EP1708866A1

EP1708866A1 - Method of swage-forming of container or preform internal threads and container and preform having such internal threads

Info

Publication number: EP1708866A1
Application number: EP20040815386
Authority: EP
Inventors: W. Bruce Larsen; Thomas E. Nahill
Original assignee: Graham Packaging Pet Technologies Inc
Current assignee: Graham Packaging Pet Technologies Inc
Priority date: 2003-12-24
Filing date: 2004-12-23
Publication date: 2006-10-11
Also published as: CA2550668A1; CN1898071A; AU2004308960A1; BRPI0418199A; WO2005063463A1; US20050139569A1

Abstract

A method of making a plastic container having an internally threaded finish. The container is made from a preform (10) having a body (12) and an integral neck (14), and the body of the preform is expanded within a mold cavity to form the body of the container. Either prior to or subsequent to blow molding the preform body, at least one internal thread (20) is formed in the neck by engaging an inner surface of the neck with a first tool (22) having a peripheral channel (28), engaging an outer surface of the neck with a second tool (24) having a peripheral bead (32), and causing relative rotation of the neck and tools to swage at least one internal thread in the neck. Such a preform and such a container are also disclosed.

Description

SWAGE-FORMING OF CONTAINER OR PREFORM INTERNAL THREADS The present application is directed to plastic containers, and preforms for blow molding plastic containers, and to a method of forming internal threads on the preform or container.

Background In the manufacture of plastic containers, such as monolayer or multilayer polyethylene terephthalate (PET) containers, it is conventional to mold a container preform having a body and a finish with one or more external threads. The finish typically is molded to its final geometry in the preform, while the body of the preform is subsequently blow molded to the desired geometry of the container body. However, this manufacturing technique is not well suited for fabrication of preforms or containers having internal threads because, among other reasons, it is difficult to strip a preform having molded internal threads from its forming mold. It would therefore be desirable to provide a method of forming internal threads in the finish of a plastic preform or container, and to provide a preform or container finish with internal threads. Summary of the Invention In accordance with one embodiment of the invention, a method is provided of forming at least one internal thread in a plastic neck of a preform or container. The method includes the steps of: a) engaging the inner surface of the neck with a first tool having a peripheral channel; b) engaging an outer surface of the neck with a second tool having a peripheral bead; and c) causing relative rotation between the neck and tools to swage at least one internal thread in the neck between the channel and bead. In various alternative implementations of the method, the step of causing relative rotation may include:

• rotating both tools;

• rotating the preform;

• rotating the preform and rotating one of the first and second tools; and

• rotating both tools and the preform. The method may be performed on a perform, and a body of the preform may subsequently be blow molded to form a container. Alternatively, the method may be performed on the neck of a container, such as a blow molded container formed from the preform. The preform may be formed by injection molding or compression molding. The preform may be molded with an external thread on the neck. This enables production of a preform or container neck having both an external molded thread and an internal swaged thread. The internal thread may be formed either with or without a change in pitch. The thread may be simply a groove, such as a continuous groove around the neck. In accordance with one method embodiment, the method may also include the step of smoothing a top surface of the neck while forming the internal thread. The smoothing step may be accomplished by the application of heat and pressure to a top end surface of the neck. In other embodiments, a separate finish ring may be provided which is assembled to the neck such that the ring is received over an outer surface of the neck. This finish ring may have an external thread, and may itself be a molded plastic article. In various method embodiments, one or more of the tools may be heated. Also, the neck of the preform or container may be heated to facilitate formation of the swaged internal thread. In accordance with another embodiment, an article is provided comprising a plastic preform or container. The article has a cylindrical neck of substantially uniform wall thickness, and at least one internal swaged thread in the neck. The article may further comprise a finish ring secured over the neck and having at least one external thread. Again, the external thread may be formed by injection molding or compression molding. The container may be a blow molded plastic container formed from the preform. The following description and accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention. Brief Description of the Drawings FIG. 1 is a perspective view of a preform molded without threads in accordance with one aspect of the present invention; FIG.2 is a schematic diagram that illustrates swaging an internal thread in the preform of FIG. 1 ; FIG. 3 is a schematic diagram that illustrates swaging an internal thread in a container molded from the preform of FIG. 1 ; FIG. 4 is a sectional view of the portion of FIG. 3 within the area 4; FIG. 5 is a perspective view of a preform and finish ring assembly having both internal and external threads in accordance with another embodiment of the invention; FIG. 6 is a schematic diagram that illustrates swaging an internal thread in a preform having a molded external thread; FIG. 7 is a sectional view of a preform having a molded external thread and a swaged internal thread; FIG. 8 is a sectional view of a preform with an internally formed horizontal groove (as the internal swaged thread) in accordance with another embodiment; FIG. 9 is a schematic diagram that illustrates various alternative relative movements of the preform and first and second tools, in accordance with various embodiments of the invention; and FIG. 10 is a schematic diagram that illustrates a combined step of swaging an internal thread in a container and smoothing the top surface of the neck of the container.

