CA2425018C

CA2425018C - Graded crystallization of container finishes

Info

Publication number: CA2425018C
Application number: CA 2425018
Authority: CA
Inventors: Thomas E. Nahill; Keith J. Barker; Brian A. Lynch
Original assignee: Graham Packaging Pet Technologies Inc
Current assignee: Graham Packaging Pet Technologies Inc
Priority date: 2002-04-12
Filing date: 2003-04-08
Publication date: 2008-01-29
Anticipated expiration: 2023-04-08
Also published as: DE60305776T2; PL359635A1; US7033656B2; EP1679176A3; ATE328718T1; KR20030081134A; CA2425018A1; AU2003203666A1; EP1352730A1; CO5450248A1; ECSP034555A; MXPA03003159A; SG120925A1; AU2003203666B2; JP2004001481A; CR6956A; JP4409198B2; US20060110558A1; NZ525296A; TW200306935A

Abstract

A container, a container preform and a method of making the container or preform in which the finish of the preform or container is at least partially of crystallizable polymer construction, and has an end portion remote from the body of the preform or container, a second end portion adjacent to the body of the preform or container, and a mid portion between the end portion The end portion of the finish forms an end surface, and the end and mid portions of the finish form continuous inner and outer surfaces. The polymer material in at least one of the end, inner and outer surfaces is crystallized, and crystallization in the finish in a direction perpendicular to such surface is graded from crystallization at the surface to an essential absence of crystallization at a position within the finish spaced from the surface.

Description

RCC:hu 17829F
GRADED CRYSTALLIZATI4N OF CC)NTAINER FINISHES

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

Background and Summary of the Invention Containers of crystallizable polynter constt uction. - e.g., PET construction -are conventionally fabricated in an injection blow molding operation, in which a preforrn 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,lJ.S.
Patents 4,618,5 15, 4,928,835 and 6,217,818. T'he uncrystallized portions of the container bodv and finish are typically translucent, while the crystallized portion(s) of the frnish contain spherulite that has a milky opaque appearance.

The term "crystaliizable polymer"in. the present application refers to any polymer that is capable of being crystallized. These polymers include not onlv polyesters such as PET, which is the crystallizable polymer most typically used to make containers, but also polyolefins such as polyethylenes and polypropylerles, polycarbonates and polyamides such as rrylons. 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.

Likewise, when referring in the present application to preforms or containers that are at least partly of crystallizable polymer construction., or to preforms or containers of crystallizable polymer construction, such language refers not only to containers that are entirely of crystallizable polymer construction, but also to multilayer containers in which inside and outside layers are of crystallizable polymer construction. Cryttter intermediate layers of the container or preform may include barrier materials against migration of gases through the container walls, layers of process regrind andfor layers that include post consumer resin. '1'hese intermediate layers may be included only in the body ot'the container, such that the container finish is of unlayered polymer construction, or may extend into the tinish of the container. See, for example, US. Patents 4,550,04' ), 4,609,516, 4,781,954, 4,990,301 and 5,098,274.

It has been proposed to crystallize the entire finish of a PET' container to improve dimensional stability of the container finish. However, such complete crystallization may induce shrinkage of the finish as a result of crystallization, which is unacceptable in the threaded section of the finish to which a container closure will ultimately be secw-ed.
Conversely, a completely amorphous finish is subject to softening and movement as the container is hot-filled and capped because the temperature of the container may rise above ttae glass transition temperature of the plastic. It is therefore an object of the present invention to provide a technique i:or selectively crystallizing portions of the container finish that substantially reduces or eliminates shrinkage of the finish as a result of crystallization, provides desired stability in the finish sealing and thread area where the container closure will ultimately be secured, and/or that reduces consumption of energy as compared with crystallization of the entire finish area. C)ther and more specific obJects of the invention are to provide a preform for blow naolding a hollow plastic container, a hollow plastic container, and a method forforrra.ing a hollow plastic container in which the container finish is selectively crystallized as described above,.

These and other objects are achieved in accordance with the present invention by selectively crystallizing the neck finisll of the preform or container in such a way as to achieve substantial crystallization in at least a tirst portion of'the finish, substantially no crystallization in a second portion of the finish, and graded crystallization between the first and s,econd portions of the finish. The term "graded crysta.llization" ref~rs to a gradual transition between substantial crystallization and substantially no crystallization, as distinguished from a sharp or distinct non-graded pattern of contrast between crystallized and uncrystallized portions of the neck finish. The gradation of crystallization is continuous, and may be either linear or non-linear with distance.

'The present invention embodies a number of aspects, that may be implemented separately from or in combination with each other.

