CA1211356A - Method and an arrangement for the heat-sealing of packing laminate - Google Patents
Method and an arrangement for the heat-sealing of packing laminateInfo
- Publication number
- CA1211356A CA1211356A CA000419047A CA419047A CA1211356A CA 1211356 A CA1211356 A CA 1211356A CA 000419047 A CA000419047 A CA 000419047A CA 419047 A CA419047 A CA 419047A CA 1211356 A CA1211356 A CA 1211356A
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- Canada
- Prior art keywords
- ridge
- zone
- working surface
- sealing
- jaw
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Laminated Bodies (AREA)
- Lining Or Joining Of Plastics Or The Like (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
In the manufacture of non-returnable packages for milk and other beverages laminated packing material is seal-ed to itself along linear sealing zones by causing outer thermoplastic layers of the packing material to fuse together.
The strength of the seal obtained depends upon the thermo-plastic surfaces being free of impurities, e.g., oxide coat-ings or residues of the contents of the package. In spite of the presence of impurities a strong seal can be obtained if the thermoplastic layers, within a limited region of the seal-ing zone, are pressed against each other with such a force that molten thermoplastic material is made to flow to adjoin-ing regions, since in this case the thermoplastics are blend-ed to such a degree that the seal-preventing layer of impuri-ties is broken.
In the manufacture of non-returnable packages for milk and other beverages laminated packing material is seal-ed to itself along linear sealing zones by causing outer thermoplastic layers of the packing material to fuse together.
The strength of the seal obtained depends upon the thermo-plastic surfaces being free of impurities, e.g., oxide coat-ings or residues of the contents of the package. In spite of the presence of impurities a strong seal can be obtained if the thermoplastic layers, within a limited region of the seal-ing zone, are pressed against each other with such a force that molten thermoplastic material is made to flow to adjoin-ing regions, since in this case the thermoplastics are blend-ed to such a degree that the seal-preventing layer of impuri-ties is broken.
Description
The present invention relates to a method of heat-sealin~ packing laminate comprising an outer thermoplastic material layer, which consists .in making the thermoplastic layers within a sealing zone lie a~ainst one another and heat-ing them temporarily tv sealing temperature.
The invention also relates to an arrangement for heat-sealing packing laminate, comprising an elonga~ed seal-ing ~aw with a working surface which can be pressed against the laminate.
Packing containers of the non-returnable type are used for milk, fruit beverages, etc., and are generally manu-factured from laminated packing material. The packing material comprises a central, relatively stiff carrier layer of paper which is covered on either side by thin layers of homogeneous plastic material. The material may also comprise layers of aluminum foil or other material. It is a comr,lon leature of all packing laminates of this type that they comprise on the outside, at least on the side which is to face towards the packaged contents, a layer of thermoplastic material, usually polyethylene r which makes it possible for two portions of the laminate resting against each other to be sealed together in a liquid-tight manner with the application of heat and pressure~
Tor the seai to have thedesired strength and liquid-tightness the two thermoplastic layers which are sealed to cach other must be clean and free of impurities. If this is the case a complete fusin~ to~ether of the thermoplastic layers can take place. This results in an optimum scal from a point of view of strength as well as ti~htness. Since on the sur-face of the thermoplastic layers ~ thin oxide coating, which is formed during the extrusion of the thermoplastic laycrs on the ~ackin~ laminate, is usually prese~lt a complete fusing to~ther of the thermoplastic layers is oEten prevented, as a ~' ~2~
result the seal does not acquire the strength and tightrless which is theoretically possible. Other types of impurities may also occur on the surface oF the thermoplas-tic layer, e.g., residues of -the contents, which Further impair thè seal. This is a particular problem in the type of package where -the seal-ing of the laminate material takes place with the contents present, that is to say where the contents have to be Forced out from the space between the thermoplastic surfaces resting against one ano~her before the sealing can take place. In practice, however~ the contents are not fully squeezed out, small residues remain embeded in the sealing area and this weakens the seal.
It is an object of the present inven~ion to provide a method which makes it possible to heat-seal a packing laminate of the aforementioned type in such a manner that the above men-tioned difficulties are alleviated.
It is a further objec~ oF the present invention to provide a method of heat-sealing a packing laminate which provides a good seal, even if the packing laminate is covered with impurities, e.g., oxides, residues of the contents of the package, or dirt.
