Ultrasonically sealed side seam on cup

A container comprising a tubular frustoconical side wall member having open ends, one of which is of smaller diameter than the other and a flat circular bottom member disposed at the open end of smaller diameter;

• said side wall member comprising a trapezoidal blank laminate of two coextensive plies, one ply comprising cardboard and the other ply comprising plastic, said trapezoidal blank having spaced, parallel top and bottom edges and symmetrically converging side edges and said blank being formed to assume said tubular frustoconical configuration with the cardboard ply at the outside and the plastic ply at the inside and with the side edges overlapping such that the plastic ply at the inner marginal edge of the outer one of the side edges is disposed in contact with the paperboard ply at the outer marginal edge of the inner one of the side edges, said side wall member having at its upper end a radially-disposed lip and at its lower end an inwardly-disposed upturned flange defining a groove peripherally of the lower end, the inner surface of which is constituted by the plastic ply and said bottom member corresponding in diameter to the open end of smaller diameter and being provided with a downturned peripheral flange turned downwardly from the plastic side such as to have contact with the inner plastic side of the side wall member at the lower end and wherein the cardboard ply at the marginal edge of the inner one of the side edges is skived and the plastic ply at said marginal edge folded to dispose the plastic ply about the end edge into contact with the plastic ply at the inner side of the outer one of the side edges and wherein the lapped ends are ultrasonically bonded using an ultrasonic horn throughout an area coextensive with the confronting overlapping surfaces thereof from the rim at the top downwardly along the overlapping surfaces at least several millimeters to reinforce the top and wherein the confronting overlapping surfaces of the lapped ends along the remainder of the distance toward the bottom are adhered to each other throughout an area corresponding in length to the remainder of the distance toward the bottom and in width from the edge of the outer one of the lapping ends toward the edge of the inner one of the lapping ends a distance less than the width of the overlapping surface such that the remainder of the confronting surfaces are unattached.