DE19511875A1 - Magnetic recording medium with high recording density - Google Patents

Abstract

A longitudinally oriented magnetic recording medium is described which is insensitive to fluctuations of the gap width of the read/write head, and in which, in the case of square-wave recording, the recording current at a wavelength corresponding to three times the electrical gap width of a reference read/write head is adjusted to the maximum level of the fundamental wave of the square-wave function and this current is used to measure a single pulse whose phase response of the Fourier transform at 2.69 times the wavelength of the reference read/write head deviates less than 15{ from the zero line and whose phase of the Fourier transform at the same wavelength deviates by less than 5{ from the previously obtained value when the head gap width is changed by 10%, the phase responses, in each case in the wavelength range from 2 to 4 times the gap width of the reference read/write head, being evaluated in such a way that their mean slope there is zero.

Description

The invention relates to a substantially longitudinally oriented magnetic Record carrier of very low layer thickness, which insensitive to Variations in the width of the read / write head is.

To address the need for increased recording density for magnetic recording media Recently, the recording wavelength has been steadily reduced Service. For example, the recording wavelength for the 8 mm video system is 0.58 μm. This results in the problem of so-called thickness loss in the signal as This means that the playback level increases as a function of increasing layer thickness not linear, but shows a saturation effect. Thus, for short wavelengths just a very thin layer needed.

To meet this demand, in the last 10 years have been magnetic Drawing support developed in which a binder-free ferromagnetic metal layer was applied in a very low thickness by means of vacuum technology. This metal eva Although porated recording media have a low thickness loss and achieve one very high reproduction level, however, the mass production of such tapes always prepares still great difficulties compared to magnetic recording media, at where the magnetic pigments are dispersed in binders. Also change These ME bands are under the influence of atmospheric oxygen.

The demand for low layer thickness, however, can be lately also by a thin magnetic layer in which the finely divided magnetic particles in a polymeric binder are dispersed and in which this layer on a non-magnetic undercoat is poured.

Such application methods are described, for example, in publications US 2,819,186, US Pat. DE-OS 43 02 516, EP 0 520 155, EP 0566 100 and the German applications Reference P 44 43 896 and file reference P 195 04 930 described.  

High density magnetic recording is becoming prevalent nowadays digitally performed. This means that in contrast to analog video recording no sinusoidal signals are recorded, but the information is transmitted through Switching the direction of the head current of the recording head to the recording Written. One calls the magnetization pattern, which at one of the like switching process arises, magnetization transition. However, this transition occurs not jumpy, but more or less soft, in the form of a Gauss curve. The Playback signal of such a magnetization transition is impulsive, because the inductive reading, which is typically used in the video system, a differential tion is made. Since the magnetization transition as described above, not suddenly, the read pulses have a certain width, which is usually indicated by the PW₅₀ value. This value indicates the distance on the up sign carrier, which lies between the two points at which the current Signal is just 50% of the maximum value as recorded in the figure. It is Clear that high-density recording requires very small pulse widths. simultaneously must ensure the highest possible pulse size to achieve sufficient levels his.

In addition, in recording such pulses, some phase distortion is observed, which is normally reversed in current recording systems. The Applicant has found, however, that the extent of the Phasenver distortions of the gap width g _{w of} the write head depends and that in such a case, such distortions can at least not be completely reversed.

Therefore, the object was a magnetic recording medium of the above to find the generic type mentioned, which as little as possible to scatters of Head gap width responds and in which at the same time a certain constant absolute value of the phase distortion is maintained.

According to the invention the object has been achieved with a recording medium in which in a rectangular recording of the recording current with one of the threefold electrical rule head gap length of a reference read / write head corresponding wavelength is adjusted to maximum level of the fundamental wave of the rectangular function and with this current a single pulse is measured, whose phase characteristic of the Fourier transform differs less than 15 ° from the zero line at the 2.69-fold wavelength g _w of the reference writing / reading head gap and whose Fourier transform phase is at the same wavelength when the head gap length is changed by 10% less than 5 ° differs from the previously obtained value, wherein the phase responses are respectively evaluated in the wavelength range of 2 to 4 times the gap length of the reference read / write head so that their average slope is zero there.

The invention will be explained in more detail below.

