JPH1021524A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having excellent electromagnetic transducing characteristics and travelling durability. SOLUTION: This magnetic recording medium is produced by forming a magnetic layer 3 containing a metal-based magnetic powder essentially composed of Fe on one surface of a nonmagnetic supporting body 2 and forming a back coating layer 4 on the other surface of the supporting body 2. The magnetic layer has >=350mT saturation magnetic flux density Bm in the longitudinal direction, 179 to 200A/m coercive force Hc, 2 to 5nm surface roughness SRa and 0.1 to 0.3μm thickness δ. The medium has <=7μm sum thickness D and >=5N strength for 5% elongation. The contribution rate TST of the magnetic layer to stiffness defined by TST=[(YM.δ/D)/(YMD.δB/D+YBC.δBC/D)]×100 is controlled to <=7%, wherein YM, YMD and YBC are Young's modulus of the magnetic layer, nonmagnetic supporting body and back coating layer, respectively, δB and δBC are thickness of the nonmagnetic base body and the back coating layer, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a coating type magnetic recording medium, and more particularly to a magnetic recording medium having excellent characteristics for high density digital recording.

[0002]

2. Description of the Related Art In recent years, especially for magnetic tapes for digital recording, the volume recording density has been improved. In order to improve the recording density, the magnetic layer has been further thinned and the magnetic tape itself has been improved. Is required to be reduced in total thickness. Regarding the improvement of the linear recording density, in order to realize a C / N and a sufficient O / W (overwrite) characteristic at which a sufficiently low error rate can be obtained in a system having a recording wavelength λ of 0.4 μm or less, magnetic recording must be performed. It is known that the layers need to be thinned. For this purpose, for example, a two-layer coating type magnetic tape in which a non-magnetic layer is provided below the magnetic layer has also been proposed, but when the total thickness of the tape is limited, the coating layer becomes thicker due to the two-layer structure. In addition, the thickness of the non-magnetic support has to be reduced accordingly, and as a result, the 5% elongation strength of the tape as a whole is reduced, and the running durability is reduced.

In this case, it is conceivable to use polyamide as a material for the non-magnetic support in order to improve the strength of the tape itself. However, this polyamide is less expensive than general-purpose polyester and polyethylene naphthalate. There was a drawback that it was extremely high. Furthermore, if the thickness of the coating layer which is to be the magnetic layer is too thick relative to the entire thickness of the tape, the magnetic powder or the like is highly filled and the rigidity is increased. Thus, there is a disadvantage in that the reproduction signal amplitude deteriorates per head such as a drop in supply.

In order to solve such a problem, a magnetic medium in which the thickness of a non-magnetic material, the elongation strength in the longitudinal direction, the surface roughness, the saturation magnetization of the magnetic powder, the coercive force, and the like are specified, and 6
No. 0-219627), and a recording medium (JP-A-6-318317) in which the stiffness of the nonmagnetic support and the entire recording medium, the coating energy of the magnetic paint, and the like are specified. The present inventor has also proposed a recording medium (see Japanese Patent Application Laid-Open No.
However, none of these conventional recording media is sufficient in terms of electromagnetic conversion characteristics and running durability. The present invention has been made in view of the above problems, and has been made in order to effectively solve the problems. An object of the present invention is to provide a magnetic recording medium having both excellent electromagnetic conversion characteristics and running durability. It is in.

[0005]

According to the present invention, in order to solve the above-mentioned problems, a magnetic layer containing a metal-based magnetic powder containing Fe as a main component is provided on one surface of a non-magnetic support. A magnetic recording medium provided with a back coat layer on the surface side,
The saturation magnetic flux density Bm in the longitudinal direction of the magnetic layer is 350 mT
As described above, the coercive force Hc is in the range of 170 to 200 A / m, the surface roughness SRa of the magnetic layer is in the range of 2 to 5 nm, and the thickness δ of the magnetic layer is in the range of 0.1 to 0.3 μm. ,
In a magnetic recording medium having a total thickness D of 7 μm or less, the magnetic recording medium has a 5% elongation strength of 5N or more, and the Young's modulus of the magnetic layer, the non-magnetic support, and the back coat layer is Y, respectively. _M , Y _MD , Y _BC , the thickness of the nonmagnetic support is δ _B , and the thickness of the back coat layer is δ _BC , the contribution T _st of the magnetic layer to the stiffness shown in Equation 1 below is Set to be 7% or less.

