CROSS REFERENCE TO RELATED APPLICATIONS This application claims the priority of Swiss patent application 0061/09, filed Jan. 16, 2009, the disclosure of which is incorporated herein by reference in its entirety.
FIELD OF THE INVENTION The invention is related to a method for manufacturing tear-open lids, comprising the steps of: providing a band of tear-open foil material, stamping a foil section with a tear-open tag out of the band, sealing the foil section onto a lid ring and folding the tear-open tab on the lid. Furthermore, the invention is related to a device for manufacturing tear-open lids as well as to a tear-open lid with a lid ring and a tear-open foil.
BACKGROUND-PRIOR ART It is known to execute lids for can-like or box-like packages as metal covers which are permanently attached on top of the package, having a lid ring with an extraction opening. The latter is kept closed until the first use of the package content by means of a foil which is applied on the lid ring by means of heat sealing and which can be torn open; such lids are called tear-open lids. The foil on the lid is called tear-open foil and may for example be a metal foil, a metal composite foil or a pure plastic foil. An additional lid made of plastic which is arranged above the metal lid makes the package resealable during the use period of the content. In order to open the tear-open lid or to tear away the sealed foil respectively, the latter has a tear-open tab. When closing a can after its filling, the pre-fabricated tear-open lid is flanged up at the body of the can. During this manufacturing step, a tear-open tab which sticks out may disturb, wrinkle and be even torn off. Furthermore, the appliance of the plastic lid is normally only possible when the tab is fold back. Therefore it is preferred that the tear-open tab is fold back onto the lid and that it keeps this position. This is possible in case of metal foils; however, even in this case, the thermal effect and the cooling process during the sterilization of the filled and sealed can may cause a deformation and an undesired sticking out of the tear-open tab. In case of composite foils made of metal and plastic or foils made only of plastic, a permanent folding back is more difficult and the result is even more likely to be a sticking out during the sterilization, because of different thermal expansions of the layers. For cans receiving dry products which don't have to be sterilized it is already known to fixate the folded back tear-open foil on the lid by means of Hotmelt adhesive material, after having sealed the tear-open foil on the lid. However, this production step is complex. In addition, it is not usable for cans which have to be sterilized, because Hotmelt adhesive material fails in sterilization conditions.
Known methods or devices respectively for the manufacturing of tear-open lids will be explained in the following by means of the FIGS. 1 to 9. Thereby, the FIGS. 2 to 8 serve for explaining the manufacturing steps.
SUMMARY OF THE INVENTION The invention has the task of enhancing tear-open lids.
The method mentioned at the beginning solves the task by applying an adhesive surface on the band before stamping out the foil section, at a position where the folded back tear-open foil comes to lie on the tear-open lid. Furthermore, the task is solved by the manufacturing device comprising a conveying installation for lid parts and lids, a sealing station wherein a band of tear-open foil material is feedable by means of feeding means wherein the sealing station is formed to stamp out a foil section with a tear-open tab out of the band and to seal the foil section with its sealable lower side onto a lid ring, a folding station wherein the tear-open tab is foldable onto the lid, characterized in that an installation is provided, by means of which an adhesive surface is applicable on the upper side of the band before stamping out the foil section. The task is further solved by a tear-open lid with a lid ring and a tear-open foil with a folded back tear-open tab, characterized in that the tear-open tab is attached on the tear-open foil by means of an adhesive surface which is formed from a piece of double sided adhesive tape whose adhesive strength is different on each of its sides, wherein the lower adhesive strength acts on the side to which the tear-open tab is attached.
It is particularly preferred to apply the adhesive surface in form of a piece of double sided adhesive tape and particularly of an adhesive tape with a different adhesive strength on each of the adhesive sides, wherein the tape is applied in such a way, that the lower adhesive strength is effective at the tear-open tab.
BRIEF DESCRIPTION OF THE DRAWINGS In the following, embodiments of the invention will be further explained by means of the figures.
FIG. 1 is a schematic side view of a device according to the prior art as well as for carrying out the present invention;
FIG. 2 to FIG. 8 are sectors of metal lids for explaining their manufacturing;
FIG. 9 is a top view on a tear-open lid according to the invention;
FIG. 10 is a partial section view of the tear-open lid of FIG. 9;
FIG. 11 is a schematic view of the appliance of the tear-open foil in the sealing station as well as further steps;
FIG. 12 is a schematic view of a stamping station for a double sided adhesive tape;
FIG. 13 is a schematic section view of the blow and suction equipment for removing the protective foil from the adhesive surface; and
FIG. 14 is a more detailed view of the removal of the protective foil.
