Note: Descriptions are shown in the official language in which they were submitted.
H-8263
MOLDS, MOLD ASSEMBLIES, STACK COMPONENTS AND MOLDED ARTICLES
FIELD OF THE INVENTION
This invention relates generally to molding apparatus and associated methods
and molded articles.
More specifically, although not exclusively, this invention relates to mold
stacks and components
thereof, mold assemblies, molds, molding systems for molding preforms and
other articles, for
example tubular articles, and to associated methods and molded tubular
articles, such as preforms.
BACKGROUND OF THE INVENTION
Molding is a process by virtue of which a molded article can be formed from
molding material, such
as a plastics material, by using a molding system, such as an injection
molding system or a
compression molding system. Various molded articles can be formed by using
such molding processes
including, for example, preforms which can be formed from polyethylene
terephthalate (PET)
material. Such preforms are capable of being subsequently blow molded into a
container, for example
a beverage container, bottle, can or the like.
As an illustration, injection molding of preforms involves heating PET
material (or other suitable
molding material for that matter) to a homogeneous molten state and injecting,
under pressure, the so-
melted material into a molding cavity defined, at least in part, by a female
cavity piece and a male
core piece. Typically, the female cavity piece is mounted to a cavity plate
and the male core piece is
mounted to a core plate of a mold. The cavity plate and the core plate are
urged together and are held
together by clamp force, the clamp force being sufficient to keep the cavity
and the core pieces
together against the pressure of the injected material. The molding cavity has
a shape that substantially
corresponds to a final cold-state shape of the molded article to be molded.
The so-injected material is
then cooled to a temperature sufficient to enable removal of the so-formed
molded article from the
molding cavity. When cooled, the molded article shrinks inside of the molding
cavity and, as such,
when the cavity and core plates are urged apart, the molded article tends to
remain associated with the
core piece.
Accordingly, by urging the core plate away from the cavity plate, the molded
article can be
subsequently demolded by ejecting it off the core piece. Ejection structures
are known to assist in
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removing the molded articles from the core halves. Examples of the ejection
structures include stripper
plates, stripper rings and neck rings, ejector pins, etc.
When dealing with molding a preform that is capable of being subsequently
blown into a container,
one consideration that needs to be addressed is forming a so-called "neck
region". Typically and as an
example, the neck region includes (i) engaging features, such as threads (or
other suitable structure),
for accepting and retaining a closure assembly (ex. a bottle cap), and (ii) an
anti-pilferage assembly
to cooperate, for example, with the closure assembly to indicate whether the
end product (ex. a
beverage container that has been filled with a beverage and shipped to a
store) has been tampered with
in any way. The neck region may comprise other additional elements used for
various purposes, such
as to cooperate with parts of the molding system (ex. a support ledge, etc.).
As is appreciated in the
art, the neck region cannot be formed easily by using the cavity and core
halves. Normally, split mold
inserts (sometimes referred to by those skilled in the art as "neck ring") are
used to form the neck
region.
A typical molding insert stack assembly that can be arranged (in use) within a
molding machine
includes a split mold insert pair that, together with a mold cavity insert, a
core insert and optionally a
gate insert, a lock ring and/or a core ring, defines a molding cavity. Molding
material can be injected
into the molding cavity from a source of molding material via a receptacle or
port in the cavity insert
or gate insert to form a molded article. In order to facilitate forming of the
neck region of the molded
article and subsequent removal of the molded article therefrom, the split mold
insert pair comprises a
pair of complementary split mold inserts that are mounted on adjacent slides
of a slide pair. The slide
pair is slidably mounted on a top surface of a stripper plate.
As commonly known, the stripper plate is configured to be movable relative to
the cavity insert and
the core insert, when the mold is arranged in an open configuration. The slide
pair, and the
complementary split mold inserts mounted thereon, can be driven laterally, via
a cam arrangement or
any other suitable known means, for the release of the molded article from the
molding cavity. One
of the functions performed by the split mold insert pair is to assist in
ejecting the molded article off
the core insert by "sliding" the molded article off the core insert, typically
into a cooling tube mounted
to a post mold cooling unit of a downstream handling device.
