The present invention refers to a hot air shrink tunnel for a heat shrinking apparatus for heat shrinking a shrink label to enclose a product, a method for heat shrinking the shrink label enclosing the product, and a heat shrinking apparatus for heat shrinking the shrink label enclosing the product, said heat shrinking apparatus comprising the hot air shrink tunnel.

A container such as a PET (Polyethylenterephthalat) bottle which is filled with liquids or other pourable materials like grains or pills generally has a label mounted thereon. The label is often formed of a shrink film (hence also termed “shrink label”) cylindrically shaped to enclose or envelop the container and has a brand name, information on the contents of the container, and the like printed on it. Such a cylindrical label is generally fitted onto the container in a sequence of steps by a label mounting system including a conveying means for conveying the container along a predetermined conveying path, a label fitting apparatus for fitting an unshrunk cylindrical label onto the container while being conveyed by the conveying means, and a heat shrinking apparatus for heat shrinking the cylindrical label fitted onto the container. In order for such a shrink label to be shrinkable, it is usually made of a thermoplastic material like polypropylene (PP), polyethylene (PE), polystyrene (PS) or polyvinyl chloride (PVC).

There are several ‘physical’ options (heat sources) known in the art to transfer heat to the shrink label to enhance its temperature to a minimum temperature to start shrinking, and there are several ‘technical’ options known in the art for technical implementation and constructive design to carry out this process more or less uniformly, that is to end up with a more or less wrinkle-free, bubble-free, and dry, i. e. a ready-to-pack final product. Difficulties are encountered in applying any of these techniques, and each of them has its own advantages and disadvantages resulting in respective ideal areas of application which directly relate to their strengths and weaknesses.

As for the physical options, a distinction must be made in terms of the heat source which determines the physical effects exploited for both the transfer of the thermal energy medium between the heat source and the product and the subsequent heat exchange at the interface or contact area between the medium and the surface of the product. Hence distinction is generally made between (a) heat transfer by infrared radiation, (b) heat transfer by hot air, i. e. by thermal convection and finally heat exchange between the hot air and the surface of the product, and (c) heat transfer by steam, i. e. by convection and finally by condensation of the water contained in the steam on the surface of the product. Correspondingly, the devices configured to apply these options usually are so called infrared tunnels (which are not further considered herein) in the case (a), ‘hot air tunnels’ in the case of (b), and ‘steam tunnels’ in the case of (c).

As for (b), the biggest assets of hot air tunnels are their relative compactness, a wide temperature range in which they can be used, the possibility to use miniature nozzles and custom hole/distribution patterns to manipulate the flow of air allowing for targeting of critical areas and helping to treat potential problem areas, and relatively low costs in view of the fact of having dry products leaving at the end, for example.

On the negative side is (b1 ) the limitation to simple shapes due to the dependency of the heat transfer from the hot air source to the product on the local flow velocity of the hot air and (b2) the heating-up of the local environment due to a continuous flow of hot air. (b1 ) is due to the fact that the overall heat transfer coefficient is dependent on the heat capacity, temperature, and flow.

Regarding (c), as noted above, the physical effect of heat exchange is condensation, that is the change of state from the gas phase into the liquid phase and that is the reverse of vaporization. Being the reverse of vaporization, the enthalpy of vaporization, i. e. the amount of energy that must be added to a liquid substance to carry out a phase transition or phase change to the gaseous phase, is regained and used to increase the temperature of the product outer skin temperature. Crucial to this process is the dew point as the temperature at which this phase transition occurs, i. e. to which a gas must be cooled to become saturated with water vapor at a given (constant) air pressure and water content. That is, the dew point is an absolute measure of the gas humidity at any temperature and relates directly to the amount of water vapor present (partial pressure of water vapor). Conversely, observation of the occurrence of condensation allows an estimation of the temperature.

Steam tunnels using water vapor as a medium to transport thermal energy by latent energy transfer allow for a very uniform transfer of heat to the product. Such a uniform transfer of heat is necessary when high-quality and distortion-free graphics, for example, are important.

