Paper receptacle

A method for forming a paper receptacle, comprising:

• preparing a paperboard material composed of a sheet material having an outer periphery of a polygonal shape with a straight portion, and a curved portion having rounded corners;
• impressing a plurality of score lines from a surface of the paperboard material to a back side of the paperboard material to approximately radially extend toward the outer periphery in a portion corresponding to said curved portion, the impressing terminating an end of the score lines at a distance between about 1 mm and about 3 mm from the outer periphery;
• after said impressing, compacting a straight peripheral portion corresponding to said straight portion in the outer peripheral portion of said paperboard materials and a curved peripheral portion corresponding to said curved portion in the outer peripheral portion of said paperboard material in such a way that said straight peripheral portion has a smaller thickness than said curved peripheral portion;
• after said compacting, forcing said compacted straight peripheral portion and said curved peripheral portion into a clearance narrower than the respective compacted thicknesses to iron and compress said straight peripheral portion and curved peripheral portion;
• and
• curling said compressed outer peripheral portion of said paperboard material to form a curled portion.

A machine for forming a paper receptacle, the paper receptacle having a bottom portion, a side wall portion connecting with said bottom portion, a flange portion connecting with said side wall portion and extending in a horizontal direction, and a curled portion formed around an outer periphery of said flange portion, comprising;

• first and second die members for pressing a paperboard material interposed therebetween to form said bottom portion, said side wall portion and said flange portion,
• said first die member and said second die member having respective surfaces facing each other, the surfaces having respective portions for forming the bottom portion of the paper receptacle, the respective portions being respectively angled toward a center of the respective die members and relative to a horizontal plane, whereby when said bottom portion and said side wall portion are formed when being pressed, an angle defined therebetween is smaller than the corresponding angle after being formed
• first and second outer frame members provided respectively around, and corresponding to, said first and second die members, said first and second outer frame members abutting on each other while pressing;
• and
• a curl ring member provided between said second die member and said second outer frame member so as to abut on an inner end of an abutting surface of said first outer frame member while pressing;
• wherein the inner end of the abutting surface of said first outer frame member and an abutting surface of said curl ring member have respective circular grooves facing each other, said grooves having inner wall surfaces curved in a curling direction, said respective grooves being formed to constitute a curling groove when abutting,
• an inner edge of the groove of said first outer frame member is formed so as to be located outside an inner edge of the groove of said curl ring member when abutting to form a clearance, with an inner wall surface of the groove of said curl ring member, as can pinch and compact the edge of the outer peripheral portion of said paperboard material,
• said first die member and said first outer frame member relatively move toward said second die member and said second outer frame member, whereby said paperboard material is held between said first and second die members and the outer peripheral portion of said paperboard is pressed and compacted between said first and second outer frame members,
• with said first and second die members holding the paperboard material therebetween, said first outer frame member, said second outer frame member and said curl ring member, while abutting, are relatively moved to the side of said second die member, whereby the outer peripheral portion of said paperboard material is forced into a clearance between an inner peripheral surface of said first outer frame member and an outer peripheral surface of said second die member and ironed and compressed,
• when the edge of the outer peripheral portion of said paperboard material is located at the inner edge of said curling groove, only said curl ring member is caused to stop moving, whereby the edge of the outer peripheral portion of said paperboard material is pinched and compacted between the inner edge of the groove of said first outer frame member and the inner wall surface of the groove of said curl ring member and the curling set in the curling direction is formed on the edge of the outer peripheral portion of said paperboard material, and
• after forming said curling set, said first outer frame member, said second outer frame member and said curl ring member are moved, while abutting, in the opposite direction, to the side of said first outer frame member, whereby the outer peripheral portion of said paperboard material is inserted into said curling groove and curled along the inner wall surface of the curling groove, so as to form the curled portion.