Note: Descriptions are shown in the official language in which they were submitted.
CA 02612365 2013-06-12
PROCESS FOR HOT FILLING A THIN-WALLED CONTAINER AND FILLED
CONTAINER THUS OBTAINED
This invention relates to a process for hot filling a light, thin-walled
container, in
particular made of polyethylene, and a filled container that is thus obtained.
A polymer, polyethylene terephthalate, PET, heavily used for the production of
containers for liquids, is known. Its primary assets are transparency, low
weight, release
of forms allowing distinctive profiles based on commercial products or
requirements,
contrary to metal boxes, all of the same shape and same dimensions. It is the
same for
the containers that are produced from cardboard whose forms are limited.
PET is unbreakable and has good mechanical properties of preservation,
permeability, which makes it very attractive and explains for the most part
its very heavy
use.
These bottles made of PET are used for still liquids such as oils and mineral
waters. In this case, the containers undergo only very few mechanical
stresses. The PET
is completely suitable. Actually, these liquids are cold filled without
pressure.
These bottles are also used in the case of carbonated drinks and are therefore
likely to pressurize the container.
Tricks of design with grooves on the body of the bottle or so-called pctaloid
bottoms make it possible to enhance mechanical strength and/or resistance to
pressure,
without increasing the weight of the container in a detrimental way.
When the manufacturers need to hot fill a container, it then is necessary to
use
different designs that require larger thicknesses, different geometries
including panels
CA 02612365 2013-06-12
placed on the body of the container to produce beams. These elements that are
necessary
for hot filling lead to high weights with high material consumptions, up to
two times the
weight of the same bottle for cold-filled liquids.
Actually, the mechanical characteristics of the PET deteriorate greatly when
the
temperature rises.
There are so-called "heat-resistant" processes, more commonly designated by
the
letters HR, which make it possible to improve the heat resistance of the
container that is
thereby produced.
A first so-called one-wheel process makes it possible to reach filling
temperatures
of 80/88 C.
A second so-called two-wheel process makes it possible to package the liquids
at
temperatures of 88/95 C.
A hot-filled bottle actually undergoes numerous mechanical stresses during
different phases.
Thus, the bottom is to withstand the hydrostatic pressure of the hot liquid
during
filling.
The container is to withstand forces produced by the evacuation caused by the
cooling of the liquid when the container has been plugged when hot to ensure
the sterile
nature of the liquid. The cooling causes a double contraction, that of the
liquid and that
of the air of the top space of said bottle.
It is for this reason that the profiles are much more complex with panels and
beams on the body, bands marked on the body as well as a shoulder between the
spout
and the body, whose shape is rather bulbous.
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The advantage of the thickness that is necessary to the mechanical strength is
also
having a higher inertia at the temperature.
The manufacture of light bottles made of PET uses the so-called extrusion/blow
molding process. This process consists in making a preform by extrusion,
whereby this
preform has a tube profile with one end formed to dimension and to the
definitive form of
the spout, and whereby the other end is closed.
After heating this preform, in particular by infrared radiation, up to 100/120
C,
the amorphous material is softened and can undergo blowing through the
interior after it
has been placed in a suitable mold.
This mold has dimensions such that the withdrawal of the material with cooling
is
taken into account so that the final container has the desired dimensions.
During this blow-molding phase, a longitudinal stretching occurs under the
action
of a stretching rod and inflation by the pressurized air that is thus
introduced. More
precisely, the air is first introduced at low pressure to ensure a suitable
deformation of the
material during high amplitudes then at high pressure to ensure plating
against the walls
of the mold during finishing and for very low amplitudes.
The molds are also cooled with water so as to dissipate the calories
transmitted by
contact, which also has the effect of immobilizing the bottle.
Actually, the bottles that are thus obtained are called bi-oriented because
they
have undergone stretching in one direction and an omni-directional inflation.
The macromolecular chains that are thus oriented in two directions lead to
excellent parameters of mechanical strength, at ambient temperature.
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The drawback of this hi-orientation is being in part reversible, and the
material
thus regains a certain freedom as soon as the temperature rises.
Actually, the material has a tendency to return to its initial form in which
it has
fewer stresses.
It is the so-called shape memory phenomenon.
