GB967266A - Improvements in or relating to packaging with thermoplastic film - Google Patents

Abstract

967,266. Wrapping-machines. H. ALEXANDER. May 17, 1963 [June 29, 1962], No. 25039/62. Heading B8C. A method of packaging articles in thermoplastic film comprises supporting the film at spaced points 2, 3, Fig. 2, heating the film to a stretchable state, dropping an article 4 on to the heated film to form a neck 6, withdrawing air from the neck by opening a valve leading to a reduced pressure reservoir so that the neck takes the shape 6a shown in Fig. 8, and bringing together sealing elements 8, 9 which seal opposed portions of the neck along a line. The sealing elements may also sever the wrapped package from the film or merely form a tear-strip for manual parting off of the package. On cooling, the wrapper shrinks to produce the package of Fig. 10. In the machine illustrated for carrying out the above method a thermoplastic film 17, Fig. 13, is fed between a fixed frame 19 and a spring-loaded frame 20 lowered by depressing a foot pedal 24, and then allowed to rise to clamp the film. Depression of the foot pedal also separates sealing elements 31, 32, with knife edges 31a, 32a, and these are held in the open position by a solenoid-operated plunger 36 entering apertures 37 in them. A heater hood 25 is then drawn forward by hand on rails 26, Fig. 11, to a position above the film, and remains there until the film has become stretchable. It is then allowed to return to its rearmost position under the action of a counterweight. An article is dropped into the sheet 17 and on to the platform 48 which was raised by forward movement of the heater hood and held raised by a detent, and contact of the article with the platform releases the detent so that the platform descends under gravity, the speed of descent being controlled by a dashpot arrangement. Descent of the platform releases spring- loaded gripper plates 69 which hold the article as it descends and these are urged apart and held by a detent when the platform reaches its lowermost position. A hollow suction cover 40 is then pivoted into air-tight engagement with the frame 19 and an enclosed space is thus defined by the base of the cover and the neck formed in the thermoplastic film as the article descends. The cover is connected via a valve 43 to a suction reservoir 44, evacuated by a pump 45. A valve 47 in the cover is opened manually or may be actuated by a device detecting closure of the hood, or by the descending article operating a switch or breaking a light beam to a photo-electric cell. The enclosed space in the neck is thus evacuated to gather in the sheet, whereupon the valve closes. The solenoid controlling the plunger 36 is activated either by the operator depressing a switch or by a pressure-controlled switch in the enclosed space or reservoir, so that blades 31, 32 are allowed to come together under the action of a counterweight to seal the web along a line and sever the package thus formed from the web. A switch may be included which allows the blades to operate only when the cover is in position. The suction cover is then raised and the cycle of operations, which may alternatively be controlled entirely by a combination of sequence timing and resultant timing, repeated. Specification 953,399 is referred to.