Plastic container

• US RE36,639 E
• Filed: 05/16/1996
• Issued: 04/04/2000
• Est. Priority Date: 02/14/1986
• Status: Expired due to Term

• Current Assignee: North American Container inc.
• Original Assignee: North American Container inc.
• Inventors: Okhai, Aziz A.
• Primary Examiner(s): Weaver, Sue A.
• Application Number:
  US08/649,918
• Time in Patent Office: 1,419 Days
• Field of Search: 220/606, 220/609, 215/373-375
• US Class Current: 215/375
• CPC Class Codes: B29C 49/12 Stretching rods
• CPC Class Codes: B65D 1/0284 having a discontinuous contact surface, e.g. discrete feet

Abstract

A container of blow-moulded oriented thermoplastic material includes a base structure comprising a convex annular surface (which may be divided into a plurality of feet (118) by radial webs (112) and a central re-entrant portion (116). In blow-moulding the container, a moulded preform is enclosed within a mould heated, and stretched such that its bottom surface impinges upon a projecting surface of the mould bottom corresponding to the topmost surface (158) of the re-entrant portion. After blow-moulding, the material of the re-entrant portion (116) remains unoriented and relatively thick in comparison to the material of the remainder of the base. The unoriented material in the base is substantially confined to the re-entrant portion (116) which itself is strengthened by its relatively thick walls and the base thus exhibits improved creep and stress cracking properties.

Claims

1. A container of blow-moulded oriented thermoplastic material of the type formed by enclosing a moulded preform in a mould corresponding to the shape of the container, heating the preform and stretching it to the full length of the mould so that its bottom surface impinges upon the bottom surface of the mould prior to blow-moulding;

said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion closing the bottom end of said side wall, wherein said base portion is defined by a figure of rotation formed by rotating a generally convex curve, extending from the bottom end of said side wall to the central longitudinal axis of the body portion, about said axis so as to define an annular, convex surface having a central re-entrant portion, the material in the vicinity of the center of said re-entrant portion being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion and wherein said annular, convex surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly from said side wall to a lowermost point and an inner wall portion extending upwardly from said lowermost point towards the center of the base portion; and

wherein said inner wall portions are generally convex, and said unoriented, relatively thick material is confined substantially to the upper most regions of said convex, inner wall portions; and

wherein said convex, inner wall portions converge to form a cusp at the center of said base portion, and said unoriented, relatively thick material is confined substantially to the point of said cusp.

31. diameter of said side wall..Iaddend..Iadd.33. The container of claim 32 wherein the diameter of said unoriented relatively thick material is in the range of 10% to 20% of the overall diameter of said side wall..Iaddend..Iadd.34. The container of claim 32 wherein said base portion is provided with a plurality of generally convex stabilizing feet spaced around said base portion and extending downwardly from the outer

32. wall portion thereof..Iaddend..Iadd.35. A container of blow-moulded oriented thermoplastic material, said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion closing the bottom end of said side wall, wherein said base portion is defined by a figure of rotation, formed by rotating a generally convex curve, extending from the bottom end of said side wall to the central longitudinal axis of the body portion, about said axis so as to define a bottom surface;

the material in the vicinity of the center of said bottom surface being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion; and

wherein said bottom surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly from said side wall and an inner wall portion extending from said outer, convex wall portion towards the center of said bottom surface;

wherein said unoriented, relatively thick material is confined substantially to the center of said bottom surface and wherein the thickness of the material in the range of up to 30% of the overall diameter of said side wall is from 1.2 times to 10 times the thickness of the material of the remainder of the base portion..Iaddend..Iadd.36. The container of claim 35 wherein the thickness of the material in the range of up to 30% of the overall diameter of said sidewall is from 1.95 times to 7.14 times the thickness

35. portion..Iaddend..Iadd.39. The container as in any of claims 1-7, 10-19, 23, 29, 30, 35, 36, or 37-38 under internal pressure provided by contents in the container..Iaddend..Iadd.40. The container of claim 39 wherein said contents comprise a liquid..Iaddend..Iadd.41. The container of claim 40 wherein said liquid is a drink..Iaddend..Iadd.42. The container of claim 41 wherein said drink is a carbonated drink..Iaddend.

