US3516218A - Packaging method - Google Patents

Description

June 23, i970 P. EISLER PACKAGING IIETHOD 3 Sheds-Sheet l Filed June 16. 1966 y i li Il Il ll .i Il

P. EISLER PACKAGING METHOD June 23, 1970 Filed June 16. 1966 3 Sheets-Sheet L l f( w f u Rm. WML Wm. \m. mv m ht, che n o A :0.1 .m.\ W\n q IML )\\\.U ml fr mmm H ub .m/.h .Vv Wm. \m. W\ O mv, I Wm? s" ST Bt O .Q Q u ,m vm# ov mv wlw, ub H Bw n, mm ,a5 3.: mn vm Bmm. QWN m mt u?? P. EISLER PACKAGING METHOD June 23, 1970 im s e n wWm e h 4 vf H Y Nm. E mE A* m o 3 D @mmf a n d o @ZM m r r 1 nu 3 Q Q G., G mv mv :w MLN .H E. u H vm. 6.9.x nln nnvnlnn urinarannnrndnnnnnnnrrnnnnr. o j mv BM Filed Junef 16, 1966 United -States, Patent O 3,516,218 PACKAGING METHOD Paul Eisler, 57 Exeter Road, London NW. 2, England Filed June 16, 1966, Ser. No. 557,988 Int. Cl. A231 3/04; B65b 55/14; H05b 3/18 U.S. Cl. 53-25 8 Claims ABSTRACT F THE DISCLOSURE Goods to be heat-processed and hermetically packed are filled into a container; the container unsealed is processed in a harmless atmosphere, while the pressure is raised to avoid pressure dependent damage, the goods are cooled under pressure reduction to avoid damage and the container her-metically sealed. The pressure medium may be a volatile ingredient, air or steam and may be recirculated. Heating may be by electric heating iilm. The apparatus includes at least three chambers, a conveyor, air gates, pipes and valves, an air compressor and electrical connections for heaters while the containers are on the conveyor.

The present invention relates to the hermetic packaging of goods needing to be heat processed at the time of packaging. Examples are foodstuffs which need to be sterilized and cooked, pharmaceutical products, chemicals which may need to react at the time of packaging, and even surgical and scientific instruments needing to be sterilized at the time of packaging.

In all such cases, if the package is hermetically sealed before heat treatment, the problems almost invariably arise of the pressure differences developing during the heating. To take the typical example of foodstuffs which generally contain water, to sterilise as well as cook them it is necessary to raise the temperature to say 240 F. (116 C.) which is well above the vapour pressure of water at atmospheric pressure. A common method is t'o effect the heat treatment with steam at the pressure corresponding to the required temperature. For the above temperature and saturated steam this is about lbs. per sq. inch (1.7 atmospheres) in value, and needs the operation to be done in an autoclave; moreover to ensure the goods being brought to the required temperature in a reasonable time requires steam at a high temperature and therefore a higher pressure to be used. At the start when the package is cold, pressure within it will be approximately atmospheric while the steam pressure is much higher, this pressure difference remains the same until the temperature within the package reaches boiling point at atmospheric pressure, whereafter as the ternperature rises within the package so does the pressure until finally the internal and external pressure balance or nearly balance. If the package is now taken out of the autoclave to cool under ambient conditions, the internal pressure will be much higher. There are thus two phases when there is a very substantial pressure difference between the inside and outside of the package and it must be strong enough to withstand this.

Similar conditions will usually arise with the other types of package referred to. Thus in the case of pharmaceutical products or chemicals there may be a solvent present other than water and the temperature needed may differ from that required with foodstuffs, but the phenomena are similar and only the parameters differ. With chemical reactions there may be gas or vapour pressures developed which at least at one stage involve a substantial difference ice in pressure between the inside and outside of the package. Even in the case of surgical or scientific instruments there will usually be air in the package which at the start is at atmospheric pressure and which needs to be brought to a high temperature so that at least at one stage (or more than one stage if steam heating is employed) there will be a substantial difference in pressure between the inside and outside of the package.

