Note: Descriptions are shown in the official language in which they were submitted.
~212~L5
DESCRIPTIO~
"PROCESS AND APPARATUS FOR PROVIDING A SEALED PACKAGE"
The present invention relates to a process and
apparatus for forming a sealed package, in particular by
fusing together layers of film material (which may
themselves be bonded multi-ply film structures) to seal
a package. Such a package may, for example, be a vacuum
pack, but equally could contain an inert gas which assists
in preserving the contents of the package, particularly
where the contents are perishable.
Various methods are known for sealing films.
In widespread use at the moment are:- clipping to close
off the neck of a bag formed of the film material, heat-
sealing by the simultaneous application of heat and
pressure to press two layers of the film together into
fusing contact, and adhesive sealin~, for example by
coating one or both of the surfaces which are to come
into contact for sealing together with an adhesive
composition so that the contacting surfaces seal when
pressed together.
In addition to heat sealing by pressing films
to~ether using heated mechanical clamping bars, it is
also known from U.S. Pa-tent Specifications Nos. 3989778
and4069080 to irradiate clam~ed layers of fi~n with energy
from a la~er to pxomote loca~ised fusing of the surfaces
~2:~261S
in contact with one another. It is also known, from
UnS~ Patent Specifications Nos. 3477194 and 3247041, to
irradiate clamped layers of film with infra~red radiation
from an adjacent source fo~ the purpose of bonding them
together.
These prior art specifications all rely on the
application of heat to portions of the films which are
already clamped in sealing relation, so the application
of such a system requires careful registration of the
.10 clamped film portions with the path of emission of energy
from the infra-red source or laser, as the case may be.
Furthermore, particularly with regard to the use of
infra-red radiation, it is difficult to avoid having
distances between the infra-red source( 3 ~ and the clamped
film portions which (in order to provide ample room for
manipulation of the packed product and the material
therearound) are so great that the radiation losses
which vary inversely in proportion to the square of the
.
distance from the heat source, become considerablen
In order to overcome the disadvantages of the
~ior art systems using radiant heat to seal plastics
mater~a~, the present invention provides a process for
~orming a package, comprising enveloping goods in a
plastics film arran~ed with corresponding film portions
~hich will be brought into contact with one anot'her to
seal the ~c~a~e~ m~intaini~ said corresponding ~ilm
~26~5
portions out of contact with one another before sealing,
heating said corresponding film portions With infra-red
radiation, then bringing said heated film portions into
contact with one another to fuse together on conkact.
Another aspect of the present invention
provides apparatus for forming a package, comprising a
su,pport for goods and an enveloping plastic3 film, at
least one infra-red radiation source positioned to
irradiate corresponding film portions of ~uch a supported
10 anvelcping film, means for maintaining said corresponding
film portions out of contact with one another during
operation of said infra-red radiation sources, and means
for subsequently bringing said corresponding film
portions into contact wlth one another to close the
package.
. Althoug'h the process and apparatus of the
present invention find application in various different
types o packaging, they are particularly suitable for
the vacuum packaging of products in a chamber.
~0 Accordingly, a further aspec~ of the present
inv~n~on provide3 a process for fonming a vacu~n package,
comprising enveloping a product in plastics film, placing
the enveloped product wi'~hin a vacuum chamber, evacuating
the ~hambe~ to redu~e the pre~sure within and around the
25 pla3tics film, and sealing corresponding portions of the
e~velopihg film to form a vacuum package, w~erein the
~2~6~5
step of sealing the film portions comprises irradiating
said corresponding film portions within the chamber with
infra-red radiation, and bringing said heated film portions
into contact with one another -to fuse on contact.
~et a fourth aspect of the present invention
provides apparatus for forming a vacuum package, comprising
a vacuum chamber, a support within the chamber for a
loaded plastics bag, means for constricting the neck of
the bag within the chamber, means for ballooning the neck
of a said bag supported on the support with its neck
constricted by said neck-constricting means, infra-red
radiation-e~itting means in said chamber energisable for
irradiating the ballooned neck of said bag to heat the
ballooned neck material, and means for releasing gas from
within the said bag to remove the bag neck from its
ballooned configuration after heating of the bag by said
infra-red radiation-emitting means and for causing the
heated ballooned neck material to contact itself and to
seal upon contact~
The invention also provides a package fol~ned
by either of the above processes, or using either of the
above apparatuses.
