Abstract: An apparatus for dielectric welding has an opposed pair of relatively movable electrodes (14, 12), each incorporating an electrically conducting element with a working surface close to and opposed to that of the other electrode. There is a gap (15) between the electrodes, such that a material to be welded may be placed in the gap and may be pressed between the electrodes, and radio frequency signals are supplied (16, 18) to the electrodes. At least one of the electrodes (14) incorporates a layer (14b) of dielectric material covering the conducting element (14a) both on the working surface and on surfaces which are alongside the working surface, so that the dielectric material (14b) defines at least part of the gap (15). The thickness covering the working surface is significantly less than that covering the alongside surfaces.

Abstract: Sachets are made from at least one thin and flexible film (10, 18) of a water-soluble and edible polymeric material, the film and/or films being shaped to define a sachet and filled with a food material (16), and being sealed to form a peripheral seal by RF welding between opposed electrodes (12, 20). The film may be of starch. The sachet and contents are added to water, without needing to be cut open, before being eaten or drunk, or cooked. For example the food material might be coffee powder or dried soup, or a mixture for making bread; the film dissolves readily and is substantially tasteless. RF welding provides reliable seals despite any powder on the surfaces of the film.