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic side view of a device 1 for manufacturing tear-open lids. It has multiple processing stations 3 to 9 on a machine framework 2. A conveying installation 10, 13, 14 transports lid parts and the finished lids in a conveying direction indicated by the arrow C, from the input of the device at the stack 11 to the output of the device where the lids reach the trays 16 or 17 via slides. Lid parts are destacked from the stack 11 in a known way and they get into the conveying installation. The latter may have two long bars 10, each of which is arranged at the side of the objects and lift up the lid parts or the lids respectively lying on the trays 10′ or in the stations to 9 respectively, during their own lift up, in the direction of arrow A, by means of the actuator 14, and subsequently shift them onwards by an amount in a forward motion in the direction of arrow B (in the same direction as arrow C) by means of a crank drive 13. Thereafter, the bars are moved downwards in the direction of arrow A, wherein the lid parts or the lids respectively are again placed onto their laydown position. Thereafter, the bars 10 are moved backwards below the object laydown positions in the direction of arrow B and antiparallel to arrow C, whereafter the described process is repeated. Between transportations, the lid parts or the lids respectively lie on their laydown positions or are located in the processing stations respectively and are processed there. A recurring conveying takes place after a processing step through all processing stations. A known conveying installation with two tooth belts according to WO 2006/017953 may be used instead of the described conveying installation. Such an endless tooth belt drive has the necessary length for the number of processing stations and the stepwise tooth belt motion which is synchronized with the processing stations is done by means of a step motor or a servo motor, which actuates the tooth belts by means of pulleys. The conveying installation with tooth belts makes it possible to manufacture lids with a higher cycle number of for example 200 lids per minute.
FIG. 2 shows stacked metal lid blanks 20, as they are provided in the stack 11 at the beginning of the conveying installation. These blanks 20 are for example round metal disks with a diameter of for example 11 cm. Evidently, other basic shapes like for example square or rectangular disks and other diameters are readily possible. The blanks 20 have already been preformed at their edge in a processing machine which is not shown, as shown in FIG. 2. In FIG. 2 and in the subsequent FIGS. 3 to 9, only a sector of the whole disk or lid respectively is shown in order to simplify the figures. In the first processing station 3 of FIG. 1, an opening is stamped into the disk by means of a stamping process with an upper and a lower tool, this being shown in FIG. 3, wherein the edge of the opening is denoted by 21 and the stamped out round disk by 27. This disk 27 is disposed of in the container 12 of FIG. 1. Thus, the result is a ring shaped lid part 20′ with an opening which forms the extraction opening of the finished lid. The stamp processing station 3 is actuated—as it is the case for the additional processing stations—by means of an actuator 15. A pulling down of the edge 21 takes place in the processing station 4, by means of which for example the shape 22 of the edge, shown in FIG. 4, is reached. The ring shaped lid parts 20′ then reach the sealing station 5. Therein, a foil section 25 is stamped out by means of stamping means 6, placed above the opening of the lid ring 20′ and attached there by means of heat sealing, this being shown in FIGS. 5 and 6. For this, a sealable plastic layer is applied onto the lower side of the tear-open foil 25 in a known way, wherein the latter may be a metal foil, a composite foil or a plastic foil. The tear-open foil 25 may for example be a multiple layer composite foil with plastic layers and aluminium layers and may for example have a layer of heat sealable polypropylene (PP) and a subsequent layer of PET, being followed by an aluminium layer and having another PET layer on the upper side of the tear-open foil. A possible print is arranged under this PET layer. A further embodiment of the tear-open foil may be a heat sealing paint layer arranged under the lid or on the contents side respectively, being followed by the aluminium layer and the PET layer on the upper side of the lid. Also further embodiments are known to the skilled person and may be used within the scope of the present invention. The needed precut foil 25, which in this example has a round shape, is normally stamped out of a wide foil web in the station 5, 6, placed above the middle cavity of the ring shaped disk, wherein the foil is pressed by the sealing station at the edge of the round cavity of the lid part 20′ under the influence of heat, such that the foil 25 is sealed tightly by melting and subsequent cooling of the sealable layer. This is known and will therefore not be explained in more detail. The tear-open lid 28 is thereby formed. A cooling process station 7 may possibly be provided for the cooling. The foil 25 may be provided with a stamp 24 (FIG. 7) in the processing station 8 and then the edge 22 is subsequently flanged to yield the finished edge 23. If the tear-open foil is provided with a tear-open tab, the tab may then be folded back such that it comes to lie on the lid. The finished lids are submitted to an inspection in an inspection station 9 which is to be considered a processing station, normally comprising a leak test for the tear-open foil 25 which is applied on the lid, wherein an air pressure gradient is created between the lower side and the upper side of the lid. If the foil is tightly attached to the lid ring, the lid thereby ends up in the tray 16 for the finished lids. If a leak is detected, the lid ends up in the waste container 17 via the other shown slide.