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Preforms intended to be blow molded into a container normally include a hollow
cylindrical body,
typically with a varying thickness and having an open end having the final
shape of the bottle neck,
and a closed end having a dome shape intended to form a base of the bottle. In
the production of plastic
bottles, biaxial molecular orientation blow molding, also referred to simply
as blow molding, is a
widely applied process. This process can either be carried out simultaneously
with the injection
molding process in an integrated system, commonly referred to as a single
stage process, or separately
using a so-called two-stage process. In the two-stage process, the preforms
are molded in a dedicated
injection molding machine, and are subsequently cooled and stored for a
predetermined period. These
preforms are later heated to a temperature sufficient to soften the body and
fed into a stretch blow
molding machine.
In the blow molding machine, the hot and deformable preform is placed in a
blow-molding cavity,
which describes the shape of the body of the final plastic bottle. A stretch
rod is inserted into the
preform via its open neck, stretches the base of the preform to a closed end
of the blow-molding cavity,
and a pressurized fluid, normally compressed air, is introduced into the
stretched preform to force the
stretched preform material against the walls of the blow-molding cavity.
The shape of the cavity varies along its length, creating variations in the
extent to which distinct
regions of the preform body are stretched. This results in variations in the
wall thickness of the finished
bottle. One technique for improving material thickness distribution is
commonly referred to as "heat
profiling". This technique involves varying the temperature to which selected
regions within the
preform are heated, in order to influence the extent to which these regions
stretch during the blow-
molding process. More particularly, regions that are hotter than others will
deform more readily, so
the aim is to align the hotter preform regions with corresponding areas of the
bottle which would
otherwise tend to have a thicker wall.
However, this technique is less effective in the domed end region of the
preform, in part since it has
a lower surface to volume ratio. This is particularly true of the region of
the gate nub.
W02020006624A1 seeks to mitigate this by providing the closed end of the
preform with elliptical
inner and outer faces each with a respective flat circular bottom portion,
which are both centered on a
vertical center axis of the preform and have a radius of equal size. This is
believed to improve material
distribution in the finished bottle.
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The applicants have observed that material distribution can be further
improved, whilst further
reducing the quantity of wasted material in the gate area.
SUMMARY OF THE INVENTION
The present invention seeks to provide, inter alia, a means by which the
distribution of material in the
gate area can be improved to increase the proportion of material that is
redistributed into the body of
a subsequently blown container. This invention is directed, in particular but
not exclusively, to mold
stacks and components thereof, molds, mold assemblies, molding systems and
associated methods for
making tubular articles, such as preforms, and the tubular articles
themselves.
The tubular article may have a hollow body portion, which may have a closed
end. The tubular article
may have a neck portion, which may have an open end. The neck portion may
include one or more
radial flanges, which may extend outwardly. The neck portion may include
engaging features, such
as threads or a snap fit finish. The tubular article and/or neck portion may
comprise any one or more
other features described above in relation to known preform designs. In
addition, any of the foregoing
features described in relation to known preforms may be incorporated within
tubular articles according
to the invention, insofar as they are consistent with the disclosure herein.
Advantageously, the closed end of the tubular article may be formed by a
truncated dome. The
truncated dome may have an axial centre that is flush or recessed relative to
a surrounding convex
surface of the truncated dome. The recess, if present, may have a diameter or
width that is at least 10
times its depth.
According to a broad aspect of the present invention, there is provided a
tubular article, e.g. a preform
for being blow molded into a container, the tubular article comprising a
closed end having an outer
surface formed by a truncated dome with an axial centre, or apex, that is
flush or recessed relative to
a surrounding convex surface of the truncated dome, wherein the recess, if
present, has a diameter or
width that is at least 10 times its depth.
