Continuous production of container preforms
A method of producing preforms for blow molding containers includes producing polyester polymer by melt phase polymerization and compression molding preforms of the polyester polymer without solidifying the polyester polymer prior to compression molding the preforms. This process has the advantage of eliminating the conventional intermediate steps of solidifying the polymer in the form of pellets, shipping the pellets to the preform manufacturer and then remelting the polymer. Furthermore, because the preforms are produced directly from melt phase polymer, the polymer can have a low intrinsic viscosity of 0.65 or less, which is particularly useful for blow molding containers for low pressure, low temperature applications.
1 . A method of producing preforms for blow molding containers, which includes the steps of:
(a) producing polyester polymer by melt phase polymerization, and
(b) compression molding preforms of said polyester polymer without solidifying the polyester polymer prior to compression molding the preforms.
2 . The method set forth in claim 1 wherein said step (a) includes producing a continuous flow of said polyester polymer in melt phase, and
wherein said step (b) includes dividing said continuous flow into individual compression mold charges in melt phase.
3 . The method set forth in claim 2 wherein said step (b) includes: (b 1 ) providing a continuous flow of compression mold cavities, (b 2 ) placing each said mold charge into an associated cavity and (b 3 ) compression molding said mold charge into a preform, such that there is a continuous flow of polyester polymer from said step (a) through said step (b) to produce a continuous flow of preforms following said step (b).
4 . The method set forth in claim 3 including the step of: (c) cooling said preforms compression molded in said step (a).
5 . The method set forth in claim 3 including the step, between said steps (a) and (b), of layering said polyester polymer in said continuous flow with at least one additional polymer to produce preforms in said step (b) having a layered wall.
6 . The method set forth in claim 3 including the steps of:
(c) blow molding containers from said preforms,
(d) filling the containers with product, and
(e) capping the containers with said product captured therein,
said steps (c), (d) and (e) being a continuous in-line continuation of said steps (a) and (b) to produce filled and capped containers of polyester polymer in a continuous operation.
7 . A method of producing preforms for blow molding plastic containers, which includes the steps of:
(a) producing a continuous flow of polyester polymer by melt phase polymerization,
(b) providing a continuous motion of preform compression mold cavities,
(c) dividing said continuous flow of polyester polymer into individual compression mold charges in melt phase,
(d) placing each said mold charge into an associated mold cavity, and
(e) compression molding each said mold charge into a preform,
such that there is a continuous flow of polyester polymer from said step (a) through said step (e) to produce a continuous flow of preforms in said step (e).