Abstract: A method and apparatus for forming a seal between layers of thermoplastic coated paperboard or the like wherein there are different numbers of layers and varying thicknesses at different locations within the area to be sealed. The apparatus includes an anvil having a work surface for engaging one outer surface of the layers and a horn that vibrates at a predetermined frequency when energized. The horn has a work surface that opposes the work surface of said anvil.

Abstract: Apparatus for forming a seal between layers of a carton of thermoplastic coated paperboard material and the like wherein the thermoplastic material in the area to be sealed serves as the sealant and is activated to flow by frictional heat generated by a vibration welding horn and is then allowed to cool and set under pressure to form the seal between the layers. The carton first moves to an activating station wherein the layers to be sealed are engaged on opposite surfaces by a vibrating horn and a back-up means for a time sufficient to activate the thermoplastic material to flow. The carton is then carried to one or more clamping and sealing stations at a different location from the activating station with the thermoplastic material in the activated state. The layers to be sealed with the activated thermoplastic is then engaged on opposite surfaces by a pressure pad and a back-up means for a predetermined period of time to permit the activated thermoplastic to cool and set and form a seal.