The provision of a closed end with a flush or slightly recessed axial centre,
or apex, effectively
eliminates the funnel shaped transition between the dome shaped base and the
gate nub. This reduces
the time needed to cool this area of the tubular article, thereby reducing
cycle time. This is also
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believed to provide a more effective delineation between the gate region and
the surrounding material
to be heated and stretched, whilst enabling the wall thickness of the gate
region at the axial end of the
base to be reduced. This is believed to be particularly true with a slightly
recessed axial centre, or
apex, as the ridge surrounding the recess further exaggerates this
delineation. As a result, thermal
profiling of the tubular article can be more effective whilst reducing the
overall weight of the tubular
article.
The tubular article may comprise a witness mark, which may comprise or
describe at least part of the
flush surface or recess. The flush surface or recess may, but need not, be
flat. In some examples, the
flush surface or recess may be conical or curved, e.g. spherical. The witness
mark may correspond to
a surface or portion formed at least in part by a valve stem. The witness mark
may comprise a circular
indentation or projection. Additionally or alternatively, the witness mark may
comprise an annular
projection. The witness mark may correspond in part to an outer surface of an
end of the valve stem.
The witness mark may correspond at least in part to a passage in a mold
insert, e.g. within which the
valve stem was received and/or through which the valve stem extended when the
tubular article was
molded.
Another broad aspect of the invention provides a mold insert. The mold insert
may, but need not, be
for molding a tubular article or preform as described above.
The mold insert may comprise a concave cavity portion, which may describe an
outer surface of a
closed end of a tubular article or preform. The mold insert may comprise a
nozzle receiving portion,
which may be for engaging an injection nozzle. The mold insert may comprise a
passage, e.g. for
receipt of a valve stem. The passage may join the concave cavity portion to
the nozzle receiving
portion.
The concave cavity portion may have a flat base or annular ridge that
surrounds and/or joins the
concave cavity portion to the passage. The annular ridge may, but need not,
have a height that is less
than one quarter, or 25%, of a diameter or width of the passage.
Another broad aspect of the invention provides a mold insert, e.g. a tubular
article or preform mold
insert, the mold insert comprising a concave cavity portion describing an
outer surface of a closed end
of a tubular article or preform, a nozzle receiving portion for engaging an
injection nozzle and a
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passage joining the concave cavity portion to the nozzle receiving portion for
receipt of a valve stem,
the concave cavity portion comprising a flat base or annular ridge that
surrounds and joins the concave
cavity portion to the passage, wherein the annular ridge, if present, has a
height that is less than one
quarter, or 25%, of a diameter or width of the passage.
As used hereinbelow, the term "tubular article" may be replaced with
"preform", although the skilled
person will appreciate that this invention may be beneficial for other tubular
articles, and is therefore
not limited to preforms. In addition, the witness mark of the preform may
comprise one or more
features corresponding substantially to features or dimensions of the passage
of the mold insert.
The annular ridge of the mold insert may be for forming part of the recess of
the tubular article. The
annular ridge of the tubular article may be for forming, or configured to
form, in use, the recess of the
tubular article with an end of a valve stem received within and/or extending
through the passage.
The annular ridge of the mold insert may, but need not, comprise a truncated
apex. The truncated apex
may describe an annular surface, which may be flat. The annular surface may be
for forming, or
configured to form, in use, with the end of the valve stem, a base of the
recess of the tubular article.
The annular surface may an outer diameter or width, which may be at least 5%
or 10% more than the
diameter or width of the passage. Alternatively, the annular surface may be
omitted or replaced with
an annular edge.
The recess of the tubular article may taper, e.g. from an annular rim
surrounding the recess toward a
base of the recess. The annular rim of the tubular article may comprise or
provide the convex surface
surrounding the axial centre or apex. The annular rim may be toroidal.
The annular ridge of the mold insert may taper, e.g. from a base of the
concave cavity portion toward
the or an apex of the annular ridge. The mold insert may comprise a toroidal
recess between the
annular ridge and a surrounding portion of the concave cavity portion.
The passage of the mold insert may form an edge with the surrounding concave
cavity portion. The
edge may describe a right or acute angle, e.g. to provide the flat base or
annular ridge. The edge may
describe a right or acute angle to provide the truncated apex or annular
surface of the annular ridge.
