Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to a process and apparatus for
packing commodities such as foodstuffs into vacuum-sealed packs,
and is particularly applicable to the smaller sized packs which are
used to contain ~oodstuffs such as rashers of bacon or small Joints -
- of meat sold through retail outlets.
Vacuum sealed packs containing foodstuffs for domestic
consumption generally consist of the foodstuff enclosed between two -
superposed films of plastics material which are sealed hermetically
together around the periphery of the pack with a margin between the
seal and the foodstuff. This margin may be as wide as 3 or 4 cm in
places. The packs are sealed under a vacuum of e.g. 4 Torr to ensure
that the food is kept fresh.
In one method of packing domestic cuts of meats such as
bacon, a continuous film of stretchable plastics material is first
deformed, for example by heat and vacuum, to provide a series of
pockets for receiving the foodstuff. The stretched pocketed film
is then fed to a packing station where the slices of bacon are loaded
in succession into the pockets, and a second continuous film is then
applied on top of the first film. The first or lower film is wider
than the second or upper film so that the lower film i8 left with
uncovered margins along opposite longitudinal edges.
The superposed films are then indexed to a vacuum sealing
station where each pocket is received in a heated die which can be
raised to bring the films into engagement with an upper die. The
webs are clamped transversely between the dies but are not at this
stage permanently sealed together; the longitudinal edges of the
dies engage the margins of the lower web only; due to its narrow
width, the upper web is not at this stage gripped along its longi-
tudinal edges.
The space within the closed dies is then evacuated through
ducts at the outer margins of the dies, and the air is drawn from
the pocket via the free outer longitudinal edges of the upper web.
A heating plate is then lowered to heat the upper web and to heat
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-- seal the-superposed edges o~ the films around the whole periphery
of the pocket; at the same time, lhe lower film is heated through
the lower die.
On heating, the material shrinks into contact with the
product in the pack and the chamber is simultaneously aerated so
that the material collapses closely around the product. The dies
are then separated and the sealed pack is moved out of the vacuum
chamber and is replaced by a succeeding pack for the next cycle of
sealing operations.
In this method, which has hiterto been applied only to
heat shrinkable films, where a transverse row of pockets are indexed
into the sealing chamber in each step evacuation of the pockets in
the central region of the web is slow and inefficient as the air
must pass across the outer pockets be~ore it is removed via the
edges of the web. In addition, relative alignment of the upper and
lower webs must be exact in order to enable the dies to engage the
margins of the lower web without trapping the upper web and prevent-
ing exhaustion of the pockets, and this is difficult to achieve in
practice.
The method and apparatus of the invention provides an
alternative means for achieving a vacuum-packed commodity in which
the risk of leakage is extremely low and which can be performed at
high speed.
According to the present invention, there ls provide-d a
process for continuously packing commodities into vacuum-sealed
packs formed from a pair of superposed flexible fi]ms each of which
comprises a laminate of two flexible layers of plastics material
one layer of which has a softening temperature below that of the
other layer. The process includes forming pockets successively in
; 30 a continuously moving web of a first film by thermoplastic deforma-
, tion of, but without stressing, the film which has the laminate
with the lower softening point on its upper surface, putting a
commodity to be packed into each of the pockets, and laying a second,
upper contlnuous web of the film onto the upper surface of the lower
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~ web~ith its lower softening poin~ layer in contact wlth the
upper surface of the lower web to overlie -the pockets containing
the coiNmodities. The superposed ~ebs are advanced to a vacuum
sealing and continuously heatéd/chamber, witll the process further
including enclosing at-~east one of the pockets in the chamber. The
chamber is hermetically sealed and the films are heat se~led around
the pocket periphery, leaving a vacuum port in that seal. The
interior of the chamber and hence the interior of the pocket is
evacuated and the two films are simultaneously heated within the
chamber and the vacuum port is closed to seal the pocket under
vacuum. The interior of the chamber is aerated to cause the heated
films to collapse around the commodity in the pocket and the films
in the chamber are heated to a temperature such as to cause the
inner layers of the films to soften and thus fuse together around
the commodity on aeration of the chamber.
During heating of the superposed films in the vacu~ ~eal-
ing and heating chamber, the temperature of the films is raised to
a ~vel such as to cause the inner laminates to become substantially
molten. The outer laminates have a much higher softening temperature
and are thus not affected by the heat applied to the films. When
the vacuum chamber is aerated, the material of the packs collapses
around the product and fuses together around the margins of the packs,
thus providing a vastly better hermetic seal than has been achieved
hitherto using conventional vacuum-packing techniques.
