MOLDED CLOSURE WITH FLEX AREAS AND METHOD

Abstract: A plastic cap (10) having a top portion and a skirt (12) with an interior surface. There are weak areas, flex areas (14) or flex panels, preferably in the interior surface of the skirt (12), to allow the skirt to expand circumferentially radially outward when the interior surface of the skirt (12) is subjected to a radially outwardly directed force as during strip-ejection of the cap from mold tooling (38). A method of molding the strip ejectable cap (10) includes providing outwardly extending members (42) on the core (38) of the mold tooling to form areas (14) in the cap that are thinner than the average thickness of the cap to allow the cap to expand radially outward when the cap is strip ejected from the mold tooling (38) with reduced smearing of the thread.

Description: MOLDED CLOSURE WITH FLEX AREAS AND METHOD FIELD OF THE INVENTION This invention is directed to a low cost molded closure or cap, and to methods and apparatus for producing the same. The invention is also directed to a molded closure or cap that is designed to be strip-ejected from the core of a mold. BACKGROUND OF THE INVENTION There has been a need for low cost containers and container components. Closure and cap components for containers may be manufactured by various processes, e.g., by thermoforming, or by compression (by itself or by (or with) overmolding) or injection molding (by itself or with overmolding). Many such components are made by injection molding processes which involve the injection of molten polymeric material under high pressure into a mold cavity having the shape of the closure or cap (hereafter, collectively referred to as "cap") that is to be formed. The injection molding apparatus includes a cavity that is formed between male tooling, often referred to as the core, that has one or more grooves extending radially inwardly into its surface to form one or more threads on the interior surface of the cap, and female tooling that forms the exterior surface of the cap. While the formed cap is on the core, it is allowed to cool. After the female tooling is pulled away from the cap, the cap is removed from the core. There have been basically three methods for removing the formed cap from mold tooling. Two methods are preferred since they remove the cap with relatively the least damage to its threads. Either the threaded cap is unscrewed from the threaded tooling or vice versa, or the core with the thread groove therein is radially collapsed to remove the groove from the thread of the cap and an axially moving stripper, e. g., a stripper ring, engages the lower rim of the cooled cap and strips the cap from the collapsed core. These methods prevent the threads on the interior of the caps from being weakened, damaged or deformed during removal of the caps from the tooling. In the third method, a stripper, which can be a knock out pin that comes up through an uncollapsed core, engages the top wall of the cap and strips it axially from the core. This can also be done by use of a stripper ring that pushes up on the bottom surface of the cap. Since the core is not collapsed, the thread of the cap is smeared and/or distorted when the thread engages the groove as the cap is axially stripped from the core. Weakened, damaged or deformed threads are acceptable for some non- or less-demanding applications but such threads are generally undesirable because they can significantly negatively affect the torque that can be applied while screwing the cap onto a container, and/or the ability of the cap to initially or repeatedly properly seal the container. It would be desirable to provide an improved cap. It would also be desirable to provide a low cost cap, as well as improved methods and apparatus for producing improved or low cost caps. It therefore is an object of this invention to provide an improved cap. Another object of this invention is to provide a low cost cap. Another object of the invention is to provide a low cost cap that is produced with less material. Another object of the invention is to provide a cap that can be manufactured of, for example, from about 30% to about 40% less material than would a conventional cap of the same size. Another object of the invention is to provide a cap that is designed to be axially removed or stripped from a core, e. g., a non-collapsed core, having a thread or other forming groove therein, without significant smearing or distortion of the thread. Yet another object of the invention is to provide a cap that has thin flex areas that allow a threaded skirt of the cap to flex, distort or expand radially outwardly to avoid significant smearing or distortion of the thread when the cap is axially removed from male tooling of a cap-forming mold. Still another object of the invention is to provide improved methods and apparatus for forming a cap. Still another object of the invention is to provide improved methods and apparatus for forming an aforementioned desired cap. Still another object of the invention is to provide methods and apparatus that allow an aforementioned desired cap to be manufactured in less time. SUMMARY OF THE INVENTION This invention is directed to a plastic cap, comprising a top portion, an annular skirt that depends from the top portion and