Method and station for sealing a lid film to a packaging tray

Abstract

Method for sealing a lid film (8) to a packaging tray (7) by means of a sealing station (2), wherein the sealing station (2) has a tool upper part (3) and a tool lower part (4) and wherein a sealing frame (5) with a heated sealing surface (5b) is arranged on the tool upper part (3), wherein the method comprises the following steps: Clamping of at least one clamping area (81) of the cover film (8) between the upper tool part (3) and the lower tool part (4), Heating a sealing area (82) of the lid film (8) by means of the heated sealing surface (5b) such that a transition area (83) of the lid film (8) located between the clamping area (81) and the sealing area (82) receives a temperature gradient increasing towards the sealing area (82), Sealing the sealing area (82) of the lid film (8) to the packaging tray (7) on a packaging tray receptacle (6), and Generating a tensile stress (σ) in the transition area (83) of the lid film (8), characterized by Separation of the lid film (8) at a warmest section (83a) of the transition area (83) if the tensile stress (σ) corresponds to at least one tensile strength (Rm) of the lid film (8).

Description

[0001] The present invention relates to a method for sealing a lid film to a packaging tray by means of a sealing station, a sealing station for sealing a lid film to a packaging tray or a packaging machine, preferably a tray sealing machine, comprising a sealing station for sealing a lid film to a packaging tray. State of the art

[0002] Sealing stations and methods for cutting a lid film are known from the prior art. For example, EP 2 441 683 A1 teaches a method for cutting a lid film with a knife that is attached to and movable with a sealing frame. Upon contact of the knife with the lid film, the knife cuts the lid film.

[0003] The disadvantage of this design is that a knife is required to separate the lid film. Furthermore, some lid films, such as lid films, cannot be cut at all or only inadequately using this method. Task

[0004] Based on the known state of the art, the technical problem to be solved is to provide a method for sealing a lid film to a packaging tray using a sealing station, a sealing station for sealing a lid film to a packaging tray, or a packaging machine, preferably a tray sealing machine, comprising a sealing station for sealing a lid film to a packaging tray, which enables simple and efficient separation of a lid film. Ideally, costs should also be reduced. Solution

[0005] This problem is solved according to the invention by a method for sealing a lid film to a packaging tray by means of a sealing station according to claim 1, a sealing station for sealing a lid film to a packaging tray according to claim 11 or a packaging machine, preferably tray sealing machine, comprising a sealing station for sealing a lid film to a packaging tray according to claim 12.

[0006] Advantageous embodiments of the invention are covered in the dependent claims.

[0007] A method for sealing a lid film to a packaging tray using a sealing station is disclosed, wherein the sealing station has a tool upper part and a tool lower part, and wherein a sealing frame with a heated sealing surface is arranged on the tool upper part.The process comprises the following steps: clamping at least one clamping area of ​​the lid film between the upper and lower tool parts; heating a sealing area of ​​the lid film using the heated sealing surface such that a transition area of ​​the lid film located between the clamping area and the sealing area experiences a temperature gradient increasing towards the sealing area; sealing the sealing area of ​​the lid film to the packaging tray at a packaging tray holder; generating tensile stress in the transition area of ​​the lid film; and separating the lid film at the warmest section of the transition area when the tensile stress is at least equal to the tensile strength of the lid film. The process allows the lid film to be separated even without a knife.Unlike cutting the lid film with a knife, the mechanism of the present method for separating the lid film is based on an interaction of tensile stress and temperature gradient in the transition zone. A heated sealing frame is typically used to seal the lid film to the packaging tray. The advantage of the present method is that the sealing frame can perform a dual function: it heats the sealing area of ​​the film to create a seal and also heats the transition zone. This reduces the number of components required and ideally lowers maintenance requirements, such as cleaning, sharpening, or replacing the knife, as well as costs.

[0008] Furthermore, a sealing station for sealing a lid film to a packaging tray is disclosed. The sealing station is designed to carry out the process in at least one of the variants disclosed in this intellectual property right.

[0009] Furthermore, a packaging machine, preferably a tray sealing machine, is disclosed. The packaging machine has a sealing station for sealing a lid film to a packaging tray.

