Method and equipment for the sealing of a film of wrapping material

Abstract: Method and equipment for the sealing of a film (4) of material for wrapping for products (2), according to which film (4), wrapped about the products (2), which are fed in ordered sequence and arranged at predetermined intervals along a packaging line (3) in order to form a tubular envelope (6) having two specific parts (7,8) respectively defined by two overlapped longitudinal edges (7a,7b) and two opposed walls (8a,8b) included between two adjacent products (2) and destined to be connected by means of a heat seal, is pre-heated at the specific parts (7,8) brushing them by means of a beam (13) of radiant electromagnetic energy.

Description: The present invention relates to a method for the sealing of a film of wrapping material. In particular, the present invention relates to a method for the sealing of specific parts of a film of material for wrapping products in packaging machines, which are fed in ordered sequence and arranged at constant intervals determined along a packaging line, and inside an envelope which is given a tubular shape equipped with two overlapped longitudinal edges obtained by folding the film about each product. The reciprocal sealing of the above mentioned specific parts of the film permits to obtain a sequence of single envelopes hermetically sealed both longitudinally along the longitudinal edges and transversally on the respective end parts, enclosing, each, one relative product. At present, along the advancement path of the packaging line, are envisaged one or more pairs of sealing rollers, which are positioned by apposed bands of the longitudinal edges, which heat and compress them until their reciprocal sealing, and there also being provided a cutting and sealing unit equipped with a pair of opposed rollers which extend transversally, and from bands opposed to the advancement path. Each roller of the cutting and sealing unit is equipped with at least a first and second cutting and sealing head interacting cyclically between each other in such a way as to seal, between each other, the opposed walls of the tubular envelope at a sealing area provided between each pair of adjacent products and, at the same time, to cut the tubular envelope in each transversal sealing area in order to obtain the above mentioned single envelopes hermetically sealed enclosing, each, one relative product. The above mentioned known method for obtaining the sealing both of the longitudinal edges and the walls of the tubular envelope has a drawback due to, above all, the functioning speed of the machine. In fact, when the speed increases the time available for the sealing decreases, and therefore it is necessary to increase the temperature of both the rollers and the sealing heads, but with the films of wrapping material currently used which have a relatively reduced thickness, the risk of burning or of completely melting the films themselves is greater. Such problem also makes the machine rigid, in that the speed reached can no longer be reduced otherwise the film will surely melt, also taking into account that the thermal inertia of the sealing elements is difficult to control. Regarding the sealing of the longitudinal edges, in order to eliminate a similar drawback, more pairs of sealing rollers have been used which are positioned one next to the other along a feeding line in such a way that the sealing of the film comes about gradually. In this way it has been possible to increase the sealing times, the functioning speed being the same and without increasing the temperature of the single rollers but, at the same time, the structure of the machine has become considerably complicated, thus causing an increase of the production and maintenance costs. Furthermore, in this case said solution would only be partial since the tubular envelope has to be sealed also transversally so as to define the single packets. The aim of the present invention is to supply a method which permits to eliminate in a simple and economic way the above mentioned drawbacks. According to the present invention, a method for the sealing of a film of material for wrapping products in packaging machines is supplied, the method comprising the phases of feeding the film along a packaging line wrapped about the products fed in an ordered sequence and arranged at predetermined constant intervals along the same packaging line making a tubular shape envelope wherein at least two types of specific parts, are identified, respectively constituted by two overlapped longitudinal edges and by at least two opposed walls included between each pair of adjacent products, and to connect between each other said specific parts by means of heat sealing; the method being characterised in that said connecting phase comprises a further pre-heating phase of at least one of said two types of specific parts brushing them by means of a beam of radiant electromagnetic energy. Furthermore, the present invention relates to an equipment for the sealing of films of wrapping material. According to the present invention, an equipment is provided for the sealing of a film of wrapping material in packaging machines, of products