has an interior surface, means for securing the cap to the neck of a container, and substantially weak areas provided in the cap to allow the skirt to expand circumferentially radially outward when the interior surface of the skirt is subjected to a radially outwardly directed force, for example, when the cap is being strip ejected from mold tooling. The invention is also directed to a cap comprised of thermoplastic material and having an interior surface and an exterior surface, comprising a top portion, an annular skirt that depends from the top portion, the skirt having an interior surface that has a radially inwardly extending thread, and a plurality of flex areas that are less thick than the average thickness of the cap, and that increase the ability of the skirt to expand radially outward such that the cap can be strip-ejected from a mold core having an exterior surface with a thread-forming groove therein, with reduced smearing or distortion of the thread of the skirt by the groove of the core than if the cap did not have the weak areas. Preferably, the flex areas are the thinnest areas of the cap, or they are substantially less thick than the minimum thickness of the rest of the cap excluding the thread. The flex areas preferably are from about 1.2 to about 4 or more times thinner than the thickness of the cap excluding the thread. The flex areas can be flex panels and can be located in the inner and/or outer surface of the top portion of the cap, in the skirt, and/or in or through the joint between the top portion and skirt. The skirt can include a lower rim, and the flex areas can comprise a plurality of circumferentially spaced panels, each continuous from the top portion of the cap or from the top of the skirt or side wall to the lower rim of the cap. The flex areas or flex panels can be narrow and elongated in the skirt and can extend in a direction substantially parallel to the longitudinal axis of the cap. The widths of the flex panels can taper inwardly as they extend toward the top portion of the cap. The thread of the cap preferably is formed of segments that are circumferentially staggered from one another. Preferably, no thread segment overlies or underlies another thread segment. The thread segments can have full portions and lead-in and lead-out portions, wherein no full portion of a segment axially overlaps an overlying or underlying full portion of a thread segment. The flex areas can be spaced equally from each other about the cap, and they can be substantially less thick than the average thickness of the cap. The flex panels can be located between the thread segments, and they can be thinner than the average vertical cross sectional thickness of the skirt, or thinner than the average vertical cross sectional thickness of the skirt measured in the non-threaded portions of the skirt. The skirt can have portions of a first thickness, and flex areas of a second thickness that are thinner than said first portions, for allowing the skirt to stretch mainly in the flex areas and thereby increase the ability of the skirt to expand radially outward more when the skirt is subjected to an internal radially outwardly directed force than if the same force were applied to said skirt without the flex areas. The invention is also directed to a method of molding a strip ejectable plastic cap, which comprises molding a cap in a tool set having a mold cavity formed by female tooling for forming the exterior surface of the cap and by a core for forming the interior surface of the cap, such that the cap will have an exterior surface, an interior surface, a top wall, and a depending annular skirt having a thread and that is in communication with the top wall, providing radially outwardly extending members on the outer surface of the core to form radially inwardly extending weakened areas in the interior surface of the cap, the members extending radially outwardly sufficiently such that the weakened areas are thinner than the average thickness of the cap, to allow the skirt to expand radially outward and thereby allow the cap to be strip-ejected from the mold tooling with reduced smearing of the thread. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front elevation of a preferred embodiment of the cap of the invention. Fig. 2 is a top plan view of the cap shown in Fig. 1. Fig. 3 is a bottom view of the cap of Fig. 1. Fig. 4 is a vertical sectional view taken through a segment of thread and a portion of the skirt of the cap of Fig. 5. Fig. 5 is a vertical sectional view taken along line 5-5 of Fig. 2 of Sheet 2 of the drawings. Fig. 6 is a vertical sectional view taken along line 6-6 of Fig. 2 of Sheet 2 of the drawings. Fig. 7 is a vertical sectional view taken along line 7-7 of Fig. 2 of Sheet 2 of the drawings. Fig. 8 is a top side perspective view of the cap of Fig. 1. Fig. 9 is a bottom perspective view of the cap of Fig. 1. Fig. 9A is a top perspective view of a second embodiment of the cap of the invention. Fig. 9B is a top view of the cap of Fig. 9A. Fig. 9C is an elevational view of the cap of Fig. 9A. Fig. 9D is a sectional view taken along line 9D-9D of Fig. 9B. Fig. 9E is a top perspective view of a second embodiment of the cap of the invention. Fig. 9F is a top view of the cap of Fig. 9E. Fig. 9G is an