In the method of the invention, it is preferred that a
plurality of pockets are formed transversely across the width of the
web, and the vacuum sealing and heating chamber is adap-ted to receive
at least one row of such pockets at a time. In practice, the vacuum
chamber can be constructed to receive at least two rows of the trans-
verse pockets, and the two films are then indexed stepwise by a dis-
tance which corresponds to the width of a double row of pockets.
In the preferred form of the invention, the method includes
slitting the upper web longitudinally prior to the films being passed
to the vacuum sealing and heating chamber, said slit extending cent-
rally along the length of the web between pockets which are adjacent
across the width of the web~ This enables the pockets to be evacuated~ -
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through the slits rather than through the edge regions of the web
and this substantially improves the air flow from the interior of
the pockets during the evacuation process. Ad~antageously, prior
to evacuation of the chamber, the two films may be heat sealed to-
gether around part of the periphery of the pocket, and where more
than one pocket is provided across the width of the web, the films
are heat sealed together prior to evacuation of the chamber by a
peripheral seal formed around the outside of each row of pockets in
the chamber, thus leaving a central or longitudinal slit through
which the pockets can subsequently be evacuated.
More than one slit may be provided in the upper web where
a large number of pockets are provided in each row.
On evacuation of the pockets through the or each slit,
the seal around the pack is completed by means of a sealing bar, which
is operable to seal the films together on either side of the respective
slit. The sealing bar may also act as an evacuation duct by the pro-
vision of ports in the outside edges of the bar.
In an embodiment of the invention, evacuation of the chamber
may continue after all the peripheral seals have been formed around
each pocket, to cause the material of the pockets to inflate for opti-
mum contact with the heated surfac~swithin the chamber.
In another embodiment of the invention, transverse seals
may be applied between adjacent rows of pockets before the pockets
are advanced into the vacuum sealing and heating chamber so as to
prevent relative movement between the upper and lower films during
the evacuation and heating operation.
Preferably, the plastics material of the upper and lower
films comprises a nylon/polythene laminate in which the nylon layer
has a softening point around 240C and the polythene layer has a
softening point around 110C.
The invention also includes apparatus for continuou,ly
p~ck.ina commodities into a succession of vacuum-sealed packs formed
from a pair of superposed films each of which comprises a laminate
of two layers of flexible plastics material one layer of which has
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a softening temperature below that of the other layer. The
apparatus includes pocket forming means for successively forming
in a first, lower continuous web of the film successive rows of
pockets across the width of the web which pockets are adapted
to receive the commodities. Means are provided for loading
commodities into the pocket and means are provided for super~osillg
a second, upper continuous web of the film onto the upper surface
of the lower film to overlie the pockets containing the commodities, -
and slitting means provide for slitting the upper web longitudin-
ally thereof along a line which extends intermediate adjacentpockets in the lower web. A vacuum sealing and contin~ously
; ,heated chamber is provided for receiving successive loaded
; pockets in the superposed upper and lower webs and heating m~ans
disposed to heat the webs are within the evacuation and heating
chamber. Sealing means are provided for sealing together the
upper and lower webs in the heated chamber along part of the
peripheries of the pockets and evacuation means evacuating
the interior of the vacuum chamber and the interior of the
partly sealed pockets. Further sealing means are provided for
sealing together the upper and lower webs along the remainder
of the peripheries of the evacuated pockets, aerating means
are provided in the interior of the chamber to cause the heated
films to collapse around the commodity in the pocket, and means
are provided for advancing the superposed webs in a step-by-step
manner successively through the app~aratus.
Preferably, the vacuum sealing and heating chamber com-
prises a fixed upper part incorpoxating heating means, and a
vertically displaceable lower part also incorporating heating
means which is provided with die surfaces which generally match
the shape of the pockets.
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In order to achieve displacement of the lower part of
the chamber, this part is preferably connected to a cylinder
and piston assembly operable to move said lower part between
a raised position in which it engages the upper part of the
chamber to form a vacuum enclosure, and a lowered position in
which entry and exit of the pockets takes place.
Advantageously the sealing means comprise mating surfaces
provided on the upper and lower parts of the vacuum chamber which
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surfaces are adapted to engage the web material when the lower part
is in the raised position. The further sealing means suitably com-
prises a sealing bar located in the upper part of the chamber which
bar extends longitudinally in -the direction of movement of the web
and is movable vertically between a raised position and a lowered
position in which the bar mates, through the web material, with a
surface formed on the lower part of the chamber. The axis of this
sealing bar is aligned with said slitting means and the sealing bar
is adapted to seal the upper and lower webs together on both sides -
of the longitudinally extending slit formed by the slitting means,
and the sealing bar may be provided with apertures communicating
with a vacuum port located in the vacuum sealing and heating chamber.
