EP1699702B1

EP1699702B1 - Apparatus for the final heat treatment of a packaging with a thermoplastic film

Info

Publication number: EP1699702B1
Application number: EP04820458A
Authority: EP
Inventors: Renato Rimondi
Original assignee: AWAX Progettazione e Ricerca SRL
Current assignee: AWAX Progettazione e Ricerca SRL
Priority date: 2003-12-18
Filing date: 2004-12-02
Publication date: 2007-08-29
Anticipated expiration: 2024-12-02
Also published as: ES2291985T3; EP1699702A1; DE602004008671D1; ATE371587T1; DE602004008671T2; WO2005058705A1

Abstract

At least the upper portion of the packaging film (2), which covers the tray and through which the product (102) is visible, is heated essentially through thermal conduction by any suitable means (3) which physically touches the outer surface of the said upper portion of the packaging film, so as to spread onto this latter, by physical contact, the minimum quantity of heat which is necessary to the heat shrinking of said surface, without substantial modification of the temperature of the inner atmosphere of the packaging. The means for effecting the thermal treatment consists preferably of a roller (3).

Description

Fresh food products are often packed to protect them from contact and prolong their life, in tubs or trays closed or wrapped in thermoplastic film. The present-day packaging techniques are fundamentally as follows:

a) the tray is completely wrapped in thermoplastic film. If the tray containing the product may be likened to a parallelepiped, the packaging film covers all six faces of this parallelepiped;
b) the tray is closed with a film welded to the open top of the tray. On the other five faces, again if likened to a parallelepiped, the tray itself is directly exposed.

The two processes are very different, not only in terms of the visual results achieved, but also as regards the differing characteristics of the films and of the trays suited to the first technique as opposed to the second. It is obvious that, since a perfectly fluid-tight packaging is very important, in the process described in point b), both the tray and the film must be impermeable to fluids, whereas in the other process this property can be limited to the film only and the tray need only have mechanical strength characteristics. Similarly, in the process in point a) care must be taken to optimize the film to make it possible to weld it leak-tightly to itself, whereas there is no such requirement of the tray. In the process in point b), however, the tray itself must have properties of leak-tight weldability to the film.
Whatever method is used to make the packaging, its attractiveness is, however, fundamentally important to its subsequent success in selling the packaged product. Large-scale distribution attaches great importance to the appearance of the packed product and to its consequent ability to attract the consumer's attention. Makers of packaging machines and films are therefore pushed to make great efforts to optimize their products from the point of view of the attractiveness of the packaging, if the packaging is to be displayed in the aisles of supermarkets. A poorly wrapped packaging with the film not properly adhering to the package, with excess material at the corners and sides, with the film's transparency limited by too many surface creases or wrinkles will be ill received by the consumer, but even before that, such a packaging will be rejected by the marketing organizations of the large distribution chains.
Thermoplastic films normally have a heat-shrink property which is prepared at the production stage and/or is the result of pre-stretching treatments at the use stage of these films, and this property can be used to improve the packaging process, i.e. to cause the film to cling very closely to the tray with the product inside. This packaging technique has the drawback that the whole of the package must be exposed to a large amount of heat by immersing it in a fluid at a very high temperature for a considerable period of time. This is necessary in order to raise all of the film around the tray to a high enough temperature to set off the shrinkage process in order to cause the film which would otherwise be loose, to cling to the tray. The consequences of applying such a large amount of heat to a package containing fresh food, which is normally kept in a cold chain that must never be broken, on the preservation of the product, may well be imagined.
The applicant is the owner of WO 03/051715 for a process and a machine capable of producing food product packagings by the method described in point a) above, with the film clinging to the tray, mainly by exploiting the stretchability properties of a thermoplastic film rather than its heat-shrink properties. In certain stages of this process it is also indicated that heat can be applied to the film to optimize the formation of the packaging. One specific problem encountered with this process, in the packaging of food products in trays, is how to achieve perfect transparency of the part of the packaging film that covers the top of the tray and through which the packaged product is seen, because the presence of creases or wrinkles, even if only local, on this part of the film would give the consumer the impression that the product was old and had deteriorated. Efforts have been made to solve the problem by applying heat to the surface of the film of the packaging using a flow of hot air which raises the temperature of the film in order to trigger the "heat shrink" phenomenon, that is to enhance the elastic memory effects resulting from the stretching to which the film was subjected during formation of the packaging, to the point where the said creases or wrinkles disappear, but this solution has the following limitations and disadvantages:

it can heat the atmosphere around the product enclosed in the film packaging;
it can heat the packaged food product to values above those allowed by the preserving cold chain;
it uses too much energy; and
it is difficult to fine-tune it to suit the varying dimensional characteristics of the packaging and those of the packaged product.