elevational view of the cap of Fig. 9E. Fig. 9H is a vertical sectional view taken along line 9H-9H of Fig. 9F. Figs. 91 through 9L are views similar to those shown in Figs. 9A through 9D, of a fourth embodiment of the cap of the invention. Figs. 9M through 90 are views similar to those shown in Figs. 9A through 9C, showing a fifth embodiment of the cap of the invention. Figs. 9P through 9S are views similar to those of Figs. 9A through 9D, showing a sixth embodiment of the cap of the invention. Fig. 10 is a front elevation, with portions in vertical section through a portion of a closed tool set of an injection molding apparatus having an empty mold cavity for forming a cap of the invention. Fig. 11 is a vertical section of the injection molding apparatus of Fig. 10 shown with the tool set open, and it is cross section of the cavity in front elevation. The skirt of the cap has spaced axial thin portions that allow the cap to distort, flex or expand radially outwardly as the cap is stripped axially, rather than unscrewed, from the core of a mold cavity. The thread preferably is segmented, i.e., discontinuous. The segments of the thread, other than the initial lead-in and terminal lead-out portions, are circumferentially staggered from one another. None of the segments of the thread (other than the aforementioned lead-in and lead-out portions) axially directly underlie another segment of the thread. This allows minimal smearing or distortion of the thread. The closure or cap (hereafter "cap") is a low cost cap. It uses significantly less material, often from about 30% to about 40% less material, to form the cap as compared to a conventional cap of similar size. Because of the reduced material employed, molding, cooling and stripping time are reduced. DESCRIPTION OF PREFERED EMBODIMENTS OF THE INVENTION Fig. 1 shows a preferred cap 10 of the invention. Although the cap shown is for a 1 " diameter tubular collapsible dispensing container, the cap of the invention is not limited to any particular sized or type of container. Cap 10 has a top wall, top panel or top portion 11 , an outer axial wall or skirt 12 with a top brim or ridge 13 and thin, preferably substantially aligned circumferentially spaced flex areas, here, generally designated 14. The flex areas are thinner than the less-flex thicker areas of the skirt. Whereas the wall thickness of the skirt of a conventional cap of the same size for a 1 " diameter tube is about 0.035" thick from the outer surface to the non- threaded portion of the inner surface of the skirt, the thickness of cap 10 is about 0.025" thick, measured in the same area through the skirt. The thickness of the thin flex area for cap 10 is about 0.009". The width of each flex area is about 0.050". It is to be understood that these thicknesses are preferred for a cap 10 having the dimensions disclosed herein for a one inch diameter tube having a neck whose diameter is 0.5 inch. Thus, if desired, one skilled in the art can adapt these dimensions and thicknesses to suit the packaging application. It is contemplated to be within the scope of this invention that the flex areas can have ribs axially circumferentially or angularly therein, thereon or thereacross. Also, one or more of the flex areas themselves can have weakened areas relative to the flex area or areas, for example, holes or gaps, with or without webs, areas of reduced thickness, or portions with pores or filled with particulate material to further weaken portions of the flex area(s) or panel(s). There can be any suitable number of flex areas. Preferably, there are two or more. The more there are, the thicker they can be. However, generally, the more there are, the less thread circumferential length there will be. Preferably, the flex areas are spaced uniformly or equally from each other about the circumference of the cap. This allows the cap to be circumferentially axially balanced and provides uniform torque relative to rotation of the cap about the threads of, for example, the neck of a container. Each of the flex areas need not be of the same thickness. Each flex area need not be of the same design or configuration, so long as the purpose of the invention is met. Thus, each, any or all of the flex areas can be of any suitable size, shape, design or configuration. For example, they can be rectangular, trapezoidal, conical, frustoconical, circular, oblong, spiral, helical, or any combination of the same. Though less preferred, there may be certain applications where it may be desirable that the flex areas encompass, lead or follow one or more of the thread segments. As shown, preferably the flex areas are rectangular, though they preferably may also be slightly frustoconical or tapered (to be wider at their lower ends). Preferably, the flex areas are axially arranged. The flex areas can be of any suitable height or length. Preferably, the flex areas are of uniform height and extend the full height or length of the skirt of the cap. As explained below, one or more of the flex areas of the skirt can extend into a portion of or diametrically across the top wall of the cap. Consistent with a main objective of the invention, the one or more flex areas can be at any suitable location(s) of the cap. For example, the one or more flex areas of the cap