Detailed Description of Preferred Embodiments

FIG. 1 illustrates an exemplary container preform 10 having a body 12 and an integral neck 14. Neck 14 preferably is cylindrical in contour, and as molded has no internal or external threads in this embodiment. The specific preform 10 illustrated in FIG. 1 is molded with an external stop bead 16 for cooperating with tamper-indicating structure in a closure secured to the final container, and a support flange 18 that facilitates handling of the preform and the container. Bead 16 and flange 18 are optional. Cylindrical neck 14 is of generally uniform radial wall thickness. Preform 10 can be injection molded or compression molded of monolayer plastic construction such as PET, or of multilayer plastic construction having matrix or structural layers of PET, for example, and one or more intermediate layers of barrier material such as ethylene vinyl alcohol (EVOH) or nylon. The barrier layers may or may not extend into the preform neck 14. In accordance with one aspect of the present invention, internal threads are swage-formed in neck 14 either prior to or subsequent to blow molding of the preform body 12. As illustrated in FIG. 2, one or more internal threads 20 are swaged in preform neck 14 prior to blow molding preform body 12. These threads 20 are swaged into the preform neck by means of a first rotary tool 22 that engages the inner surface of neck 14, and a second rotary tool 24 that engages the outer surface of neck 14. Inner tool 22 includes a disk 26 with a peripheral channel 28. Outer tool 24 includes a disk 30 having a peripheral bead or rib 32. With tool 22 in engagement with the internal surface of neck 14 and tool 24 engaged with the external surface of neck 14, the tools (and preform) are rotated so that bead 32 deforms or swages the plastic material of neck 14 into channel 28 on tool 22. This deformation can be assisted and promoted, if desired, by heating one or both of the tools 22, 24; alternatively the swaging can be a cold-forming operation. After the internal threads 20 are formed in neck 14, preform 10 is placed in a suitable blow mold, and the heated preform body 12 is blow molded to form the body 12a (FIG. 3) of a container. FIG. 3 illustrates an alternative technique for swaging internal threads 20 in preform neck 14 after blow molding container body 12a. Reference numerals in FIG. 3 that are identical to those in FIGS. 1-2 indicate identical parts. Whether the internal threads are swaged in the preform neck prior to or subsequent to blow molding the preform body, the neck 14 remains of substantially uniform radial thickness as illustrated in FIG. 4. FIG. 5 illustrates a method of forming a preform or container having both internal and external threads in the preform or container finish. After swaging one or more internal threads 20 into the neck 14 of the preform or container (FIG. 2 or FIG. 3), a separately made finish ring 34 is secured over the external surface of neck 14. Finish ring 34 has one or more external threads 36 preformed therein. As a modification to FIG. 5, stop bead 16 and/or support flange 18 may be formed in ring 34 rather than in the preform. Thus, the final container in accordance with the embodiment of FIG. 5 includes both internal and external threads, with the internal threads being swaged into the container neck and the external threads being formed on a separate finish ring. FIGS. 6 and 7 illustrate another method of making a preform having both internal and external threads. In this preform 40, the preform is molded with external threads 42 on the preform neck 44. After molding, and either prior to or subsequent to blow molding the preform body, swage tools 22, 24 are used to form internal threads 46 on neck 44. It may be desirable to heat neck 14 prior to or during the thread forming operation. This heating may be carried out by conduction from tools 22, 24. The neck