This ensures that air is drawn from the interior of the pockets by
a port located closely adjacent to the longitudinal slit. Air ports
are also provided in the lower dies.
Advantageously, the heated surfaces in the chamber are
coated with a non-stick material such as PTFE to prevent the softened
plastics material from sticking to the die surfaces.
Preferably, operation of the sealing bar is controlled by
means sensitive to the degree of vacuum within the evacuation cham-
ber. The period during which the lower die is in the raised position
is also suitably controlled by the degree of vacuum within the chamber.
The apparatus suitably includes transverse sealing means
located upstream of the vacuum sealing and heating chamber adapted
to make transverse seals between adjacent rows of pockets across the
width of the web prior to the pockets passing to the vacuum sealing
and heating chamber. This prevents relative movement between the
upper and lower webs during the vacuum sealing operation.
The apparatus also suitably includes severing means for
separating the individual packs from the web after the vacuum sealing
operation is completed.
In order that the invention may be more fully understood,
an embodiment in accordance therewith will now be described by way
of example with reference to the accompanying diagrammatic drawings,
in which:-
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- Fi~ure 1 is a schematic represen-tation o~ the
apparatus according to the invention
in operat.ion, showing parts of the
apparatus in longltudinal section;
Figure 2 is a transverse cross-sectional view
of the upperpart of the vacuum sealing
~ chamber;
: Figure 3 is a transverse cross-sectional view o~
the lower par-t of the vacuum sealing
chamber; and
Figure 4 is a pl.an view of the lower part of the
:: . vacuum sealing chamber shown in Figure 3.
.
Referring to the drawings, Figure 1 shows apparatus for
. continuously packing rashers of bacon or small joints of meat into
vacuum sealed packs formed from two superposed sheets each of which
comprises a two-layer laminated plastics material.
;~ It will be appreciated that while the invention is des. cribed in connection with.the packaging of ~oodstuf~s, it is eqlally
. applicable to other commodities which must be packed and maintained
under vacuum.
.. Sheet plastics material intended to form the ba.se part of
the packs is drawn from a reel 10 and after passing o~er a roller 11 ;
is advanced horizontally through the various stages of operation in
the form of a continuous base web 12.
- The material is a t~ layer laminated plastics film hav- ~:
ing one layer which has a much lower softening temperature than the
: other layer. In the case of the base web 12, the layer with the
.: . lower softening point is disposed on the upper side of the web.
..
. A sui-table plastics laminate film is a nylon/polythene
;,~ 30 laminate having a first lay~r of nylon of a thickness of 30 microns
with a softening point of 240~ and a second layer o~ polythene
: which is 70 microns thick and with a softening point of 115C.c A
.. ~ lower melting point polythene of 70 microns thickness with a soften~
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-ing point oE 105C may also be used for -the low-meltin~ polnt layer.
The first stage of the operation is conven~ional and com-
prises the forming oE successive pockets in the lower film in a
pocke-t-forming apparatus generally indicated a-t 13. l'he pocket-
forming apparatus comprises a vacuum chamber formed by a fixed upper
part 14 and a vertically displaceable lower part 15 which incorporates
a die 16. A heating element 17 is located in the upper part 14.
The base web 12 is indexed through the pocket-forming
device in a step-by-step manner, entering and leaving the chamber
with the lower part 15 in the down position shown in Figure 1. ~en
the web to be formed passes into the device 1~, the lower part 15 is
raised to close the chamber onto the base web 12, Eorming a hermetic
seal around the margins of the chamber, and the heating plate 17
(which is continuously heated) softens the material of the web. The
chamber is then evacuated through apertures in the die 16, and the
softened material is sucked into the lower part of the chamber~ con
Eorming to the shape of the die 16. The softened material cools on
contact with the die surface, and the vacuum is then released, to
leave the formed pocket in the web. The lower part 15 is displaced
downwardly to allow removal o~ the formed pocket, and the pocket is
indexed out of the apparatus.
In the device 13, pockets are Eormed in adjacent pairs
across the width of the web in a single operation o~ the pocket-
Eorming device, although they may be formed singly or in any number
(either transversely across or in the direction of mo~ement of the
web) depending on the size of the pockets and the dimensions of the
apparatus. For example, in one form of the apparatus, the pocket-
forming device 1~ is adapted to form pockets in sets of four, two
transversely across the web and two longitudinally in the direction
of the web. The die 16 is exchangeable so that dif:Eerent shapes and
numbers of pockets can be formed to suit the co~modities to be paGked.
