DE2606418A1 - PROCESS FOR PRODUCING MAGNETIC RECORDING MEDIA WITH WEAR-RESISTANT SURFACE - Google Patents

Description

BASF Aktiengesellschaft

Our reference: OZ 31 860 Sob / Gl 6700 Ludwigshafen, February 17th, 1976

Process for the production of magnetic recording media with a wear-resistant surface

The invention relates to a method for producing wear-resistant magnetic recording media with a dimensionally stable carrier, a ferromagnetic one firmly bonded to it Metal thin layer, and a thin protective layer applied thereon.

Magnetic recording media containing a cobalt-containing ferromagnetic Have a thin metal layer on a dimensionally stable carrier, e.g. a non-magnetic metal plate, have been known for a long time. Such recording media can be used in various magnetic recording systems and have found particular interest in electronic data recording. One of the problems of the However, the use of magnetic metal thin-film storage devices lies in their sensitivity to corrosion and mechanical damage.

It has therefore already been proposed to protect the ferromagnetic thin metal layer against corrosion and damage by applying a protective layer. DT-PS 1 297 427 describes the protection of surfaces of cobalt-containing ferromagnetic metal thin layers by producing a continuous protective layer consisting _{of Co-O 11.} According to US-PS 3,533,166 and DT-OS 2250460 the metallic magnetic layer is formed an oxide layer and stabilized by a subsequent heat treatment at 300 ⁰ C to 48O ° C in a similar manner on the surface. The magnetogram carriers protected in this way show a longer service life than untreated magnetogram carriers of the same type, but they do not meet the high requirements in practical use of the magnetic disks.

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In particular, if the magnetic head is in constant contact with the magnetic layer, local scratch marks become visible after some time, which quickly spread over the entire recording area. It is also known from DT-AS 1 282 08 ¹ J to give the surfaces of thin ferromagnetic metal layers an improved resistance to abrasion and other damage by applying a thin layer of natural or synthetic waxes. However, since waxes adhere poorly to metal layers, an intermediate layer of a polymer is first applied to them, which on the one hand has good adhesion to the metal layer and on the other hand is intended to be an adsorptive substrate for the wax sliding layer. The combination of oxidation of the metallic surface with aqueous solutions of oxidizing acids with the heat treatment of the resulting oxide layer and the application of substances which form a lubricating film is also known (DT-AS 1 965 482, DT-OS 2 135 899). Although it results' magnetogram carriers with an improved sliding behavior, they do not have the necessary resistance to withstand repeated landings of the flying magnetic heads and repeated head edge contacts at the usual rotational speeds of the disks of 1500 to 36ΟΟ rpm without mechanical damage. After a while, local damage occurs to the thin metal layer, which is usually the starting point for a total destruction of the magnetogram carrier. It is also known to coat magnetogram carriers with thin magnetic metal layers with a thin layer of rhodium, but these magnetogram carriers were not yet sufficiently resistant to mechanical damage either. Finally, from US Pat. No. 3,498,837 it is also known to coat recording media with ferromagnetic thin metal layers in a vacuum with a vapor-deposited chromium-chromium oxide layer. However, the process is complex and often does not achieve satisfactory results.

The object of the invention was to provide a method for producing magnetic recording media, the ferromagnetic metal layer with a thin, but equally

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moderate, mechanically stable and wear-resistant protective layer is provided. The production of the protective layer should also be possible at the lowest possible temperatures, so none Damage or even change to the recording medium occurs. Furthermore, the process should be simple and economical be.

It has now been found that the object is achieved in that the thin metal layer is anodically oxidized in an electrically conductive solution and subjected to ^{a heat treatment at 150 to 300 ° C. after washing and drying.}

All customary supports for magnetic thin metal layers which are largely dimensionally stable ^{at temperatures of up to 300 ° C. are suitable as thermally stable supports.} May be are preferably plates or discs made of aluminum or aluminum alloys in the conventional starches, which are also pretreated, for _o example, with a chemically or electrolytically deposited copper layer provided. These intermediate layers expediently have an electrical conductivity greater than 0.1 S / cm. Carrier materials made from other metals and plastics, such as copper or polyethylene terephthalate foils, can also be used. In this case, adhesion-promoting layers are mostly used between the carrier and the magnetic layer.