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Another broad aspect of the invention provides a mold insert, e.g. a tubular
article or preform mold
insert, the mold insert comprising a concave cavity portion describing an
outer surface of a closed end
of a tubular article or preform, a nozzle receiving portion for engaging an
injection nozzle and a
passage joining the concave cavity portion to the nozzle receiving portion for
receipt of a valve stem,
wherein the passage forms an edge with the surrounding concave cavity portion
which describes a
right or acute angle.
The recess or witness mark of the tubular article may have a diameter or width
that is at least 10 times
the depth of the recess. Preferably, the recess or witness mark of the tubular
article has a diameter or
width that is at least 20 times the depth of the recess. For example, the
recess or witness mark of the
tubular article has a diameter or width that is at least 30 times the depth of
the recess, for example at
least 35 times the depth of the recess.
In some examples, the passage of the mold insert corresponds substantially to
an outer diameter or
width of the annular ridge, e.g. an outer diameter of the truncated apex or
annular surface of the
annular ridge. In such examples, a valve stem received within and/or extending
through the passage
may be configured to form a base, e.g. the entire base, of the tubular
article. The edge formed between
the passage and the surrounding concave cavity portion may therefore comprise
an acute angle.
The annular ridge, or the truncated apex or annular surface of the annular
ridge, of the mold insert
may have a diameter or width, e.g. an outer diameter or width, that is at
least 10 times its height.
Preferably, the diameter or width of the annular ridge, truncated apex or
annular surface is at least 20
times its height. For example, the diameter or width of the annular ridge,
truncated apex or annular
surface may be at least 30 times its height, e.g. at least 35 times its
height. Additionally or alternatively,
the diameter or width of the passage of the mold insert may be at least 10
times, preferably at least 20
times, for example at least 30 or even 35 times, the height of the annular
ridge or the truncated apex
or annular surface of the annular ridge.
Additionally or alternatively, the annular ridge of the mold insert may have a
height that is less than
10% of the diameter or width of the passage, preferably less than 5% of the
diameter or width of the
passage.
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The mold insert may be for incorporation within a mold stack.
Another aspect of the invention provides a mold stack, e.g. a tubular article
or preform mold stack.
The mold stack may, but need not, be for molding a tubular article or preform
as described above. The
mold stack may, but need not, comprise a mold insert as described above. The
mold insert may
comprise or be a cavity insert or a gate insert. The mold stack may comprise a
core insert.
The tubular article may comprise an inner surface. The inner surface may
comprise a flat or bulged
portion. The flat or bulged portion may be aligned with the axial centre of
the outer surface. The
thickness of the base through the axial centre of the tubular article is
preferably within 10% of the
radial thickness of the base through the surrounding convex surface of the
truncated dome. Preferably,
the axial thickness of the base described between any point of the recess and
the flat or bulged portion
of the inner surface does not vary more than 10%. More preferably, the axial
thickness of the base
described between any point of the recess and the flat or bulged portion of
the inner surface does not
vary more than 5%.
The core insert of the mold stack may comprise a flat or recessed end portion.
The flat or recessed end
portion may be aligned with the flat base or annular ridge of the
aforementioned mold insert, e.g. when
the mold stack is in a molding configuration.
The flat or bulged portion of the inner surface of the tubular article may
have a larger diameter or
width than that of the recess, or of a base or flat base of the recess. The
flat or bulged portion of the
inner surface of the tubular article may have a diameter or width that is at
least 10% larger than that
of the recess, or of a base or flat base of the recess.
The flat or recessed end portion of the core insert of the mold stack may have
a larger diameter or
width than the or an outer diameter or width of the flat base or annular
ridge, or the truncated apex or
annular surface of the annular ridge, of the mold insert. The flat or recessed
end portion of the core
insert of the mold stack may have a diameter or width that is at least 10%
larger than the or an outer
diameter or width of the flat base or annular ridge, or the truncated apex or
annular surface of the
annular ridge, of the mold insert.