can be located only in the top wall of the cap or only at the joint of the top wall and skirt of the cap. If the flex areas are located in the top wall of the cap, preferably they extend to the joint of the top wall and more preferably into the skirt of the cap. For example, as shown in Figs. 9E-9H, the top wall 11 ' can have flex areas 14' that preferably are arranged in a starburst pattern in top wall 11", and that extend to the upper brim or ridge 13' of skirt 12'. The entire area of the top wall can be of reduced thickness and can be considered a flex area within the scope of the invention to allow the skirt to flex radially outward to facilitate stripping of the side wall of the cap without distortion or smearing of the cap. Fig. 2 is a top view of the cap of Fig. 1. Fig. 2 shows that cap 10 has a top wall 11. Fig. 3 is a bottom view of the cap of Fig. 1. Skirt 12 has an outer surface 16 and an inner surface 18. Fig. 4 is a vertical section through a segment 20 of a thread 22. The thread preferably but need not be a buttress thread. The thread preferably is sufficiently long enough to support itself during the strip ejection process. Its thickness preferably is about 0.015". Fig. 5 shows a segment 20 of thread 22. Figs. 6 and 7 show staggered thread segments 20 that straddle flex areas 14. These Figures also show lead-out portion 24 of a segment 20 overlying lead-in portion 26 of a lower segment 20. Since the lead-in and lead-out portions are tapered radially outward (progressively thinner) toward the inner surface of the skirt, they do not pose an interference or stripping problem. Figs. 8 and 9 are perspective views of cap 10. Fig. 9 shows that flex areas 14 are located between thread segments 20, and that the flex areas preferably extend to the bottom edge or rim 17 of the skirt. Figs. 9A through 9D show a second embodiment of the cap of the invention, generally designated 10' having flex panels 14' extending from outer surface 16' of skirt 12' radially into the wall of skirt 12' of cap 10'. Flex panels 14' extend from the top edge or rim 13' to the bottom edge 17' of the skirt. The flex panels are substantially parallel to the axis of cap 10' and are spaced equally about the circumference of the cap. Figs. 9E through 9H show a third embodiment of the cap of the invention, generally designated 10". Cap 10" is similar to cap 10' except that cap 10" has a plurality of flex panels that extend downwardly into and are arranged in a starburst or radial pattern in top wall 11 ". Flex panels 14' are shown interrupted by a central portion 15' that is of the normal thickness of top panel 11 ". Although, flex panels 14' could, in these Figures they do not enter rim 13' of side wall or skirt 12', nor do they join flex panels 14'. Providing one or more flex panels downwardly into the upper, outer surface of top portion 11 " as shown in Figs. 9E through 9H, or upwardly into the inner surface thereof, helps to meet the objectives of the invention because it weakens the hoop strength of the side wall or skirt. Flex panels 14' can extend into one another by eliminating central portion 15. Figs. 91 through 9L show a fourth embodiment of the cap of the invention, generally designated 10'". Cap 10'" does not have a top rim such that top panel 11 '" directly joins skirt 12'". In this embodiment, flex panels 14'" in top wall 11 '" and skirt 12'" adjoin each other and form one continuous flex panel. This flex panel arrangement enables the opposed portions of cap 10'" on either side of the flex panels to be moved away from each other in a hinging fashion from the area adjacent top panel 11 '", to facilitate strip ejection of the cap from a core of mold tooling. Figs. 9M through 90 show a fifth embodiment of the cap of the invention, here generally designated 100. This embodiment shows that flex panels 14' can be advantageously employed with continuous flex panel 14'", the former allowing the skirt to expand circumferentially radially outwardly, and the latter enabling the skirt to hinge adjacent top panel 11 '", and thereby cooperatively allowing or facilitating strip ejection of cap 100 from the core of mold tooling. Figs. 9P through 9S show a sixth embodiment of the cap of the invention, generally designated 100'. Cap 100' has flex panels 114 extending from an outer peripheral portion of top panel 111 through joint 117 and downwardly into the outer surface of the upper portion of skirt 112. This configuration of flex panels arranged circumferentially about the joint of the top wall and skirt creates pivot points which allow the skirt to move outwardly to facilitate strip ejection. Flex panels 114 can be of any suitable length in the top wall and skirt. For example, they may be configured as merely a plurality of circumferentially spaced notches (not shown) formed in the joint 117 between the top panel 111 and skirt 112. Thus, the embodiments of Figs. 9A through 9S show that the flex panels can be of any suitable size, configuration and location that meets the objective of the invention, that of reducing the hoop strength of the side wall or skirt to facilitate strip ejection of the cap. A main concept of the invention is that the cap of the invention can easily be stripped axially from the male tool or core on which it is molded. As