Method of forming a container having a rolled rim
Method of forming a container having a rolled rim, including providing a thermoformable sheet, and thermoforming the sheet to form a hollow body. The hollow body has an open first end and an opposite closed second end with a sidewall extending between the first end and the second end, and a rim structure formed at the first end of the hollow body. The rim structure includes an inner wall portion, a flange, and a skirt. The method further includes coining an upper section of the inner wall portion of the rim to form a controlled inner diameter, and rolling the rim structure to form a rigid rolled rim along an outer diameter of the open first end of the hollow body, the skirt extending toward the sidewall after being rolled.
1 . A method of forming a container having a rolled rim, comprising:
providing a thermoformable sheet comprising a polymeric material;
thermoforming the sheet to form a hollow body having an open first end and an opposite closed second end with a sidewall extending between the first end and the second end, and a strengthening rib on the sidewall, the strengthening rib disposed closer to the first end than the second end, the hollow body further having a rim structure formed at the first end of the hollow body, the rim structure including an inner wall portion extending upwardly from the sidewall, a flange extending outwardly from the inner wall portion, and a skirt extending downwardly from the flange;
coining an upper section of the inner wall portion of the rim structure to form a controlled inside diameter to a depth “d” from a top surface of the flange along an inner diameter of the open first end of the hollow body; and
rolling the rim structure to form a rigid rolled rim along an outer diameter of the open first end of the hollow body, wherein the skirt extends toward the sidewall after being rolled, the rolled rim and controlled inside diameter defining a lid-engaging surface;
wherein the strengthening rib has a first concave portion extending radially outwardly from an interior of the container and a first convex portion extending radially inwardly toward the interior of the container;
wherein the container has an overall height between the first end and the second end, and wherein the strengthening rib is disposed approximately between ½ and ¾ the overall height.
2 . The method of claim 1 , wherein the strengthening rib has a “∠”-shape in side cross-section.
3 . The method of claim 1 , wherein the concave portion of the strengthening rib is closer to the second end of the container than the convex portion of the strengthening rib.
4 . The method of claim 1 , wherein the concave portion of the strengthening rib has a greater depth than the convex portion of the strengthening rib.
5 . The method of claim 1 , wherein the sidewall has a bottom frustoconical portion below the strengthening rib and a top frustoconical portion above the strengthening rib, the bottom frustoconical portion defining a first taper line in side profile and the top portion defining a second taper line in side profile, wherein the first taper line is parallel to the second taper line.
6 . The method of claim 5 , wherein the first taper line is offset from the second taper line by a taper line offset.
7 . The method of claim 6 , wherein the taper line offset is approximately 0.080 to 0.100 inches.
8 . The method of claim 1 , wherein the flange defines a flange thickness and the skirt defines a skirt thickness, the flange thickness being greater than the skirt thickness.
9 . The method of claim 5 , wherein the parallel taper lines allow for printing on an outer surface of the top frustoconical portion and an outer surface of the top frustroconical portion simultaneously and in a single pass.
10 . The method of claim 1 , wherein coining an upper section of the inner wall portion of the rim structure forms a coined ledge at the depth “d” to define a portion of the lid engaging surface.