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The bulged portion of the tubular article may comprise at least one curved
surface, e.g. a convex
surface. The convex surface may have a radius of curvature which is at least
twice or three times the
diameter or width of the recess. In some examples, the convex surface
comprises a toroidal surface,
in which case the radius of curvature may be in the poloidal direction. In
other examples, the convex
surface may comprise a spherical surface, in which case the radius of
curvature may be at least 20
times, or even 40 or 50 times, the diameter or width of the recess.
The end portion of the core insert of the mold stack may comprise a recess
having at least one curved
surface, e.g. a concave surface. The concave surface may have a radius of
curvature which is at least
twice or three times the diameter or width of the passage or an outer diameter
or width of the flat base
or annular ridge, or truncated apex or annular surface of the annular ridge,
of the mold insert. In some
examples, the concave surface comprises a toroidal surface, in which case the
radius of curvature may
be in the poloidal direction. In other examples, the concave surface may
comprise a spherical surface,
in which case the radius of curvature may be at least 20 times, or even 40 or
50 times the diameter or
width of the passage or an outer diameter or width of the flat base or annular
ridge, or truncated apex
or annular surface of the annular ridge, of the mold insert.
The tubular article may comprise a neck finish, which may be adjacent the open
end. The neck finish
may comprise securing means or a securing feature, for example a thread or
snap fit bead. The neck
finish may comprise a radial flange or a support ledge, which may be between
the securing means or
feature and the closed end.
The mold insert may be or comprise a gate insert. The mold stack may further
comprise a cavity insert,
which may describe a body of the preform. The mold stack may comprise a split
mold insert, which
may describe a neck region of the preform.
Another broad aspect of the invention provides a mold, e.g. a tubular article
or preform mold. The
mold may comprise one or more, e.g. a plurality of, mold inserts or mold
stacks as described above.
The mold may comprise a cavity plate, e.g. to which the or each mold insert is
mounted. The mold
may comprise a core plate, e.g. to which the or each core insert is mounted.
The mold may comprise
a stripper plate assembly, e.g. to which the or each split mold insert is
movably mounted. The stripper
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plate assembly may be movable, e.g. along the core insert(s), to remove a
molded tubular article from
the or each core insert.
The stripper plate assembly may comprise a stripper plate and/or one or more,
e.g. a pair of, slides,
which may be movably mounted to the stripper plate. The or each split mold
insert may comprise two
or more parts, e.g. halves. Each part may be mounted to a respective one of
the slides. The slides may
be movable, e.g. as the stripper plate assembly is moved along the core
insert(s), to separate the parts
of the or each split mold insert, thereby to release a molded tubular article
from between the parts.
Another aspect of the invention provides a computer program element comprising
and/or describing
and/or defining a three-dimensional design, e.g. of the mold, mold stack or
mold insert described
above or an embodiment thereof. The three-dimensional design may be for use
with a simulation
means or an additive or subtractive manufacturing means, system or device.
.. The computer program element may be for causing, or operable or configured
to cause, an additive or
subtractive manufacturing means, system or device to manufacture the mold,
mold stack or mold
insert described above or an embodiment thereof. The computer program element
may comprise
computer readable program code means for causing an additive or subtractive
manufacturing means,
system or device to execute a procedure to manufacture the mold, mold stack or
mold insert described
.. above or an embodiment thereof.
For the avoidance of doubt, any of the features described herein apply equally
to any aspect of the
invention. Within the scope of this application it is expressly intended that
the various aspects,
embodiments, examples and alternatives set out in the preceding paragraphs, in
the claims and/or in
.. the following description and drawings, and in particular the individual
features thereof, may be taken
independently or in any combination. That is, all embodiments and/or features
of any embodiment
can be combined in any way and/or combination, unless such features are
incompatible.
