JPH0927111A - Magnetic recording medium with high packing density - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a recording medium having a high recording density by executing square wave recording in such a manner that the single phase deviating less than 5 deg. from the numerical value at which the phase of Fourier transform at the same wavelength is previously obtd. is measured in the case the square wave recording is executed. SOLUTION: The square wave signals having a frequency of 96kHz are recorded on a tape. These signals are then scanned by a digitizer read by a reading head. The pulses are obtd. by averaging the read pulses at the center. The average values of the 126 pulses in total number is obtd. In such a case, the phase response is (for example, about 5MHz) inclination 0 at the average frequency. The distinct comparison of different curves is thereby made possible.

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 which has an extremely small layer thickness and is insensitive to variations in the width of a read / write head, and is basically oriented in the longitudinal direction.

Recently, recording wavelengths have been consistently reduced to meet the increasing demands on recording density of magnetic recording media. For example, the recording wavelength for an 8 mm video device is 0.58 μm. This causes the problem of thickness reduction in recording and playback of signals. That is,
The playback level does not increase linearly as a function of increasing layer thickness, indicating a saturation effect. Thus, only very thin layers are required for short wavelengths.

In order to meet this demand, a magnetic recording medium in which a ferromagnetic metal layer having no binder is used in a very small thickness by using a vacuum method has been developed in the past 10 years. Although these metal-deposited recording media provide a slight reduction in thickness and achieve extremely high recording and playback levels, mass production of tapes of this type shows that magnetic pigments are dispersed in the binder. In comparison with the magnetic recording media
Still, it poses considerable difficulties. On the contrary, these metallized tapes are transformed under the influence of atmospheric oxygen.

[0004]

However, recently it has become possible to meet the demand for thin layer thicknesses by means of a thin magnetic layer in which finely divided magnetic particles are dispersed in a polymeric binder. This layer is provided on the non-magnetic base layer.

Such a method of use is described, for example, in US Pat. No. 2819186, German Patent Application Publication No. 43.
02516, EP 0520155, EP 0566100 and German patent application 444.
3896 and 19504930.

Magnetic recording having a high recording density is now predominantly performed by a digital method. This means that, in contrast to analog video recording, the sinusoidal signal is not recorded, but instead the information is recorded on the recording medium by switching the direction of the current in the recording head. The pattern of magnetization created in such a switching process is called a magnetization transition. However, this transition does not occur rapidly, more or less,
It occurs gradually, for example in the form of a Gaussian curve. The recording / reproducing signal of such a magnetic transition is pulse-like because the inductive reading used as a characteristic of a video system is based on differentiation. Since the above-mentioned magnetization transition does not occur suddenly, the read pulse has a constant width which is usually defined by the value of PW ₅₀ . This numerical value indicates the distance between two points on the recording medium when the actual signal takes exactly 50% of the maximum numerical value as shown in the drawing. Clearly, high density recording requires a very small pulse width. At the same time, a very large pulse amount must be ensured in order to achieve a sufficient output level.

Furthermore, some phase distortion, which is eliminated in conventional recording schemes, is observed in recording such pulses. However, Applicants have found that the degree of phase distortion depends on the gap width g _w of the recording head, and in such cases this type of distortion cannot be eliminated at least completely.

[0008]

The object of the invention is to exhibit a very slight reaction to head gap variations, while at the same time maintaining a certain constant absolute value of the phase distortion. It is to provide a recording medium of the general type described at the beginning.

[0009]

According to the present invention, when square wave recording is performed, the recording current has a maximum level of the fundamental wave of the square wave function at a wavelength corresponding to three times the electric head gap width. And the phase response of the Fourier transform at a wavelength of 2.69 times that of the reference read / write head deviates less than 15 ° from the zero line,
And when the head gap width is changed by 10%,
The phase of the Fourier transform at the same wavelength is deviated by less than 5 ° from the previously obtained number, a single phase is measured, and the phase response is twice the gap width of the reference read / write head. Is solved in each case in the wavelength range from 1 to 3 times, in such a way that its mean slope there is zero.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described below with reference to examples.

An important parameter of the recording head is its head gap width, that is, the wavelength at which the read signal becomes zero. In order to ensure that the change in recording quality is as small as possible, it is desirable that the response of the medium to the change in electric head gap width is as small as possible. That is, the phase distortion should be independent of the head gap. At the same time, as mentioned above, some absolute value of the phase distortion must be maintained.