In order that the present invention may more
readily ~e understood the following description is given,
merely by ~ay of example, with reference to the
accompanying drawings in which:-
~Z126~5
~ igure 1 is a side eleva-tional view, in
schematic form, of one form of vacuum chclmber in which
the process of the present invention can be carried out;
Fi~ure 2A is a detail,in sectlonal form, of the
sealing mechanism incorporated in the chc~mber of Figure l;
Figure 2B is an end elevational view of the
sealing mechanism of Figure 2A;
Figure 3 i5 a top plan view, in schematic form,
of an alternative form of vacu~l chamber i.n which the
process in accordance with the present invention can be
carried out,
Figure 4 is a view, similar to Figure 3, but
showing yet a further embodiment of vacuum chamber in
which the process can be carried out; and
~ Figure 5 is a clrcult diagram of a slmple
form~of control system for the infra-red heat sources
used in Flgures 1 to 4.
Referring now to Figure 1, there can be seen
a va~uu~ chamber ~ comprising a hase portlon 2 and a
~ovèr 3 which are ~losed together and seal around their
rims ~0 to form a sealed enclosure within which two plastic
bags 4(in thi~ case formed of a heat--shrinkable material~
encl~ p~od~ct articles 21 can be evacuated and seale~.
~hrinkin~ heat is imparted to each bag 4 by
means of t~ fans 6 and 7 driven ~y respective motors 8
and 9 and ~ lati~g air by way of circular heating
~2~
-- 6 --
elements 10 and 11 which,,while shown in side elevation
in Figure 1, are identical ko the construction o:E the
corresponding heating elements 10 and 11 shown in'plan
view in Figures 3 and 4. The radially outward airflow
from the centrifugal fan rotors 6 and 7 passes over the
heating elements 10 and 11, becomes heated thereby, and
then contacts the bags4 above a support grid 12 in the
chamber. The bag~then acquire heat from the air and
shrinks to the desired extent, depending on the extent
'10 to which the film was oriented during manufacture.
The chamber further includes upper and lower
heating units 13 and 14 incorporating infra~red heat-
emitting strip lamps. (37 and 38 in Figure 2A) which
radiate heat to the spaced film portions of the neck
regionsof the baa,s4 and heat the neck regionsto a
suffiQient extent so that when these film portions
subsequently contact one another, for example, during
repressurisation of the cham~e.r 1, the film layers
automatically fuse together.
~ The detailed construction of these upper and
lower he~ating units 13 and 14 will be described with
refèr~ncè to the detailed drawin~s of Figures 2A and 2B.
The mouth region of each bag is clamped by a
yieldable bag holdin~ means ha~i.ng upper and lower
members 33 a~d 35, also shown in Figures ~A and
2B, in such a way that air lS able to escape from the
lZ~61~i
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interior of the bag 4 between the upper and lower heating
units 13 and 14 and the upper and lower me~ers 33 and 35,
but by virtue of the yieldable bag holding action air is not
able to re-enter the bag through the mouth regionO
The evacuation cycle u~ed in the ch~er of
Figure 1 can be one of several different forms.
As a first example, it is possible -for the
shrinking heat to be applied to the bag 4, ~y a~tivation of
the fan motors 8 and 9 and the heaters 10 and 11, before
evacuation of the chamber 1. This will result in the heat-
shrinking of the bag material. This heat-shrinking tends to
compress the air trapped between the pro~uct ~1 and the bag
4 and~the trapped air holds the bag ~Iballooned~ out of
contact with the relatively cold product while the tension
in the heat-shrinking bag 4 builds up.
The air trapped within the bag 4 i9 then released
when its pressure overcomes the resilient blade 33, allowing
the shrink ener~y pent up ïn ~he taut bag to force the bag
material down onto the product 21. The vacuum pump is then
startod and evacuation of chamber 1 takes place. After a
suitable del~y, the shaped wire 48 i3 energised rupturin~
the bag ~eck to allow further evacuation o~ the bag through
the ne~X. The chamber 1 contin~e~ to be evacuated in
order to e~t~a~t t~e remaining air from within the bag 4
and to allow the b~g to be sealed~ Such a cycle is the one
described in
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-- 8 --
relation to Figures 2A and 2B.
