Plastic container with noneverting bottom

Abstract

A plastic container having a lower side wall of ogival configuration merging into a bend-load resistant thickened annulus at the juncture of a base of a conical inverted dome center section of the bottom.

Description

DISCUSSION OF THE PRIOR ART

In the construction of plastic bottles, the weakest portion is the bottom of the bottle. Various configurations have been suggested including the so called champagne bottle structure which incorporates an inverted dome connected at its base to the lower edges of the side wall of the bottom. The problem with such construction is that invariably during the blow molding process, the juncture area between the base of the inverted dome and the side wall of the bottom stretches and becomes thinned out. Also this juncture area is subjected not only to tensile stresses but to severe dome loads since the inverted dome tends to revert to a hemispherical shape into what is commonly known as a bulged bottom and the bottle becomes a rocker in that it cannot stand up. In this juncture area the compressive stresses on the domed section are changing to tensile stresses and to flexural (bending) stresses. Since plastic material is weakest in tension, the critical tensile stresses are reached first and they are followed by critical flexural stresses before critical compressive stresses develop.

SUMMARY OF THE INVENTION

This invention is directed to a novel construction of a plastic bottle for containing pressurized liquid such as carbonated drinks or beer.

The invention contemplates the provision of a novel bottom structure for such bottle which will withstand the developed pressures and will not bulge or crack.

A specific object of the invention is to provide a novel bottom construction for a plastic container by forming an integral reinforcing ring at the juncture of the inverted dome and the ogival section of the side wall of the bottle in order:

1. TO ARRANGE THE COMPONENTS IN SUCH MANNER THAT IS SUBJECTED TO ESSENTIALLY COMPRESSIVE STRESSES;

2. TO INHIBIT DEVELOPMENT OF TENSILE AND BENDING STRESSES AT THE BASE OF THE DOME;

3. TO MINIMIZE THE MATERIAL CONTENT OF THE BOTTOM OF THE CONTAINER AND PROVIDING A SATISFACTORY STRUCTURE BY STRATEGICALLY LOCATING THE MATERIAL TO RESIST THE DESTRUCTIVE STRESSES.

These and other objects and advantages inherent in and encompassed by the invention will become more apparent from the specification and the drawings wherein:

FIG. 1 is an elevational view of a plastic bottle made in accordance with the invention shown partly in axial section;

FIG. 2 is an enlarged axial section of the lower and bottom portions of the bottle shown in FIG. 1;

FIG. 3 is a bottom end view of the bottle;

FIG. 4 is an enlarged diagrammatic elevational view of the bottom portion of the bottle;

FIG. 5 is a longitudinal section of an apparatus for making the bottle; and

FIG. 6 is an enlarged longitudinal section of another mold assembly shown in closed position for making the bottle.

DESCRIPTION OF THE INVENTION

Referring to the drawings, there is shown in FIGS. 1 and 2 the preferred themoplastic bottle structure generally designated 1 which is a hollow container having a pour opening 2 at one end defined by a lip 3 at the top of a narrow cylindrical neck 4 which is joined to a cone frustrum section 5. The cone section 5, which forms the upper section of the side wall of the bottle, merges at its base end into a cylindrical intermediate section 7 which in turn merges at its lower end into a truncated hemispherical or ogival lower section 8.

The bottom generally designated 9 comprises a central conical section 10 centered on the center line X--X of the bottle and comprises a top apex 13 and a downwardly sloping conical wall section 14 which merges into a thick annulus or junction ring 15 which interconnects with the base edge portion 16 of conical wall section 14 and the inturned lower edge portion 17 of an ogival section 8 of the lowermost portion of the side wall of the bottle.

The reinforcing junction ring is flattened at 19 to provide a seat normal to the axis X--X of the bottle and has a transversely arcuate upper surface contour 20 which provides a stress resistant structure. The thickest section identified at 22 is centered in the junction area and the ring is feathered or blended at its inner circumference 24 into the interior surface 25 of the conical section above its base edge 16 and also blends at its outer circumference 21 into the inner face 28 of the ogival section above its lower edge.

FIG. 4 is a diagrammatic representation of the displacement of different sections of the bottom portion of the bottle due to pressurizing of the bottle. It will be noted that the height C-D of the dome can decrease to C' D only if the base diameter A-B and the circumference of the dome at these points elongate to A'-B' concurrent with bending of the lower ogival section of the dome outwardly so that points A', B' would move to positions A.sup.2, B.sup.2 respectively. The provision of the reinforcing ring 15 of the same material as the container and at the junction or transition area between the base of the conical portion and the ogival portion not only provides a practical structure, but also a construction which resists the expansion, this being done by thickening the critical area to provide adequate strength.