FIG. 9 shows a finished tear-open lid 28 in a top view. Thereby, the tear-open foil 25 has a tear-open tab 29 which is folded back onto the lid. According to the invention, the tear-open tab at the lid is attached by means of an adhesive surface 30 which is preferably formed by a double sided adhesive tape, particularly with different adhesive strengths of each of its tape sides. An adhesive surface formed by a sealing paint may also be provided. FIG. 10 shows a zoomed view of the area of the tear-open lid with the tear-open tab 29 which, in its folded back position, is detachable attached to the adhesive surface formed by a piece of double sided adhesive tape. The tab 29 sticks out over the adhesive surface 30, such that the tab for opening the tear-open lid may be grasped and detached from the adhesive surface 30 in a simple way. The adhesive tape 33 is preferably differently adhesive on each of its sides, such that the bond of the adhesive tape on its lower side (shown in FIG. 10) or at the tear-open foil surface respectively, is higher than at its upper side to which the tear-open tab 29 is held in an adhering way. This makes sure that the tab 29 may easily be removed from the adhesive surface, while the adhesive tape remains bonded on the tear-open foil of the lid. In this example, the edge of the extraction opening has a different shape 23′ than in FIG. 7.
The procedure of providing a preferred adhesive surface 30 in form of a piece of double sided adhesive tape on the tear-open lid is explained in FIG. 11. Different types of adhesive surfaces, like particularly sealing paint surfaces, may be applied as well. FIG. 11 shows in a broad schematic way a part of a device for manufacturing tear-open lids, which may for example be a device according to FIG. 1. Four rows of lid parts 20, 20′ or lids 28 respectively are conveyed parallel in the conveying direction C by means of the conveying installation which is not shown in FIG. 11. In the area of the sealing station which is not shown here as an apparatus (accordingly like the sealing station 5 and 6 of FIG. 1) a band 35 of the tear-open foil material runs into the sealing station and is stamped there, in order to form the foil sections 25 with the tear-open tab 29. The stamping pattern is thereby chosen in such a way that as little stamping waste as possible is left over. The foil sections 25 for the uppermost row of lid rings 20′ of FIG. 11 are in this example stamped out of the band 35 in the leftmost row at the edge of the band. After that, the empty regions 25′ are left. The foil sections 25 for the second uppermost row of lid rings 20′ are stamped out in the row left of the middle axis of the band 35 and the foil sections for the second lowest row of lid rings 20′ are stamped out in the row right of the middle axis of the band 35. The foil sections 25 for the lowest row of lid rings 20′ are stamped out in the rightmost row of the band 35. The stamped out foil sections are each sealed onto the respective lid ring, as known to the skilled person. The band 35 may be conveyed by means of actuating rollers 36 or by other known means. The adhesive surfaces 30 are applied onto the band 35 on its upper side 26 before the stamp out of the foil sections 25. This takes place in such a way, that at least one such adhesive surface is applied onto the band 35 at each foil section 25 which has to be stamped out later, namely at the position on the foil section 25, whereat the folded back tab 29 of the finished tear-open lid 28 comes to lie. The stamping of the individual foil sections 25 in the sealing station may for example be controlled by marks printed on the band. These printed marks may also be used as helpers for the correct positioning of the adhesive surfaces 30, if necessary. However, a print on the tear-open foil sections themselves may serve as a mark.
In the shown example, a double sided adhesive tape is guided transversally to the tear-open foil band 35 over the same. This is a preferred example, the adhesive tape could however be also guided obliquely or in the same direction over the band 35. Also multiple single bands could be provided instead of a tape 33. The double sided adhesive tape has no protective foil at its lower side located opposite of the band 35, which preferably has the higher adhesive strength than the upper side. On the contrary, a protecting foil 37 is provided on the upper side, being shown in the top view of FIG. 11. A double sided adhesive tape with a respective different adhesive strength on both sides and with a single sided protective foil on the side with a lower adhesive strength, being adequate for being applied on the band 35, is for example the adhesive tape tesafix 6917 of the company teas bandfix AG, Bergdietikon, Switzerland. This adhesive tape is knowingly used for the reversible sealing of foil bags. The adhesive tape running over the band 35 is stamped by means of a stamping installation (FIG. 12), such that the adhesive surfaces 30 are stamped out of the adhesive tape 33. Preferably, they are applied directly onto the band 35 by the stamping tool, where they stick by means of their lower side which is free of protective foil. The upper side of each adhesive surface stays covered by means of the equally stamped protective foil 37. The empty regions 33′ remain in the tape 33.
