Abstract:
A method of wrapping an object with a heat-shrinkable material. A sheet of the heat-shrinkable material is heated to its frosting temperature and then fitted around the object like a sleeve so that leading and trailing ends of the sheet overlap and are welded together. The object and the sleeve are allowed to cool to shrink the sleeve onto the object.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a division of copending application Ser. No. 09/454,637 filed Dec. 6, 1999. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a method for packaging objects by means of sheets of heat-shrink material, and a corresponding packaging machine.  
           [0003]    More particularly, the present invention is included in the specific field of operative methods for packaging objects such as boxes or batches of products (e.g. casks, cans, bottles, etc), by means of sheets of heat-shrink material, in which individual sheets are wound in the form of a “sleeve” around corresponding objects to be packaged, in order then to heat-shrink the said sheets onto the corresponding objects, using the so-called phenomenon of “memory” (“resilient memory”) with which specific plastics materials are provided, in order to consolidate the packaging.  
         BACKGROUND OF THE INVENTION  
         [0004]    At present, see for example patents U.S. Pat. Nos. 503,144, 5,203,146, 5,463,846 and patent application IT-BO98A-000277 (correspond to EP-99,105229.1 and US-98.09/271,773) in the name of the same applicant as the present patent application, in order to package objects with sheets of heat-shrink material (for example by means of shrinkable polyethylenes), firstly, a piece of heat-shrink material in sheet form is wound around an object in the form of a “sleeve”, and subsequently, the object-piece assembly obtained, is conveyed by means of a belt conveyor into and through a tunnel oven of the convection type (e.g. with forced circulation of hot air), or of the irradiation type (e.g. with infra-red lamps), which has an intake door and an output door, such as to heat the piece during passage inside the said tunnel, to a specific temperature, which varies in relation to the type of shrinkable material, such as to weld to one another the head portion to the tail portion of the piece, which overlap one another and are disposed beneath the object, in order then, after output from the tunnel oven, during cooling, to shrink the said piece onto the object, as a result of the above-described phenomenon of “memory”, and consequently to consolidate the packaging.  
           [0005]    This method and the corresponding machines have a series of disadvantages.  
           [0006]    A first disadvantage is caused by the fact that an enormous amount of energy is consumed by the said tunnel oven, inside which there must be formed and maintained during operation, forced air circulation at an indicative temperature of approximately 200-250°, such as to heat the piece of heat-shrink material in sheet form, to an indicative temperature of 110-130° C. in acceptable times, i.e. during the period of time which the object-piece assembly takes to travel from upstream to downstream of the tunnel itself.  
           [0007]    In addition, in relation to the above-described disadvantage, it must be emphasised that during operation, the intake door and the output door of the tunnel oven open periodically, in order to permit intake and output of the object-piece assemblies, with consequent dispersion of some kilocalories produced, and thus with a relatively large consumption of energy for production of the said dispersed kilocalories.  
           [0008]    A second disadvantage is caused by the fact that some of the kilocalories produced are absorbed by the conveyor which transports the object-piece assemblies, with consequent energy consumption for production of new kilocalories designed to compensate for the said absorption.  
           [0009]    A third disadvantage is owing to the fact that a further portion of the kilocalories produced is absorbed by the object wrapped, with consequent energy consumption for the production of new calories designed to compensate for the said absorption.  
           [0010]    In addition, in relation to the above-described disadvantage, it must be emphasised that these methods and these devices can be used only to package objects and/or products which, without deteriorating and/or being damaged, can undergo the heating which takes place inside this tunnel oven, i.e. in other words, these methods and these devices cannot under any circumstances be used to package objects and/or products which are degradable in heat and/or heat-sensitive, or inflammable products.  
         OBJECT OF THE INVENTION  
         [0011]    The object of the present invention is to eliminate the above-described disadvantages.  
         SUMMARY OF THE INVENTION  
         [0012]    The invention, which is characterised by the claims, solves the problem of creating a method for packaging objects by means of sheets of heat-shrink material, which are wrapped in the manner of a sleeve around the objects, and shrunk onto the latter, in which the said method is characterised in that it provides the use of a sheet of heat-shrink material which is heated to a temperature which is at least equivalent to its “defrosting” temperature, in that the said heated sheet is wrapped around an object to be packaged in the manner of a sleeve with a front portion and a rear portion of the said sheet overlapping one another; in that the said front portion is welded to the said rear portion of the sheet; and in that the assembly obtained is allowed to cool until the sheet shrinks onto the object.  