In accordance with this invention, the pockets are Eormed
by thermoplastic deEormation of the web 12, and the web is unstressed
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~ fter the pocket-forming operation, unlike similar operations with
- shrink films in which the material is stretched when the pockets
are formed and left in a stressed condition.
me lower web 12 with the pockets 18 formed in this opera-
tion passes from the pocket-forming device 13 to a filling station
generally indicated at 19 where they are filled either by hand or
automatically by machine with the commodity 20 to be packed, which
in this case is either bacon or small joints of meat.
Beyond the filling station 19 the upper web material 21
is applied to overly the lower web 12, covering the commodities
filling the pockets 18. me upper web 21 is of the same laminated
plastics material as the lower web, and is drawn from a reel 22,
passing over a roller 23 before it is laid over the web 12. In this
case the laminate with the lower softening point is on the lower side
of the web, so that the low-softening point layers of the two webs
face each other and contact each other around the margins ~f the --
pockets.
Simultaneously with passing over the roller 23, the upper
web i8 slit longitudinally by a knife 24 so that the web approaches
the vacuum sealing station generally indicated at 28 with a central
dividing slit (the position of which is æhown in dotted line 26 in
Figure 4), the dividing slit extending centrallybetween transverse
pairs of pockets 18.
Before passing to the vacuum sealing station 28, the
superposed films pass between a pair of impulse sealing bars 29 which, ~
as the webs are indexed step-by-step through the apparatus, seal the ~-
two films together in a transverse direction between each pair of
pockets. mese seals, which extend across the full width of the
web, ensure that the webs maintain their relative position as they
pass through the remaining stages of operation.
The vacuum sealing chamber 28 is shown in detail in trans-
verse section in Figures 2 and 3 and comprises an upper part 30
(Figure 2) and a lower part 31 (Figure 3). Both parts are formed
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from a material such as aluminium alloy having good heat conducting
properties. The upper part 3O is fixed and is provided with a peri-
pheral sealing wall 32 defining a space 33 in which are located a
pair of heating plates 34 incorporating resistance heating elements.
The space 33 is provided with a main vacuum port 35, and water cool-
ing ducts 36 are located in the upper part 30 connected to a common
water supply (not shown).
~ ue to the restricted space within the vacuum sealing
chamber, the heating plates 34 are only around 5 mm in thickness and
are formed from an electrically conductive mesh or film embedded in a
sheet rubber material which is sandwiched between a pair of metal
plates. The outer surfaces of the plates which contact the web
material may be coated with a non-stick layer such as PTFE
(polytetrafluoroethylene) .
The lower part 31 of the vacuum chamber comprises a base
; 37 provided with vacuum ports 38 and boundary wall members 39 having
; upper edges 4O which are engageable with the peripheral sealing wall
32 of the upper part 30. The lower part 31 also has a lo~gitudinal
dividing wall 41 extending in the direction of movement of the webs
and having an upper surface 42 which is engageable (as will be des-
cribed) with a movable sealing bar 45 located in the upper part 3O.
The entire lower section 31 is vertically movable (as
illustrated in Figure 1) between a down position in which entry and
exit of the pockets 18 into the chamber takes place, and a raised
position adopted during the vacuum sealing operation. To this end,
the lower part 31 is mounted on the piston rod of an air cylinder
and piston assembly 46 and this vertical movement is controlled in
timed relation with the step-by-step advance of the pockets through
the vacuum sealing station.
The boundary walls 39 and wall 41 divide the lower part
31 into two sections 43, 44 and dies 48, 49 each shaped to receive
a pocket 18 are located respectively in these sections.' These dies
are interchangeable to suit the size of the pockets and two different
die sections are shown in Figure 3, the die 49 on the right-hand side
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~f the drawing being intended for bacon rashers and the die 48 on
the left-hand side of the drawing being intended for meat joints.
In practice, the dies will generally be the same in each section.
The dies are located only by the walls 39 and 41 and can be removed
by simply lifting them out of the appropriate sections.
The dies are provided with vacuum ports 50 communicating
with the vacuum ports 38.
