CA1212615A - Fusion sealing with infra-red lamps - Google Patents

Abstract

ABSTRACT
"PROCESS AND APPARATUS FOR PROVIDING A SEALED PACKAGE"

Plastic bags (4) are sealed in the neck region by ballooning of the neck region and exposure of the ballooned neck portions to infra-red radiation emitted by heating units (13 and 14). The thus heated neck region is then collapsed onto itself to seal upon contact.

Description

~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~

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 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 ~Z~ 5 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~

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~

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 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 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 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 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 .

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

Claims (27)

The embodiments of the invention, in which an exclusive privilege or property is claimed, are defined as follows.

1. A process for forming a package, comprising the steps of:
(a) enveloping goods in a plastics film arranged with corresponding film portions which will be brought into contact with one another to heat seal the package;
(b) maintaining said corresponding film portions out of contact with one another before sealing;
(c) heating said out-of-contact corresponding film portions with infra-red radiation; and then (d) bringing said heated film portions into contact with one another to fuse together on contact.

2. A process according to claim 1, wherein said plastics film is in the form of a bag having a neck defining said film portions to be sealed together.

3. In a process for forming a vacuum package, comprising the steps of:
(a) enveloping a product in plastics film;
(b) placing the enveloped product within a vacuum chamber;
(c) evacuating the chamber to reduce the pressure within and around the plastics film; and (d) sealing corresponding portions of the enveloping film to form a vacuum package, the improvement wherein the step of sealing the corresponding film portions comprise irradiating said corresponding film portions within the chamber with infra-red radiation and bringing the thus heated corresponding film portions into contact with one another to fuse on contact.

4. A process according to claim 3, wherein said plastics film is in the form of a bag having a neck held constricted in the chamber so as to retard escape of gas from within the bag whereby the bag is subjected to a ballooning action upon evacuation of the chamber, and said infra-red radiation is emitted by infra-red sources placed close to the neck of the bag to heat the neck ballooned by the retarded escape of gas from within the bag, and the gas is then allowed to escape from the ballooned bag until the neck portions contact with one another to seal upon contact.

5. A process according to claim 4, wherein said escape of gas from the bag is achieved by yieldably holding the bag neck to restrict escape of gas until the pressure differential between the interior and exterior of the bag reaches a value at which the bag neck-holding yields to allow escape through the bag mouth.

6. A process according to claim 4, wherein said ballooning of the bag neck is caused by applying heat to the bag material using additional heating means, and wherein said escape of gas from the bag is effected by rupturing the ballooned bag to allow substantially unhindered escape of gas from the interior of the ballooned bag.

7. A process according to claim 6, wherein said film material is a heat-shrinkable film.

8. A process according to any one of claims 4 to 6, wherein the step of subjecting said bag to a ballooning action includes heat-shrinking the bag material while the bag neck is held constricted.

9. A process according to claim 4, wherein the step of subjecting said bag neck to a ballooning action includes evacuating air from within the chamber causing a differential pressure across the bag film material by virtue of the constricted bag neck.

10. A process according to any one of claims 1 to 3, wherein the film material is a multi-layer film comprising at least an ethylene-vinyl acetate layer, and a layer of polyvinylidene chloride, and a layer of irradiated ethylene vinyl acetate; and wherein the wavelength of the infra-red radiation is from 3 to 4 microns.

11. Apparatus for forming a package, comprising:
(a) support means for supporting goods and an enveloping plastics film;
(b) infra-red radiation source means positioned to irradiate corresponding film portions of such an enveloping plastics film on goods supported by the support means;
(c) means for maintaining said corresponding film portions out of contact with one another during operation of said infra-red radiation source means; and (d) means for subsequently bringing said corresponding film portions into contact with one another to seal the enveloping film and thereby close the package.

12. Apparatus for forming a vacuum package, comprising:
(a) a vacuum chamber;
(b) support means within the chamber for a loaded plastics bag;
(c) means for constricting the neck of the bag within the vacuum chamber;
(d) means for ballooning the neck of a said bag which is supported on the support means and has its neck constricted by said neck-constricting means;

(e) infra-red radiation-emitting means in said chamber energisable for irradiating said ballooned neck of said bag to heat the ballooned neck material; and (f) 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, whereby the heated ballooned neck material contacts itself and seals upon contact.

