US1702564A - Record disk for talking machines and the like - Google Patents

Description

Patented Feb. 19, 1929.

' UNITED S TATE S PATENT OFFICE.

WILLIAM EORSE, OF LONDON, ENGLAND, ASSIGNOB TO COLUMBIA PHONOGRAPH CQM .TPANY, INC., 01 BRIDGEPORT, CONNECTICUT, A CORPORATION OF NEW YORK.

RECORD DISK FOR TALKING MACHINES AND THE LIKE.

No Drawing.

conditions, and be free from the difficulties;

that have been associated with records produced from the usual shellac mixtures.

The invention relates more especially to record disks having an inner core or disk made of a cheaper material than is used for the surface on which the record sound groove is impressed.

Disks of this class are constructed in many different ways, some having a cardboard disk prepared with a suitable filler or gum, and then coated on the surface with a high-grade mixture comprising shellac, pigment, flock, or shoddy, together with certain mineral earths and clays.

Another well-known method for making records of this class is by pulverizing a shellac mixture similar to the above, and then dusting, the powder by means of a sieve onto one surface of thin paper disks which have been out about the size of a finished record and treated with a suitable gum to hold the shellac powder when so duste A sheet prepared in the above manner is placed with the shellac face downwards on the matrix plate in the record forming die, a disk or piece of cheaper material (such as powdered earths, clays and shoddy, bound together with a suitable gum so as to form a thermoplastic mass) is softened by heat and placed on the back of the shellac coated paper sheet. The other half of the record forming die-isthen placed in position, and the whole Y subjected to hydraulic or other pressure so as to impress the shellac surface of the coated paper sheet with the sound record line on the matrix, the cheaper material beingextended out to form the inner body of a record disk of suitable thickness and strength for comniercial use. Laminated-records having a shellac mixture surface as described above, invariably have a'serious fault in that the record surface is not stable. Particles of mineral or flock that are too large to com ress between the very fine consecutive recor grooves and that rocess of Application filed October 17, 1924. Serial No. 744,257.

cannot be properly worked up on the record surface owing to the inefficient mixing, alter in shape by shrinkage or expansion and when exposed to the heat or damp as certain partic es that are not sutficiently covered with shellac get loose or form slight projections or recesses, thus producing a miscroscopically rough surface which, while being passed over by a reproducer stylus, produces undesirable scratching noises.

In the manufacture of records in the past this fault has arisen from the use offlock or other fibrous material in combination with the shellac and other ingredients for the pur-. pose of binding the small particles together as the particles of mineral earths and the like were not ground fine enough to give suflicient granular surface to enable such to be bound efi'ectively by the shellac. This difiiculty has even arisen if only a very small proportion of the unbound material exists, as such will invariably work up on the surface of the recordand break away or give roughness.

This serious fault has not, up to the present, been successfully overcome, owing to the difficulty in preparing a sufficiently fine and powdered record material that is entirely free from large grains of mineral or other material, as grains having a diameter of about -180 mm. would be likely to work loose when in use. The present invention inconnection with the manufacture of records provides for the production of grains having a maximum size of .1 mm. and of averaging about .025 mm. in diameter. By this means, the necessity of using flock, or other fibrous binding material is eliminated, as the granular surface is suflicient to be tightly bound by shellac alone, while the particles of mineral earths and the like are all so small that they do not present a surface rough enough to cause the stylus to vibrate to any audible note.

When manufacturing the improved records, there is employed paper sheets that are coated with powder having a maximum granular size of less than .1 mm. and free from any fibrous materials, and the disks or sheets This backing material may contain flock or other binding material, but this backing or strengthening material forms no part of produced by mixingthe materials, for instance, mineral earths, resins and coloring matter, in their correct proportlons and in the usual way by first heating and rolling the product out into slabs, and then grinding such slabs to a fine powder by passing them through impact mills, rolling mills or the like. Having thus secured a fine powder, it is passed into a separating box to enable the fine granules to be separated from the coarser granules by air flotation.

The separation is effected by air flotation by passing the powder direct from the grind-' ing mills into a separating box at a point about half way up its height, and there is mounteda suction fan or exhauster on the top of the separating box above the powder inlet. By the operation of this fan or exhausting device there is created a partial vacuum which causes the air to be removed from the separating box at a high velocity. This air displacement, when used in conjunction with apparatus of suitable size, will create a current of air having the necessary force to carry away all particles of powder entering the chamber which are under a given size (.1 mm. in diameter for example), while the heavier particles fall to the bottom of the chamber to be returned by conveyor means back to the grinding mills, where it is reground and repassed through the separating chamber again and again until it is of sufficient size to pass over with the air current into a receptacle adapted to collect the very fine powder which is required for the invention.

It must be understood that the action and construction of 'the powder separating mechanism is described by way of example only, and may be varied in many ways, or a sieve of suitably fine mesh or any otherwell-known means for obtaining fine powder of a defined .maximum size may be used.

' The finely divided powdered shellac material thus obtained is dusted by any well known mechanical means on to disks of paper of suitable size for forming records. The coated paper sheets, while warm, may then be passed between cold (preferably watercooledi rollers under pressure to give an even surface to the powder, and to distribute the powder evenly over the paper disk.

This improved cold rolling process has not hitherto been practicable with the coarser grained powder, owing to the large particles becoming depressed temporarily into the paper sheet and then rising again when released and forming excretions or irregularities that were damaging to the surface of the powdered sheet.

The thermoplastic powder having the char acteristics as described herein, may be used for manufacturing sound record disks in various well-known ways; and although primarilycintended for use in combination with paper disks to limit the use of the high-grade powder in the sound records surface, it must be understood that such finely divided and separated powder as hereinbefore described can also be applied to various forms of core or disk without necessarily using paper sheets.

It is to be understood that the foregoing description given for securing a complete adhesion of the finely divided homogeneous material without the necessity of using a foreign binding material, such as flock, is set forth by way of example or illustration, and

not of limitation, and that the powder may be composed of various ingredients and produced in various ways to suit t-heparticular purpose for which it is required.

Having now particularly described and ascertained the nature of the invention, and in what manner the same is to be performed, what is claimed is:

1. A. sound record comprising a base of material containing a fibrous binder, the layer of said base into which the record groove is pressed being of smoother texture than the material of the base said layer comprising shellac and a granular filler free of fibrous binders the granules having a size not exceeding one-tenth mm. indiameter.

2. A. sound record having an outer layer into which the record groove is pressed, said layerv consisting of a compressed dried mechanical mixture of granules composed of sirellac and crocus having a size not exceeding mm.

3. A sound record having a base with fibers therein and an outer layer into which the record groove is pressed, said layer consisting of a compressed granular mixture of shellac and filler, said mixture being free of fibrous binding materials, and the granules of said mixture having a size not exceeding .1 mm;

Signed at London, England, this sixth day of Uctober A. D. 1924.

. 7 WILLIAM FORSE.