According to a first aspect oF the invention there is provided a method of heat-sealing packing laminate having an outer layer of thermoplastic material, comprising heating and pressing together the thermoplastic layers of adjacent laminates with a sealing jaw, said sealing jaw having a working surface with an outer unheated zone, an inner heated zone, and a narrow linear ridge in said heated zone, said thermoplastic layers being pressed together with sufficient force to cause molten 3~ therrnoplastic material to flow away from the ridge into ad-joining heated and unheated regions also under pressure where further outward flow is stopped by non-molten material in the unheated zone, an accurnulation oF theremoplastic material being formed alongside the ridge.
With this method the molten -thermoplas-tic material, whilst being forced from the linear region to adjolning parts o-f the sealing zone, entrains with it any impuri-ties whi'lst the two thermoplastic layers of the 'laminate placed against one another are effectively blended to such a degree that a com-plete fusing together can be achieved. Within the linear region only a very thin thermoplastic layer remains, which is free of impurities and which is in close contact with the carrier layer of the packing laminate, whilst in the adjoining regions of the sealing zone an accumulation of well-blended thermoplas-tics from both thermoplastic layers guarantees a sea'l of good strength and tightness.
It is a further object of the present invention to provide an arrangement for the heat-sealing of packing laminat'e of the above mentioned type. The arrangelnent ensures that a seal of good properties is obtained, even if the malerial which is to be sealed is not wholly free of impurities.
It is a further object of the present inven~ion to provide an arrangement for the heat-sealing of packing 'larninate, which is not subject to the disadvantages of arrangements known earlier and is simple and reliable in design. The arrangement is capable, moreover, of being used with known types of packing machines and being manufactured at low cost.
Accordingly, the invention also provides an arrangement for heat-sealing packing laminate having an outer layer of thermoplastic material comprising an elongate sealing jaw having a working surface adapted to be pressed against the laminate, said working surface having an outer unheated zone, an inner heated zone, and a~narrow linear ridge projecting from the working surface in the heated ~one, and a counter-jaw with a plane working surface co-operating with said sealing jaw, whereby when the thermoplastic layers of adjacent laminates are pressed toge-ther between said jaws with suffic;ent -Force, mol~en thermoplastic rnaterial flows away from the ridge into adjoining regions under pressure between said jaws where fur'~her outward Flow is stopped by non-nlolten material in the unheated zone.
By providing the sealing jaw with the said ridge, or elongated raised surface, a jaw is obtained which, when pressed against two combined packing laminates, brings about a sealing zone with a linear portion wherein the laminates - 3a -: ~ .
351~
are pressed a~ainst one another at very high pressure. Since the sealiny jaw comprises a region heating the laminate, which includes not only the linear ridge, but also an adjoin-ing region, the heated thermoplastics is forced at high speed from the linear re~ion to the adjoining re~ion so that an effective ~lending, and consequently a c~ood seal, is obtained in the manner described earlier.
The invention ~ill now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:-Fig. 1 is an enlarged cross~section through a pack-ing laminate of a type which can be heat-sealed by the method in accordance with the invention;
Fig. 2 i5 an enlarged cross-section through a seal-ing jaw forming part of a seaiing arrangement;
Fig. 3 is a section through two packing laminates of the type shown in Fig. 1, which are heat-sealed in accor-dance with the method of the invention; and Fig. 4 is an enlarged cross-section through a second embodiment of a sealing jaw.
The packing laminate shown in Fig. 1 is of a type used fre~uently for packaging mil~ and other beverages. The pac~ing laminate has an overall thickness of 0.4-0.5 mm and comprises a central carrier layer 1 of fibrous material, covered on either side by comparatively thin, homogeneous layers 2,3 of thermoplastic material, in particular polyethyl-ene. Between one outer plastic layer 3 and the carrier layer 1 a further layer 4 o$ aluminum foil is often present. This layex is ~oined to the carrier layer by mcalls of tllermoplastics (not shown~ and completely covered by the outer "lor~logeneous layer 3O O~ing to the presence o~ thc two outer thermoplastic layers 2,3 the packing laminate can be si~ply heat--sealed by pressing together the parts which are to be sealed to on~ an-other and simultaneous heating the thermoplast.ics to its melt-i~lg temperature. It is of course also possible to seal pack-ing laminates of other types w~th the aid of the method and the arrangement in accordance with the invention, but the pack-ing laminates must have a layer o~ thermoplastic material.