The present invention avoids substantial pressure difference between the inside and outside of the container by effecting heating with the container unsealed. Merely to leave the container open is in general not a satisfactory solution. For one thing while the contents of the container are at a lower temperature than the temperature of satu rated steam at the pressure of the steam, condensation into the container will occur which may contaminate, dilute or otherwise damage the contents, and similar objections may arise to the use of other vapours than steam. If highly heated air or inert gas were used instead of steam, it would not be necessary to have it under pressure to heat it to the required temperature and there would be no contamination, dilution or similar damage, but now as the contents of the container reached a certain temperature evaporation of volatile ingredients, leading to drying, decomposition or other damage and possibly other forms of pressure dependent damage might occur.

The present invention, which as above stated effects heating of the container and its contents with the container unsealed, also avoids pressure dependent damage by appropriate choice of the pressure conditions under which the heat treatment is elfected.

The method according to the invention includes filling the goods into a container capable of being hermetically sealed, enclosing the lilled but unsealed container in an atmosphere of a medium which will be harmless to the goods at the temperature of processing, heating the goods to the temperature and for the time required by the heat processing, increasing the pressure of the medium in the enclosure which throughout the rise in temperature is at a rate sufiicient to prevent pressure-dependent damaging phenomena occurring in the goods, thereafter cooling the goods and reducing the pressure of the medium in the enclosure to at least approximately ambient atmospheric pressure at a rate which still prevents damaging phenomena arising in the goods during cooling, hermetically sealing the container, and removing it from the enclosure. If the goods contain a volatile ingredient, the pressure in the enclosure will be maintained above the vapour pressure thereof throughout the whole of the heating and cooling. In some cases it may still be possible to use steam as the medium, for example where contamination or dilution will not occur due to the nature of the goods. However, the function of the medium usually makes it necessary to use a gaseous medium and if possible air will be used on economic grounds. Such a medium is not so good a heating agent as steam. Nevertheless some of the heat may be supplied by the medium itself, but preferably heating is effected at least to a major extent by an electric heater in contact with the package, especially an electric heating iilm forming part of the container such as a iilm of the kind disclosed in the specification of my Pats. Nos. 3,020,378, 3,026,234 and 3,149,406, and my application Ser. No. 165,736 filed Jan. 12, 1962 now Pat. No. 3,283,284 issued Nov. 1, 1966 or a package as disclosed in the specifications of my Pat. No. 3,100,711.

An electric heater such as a film may be immersed in the goods, or line the internal wall of the package or be incorporated within the wall of the package. In all such cases the film can remain part of the package and can be re-used to reheat the contents of the package at some subsequent period. But even if the iilm is not to be reused in this way it can be made cheap enough to be dispensed with after it has been used in the packaging operations. When an immersed film is used, it can if desired be withdrawn between the heating and sealing operatons.

Where access of steam or other vapor to the goods during heating is permissible i.e. where contamination or dilution due to condensation or undesirable reactions are not to be feared, steam or other vapour may be used alone or mixed with air. As the medium and this may facilitate the transfer of heat to the goods, a smaller proportion though still preferably a major proportion being supplied electrically.

Since the package does not have to resist pressure it can be made of less strength and more cheaply than a conventional can. The choice of materials is Wider. It must resist the temperature involved, not be damaged by or damage the contents, be capable of hermetic sealing, and withstand such handling and storage as may be necessary. Laminated paper and plastics materials are suitable in many cases, including transparent plastics materials which render the contents visible. The packages may be in the form of bags in many cases. When the package incorporates a heating iilm it becomes a selfheating package for use anywhere where a supply of current at a suitable voltage is available.

The invention provides particular constructions of packages and material for making packages for use in the methods of the invention.