For the avoidance of doubt, the terms "may", "and/or", "e.g.", "for example"
and any similar term as
used herein should be interpreted as non-limiting such that any feature so-
described need not be
present. Indeed, any combination of optional features is expressly envisaged
without departing from
the scope of the invention, whether or not these are expressly claimed. The
applicant reserves the
right to change any originally filed claim or file any new claim accordingly,
including the right to
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amend any originally filed claim to depend from and/or incorporate any feature
of any other claim
although not originally claimed in that manner.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described by way of example only with
reference to the
accompanying drawings in which:
FIG. 1 depicts a cross-sectional view of a preform according to an embodiment
of the invention;
lo
FIG. 2 depicts an enlarged view of gate area A the preform of FIG.1;
FIG. 3 depicts an enlarged view, similar to that of FIG. 2, but illustrating
an alternative
configuration of gate area A;
FIG. 4 depicts a cross-sectional view through a mold stack for making the
preform of FIG. 1;
FIG. 5 depicts a cross-sectional view of the gate insert of the mold stack of
FIG. 4;
FIG. 6 depicts an enlarged view of gate area B of the gate insert of FIG. 5;
FIG. 7 depicts a cross-sectional view of an end portion of the core insert of
the mold stack of
FIG. 4; and
FIG. 8 depicts an enlarged view of the end portion C of the core insert of
FIG. 7.
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIG. 1, there is depicted a non-limiting example of a
preform 1 according to an
embodiment of the invention. The preform 1 is for being blow molded into a
container, and includes
a central longitudinal axis L, a body portion 10, a base portion 11 describing
a closed end 1 1 a and a
neck portion 12 describing an open end 12a. The neck portion 12 includes
threads 12b adjacent the
open end 12a for cooperating with a corresponding screw thread of a closure
cap (not shown) in the
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usual way. The neck portion 12 also includes a radial flange, or support ledge
12c for handling the
preform, as is well known in the art.
The base portion 11 has an outer surface 13 formed as a truncated dome with an
axial centre, or apex
14, that is recessed relative to a surrounding annular rim 15 of the truncated
dome, as shown more
clearly in FIG. 2. The overall length of the preform 1 is described from the
open end 12a of the neck
portion 12 to a peak of the annular rim 15. The annular rim 15 describes a
convex surface 15a, which
is toroidal in this example, that surrounds and tapers toward a recess 16
having a flat or substantially
planar base the centre of which forms the recessed apex 14. In other examples,
the recess 16 or surface
describing the apex 14 may be conical or curved or spherical, or the apex 14
may be flush with a
surrounding, convex surface of the truncated dome, and either surrounded by
the annular rim 15 or
the annular rim may be omitted, for example if the apex 14 is described by a
flat or planar surface that
is flush relative to the surrounding convex surface of the truncated dome.
.. The base portion 11 also has an inner concave surface 17, which
approximates the outer surface 13,
but describes therewith a gradual increase in thickness from the closed end
lla to the body portion
10. The inner surface 17 includes a bulge 18 with an axial centre or apex 19,
opposite the recessed
apex 14. A first thickness Ti is described between the outer apex 14 and the
inner apex 19, and a
second thickness T2 is described between the peak of the rim 15 and the base
of the bulge 18. The first
thickness Ti is preferably the same or less than the second thickness T2, but
this is not critical.
In this example, the bulge 18 is toroidal and is formed with a radius R in the
poloidal direction that
results in the inner apex 19 being recessed slightly. However, the bulge 18'
may be spheroidal, with
a much larger radius R', as shown in FIG. 3. This can vary the relationship
between the first and
second thicknesses Ti', T2', but it is still preferable that the first
thickness Ti' is less than, or
substantially the same as, the second thickness T2'.
The flat base of the recess 16 has a depth D and a diameter, or width Wi
delineated by the rim 15. The
bulge 18 also has a diameter, or width W2, which is larger than the diameter
or width Wi of the base
of the recess 16. In this example, the diameter or width W2 of the bulge 18
corresponds substantially
with the diameter of the peak of the annular rim 15. The recess 16 is shallow,
in this case having a
depth D that is approximately 2.5% of its diameter or width Wi. It has been
determined that this
relationship can vary, but increasing the relative depth D of the recess 16,
for example in order to
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provide a more effective delineation between the gate region and the
surrounding material to be heated
and stretched, can create other issues.