[0010] One aspect of the invention relates to a method for sealing a lid film to a packaging tray using a sealing station, wherein the sealing station comprises a tool upper part and a tool lower part, and wherein a sealing frame with a heated sealing surface is arranged on the tool upper part. The method includes the following steps: - Clamping of at least one clamping area of ​​the lid film between the upper and lower tool parts, - Heating a sealing area of ​​the lid film by means of the heated sealing surface in such a way that a transition area of ​​the lid film located between the clamping area and the sealing area receives a temperature gradient increasing towards the sealing area, - Sealing the sealing area of ​​the lid film to the packaging tray on a packaging tray holder, - Creating a tensile stress in the transition area of ​​the lid film, and - Separation of the lid film at the warmest section of the transition area, if the tensile stress corresponds to at least one tensile strength of the lid film.

[0011] This method allows the lid film to be separated easily and efficiently at the warmest section of the transition zone. This warmest section is determined by the temperature gradient and the tensile stress prevailing in the transition zone. In the context of the invention, the tensile strength of the lid film can be its tear strength. It can indicate the maximum mechanical tensile stress with which the lid film can be subjected before it tears.

[0012] By heating the lid film, its tensile strength can be locally reduced. Preferably, the heating is carried out such that the tensile strength of the lid film at its warmest section of the transition area is reduced by 4–15 N / mm². 2 is reduced compared to the tear resistance of the lid film in its cold state (i.e. at room temperature).

[0013] For example, the tear strength of the lid film in a cold state can be approximately 20 N / mm². 2 for example, the warmest section of the lid film can be heated to a temperature at which the tear strength is only approximately 10 N / mm². 2 up to 16 N / mm 2 amounts.

[0014] The process also offers the advantage that no additional components, such as a knife, are required to cut the lid film. Ideally, the installation space of the sealing station can be reduced, thus minimizing maintenance, such as sharpening or changing the knife. This results in a cost-effective lid film separation process.

[0015] The packaging tray can be flat or at least have a contour, in particular a depression, with an edge in some sections.

[0016] The clamping area can be completely enclosed. Multiple clamping areas, particularly opposing clamping areas, can also be provided.

[0017] An area of ​​the lid film between at least one clamping area can be suctioned to an inner surface of the sealing tool by means of a suction device.

[0018] The inner surface of the sealing frame can be heated by means of a heating device, in particular an electric one. The sealing surface of the sealing frame can be heated by means of a heating device, in particular an electric one. The sealing surface and the inner surface can be heated by means of a common heating device or by means of separate heating devices.

[0019] The temperature of the heating device and / or the inner surface of the sealing frame and / or the sealing area of ​​the sealing frame can depend on the lidding film, in particular its material and / or thickness. The temperature of the inner surface of the sealing frame can be lower than the melting point of the lidding film. The temperature of the inner surface can be at least equal to the temperature at which the lidding film is deformable.

[0020] The temperature of the sealing surface can correspond to the melting point of the lid film. The temperature of the sealing surface or sealing area can be greater than 150 °C, in particular greater than 180 °C. The temperature of the sealing surface or sealing area can be less than 220 °C, in particular less than 200 °C.

[0021] The temperature at the warmest section of the transition zone can be equal to or less than the temperature of the sealing zone. The temperature at the warmest section of the transition zone can be at least 70%, and in particular at least 80%, of the temperature of the sealing zone. The temperature gradient at the transition zone can be less than 90°C, and in particular less than 70°C. The temperature gradient at the transition zone can be greater than 40°C, and in particular greater than 30°C.

[0022] The film material can be any suitable material. For example, the material can be or include polyethylene (PE) or ethyl vinyl alcohol (EVOH). Optionally, the film can consist of a composite material made of several films, for example, polyethylene (PE) or ethyl vinyl alcohol (EVOH).

[0023] The thickness of the lid film can be less than 100 µm, in particular less than 90 µm. The thickness of the lid film can be greater than 70 µm, in particular greater than 80 µm. The thickness of the lid film can be constant.

[0024] The tensile stress required to separate the lid film in the transition area of ​​the lid film can depend on the temperature of the sealing surface.