The measured values are, among other things, two video recording heads, a V8 type and an H type, under the following conditions:
It was obtained using the experimental setup for type i8. Relative head / tape speed: v = 3.17 m / s Write / read head A: V8 type, measured gap zero point g _w = 236 nm Write / read head B: Hi8 type, measured gap zero. Position gr = 150nm The recording current has a wavelength of λ at the fundamental wave level of the square wave signal.
= 708 nm was tuned to be the maximum in square wave recording. The measurement is performed by a spectroscopic analyzer (resolution bandwidth:
30 kHz).

A square wave signal having a frequency of 96 kHz was recorded on the tape. This signal was then read by the read head and scanned by the digitizer. The scanning speed was 5 ns. A single pulse was calculated from the scanned signal. This pulse is obtained by averaging the central read pulse. In total, 126 pulses were averaged. The averaged single pulse was then subjected to a Fourier transform. The FFT algorithm was used for this purpose. Such algorithms are as found in standard books on numerical mathematics. The trigonometric function (Parzen window) was used as the window function. The phase response as a function of frequency obtained in the single pulse measurement after the Fourier transform was of interest. It is also known from the communication art that, in the case of a distortion-free system, it is possible to sum the phase response which varies linearly with frequency without changing the information content. In the measurement, such phase responses were summed so that the phase response has zero slope at the average frequency (about 5 MHz in the example). This allows a clear comparison of different curves.

The reading point used was f = 5 MHz, which corresponds to 2.69 times the wavelength of the electrical gap g _w of the reference head (236 nm in this example). The comparative head has a gap width of 150 nm, which corresponds to about 0.64 times the numerical value of the reference head. The measurement with the reference head was likewise carried out at a wavelength of 708 nm, since otherwise it would not actually fit.

In principle, there is no restriction on the composition of the magnetic recording medium, but it is desirable that the composition comprises a layer containing a magnetic pigment and a non-magnetic base layer.

Iron oxides, iron oxides with Co additions, metallic pigments and metal alloys, chromium dioxide and other prior art magnetic pigments can also be used, which are conventional polymeric binders or binders. The same applies to the mixture and other additives such as dispersants, non-magnetic pigments, lubricants, curing agents, wetting agents and solvents.

Suitable components of the magnetic and non-magnetic layers are described, for example, in DE-A-4302516.

Known materials such as polyethylene terephthalate or polyethylene naphthalate, and polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamide imide, polysulfone, aramid or aromatic polyamide are known. Polyester is used as the base layer. The base layer was previously corona discharge treated,
Plasma treatment, light adhesion treatment, heat treatment, dust removal treatment, etc. can be performed. To achieve the objects of the invention, the non-magnetic underlayer is generally 0.03 μm or less, preferably 0.02 μm or less, especially 0.01 μm.
Or having a center line average surface roughness of less than that. Therefore, it is desirable that the base layer not only have a slight centerline average surface roughness, but also not have large protrusions of 1 μm or more. The surface roughness profile of the base layer can be freely controlled, if necessary, by the size and amount of the filler added to the base layer. Examples of suitable fillers are oxides and carbonates of Ca, Si and Ti, and organic fines of acrylics.

The process for preparing the magnetic dispersion is
It is composed of at least one kneading stage, one dispersing stage, and one further mixing stage which can be installed before or after each preceding stage as required. The individual stages can each have two or more stages. In preparing the ingredients, all starting materials, i.e.,
Ferromagnetic powders, binders, carbon black, abrasives, antistatic agents, lubricants and solvents can be added to the reactor immediately at the beginning of the process or in the course of subsequent processes. The individual starting materials can be divided into parts in stages that are added in two or three stages to the process. For example, polyurethane is divided into a plurality of parts and added in a kneading step and a dispersing step, and also in a mixing step for adjusting viscosity after dispersion.

In order to achieve the object of the invention, the known techniques of the prior art can also be used as part of the process for the production of this new magnetic recording medium. For example, a kneading device having a high kneading capacity, such as a continuous kneader or a pressure kneader, can also be used in the kneading step to obtain a novel magnetic recording medium having a high Br value. When such a continuous kneader or pressure kneader is used, it is desirable that the ferromagnetic powder be kneaded with the entire binder, preferably 30% by weight or more. For example, the ferromagnetic powder 100 is kneaded with 15 to 500 binders by weight.

After microfiltration with a narrow mesh filter having a mesh size of less than 5 μm, the dispersion is usually 10
Processed by a conventional coating machine at a speed of 0-500 m / min, oriented essentially in the longitudinal recording direction in a magnetic field, then dried and calendered, If necessary, surface smoothing treatment is further performed.

Oriented in the recording direction means that the magnetic particles are basically oriented in the recording direction in the plane of the layer, but oriented with a tilt of up to 25 ° with respect to the layer plane. It is also meant to mean being.

