Abstract:
A method of making a preform assembly including providing a finish ring of plastic construction, placing the finish ring onto a core pin, introducing a preform polymer into a mold cavity that includes the core pin, and compression molding the preform polymer to the finish ring. A resulting preform assembly, and container assembly blow-molded from the preform assembly, are also disclosed.

Description:
[0001]     The present invention is directed to preform assemblies for blow molding plastic container assemblies, to plastic container assemblies blow molded from such preform assemblies, and to methods of making such preform assemblies and container assemblies.  
       BACKGROUND AND SUMMARY OF THE INVENTION  
       [0002]     In the manufacture of plastic containers, it is conventional to injection mold or compression mold a container preform having a body and a neck finish with one or more external threads or other closure attachment means. The preform neck 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 neck finish of the preform. U.S. Pat. Nos. 4,609,516, 4,710,118 and 4,954,376 illustrate injection molding of multilayer container preforms.  
         [0003]     Molding the neck finish portion of a container as part of the container 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 mold cavity into the area in which the neck finish is molded. The neck finish typically requires more accurate and stable dimensioning than the body of the preform, which can limit the cycle time of the preform molding process. Furthermore, the neck finish of the preform is of the same material as a monolayer preform body, and of the same material as at least the outer layers of a multilayer preform body, which limits the ability to obtain the most desirable material characteristics at the neck finish. When the preform is of polyester construction, such as polyethylene terephthalate (PET), the neck finish of the preform can be wholly or partially crystallized to improve the operating characteristics of the neck finish area, particularly in hot-fill container applications. However, the requirement that the neck finish be of the same material as at least the outer layers of a multilayer preform body still limits the design capabilities of preform manufacture.  
         [0004]     A method of making a preform assembly in accordance with one aspect of th present invention includes providing a finish ring of plastic construction, placing the finish ring onto a core pin, introducing a preform polymer into a mold cavity that includes the core pin, and compression molding the preform polymer to the finish ring.  
         [0005]     In accordance with a second aspect of the present invention, there is provided a preform assembly for blow molding a container assembly, which includes a molded plastic finish ring and a plastic preform compression molded to the finish ring such that a neck portion of the plastic preform radially interengages the finish ring.  
         [0006]     In accordance with a third aspect of the invention, there is provided a container assembly blow molded from a preform assembly which is produced from compression molding a preform to a molded plastic finish ring. The container assembly includes the molded plastic finish ring, and a plastic container having a neck portion thereof radially interengaging said finish ring.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     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:  
         [0008]      FIG. 1  illustrates a side elevational view of a preform assembly according to one exemplary embodiment of the present invention;  
         [0009]      FIG. 2  illustrates a side elevational view of a container assembly, blow-molded from the preform assembly of  FIG. 1 , according to another exemplary embodiment of the present invention;  
         [0010]      FIG. 3  illustrates a side elevational view of a finish ring for the preform and container assemblies of  FIGS. 1 and 2 ;  
         [0011]      FIG. 4  illustrates a top view of the finish ring of  FIG. 3 ;  
         [0012]      FIG. 5  illustrates a cross-sectional view of the finish ring of  FIG. 3 , taken along line  5 - 5 ;  
         [0013]      FIG. 6A  illustrates a compression molding apparatus for use in accordance with an exemplary method of the present invention, wherein the apparatus is shown in an open position in which a charge of preform material is located within a mold cavity and a pre-made finish ring is loaded to a core pin;  
         [0014]      FIG. 6B  illustrates the compression molding apparatus of  FIG. 6A  wherein the apparatus is shown in a closed position in which the preform material is compression molded within a portion of the pre-made finish ring;  
         [0015]      FIG. 7  illustrates a fragmentary cross-sectional view of a portion of the compression molding apparatus of  FIGS. 6A and 6B  and a cross-sectional view of the resulting preform assembly, wherein the preform assembly has been retracted and is carried on the compression core pin; and  
         [0016]      FIG. 8  illustrates an enlarged cross-sectional view of the preform assembly of  FIG. 7 , taken from circle  8  thereof. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0017]      FIG. 1  illustrates a preform assembly  20  in accordance with one presently preferred embodiment of the invention as comprising a preform  22  and a separate finish ring  24  secured thereover. The preform  22  may be injection molded, but is preferably produced by compression molding as will be discussed in greater detail below. The preform  22  is composed of any suitable plastic material such as monolayer polyethylene terephthalate (PET) or the like, or multilayer PET or the like in which matrix layers of PET, for example, alternated with one or more layers of a barrier resin material such as ethylene vinyl alcohol (EVOH), nylon or the like. The finish ring  24  is injection or compression molded or the like, and is composed of any desired material such as PET, post consumer resin (PCR), process regrind (REG), polypropylene (PP), polyethylene (PE), polyethylene napthalate (PEN), or the like. Preferably, however, the finish ring  24  is composed of a material different than that of the preform  22 , such as amorphous PET for preform  72  and crystalized PET for finish ring  24 .  FIG. 2  illustrates a container assembly  120  that is blow molded from the preform assembly  20  of  FIG. 1  in accordance with another presently preferred embodiment of the present invention, and includes the finish ring  24  secured to a container  122  in a manner that is in all significant respects identical to that of the preform assembly  20  from which the container assembly  120  is blow-molded. Accordingly, such securement details will not be repeated for this embodiment.  