An alternative operating cycle for the chamber
in Figure 1 is one in which the evacuation of the chamber
1 starts simultaneously with the activation of the
heaters 10 and 11 and of the ~an motors 8 and 9 and
proceeds in such a way that the restriction of the bag
mouth by the yieldable bag holding means results in
delayed extraction of air from within the bag 4. This
causes the bag 4 to balloon outwardly away from the product
21 as the pressure in the chamber around the bag 4 drops
more rapidly than t,he pressure of the air within the bag 4.
Once ~he bag has ballooned to a desired extent (as can be
detected either by having a cycle timer which relies on the
fact that a batch of similar product articles packaged in a
similar film and subject to chamber evacuation at a similar
rate will take the same time to balloon~ or as detected by
means of mechanical sensors responsive to ball.ooning bag 4)~
the evacuation of the chamber ceases so that the ballooned
state of the bag is held during circulation of the remaining
air in the chamber 1 by way of the fan rotors 6 and 7. This
circulation of hot air causes further heat transfer to the
material of the bag 4 with resulting recovery of the shrink
energy in the bag 4 because the bag is still
~2~ 5
maintained out of contact with the product article 21 therein.
Once this heating of the bag 4 has proceeded to a desired
degree 3 evacuation of the chamber resumes and then the bag
neck is eventually sealed when the interior of the bag has
reached a sufficiently low residual pressure (high vacuum).
Other possible operating cycles can be envisaged,
for example in which the evacuation and hot air circulation
begin simultaneously and continue uninterrupted until a
sufficiently low residual pressure (high vacuum) is obtained,
and the bag is then sealed.
With each of the above forms of operating cycle,
the chamber of Figure 1 will preferably include the upper
and lower heating units 13 and 14 shown in Figures 2A and
2B.
As shown in Figure 2A, the yieldable bag-holding
means 30 is supported by an upper support member 31 forming
part of the chamber cover 3 and a lower support member 32
of the lower chamber part 2 As the cover 3 closes onto
t.he lower chamber 2 the upper support member 31 descends
towards the lower support member 32 to adopt the
~2~
-- 10 --
configuration shown in Figure 2A.
A resilient bag-holding blade 33 of a suitable
rubber-like material is carried by the upper support
member 31 and is secured thereto by a set of screws 34.
Along its lower edge, the resilient blade 33 contacts a
counter member 35 carried by the lower support member 32.
The counter member may alternatively be a blade similar to
the blade 33. After the neck of a plastics bag is placed
on the counter men~er 35 while the chamber cover 3 was in
lQ the raised position, lowering of the chamber cover 3 to
bring the upper and lower suppor-t members 31 and 32 into
the Figure 2A configuration automatically causes the bag
neck to be held on the counter member 35 such that any
build-up differential air pressure within the bag above a
certain value can be vented by displacement of the blade 33.
Retraction of the bag neck lef-twardly between the blade 33
and the counter member 35 is resisted by spring-loaded
plungers, one (36) of which is shown in Figure 2A, pressing
the back neck firmly onto the counter member 35.
The angle of inclination of the yieldable blade
33 is such that air under a sufficient differential pressure
is able to escape f~om within the bay at least in the mouth
regions between successive plungers 36.
Sealing of the bag neck, in such a way that the
2~ minimum of air space results within the bag around the
neck, is achieved by means of upper and lower heat sources
Z~;:6~S
37 and 38, respectively, in -the form of strip lamps w~lich
radiate infra-red heat at a wavelengtll w~lich cJiVe5 optimum
heat absorption by the plastics composi~ion of -the bags 4
within ~he chamber.
The wavelength of the li~ht emitted hy the lamps
37 and 38 i.s advantageously chosen to coincide with the
wavelength most readily absoxbed by the material o~- the
bag. Conveniently the wavelengt~ in question is in the
range from 3 to 4 microns for most plastics films,
including multi-ply films and laminates such as a heat~
shrinkable (i.e. oriented) three-ply laminate of ethylene-
vinylacetate, polyvinylidene chloride and irradiated.ethylene-vinylacetate.
~ brief exposure of the bag neck region to the
radiation from the heat ~mitters 37 and 38 will be
suf~icient to heat the bag material to its softening
point so that wl~en the panels of bag material are pressed
together t~ley will s~al at the mouth and neck regions.