Fig. 2 is a cross-section through a sealing jaw 5 in an arrangement according to the invention. The sealing jaw 5 comprises a main body 6 made of an electrically non-conduct-ing material and provided in one lateral surface with a grooveinto which a bar 7 of electrically conductive material, pre-ferahly copper, .is inserted. The bar 7, which is located centrally in the one lateral surface of the main body, forms together with the surrounding parts of the main body 6 the work-ing surface 8 of the sealing jaw 5. The working surface 8 is proviued with a linear rid~e 9 formed in the bar 7. The ridge 9 is of substantially rectangular cross-section an~ of a height which extends to 0.2 to 0.8 times the thickness of the lamin-ate, but preferably O.S times the thickness of the laminate and of a widt~ which is substantially equal to the thickness of the packing laminate. The working surface 8 of the sealing ]aw 5 thus comprises a centrally situated region heating the lam-inate, which includes on the one hand the linear ridge 9, on the other hand at least one adjoining region at the side of ~e ridge~
The region heating the laminate can be connected via the mater-ial in the ~ar 7 to a power source which may be of the high-frequency type, so as to make possible the high-frequency ~eld-ing of laminate containing aluminum foil. The re~ion heating the laminate or the bar 7 may also be hcatable and consist, ~or examp]e, of an electric resistance material, when packing lamin~te ~ithout aluminum foil or other electrically conduct ing layers is to be joined togetller 3S~
The sealing jaw ma~ ~e modified within the concept of the invention in different ways 50 as to meet requirements which the sealing of different materials and di~ferent types of packing containers may make. ~ typical modification of this kind may be that the sealing jaw is provided with one or more ducts for a cooling medium, e.g. water, which prevents harm-ful rises in temperature or undesirable spreadin~ of heat to the adjoining region, which should rernain unheated. It is also possible to design the sealing jaw in several, mutually movable parts. The portions of the sealing jaw situated on either side of the ridge 9, for example, may be made movable in relation to the ridge 9 and be spring-loaded in a direction towards the material, so that a suitable contact pressure is automati-cally produced. The sealing jaw may also be doubled, that is to say it may comprise two main bodies of the type described arranged at a distance lrom each other. This embodiment is particularl~ suitable when a packing material tube is to be sealed off, that is to say sealed in two transverse zones and cut off between these, since a knife or some other appropriate cutting device can then operate in the space between the two main bodies of the sealing jaw.
Fig. 3 illustrates the sealing sequence during the sealing together of two packin~ laminates. Two packiny lamin-ates 10,11 (or two parts of the same, folded, packing laminate) are joined together in preparation for sealing so that their outer thermoplastic layers 3 lie against each otherO The pack-ing laminate is pressed together with the help of a sealing jaw 5 and a counter-jaw 12 restiny against the op~osite side of the packing laminate (indicated by means of dash-dotted lines). The sealing ja~ 5 i~ of the type shown in Fig. 2, whilst the counter-jaw 12 is provided with a plane working sur-face resting against the laminate 11. The jaws 5,12 are sus-35il~
pended in the fra~e (not shownl o~ the packing machine in such a manner that they can be given a reciprocating movement by means of ~ydraulic or mechanical driving devices, so that dur-ing the sealing they can be pressed together with a certain, adjusta~le force. At t~e same time, as the jaws are moved towards one another and start to press together the packing larninate 10,11 situated in ~etween, the bar 7 of the sealing jaw 5 is connected to a hiyh-frequency power source. In this way an alternating electric field is induced in the aluminum layer 4 of the packing laminates. ~s a result these are heated within a region corresponding to the surface of the bar 7 to a temperature which is apprecia~ly ~igher than the melting tem-perature of the adjacent thermoplastic layers. The heat gener-ated is transmitted directly to the thermoplastic layers 3 located between the aluminum layers, so that these melt and become fluid. Owing to the high force (approx. 100 kg/cm ) with which the packing laminates are pressed together under the ridge 9, the molten thermoplastic runs or flows from the region 13 of high pressure to adjoining parts 14 of tlle total sealing 2Q zone 13,14~ Since the thermoplastic layers 3 lying against one another in the region outside the sealing zone 13,14 con-tinue to be in solid state and are pressed against one another, the molten thermoplastics cannot flow any further outside the sealing zone, but remains in the two regions indicated by refer-ence numeral 14, where it forms bulges 15 runniny parallel with the elongated pressure region 13 wherein the two layers to be sealed to each other are blended. In the region 13 only insigni-ficant amounts of plastic material remain which, because o~ the unevenness of the surface etc., cannot be squeezed out, whilst the bul~es 15 formed on either side of the region contain an cxcess of well-blended plast;~cs, providing a very strong and, in ~ractice, unbreakable seal between the two layers. Since 3~
the flo~ fro~ the region 13 tv the regions 14 is so rapid, turbulence occurs in the flowi~g plastic material which ensures that the plastic material from the two layers reskin~ against one another is well blended, so tha~ any surface oxidation or other impurities present on the surface (e.g. from remaining residues of the contents of the packages) are effectively blend-ed into ~e plastics. Any coherent film of impurities impairing the strength of the seal w-ill not survi~e.
