A heating device for heat-sealing containers by heating an end forming portion 13 of a tubular container having a rectangular to square cross section, the end forming portion 13 having four generally quadrilateral first to fourth panels 21 to 24 continuous with one another and each having a heating region 31, 32, 33 or 34 to be heated on an inner surface thereof. The heating device has a hot air nozzle 71 in the form of a bottomed tube and fittable into the container end forming portion 13 for heating an inner surface of the container. The nozzle 71 has four side walls 81 to 84 continuous with one another and corresponding to the first to fourth panels 21 to 24 respectively, at least one of the side walls 81 to 84 being provided with a hot air discharge portion 121, 122, 123 or 124 having orifices 111 and to be opposed to the heating region of the corresponding panel 21, 22, 23 or 24 and with a hot air nondischarge portion 125, 126, 127 or 128 other than the discharge portion, the hot air nondischarge portion being at least partly provided with a hot air escape portion 95, 96, 97 or 98.

A hollow heating head for insertion into an open, spouted, top end closure of a carton comprises an interior chamber with slot-form outlets for hot air supplied to the chamber. The slots include a U-shaped, narrow slot, or its equivalent, extending generally horizontally around two lateral vertical walls and an end vertical wall of the head. Each limb of the U-shape includes horizontal, upper and lower sections and a vertical intermediate section. The base of the U-shape is adjacent the lower sections, is at substantially the same level as the lower sections and is of a shallow V-shape in a vertical plane. The slots also include several vertically extending slots above each of the base and the lower sections of the U-shaped slot.

A heating device for heat-sealing bottom portions of containers has a hot air nozzle 62. The nozzle 62 is positionable as opposed to a bottom forming end portion 14 of a tubular blank 11 of square cross section as fitted around an intermittently drivable mandrel 52 for heating a region of the blank end portion. The nozzle 62 is movable toward or away from the end portion 14 on the axis of the blank 11. The nozzle 62 has orifices 101, 102, 131, 132, 133 directed toward a plurality of parts within the region when the nozzle is positioned close to the end portion. Among the orifices 101, 102, 131, 132, 133 of the nozzle 62, those 101, 131 directed toward the part of the region remote from an extremity of the blank when the nozzle is so positioned have a greater open area ratio than those 102, 133 directed toward the part of the region proximate to the blank extremity when the nozzle is so positioned.

An inner seal portion (30a) of an open edge portion (1a, 1b) of a paper container (1) is aligned face-to-face with an inner peripheral heating portion of a seal-heating apparatus. An outer seal portion (30b) of the open edge portion is aligned face-to-face with an outer peripheral heating portion (4, 5, 6, 7, 13, 14, 15, 16) of the seal-heating apparatus. At least the inner peripheral heating portion (8, 17) is oscillated about an axial line thereof so as to vary the hitting position of the inner seal portion against which hot air blown from the hot air blowing holes (8a) of the inner peripheral heating portion (8) hits. Thus, the seal portion (30) of the paper container (1) can be equally and properly heated.

A gable top carton employs a stake joint having spaced apart legs disposed longitudinally on opposite sides of a channel, the channel being formed when a carton blank is folded to form the gable top carton. The spaced apart legs urge the material at the sides of the channel toward the center of the channel to effect a channel seal. The stake seal may be in the form of an inverted U-shaped stake seal. A method and apparatus for forming the stake seal are also contemplated.