Note: Descriptions are shown in the official language in which they were submitted.
CA 02366986 2001-10-11
MOLDING MULTI-LAYERED ARTICLES
USING COINJECTION TECHNIQUES
s Field of the Invention
This invention relates generally to coinjection molding and particularly
relates to an improved apparatus for molding multi-layered articles which
minimizes the effects of wall friction on contiguously flowing injection
molding
materials for supply to injection molding cavities.
to
Definitions
As used herein:
"First and second materials" is intended to cover at least two materials
which are sequentially supplied to an injection mold, it being entirely
possible
15 that one or more other materials may be sequentially supplied before,
between,
or after the first and second materials;
"Balanced Hot Runnel" is a temperature controlled heated uninterrupted
material conveying system extending from a single input (e.g. a material
source
or metering valve) to a plurality of outputs (e.g. metering valves or
injection
2 o mold cavities) comprising a single passage branched into a plurality of
passages with each of said plurality of passages, communicating with one of
the plurality of outputs, for conveying material therethrough to
simultaneously
supply equal quantities of the material to each of the outputs;
"Unbalanced Hot Runnel' is a temperature controlled heated material
2 s conveying system, for the passage of material from an input (e.g. material
supply source) to a plurality of outputs (e.g. metering valves for metering
the
material for supply of metered quantities of the material to injection mold
cavities), which is not
branched to provide passages of identical cross-section and length and does
3 o not divide the supplied material into equal quantities for the
simultaneous
supply of these quantities each to one of outputs.
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Background of the Invention
The manufacture of pure, or virgin, resin preforms for blow molding
containers is well known within the prior art. But since the advent of
recycling,
it is now possible to manufacture preforms with materials that are
compositionally less pure than virgin materials. Such degraded, or recycled,
materials not only yield positive environmental benefits in an ecologically
fragile
era but provide manufacturers with an alternative manufacturing method which
allows for substantial reductions in costs.
But, since recycled materials are obtained from post consumer solid
io waste, certain new manufacturing problems have been encountered that were
heretofore previously unknown. For example, manufacturers must now
provide, at increased costs, additional equipment for keeping the virgin and
recycled materials separate from each other. In addition, multi-layered
articles,
such as preforms, that are eventually used to form containers for food stuffs,
have even further impediments by way of rigid statutory guidelines. The
guidelines, enacted by the Food and Drug Administration (FDA), require that
certain minimums must be met, or exceeded, before the containers can be
approved as "qualified" to contain food stuffs and before the foods are
allowed
to be distributed to the consumer population. One extremely noteworthy FDA
2 o provision enacted theretowards provides for the assurance of product
"cleanliness".
Currently, in order to meet the FDA cleanliness standards, a container
must be configured such that only surfaces of virgin materials contact the
foods
and beverages therein. Other container surfaces, such as areas for contacting
2 s the human mouth, e.g. the dispensing orifice on a soda container, also
require
virgin material surfaces. As a result, it is economically desirable to provide
v
manufacturers with a apparatus capable of utilizing recycled materials within
containers while, at the same time, preventing recycled materials from
~
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contacting the very foods and liquids that are to be distributed to, and
consumed by, the public.
Some advances towards the aforementioned goal have been attained
by using coinjection molding techniques to manufacture multi-layered
containers. The multi-layered containers thence produced have interior and
exterior surfaces of the container comprised of virgin materials while the
fill and
support materials located within the interior of the container walls comprise
the
degraded, less than pure, recycled materials. Consequently, the economies
and conservation of utilizing recycled materials is thereby achieved while
io simultaneously meeting the strict FDA statutory requirements.
Prior art coinjection molding techniques that produce the multi-layered
containers described above, often first manufacture a multi-layered preform
and then blow mold the preform into the final container. The formation of
multi-
layered containers are described in detail, for example, in Applicant's United
States Patent Nos. 4,550,043 and 5,221,507.