The coating can be carried out by a doctor blade coating machine, a knife type coating machine, a doctor, an extrusion coating machine, a reverse roll coating machine, or a combination thereof.
The two layers are preferably applied simultaneously in the wet-on-application form.

The magnetic recording medium thus obtained is
It is then longitudinally cut, stamped to its normal working width and subjected to conventional electroacoustic and mechanical testing.

Particularly advantageous results are obtained when a very thin upper magnetic layer having a thickness of 1 μm or less is applied to a nonmagnetic base layer having a thickness of 1-8 μm.

Although the present invention is described in connection with the examples and comparative examples, the present invention is not limited to any particular formulation and apparatus for the production of such magnetic recording media.

A magnetic recording medium comprising a thin magnetic upper layer coated on a non-magnetic base layer is described in German Patent Application No. 19504.
Produced by the apparatus described in more detail in No. 930. The two layers are based on the following formulation.

A) Composition of lower layer Weight ratio Vinyl polymer having polar group 85 Polyurethane having polar group 85 TiO ₂ (55 m ² / g BET) 1000 Lubricant 25 Polyisocyanate 30 Solvent (tetrahydrofuran, dioxane) 2209

The viscosity of this lower layer is 50 mPa.s. s and the fluidity limit is 18 Pa.

B) Composition of upper layer Weight ratio Magnetizable metal pigment 1000 α-Al ₂ O ₃ (particle size = 0.2 μm) 70 Vinyl polymer having polar groups 77 Polyurethane 77 having polar groups 77 Phosphate ester 10 Lubricant 25 Polyisocyanate 22.5 Solvent (tetrahydrofuran, dioxane) 6170

The viscosity of this upper layer is 8 mPa.s. s,
The fluidity limit is 2.5 Pa.

Carri-Med CSL rheometer (Carri-Med CSL)
Rheometer) and a plate-and-cone measuring device 25
It was carried out at a temperature of ° C and evaluated according to Bingham (down curve).

[0033]

[Table 1]

Table 1 shows the magnetic and mechanical data of the magnetic recording media obtained by using the different magnetic pigments shown in the table. d in μm unit is the dry layer thickness of the upper layer, and the average particle length (nanometer unit) of the magnetic particles after volume averaging is displayed in the last column. The particle size is
It was measured with an electron microscope having a magnifying power of 100,000 times.

Table 2 below shows various information regarding the difference in the phase position between the head A and the head B and the difference in the phase position when the head gap width g _w or gr changes by 10% in each case. It shows the results obtained with various magnetic recording media. Marketed under the name of Fuji SDC, and Hi-8
The magnetic recording media intended for recording by mold are also included in the table for comparison.

[0036]

[Table 2]

[Brief description of drawings]

FIG. 1 shows a read pulse, indicated by the numerical value PW ₅₀ .

[Procedure amendment]

[Submission date] June 24, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

[0009]

According to the present invention, when square wave recording is performed, the recording current has a maximum level of the fundamental wave of the square wave function at a wavelength corresponding to three times the electric head gap width. And the phase response of the Fourier transform at a wavelength of 2.69 times that of the reference read / write head deviates less than 15 ° from the zero line,
And when the head gap width is changed by 10%,
The phase of the Fourier transform at the same wavelength is deviated by less than 5 ° from the previously obtained number, a single phase is measured, and the phase response is twice the gap width of the reference read / write head. To 4 times the wavelength range in each case solved by a recording medium which is evaluated in such a way that its mean slope there is zero.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Werner, Lenz Germany, 67098, Bert, Dürkheim, Heinrich-Bermann-Strasse, 14 (72) Inventor Ronald, John, Bich Germany, 67133, Maxdorf, Karl-Schumann- Ring, 18

Claims (1)

[Claims] 1. A magnetic recording medium is insensitive to the width of a read / write head, and when performing square wave recording, the recording current has a square wave function at a wavelength corresponding to three times the electric head gap width. Adjusted to the maximum level of the fundamental wave,
Moreover, the phase response of the Fourier transform at the wavelength of 2.69 times that of the reference read / write head is 1 from the zero line.
When deviating less than 5 ° and also when the head gap width is changed by 10%, the phase of the Fourier transform at the same wavelength deviates less than 5 ° from the previously obtained value. A single phase is measured and the phase response is between 2 and 3 times the reference read / write head gap width.
For high density recording, evaluated in such a way that the average tilt is zero in each case in the double wavelength range,
And a magnetic recording medium in which magnetizable particles present in the magnetic layer are basically oriented in the vertical direction.