For certain kinds of contents, it may be advantage-ous to transfer the flo~ of melted, thermoplastic materi~lfurther awa~ from the ridge area in order to produce a wider, flatter ~ulye 15. ~ith this technique it is possible to achieve a smoother and more fiexible seal, compared with the embodiment discussed above. This also results in a more rectilinear seal edge. As a result the seal is stronger, since no protruding "attack points" for external forces are created.
The above mentioned advantages are achieved in accor-dance with a second embodiment in that one longitudinal edge of the ridge 9 mainly coincides with one ~dge of the heatable region of tfie working surface 8 ~Fi~. 4), whereby the heatable region adjacent to the ridge 9 is situated at a higher level than the level of the working surface at the other side of the ridge. According to a further feature of the second embodi~
ment, the distance between the level of the heatable area and the level of the ridge 9 is roughly equal to the distance be tween the heatable area and the level of the wor~ing surface on the other side of the r;dge, i.e., the distance (a) is simi-lar to the distance (bl CFig. 4~-When the second cr,lbodiment is used, the asymmetric posit~oning of the ridge 9 in relation to the hc~table arearesults in tfie ma~or ~art of the flow of melted tll~rmoplastic mat:erial being directed towards the heated side of the ridge~
~2~3~;i6 The higher l~vel ~compared with the ~irst embodiment of theinvention~ of the heata~le area leaves a smaller and more elongated space for the flQwing of ther~oplastic material be-ore it reaches the thexmoplastic layers that are situated out side the heataBle area and thus are in the solid state. Conse-quently, the elongated ~ulge or accumulation 15 of thermo-plastic material squeezed away from the high pressure zone immediately in front of the ridge 9 is given a flatter and more elongated cross-sectional form, thus rendering the bulge more 1exi~ility and results in a stronger seal.
To ensure further that the bulges or accumulations 15 of molten thermoplastics are of a limited, linear appear-ance, the parts of the two plastic laminates situated outside the sealing zone 13,14 may be coo~ed. This can be achieved either by providing the two jaws 5,12 with cooling ducts situ-ated outside the sealing region through which liquid is con-ducted or, in the type of sealing performed with simultaneous forcing out of the contents, by allowing the contents to cool adjacent parts of the packing lamina~e.
To ensure an effective flow of molten thermoplastic material from the central region 13 to the adjoining regions 14, the pressing of the ridge 9 against the packing laminate must take place with such a force that the surface pressure in the linear re~ion 13 of the sealing zone amounts to approx. 100 kg~c~ at the same time as the temperature of the thermoplastics should exceed approx. 130C.
The invention also relates to an arrangement for heat-sealing packing laminate, comprising an elonga~ed seal-ing ~aw with a working surface which can be pressed against the laminate.
