Patent attributes
A method and apparatus for the formation of double-walled containers with the structure of two integrally connected and adjacent containers extending in the same direction with an air gap between them, stretch-blow moulded as single bodies out of thermoplastic material, and suitable for mass-production. A thermoplastic tubular blank is formed and then heat-conditioned. The heat-conditioned tubular blank is then mechanically stretched longitudinally and blow-formed outwards by gas pressure to conformingly and stretchingly assume the tubular blank to the shape of a first dual-container shaped mould cavity set in order to form a stretch-blow moulded first container integrally connected to a second container, with both containers extending in opposite directions. Next, additional heat-conditioning is applied to further heat-condition as necessary the stretch-blow moulded second container and if deemed an advantage, at least part of the first container. Then at least one profiled inversion piston shaped as a male mould member with an outer surface configuration that defines the inner surface configuration of the article being formed and a second container shaped mould cavity set with a single-container shaped configuration are provided along with one or more wall stability devices which are applied to at least part of the wall surface(s) of either or both of the two integrally connected stretch-blow moulded containers, such that the second smaller container side wall(s) are at least substantially not in contact with the second container shaped mould cavity set and may be inverted at least partially inside-out, while at the same time the second smaller container bottom wall at least substantially does not invert, in order for the second smaller container to become a substantially mirror-image inverted second smaller container extending in the same direction as, and interior to, the first container.
