GB2094745A - Packaging - Google Patents

Abstract

A package is formed by loading a bag, preferably of heat-shrinkable material, in a vacuum chamber 2,3 and operating hot air fans 9 to circulate air over heats 16 within the closed chamber to apply heat which causes air trapped within the container by bag- mouth restoration means 33,35, to expand and balloon up the container away from contact with the product (21) so that further forced convection heat is more readily able to shrink back the bag into contact with the product. The closed, ballooned bag is then ruptured, the chamber evacuated, and the bag finally sealed before repressurisation and opening of the chamber. The bag mouth restricting means may comprise a resilient leaf 33 biassed against a counter-support to releasable hold the bag-mouth closed whilst allowing venting of any excessive pressure built-up in the bag. <IMAGE>

Description

SPECIFICATION Packaging process and apparatus The present invention relates to a process and apparatus for forming packages.

It is known, in the field of packaging articles in flexible plastics film to evacuate the interior of the package both to improve the shelf life of the packaged product and to give the package a good appearance. It is also known to improve the appearance of the sealed package by using a heatshrinkable (i.e. oriented) film as envelope for the package and subjecting the evacuated, sealed package to a shrinking operation in a hot water bath or a hot airtunnel after sealing in which shrinking operation the plastics film is heat-shrunkto bring it more intimately in contact with the article therein.

British Patent Specification No. 1,561,837 discloses a combined shrinking and evacuation system in which a loaded flexible container is placed in a vacuum chamber which is then evacuated to reduce the residual pressure of air both within and outside the container to a value of the order of 4 Torr, after which the package is sealed. and the chamber further evacuated which causes the container surrounding the product to balloon away from the product and to contact conductive heating plates which achieve heating of the film to a self-welding temperature.

Our own British Patent Application No. 8023465 discloses a cycle in which the extraction of air from within a vacuum chamber proceeds while the neck of a container (formed of a heat-shrinkable or self-welding material) therein is constricted so as to allow only limited removal of air from within the package, thereby causing the container material to balloon away from the product and this ballooning is then held during a container-heating phase when the residual air in the chamber is circulated by means of a fan and heaters within the chamber.Particularly when applied to fresh red meat, these known processes have the disadvantage that the reduction of pressure within the container during the early stages extracts moisture from the surface regions of the product as mist, and consequently when the bag balloons away from the surface of the product the inside of the container assumes a misty appearance which is not lost when the container is collapsed onto the product.

It is an object of the present invention to provide a packaging process and apparatus enabling the risk of entrapped gas in the package to be eliminated and the appearance of the finished package to be improved.

Accordingly, one aspect of the present invention provides a process of packaging a product comprising placing the product in a flexible container with a gas around the product; applying heat to the flexible container while resisting escape of gas therefrom; releasing the gas from within the flexible container and causing the container to collapse into contact with the product; and sealing the flexible container.

The gas around the package will normally be atmospheric air, but any other suitable gas may be used as desired.

A second aspect of the present invention provides apparatus for packaging a product comprising a chamber; means for evacuating the chamber; a support for a loaded bag in the chamber; means for circulating hot air around the interior of the chamber; means for closing the neck of the bag in the chamber and for subsequently opening the bag; means for sealing the flexible container after operation of said closing and opening means; and programming means for ensuring the operation of said hot air circulating means before evacuation of the chamber, and for ensuring that the container-closing means hold the container closed during operation of the air circulating means and operate to open the container before operation of the chamber evacuating means.

The invention also provides a package formed by the method of the present invention, or by using the apparatus of the present invention.

In order that the present invention may more readily be understood the following description is given, merely by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic illustration of apparatus for forming a shrunk, vacuum sealed package comprising an envelope of heat-shrinkable film surrounding a product article; Figure 2A is a detail of the envelope-holding means of Figure 1; Figure 2B is an elevational view of the envelopeholding means of Figure 2A as viewed along arrow B of Figure 2A; Figure 3 is a plan view of the chamber lower part; and Figure 4 is a graph plotting the reduction of residual air pressure in the shrink chamber as a function oftime.