The usual ferromagnetic thin metal layers are used with layer thicknesses of about 600 to 6OOO S in question, which in an known way by chemical deposition, galvanic deposition or by vapor deposition, i.e. deposition of the metals or metal alloys can be deposited from the gas phase in a high vacuum on optionally pretreated supports. Preferred chemical and galvanic deposition is used here.

Suitable cobalt-containing ferromagnetic metal thin layers are mainly cobalt-phosphorus, cobalt-boron and cobalt-nickel, cobalt-nickel-iron, cobalt-iron and phosphorus, boron and / or

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Nitrogen-containing alloys of the type mentioned, e.g. alloys of about 90 to 98 % cobalt and 2 to 10 % phosphorus, about 30 to 20 % nickel and 70 to ÖO % cobalt, about 90 % cobalt, 9 % nickel and 1 % phosphorus, about bö % cobalt, 9 % nickel and 3 % boron or about 40 to 50 % cobalt, 40 to 50 % nickel and 1 to 5 % boron. 6 to produce thickness with, for example, a coercive force of 300 to 900 Oe and a magnetization 4ττΐ of 10,000

up to 15,000 gauss.

A ferromagnetic metal layer which is particularly preferred in the context of the invention consists of 90 to 98.5 % cobalt and 1.5 to 10 % phosphorus and was deposited onto a carrier in a thickness of 0.0 to 0.5 μm by galvanic or electroless deposition Applied from copper-plated aluminum alloy.

According to the method of the invention, the magnetic recording medium, produced from the carrier material described, an intermediate layer optionally located thereon and the as stated, applied ferromagnetic metallic layer, anodically oxidized in an electrolyte solution. This can happen after the chemically or galvanically deposited magnetic layer has already been washed and dried. Particularly However, it is expedient if the recording medium is immersed in the electrolyte immediately after the deposition of the magnetic layer is introduced. In this way, the layer surfaces are constantly wetted with liquid, so that, for example, contamination is largely avoided by dirt particles.

The treatment according to the invention is expediently carried out by means of a device that allows a movement e.g. rotating, the recording medium in the electrolyte with simultaneous switching as Anode allowed. The treatment can be potentiostatic or done galvanostatically.

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The arrangement of the electrodes in the electrolytic cell can be vertical or horizontal. There is a simple arrangement in that the walls of the cell can be connected as cathodes at the same time, provided they are made of the appropriate material are made. Cathodes are attached to both sides of the workpiece to be oxidized and should be approximately the size of the Have anode to ensure an even current distribution. A preferred embodiment of the cell is that the disk to be coated is allowed to rotate through a U-shaped cathode in the form of a ribbon. This is a particularly easy one Replacing the anode guaranteed.

In addition to iron, steel, nickel, zinc, graphite and noble metals _{, Z 0} B _{0 are} suitable as cathode materials. Electrodes that have a high hydrogen overvoltage, such as, for example, have proven to be advantageous. Lead, cadmium, amalgamated lead, zinc, steel, iron and mercury, in order to avoid or greatly reduce the occurrence of hydrogen during the electrolytic treatment of magnetic recording media.

The duration of the power supply can be very different. Depending on the current strength used, both fractions of a second or fractions of a second or periods of a few minutes may be appropriate. Has been found to be particularly advantageous in the context of the invention

a current density of 1-6 mA / cm revealed an anodic oxidation of 15 seconds to 2 minutes.

As a rule, direct current of constant current strength will be used, which can also be superimposed by a stream of animals »The superimposed alternating current can have the characteristic of a Have a sine as well as a triangle or square function. Frequency and amplitude are depending on the desired layer thickness and properties freely selectable. Pure alternating current can also be used if the cathodic current components are smaller than the anodic. Various functions can also be used here, as with superimposed alternating current.