In accordance with a first aspect of' the present invention, a finish on a hollow plastic container or preform has an integral body, a first end portion with an end surface spaced from the body, a second errd portion adjacent to the body and a mid portion between the end portions. The first end and the mid portions form continuous inner and outer surfaces. The finish is crystallized at at least one of the end, inner and outer surfaces, and crystallization in the finish in a direction perpendicular to the one surface is graded from crystallization at the one surface to an essential absence of crystallization at a position within the finish spaced from the one surface.

'Yet another aspect ofthe present invention provides a method of'making a hollow plastic container, which includes molding a preform at least partially of crystallizable polymer construction and blow molding the preform to forrri the hollow plastic container. Either prior to or subsequent to blow molding the preform, the finish is crystallized in such a way that at least the first end portion of the finish is crystallized, and crysta.llization in the finish is graded from crystallization in the first end portion.

..... . . . . ,,.,, .a.
,.. õ _ In accordance with a further aspect of the invention, a finish on a liollow plastic container or preform is at least partially ot'crystallizable polymer construction ancC is coupled to a body integral with the finish. "I'he finish has an erid portion remote from the body, a capping flange adjacent to the body, and a mid portion between the end portion and the capping flange.

At least a portion of the end portion, the mid portion, or both the erad portion and the mid portion is crystallized, and the capping flange is essentially free of'crystallization.

Brief Description of the Drawines 7'he invention, together with additional objects, features and advantages thereof, will be best understood from the following descriptiori, the appended claims and the accompanying drawings in which:

FIG. I is a cross sectional view of a prefornl 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;

FIG. 3 is an enlarged fragmentary sectional view ot'the neck finish in the preform of FIG. 1; and FIGS. 4-11 are fragmentary sectional views similar to that o:t' FI:G. 3 but illustrating respective additional embodiments of'the invention.

Detailed Description of Preferred Embodiments, 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 iritegrally formed in an injection molding operation, for example, and are either of monolayer or rnultil.ayer construction as previously described. Patents noted above illustrate various automated techniques for fabricating prefor ms 20. Finish 22 ofpreform 20 includes a first end portion 26 remote from body 24, a mid port:ion 28, and a second end portion 30, which preferably includes a capping ring or flange 30, adjacent to body "24. First end portion 26 defines an end surface 32.
First end portion 26 and mid portion 28 also define a continuous external surface 34 that includes at least one external thread f'or ultimate securernent of a container closure, and an internal surface 36 that will form the mouth of the container. FIG. 2 illustrates a container 20a blow malded 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 ;.xternal 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 (ancl 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 thc finish is essentially uncrystallized or amorphous, means that there is an absence of intended crystallization, ,:uid that any crystallization is an unintended and insubstantial minor result of variations in the manufacturing process. The degree of crystallization will depertd upon application. In other worcCs, the darkest areas of the drawings may possess 50% crystallization, decreasing to substantially zero through the graded area..

In FIG. 3, there is substantial crNlstalliz.ation at the outside edge of first end portion 26 of finish 22, and graded crystallization from the upper outside edge of first end 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 'dcawnward." 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. Second end portion 30, including the capping flange, is essentially free of crystallization in this embodirne:nt. Thus, in the embodiment of FIG. 3, there is heavy crystallization along outer surface 34 in first finisf- end portion 26 and the upper part of mid portion 28, graded crystallization radially inwardly to surface 36, where there is partial crystallization in first end portion 26 and the upper part of' mid portion 28, and axially graded crystallization along surface 34 in the niiddle 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 crystallizatiorn. at inner surface 36.
(It will be understood that crystallization around the circumference of finish 22 is the same as illustrated ir- the cross section of FIG. 3 (as well as the cros,3 sections of FI-.iS, 4-8) within manufactw=ing tolerance variations.) F'IG. 4 illustrates a finish 22a, in which crystallization is similar to that in FIG. 3, The uncrystallized inner area of mid portion 28 extends upwardly irrto first end portion. 26, while the partially crystallized lower end of mid portion 28 extends to a position adjacent to second end 30. Again, the capping flange is essentially free of c--,ystallization. FIG. 5 illustrates a finish 22b, in which there is full crystallization along outer surface 34 ftom first end portion 26 through mid portion 28, with second end portion 30 being essentially free of crystallization. Crystallization is graded from substantial crystallization at outer surface 34 to no crystallization at and near iriner surface 36. Crystallization is also graded in the axial direction from substantial crystallization in mid portion 34 to essentially no crystallization at second end 30. lIG. 6 illustrates a finish 22c that has full crystallization at inner surface 36 in both first end portion 26 and rrad portion 28.
Crystallization is graded in the radial direction from substantial crystallization at inner surface 36 to absence of crystallization at and adjacent to outer surface 34.
Crystallization is also graded in the axial direction, with ttiere being partial crystallization at inner surface 36 radially inwardly of the capping flange.

