GB471640A - Improvements in or relating to methods and apparatus for drying webs that are subject to shrinkage during the drying thereof - Google Patents

Abstract

471,640. Drying films. BRITISH CELLOPHANE, Ltd. Oct. 13, 1936, No. 27818. Convention date, Oct. 23, 1935. [Class 34 (i)] The invention relates to a method of and apparatus for drying a non-fibrous self-supporting transparent web or film subject to shrinkage in drying, including regenerated cellulose films and also non-cellulosic sheets of a similar nature. The web is passed into contact with one or more drying rolls subject to external heat treatment for maintaining the peripheral roll surface in a substantially dry state. Preferably the web is preliminarily dried to prevent sticking to the rolls. Materials may be applied to the sheets to make them waterproof and prevent transmission of ultra-violet light and to anchor subsequent coatings to the film. Fig. 1 shows apparatus in which there is preliminary heating of the film. A comparatively wide regenerated cellulose film 10 undried is led through a liquid bath 11 to squeeze rolls 13 and thence through a drying chamber of the type described in Specification 471,641. The web is unsupported between rolls 13 and 16. A plurality of headers 18 extend preferably obliquely towards the web and supply hot air or gas flames for drying the film. When burners are used they are so spaced that there is space for an ample supply of secondary air to reach the flames and allow combustion gas to escape. The burners may be adjustable. A number of openings 22 are allowed for hot gas to escape, assisted by a fan. The web passes from the roll 16 to a series of drying rolls 40. The first set of rolls are preferably confined in a chamber 46, in which hot gas jets are provided and suction means 44 for withdrawing products of combustion by conduits 49, 50. The jets 42 are directed against the peripheral parts of the rolls out of contact with the web 10 while the suction means 44 are arranged adjacent the webs. This prevents adhesion between the web and the rolls. Additional drying rods 40 unenclosed are used to remove most of the remaining moisture content leaving sufficient to be desirable. The web is wound on a shaft 51. The speed of the rolls may be regulated to allow for shrinkage. Requisite heat may be by gas or electricity or by heated air or other gas over steam coils or by combustion. The heat supplied must be by convection and/or radiation and not conduction. The wet web may contain more than 300 per cent of water and the dried one less than 10 per cent. In a modified form of apparatus, Fig. 2, the preliminary drying chamber is omitted.