METHOD AND DEVICE FOR SEALING PACKAGES OF THERMOPLASTIC MATERIAL

Abstract: Packages (2) preferably joined in a belt (1) of weldable thermoplastic material display two opposite walls (5, 6) which are joined to edge portions (10, 11) in the vicinity of the openings of the packages. In accordance with the invention the material is heated to a welding temperature in ribbon-shaped, opposite regions (12, 19) in the vicinity of the openings of the packages during the enclosure of both the regions between two pressing ribbons. The material in the ribbon-shaped regions is pressed together by the pressing ribbons, whereby a ribbon-shaped welded region (120) is formed and the packages sealed. In a central area (121) within the welded region the pressing ribbons displace materials, whereby separation of the edge portions (10, 11) from the sealed packages is obtained or made possible.

Description: Method and device for sealing packages of thermoplastic material The present invention relates to a method and a device for both seal¬ > ing of packages, preferably forming part of a belt, of weldable ' » thermoplastic material whereby the packages display two opposite walls, and separation of superfluous packaging material from the 5 sealed packages. In particular, the invention relates to sealing the packages by welding them together in ribbon-shaped regions close to the openings of the packages, and thereafter separating superfluous material from the packages. US Patent No. 4 260 447 reveals a device for sealing plastic bags, 10 where the latter are introduced by their upper portion between two pairs of V-belts, between which the walls of the bag are fixed, whereby the walls of the bag are uncovered in the space between the pairs of V-belts, and thereby accessible for heating and welding to¬ gether. When welding the walls together a contact pressure is 15 achieved between the walls of the bags in a heated region in that a wheel with a peripheral flange displaces the material at right-angles to the direction of displacement of the bags. The weld is then cooled and a knife cuts away excess material by means of a cut in the actual weld. The solution shown in the publication produces internal stres- 20 ses into the material in the heating, stretching and welding proce¬ dures, which stresses cause the weld to become more or less wrinkled due to the fact that the inbuilt stresses contact the weld during the cooling procedure. The purpose of the present invention is to achieve an improved method 25 and an improved device for sealing filled packages of thermoplastic material. The invention makes it possible to achieve a completely wrinklefree seal. OMPI The required result is obtained by means of a method that is revealed in claim 1 and by means of a device that is revealed in claim 6. The invention is decribed in greater detail in conjunction with a number of figures, where: fig. 1 shows a belt viewed from the side, fig. 2 shows an enlarged detail of the marked region II-II in fig. 1, fig. 3 shows a device in accordance with the invention viewed from above, fig. 4 shows the section IV-IV in fig. 3, figs. 5 - 8 show the sections V-V, VI-VI, VII-VII and VIII-VIII in fig. 3 and fig. 9 shows an enlarged detail of the region marked by IX in fig. 7. Figs. 1 and 2 disclose a section of a continous belt 1 of thermo¬ plastic material with a number of packages 2. The belt has been formed by folding a wider belt of material along its centre line 3 for the formation of the bottom portion 4 of the packages which in figure 1 is shown in an embodiment with a folded-in bottom during the formation of the lower edge 38 of the belt. The opposite walls 5,6 obtained by folding are joined to one another at regular intervals for the formation of connection zones 7,8 which extend at right- -angles to the bottom portion 4 of the packages. The connection OAΪPI zones, which can be formed by welding or glueing or by some other suitable manner, delimit each package laterally and extend from the bottom portion 4 up to an upper site that is located at a predeter¬ mined distance from the upper edge 9 of the belt. The continous belt further includes two longitudinal edge portions 10,11 which comprise the upper regions of the walls obtained by folding. In or between the connection zones 7,8 there are vertical slotted portions 14 disposed, whereby each slotted portion in certain embodi¬ ments is interrupted by one or more flaps 15 that retain the packages in a continous line. Moreover, in certain embodiments horizontal slotted portions 16 are disposed in the region of the transition between the packages and the upper edge portions 10,11, whereby these horizontal slotted portions 16 are located next to the vertical slotted portions 14 and are joined thereto in the shape of a T. As will be evident from fig. 1, two adjacent horizontal slotted portions 16 are disposed at a distance from one another. The slotted portions are disposed in the two walls 5,6. In certain embodiments certain or all slots 'are replaced by perforations. Figures 1 and 2 further show the two wall portions 10,11, formed in their upper edges with double walls of material 17,18 which have been formed in that the belt of material before passing into a seal¬ ing device in accordance with the invention, has been disposed with tunnel-shaped support devices which had interacted with special guide devices over which the tunnel-shaped support devices slid as the belt passed by a filling station. In conjunction with the belt leaving this filling station, the tunnel -shaped support devices were cut open, whereby the double material walls 17,18 shown in the figure were produced. The embodiment with double material walls is on its own account only of importance in the application of the invention in OΛ-PI embodiments where the sealing device in accordance with the invention interacts directly with a filling station supporting the belt by means of the aforesaid support devices. Fig. 2 shows in dashed lines ribbon-shaped regions 12,19 in which the material walls in a belt in a device in accordance with the invention are heated in order for the walls to be welded together, and the packages thereby sealed. The reference