Disadvantageous conceivably is that (c1 ) the products are wet from condensation upon exiting the tunnel requiring drying before packaging (dryer is needed), printing or secondary labelling, possibly causing corrosion of metal components, and rendering the application to dry goods such as herbs and grains at least problematic, that (c2) high energy is needed for steam generation (steam boiler) which usually is fossil energy, that (c3) steam tunnels generally have a smaller physical footprint than infrared or hot air tunnels. In fact, the physial footprint is smaller due to the intense energy being higher by a factor of ten compared to hot air and six compared to infra red. It should be noted, however, that infra red is not adapted for shrinking due to the print colors on the sleeve. Infra red can be used only for pre-heat or evaporation of condense drops.

It is an object of the present invention to provide a hot air shrink tunnel with steam support in the most critical moments in the shrink process where a low temperature and low flow without reduced total energy is required, for a heat shrinking apparatus for heat shrinking a shrink label to firmly enclose a container, a product in the terminology of the present invention, while securing the advantages and avoiding the disadvantages described above, a method for heat shrinking said plastic sleeve to enclose said product by means of said hot air shrink tunnel, and a heat shrinking apparatus for heat shrinking a shrink label comprising the hot air shrink tunnel. Specifically, the above object is intended to be solved taking into account the following boundary conditions: reduction of energy consumption, preference of electric energy vis- a-vis fossil energy, provision of dry end products out of the hot air shrink tunnel, application to non-regular surfaces having undercuts, for example, simplification of the design of the hot air shrink tunnel to minimize the need for a service technician and to be as self-sufficient as possible.

A hot air shrink tunnel, a method, and a heat shrinking apparatus according to the preambles of claims 1 , 16, and 17, respectively, are described in EP 2 103 527 A1 titling “heart shrinkage apparatus for shrink film”.

This object is solved by the hot air shrink tunnel of claim 1 and the method of claim 16, respectively. Advantageous modifications are defined in the dependent claims.

According to a first aspect of the present invention (claim 1 ), a hot air shrink tunnel for a heat shrinking apparatus for heat shrinking a shrink label to enclose a product, wherein the hot air shrink tunnel surrounds a conveying path of the product, is characterized by a moist air zone and a dry air zone arranged in this order in a conveying direction of the product through the hot air shrink tunnel wherein (i) the moist air zone includes heating means for heating air flowing within the moist air zone, and water diffusion means for diffusing an amount of water in the air flowing within the moist air zone to produce an air- steam-mixture, and (ii) the dry air zone includes heating means for heating air flowing within the dry air zone.

The expression “hot air shrink tunnel” (hereafter briefly “tunnel”), that may be understood in a sense to be a continuous oven, as used herein refers in an more abstract and non- structural sense to a connection of a plurality of zones - according to the present invention a moist air zone and a dry air zone (to be understood, as a matter of course, as “at least one” in each case) - each embodied by a respective module. In other words, the term “module” refers to a structural portion of the tunnel arranged in the conveying direction, while the term “zone” refers to an atmosphere or environment generated therein and may be understood in a more functional sense by referring to a part of a shrinkage process to be carried out inside the tunnel. Furthermore, hereafter, the three-dimensional space within a module where the product is to be subjected to said atmosphere or environment is called “chamber”.

The tunnel is adapted to be feeded from an infeed side thereof by the product as an initial product (hereafter briefly “product”) to be enclosed firmly during its passage therethrough by a shrink label, herein called “sleeve”, that is heat shrunk or, synonymous, thermally shrunk into tight contact with the product to form a final product. As a matter of course, a plurality of products are usually fed one after the other by and in a conveying direction of some conveying means like a production line or a conveyor belt representing a concretization or concrete design of the conveying path.

Preferably, the shrink label - in order to be thermally shrinkable - is a thermoplastic material, for example PP, PE or PS.

As for the “product”, this preferably is a bottle-like container for liquids, for example, of either constant or varying cross-section perpendicular to the axis of symmetry, where said cross-section may have any shape like a circular, a square and a rectangular shape, for example, wherein size, shape and changes of both of the cross-section along a longitudinal axis of a product are important to be considered in terms of the different contact points of time and the different strength of adhesion and elongation of the shrink label.

The term “hot air” as used herein refers to air having a temperature higher than ambient temperature, specifically a temperature in a range - depending on the type of zone (production step) - between 80°C and > 200°C with improved insulation, for example, where it should be noted that in view of the relative short residence time of a product within an individual zone of only a few second, for example, the sleeve temperature usually is below this temperature range and the product outer temperature is even lower.