The packaging apparatus 1 illustrated in Figure 1 comprises a vacuum chamber consisting of a lower chamber part 2 and an upper chamber part or cover 3.

In this case, two packages are introduced into the chamber 1 as loaded but unsealed containers, in this case heat-shrinkable bags 4. Raising of the chamber cover 3 allows each bag 4to be placed on a support grid 5 where the package is positioned clear of the side walls of the chamber 1 and the shrinking operation can then be carried out.

The apparatus illustrated in Figure 1 further includes a temperature sensing themocouple 6 which provides an indication of the air temperature inside the chamber, as of course this will be an important factor in the shrinking of the package. The temperature sensor may form part of a control circuit for controlling the temperature of the air in the chamber 1.

The chamber also includes a pressure sensor 7 to determined the residual gas pressure in the chamber as this pressure may if desired be used for controlling the evacuating cycle.

The chamber 1 further includes heating means, in the form of two circular arrays of electrical resistance heaters 16 concentrically around respective fan rotors 9 in the lower part 2 of the chamber to circulate hot air within the interior of the chamber 1 in order to heat-shrink each bag 4 to cause it to contact the product article 21 therein intimately, thereby provided a pleasing appearance and effectively cavity-free contact between the bag 4 and the product. Further heaters may be provided, if desired.

Under the bottom part of the chamber is a vacuum pump 10 which is required in order to be able to reduce the pressure of the gas remaining in the vacuum chamber 1 to the order of 5 Torr or less for the purposes to be described below.

The various electrical resistance heaters 16 around the fans are located so that airflow leaving the fans and about to pass over the package in the chamber is also heated by the heaters 16. The thermocouple 6 (Figure 3) monitors the temperature of the chamber heating means, in order to maintain its temperature at the value required for shrinking of the bag material.

Although not shown in Figure 1, loaded bags can be conveyed in a continuous succession to the vacuum chamber 1 by way of an in-feed conveyor, and can equally be discharged from the vacuum chamber 1 by way of a delivery conveyor.

The chamber of Figure 1 is designed to ensure that, when the fans 9 are in operation, the air flow will be in a re-circulating path which takes the air directly over the various heaters 16, then over the surface of the loaded bags 4 and then back to the fan inlet.

Figures 2A and 2B show the yieldable bag-holding means 30 and bag neck heating units 13 and 14 used in the embodiment of the invention shown in Figure 1.

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 the lower chamber 2 the upper support member 31 descends towards the lower support member 32 to adopt the 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 member 35 while the chamber cover 3 was in the raised position, lowering of the chamber cover 3 to bring the upper and lower support 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 ieftwardly 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 from within the bag at least in the mouth regions between successive plungers 36.

Sealing of the bag neck, in such a way that the minimum of air space results within the bag around the neck, is achieved by means of upper and lower heat sources 37 and 38, respectively, in the form of strip lamps which radiate infra-red heat at a wavelength which gives optimum heat absorption by the plastics composition of the bags 4 within the chamber.

The wavelength of the light emitted by the lamps 37 and 38 is advantageously chosen to coincide with the wavelength most readily absorbed by the material of the bag. Conveniently the wavelength 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) threeply laminate of ethylene-vinylacetate, polyvinylidene chloride and irradiated ethylene-vinylacetate.

A brief exposure of the bag neck region to the radiation from the heat emitters 37 and 38 will be sufficient to heat the bag material to its softening point so that when the paneis of bag material are pressed together they will seal at the mouth and neck regions.

Contact of the bag material with the upper and lower heat sources 37 and 38 is prevented by means of wire screens 39 and 40 carried by respective upper and lower pairs of carrier plates 41 and 42 pivoted on pins 41a, 42a. Each carrier plate 41,42 has a slot 41b, 42b, which slidably co-operates with a respective cam pin 43 or 44 carried at the associated end of a vertically movable upper or lower clamping bar 45 or 46, respectively. The lower clamping bar 46 includes a main 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 member 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 ruptures the bag neck to allow escape of the gas (usually air) within the ballooned neck before sealing. The wire 48 may, for example, have a saw-tooth shape or a sinusoidal undulating shape.