           [0013]    In addition, according to one of its variants, the same invention solves the problem of creating a further correlated method for packaging objects by means of sheets of material, which are wrapped in the manner of a sleeve around the objects and shrunk onto the latter, in which the said method is characterised in that it provides the use of a sheet of heat-shrink material heated in a differentiated manner, in which some areas of the sheet are heated at a different temperature from other areas of the same sheet, and in which the arrangement of these areas is selected in relation to the position which the areas themselves assume relative to the object to be packaged, when the said sheet thus heated is wrapped accordingly around the object to be packaged; in that the said sheet of heat-shrink material heated in a differentiated manner is wrapped around the object to be packaged in the form of a sleeve with a front portion and a rear portion of the said sheet overlapping one another; in that the said front portion is welded to the said rear portion of the sheet, and in that the assembly obtained is allowed to cool until different percentages of heat shrinkage are obtained amongst the said areas previously heated in a differentiated manner.  
           [0014]    In addition, the same invention also solves the problem of creating a machine for packaging objects by means of sheets of heat-shrink material obtained from a continuous tape of heat-shrink material, which are wrapped in the manner of a sleeve around the objects and shrunk onto the objects themselves, in which the said machine comprises: first conveyor means, which are disposed upstream and can translate and supply the objects longitudinally along a transport plane; second conveyor means, which are disposed downstream and are slightly spaced relative to the said first conveyor means, giving rise to a first aperture between the said first and the said second conveyor means, which can receive the objects presented by the said first conveyor means and translate them longitudinally along a second wrapping plane, which has an intake end and an output end; third conveyor means, which are disposed downstream and slightly spaced relative to the said second conveyor means, giving rise to a second aperture between the said second and the said third conveyor means, which can receive the objects presented by the said second conveyor means, and translate them longitudinally along a transport plane; wrapping means, which are disposed in the vicinity of the said second conveyor means, including suspended wrapping bars, which are oriented transversely relative to the direction of longitudinal advance of the object, and are translated through the said first and the said second aperture, along an orbital path which circumscribes the second conveyor means, and can transport the sheets of packaging material, for wrapping around the objects to be packaged; supply means, which are disposed beneath and aligned in the vicinity of the said first aperture, and can supply a tape of packaging material; cutting means, which are disposed between the supply means and the said first aperture, and can cut the tape of packaging material transversely; and synchronisation means, which can synchronise the said conveyors and the said operative means with one another; in which the said machine is characterised in that it comprises heating means which are disposed upstream from the said wrapping means in order to heat a cold tape of packaging material to a temperature which is at least equivalent to its “defrosting” temperature.  
           [0015]    By means of use of the method and the machine, which is the subject of the present invention, the following results are obtained: the tunnel oven is eliminated; and the objects to be packaged are not heated.  
           [0016]    The advantages obtained by means of a the present invention consist, substantially, in that there is a reduction of the overall cost of the packaging machine, in that there is an enormous reduction of the energy consumed in order to carry out the packaging, in that a regular shrinkage of the packaging sheet is obtained, and in that even objects and/or products which are heat-sensitive can be packaged with heat-shrink material in sheet form.  
           [0017]    In addition, with reference to the variant embodiments of the operative method which is the subject of the present invention, and the variant embodiments of the packaging machine which is also the subject of the present invention, in addition to the above-described results, the result is obtained of heating a sheet of packaging material in a differentiated manner, in which some areas of the said sheet are heated at different temperatures from the others.  