Typically, the preforms are injection molded in multi-cavity molds which
may have as many as 9fi cavities. These preforms are then simultaneously
produced by injecting appropriate amounts of a first and second material, i.e.
virgin and recycled, into each of the cavities. To this end, the mold defines
a
2 o manifold arrangement to convey the two materials to each of the singular
cavities. Such an arrangement, as in Applicant's prior patents, is known to
convey each of the first and second materials into a singular hot runner
before
contiguously conveying the materials to the cavities. The combination then
allows for a reduction in equipment costs due to the singular hot runner
arrangement. The singular conduit repeatedly divides the materials flowing
therein into a plurality of flow paths for delivery to each cavity and to
thereby
ultimately provide each cavity with a substantially equal amount of metered
material at substantially the same temperature and at substantially the same
time as every other cavity. Yet, with mold arrangements containing large
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numbers of cavities, such as with forty-eight and ninety-six cavities, the two
materials contiguously flowing within a singular conduit have been known to
have interface boundary problems between the virgin and recycled materials
when conveyed over lengthy distances.
s Fig.1 illustrates potential interface boundary problems encountered with
sequentially and contiguously flowing materials A and B in singular conduit 2.
Flow is in the direction of arrow 4 with overlapping tails 6 lagging the core
flow
of the materials to such an extent that a transverse cross-section (Fig. 2) of
the
flowing materials may contain two or more layers in a radial material
to distribution A-B-A (or even A-B-A-B or more) of materials A and B in
lengthy
conduits. This problem complicates the injection molding of preforms for blow
molding containers meeting the aforementioned FDA requirements in
multi-cavity mold constructions utilizing contiguously flowing material
distribution systems.
i s Other prior art multi-cavity mold apparatus, that use coinjection molding
to form multi-layered preforms, utilize molds in which a completely separate
manifold system for each material, i.e. virgin and recycled, is used to
separately
convey that specific material to the singular cavities. The separate materials
are then injected sequentially into the cavities utilizing a valve arrangement
2 o dosely adjacent each cavity to control the flow from the separate
manifolds into
multi-orifice nozzles. Such arrangements result in molds that are expensive
and complex.
Objects and Summar)r of the Invention
2 s It is an object of the present invention to provide a more distinct
division
between the recycled and pure materials being contiguously conveyed within
the same conduit to the individual mold cavities in ot~der to more accurately
provide a substantially equivalent amount of molding materials to each cavity.
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It is also an object of the present invention to provide a method and
apparatus that yields a delivery method for a first and second material that
delivers the respective materials at substantially the same temperature and at
reduced costs while conveying substantially equal amounts of the respective
s materials at substantially simultaneous delivery times.
Summary of the Invention
According to the invention, there is provided a multi-cavity coinjection
mold for simultaneously producing a plurality of multi-layered articles
comprising: a mold structure defining a plurality of mold cavities; a first
supply
source for supplying a first molding material; a second supply source for
supplying a second molding material; a hot runner system in communication
with said first and second supply sources for conveying timed metered
quantities of said first and said second materials separately to a region
1 s proximate each cavity; and each said region comprising a contiguous gate
and
adjacent passage with a reciprocal pin closely housed in the passage for
movement between a fully retracted position, in which the first and second
materials are conveyed contiguously through said passage and said gate to the
proximate cavity, and a gate closure position, in which the pin has ejected
all
20 of the first and second materials from the passage into the proximate
cavity,
the passage and -gate having the same cross-section and size without
restriction therebetween.
Also according to the invention, there is provided a multi-cavity
coinjection mold for simultaneously producing a plurality of multi-layered
2 s articles comprising: a mold structure defining a plurality of mold
cavities; a first
supply source for supplying a first molding material; a second supply source
for
supplying a second molding material; a hot runner system in communication
with said first and second supply sources for conveying said first and said
second materials separately to a region proximate each cavity; a valve
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mechanism per cavity for receiving said first and said second materials from
said hot runner system and for sequentially supplying desired quantities of
said
first and said second materials contiguously to a hot runner to a region
proximate each cavity, wherein each hot runner communicates with a single
cavity only; and each said region comprising a contiguous gate and adjacent
passage with a reciprocal pin closely housed in the passage for movement
between a fully retracted position, in which the first and second materials
are
conveyed contiguously through said passage and said gate to the proximate
cavity, and a gate closure position, in which the pin has ejected all of the
first
1 o and second materials from the passage into the proximate cavity, the
passage
and gate having the same cross-section and size without restriction
therebetween.
