JPH07105525A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To suppress a noise level by forming a magnetic layer in such a manner that the polarity of the peak value of magnetic interaction between ferromagnetic particles in the orientation direction is made different from the polarity of the peak value of magnetic interaction in the perpendicular direction to the orientation direction. CONSTITUTION:This magnetic recording medium has a magnetic layer essentially comprising ferromagnetic particles formed on a supporting body. The polarity of the peak value (Angstrom Mpmax) of magnetic interaction between ferromagnetic particles in the orientation direction is different from the polarity of the peak value (Angstrom Mvmax) of magnetic interaction in the perpendicular direction. Further, the peak value Mpmax is 0.3-0.7. The ferromagnetic particles essentially consist of barium ferrite particles and d/t of the particle (d) is the average paticle diameter and t is thickness of the particle is specified to 2 to 6. By this method, a medium having excellent noise characteristics and good SFD suitable for high density recording can be obtd.

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 having a magnetic layer provided on a support represented by a magnetic tape.

[0002]

2. Description of the Related Art A magnetic recording medium having a magnetic layer provided on a support is the most effective means for recording a large amount of information in various fields such as an audio recording device, a video recording device or a data recording device. It's being used.

Among them, a magnetic recording medium provided with a magnetic layer mainly composed of ferromagnetic particles is superior in durability and environmental resistance to a magnetic recording medium formed by using a vacuum technique, and also coated. Since it can be mass-produced with manufacturing technology such as this, it can be supplied at a low price, so it is on the market in large numbers.

In order to achieve the demand for higher density recording on these magnetic recording media, it is necessary to improve the linear recording density or the track density. Combination with various servo technologies is used to improve track density, and improvement of ferromagnetic particles that compose a magnetic recording medium, improvement of its volume content, or improvement of magnetic recording medium surface smoothness to improve linear recording density. The reproduction output is being increased by improving it.

[0005]

By the way, in recent years,
With the progress of recording / reproducing technology and the spread of digital recording / reproducing technology, especially in a device for high-density recording,
In addition to high playback output, noise level reduction and excellent S
The securing of FD (Switching Field Distribution) has been required for magnetic recording media.

However, regarding the reduction of the noise level, only the degree of eliminating the agglomeration of the ferromagnetic particles has been studied, and the noise level is still reduced depending on how the magnetic recording medium is constructed. At present, it has not been found whether the SFD is reduced and excellent SFD is secured.

The present invention has been made in view of the above technical problems, and an object thereof is to provide a magnetic recording medium whose noise level is suppressed to a low level and which is optimum for high density recording.

[0008]

According to a first aspect of the present invention, there is provided a magnetic recording medium having a magnetic layer mainly composed of ferromagnetic particles on a support, wherein the ferromagnetic particles are aligned in the orientation direction. The polarity of the peak value (ΔMpmax) of the magnetic interaction of is different from the polarity of the peak value (ΔMvmax) of the magnetic interaction in the direction orthogonal thereto, and the peak value (ΔMpmax)
Mpmax) is 0.3 to 0.7.

The invention described in claim 2 is characterized in that the ferromagnetic particles described in claim 1 are mainly composed of barium ferrite particles. The invention described in claim 3 is characterized in that the ratio (d / t) between the average particle diameter (d) and the plate thickness (t) of the barium ferrite particles according to claim 2 is 2 to 6. It is a thing.

[0010]

The present inventors conducted a sincere study focusing on SFD characteristics and noise characteristics in order to achieve high-density recording of magnetic recording media. The polarity of the peak value (ΔMpmax) of the magnetic interaction is different from the polarity of the peak value (ΔMvmax) of the magnetic interaction in the direction orthogonal thereto, and the peak value (ΔMpma)
It was found that a magnetic recording medium excellent in both SFD characteristics and noise characteristics can be obtained by setting x) to 0.3 to 0.7, and the present invention has been completed.

Magnetic interaction between ferromagnetic particles (ΔM)
Is the value obtained by normalizing the residual magnetization from the state of the medium being saturated with direct current magnetization in a certain direction by the saturated residual magnetization (Mr0).
(H), when the value obtained by normalizing the residual magnetization from the demagnetized state by the saturated residual magnetization (Mr0) is Mr (H), ΔM = Md (H)-{1-2 × Mr (H)} Is required in.