Packing containers of the non-returnable type are used for milk, fruit beverages, etc., and are generally manu-factured from laminated packing material. The packing material comprises a central, relatively stiff carrier layer of paper which is covered on either side by thin layers of homogeneous plastic material. The material may also comprise layers of aluminum foil or other material. It is a comr,lon leature of all packing laminates of this type that they comprise on the outside, at least on the side which is to face towards the packaged contents, a layer of thermoplastic material, usually polyethylene r which makes it possible for two portions of the laminate resting against each other to be sealed together in a liquid-tight manner with the application of heat and pressure~
Tor the seai to have thedesired strength and liquid-tightness the two thermoplastic layers which are sealed to cach other must be clean and free of impurities. If this is the case a complete fusin~ to~ether of the thermoplastic layers can take place. This results in an optimum scal from a point of view of strength as well as ti~htness. Since on the sur-face of the thermoplastic layers ~ thin oxide coating, which is formed during the extrusion of the thermoplastic laycrs on the ~ackin~ laminate, is usually prese~lt a complete fusing to~ther of the thermoplastic layers is oEten prevented, as a ~' ~2~
result the seal does not acquire the strength and tightrless which is theoretically possible. Other types of impurities may also occur on the surface oF the thermoplas-tic layer, e.g., residues of -the contents, which Further impair thè seal. This is a particular problem in the type of package where -the seal-ing of the laminate material takes place with the contents present, that is to say where the contents have to be Forced out from the space between the thermoplastic surfaces resting against one ano~her before the sealing can take place. In practice, however~ the contents are not fully squeezed out, small residues remain embeded in the sealing area and this weakens the seal.
It is an object of the present inven~ion to provide a method which makes it possible to heat-seal a packing laminate of the aforementioned type in such a manner that the above men-tioned difficulties are alleviated.
It is a further objec~ oF the present invention to provide a method of heat-sealing a packing laminate which provides a good seal, even if the packing laminate is covered with impurities, e.g., oxides, residues of the contents of the package, or dirt.
According to a first aspect oF the invention there is provided a method of heat-sealing packing laminate having an outer layer of thermoplastic material, comprising heating and pressing together the thermoplastic layers of adjacent laminates with a sealing jaw, said sealing jaw having a working surface with an outer unheated zone, an inner heated zone, and a narrow linear ridge in said heated zone, said thermoplastic layers being pressed together with sufficient force to cause molten 3~ therrnoplastic material to flow away from the ridge into ad-joining heated and unheated regions also under pressure where further outward flow is stopped by non-molten material in the unheated zone, an accurnulation oF theremoplastic material being formed alongside the ridge.
With this method the molten -thermoplas-tic material, whilst being forced from the linear region to adjolning parts o-f the sealing zone, entrains with it any impuri-ties whi'lst the two thermoplastic layers of the 'laminate placed against one another are effectively blended to such a degree that a com-plete fusing together can be achieved. Within the linear region only a very thin thermoplastic layer remains, which is free of impurities and which is in close contact with the carrier layer of the packing laminate, whilst in the adjoining regions of the sealing zone an accumulation of well-blended thermoplas-tics from both thermoplastic layers guarantees a sea'l of good strength and tightness.
It is a further object of the present invention to provide an arrangement for the heat-sealing of packing laminat'e of the above mentioned type. The arrangelnent ensures that a seal of good properties is obtained, even if the malerial which is to be sealed is not wholly free of impurities.
It is a further object of the present inven~ion to provide an arrangement for the heat-sealing of packing 'larninate, which is not subject to the disadvantages of arrangements known earlier and is simple and reliable in design. The arrangement is capable, moreover, of being used with known types of packing machines and being manufactured at low cost.
Accordingly, the invention also provides an arrangement for heat-sealing packing laminate having an outer layer of thermoplastic material comprising an elongate sealing jaw having a working surface adapted to be pressed against the laminate, said working surface having an outer unheated zone, an inner heated zone, and a~narrow linear ridge projecting from the working surface in the heated ~one, and a counter-jaw with a plane working surface co-operating with said sealing jaw, whereby when the thermoplastic layers of adjacent laminates are pressed toge-ther between said jaws with suffic;ent -Force, mol~en thermoplastic rnaterial flows away from the ridge into adjoining regions under pressure between said jaws where fur'~her outward Flow is stopped by non-nlolten material in the unheated zone.
By providing the sealing jaw with the said ridge, or elongated raised surface, a jaw is obtained which, when pressed against two combined packing laminates, brings about a sealing zone with a linear portion wherein the laminates - 3a -: ~ .
351~
are pressed a~ainst one another at very high pressure. Since the sealiny jaw comprises a region heating the laminate, which includes not only the linear ridge, but also an adjoin-ing region, the heated thermoplastics is forced at high speed from the linear re~ion to the adjoining re~ion so that an effective ~lending, and consequently a c~ood seal, is obtained in the manner described earlier.