As 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-clockwise direction to swing the heat source 37 and its wire screen 39 rightwardly away from the path of descending travel of the upper clamping bar 45.

Similarly, as the lower clamping bar 46 ascends its cam pins 44 co-operate with the slots 42b of the lower carriers 42 to swing those carriers aside and to move the lower heat source 38 and its wire screen 40 away from the path of travel of the rising clamping bar 46. This allows the film material to be clamped between the two clamping bars 45 and 46. At the same time, a blade 47 carried by the main body portion of the lower clamping bar 46 is exposed above the yieldable jaw 46a due to yeilding of the compression springs 46b and is able to cut the surplus bag material from the neck during sealing.

Figure 2B shows the drive 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 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 of a secondary drive strut 56.

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 53 and 54 above-described.

A primary drive strut 58 is connected between the piston rod 59 of a ram 60 and a further articulation pin 61 on the righthand double bell-crank assembly 52'. Extension and retraction of the piston rod 59 causes anti-clockwise or clockwise motion, respectively, of the bell-crank assemblies 52, 52' and consequently raising and lowering movement of the clamping bars 45.

A similar 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 which the blade 47 can enter when the upper and lower clamping bars 45 and 46 come together.

The holding means 30 of Figure 2A and Figure 2B operate at several stages during the cycle of the entire machine as will be described later.

The operation of the apparatus shown in Figure 1, when using bags 4 formed of a heat-shrinkable i.e.

orientated, film material is as follows: A loaded but unsealed bag 4 of heat-shrinkable packaging film 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.

One form of a heat shrinkable (i.e. oriented) film used for the bag 4 may be a three-ply laminate of ethylene vinyl acetate, polyvinylidene chloride and irradiated ethylene-vinylacetate, as disclosed in United States Patent No.3,741,253 and as sold by W.R.

Grace & Co, under the Trade Mark "Barrier Bag".

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 surface 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.

Shrinking heat is applied to the exterior of the bag before any substantial evacuation of air from the interior of the chamber and the applied heat causes the bag material to begin to shrink. The air enclosed within the effectively sealed bag (held by the resilient blade 33) resists the shrinking action and holds the bag material "ballooned" away from the surface of the product (for example a cut of fresh red meat) therein. While the bag is thus maintained clear of the surface of the product, the circulation of hot air around the outside of the ballooned bag material imparts further heat to the bag material and completes the heat-shrinking operation to draw the film material back down against the surface of the product.However, the bag material will have been ballooned away from the surface of the product for long enough to allow adequate heat transfer to the ballooned film which is not able to give up any appreciable heat to the product 21, and to have raised the film to its shrinking temperature so that a very high proportion of the shrink energy can be recovered.

During this time, the heat sources 37 and 38 will either be de-energised or more preferably energised to a low heating level which will now enable them to heat the film material of the bag neck to a temperature sufficient to achieve fusion.

The constriction of the bag mouth when engaged by the yieldable holding means 30 ensures that, as the application of heat by convection to the exterior of the bag proceeds, any excessive pressure differential built up within the bag can be controlled by venting of gas (usually air) from the interior of the bag 4to an extent which will still maintain the bag material "ballooned" away from the surface of the product 21 therein.Since the ballooning action will depend upon factors common to a particular batch of products 21 (for example the surfae temperature, the amount of air contained within the product, and the surface nature, -e.g. tackiness - of the product) it may be convenient to determine, by observation, when ballooning is likely to occur and then to time the process such that the evacuation begins at the same time for all the products of a batch and is timed by a suitable timer. Any other control means may be employed, as desired.