For the thick bottles that are designed to be used for hot-filled drinks, use
is also
made of extrusion/blow molding, but with more sophisticated and more complex
behavior parameters.
Actually, the preform is heated to a higher temperature than in the case of
light
containers, close to the crystallization so as to reduce this PET shape memory
and to
relieve the stresses due to the blow molding.
In the case of manufacture with one wheel, so as to increase its strength at
temperature, the initially amorphous material of this container is made to
undergo a heat
treatment, during and after its shaping.
The material, when it is stretched after softening, generates an induced, but
reversible crystallinity, whereby the material remains transparent. The
mechanical
properties are enhanced.
Thus, if the heating is maintained after having generated this induced
crystallization, a spherolitic crystallization occurs, causing a certain
crystallinity of chains
that are already organized by bi-orientation.
Contrary to the direct spherolitic crystallization of the PET, the spherolitic
crystallization subsequent to a hi-orientation perfectly preserves the
transparency of the
material.
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In the case of two-wheel manufacture, the process makes it possible to reach
higher performance levels, but at the cost of a succession of more complex
stages.
Actually, in this case, a blank of much larger volume than the volume of the
final
container, two to three times as much, i.e., with a proportional stretching
rate, is first
worked up.
This blank is then heated beyond the vitreous transition to relieve the
stresses,
which brings about a reduction of volume and a return to the dimensions of the
preform,
but with a high rate of spherolitic crystallinity, whereby this leads in a
proportional way
to a homothetic container. There is self-regulation with the PET.
When this restricted blank is at temperature, a blowing stage with a mold with
the
dimensions of the final container to be obtained, aside from recesses, makes
it possible to
manufacture the final container.
The high rate of crystallinity imparts to this container an improved
resistance to
hot filling.
It is noted that such a process is much more burdensome to put into place.
'Hie
process requires behavior always at the limits of values, requires cleaning of
molds, as
well as intensive and regular maintenance.
In addition, it should be noted that the bottles that are obtained by the HR
process
have a tendency to absorb water as soon as they are manufactured, which
reduces their
characteristics of mechanical strength and therefore temperature resistance.
It thus is
possible to obtain manufacture of a container that initially withstands a
temperature of
88 C and that, after uptake of water, withstands only 82 C. Actually, the
transition
temperature TG drops.
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Whereby storage should be reduced as much as possible, the bottles are
generally
produced on the filling site, for just-in-time use, which is another
constraint.
Once these containers are manufactured, there are several filling methods and
various properties of the liquids to be packaged.
There are liquids that are sensitive to light, such as milk or beer, sensitive
to
oxygen absorption and therefore oxido-sensitive, such as fruit or vegetable
juices, beer,
oil, but also sensitive to the uptake of water, to the loss of gas, to the
development of
yeast, mold or bacteria.
The liquids can include preservatives and are thereby not very sensitive; in
contrast, certain so-called still and delicate liquids - such as milks,
juices, coffee, tea, fruit
drinks, and certain waters - do not include any preservative and should still
be packaged
under the best conditions.
To ensure such packaging under conditions of suitable hygiene and with all of
the
guarantees of good preservation, two primary methods are known: one called
"aseptic
tilling," and the other called "hot filling."
The aseptic filling is simple in theory because it consists in filling the
container
with a sterilized liquid and in plugging said container, whereby the packages
just like the
plugs are sterilized, and the operation is conducted in a sterile environment
in its entirety.
Nevertheless, it is understood that the chain is complex to install, difficult
to keep
always under the same aseptic conditions over time, require a very high
monitoring and
high maintenance producing high costs. In such a chain, it is necessary to use
chemical
sterilizations that use chemical products with treatments that are derived
therefrom,
expertise of personnel, low yield due to treatment speeds that are not very
high. The
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yield is 40 to 50% of that of a hot filling chain. The investments are also
very large, two
to three times larger than that of a hot -filling chain.
A very significant drawback of this process resides in the impossibility of
monitoring online the sterility of the contents in each container. At the very
most, the
monitoring can be done by sampling.
The advantage of this cold aseptic filling is to require only thin-walled
bottles of
low weight and of free form since the cold filling prevents the deformations
due to the
temperature.
The other method, the hot filling, also guarantees a quality of asepsis, since
the
monitoring of the temperature of the contents is simple and easy at any time.