As defined above, as a consequence of the stream of hot air and the water diffused within each of the chambers, an air-steam -mixture defined and specified by a set of intensive thermodynamic variables like temperature, pressure, concentration, and absolute humidity is generated in the chambers, where hot air and water vapor together can be referred to as a gaseous fluid.

Therefore, according to the present invention, the sleeve is shrunk by heat, wherein the heat to enhance the temperature to an appropriate temperature of the sleeve (i) is transported to the sleeve via the flow of hot air, i. e. by heat convection, and - in synergetic cooperation - (ii) is supplied by condensation of the water in the form of so called enthalpy of vaporization, heat of vaporization or latent heat. To emphasize, in the moist air zone, two physical effects (convection and condensation) are employed, while in the dry air zone, wherein the curve of the dependency of the shrinkage (in %) on the temperature shows a steep characteristics in the temperature range where latent heat is responsible for the effect and a flat characteristics in the temperature range where convection is essential, both effects overlapping to a certain degree. Due to the combined effect of hot air and water vapor, with the purpose to achieve appropriate temperatures, the hot air need not to be heated as much as it would have to be without the thermodynamic support of the water vapor. It should be noted that in order for condensation to take place, the dew point of water must be undercut, where the dew point is the temperature to which water containing air must be cooled to become saturated with water vapor, constant air pressure and water content assumed. To achieve this, fortunately, the sleeve temperature must become only slightly lower than the dew point.

According to the present invention, the air and the water vapor or steam are mixed inside the tunnel. Alternatively, it is conceivable to carry out this step outside of the tunnel. Advantageously, for the fluids to be controllable not only in terms of temperature and flow rate, but also in terms of flow direction into and, consequently, within the modules, the fluids are introduced into the respective modules (moist air zones) via nozzles adjustable in position in angle. Correspondingly, the modules may be referred to as “nozzle modules”.

Advantageously, once the fluids are introduced into a chamber, they may be circulated therein by means of a fan, a blower, a ventilator or the like. According to the present invention, each of the moist air zone and the dry air zone “includes” heating means for heating air flowing within the respective zone. In view of the functional interpretation of the term “zone” as explained above, the heating means may be arranged inside or outside the respective chambers.

To refer back to said air-steam mixture, it should be emphasized that according to the present invention, due to the synergetic interaction of the hot air and the water vapor, the temperature of each of these fluids can be relatively low as compared for example with the prior technique using superheated steam where a superheat steam, as is well known in the art, is a steam at a temperature higher than its vaporization point at the absolute pressure where the temperature is measured (pressure dependency of the vaporization point). This has a positive influence both on energy consumption and on service life of the components of the shrink tunnel. That is, although superheated steam, in contrast to saturated steam, for example, is adapted to prevent moisture or water droplets from adhering to the surface of the shrink label and the product, energy consumption is high and, as a consequence, the life times of the components shortened. In fact, superheated steam means high temperature. Sleeve fixation at high temperature is difficult with the time exposed to the temperature depending on the temperture (0,5 s at 90°C and 0,1 s at 100°C, for example). Therefore, superheated steam is an option for shrink finish, but a less good choice for sleeve fixing and moving. This disadvantage entails another disadvantage, namely the shortening of maintenance intervals and, therefore, increased costs. The present invention differs, therefore, from the prior art in that well-known hot air shrink tunnels are modified in that a defined amount of water is injected into hot air.

As for energy consumption, it should be noted that the water content of the moist air is directly related to the electric power used to evaporate water. That is, the amount of water evaporated quickly changes with a change in electric energy supplied for that purpose.

Furthermore, important and critical to the present invention, it should be noted that the pressure as variously mentioned is always normal pressure, i. e. all processes according to the present invention are carried out only without overpressure. Only without overpressure, a hot air recycling system can be used. Common for steamtunnels is steam exhaust. In a preferred modification (claim 2), the moist air zone heating means is configured to adjust a temperature of the air flowing in the moist air zone to a given target temperature, and the water diffusion means is configured to adjust the amount of water depending on the given target temperature, to such extent that a given absolute humidity of the air- steam-mixture within the moist air zone is achieved with the air-steam-mixture being kept at normal pressure. Here, the absolute humidity is given in “kg water I kg dry air”. Alternatively, the absolute humidity can be given in “kg water I (kg dry air + kg water)”. That is, rather than manually, control according to the present embodiment is preferably carried out automatically by the moist are zone heating means and the water diffusion means in synergetic cooperation with each other to achieve the desired environment of each zone (within each chamber) with a minimum of resources (for example electric power). As an example, the combination of hot air and water steam in zones 1 and 2 (only) yields better results compared with classical steam tunnels (without water steam) without the necessity to resort to fossil energy at all and with an overall energy reduction by 65 % and water reduction by 75% with respect to the classical variant.