2. A container of blow-moulded oriented thermoplastic material of the type formed by enclosing a moulded preform in a mould corresponding to the shape of the container, heating the preform and stretching it to the full length of the mould so that its bottom surface impinges upon the bottom surface of the mould prior to blow-moulding;

said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion closing the bottom end of said side wall, wherein said base portion is defined by a figure of rotation formed by rotating a generally convex curve, extending from the bottom end of said side wall to the central longitudinal axis of the body portion, about said axis so as to define an annular, convex surface having a central re-entrant portion, the material in the vicinity of the center of said re-entrant portion being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion and wherein said annular, convex surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly from said side wall to a lowermost point and an inner wall portion extending upwardly from said lowermost point towards the center of the base portion; and

wherein said inner wall portions are generally convex, and said unoriented, relatively thick material is confined substantially to the uppermost regions of said convex, inner wall portions;

wherein the diameter of said re-entrant portion is in the range 5% to 30% of the overall diameter of said base portion.

3. A container as claimed in claim 2 wherein the diameter of said re-entrant portion is in the range 10% to 20% of the overall diameter of said base portion.

4. A container of blow-moulded oriented thermoplastic material of the type formed by enclosing a moulded preform in a mould corresponding to the shape of the container, heating the preform and stretching it to the full length of the mould so that its bottom surface impinges upon the bottom surface of the mould prior to blow-moulding;

said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion enclosing the bottom end of said side wall, wherein said base portion is defined by a figure of rotation formed by rotating a generally convex curve, extending from the bottom end of said side wall to the central longitudinal axis of the body portion about said axis so as to define an annular, convex surface having a central re-entrant portion, the material in the vicinity of the center of said re-entrant portion being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion and wherein said annular, convex surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly from said side wall to a lowermost point and an inner wall portion extending upwardly from said lowermost point towards the center of the base portion; and

wherein said inner wall portions are generally convex, and said unoriented, relatively thick material is confined substantially to the uppermost regions of said convex, inner wall portions; and

wherein the upper ends of said upwardly extending, convex inner wall portions are closed by a topmost surface extending therebetween, and wherein said unoriented relatively thick material is confined substantially to said topmost surface and the adjacent uppermost ends of said inner wall portions; and

wherein the diameter of the re-entrant portion is in the range 10% to 20% of the overall diameter of said base portion.

5. A container as claimed in claim 4, wherein said topmost surface is substantially flat.

6. A container as claimed in claim 4, wherein said topmost surface is upwardly concave.

8. A container as claimed in any one of claims 4 or 7, wherein the upper ends of said inner wall portions converge toward the longitudinal axis at an angle less than 60°

.

9. A container as claimed in any one of claims 4 or 7, wherein the ratio of the thickness of said unoriented material to said oriented material is in the range of about 10:

1.

7. A container of blow-moulded oriented thermoplastic material of the type formed by enclosing a moulded preform in a mould corresponding to the shape of the container, heating the preform and stretching it to the full length of the mould so that its bottom surface impinges upon the bottom surface of the mould prior to blow-moulding;

said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion closing the bottom end of said side wall, wherein said base portion is defined by a figure of rotation formed by rotating a generally convex curve, extending from the bottom end of said side wall to the central longitudinal axis of the body portion, about said axis so as to define an annular, convex surface having a central re-entrant portion, the material in the vicinity of the center of said re-entrant portion being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion and wherein sad annular, convex surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly from said side wall to a lowermost point and an inner wall portion extending upwardly from said lowermost point towards the center of the base portion;

wherein said inner wall portions are generally convex, and said unoriented, relatively thick material is confined substantially to the uppermost regions of said convex, inner wall portions; and

wherein the upper ends of said upwardly extending, convex inner wall portions form a truncated cusp having a closed topmost surface, said unoriented relatively thick material being confined substantially to said topmost surface of said truncated cusp and the adjacent uppermost ends of said inner wall portions; and

wherein the diameter of the re-entrant portion is in the range 10% to 20% of the overall diameter of said base portion.