If the film has barrier or fluid-impermeability properties and is heated by convection by a stream of hot air, there will inevitably be an increase in the temperature of the atmosphere contained within the film envelope, tending to increase the volume and consequently the internal pressure of the packaging precisely because of this impermeability of the film to fluids. This increase in the internal pressure stretches the packaging film, which deforms much like a balloon being inflated. When the atmosphere inside the packaging cools down and the internal pressure is removed, the creases and wrinkles that existed before the heat treatment return, sometimes worse than before.
Document US 2 785 519 A discloses an apparatus for the final heat treatment of packagings with thermoplastic film, said packagings presenting at least one top surface, whereby there are provided means for transferring an amount of heat to at least said top surface, by heat conduction, in such a way that a sufficient amount of heat is transferred quickly directly onto the intended surface, to achieve the desired effects, without harmfully modifying the temperature of the atmosphere.
The idea of solution of the present invention appears in the appended claim 1 and in the dependent claims.
Other features of the invention, and the advantages that follow therefrom, will become more clear in the course of the following description of two preferred embodiments of the invention, illustrated purely by way of non-restrictive example, in the figures of the accompanying sheets of drawings, in which:

Fig. 1 is a perspective view of the present apparatus; and
Fig. 2 shows the apparatus in plan view from above and with parts in section.
Figures 3 and 4 are views respectively in side elevation and in plan view from above of another embodiment of the invention.