More particularly, the skilled person will appreciate that reducing the first
and second thicknesses Ti,
Tz, Ti', Tz' excessively could be detrimental to the ability of the base 11 of
the preform 1 to withstand
the force applied by the stretch rod (not shown), during the blow molding
process. An increase in the
depth D would therefore necessitate a corresponding increase in the height of
the bulge 18, to maintain
the requisite thickness. If such an increase is substantial, the skilled
person will appreciate that this
will increase the volume, and therefore the weight, of material required to
make the preform 1.
It has been determined that an increase in depth D of the recess to a value
over 10% that of the its
diameter or width W can be particularly detrimental. As such, recess 16 should
have a diameter or
width Wi that is at least 10 times its depth D, preferably at least 20 times
its depth D and more
preferably at least 30 times its depth D.
Whilst it is possible to reduce the depth D of the recess to zero, thereby
providing a flat base in place
of the recess 16, this is less preferable as it can reduce substantially the
effectiveness of the
aforementioned delineation between the gate region and the surrounding
material to be heated and
stretched.
Turning now to Figure 4, there is shown a mold stack MS for molding the
preform 1 of Figures 1 and
2. The mold stack MS includes a core assembly 2, a split mold insert 3, a
cavity insert 4 and a gate
insert 5. It is, however, envisaged that the cavity insert 4 and gate insert 5
may be provided as a single
mold insert.
The core assembly 2 includes a core insert 20, a core ring 21 surrounding an
intermediate part of the
core insert 20 and a lock ring 22 surrounding the core insert 20 and core ring
21 for securing the core
assembly 2 to a core plate (not shown). The core ring 21 is mounted on a step
of the core insert 20
and has a male taper 21a that cooperates with a female taper 22a of the lock
ring 22 in a manner that
is known in the art and will not be described further herein. The lock ring 22
also has a further female
taper 22b on its split-mold facing side. The core insert 20 has a molding
surface 23 describing an inner
surface of the preform 1. The molding surface 23 includes a base molding
portion 24 for molding the
inner surface of the base portion 11 of the preform 1.
13
Date Recue/Date Received 2023-03-14
H-8263
The split mold insert 3 includes two parts 30, 31 each describing half of the
outer surface of the neck
portion 12 of the preform 1, and the cavity insert 4 describes the outer
surface of the body portion 10
of the preform 1, in the usual way. The split mold insert 3 in this example
includes a male taper 32,
33 on each of its core-facing and cavity-facing sides. The male taper 32 on
the core-facing side of the
split mold insert 3 cooperates with the further female taper 22b of the lock
ring 22. The male taper 33
on the cavity-facing side of the split mold insert 3 cooperates with a female
taper 40 at a first end of
the cavity insert 4.
The gate insert 5 abuts a second end of the cavity insert 4, and includes a
concave cavity portion 50
with a molding surface 51 describing the outer surface of the base portion 11
of the preform 1. As
illustrated more clearly in FIG. 5, the gate insert 5 also includes a nozzle
receiving portion 52 for
engaging an injection nozzle (not shown) and a passage 53 joining the concave
cavity portion 50 to
the nozzle receiving portion 52.
A gate area B, including the passage 53 and adjacent portions of each of the
concave cavity portion
50 and the nozzle receiving portion 52, is illustrated more clearly in FIG. 6.
The concave cavity portion
50 in this example includes an annular ridge 54 with a truncated, flat peak 55
that surrounds and joins
the concave cavity portion 50 to the passage 53. The annular ridge 54 is
joined to the concave cavity
portion 50 by a curved transition, which defines an inflection in the
direction of the adjoining region
of the concave cavity portion 50 to form a toroidal molding surface 51a
corresponding to the convex
surface 15a of the annular rim 15. As a result, the annular ridge 54 tapers
from the concave cavity
portion 50 toward its truncated, flat peak 55.
The annular ridge 54 has a height H and a diameter or width W3 that
correspond, respectively, to the
depth D and diameter or width Wi of the flat base of the recess 16 of the
preform 1 of Figure 1. As
explained in relation to the preform 1, the depth D and diameter or width Wi
of the recess 16, and
therefore the height H and diameter or width W3 of the annular ridge 54, may
vary within the
aforementioned ranges.