In a preferred modification (claim 3), the hot air shrink tunnel further comprises a detecting means for detecting the absolute humidity of the air-steam-mixture within the moist air zone. That is, the absolute humidity is the controlled or measured variable. Alternatively, other physical values like partial pressure, oxygen content or nitrogen content could serve as such.

In a preferred modification (claim 4), the hot air shrink tunnel comprises a control means configured to control the absolute humidity of the air-steam-mixture as a controlled variable within the moist air zone to adjust the mass concentration of water in dry air water while keeping the temperature at the target temperature. That is, according to the present embodiment, as already suggested above, the “ultimate goal”, that is the goal that is ultimately desired and wished to be achieved - with as little energy as possible -, is a temperature appropriate for the materials used in order for the sleeve to become firmly shrunk without wrinkles onto the product during its passage of the tunnel. This is achieved in a controlled fashion by optimally match temperature and humidity. It should be noted that the passage time for travelling through the tunnel is only a few seconds. In a preferred modification (claim 5), any of the heating means of the moist air zone and/or of the dry air zone is configured to generate hot air controllably in terms of temperature and flow rate. It should be noted here that heat transfer from the atmosphere of a zone to the sleeve depends, in case of the hot air, on its flow rate or flow velocity, temperature and flow direction, while it depends, in case of the water vapor, less on the flow rate but rather on the absolute humidity.

In a preferred modification (claim 6), any of the heating means of the moist air zone and/or of the dry air zone includes flow generating means for generating air flow circulation in a plane perpendicular to said conveying direction. Specifically, the direction perpendicular to the conveying direction essentially is also perpendicular to the above referred to symmetry or main axis of the product. That is, most of the hot air and also the flow of diffused water hits the sleeve without or with only a small component tangential to the symmetry or main axis. As a result, no or only a small amount of water vapor gets into the gap between the sleeve and the product at the begin of the shrinkage process. However, by the heating process itself, the air in the gap expands and presses the water vapor that nevertheless has succeeded to penetrate into the gap out of it resulting in a dry contact area between the sleeve and the product at the end of the shrinkage process when the sleeve gets into contact with the product. Preferably, the flow of the fluids hitting the product may be adjusted in terms of angle and/or direction to locally obtain heat appropriate for each product spot. Furthermore, more than a single nozzle may be used to cooperate with each other to achieve the required temperature at a specific product spot. To be specific, for each individual product spot, the number of nozzles used, their respective distance and angle with respect to the individual product spot may be controlled.

In a preferred modification (claim 7), the moist air zone includes at least a first moist air chamber and a second moist air chamber arranged in this order in the conveying direction of the product, which are defined by their respective moist air atmospheres individually controllable at least in terms of temperature, humidity and flow. It should be noted that the basic design or constructive concept is modularity. Hence, not only moist air chambers (modules) but dry air chambers (modules) may be inserted between two already existing modules (chambers) (or taken away from that position) in order to lengthen (shorten) the total length of the tunnel and, thereby, adapt it to the specific conditions, i. e. the materials of the sleeve and the product, conveying speed, times within the zones. As already mentioned above, the tunnel consists of a plurality of modules (modular concept) forming chambers inside them. Within the chambers, zones having specific atmospheres or environments are generated that are controllable in terms of their thermodynamic state which again is defined by intensive thermodynamic variables (variously called state variables or state parameters). Intensive thermodynamic variables are variables that are independent from the size of the physical system (tunnel) like temperature and pressure. The concept of state, as a matter of course, presupposes a certain constancy and continuity in terms of the values of the variables.

In a preferred modification (claim 8), a first moist air chamber and a second moist air chamber are separated from each other by a pass through for the product to be conveyed from the first moist air chamber to the second moist air chamber. The pass throughs are adapted to separate adjoining different atmospheres to be controllable individually.

