Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: METHOD FOR PRODUCING FILLED RIGID CONTAINERS OF PLASTIC
BACKGROUND OF THE INVENTION
In the process of producing a filled plastic container, for
example, rigid plastic bottles of polyethylene terephthalate
(PET), polypropylene or the like, the steps of producing the
container are conventionally separated from the filling
operation for many reasons. Production of the containers, as by
injection blow molding or injection stretch blow molding, is
typically and necessarily carried out at a different rate than
the filling operation if both of these operations are to be
performed at optimal efficiencies. The container molding
operation, for example, is best performed without interruption,
if major start-up losses are to be considered. This applies
particularly to the process for injection molding of preforms
which precedes the blowing operation. In fact, the injection
molding procedure is primarily responsible for the disparity in
the operating cycles.
It is well known in for example the milk carton technology
to couple the forming of the containers with the filling
processes. For example, for this operation a blank is
conventionally supplied to a machine that sequentially erects
the container, fills the container and seals the container.
This procedure may be performed in adjacent and in-line
sequential operations.
It would be highly desirable to provide a process for
producing filled plastic containers which includes the
preparation of these containers in a sequential and physically
proximate operation.
Accordingly, it is the principal object of the present
invention to provide a process for producing filled plastic
containers including the preparation of these containers in a
sequential and physically proximate operation without
contaminating the substance that is filled thereinto.
Further objectives and advantages of the present invention
will appear hereinbelow.
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SU1~IARY OF THE INVENTION
In accordance with the present invention, the foregoing
objects and advantages are readily obtained.
The present invention provides a process for producing a
filled plastic container, which comprises: preparing a plastic
preform by compression molding in a preform production station;
blow molding said preform into the configuration of a final
container in a blow molding station; and filling said blow
molded container in a filling station, wherein said preform
preparation, blow molding and filling are performed sequentially
in physically proximate operations, preferably under conditions
whereby the substance to be contained therein is not
contaminated.
In a preferred embodiment, the process of the present
invention includes the step of preparing a precursor prior to
preparing the preform and preparing the preform from the
precursor. Desirably, the precursor is heated to compression
molding temperature prior to preparation of the preform, said
temperature being insufficient to cause substantial change in
the morphology of the plastic. In addition, the process of the
present invention preferably includes the step of maintaining
the preforms at blow molding temperature in the compression
molding step. Also, desirably the compression molding, blow
molding and filling steps are simultaneously performed,
preferably with the compression molding, blow molding and
filling steps carried out at approximately the same rate.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be more readily understood from
a consideration of the accompanying illustrative drawings,
wherein:
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Figure 1 is a partly schematic view of a thermoforming
process which may be used for forming thermoplastic precursors
in accordance with the present invention;
Figure 2 is a partly schematic sectional view of one
embodiment of the step of preparing the preform from the
precursor by compression molding;
Figure 3 is an elevational view of the preform prepared in
Figure 2;
Figure 4 is a partly schematic view of the blow molding
step; and
Figure 5 is a side view of the filling step.
DETAILED DESCRIPTION OFPREFERRED EMBODIMENTS
It is a particular advantage of the present invention that
means are provided to perform every operation required to
produce the container at the same rate and mold cavity cycle and
to fill the containers at a rate that is an even multiple of the
output of a single cavity mold set, said set typically
consisting of a preform mold and a finishing blow mold. This is
accomplished in accordance with the present invention by
producing the preform by compression molding instead of
injection molding, and by performing the sequential operations
of preform preparation by compression molding, blow molding the
preform into the final container form and filling the blow
molded container in a filling station.
As is commonly known, injection molding requires that the
plastic be melted, i.e., heated to a high enough temperature to
enable the plastic to flow through the channels of a hot runner
system and through injection nozzles followed by injection
gates, and finally into chilled mold cavities. The rates for
accomplishing this and the pressures for accomplishing this must
permit the cavities to be filled completely without the chilled
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walls of the cavities inhibiting sufficient flow. When the
plastic is thus heated, the molecular structure of the plastic
changes due to thermal degradation. The result of this is that
the plastic has changed and usually decreased in quality. In
addition, this procedure is accompanied by the generation of
volatile degradation products which are undesirable. Thus,
conventionally one carries out the injection molding of the
preforms at a location different from the filling operation and
therefore does not perform the container preparation
sequentially and in physically proximate operations with the
filling operation. Many if not most beverages and some food
products absorb the volatile degradation products described
above, with the effect that even small quantities of these
degradation products influence taste and odor unfavorably. Even
small quantities of these volatile degradation products are
sufficient to do a considerable amount of damage.
Therefore, as indicated above, the direct coupling of the
filling and rigid container production procedures is
insufficiently effective with the current state of the art.
Some reasons for this include the fact that the rate of filling
is very difficult, if at all possible, to match with the rate of
the several steps of container forming. In addition, as
indicated hereinabove, container forming by injection blow
molding or injection stretch blow molding causes degradation of
the plastics which necessitates the use of expensive materials
that provide the required properties of the container after
their degradation. This is economically undesirable. In
addition, degradation of the commonly used plastics is
accompanied by the generation of volatile degradation products
that may be harmful to the substance being filled into the
containers. This precludes the physically proximate placement
of the steps of rigid container production that cause such
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degradation at the filling line, resulting in a more expensive
and inconvenient process.