preferably is heated to a level above room temperature, such as in the range of 50° C to

100° C for PET finishes. The temperature of the finish neck preferably should not

exceed the glass transition temperature Tg of the neck material by more than about 40

to 50° C. For example, finish neck heating to a level of 120° C or above can cause

distortion and warping of the neck. Five seconds of contact time may be ample for thread formation when neck 14 has a thickness of 0.5 to 1 mm (0.019 to 0.039 inch). A lesser contact time, such as on the order of one second, may not be adequate unless the finish neck is very thin; this may not be desirable in the embodiments of FIGS. 1 -4, but could be accommodated in the embodiment of FIG. 5. Thus, one or more internal threads are swage formed on the E wall of preform and container neck 14. All or a portion of the preform or container neck can be crystallized before or during formation of internal threads 20 to prevent shrinkage or distortion. This would be particularly desirable in hot-fill applications, where the temperature of the material placed in the container otherwise might cause shrinkage or distortion of the container finish. Crystallization of the container finish can extend throughout the radial thickness and the axial length of the neck, including stop bead 16 and/or support flange 18 where provided, if desired. In another alternative embodiment, FIG. 8 shows the cross section of a perform 50 having a body 52 and a neck 54. In the neck there has been formed an internal thread in the form of a horizontal continuous groove 56 around the circumference of the neck.

FIG. 9 is similar to FIG. 2 in illustrating the swaging operation. However, FIG. 9 shows various directions of movement of the first tool 22 (arrows 22a, 22b), second tool 24 (arrows 24a, 24b) and perform neck 14 (arrow 14a). The preform as illustrated has a body 12 and a neck 14 with a swage formed internal thread. The preform has a longitudinal axis CL. The first tool 22 can be rotated about an axis substantially parallel to the longitudinal axis of the perform (arrow 22a), and the first tool can also be moved axially along the longitudinal axis of the perform (arrow 22b). The second tool 24 has similar directions of movement as the first tool (arrows 24a and 24b), but it is understood that the second tool will be rotating in the opposite direction as the first tool in any given operation. Overall, the second tool moves in a large arc around the perform neck (arrow 31 ) as the internal thread is formed. The preform itself may be rotated about its longitudinal axis (arrow 14a), in combination with one or both of the tools. As a result of these relative directions of movement, it is possible to form a thread having either a horizontally aligned thread or groove, or a thread or groove which is pitched with respect to the longitudinal axis of the preform. Fig. 10 shows a further alternative embodiment in which an internal swaged thread 62 is being formed in the neck of a container 60. While the internal thread is being formed, the first tool 80 is also smoothing the top surface 64 of the neck 66 of the container by means of a smoothing tool 82 positioned adjacent the top surface 64 of the neck. The smoothing plate 82 is held in position against the top surface of the neck by a compression spring 84, and the smoothing plate may be heated in order to warm the top surface and facilitate the smoothing. The first and second tools 80, 90 are shown rotating about parallel axes, in opposite directions. The internal thread may be useful for attaching a closure such as a cap to seal the container, or a fitment such as a pouring spout. Preforms may be of any suitable plastic construction, such as monolayer PET or multilayer construction of PET layers alternating with layers of barrier resin such as ethylene vinyl alcohol (EVOH) or nylon. Preforms may be injection molded or compression molded. Likewise, finish rings may be of injection or compression molded plastic construction. By providing finish rings separate from preforms, the finish rings may be of any desired material construction, either the same as or more preferably different from the material construction of the preform. For example, the finish ring can be of PET, post consumer resin (PCR), process regrind (REG), polypropylene (PP), polyethylene (PE) or polyethylene naphthalate (PEN) construction. Where the finish ring is of polyester construction (e.g., PET, PEN or process regrind), the finish ring may be wholly or partially crystallized as molded. This may be accomplished by employing fast-crystallizing materials, or suitably setting process conditions for manufacture of the finish ring, such as high mold temperature, slow mold cooling, heated areas in the mold cavity, etc. The finish ring alternatively may be wholly or partially crystallized in a post- molding operation. In other words, the material and conditions of fabrication of the finish ring may be selected separately from the material and manufacturing conditions of the preform to achieve desired operating characteristics at the finish area of the preform and the final container. Furthermore, the preform can be molded with thin wall sections without having to accommodate flow of material into a thicker finish area, which reduces material cost and mold cycle time. The finish ring is secured to the neck of the preform by interference fit (e.g., press fit or shrink fit), adhesive or welding.. The finish ring and/or the preform neck can be provided with suitable means for preventing rotation of the ring on the neck. Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims.