The lower part 31 and hence the dies 48, 49 are electrically-
heated by heating elements 51 loGated on the outside of the lower part
31. These heating elements are of the same construction as the heat-
ing plates 34. ~uring operation of the apparatus these heating ele-
ments are operated continuously, as are the heating plates 34. me
elements 51 raise the temperature of the die surfaces to around 120C,
and in order to improve the heat transfer properties of the base part
31, the dies are suitably made of a good heat-conducting material
such as aluminium alloy~ Thermocouples 53 are provided in the upper
part 30 and on the outside of the base part 31 for monitoring the
temperatures of these parts, and these thermocouples may be operable
to control the current supply to the heaters for example to maintain
a constant pre-set temperature. As fusion is not required at the
bottoms of the pockets, the bases 52 of the dies are formed of a non-
heat conductive material to reduce overheating of the commodity.
As the pockets are advanced into the vacuum sealing
station, the lower part of the chamber 31 is in the down position as
shffwn in Figure 1. Following the indexing operation, the air cylinder
46 is operated and the lower part 31 is raised into engagement with -
the upper part 30, trapping the upper and lower webs between the hot
upper surfaces 40 of the walls 39, and the peripheral wall element
32 of the upper part 30, and hermetically sealing the inside of the
vacuum chamber. The two webs fuse alor,g this line of contact, and
a seal is formed extending completely around the periphery of the
pockets within the vacuum chamber. The interior of the pockets re-
main open to the interior of the vacuum chamber only through the
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~; central longitudinal slit extending along the dotted line 26 in
Figure 4.
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In the closed position of the parts 30, 31, the upper
web 21 is in contact with the heating plates 34, and the pockets 18
are in close contact with the walls of the dies 4~, 49. The heat
imparted by the plates and the dies quickly raises the temperature
of the web material, and simultaneously the interior of the vacuum
chamber is evacuated through main vacuum port 35 and vacuum ports 38.
Air is drawn out of the poc~ets through the central slit, and the
interior of the vacuum chamber and the pockets is evacuated to a
value of around 4 Torr.'
During operation, the longitudinal slit extends in the
same direction and slightly below the sealing bar 45, and in order
to speed up the evacuation of the pockets, the transverse sealing
bar 45 is provided with drillings 54 which terminate in bores 55
which communicate with the central cavity 33 of the vacuum chamber.
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The location of the sealing bar 45 also prevents the free edges of the
upper web on either side of the slit from "curling" in the air stream
and preventing subsequent sealing.
The sealing bar 45 is mounted on the base of a plate 56
connected to the upper part of the vacuum chamber by bellows 57 which
are normally urged into a collapsed position (shown in Figure 2) by
compression springs 58; the interior 59 of the bellows is connected ' '
to a compressed air port 60, and on reaching a predetermined level
of vacuum in the vacuum chamber (and hence in the pockets), the `
.. . .
' compressed a~r line connected to port 60 is energised, and the seal-
ing bar 45 is forced downward against the pressure of the springs 5S
into contact with the upper web on either side of the slit. The bar
45 presses the web material against the hot upper surface 42 of the
dividing wall 41, forming a seal along both sides of the slit, which
completes the peripheral seal around the boundaries of the individual
pockets.
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At this stage of the operation, the heat imparted to the
webs by the heated surfaces in the chamber has caused the inner, low-
melting point layers to become molten, and at a predetermined vacuum
the valves controlling the vacuum ports are opened, aerating the
chamber and causing the web material to collapse around the product
in the pockets. At the contacting margins of the webs i.e. in the
zones between the pockets and at the sides of the pockets the web
material fuses together, forming a perfect hermetic seal around the
commodity. me lower part 31 of the vacuum chamber is then displaced
downwardly into the position shown in Figure 1, and the evacuated
and fused packs 62 are indexed out of the machine and passed to a
slitting station where they are separated from each other and from
the remainder of the wek material.
By virtue of the complete fusing of the opposite films
around the commodities, the number of leaking packs produced in this
apparatus is extremely low compared to most known methods of packing;
in practice, a reduction in the number of leaking packs of around
95% has been achieved with the apparatus and method of the invention.
A number of modifications to the method and apparatus des-
cribed are possible without departing ~rom the scope o~ the invention.For example, in one embodiment, once the peripheral seals have been
formed around the packs vacuum may continue to be drawn through the
vacuum ports, causing the air pressure in the vacuum chamber to be
reduced to a value below that present in the sealed pockets. This
causes the sealed web material to inflate, forming optimum contact
; conditions between the material and the heated surfaces of the plates
~4 and dies 48, 49.
In a further modification, the web material may be per-
forated along lines which are located in the margins of the sealed
packs in order to assist in the evacuation of the pockets. Due to
the ultimate fusing of the films, these holes are closed when the
packs are finally formed.
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