. Contact of the bag material w:i.th the
upper and lower heat sources 37 and 38 is prevented by
means of wire screens 39 and Llo carried by respective
up~ë~ an~ lower pairs of carrier pla-tes 41 and 42 pi.voted
on pin~ 41a, 42a. Each carrier plate 41, 42 has a slot
41b, 42b, which slidably co-operates with a xespective
cam pin 43 or 44 carried at the associated end of a
vPrtically movable upper or lower.clamping bar 45 or 46,
respective~y. ~he lower:clampillg bax 46 includes a main
~2~
-12 -
body having a resiliently biased jaw member 46a connected
thereto by means of helical compression springs 46b which
- ensure that as the two pressure bars 45 and 46 come into
contact with one another the jaw member 46a yields.
The holding means 30 furthermore includes a
shaped wire 48 carried by the counter mel~ber 35 and which
in the Figure 2A configuration of the holding means contacts
the ballooned bag neck. When energised with a current
pulse the wire ru.ptures the bag neck to allow escape of
the gas (usually air) within the ballooned neck be~ore
sealing. The wire 48 may, for example, have a saw-tooth
shape or a sinusoidal undulating shape.
~ s the upper clamping bar 45 descends, its cam pins
43 slide down the slots 41b and causes the upper pivotable
carrier members 41 to pivot in the anti-clockwisQ direction
to swing the heat source 37 and its wire screen 39 xight-
wardly away from the path of descending travel of the
upper cla~ping bar 45~
~ Similarly, as the lower clc~nping bar 46 ascends
its cam pins 44 co-operatè with the slots 42b of the lower
carriers ~2 ~o swing those carriers aside and to move the
lower he~t source 38 and its wire screen 4G away ~rom the
pa~h ~ ~ravel of the rising clamping bar 46. This allow.s
the film ma~erial to be clamped between the two clamPing
25 bars 45 ~nd ~6. ~t the sarne time, a blade 47 carried by
the mai~ body portion of the lower clamping bar 46.is
exposed above the yieldable jaw 4~a due to yielding o-f the
com~ressio~ sprin~6 46b and is able to cut the surplus bag
material ~ro~ ~h~ neck dur.in~ sealing~
, .
~z~
Figure 2B shows the drlve mechanism by virtue
of which the upper clamping bar 45 is driven for its
vertical movement.
As shown in Figure 2B, the upper clamping bar
45 is in two separate parts supported by a central bearing
portion 49 on a vertical guide pin 50 to allow vertical
sliding of the two parts of the upper clamping bar 45.
The two clamping bar parts are connected to the
lower ends of respective thrust links 51 which in turn
. 10 have their upper ends articulated to respective double
bell-crank assemblies 52, 52' of which one, 52, can be
seen in Figure 2A.
The lefthand of the bell-cranks 52 has a fixed
pivot pin 53 at one corner, a pivot pin 54 at another
corner articulating it to the thrust link 51, and a
further pivot pin 55 at the third corner articulating it
to one end o~ a secondary drive strut S6.
The other end of the secondary drive strut 56
is articulated at 57 to a corresponding corner of the
righthand double bell-crank assembly 52' which also has
counterpart pivot pins 53' and 54' to correspond to the
pins S3 and 54 above-described.
A primary drive strut 5~ is connected between
the piston rod 59 of a ram 60 and a further articulation
pin 61 on the righthand double bell-crank assembly 52lo
Extension and retraction of the piston rod 59 causes
~21;2~1S
- 14 _
anti-clockwise or clockwise motion, respectively, of the
bell-crank assemblies 52, 52l and consequently raising
and lowering movement o-f the clamping bars 45~
~ ~ sirnilar drive linkage and drive ram will be
provided to drive the main body of the lower clamping bar
46 upwardly and downwardly.
As also shown in Figure 2B, the upper clamping
bar 45 has a guard member 62 screwed thereto~ for the
purpose of defining a gap into w~ich the
blade 47 can enter when the upper and lower clam~ing
bars ~5 and 46 come together.
The holding means 30 o-f Fiyure 2A and Figure 2B
operate at several stages during -the cycle of the erltire
machine as will be described later.