In the present invention, the peak value (ΔMpm) of the magnetic interaction between the ferromagnetic particles in the orientation direction.
ax) is the orientation direction having the largest squareness ratio among the three directions of the longitudinal (X) direction, the width (Y) direction and the vertical (Z) direction with respect to the magnetic layer film surface, and the measurement is made in this direction. It was done. In the case of measuring in the vertical (Z) direction, the measured value is after the demagnetizing field is corrected.

Magnetic interaction between these ferromagnetic particles (Δ
M), IEEE Trans on Magn, vol MAG-26 No.5
In 1990, PI Mayo et al. Again, Journal of Magneti
D. Spel in sm and Magnetic Materials 120 (1993)
Reported by iotis and others.

For example, in a magnetic recording medium in which barium ferrite particles are used and longitudinally oriented, D. Speliotis et al. Shows that the peak value (ΔMpmax) of magnetic interaction in the longitudinal direction, which is the orientation direction, shows a positive polarity. , The peak value of magnetic interaction in the width direction orthogonal to it (ΔMvmax)
Indicates that it exhibits a negative polarity.

As reported in PI Mayo et al. Or D. Speliotis et al., The magnetic interaction between ferromagnetic particles is
Although various magnetic recording media behave differently, according to experiments by the present inventors, the peak value (ΔMpmax) of magnetic interaction between ferromagnetic particles in the orientation direction and the SFD characteristics,
The peak value (ΔMpmax) of the magnetic interaction between the ferromagnetic particles in the orientation direction and the noise characteristics are shown in FIG.
It was found for the first time that they had a completely different relationship as shown in.

The SFD value in FIGS. 1 and 2 is VSM.
(Vibrating Sample Magnetometer: Digital Measureme
M-measured by nt System model 1660)
The demagnetization curve of the H loop was differentiated, and the full width at half maximum of the obtained curve was normalized by the coercive force (Hc). To measure the noise level, use a drum tester to subject the tape to be measured to saturation DC magnetization in the orientation direction, and then re-magnetize the same area in the opposite direction with a current smaller than the saturation recording current, and then reproduce the spectrum. The reproduced signal was measured with an analyzer, and the spectrum was obtained by integrating from 0 to 5 MHz.

By analyzing these experimental data, the conditions for satisfying both the excellent SFD characteristics and the noise characteristics necessary for achieving high density recording are to determine the magnetic interaction between the ferromagnetic particles in the orientation direction. Peak value of (ΔMpma
The inventors of the present invention have found that it can be achieved by controlling x) within the range of 0.3 to 0.7, and have arrived at the present invention.

That is, when the peak value (ΔMpmax) of the magnetic interaction between the ferromagnetic particles in the orientation direction is smaller than 0.3, the SFD characteristic is significantly deteriorated, and therefore, the signal is recorded. The width of the magnetic transition is widened, and the reproduction output, especially the short wavelength output is reduced. On the contrary, the peak value of the magnetic interaction between the ferromagnetic particles in the orientation direction (ΔMpm
If ax) is larger than 0.7, it causes an increase in noise level, and has an optimum value of 0.3 to 0.7.

Particularly preferably, the peak value of the magnetic interaction between the ferromagnetic particles in the orientation direction (ΔMpma
x) should be controlled within the range of 0.4 to 0.6. In addition, the polarity of the peak value (ΔMpmax) of the magnetic interaction between the ferromagnetic particles in the orientation direction is controlled to be different from the polarity of the peak value (ΔMvmax) of the magnetic interaction in the direction orthogonal thereto. This is because the magnetization is stably left in the orientation direction, but the magnetization is hard to remain in the other directions, and the reproduction signal at the time of high-density recording is made higher.

The polarity of the peak value (ΔMpmax) of the magnetic interaction between the ferromagnetic particles in the orientation direction or the polarity of the peak value (ΔMvmax) of the magnetic interaction in the direction orthogonal thereto is used. It depends on the shape of the ferromagnetic particles, and can be controlled by using ferromagnetic particles such as barium ferrite particles having an easy axis of magnetization in a direction substantially perpendicular to the plate surface.

Further, the peak value (ΔMpmax) of the magnetic interaction between the ferromagnetic particles in the orientation direction largely depends on the shape of the ferromagnetic particles, and is greatly influenced by the existing state.

