Patent GB-744748-A (GB)
Title: Improvements in and relating to plastic containers filled with fluid material
IPC: A23L7/20
Filed: 1952-03-10
Abstract: Containers filled with fluid material are made by a process in which a tube of flexible thermoplastic material, after being filled with fluid material, is welded both along transverse lines and along one or more longitudinal lines so as to divide it into sections joined together end to end and each subdivided into two or more containers joined together side by side.  The fluid filling material may be a liquid, a paste, or air or other gas, for example detergents or medicaments.  If the welding tool has the general form of a letter T the welds will be such as to divide a still unclosed part of the tube into two pockets and to close the open ends of the pockets formed by the previous weld.  If the T has more than one stem more than two pockets may be formed, and if the stem is short the pockets will be partly formed in one welding operation and completed in the next. The welding tool may be shaped to give containers of a desired form, such as one including a shoulder and neck.  To facilitate subsequent separation of the containers the tools may be ribbed to form a line of weakness in the weld.  If one tool is flat and the other V-shaped the material displaced thickens the walls near the weld. To ensure complete expulsion of air the tube should be filled with the fluid before closing it at either end.  In one method the tube is wound round a rotatably mounted tank with which one end communicates and is unreeled as welding proceeds along its length, excess fluid discharging into the tank.  In another arrangement the end of the tube remote from the first weld is in communication with a reservoir of the filling fluid with a head sufficient to maintain the required pressure within the tube.  A pressure-release valve may be fitted. In a third arrangement the tube communicates with a vessel containing gas under pressure, preferably an inert gas such as nitrogen when the fluid to which pressure is imparted is inflammable.  To avoid variation in the capacity of different containers a filled length of tube, already closed at one end by welding, is temporarily isolated by clamping the opposite walls together and the welding operation performed on this isolated length, which should be at least 30 per cent greater than the distance between successive welds, to avoid excessive pressure, but should not exceed 20 times that distance.  To reduce fire risk there may be interposed between the walls of the tube and the welding tools flexible sheets of a material which is a bad electrical conductor, does not contain molecules of free carbon and melts above 100 DEG C., suitable materials being polytetrafluorethylene and glass fibre fabric impregnated with silicon rubber.  The interposed sheets may have a rough or patterned surface which, when impressed on the portions of the tube softened during welding, provides a better grip for eventually tearing the container open.  When the containers are filled with a pasty substance short slits may be cut in them near the welds so that a container may be squeezed to force out some of the paste. Specification 747,750, [Group XVII], is referred to.