           [0018]    The advantages obtained by means of the said variants substantially consist in the fact that it is possible to optimise and pre-select the areas of heat-shrinkage of the sheet, in order to obtain cooled packaging which is heat shrunk only in specific areas and not in other areas, as well as packaging which has different required percentages of heat shrinkage in different specific areas, in which the said areas and the said percentages of heat shrinkage are selected in relation to the type or shape of the object to be packaged. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    Further characteristics and advantages of the present invention will become more apparent from the following detailed description of some preferred practical embodiments, provided purely by way of non-limiting example, with reference to the Figures of the attached drawings, in which:  
         [0020]    [0020]FIG. 1 is a schematic perspective view of the packaging machine which is the subject of the present invention, according to a first practical embodiment;  
         [0021]    FIGS.  2  to  10  are schematic lateral views which are designed to illustrate the operative method which is the subject of the present invention, implemented in conformity with the machine in FIG. 1;  
         [0022]    [0022]FIG. 11 is a schematic perspective view of the packaging machine which is the subject of the present invention, similar to FIG. 1, but provided with a further particular device;  
         [0023]    [0023]FIG. 12 is a schematic perspective view of the machine which is the subject of the present invention, similar to FIG. 1, but provided with different operative means;  
         [0024]    [0024]FIG. 13 is a schematic perspective view of the machine which is the subject of the present invention, similar to FIG. 1, but provided with different operative means;  
         [0025]    [0025]FIGS. 14, 14A,  14 B,  14 C and  14 D are schematic views which are designed to illustrate a variant of the method and the machine which are the subject of the present invention; and  
         [0026]    [0026]FIGS. 15, 15A,  15 B,  15 C and  15 D are schematic views which are designed to illustrate a further variant of the method and the machine which are the subject of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]    With reference to the following description, it should firstly be noted that the films of heat-shrink packaging material in sheet form, such as PVC, heat-shrink polyethylenes, LDPEs, etc, have a stretched and frozen molecular structure, such that, if the said films are heated at least to a temperature at which the molecules acquire a specific level of freedom, which is defined here as the “defrosting” temperature, during the cooling stage, as a result of the so-called phenomenon of “memory” or “resilient memory”, the said molecules tend to assume their original orientation, with consequent heat-shrinkage of the film itself.  
         [0028]    In addition, in the case of specific heat-shrink films, the percentile value of the heat-shrinkage depends on the value of the heating temperature, and consequently, the said heating temperature of the film is selected by the user in relation to the percentage of the heat shrinkage to be obtained.  
         [0029]    With reference to FIG. 1, the packaging machine which is the subject of the present invention comprises three conveyors, indicated as  1 ,  2  and  3 , which are disposed in series one after another, and are slightly spaced longitudinally from one another, in order to define a first aperture  4  between the conveyors  1  and  2 , and a second aperture  5  between the conveyors  2  and  3 .  
         [0030]    A first servomotor  6 , of an electric type, actuates a shaft-roller  7 , around which the second conveyor  2  is wound. -At its opposite ends, the said shaft-roller  7  has keyed onto it two respective crown wheel, indicated as  8  and  9 , around which there are wound respective chains  10  and  11 , such that the first chain, indicated as  10 , is wound onto a crown wheel  12 , keyed onto a shaft-roller  13 , around which the first conveyor  1  is wound, and the second chain, indicated at  11 , is wound around a crown wheel  14 , keyed onto a shaft-roller  15 , around which the third conveyor  3  is wound.  
         [0031]    The second conveyor  2  or winding conveyor, is associated with wrapping means, indicated as  16  as a whole, which substantially consist of transverse wrapping bars  17 , which orbit around the said second conveyor  2 , passing through the said first aperture  4  and the said second aperture  5 , wherein the bars  17  themselves have their own opposite ends supported by two respective chains  18   a  and  18   b , which are disposed facing one another, and are wound in respective parallel planes which extend longitudinally and vertically, and are disposed respectively on the two longitudinal sides of the second conveyor  2  itself, wherein the said chains  18   a  and  18   b  are designed to slide inside guide grooves provided by respective frames which are indicated as  19   a  and  19   b , and are illustrated schematically in this case.  
         [0032]    The chains  18   a  and  18   b  are actuated by means of a pair of sprockets  20   a  and  20   b , keyed onto the opposite ends of a single shaft  21 , which in turn is actuated by a second servomotor  46 , which is also of the electrical type.  
         [0033]    Along one side of the conveyor  2 , at a height equivalent to that at which the objects to be packaged  50  are conveyed, there is disposed a position sensor  22 , for example of the opto-electronic type, which extends longitudinally until it meets the transport section configured by the conveyors  2  and  3 .  
         [0034]    In the area beneath the conveyor  2 , in the vicinity of its intake end, there are disposed means for supplying the packaging material, which include cutting means, which are indicated as  23  as a whole, and, disposed further upstream in relation to the direction of supply of a continuous tape  38 - 39 , there are disposed the supply means  25 .  
         [0035]    The cutting means  23  substantially comprise a counter-blade  26  and a blade  27 , which extend transversely relative to the tape  39 , in which the blade  23  is actuated by an actuator  24  of the electromagnetic type and/or pneumatic type and/or of a known type. -These cutting means  25  can also be of the rotary blade type.  
