Process For Forming Magnetic Metal Deposits On A Flexible Base For Use As Information Data Carrier Product Thereof

Abstract

A metal coated base is passed at a substantially constant speed through an electrolytic bath formed by a solution of metal salts to which 2 to 30 g/l of disodium-dihydrogenethylenediaminetetraacetate has been added and which is at a pH between 2.5 and 6. The metal coated base is then made the cathode by connecting it to the negative pole of a current source and the electrolytic deposit is formed on the metal coated carrier by passing a square wave impulse current through the bath which has A. a frequency between 2 and 10 Hz; B. an amplitude changing from negative 1 to positive 2 values; C. a keying ratio t between 2 and 4 and corresponding to the relationship t = .delta./(T - .delta.) (I) wherein T is the duration of a period and .delta. is the time during which the cathode current density is effected within one period; D. an effective current density (i.sub.W) of 0.5 to 7 A/dm.sup.2 with a high cathodic current density (i.sub.S ) of at least 10 A/dm.sup.2, and E. an anodic current density (i.sub.S ) corresponding to the relationship i.sub.S = (i.sub.S .sup.. .delta./T - i.sub.W)/(1 - .delta./T) [A/dm.sup.2] (II)

Description

BACKGROUND OF THE INVENTION

The present invention relates to a process for making thin magnetic coatings of high magnetic hardness by means of an electrolytic operation.

A process is known for making hard magnetic metal deposits particularly of cobalt-phosphorus or cobalt-nickel-phosphorus composition whereby a metal coating is first applied by vacuum evaporation or cathode evaporation on a flexible ribbon. The thus treated flexible ribbon is then made the cathode in a circuit by connecting it to the negative pole of a direct current source. The ribbon is moved at a continuous rate of speed through an electrolytic bath in which solutions of the particular metal salts constitute the electrolyte. The hard magnetic metal deposit is formed on the metal coated flexible ribbon by the action of the direct current.

However, the hard magnetic metal deposits made by this process possess a comparatively low magnetic hardness. The maximum obtainable coercive force is about 800 Oe. The ratio of remanence induction to saturation induction is at best 0.6. With these magnetic materials it is possible only to obtain a low information data density on these deposits.

It is therefore an object of the present invention to increase the maximum data density on hard magnetic metal deposits. More specifically the invention has the object to provide for a process for making thin hard magnetic metal deposits on a flexible base which are characterized by a high coercive force and high remanence.

SUMMARY OF THE INVENTION

According to the invention a metal-coated base is moved at a substantially constant speed through an electrolytic bath formed by a solution of metal salts to which 2 to 30 g/l of disodiumdihydrogenethylene diaminetetraacetate have been added and which is at a pH between 2.5 and 6. The metal coated base is then made the cathode by connecting it to the negative pole of a current source. The electrolyte deposit is formed on the metal-coated carrier by passing a square wave impulse current through the bath, said current having

a. a frequency between 2 and 10 Hz;

b. an amplitude changing from negative 1 to positive 2 values;

c. a keying ratio t between 2 and 4 and corresponding to the relationship

t = .delta./(T - .delta.) (I)

wherein T is duration of period and .delta. is the time during which the cathode current density is effective within one period;

d. an effective current density (i.sub.W) of 0.5 to 7 A/dm.sup.2 with a high cathode current density (i.sub.S ) of at least 10 A/dm.sup.2 ; and

e. an anodic current density (i.sub.S ) corresponding to the relationship

i.sub.S = (i.sub.S .sup.. .delta./T - i.sub.W)/(1 - .delta./T) [A/dm.sup.2 ] (II)

BRIEF DESCRIPTION OF THE DRAWING

The drawing illustrates the square wave of the impulse current employed in the method of the invention.

DETAILS OF THE INVENTION AND PREFERRED EMBODIMENT

The impulse current employed in the method of the invention causes a switching between cathodic deposit formation and anodic deposit removal resulting in a finely crystalline coating which meets the requirements for obtaining desirable magnetic properties in the plane of the deposit. By changing the frequency, the keying ratio and the effective or the cathodic current density it is possible to affect the character of the deposit formation. Depending on the intended use of the thin hard magnetic coating it is possible to obtain maximum values for the cohercive force or for the remanence ratio or an optimum of both parameters.

In carrying out the process of the invention it is preferred to add 10 g/l of disodiumdihydrogenethylene-diaminetetraacetate to the electrolyte and to adjust the pH in case of a chloride bath to 3.5 and in case of a sulfate bath to 5.5. The operation is preferably carried out at a frequency of 4 Hz and a keying ratio of 3 and an effective current density of 1.5 A/dm.sup.2. It is of advantage to proceed at a temperature of the electrolytic bath between 15.degree. and 30.degree.C and preferably at a temperature of 22.degree.C.