10. A container of blow-moulded oriented thermoplastic material of the type formed by enclosing a moulded preform in a mould corresponding to the shape of the container, heating the preform and stretching it to the full length of the mould so that its bottom surface impinges upon the bottom surface of the mould prior to blow-moulding;

said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion closing the bottom end of said side wall, wherein said base portion is defined by a figure of rotation formed by rotating a generally convex curve, extending from the bottom end of said side wall to the central longitudinal axis of the body portion, about said axis so as to define an annular, convex surface having a central re-entrant portion, the material in the vicinity of the center of said re-entrant portion being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion and wherein said annular, convex surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly from said side wall to a lowermost point and an inner wall portion extending upwardly from said lowermost point towards the center of the base portion; and

wherein said inner wall portions are generally convex, and said unoriented, relatively thick material is confined substantially to the uppermost regions of said convex, inner wall portions; and

wherein said base portion includes a plurality of radial webs extending from the bottom of said body portion towards the centre of said base portion and including means dividing said convex annular surface into a plurality of feet spaced around the circumference of said base portion; and

wherein said convex, inner wall portions converge to form a cusp at the center of said base portion, and said unoriented, relatively thick material is confined substantially to the point of said cusp.

11. A container of blow-moulded oriented thermoplastic material of the type formed by enclosing a moulded preform in a mould corresponding to the shape of the container, heating the preform and stretching it to the full length of the mould so that its bottom surface impinges upon the bottom surface of the mould prior to blow-moulding;

said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion closing the bottom end of said side wall, wherein said base portion is defined by a figure of rotation formed by rotating a generally convex curve, extending from the bottom end of said side wall to the central longitudinal axis of the body portion, about said axis so as to define an annular, convex surface having a central re-entrant portion, the material in the vicinity of the center of said re-entrant portion being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion and wherein said annular, convex surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly from said side wall to a lowermost point and an inner wall portion extending upwardly from said lowermost point towards the center of the base portion; and

wherein said inner wall portions are generally convex, and said unoriented, relatively thick material is confined substantially to the uppermost regions of said convex, inner wall portions; and

wherein said base portion includes a plurality of radial webs extending from the bottom of said body portion toward the centre of said base portion and including means dividing said convex annular surface into a plurality of feet spaced around the circumference of said base portion; and

wherein the diameter of said re-entrant portion is in the range 5% to 30% of the overall diameter of said base portion.

12. A container as claimed in claim 11, wherein the diameter of said re-entrant portion is in the range 10% to 20% of the overall diameter of said base portion.

13. A container as claimed in claim 11, wherein said container has a capacity of at least one liter.

14. A container of blow-moulded oriented thermoplastic material of the type formed by enclosing a moulded preform in a mould corresponding to the shape of the container, heating the preform and stretching it to the full length of the mould so that its bottom surface impinges upon the bottom surface of the mould prior to blow-moulding;

said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion closing the bottom end of said side wall, wherein said base portion is defined by a figure of rotation formed by rotating a generally convex curve, extending from the bottom end of said side wall to the central longitudinal axis of the body portion, about said axis so as to define an annular, convex surface having a central re-entrant portion, the material in the vicinity of the center of said re-entrant portion being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion and wherein said annular, convex surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly from said side wall to a lowermost point and an inner wall portion extending upwardly from said lowermost point towards the center of the base portion; and

wherein said lower wall portions are generally convex, and said unoriented, relatively thick material is confined substantially to the uppermost regions of said convex, inner wall portions; and

wherein said base portion is provided with a plurality of generally convex stabilizing feet spaced around said annular, convex surface and extending downwardly from the outer wall portions thereof;

wherein the upper ends of said upwardly extending, convex inner wall portions are closed by a topmost surface extending therebetween, and wherein said unoriented relatively thick material is confined substantially to said topmost surface and the adjacent upper ends of said inner wall portions; and

wherein the diameter of the re-entrant portion is in the range 10% to 20% of the overall diameter of said base portion.

