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The present invention relates to an apparatus and method for vacuum
packaging a product in a flexible receptacle, such as a bag.
BACKGROUND OF THE INVENTION
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A number of methods and apparatuses are available in the prior art for vacuum
packaging food products in flexible containers such as bags or pouches. For instance,
US 3,832,824 discloses a method and an apparatus wherein a filled bag is placed in a
vacuum chamber which has two portions, the first portion enclosing the mouth of the
bag and the second portion enclosing the product-containing part of the bag. Initially
vacuum is applied only in the portion of the chamber in which the product is
contained causing the wall of the bag to "balloon" away from the enclosed product
thereby allowing a more efficient removal of air from within the bag; vacuum is then
applied also in the portion of the chamber in which the mouth of the bag is located,
consequently evacuating the interior of the "ballooned" bag; when the evacuation of
the bag is complete the bag can be closed and atmospheric pressure re-established
inside the chamber. Such a process can be succesfully applied only to products that
can tolerate a long evacuation step or a high vacuum, wherein the term high vacuum
indicates a very low pressure level. In fact, when packaging products having a porous
structure, such as certain types of cheeses, the high vacuum applied can remove air
out of the product so that the structure of the product will be damaged. Methods for
the vacuum packaging of sensitive products are disclosed in US 4,583,347 and in US
4,922,686, both describing a single-chamber apparatus having an air admission valve
located on the cover of the vacuum chamber for allowing air inside the chamber
during the vacuumization step. The admission of air in the vacuum chamber once or
more times during the vacuumization stage of the process generates a pulsating effect
which facilitates the extraction of air from within the bag without the need of
generating a high level of vacuum. To carry out such process the apparatus described
in US 4,583,347 and in US 4,922,686 relied on one air extraction duct located close to
the mouth of the bag, so that the amount of air extracted form the side of the chamber
holding the product and the speed of air extraction depend on how much the passage
between one side of the chamber and the other is obstructed by the bag and the
product, often leading to non uniform levels of vacuum from one package to the other
during high speed packaging operations. Therefore the need still exsist for an
apparatus and a method for reliably packaging articles under vacuum in a flexible
receptacle, such as a bag.
SUMMARY OF THE INVENTION
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Accordingly, a first object of the present invention is an apparatus for vacuum
packaging a product in a flexible receptacle, such as a bag, comprising a first vacuum
chamber and a second vacuum chamber adjacent to it and an aperture connecting the
two chambers for passing the neck of the receptacle, means to evacuate the first and
second chambers and means to close the package when its evacuation is completed
characterised in that means are present in the aperture to prevent the passage of air
from one chamber to the other and air admission means are present in the first
chamber.
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A second object of the present invention is a method of vacuum packaging a
product in a flexible receptacle, comprising the steps of loading the article in the
receptacle, extracting gas from around the exterior of the receptacle to lower the
surrounding pressure, extracting gas from within the receptacle, partially restoring the
pressure surrounding the exterior of the receptacle, further extracting gas from around
the exterior of the receptacle, and again partially restoring the pressure surrounding
the exterior of the receptacle, then further extracting gas from around the exterior of
the receptacle before closing the receptacle characterised in that the extraction of air
from within the receptacle is independent of the extraction of air from around the
receptacle and constant in time.
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These and other objects, advantages, and features of the invention will be
more readily understood and appreciated by reference to the detailed description of
the invention and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
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- Fig. 1 is a section of an apparatus according to the present invention in which the
vacuum chambers of the apparatus are closed;
- Fig. 2 is a view similar to Fig. 1 showing the apparatus during operation when
vacuum is applied in the chamber containing the product.
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DETAILED DESCRIPTION OF THE INVENTION
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Figure 1 shows a section of the vacuum packaging apparatus 1 of the invention.
As used herein, the phrase "vacuum packaging" refers to a method wherein at least
one product is placed in a receptacle having one opening, such as a bag, then the
receptacle is evacuated and closed.
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Vacuum packaging apparatus 1 includes a cover 2 hinged to base member 3 which
is divided by lower chamber divider wall 12 which cooperates with the upper divider
wall 11 to separate apparatus 1 into the two chambers 4 and 5. Upper divider wall 11
is optionally removable from cover 2. The first and larger chamber 4 is the product
chamber in which the portion of a receptacle or bag 9 containing a product 8 is
placed. The receptacle opening (9a) or bag neck is extended into the second and
smaller chamber 5 through aperture 15. Aperture 15 is formed in the wall which
divides chambers 4 and 5 when the cover 2 is rotated into position. Gaskets 16 and
16a on the lower divider wall (12) and on the upper divider wall (11), respectively,
hold the bag neck in place without choking it and isolate first chamber 4 from second
chamber 5. The first chamber 4 is evacuated through vacuum port 6 and the second
chamber is evacuated through vacuum port 7. Air admission port 10 admits air into
the first chamber. A receptacle-closing unit 21 is located in one of the chambers.