The operation of the apparatus sho~ in Figure
1, when using bags 4 formed of a heat-shrinkable,
i.e.~orientated, film material is a~ follows:~
A loaded but unsealed bag 4 of heat-shrinka~le
packaging ~i~n is placed in the vacuum chamber 1, and the
chamber cover 3 is driven downwardly to close the chamber
and to allow sealing of the chamber at its rim 20.
bne form ot a heat shrinkable (i.e. oriented~
film used for the bag 4 may be a -three~ply laminate of
ethylene vinyl aceta-te, polyvinylidene chloride and
irradiated ethylene-vinylacetate. as disclosed in
Unit~ States Patent No. 3,741,253 and as sold by
W.R~ Grace & ~o, under the Trade Mark "Barrier Bag".
~Z~;:6:~5
- 15 --
As explained above, the lowering of the chamber
cover 3 brings the resilient blade 33 down against the
bag neck to hold the neck firmly on the top surE~ce of
the-counter member 35. At this stage the upper and lower
clamping bars 45 and 46 are retracted and the heat sources
37 and 38 are in the configurations shown in'Figure 2A.
Shrinkin~ heat is applied to the exterior of the
bag before any substantial evacuation of air Irom the
interior of the chamber and the applied heat causes the
bag material to begin to shrink. The air enclosed within
the e~fectively sealed bag (held by the resiliellt blade
33) resists the s'hrinking action and holds the bag material
"ballooned" away rom the surface of the product (or
example a cut of fresh red meat) therein. While the bag
15 ' is thus maintained clear of the surface of the product,
the circulation of hot air around the outside of the
ballooned ba~ material im~arts further heat to the bag
mat~rial and completes the heat-shrinking operation to
draw the film material back down agai}lst the surface of
the product r However, the bag material will have been
ballooned away from the sur~ace of t'he product for long
enou~h to allow ade~quate heat transfer to the ballooned
film whiCh is not able to give up any appreciable heat
to the prod~t 21, and to have raised the film to i-ts
shrinking tè~perature so that a very hi~l proporti.on of
the shr~n~ ene~gy can be recovered.
s
~ 16 -
During this time, the heat sources 37 arld 38
- will either be de-energised or more preferably energised
to a low heating level which will not ena~le them to heat
the fiLm material of the bag neck to a temperature
sufficient to achieve fusion.
The constriction of~the bag mouth ~len engaged
by the yieldable holding means 30 ensures that, as the
application of heat by convection t.o the exterior o-~ the
~ag proceeds, any excessive pressure diff~rential built
up within the bag can be controlled by ventin~ o~` gas
(usuàl~ly ai~) from the interior of the bag 4 to an ex-tent
~hich will s-till maintain the bag material"balloc>ned" away
~rom the surface of the produc~ 21 therein. Since the
ballooning action will depQnd upon factors con~non to a
particular batch o~-products 21 ~for example the surface
tem~erature, the amount of air contained within the product,
and ~he surface nature, -e.~. tackin~ss - of tlile ~roduct)
it ~ày be convenient to determi.ne, by observation, when
ballooning is likely to oc~ur and then to time: the process
2~ such that the evacuation begins at the same time for all
the ~r~duc~ o~ a batch and is timed by a suitable tirner~
Any othèr control means may be e~ployed, as desired.
~ ecause, during the heat-shrinking step, the
bag 1~ ~tl~1 y~ldably held across its neck, further escape
12~2~5
_ 17 -
Ol alr ~rom within the bag may occur through the neck in
the unlikely event of an excessi~e pressure differential
across the bag material, while the remainder of the bag
will shrink ~ack onto the surface of the product article
21 so as to provide a substantially wrinkle-free surface
covering to the product article 21 and neverthelas~ lea~e
the bag neck capable of sealing when the cla~ping baxs 45
and 46 close together to contact one another.
At the end of the ~allooning phase, and before
evacuation of the bag is to commence, the shaped wire 48
is briefly energised to rupture the bag neck and to release
the trapped gas therewithin.
Evacuation of the chamher atmosphere ~and of the
now ruptured bag ~) proceeds until the desired vacuum
level has been reached~ At, or sli~htly before, the end
of the evacuation phase the larnps 37, 38 can be energised
to their maximum level to e~it radiant heat at the desired
wavelength for optimum heat absorption by the film matexial,
and thereby to heat the pierced bag neck to fusion
temperature~
The rams 60 are then operated to brin~ the upper
and lower clamping members 45 and 46 together J
simultaneo~ swinging away the sourcss 37 and 38 and
their associated wire screens 39 and 40~ .
once the upper clamping bar 45 has come into
cont~t ~ith the biased clamping jaw 46a, further
lZ~ S
- l$ -
operation of the rams 60 results in the blade 47 severing
- the bag neck to detach the surplus material therefrom.
