Ultrasonic welding device and method of producing disposable diaper using same

An ultrasonic welding device for ultrasonically welding an object to be welded, comprising:

• a holding member that holds an object to be welded;
• a pair of welding tools having an ultrasonic horn that has an output surface that applies ultrasonic vibration to the object to be welded, and an anvil having a welding surface over which the object to be welded is welded between the output surface of the ultrasonic horn and the anvil, the pair of welding tools being configured such that a moving welding tool that is one of the pair of welding tools can move, with respect to the holding member, over a welding area at which the output surface or the welding surface of the moving welding tool overlaps, in a plan view, the object to be welded that is held by the holding member, and over which the object to be welded is welded between the moving welding tool and a counterpart welding tool that is the other of the pair of welding tools, and a non-welding area that is spaced from the welding area in a plan view;
• and
• a displacement mechanism that displaces the moving welding tool with respect to the counterpart welding tool, in such a manner that the output surface and the welding surface approach each other in the welding area, and the output surface and the welding surface move away from each other in the non-welding area,
• wherein an end section of the counterpart welding tool including the output surface or the welding surface is branched, in a direction perpendicular to a movement direction of the moving welding tool, by a slit that extends in the movement direction, and has a pair of end faces positioned on both sides of the slit and functioning as the output surface or the welding surface,
• the displacement mechanism includes an urging mechanism that urges the moving welding tool toward the counterpart welding tool, in such a manner that the output surface and the welding surface move closer in the normal direction thereof, and a pressed member that has a pressed surface against which an outer surface of the moving welding tool, positioned within the non-welding area, is pressed by an urging force of the urging mechanism, the pressed member being fixed to the holding member in a state where the pressed surface is disposed within a width-direction range of the slit, and
• at least one of the pressed surface of the pressed member and the outer surface of the moving welding tool functions as a guide surface which, in response to the movement of the moving welding tool from the welding area to the non-welding area, guides the moving welding tool in a direction in which the output surface and the welding surface move away from each other.