In a preferred modification (claim 9), the dry air zone includes at least a first dry air chamber and a second dry air chamber arranged in this order in the conveying direction of the product, which are defined by their respective dry air atmospheres individually controllable at least in terms of temperature. Especially for dry zones, a pass through therebetween can be dispensed with (see below), resulting in an extended heating zone of uniform temperature and (rest) humidity.

In a preferred modification (claim 10), the moist air zone and the dry air zone are separated from each other by a pass through for the product to be conveyed from the moist air zone to the dry air zone. As noted above, the pass through serves to be able to clearly separate the different zones (atmospheres) generated within the chambers.

In a preferred modification (claim 11 ), the hot air shrink tunnel further comprises an infeed zone arranged ahead of the moist air zone in a conveying direction of the product and including heating means for heating the interior of the infeed zone. Advantageously, the infeed zone is employed as a “pre-heat zone” pre-heating the product to a temperature that is only moderately higher than the ambient temperature, i. e. to about 80°C, for example. Furthermore, the infeed zone has a length of at least 1.000 mm, for example, in the conveying direction in order to ensure work safety.

In a preferred modification (claim 12), the infeed zone and the moist air zone are separated from each other by a pass through for the product to be conveyed from the infeed zone to the moist air zone. To be sure, a pass through between a moist air zone and a dry air zone is essential in view of the significant difference between the environments created therein which is greater than that between principal equal zones, i. e. between two moist air zones or between two dry air zones.

In a preferred modification (claim 13), the hot air shrink tunnel further comprises an outfeed zone arranged after the dry air zone in a conveying direction of the product and including heating means for heating the interior of the outfeed zone. The heating means is configured to evaporate rest condensation that has not yet been removed within the dry air zones.

In a preferred modification (claim 14), the dry air zone and the outfeed zone are separated from each other by a closable/openable pass through for the product to be conveyed from the dry air zone to the outfeed zone. Optionally, the pass throughs are either permanently open having only a small opening surface matching to the outline or contour of the product, or are open only in the very moment the product is moved between chambers and otherwise closed. As a matter of course, in the latter case also, the pass through is as small as possible and correspondingly shaped.

In a preferred modification (claim 15), the pass through is adapted to be closed and opened in the transition of the product from one zone to the next.

In a preferred modification (claim 16), the hot air shrink tunnel further comprises a recycling zone arranged between the moist air zone and the dry air zone which is configured to recycle moist air leaving the moist air zone to an infeed zone arranged ahead of the moist air zone in a conveying direction of the product, and/or to the moist air zone. To this end, a tube or a pipe leading from the recycling zone to the infeed zone and/or a second pipe leading from the recycling zone to the moist air zone may be provided.

As above outlined, the infeed zone is employed as a pre-heat zone pre-heating the product to a temperature that is only moderately higher than the ambient temperature, i. e. to about 80°C, for example. In particular, the energy stored in the recycled moist air leaving the moist air zone may lift the sleeve temperature in the pre-heat zone from room temperature to a shrink start temperature of about 70°C. Therefore, by recycling moist air leaving the moist air zone from the recycling zone to the pre-heat zone, energy required to shrink the sleeve can be saved overall.

In case the energy contained in the moist air leaving the moist air zone into the recycling zone exceeds an amount of energy needed in the pre-heat zone to lift the sleeve temperature from room temperature to a shrink start temperature of about 70°C, the energy of the moist air not needed in the pre-heat zone can be used in the moist air zone to heat up the air, so that energy can be saved overall. Further, as the recycled moist air already contains water (i.e. evaporated water = steam), the amount of water used by the water diffusion means to produce an air-steam mixture in the moist air zone can also be reduced. Alternatively or additionally to using the recycled energy of the moist air leaving the moist air zone into the recycling zone in the infeed zone and/or the moist air zone to heat up air, the energy of the recycled moist air may be used to heat up the (infeed) water used by the water diffusion means in the moist air zone.

Another benefit of the recycling zone is that it creates a structural separation of the moist air zone and the dry air zone. The conditions, i.e. the enviroments, and temperatures in the moist air zone and dry air zone strongly differ from each other. At the end of the moist air zone, the air is moist and has a temperature in the range of 110°C, and at the beginning of the dry air zone, the air is dry and has a temperature in the range of 180°C. By providing the recycling zone, it is possible to prevent the different temperatures and conditions (moist - dry) in the moist air zone and dry air zone from negatively affecting each other. Specifically, the recycling zone prevents moist air entering the dry air zone. As a result, the overall shrink conditions can be improved and better shrink results can be achieved. In a preferred modification (claim 17), in case the moist air zone includes a first moist air chamber and a second moist air chamber arranged in this order in the conveying direction of the product, the recycling zone is configured to recycle moist air to the first moist air chamber.