being fed in ordered sequence and arranged at predetermined constant intervals along a packaging line, the packaging machine comprising advancing means so as to feed the film, along the packaging line, wrapped about the products, thus making a tubular shape envelope wherein at least two types of specific parts are identified respectively constituted by two overlapped longitudinal edges and by at least two opposed walls included between each pair of adjacent products; the sealing equipment comprising a sealing unit for connecting said specific parts between each other by means of heat sealing, the equipment being characterised in that it comprises means shaped in such a way so as to release a beam of radiant electromagnetic energy in order to brush at least one of said two types of specific parts by pre-heating said type of part before it reaches the area of the respective sealing unit. The present invention will now be described with reference to the accompanying drawings which represent a preferred embodiment in the form of a non-limiting example in which: figure 1 shows a schematic perspective view, with some parts removed so as to better evidence others, of a first preferred embodiment of the equipment of the present invention; figure 2 shows a schematic plan view, with some parts removed so as to better evidence others, of a second preferred embodiment of the equipment in figure 1. With reference to the appended figures, 1 denotes as a whole a packaging machine of products 2 fed in an ordered sequence and arranged at predetermined constant intervals (not shown) along its packaging line 3. The packaging machine 1 comprises known means, not shown, for feeding a film 4 of wrapping material along the packaging line 3 according to the direction indicated with F and for wrapping it about the products 2 making a tubular shape envelope 6, and advancing means 5 (only shown in figure 2) capable of moving the envelope 6 forward with the relative products 2. Along the packaging line 3 the products 2 are therefore spaced between each other, in such a way that the envelope 6 also wraps an empty space (not shown) which is created between each pair of adjacent products 2. In the tubular envelope 6 obtained for folding the film 4, two different types of parts are therefore obtained destined to be connected between each other by means of heat sealing, in order to make the sealed packets 19 of the products 2. These parts of the envelope 6 will be referred to in the detailed description that follows as specific parts 7 and 8. In particular, the envelope 6 is equipped with two overlapped longitudinal edges 7a, 7b, positioned below, which constitute the above mentioned specific parts 7 and respectively of two opposed walls 8a 8b positioned transversally to the envelope 6 between each pair of adjacent products 2 which constitute the above mentioned specific parts 8. The opposed walls 8a, 8b are therefore found located in the above mentioned empty spaces. The advancing means 5, for example a pair of rollers, are normally positioned under the packaging line 3 and they act on the overlapped edges 7a, 7b. Downstream from the advancing means 5 a first sealing equipment 9 is provided for the sealing of the specific parts 7 of the film 4, or for the longitudinal sealing of the overlapped edges 7a, 7b of the tubular envelope 6. Downstream from the first sealing equipment 9, a pair of folding rollers and a second sealing equipment 23 are provided for the sealing of the specific parts 8, or for the transversal sealing of the film 4 at the opposed walls 8a, 8b of the tubular envelope 6. In this transversal sealing phase, the part of the tail end of the packet 19 positioned downstream is made and separated from the part of the head end 19a of the packet 19 positioned upstream with respect to the advancement direction F along the packaging line 3. In the description that follows the sealing equipment 9 and 23 will be described, following their position order along the packaging line 3 of the packaging machine 1. With reference, in particular, to figure 2, the sealing equipment 9 comprises a source (10) of radiant electromagnetic energy, and a sealing unit 11. The sealing unit 11 includes a pair of rollers 12 substantially in mutual contact and heated which carry out the sealing of the longitudinal edges 7a and 7b of the envelope 6. The source 10 is capable of releasing a beam 13 of radiant electromagnetic energy which, as will be described in detail in what follows, through appropriate reflection 14 and focusing 115 means, can be exclusively directed towards the specific parts 7 to be sealed and it can be moved along and with respect to said specific parts in such a way as to brush them on all of their surface. The beam 13 released by the source 10 is capable of increasing the temperature of the specific parts 7 until reaching the best possible temperature value in order to permit their subsequent heat sealing by means of the rollers 12. The temperature reached by the specific parts 7 under the action of the beam 13 is lower by a delta t value than the best possible temperature for the sealing of the specific parts 7 by the the rollers 12 rotating at a predetermined angular