In Figure 1, reference 1 denotes the belt conveyer which travels in the direction F carrying the packaging 2 with the product 102 inside a tray packed in a thermoplastic stretch film, which may optionally also have a barrier effect or fluid-tightness properties, coming from the packaging machine. In other words, the stretch film wrapped around the product may be of the usual type that allows all gases to pass through it, or of the type impermeable to all gases or of the type that allows some gases to pass through it and others not. To solve the problem set out in the introduction, good results have been achieved by providing above the conveyer 1, in a transverse arrangement and at a distance from the belt correlated with the height of the packaging 2 and adjustable (see below), at least one preferably rolling means, such as for example a belt, or preferably a roller 3 of suitable diameter, which may be idle, constructed at least superficially with any material that does not stick to the packaging film and that is heated by any suitable means to a temperature at which, when this roller is rolled over the top surface of the packaging and touches it with slight interference (see below), it transfers to this surface directly, by conduction, the moderate amount of heat necessary to remove any creases or wrinkles from this surface without significantly modifying the temperature of the atmosphere inside the packaging.
The roller 3 may have its own heat sources, which may be internal to it, or may receive its heat from a stream of hot fluid striking it, produced for example by the apertures B1 and B2 on the sides of the intermediate-final part of the conveyer 1, which dispense hot air at the right temperature onto the perimeter of the packaging 2, also flowing over the roller 3 and transferring to it the heat required for the heat treatment of the top of the packaging 2. The roller 3 must not only be non-stick towards the film of the packaging 2 but also light enough not to induce harmful interference with the said packaging and must have good thermal inertia. Good results have been obtained for example with aluminium rollers covered with silicone rubber or with rollers made of carbon-fibre composite and epoxy matrix, which has the great advantage of reducing their weight.
The roller 3 is supported rotatably in bearings or other means with a low coefficient of friction 4, by a spindle 5 attached to the free end of a U-shaped arm 6, which extends from the roller in the direction from which the packaging has arrived and which at the other end is mounted rotatably, via bushes 7 with a low coefficient of friction, on a horizontal shaft 8 parallel to the said roller. The shaft 8 passes through straight vertical slots 10, 110 in brackets 11, 111 attached to the sides of the frame of the conveyer 1, and attached to the insides of these brackets are vertical racks 12, 112 meshing with pinions 13, 113 keyed to the said shaft 8, which last has on at least one end a knob 108 which can be turned to rotate the shaft 8 and modify its distance from the conveyer 1. The shaft 8 is stabilized at the height selected by rotating it in this way by means of the friction exerted against the brackets 11, 111 by pairs of washers 9, 109 which are made of a material suitable for the purpose, are mounted on this shaft 8, and touch the opposite faces of the said brackets. One washer of each pair presses, for example, against the pinions 13, 113, while the other washers can move axially and are pushed towards the said brackets 11, 111 by elastic means such as, for example, diaphragm springs 14, 114 loaded by nuts 15, 115.
It will be understood that the height adjustment of the shaft 8, which is necessary in order to position the roller 3 correctly, as the height of the incoming packagings 2 varies, can be effected differently automatically by a remote-controllable electric motor unit, e.g. of stepper motor or equivalent type, conveniently arranged so as not to be affected by the temperatures of the operating station in which it operates and controlled by the processor at the packaging machine which with the aid of means normally present in the said packaging machine knows the dimensions of the various products inserted into the packaging cycle.
The said height adjustment of the shaft 8 also modifies the height of the roller 3 and its distance from the conveyer 1, as does the possibility of pivoting upwards, by the device which will now be described. On the side of the arm 6, there is mounted rotatably on the shaft 8 via its inverted U-shaped intermediate part 116, a lever 16, formed for example from a metal sheet by cutting and bending. This is provided with a projection 216 bent parallel to the shaft 8, the said projection sliding in a vertical slit 17 in the neighbouring bracket 111 and provided with an extension 316 alongside the arm 6 terminating in a U-shaped head 416, on the lower flange of which the said arm 6 normally rests but is free to pivot upwards through an angle proportional to the height of the said head 416.
It will be obvious that the roller 3 turns and is suspended from a structure that enables its minimum distance from the conveyer 1 to be adjusted in such a way that the roller can operate in contact with that part of the packaging 2 film which closes the top of the tray with the product inside, without significantly touching the tray itself. In contact with the packaging film, the roller 3 rotates because of friction between it and the packaging and spreads onto the said film the heat necessary for neutralizing any creases or wrinkles. Good results have been obtained when packaging with film having a thickness of approximately 40 microns, with the film being treated by the roller 3 at a temperature of between approximately 40° and 80°C, the said packaging being advanced by the conveyer 1 at a speed of between 0.05 and 0.5 m/s.
A modified atmosphere is created inside the packaging to prolong the life of the packaged product. This atmosphere is at a slightly higher pressure than the external atmosphere, so the top of the film of the packaging is not perfectly flat but slightly domed, with a slight outward convexity. The roller 3 will therefore on average touch the highest part of this dome of film, without significantly interfering with the tray, as any serious interference between these two parts could result in impact damage to the packaging or could stop the packaging on the conveyer 1, with obvious negative consequences. The entire moving part of the device, including the roller 3 and the arm 6, must be kept as light as possible so that it can be raised with the least possible effort during the interference between the roller and the incoming packaging 2. The objective of lightening the said moving part can be achieved, in combination with or as an alternative to the matters described with reference to limiting the weight of the roller 3, by the additional application of a suitable counterweight (not shown), for example on the crossbar 106 of the arm 6. To damp the downward oscillation of the roller 3 after the packaging 2 has left it, one possibility would be to use a small damper (not shown), which could be placed on the lower flange of the head 416 of the lever 16. These latter parts have not been illustrated on the grounds that they are obvious and can easily be made by those skilled in the art.