[0006]

(Equation 1)

As a result, it is possible to improve the electromagnetic conversion characteristics at the time of high-density recording with a recording wavelength of 0.5 μm or less, to improve head contact, and to improve running durability. In this case, the Young's modulus Y _MD in the longitudinal direction of the nonmagnetic support
Is desirably set so that Y _MD ≧ 1500 (kg / mm ² ). Further, it is desirable that the magnetic layer contains a binder having the structural unit shown in Chemical formula 1 or Chemical formula 2.

[0008]

Embedded image

R1 is any of an alkyl group, an aralkyl group and a phenyl group.

[0010]

Embedded image

R2 is an alkylene group or a phenylene group.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the magnetic recording medium according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a partially enlarged sectional view of a magnetic recording medium according to the present invention. According to the present invention, when the magnetic recording medium has a total thickness of 7 μm or less, by securing 5% elongation strength, running durability is obtained and at the same time sufficient head contact is obtained in a helical scan type recording system. The present invention relates to a magnetic recording medium that satisfies the mechanical conditions while satisfying the short-wavelength recording conditions.

That is, the magnetic recording medium 1 has a non-magnetic support 2 made of a polymer film such as a polyester resin. A magnetic layer 3 is formed on one side and a back coat layer 4 is formed on the opposite side. It is configured. The layers to be formed are not limited to these. Here, the saturation magnetic flux density Bm of the magnetic layer 3 in the longitudinal direction of the medium is 350 mT.
As described above, the coercive force Hc is 170 to 200 A / m, the surface roughness SRa of the magnetic layer 3 is 2 to 5 nm, and the thickness δ of the magnetic layer 3 is 0.
1 to 0.3 μm, and the total thickness D of the medium is set to 7 μm or less. Further, the 5% elongation strength of the recording medium is set to 5N or more, the Young's modulus of the magnetic layer 3, the non-magnetic support 2 and the back coat layer 4 are set to Y _M , Y _MD and Y _BC respectively. When the thickness is δ _B and the thickness of the back coat layer 4 is δ _BC , the contribution T _ST of the magnetic layer 3 to the stiffness shown in Expression 1 is set to be 7% or less.

[0014]

(Equation 1)

In the future digital recording media, it is desired to improve the volume recording density. For that purpose, the improvement of the linear recording density and the thinning of the medium itself have been studied. To improve the linear recording density, the saturation magnetization σ _S
The method of making metal magnetic material with high particle size into fine particles and filling them with high density has become mainstream. In order to realize a digital recording system having a recording wavelength λ of 0.5 μm or less, the saturation magnetic flux density Bm required for a recording medium such as a magnetic tape needs to be 350 mT or more, and the coercive force Hc needs to be 170 A / m or more. This has been confirmed by the present inventors. Further, in the digital overwriting system, due to its O / W characteristics,
It is necessary to limit the upper limit of the coercive force Hc and the thickness of the magnetic layer,
The coercive force Hc is 200 A / m or less, and the thickness of the magnetic layer is 0.3
μm or less is a necessary condition. Naturally, in order to obtain a sufficient output, the thickness of the magnetic layer is required to be at least 0.1 μm or more. The surface roughness SRa of the magnetic layer is demagnetized due to the spacing loss, so that the recording wavelength λ is 0 μm. It has so far been studied by the present inventors that when it is smaller than 0.5 μm, it must be smaller than 5 nm.

Here, if the total thickness of the tape is too thin, the running durability and the strength sufficient to satisfy the head contact cannot be obtained, and a problem occurs. The inventors of the present invention have found that the setting of is particularly effective in ensuring running durability (tape plastic deformation resistance represented by tape damage). However, in principle, sufficient strength is ensured by a magnetic layer or a non-magnetic support capable of taking a strength. However, when the total thickness of the medium is 7 μm or less, the thickness ratio of the magnetic layer having a high filling degree is reduced. It was found that when the temperature was increased, the flexibility of the magnetic layer could not be obtained for high-speed tracing of the head, but rather the head contact and edge damage were worsened. Many studies have shown that the magnetic layer contributes 7% to the tape stiffness.
It has been found that when designed to be as follows, it is possible to secure the strength and not to deteriorate the head contact. More preferably, the contribution ratio is in the range of 1% to 6%. Further, as described above, a binder having a structural unit represented by the following chemical formulas 1 and 2 containing amine quinone as a binder in a thin, rigid, and flexible magnetic layer is effective. I discovered that.

