METHOD OF FORMING RETORTABLE PLASTIC CONTAINER HAVING IMPROVED BASE STABILITY
A method of forming a retortable plastic container, the container including a main body and a bottom. The bottom defines a raised inner portion and at least one substantially flat bottom support surface. The substantially flat bottom support surface is curved and positioned near a radially outermost edge on the bottom when viewed in bottom plan. A groove is defined in the substantially flat bottom support surface. In addition, a first side wall portion that extends upwardly from the radially outermost edge of the bottom is shaped as a truncated cone, giving the bottom portion greater dimensional stability under retort conditions. The container bottom exhibits superior dimensional stability with respect to predecessor designs.
1 . A method of forming a retortable plastic container, comprising the steps of:
disposing a polymeric material in a mold;
blow molding the polymeric material in the mold to form a container comprising:
a main body, and
a bottom having a raised inner portion and at least one support surface defining a reference plane, the support surface having a radially inward portion and a radially outward portion each co-planar with the reference plane, the support surface further having a curved portion near a radially outermost edge of the bottom as viewed in longitudinal cross-section, the bottom having a groove defined in the support surface between the radially inward portion and the radially outward portion; and
removing the container from the mold.
2 . The method of forming a retortable plastic container according to claim 1 , wherein the polymeric material comprises polypropylene.
3 . The method of forming a retortable plastic container according to claim 1 , wherein disposing the polymeric material includes extruding the polymeric material.
4 . The method of forming a retortable plastic container according to claim 4 , wherein the mold defines a mold parting line in the container, and the bottom surface extends continuously around a periphery of the bottom, further wherein a pair of opposed tunnel recesses are defined in the support surface proximate the mold parting line.
5 . The method of forming a retortable plastic container according to claim 1 , wherein a bottom of the support surface has a width between the raised inner portion and the curved portion, and the retortable plastic container has a maximum outer diameter, and further wherein a ratio of the width to the maximum outer diameter is substantially within a range of about 0.035 to about 0.2.
6 . The method of forming a retortable plastic container according to claim 1 , wherein the groove is substantially concentric with the support surface.
7 . The method of forming a retortable plastic container according to claim 1 , wherein the groove has a curved inner surface having a maximum width, and a bottom of the support surface has a width between the raised inner portion and the curved portion, and further wherein a ratio of the maximum width of the groove to the width of the bottom of the support surface is substantially within a range of about 0.1 to about 0.9.
8 . The method of forming a retortable plastic container according to claim 1 , wherein the groove has a curved inner surface having an average radius of curvature in longitudinal cross-section and a bottom of the support surface has a width between the raised inner portion and the curved portion, wherein a ratio of the average radius of curvature to the width of the bottom of the support surface is substantially within a range of about 0.05 to about 1.0.
9 . The method of forming a retortable plastic container according to claim 1 , wherein the groove has a maximum depth in longitudinal cross-section and a bottom of the support surface has a width between the raised inner portion and the curved portion, and wherein a ratio of the maximum depth of the groove to the width of the bottom of the support surface is substantially within a range of about 0.01 to about 0.3.
10 . The method of forming a retortable plastic container according to claim 1 , wherein the groove has a maximum depth in longitudinal cross-section and the radially outermost edge of the support surface is convex and has an average radius of curvature, and a ratio of the average radius of curvature of the outermost edge to the maximum depth of the groove is substantially within a range of about 0.5 to about 10.
11 . The method of forming a retortable plastic container according to claim 1 , wherein the container further comprises a first side wall portion extending upwardly from the radially outermost edge, and wherein the first side wall portion is substantially straight when viewed in longitudinal cross-section.
12 . The method of forming a retortable plastic container according to claim 11 , wherein the first side wall portion defines an angle with respect to a vertical axis extending perpendicular to the reference plane, the angle being substantially within a range of about 0° to about 15°.
13 . The method of forming a retortable plastic container according to claim 11 , wherein the first side wall portion is shaped substantially as a truncated cone.
14 . The method of forming a retortable plastic container according to claim 11 , further comprising a second side wall portion extending upwardly and outwardly from the first side wall portion.
15 . The method of forming a retortable plastic container according to claim 14 , wherein the second side wall portion is convexly curved in longitudinal cross-section
16 . The method of forming a retortable plastic container according to claim 15 , wherein the second side wall portion is shaped substantially as a bowl.
17 . The method of forming a retortable plastic container according to claim 15 , wherein the second sidewall extends from the first side wall portion to a sidewall groove.
18 . The method of forming a retortable plastic container according to claim 17 , wherein the sidewall groove extends about an entire circumference of the main body portion.
19 . The method of forming a retortable plastic container according to claim 17 , wherein a third sidewall extends upwardly and radially inwardly from the sidewall groove.
20 . The method of forming a retortable plastic container according to claim 19 , wherein the third sidewall is shaped substantially as a truncated cone.