The invention ~ill now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:-Fig. 1 is an enlarged cross~section through a pack-ing laminate of a type which can be heat-sealed by the method in accordance with the invention;
Fig. 2 i5 an enlarged cross-section through a seal-ing jaw forming part of a seaiing arrangement;
Fig. 3 is a section through two packing laminates of the type shown in Fig. 1, which are heat-sealed in accor-dance with the method of the invention; and Fig. 4 is an enlarged cross-section through a second embodiment of a sealing jaw.
The packing laminate shown in Fig. 1 is of a type used fre~uently for packaging mil~ and other beverages. The pac~ing laminate has an overall thickness of 0.4-0.5 mm and comprises a central carrier layer 1 of fibrous material, covered on either side by comparatively thin, homogeneous layers 2,3 of thermoplastic material, in particular polyethyl-ene. Between one outer plastic layer 3 and the carrier layer 1 a further layer 4 o$ aluminum foil is often present. This layex is ~oined to the carrier layer by mcalls of tllermoplastics (not shown~ and completely covered by the outer "lor~logeneous layer 3O O~ing to the presence o~ thc two outer thermoplastic layers 2,3 the packing laminate can be si~ply heat--sealed by pressing together the parts which are to be sealed to on~ an-other and simultaneous heating the thermoplast.ics to its melt-i~lg temperature. It is of course also possible to seal pack-ing laminates of other types w~th the aid of the method and the arrangement in accordance with the invention, but the pack-ing laminates must have a layer o~ thermoplastic material.
Fig. 2 is a cross-section through a sealing jaw 5 in an arrangement according to the invention. The sealing jaw 5 comprises a main body 6 made of an electrically non-conduct-ing material and provided in one lateral surface with a grooveinto which a bar 7 of electrically conductive material, pre-ferahly copper, .is inserted. The bar 7, which is located centrally in the one lateral surface of the main body, forms together with the surrounding parts of the main body 6 the work-ing surface 8 of the sealing jaw 5. The working surface 8 is proviued with a linear rid~e 9 formed in the bar 7. The ridge 9 is of substantially rectangular cross-section an~ of a height which extends to 0.2 to 0.8 times the thickness of the lamin-ate, but preferably O.S times the thickness of the laminate and of a widt~ which is substantially equal to the thickness of the packing laminate. The working surface 8 of the sealing ]aw 5 thus comprises a centrally situated region heating the lam-inate, which includes on the one hand the linear ridge 9, on the other hand at least one adjoining region at the side of ~e ridge~
The region heating the laminate can be connected via the mater-ial in the ~ar 7 to a power source which may be of the high-frequency type, so as to make possible the high-frequency ~eld-ing of laminate containing aluminum foil. The re~ion heating the laminate or the bar 7 may also be hcatable and consist, ~or examp]e, of an electric resistance material, when packing lamin~te ~ithout aluminum foil or other electrically conduct ing layers is to be joined togetller 3S~
The sealing jaw ma~ ~e modified within the concept of the invention in different ways 50 as to meet requirements which the sealing of different materials and di~ferent types of packing containers may make. ~ typical modification of this kind may be that the sealing jaw is provided with one or more ducts for a cooling medium, e.g. water, which prevents harm-ful rises in temperature or undesirable spreadin~ of heat to the adjoining region, which should rernain unheated. It is also possible to design the sealing jaw in several, mutually movable parts. The portions of the sealing jaw situated on either side of the ridge 9, for example, may be made movable in relation to the ridge 9 and be spring-loaded in a direction towards the material, so that a suitable contact pressure is automati-cally produced. The sealing jaw may also be doubled, that is to say it may comprise two main bodies of the type described arranged at a distance lrom each other. This embodiment is particularl~ suitable when a packing material tube is to be sealed off, that is to say sealed in two transverse zones and cut off between these, since a knife or some other appropriate cutting device can then operate in the space between the two main bodies of the sealing jaw.