An essential parameter of the write head is its electrical head gap width, the is the wavelength at which the read signal becomes zero. So that the recording quality changes as little as possible, the aim is that the media as little as possible Changes in the electric head gap lengths to respond, that is, that the phases distortions from the head gap should be independent. At the same time, a certain Absolute value of the phase distortion can be met, as stated above.

The measured values were now given an experimental setup under the following conditions won for two different video recording heads, namely for V8 and Hi8.

Head-band speed: v = 3.17 m / s
Read / write head A: V8 type, measured gap zero at g _w = 236 nm
Read / write head B: Hi8 type, measured gap zero g _r = 150 nm.

The recording current was adjusted so that in a rectangular recording with the Wavelength λ = 708 nm, the level of the fundamental wave of the square wave signal becomes maximum. The measurement was done with a spectrum analyzer (resolution bandwidth 30 kHz).

A rectangular signal with a frequency of 96 kHz was written on the tape. Subsequently, the signal was read with the read head and with a digitizer sampled. The sampling rate was 5 ns. The sampled signal became a single pulse calculated by averaging the centered read pulses. There were a total of 126 pulses averaged. The average single pulse was only a Fourierrans  undergone formation. An FFT algorithm was used for this. Examples of such Algorithms can be found in standard works on numerical mathematics. As a window radio tion a triangular function ("Parzen window") was used. Of interest was now the Phase response as a function of the frequency that occurs when measuring a single pulse Fourier transform results. From the telecommunications is known that one at a distortion-free system addie a linear with the frequency running phase response can change without changing the information content. The measurements were a derar tiger phase response added, so that at medium frequencies (in the example about 5 MHz) of the Phase transition the slope has zero. This allows a defined comparison of different curves.

The reading point used was f = 5 MHz, which corresponds to the 2.69-fold wavelength of the electrical gap width g _{w of} the reference head (in this example, 236 nm). A comparison head has the gap length 150 nm, which corresponds approximately to 0.64 times the value of the reference head. The measurement with the comparison head was also carried out with the wavelength 708 nm, otherwise this would not correspond to a practical comparison.

For the composition of the magnetic recording medium, preferably best From the magnetic pigment containing layer and an unmagneti In principle, there are no restrictions on the lower class.

It may be known from the prior art magnetic pigments such as iron oxide, Co-doped iron oxides, metal pigments and alloys, chromium dioxide and others be used, as well as the usual polymeric binders or mixtures and Other additives such as dispersing agents, non-magnetic pigments, lubricants, Hardeners, wetting agents and solvents are used.

Candidate constituents of the magnetic as well as the non-magnetic layer are For example, see DE-A 43 02 516.

As a support are known films of polyesters, such as polyethylene terephthalate or Polyethylene naphthalate and polyolefins, cellulose triacetate, polycarbonates, polyamides, Polyimides, polyamidoimides, polysulfones, aramids or aromatic polyamides. The support may be preceded by a corona discharge treatment, a plasma treatment  treatment, a light adhesion treatment, a heat treatment, a Staubentfer treatment or the like. To the goal of the present He The non-magnetic substrate is one with a medium Centerline surface roughness of generally 0.03 μm or less, preferably of 0.02 μm or less, especially 0.01 μm or less. Besides, it is he desires that the wearer not only have such a low centerline surface area Roughness, but also no large protrusions (protrusions) of 1 micron or owns more. The roughness profile of the surface of the carrier may, if desired, be free be controlled (controlled) according to the size and amount of the filler that the Layer support to be added. Examples of suitable fillers are oxides and Carbonates of Ca, Si and Ti as well as organic fine powders of acrylic substances.

The process for producing the magnetic dispersion comprises at least one Ver kneading stage, a dispersion stage and optionally a mixing stage before and after may be provided in the preceding stages. The respective levels can each be composed of two or more stages. In the production of the together All starting materials, namely the ferromagnetic powder, can be used Binder, the carbon black, the abrasive, the antistatic agent, the lubricant and the Solvent, right at the beginning of the process or later during the expiration of Ver be added to the reactor. The individual starting materials can be used in divided into several portions, the process in two or more stages be set. For example, the polyurethane is divided into several portions and in the kneading stage and in the dispersion stage and also in the mixing stage for Ein Adjust the viscosity after dispersion.