Because, during the heat-shrinking step, the bag is still yieldably held across its neck, further escape of air from within the bag may occur through the neck in the unlikely event of an excessive pressure differential across the bag material, while the remainder of the bag will shrink back onto the surface of the product article 21 so as to provide a substantiallywrinkle-free surface covering to the product article 21 and nevertheless leave the bag neck capable of sealing when the clamping bars 45 and 46 close together to contact one another.

At the end ofthe ballooning 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 chamber atmosphere (and of the now ruptured bag 4) proceeds until the desired vacuum level has been reached. At, or slightly before, the end of the evacuation phase the lamps 37,38 can be energised to their maximum level to emit radiant heat at the desired wavelength for optimum heat absorption by the film material, and thereby to heat the pierced bag neck to fusion temperature.

The rams 60 are then operated to bring the upper and lower clamping members 45 and 46 together, simultaneously swinging away the sources 37 and 38 and their associated wire screens 39 and 40.

Once the upper clamping bar 45 has come into contact with the biased clamping jaw 46a, further 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 firm holding of the neck alongside the blade 47 to effect sealing. Throughout this operation, the mouth portion of the bag 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 retraction of the upper and lower clamping bars 45 and 46 will bring the heat sources 37 and 38 and their wire screens 39 and 40, respectively, back into the Figure 2R configuration. The evacuation of the chamber takes place after this retraction of the clamping bars 45,46 so that unhindered escape of any residual air from the bag can take place.

When the vacuum chamber is re-pressurised, upon opening, the heated neck portions of the bag to the left of the clamping members 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 3 tidy appearance to the finished pack.

The surplus bag material severed by the blade 47 is still held between the resilient blade 33 and the counter member 35 and can be removed during or after removal of the package from the opened chamber.

The above-described process is particularly convenient for use with wet products such as fresh red meat in heat-shrinkable bags because the pressure increase on the surface of the meat, during the bag-ballooning action, tends to hold the moisture in the product and avoids misting of the inner surface ofthe bag when 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 wrinklefree nature of the product is enhanced through the adoption of a preliminary shrinking step followed by subsequent evacuation (as opposed to the conventional sequence of vacuum-sealing first and shrinking afterwards).

The finished package in accordance with the present invention is moreover much improved over prior art shrink-tidied packages in which a water shrink bath is used in order to alleviate the "heatsink" effects of the relatively cool and high thermal capacity product, because shrinking of the film in contact with air allows a greater recovery rate of the shrink energy, and consequently a greater increase in thickness, with the result that the barrier properties of the bag (important in order to maintain hermetic sealing of the product and freshness up to the time of consumption) are more effective. Furthermore, the abuse-resistance of such a bag is better because of the increased thickness.

Because the air pocket trapped inside the bag during the pre-heating shrink phase resists the collapsing of the bag and postpones contact of the bag with the cold product, this thickness-increasing effect is even more noticeable and so also is the wrinkle-.ree appearance of the bag which again depends on the extent of recovery of latent shrink energy in the film material. Moreover, because the shrink is provoked by air currents moving around the whole of the product, the shrinkage of the bag will be uniform around the product and this will eliminate risk of entrapment of air pockets behind the "equator" of the product (i.e. the area of largest cross-section in a plane perpendicular to the longitudinal axis of the bag).

Furthermore, the above-mentioned characteristic of having little or no water vapour in the air between the product and the shrinking bag (caused by the onset of shrink before any pressure reduction and even causing a slight pressure increase as evident from Figure 4) 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.

Because the lower and upper support members 31 and 32 of the yieldable 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 when the chamber is closed and all that the operator needs to do is to ensure that the neck of the bag 4 is placed on the counter member 35 before the chamber closes.

If desired, where the loaded bags are introduced by a conveyor into the chamber 1 the conveyor may be one which ensures that, when the bag 4 is stopped, the bag neck is correctly positioned for constricted clamping withoutthe need for careful positioning by an operator.