         [0036]    The supply means  25  substantially comprise a pair of rollers  28  and  29 , which are preferably rubberised with particular material, between which the continuous tape  39  is engaged, wherein the roller  29  is actuated by a third servomotor  45 , which is also of the electrical type.  
         [0037]    Upstream from the said supply means  25 , there are disposed heating means, which are indicated as  30  as a whole, and are designed to heat the cold tape  38  which enters cold in the vicinity of the upstream end  30   a  of the said heating means  30 , and is then output heated, as described in greater detail hereinafter, in the vicinity of the downstream end  30   b  of the heating means  30  themselves.  
         [0038]    The heating means  30  comprise a heating drum  31 , which is supported by a shaft  32 , and two return rollers  33  and  34 , wherein the said drum  31  and the said rollers  33  and  34  are oriented transversely relative to the direction F 2  of travel of the tape  38 - 39 .  
         [0039]    By way of example, the aforementioned heating drum  31  can be produced by means of a plurality of thermostatic, resistor-type heaters  35 , which are accommodated in axial holes provided in the vicinity of the shell  36  of the drum  31  itself, with an equidistant circumferential arrangement, wherein the said heaters  35  are interconnected and are supplied by means of sliding contacts  35   b  disposed on the sides of the drum  31 , in order to be able to power supply the said resistors whilst the drum  31  is rotating.  
         [0040]    During functioning of the machine, as described in greater detail hereinafter, the said heater drum  31  heats by means of thermal conduction the cold tape  38  of heat-shrink material which is wound onto the shell  36 , in order then to supply to the supply means  25 , the cutting means  23  and the wrapping means  16 , a heated tape  39  of heat-shrink material, the temperature of which is at least equivalent to the said temperature of “defrosting”, or to a higher temperature, as described in greater detail hereinafter.  
         [0041]    If required, in order to improve the heating of the tape  38 , the heating means  30  can also include a plurality of pressure rollers  37 , which are designed to keep the cold tape  38  pressed against the shell  36  of the said drum  31 , and also, again if required, the said pressure rollers  37  can be hot, such as to heat also the other surface of the tape  38 , and thus heat the tape  38  itself by means of thermal propagation, by conduction, by acting on both surfaces of the tape.  
         [0042]    Again with reference to the heating means  30 , and also if required, it is also possible to make the return roller  34  hot, or to make the return roller  33  hot, or to make both these rollers  34  and  33  hot, again in order to heat the other surface of the tape  38 , and thus to increment the propagation of heat towards the cold tape  38  by thermal conduction, by acting on both its surfaces.  
         [0043]    Upstream from the said heating means  30  there are disposed devices to control the unwinding of the continuous cold tape  38  from the respective bobbin, which devices are not described and illustrated here, since they are beyond the scope of the present invention, and are known to persons skilled in the art.  
         [0044]    Optionally, if required, the third conveyor  3  can have heating-welding means  42 , which, by way of example, can consist of a conveyor belt  3   a , which is wound in a closed path, and is made of flexible, anti-adhesive and heatable material, such as glass-silicon and/or teflon glass and/or similar materials, in which the upper section of the said path is in contact with a heating element  43  beneath, for example an electrical resistance heater and/or an irradiation heater and/or a convection heater, which is designed to heat at least the upper section of the said conveyor belt  3   a , for the reasons which will become apparent hereinafter.  
         [0045]    In addition, the said machine is also provided with a control system (electrical, mechanical, electronic), in order to actuate in phase ratio the various servomotors, actuators and transducers of an electrical/electronic system, such as to vary and regulate the temperature of the resistors  35 , and thus the temperature of the shell  36  of the heating drum  31 , as well as, optionally, if required, of similar electrical/electronic systems, in order to vary and regulate the temperature of the pressure rollers  37 , the temperature of the first return roller  34 , and the temperature of the second return roller  33 ; wherein the temperature of each and/or all of the said elements  36 ,  37 ,  34  and  33  is selected in accordance with the type of heat-shrink material used, in relation with the thickness of the latter, and in relation with the speed of advance of the tape  38 - 39 , since this last variable determines the heating time of the cold material  38  by thermal conduction, as will become more apparent hereinafter.  
         [0046]    With reference to the optional heating-welding means  42 , the said machine is also provided with an electrical/electronic system in order to vary and regulate the temperature of these means, and more particularly the heating element  42 .  