As shown in FIG. 11 in case of the tear-open lids which are viewable in conveying direction C directly after the band 35, an individual lid 28 is formed in this way, with a tear-open foil 25, from which a tab 29 sticks out over the edge of the lid and whereat an adhesive surface 30, which is still covered by a protective foil 37, is provided. Thereby the protective foil 37 allows a failure-free sealing of the tear-open foil 25 onto the lid ring and protects the adhesive surface 30.
After that, the protective foil 37 is removed and the tab 29 is folded back onto the free adhesive surface 30, where it is fixed by the adhesive material, leading to the lid 28 shown in FIGS. 9 and 10. In the example of FIG. 11, the removal of the protective foil 37 takes place in the station 40 and the folding back of the tab 29 in station 41. In between, the lid is turned into a defined position for the folding back, which may however be equally done before. The lid 28 with the adhering and folded back tab is viewable at the end of the conveyor line of FIG. 11. The folding back of the tab is already known to the skilled person and is not explained in more detail here. On the other hand, the stamping out of the adhesive regions and the removal of the protective foil 37 is elaborated in more detail in the following.
Equally, an adhesive surface in form of a surface 30 of sealing paint may be provided for fixing the tab 29 onto the lid 28 instead of the preferred double sided adhesive tape. An adhesive material may also be applied instead of a sealing paint. The adhesive surface 30 is also applied onto the band 35 before the stamping out of the foil section 25 and the applying on a region of the band 35, onto which the tab 29 is being folded back for the finished lid 28, also takes place in these cases. The sealing paint or the adhesive material may be imprinted on the band 35, for example by means of printing rollers or by means of pad printing or they may be sprayed on it. This may occur directly before the sealing of the foil section 25, as shown in FIG. 11 for the adhesive tape. The applying of the adhesive surface 30 by means of sealing paint or of an adhesive material may however take place beforehand, particularly during the manufacturing of the band 35 out of the tear-open foil material, wherein a covering with a protective foil may be provided in case of using an adhesive material, this not being necessary in case of forming the adhesive surface 30 with sealing paint, because the latter doesn't cause an adherence until the sealing.
A further sealing process at the adhesive surface 30 is necessary in case of the sealing paint, when the tab is folded back. This may take place in the station wherein the stamping is applied (FIG. 7). A separate sealing station for this step may also be provided, for example instead of the removal of the protective foil shown in FIG. 11, wherein in this case 40 may identify a station for folding back and sealing of the tab 29 and the station 41 would be obsolete.
FIG. 12 shows the stamping out of the parts of the double sided adhesive tape 33 forming the adhesive surfaces 30. The double sided adhesive tape 33 is peeled off from a roll 34 and lead over the band 35, this being viewable in FIG. 12 as a cut from the drawing plane. The band 35 runs over a supporting surface 36 in the region of the four actuated stamping machines 38, in order for the stamping tools to be able to press the stamped out piece of adhesive tape onto the band 35. The structure of actuated stamping tools 38 for the adhesive tape 33 is a technical measure. The tape 33 is not adhering on the surface of the tape 33 because of the protective foil 37, such that the stamp of each stamping tool doesn't have to be protected against an adherence to the adhesive tape. The lower side of the adhesive tape is adhesive, such that the die and the vicinal regions of the stamping tool have to be furnished with an anti-adherence coating, for example a Teflon coating, in order for the adhesive tape not to adhere to the die or to its vicinity during the stamping out.
The removal of the protective foil 37 from the adhesive surface 30 is explained by means of FIGS. 13 and 14. For this, on the one hand, an air jet 43 is blown obliquely from the side onto the adhesive surface 30, thus lifting and loosening the protective foil. On the other hand, a suction flow 46 is generated and therefore air above the adhesive surface is aspirated, thus removing the loosened protective foil 37. FIGS. 13 and 14 show a partially cut view of a station 41 without the conveying installation or the support means for the lid 28 respectively. Preferably, the pressurized air, indicated with arrows 43, is blown around and obliquely onto the border of the adhesive surface 30 via an annular nozzle 44. The border of the adhesive surface is preferably enlarged compared to a round adhesive surface, by stamping out the adhesive tape star-shaped or toothed wheel shaped. This enhances the removal of the protective foil 37 from the adhesive tape if the air is blown from the side on the adhesive surface. A suction opening 45 arranged centred above the adhesive surface 30 can suck off the loosened protective foil 37 by means of a suction flow 46 generated by under pressure. Additionally to the removal of the protective foil 37 by means of air, a mechanical removal by means of grippers or fingers may be provided, lifting the protective foil at least at the border of the adhesive surface.
During the manufacturing of tear-open lids 28 out of lid rings 20′ with sealed tear-open foil 25 with a tear-open tab 25 on it, the tear-open tab is thereby fixed by an adhesive surface 30 which is applied out of a band 35 of this material onto the tape. In this way, a simple and suitable tab fixing for the production of tear-open lids with high speed results.