Some other bag-holding and -closing mechanism may be provided if desired. For example, the bag neck may be tightly gathered in the chamber when the chamber is closed, to an extent consistent with the desire for ballooning of the bag away from the product during the very early stages of evacuation of the chamber, and a clip may then be attached to the neck of the bag after the evacuation and shrinking operations have been completed. Such in-chamber clipping means is for example disclosed in our British Patent Specification No. 1,353,157.

The product is supported on rollers which define the air-pervious grid 5 to support the article but nevertheless allow the hot shrinking air circulation to pass right around the surface of the article.

In any conventional post-sealing shrinking process, the degree of recovery of the available shrink in the film (i.e. the extent to which the film is able to return to its original configuration before the orienting stretching) is limited by the drop in temperature of the film as it contacts the product. By ensuring that, in the present invention, the heating step takes place while the heat-shrinkable film is in a ballooned condition and while the air pressure within the chamber is substantially at atmospheric pressure during the heat-shrinking air circulation, it is possibleto recover much more ofthe available shrink in the film during only a very short duration heating phase.

In the preferred embodiment, we have referred to the process as evacuating air from within the chamber and air from within the package. It will of course be appreciated that some other gas may, if desired, be used. In any case some products may give off gas such as carbon dioxide to be extracted during the evacuation step, or the product may be flushed with an inert gas, even if air is the principal component gas within the chamber and/or bag.

Throughout the description of the preferred embodiment of process, the use of the air-circulating fans 9 to enhance convective heat transfer has been described. However, it is of course possible for the heat to be applied to the packaging film by convention without the use of fan-assisted circulation, or by some other mechanism, for example by heat radiation with or without some form of air circulation such as circulation-boosting by the fans 9. The process in accordance with the present invention relates to the hitherto unheard of step of applying shrinking heat before any substantial evacuation of the chamber, and the precise mechanism by which heat is imparted to the packaging film may therefore be varied without departing from the scope of the invention as claimed.

If desired, the chamber may have the heating units 13 and 14 and yieldably holding means 30 at only one end, or along one or both sides, or at both ends and along one side in order to allow the operator to vary the positioning of the bag or bags 4 to be sealed. Arranging the heaters 13, 14 and yieldably holding means along a side of the chamber ensures that several short bags can be place side-by-side along the chamber.

The ballooning action during the heating step ensures that the plastics material of the envelope quickly clears the relatively cool product article 21 therein, and is therefore much more readily able to undergo the shrinking because the heat transferred to the bag material from the hot air flow will not be transferred immediately to the article 21 by conduction.

The application of shrinking heat lasts for a brief period, for example from 2 to 8 seconds, preferably from 3 to 4 seconds, and evacuation proper is then begun once the ballooned area has returned into contact with the surface of the article 21 by the shrinking action of the film and/or the equalisation of pressures within and around the bag.

Evacuation of the chamber then proceeds by operation of the vacuum pump 10 until the residual pressure in the vacuum chamber 1 has dropped to a finishing value of, for example, 5% residual air mass.

In the embodiment of the process where the gas in the chamber undergoes fan-assisted circulation, during this continued evacuation of the chamber the fans 9 may if desired be in constant operation so that, as the density of the air remaining in the chamber 1 gradually reduces, that air is still able to carry out some further shrinking of the bag material onto the external contour of the article 21.

Upon termination of the vacuum phase, the bag neck is sealed, in this case by operation of the welding heaters 37, 38 or else by operation of any other suitable welding device such as conventional welding bars.

The valve 14 is then opened to allow the chamber 1 to be repressurised. The chamber cover 1 is then raised in order to allow the resulting shrunk and sealed package to be removed from the vacuum chamber 1.

The heaters 16 within the chamber serve to keep the temperature of the air around the package at a value sufficient for the necessary exchange of heat to the ballooned bag material to achieve shrinking.

However, where fan-assisted circulation of air in the chamber is used, the heaters 17 need not be in continuous operation provided that, by the time the bag 4 has ballooned away from the product article 21, the temperature of the air in the chamber 1 is at a temperature adequate for shrinking the package.