[0025] Preferably, the sealing frame is moved relative to the lower part of the tool to generate the tensile tension in the transition area of ​​the lid film. For this purpose, the sealing frame can be driven by a drive device, particularly an electric or hydraulic one. The advantage of this design is that no additional component is required to tension the lid film. The sealing frame can therefore perform a dual function: on the one hand, it seals the sealing area of ​​the lid film to the packaging tray, and on the other hand, it generates the tensile tension in the transition area of ​​the lid film. Ideally, The installation space is reduced, maintenance effort is reduced, and costs for the process are lowered.

[0026] Preferably, the sealing frame and the packaging tray holder are moved together with the sealing area of ​​the lid film and the packaging tray relative to the lower tool body to generate the tensile stress in the transition area of ​​the lid film when the sealing area of ​​the lid film and the packaging tray are clamped. For this purpose, the packaging tray holder can be movable relative to the lower tool body, in particular via at least one (compression) spring connected to the lower tool body and the packaging tray holder. Depending on the type of lid film used or the temperature gradient present in the transition area of ​​the lid film, a mere movement of the sealing frame relative to the lower tool body may not be sufficient to generate a tensile stress in the transition area of ​​the lid film that is large enough to reach or exceed the tensile strength of the lid film.In such a case, it may be necessary to further increase the tensile stress until the tensile strength of the lid film is reached or exceeded. The method therefore offers a simple and efficient way to generate or increase the tensile stress in the transition area of ​​the lid film.

[0027] Preferably, the temperature gradient at the transition zone is generated contactlessly by radiant heat from the sealing frame and / or by heat conduction in the lid film originating from an area of ​​the lid film contacted by the sealing frame. Contactless heating prevents wear or damage to the sealing frame, for example, if the lid film sticks to the warm sealing frame. This reduces maintenance and repair costs for the sealing frame. A gap between the sealing frame and the transition zone of the lid film ensures that the transition zone is not exposed to excessive heat from the sealing frame. This prevents overheating or even melting of the transition zone. The distance of the transition zone from the sealing frame can influence the temperature gradient within the transition zone.The gap can decrease while tensile stress is generated in the transition area of ​​the lid film. The minimum gap can be at least 1.00 mm, in particular at least 2.00 mm. The minimum gap can be at most 10.00 mm, in particular at most 5.00 mm.

[0028] Preferably, the transition area of ​​the lid film is located near or adjacent to the sealing area. This offers the advantage that the transition area can be heated easily and efficiently. The sealing area is heated for sealing by means of the heated sealing surface of the sealing frame. If the transition area of ​​the lid film is located near or adjacent to the sealing area, the heat from the sealing area can be at least partially transferred to the transition area. The method thus offers a simple way to generate a temperature gradient at the transition area of ​​the lid film that increases towards the sealing area.

[0029] Preferably, the lid film is separated while the sealing area of ​​the lid film and the packaging tray are clamped. This increases the reliability of the process. Separating the lid film while the sealing area of ​​the lid film and the packaging tray are clamped ensures that the sealing area of ​​the lid film and the packaging tray can be reliably sealed.

[0030] Preferably, the lid film is separated before or during the sealing process to the packaging tray. A seal is created between the sealing area of ​​the lid film and the packaging tray. If the lid film is separated after sealing, the seal can be damaged. This method therefore offers the advantage of avoiding incomplete and / or damaged seals and increasing the quality of the seal. Ideally, the process time can also be reduced and productivity increased.

[0031] Preferably, the interior of the packaging tray is evacuated and / or gassed before sealing. This has the advantage that the quality and / or shelf life of the contents of the packaging tray and the lid film can be specifically influenced, and in particular improved. Furthermore, the appearance of the sealed packaging tray and the lid film can be influenced, and in particular improved.

[0032] Preferably, the tensile stress is constant across the entire transition area. This prevents varying tensile stresses from occurring at the transition point, which could hinder reliable separation of the lid film at a desired section. This improves the reliability and efficiency of the process.

[0033] The characteristics or explanations described for one of the aspects (process, sealing station or packaging machine) can be transferred to and combined with the other aspects, either individually or in combination.

[0034] The invention is explained below using exemplary embodiments. The following are shown: Fig. 1 a schematic side view of a packaging machine according to one embodiment; and Fig. 2a-2c a schematic partial side view of a sealing station according to one embodiment.

