SEALING SUPPORTED BY PRESSURIZED AIR

Abstract

A method of closing a packaging tray comprises arranging a packaging tray between a lower tool and an upper tool of a sealing station, positioning a cover film above the packaging tray between the lower tool and the upper tool, and pressing together the cover film and the packaging tray by a lower sealing surface of the lower tool and an upper sealing surface of the upper tool cooperating with the lower sealing surface. During the pressing together, a connection is established between the cover film and the packaging tray along a sealing seam. While the cover film and the packaging tray are being pressed together, an overpressure is locally generated by supplying pressurized gas from a pressurized-gas source, the overpressure cooperating as a counterpressure with the lower sealing surface or with the upper sealing surface so as to press the cover film and the packaging tray together.

Claims

1. A method of closing a packaging tray, the method comprising: arranging a packaging tray, which is filled with a product to be packed, between a lower tool and an upper tool of a sealing station; positioning a cover film above the packaging tray between the lower tool and the upper tool of the sealing station; and pressing together the cover film and the packaging tray by a lower sealing surface of the lower tool and an upper sealing surface of the upper tool cooperating with the lower sealing surface, a connection between the cover film and the packaging tray being established along a sealing seam during the pressing together; wherein an overpressure is locally generated by supplying pressurized gas from a pressurized-gas source while the cover film and the packaging tray are being pressed together, the overpressure cooperating as a counterpressure with the lower sealing surface or with the upper sealing surface so as to press the cover film and the packaging tray together.

2. The method according to claim 1, wherein the overpressure is generated in an area in which the packaging tray locally has a reduced thickness.

3. The method according to claim 1, wherein the packaging tray comprises at least two superimposed material layers, wherein the overpressure is generated in an area in which at least one material layer of the packaging tray is omitted.

4. The method according to claim 1, wherein the overpressure is generated at at least one corner of the packaging tray.

5. The method according to claim 1, wherein the lower sealing surface or the upper sealing surface has provided therein a pressurized-gas aperture and the overpressure is provided via the pressurized-gas aperture.

6. The method according to claim 1, wherein generation of the overpressure by supplying the pressurized gas only takes place after the cover film and the packaging tray have been pressed together by the lower sealing surface and the upper sealing surface at least for a first period of time.

7. The method according to claim 1, wherein the overpressure is reduced again before the pressing together of the cover film and the packaging tray by the lower sealing surface and the upper sealing surface is terminated.

8. The method according to claim 1, wherein the overpressure is a pressure of at least 4 bar.

9. The method according to claim 1, wherein the overpressure is a pressure of at least 5 bar.

10. The method according to claim 1, wherein the overpressure is a pressure of at least 6 bar.

11. The method according to claim 1, wherein the pressurized gas is actively heated before it is supplied.

12. A sealing station comprising: a lower tool provided with a lower sealing surface; an upper tool provided with an upper sealing surface and arranged above the lower tool; a drive unit configured to move the lower tool and the upper tool towards each other, or to move one of the lower and upper tools toward the other, so that a packaging tray and a cover film for closing the packaging tray may be pressed together between the lower sealing surface and the upper sealing surface when the packaging tray and the cover film are positioned between the lower tool and the upper tool; and a pressurized-gas source, wherein the lower sealing surface or the upper sealing surface has provided therein a pressurized-gas aperture, which is configured to allow an escape of pressurized gas provided by the pressurized-gas source.

13. The sealing station according to claim 12, wherein the lower sealing surface or the upper sealing surface comprises a depression, and wherein the pressurized-gas aperture is arranged in the depression.

14. The sealing station according to claim 12, further comprising a valve configured to selectively prevent or allow a flow of the pressurized gas from the pressurized-gas source to the pressurized-gas aperture, and a control unit configured to control the drive unit for pressing the packaging tray and the cover film together by means of the lower sealing surface and the upper sealing surface and to control the valve for allowing the flow of the pressurized gas to the pressurized-gas aperture after the cover film and the packaging tray have been pressed together at least for a predetermined first period of time.

15. The sealing station according to claim 12, wherein the lower tool is configured as a tray holder for receiving the packaging tray, wherein the lower sealing surface provides a support surface for a flange of the packaging tray.