According to a second aspect of the present invention (claim 16), a method for heat shrinking a plastic sleeve enclosing a product while said product is conveyed through a hot air shrink tunnel according to any one of the preceding claims is characterized in that (i) an air atmosphere within the moist air zone is heated to adjust its temperature to a given target temperature, and (ii) depending on the target temperature, the amount of water diffused in the moist air zone is adjusted so that by latent heat release due to condensation of water on a sleeve surface a desired sleeve surface temperature is achieved. That is, as already pointed out above, the processes of (i) and (ii) are carried out together to achieve the target temperature in cooperation with the lowest possible total energy consumption.

According to a third aspect of the present invention (claim 17), a heat shrinking apparatus for heat shrinking a shrink label enclosing a product comprises a hot air shrink tunnel as recited above, and a conveying means for conveying a shrink label covered product through the hot air shrink tunnel.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is photo showing in a perspective view a hot air shrink tunnel according to the present invention;

Fig. 2 schematically shows a perspective view of a module as part of said hot air shrink tunnel serving to generate a moist or a dry atmosphere inside;

Fig. 3 is a longitudinal section along a conveying or running direction of a product of the module shown in Fig. 2; Fig. 4 is a diagram showing a time-temperature-relationship along the path through the hot air shrink tunnel according to the present invention;

Fig. 5 is a diagram showing a time-temperature-relationship along the conveying direction;

Fig. 6 is another perspective view of the hot air shrink tunnel according to the present invention;

Fig. 7a is a front view of the hot air shrink tunnel according to the present invention;

Fig. 7b is a side view of the hot air shrink tunnel according to the present invention; and

Fig. 8 is a perspective view of a hot air shrink tunnel according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A hot air shrink tunnel (hereafter simply „tunnel“) 10 for a heat shrinking apparatus according to an exemplary embodiment of the present invention is shown in Figs. 1 to 7b.

Fig. 1 is a photo showing, in a perspective view, the tunnel 10 as seen from an infeed side thereof, with an entrance 12 leading into it. Fig. 6 shows another perspective view of the tunnel 10 as seen from an infeed side thereof.

In the tunnel 10, a shrinkage process, in which a plastic film or shrink label (hereafter referred to as „sleeve“) made of polypropylene (PP), polyethylene (PE) or polystyrene (PS), for example, is thermally shrunk onto and brought in tight contact with a product (for example a bottle) in successive stages during the movement of the product in a conveying direction through the tunnel 10.

The heat shrinking apparatus housing the tunnel 10 comprises an infeed module 16, a first nozzle module 18, a second nozzle module 20, a third nozzle module 22, a fourth nozzle module 24, and an outfeed module 25 (only a small part thereof is visible leftmost in Fig. 1 ) that are arranged in this order along a conveyor means 14 (conveying path), which in this exemplary embodiment is lower part of the tunnel 10, in a conveying direction thereof. As shown in Fig. 1 , all modules 16 to 25 straddle the conveyer means 14 thereby “surrounding a conveying path of the produce” as recited above.

Each of the modules forms a specific chamber (or zone in a process-focusing language), as noted above, in which a well-defined atmosphere, that is controllable in terms of intensive thermodynamic variables like temperature, humidity, and - optionally - pressure and that is adapted to carry out a specific part of a shrinkage process, can be created. That is, the term “module” refers to a structural portion of the tunnel 10, while the term “zone” refers to a respective atmosphere generated therein and may be understood in a more functional sense referring in this reading to a part of the shrinkage process.

Therefore, located at the infeed side and at an outfeed side of the tunnel 10 and forming a structural bracket enclosing nozzle modules 18, 20, 22, and 24, are the infeed module 16 and the outfeed module 25 which are not nozzle modules, i. e. modules without any fluid circulating therein. Modules 16 and 25 that form an infeed zone and an outfeed zone, respectively, are configured (i) as functional modules in terms of the shrinkage process in that the temperature is such that condensation takes place (for example, as shown in Fig. 2, in the present embodiment, the temperature in module 16 acting as a pre-heating zone is selected to be 80°C) and (ii) as safety-zones for the workers in charge with the operation of the heat shrinking apparatus. As for module 25, point (i) is realized by means of some sort of heating device in order to remove residual moisture by vaporization, while point (ii) is realized particularly by its relatively long extension of 1000 mm in the conveying direction in this embodiment. The same in terms of safety holds for module 16, as shown in Fig. 2.