In accordance with the present invention, one readily
produces filled plastic containers in-line and sequentially with
the preparation of rigid plastic containers.
Figure 1 illustrates a procedure for producing a precursor
to a preform in a first station in the sequence of stations.
The precursor preparation station need not be adjacent to the
subsequent stations. Instead, it may be located next to the
facility that produces the plastic, depending on applicable
economics.
As shown in Figure 1, precursors 10 are thermoformed in
step 12. Thus, a sheet 14 of thermoplastic material 16, which
may for example be PET or polypropylene, which may have two,
three or more layers of different materials to provide a multi-
layered material, is supplied to thermoforming means 18. A
plurality of thermoformed precursors 10 are formed in the
thermoforming means 18 from thermoplastic material 16 in sheet
22 which is severed by conventional trim-cutting means 24. The
precursors may also be made by other means, as by pressure
molding or tabletting, in known ways. In tabletting, one makes
tablets by compressing particulate material, which is a well
known technology.
Figure 2 shows a second station for preparing a preform
from the precursor by compression molding, which as indicated
hereinabove, is physically independent of the precursor
preparation station.
Prior to preparation of the preform, the precursor is
desirably heated to compression molding temperature by known
heating means (not shown), to a temperature that does not cause
degradation of the plastic or the release of volatile
degradation products. The heating means are preferably provided
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by radio-frequency current (RF heater), which is particularly
efficient, but it may also be a convection, radiation, or
fluidized bed heater.
As shown in Figure 2, compression molding assembly 28 is
provided, which is desirably openable as indicated by the arrow,
and having a cavity 30 therein in the desired preform shape,
including threaded neck portion if desired (not shown). The
precursor 10 may have two or more layers. RF heating is
preferred, particular for thick-walled precursors, because it
does not rely on the heat conductivity of the plastic, which is
poor. As shown in Figure 2, mold core 38 is inserted into the
cavity of the heated precursor 10, as placed into cavity 30, to
compression mold preform 42. The shown preform 42 is
representative only and naturally any suitable shape may be
produced.
Compression molding, being a process carried out in the
solid state, may be performed within the temperature range of
blow molding. Accordingly, the precursor is in condition to be
moved by conventional means directly to blow molding, preferably
at constant temperature.
Thus, the precursors may be heated in a separate heating
station to compression molding temperature as indicated above,
transported from the heating station to the compression molding
station as shown in Figure 2, and therein reshaped into
preforms, as preforms 42 shown in Figure 3. The components of
the compression mold in Figure 2 are preferably held at a
temperature which is not lower than the temperature at which the
next step is performed, i.e., the blow molding step as shown in
Figure 4. The compression molding step shown in Figure 2 may be
adjusted to be an even multiple of the filling step. Hence, a
number of compression molds may be assembled for conformance
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with the rate of filling. The blow molding step is shorter
than the compression molding step.
Following compression molding of the preform in Figure 2,
the preform 42 is transferred to the blow molding station, shown
in Figure 4, adjacent and desirably in-line with the compression
molding station. Thus preform 42 is_transferred to blow mold
44, which may be separable along parting line 46 and which may
include strength rod 47, and expanded into the shape shown by
dashed line 48, into conformance with the blow mold cavity 50,
by means well known, as by blow air through channel 49. The
operating cycle of the blow molding station shown in Figure 4 is
typically shorter than that of the compression molding cycle
shown in Figure 2. Thus, if these operations are performed
sequentially, in adjacent or physically proximate operations,
preform production, blow molding and filling can in fact be
carried out at the same rate, and each operating station is
capable of economic operation at the same rate as the other to
provide an efficient and highly desirable in-line system.
The blow molding operation shown in Figure 4 is followed by
a filling operation shown in Figure 5 wherein filling head 52 is
applied to container 48 to fill same in a simple manner at a
physically proximate location with the blow molding and preform
preparation steps. This may be followed by other operations,
e.g., inspection, packaging, etc. in one or more of following
operations which desirably may be in a location physically
proximate with the filling operation.
If the filling operation needs to be interrupted, the
entire sequence may also be conveniently interrupted without
loss of any material or shutdown penalty, and then restarted
when the filling operation is restarted. Due to the low
temperatures at which all of the molding steps are carried out,
no degradation of the plastic occurs and hence no volatile
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degradation products. Therefore, the plastic introduced into
the process may be of substantially the same molecular weight as
that desired for the finished container. Also, a highly
advantageous sequential operation is provided where the preform
preparation, blow molding and filling steps are performed
sequentially in physically proximate_operations. This results
in a highly advantageous and economical procedure.
It is to be understood that the invention is not limited to
the illustrations described and shown herein, which are deemed
to be merely illustrative of the best modes of carrying out the
invention, and which are susceptible of modifications of form,
size, arrangement of parts and details of operation. The
invention rather is intended to encompass all such modifications
which are within its spirit and scope as defined by the claims.
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