Method of heat shrinking thermoplastic sleeve wraps on glass containers

Abstract

A method of heat shrinking a sleeve of pre-oriented polyolefin plastic over the outer surface of a bottle by heating the plastic in annular regions along the height thereof in successive stages while conveyed in vertical upright position along the length of an oven. Infrared radiant heat is directed onto a mid body annular region of the plastic sleeve overlying the large dimension of the bottle. The mid body portion is firmly shrunken around this region of the bottle. Also, the first zone of the oven applies some heat in an upper annular region of the sleeve to soften the plastic thereat and raise its temperature to near the shrinking condition while the bottle and sleeve are rotating at a speed that will hold the upper region opposite the neck of the bottle erect and avoid foldover or collapse. Next, the bottle is conveyed in front of infrared burners in a second control zone of the oven, wherein the radiant heat is directed individually against the upper and lower annular regions of the sleeve. This second zone heating is concentrated to completely shrink the upper portion on the neck and the lower portion over the heel and on the bottom of the bottle, and avoid damage to the surface of the shrunken mid body. High production rates are experienced with the controlled heating, and a superior finish of the plastic wrap over substantially all of the outer surface of the bottle is obtained.