         [0047]    With reference to the drum  31 , it should be noted that the system for obtaining heating of its shell  36  can also be implemented by means of other heating systems (dielectric, by induction, circulation of hot fluid etc), which are designed to heat the said shell  36 , and keep it hot whilst the drum  31  rotates.  
         [0048]    With reference to FIGS.  2  to  10 , the objects  50   a ,  50   b  and  50   c  are supplied in individual succession from upstream in the downstream direction of the machine, with a direction of advance Fl, with longitudinal translation of the objects along the conveyors  1 ,  2  and  3 .  
         [0049]    With reference to FIG. 2, an object  50   a  from the first conveyor  1  is translated onto the second conveyor  2 , whereas a front portion  39   a  of tape  39 , which has previously been heated at least to its “defrosting” temperature or to a higher temperature, by means of the heating means  30  as described in greater detail hereinafter, is being supplied to the initial end of the second conveyor  2 .  
         [0050]    With reference to FIG. 3, when the object  50   a  reaches the position between the first conveyor  1  and the second conveyor  2 , the supply means  23 , which consist of the rollers  28  and  29 , supply the heated tape  39  towards the conveyor  2 , such that the said front portion  39   a  is disposed between the second conveyor  2  and the object  50   a  which is advancing, and during this operation, upstream in relation to the direction of advance of the tape  39 - 38 , the heating means  30  heat the cold tape  38  which is disposed inside the said heating means  30 , and subsequently heat the tape  38  which advances inside the said heating means  30 , during the successive wrapping steps described hereinafter.  
         [0051]    With reference to FIG. 4, the object  50   a  has advanced downstream, with the front portion  39   a  of the heated tape  39  interposed between the base of the object  50   a  and the transport plane of the conveyor  2 , and upwards the transverse wrapping bars  17  of the wrapping means  16  have brought a portion of heated tape  39  above the object  50   a .  
         [0052]    With reference to FIG. 5, when the transverse bars  17  reach a specific position of their path of longitudinal advance in the downstream direction, in which a required length of heated tape  39  has been extracted, the actuator  24  brings the blade  23  against the counter-blade  26 , in order to cut off the tape  39 , thus providing a sheet  40  of heat-shrink material, which is heated at least to the “defrosting” temperature, or to a higher temperature.  
         [0053]    With reference to FIGS. 6, 7 and  8 , the heated sheet  40  thus obtained is wrapped around the object  50   a , and when the object-sheet assembly  50   a - 40  obtained passes onto the third conveyor  3 , the final portion  41  of the said sheet  40  is folded beneath the front portion  39   a  of the sheet  40  itself, see in particular FIG. 8.  
         [0054]    With reference to FIG. 9, the assembly obtained of the object  50   a  and sheet  40  is translated onto the third conveyor  3 , and advanced in the downstream direction, and, optionally, when the said two end portions  39   a  and  41  which are overlapping one another and are pressed onto one another reach the vicinity of the heating means  42  which heat the conveyor  3   a , welding takes place between the two end portions  39   a  and  41  of the sheet  40 .  
         [0055]    Then, see FIG. 10, the sheet  40  which is thus wrapped around the object  50   a , with the end portions  39   a  and  41  welded to one another, is allowed to cool, with consequent heat shrinkage of the sheet  40  itself, and consolidation of the packaging.  
         [0056]    Whilst the above-described operations are taking place, with reference to the object  50   a , again see FIGS.  2  to  10 , upstream from the object  50   a  itself other successive objects  50   b  and  50   c  are gradually being packaged in the manner previously described.  
         [0057]    The heating-welding means  42  which are designed to weld the end portions  39   a  and  41  of the sheet  40  can be eliminated if specific heat-shrink materials and/or specific thicknesses are used, since it is possible to obtain self-welding between the said portions  39   a  and  41 , including by means of simple reciprocal overlapping with pressing, wherein the latter depends on the weight of the object  50  to be packaged. -In order to obtain this effect, the cold tape  38  of material in sheet form can sometimes be heated, again by means of the heating means  30 , to a temperature higher than that of “defrosting”, i.e. to a temperature such as to render the portions  39   a  and  41  self-welding, when they are overlapping one another and are pressed (compressed) beneath the object.  
         [0058]    Longitudinal Stretching  
         [0059]    With reference to the operative method and to the above-described preferred practical embodiment, if it is necessary or appropriate, it is possible to carry out longitudinal stretching of the heated tape  39  before cutting off the sheet  40  and wrapping it around the object  50   a.    