shown in Figs. 10 and 11 , the male mandrel 38 has staggered grooves 40 therein and in which the staggered thread segments are formed. Mandrel 38 also has radially outwardly extending axial ribs 42 protruding from its outer surface. Ribs 42 form flex areas 14 in cap 10. Fig. 10 shows the tool set closed, prior to injection of plastic into the mold cavity. Fig. 11 shows the tool set opened and the cap stripped from the mandrel, after stripper plate 44 has moved upwardly and has engaged the bottom edge of skirt 12 of the cap. Although the male tool or core has been discussed in connection with an injection molding apparatus, it is to be understood that the caps of the invention and the improved apparatus and methods can be employed as well in connection with compression molding and thermoforming apparatus and methods. In accordance with the invention, the cap can be easily stripped from the mandrel because of its overall reduced wall thickness and particularly because of the very thin flex areas. This allows the skirt to expand radially outward and thereby allow the each thread to leave the groove in which it is formed and be axially stripped from the mandrel without encountering another groove above it and thus without significant smearing of the threads. The thread preferably has an extended axial length to allow it to be functional for providing sufficient torque for threadedly securing the cap to the neck of a container, even if there is some smearing of a thread segment. Those skilled in the art of strip ejection of caps will understand how to apply the disclosure of this invention to caps of different sizes, types and applications. The factors that may apply and may need to be considered and balanced, include the wall or skirt strength, e.g., column strength, required for the particular application, the materials employed, the overall diameter of the cap, the number of flex areas, their dimensions (height, thickness and width), and the size, thickness, and profile or shape of the cap and thread. The height and taper of threaded skirt or side wall of the cap is also a factor, since it affects the amount of expansion of the skirt and the ease of stripping. Other interrelated factors include whether the cap has a continuous or segmented thread, and the level of stripping force, thread distortion, and torque retention desired for the application being considered. The weakened areas, flex areas or panels preferably are the thinnest areas of the cap. They are substantially less thick than the minimum thickness of the cap, excluding the thread. They preferably are substantially thinner, preferably 1.2 to about 4 or more times thinner than the thickness of the cap excluding the thread. The thickness of the thin flex areas, here panels, of the skirt, preferably and usually are the thinnest portions of the skirt. The flex areas or panels preferably and usually are thinner than the average vertical cross sectional thickness of the skirt. With respect to the skirt 12 of cap 10, flex areas 14 preferably and in fact are thinner than the average thickness of the skirt measured in non-threaded portions of the skirt. Flex areas 14 also preferably are thinner than the otherwise thinnest portions of the skirt, i. e., those portions measured from the depths of the grooves of the serrated surface of the cap to the inner, non-threaded surface of the skirt. Preferably, the flex areas are generally less thick, preferably substantially less thick than the minimum thickness of the general side wall. The objective is that the flex areas be designed to be focused, built in weak areas that will provide greater flexibility than the rest of the skirt, or sufficient flexibility, that the skirt has reduced hoop strength and allows the cap to be stripped with less force and less thread distortion or disruption than without the flex areas. In cap 10, flex areas 14 are weaker than the serrated portions of the cap. Flex areas 14 desirably are as thin as possible to meet the objectives of the invention, but not so thin that they tend to split or break during stripping or the application of torque. A flex area 14 need not be of uniform thickness. And, each flex area 14 need not be the same thickness as the other flex areas. Flex areas 14, especially when they are very thin, preferably occupy only a minor portion, i.e., less than about 50%, of the circumference, periphery or breadth of the cap. Otherwise, the cap may be too weak and/or may not have enough thread to sufficiently engage the mating thread(s), e.g., on the neck of the container, or enough hoop strength to hold the cap on or properly seal the container. In preferred embodiments that employ segmented threads, flex areas 14 preferably are narrower than the width or arcuate extent of the shortest of the segments of the threads. Although it is generally true that the wider the flex area or panel, the greater the flexibility of the skirt, it is considered to be within the scope of the invention to provide many narrow axial flex panels that would not unduly limit the number of thread segments or unduly weaken the side wall of the skirt. With wide flex areas or panels, the thicker panels between the flex areas are more free to expand, flex or pivot independently or in combination outwardly and avoid smearing