Method and device for sealing a narrow tape to a heatsealable strip

Abstract: The method and device for sealing a narrow tape (2) to a strip (3) of heatsealable material in cigarette packing machines, which produce packets of cigarettes protected by an external wrapper made of plastic which can be torn using the said tear tape; to avoid a thermal degradation in the sections of heatsealable strip adjacent to the sealing zone, the present invention envisages sealing the narrow tape (2) to the strip (3) by passing them through a sealing unit (15), in contact with one another, and joining them with an ultrasound sealer (5) which directs the ultrasound to at least a zone in which the narrow tape (2) and strip (3) overlap; the intensity of the heatsealing action of the ultrasound is controlled and adjusted by elements (6) which detect the feed speed of the narrow tape (2) and strip (3).

Description: The present invention relates to a method for sealing a narrow tape to a heatsealable strip. In particular, the present invention relates to a method for sealing a so-called narrow tear tape to a strip of heatsealable material intended, in particular, for use in the creation of a protective external wrapper for cigarette packets in machines which produce the said packets. As is known, when a cigarette packet of the afore-mentioned type must be opened, the tear tape allows the external wrapper (also commonly known as the overwrap) on the packet to be torn in an easy and immediate manner. The application by heatsealing of a narrow tear tape to a strip of wrapping material is common practice in the sector for the machines or systems which produce cigarette packets, exploiting the physical characteristics of the strip of material envisaged to form the external wrapper, or overwrap. For example, the application for a British patent No. GB-A-2 290 498, dated 30 May 1995, envisages that a narrow tear tape and a strip of wrapping material be fed in a continuous manner to sealing means which consist of a heating plate with ring-crown shaped sectors and operates in conjunction with a sector of a rotating drive roller which, at least at the said sector, sucks both the narrow tape and the strip against its revolving surface. The plate, which is kept at a preset operating temperature, heats the narrow tape and the strip until they are sealed together. The above method is not very flexible faced with variations in the feed speed of the narrow tape and the strip of heatsealable material. In fact, the feed speed of the said narrow tape and strip may drop temporarily for various reasons. As a result, the time for which the narrow tape and strip remain between the drive roller and the sealing means increases, and may result in excessive, unwanted fusion of the materials on some areas of the narrow tape and strip. Moreover, given that the strip of wrapping material is much wider than the tear tape, the former is also subjected to significant thermal stress in the areas adjacent to the zone sealed to the tear tape. The said phenomenon may lead to a thermal degradation in the material in these areas. The portions of the wrapping strip near to the tear tape which do not actually overlap the latter are thinner than the sealing zone where the tear tape and the strip overlap, and so, even if they absorb the same amount of heat, they are less resistant to thermal degradation than the sealing zone. To reduce the risk of damage to the portions of strip adjacent to the sealing zone, the operating temperature of the sealing means must be reduced, leading to an increase in the amount of time for which the tear tape and strip must be held in front of the sealing means and, ultimately, slowing down the process. It may also happen that the portions of strip adjacent to the sealing zone are easily wrinkled and creased by the heat to which they are subjected. It is also known from document WO-A-8909730 a method and apparatus for bonding tear-open system to packaging film in tape form. In particular the invention relates to a method and apparatus for bonding a twisted yarn consisting of thermoplastic fibers to the inner surface of a packaging film in the tape form in place of a conventional cut tape by use of ultrasonic sealing apparatus or a high frequency sealing apparatus. The main object of the present invention is, therefore, to overcome the afore-mentioned disadvantages. The present invention provides a method for sealing a narrow tape to a heatsealable strip, especially in cigarette packing machines, as described in claim 1. Some advantages of the present invention are its speed, the notable flexibility to variations in the feed speed of the narrow tape and strip, and the reduced thermal stress on the portions of strip adjacent to the zone in which it is sealed to the tear tape. The present invention also relates to a device for sealing a narrow tape to a heatsealable strip, especially in cigarette packing machines, as described in claim 3. The technical features of the present invention are described in the detailed description below, with reference to the accompanying drawings, which illustrate an embodiment by way of example only, and in which: figure 1 is a perspective view of the overlap between the tear tape and the strip of wrapping material to be sealed together; figure 2 is a schematic perspective view of a cigarette packet externally protected by a wrapper which has a tear tape; figure 3 is a schematic side view of a first possible embodiment of the device disclosed for the actuation of the invention disclosed; figure 4 is a schematic side view of a second possible embodiment of the device disclosed for the actuation of the invention disclosed. With reference to the accompanying drawings, the number 1 denotes a device for sealing a narrow tape 2 to a strip of heatsealable material 3; the narrow tape 2 and strip 3 arriving together at a sealing unit, denoted by 15, as shown in figure 1. The strip 3 of heatsealable material is the strip of wrapping material from which the sections intended to form the wrappers 12 for cigarette packets 11 are taken, whilst the tear tapes 13 for the wrappers 12 are taken from the narrow tape 2 (see figure 2). As is known, to open a packet 11, a free, deliberately unsealed tab of the tear tape 13 can be gripped and pulled to unwind the tear tape 13; in this way the tear tape 13 tears the wrapper 12, dividing it into two parts, at least one of which, illustrated with a dashed line in figure 2 and which may be defined the top of the wrapper 12, can then be removed from the packet 11 so that the packet may be opened and the cigarettes removed. The sealing unit 15 has ultrasound heatsealing means 5, located on the trajectory followed by the narrow tape 2, in contact with the strip 3 and at the same feed speed, along a path which leads through the sealing unit in a direction indicated by the arrow 7 in figures 3 and 4. The said ultrasound heatsealing means 5 are envisaged configured and angled in such a way that they operate only upon the zone where the narrow tape 2 and the strip 3 overlap, and usually include a sealer with a generator, designed to send an alternating current with preset frequency to a sound vibration transducer. The ultrasound is usually directed, within certain limits, to a zone in which the narrow tape 2 and the strip 3 overlap by a width approximately equal to the width of the narrow tape 2. Moreover, the heatsealing means 5 are controlled and checked by at least one sensor 6 attached to the timing shaft of the cigarette packing machine or system, or to a rotating axis which is kinematically connected to the timing shaft and is part of the feed and handling means of at least the narrow tape 2 or strip 3. The said sensor 6 detects the feed speed of the narrow tape 2 and/or the strip 3, as well as automatically adjusting the ultrasound sealing intensity according to this speed, by means of a logic unit 18. The sensor 6, which may include, for example, a decoder attached to the afore-mentioned timing shaft, acts upon the frequency of the generator. Supporting means 4 are envisaged at the heatsealing means 5, so that the overlapping narrow tape 2 and strip 3 are fed to the sealing unit 15 between the supporting means 4 and the ultrasound heatsealing means 5. In the embodiment illustrated in figure 3, the supporting means 4 consist of a fixed element 9, whilst in the embodiment in figure 4, they consist of the curved surface of a rotating cylinder 10 with axis normal to the feed trajectory of the narrow tape 2 and strip 3 where they pass through the sealing unit 15. In this case, the unit 15 is defined by a concave sealing surface 16, set opposite the afore-mentioned curved surface of the cylinder 10 and with a radius of curvature substantially equal to the radius of the cylinder 10 itself. The infeed of the sealing unit 15 may be fitted with at least one pair of opposite guide rollers 17, between which both the narrow tape 2 and the strip 3 are passed. The curved surface of at least one of the said opposite rollers 17, usually that located on the same side as the narrow tape 2, may have at least one groove which extends over the entire circumference to house the narrow tape 2 and guide it towards the sealing unit 15.