         [0018]     In  FIG. 1 , the preform  22  includes a closed lower end  26  and extends upwardly therefrom in the form of a body  28  that terminates in a cylindrical neck  30  that is integrally molded with the body  26 . (Directional words such as “upper” and “lower” are employed by way of description and not limitation with respect to the upright orientation of the preform assemblies and components illustrated in the drawings. Directional words such as “radial” and “circumferential” are employed by way of description and not limitation with respect to the axis of the preform neck or finish ring as appropriate.) As also shown in  FIGS. 3-5 , the finish ring  24  is circumferentially continuous and includes an annular cylindrical wall  32  having one or more external threads or thread segments  34 . In the preferred embodiment illustrated in the drawings, a circumferential bead  36  extends around the outer surface of the wall  32  beneath the threads  34  for cooperating with a tamper-indicating mechanism on a closure (not shown) to be secured to the finish portion of the final container. A capping or support flange  38  extends radially outwardly from the lower end of the wall  32 , giving the finish ring  24  a generally L-shaped lateral cross section in the illustrated embodiments of the invention. As best shown in  FIG. 5 , the finish ring  24  includes a cylindrical internal surface  40  and a tapered internal surface  42  extending between top and bottom ends  44 ,  46 . Annular grooves  48  are provided in the tapered internal surface  42 , as will be further described in reference to  FIGS. 6A-8  below.  
         [0019]     Referring now in general to  FIGS. 6A-8 , there is illustrated a compression molding apparatus  50  for use in accordance with an exemplary method of the present invention. In  FIG. 6A , the apparatus  50  includes a core pin  52  positioned above a compression mold  54 . The compression mold  54  includes a closed bottom end  56 , a body portion  58 , and a partial finish portion  60  that together define a mold cavity  62 . The apparatus  50  occupies an open position in  FIG. 6A , in which a charge of preform material  64  is introduced into the compression mold cavity  62  and the pre-made finish ring  24  is placed on to the compression core pin  52 , as shown. The charge  64  is soft or molten, and thereby conforms to and fills the lower end of the mold cavity  62 . The core pin  52 , with the finish ring  24  mounted thereto, and the mold  54  are positioned in vertical alignment.  
         [0020]     As shown in  FIG. 6B , the core pin  52  and finish ring  24  are then moved into the mold  54  to compression overmold the charge  64  partially within the finish ring  24 . The term “overmold” is a term of art and, as used herein, means to mold one component from a soft or molten state to another component in a solid or finished state. The molten preform material charge  64  flows in an upward or forward direction between the core pin  52  and mold  54 . As a result, the preform  22  is formed including the closed bottom end  26 , the body  28  and the neck  30 . More significantly, however, the preform assembly  20  is formed from the overmolding of the preform  22  to the finish ring  24 . Thereafter, and as shown in  FIG. 7 , the core pin  52  is retracted with the preform assembly  20 , including the preform  22  and finish ring  24 , mounted thereto.  
         [0021]     As shown in  FIG. 8 , the preform assembly  20  includes the preform  22  compression molded partially within a portion of the finish ring  24 . More specifically, the neck  30  of the preform  22  includes an upper portion  66  having annular projections  68  that extend into the annular grooves  48  of the finish ring  24  so as to positively radially interlock or interengage the finish ring  24  to the preform  22 . The annular grooves  48  in the finish ring  24  can also be referred to as radial recesses or radial interengagement features. The radial interengagement between the preform  22  and finish ring  24  provides positive resistance to any axially applied force tending to separate the components  22 ,  24 . The preform  22  also includes a tapered or conical external surface  70  that corresponds to the tapered or conical internal surface  42  of the finish ring  24 . The tapered internal surface  42  of the finish ring  24  is greater in diameter than the corresponding portion of the core pin  52 . Accordingly, a small gap  72  is provided between the core pin  52 , tapered internal surface  42  of the finish ring  24 , and a leading edge  74  of the preform  22 . In terms of the preform assembly  20 , the gap  72  is provided between a transition point  76  of the finish ring  24  and the forward edge  74  of the preform  22 , wherein the transition point  76  is defined by the intersection of the cylindrical or straight internal surface  40  and the tapered internal surface  42 . The gap  72  is intentionally provided to accommodate within-tolerance variation of the size, volume or weight of the molten preform charge. In other words, at least some gap  72  should always be present under maximum material conditions of both the preform  22  and the finish ring  24 , to ensure a proper fit therebetween without any distortion due to overpacking of the preform material into the finish ring  24 . The term “overpack” is a term of art and, as used herein, refers to a condition where an excessive amount of molten polymer is compression molded and tends to lead to difficulties in ejecting the finished formed part or parts from the compression molding apparatus. Overpacking also tends to lead to warpage of, and residual stress within, the finished part or parts.  
         [0022]     With one or more of the embodiments described above, the present invention provides a number of advantages. The present invention facilitates production of preform assemblies and container assemblies wherein a finish ring is composed of a material different from that of a preform or container to which the finish ring is radially interengaged. Likewise, the present invention facilitates application of finish rings of various sizes and/or materials, to a common size preform and/or container. Moreover, the present invention enables a decrease in the cycle time required to produce a preform because the constraint of the process—forming the neck finish portion—can be subordinated to a separate, parallel production process for producing just finish rings. In the same vein, the present invention enables a reduction in the piece price of each preform because the mold tooling can be simplified, and reduced in cost, to omit the complex thread split features typically required for the threaded finish portion of the preform.  
         [0023]     There have thus been described preform assemblies for blow molding plastic container assemblies, plastic container assemblies blow molded from such preform assemblies, and methods of making such preform assemblies and container assemblies that fully satisfy all of the objects and aims previously set forth. The present invention has been disclosed in conjunction with presently preferred embodiments thereof, and a number of modifications and variations have been discussed. Other modifications and variations will readily suggest themselves to persons of ordinary skill in the art in view of the foregoing description. Indeed, the invention is intended to embrace all modifications and variations as fall within the spirit and broad scope of the appended claims.