Abstract:
A preform includes a tapered surface having projections formed thereon for contacting an adjacent, nested preform. The projections facilitate removal of a preform that has been inserted into an adjacent preform during shipping or handling prior to the reheat stage. A mold for forming the preforms all includes the projections.

Description:
BACKGROUND  
         [0001]    The invention relates to plastic articles and machinery for making the same, and more particularly to plastic preforms having features to inhibit or prevent locking of nested preforms or to diminish the force required to separate nested preforms.  
           [0002]    Plastic containers are often formed in a two stage process. The first stage encompasses injection molding a preform into a predetermined shape. The second stage encompasses reheating the preform, inserting the preform in a mold, and blowing the preform against the mold walls to form a desired container shape. Often, the finish of the container is formed in the injection molding stage. However, the threaded area of the finish may be formed by blow molding for large mouth containers.  
           [0003]    Between the injection molding stage and the reheat stage, preforms are often handled and shipped loose. During handling or shipping, nesting of one preform into an adjacent preform sometimes occurs. In this regard, FIG. 1 shows a preform  110  nested into an adjacent preform  110 ′, the latter of which is shown in cross section for clarity.  
           [0004]    Preform  110  includes an open end portion  112 , a transition portion  114 , and a body  116 . Open end portion  112  is shown in FIG. 1 having an injection molded finish, although the nesting phenomena is not limited to such preforms. An opening  120  is formed at open end portion  112 , and body  116  terminates in an enclosed end  118 . For preforms having a particular relationship between the outside diameter of body portion  116  near enclosed end  118  and an inside diameter of opening  120 , enclosed end  118  is insertable into opening  120 ′ of an adjacent perform  110 ′, thereby enabling the nesting shown in FIG. 1.  
           [0005]    Once a first preform  110  nests into adjacent preform  110 ′, the combination of performs  110  and  110 ′ may travel together, which enhances the ability of a third preform to nest in the combination. Further nesting sometimes produces long combinations or chains of preforms.  
           [0006]    Un-scrambling equipment, which may be employed prior to the reheat process to orient and position the preforms, often includes a wheel-like device intended to separate nested preforms. However, such devices are not always effective, which may cause the preform feeding equipment to jam, thereby interrupting the preform feeding process. Long combinations of nested preforms or tightly nested preforms exacerbate separation problems of nested preforms. Heat and humidity conditions either at the un-scrambling stage or during shipping may exacerbate un-scrambling problems.  
           [0007]    Because of the high production rate of commercial blow molding machines, which is typically several thousand per hour, even a short interruption in the feeding process may result in the interruption in the entire manufacturing process.  
           [0008]    U.S. Pat. Nos. 5,366,774 and 5,756,172 disclose preforms having features to prevent nesting. The anti-nesting feature of the &#39;774 patent is axially extending ribs disposed near the opening thereof. The ribs project toward the longitudinal centerline of the preform. Unfortunately, some spindles and blowing nozzles that enter into the preform throat during air injection of the blow molding process are configured to be inserted into a preform throat having a circular cross sectional surface, and the protruding ribs disclosed in the &#39;774 patent may interfere with spindle insertion or performance. As each typical blow molding machine has hundreds of spindles, replacing the spindles would require significant cost and downtime, as well as possibly significant redesign costs. Further, the effectively reduced diameter may interfere with filling equipment, which also often is inserted into the throat.  
           [0009]    The &#39;172 patent also discloses features formed on the preform that prevent nesting. The anti-nesting features are protrusions formed on the exterior surface of the preform near its enclosed end. The protrusions act as obstacles to the insertion of the narrow end of the preform into the open end of an adjacent preform. Because the protrusions are on the outside of the perform, they may be subject to fracture during shipping and handling, thereby producing loose plastic bits. The loose plastic bits may fall into the preforms and remain in a blown bottle as a contaminant. Further, the protrusions may add difficulty to the manufacturing process and, under particular conditions (such a local cold spot on a mold surface and insufficient heating of the protrusion area of the preform), the protrusions may not fully disappear upon blow molding.  