Claims: A method for sealing a narrow tape (2) to a heatsealable strip (3), especially in cigarette packing machines, the method including the phase for feeding the narrow tape (2) and heatsealable strip (3) to a sealing unit (15) in such a way that they arrive at the sealing unit (15) overlapped and correctly positioned, said narrow tape (2) being sealed to the heatsealable strip (3) by feeding the narrow tape (2) and the strip (3), in contact with one another and at the same speed, through the said sealing unit (15), joining them with a heatsealer (5) located along the trajectory followed by the narrow tape (2) characterised in that said heatsealer is an ultrasound sealer which direct the ultrasound at least in a zone where the narrow tape (2) and the strip (3) overlap and in that said method comprises the phase of checking the ultrasound sealing intensity with means (6) which control the sealer (5), detect the feed speed and automatically adjust the ultrasound sealing intensity according to the said speed. The method for sealing a narrow tape (2) to a heatsealable strip (3) as described in claim 1, characterised in that the narrow tape (2) is sealed to the heatsealable strip (3) by feeding the narrow tape (2) and the strip (3), in contact with one another and at the same speed, through the said sealing unit (15), joining them with an ultrasound sealer (5) located along the trajectory followed by the narrow tape (2) so as to direct the ultrasound at least to a zone where the narrow tape (2) and the strip (3) overlap by approximately the width of the narrow tape (2). A device for sealing a narrow tape (2) to a heatsealable strip (3), especially in cigarette packing machines, the device including: means for feeding the said narrow tape (2) and heatsealable strip (3), designed to make the narrow tape (2) and the strip (3) overlap; heatsealing means (5), attached to a sealing unit (15) located on the trajectory followed by the narrow tape (2) which overlaps the strip (3) and is fed with it at the same speed along the path through the said sealing unit (15), characterised in that the heatsealing means (5) is an ultrasound sealer envisaged configured and angled so as to act only upon the zone in which the narrow tape (2) and the strip (3) overlap, and in that the heatsealing means (5) are also controlled and checked by at least one sensor (6), said sensor being attached to a timing shaft on the machine, or to a rotating axis kinematically connected to the said timing shaft and forming part of the feed means for the narrow tape (2) or the strip (3), or both, the sensor being able to detect the feed speed as well as automatically adjust the intensity of ultrasound sealing according to the said speed. The device as describad in claim 3 characterised in that the ultrasound heatsealing means (5) include a generator designed to send an alternating current at a preset frequency to a sound vibration transducer, and in that the sensor (6) acts upon the said frequency. The device as described in claim 3 or 4, characterised in that it includes supporting means (4), these means being located at the heatsealing means (5) so that the overlapping narrow tape (2) and strip (3) are fed to the sealing unit (15) between the supporting means (4) and the heatsealing means (5). The device as described in claim 5, characterised in that the supporting means (4) consist of the curved surface of a cylinder (10) with axis normal to the feed trajectory of the narrow tape (2) and the strip (3) where they pass through the sealing unit (15); and characterised in that the means (5) have a sealing surface (16), being opposite the curved surface, and being concave with a radius of curvature substantially equal to the radius of the said cylinder (10), the concavity intended to match the zone of the curved surface opposite the sealing body (15). The device as described in any of the claims 3 to 6, characterised in that it includes, at the infeed of the sealing unit (15), at least one pair of opposite guide rollers (17) for the narrow tape (2); both the narrow tape (2) and the strip (3) being passed through the said rollers (17), the curved surface of at least one of the opposite guide rollers (17) having at least one groove which extends over the entire circumference to house the narrow tape (2) and guide it towards the sealing unit (15).

Inventors: DRAGHETTI FIORENZO, STIVANI EROS, DRAGHETTI, FIORENZO, STIVANI, EROS
Applicants: GD SPA, G.D. S.P.A.
Application year: 1996
Main classification: B65B61
IPC codes: B29C65, B31B1, B65B61