13. Apparatus according to claim 12, wherein said neck-restricting means comprise bag neck gathering means adapted to constrict the bag neck by gathering to achieve sealing after energisation of said infra-red radiation-emitting means.

14. Apparatus according to claim 13, and including clipping means operable to apply a clip to close the bag neck after said removal of the bag neck from its ballooned configuration.

15. Apparatus according to claim 12, wherein said means for removing the bag neck from its ballooned configuration include means for rupturing the ballooned bag neck.

16. Apparatus according to claim 15, wherein said means for removing the bag neck from its ballooned configuration include first and second co-operating holding jaw means positioned adjacent said bag neck rupturing means between said bag neck rupturing means and said bag support means, for clamping said bag neck to reclose it after escape of gas through the ruptured neck portion thereof.

17. Apparatus according to claim 12, wherein said infra-red radiation-emitting means comprise first and second strip lamps positioned parallel to one another, and including means defining a space between said first and second strip lamps to accommodate the ballooned neck material of the said bag.

18. Apparatus according to claim 17, wherein said neck-constricting means comprise first and second parallel clamping bars arranged adjacent said bag neck-accommodating space between said strip lamps, said first and second parallel clamping bars being operable to clamp the neck of a said bag therebetween.

19. Apparatus according to claim 18, wherein said first clamping bar includes a yieldable clamping bar portion to allow escape of gas from within the bag in the event of excessive pressure differential building up across the film material of the bag.

20. Apparatus according to any one of claims 17 to 19, wherein said means for removing the bag neck from its ballooned configuration include first and second co-operating holding jaw means positioned adjacent said bag neck rupturing means between said bag neck rupturing means and said bag support means, for clamping said bag neck to reclose it after escape of gas through the ruptured neck portion thereof; and including means mounting said holding jaw means for movement towards and away from one another along a path of action, and means mounting said strip lamps for movement between an operative position in which they are disposed along said path of movement between first spaced-apart positions of said holding jaw means and second positions in which said strip lamps are clear of said path of action to allow said holding jaw means to close together.

21. Apparatus according to any one of claims 17 to 19, and including screens associated with said strip lamps for preventing physical contact of said strip lamps with said ballooned bag neck material during heating.

22. Apparatus according to any one of claims 17 to 19, wherein said means for removing the bag neck from its ballooned configuration include first and second co-operating holding jaw means positioned adjacent said bag neck rupturing means between said bag neck rupturing means and said bag support means, for clamping said bag neck to reclose it after escape of gas through the ruptured neck portion thereof;

including means mounting said holding jaw means for movement towards and away from one another along a path of action; means mounting said strip lamps for movement between an operative position in which they are disposed along said path of movement between first spaced-apart positions of said holding jaw means and second positions in which said strip lamps are clear of said path of action to allow said holding jaw means to close together; and screens associated with said strip lamps for preventing physical contact of said strip lamps with said ballooned bag neck material during heating.

23. Apparatus according to any one of claims 17 to 19, wherein said first and second strip lamps each include reflector means to direct all the radiation from each strip lamp towards the said space between the first and second strip lamps.

24. Apparatus according to any one of claims 17 to 19, and including means for energising said first and second strip lamps at a first level in which they emit infra-red radiation with a first intensity sufficient to achieve heating of said ballooned bag neck, and a second level in which they are operating at a much reduced intensity in standby condition.

25. Apparatus according to any one of claims 17 to 19, and including timer means for timing the duration of emission of infra-red radiation from said strip lamps, and means for adjusting said first intensity with which they emit said bag heating infra-red radiation.

26. Apparatus according to any one of claims 12 to 14, including air-circulating fan means within said chamber and heater means for heating the air circulated by said fan means.

27. Apparatus according to any one of claims 12 to 14, and including means for severing surplus bag neck material from the package after operation of the infra-red radiation-emitting means.