         [0060]    In order to obtain longitudinal stretching of this type, for example, again see the embodiment of the machine illustrated in FIG. 1, for the heating drum  31  a peripheral speed is adopted which is lower than that of the drive rollers  28  and  29 , with consequent longitudinal stretching of the heated tape  39 .  
         [0061]    Transverse Stretching  
         [0062]    With reference to FIG. 11, which illustrates a second practical embodiment of the machine and method which are the subject of the present invention, between the supply means  25  and the heating means  30  there are disposed means for transverse stretching indicated as  53 .  
         [0063]    More particularly, the said means  53  for transverse stretching are of the so-called “rameuse” type, in which two chains or belts  51   a  and  51   b , which are disposed at the longitudinal sides of the tape  39  and diverge in the downstream direction, are provided with respective pluralities of clamps  52   a  and  52   b  which are designed to grasp respectively the two transverse ends of the heated tape  39 , after it has been output from the heating means  30 , in order then to stretch it transversely whilst it is moving in the downstream direction, and thus to present to the supply means  23  a tape  39   c  which is stretched transversely.  
         [0064]    First Variant Embodiment—Means for Heating by Irradiation  
         [0065]    [0065]FIGS. 12 and 12A illustrate a different embodiment of the machine which is the subject of the present invention, in which the heating means  130  are designed to heat the tape  38  by means of thermal irradiation.  
         [0066]    More particularly, in this embodiment, the heating means  130  consist of two supports  130   a  and  130   b , which are hollow internally, have a transverse length equivalent to that of the cold tape  38 , and are designed to support respective pluralities of irradiating lamps, for example infra-red lamps  131   a ,  131   b , which are disposed facing one another, between which the cold tape  38  moves freely, in order to be able to heat the tape by irradiation whilst it is advancing in the downstream direction.  
         [0067]    Second Variant Embodiment—Means for Heating by Convection  
         [0068]    [0068]FIGS. 13 and 13A illustrate a different embodiment of the machine which is the subject of the present invention, in which, schematically, heating means  230  are designed to heat the tape  38  by means of thermal convection.  
         [0069]    More particularly, in this embodiment, the heating means  230  consist of two cases  230   a  and  230   b  which are hollow internally, have a transverse cross-section in the shape of a “C”, are disposed facing one anther, and have a length equivalent to the length of the cold tape  38 .  
         [0070]    The opposite transverse end sides of the said two cases, the end sides  232   s - 232   d  of the case  230   a , and the end sides  234   s - 234   d  of the case  230   b  support ducts, indicated as  235   s  and  235   d , which are connected in a closed circuit to an air heater, not shown, in order to create forced circulation of hot air inside the chambers of the said two cases  230   a  and  230   b.    
         [0071]    Thus, the tape  38  which moves freely between the said two hollow cases  230   a  and  230   b  is heated by the circulating forced hot air, and is thus heated to the required temperature.  
         [0072]    Third Variant Embodiment—Longitudinal Strips Heater  
         [0073]    [0073]FIGS. 14, 14A and  14 B illustrate a different embodiment of the above-described method and machine, which are the subject of the present invention.  
         [0074]    Substantially, with reference to this variant, from a heated tape  339  of heat-shrink material, which is heated in a manner described in greater detail hereinafter, there is obtained a sheet  340  which extends along a longitudinal supply and wrapping axis indicated as “Y”, which has first longitudinal strips  340   b ,  340   d  heated to a first, higher temperature, and second longitudinal strips  340   a ,  340   c  and  340   e  heated to a second, lower temperature.  
         [0075]    The said first and second heating temperatures are thus different from one another, but higher than the “defrosting” temperature, such that, after the said heated sheet  340  has been wrapped in the manner of a “sleeve”, and is in the correct position around an object, after welding to one another has taken place of the reciprocally overlapping front portion  339   a  and the rear portion  341 , and after the said wrapped sheet  340  has been allowed to cool, see in particular FIG. 14B, a heat-shrunk packaging  342  is obtained, which has first longitudinal strips  342   b  and  342   d  which correspond to the original first longitudinal strips  340   b  and  340   d , and are considerably heat-shrunk, i.e. which have substantial accumulation of material, and second longitudinal strips  342   a ,  342   c ,  342   e , corresponding to the original longitudinal strips  340   a ,  340   c  and  340 , which are slightly heat-shrunk, i.e. which have a low accumulation of material.  