The invention will be further described with reference mainly to foodstuffs. Such changes as are necessary to apply it to other goods will in some cases at least, be obvious but where necessary further details, will be given for other goods.

In the description which follows reference will be made to the accompanying diagrammatic drawings illustrating the invention by way of example.

-In the drawings:

FIG. 1 is a diagram illustrating a simple form of apparatus for carrying out the method of the invention;

FIGS. 2 to 5 are diagrams illustrating a more elaborate form of apparatus suitable for continuous operation;

FIGS. 6 to 8 illustrate details of several forms of package in accordance with the invention.

The example illustrated by FIG. 1 is that of a container 11 incorporating a heating film, having terminal tabs 12, 13 such as described in my patents and application above referred to or a container with a heating iilm v as described further below, and this container when lled with the goods e.g. foodstuff is connected to a low voltage electricity supply 14 while it is subjected to a high air pressure. The package is not closed, or is at least not hermetically closed while it is under that pressure which thus does not stress the container wall, since it reaches the inside or the contents of the container as well as acting on the outside of the container.

The air pressure is kept at least as high, and preferably a little higher than the value of the vapour pressure, for the maximum temperature the food (or chemical) has to reach in the packaging procedure. Subsequently the package is closed and can be hermetically sealed, and the pressure is released, but only after the contents have cooled down to below their boiling point at atmospheric pressure (for food or other water containing material below 100 C.).

The temperature of the compressed air is of minor importance for the whole process, but it is, of course, desirable that `the air be as clean and sterile as possible. This applies particularly for the air in the space where the packages are held during the whole cooking period from the last stage of the heating cycle, which last stage includes the iinal point of maximum temperature to which the package is heated, until the point when the packages are cooled down to below boiling point at atmospheric pressure.

In order to carry out this heating of the open containers under high air pressures and the subsequent safe closing of the packages the containers are carried e.g. by a conveyor from a lling station 15 through a high pressure chamber 16 in which a cycle of at least three stages takes place, namely:

-(a) Pressuring while the open packages are not heated at all or are heated only in controlled relation to the rise of pressure-The heating ilms of the packages are already connected to a busbar arrangement 17, but the electricity supply is still switched olf at a control box 18 or only allowed in relation to and under control of the air pressure and temperature reached. Thus a pressure sensing element is indicated at 19 and a temperature sensing element 21 in contact with one of the packages, these elements being connected to the box 18. The stage (a) can be quite short and comprise only the time required for the transfer of the packages into the pressure chamber, for the closing of the door 22 of the chamber 16 and for the raising of the air pressure in the chamber to the maximum level desired by a pump 23 equipped with a iilter or the like 24 on its inlet to clean and sterilise the air, and driven by a motor 25. Any heating of the packages, if started at all, during this stage (a) does not prolong this stage of rising pressure.

(b) Heating under maximum air pressure--During this stage the air pressure is at least as high as the vapour pressure corresponding to the maximum temperature to be reached by the contents of the package, or as prescribed by the sterilising, preserving or other heat treating process carried out. The electric current to the heating iilms of all the packages is switched on and heat is disseminated into the food or other content. When the desired maximum temperature is reached the current is switched otf or decreased and the temperature is kept as constant as possible by thermostatic control for as long as prescribed by the process, e.g. under the control of the element 21 and a time switch incorporated in the box 18.

(c) Cooling under air premura- During this stage the electric current to the heating films is switched oi iinally. Where available, artificial cooling can be used to speed up the cycle, for instance by passing cold water through a hollow shelf 26 on which the packages rest, or by passing the packages over cold panels within the chamber. The air pressure is maintained and can only be gradually released (for example by a valve Z7), as the temperature of the content of the packages drops, but never below the value at any instant of the vapour pressure at the particular temperature of the contents of the container. It is preferred to keep the air pressure at the maximum vapour pressure level for the iirst part of the cooling period, then to drop it in stages until the packages are cooled to below the boiling point at atmospheric pressure, when they can be sealed after opening the door 22. The valve 27 may have its own control mechanism 28 controlled from the element 21 and a time switch or the like.