           [0010]    There is a need for improved features to alleviate drawbacks relating to nesting.  
         SUMMARY  
         [0011]    The inventors have discovered a relationship between the contact surface areas of nested preforms. As illustrated in FIG. 2, an outer surface  104  of prior art perform  110  may contact an inner surface  122 ′ of adjacent prior art preform  110 ′ in a line contact, in longitudinal cross section, as indicated by reference numeral  104 . Even if the design geometry of preforms  110  and  110 ′ would provide for contact between the surfaces at merely one circumferential line (that is, at a point when viewed in cross section), preform surfaces  104  and  122 ′ may deflect to form a line contact, in longitudinal cross section, between points  105   a  and  105   b.  Such line contact may contribute to the difficulty in separating preforms  110  and  110 ′. The present invention is not, however, limited to circumstances in which such line contact of locking occurs (unless specifically recited in the claims), but rather encompasses any preforms in which nesting may occur.  
           [0012]    A preform is provided that inhibits locking of one preform nested in another or that diminishes the force required to separate nested preforms. In this regard, the projections may prevent locking (that is, sticking or adhering) of a preform that is inserted into the throat of an adjacent preform, may provide for point contact that inhibits or prevent such locking, or that facilitates separation upon locking by conventional separation equipment prior to the reheating stage. The projections may be formed anywhere in the preform such that the projections do not form an undercut that would interfere with removal of the preform from the mold, and preferably are formed in the preform transition area.  
           [0013]    For example, a preform for forming a blow-molded container may include a body internal diameter that is smaller than its throat internal diameter. An internal surface of a transition portion between the body and throat yields to the throat internal diameter at an upper end and to the body diameter at an opposing lower end thereof. Plural projections that are disposed on the transition internal surface extend inwardly therefrom. The projections are spaced apart from the throat opening such the projections are configured to contact an adjacent preform prior to blow molding (such as during handling) to diminish the force required to separate the preform from the adjacent preform upon nesting thereof.  
           [0014]    The projections may substantially form point contact with a body external surface of the adjacent or nested preform. The projections may be limited to the transition surface such that the throat lacks projections. In some configurations, the projections are disposed entirely below a circumferential support ring formed on the throat. The projections, in front elevation view, preferably form a substantially downwardly tapered, rounded shape or other suitable geometry. The projections preferably do not form an undercut.  
           [0015]    Further, an injection mold for forming a preform is provided. The injection mold defines a cavity comprising a throat and a tapered surface disposed on inside the preform and extending downwardly from the throat. The preform comprises plural projections disposed on the tapered surface. The projections are spaced apart from the throat opening such that the projections are configured to contact an adjacent preform during handling to diminish the force required to separate the preform from the adjacent preform upon nesting thereof. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0016]    [0016]FIG. 1 illustrates nesting of conventional preforms;  
         [0017]    [0017]FIG. 2 is an enlarged view of a portion of conventional nested preforms;  
         [0018]    [0018]FIG. 3 is a perspective view of a preform illustrating an embodiment of the present invention;  
         [0019]    [0019]FIG. 4 is a side view of the preform shown in FIG. 3;  
         [0020]    [0020]FIG. 5 is an end view of the preform shown in FIG. 3 taken along lines  5 - 5 ;  
         [0021]    [0021]FIG. 6 is an enlarged, cross sectional view of the preform shown in FIG. 3 with another preform nested therein; and  
         [0022]    [0022]FIG. 7 is an enlarged view of a portion of that shown in FIG. 6. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0023]    As best shown in FIGS. 3 and 4, a preform  10  includes a throat  12 , a transition portion  14 , and a body  18 . Throat  12  is illustrated in FIGS. 3 and 4 having a finish  21 , even though the present invention encompasses preforms that lack a finish, such as preforms adapted for forming wide mouth container in which the thread portion is blown, as will be understood by persons familiar with such wide mouth forming processes in view of the present disclosure. Throat  12  forms a throat opening  20  formed therein. A circumferential support ring  23  is formed on an exterior surface of throat  20  below finish  21 .  
