Method for blow molding of thermoplastic articles

DETAILED DESCRIPTION What is claimed is: 1.
In a method comprising the step of introducing pressurized air interiorly of a parison of thermoplastic material at a sufficient pressure to transform the parison into a hollow article, the improvement comprising the steps of: (a) providing a mixture of water and surface active matter, said mixture including said surface active matter in percentage of from 0.
023 percent to 0.
36 percent of the liquid volume of said mixture; and (b) introducing said mixture into the interior surface of said parison in the course of air pressurization of said parison.
2.
The invention claimed in claim 1 wherein said surface active matter is non-crystallizing.




Description:
FIELD OF THE INVENTION This invention relates to the making of plastic articles and, more particularly, to improvements in the blow molding of containers.
BACKGROUND OF THE INVENTION In long-standing practice, as shown for example in commonly-assigned U.
S.
Pat.
No.
3,733,384, plastic containers are formed by introducing a molten plastic tube (parison) between spaced dies and closing the dies upon the parison.
The dies define a cavity which imparts desired exterior shape to the parison, inclusive of a cavity part providing a container filling/emptying opening.
A blow pin is supported in the paths of movement of the parison to be sealably encircled by the parison on closure of the dies.
As the dies close, the blow pin conducts pressurized air into the parison, forcing it to conform to the shape of the die cavity.
A measure of dimensional stability of the thus-formed container need of course to be attained prior to withdrawing the container from the dies, i.
e.
, the plastic substance need be cooled to effect a transition from its flowable parison state to a substantially less flowable condition.
For this purpose, coolant is continually circulated through the dies to extract heat from the plastic material.
The time of closure of the dies is the dominant factor in the commercially-significant cycle time for making a plastic blow-molded container