As shown in Fig. 2, adjacent two zones (modules) are either connected directly (as zones 3 and 4 in the present embodiment) or coupled with each by a partitioning element 26, having provided therein pass-throughs configured to correspond or to be flexibly adaptable to correspond in size and shape to the product conveyed. That is, nozzle modules 3 and 4 are connected in such a way as to form a combined module having the added lengths of both modules. The pass-throughs are arranged to be open during the movement of the product from one module to the next one in order to keep their respective atmospheres as constant as possible, and are closed again afterwards.

As shown in Fig. 2, in each of nozzle modules 1 and 2 there is created a moist air zone while in each of nozzle modules 3 and 4 there is created a dry air zone, the latter two forming a combined dry air zone of twice the length of a distance that may be called a “standard modular distance” within the modular concept of the present invention. Although not shown in Fig. 2, each of nozzle modules 1 and 2 comprises (a) a heating means, (b) a flow generating means, and (c) a water ejecting means (nozzles) while each of nozzle modules 3 and 4 comprises only (a) and (b). Furthermore, each of modules 16 and 25, being no nozzle modules as already mentioned above, comprises only (a).

In order to get an idea of the size and the temperature regime of the individual modules, as an example, according to the present embodiment, all modules except the infeed module 16 and the outfeed module 25 which each have, as stated above, a length of 1000 mm, have a length in the conveying direction of 500 mm. Furthermore, the pre-heat- temperature in the infeed-zone is about 80 °C, that of zone 1 (first moist air zone) about 90 °C -130 °C, that of zone 2 (second moist air zone) about 90 °C - 170 °C, and that of zone 3 (first dry air zone) and zone 4 (second dry air zone) about 220 °C. As a matter of course, the above data are only to be understood as an example. Specifically, the “standard modular distance” may differ from the above mentioned 500 mm. Furthermore, the modular concept may include modules of different lengths to be flexibly added to various overall lengths adapted to needs and products, for example.

Fig. 3 schematically shows a perspective view of one of said nozzle modules as part of the tunnel 10 in which either a moist or a dry atmosphere is created. Clearly visible are inlets 28 with nozzle-designed tip ends (see Fig. 4).

As shown in Fig. 4, the inlets are directed in a direction perpendicular to the conveying direction in order to generate a circulation in a plane perpendicular to the conveying direction. The atmosphere inside each of the nozzle modules may be circulated by means of a ventilator 32, a top portion thereof extending outside and being visible in Fig. 3. Although not illustrated in the drawings, according to the present invention, an air-steam- mixture is generated individually only inside the respective nozzle modules. As a matter of course, alternatively, the air-steam-mixture may be generated outside thereof.

Fig. 5 is a diagram showing a time-temperature-relationship along the conveying direction. It should be noted that the regions named “pre-heat”, “fixation match”, “move match”, and “finish and dry” are not to be associated in a one-to-one relationship to zones 1 to 4. Instead, the process of shrinking starts with a pre-heat process (“shrink none”) in the infeed module and ends in the outfeed module (“shrink strong and dry”).

The regions shown in Fig. 5 may be defined, exemplarily, according to the following characteristics: (i) product, (ii) product content, (iii) sleeve state, (iv) sleeve characteristic, (v) process, and (vi) length of time.

In line with this definition, the characteristics of the pre-heat-region are: (i) dry and at room temperature, (ii) liquid or granulate at room temperature or product empty, (iii) unstable, undefined contact points with the product, standing on transport belt, (iv) shrinkage time 70°C for 4 s, 80°C for 1 s, 90°C for 0,5 s, 100°C for 0,1 s, melting point 120°C, (v) heating of the sleeve from room temperature to a temperature of 70°C where shrinkage starts, and (vi) 1 s - 4 s.

