Note: Descriptions are shown in the official language in which they were submitted.
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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
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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.
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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
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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.
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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.
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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.
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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.
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
10 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
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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
areas) 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
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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 locations) 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
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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
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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.
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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
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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.
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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.
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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
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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
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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 materials) 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
materials) 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 vamped lead-in portion,
and a trailing terminal groove segment having a gradually shallowing,
tapered or vamped lead-out portion. Preferably, no full portion of a groove
segment axially overlies or underlies another full portion of another groove
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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
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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.
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