The bottling line is simple, and the treatments of the container and the plug
are
limited in scope since the sterilization is obtained by the hot liquid itself,
introduced into
the container that is immediately closed after filling. A tipping of the
bottle also ensures
the sterilization of the inside surface of the plug in contact with the
liquid.
In contrast, it is necessary to use containers that are able to withstand the
filling
temperature of between 60 and 95 C, more particularly between 80 and 92 C,
based on
the products.
In addition, the bottles have high weights with approximately identical shapes
linked to the resistance constraints, which allows only a very slight
differentiation
between the marketed products.
Also, it is concluded that there are two processes that have advantages and
disadvantages. Nevertheless, the additional expense produced by the particular
characteristics of the containers currently used and necessary for the hot
tilling tend to
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orient the manufacturers involved toward the activation of filling lines by
the aseptic
method.
It is important to set an estimate of the material weight. Fifteen years
previously,
a 1.5 liter container required 49 g of cold filling material and 55 g of hot
filling
material, HR treatment.
Since then, important gains have been made for the cold filling reaching 28 g,
while the amount of material for hot filling has stayed almost the same.
The compromise sought by the manufacturers would consist in being able to fill
hot liquids to obtain the guarantee of asepsis but in thin-walled bottles that
are designed
for cold filling to limit the costs of the containers as well as the packaging
line.
In accordance with one aspect of the present invention, there is provided a
process for hot filling a container with a sterilized liquid, comprising the
following
stages: a. providing a container that is made of a polymer and following a
process that
can make it able to withstand the hot filling of said liquid, whereby the
container has
residual stresses obtained from its manufacture; b. filling the container with
said hot
liquid; c. closing the filled container immediately after filling; d. allowing
the container
to cool at least below a transition temperature of the container that is on
the order of
from 40 C to 50 C and forming a depression inside the container, resulting
in visible
deformation of the container; and e. heating the container to bring about a
relief of the
residual stresses, whereby this relief leads to a shrinkage and consecutively
generates an
internal pressurization of the container that compensates for at least the
deformation
undergone by the effects of the depression of stage d.
In accordance with another aspect of the present invention, there is provided
a
process for hot filling a container with a liquid, generally at a temperature
that is
between 60 C to 95 C, comprising the following stages: a. providing a
polymer
container having residual stresses incurred from its manufacture; b. filling
the container
with said hot liquid; c. closing the filled container immediately after
filling; d. allowing
the container to cool such that the interior liquid passes below a transition
temperature
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8a
that is on the order of from 40 C to 50 C; and e. heating the container to
bring about a
relief of the residual stresses, whereby the relief leads to a shrinkage and
consecutively
generates an internal pressurization of the container.
In accordance with another aspect of the present invention, there is provided
a
lightweight, thin-walled heat resistant plastic container containing hot-
filled liquid
contents, comprising: a spout for filling the container with liquid contents;
a closure
configured to seal the spout; a base including a bottom portion that is bent
toward the
spout, the base including a structural reinforcement configured to withstand
hydrostatic
pressure from the hot-filling of liquid and configured to prevent significant
deformation
in the base upon the cooling of the hot liquid; and a sidewall extending
upwardly from
the base toward the spout, the sidewall including a zone of deformation,
wherein the
zone of deformation in the sidewall is configured to accommodate an initial
deformation due to the cooling of the contents and to substantially regain its
initial
shape upon the relieving of immobilized stresses.
In accordance with another aspect of the present invention, there is provided
a
lightweight, thin-walled heat resistant plastic container containing hot-
filled liquid
contents, comprising: a spout for filling the container with liquid contents;
a closure
configured to seal the spout; a base including a bottom portion that is bent
toward the
spout, the base including a structural reinforcement configured to withstand
hydrostatic
pressure from the hot-filling of liquid and configured to prevent significant
deformation
in the base upon the cooling of the hot liquid; a sidewall extending upwardly
from the
base toward the spout; and a zone of deformation, which is configured to
accommodate
an initial deformation due to the cooling of the contents and to substantially
regain its
initial shape upon the relieving of immobilized stresses.
