Patent Application
20050142311
The present invention is directed to finishes for plastic containers or preforms, to preform assemblies for blow molding plastic containers, to plastic containers blow molded from such preform assemblies, and to methods of making such finishes, preform assemblies and containers.
In the manufacture of plastic containers, it is conventional to injection mold or compression mold a container preform having a body and a finish with one or more external threads or other closure attachment means. The preform finish typically is molded to its final geometry, while the body of the preform subsequently is blow molded to the desired geometry of the container body. The preform may be of monolayer construction, or may be of multilayer construction in which one or more intermediate layers in the preform body may or may not extend into the finish area of the preform. U.S. Pat. Nos. 4,609,516, 4,710,118 and 4,954,376 illustrate injection molding of multilayer container preforms.
Molding the finish portion of the container as part of the preform presents a number of problems. For example, when the preforms are formed by injection molding, the plastic material typically is injected into a mold cavity at the closed end of the preform body, so that the material must flow along the sides of the preform cavity into the area in which the finish is molded. The finish typically requires more accurate and stable dimensioning than the body of the preform, which can limit the cycle time of the molding process. Furthermore, the finish portion of the preform is of the same material as at least the outer layers of the preform body, which limits the ability to obtain the most desirable characteristics at the finish. When the preform is of polyester construction, such as polyethylene terephthalate (PET), the finish portion of the preform can be wholly or partially crystallized to improve the operating characteristics of the finish area, particularly in hot-fill container applications. However, the requirement that the finish be of the same material as at least the outer layers of the preform body (in a multilayer preform) still limits the design capabilities of preform manufacture.
U.S. application Ser. Nos. 10/351,671, 10/375,376, 10/375,758 and 10/403,415, assigned to the assignee of the present application, disclose finish assemblies for preforms and containers in which the preform neck has an external flange around its open end, and a separate plastic finish ring is assembled over the preform neck in abutment with the external flange. The finish ring has one or more external threads or other means for securement of a closure, and can be of a plastic construction different from the plastic construction of the preform. The preform body and neck may be of thin plastic construction. However, liquid that spills on the finish during filling of the container can flow between the finish ring and the preform flange, and collect between the finish ring and the preform neck. Such fluid is unsightly and can encourage the growth of mold. It is a general object of the present invention to provide a finish assembly for a plastic preform or container, a method of making a plastic preform or container, and a preform assembly that reduce or eliminate the likelihood of leakage of fluid between the finish ring and the preform/container neck.
A method of making a preform assembly for blow molding a container, in accordance with a first aspect of the present invention, includes providing a plastic preform having a body with a closed end and a neck extending from the body. The neck has an open end and a radially outwardly extending flange surrounding the open end. The flange has an open axially facing channel adjacent to the outer surface of the neck. A finish ring has an annular body, an outer surface with at least one external thread, bead or other means for securing a closure, and an annular lip extending axially from the body. The finish ring is assembled to the preform until the ring abuts the flange, such that the finish ring is received over the outer surface of the neck and the annular lip is received in the neck flange channel to seal the finish ring against the flange. In the preferred embodiments of the invention, the channel in the flange is formed in part by a radially inwardly and axially facing conical surface, and the lip on the finish ring has a radially outwardly and axially facing conical surface in facing engagement with the radially inwardly facing conical surface on the flange to seal the finish ring against the flange and retard or prevent entry of liquid between the finish ring and the neck of the preform.
A finish assembly for a plastic container or preform in accordance with a second aspect of the invention includes a plastic neck having an open end surrounded by an external flange. The flange has an open axially facing channel adjacent to the outer surface of the neck. A plastic finish ring has an annular body, an inner surface opposed to the outer surface of the neck, an outer surface with at least one external thread, bead or other means for attachment of a closure, and an annular lip extending axially into the channel. In the preferred embodiments of the invention, the channel is formed in part by a radially inwardly and axially facing conical surface on the flange, and the lip has a radially outwardly and axially facing conical surface in facing engagement with the radially inwardly facing conical surface on the flange to seal the finish ring against the flange against entry of liquid between the finish ring and the neck.
The invention, together with additional objects, features, advantages and aspects thereof, will be best understood from the following description, the appended claims and the accompanying drawings, in which:
Finish ring 14 preferably is of molded plastic construction, having an annular body 34 with an integrally formed axially extending lip 36. Ring body 34 and lip 36 preferably are circumferentially continuous. Lip 36 has an inner surface 38 (
Preform 12 preferably is formed in a compression or injection molding operation. Finish ring 14, which preferably is itself formed in a suitable plastic molding operation, is assembled over the closed end of the preform so that the radially inner surface 40 of preform body 34 is in close sliding engagement with the outer surface 28b of preform neck 20. The above-noted pending applications disclose various techniques for assembling finish ring 14 over neck 20 and securing the finish ring to the neck, such as by interference press fit. The assembly of finish ring 14 over preform neck 20 continues until lip 36 on finish ring 14 is received within channel 24 on preform neck flange 22 and conical surfaces 44, 32 are brought into abutting facing engagement. Such abutting facing engagement of surfaces 44, 32 helps prevent any flow of liquid between the opposing surfaces of the finish ring and the preform neck. The axial dimension of channel 24 preferably is coordinated with the axial dimension of finish ring lip 36 so that there is a gap 56 (
There have thus been disclosed a method of making a preform assembly, a finish assembly for a plastic container or preform, and a preform assembly that fully satisfy all of the objects and aims previously set forth. The invention has been disclosed in conjunction with several exemplary presently preferred embodiments, and a number of additional modifications and variations have been discussed. Other modifications and variations will readily suggest themselves to person of ordinary skill in the art. The invention is intended to embrace all such modifications and variations as fall within the spirit and broad scope of the appended claims.