In order to achieve the object of the present invention, a known herkömm Liche technology as part of the process for the preparation of the magnet according to the invention be used recording medium. So, for example, in the kneading stage a kneading device having a high kneading force, such as a continuous one Licher kneader or a pressure kneader can be used to an inventive Ma gnet recording medium with a high Br value. If such a conti is used with a kneader kneader or pressure kneader, the ferromagnetic powder with the entire binder, preferably 30 wt .-% or more, kneaded. So be with  For example, 100 parts by weight of a ferromagnetic powder with 15 to 500 parts by weight a binder mixed.

After fine filtration through narrow mesh filters with a width of at most 5 μm the dispersions by means of a conventional coating device with speed applied in the usual range of 100-500 m / min, in the magnetic field in Aufzeich aligned and then dried and a calender treatment and optionally further surface smoothing treatment.

To be substantially longitudinally aligned means that the magnetic particles although essentially oriented in the layer plane in the direction of recording, However, also up to 25 ° can be arranged obliquely oriented to the layer plane.

The coating can be carried out by means of squeegee, knife pourer, Abstreifgießer, Extruder casters, reverse roll coaters or combinations. Both layers can preferably be applied simultaneously in the wet-wet process.

Subsequently, the magnetic recording medium thus obtained is in the usual Use width slit or punched and the usual electro-acoustic and subjected to mechanical tests.

Particularly favorable results are obtained when a very thin magnetic Upper layer, whose layer thickness is less than 1 micron, on a non-magnetic sub layer whose layer thickness may be 1-8 microns, to be poured.

The invention will now be explained in more detail by practical examples and comparative examples, However, without the invention to the specific recipe examples and the device for Her Position of such a magnetic recording medium to limit it.

By means of a device, as in the German application number P 195 04 930 is described in more detail, a magnetic recording medium was made, consisting from a thin magnetic top layer, which faces a non-magnetic underlayer was poured. The two layers are based on the following recipes:

a) Composition of the lower layer parts by weight Vinyl polymer with polar groups 85 Polyurethane with polar groups 85 TiO₂ (55 m² / g BET) 1000 lubricant 25 polyisocyanate 30 Solvents (tetrahydrofuran, dioxane) 2209

The viscosity of this lower layer is 50 mPa · s, the yield point is 18 Pa.

b) composition of the upper layer parts by weight magnetizable metal pigment 1000 α-Al₂O₃ (TG = 0.2 μm) 70 Vinyl polymer with polar groups 77 Polyurethane with polar groups 77 organophosphate 10 lubricant 25 polyisocyanate 22.5 Solvents (tetrahydrofuran, dioxane) 6170

The viscosity of this upper layer is 2.5 mPa · s, the yield point 8 Pa.

The measurement of the viscosity and the flow limits was carried out with a Carri-Med CSL Rheometer in the measuring system cone / plate at a temperature of 25 ° C and the Auswer This happened to Bingham (downhill).  

Table 1

In Table 1, the magnetic and mechanical data are different Magnetic pigments, which are evident from the table, obtained magnetic Record carrier listed. d in μm, the dry film thickness means the upper layer, in the last column is the mean particle length after volume averaging (in Nanometer) of the magnetic particles. The particle size was in Electron microscope at 100 000 magnification measured.

Table 2 below shows the results obtained with the various magnetic recording media with respect to the difference between the phase positions between head B and A and with respect to the phase differences, each based on 10% change in the head gap width g _w or g _r . In addition, a marketed Hi8 recording specific magnetic recording medium called Fuji SDC is listed.

Table 2

Claims (1)

For high-density recording of certain magnetic recording media whose magnetizable particles are oriented substantially longitudinally, and wherein the magnetic recording medium is insensitive to the width of the read / write head, characterized in that the recording current in a rectangular recording has a wavelength corresponding to three times the electric head gap length is matched to maximum level of the fundamental wave of the rectangular radio tion and that while a single pulse is measured, the phase transition of the Fourierransformierten at 2.69 times the wavelength of the reference read / write head deviates less than 15 ° from the zero line and its phase Fourier transforms at the same wavelength as the head gap length changes by 10% less than 5 ° from the previously obtained value, the phase responses each in the wavelength range of 2 to 4 times the gap length of the reference read / write head be evaluated so that their mean slope is zero there.