designation 120 further indi¬ cates the welded region which thus occurs, and the reference designa¬ tion 121 a central region of this welded region. In the central region the material thickness has been reduced after welding together of the walls in that material has been moved to one side. The central region 121 either separates the filled and sealed packages from the longitudinal edge portions 10,11 or causes sufficient weakening of the connection between the packages and the edge portions so that a later separation should easily be able to take place by simply pulling apart the packages and the edge portions. Once the central region 121 is formed the sealed package is in principle completed. Figures 3-9 disclose a frame 42 on which there are disposed next to one another drive wheels 43,44 for both two retaining ribbons 80 and 81 forming endless loops, and two pressing ribbons 40 and 41 of e.g. Teflon material; they too forming endless loops. The retaining ribbons and pressing ribbons turn over their own trailing wheel 85,86 and 45,46, respectively. The retaining and pressing ribbons form pairwise loop portions 800, 810 and 400, 410, respectively, that run parallel to one another, and at a distance from one another adapted to the thickness of the material belt in order to fix the belt under a certain compression of the material therein. The retaining and pressing ribbons are further so located that a smaller distance is formed between adjacent retaining and pressing ribbons. In the figures the retaining ribbons are shown located below the pressing "BUREA Oft'.PI ribbons. In the drive wheels 43, 44 the peripheries of the contact surfaces for the retaining ribbons, and the pressing ribbons, and the rotational speeds of the wheels are so selected that the speeds agree in the loop portions 800, 810 and 400, 410, respectively, of the re- 5 taining ribbons and pressing ribbons. The direction of rotation of the drive wheels 43,44 is so selected that the pressing ribbons in the parallel loop portions 400,410 are displaced from the trailing wheels 45,46 towards the drive wheels. The frame is preferably designed with two plates 422,423 level with 10 one another and separated by a continous aperture 424 which in the figures is located below the parallel loop portions 800, 810 of the retaining ribbons 80,81. As the packages pass through the device the aperture section of the packages that is compressed by the retaining ribbons is located in the continous aperture, while the remaining and 1 . 5 normally filled portion of the packages is located below the conti¬ nous aperture with the orientation shown in the figures. The heating and welding devices, hereinafter termed welding devices, 50,51 are disposed on each side of the loop portions 400, 410 of the pressing ribbons 40,41 that run parallel to one another. The welding 0 devices are further journalled for motion towards one another during enclosure of the pressing ribbons. In the embodiment shown in the figures the welding devices have a continous shape along the loop portions 400, 410 ' , and are rotatably journalled in journalling de¬ vices 54,55 in the vicinity of the ends that are located nearest the 5 trailing wheels 45,46. The welding devices are pressed against one another by means of springs 52,53. In the embodiment shown in the figure the welding devices are disposed with ducts 500,510 for a heating fluid. Other known heating devices are also applicable within the scope of the invention. " BUR£ Immediately after the welding devices separating devices 60,61 (cf fig. 7) are disposed in the direction of motion of the loop portions 400, 410. The separating devices comprise in the embodiment shown two free-running wheels 64,65 which are ' pressed against one another by a spring 62 during enclosure of small regions of the loop portions 400,410 of the pressing ribbons. One of these wheels has preferably a slightly rounded peripheral surface 640 while the other has prefera¬ bly a relatively narrow peripheral surface 650 for interaction with the rounded surface. In certain embodiments at least one of the pulleys is replaced by a stationary mechanical device with an anti- -f riction coated surface for abutment against the pressing ribbons. In the embodiment shown in the figures cooling devices 70,71 are disposed immediately after the separating devices in the direction of motion of the loop portions 400,410. The cooling devices are also pressed against one another by means of springs 72,73 during enclo¬ sure of the pressing ribbons (cf fig. 8). The cooling devices are disposed with cooling ducts 700,710 for conduction of thermal energy from the cooling devices and the heated thermoplastic material. It will be evident from figures 5-8 that the retaining ribbons 80,81 are located with their loop portions 800,810 in preferably continous grooves 420,421 disposed in support plates 425,426 attached to plates 422,423 in the frame and located close to the continous aperture 424. A number of springs 47,48 are disposed in the grooves in order to press the loop portions 800,810 against one another during enclosure of the material in the belt of blanks and fixing of the latter. Fig. 3 further shows a belt 1 passing into the device in the π ' ght- -hand section of the figure and sealed packages emerging from the device in the left-hand part of the figure. When the belt is passing 15URE4 " through the device the longitudinal edge portions 10,11 of the belt protrude above the loop portions 400,410 of the pressing ribbons 40,41. These protruding edge portions have however, in order to render the figure clearer, been omitted in respect of that part of the belt that is compressed by the pressing devices. Likewise for the same reasons, in the figure as in figure 4, the loop portions 400,410 of the pressing ribbons and the loop portions 800,810 of the retain¬ ing ribbons are completely or partially omitted. A belt 1 is inserted between the retaining ribbons 80,81 (cf fig. 5) which press the material walls of the belt against one another and fix the belt. When the retaining ribbons are displaced successive portions of the belt are continously drawn into the device. During the continuing leftwards