The pressure chamber 16 in this example is stationary and the above described stages (a), (b) and (c) of the heating and pressure cycle are performed at least partly under outside control, while the packages are stationary in the chamber. This is akin to present day pressure cooking provisions, autoclaving or most vapour treatment arrangements.

In principle the above method could be practised with an atmosphere of a gas other than air or even with a vapour, but for the sake of economy closed circuit circulation would be desirable, which cannot easily be effected with the equipment shown in FIG. 1 because of the need to open the door 22 at intervals. Equipment described later provides for closed circuit circulation of the atmosphere within it.

The fact that the present invention uses direct heating of the packages and compressed air which does not get too lhot in the process, permits such air pressure vessels and batteries of such vessels side by side readily to be used in the field and makes canning and sterilising a much less cumbersome, cheaper, better controllable process. The equipment can for example be mounted on a truck to render it mobile and thus enable it to be used in the packaging of sensitive products such as various fruits and vegetables, when they are not merely fresh, but almost immediately after they have been harvested.

The invention also 4makes it much less difficult to use flow line processing than it would be with steam, quite apart from the incompatibility of steam with many types of packages and contents if not first sealed.

In a flow line the packages travel continuously or step by step through the above three stages in a tunnel in which these stages take place in compartments traversed by the packages in succession. Step by step working is simpler, and the mechanical provisions for travel as well as the inlet and outlet closures or doors of the several parts of the tunnel in which the air pressure is different, can be quite robust. In the following description of the examples shown in FIGS. 2 to 5 these closures or doors will be referred to as gates The flow line type of pressure chamber consists of at least three, but preferably of at least four compartments adjacent to each other in the direction of flow with gates which, when closed, hermetically seal each compartment from the others, and from the outside. The compartments are interconnected by pipes and valves and with a cornpressor so that the air pressure in any combination of compartments can be controlled, equalized and air be shifted from one compartment to the other for equalising pressure without using the compressor. The four compartments are designated I, II, III and IV in FIG. 2.

The containers 11a after having passed the filling station 15a and a station 31 at which the terminals 12a, 13a of their heating lms are connected to a busbar arrangement 17a not yet alive, are pushed intocompartment I of the pressure chamber by a conveyor, a moving platform or equivalent handling device 32. The gate 33 between compartments I and II is closed. This condition is shown in FIG. 2.

When the compartment is full the entrance gate 34 is also closed, and compressed air is let into compartment I first by equalising this compartment with compartment IV through values 35, 36 and then with cornpartment III through valves 37, 36 and finally with compartment II through ' valves 38, 36 after which the gate 33 between compartments I and II is raised, all packages are transferred into compartment II and the gate between compartments I and II is closed again, thus reaching the condition indicated in FIG. 3.

The air in the empty compartment I which is at about maximum pressure owing to the equalisation with the maximum pressure compartment II is noiw shifted to compartment III by means of valves 36, 37 and then to compartment IV through the valves 36, 35, before what s left is let out of the compartment I to atmosphere by opening the entrance gate 34 for the reception of the next batch of packages whereupon the above described cycle is repeated.

The air pressure in compartment I is preferably always maintained a little above atmosphere pressure, even when the entrance gate 34 is open, while a batch of packages is pushed into the compartment. The airflow when the entrance gate is open is out of the tunnel, not in it, a ow of clean or sterilised air which has been through cleaning or sterilising equipment 24a arranged in front of the cornpressor 23a. For this purpose there may be a direct connection from the compressor 23a to the compartment I through a pressure reducing valve 39.