Temperatures of 90"C to 140"C at ballooning may be required to achieve shrinking in the case of a biaxially oriented shrinkable film. The precise value of the temperature will depend upon factors such as the nature of the film orthe degree of orientation.

A fully automatic version of the apparatus can be envisaged, in which all the various process parameters are controlled and the apparatus is timed to operate automatically from introduction of a loaded bag into the chamber to delivery of the sealed package automatically from the chamber.

The precise duration of the heating phase is variable within certain limits.

For example, Figure 4 shows a graph plotting the pressure within the chamber against time. At time to the chamber closes, and time t1 indicates the time at which, after shrinking of the bag, evacuation of the chamber begins. At time t2 the shaped wire 48 is energised to rupture the bag neck before full vacuum is reached by time t. At time 4 the lamps 37,38 are energised and the clamping bars 45,46 are then brought together to seal the neck and trim the excess material. At time tS the chamber is repressurised.

The broken line 101 in Figure4showsthe pressure within the bag and from this it will be seen that the pressure rises above the atmospheric starting pressure value of said line 100 denoting the chamber pressure. It is this increase in pressure, caused by the application of shrinking heat to the outside of the chamber, which causes the bag to balloon.

For any given product batch, the constricting effect of the yieldable holding means 30 on the bag neck should be such as to cause the bag to undergo ballooning to an extent to ensure that heat transferred to the ballooned bag material by contactwith the hot air flow is not immediately iost by conduction to the relatively cool product within the bag.

Since the application of heat relies upon circulation of hot air over the ballooned packaging film, the fact that the exterior of the bag is substantially at atmospheric pressure ensures that the thermal capacity of the air in the chamber 1 during the shrinking operation at that intermediate pressure is as high as possible for effective heat transfer.

As indicated above, the temperature of the product, the nature of the packaging film (e.g. the bag 4) and the volume of gas contained in the product, will also affect the ballooning action.

In general, the apparatus will be adjustable to allow for different values of the duration of the shrink-heating time to ensure that the bag will always have ballooned and collapsed back adequately by the time the main evacuation step begins.

If desired, for example when packaging particularly soft articles such as cream cheeses, a "soft vacuum" pack may result in that the evacuation step is curtailed very soon after resumption of pressure drop below the "intermediate pressure" value.

It may if desired be arranged for hot air to be introduced into the chamber 1 (by means not shown) while the cover 3 is descending and up to and including the instant at which the cover 3 closes onto the lower chamber portion 2 to seal at the rim 20.

This will provide the best possible supply of hot air within the chamber 1 at the start of the heatshrinking operation.

If desired, the package may include several product articles enclosed within one wrapper (for example in one bag 4).

It may be desirable to modify the process for use with so-called self-welding films, referred to in our said British Patent Application No.8023465.

Claims (1)

1. A process of packaging a product comprising placing the product in a flexible container with a gas around the product; applying heat to the flexible container while resisting escape of gas therefrom; releasing the gas from within the flexible container and causing the container to collapse into contact with the product; and sealing the flexible container.

2. A process according to claim 1, wherein after escape of the gas from within the flexible container, the interior and exterior of the flexible container are evacuated after which the container is sealed to enclose the product under vacuum conditions.

3. A process according to claim 1 or claim 2, wherein said flexible container is clamped along its mouth to prevent escape of gas during the heating step.

4. A process according to claim 1 or 2, wherein the mouth of the flexible container is clamped to restrict escape of gas during heating, to an extent which will provoke ballooning of the container away from the surface of the product during the heating step.

5. A process according to claim 3 or 4, wherein the gas is released from within the bag by cutting the bag alongside its clamped mouth, to allow unobstructed escape of gas, and the cut container is subsequently sealed to the side of the cut region which is nearer the product to re-seal the bag.