To increase the area of contact between hot roller and film, the arm 6 may support one after the other, two or more mutually parallel rollers 3, as illustrated in dashes in Figure 1, in such a way as to create a rotating grid which limits the direct exposure of the top of the packaging to the external environment and is therefore better able to treat this part essentially by heat conduction. In this version, the pivoting arm 6 may advantageously be replaced by a parallel-motion mechanism and the array of rollers 3 will be supported by that side of the parallelogram which is opposite the fixed side, so that the said array of rollers can pivot while always remaining parallel to the conveyer 1 beneath it. In another constructional variant, the roller or rollers 3 may be driven in some suitable way rather than being idle.
According to the embodiment which will now be described with reference to Figures 3 and 4, there are provided means for automatically adapting the height position of the rollers for the final heat treatment of the packaging to the different sizes of the said packagings. In Figures 3 and 4, reference numeral 1 indicates the belt conveyer which travels in the direction of arrow F and onto which there rests the packaging F with the product arranged at the interior of a tray and tightly wrapped by a thermoplastic film which is stretchable and can be also of the barrier effect or fluid tight. The stretchable film which wraps the product can be of the common type which permits the passage or all gases or of a type impermeable to all gases or of the type which permits the passage of some gases and not of other gases. According to the invention, to top portion of the packaging 2 is thermally treated by a set of rollers 3 of suitable diameters, for example freely rotatable, constructed at least superficially with any material that does not stick to the packaging film and that is heated by any suitable means to a temperature at which, when this roller is rolled over the top surface of the packaging and touches it with slight interference (see below), it transfers to this surface directly, by conduction, the moderate amount of heat necessary to remove any creases or wrinkles from this surface without significantly modifying the temperature of the atmosphere inside the packaging. As above said with reference to the embodiment of Figures 1 and 2. The rollers 3 may have their own heat sources, which may be internal, or may receive the heat from a stream of hot fluid striking it, produced for example by the apertures B1 and B2 on the sides of the intermediate-final part of the conveyer 1, which dispense hot air at the correct temperature onto the perimeter of the packaging 2, also flowing over the rollers 3 and transferring to them the heat required for the heat treatment of the top of the packaging 2. The rollers 3 and the conveyer 1 are preferably insulated from the outer environment by a removable hood 18 preferably of suitable transparent plastic material, open at both ends, which has the function of maintaining the heat produced by the apertures B1 and B2 suitably concentrated onto the travelling packages and onto the rollers 3.
The rollers 3 are mounted rotatable the one following the other, co-planarly and at a short distance the one from the other onto the horizontal portion of side members 19, 119, for example having the shape of a rectangular triangle or of a square and they are hinged at 20 and 120 to parallel link rods 21, 121, of which the upper ones 21 are rotatably mounted by their other end to a rod 22 parallel to the hinge points 20, 120 and secured by its end to supports 23, 123 which on their turn a secured to the side members of the frame of the conveyer 1, while the lower link rods 121 are secured by their other end, for example by means of a stop dowel 24 to a shaft 25 parallel to the said rod 22, which by its ends is rotatably supported by the supporting members 23,123. The link rods 121 carry on their end keyed to the shaft 25, appendices 221 directed upwards and provided with circular sector slots, having their axes of curvature on the axis of shaft 25 and traversed by the rod. At the said appendices 221, one of the link rods 121 carries an appendix 321 directed downwardly, linked to a fork 27 secured to the stem of a linear actuator 28, for example to a simple-action cylinder and piston group, the body of which is secured by a bracket 29 to the near support 23. When the cylinder 28 is acted in the expansion run of its stem, the parallelogram structure which carries the roller 3 is lifted to the maximum position indicated in Figure 3 by the dotted lines, which is limited by the co-operation of the slots 26 with the rod 22 and which is such that beneath said rollers there may pass without any interference even the maximum height packaging which can be handled by the packaging machine. Whenever instead the cylinder 28 is acted into the braked retraction run of its stem (see further) due to the weight of the unit of the rollers 3, the said rollers are lowered and bear with their weight onto the top of the packaging so as to transfer onto it the heat which is necessary for effecting the correct smoothening of the said packaging. The slots 26 and the fork 27 which constitute the articulation of the appendix 321, add to the system a correct degree of freedom in the vertical displacement of the unit of rollers, which in this manner can bear by gravity onto the packaging to be treated and adapt itself to possible irregularities thereof.
In order to correctly actuate the cylinder 28, upstream of the unit of rollers 3 there is provided, laterally with respect to the conveyer 1, a photocell 30 which is acted upon by the passage of the packaging 2. The photocell 30 is connected to a processor 31 which is connected to the motor 32 which controls the conveyer 1, and to the same processor there is connected also the electro-valve 33 which controls the cylinder 28. ln correct time relationship therefore the processor will control the operation of the valve 33, by properly causing the lifting and lowering of the unit of roller 3, upon the passage of any packaging to be treated.