         [0024]    Throat  12  yields to transition  14 , which yields to body  16 . Body  16  is generally cylindrical, even though the present invention is not limited to employing any particular geometry of the body. Body  16  terminates in an enclosed end  18 . Preform  10  has an interior surface  22  and an external surface  40 . Internal surface  22  includes a throat internal surface  32 , a transition internal surface  34 , and a body internal surface  36 . In general, throat internal surface couples to transition internal surface, which couples to body internal surface. The term “couple” when used herein to describe relationships of corresponding surfaces, encompasses having another surface disposed between the surfaces that are the objects of the term. Further, the present invention encompasses radiused portions or other transitions between coupled surfaces.  
         [0025]    External surface  40  includes a throat external surface  42 , a transition external surface  44 , and a body external surface  46 . Body external surface defines a diameter D1, throat opening  20  defines an opening diameter D2, and body internal surface defines a body internal diameter D3. In a most preferred embodiment, and as shown in the figures, body internal diameter D3 is less than throat opening diameter D2 such that transition internal surface  34  makes the transition therebetween.  
         [0026]    Throat  20  preferably has a smooth bore such that throat inner surface  32  without protrusions. Throat internal surface  32  and the upper portion of body internal surface  36  are illustrated as defining substantially tight circular cylinders. The present invention is not limited to such configurations, but rather encompasses any geometric or irregular shape. Further, transition internal surface  34  is illustrated as having a substantially frusto-conical shape, although the present invention encompasses any shape, including a curved shape (in longitudinal cross section), steps, irregularities, and the like, as will be understood to persons familiar with preform and blow molding technology considering the present disclosure.  
         [0027]    Plural projections, such as elongate embosses  26 , are disposed on transition internal surface  34 . Preferably, as best illustrated in FIG. 5, three projections  26  are disposed circumferentially equidistant apart. As best shown in FIGS. 6 and 7, each projection preferably forms a point contact  27  with an adjacent preform  10 ′ that is insertable into throat  12 . Each projection  26  includes an upper rounded surface, such as half a hemisphere  28 , and a downwardly extending longitudinal tail or lower portion  30 .  
         [0028]    As best shown in FIG. 7, projection  26  in longitudinal cross section, defines an inner edge  31  opposite transition internal surface  34 . Preferably, inner edge  31  is substantially rectilinear. Inner edge preferably is either parallel to preform longitudinal centerline C or inclined at a positive angle A thereto. A longitudinal line C′ that is parallel to preform centerline C is shown in FIG. 7. Angle A is referred to as a positive angle to indicate that projection lower portion  30  does not form an undercut, but rather is formed to facilitate removal of preform  10  from the mold.  
         [0029]    Because projections  26  preferably are disposed in transition portion  14 , projections  26  are disposed in a portion of the preform that will likely be stretched and are likely to diminish or disappear during the blowing process. Projections preferably are not disposed on body internal surface  36  where body internal surface forms a right circular cylinder, as a projection in such geometry would cause an undercut that would interfere with removal of preform  10  from the mold during injection molding or like process.  
         [0030]    Further, the dashed lines, indicated schematically by reference numeral  11 , about preform  10  in FIG. 4 illustrate a mold  11  employed for forming preform  10 . Mold  11  forms a cavity that has the attributes of preform  10  described herein. Mold manufacturing for anti-locking features described herein is generally easier and less expensive than for conventional anti-nesting features. The present invention, however, is not limited to molds that are easier and less expensive to manufacture, but rather encompasses any mold configuration subject to the description herein with respect to preform  10 .  
         [0031]    The description of the embodiment shown in the figures is provided to illustrate an embodiment of the present invention. However, the present invention is not limited to the particular attributes described herein. For example, projections  26  encompass any shapes that can provide point contact with preform  10 ′. Further, point contact between projections  26  and preform  10 ′ is not required. Rather, the present invention encompasses any contact between projections  26  and preform  10 ′. Further, the present invention encompasses any geometry and location of projections  26 .