         [0076]    In addition, if required, on the cooled packaging  342 , it is also possible to obtain the said longitudinal strips  342   a ,  342   c ,  342   e , free from heat-shrinkage, by using an operative method which does not involve heating the corresponding longitudinal strips  340   a ,  340   c ,  340   e  of the sheet  340 , or which involves heating the said strips  340   a ,  340   c  and  340   d  to a temperature lower than the so-called “defrosting” temperature.  
         [0077]    In order to implement this variant method, by way of example, see FIG. 14, the corresponding machine is provided with different heating means, in this case indicated as  330 , which include a specific heating drum, indicated as  331 , formed from a plurality of cylinders  331   a ,  331   b ,  331   c ,  331   d ,  431   e , which are heated individually, disposed adjacent to one another axially, and separated from one another by a thermal insulating material, wherein the cylinders  331  b and  331  d are heated to a higher temperature than the cylinders  331   a ,  331   c  and  331   e , such that when the cold tape  338  is wound onto the shell formed by the drum  331  in sections  331   a ,  331   b ,  331   c ,  331   d ,  331   e , is heated by thermal conduction, in the above-described differentiated manner.  
         [0078]    This specific embodiment, for example, see again FIG. 14 b , can advantageously be used in packaging of objects such a bottles or similar products, in which the strips  340   b  and  340   d  which are heated most, provided on the tape  339 , and thus on the corresponding sheet  340 , are correctly disposed and spaced transversely such as to be provided on the corresponding batch of bottles, in the vicinity of the areas of separation between the longitudinal rows of the bottles themselves, in order, after the conventional operations of wrapping and heat shrinking, to obtain cooled packaging  342 , which in the areas  342   b  and  342   d  has considerable accumulation of material, with considerable shrinkage, and thus little transparency, and, simultaneously, in the areas  342   a ,  342   c  and  342   e , minimal accumulation of material, with consequent good transparency.  
         [0079]    By this means, the packaging  342  thus obtained has a more pleasing external appearance, and, simultaneously, a potential purchaser who looks at the said packaging can distinguish more clearly the bottles it contains, since the said strips  342   a ,  342   c ,  342   e , i.e. the ones which are more transparent, are disposed against the shafts of the said bottles. -In addition, in this context, it should also be pointed out that any labels which are applied to the shafts of the bottles, and which are correctly oriented towards the exterior before packaging takes place, are more intelligible.  
         [0080]    These specific embodiments, see also FIGS. 14 c  and  14   d , can also advantageously be applied when strips of heat-shrink material which are printed with decorative and/or advertising patterns  370  are used, since it is possible to heat only the areas  340   b  and  340   d , in which the images are not present, without heating the areas  340   a ,  340   c  and  340   e  in which the said images are present, in order, during cooling, to obtain heat shrinkage only in the said non-printed areas  340   b  and  340   d , whereas, on the other hand, in the areas  340   a ,  340   c  and  340   e , in which the printing  370  is present, heat shrinkage, and thus deformation of the said images  370 , is avoided.  
         [0081]    By this means, the patterns  370  do not undergo deformation by heat shrinkage, and are thus perfectly legible and visually attractive even on the heat-shrunk packaging  342 .  
         [0082]    Fourth Variant Embodiment—Transverse Strips Heater  
         [0083]    [0083]FIGS. 15, 15A and  15 B illustrate a different embodiment of the above-described method and machine, which are the subject of the present invention.  
         [0084]    Substantially, with reference to this variant, from a heated tape  439  of heat-shrink material, which is heated in a manner described in greater detail hereinafter, there is obtained a sheet  440 , which extends along a longitudinal supply and wrapping axis indicated as “Y”, which has first transverse strips  440   b ,  440   d  heated to a first, higher temperature, and second transverse strips  440   a ,  440   c  and  440   e  heated to a second, lower temperature.  
         [0085]    The said first and second heating temperatures are thus different from one another, but higher than the “defrosting” temperature, such that, after the said heated sheet  440  has been wrapped in the manner of a “sleeve”, and is in the correct position around an object, after welding to one another has taken place of the reciprocally overlapping front portion  349   a  and the rear portion  441 , and after the said wrapped sheet  440  has been allowed to cool, see in particular FIG. 15B, a heat-shrunk packaging  442  is obtained, which has first transverse strips  442   b  and  442   d , which correspond to the original first transverse strips  440   b  and  440   d , and are considerably heat-shrunk, i.e. which have substantial accumulation of material, and second transverse strips  442   a ,  442   c ,  442   e , which correspond to the original transverse strips  440   a ,  440   c  and  440   e , and are slightly heat-shrunk, i.e. which have low accumulation of material.  