20. A container as claimed in any one of claim 14, 15, 18 or 19 wherein the outer convex wall portion and inner convex wall portion of the base portion form a continuous curve, the radius of which is greater than half of the radius of said cylindrical body portion.

21. A container as claimed in any one of claims 14, 14, 18 or 19 wherein a straight line portion is incorporated into the outer convex wall portions of the base portion to form an upwardly diverging frusto-conical section around the outside portion of the base portion.

22. A container as claimed in any one of claims 14, 15, 18 or 19 wherein the outer convex wall portion and inner convex wall portion of the base portion form a continuous curve, the outer convex wall portion of the base portion including a first convex arcuate portion having a radius greater than half of the radius of said cylindrical body portion and extending from the bottom of the cylindrical wall portion of the container;

second convex arcuate portion which forms a lower apex of the base portion and has a radius less than the radius of said cylindrical body portion; and

a third convex arcuate portion formed as part of the inner convex wall portion of the base portion, having a radius greater than the radius of said cylindrical body portion and extending upwardly towards the centre of the bottle.

24. A container as claimed in any one of claims 14, 15, 19 or 23 wherein said topmost surface is substantially flat.

25. A container as claimed in any one of claims 14, 15 19 or 23 wherein said topmost surface is upwardly concave.

26. A container as claimed in any one of claims 14, 15, 19 or 23 wherein the upper ends of said inner wall portions converge toward the longitudinal axis at an angle less than 60°

.

27. A container as claimed in any one of claims 14, 15, 19 or 23 wherein the ratio of the thickness of said unoriented material to said oriented material is in the range of about 10:

1.

28. A container as claimed in any one of claims 14, 15, 19 or 23 wherein there are six equally spaced feet provided around the base portion. .Iadd.

15. A container of blow-moulded oriented thermoplastic material of the type formed by enclosing a moulded preform in a mould corresponding to the shape of the container, heating the preform and stretching it to the full length of the mould so that its bottom surface impinges upon the bottom surface of the mould prior to blow-moulding, said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion closing the bottom end of said side wall wherein said base portion is defined by a figure of rotation formed by rotating a generally convex curve, extending from the bottom end of said side wall to the central longitudinal axis of the body portion, about said axis so as to define an annular, convex surface having a central re-entrant portion, the material in the vicinity of the center of said re-entrant portion being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion and wherein said annular, convex surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly from said side wall to a lowermost point and an inner wall portion extending upwardly from said lowermost point towards the center of the base portion;

and wherein said inner wall portions are generally convex, and said unoriented, relatively thick material is confined substantially to the uppermost regions of said convex, inner wall portions; and

wherein said base portion includes a plurality of radial webs extending from the bottom of said body portion towards the centre of said base portion and including means dividing said convex annular surface into a plurality of feet spaced around the circumference of said base portions; and

wherein the diameter of the re-entrant portion is in the range of 10% to 20% of the overall diameter of said base portion; and

wherein the upper ends of said upwardly extending, convex inner wall portions form a truncated cusp having a closed topmost surface said unoriented relatively thick material being confined substantially to said topmost surface of said truncated cusp and the adjacent upper ends of said inner wall portions.