Therefore, the peak value (ΔMpmax) of the magnetic interaction between the ferromagnetic particles in the orientation direction is 0.3 to
In order to control in the range of 0.7, the plate ratio (d / t) is 2 to
It is effective to use barium ferrite particles having a relatively small plate ratio such as 6.

By using barium ferrite particles having a small plate-like ratio, stacking between particles can be suppressed, and thereby it is possible to control the existence state in which an appropriate peak value (ΔMpmax) can be obtained.

However, the plate ratio (d / t) is simply 2
When the barium ferrite particles of ~ 6 are used, the peak value of the magnetic interaction between the ferromagnetic particles in the orientation direction (Δ
Mpmax) is not always controlled within the range of 0.3 to 0.7, and the selection of materials such as binder resin according to the ferromagnetic particles, magnetic properties such as drying temperature, orientation conditions and calendar conditions. The setting of recording medium creation conditions is also important.

In any case, the material or processing conditions should be controlled so that the peak value (ΔMpmax) of the magnetic interaction between the ferromagnetic particles in the orientation direction is controlled within the range of 0.3 to 0.7. Selection is necessary.

Examples of barium ferrite particles suitable for the present invention include M type, W type, and solid solutions or ion-substituted products thereof. The barium ferrite particles, for example, the following general formula _{AO · n (Fe 12-p} M p O 18-) ( however, A is at least one metal element selected from the group consisting of Ba, Sr, Pb and Ca And M is 2
To at least one metal element selected from hexavalent metal elements, P is a substitution amount per chemical formula and is a number of 0 or more,
n is 0.7 to 4, and α is a number of 0 or more).

Further, more preferably, a part of Fe atom is replaced by a specific metal element, for example, the following general formula AO.n (Fe _{12 -XYZ} Co _X M (I) _Y M (II) _Z O
_18- ) (wherein A represents at least one element selected from Ba, Sr, Pb and Ca, and M (I) represents Zn, Ni
M (II) is at least one metal element selected from tetravalent to hexavalent metal elements, X, Y, and Z are Co, M (I), and M (, respectively). The substitution amount per one chemical formula of II), n is 0.7 to 4, and α is a number of 0 or more) is preferable.

In this case, the substitution amount X per chemical formula is 0.
By setting the above to 0.7 or less and Y to 0.5 or more and 2.0 or less, the change of the coercive force (Hc) with respect to temperature is reduced. Furthermore, when a part of the Fe atoms is replaced with the Co atoms, the saturation magnetization (σs) is not significantly reduced as compared with the case where a part of the Fe atoms is not replaced with the Co atoms, and the temperature coefficient (δHc Is particularly preferable because it can be easily controlled.

As the tetravalent metal element, Ti, Zr,
Hf, Sn, etc. are Nb, Sb,
Examples of hexavalent metal elements such as Ta and V include W and Mo.

If the coercive force (Hc) of the barium ferrite particles is less than 200 (Oe), the residual recording signal on the magnetic recording medium is likely to be insufficient, and 300
When it exceeds 0 (Oe), the signal is written by the magnetic head.
200 to 3000 because it tends to be difficult to erase
(Oe) is preferred.

Further, such barium ferrite particles can be produced by a known method such as a glass crystallization method, a hydrothermal synthesis method or a coprecipitation method. Further, the average particle size of such barium ferrite particles is 0.02 to
It is preferably 0.2 μm. Average particle size is 0.02
If it is less than μm, saturation magnetization (σs) and coercive force (Hc)
Becomes smaller, the reproduction output of the magnetic recording medium tends to decrease,
On the other hand, if it exceeds 0.2 μm, noise tends to be remarkably generated during reproduction in high density recording.

[0032]