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The electrolyte solution is expediently moved during the production of the recording media according to the invention. This can e.g. can be achieved by stirring, pumping the electrolyte, rotating the substrates or blowing gases through. Come as gases inert gases such as nitrogen, noble gases, air or other gas mixtures can be considered. The presence of dissolved oxygen in the electrolyte can e.g. be advantageous to achieve a thin oxide layer on the pilm surface.

In the context of the invention, an electrolyte solution is to be understood as an electrically conductive solution whose specific conductivity is greater than approximately * -iq ^o q = 0.01 [/ 2. ~ cm ~ J should be. Aqueous solutions are preferred. Salts, acids, bases or mixtures thereof are used to prepare the aqueous electrolyte solutions. The dissolved substances and ions should be largely electrochemically stable under the chosen process conditions.

Preferred salts are sulfates, phosphates, borates, fluorides, halides, perchlorates, silicates and hexafluorosilicates, acetates, Carbonates and Tetrafluoroborates »

The cations belonging to the salts should not be separable from aqueous solution under the chosen conditions. Examples are alkali cations, ammonium or magnesium ions. In addition to the Electrochemical stability of the ions in the electrolyte must also be based on sufficient solubility to achieve the required electrical conductivity must be respected. Depending on the type of electrolyte solution, the method of the invention is carried out in neutral, acidic or alkaline medium. If a pH value that deviates from the neutral point is selected, the selection must be made the acids and bases care must be taken that undesired metal or oxide dissolution in the acidic range or precipitation of hydroxides in the alkaline range should be avoided.

If a change in pH occurs in divided cells during anodic oxidation, it may be useful prove to use buffer systems. Such buffer systems are

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however, it is generally particularly advantageous because it makes the anodic Treatment of the magnetic recording media takes place under constant conditions and, in particular, reproducibly. As buffer solutions the known, usually borate and phosphate buffers can be used. In some cases, in particular in the basic range, the additional use of the usual complexing agents can be useful to prevent precipitation of Avoid hydroxides or basic salts. The chemical or galvanic deposition agents are used as complexing agents well-known compounds such as citrate, tartrate, etc. in question.

Organic solutions of sufficient conductivity can also be used. Organic solvents which cannot be oxidized or reduced under the electrolysis conditions used are preferred. Mixtures of organic solvents and water can also be used. Solvents are preferably used which absorb electrolyte salts in sufficient concentration, such as alcohols, for example, in order to ensure sufficient conductivity. Electrolyte salts that can be used are above all those with anions and cations that are stable under electrolysis conditions, such as N (CH-,) u CH ^ SO _1. , NCCH-zJ-zH-p-toluenesulfonate or N (C ₂ H ₁ -) ^ - p- Toluenesulfonate are used.

The temperature of the electrolyte solution is expediently 20 to 2 ° C. Electrolytes with temperatures above their solidification point and below their boiling point can be used. However, temperatures that are too high can be unfavorable, for example because of increasing solvent losses. Likewise, in some cases poorer results are obtained at elevated temperatures. In aqueous systems should therefore the working temperature below about 70 ⁰ C, and in particular be below about 5O ⁰ C. The passivation can also take place in used deposition baths, for example depleted in reducing agents.

After the anodic treatment, the magnetic recording medium becomes washed with water and organic solvent and dried.

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In the further course of the method according to the invention, the magnetic recording medium which is anodically oxidized on the surface is now used subjected to a heat treatment. Depending on the thickness of the protective layer forming the wear-resistant surface and the Thermal properties of the carrier material are the temperatures of the heat treatment at 150 to 300 ° C, preferably at 170 to 280 ° C. The duration of the heat treatment is dependent to choose from protective layer thickness and temperature and takes 5 minutes to 15 hours, usually 10 minutes to about 8 hours. The temperature and duration are expediently chosen so that the thickness of the protective layer is 0.01 to 0.2. is preferably 0.01 to 0.1 µm. The heat treatment in the context of the production of the magnetic recording medium according to the invention can be carried out both in inert gases and in an oxygen-containing atmosphere.