16. A method of closing a packaging tray, the method comprising: using pressurized gas for providing a counterpressure upon connecting a packaging tray and a cover film along a sealing seam by pressing the packaging tray and the cover film together by a lower sealing surface and an upper sealing surface.

17. The method according to claim 16, wherein, with respect to a length of the sealing seam, the pressurized gas is supplied only locally, so as to compensate for a local irregularity in the packaging tray.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In the following, the present disclosure will be explained in more detail on the basis of an embodiment with reference to the figures, in which

[0030] FIG. 1 shows a schematic perspective view of a packaging machine including a sealing station according to an embodiment;

[0031] FIG. 2 shows a schematic top view of a package, which has been closed by means of the sealing station, according to the embodiment;

[0032] FIG. 3 shows a schematic sectional detail view of the package, the section line being depicted as I-I in FIG. 2;

[0033] FIG. 4 shows the package according to FIG. 2 in a schematic perspective view from below;

[0034] FIG. 5 shows a detail view of the area F according to FIG. 4;

[0035] FIG. 6 shows a schematic top view of the lower tool of the sealing station according to the embodiment; and

[0036] FIG. 7 shows a schematic sectional view during the sealing process, the position of the section being identified by II-II in FIG. 6.

DETAILED DESCRIPTION

[0037] FIG. 1 shows a packaging machine 1 according to an embodiment. The packaging machine 1 comprises a feed device 3 for packaging trays 4 to be closed, which are filled with a product, (cf. FIG. 2). The packaging trays 4 are transferred from the feed device 3 along a production direction P by means of a gripper system to a sealing station 5. In the sealing station 5, the packaging trays 4 are sealed with a cover film 7. The cover film 7 may be a plastic film. The cover film 7 is fed to the sealing station 5 from a supply roll (not shown), which is attachable to a film holder 8 of the packaging machine 1. The sealing station 5 comprises a lower tool 9 and an upper tool 11. The lower tool 9 and the upper tool 11 are arranged one above the other. By means of a drive unit 13, the sealing station 5 can be moved between an open position and a closed position. In the open position, the lower tool 9 and the upper tool 11 are spaced apart from each other along a vertical direction so that packaging trays 4 to be closed may be transferred to the lower tool 9 and a corresponding section of the cover film 7 for closing the packaging trays 4 may be moved to an area between the lower tool 9 and the upper tool 11, so as to extend above the packaging trays 4. From the open position, the sealing station 5 is moved to a closed position or sealing position in that the drive unit 13 moves the lower tool 9 and the upper tool 11 towards each other along the vertical direction. It should be noted that both the lower tool 9 and the upper tool 11 may be moved, or only either the lower tool 9 or the upper tool 11 may be moved.

[0038] During a sealing process, a packaging tray 4 and the cover film 7 are pressed together and connected to each other by means of the lower tool 9 and the upper tool 11. This is preferably done under the action of heat. For example, the lower tool 9 and/or the upper tool 11 may be heated to support the sealing process.

[0039] When the sealing process has been finished, the sealing station 5 is opened again and the sealed packaging trays 4 are transferred to a discharge device 15.

[0040] FIG. 2 shows a schematic top view of a finished package 16, which has been sealed in the sealing station 5. The package 16 comprises the packaging tray 4 and the cover film 7 closing the packaging tray 4. The packaging tray 4 is shown as a rectangular packaging tray. It goes without saying that also arbitrary other shapes of packaging trays 4 are imaginable. The packaging tray 4 includes a flange 17 which runs around the packaging tray 4. The flange 17 provides a connection area for connection to the cover film 7. As shown in FIG. 2, the packaging tray 4 and the cover film 7 have been connected to each other along a circumferentially extending sealing seam 19 during the sealing process. The sealing seam 19 extends fully around the packaging tray 4 along the flange 17.