The magnetic recording medium of the present invention will be described below with reference to specific examples and comparative examples. [Specific Example 1] (Coating composition) Co-substituted Ba-ferrite magnetic powder (average particle size 45 nm, plate ratio 3.2, coercive force 1350 Oe) 100 parts by weight metal sulfonate-containing polyurethane 8 〃 (average molecular weight 25,000) vinyl chloride -Vinyl acetate copolymer 4 〃 (average molecular weight 25,000) Aluminum oxide 5 〃 Lubricant 1 〃 Dispersant (lecithin) 1 〃 Methyl ethyl ketone 45 〃 Toluene 45 〃 Cyclohexanone 45 〃 Stir the above magnetic coating composition components Then, the magnetic powder is sufficiently dispersed, 4 parts by weight of isocyanate is added to adjust the magnetic paint, and then this magnetic paint is applied on the surface of the base film having a thickness of 9 μm by using a reverse coater, and magnetic poles of the same polarity are obtained. Are dried while applying a longitudinal alignment magnetic field of 4 K gauss by an alignment treatment device arranged opposite to each other, and calendered at a linear pressure of 300 Kg and a temperature of 80 ° C. Forming a magnetic layer of 2 [mu] m, and a magnetic recording medium by curing in a thermostat at temperature 60 ° C.. [Comparative Example 1] Ferromagnetic particles having an average particle diameter of 50 nm,
A magnetic recording medium was prepared in the same manner as in Example 1 except that Co-substituted Ba-ferrite particles having a plate ratio of 7 and a coercive force of 1220 (Oe) were used. [Comparative Example 2] A magnetic recording medium was prepared in the same manner as in Example 1 except that the alignment treatment was not performed. [Comparative Example 3] Ferromagnetic particles having an average particle length of 0.1 μm
A magnetic recording medium was prepared in the same manner as in Example 1 except that metal particles having m, an axial ratio of 7, and a coercive force of 1400 (Oe) were used.

Orientation direction of the obtained various magnetic recording media, polarity and peak value (ΔMpmax) of magnetic interaction between ferromagnetic particles in the orientation direction, and polarity and peak of magnetic interaction in the direction orthogonal thereto. Value (ΔMvm
ax), SFD, reproduction output ratio (EP) and noise level were measured, and the results are shown in Table 1.

Orientation direction, peak value (ΔMpmax),
(ΔMvmax) and SFD are measured by VSM (Vibrat
ing Sample Magnetometer: Digital Measurement Syst
The model 1660 manufactured by em was used.

Regarding the reproduction output ratio, a drum tester equipped with a magnetic head having an 8 mm VTR MIG head having a gap length of 0.3 μm was used to record a digital signal having a recording wavelength of 0.54 μm at the optimum current of each magnetic recording medium. From the reproduction output at that time, the noise level was saturated with direct current magnetization of each magnetic recording medium in the orientation direction, and the same area was directly reverse-current magnetized with a current smaller than the saturated recording current in the opposite direction.
Play back, measure the playback signal with a spectrum analyzer,
It was determined by integrating the spectrum from 0 to 5 MHz.

[0036]

[Table 1]

It can be understood from Table 1 that the magnetic recording medium of the specific example satisfies both the SFD and the noise level as compared with the magnetic recording medium of each comparative example.
In the magnetic recording medium of the above specific example, only the magnetic recording medium composed of a single magnetic layer has been described, but the present invention is not limited to this, and it is composed of a plurality of magnetic layers. It may be a magnetic recording medium, and in such a case, the constitution of the outermost magnetic layer may be adjusted so as to be controlled within the scope of the present invention.

[0038]

As described above, according to the present invention, it is possible to provide a magnetic recording medium having excellent noise characteristics and good SFD, which is optimum for high density recording. Since the present invention is excellent in both noise characteristics and SFD characteristics, it is most suitable for a magnetic recording medium for digital recording / reproduction.

[Brief description of drawings]

FIG. 1 is a graph showing the dependence of SFD on magnetic interaction (ΔMpmax), with the vertical axis representing SFD and the horizontal axis representing magnetic interaction (ΔMpmax) in the orientation direction.

FIG. 2 is a diagram showing the magnetic interaction (ΔMpmax) dependency of the noise level, with the vertical axis representing the noise level and the horizontal axis representing the magnetic interaction (ΔMpmax) in the orientation direction.

Claims (3)

[Claims] 1. In a magnetic recording medium having a magnetic layer mainly composed of ferromagnetic particles on a support, the polarity of the peak value (ΔMpmax) of magnetic interaction between the ferromagnetic particles in the orientation direction is A magnetic recording medium characterized in that the peak value (ΔMpmax) is different from the polarity of the peak value (ΔMvmax) of the magnetic interaction in the direction orthogonal thereto and the peak value (ΔMpmax) is 0.3 to 0.7. 2. A magnetic recording medium, wherein the ferromagnetic particles according to claim 1 are mainly composed of barium ferrite particles. 3. The barium ferrite particles according to claim 2, wherein the ratio (d / t) between the average particle diameter (d) and the plate thickness (t) is 2.
A magnetic recording medium characterized in that