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 and method for forming sealed joints by welding layers of thermoplastic coated paperboard together. One outer surface of the paperboard layers is placed in engagement with back-up means, and the opposite outer surface of the paperboard layers is engaged by vibrating means so that the thermoplastic coating of the paperboard is heated by the vibration to weld the layers together. The apparatus and method is particularly useful in forming sealed joints for paperboard cartons, such as milk cartons of the type shown, for example, in U.S. Pat. No. 3,309,841. The vibrating means may be an ultrasonic transducer of the type disclosed in U.S. Pat. No. 3,526,792, for example.