The clamping members 45 and 46 ensure film holding of the
neck alongside the blade 47 to ef~ect sealing~ Throughout
this operat.i.on, the mouth portion of the bacf will still
have been clamped between the yieldable blade 33 and the
counter member 35 so that the bag will still be securely
located within the holding means 30.
The ret:raction of the upper an~ lower clam~ing
bars 45 and 46 wîll brin~ thc heat sources 37 and 38 and
their wire screens 39 and 40, respecti.vely, back into the
Figure 2A configuration. The e~acuation of the ch~nber
takes place after this retraction of the clam~ing bars
45, 46 so that unhindered escape of any residual air from
the bag can take place.
When the vacuum chamber is re-pressu.rised,
upon opening, the heated neck portions of the bag to the
left of the clamping memb~ers 45 and 46 are thrust together
to achieve fusion welding and to reduce the size of any
surplus bag material around the sealing zone to achieve
a ti~y appearance to the finished pack.
The surplus bag material severed by the blade
47 is still held between the resilient blade 33 and the
cvunter member 3S and can be removed during or after
remo~al of the package from the opened chamber.
~2~ 5
- 19 -
The above-described process is particularly
convenient for use with wet produc-ts such as fresh red meat
in heat-shrinkable bags because the pressure increase on the
sur-face of the meat, during the ~ag-ballooning action, tends
to hold the moisture in the product and avoids misting of the
inner surface of the bag ~hen in the ballooned condition.
Furthermore, the rapid venting of the trapped air upon
bag piercing allows the bag material to contact the product
rapidly and before any such misting occurs. Consequently,
the appearance of the finished package is particularly
attractive in the case of moist products such as fresh
red meat.
In the case of all products packed by -this
process, the wrinkle-free nature of the product is enhanced
through the adoption of a prelimin~ry shrinking step
ollowed by subsequent evacuation (as opposed to the
conventional sequence of vacuum-sealing first and shrinking
a~terwards).
The finished package in accordance with the
present invention is moreover much improved over prior
art shxink-tidied packages in which a water shrink bath
is used in order to alleviate the "heat-sink" effects of
the relatively cool and high thermal capacity product,
beca~ shrinking of the film in contact with air allows
a greater recovery rate of the shrink energy, and .
consequent1y a greater increase in thickness, with the
- u
~2:~26~5
-- ~o --
result that tlle barrier properties of t~-le bag (importarlt
in order to maintain hermetic sealing of the procluct and
freshness up to the time of cons-lmption) are more effective.
Furthermore, the abuse-resistance of such a hay is better
because of the increased th.ickness.
Because the air pocket trapped inside the bag
during the pre-heating shrink pllase resists the collapsing
of the bag and postpones contact of the bag with the cold
. product, this~tnickness-increasing effect is even more
noticeable and so also is the wrinkle-~ree appearance of
the bag ~ich again depends on the exte~nt of recovery of
latent shrink energy in the film material. Moreover,
because the shrink is provo]~ed by air currents moving
around the whole of the produc-~, the shrinlcage o:E the
bag will be uniform around the produc-t and this ~i.ll
eliminate risk of entrapmen-t o~ air pockets behind the
"equatos" of the product (i.e. -the arecl oE largest cross-
section in a plane perpendicular to -the loncJitudinal axis
of the bag).
Furthermore, the above-mentioned characteristic
of having little or no water vapour in the air between
the product and the.shrili~ing bag (causedby the onset of
shrink before any pressure reduction and even causing h
slight pressure increase) ensures that less shrink heat
is required because the dry air on the inside of the bag
absorbs less heat than would moisture-laden air.
~ ~Z1261S ` .
,
Because the lower and upper support members
32 and 31 of the yleldable holding means 30 are carried
by the lower chamber portion 2 and the chamber cover
portion 3, respectively, they automatically close together
to contact one another ~nen the chamber is closed and all
that the operator needs to do is to ensure that the neck
of eachbag 4 is placed on the respective counter members
35 before the chambèr closes~
If desired, where the loaded bags are introduced
by a collveyor into the chamber 1 t~e conveyor may be one
which ensures that, when the bag 4 i~ stopped~ the bag
neck is correctly positioned for constricted clamping
without the need for careful positioning by an operator.
