METHOD OF FORMING RETORTABLE PLASTIC CONTAINER HAVING IMPROVED BASE STABILITY

Abstract

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.

Claims

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a perspective view of a retortable plastic container that is constructed according to a preferred embodiment of the disclosed subject matter;

[0015] FIG. 2 is a bottom plan view of the retortable plastic container that is depicted in FIG. 1;

[0016] FIG. 3 is a cross-sectional view taken along lines 3-3 in FIG. 2; and

[0017] FIG. 4 is an enlarged portion of the area 4-4 that is depicted in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0018] Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to FIG. 1, a retortable plastic container 10 that is constructed according to a preferred embodiment of the disclosed subject matter includes a main body 12 and a bottom 14 that is unitary with the main body 12. The bottom 14 is constructed and arranged so as to be stable when placed on an underlying horizontal surface such as a tabletop or retail shelf

[0019] Referring again to FIG. 1, the retortable plastic container 10 includes an upper rim 16 defining an opening 18. The main body 12 and the bottom 14 are preferably fabricated from a single unitary sidewall 17 having an outer surface 19 and an inner surface 21 that defines an interior space within the container that is accessible through the opening 18. After the retortable plastic container 10 has been filled, a lid 31 is mounted to the rim 16 in order to seal the plastic container 10 prior to the heat sterilization process. Lid 31 is diagrammatically shown in FIG. 3.

[0020] The retortable plastic container 10 is preferably fabricated using an extrusion blow molding process from a plastic material that is compatible with the heat sterilization process, most preferably polypropylene. Most preferably, a multilayer material containing polypropylene and additional layers, such as a barrier layer with low oxygen permeability, may be used to form the sidewall 17 of the plastic container 10.

[0021] Referring now to FIGS. 2-4, the container bottom 14 is preferably shaped to define a raised inner portion 20 and at least one substantially flat bottom support surface 22 that is curved when viewed in bottom plan, as is shown in FIG. 2. The substantially flat bottom support surface 22 is preferably positioned near a radially outermost edge 23 of the bottom 14 and further preferably has a groove 24 defined therein.

[0022] Groove 24 is preferably shaped so as to be substantially concentric with respect to the curvature of the substantially flat bottom support surface 22, as is best shown in FIG. 2. In the preferred embodiment, the container 10 has a mold parting seam 26 as a result of the extrusion blow molding process, and a pair of opposed tunnel recesses 28, 30 are defined in the substantially flat bottom support surface 22 in the area of mold parting seam 26. Otherwise, the substantially flat bottom support surface 22 has a substantially annular shape defined by a substantially constant inner radius and a substantially constant outer radius, and preferably extends continuously around the outer periphery of the container bottom 14.

[0023] As FIG. 4 best shows, the substantially flat bottom support surface 22 has a width W.sub.S, which is defined as the radial distance of the lowermost surface of the support surface 22. The surface preferably resides substantially within a plane that will contact an underlying horizontal surface on which the container 10 is resting. The container 10 has a maximum outer diameter D.sub.MAX, as is depicted in FIG. 3. Preferably, a ratio W.sub.S/D.sub.MAX of the width W.sub.S to the maximum outer diameter D.sub.MAX is substantially within a range of about 0.035 to about 0.2, more preferably substantially within a range of about 0.0425 to about 0.01 and most preferably substantially within a range of about 0.05 to about 0.008.

[0024] The groove 24 preferably has a maximum width W.sub.G, which is best shown in FIG. 4. Preferably, a ratio W.sub.G/W.sub.S of the maximum width W.sub.G of the groove to the width W.sub.S of the support surface is substantially within a range of about 0.1 to about 0.9, more preferably substantially within a range of about 0.25 to about 0.75 and most preferably substantially within a range of about 0.40 to about 0.60.

[0025] The groove 24 preferably has a curved inner surface 32 that has an average radius of curvature R.sub.G, as is best shown in FIG. 4. Preferably, a ratio R.sub.G/W.sub.S of the average radius of curvature R.sub.G to the width W.sub.S of the support surface is substantially within a range of about 0.05 to about 1.0, more preferably substantially within a range of about 0.25 to about 0.75 and most preferably substantially within a range of about 0.40 to about 0.60.