The bottle shown may be made of the type of plastic material such as Du Pont NR-16 material or Barex-210 sold by Vistron Corporation.

The bottle may be formed by the blow molding process wherein the plastic is extruded through an extruder 35 which comprises a shell 36 having a bore 37 into which the melted plastic is force fed from an inlet 38. The plastic material exits through an annular slot 39 which is defined between the bore surface 37 and a core blank 40. The core element 40 is axially movably by a motor 42 and the motor is connected to a programmer 44 of well known type which is effective to adjust the position of the core and particularly to vary the cross-sectional area of the metering slot 39 by displacing the position of the frusto-conical head 45 of the core element.

The plastic material is extruded to form a parison or tubular preform 46 of generally uniform thickness except for a predetermined bulge of material at 47 which is to form the reinforcing ring 15 at the bottom of the bottle. This bulge or thickness is an annulus which is between 2 or 3 times the thickness of the remainder of the parison length 46.

The thickened portion is formed by opening the clearance between the core blank 40 and the bore 37 to enlarge the metering slot 39.

As best seen in FIG. 5 the annulus is positioned in relation to the bottom forming surfaces 50, 50 of the mold halves 51, 51 such that when the molds are closed as seen in FIG. 6 and the air is blown into the bottle by the air nozzle 53, the thickened portion will locate, due to the stretch of the material and the formation of the dome portion on the core inset 55, in the groove 56 of the molds 51 at the juncture of the truncated hemicylindrical portion 8, the mold providing in the groove 56 an annular surface 57 which forms the seating area of the bottle and causes the material of the ring to bulge inwardly of the bottle and located essentially tangentially to the hemispherical surface section of the side wall of the bottom. The inward displacement of the ring-forming material thus does not modify the spherical maximum-pressure-accommodating contour of the bottom section of the bottle and being of thicker section than the dome portion which is loaded in compression and being located at the base of the dome portion is effective to resist the hoop stresses. Tests on NR-16 material 42 mils thick at 140.degree.F for 1 hour withstood stresses of about 4000 psi, a stress load of about 6500 psi was withstood by material 25 mils thick and material 32 mils thick withstood a stress load of about 5200 psi. Thus it was empirically established that a ring thickness of 2 or 3 times the wall thickness would be adequate to contain the selected pressurized beverage or liquid without eversion.

A preferred form of the invention has been described for purposes of best illustrating the invention. It will be realized that other modifications will now become apparent which come within the scope of the appended claims.

Claims

I claim:

1. In a generally cylindrical thermoplastic container biaxially oriented, at least in the generally cylindrical section, the improvement wherein the bottom configuration comprises essentially of a series of connected geometric curves rotationally symmetrical about the center line of the bottle comprising:

a truncated hemispherical section at the lower end of said bottom;

an inwardly concaved bottom section within said hemispherical section having an upwardly directed apex and a base adjacent to the lower end of said hemispherical section;

an arcuate toroidal juncture section between the base and the lower edge of said hemispherical section; and

a strength-imparting thick annulus located at and integrated with said juncture section and thicker than said sections.

2. The invention according to claim 1 and said annulus projecting widthwise into the container.

3. The invention according to claim 2 and said annulus formed of thermoplastic material of said container.

4. The invention according to claim 3 and said annulus merging into the internal surfaces of said conical section and said hemispherical section.

5. The invention according to claim 4 and said annulus located in the high stress area between said conical section and said hemispherical section.

6. The invention according to claim 5 and said annulus projecting widthwise into the bottle.

7. The invention according to claim 6 and said bottom having a continuous smoothly blended uninterrupted exterior surface contour on the conical section and hemispherical section and said surface contour being substantially flat in axial alignment with the annulus and providing a seating surface for the bottle normal to the axis thereof.

8. The invention according to claim 7 and said hemispherical section and conical section having an area of intersection inwardly of the cylindrical side wall of the bottle and said annulus providing an arcuate pressure-distributing surface area within the container.

9. The invention according to claim 8 and said surface area being essentially in axial alignment with the base edge portion of said conical section.

10. The invention according to claim 1 and said strength-imparting annulus being essentially centered between the lower edge portions of said center section and said hemispherical section and providing extended surface areas converging into the container and sloping toward the adjacent walls of the conical and hemispherical sections transversely of the axis of the container.