Claims

Apparatus for the final heat treatment of packagings with thermoplastic film, said packagings presenting at least one top surface, comprising:
- means for transferring an amount of heat to at least the said top surface, by heat conduction, in such a way that heat is transferred quickly directly onto the intended surface, to achieve the desired effects, without harmfully modifying the temperature of the atmosphere inside the packaging; said means being arranged above the conveyer (1) which collects the finished packaging (2) as it leaves the forming cycle and carries it away for discharge and being such as to operate on the said film with a rolling action;

- said heat transferring means comprising at least one roller (3) which rotates in contact with the top film of the packaging (2) and whose axis is parallel to the axes of the pulleys of the conveyer (1) on which the said packaging travels;

- further means being provided for adjusting the height of the said roller (3) as the height of the packagings (2) varies, in such a way that the roller basically touches the top film of the packaging without significantly interfering with the tray containing the packaged product;
characterized by the fact that
the said roller (3) is mounted rotatably on an arm (6) that pivots on a shaft (8) supported by the said height-adjustment means which carry a device (16) on which the said arm rests and which limits the amplitude of the upward pivoting of the said arm, the whole pivoting assembly being designed, including in the physical characteristics of its component parts, to be raised with very little effort when the roller interferes with the top film of the packaging undergoing the heat treatment.
Apparatus according to Claim 1, characterized in that the said means that transmit the heat to the top film of the packaging by heat conduction have their own means of heating, for example electrical resistances.
Apparatus according to Claim 1, characterized in that the said means that transmit the heat to the top film of the packaging by heat conduction are heated by a stream of hot air that strikes them, for example the stream of hot air dispensed by apertures (B1, B2) on the sides of the conveyer (1) carrying the packaging (2), these apertures acting on the perimeter of the packaging protected by the tray.
Apparatus according to Claim 1, characterized in that the said roller (3) is idle.
Apparatus according to Claim 1, characterized in that the said roller (3) is connected to means which make it rotate with a peripheral speed equal to or slightly different from the linear speed of advance of the conveyer (1) on which the packaging (2) is travelling and in a direction that accords with the direction of travel of the said packaging.
Apparatus according to Claim 1, characterized in that the said roller (3) has sufficient thermal inertia.
Apparatus according to Claim 1, characterized in that the said roller (3) is made of or at least covered with a material that does not stick to the film of the packaging undergoing the heat treatment.
Apparatus according to Claim 1, characterized in that the said roller (3) is made of aluminium and is covered with silicone rubber.
Apparatus according to Claim 1, characterized in that the said roller (3) is made of a carbon-fibre composite in an epoxy matrix.
Apparatus according to Claim 1, characterized in that there may be balancing means such as, for example, counterweights on the pivoting arm (6) carrying the roller (3), to limit the effort necessary to raise the said roller while it is acting on the top film of the packaging undergoing the heat treatment.
Apparatus according to Claim 1, characterized in that the fulcrum shaft (8) of the arm (6) with the heat-treatment roller (3) passes through straight vertical slots (10, 110) in brackets (11, 111) attached to the sides of the frame of the conveyer (1) on which the packaging (2) is travelling, and attached to, for example, the insides of these brackets are vertical racks (12, 112) meshing with pinions (13, 113) keyed to the said shaft (8), which latter has on at least one end a knob (108) which can be turned to rotate this shaft, modify its distance from the underlying conveyer (1) and keep it permanently horizontal, this shaft (8) being stabilized at the height selected by rotating it in this way by means of the friction exerted against the said brackets (11, 111) by pairs of washers (9, 109) which are made of a material suitable for the purpose, are mounted on the said shaft (8), and touch the opposite faces of the said brackets; one washer of each pair being for example pressed against the said pinions (13, 113) while the other washers can move axially and are pushed towards the said brackets (11, 111) by elastic means (14, 114) loaded by nuts (15, 115).
Apparatus according to Claim 11, characterized in that on the fulcrum shaft (8) of the arm (6) carrying the treatment roller (3), on the side of this arm, there is mounted rotatably, via its intermediate part (116), a lever (16) provided with a projection (216) bent parallel to the said shaft (8), the said projection sliding in a vertical slit (17) in the neighbouring bracket (111) and provided with an extension (316) alongside the said arm (6) ending in a U-shaped head (416), on the lower flange of which the said arm (6) normally rests but is free to pivot upwards through a sufficient angle permitted by the height of the said head (416).
Apparatus according to Claim 11, characterized in that in a variant of construction, the height adjustment of the fulcrum shaft (8) of the arm (6) with the heat-treatment roller (3) can be effected automatically by a remote-controllable electric motor unit, e.g. of stepper motor or equivalent type, controlled by the processor at the packaging machine which with the aid of means normally present in the said packaging machine knows the dimensions of the various products inserted into the packaging cycle.
