Graded crystallization of container finishes

#The present invention is directed to containers of molded polymer construction, and more particularly to crystallization at the container neck finish.

#Containers of crystallizable polymer construction—e.g., PET construction—are conventionally fabricated in an injection blow molding operation, in which a preform is fabricated by injection molding, and the preform is then subjected to a blow molding operation to form the container. The container finish is formed to final geometry or substantially final geometry in the injection molding operation, and generally is of amorphous polymer construction. The body of the container is subjected to stretching during the blow molding operation so that the body is of oriented polymer construction. It has been proposed to strengthen and rigidify the finish portion of the container by crystallizing all or selected portions of the neck finish. See, for example, U.S. Pat. Nos. 4,618,515, 4,928,835 and 6,217,818. The uncrystallized portions of the container body and finish are typically translucent, while the crystallized portion(s) of the finish contain spherulite that has a milky opaque appearance.

#The term “crystallizable polymer” in the present application refers to any polymer that is capable of being crystallized. These polymers include not only polyesters such as PET, which is the crystallizable polymer most typically used to make containers, but also polyolefins such as polyethylenes and polypropylenes, polycarbonates and polyamides such as nylons. Thus, although specific embodiments of the invention are disclosed in conjunction with polyesters—i.e., PET—the invention is by no means limited specifically to this polymer or family of polymers.

#The invention, together with additional objects, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:

#FIG. 1 is a cross sectional view of a preform for blow molding a container in accordance with one aspect of the present invention;

#FIG. 2 is a partially sectioned view of a container blow molded from the preform illustrated in FIG. 1;

#FIGS. 1 and 3 illustrate a preform 20 in accordance with one aspect of the present invention as comprising a finish 22 and a body 24. Finish 22 and body 24 are integrally formed in an injection molding operation, for example, and are either of monolayer or multilayer construction as previously described. Patents noted above illustrate various automated techniques for fabricating preforms 20. Finish 22 of preform 20 includes an end portion 26 remote from body 24, a mid portion 28, and a capping ring or flange 30 adjacent to body 24 that generally separates finish 22 from body 24. End portion 26 defines an end surface 32. End portion 26 and mid portion 28 also define a continuous external surface 34 that includes at least one external thread for ultimate securement of a container closure, and an internal surface 36 that will form the mouth of the container. FIG. 2 illustrates a container 20a blow molded from preform 20. Container 20a includes finish 22 and a body 24a that is blow molded from preform body 24. The exemplary finish of FIGS. 1-3 (as well as the finishes of FIGS. 4-9) also have an external thread for later securement of a closure, and a retaining bead for cooperating with tamper-indicating structure on the closure.

#Referring in particular to FIG. 3, and in accordance with one presently preferred embodiment of the invention, preform finish 22 (and therefore ultimately container finish 22) is selectively crystallized for enhanced dimensional stability of the thread and sealing surface areas of the finish. Crystallization in FIG. 3 (and in FIGS. 4-11) is illustrated by shading or stippling, with the density of the shading or stippling indicating the degree of crystallization, and with the absence of shading or stippling indicating an absence of substantial crystallization. Reference to an absence of crystallization, or to the fact that a portion of the finish is essentially uncrystallized or amorphous, means that there is an absence of intended crystallization, and that any crystallization is an unintended and insubstantial minor result of variations in the manufacturing process. The degree of crystallization will depend upon the intended application. In other words, the darkest areas of the drawings may possess 50% crystallization, decreasing to substantially zero crystallization through the graded area.

#In FIG. 3, there is substantial crystallization at the outside edge of upper portion 26 of finish 22, and graded crystallization from the upper outside edge of upper portion 26 both radially inwardly and axially downwardly with respect to finish 22. (Directional words such as “axial” and “radial” are employed by way of description and not limitation with respect to the central axis of the container finish. Directional words such as “upper” and “downward” are employed by way of description and not limitation with respect to the upright orientations of the preforms and containers illustrated in the drawings.) In mid portion 28 of finish 22 in FIG. 3, there is some crystallization along outside surface 34, but an absence of crystallization along at least the lower portion of inside surface 36. Capping flange 30 is essentially free of crystallization in this embodiment. Thus, in the embodiment of FIG. 3. There is heavy crystallization along outer surface 34 in upper finish portion 26 and the upper part of mid portion 28, graded crystallization radially inwardly to surface 36, where there is partial crystallization in upper portion 26 and the upper part of mid portion 28, and axially graded crystallization along surface 34 in the middle and lower sections of mid finish portion 28. In these mid and lower sections of mid portion 28 crystallization is graded radially inwardly to about the center of the finish thickness, and no crystallization at inner surface 36. (It will be understood that crystallization around the circumference of finish 22 is the same as illustrated in the cross section of FIG. 3 (as well as the cross sections of FIGS. 4-8) within manufacturing tolerance variations.)