speed. Said delta t temperature difference corresponds to the heat quantity that the heated rollers 12 are capable of appropriately transmitting to the specific parts 7, during the short period of time in which they are in contact with the specific parts 7 during the phase of their connection by means of heat sealing. In actual practice, the source 10 will brush the specific parts 7 with its own beam 13 and it will increase the temperature to a predetermined value. Subsequently, the rollers 12 will come into contact with the same specific parts 7 and they will increase their temperature by the envisaged delta t value until they provoke their reciprocal heat sealing. The electromagnetical energy released by the source 10 can be of different types, for example it can be electromagnetical energy relative to the part of spectrum which borders with the limit of the red visible radiation or to the part of spectrum which borders with the limit of the violet visible radiation. In the first case there will be, as conventionally known, a beam 13 of ultrared light and in the second case a beam 13 of ultraviolet light. As an alternative, the source 10 can be a source of laser beam. Furthermore, the source 10 can be capable of releasing both a beam 13 of a punctiform type, and of a light-blade type. Both these types of sources 10 are shown as examples in the appended figures, wherein 10a denotes the punctiform source and 10b denotes the light-blade type source. Regardless of the type of source 10 used, as previously mentioned reflection means 14 of the beam 13 towards the specific parts 7 are envisaged. Usually, the reflection means 14 are constituted by a mirror 15. The mirror 15 is interlocked to a pair of actuators (not shown) capable of making it rotate about two axes 15a, 15b perpendicular between each other and it reflects the beam 13 by means of a focusing lens 115 unitedly mobile with the mirror 15 itself. The focusing lent 115 is positioned and structured in such a way that its focus, punctiform in the case of the source 10a and linear in the case of the source 10b, is substantially found at the overlapped edges 7a, 7b in order to obtain the maximum pre-heating efficiency. Always with reference to figure 2, wherein the source 10 has been illustrated relatively to the longitudinal sealing equipment 9, the mirror 15 relative to the punctiform source 10a is made to continuously oscillate about its own axis 15a in order to move the focus of the relative focusing lent 115 along a line transversal to the overlapped longitudinal edges 7a, 7b themselves. The mirror 15 relative instead to the light-blade source 10b is made to oscillate about its axis 15a depending on the amplitude of the light-blade which comes out from the relative focusing lens 115 with respect to the width of the longitudinal edges 7a, 7b. Since the sealing of the longitudinal edges 7a, 7b is made during the advancement of the envelope 6 along the packaging line 3, the mirror 15 is also made to oscillate about its respective axis 15b in such a way as to brush one or more times the same parts of the overlapped longitudinal edges 7a, 7b by means of the beam 13 making the focus of the relative focusing lens 115 move forward and backwards along the overlapped longitudinal edges 7a, 7b themselves. In actual practice, the beam 13 will follow the overlapped edges 7a, 7b. The oscillation of the mirror 15 about the axis 15b permits, as already mentioned, to brush more than once the same areas of the overlapped longitudinal edges 7a, 7b by means of the beam 13. In this way the temperature of the overlapped longitudinal edges 7a, 7b can be raised further in the space of the same period of time so as to reduce the delta t temperature difference between the temperature value reached by the overlapped edges 7a, 7b at the end of the pre-heating phase and the value of the best possible sealing temperature of the same overlapped edges 7a, 7b. This means that the quantity of heat that the rollers 12 have to transmit to the overlapped longitudinal edges 7a, 7b during the sealing phase is reduced. This aspect is particularly interesting since it permits to increase the advancement speed of the tubular envelope 6 much further than the actual limits. On the contrary, that is by increasing the delta t temperature difference, it is possible to intervene on the whole of the sealing phase whenever the packaging machine 1 moves at an operating speed which is lower than that of the standard running speed, for example during the transition periods before the starting or the stopping of the packaging machine 1, and increase the time of the rollers 12 remaining in contact with the overlapped longitudinal edges 7a, 7b. In the appended figures, 16 denotes a control unit to which the source 10 and (in a way that is not illustrated) the movement actuators of the mirrors 15 are interlocked in order to establish the temperature value that the longitudinal edges 7a, 7b have to reach at the end of the pre-heating phase and in order to establish said delta t value. With reference to figure 1, wherein the source 10, has been illustrated relatively to the transversal sealing equipment 23 acting on the specific parts 8, it can