Meanwhile the batch of packages stay in the high pressure compartment II together with batches of packages from previous cycles, the heating period of which has not yet been completed. The air pressure is maintained in compartment II by the compressor 23a and is not allowed to fall, even during the equalisation with other compartments below the value of the vapour pressure at the maximum temperature of the material in the packages. The busbar arrangement 17a to which all terminals of the heating films of a batch of packages are connected, is switched on, and the heating proceeds while the batch of packages is moved, step by step to the gate 41 between compartments II and III, as new batches of packages come into compartment II and others leave it and pass into compartment III.

The electric current supply to and the thermostatic control thereof are nally switched off from a batch, after it has been heated for the prescribed time at the prescribed temperature, while it is still only halfway or part -way through compartment II, or more accurately stated, while it has still some time to` pass in compartment II cooling down from the maximum temperature it has reached, to a temperature `which is less than the boiling point under the air pressure to be encountered in the next compartment III. Where, as in the present example, there are four compartments and the pressure in compartment III is above atmosphere, the cooling time in compartment II can be short. Prior to the shifting of the cooled batch of packages the air pressures in compartments II and III are equalised through valves 37 and 38, the gate 41 between compartments II and III is lifted and closed immediately after the batch of packages has been transferred, so reaching the position shown in FIG. 4.

The air pressure in compartment III is dropped at once by equalizing with compartment I through valves 37, 36 and after the packages have cooled down to below atmospheric boiling point, it is dropped again by equalizing with compartment IV through valves 37, 35 to near atmospheric pressure. 'The gate 42 between compartments III and IV is then opened, the batch of packages is shifted into compartment IV, the gate 42 is closed-and provided the timing of the cycle in compartment I is run accordingly-the second air pressure equalizing between compartments I and III through valves 37, 36 is effected while both these compartments are just empty, FIG. 5.

Compartments I and II are preferably of a size containing just one batch of packages, while compartment II is large enough to hold as many batches as are required to permit the prescribed heating period and to permit their cooling down under maximum air pressure to atmospheric boiling point temperature or to the safe temperature for compartment III. The platforms and walls in compartment III can be kept constantly cooled, and during equalisingair coming into III from I through the pipeline can also be cooled while owing through the pipe. Jackets through which a coolant can flow are indicated at 43, 44 respectively.

Compartment IV is preferably a wide motion of the tunnel in which the operations of disconnecting the terminals from the busbar arrangement and the closing (sealing) of the packages takes place. The air pressure in this compartment is preferably kept a little above atmospheric pressure suitably by a connection from the compressor through a pressure reducing valve 45 in order to keep outside air out and enable the closure of the packages to be effected in the clean air, all of which including the air flowing into compartment IV from cornpartments I and III when equalising the air pressure compartments I and IV or compartments III and IV has gone through cleaning and sterilising station 24a before passing the compressor 23a. The exit gate 46 is therefore opened only for as short a time as possible for removal of the sealed packages.

For both entrance and exit gates 34, 46, revolving doors or similar devices which decrease the loss of air from the tunnel are preferred arrangements.

The above description of FIGS. 2 to 5 assumes that the heat carried by the air released when the gate 34 or 46 is opened is lost with the air as well as all the air used having to be cleaned and sterilised. Some heat can be recovered by arranging for the air drawn by the compressor to recover heat at super ambient temperature from the containers being cooled by counter-current heat exchange. However, by providing for recirculation of the air, heat can be conserved and the burden of cleaning be reduced. Thus there may be a further enclosure into which the gates 34 and 36 open, from which enclosure the compressor 23 draws, while the heat carried by the air is retained in the circuit. The air drawn by the compressor as Well as any make-up air needed to replace leakage can again iiow counter current with the heat processed packages in the stage where they are being cooled down, for instance through the jacket 43, and thence to the 'equipment 24a. Such total enclosure facilitates the application of the invention to cases in which the medium is not air but some other gas, for instance an inert gas or a vapour, for instance steam. Steam may be desirable in certain types of food processing, for example in the packaging of previously dried foodstuff such as potatoes which are to be at least partly reconstituted and cooked at the time of packaging. In such cases the vapour can be confined to compartments II and III while air is used in compartments I and IV, corresponding modification in the piping and controls being provided since equalisation between compartments containing vapour and compartments containing air would not be suitable. The pressure conditions would be maintained to satisfy the general requirements of the operations to avoid pressure-dependent damage to the goods.