Fig. 3 illustrates the sealing sequence during the sealing together of two packin~ laminates. Two packiny lamin-ates 10,11 (or two parts of the same, folded, packing laminate) are joined together in preparation for sealing so that their outer thermoplastic layers 3 lie against each otherO The pack-ing laminate is pressed together with the help of a sealing jaw 5 and a counter-jaw 12 restiny against the op~osite side of the packing laminate (indicated by means of dash-dotted lines). The sealing ja~ 5 i~ of the type shown in Fig. 2, whilst the counter-jaw 12 is provided with a plane working sur-face resting against the laminate 11. The jaws 5,12 are sus-35il~
pended in the fra~e (not shownl o~ the packing machine in such a manner that they can be given a reciprocating movement by means of ~ydraulic or mechanical driving devices, so that dur-ing the sealing they can be pressed together with a certain, adjusta~le force. At t~e same time, as the jaws are moved towards one another and start to press together the packing larninate 10,11 situated in ~etween, the bar 7 of the sealing jaw 5 is connected to a hiyh-frequency power source. In this way an alternating electric field is induced in the aluminum layer 4 of the packing laminates. ~s a result these are heated within a region corresponding to the surface of the bar 7 to a temperature which is apprecia~ly ~igher than the melting tem-perature of the adjacent thermoplastic layers. The heat gener-ated is transmitted directly to the thermoplastic layers 3 located between the aluminum layers, so that these melt and become fluid. Owing to the high force (approx. 100 kg/cm ) with which the packing laminates are pressed together under the ridge 9, the molten thermoplastic runs or flows from the region 13 of high pressure to adjoining parts 14 of tlle total sealing 2Q zone 13,14~ Since the thermoplastic layers 3 lying against one another in the region outside the sealing zone 13,14 con-tinue to be in solid state and are pressed against one another, the molten thermoplastics cannot flow any further outside the sealing zone, but remains in the two regions indicated by refer-ence numeral 14, where it forms bulges 15 runniny parallel with the elongated pressure region 13 wherein the two layers to be sealed to each other are blended. In the region 13 only insigni-ficant amounts of plastic material remain which, because o~ the unevenness of the surface etc., cannot be squeezed out, whilst the bul~es 15 formed on either side of the region contain an cxcess of well-blended plast;~cs, providing a very strong and, in ~ractice, unbreakable seal between the two layers. Since 3~
the flo~ fro~ the region 13 tv the regions 14 is so rapid, turbulence occurs in the flowi~g plastic material which ensures that the plastic material from the two layers reskin~ against one another is well blended, so tha~ any surface oxidation or other impurities present on the surface (e.g. from remaining residues of the contents of the packages) are effectively blend-ed into ~e plastics. Any coherent film of impurities impairing the strength of the seal w-ill not survi~e.
For certain kinds of contents, it may be advantage-ous to transfer the flo~ of melted, thermoplastic materi~lfurther awa~ from the ridge area in order to produce a wider, flatter ~ulye 15. ~ith this technique it is possible to achieve a smoother and more fiexible seal, compared with the embodiment discussed above. This also results in a more rectilinear seal edge. As a result the seal is stronger, since no protruding "attack points" for external forces are created.
The above mentioned advantages are achieved in accor-dance with a second embodiment in that one longitudinal edge of the ridge 9 mainly coincides with one ~dge of the heatable region of tfie working surface 8 ~Fi~. 4), whereby the heatable region adjacent to the ridge 9 is situated at a higher level than the level of the working surface at the other side of the ridge. According to a further feature of the second embodi~
ment, the distance between the level of the heatable area and the level of the ridge 9 is roughly equal to the distance be tween the heatable area and the level of the wor~ing surface on the other side of the r;dge, i.e., the distance (a) is simi-lar to the distance (bl CFig. 4~-When the second cr,lbodiment is used, the asymmetric posit~oning of the ridge 9 in relation to the hc~table arearesults in tfie ma~or ~art of the flow of melted tll~rmoplastic mat:erial being directed towards the heated side of the ridge~
~2~3~;i6 The higher l~vel ~compared with the ~irst embodiment of theinvention~ of the heata~le area leaves a smaller and more elongated space for the flQwing of ther~oplastic material be-ore it reaches the thexmoplastic layers that are situated out side the heataBle area and thus are in the solid state. Conse-quently, the elongated ~ulge or accumulation 15 of thermo-plastic material squeezed away from the high pressure zone immediately in front of the ridge 9 is given a flatter and more elongated cross-sectional form, thus rendering the bulge more 1exi~ility and results in a stronger seal.
To ensure further that the bulges or accumulations 15 of molten thermoplastics are of a limited, linear appear-ance, the parts of the two plastic laminates situated outside the sealing zone 13,14 may be coo~ed. This can be achieved either by providing the two jaws 5,12 with cooling ducts situ-ated outside the sealing region through which liquid is con-ducted or, in the type of sealing performed with simultaneous forcing out of the contents, by allowing the contents to cool adjacent parts of the packing lamina~e.
