Method of controlling shrinkage of a sleeve wrap on a container

Abstract

A method of forming a substantially encapsulating layer of a heat shrinkable polyolefin plastic on a glass container in which the neck, shoulder and body onto the bearing bottom surface of the container is covered. The body of the container is substantially greater in diameter compared with the neck. A cylindrical sleeve of the polyolefin is telescopically placed along the outer surface of the container and the two are conveyed together into a heating oven for shrinking the sleeve snugly over the container. Upon application of heat in the oven, the polyolefin initially softens and becomes limp such that the sleeve tends to fold over or upon shrinking creates wavy top margins on the shrunken covering. The invention includes controlled rotation of the bottle and sleeve in the oven to apply a centrifugal force to the limp plastic which remains erect and billowed outwardly to give the material time to react with the heat such that the sleeve material shrinks into overall even, snug contact about the contour of the container without folds and wrinkles. By way of example, heat shrinkable foam polyethylene sleeve material on the order of 4-5 inch diameter sleeve (bottle body diameter 4-5 inch and neck diameter 1-2 inch) and 14-15 mil thickness which is pre-oriented in machine direction (sleeve circumference) 60-80% and cross dimension 0-15% shrinks evenly and suitably onto the neck with good upper marginal control at a bottle rotation in the range of 150-300 RPM while immersed in the heat atmosphere of the oven at a production rate of approximately 100-250 BPM.