The apparatus shown in FIGS. 2 to 5 can be somewhat simplified for operation with a common medium, especially air, at the cost of less convenience and possibly less economy by reducing it to three compartments by combining compartments II and III into a single compartment of the same length as the two combined. It is believed the mode of' operation will be sufiiciently clear from the previous description without any further description, since this modification comes between that of FIG. 1 and that of FIGS. 2 to 5.

The present invention has manifold advantages. In any of the forms above described, the enclosure and the supply of clean compressed air is so simple and cheap that, together with the use of the low voltage heating film as the heating medium, or together with equivalent equally practical heating means, it opens the possibility of packaging in the field. All that is needed is a wheeled carrier for what amounts to a simple mobile packaging factory comprising a low Voltage electric generator, a water pump, a compressor with air cleaner and at least one air pressure vessel, piping, a store of empty packages with heating films and closures and implements for cleaning, cutting and otherwise preparing the goods, before it is filled into the packages, including benches, tools and such additives as may be needed for instance for food. Such a carrier can be towed to a place near a field where the vegetables, fruit or other goods are gathered in and where a supply of Water can be pumped up for cleaning the raw food which can then be prepared and directly filled into packages within hours of having been harvested.

This decentralising of the packaging process should not only be economically advantageous to the grower, but give a better product by cutting down the time between gathering and packaging and eliminate much transport and storage. The use of air pressure instead of steam pressure also contributes to giving a better product and permits optimal sterilizing treatments to be reliably programmed and controlled.

It will be clear that some of these advantages are also obtained in fixed factory-type packaging plants using the present invention instead of steam autoclaving, and that the invention can be carried out with other heating means than films for effecting direct heating of the packages and their contents while under the required pressure medium. Such heating means can be high frequency heating arrangements in the pressure vessel,or standard type electric immersion heaters which dip into every package while it is in the pressure chamber (compartment II in FIGS. 2 to 5). Food or chemicals in metallic containers can be heated by hot plates on which they are placed in the pressure vessel, by radiant heaters or by eddy current producing arrangements in the compartment II. None of these means of heating, however, is as advantageous for the processing according to the present invention as the heating film which is a part of the package itself and remains part of the package after it has left the pressure chamber and is hermetically sealed. In addition to all the processing advantages it makes for a package which can be heated again later on by the consumer or user.

A particularly suitable type of such self-heating package comprises a container with a cylindrical or similar laminated wall of which at least one of the laminae is a heating film. The wall is usually a tube of circular crosssection (drum), but it can have any desired cross-section-square, rectangular, hexagonal, ete-preferably with rounded corners.

Such a wall can be produced by convolute or spiral winding of thin layers of strip materials, the strips being coated with an adhesive during the winding operation, if they do not already have a self-adhesive -character or do not adhere to the other laminae by heat or other means. The winding process and the winding machinery are very similar, or the same, as used for manufacturing convolute or spiral-wound cardboard tubes. Indeed, the walls of one of the types of the self-heating tubular containers are small lengths of such cardboard tubes with special inner linings. These inner linings are (a) strips which form an impermeable inner skin so that the contents of the container cannot leak through, or so that a hermetic sealing of the package becomes possible, and (b) strips of heating film which give to the package its self-heating character. The outer layers of the cylindrical wall are strips of cardboard for stiifening, and other conventional strip materials.