Also according to the invention, there is provided a method of multi-
cavity coinjection molding for simultaneously producing a plurality of multi-
ls layered articles comprising: a) providing a mold structure defining a
plurality
of mold cavities; b) providing a first supply source for supplying a first
molding
material; c) providing a second supply source for supplying a second molding
material; d) separately conveying said first and second materials through a
hot
runner system from said first and second supply sources to convey timed
2 o metered quantities of said first and said second materials separately to a
region
proximate each cavity; wherein each said region comprising a contiguous gate
and adjacent passage with a reciprocal pin closely housed in the passage,
the passage and gate having the same cross-section and size without
restriction therebetween; and e) and moving the pin between a fully retracted
2 s position, in which the first and second materials are conveyed
contiguously
through said passage and said gate to the proximate cavity, and a gate closure
position, in which the pin has ejected all of the first and second materials
from
the passage into the proximate cavity.
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Brief Description of the Drawin4s
The invention will now be described, by way of example, with reference
to the accompanying drawings, in which:
Figs.1 and 2 illustrate the distribution of contiguously flowing materials A
and B in a relatively long conduit;
Fig. 3 is a diagrammatic cross-section of a multi-cavity coinjection mold
system according to one embodiment of the invention;
Figs. 4, 5, 6, 7 and 8 are diagrammatic views of cavity arrangements
having passage and pin arrangements associated with a mold cavity, according
1 o to variations of the invention;
Fig. 9 is a diagrammatic illustration of a further embodiment of a mold
of the present invention in which additional materials are used in the
coinjection
process; and
Fig. 10 is a variation of Fig. 4.
Detailed Description of the Preferred Embodiments
With reference to the embodiment of Fig. 3, a cavity mold 8 for the
sequential coinjection molding of multi-layered preforms for the blow molding
of multi-layered containers comprising interior and exterior surfaces of a
virgin
2o material, e.g. polyethylene terephthalate (PET) is illustrated as having
four
cavity arrangements 10. It will be appreciated by those skilled in the art
that,
in practice, the multi-cavity mold 8 depicted may have a greater number of
cavities including both odd (e.g. 71 ) or even (e.g. 9fi) numbers. Four cavity
arrangements 10 are used in this example to simplify explanation of the
present invention which is applicable to molds having any number of cavities.
Each cavity arrangement comprises a cavity 12 (e.g. Fig. 4) of a form is
itself
well known to those skilled in the art and is not described in detail herein.
At
the base of each cavity is a gate 14 through which passes the materials which
will form the preform in that particular cavity. The particular gate cross
section
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is a function of the properties of materials conveyed and of how much material
is to be injected. All of which are well known within the art.
The mold 8 defines a plurality of hot runner passages 16 (e.g. Fig. 4)
each for conveying timed sequential quantities of alternating first and second
molding materials contiguously and simultaneously to all cavities.
In operation, each passage 16, receives first and second materials
through a hot runner manifold system 20 by way of hot runners 22, 24. The
first and second materials (A and B) are supplied by plasticizers 26 and 28
under control of ram pots 30 and 32, respectively. So that the two materials
i o are sequentially supplied in timed metered quantities through the passages
16
of the associated cavity (Fig. 4).
An example of a cavity arrangement 10 is diagrammatically illustrated
in Fig. 4 in which one only of a plurality of cavities 12 of a multi-cavity
mold is
shown, the other cavities being identical as to form and material supply
i5 arrangements. In this embodiment an essentially nozzleless material supply
arrangement is provided in that material A and B reach the gate 14 through a
passage 16 of the same cross-section and size as the gate 14, without the
reduction in cross-section inherent in a nozzle such as the nozzles of the
prior
art. Hereinafter in this preferred description, the preferred cross-section of
2 o passage and gate as being circular will be referred to.
In this embodiment materials A and B are separately and sequentially
conveyed through hot runners 22, 24 in timed metered quantities to
passage 16 through which they are conveyed contiguously to and through
gate 14 to cavity 12 for the coinjection molding of a multilayer preform as
25 previously described.
A pin 30 is reciprocally mounted in passage 16 and is shown in full in its
retracted position and in ghost in its gate closure position. The pin is
cylindrical
and has a diameter about 0.0005 inches (0.013 mm) to about 0.001 inches
(0.025 mm) less than the diameter of passage 16 and gate 14.