~s indicated above, other bag closing mechanisms
may be provided for u~e with the radiant heat sealing
. .
units 13 and 14 described above.
For exa~ple, the bag neck may be closed by a
conventional trim-sealing bar 70 (Figure 3) w~ich both
cuts off ex~ess material and seals the bag mouth along
the line of pressure betwee~ upper and lower clamping
bar~ ~b~ ~è~h~ af a resistance heater). The
applicatlon of heat to the neck region between the trim-
sealing unit 70 and the product 21 has the result that
~hen the ~hamber 1 is re-pressurised the bag material
in the neck re~ion will have been heated to an extent
that it will f~B~ to itself on collapsing, leaving a
~2~26g~i
- 22 -
much tidier neck region to the package.
Alternatively, the bag neck may be placed in a
gathering unit 71 (Figure 4~ so as to be gathered in a
~acuum chamber when the chamber closes~ and has a clip
5 attached to the neck of the bag b~ the clipping unit 71a
after the evacuation and shri~king operakions have been
completed. Such in-chamber clipping mean~ is for ex~mple
disclosed in our British Patent Specification No. 1,3S3,157
Yet a further pos~ibility is for the clippin~
unit 71a to be omitted from Figure 4 and for the gathering
action to be carried out after the energisation of the
infra-red heat sources has achieved heatin~ of the bag
neck in the region which is about to be gathered. When
the thus heated and softened bag neck regions are drawn
together by operation of the gatherin~ unit 71(which may
for example be of the kind described and c~laimed in Briti~h
Patent Spe~ifications Nos. 1,353,157, 1~361,142 and
1,496,740) the gathering action is sufficient to cause
the neck material to adhere to itself and to resemble the
configuration of a clipped neck but without a clip. The
mere heat-sotening of the bag neck region will be
sufficient to cau3e intimate contact and sealing of the
gathe~ing nè~k reglon~ ;
~he schematically illustrated gathering unit 71.
may for example operate in two stages, as disclo~ed in
British Patent 5pecification ~o. 1,353~157, in that it
.i ~2~6~
. - 23
first of all gathers the bag into a horizontal slot-like
configuration as the chamher closes, and achieves sufficient
restriction of the flow of gas from the bag interior to
promote the desired ballooning effect before energisation
of the infra-red radiation sources, Then tha second stage
of gathering reduces the Length of that slot to bunch the
bag neck into a self-adhering gathered coniyurat.ion~
Alternatively, some other bag mouth-constricting action
may be exerted on the bag and the gathering unit 71 t'nen
operated to completely gather the bag neck after the
ballooning heating action.
The above description of the various cycles of
operation possible.with the chamber 1 o Figure 1 refers
throughout ~o the use of a heat-shrinkable film~ However
~5 it may be possible.to use the process according to the
present invention with other films, ~or ex~lp~e self~
weldlng fi.lms which are heat-softened and will then weld
when they come into contact with one another4
Likewise, the alternative chamber constructions.
shown in Figures 3 ànd 4 can be used wi.th any suitable ..
~ilm, in~lu~ing heat shrinkable Eilm and self-welding ~ilm.
~ lgure 5 shows a scnematic view of one possible
control circ~it for energisation of the radiant heat~emittiny
l~mps 37 ~d 38~ A varia~le transformer 72 ;.s connected
2~ a~ross input termina~s 73 and 74, and across the same two
terminals 73 ahd 74 there i9 connec'ed a shunt line
including a m~ro~witch 75 and a timer 76, A further shunt
~` line includes a ~ 'h 77 and a circuit breaker 78; the
~2~
- 24 _
circuit breaker being itself connected to switch contacts
79 and 80 in the secondary circui-t of the variable
transformer 72. Thus the two switch contacts 79 and 80
control energisation of the infra-red emitting lamps 37
and 38 which are connected in parallel in the secondary
circuit of the variable transformer 72.