[0017]

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R1 is any one of an alkyl group, an aralkyl group and a phenyl group.

[0019]

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R2 is an alkylene group or a phenylene group. As the resin of the binder into which the amine quinone can be introduced, a known resin used in a conventional magnetic recording medium can be used, but it is preferable to use a vinyl chloride resin, a polyurethane resin, or a polyester resin. The weight ratio of the constituent monomer having an amine quinone structure in the resin is not particularly limited,
It is desirable from 0.1 to 50% by weight from the viewpoint of mechanical strength. Further, in order to improve running durability, it is essential to secure 5% elongation strength as described above, and the means for that is not strictly limited. Under the condition where the contribution is reduced to less than 5%, the improvement of the rigidity of the non-magnetic support is most effective, and the Young's modulus in the longitudinal direction of the non-magnetic support needs to be 1500 (kg / mm ² ) or more. Further, in order to secure the head per head, it is necessary to secure the strength in the medium width direction. For this purpose, the total of the Young's modulus in the vertical and horizontal directions of the non-magnetic support must be 1900 (kg / mm ² ) or more. Is desired.

<Examples> Examples of the present invention and comparative examples for comparison will be specifically described below. Incidentally, the composition and the manufacturing method of the medium shown here are not particularly limited, and changes thereof can be easily estimated. The following Examples and Comparative Examples were prepared by sufficiently kneading and dispersing a magnetic coating composition having the composition components of the magnetic layer shown below using a kneader, a bead mill, and the like. It was applied to the thickness shown, then oriented, dried and calendered, then cut to 3.81 mm width and taped. The magnetic powder used was an Fe-based ferromagnetic powder containing Fe as a main component (50 wt% or more).

Magnetic coating composition Fe-based ferromagnetic powder 100 parts Vinyl chloride copolymer (MR110 manufactured by Nippon Zeon) 10 parts Binder (designated in table) 10 parts Polyisocyanate (Coronate L manufactured by Nippon Polyurethane) 5 Part alumina 5 parts myristic acid 1 part butyl stearate 1 part methyl ethyl ketone 100 parts toluene 100 parts The back coat composition is as follows. Back coat composition Carbon black 100 parts Vinyl chloride copolymer (MR110 manufactured by Zeon Corporation) 100 parts Methyl ethyl ketone 400 parts Toluene 400 parts

The magnetic tapes of the examples and comparative examples were prepared using R-DAT.
The cartridge was wound into a cassette, and the electromagnetic conversion characteristics (C / N, O / W) and edge damage were evaluated using a D-DAT drive (manufactured by Victor Company of Japan). The C / N uses 4.7 MHz as a carrier signal, and the O / W overwrites a 4.7 MHz signal after writing a 130 kHz signal, and
The residual level of z was measured and expressed as the amount of 130 kHz signal attenuation. C / N is a target level of 4 dB or more, and 0 / W is a target level of −30 dB or more. Edge damage is 1
The damage status of the edge after the repeated running of 000 passes was visually judged, and a slight and no change was evaluated as 、, a medium was evaluated as Δ, and a damage was evaluated as ×. △
The above are the required characteristics that can be used. Saturation magnetic flux density Bm, coercive force Hc, the surface roughness SRa of the magnetic layer, the Young's modulus Y _MD of the non-magnetic support, the magnetic layer thickness [delta], a non-magnetic support thickness [delta] _B including the construction materials and process conditions of the Adjusted media were prepared to obtain tapes shown in Examples 1 to 6 and Comparative Examples 1 to 7 as shown in Table 1. Table 1 shows the evaluation results of these examples and comparative examples.