or distortion of single or multiple threads. Desirably, the skirt should be able to expand, or pivot, as from the weakest point near the top wall of the cap, a distance that is at least about one-half the radial thickness of the thread on the inner surface of the cap. Preferably, the skirt is capable of expanding a distance that is most of, the entire or greater than the entire radial thickness of the thread, threads or thread segments. The flex areas preferably extend from the inside surface of the cap radially outward toward the outer surface of the cap. However, it is within the purview of this invention that the one or more or all of the flex areas can extend from the outside surface radially inward toward the inside surface of the cap. A combination of these types of flex areas may also be employed. The caps of the invention are highly suitable for containers for products that are packaged with low internal pressure. The caps are also highly suitable for containers and packaging applications with limited life. It is to be understood that closure or cap herein includes any cover for an opening of an article or container. It is contemplated that a closure or cap includes a closure with a base and a flip top cap, secured to the cap by living or other hinges or straps. Closures or caps of the invention are not limited by the means by which the cap is secured or held onto the article or container. Thus, the closures or caps of the invention can have any suitable means for securing the closures or caps to the neck of a container or to a base of a cap that in turn in secured to a container. The skirt or side wall of the cap may not be threaded and may include a radially inwardly extending member, e. g., a bead for engaging or friction snapping onto or holding a cooperative portion of a neck or other portion of an article or container. The cap of the invention preferably is threaded on the interior surface of the skirt. Any suitable type of threading can be employed. The thread profile can be rounded, V- or angularly-shaped, buttress, or modified buttressshaped or a combination of these or other shapes. As stated above, preferably a buttressed, more preferably a modified buttressed thread is employed. The thread engagement surfaces of the buttress thread preferably are tapered at an angle of about 15 to about 25 degrees relative to the inside surface of the skirt of the cap. This thread is desirable because it provides higher torque resistance than say a V-shaped or rounded thread. Although the latter are easier to strip from a core, they provide less torque resistance and may not provide sufficient seals. The modified buttress thread can be employed to advantage yet it can be easily stripped from a core with minimum distortion or smearing when employed on a cap of the invention. Although the thread employed on the cap of the invention can be continuous, with or without changing depth or profile, preferably the thread is staggered or segmented, with or without changing depth or profile. The thread segments can be uniformly or non-uniformly distributed about the circumference of the skirt of the cap. The flex areas 14 preferably extend axially between the thread segments. The pitch of the thread or thread segments preferably is coarse rather than fine, and the preferred pitch for the segmented modified buttress thread of cap 10 is about 12 turns per inch. It is generally accepted to provide at least one turn of thread engagement for a uniform, balanced torque and for uniform axial pull down force. For the embodiment with the segmented thread shown in the drawings, the thread segments preferably extend circumferentially about the skirt for a total of two full turns, but roughly half of the length of the thread has been removed. The one segmented thread is spread over a distance of two thread rotations (720 degrees), with a net result similar to one full turn of continuous thread. Preferably, no portion of a full thread segment axially overlaps (overlies or underlies) another portion of another full thread segment. By a full thread segment is meant the portion of a segment that is of full axial height and radial thickness. Thus, with the segmented thread 22 of cap 10, preferably no portion of a segment 20 of the thread 22, other than a tapered lead-in or lead-out portion thereof, axially overlaps an overlying or underlying full thread segment. In cap 10, the full thread thickness is about 0.015 inch measured from the interior surface of the skirt. The full thread height of a segment is about 0.042 inch. Some full thread segment overlap can be tolerated, at the expense of increased thread smearing or distortion unless the skirt of the cap is more inclined at an angle to the vertical to facilitate stripping of the cap from the core, and/or a more tapered core is employed. The skirt of the cap 10 of the invention generally can be at an angle of about 0 to about 4 or 5 degrees, preferably about 3 degrees, and most preferably about 2.5 degrees. The greater the angle, the easier it is to strip the cap from a core, but the less torque resistance of the thread relative to the mating thread of the container. Too steep a taper reduces torque and cap retention and seal. Any suitable cap can be provided with weakened areas, for example, flex