16. A container of blow-moulded oriented thermoplastic material of the type formed by enclosing a moulded preform in a mould corresponding to the shape of the container, heating the preform and stretching it to the full length of the mould so that its bottom surface impinges upon the bottom surface of the mould prior to blow-moulding;

said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion closing the bottom end of said side wall, wherein said base portion is defined by a figure of rotation formed by rotating a generally convex curve, extending from the bottom end of said side wall to the central longitudinal axis of the body portion, about said axis so as to define an annular, convex surface having a central re-entrant portion, the material in the vicinity of the center of said re-entrant portion being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion and wherein said annular, convex surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly from said side wall to a lowermost point and an inner wall portion extending upwardly form said lowermost point towards the center of the base portion; and

wherein said inner wall portions are generally convex, and said unoriented, relatively thick material is confined substantially to the uppermost regions of said convex, inner wall portions; and

wherein said base portion is provided with a plurality of generally convex stabilizing feet spaced around said annular, convex surface and extending downwardly from the outer wall portions thereof; and

wherein said convex, inner wall portions converge to form a cusp at the center of said base and said unoriented, relatively thick material is confined substantially to the point of said cusp.

17. A container of blow-moulded oriented thermoplastic material of the type formed by enclosing a moulded preform in a mould corresponding to the shape of the container, heating the preform and stretching it to the full length of the mould so that its bottom surface impinges upon the bottom surface of the mould prior to blow-moulding;

said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion closing the bottom end of said side wall, wherein said base portion is defined by a figure of rotation formed by rotating a generally convex curve, extending from the bottom end of said side wall to the central longitudinal axis of the body portion, about said axis so as to define an annular, convex surface having a central re-entrant portion, the material in the vicinity of the center of said re-entrant portion being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion and wherein said annular, convex surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly form said side wall to a lowermost point and an inner wall portion extending upwardly from said lowermost point towards the center of the base portion, and wherein said inner wall portions are generally convex, and said unoriented, relatively thick material is confined substantially to the uppermost regions of said convex, inner wall portions; and

wherein said base portion is provided with a plurality of generally convex stabilizing feet spaced around said annular, convex surface and extending downwardly from the outer wall portions thereof; and

wherein the diameter of said re-entrant portion is in the range 5% to 30% of the overall diameter of said base portion.

18. A container as claimed in claim 17 wherein the diameter of said re-entrant portion is in the range 10% to 20% of the overall diameter of said base portion.

19. A container of blow-moulded oriented thermoplastic material of the type formed by enclosing a moulded preform in a mould corresponding to the shape of the container, heating the preform and stretching it to the full length of the mould so that its bottom surface impinges upon the bottom surface of the mould prior to blow-moulding;

said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion closing the bottom end of said side wall, therein said base portion is defined by a figure of rotation formed by rotating a generally convex curve, extending from the bottom end of said side wall to the central longitudinal axis of the body portion, about said axis so as to define an annular, convex surface having a central re-entrant portion, the material in the vicinity of the center re-entrant portion being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion and wherein said annular, convex surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly from said side wall to a lowermost point and an inner wall portion extending upwardly from said lowermost point towards the center of the base portion; and

wherein said inner wall portions are generally convex, and said unoriented, relatively thick material is confined substantially to the uppermost regions of said convex, inner wall portions; and

wherein said base portion is provided with a plurality of generally convex stabilizing feet spaced around said annular, convex surface and extending downwardly from the outer wall portion thereof; and

wherein the upper ends of said upwardly extending, convex inner wall portions are closed by a topmost surface extending therebetween, and wherein said unoriented relatively thick material is confined substantially to said topmost surface and the adjacent upper ends of said inner wall portions, and wherein the diameter of said re-entrant portion is in the range 10% to 20% of the overall diameter of said base portion.