In accordance with another aspect of the present invention, there is provided
a
lightweight, thin-walled heat resistant plastic container configured to
receive hot-filled
liquid contents, comprising: a spout for filling the container with liquid
contents; a base
including a bottom portion that is bent toward the spout, the base including a
structural
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8b
reinforcement configured to withstand hydrostatic pressure from the hot-
filling of liquid
contents and configured to prevent significant deformation in the base upon
the cooling
of such liquid; a sidewall extending upwardly from the base toward the spout;
and a
zone of deformation, which is configured to accommodate an initial deformation
due to
post-sealing cooling of hot-filled liquid contents, and the zone of
deformation is
configured to substantially regain its initial shape upon the relieving of
immobilized
stresses that manifest with the post-sealing cooling of hot-filled liquid
contents.
In accordance with another aspect of the present invention, there is provided
a
process for filling a container with a liquid, comprising the following steps:
(a)
providing a plastic container comprising a spout, a base including a bottom
portion with
a portion that extends upwardly toward the spout, and a sidewall extending
upwardly
from the base toward the spout; (b) filling the container with a liquid; (c)
sealing the
spout with a closure; (d) permitting the formation of a depression or creation
of a
vacuum inside the container, resulting in visible deformation of the
container; and, (e)
when the liquid is at least below a transition temperature that is on the
order of from
40 C to 50 C, applying heat to the container to bring about internal
pressurization of
the container to compensate for at least the depression or vacuum of step (d).
In accordance with another aspect of the present invention, there is provided
a
process for filling a container with a liquid, comprising the following steps:
(a)
providing a plastic container comprising a spout, a base including a bottom
portion with
a portion that extends upwardly toward the spout, and a sidewall extending
upwardly
from the base toward the spout; (b) filling the container with a liquid; (c)
sealing the
spout with a closure; (d) visibly deforming the container sidewall; and, (e)
when the
liquid is at least below a transition temperature that is on the order of from
40 C to
50 C, applying heat to the container to bring about internal pressurization
of the
container to compensate for at least the deformation of step (d).
In accordance with another aspect of the present invention, there is provided
a
heat resistant plastic container containing hot-filled liquid contents,
comprising: a spout
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8c
for filling the container with liquid contents; a closure configured to seal
the spout; a
base including a bottom portion that is bent toward the spout, the base
including a
structural reinforcement configured to withstand hydrostatic pressure from the
hot-
filling of liquid and configured to prevent significant deformation in the
base upon the
cooling of the hot liquid; and a sidewall extending upwardly from the base
toward the
spout, the sidewall including a zone of deformation, wherein the zone of
deformation in
the sidewall is configured to accommodate an initial deformation due to the
cooling of
the contents and to substantially regain its initial shape upon the relieving
of
immobilized stresses.
In accordance with another aspect of the present invention, there is provided
a
lightweight, thin-walled plastic container containing liquid contents,
comprising: a
spout for filling the container with liquid contents; a closure configured to
seal the
spout; a base including a bottom portion that is bent toward the spout, the
base
including a structural reinforcement; a sidewall extending upwardly from the
base
toward the spout; and a zone of deformation, which is configured to
accommodate an
initial deformation due to post-sealing internal vacuum and to substantially
regain its
initial shape upon the relieving of immobilized stresses.
In accordance with another aspect of the present invention, there is provided
a
lightweight, thin-walled heat resistant plastic container configured to
receive hot-filled
liquid contents, comprising: a spout for filling the container with liquid
contents; a base
including a bottom portion that is bent toward the spout, the base including a
structural
reinforcement; a sidewall extending upwardly from the base toward the spout;
and a
zone of deformation, which is configured to accommodate an initial deformation
due to
the post-sealing cooling of hot-filled liquid contents, and the zone of
deformation is
configured to substantially regain its initial shape upon the relieving of
immobilized
stresses that manifest with the post-sealing cooling of hot-filled liquid
contents.
This is what the process and container according to this invention proposes,
which is now described in detail according to a preferred, nonlimiting
embodiment.
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8d
A set of figures makes it possible to illustrate the process diagrammatically,
whereby these figures show:
- Figure 1: A view of a container before filling,
- Figure 2: A view of the same container as that of Figure 1 once
filled
with a hot liquid before cooling,
- Figures 3A and 3B: Two views at 900 of the filled container, after
cooling and having undergone the collapse phenomenon,
- Figure 4: The collapsed container of Figures 3A and 3B after
treatment
according to the process of this invention that regains its initial shape.
