Preform and mold stack

1. A preform suitable for subsequent blow molding, the preform comprising:

a neck, a base and a body extending therebetween, the neck, the body and the base each having inner and outer faces defining a wall thickness therebetween,

the base having an elliptical inner face with a first flat circular bottom portion, and an elliptical outer face with a second flat circular bottom portion, and

the first and second flat circular bottom portions each having a center on a vertical center axis of the preform and a radius R of equal size.

2. The preform according to claim 1 , wherein

the elliptical inner face of the base extends tangentially from a distal end of an inner face of the body, and the elliptical outer face of the base extends tangentially from a distal end of an outer face of the body, and

a first ellipse defining the elliptical inner face and a second ellipse defining the elliptical outer face each have a center spaced from the vertical center axis of the preform by a radius equal to the radius R of the first and second flat circular bottom portions.

3. The preform according to claim 2 , wherein

the first ellipse defining the elliptical inner face has a first radius IR 1 being parallel to the vertical center axis of the preform and a second radius IR 2 being perpendicular to the vertical center axis of the preform, the first radius IR 1 being greater than both the second radius IR 2 and a radius of a cylindrical inner face of the body, and

the second ellipse defining the elliptical outer face has a first radius OR 1 being parallel to the vertical center axis of the preform and a second radius OR 2 being perpendicular to the vertical axis of the preform, the first radius OR 1 being greater than both the second radius OR 2 and a radius of a cylindrical outer face of the body.

4. The preform according to claim 3 , wherein

the radius R of the first and second flat circular bottom portions is equal to 0.4 times of the radius of the cylindrical outer face of the body.

5. The preform according to claim 1 , wherein the body consists of a body main portion, and a transition portion extending from the neck.

6. The preform according to claim 5 , wherein

the transition portion has a cylindrical outer face with a diameter equal to a diameter of a cylindrical outer face of the body main portion, and a conical inner face with a continuously decreasing diameter, and wherein

the inner face of the body main portion extends tangentially from the conical inner face of the transition portion.

7. The preform according to claim 6 , wherein

the neck has cylindrical inner and outer faces, and

the outer and inner faces of the transition portion extend tangentially from the outer and inner faces of the neck.

8. The preform according to claim 1 , wherein

the neck on its outer face carries a neck finish and a support ledge.

9. A mold stack for injection molding a preform having a neck, a body and a base, the mold stack comprising:

a core insert comprising a first cavity defining portion configured to define an inner face of the neck and the body of the preform and, via a gate defining portion thereof, an inner face of the base of the preform,

a split mold insert pair configured to define an outer face of the neck of the preform,

a cavity insert configured to define an outer face of the body of the preform, and

a gate insert comprising a second cavity defining portion configured to define an outer face of the base of the preform;

the gate defining portion of the first cavity defining portion of the core insert having a first elliptical curvature with a first flat circular bottom portion, and the second cavity defining portion of the gate insert having a second elliptical curvature with a second flat circular bottom portion, and

the first and second flat circular bottom portions each having a center on a vertical center axis of the mold stack and a radius R of equal size.

10. The mold stack according to claim 9 , wherein

the first elliptical curvature of the gate defining portion of the core insert is tangent with a distal end of the first cavity defining portion of the core insert, and the second elliptical curvature of the second cavity defining portion is tangent with a distal end of an inner surface of the cavity insert defining the outer face of the body of the preform, and wherein

a first ellipse defining the first elliptical curvature and a second ellipse defining the second elliptical curvature each have a center spaced from the vertical center axis of the mold stack by a radius equal to the radius R of the first and second flat circular bottom portions.

11. The mold stack according to claim 10 , wherein

the first ellipse defining the first elliptical curvature has a first radius IR 1 being parallel to the vertical center axis of the mold stack and a second radius IR 2 being perpendicular to the vertical center axis of the mold stack, the first radius IR 1 being greater than both the second radius IR 2 and a radius of the first cavity defining portion of the core insert defining at least in part a cylindrical inner face of the body of the preform, and

the second ellipse defining the second elliptical curvature has a first radius OR 1 being parallel to the vertical center axis of the mold stack and a second radius OR 2 being perpendicular to the vertical center axis of the mold stack, the first radius OR 1 being greater than both the second radius OR 2 and a radius of an inner surface of the cavity insert defining a cylindrical outer face of the body of the preform.

12. The mold stack according to claim 11 , wherein

the radius R of the first and second flat circular bottom portions is equal to 0.4 times of the radius of the cavity insert defining the cylindrical outer face of the body of the perform.

13. The mold stack according to claim 9 , wherein

the first cavity defining portion of the core insert defining the inner face of the neck and the body of the preform, further comprises a transition portion being tangent with a neck defining portion of the first cavity defining portion, and a main portion being tangent with the transition portion of the first cavity defining portion.

14. The mold stack according to claim 13 , wherein

the transition portion is conical in shape and configured to define a conical inner face with decreasing diameter of a transition portion of the body of the preform, and

the main portion is configured to define a cylindrical inner face of a main body portion of the body of the preform.

15. The mold stack according to claim 14 , wherein

the split mold insert pair in configured to define a cylindrical outer face with a neck finish and a support ledge of the preform neck, and

a neck defining portion of the first cavity defining portion of the core insert is configured to define a cylindrical inner face of the preform neck.