[0026] The groove 24 also preferably has a maximum depth D.sub.G, also best shown in FIG. 4. Preferably, a ratio D.sub.G/W.sub.S of the maximum depth of the group 24 to the width W.sub.S of the support surface is substantially within a range of about 0.01 to about 0.30, more preferably substantially within a range of as 0.03 to about 0.20 and most preferably substantially within a range of about 0.05 to about 0.15.

[0027] As FIG. 4 also best shows, the outermost edge 23 of the of support surface 22 is preferably convex and has an average radius of curvature R.sub.O. Preferably, a ratio R.sub.O/D.sub.G of the average radius of curvature R.sub.O of the outermost edge 23 to the maximum depth D.sub.G of the groove 24 is preferably within a range of about 0.5 to about 10.0, more preferably substantially within a range of about 0.75 to about 5.0 and most preferably substantially within a range of about 1.0 to about 3.0.

[0028] As FIG. 4 also shows, the sidewall 17 in the area of the bottom 14 preferably has an average thickness W.sub.T. Preferably, a ratio of the average thickness W.sub.T to the average radius of curvature R.sub.G is substantially within a range of about 0.5 to about 2.0, more preferably substantially within a range of about 0.7 to about 1.8 and most preferably substantially within a range of about 0.9 to about 1.6.

[0029] Preferably, a ratio W.sub.G/W.sub.T of the maximum width of the groove 24 to the average thickness of the side wall 17 is substantially within a range of about 0.1 to about 1.0, more preferably substantially within range of about 0.2 to about 0.85 and most preferably substantially the range about 0.3 to about 0.65.

[0030] Referring again the FIG. 4, it will be seen that the sidewall 17 above the outermost edge 23 of the support surface 22 has a first sidewall portion 40 and a second sidewall portion 42. The first sidewall portion 40 is preferably substantially straight when viewed in side elevation and extends circumferentially about the outer periphery of the lower end of the container 10 directly above the outermost edge 23 to form a truncated inverted cone shape. As viewed in longitudinal cross-section as shown in FIG. 4, the first sidewall portion defines an angle a with respect to a vertical axis that preferably substantially within a range of about zero degrees to about 15 degrees, more preferably substantially within a range of about zero degrees to about 12 degrees and most preferably substantially within a range of about zero degrees to about 8 degrees.

[0031] The first sidewall portion further has a height H.sub.1. Preferably, a ratio H.sub.1/D.sub.MAX of the height H.sub.1 of the first sidewall portion to the maximum outer diameter D.sub.MAX of the container 10 is substantially within a range of about 0.015 to about 0.040, more preferably substantially within a range of about 0.020 to about 0.035 and most preferably substantially within a range of about 0.025 to about 0.030.

[0032] The second sidewall portion 42 is unitary with the first sidewall portion 40 and a connected thereto by a concave fillet having an average radius of curvature R.sub.B. Preferably, a ratio R.sub.B/D.sub.MAX of the average radius of curvature R.sub.B to the maximum outer diameter D.sub.MAX of the container 10 is substantially within a range of about 0.0045 to about 0.065, more preferably substantially within a range of about 0.007 to about 0.04 and most preferably substantially within a range of about 0.0092 to about 0.02.

[0033] The presence of the groove 24 and the division of the support surface 22 into inner and outer portions in conjunction with the truncated cone shape of the first sidewall portion 40 has the effect of stiffening the bottom 14 during the heat sterilization process, and also has the tendency to preserve the flatness of the support surface 22 both during the heat sterilization process and during subsequent use of the container 10. The stiffening effect is particularly pronounced when using polypropylene.

[0034] It is to be understood, however, that even though numerous characteristics and advantages of the present disclosed subject matter have been set forth in the foregoing description, together with details of the structure and function of the disclosed subject matter, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the disclosed subject matter to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.