The process of the invention permits obtaining thin hard metal coatings having a cohercive force > 1,500 Oe and a remanence ratio > 0.7 and to accomplish this is an economical way. The process of the invention also permits to obtain cobalt-tungsten or cobalt-nickel-tungsten composition type deposits.

For the deposit formation either metal chloride or metal sulfate salts are useful.

A particular advantage of the process is that the electrolysis can be carried out at room temperature and that therefore an additional heating of the electrolyte is not necessary.

The process of the invention can also be used for making bilaterally coated flexible carriers.

The following example will further illustrate the invention. A polyester ribbon which was provided on one face with a copper coating and had a width of one-quarter inch was placed in an electrolytic bath and connected as the cathode to the negative pole of a current source. The electrolyte had the following composition:

100 g/l CoSO.sub.4 .sup.. 7H.sub.2 O

50 g/l NiSO.sub.4 .sup.. 7H.sub.2 O

30 g/l NaH.sub.2 PO.sub.2 .sup.. H.sub.2 O

25 g/l (NH.sub.4).sub.2 SO.sub.4

10 g/l disodiumdihydrogenethylene diaminetetraacetate ("Komplexon III").

The salts employed in this composition were all of the highest purity. The temperature was adjusted to 20.degree.C. The pH value of the bath was set for 5.5. The current source was constituted by an electronically stabilized currents producing apparatus which produced square wave negative 1 and positive 2 impulses. The impulse current had a frequency of 4 Hz and a keying ratio of 4:1. As an effective current density (i.sub.W) 1.5 A/dm.sup.2 and as the cathodic current density (i.sub.S ) 10.5 A/dm.sup.2 were selected. According to the Equation II found in the abstract and in claim 1 this resulted in an anodic current density (i.sub.S ) of 34.5 A/dm.sup.2.

After switching on the impulse current the ribbon was passed at a constant speed of 23.4 cm/min through the bath.

The operation resulted in the deposit of a cobalt-nickel-phosphorus layer on the copper base of a thickness of 0.1 .mu.m. This layer had a cohercive force of 1,530 Oe and a remanence ratio of 0.76.

If the electrolyte was used under otherwise the same conditions with a direct current a deposit was formed which had only a cohercive force of 800 Oe at a remanence ratio of 0.6.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

Claims

What is claimed as new and desired to be protected by Letters Patent is set

1. The process of making an information data receiving carrier consisting of a thin metal deposit of high magnetic hardness on a flexible base, the said process comprising passing a metal-coated base at a substantially constant speed through an electrolytic bath formed by a solution of metal salts to which 2 to 30 g/l of disodiumdihydrogenethylene diaminetetraacetate have been added and which is at a pH between 2.5 and 6, the metal-coated base constituting the cathode by connection to the negative pole of a current source, and forming an electrolytic deposit on said metal-coated carrier by passing a square wave impulse current through the bath of

a. a frequency between 2 and 10 Hz;

b. an amplitude changing from negative 1 to positive 2 values;

c. a keying ratio t between 2 and 4 and corresponding to the relationship

t = .delta./(T - .delta.) (I)

wherein T is the duration of a period and .delta. is the time during which the cathode current density is effected within one period;

d. an effective current density (i.sub.W) of 0.5 to 7 A/dm.sup.2 with a high cathodic current density (i.sub.S ) of at least 10 A/dm.sup.2, and

e. an anodic current density (i.sub.S ) corresponding to the relationship

i.sub.S = (i.sub.S .sup.. .delta./T - i.sub.W)/(1 - .delta./T) [A/dm.sup.2 ] (II)

2. the process of claim 1 wherein the said metal coating formed in said electrolytic bath is a cobalt-phosphorus or cobalt-nickel-phosphorus

3. The process of claim 1 wherein the said flexible base is a polyester

4. The process of claim 1 wherein the amount of disodiumdihydrogenethylene

5. The process of claim 1 wherein the electrolyte in said bath is in the form of a chloride bath and the pH of the bath is adjusted to about 3.5.

6. The process of claim 1 wherein the electrolyte in said bath is formed by

7. The process of claim 1 wherein the frequency of said square wave impulse

9. The process of claim 1 wherein the effective current density is 1.5

10. The process of claim 1 wherein the temperature of the electrolytic bath

11. The process of claim 10 wherein the temperature of the electrolytic

12. An information data receiving carrier consisting of a deposit of a hard magnetic material on a flexible base, the said data receiving carrier having been made by the process of claim 1.