According to the method according to the invention, surprisingly an extremely uniform oxide layer on the ferromagnetic Film surface generated. The reaction behavior, which is uniform over the entire surface, can already be seen visually on the uniform colorations of the oxidized layer surfaces, which can, for example, have a yellowish or blue appearance. At the same time, in addition to an extremely good adhesive strength between the magnetic layer and the applied protective layer, a excellent wear resistance of the surfaces achieved.

The invention is explained in more detail using the following examples, The magnetic values, coercive force H in fkA / ml

_ r -ι C L J

and saturation _{flow J> m} / b in InWb / ml, measured at a field strength of 160 kA / m. To determine the wear resistance, the plates are mounted on a turntable. The wear load is generated by a spherically ground grinding body made from conventional magnetic head materials, which slides on the plate surface under suitable pressure conditions. A vibration transmitter is mounted on the grinding wheel, the signal of which is recorded on a laboratory recorder as a function of time after suitable amplification. With undamaged

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The plate surface is caused by the friction between the plate surface and the specimen surface of the specimen in Displaced vibrations that are detected by the vibration transmitter. The amplitude of these oscillations reacts very sensitively to disturbances in the frictional behavior and increases when the Plate surface strongly due to wear. This is the time from the beginning of the wear and tear to the occurrence of the sudden increase in the oscillation amplitude a measure of the Stability of the surface.

example 1

One on both sides with an approximately 0.4 µm thick cobalt-phosphorus alloy coated copper foil with a surface on both sides

2 ~ * i

of 18 cm is placed in a glass vessel with a volume of 250 cm between

two platinum cathodes fixed at a distance of 3 cm. The film coated with Co / P is connected as an anode. The electrolyte is 1 molar aqueous NapSO ^ solution, which has been adjusted to a pH of 5 _{by adding H 2} SO _1+. At 22 ^° C., the film is anodically loaded for 6 seconds while the potential is kept constant. The given potential is U =

1000 mV. Related to a saturated calomel reference electrode. It

2 shows an average current density of 72 mA / cm. a. The current curve during the electrolysis time corresponds approximately to a square pulse. The converted amount of electricity results

accordingly with 432 mAsec / cm. After the anodic treatment the film is rinsed with water and alcohol and air-dried at room temperature. The electrochemical applied Oxide layer has a black-gray color and is very even. Type and results of the heat treatment of the so anodized metallic magnetic layers are shown in Table 1.

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Table 1

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Sample type of treatment

[kA / mJ [nWb / m]

Color after tempering

Blank sample without anodic treatment; 30 minutes at 240 ° C under nitrogen

390 shiny metallic

B treated anodically. 30 minutes at 240 ^° C. under nitrogen

37, B 368

evenly brown

anodized, 30 minutes in air at 240 ° C

41.5 294

evenly brown

Example 2

A 1 molar aqueous sodium acetate solution is poured into the arrangement described in Example 1 as the electrolyte. A Co / P-coated copper foil as in Example 1 is used for the electrochemical treatment. The layer thickness of the Co / P film is 0.15 / µm. Constant direct current is used for the anodic oxidation of the Co / P layer. The current density is 5 mA / cm with an electrolysis time of 30 seconds.

2 The amount of current converted is 150 mAsec / cm. The temperature of the electrolyte was 22 ° C. After the anodic treatment, the film is rinsed and air-dried at room temperature. The surface is covered with a golden yellow oxide layer. Some results found after tempering under inert gas or in air are shown in Table 2.

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Table 2 ; Type of treatment TkA / m] 0 _m / b
InWb / iü oz 31 860
2606418 sample no anodic loading
plot, 30 minutes
in nitrogen
24O ⁰ C 42.7 165 Color according to
Tempering D. treated anodically,
30 minutes in stick
fabric at 24o ° C 44.8 118 metallic
glittering E. treated anodically,
30 minutes in the air
at 240 ° C 43.9 103 golden yellow F. Example 3 golden yellow

In a device according to Example 1, a solution of 1 mol ITapSO ^ is used as the electrolyte. and 117 g of tri-sodium citrate-5,5-hydrate with a temperature of 25 ⁰ C filled. A polyethylene terephthalate film provided with a 0.3 μm thick cobalt-phosphorus layer is placed between two copper cathodes. The anodic treatment according to Example 2 of the cobalt-phosphorus layer takes place

ρ
at a current density of 3 mA / cm for a total of 60 seconds. The magnetic foil is then rinsed with water and alcohol and dried in air at room temperature. The magnetic layer, which originally had a metallic sheen, has a black-gray appearance after the anodic treatment. The subsequent heat treatment results after 4 hours at l80 ^c C in air, a uniform, gold-colored coating layer.