The given example relates to the PET bottles but could be applied to any
container made of polymer material of the same nature and having similar
properties.
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The process consists in carrying out hot filling of a thin-walled container,
whereby this container should have suitable characteristics as described
above.
This container is cylindrical in shape, optionally with grooves for making the
body rigid, with a light bottom like that of the containers for still mineral
waters, but
reinforced, whereby the total weight of the container is approximately that of
the
containers that are used for the mineral water containers, with equal
capacity.
The reinforced bottom generally consists of a bottom that is bent toward the
spout
with reinforcements to prevent its return under slight pressure.
This container is manufactured starting from one or the other of the two so-
called
one- or two-wheel "HR" treatment methods, based on the packaging temperatures.
'['he container thus has good hot strength and still has a reduced weight.
In addition, the absence of the characteristic elements of the PET bottles of
the
prior art that were hot packaged, such as a band, a bulb with a shoulder,
panels, is noted.
The container, shown in Figure 1, uses a simple geometry.
The filling is carried out from the reservoir of a filling device of known
type,
generally by gravity directly into the container, whereby the liquid is
carried and kept at a
temperature of 60 to 95 C based on the targeted applications.
When the liquid at temperature penetrates the container, three actions occur:
Quick rise in temperature of the wall since the thickness is slight and the
corresponding inertia is limited.
Action of the hydrostatic pressure due to the load resulting from the
gravity flow, and
Action due to the load of the liquid volume introduced into the container.
=
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The container deforms little under the effect of the rise in temperature under
the
filling effect, because the container is manufactured to meet this rise in
temperature, at
the very most a very slight barrel shaping at the time it is closed. This is
the
representation of Figure 2.
It is known that the crystallinity can be improved as indicated in the
introductory
clause ofthis application, which greatly improves the mechanical strength. It
is also
known that if the container is used after its manufacture, the uptake of
moisture is very
limited, and the initial temperature resistance remains almost unchanged.
The bottom having been designed with an improved mechanical strength as well
as its "FIR treatment" prevents the restoration of the bulge of this bottom
under the effect
of the load and the increase in pressure once said container is closed.
Actually, the
increase in temperature brings about a quick shrinkage of the volume of the
container
while the liquid that is contained preserves its volume, which generates
pressurization of
the interior of the container.
Actually, the bottom that is designed to withstand preserves its shape while
the
body of the container has a significant deformation during the cooling of the
liquid and
the head space. It should be noted that this deformation is not irreversible,
since if the
container is open, the body regains its initial shape.
It is known that the deformation is located in the zone that is the most
favorable to
the mechanical deformation such as the walls, for example, in the case of
known
containers and for which no particular modification has been provided.
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It is also noted that in the case of a zone that is less resistant
mechanically, the
deformation can be reproduced on all of the identical containers that are
filled under the
same conditions.
It is therefore possible to create a zone voluntarily that is suitable in any
container
so as to carry the deformation to this specific and determined zone in a
reproducible way.
It is known that a square or cylindrical container withstands pressure well
but
withstands vacuum poorly except in providing devices such as grooves or folds.
According to the process of the invention, a container is therefore obtained
with a
bottom and a band for joining the bottom and said non-deformed body thanks to
the
strength of the fold formed at this junction. The container is stable on its
bottom but with
a deformed body, collapsed as it is referred to in the trade, which makes it
unsuitable for
sale. These are the representations of Figures 3A and 3B.
The process according to this invention consists in reducing the volume of the
container by bringing about a reduction of the volume of the container after
partial or
total cooling of the liquid.
It was noted that the bottle, even if it receives a -Heat Resistance" (HR)
treatment, makes it possible to minimize the shape memory effect of the PET
without
thereby eliminating it integrally.
The process consists in relieving the immobilized stresses so that the
container
tends to regain its initial shape, that of the preform, and therefore tends to
regain a
smaller volume. This is the particularly surprising and attractive approach of
this
invention.
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For this purpose, once the liquid is introduced when hot, then once the
container
is closed and a partial or total cooling is performed, the container is
subjected to a rise in
temperature of at least a portion of said container so as to relieve the
stresses and to
deform irreversibly the container on all or part of its surface.
