GB617968A - Improvements in the drying of printed matter by dielectric heating - Google Patents

Abstract

617,968. Dielectric heating. HOE & CO., Ltd., R. Nov. 29, 1945, No. 32271. Convention date, Nov. 29, 1944. [Class 39 (iii)] An electrical drying system for freshly printed surfaces comprises electrode elements arranged in two or more sets spaced apart along the path of movement of the surface, each set comprising pairs of electrodes opposed to one another about the path of movement, each pair being at the same potential, and the sets being connected across a source of high frequency energy. In an example, a sheet 11, to be printed on one or both sides, passes between printing cylinders 13, 14 and lower and upper sets of rod-like electrodes 62, 72, 67, 77, 42, 52, 47, 57 of semi-circular cross-section which are joined by arcuate connectors 66, 76, 71, 81, 46, 56, 51, 61. The electrodes 42, 52 and 47, 57 are connected respectively to an oscillator 22 by the inner and outer conductors 37, 39 of a co-axial cable 32. The electrodes 62,72,67,77 are similarly connected to an oscillator 23. Thus each pair of electrodes which face one another on opposite sides of the sheet are of the same potential and the high frequency electric field is induced between adjacent electrodes. Preferably the upper set of electrodes operate at a higher voltage than the lower set The oscillators 22, 23 are connected to power lines L1, L2 through a centrifugal switch 27 actuated by the shaft 29 of the cylinder 13 and serving to close the circuit when the printing speed is attained. To vary the electric power with the speed of the printing machine, a pilot motor 114 and a rheostat 113 which regulate the speed of the printing machine are coupled by a shaft 112 to a Selsyn or similar transmitter 111 which is electrically connected to a Selsyn or similar receiver 115 coupled by a shaft 116, couplings 119 and gearings 117, 118 to shafts regulating the output of the oscillators 22, 23. The couplings 119 e@ble one or both of the oscillators to be regulated by the receiver 115. The electrodes may be at right angles to the direction of movement of the sheet, as shown, or at an angle thereto. In a modification, electrodes are formed by a number of concentric rings of consecutively opposite potential. The dielectric heating can be increased by the use of a printing ink containing a material of high power factor, such as a soluble resin, or by the use of spray guns for spraying the sheet with, for example, a quick-drying volatile solution of a colourless resin. After heating the sheet passes through a cooling box 21 which houses refrigerating pipes 84, baffles 86, deflectors 87 and air circulating fans 88.