claims] 1. A tape-shaped magnetic recording medium having a thickness of 5 to 10 μm, comprising a nonmagnetic support and a magnetic layer containing a ferromagnetic powder, carbon black, a fatty acid ester-based lubricant and a binder provided thereon. The magnetic recording medium has a bending rigidity DL in a longitudinal direction and a bending rigidity DW in a width direction satisfying the following formulas (1) and (2), respectively. The magnetic recording medium is immersed in n-hexane at 25 ° C. for 1 minute. The amount of the extracted fatty acid ester-based lubricant is 5
550 mg / m ² , and the magnetic layer side has a surface electric resistance of 1
The magnetic recording medium comprising a 0 ^6-10 is ^{10 Ω} / □. (Equation 1) (Equation 2) 2. The method according to claim 1, wherein the non-magnetic support and the magnetic layer are
2. The magnetic recording medium according to claim 1, further comprising an intermediate layer containing carbon black and a binder. 3. The oil absorption of carbon black contained in the magnetic layer is 50 to 200 ml / 100 g, and the oil absorption of carbon black contained in the intermediate layer is 250 to 200 ml.
3. The magnetic recording medium according to claim 1, wherein the weight is 600 ml / 100 g. 4. The ratio (former / latter) of the oil absorption of carbon black contained in the intermediate layer to the oil absorption of carbon black contained in the magnetic layer is 2 to 5.
The magnetic recording medium according to the above. 5. A backcoat layer is provided on a surface of the nonmagnetic support opposite to the surface on which the magnetic layer is provided, and the backcoat layer has a surface electric resistance of 10 ⁹ Ω.
The magnetic recording medium according to claim 1, wherein the ratio is not more than / □.