apparatus for sealing deformable sheet material blanks comprises ultrasonic energy means having a sonotrode mounted for relative movement toward and away from an anvil surface carrying projections thereon . the anvil projections enable maximizing sonic energy from the sonotrode to form rapid and efficient seals in carton blanks . the carton blanks preferably carry a varnish having thermoplastic solvents in a liquid vehicle with the solids being present in sufficient amount to form a thermoplastic seal when processed in the ultrasonic apparatus . the method of forming the carton blanks utilizes printing techniques to apply the varnish and preferably the novel ultrasonic apparatus to enable rapid seals with minimized requirement for ultrasonic energy application due to compressing of sheet material at the seals to be formed .