[0041] FIG. 3 shows a sectional detail view through the package 16, which is shown in FIG. 2, with respect to the section line I-I. From FIG. 3 it can be seen that the packaging tray 4 consists of two superimposed layers of material, a first material layer 21 and a second material layer 23. The first material layer 21 represents a structural layer, which determines the shape of the packaging tray 4 and provides the necessary rigidity. The first material layer 21 may, for example, be configured as a cardboard layer or a paper layer. The second material layer 23 is arranged on top of the first material layer 21 on the side facing the product. The second material layer 23 may be configured as a film layer, so as to provide an oxygen barrier between the product and the surroundings. In particular, the second material layer 23 may be a plastic film layer. In the illustrated embodiment, sealing between the cover film 7 and the packaging tray 4 takes place along the sealing seam 19 between the cover film 7 and the second material layer 23 of the packaging tray 4.

[0042] FIG. 4 shows the package 16 in a perspective view from below. In FIG. 4, it can be seen that the first material layer 21 of the packaging tray 4 is not configured as a continuous layer. In the area of the corners of the packaging tray 4, the first material layer 21 has slits 25. The slits 25 are provided to facilitate folding of the first material layer 21 into the packaging tray 4. The slits 25 also extend across the flange 17. In particular, the slits 25 extend substantially radially outwards across the flange 17.

[0043] FIG. 5 shows a detailed view of the area F in FIG. 4. In FIG. 5, it can be seen that the second material layer 23 extends across the slits 25. This ensures that the packaging tray 4 will be tight also in the area of the slits 25. In particular, the second material layer 23 is configured such that it is continuous across the flange 17.

[0044] FIG. 6 shows a schematic top view of the lower tool 9 of the sealing station 5. The lower tool 9 defines a tray holder for receiving the packaging tray 4. The body of the packaging tray 4 may be received in a receiving space 27 of the lower tool 9, while the flange 17 of the packaging tray 4 rests on a lower sealing surface 29 of the lower tool 9. The lower sealing surface 29 defines a support for the flange 17 of the packaging tray 4.

[0045] FIG. 7 is a sectional view with respect to the section line II-II of FIG. 6 during the sealing process. FIG. 7 also shows the packaging tray 4, the cover film 7 and the upper tool 11, which have been omitted in FIG. 6 for the sake of clarity. The upper tool 11 includes an upper sealing surface 31 that faces downwards. The lower sealing surface 29 and the upper sealing surface 31 face each other. The lower sealing surface 29 and the upper sealing surface 31 may each be configured as horizontal, flat surfaces. During the sealing process, the packaging tray 4 and the cover film 7 are pressed together between the lower sealing surface 29 and the upper sealing surface 31 and are thus connected. Preferably, this is done under the action of heat, so as to facilitate the process. For example, the lower tool 9 and the upper tool 11 may be heated by means of an integrated heating device 33.

[0046] In the areas of the flange 17 where the packaging tray 4 is formed by both the first material layer 21 and the second material layer 23 superimposed thereon, i.e., everywhere except in the area of the slits 25, there is direct contact between the lower sealing surface 29 and the flange 17 and direct contact between the upper sealing surface 31 and the cover film 7 during the sealing process. When the packaging tray 4 and the cover film 7 are pressed together, the lower sealing surface 29 will act as a counterpressure element for the upper sealing surface 31 and the upper sealing surface 31 will act as a counterpressure element for the lower sealing surface 29 in these areas. In the area of the slits 25, this is not the case due to the reduced thickness of the packaging tray 4 (because of the local absence of the first material layer 21). In the area of the slits 25, the packaging tray 4 does not rest against the lower sealing surface 29. Thus, the lower sealing surface 29 cannot effectively act as a counterpressure element during sealing in the area of the slits 25. Without additional measures, this would lead to a weak point in the sealing seam 19 with a smaller connection strength in the area of the slits 25. In the area of the slits 25, leaks could occur in the connection between the packaging tray 4 and the cover film 7.

[0047] To cope with this problem, pressurized-gas apertures 35 are provided in the lower sealing surface 29 in the area of the corners, at the points where the slits 25 of the packaging tray 4 are located during the sealing process. The pressurized-gas apertures 35 communicate with a pressurized-gas source 37 shown schematically in FIG. 1 and are configured to allow an escape of pressurized gas provided by the pressurized-gas source 37. The sealing station 5 further comprises a valve 39, schematically shown in FIG. 1, which is configured to selectively prevent or allow a flow of the pressurized gas from the pressurized-gas source 37 to the pressurized-gas apertures 35. During the sealing process, the valve 39 is controlled to allow pressurized gas to escape through the pressurized-gas apertures 35 and to locally generate an overpressure in the area of the slits 25. This overpressure cooperates as a counterpressure element with the upper sealing surface 31 in the area of the slits 25 during the sealing process and ensures that the sealing seam 19 will reliably be established with sufficient connection strength and tightness also in the area of the slits 25. In the illustrated embodiment, the pressurized gas presses the second material layer 23 in the area of the slits 25 from bottom to top against the cover film 7 and ensures, together with the upper sealing surface 31, that the packaging tray 4 and the cover film 7 will be pressed together in the area of the slits 25.