CA 02366986 2001-10-11
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Friction of the materials A and B contiguously flowing through
passage 16 causes the interfaces of materials in passage 16 to form tails
adjacent the wall of passage 16 which lag the more centrally located core
portions of the interfaces. These tails are undesirable as they have a
potential
s of adversely affecting material distribution in the preform produced in the
cavity 12. The further the materials are contiguously conveyed, the worse is
the adverse effect. In the embodiment of Fig. 4, the adverse effect of the
tails
is minimized as a result of the materials A and B being separately supplied to
passage 16 and the passage 16 being kept as short as possible with the
to consequence that the contiguous contact of materials A and B is minimized
with the consequent minimization of the tails.
When the metered quantities of materials A and B, for injection molding
a preform, have been conveyed to the passage 16 and cavity 12, the
passage 16 is full. At this time, the pin 30 is moved by actuator 32 in the
1 s direction of arrow 34 to drive the material remaining in passage 16
through the
gate 14 to completely fill the cavity 12 with the pin 30 then closing the gate
14.
By this means, the pin 30 ejects all material from passage 16 and thus
eliminates all residual tails which would otherwise remain pending the next
molding cycle. With the pin 30 in this position, the cavity is full. The pin
30
2 o then is applying and continues to apply a packing pressure (produced by
actuator 32) to the material in the cavity 12 while that material is
solidifying,
thereby to ensure complete filling of the cavity 12 and formation of a
complete
preform therein. The pin 30 remains in this position until the next molding
cycle
is about to commence, at which time the pin 30 is withdrawn by actuator 32 to
2 s its fully retracted position with ports 36 and 38 fully open for the
conveyance,
in timed metered sequence, of materials A and B to passage 16. It should be
noted that pin 30 does not control flow of either material A and 8 to passage
16
as these materials are only supplied to passage 16 while the pin 30 is fully
retracted.
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It will be appreciated that while hot runners 22, 24 only for materials A
and B (e.g. virgin and recycled PET) are shown, the provision of hot runners
for the timed metered supply of a third (e.g. a barrier material) material
etc.
could be provided within the scope of the invention. Also while the hot
s runners 22, 24 are shown as ported into the side of passage 16, annular or
other port configurations could be used.
Referring now to Fig. 5 which illustrates a variation of the embodiment
of Fig. 4, only distinguishing features will be described. Here a timed valve
mechanism 18, hereinafter described in more detail, supplies metered
1 o quantities of materials A and B, from hot runner systems 20 (balanced or
unbalanced) for contiguous conveyance to passage 16 by way of hot
runner 40, where this contiguous supply of materials A and B is sequenced
with a timed metered supply of material C (e.g. a barrier material) from a
further
material supply source 42 by way of hot runner 44 for the contiguous supply of
15 materials A, B and C in a desired sequence through gate 14 to cavity 12.
It will be appreciated that a further timed valve mechanism 18 (Fig. 6)
could be employed to provide a contiguous supply of materials (e.g. C and D
or C with A or B, etc.) in place of the metered supply of material C.
The valve mechanisms 18 are as closely adjacent their respective
2 o cavities 12 as possible. It will be appreciated that separate conveyance
of the
first and second materials to the valve mechanisms proximate their respective
cavities will minimize any interface boundary difficulties between the first
and
second materials since the two materials are not contiguous within a singular
conduit prior to reaching the valve mechanisms. Once combined by the valve
2 s mechanisms 18, the distance traveled by the contiguous first and second
materials within the hot runners 40, 44 and passages 16 is minimal and the
difficulties of lengthy contiguous travel are minimized. Simultaneously,
equipment cost advantages are realized since each hot runner 40, 44 is a
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single undivided channel dedicated to a single cavity. In addition, hot runner
manifold system 20 need not be a balanced conveyance system.
Timing control mechanism 46 facilitates the coordination of simultaneous
switching of the plurality of valve mechanisms 18 so that substantially equal
s amounts of the materials will be supplied simultaneously to each individual
cavity 12. Actuators 32 and timing mechanism 46 may be any one of a variety
of electro-mechanical mechanisms as will be well known to those skilled in the
art and will not be described here in detail.
Further construction details of mold 8, particularly its hot runners,
io together with the heating and cooling arrangements therefore are also
conventional within this technology and will be readily apparent to those
skilled
in the art. Likewise, the plasticizers and ram pots are of conventional
construction as are the general engineering details of valve mechanisms.
