Injection molded preform and manufacture thereof

An injection moulded thermoplastic preform for blow moulding to form a container, the preform comprising a lower closed base portion, a hollow body portion having an annular wall, a hollow transition portion between the lower closed base portion and the hollow body portion, and an upper open end portion adjacent to an upper part of the hollow body portion, wherein the closed base portion comprises a central portion which extends over at least 50% of an internal radius of a lower end of the hollow body portion and is either substantially flat or has a shallow concave or convex internal curvature, and the transition portion consisting essentially of an upwardly and radially outwardly tapering portion extending away from the central portion to connect to the hollow body portion, the tapering portion having a lower end adjacent to the central portion and an upper end adjacent to the hollow body portion, the tapering portion being frustoconical and defined between outer and inner frustoconical walls, the tapering portion increasing in wall thickness, measured between the outer and inner frustoconical walls, from the lower end adjacent to the central portion to the upper end adjacent to the hollow body portion so that the wall thickness, measured between the outer and inner frustoconical walls, at the upper end is greater than the wall thickness, measured between the outer and inner frustoconical walls, at the lower end, wherein the outer frustoconical wall is inclined at an angle, measured between the lower and the upper end, of from 18 to 24 degrees to a longitudinal axis of the preform and the inner frustoconical wall is inclined at an angle, measured between the lower end and upper end, of from 12 to less than 18 degrees to the longitudinal axis of the preform, and the outer frustoconical wall has a length, measured along the outer frustoconical wall between the lower closed base portion and the hollow body portion, of from 3 to 5 times the wall thickness of the annular wall of the hollow body portion and wherein the wall thickness of the tapering portion, measured at the upper end thereof adjacent to the hollow body portion, is less than the wall thickness of the hollow body portion.