motion of the belt in fig. 3 the longitudinal edge portions 10,11 are inserted between the pressing ribbons 40,41 which enclose the edge portions and during continuing motion insert the enclosed edge portions between the welding devices 50,51. The welding devices displace the pressing ribbons against one another whilst simultaneous fixing the material in the belt and heat¬ ing the material in the ribbon-shaped regions 12,19. In the disclosed embodiment the journal ling of the welding devices and the design of their contact surfaces against the pressing ribbons ensure that the force for compressing material walls is at its greatest when the belt is in the final stage of its passage of the welding devices, which in turn ensures a secure and reliable welding together of the material walls for the realisation of the ribbon-shaped welded region 120. While continuing to be fixed by means of the pressing ribbons 40,41 the still warm welded region 120 is moved in between the free-running wheels 64,65 of the separating device 60 (cf fig. 9), which wheels are pressed against one another by the spring 62, thereby deforming the pressing ribbons in two opposite local regions, whereby the ϊURE OMPI - distance between the pressing ribbons is reduced preferably to an extent causing the pressing ribbons to abut one another. The still warm material in the ribbon-shaped welded region 120 is thus dis¬ placed into the central part 121 of the region, at the same time as the sealing of the package which the welded region has made is re¬ tained intact. The filled and sealed packages are thus separated from the longitudinal edge portions 10,11, whereby the sealed package is in principle completed. Alternatively, there remains such a weak con¬ nection to the longitudinal edge portions 10,11 that a later separa- tion is achieved if the packages and the edge portions are drawn apart. The sequences described in the immediately preceding paragraphs are revealed in fig. 2 where the right-hand part of the figure contains the ribbon-shaped regions 12,19 in which the welding devices 50,51 raise the material temperature to a welding temperature, and where the left-hand half of the figure contains the ribbon-shaped welded region 120 and the central region 121 of reduced material thickness. With retained fixing of the blank walls in the welded region, the belt is moved in between the cooling devices 70,71 where the material in the weld region is cooled down to primarily room temperature. The completed packages and the normally separated edge portions 10,11 then leave the device when the pressing ribbons and the retaining ribbons relax their grip around the separated edge portions and the sealed packages respectively. The edge portions are then preferably wound onto rollers while the completed packages, preferably supported by a conveyor belt, are carried away from the device. The fixing of the material walls which is achieved by the retaining ribbons 80,81 in combination with the pressing ribbons 40,41 ensures that as the material belt passes through the device the distribution which the material has in the belt when the material in conjunction with its insertion in the device is fixed between the retaining ribbons 80,81 and the pressing ribbons 40,41, is primarily retained. This fixing ensures that any possible internal stresses that have been built into the material in conjunction with its passage through the device are not allowed to deform the weld or the region around it. As the material cools down to room temperature the internal stresses are "frozen" and the potential of the material for permanent changes in shape ceases. The pressing devices also operate as forming devices that ensure an even residual weld for sealing the package as the separating device displaces material in the ribbon-shaped welded ' region. In a preferred embodiment of the invention the device described here¬ tofore is preceded by devices (e.g. a filling device of the type that is described in the international application PCT/SE81/00187 with publication No. WO 82/00129) which cause the material in the belt to be subjected to stretching forces, at least in the vicinity of the longitudinal edge portions of -the belt, thereby obtaining a certain longitudinal extension in the belt in conjunction with its insertion into the device. This ensures that the material in the blank walls, prior to its being fixed between the retaining ribbons 80,81 and the pressing ribbons 40,41, is smooth and without wrinkles. The continous fixing of the distribution of the material as it passes through the device, described in the preceding paragraph, ensures that despite any stresses which may have been built into the material through stretching, an even and smooth sealing weld is obtained in the com¬ pleted package. The invention is described above in conjunction with sealing of packages joined in a belt. It will however be evident from the de- scription that the invention as such is also applicable in the case of individual feeding of packages into the device described. In the embodiment of the invention where the blank material is prestretched prior to feeding into the device such prestretching is achieved in the case of individual feeding of packages by means e.g. of two pairs of elastic ribbons, which once they have fixed the material in the package are stretched during simultaneous extension of the material in the package. The pressing ribbon then fixes the packages in their stretched state in a region between the two pairs of elastic ribbons before the packages are loosened from the elastic ribbons. Embodiments of the invention have been described above in which the material in the packages is stretched in the direction of movement of the packages prior to insertion in the device. The idea of the inven¬ tion as such is however not restricted to the direction of stretching described but is also applicable in the case of other directions of stretching. The introductory section of the description has already described a number of embodiments of the invention. In addition to the embodi¬ ments described the invention is adaptable to a large number of embodiments within the scope of the claims.