Accordingly, these matters are again not described herein in detail.
i5 It will be further appreciated by those skilled in the art that the
separate
and distinct hot runners 22, 24 may be used to convey different materials from
respective plasticizers 26 and 28 wherein the materials supplied from the
plasticizers are of substantially different processing temperatures. Such an
alternative arrangement, while providing distinct hot runners for materials of
2 o differing temperatures, may also be used if the materials are of the same
processing temperature. The conveyance of the specific materials are kept
separate until conveyed to the appropriate proximate cavity regions. Conveyed
first and second materials are then likewise supplied to a timed valve
distribution system 18 for combining the materials into hot nrnners 40,
2 s passages 16 and eventually to the appropriate individual cavities 12.
Fig. 7 illustrates a cavity arrangement 10 in which valve 18 at least
partially encompasses passage 16 and pin 30 and is operated by rotation
about central axis 48 of pin 30. This arrangement provides the shortest
possible path for the contiguous supply of materials A and B to cavity 12
while
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In all embodiments disclosed, it will be appreciated that passages 16 are
hot runners suitably temperature controlled, as is the hot runner system 20
and
hot runners 22, 24, 40, 44, 52, 54, etc. by temperature controllers 56 and
appropriate insulation 58 (these being shown diagrammatically only in
s Figs. 3, 4 and 10).
Referring now to Fig. 9, four plasticizers 70, 72, 74 and 76 which may
each be associated with a ram pot (not shown in Fig. 9) separately supply a
plurality of up to four different materials by way of one or both of balanced
and
unbalanced hot runner system to supply cavities 12 of cavity arrangements 10
i o with time metered contiguous quantities of materials A, B, etc. in
accordance
with the above described embodiments.
In an embodiment employing an unbalanced hot runner and a balanced
hot runner the plasticizers may provide three different materials, for
example,
virgin PET recycled PET and another material, such as a barrier material.
is Alternatively, two of the plasticizers could supply virgin PET. In either
circumstance virgin PET is supplied separately by way of the unbalanced hot
runner to the valve mechanisms of the assemblies 10 while the other materials
are metered by a diverter valve to the balanced hot runner for contiguous flow
therethrough to supply the materials simultaneously and sequentially in equal
2 o quantities to the valve mechanisms of the assemblies 10 for metering, with
the
virgin PET from the unbalanced hot runner, to provide the contiguous supply
of the materials from the valve mechanisms of the assemblies 10. Operation
of all of the valves is preferably synchronized to ensure appropriate material
metering.
2 s In the event of the material from two of the materials both being virgin
PET, this arrangement can advantageously be used to supply virgin PET
through an unbalanced hot runner to valve mechanisms of the assemblies 10
without any possible contamination by the recycled PET, thereby to facilitate
the formation of the inner surface of a multi-later article molded in the
cavities
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and to supply virgin and recycled PET through a balanced hot runner for use
in the article where contamination of the virgin PET is less critical.
It will be appreciated that, for example, a single plasticizer could be used
to supply the same material to both the unbalanced hot runner and the diverter
s valve of the balanced hot runner and that similar variations are possible in
other embodiments. In addition the balanced hot runners may be identical, in
order to balance the contiguous supply of metered material therethrough,
or may be different from each other andlor controlled at different
temperatures
to provide desired characteristics of material flow to the cavities.
1 o The valve mechanisms may be provided with an "off" or closed position
as well as a position for the supply of each material sequentially and
contiguously.
Of course it will be appreciated that diverter valve operation could be
adjusted, if injection molding in different cavity groups is unbalanced
thereby
~ s causing non-uniform layers and or parts from cavity group to cavity group,
by
sequentially operating the valves andlor changing valve timing to adjust
material flow from one cavity group to another, for example, so that cavity
groups that would receive the most material would have their diverter valve
operation delayed to compensate and balance the flow of material to the
2 o groups.
One of the materials may be recycled PET or a barrier material e.g.
ethylene vinyl alcohol (EVOH) disposed intermediate polyester layers of the
article.
Fig.10 shows a variation of Fig. 4 in which hot runners 22, 24 conveying
2 s materials A and B are increased in cross-sectional area upstream of the
ports 36, 38 in order to reduce frictional effects on the material flows. A
similar
increase in cross-sections material supply hot runner could be utilized in
other
embodiments of this invention.