be noted that the sealing equipment 23 comprises a source 10 capable of releasing a beam 13 of radiant electromagnetic energy, and a sealing unit 24. The sealing unit 24 is constituted by two sealing heads 17 rotating about axes which are parallel between each other. The two sealing heads 17 are equipped, along their generatrixes, with a pair of sealers 18. Each pair of sealers 18 has an external surface substantially shaped as a cylinder sector and capable of completely covering a respective wall 8a or 8b of the tubular envelope 6. Each pair of sealers 18 acts on the envelope 6 at said empty spaces which are to be found between two adjacent products 2. As already mentioned and with reference to any one of the empty spaces between the two adjacent products 2, each pair of sealers 18 is designed to seal the "tail" of the packets 19 of the product 2 downstream and respectively the "head" of the packets 19 of the product 2 upstream (see figure 1 where, downstream from the sealing equipment 23, a product 2 wrapped in its packet 19 is shown). Between each pair of sealers 18 a blade 20, coupled to one of the sealing heads 17 and a corresponding counterblade 21 coupled to the other sealing head 17 are envisaged. Each blade 20 and the corresponding counterblade 21 separate the packet 19 already complete with the remaining envelope 6 as shown in figure 1. The source 10 is capable of releasing a beam 13 of radiant electromagnetic energy of a punctiform type or of a blade-light type, exactly as in the case of the longitudinal sealing equipment 9. As described and made with reference to figure 2, reflection means 14 constituted by a mirror 15 are provided. Furthermore, the mirror 15 is controlled by two actuators, not illustrated, to oscillate about two axes 15a, 15b which are perpendicular between each other. The mirror 15, as in the previous case, comprises a respective focusing lens 115. The source 10, different from what has already been described with reference to figure 2 and to the longitudinal sealing equipment 9, is intermittently activated in phase synchronism with the passage of the specific parts 8, or of the opposed walls 8a, 8b. In this case the control unit 16 is connected to the sealing unit 24 in such a way as to guarantee the phase synchronism between the movement of the opposed walls 8a, 8b and the activation of the source 10. The mirrors 15 are moved exactly as already described with reference to figure 2 also as regards to the efficiency of tracking of the envelope 6 on behalf of the beam 13. In the appended figures in order to point out the equality of the sources 10 for both the longitudinal 9 and transversal 23 sealing equipment, apart from the continuous or intermittent activation, the same reference has been made. In the appended figures, the folding rollers 22 are also illustrated, which are positioned between the first sealing equipment 9 and the second sealing equipment 23 and they fold the overlapped longitudinal edges 7a, 7b already sealed under the envelope 6 and in close contact with it. In addition, additional check and control means are also part of the packaging machine 1 and of the sealing equipment 9 and 23, which are not illustrated since they are not part of the present invention. The functioning of the sealing equipment 9 and 23 can be easily inferred from what has been described so far and therefore does not require further explanation.

Claims: A method for the sealing of a film (4) of material for wrapping products (2) in packaging machines (1), said method comprising the phases of feeding the film (4) along a packaging line (3) wrapped about the products (2) fed in an ordered sequence and arranged at predetermined constant intervals along the same packaging line (3) making a tubular shape envelope (6) wherein at least two types of specific parts (7,8) are identified, and respectively constituted by two overlapped longitudinal edges (7a,7b) and by at least two opposed walls (8a,8b) included between each pair of adjacent products (2), and of connecting said specific parts (7,8) by means of heat sealing; said method being characterised in that said connecting phase comprises a further pre-heating phase of at least one of said two types of specific parts (7,8) brushing it by means of a beam (13) of radiant electromagnetic energy. A method as claimed in claim 1, characterised in that during said pre-heating phase said beam (13) of radiant electromagnetic energy brushes the same said specific parts (7,8) one or more times depending on the temperature that said specific parts (7,8) have to reach and depending on the advancement speed of said tubular shape envelope (6). A method as claimed in claim 2, characterised in that said beam (13) of radiant electromagnetic energy brushes more than once said specific parts (7,8) advancing and moving backwards along the same mobile specific parts along said packaging line (3). A method as claimed in claim 3, characterised in that said beam (13) of radiant electromagnetic energy brushes said overlapped edges (7a,7b) of said tubular shaped envelope (6) and is released continuously, by activating a control unit (16), towards the same. A method as claimed in claim 3, characterised in