초록 ▼

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 wi

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.

대표청구항 ▼

[ I claim:] [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 bas

[ I claim:] [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.