         [0086]    In addition, if required, on the cooled packaging, it is also possible to obtain the said transverse strips  442   a ,  442   c ,  442   e  free from heat-shrinkage, and in this case, according to the operative method, there is no heating of the corresponding transverse strips  440   a ,  440   c ,  440   e  of the sheet  440 , or heating of the strips  440   a ,  440   c  and  440   e  to a temperature lower than the so-called “defrosting” temperature.  
         [0087]    In order to implement this variant method, by way of example, see FIG. 15, the corresponding machine is provided with different heating means, in this case indicated as  430 , which have a specific heating drum, indicated as  431 , formed from a cylindrical sleeve  436 , in which there are embedded peripherally two transverse bars  436   b  and  436   d , which are heated in a manner differently from the remainder of the shell, are disposed spaced circumferentially, and thermally insulated, wherein the said bars  436   b  and  436   d  are heated to a higher temperature than the remainder of the shell  436 , such that the cold tape  438  wound onto the shell formed by the drum  431  is heated in the above-described differentiated manner.  
         [0088]    This particular embodiment, for example, again see FIG. 15B, can advantageously be used in packaging of objects such as bottles or similar products, in which the first transverse strips  440   b  and  440   d , which are heated more, provided on the tape  439 , and thus on the corresponding sheet  440 , are correctly spaced longitudinally such as to be disposed on the corresponding batch of bottles in the vicinity of the areas of separation between the transverse rows of the said bottles, in order, after the above-described operations of packaging and heat-shrinkage have taken place, to obtain cooled packaging  442 , which in the areas  442   b  and  442   d , has a greater accumulation of material with considerable retraction, and thus has poor transparency, and, simultaneously, in the areas  442   a ,  442   c  and  442   e , a lesser accumulation of material, with consequent good transparency.  
         [0089]    By this means, the packaging  442  thus obtained has a more pleasing external appearance, and, simultaneously, a potential purchaser who looks at this packaging can distinguish more clearly the bottles it contains, since the said strips  442   a ,  442   c ,  442   e , i.e. the ones which are more transparent, are disposed against the shafts of the said bottles. In addition, in this context, it should also be noted that any labels applied to the shafts of the bottles, and which are correctly oriented towards the exterior before the packaging takes place, are more intelligible.  
         [0090]    These specific embodiments, see also FIGS. 14C and 14D, can also advantageously be applied when strips of heat-shrink material which are printed with decorative and/or advertising patterns  470  are used, since it is possible to heat only the areas  440   b  and  440   d  in which the images are not present, without heating the areas  440   a ,  440   c  and  440   e  in which the said images are present, in order, during cooling, to obtain heat shrinkage only in the said non-printed areas  440   b  and  440   d , whereas, on the other hand, in the areas  440   a ,  440   c  and  440   e  in which the printing  470  is present, heat-shrinkage, and thus deformation of the said images, is avoided.  
         [0091]    By this means, the patterns  470  do not undergo deformation by heat shrinkage, and are thus perfectly legible and attractive, even on the finished, heat-shrunk packaging  442 .  
         [0092]    With reference to the above-described variants to the method and machine, which are designed to package objects by means of sheets of heat-shrink material heated in a differentiated manner, in general, the operative method used substantially consists in the fact that a sheet of heat-shrink material is used which is heated in a differentiated manner, in which some areas of the said sheet are heated at a different temperature from other areas of the same sheet, in which the arrangement of the said areas on the said sheet is determined in relation to the position which the areas themselves assume relative to the object to be packaged, when the said sheet, thus heated, is correctly wrapped round the object to be packaged, in order then to be able to wrap in a correct position this sheet of heat-shrink material heated in a differentiated manner around the object to be packaged in the manner of a sleeve, with a front portion and a rear portion of the said sheet overlapping one another, to weld the said front portion and the said rear portion of the sheet to one another, and to allow the assembly obtained to cool, until different percentages of heat shrinkage are obtained amongst the said areas previously heated in predetermined areas of the packaging.  
         [0093]    The preceding description of the operative method and of the machine, as well as the descriptions provided of all the variants of methods and machines, are provided purely by way of non-limiting example, and it is thus apparent that there can be made to these methods and machines any changes and/or variants suggested by practice and by their utilisation or use, within the context of the scope of the following claims.