GB630563A - Magnetic recording medium and methods for making the same - Google Patents

Abstract

630,563. Electrodepositing magnetic recording medium. BRUSH DEVELOPMENT CO. June 28, 1946, No. 19460. Convention date, Aug. 30, 1945. [Class 41] [Also in Group XXXVIII] A magnetic recording medium (see also Group XXXVIII) comprises a thin elongated, preferably tapelike reelable core 10 on which is electrolytically deposited a layer of magnetic material from the group comprising cobalt, nickel, iron, molybdenum, manganese and tungsten, the electrolyte comprising an aqueous solution containing boric acid and a sulphate salt or chloride salt of the metal to be deposited or a mixture of the salts. A pulsating current is passed through the solution with the core as cathode, the R.M.S. value of the alternating current being from 2 to 5 times the average direct current and the current density being between 20 and 300 amperes per sq. ft. The solution is maintained at a pH value between 2 and 6 and with a metal concentration between 25 and 150 grams per litre. The tape 10 is guided through plating both vessels 21 by members 22, 23, 24, 25, the members 24 serving also as polishing members and the members 25 conveying current to the tape as cathode. The anode 31, in the case of two or more metals being deposited, may be an alloy or a plurality of ba,rs of the metals. Barriers 35 consisting of perforated plates or screens of ceramic material are provided to compensate for voltage drop in the tape, and to equalize the current distribution along the portion of the tape passing through the bath. The plating may be done on one side only of the tape in which case the other side is prevented or protected from contact with the solution. When both sides of the tape are to be plated means are provided for passing the tape in reverse direction through the baths with the other side of the tape facing the anode. Each plating vessel 21 has an inclined base terminating in an outlet 42 through which impurities may be discharged into a collecting vessel 41. The controls of this vessel are pumped to a purifying apparatus 46 where the solution is filtered and purified and restored to its original composition and hydrogen-ion concentration before return to the plating vessels. The tape 10 instead of passing along the top of a plating vessel may pass around a rotatable cylindrical guide immersed in the solution. In the arrangement shown in Fig. 5, the tape passes several times around a cylinder 23, a smaller cylinder 26 being provided so that only one side of the tape is exposed to the solution. The tape before being plated is subjected to polishing, degreasing by trichlorethylene vapour and chemical cleaning in a bath of potassium hydroxide and potassium cyanide.