Similarly, the characteristics of the fixation-region are (i) dry and at room temperature, (ii) liquid or granulate at room temperature or product empty, (iii) unstable, undefined contact points with the product, standing on transport belt, (iv) shrinkage time 70°C for 4 s, 80°C for 1 s, 90°C for 0,5 s, 100°C for 0,1 s, melting point 120°C, (v) very low flow, sleeve temperature 70°C - 80°C, homogeneous condition, high energy, and (vi) 1 s - 2 s second condition time to keep shrink control.

Furthermore, the characteristics of the move-region (where “move” is to be understood as the movement of the shrink label towards the product) are: (i) dry and at room temperature, (ii) liquid or granulate at room temperature or product empty, (iii) stable, defined and firm contact with the product, continuation of movement towards product, (iv) shrinkage time 70°C for 4 s, 80°C for 1 s, 90°C for 0,5 s, 100°C for 0,1 s, melting point 120°C, (v) mild flow, sleeve temperature 80°C - 90°C, homogeneous condition, high energy, and (vi) 1 s - 4 s condition time to keep shrink control.

Finally, the characteristics of the finish-region are (i) dry and at room temperature, (ii) liquid at room temperature, granulate at room temperature or product empty, (iii) stable, even contact with the product, sleeve smoothes out and evaporation of mini droplets, (iv) shrinkage time 70°C for 4 s, 80°C for 1 s, 90°C for 0,5 s, 100°C for 0,1 s, melting point 120°C, (v) high flow, sleeve temperature 90°C - 120°C, homogeneous condition, high energy, and (vi) 2 s - 3,5 s second condition time to get excellent shrinkage and dry products.

Although it is not shown and discussed above, it should be noted that the control and adjustment possibilities to control the heat shrinking apparatus and the processes to be carried out by and within it may be either manually or automatically or a combination of both.

Second embodiment

Fig. 8 shows a perspective view of a hot air shrink tunnel 100 according to a second embodiment of the present invention. The following description focuses on the differences to the exemplary embodiment as shown in Figs. 1 to 7b. Elements of the second embodiment corresponding to elements of the exemplary embodiment have same reference signs.

In contrast to tunnel 10, tunnel 100 comprises a recycling zone 21 arranged between the moist air zone and the dry air zone, in particular between nozzle module 20 and nozzle module 22. A pipe 102 leading from the recycling zone 21 to the infeed zone 16 is provided, through which moist air leaving nozzle module 20 is fed back (recycled) to the infeed zone 16. Further, a second pipe 104 leading from the recycling zone 21 to the nozzle module 18 is provided, through which moist air leaving nozzle module 20 is fed back (recycled) to nozzle module 18. Energy stored in the recycled moist air leaving nozzle module 20 lifts the sleeve temperature in the infeed zone 16 (pre-heat zone) from room temperature to a shrink start temperature of about 70°C. Therefore, by recycling moist air leaving the nozzle module 20 from the recycling zone 21 to the infeed zone 16, energy required to heat up air in the infeed zone 16 can be reduced and thus, energy to shrink the sleeve can be saved overall. Further, by feeding back (recycling) moist air leaving nozzle module 20 to nozzle module 18, energy required to heat up air in the nozzle module 18 can be reduced. Further, as the recycled moist air already contains water (i.e. evaporated water = steam), the amount of water used by the water diffusion means to produce an air-steam mixture in the nozzle module 18 can also be reduced.

Further, the recycling zone 21 creates a structural separation of the moist air zone and the dry air zone, in particular of nozzle module 20 and nozzle module 22. The conditions, i.e. the enviroments, and temperatures in nozzle module 20 and nozzle module 22 strongly differ from each other. In the second embodiment, at the end of nozzle module 20 in the conveying direction of the product, the air is moist and has a temperature in the range of 110°C, and at the beginning of nozzle module 22, the air is dry and has a temperature in the range of 180°C. Furthermore, in order to get an idea of the condition and temperature regime of the further modules in the second embodiment, it should be noted that in nozzle module 18, the air is moist and has a temperature of about 90°C, and in nozzle module 24, the air is dry and has a temperature of about 200°C. By providing the recycling zone 21 , it is possible to prevent the different temperatures and conditions (moist - dry) in nozzle module 20 and nozzle module 22 from negatively affecting each other. Specifically, the recycling zone 21 prevents moist air leaving nozzle module 20 from entering nozzle module 22. As a result, the overall shrink conditions can be improved and better shrink results can be achieved.