To ensure an effective flow of molten thermoplastic material from the central region 13 to the adjoining regions 14, the pressing of the ridge 9 against the packing laminate must take place with such a force that the surface pressure in the linear re~ion 13 of the sealing zone amounts to approx. 100 kg~c~ at the same time as the temperature of the thermoplastics should exceed approx. 130C.
Claims (14)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of heat-sealing packing laminate having an outer layer of thermoplastic material, comprising heating and pressing together the thermoplastic layers of adjacent laminates with a sealing jaw, said sealing jaw having a working surface with an outer unheated zone, an inner heated zone, and a narrow linear ridge in said heated zone, said thermoplastic layers being pressed together with sufficient force to cause molten thermoplastic material to flow away from the ridge into adjoining heated and unheated regions also under pressure where further outward flow is stopped by non-molten material in the unheated zone, an accumulation of thermoplastic material being formed alongside the ridge.
2. A method according to claim 1, wherein the sealing pressure in under the ridge is about 100 kg/cm2.
3. A method according to claim 1, wherein the thermoplastic material is heated to a temperature of at least 130°C.
4. A method according to claim 1, 2 or 3, wherein the unheated zone of the working surface is cooled with a cooling medium.
5. An arrangement for heat-sealing packing laminate having an outer layer of thermoplastic material comprising an elongate sealing jaw having a working surface adapted to be pressed against the laminate, said working surface having an outer unheated zone, an inner heated zone, and a narrow linear ridge projecting from the working surface in the heated zone, and a counter-jaw with a plane working surface co-operating with said sealing jaw, whereby when the thermoplastic layers of ad-jacent laminates are pressed together between said jaws with sufficient force, molten thermoplastic material flows away from the ridge into adjoining regions under pressure between said jaws where further outward flow is stopped by non-molten material in the unheated zone.
6. An arrangement according to claim 5, wherein the ridge has a height of 0.2-0.8 times the thickness of the lamin-ate.
7. An arrangement according to claim 5, wherein the width of the ridge is substantially equal to the thickness of the laminate.
8. An arrangement according to claim 5, wherein in the inner zone, the jaw has a surface of electrically conductive material for connection to a high-frequency power source.
9. An arrangement according to claim 5, wherein in the inner zone the jaw has a surface made of electric resistance material for connection to a power source.
10. An arrangement according to claim 5, wherein said ridge is asymmetrically disposed in relation to said inner zone.
11. An arrangement according to claim 10, wherein the working surface of the one side of the ridge is recessed in relation to the working surface on the other side of the ridge, the recessed portion being in said outer zone.
12. An arrangement according to claim 11, wherein the recessed portion of the working surface is recessed relative to the working surface on the other side of the ridge by an amount which is approximately equal to the projection of said ridge relative to working surface on said other side of the ridge.
13. An arrangement according to claim 5, 6 or 7, further comprising cooling means for cooling said working surface in the unheated zone.
14. An arrangement according to claim 5, wherein the portions of the sealing jaw situated on either side of the ridge are displaceable with respect to the ridge in a direction to-.
wards the counter-jaw and spring-loaded to maintain a desired working pressure.
wards the counter-jaw and spring-loaded to maintain a desired working pressure.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000419047A CA1211356A (en) | 1981-10-08 | 1983-01-06 | Method and an arrangement for the heat-sealing of packing laminate |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE8105960-2 | 1981-10-08 | ||
| SE8105960A SE433322B (en) | 1981-10-08 | 1981-10-08 | DEVICE FOR HEAL-SEALING PACKAGING LAMINATE - DESIGN OF THE SEAL BACK |
| CA000412928A CA1200749A (en) | 1981-10-08 | 1982-10-06 | Method and an arrangement for the heat-sealing of packing laminate |
| CA000419047A CA1211356A (en) | 1981-10-08 | 1983-01-06 | Method and an arrangement for the heat-sealing of packing laminate |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1211356A true CA1211356A (en) | 1986-09-16 |
Family
ID=25669833
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000419047A Expired CA1211356A (en) | 1981-10-08 | 1983-01-06 | Method and an arrangement for the heat-sealing of packing laminate |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1211356A (en) |
-
1983
- 1983-01-06 CA CA000419047A patent/CA1211356A/en not_active Expired
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