areas, in accordance with the invention. The cap can have a skirt, side wall or annular ring or shell with a vertical, conical or tapered threaded interior surface. The exterior shape of the cap can be of any suitable shape, e.g., round, oval or square. The cap can be a flip-top, dispensing or other single or multiple component article. Its wall thickness can be uniform or non-uniform. For example, it can be ribbed or serrated, or patterned. The cap can include or be employed in combination with child resistant or tamper evident features. The weakened areas, for example, the flex areas can be or be part of such a feature or features. The cap can be formed of any suitable material(s) utilizable for forming caps. Examples of such materials include propylene and ethylene polymers and copolymers, including high, medium, low, very low and ultra low density polyethenes, polypropylenes, ethylene-propylene copolymers, filled or unfilled, and polyesters for example, polyethylene terephthalates. Preferably, the cap is comprised of one or more thermoplastic materials. The caps can be single or multiple layer, barrier or non-barrier. The material(s) of the cap can include polymers made from single site catalysis systems, for example, metallocene catalysts. Suitable such materials for forming caps are disclosed in U.S. patent application Serial No. 09/144/713, filed on September 1 , 1998, the entire disclosure of which is incorporated herein by reference. The apparatus of the invention can be any suitable apparatus for molding a cap. The apparatus includes a female tool and a core operable therein to form a mold cavity for forming a cap. Either the female tool or the core or both can be formed with or modified to form the flex areas on the interior, exterior or both surfaces of the cap. Preferably, the core has an outer surface with a plurality of groove segments formed radially into the surface for forming on the core, a cap having a skirt or annular wall with an interior surface that has a radially inwardly extending segmented thread. The segments of the thread are formed in the groove segments. The groove segments of the core preferably include a first or leading groove segment having a gradually deepening, tapered or ramped lead-in portion, and a trailing terminal groove segment having a gradually shallowing, tapered or ramped lead-out portion. Preferably, no full portion of a groove segment axially overlies or underlies another full portion of another groove segment. The full portion of a thread segment is that portion of a thread segment that is not a lead-in or lead-out portion of the thread segment. The core of the apparatus of the invention can be a strip core, a collapsing core, an unscrewing core or a combination of the same. The outer surface of the core need not be, but preferably is tapered with a slightly decreasing diameter toward the end of the core that forms the upper portion of the cap, to facilitate removal of the cap from the core. The outer surface of the core of the invention generally can be tapered at an angle of about 0 to about 4 or 5 degrees, preferably about 3 degrees, and most preferably about 2.5 degrees. If flex panels are to be provided in the exterior surface of the cap, the female tool is provided with radially outwardly extending ribs or nubs, etc. as appropriate for forming the desired type, shape, etc. of flex panels in the exterior surface of the cap. Preferably, the flex panels extend axially along the skirt in locations circumferentially between thread segments. This application is related to a U.S. provisional application titled "Improved Container and Method and Apparatus for Forming the Container. The application is being filed on the same date as the subject application and is assigned to the same assignee. Strip ejection of a threaded closure reduces the molding cycle as compared to unscrewing. Thin wall "flex" areas allow the cap to distort during strip ejection. A modified buttress thread is preferred because it provides higher torque integrity as compared to "round" thread. The discontinuous thread is molded on a tapered wall and is staggered to insure the next pitch of thread will not smear the thread wall during strip ejection. The discontinuous thread is staggered, but will still provide a balanced torque and uniform axial pull down force when applied to a continuous, mating thread of a container. The cap is designed to be strip ejected. Typical strip mold closures employ continuous round threads on a taper. The closure of the invention is designed with a modified buttress thread to provide better torque retention when applied to the container. The modified buttress thread is segmented on a preferably tapered wall in a pattern that does not allow one thread to be directly above another. This pattern will allow strip ejection with minimal smearing/distortion of the thread. The closure wall will flex outwardly during ejection due to preferably symmetrical thin segments in the wall preferably parallel to the axis of the cap. These segments are designed to flex during ejection (hot polypropylene), but recover while cooling. The continuous cap wall will provide sufficient hoop strength to maintain the required thread engagement, torque and seal integrity when applied to a container.