Apparatus according to Claim 1, characterized in that to increase the surface area of contact with the top film of the packaging, the heat treatment of this surface is effected by two or more rollers (3) set one behind the other and parallel with each other in such a way as to create a rolling grid which limits the contact by convection of the top of the packaging with the external environment and which therefore heat-treats this part essentially by heat conduction.
Apparatus according to Claim 14, characterized in that the array of heat-treatment rollers (3) is supported on that side of a parallel-motion arm which is opposite the fixed side, so that the said array of rollers can pivot while always remaining parallel to the conveyer (1) beneath it.
Apparatus according to Claim 1, characterized in that it comprises means such that, when presented with, for example a packaging (2) made with a stretch film with a barrier effect and having a thickness of approximately 40 microns, the temperature at which the said film is heated by the roller or rollers (3) is proportionally between approximately 40°-80°C, while the conveyer (1) beneath it carries the said packaging (2) at a speed of between 0.05 and 0.5 m/s.
Apparatus according to claim 1, characterized by the fact that the said at least one rollers (3) are mounted on an up-and-down device which maintains same parallel to the conveyer on which the packaging to be treated is carried and which upon control can lift them up or lower them down under the action of an actuator which at the starting of each cycle maintains the said roller lifted up to a maximum predetermined position correlated to the maximum height of the packagings to be treated, so that in this position there does take place any interference between the said packagings and the said lifted rollers, means being provided in order that whenever a packaging comes beneath said roller, same are lowered in correct phase relationship until they touch the packaging with sufficient pressure and with a suitable degree of freedom in their vertical displacement, and means being provided in order that at the end of the treatment of a packaging, before that the packaging completely leaves the said thermal treatment rollers, the said rollers are lifted by the actuator (28) up to the maximum starting cycle position.
Apparatus according to claim 17, characterized by the fact that the rollers are arranged in a bank, the one following the other, co-planarly and parallelly both between them and with respect to the conveyer (1) onto which there travel the packagings to be treated, the said bank or battery of rollers (3) being mounted on an articulated parallelogram structure which can be lifted or lowered by an actuator (28) with a correct degree of freedom in the vertical displacement, in such a manner that when same is in its low position, the rollers (3) bear by gravity on the travelling packaging.
Apparatus according to claim 18, characterized by the fact that the rollers 3 are mounted rotatable onto the horizontal portion of side members (19, 119) for example having the shape of a rectangular triangle or of a square and they are hinged to parallel link rods (21, 121) of which the upper ones (21) are rotatably mounted by their other end to a rod (22) parallel to the hinge points (20, 120) and secured by its end to supports (23, 123) which on their turn are secured to the side members of the frame of the conveyer (1), while the lower link rods (121) are secured by their other end, for example by means of a stop dowel (24) to a shaft (25) parallel to the said rod (22), which by its ends is rotatably supported by the supporting members (23, 123) the link rods 121 carrying, on their end keyed to the shaft (25), appendices (221) directed upwards and provided with circular sector slots, having their axes of curvature on the axis of shaft (25) and traversed by the rod (22), there being provided, at the said appendices (221), that one of the link rods (121) carries an appendix (321) directed downwardly, linked to a fork (27) secured to the stem of a linear actuator (28), for example to a simple-effect cylinder and piston group, the body of which is secured by a bracket (29) to the near support (23).
Apparatus according to claim 19, characterized by the fact that the piston and cylinder group (28) is secured by its body and by a bracket (29) to the near support (23) and it carries on its stem a fork (27) which co-operates with the said appendix (321) of the articulated parallelogram structure which carries the set of rollers (3).
Apparatus according to claim 17, characterized by the fact that in order to correctly actuate the cylinder (28), upstream of the unit of rollers (3) there is provided, laterally with respect to the conveyer (1), a photocell (30) which is acted upon by the passage of the packaging (2), said photocell (30) being connected to a processor (31) which is connected to the motor (32) which controls the conveyer (1), to the same processor there being connected also the electro-valve (33) which controls the cylinder (28), whereby in correct time relationship the processor will control the operation of the valve (33), by properly causing the lifting and lowering of the unit of rollers (3), upon the passage of any packaging to be treated.
Apparatus according to claim 17, characterized by the fact that the thermal treatment rollers (3) have their own means of heating, for example electrical resistances or are heated by a stream of hot air that strikes them, for example the stream of hot air dispensed by apertures (B1, B2) on the sides of the conveyer (1) carrying the packaging (2), these apertures acting on the perimeter of the packaging protected by the tray, the rollers (3) and the conveyer (1) being preferably insulated from the outer environment by a removable hood (18) of suitable transparent plastic material, open at both ends, which has the function of maintaining the heat produced by the apertures (B1, B2) suitably concentrated onto the travelling packages and onto the rollers.