6. A process according to any one of the preceding claims, wherein the step of applying heat is carried out within a vacuum chamber before any vacuum is drawn in the chamber.

7. A process according to any one of the preceding claims, wherein the step of applying heat is carried out by forced convection of hot air over the external surface of the flexible container.

8. A process according to any one of the preceding claims, wherein the flexible container is sealed by the application of softening heat to the neck region followed by closing of the softened neck region to cause fusion welding.

9. A process according to any one of the preceding claims, wherein the flexible container is formed of a heat-shrinkable plastics film and the step of applying heat to the container induces shrinking of the film placing the container under tension around the entrapped gas, so that this tension is released only when the gas is itseif released.

10. A process of packaging a product, substantially as hereinbefore described with reference to the accompanying drawings.

11. Apparatus for packaging a product comprising a chamber; means for evacuating the chamber; a supportfora loaded bag in the chamber; means for circulating hot air around the interior of the chamber; means for closing the neck of the bag in the chamber and for subsequently opening the bag; means for sealing the flexible container after operation of said closing and opening means; and programming means for ensuring the operation of said hot air circulating means before evacuation of the chamber, and for ensuring that the container-closing means hold the container closed during operation of the air circulating means and operate to open the container before operation of the chamber evacuating means.

12. Apparatus according to claim 11, wherein said container-closing and -opening means comprise means for holding the mouth of a container closed during the operation of said hot aircirculating means, and means for rupturing a said flexible container to that side of the closing means which is nearer the said bag support in the chamber.

13. Apparatus according to claim 12, wherein said sealing means comprise means for sealing the neck of a container on the side of said rupturing means nearer the bag-support in the chamber.

14. Apparatus according to claim 13, wherein said sealing means comprise radiant heat sources for applying radiant heat to the neck region of a said flexible container.

15. Apparatus according to any one of claims 11 to 14, wherein said holding means comprise a yieldable holding member and a counter member against which the yieldable holding member presses the neck of a said flexible container, and wherein the rupturing means include electrical heating means positioned between the holding means and the sealing means and energisable for heat rupturing the neck of a bag held by said holding means.

16. Apparatus according to claim 15, wherein said heat sources are strip infra-red lamps disposed opposite one another to either side of an intended position of the neck material of a said flexible container; the rupturing means include clamping members which are parallel spaced clamping bars having a rest position in which the strip lamps are disposed between the two bars and an operative position in which the bars close together to occupy the positions held by the strip lamps in the rest position of the clamping bars; and wherein severing means are carried by one of said clamping bars for severing surplus neck material of a said flexible container.

17. Apparatus according to claim 16, wherein said severing means comprise a knife blade carried by said one clamping bar and said one clamping bar includes a yieldable supported clamping portion allowing further displacement of said knife blade after contact of said yieldable clamping portion with the other clamping bar.

18. Apparatus according to claim 16 or 17, wherein said strip lamps are carried by movable supports; and means are provided, operated by said clamping bars, for moving the strip lamps aside during closing together of the clamping bars.

19. Apparatus according to any one of claims 11 to 18, wherein said hot air-circulating means comprise a pair of centrifugal fans having heating elements disposed at the air outlet thereof.

20. Apparatus according to claim 19, wherein said heating elements are in circular arrays concentric with the respective fans.

21. Apparatus according to any one of claims 11 to 20, and including a timer for delaying operation of the evacuating means for a predetermined time interval after closing of the chamber and initiation of the hot air-circulating means.

22. Apparatus for packaging a product, substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

23. A package formed using the process of any one of claims 1 to 10, or the apparatus of any one of claims 11 to 22.

New claims or amendments to claims filed on 8 March 1982 Superseded claims 1 New or amended claims:

1. A process of packaging a product comprising placing the product in a flexible container with a gas around the product; substantialiy before reducing pressure around the exterior of the flexible container applying heat to the flexible container while resisting escape of gas therefrom; releasing the gas from within the flexible container and causing the containerto collapse into contact with the product; and sealing the flexible container.