Claims: CLAIMS 1. Method of sealing packages (2) preferably forming part of a belt (1) where the packages display two opposite walls of thermo¬ plastic material which comprise longitudinal edge portions (10,11) at the openings of the packages, and connected with opposite walls (5,6) of the packages, whereby for sealing the packages ribbon-shaped opposite regions (12,19) adjacent to the openings are gradually enclosed between loop portions (400,410) of two pressing ribbons (40,41), in addition to which the mate¬ rial in the enclosed regions (12,19) is heated to a welding tem- perature and the regions joined to one another by compression, whereby a ribbon-shaped welded region (120) is formed that seals each individual package, characterised in that for separation of the longitudinal edge portions (10,11) from the packages the material thickness in a central region (121) of the ribbon- -shaped welded region (120) is reduced by means of mechanical devices and with the material in a warm state. 2. Method as claimed in claim 1, characterised in that the material in the ribbon-shaped regions (12,19) as well as in adjoining regions is fixed between pressing ribbons (40,41) during heating of the material in the ribbon-shaped regions (12,19). 3. Method as claimed in claim 1 or 2, characterised in that the material in the opposite regions (12,19) is stretched before it is fixed in a stretched state between the loop portions (400,410) which fixing is removed when the weld formed on each package has been cooled. 4. Method as claimed in any of claims 1-3, characterised in that the opposite regions (12,19) enclosed and fixed in the loop portions (400,410) are moved continously by means of loop move¬ ments in the pressing ribbons (40,41). O 5. Method as claimed in any of claims 1-4, characterised in that the packages (2) are moved in between the pressing ribbons (40,41) in that tensile forces imparted in the direction of movement of the blanks are applied to the edge portions (10,11). 5 6. Device for sealing packages (2) where the device includes two endless flexible pressing ribbons (40,41) with parallel loop portions (400,410) close to one another and running in the same direction, between which during movement the packages (2) are, in the vicinity of their openings, enclosed and fixed, and weld- 10 ing devices (50,51) for formation of a ribbon-shaped welded region (120) in the vicinity of each package opening as well as of edge portions (10,11) outside the welded region, in addition to which the device preferably includes cooling devices (70,71), characterised in that a separating device (60,61) is disposed at ■ J5 the loop portions (400,410) and seen in the direction of move¬ ment of the packages after the welding device (50,51), that the separating devices are disposed for abutment against a local region of the loop portions (400,410) running between them, for setting the distance between the loop portions in the local 20 region to a value below that of the total material thickness of the welded region (120), by which means the separation of the longitudinal edge portions (10,11) is obtained or made possible. 7. Device as claimed in claim 6, characterised in that the heating and welding devices (50,51) and the cooling devices (70,71), 5 respectively, are disposed at a mutal distance adapted to the thickness of the pressing ribbons (40,41) as well as the materi¬ al in the packages (2) for formation of gaps whose widths cause the abutment of the pressing bands against the packages in ribbon-shaped regions (12,19) during the fixing thereof. 0 8. Device as claimed in claim 7, characterised in that the heating and welding devices (50,51) and the cooling devices (70,71), respectively, are disposed movable towards each other and that pressure devices (52,53 and 72,73) achieve movement of the devices towards one another for their abutment against the pres¬ sing ribbons and the letter ' s fixing of the packages (2). 9. Device as claimed in claim 6, characterised in that the separa¬ ting device (60,61) includes two opposing pulleys (64,65) between which the pressing ribbons (40,41) in a limited surface region pass during abutment of the pressing ribbons against one another or at a minimum distance smaller than the thickness of the material of the welded region (120). 10. Device in accordance with any of claims 6-9, characterised by two endless retaining ribbons (80,81) whose movement is syn¬ chronised with that of the pressing ribbons, in addition to which the retaining ribbons are disposed with opposite loop portions (800,810), running parallel to one another, between which the aperture regions of the packages are enclosed in a region closer to the centre of the packages than the ribbon- -shaped regions (12,19). _OMPI

Inventors: BRODEN INGEMAR, BRODEN, INGEMAR
Applicants: JOKER SYSTEM AB, JOKER SYSTEM AKTIEBOLAG
Application year: 1983
Main classification: B65B51
IPC codes: B29C65, B65B51