Example 4

The procedure is as in example 2. The cobalt-phosphorus magnetic layer with a thickness of 0.13 / µm is located on a copper foil. The electrolyte consists of isopropanol and contains 20 g of trimethylphenylammonium chloride per liter. Is at 2O ⁰ C.

ρ for 30 seconds at a current density of 2mA / cm the magnet

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layer treated anodically. After a one-hour heat treatment at 240 ^° C. in air, a uniformly brown-violet wear-resistant protective layer is formed.

Example 5

As described in Example 2, a cobalt-phosphorus magnetic layer with a thickness of 0.45 / μm is applied to a copper foil at 23 ° C. in an electrolyte made from a glycocolla-sodium hydroxide buffer solution (pH = 13) with a current density of ImA / cm 120 Anodized for seconds. The heat treatment is carried out in air at 2 ¹ JO ⁰ C for one hour. The uniform protective layer has a deep yellow color.

Example 6

In a metallization bath of aqueous sodium hydroxide solution with a pH of 11.5, which contains 24 g of CoCl ₂ per liter. 6H ₃ O, NiCl ₃ . 6H ₃ O, and containing 220 g of trisodium citrate-5,5-hydrate, is applied to a copper foil by means of 0.6 g of NaBH ^ per liter at 65 ⁰ C, a cobalt-nickel-boron magnetic layer (Co: Ni = 82:18 ) deposited. After the NaBHn has been consumed, the magnetic layer is anodized in the same bath composition against copper cathodes with a current density of 3.4 mA / cm for 60 seconds. After a heat treatment in air at 24O ⁰ C for two hours, a uniform golden yellow top layer is obtained.

Example 7

Two polished 14-inch aluminum alloy discs, as they are usually used in the production of magnetic storage disks, are in a known manner with a Provided with a cobalt-phosphorus magnetic layer. (Thickness for sample G: 0.15 µm and Sample H: 0.4 µm). These magnetic layers are used in a rectangular container made of V2A steel, which also serves as a cathode, treated anodically. The experimental conditions are

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as well as the results of the abrasion test in Table 3 summarized. Regarding the wear resistance is in the table 3 also the test result of a commercially available one with an iron oxide dispersion coated magnetic storage disk (type IBM 3336).

Tabel

Thickness of anodic Co / P layer treatment

Heat treatment

Wear resistance / TninJ

Sample G

0.15

Electrolyte: 0.25 m aqueous NapSO ^ -
solution

T: 2O ⁰ C current density:

2mA / cm ²

Duration: 2 minutes

4 hours
at 240 C

> 30

Sample H

0.4

as with G

as with G

commercially available magnetic storage disk

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Claims (3)

Process for the production of a magnetic recording medium provided with a uniform, wear-resistant protective surface layer, consisting of a carrier which is thermostable up to 300 ° C and a ferromagnetic thin metal layer firmly bonded to it, characterized in that the thin metal layer is anodically oxidized in an electrically conductive solution and after washing and drying a heat treatment at 150 to 30O ⁰ C is subjected. 2. The method according to claim 1, characterized in that the anodic oxidation takes place in an electrically conductive solution which consists essentially of water and / or organic solvents as well as of electrochemically stable compounds dissolved therein, causing the conductivity. 3. The method according to claim 1 and 2, characterized in that the anodic oxidation of about 0.1 seconds up to 6 minutes at a current density of 0.5 to 50 mA / cm and a temperature of less than 70 ⁰ C takes place. BASF Aktiengesellschaft ^ 709835/0055