[0048] In the following, the sequence of steps of a sealing process in the sealing station 5 will be described. The sealing process is preferably controlled by means of a control unit 41 (cf. FIG. 1) of the sealing station 5. The control unit 41 may be a separate control unit of the sealing station 5 or may, as regards its function, be part of an overall control unit of the packaging machine 1. It is possible, but not necessary, that the control unit 41 is functionally or physically separate from an overall control unit of the packaging machine 1. As one skilled in the art would understand, the control unit 41 may include suitable hardware and software, such as one or more processors (e.g., one or more microprocessors, microcontrollers and/or programmable digital signal processors) in communication with, or configured to communicate with, one or more storage devices or media including computer readable program instructions that are executable by the one or more processors so that the control unit 41 may perform particular algorithms represented by the functions and/or operations described herein. The control unit 41 may also, or instead, include one or more application specific integrated circuits, programmable gate arrays or programmable array logic, programmable logic devices, or digital signal processors.

[0049] When the sealing process starts, the drive unit 13 is activated by the control unit 41, so as to move the lower tool 9 and the upper tool 11 to the closed position and press them together. The packaging tray 4 and the cover film 7 are thereby pressed together along the course of the sealing seam 19 to be established between the lower sealing surface 29 and the upper sealing surface 31. This is done under the action of heat. After the packaging tray 4 and the cover film 7 have been pressed together in this way for a first period of time, the control unit 41 controls the valve 39 to release the flow of pressurized gas to the pressurized-gas apertures 35. As has been described, a local overpressure is built up in the area of the slits 25, so as to press the second material layer 23 of the packaging tray 4 against the cover film 7 from below in these areas. The local overpressure is maintained for a second period of time. After the second period of time has elapsed, the control unit 41 controls the valve 39 to again stop the flow of pressurized gas to the pressurized-gas apertures 35. After the flow of pressurized gas to the pressurized-gas apertures 35 has been stopped, the control unit 41 controls the drive device 13, to open the sealing station 5 again.

[0050] Preferably, the pressurized gas is heated by means of a pressurized-gas heating device 43 before it arrives at the pressurized-gas apertures 35 in order to prevent the sealing area to be cooled down by the pressurized gas. In the illustrated embodiment, the pressurized-gas heating device 43 is provided at the pressurized-gas source 37.

[0051] In the illustrated embodiment, a thickness of the packaging tray 4, which is locally reduced due to a local opening in the first material layer 21, is compensated for by the local supply of the pressurized gas. However, an embodiment according to the disclosure could also be used for compensating other local irregularities in the structure of the packaging tray 4 in the area of the sealing seam 19. For example, instead of an opening in a lower material layer 21 of the packaging tray 4, an opening in an upper material layer 23 of the packaging tray 4 could be compensated for. It would also be imaginable, for example, to compensate irregularities caused by local material differences (with or without thickness differences) of the packaging tray 4 in the area of the sealing seam 19 by locally providing the pressurized gas during the sealing process. For example, a locally increased compressibility of the packaging tray 4 in the area of the sealing seam 19 could be compensated for.

[0052] In the illustrated embodiment, the pressurized-gas apertures 35 are provided in the lower sealing surface 29. In this case, the local overpressure generated by the supply of pressurized gas may cooperate as a counterpressure element with the upper sealing surface 31 during the sealing process. Depending on the respective case of use, it would also be imaginable, alternatively or additionally, to provide suitable pressurized-gas apertures 35 in the upper sealing surface 31. By supplying pressurized gas through these pressurized-gas apertures 35, an overpressure could locally be generated, which could cooperate as a counterpressure element with the lower sealing surface 29 during the sealing process.