Claims: WHAT IS CLAIMED IS: 1. A plastic cap, comprising a top portion, an annular skirt that depends from the top portion and has an interior surface, means for securing the cap to the neck of a container, and substantially weak areas provided in the cap to allow the skirt to expand circumferentially radially outward when the interior surface of the skirt is subjected to a radially outwardly directed force. 2. A cap comprised of thermoplastic material and having an interior surface and an exterior surface, comprising: a top portion, an annular skirt that depends from the top portion, the skirt having an interior surface that has a radially inwardly extending thread, and a plurality of flex areas that are less thick than the average thickness of the cap, and that increase the ability of the skirt to expand radially outward such that the cap can be strip-ejected from a mold core having an exterior surface with a thread-forming groove therein, with reduced smearing or distortion of the thread of the skirt by the groove of the core than if the cap did not have the weak areas. 3. The cap of claim 2, wherein the flex areas are the thinnest areas of the cap. 4. The cap of claim 2, wherein the flex areas are substantially less thick than the minimum thickness of the rest of the cap excluding the thread. 5. The cap of claim 2, wherein the flex areas are from about 1.2 to about 4 or more times thinner than the thickness of the cap excluding the thread. 6. The cap of claim 2, wherein the flex areas are located in the top portion of the cap. 7. The cap of claim 2, wherein the flex areas are located in the skirt. 8. The cap of claim 2, wherein there is a joint between the top portion and skirt of the cap, and the flex areas are located in the joint. 9. The cap of claim 1 , wherein the weak areas are flex panels. 10. The cap of claim 2, wherein the flex areas are flex panels. 11. The cap of claim 10, wherein the flex panels are formed in the inner surface of the skirt. 12. The cap of claim 10, wherein the flex panels are formed in the outer surface of the skirt. 13. The cap of claim 10, wherein the flex panels are formed in the top portion of the cap. 14. The cap of claim 10, wherein the top portion of the cap has an outer surface and an inner surface, and the flex panels are formed in the outer surface of the top portion of the cap. 15. The cap of claim 10, wherein the top portion of the cap has an outer surface and an inner surface, and the flex panels are formed in the inner surface of the top portion of the cap. 16. The cap of claim 2, wherein the skirt includes a lower rim, the flex areas comprise a plurality of circumferentially spaced panels and each of the flex panels is continuous from the top portion of the cap to the lower rim of the cap. 17. The cap of claim 2, wherein the flex areas are narrow elongated flex panels, that are formed in the skirt and extend in a direction substantially parallel to the longitudinal axis of the cap. 18. The cap of claim 17, wherein the widths of the flex panels taper inwardly as they extend toward the top portion of the cap. 19. The cap of claim 2, wherein the thread is formed of segments that are circumferentially staggered from one another. 20. The cap of claim 19, wherein no thread segment overlies or underlies another threaded segment. 21. The cap of claim 19, wherein no thread segment directly underlies another thread segment. 22. The cap of claim 19, wherein the thread segments have full portions and lead-in and lead-out portions, and no full portion of a segment axially overlaps an overlying or underlying full portion of a thread segment. 23. The cap of claim 19, wherein the flex panels are located between the thread segments. 24. The cap of claim 19, wherein the flex areas are spaced equally from each other about the cap. 25. The cap of claim 10, wherein the flex panels are formed in the skirt and are thinner than the average vertical cross sectional thickness of the skirt. 26. The cap of claim 10, wherein the flex panels are thinner than the average vertical cross sectional thickness of the skirt measured in the non- threaded portions of the skirt. 27. The cap of claim 10, wherein the flex areas are substantially less thick than the average thickness of the cap. 28. A cap, comprising a top portion, and a skirt that depends from the top portion, the skirt having a sidewall with an interior surface with a radially inwardly extending thread, for securing the cap to the threaded neck of a container, the thread of the cap being comprised of full segments that are circumferentially spaced from one another such that no portion of a full segment axially overlaps a portion of another full segment. 29. The cap of claim 28, wherein the skirt has portions of a first thickness, and has flex areas of a second thickness that are thinner than said first portions, for allowing the skirt to stretch mainly in the flex areas and thereby increase the ability of the skirt to expand radially outward more when the skirt is subjected to an internal radially outwardly directed force than if the same force were applied to said skirt without the flex areas. 30. The cap of claim 29, wherein the flex areas include flex panels. 31. A method of molding a strip ejectable plastic cap, which comprises: molding a cap in a tool set having a mold cavity formed by female tooling for forming the exterior surface of the cap and by a core for forming the interior surface of the cap, such that the cap will have an exterior surface, an interior surface, a top wall, and a depending annular skirt having a thread and that is in communication with the top wall, and providing radially outwardly extending members on the outer surface of the core to form radially inwardly extending weakened areas in the interior surface of the cap, the members extending radially outwardly sufficiently such that the weakened areas are thinner than the average thickness of the cap, to allow the skirt to expand radially outward and thereby allow the cap to be strip-ejected from the mold tooling with reduced smearing of the thread.

Inventors: JACKSON DOUGLAS J, KING DANIEL L, JACKSON, DOUGLAS, J., KING, DANIEL, L.
Applicants: JACKSON DOUGLAS J, KING DANIEL L, PECHINEY PLASTIC PACKAGING INC, JACKSON, DOUGLAS, J., KING, DANIEL, L., PECHINEY PLASTIC PACKAGING, INC.
Application year: 2000
Main classification: B65D41
IPC codes: B29C45, B29L31, B65D41