Patent GB-241676-A (GB)
Title: Improvements in sound records and processes of making same
IPC: G11B3/70
Filed: 1924-09-11
Abstract: 241,676. Gramophone Co., Ltd., (Victor Talking Machine Co.). Sept. 11, 1924. Records, blanks for; records, duplicating; record tracks, form of; tools for recording.-Relates to the production of master records and of matrices for making duplicate records, and particularly to the method in which the sound trace produced by a stylus upon a blank is in the form of undulations in the side walls of a spiral groove. The blank upon which such a trace is formed consists of a tablet of impressible material covered with a pliable skin. The tablet may consist of celluloid, the surface of which has been softened and thus rendered plastic or compressible by means of a solvent, a skin of metal being applied to the softened surface. The recording stylus, which is preferably a sapphire having a smooth ball-shaped or like rounded tip, acts upon the skin, drawing it into the compressible material so as to produce a laterally undulating soundtrace bounded by rounded edges. The sound groove thus produced is of uniform width, so that a recording stylus can be used repeatedly without substantiaL wear, and the abrading action of a reproducing needle upon a record is also lessened. Figs. 11 and 12 show the preferred method of making a blank for a master record. Upon a polished disc 12 of wax or metal a layer of metal 4 is deposited electrolytically. A preliminary chemical or other treatment of the, surface of the disc 12 is in some cases necessary (e.g. if the disc is of copper or nickel, the surface may be oxidized) in order that the electrodeposit 4 may be subsequently stripped therefrom. One surface of a disc 1 of celluloid is then treated with a solvent such as acetone or amyl acetate until a layer 3 is softened. On to this softened surface the metallic skin 4 is transferred from the base 12 by rolling the prepared celluloid firmly upon the coated base 12, by means of a squeegee 14 or the like, after having first coated the skin 4 with acetone or like celluloid solvent. On pulling the celluloid sheet away from the base 12, the metal skin 4 adheres to the softened side of the celluloid, as shown in Fig. 12. Upon the blank thus obtained a record is produced, using a roundended stylus as described above. The metal surface of the blank is preferably lubricated with soapy water before recording. An alternative method of producing the blank consists in applying to a disc or base of suitable material a layer of soft material by coating, painting, &c., and thereafter forming upon the soft surface a thin layer of impressible material. This upper layer may consist of varnish, or may be formed out of the soft material itself with which the base is coated. For example, a mixture of linseed oil and wax melted together, with a filler such as lamp black, may be poured upon a smooth base-plate, and a skin or crust is allowed to form on the surface by oxidation of the oil. The skin, which is capable of receiving sound impressions, prevents further change in the soft layer. Instead of adopting the method last described, a thin sheet of metal such as copper, nickel, aluminium, or gold or silver leaf may be laid upon a layer of soft material consisting e.g. of asphaltum varnish or the substance known by the registered Trade- Mark "Bakelite " varnish. After a record has been made directly upon the blank by means of a stylus, the record may be left for a sufficient time to allow the soft material to set or harden to produce a permanent master record, if the substance used has this quality. For duplicating, a master matrix may be formed by electrolytically depositing upon the original master record a plating of metal, stripping off the electroplate, and providing it with a suitable backing. Fig. 21 shows this stage, the matrix 8 with its backing 9 being shown separated from the original master 19 comprising a base 1 with a skin 4. Steps are taken if necessary, before the electrodeposition, to ensure that the plating 8 may be readily stripped from the surface 4, e.g. by treatment of the surface with certain liquids. On the other hand, it may be preferred to ensure permanent adherence between the layers 8, 4, so that both may be stripped away from the base 1 together. Alternatively, instead of using the electroplating process, a melted alloy, having relatively low melting-point, may be poured over the skin 4. The skin and backing together are then separated from the support 1, and electroplated. A further variation consists in removing the metal skin of the original record, e.g. by etching, so as to leave a master record entirely of celluloid or the like. The metal skin of the original blank may be formed, by controlling the electrodeposition, of gradually diminishing thickness towards the centre, so that when a recording stylus acts upon it, the depth of the groove increases towards the centre of the record, as shown in Fig. 23. The object of this is to decrease the risk of a reproducing stylus jumping out of the sound groove when nearing the centre. A further form of blank for direct recording is shown in Fig. 29, and consists of a shell 4, 9<1>, both sides of which may be of metal, enclosing a liquid or semiplastic substance such as celluloid 3<1>. The blank may be formed by electrolytically depositing a skin of metal on a polished base, spraying a solution of celluloid thereon and, after allowing the celluloid partially to harden, depositing a relatively heavy metal backing upon and round the edges of the celluloid. The blank thus formed is separated from the base.