In both convolute and spiral winding of the cylindrical wall material for self-heating containers of the present invention the combination of any strip materials can be effected which will give to the wall the desired character. As shown for example in FIG. 6 the outer layers may comprise an aluminium foil strip 51 for improved thermal insulation, or for decoration, or for other qualities of the foil, they may include plastic or elastomeric films, a cellular material, or strong reinforcing steel strips. In general these outer layers will, as in conventional fibre and cardboard drums, consist mainly of cheap paper layers such as 52, 53, spiral-wound and adhesively laminated together to a rigid long tube. The first layer of this spiralwound tube is either a narrow strip of aluminium foil 54, the edges of which are tightly seamed together as at 55 as in any of the well known varieties of foil cans or a plastic film 56, FIG. 7, such as a polypropylene film which is compatible with the contents of the package and able to stand the processing temperatures. The film strip edges are sealed together as at 57 during winding (and could be overlapped) so that the film forms an impermeable inner skin of the drum. The heating film itself is not shown in FIGS. 6 and 7 but can be at any position on or Within the wall, in particular between the layers 54, 53 or 56, 53.

Instead of using a separate aluminium foil strip or a separate plastic film to provide the inner lining and of winding on top of this first strip a heating film as second separate layer, such inner layers can be combined in the form of a heating film 61, FIG. 8, at least one wide busbar margin 62 of which is folded over and is slightly wider than the rest of the heating film and insulated therefrom. The folded-over busbar 62 can be bare aluminium foil or aluminium foil backed by a plastic film 63 which has been laminated to it, or produced by coating it. Thus the heating film, or rather one busbar of the heating film can provide the leak-proof inner tube lining. Connection to the busbar could be through a metallic end closure of the container.

Where the film is on the outside or within the thickness of the wall, electrical contact with the heating film is made by baring the foil pattern on at least two terminal areas, e.g., at the end or ends of the drum and clipping supply leads on. When a metallic top or bottom closure of the drum is used, the spiral-wound tube is cut, for instance at an angle, so that the heating film proper does not touch the closure, or it may be isolated from it by a coating or tape.

The line of the bridges in the heating film pattern, such as described in my application Ser. No. 165,736 aforesaid is at right angle to the direction of the length of the heating film strip which is the direction of the arms of the heating film pattern as well. In tubes having such a film spirally-wound, the line of the bridges will therefore be at an angle to the tube axis depending on the lead angle of the helix. The arms of the heating film pattern between this line and the bottom and top of the tubular wall are cut and consequently remain unheated. A triangular area at the top and bottom of the container wall therefore remains cold.

This requirement brings up the problem of sensing the line of bridges, particularly when the heating film is the second or third layer, or even deeper within the laminated tube wall.

According to the present invention the sensing is made readily possible by arranging during the actual process of spiral winding of the heating film on the revolving mandrel to make a register mark or to attach a readily sensed sign preferably on or through the innermost layer, at the exact location or in fixed relationship to the exact location of the desired cutting line through the centre of the bridges. The preferred sign is a cut-out in the inner layer through which the heating film can be contacted and thus be sensed electrically. The cut-out can be used later on for access to a terminal area when the container is heated, saving a baring operation.

It is often desirable to produce a simple drum container with a plain paper or asbestos paper backed heating filth as the innermost spiral-wound layer and to produce various inner skins in the container which are impermeable or desirable for other reasons after it has been cut off from the tube and been provided with a bottom cover. Such an inner skin can be produced by blow moulding a plastic material into the drum, by pouring a resin, varnish or emulsion in and pouring it out, by following a resin film with a hardener, by repeating such procedures or by gelling a liquid film-forming material, etc. The advantage which the self-heatable drum offers for these methods is tht the heating film can be switched on during these procedures and thereby facilitate the cladding, curing, solidifying, or adhesion of the inner skin and its formation by a controlled heat cycle at the very base of this skin. Similar advantages are obtainable when the inner skin is to be formed from water soluble materials, such as waterglass, gelatine, etc., or from foam forming compounds which may be desired for packing of instruments or the like.