Controlled crystallization in the embodiments ofFIGS. 3-6 (and F'IGS. 7-8) can be obtained in any suitable manner, including for example directing heat from a quartz lamp onto the area to be crystallized while cooling the opposing area ol' the finish that is to remain uncrystallized. For exampie, in the embodirnent of FIG . 3, hot air can be directed against the outside surface and the upper portion of the inside surface ot'the iinish, while a chill plug or the like is employed to chill the lower portion of' t.he inside surf'ace. Heat sh.ield:9 can also be employed to prevent crystallization, as illustrated for example in above-notecl U.S. Patent 4,928,835. Likewise, in the embodiment ofFlCi. 6, hot air can be directed onto the inside surface of the preform finish, while the interior of the preforrn body and the outside surface of the preform body are suitably shielded and/or cooled to prevent crystallization.

F'IG. 7 illustrates a preform finish 22d in accordance with a modified embodinient of the invention, in which first end portion 26 ofthe finish is crystallized at and beneath end surface 32, while graded crystallization extends through mid portion 28 to a position at or slightly into second end portion 30. FIG. 8 illustrates a finish 22e in which first end portion 26 is crystallized at surface 32, and crysta;llization is axially graded from surface 32 to a substantial absence of crystallization in mid portion 28. The erribodiments of FIGS. 7 and 8 arc:. particularly useful for stabilizing only the sealing portion at the end of the container finish.

FIG. 9 illustrates a preform (or contain.er) finish 2N?f in which first end portion 26 is essentially uncrystallized, while ni'rd portion 28 and second end portion :30 are crystalii.zed.
Crystallization is graded axially between mid portion 28 and end portion 26, and is graded radially inwardly and axially downwardly from mid portion. 28 radially inwardly of the capping flange.

FIG. 10 illustrates a finish 22g having an external snap bead rather t11an. a external thread for securing a closure. First end portion 26 is crystallized throughout its thickness, and the upper part of mid portion 28 ss crystallized at the outer surface wllere the closure-attachment bead is disposed. Crystallizatiord is graded radially inwardlar and axially downwardly from the upper part of mid portion 28, and second end portion 30, including the capping flange, is essentially uncrystallized. , F'IG. 11 illustrates implementation of the invention in a crown type finish 22h often used on beer bottles, for example. First finish portion 26, including the finish crown, is substantially crystallized throughout its thickness. '1"he upper and outer surface portions ofmid portion 28 are crystallized, while the radially inner part of mid portion 28 is graded axially downwardly and radially inwardly. Second end 30 is essentially uncrystallized.

Although the preferred embodiments of the invention have been discussed in conjunction with crystallizing the finish of the preform, which is preferred for process handling purposes, it will be understood that the crystallization operation could take place in the neck finish after the container is blown to final form. Such a modificatiori would be particularly useful in situations in which the finish geometry is modifieci during the blow molding operation. Thus, crystallization in accordance with the present invention can be implemented on either amorphous or oriented finishes.

There has thus been described preforrns, containers and methods of'manufacture that fully implement all of the objects and airns previously set fi:,rth. The invention has been disclosed in corijunction with a number of presently preferred embodiments., and several additional modifications and variations have been discussed. Other modific:ations and variations will readily suggest themselves to persons of ordinary skill in the art. I'he invention is inteilded to embrace all such modifications and variations as fall within t.ht: spirit and broad scope of'the appended claims.

c~

Claims

1. A preform for blow molding a hollow plastic container, said preform being at least partially of crystallizable polymer construction and including:

a neck finish and a body integral with said neck finish, said neck finish having an end portion remote from said body, a capping flange adjacent to said body, and a mid portion between said end portion and said capping flange, said end and mid portions forming a continuous outer surface and a continuous inner surface, one of said inner and outer surfaces being crystallized throughout its length and the other of said inner and outer surfaces including at least a portion that is substantially uncrystallized, crystallization in at least said mid portion of said neck finish being graded between said crystallized surface and the uncrystallized portion of the other surface, said body and said neck finish below said capping flange being substantially free of crystallization.

2. The preform set forth in claim 1 wherein said outer surface is crystallized throughout its length and at least a portion of said inner surface is crystallized.

3. The preform set forth in claim 2 wherein said end portion of said neck finish is crystallized throughout its thickness between said inner and outer surfaces.

4. The preform set forth in claim 2 wherein crystallization in said end portion of said neck finish is graded between said outer and inner surfaces, being crystallized at said outer surface and uncrystallized at said inner surface.