The variable transformer is permanently
energised, and the start of the cycle is triggered by
operation of the microswitch 75, responsive to some moving
mechanical component, for example the closing of chamber
cover 3. Closing of the microswitch 75 starts the timing
cycle of the timer 76 so that the switch 77 immediately
closes, energising the circuit breaker 78 which closes
contacts 79 and 80 to energise the lamps 37 and 38.
After a time delay determined by the timer 76,
the switch 77 is opened, breaking the circuit to the
circuit breaker 78 which then opens contacts 79 and 80
to de-energ.ise the lamps 37 and 38.
In a particularly convenient modification of
the circuit of Figure 5, arrangements may be made for
the lamps 37 and 38 to be reduced to a standby power
setting ~for example at 20% of their full power) rather
than be completely de-energised when the circuit breaker 78
is de-energised. This may, for example, be achieved by
having a two way switching system at the contacts 79 and
80 so that in one position of the moving contacts a
12~2~
"standby" circuit is completed -to ener~ise the lamps 37
and 38 at their standby power setting, and in the other
position of the movable contact -the main circuit shown
in Figure 5 may be energised.
Adjustment of the variable transformer 72 can
allow the power of the lamps to be varied, ~d
similarly the timer 7~ may be ad~ustable to allow a
time delay, for example of from 2 to 6 seconds, for the
operation of the lamps 37 and 38.
One preferred type o~ lamp for use as lamps 37
and 38 is a Philips type 13195 X/98 lamp, obtainable
from the Philips Electrical Company.
Advantages of using the fusiQn sealin~ syste~
described and illustrated herein include the fact that
the thermal inertia of the infra-red lamps 37 and 38 is
very low so it is possible to turn thern on onl.y when
fusion sealing is requlred. Furthermore, fusion sealing
has the advantage that there is no physical contact
between the lamps supplying the hea-t and the plastics
material to be bonded.
It is a parti.cularly important advantage of the
present lnvention that -the heat is applled by radiation
to the films befare they are put into con-tact wi-th one
another, thereby ensùrln~ that the shortest possible
~5 radiant energy path from the lamps to the clamped films
~2~ 5
- 26 -
can'be provided without the lamps 37 and 38 needing to
be placed close together. Instead the lamps may be
~uite widely spaced and the bag neck material ballooned
into the vicinity of the lamps so as to cut down the
S distance from the heat source to the bag material~ This
provides a much less ~umbersome apparatus from the point
of view of (a) loading the bag into the chamber, or ~b)
more generally (where the,fusion sealing of a film
enclosure to form a package is carried out without the
use of a vacuum chamber) positioning any two film
portions to be welded in a position ready for fusion
heating with the apparatus in accordance with the present
invention.
` Furthermore, the amount of energy imparted to
the:films can quickly and easily be adjusted either by
varying the supply voltage to the lamps, or by varying
the,time for which they are "on", or by adjusting both
paràmeters.
' If desired, the neck region of thè bag may be
print~d with a material which has a high absorption
co-èfficient so as to provide even more intense localised
heat ~ptake.
Thé ~acuu~ levels envisaged for the processes
desc~ibed above will be o~ the order of 5 TorrO However,
the vacuum can be much softer (higher residual pressure)
, if desire~ ~for example when packaging products such as
. .
.
'
~ZlZ6~ ~S .
- 27 -
so called high-gassing cheeses which wi.ll naturally exude
gas - for example carbon dioxide - and will do so at a
much higher rate if packed under high vacuum conditions),
In Figures 1, 3 and 4, the means for applying
~heat to the ~ag material comprise fans circulatin~ hot air.
Alternatively, other ~ag heating means may be used in
association with the radian~ heat-emitting heating units
13 and 14.
Temperatures of 90~C to 140C in the ballooned
film will be required in order to achieve heat-shrinking
in the case of a biaxially oriented shrinkable ilm.
However, higher temperatures may be imparted by the
radiant heat-emit.ting heating units 13 and 14 in the neck
region of the film to promote fusion sealing~
The above description generally xefers to the
action on an indi~idual bag 4 in the chamber, although it
i3.made quite clear that in Figure 1 two separate bags 4
are provided. The method ~nd apparatus of the invention
can be conceived for use with one package, or with two
or more packages sealed simultaneously, and this
ver~atilit~ wil~ apply equally to the three separate
embodiments depicted by Figures 1, 3 and 4, as well as to
a~ ~ther embodiments falling within the scope of the
c l ~ ; d
