Adhesive-free bonding of continuously moving webs to form laminate web

Abstract

Method and apparatus for ultrasonically bonding continuously moving webs to one another using a stationary vibrating horn and a relatively slick, non-thermally softenable moving slip layer interposed between the webs to be bonded and the horn to prevent web damage. Interposing the slip layer between the webs to be bonded and the ultrasonic horn improves both the quality and efficiency of web bonding. It reduces friction between the travelling webs and the substantially stationary ultrasonic horn not only due to its relatively slick surface, but also due to the compressive force which the slip layer exerts upon the webs to be bonded. This in turn minimizes jamming and hangups in the very limited clearance existing between the rotating anvil roll and the substantially stationary vibrating ultrasonic horn. In addition, the slip layer maximizes retention of heat either generated in the laminate web by the ultrasonic horn or transferred to the laminate web structure by preheating one or more of the webs. If desired, the slip layer may be comprised of a continuous belt which rotates about the ultrasonic horn. In addition, a secondary slip layer may be provided intermediate the webs to be bonded and the rotating anvil roll to minimize heat transfer from the webs to the anvil roll and to prevent sticking of the webs to the anvil roll. In a particularly preferred embodiment the peripheral edges of the raised anvil bosses are relieved slightly to minimize web tearing and to enhance bond strength. In still another preferred embodiment the anvil roll is heated to a temperature approximating the maximum temperature achieved by the webs being bonded to minimize heat transfer from the webs to the anvil roll during the bonding operation. Novel laminate products bonded on-the-fly without the use of an ancillary adhesive may also be produced.