[0024]

[Table 1]

In the column of the binder in Table 1, 1 is a polyurethane resin into which the above-mentioned chemical formula 1 is introduced, 2 is a polyurethane resin into which chemical formula 2 is introduced, and 3 is a polyurethane resin (N2304 manufactured by Nippon Polyurethane). I have. Also, Y
_BASE is the sum of the Young's modulus Y _MD in the length direction of the non-magnetic support and the Young's modulus in the width direction, and F5 indicates the 5% elongation strength of the medium. As is clear from Table 1, the magnetic conversion characteristics (C / N, O / W) of Comparative Example 1 in which the thickness of the magnetic layer is increased and the stiffness contribution ratio T _ST of the magnetic layer is too large than 7%.
However, the head contact and edge damage are degraded even if good. In Comparative Example 2 in which the thickness of the magnetic layer is further increased and the stiffness T _ST of the magnetic layer and the thickness δ of the magnetic layer are respectively larger than 7% and 0.3 μm, the head contact and the edge damage are only deteriorated. , Electromagnetic conversion characteristics, O / W,
C / N is remarkably deteriorated. Coercive force Hc is 200 A /
In Comparative Example 3, which is too large than m, O / O
The W characteristic is remarkably deteriorated. Saturation magnetic flux density Bm is 35
Comparative Example 4, which is too small than 0 mT, has the following electromagnetic conversion characteristics:
C / N is remarkably deteriorated. Further, in Comparative Example 5 in which the surface roughness SRa was too large than 5 nm, the C / N was significantly deteriorated.

The 5% elongation strength of the medium is too low than 5N, the stiffness contribution T _ST of the magnetic layer is more than 7%, and the Young's modulus Y _{MD in} the length direction of the nonmagnetic support is 150.
0 (kg / mm ² ), and the sum Y of the Young's modulus Y _{MD in} the length direction and the Young's modulus in the width direction of the nonmagnetic support.
_In Comparative Examples 6 and 7 in which _BASE is smaller than 1900 (kg / mm ² ), head contact and edge damage are significantly deteriorated. Examples 1 to 5 in which a polyurethane resin into which Chemical Formulas 1 and 2 are introduced as a binder among the Examples.
Is superior to Example 6 using a commercially available polyurethane resin in terms of head contact and edge damage.

As is clear from Table 1, the edge damage is deteriorated when F5 is smaller than 5N when T _ST
Is too high and the flexibility is inferior, the Young's modulus of the non-magnetic support may be too low, and it is found that by improving these parameters, edge damage is suppressed.

[0028]

As described above, according to the magnetic recording medium of the present invention, the following excellent functions and effects can be exhibited. By setting the 5% elongation strength to 5N or more and the contribution ratio T _ST of the magnetic layer to the stiffness to 7% or less, the electromagnetic conversion characteristics, head contact characteristics, and running durability can be significantly improved. For example, a magnetic recording medium suitable for high-density digital recording with a recording wavelength of 0.5 μm or less can be provided. Further, the Young's modulus of the non-magnetic support is set to 1500 kg / mm ² or more,
By defining the binder, the head contact property and the edge damage property can be improved.

[Brief description of the drawings]

FIG. 1 is a partially enlarged sectional view showing an example of a magnetic recording medium according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic recording medium, 2 ... Non-magnetic support, 3 ... Magnetic layer, 4
... Back coat layer.

Claims (3)

[Claims] 1. A magnetic recording medium comprising: a magnetic layer containing metal magnetic powder containing Fe as a main component provided on one surface of a nonmagnetic support; and a backcoat layer provided on the other surface. The magnetic layer has a saturation magnetic flux density Bm in the longitudinal direction of 350 mT or more, a coercive force Hc in the range of 170 to 200 A / m, a surface roughness SRa of the magnetic layer in a range of 2 to 5 nm, and a thickness δ of the magnetic layer. Is in the range of 0.1 to 0.3 μm and the total thickness D is 7 μm or less, the magnetic recording medium has a 5% elongation strength of 5 N or more, and
The magnetic layer, the nonmagnetic support, the Young's modulus of the backcoat layer, respectively Y _M, Y _MD, and Y _BC, the thickness of the nonmagnetic support [delta] _B, the thickness of the back coat layer [delta] _BC
Wherein the contribution T _st of the magnetic layer to the stiffness represented by the following expression 1 is 7% or less. (Equation 1) 2. The non-magnetic support according to claim 1, wherein the Young's modulus Y _MD is Y
^2. The magnetic recording medium according to claim 1, wherein _MD ≧ 1500 (kg / mm ² ). 3. The magnetic recording medium according to claim 1, wherein the magnetic layer contains a binder having a structural unit represented by Chemical Formula 1 or Chemical Formula 2. Embedded image R1 is any one of an alkyl group, an aralkyl group and a phenyl group. Embedded image R2 is an alkylene group or a phenylene group.