23. A container of blow-moulded oriented thermoplastic material of the type formed by enclosing a moulded preform in a mould corresponding to the shape of the container, heating the preform and stretching it to the full length of the mould so that its bottom surface impinges upon the bottom surface of the mould prior to blow-moulding;

said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion closing the bottom end of said side wall, wherein said base portion is defined by a figure of rotation formed by rotating a generally convex curve, extending from the bottom end of said side wall to the central longitudinal axis of the body portion, about said axis so as to define an annular, convex surface having a central re-entrant portion, the material in the vicinity of the center of said re-entrant portion being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion and wherein said annular, convex surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly from said side wall to a lowermost point and an inner wall portion extending upwardly from said lowermost point towards the center of the base portion; and

wherein said inner wall portions are generally convex, and said unoriented, relatively thick material is confined substantially to the uppermost regions of said convex, inner wall portions; and

wherein said base portion is provided with a plurality of generally convex stabilizing feet spaced around said annular, convex surface and extending downwardly from the outer wall portions thereof; and

wherein the upper ends of said upwardly extending inner wall portions forms a truncated cusp having a closed topmost surface, said unoriented relatively thick material being confined substantially to said topmost surface of said truncated cusp and the adjacent upper ends of said inner wall portions; and

wherein the diameter of the re-entrant portion is in the range 10% to 20% of the overall diameter of said base portion.

29. A container of blow-moulded oriented thermoplastic material, said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion closing the bottom end of said side wall, wherein said base portion is defined by a figure of rotation, formed by rotating a generally convex curve extending from the bottom end of said side wall to the central longitudinal axis of the body portion, about said axis so as to define a bottom surface having a central re-entrant portion;

the material in the vicinity of the center of said re-entrant portion being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion; and

wherein said bottom surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly from said side wall and an inner wall portion extending from said outer, convex wall portion towards the center of the base portion;

wherein said unoriented, relatively thick material is confined substantially to said re-entrant portion and wherein the diameter of said re-entrant portion is in the range of 5% to 30% of the overall diameter of said side wall..Iaddend..Iadd.

30. The container of claim 29 wherein said base portion is provided with a plurality of generally convex stabilizing feet spaced around said base portion and extending downwardly from the outer portion thereof..Iaddend..Iadd.31. The container of claim 29 wherein the diameter of said re-entrant portion is in the range of 10% to 20% of the overall diameter of said side wall..Iaddend..Iadd.32. A container of blow-moulded oriented thermoplastic material, said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion closing the bottom end of said side wall, wherein said base portion is defined by a figure of rotation, formed by rotating a generally convex curve extending from the bottom end of said side wall to the central longitudinal axis of the body portion, about said axis so as to define a bottom surface;

the material in the vicinity of the center of said bottom surface being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion; and

wherein said bottom surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly from said side wall and an inner wall portion extending from said outer, convex wall portion towards the center of said bottom surface;

wherein said unoriented, relatively thick material is confined substantially to the center of said bottom surface wherein the diameter of said unoriented relatively thick material is in the range of 5% to 30% of the overall

33. of the material of the remainder of the base portion..Iaddend..Iadd.37. A container of blow-moulded oriented thermoplastic material, said container comprising a generally cylindrical body portion with a central longitudinal axis, said body portion having a side wall, a radius and a base portion closing the bottom end of said side wall, wherein said base portion is defined by a figure of rotation, formed by rotating a generally convex curve, extending from the bottom end of said side wall to the central longitudinal axis of the body portion, about said axis so as to define a bottom surface;

the material in the vicinity of the center of said bottom surface being unoriented and relatively thick in comparison with the oriented material of the remainder of the base portion; and

wherein said bottom surface comprises, in transverse cross-section, first and second downwardly convex portions each comprising an outer, convex wall portion extending downwardly from said side wall and an inner wall portion extending from said outer, convex wall portion towards the center of said bottom surface;

wherein said unoriented, relatively thick material is confined substantially to the center of said bottom surface and wherein the thickness of the material in the range of up to 20% of the overall diameter of said side wall is from 1.2 times to 10 times the thickness of

34. the material of the remainder of the base portion..Iaddend..Iadd.38. The container of claim 37 wherein the thickness of the material in the range of up to 20% of the overall diameter of said sidewall is from 1.95 times to 7.14 times the thickness of the material of the remainder of the base