5. The preform set forth in claim 1 wherein said inner surface is crystallized throughout its length and said outer surface is substantially uncrystallized.

6. The preform set forth in claim 1 wherein said capping flange is substantially uncrystallized.

7. A preform for blow molding a hollow plastic container, said preform being at least partially of crystallizable polymer construction and including:

a neck finish and a body integral with said neck finish, said neck finish having an end portion remote from said body, a capping flange adjacent to said body, and a mid portion between said end portion and said capping flange, said end and mid portions forming a continuous outer surface that is crystallized throughout its length, and a continuous inner surface at least a portion of which is substantially uncrystallized, crystallization in at least said mid portion of said neck finish being graded between said outer and inner surfaces and between said mid portion and said capping flange, said body and said neck finish below said capping flange being substantially free of crystallization.

8. The preform set forth in claim 7 wherein said end portion of said neck finish is crystallized throughout its thickness between said inner and outer surfaces.

9. The preform set forth in claim 7 wherein crystallization in said end portion of said neck finish is graded between said outer and inner surfaces, being crystallized at said outer surface and substantially uncrystallized at said inner surface.

10. The preform set forth in claim 7 wherein said capping flange is substantially uncrystallized.

11. A preform for blow molding a hollow plastic container, said preform being at least partially of crystallizable polymer construction and including:

a neck finish and a body integral with said neck finish, said neck finish having an end portion remote from said body, a capping flange adjacent to said body and a mid portion between said end portion and said capping flange, at least said end portion of said neck finish being crystallized, and crystallization in said neck finish being graded axially of said neck finish from crystallization at said end portion, said body being substantially free of crystallization.

12. A preform for blow molding a hollow plastic container, said preform being at least partially of crystallizable polymer construction and including:

a neck finish and a body integral with said neck finish, said neck finish having a first end portion remote from said body, a second end portion adjacent to said body, and a mid portion between said first and second end portions, said first end and mid portions forming a continuous outer surface and a continuous inner surface, said outer surface being crystallized throughout its length and said inner surface including at least a portion that is substantially uncrystallized, crystallization in at least said mid portion of said neck finish being graded between said crystallized outer surface and the uncrystallized portion of said inner surface, said body being substantially free of crystallization.

13. The preform set forth in claim 12 wherein said first end portion of said neck finish is crystallized throughout its thickness between said inner and outer surfaces.

14. The preform set forth in claim 12 wherein crystallization in said first end portion of said neck finish is graded between said outer and inner surfaces, being crystallized at said outer surface and uncrystallized at said inner surface.

15. A preform for blow molding a hollow plastic container, said preform being at least partially of crystallizable polymer construction and including:

a neck finish and a body integral with said neck finish, said neck finish having a first end portion remote from said body, a second end portion adjacent to said body, and a mid portion between said first and second end portions, said first end and mid portions forming a continuous outer surface that is crystallized throughout its length, and a continuous inner surface at least a portion of which is substantially uncrystallized, crystallization in at least said mid portion of said neck finish being graded between said outer and inner surfaces and between said mid portion and said second end portion, and said body being substantially free of crystallization.

16. The preform set forth in claim 15 wherein said first end portion of said neck finish is crystallized throughout its thickness between said inner and outer surfaces.

17. The preform set forth in claim 15 wherein crystallization in said first end portion of said neck finish is graded between said outer and inner surfaces, being crystallized at said outer surface and substantially uncrystallized at said inner surface.

18. A preform for blow molding a hollow plastic container, said preform being at least partially of crystallizable polymer construction and including:

a neck finish and a body integral with said neck finish, said neck finish having a first end portion remote from said body, a second end portion adjacent to said body and a mid portion between said first and second end portions, at least said first end portion of said neck finish being crystallized, and crystallization in said neck finish being axially graded from crystallization at said first end portion, said body being substantially free of crystallization.

19. The preform set forth in claim 18 wherein crystallization in said first end portion of said neck finish is graded between said outer and inner surfaces, being crystallized at said outer surface and substantially uncrystallized at said inner surface.

20. The preform set forth in claim 18 wherein said first end portion of said neck finish is crystallized throughout its thickness between said inner and outer surfaces.

21. The preform set forth in claim 20 wherein graded crystallization in said neck finish extends into said mid portion of said neck finish.

22. The preform set forth in claim 18 wherein said first end and mid portions of said neck finish form a continuous outer surface and a continuous inner surface, one of said inner and outer surfaces being crystallized throughout its length and the other of said inner and outer surfaces including at least a portion that is substantially uncrystallized.

23. The preform set forth in claim 15 wherein crystallization in at least said mid portion of said neck finish is graded between said surfaces.