that said beam (13) of radiant electromagnetic energy brushes said opposed walls (8a,8b) of said tubular shaped envelope (6) and is released intermittently, by activating a control unit (16), towards the same and in phase synchronism with the advancement of said opposed walls (8a,8b). A method as claimed in claim 1, characterised in that said beam (13) of radiant electromagnetic energy is constituted by a beam of electromagnetic energy relative to the part of the spectrum which borders with the limit of the red visible radiation. A method as claimed in claim 1, characterised in that said beam (13) of radiant electromagnetic energy is constituted by a beam of electromagnetic energy relative to the part of the spectrum which borders with the limit of the violet visible radiation. A method as claimed in claim 1, characterised in that said beam (13) of radiant electromagnetic energy is constituted by a heating laser beam. An equipment for the sealing of a film (4) of wrapping material in packaging machines (1) for products (2), fed in ordered sequence and arranged at predetermined constant intervals along a packaging line (3), the packaging machine (1) comprising advancing means (5) so as to feed the film (4) along the packaging line (3) wrapped about the products (2), thus making a tubular shape envelope (6) wherein at least two types of - specific parts (7,8), are identified, respectively constituted by two overlapped longitudinal edges (7a,7b) and by at least two opposed walls (8a,8b) included between each pair of adjacent products (2); said sealing equipment (9,23) comprising a sealing unit (11,24) for connecting said specific parts (7,8) by means of heat sealing, said sealing equipment (9,23) being characterised in that it comprises means (10) shaped in such a way as to release a beam (13) of radiant electromagnetic energy in order to brush at least one of said two types of specific parts (7,8) pre-heating it before it reaches the area of the respective sealing unit (11,24). An equipment as claimed in claim 9, characterised in that said source (10) of radiant electromagnetic energy comprises reflection means (14) for directing said beam (13) of radiant electromagnetic energy released by said source (10) towards said specific parts (7,8) for brushing them one or more times. An equipment as claimed in claim 10, characterised in that said source (10) is of a type for releasing a punctiform beam (13) and said reflection means (14) are meant to move said punctiform beam (13) according to at least two directions that are inclined between each other for brushing one or more times the same said specific parts (7,8). An equipment as claimed in claim 10, characterised in that said source (10) is of the type for releasing a beam (13) shaped as a blade-light and said reflection means (14) are meant to move said blade-light beam (13) at least according to a right-angled direction to said blade-light shape for brushing one or more times the same said specific parts (7,8). An equipment as claimed in claims 11 or 12, characterised in that said source (10) is continuously activated for brushing between the respective beam (13) of radiant electromagnetic energy a first type of specific parts (7) constituted by said overlapped longitudinal edges (7a,7b) of said tubular shaped envelope (6). An equipment as claimed in claims 11 or 12, characterised in that said source (10) is intermittently activated in phase synchronism with the advancement of said opposed walls (8a,8b) of said tubular shaped envelope (6) for brushing between the respective beam (13) of radiant electromagnetic energy a second type of specific parts (8) constituted by said opposed walls (8a,8b). An equipment as claimed in claim 11, characterised in that said reflection means (14) are constituted by a deflector (15) interposed between said source (10) and said packaging line (3) and oscillating about two respective axes (15a,15b) which are oblique or perpendicular between each other. An equipment as claimed in claim 12, characterised in that said reflection means (14) are constituted by a deflector (15) interposed between said source (10) and said packaging line (3) and oscillating about at least one respective axis (15a,15b). An equipment as claimed in any of the claims from 9 to 12, characterised in that said source (10) is a source of infrared energy for releasing a respective beam (13) of electromagnetic energy relative to the part of spectrum which borders with the limit of the visible red radiation. An equipment as claimed in any of the claims from 9 to 12, characterised in that said source (10) is a source of ultraviolet energy for releasing a respective beam (13) of electromagnetic energy relative to the part of spectrum which borders with the limit of the visible violet radiation. An equipment as claimed in any of the claims from 9 to 12, characterised in that said source (10) is a laser source for releasing a respective laser beam (13).

Inventors: BERTI ANDREA, SPATAFORA MARIO, BERTI, ANDREA, SPATAFORA, MARIO
Applicants: AZIONARIA COSTRUZIONI ACMA SPA, AZIONARIA COSTRUZIONI MACCHINE AUTOMATICHE-A.C.M.A.-S.P.A.
Application year: 1996
Main classification: B65B51
IPC codes: B29C65, B65B51