Although figures 1 and 2 show the receptacle-closing unit 21 located in chamber 5,
the mechanism could also be located in chamber 4. Suitable receptacle-closing units
are for instance heat sealing bars, impulse sealing bars or clipping mechanisms. In a
preferred embodiment of the apparatus of the invention the receptacle-closing unit 21
is a pair of opposed heat sealing bars. The apparatus further includes a pressure
sensing mean 22 in chamber 4 and optionally a second pressure sensing mean 23 in
chamber 5 and a programmable logic control system (not shown) which monitors and
sequences each phase of the apparatus during operation and in particular controls the
operation of vacuum ports 6 and 7, of air admission port 10 and of heat sealing bars
21.
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To perform the process according to the present invention the operator of
apparatus 1 places the bag 9 filled with product 8 in the first chamber 4 and brings the
neck of the bag down over gasket 16 and across sealing bars 21, so that the open end
of the bag 9a is located in the second chamber 5. When cover 2 is rotated in the closed
position, the neck of the bag will be held in place, without being choked, by gaskets
16 and 16a on the lower and upper dividing walls, respectively. Suitable materials for
gaskets 16 and 16a are for instance flexible plastic materials such as rubber and
foams. Gaskets 16, 16a and the bag neck fill the aperture between chambers 4 and 5
so that very little air is leaked from one chamber to the other. Once the chamber is
closed evacuation of chamber 4 begins through vacuum port 6. Any conventional
vacuum pump which is well known in the art may be used to evacuate chamber 4. In
this first phase, shown in Fig. 2, bag 9 will balloon outwardly due to the pressure
difference between the interior of the bag 9 and the chamber 4. When the pressure in
chamber 4 reaches a value P1, set by the operator, evacuation of the second chamber
5 begins through vacuum port 7. Due to its smaller size the evacuation of chamber 5
will proceed more rapidly than the evacuation of chamber 4, so that the vacuum level
in chamber 5, and consequently within bag 9, will drop below that in chamber 4
causing the bag to collapse back onto product 8. When the pressure in chamber 4
reaches a value P2 a signal is sent to a control unit to stop evacuation of chamber 4.
Due to the time needed for the effective closing of vacuum port 6 and to the minimal
passage of air from one chamber to the other, the pressure in chamber 4 will drop
further from value P2 to value P3. When the pressure inside chamber 4 reaches value
P3 air is allowed into the chamber through air admission port 10 to return to pressure
value P2. Air admission port 10 is then closed and vacuum is applied again through
port 6 until the pressure is reduced to value P3. The air admission-evacuation cycle
between pressure values P2 and P3 respectively is repeated at least once and usually
more times until the desired packaging result is obtained, at which time bag 9 is
closed by operation of heat sealing bars 21. Vacuum port 7, connected to chamber 5,
is held in the open position throughout the air admission-evacuation cycles carried out
in chamber 4. Pressure values P1, P2, P3 and the time during which the air admission-evacuation
cycles are repeated are set by the operator in the programmable logic
control at the beginning of the operations and are chosen according to the nature of
the product being packaged. In general pressure value P1 ranges from 500 to 950
mbar, preferably from 600 to 900 mbar; pressure value P2 ranges from 200 to 800
mbar, preferably from 250 to 650 mbar; pressure value P3 is set to be from 20 to 130
mbar lower than P2, preferably from 30 to 100 mbar lower than P2. The time period
during which the air admission-evacuation cycles are repeated is usually from 3 to 20
seconds, preferably from 5 to 15 seconds.
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Suitable settings for the packaging of sensitive products such as Raclette cheese
and pate according to the process of the invention are reported in the following table:
PRODUCT | P1 (mbar) | P2 (mbar) | P3 (mbar) | Time (s) |
Raclette cheese | 800 | 450 | 400 | 5 |
Pate | 800 | 500 | 400 | 12 |
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In one embodiment of the apparatus of the present invention, upper chamber
divider wall 11 is connected to vacuum chamber cover 2 through a lateral guide and
held in place by means of a clamp. When needed it can be disengaged from cover 2
and removed from the apparatus by manually releasing the clamp. This can be
conveniently done when the products to be packaged are hard, non-porous products
and therefore are not damaged by a high vacuum packaging process.
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The apparatus described above offers several advantages with respect to prior art
ones. First of all it allows to pack both sensitive and non-sensitive products by simply
removing upper chamber divider wall 11. Furthermore, when packaging sensitive
products, the possibility of independently controlling the level of vacuum in the two
chambers offers a great reliability in the end result in particular in packaging
processes with high turnovers.