The sealing of the container after filling and heat processing of the contents may itself be effected with a heat sensitive adhesive, since the package can be sealed when it is still hot, in the case of a foodstuff typically at a temperature a little below 100 C. when the package is released from super atmospheric pressure.

What I claim is:

1. A method of hermetic packaging of goods needing to be heat processed at the time of packaging, which includes:

(A) filling the goods into a container formed of laminated paper or plastic and capable of being hermetically sealed;

(B) enclosing the filled but unsealed container in an atmosphere of a medium which will be harmless to the goods at the temperature of processing;

(C) re-circulating the medium through the enclosure;

(D) heating the goods while in the filled but unsealed container to the temperature and for the time required by the heat processing;

(E) increasing the pressure of the medium in the enclosure acting on the container in turn concomitant with the rise in temperature of the goods in the container and at a rate which throughout is sufficient to prevent pressure dependent damaging phenomena occurring in the goods; thereafter (F) cooling the goods in the container; and

(G) reducing the pressure of the medium in the enclosure acting in the container, to ambient atmosphere pressure at a rate which still prevents damaging phenomena arising in the goods during cooling; thereafter (H) hermetically sealing the container; then (I) removing the container from the enclosure; and

(J) making up heat losses in the re-circulating medium with fresh, heated quantities of the same medium thereby to recover, at least, a fraction of the processing heat carried by the container from the enclosure.

2. The method of claim 1 wherein said goods of step A include a volatile ingredient, and wherein the increase of pressure in step E is to a pressure above the vapor pressure of the volatile ingredient.

3. The method of claim 1 wherein said atmosphere of step B is clear air.

4. The method of claim 1 wherein said atmosphere of step B is steam.

5. The method of claim 1 wherein heating of step D is effected, in part, by the atmosphere of the medium which will be harmless to the goods at the temperature of processing.

6. The method of claim 5 wherein heating of step D is effected to a major extent by an electric heater in contact with the container.

7. The method of claim 6 wherein the electric heater is a film forming part of the container.

8. A method of hermetic packaging of goods needing to be heat processed at the time of packaging, which includes:

(A) filling the goods into a succession of containers capable of being hermetically sealed;

(B) enclosing the filled but unsealed container successively in an atmosphere of a medium which will be harmless to the goods at the temperature of processing;

(C) re-circulating the medium through the enclosure;

(D) heating the goods while in the filled but unsealed container to the temperature and for the time required by the heat processing;

(E) increasing the pressure of the medium in the enclosure acting on each container in turn concomitant with the rise in temperature of the goods in that container and at a rate which throughout is suficient to prevent pressure dependent damaging phenomena occurring in the goods; thereafter (F) cooling the goods in each container in turn; and

(G) reducing the pressure of the medium in the enclosure acting on each container in turn to ambient atmosphere pressure at a rate which still prevents damaging phenomena arising in the goods during cooling; thereafter (H) hermetically sealing each container in turn; then (I) removing each container from the enclosure; and

(J) making up losses in the medium in the enclosure 11 with fresh quantities of the same medium which are caused rst to 110W in contact with the container removed from the enclosure thereby to recover atleast a fraction of the processing heat carried by the containers.

References Cited UNITED STATES PATENTS 2,386,676 10/1945 French 21-56 2,855,314 10/1958 Martin 21-56X 10 2,862,821 12/1958 Wilbur 99H216X 3,232,770 2/1966 schaak 21-56X 3,348,905 10/1967 Reveley.

3,356,510 12/1967 Bamby 53-22 X 15 3,365,311 1/1968 schmidt 99-216X Burton 21-56 X Eisler 219-386 X Eisler 29-611 Welch 219--387 X Martin 99--182 Martin 99-182 Martin 99-182 Martin 99-182 Martin 99-182 WAYNE A. MORSE, JR., Primary Examiner U.S. C1. X.R.

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