Claims

Claims 1. A method of forming at least one internal thread in a plastic neck of a preform or container comprising: (a) engaging the inner surface of the neck with a first tool having a peripheral channel, (b) engaging an outer surface of the neck with a second tool having a peripheral bead, and (c) causing relative rotation between the neck and tools to swage at least one internal thread in the neck between the channel and bead.

2. The method of claim 1 , wherein the step of causing relative rotation comprises: (a) rotating both tools; (b) rotating the preform; (c) rotating the preform and rotating one of the first and second tools; and (d) rotating both tools and the preform.

3. The method of claim 1 , wherein the method is performed on the neck of a preform.

4. The method of claim 3, wherein the preform includes a body and the method includes, subsequent to forming the swaged internal thread, blow molding the body of the preform to form a container.

5. The method of claim 1 , wherein the method is performed on the neck of a container.

6. The method of claim 1 , wherein the preform is formed by injection molding or compression molding.

7. The method of claim 1 , further comprising the step of smoothing a top surface of the neck while forming the internal thread.

8. The method of claim 1 , wherein the thread is formed with or without a change in pitch.

9. The method of claim 1 , wherein the thread is a groove.

10. The method of claim 1 , wherein the groove is a continuous groove around the neck.

11. The method of claim 1 , further comprising: (d) providing a finish ring, and (e) assembling the finish ring to the neck such that the ring is received over an outer surface of the neck.

12. The method of claim 11 , wherein the finish ring has an external thread.

13. The method of claim 11 , wherein the finish ring is a molded plastic finish ring having an external thread.

14. The method of claim 1 , wherein the neck is a molded neck having an external thread.

15. The method of claim 14, wherein the molded external thread and the swaged internal thread are axially displaced.

16. The method of claim 1 , which includes heating one or both of the tools.

17. The method of claim 1 , which includes heating one or more of the neck, the first tool and the second tool.

18. The method of claim 1 , wherein the preform has a body and the method further comprises blow molding the body to form a container either prior or subsequent to forming the swaged internal thread.

19. A plastic preform or container made in accordance with the method of claim 1 , having at least one swaged internal thread in the neck, alone or in combination with an external molded thread in the neck.

20. An article comprising a plastic preform or container having: (a) a cylindrical neck of substantially uniform wall thickness; and (b) at least one internal swaged thread in the neck.

21. The article of claim 20, further comprising a finish ring secured over the neck and having at least one external thread.

22. The article of claim 20, wherein the neck is formed by injection molding or compression molding.

23. The article of claim 20, wherein the neck has an integrally molded external thread.

24. The article of claim 20, wherein the article is a blow-molded container.