The rise in temperature should be quick so as not to cause the rise in
temperature
of the liquid, which would cancel the necessary differential for compensating
for the
depression.
Nevertheless, the selection of means for carrying out this rise in temperature
remains very broad because the ratio of the weights put into play is very
large. The few
grams of PET of a container vs. hundreds of grams of the content necessarily
lead to a
faster temperature hike of the jacket than of the contents. In addition, in
the case of
heating by radiation in particular, the jacket is the first item that is
subjected to infrared
radiation and primarily absorbs the calories.
It is suitable only for avoiding the means of heating by transmission, such as
the
water bath or pasteurization. In this case, it is another parameter that is no
longer
suitable: it is the time that is necessary, much too long with this type of
technique.
Another prejudice to overcome is the compensation volume that is necessary.
Considering the container after cooling, the deformation allows one to think
that it is
necessary to generate a significant volume reduction.
For a 500 ml bottle, the volume reduction after cooling is 3.5% only of the
liquid
volume, therefore 17 ml.
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Actually, on such a bottle, generally about 60 mm of diameter to give an
estimate,
it is possible to provide the shrinkage on the so-called labeling height,
i.e., in the zone for
affixing a label.
The band between the labeling zone and the bottom as well as the shoulder zone
being indefortnable, it is sufficient to provide a retraction of 1 to 2 mm of
the diameter. It
is even possible to impose a slight overpressure to compensate for the
possible additional
shrinkage that may occur when such a container is put into the refrigerator.
It should also be noted that during the hot filling, there is always an air-
filled top
space.
Also, it is possible to lay the bottle down so as to systematically direct
this air
along a generatrix of said bottle in the upper part. Actually, the process can
implement
hot-air heating because the transmission of calories between the wall and the
air is very
difficult, whereby the air is very insulating. The calories are concentrated
in the wall of
said bottle in the zone that is concerned and very quickly brings about the
desired
shrinkage.
So as not to have to initiate a total raising of the temperature, it is also
possible to
carry out this heating of the jacket as soon as the interior liquid has passed
below the
transition temperature on the order of 40 to 50 C.
It is also possible to note that the process according to this invention makes
it
possible to produce contents of the square section, the shrinkage then causing
a
deformation of the container by triangulation, which is also compensated for
during the
relief of the stresses and during the shrinking of the container.
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Thus, according to this invention, the process consists in using a container
that
can mechanically withstand, without deformation, hot .filling of a liquid in a
range of
temperatures of a sterilized liquid, generally from 80 to 95 C, for example a
polyethylene
container, whereby said container is produced by extrusion/blow molding and
has a shape
memory before blow molding to fill said container with said hot liquid, to
close this filled
container, and to allow it to cool at least below a solidification temperature
of the
container, then bringing about a deformation by formation of a depression
inside the
container, then in heating the container to bring about a relief of the
stresses and a return
to the shape before blow molding that generates a shrinkage and an internal
pressurization of the container that leads at least to compensating for the
deformations
undergone by the effects of depression.
Thus, according to this invention, a container that is filled with a
pasteurized
content, of which it is possible to guarantee the pasteurization by a simple
filling
temperature measurement, is obtained. The cost of the container for the
implementation
of the process is not detrimental since it is perfectly comparable to that of
the containers
that can undergo aseptic filling.
The advantage is to be able to meet the manufacturers' requirements as regards
filling rates and guaranteed asepsis without requiring high-investment
bottling lines, also
costly and complex in operation.
Thus, using the process according to this invention, not only is the cost of
raw
material for manufacturing a hot filled container reduced, but this lesser
amount of raw
material leads to subsequent reduced recycling costs for the same bottled
volume.
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According to this invention, it should be noted that it is possible to provide
a
suitable device for the implementation of the process.
A solution consists in producing shells that comprise at least two parts so as
to
encase the container, whereby said shells are heated by any suitable means so
as to
release the necessary calories.
The shells have a profile that approximately matches that of the container to
release the calories close to the walls, and even in a localized zone of this
wall, whereby
these shells are oriented horizontally if the heating is carried out on a
generatrix with air
in the upper part. In this case, it is then possible to bring about a more
intense heating in
a particular zone.