In this example, the truncated, flat peak 55 of the annular ridge 54 forms a
right angle edge 56 with
the passage 53. The outer diameter or width W3 of the flat peak 55 in this
case is approximately 15%
larger than a diameter or width W4 of the passage 53. The passage 53 is sized
for slidably receiving a
14
Date Recue/Date Received 2023-03-14
H-8263
valve stem (not shown) of an injection nozzle (not shown) with minimal
clearance such that, in its
deployed position, the flat end of the valve stem (not shown) is aligned with
the surrounding flat peak
55 of the annular ridge 54, thereby to describe therewith a substantially
planar recess 16.
The skilled person will appreciate that the recess 16 may include a shallow
witness mark, for example
from a small gap between the end of the valve stem (not shown) and the
surrounding end portion of
the passage 53, but this would be minimal and, if present, this witness mark
is expected to be recessed
with respect to the surrounding rim 15. Thus, the forementioned gate nub
present in typical preforms
is effectively eliminated, together with its funnel shaped transition to the
preform base. The skilled
person will appreciate that this reduces the weight of the base portion 11 of
the preform 1, and is
believed to improve material distribution for the reasons given above.
It is envisaged that this width may be reduced, even to the point of omitting
the flat peak 55 altogether,
resulting in an acute or sharp edge between the outer, curved and tapering
side of the annular ridge 54
and the passage 53. In such cases, the end of the valve stem (not shown) alone
would describe the
recess 16. Whilst this may be advantageous, for example because the edges of
any resulting witness
mark would be aligned with the outer edge of the recess, the resulting sharp
edge of the gate insert 5
between the outer side of the annular ridge 54 and the passage 53 is
undesirable for reasons that would
be appreciated by those skilled in the art. To mitigate this, the outer
diameter or width W3 of the flat
peak 55 is preferably, although not necessarily, at least 5% larger than a
diameter or width W4 of the
passage 53.
Turning now to FIG. 7, the core insert 20 includes an end portion C, shown
more clearly in FIG. 8,
that is truncated. More specifically, the base molding portion 24 of the
molding surface 23 is in the
form of a truncated dome, in which its end is truncated by a distance T. In
this example, the truncated
outer surface 13 of the base portion 11 of the preform 1 is also truncated by
a similar distance. The
diameter or width Ws of truncated end corresponds to the diameter or width W2
of the bulge 18 of the
closed end lla of the preform 1, and is therefore larger than the outer
diameter or width W3 of the flat
peak 55 of the annular ridge 54 of the gate insert 5.
A shallow, toroidal recess 25 describes or delineates the truncated end in
this case. The recess 25 has
a poloidal radius R, configured to ensure that the axial thicknesses Ti, T2 of
the end of the preform
base 11 are substantially the same. This configuration corresponds to the
closed end 1 1 a of FIG. 2.
Date Recue/Date Received 2023-03-14
H-8263
The skilled person will appreciate that a similar core insert 20 to that shown
in FIGs 7 and 8 could be
used to make the closed end 11 a' of FIG. 3, but in such a case the toroidal
recess 25 would be replaced
with a spherical recess for making the spherical bulge 18' of the closed end
11 a'.
It will be appreciated that the configuration of the preform 1, particularly
of the closed end 11a, 11 a'
thereof, may vary, particularly although not exclusively as described above.
Similarly, the mold stack
MS or molding surface described by the mold stack MS, particularly by the core
insert 20 and/or the
gate insert 5, may also vary, particularly although not exclusively as
described above.
It will also be appreciated by those skilled in the art that several
variations to the construction and/or
use of aforementioned examples are envisaged without departing from the scope
of the invention. It
will also be appreciated by those skilled in the art that any number of
combinations of the
aforementioned features and/or those shown in the appended drawings provide
clear advantages over
the prior art and are therefore within the scope of the invention described
herein.
16
Date Regue/Date Received 2023-03-14