[0035] Fig. Figure 1 shows a schematic side view of a packaging machine 1 according to one embodiment. This can be, as in the present example, a tray sealing machine. It can include a frame 10. The packaging machine 1 can further have a feed conveyor 12. It can also have a sealing station 2, which will be described in more detail later. Filled but at this point still unsealed packaging trays 7 can be conveyed to the sealing station 2 by the feed conveyor 12. The packaging trays 7 can be transferred to the sealing station 2 by a gripper device 11 and sealed there with a lidding film 8 fed from above, for example by sealing the lidding film 8. Before or during the sealing of the lidding film 8, areas of the lidding film 8 corresponding to the packages or packages can be cut out from the web of the lidding film 8 in the sealing station 2.A residual film grid of the top film 8 remains, which is wound up using a device 13 for winding the film 8. The packages thus completed can be transferred from the sealing station 2 to a discharge conveyor 15 via the gripper device 11.

[0036] In the Fig. 2a-2c shows a sealing station 2 in a schematic sectional view at different phases of the sealing process. Fig. Figures 2a-2c each show only a first section of the sectional view of sealing station 2. This first section can be mirrored on the right edge of the image to show the complete sectional view.

[0037] In Fig. Figure 2a shows a tool upper part 3 with a sealing frame 5, a tool lower part 4, and a packaging tray holder 6. The sealing frame 5 has an inner surface 5a and a heated sealing surface 5b, each heated by a heating device (not shown). A packaging tray 7 is arranged on the packaging tray holder 6. In this exemplary embodiment, the packaging tray 7 is flat. Fig. Figure 2a further shows a cover film 8 with a circumferentially closed clamping area 81, which is clamped between the upper tool part 3 and the lower tool part 4. The cover film 8 consists, for example, of a composite material made of, for example, three films, of which the two outer films are made of polyethylene (PE) and the middle film of ethyl vinyl alcohol (EVOH). The thickness of the cover film 8 is, for example, 95 µm and is constant throughout the entire transition area 83. The melting point of this cover film 8 is approximately 170 °C. The tensile strength Rm of the cover film 8 in a cold state is approximately 20 N / mm². 2The lid film 8 can be deformed at a temperature of approximately 80 °C. The specifications regarding the material, temperature, and thickness of the lid film 8 are merely examples and do not restrict the protected area. An inner area 84 of the lid film 8, located between the clamping area 81, is drawn against the inner surface 5a of the sealing tool 5 by means of a suction device (not shown). has a temperature of approximately 85 °C. Fig. 2a the sealing surface 5b of the sealing frame 5 does not contact the lid foil 8.

[0038] In Fig. Figure 2b shows the sealing station 2 in a position where the sealing frame 5 is moving towards the lower tool part 4. During this movement, the sealing surface 5b of the sealing frame 5 contacts a sealing area 82 of the lid film 8 and heats it. A transition area 83 is located between the clamping area 81 and the sealing area 82. In this embodiment, the transition area 83 borders the sealing area 82. As the sealing frame 5 moves, it approaches not only the sealing area 82 but also the transition area 83. However, there is no contact between the sealing frame 5 and the transition area 83. The transition area 83 is heated without contact by radiant heat from the sealing frame 5, so that the temperature at the warmest section 83a of the transition area 83 is approximately 160 °C.Towards the clamping area 81, the temperature of the transition area 83 decreases steadily to approximately 80 °C, as no heat acts on the transition area 83 there. Thus, the transition area 83 of the lid film 8 experiences a temperature gradient of approximately 80 °C, increasing towards the sealing area 82. During the movement of the sealing frame 5, an increasing tensile stress σ is generated in the transition area 83 of the lid film 8. Since the thickness of the lid film 8 is constant throughout the entire transition area 83, the tensile stress σ is constant over the entire transition area 83.

[0039] In Fig. 2c shows the sealing station 2 in a position where the sealing frame 5 is positioned starting from the Fig. 2b is moved even further towards the lower part of the tool 4. The sealing frame 5 moves the sealing area 82 along with it until the sealing area 82 of the lid film 8 and the packaging tray 7 contact and are clamped at the packaging tray receptacle 6. The movement of the sealing frame 5, or rather the sealing area 82, further increases the tensile stress σ in the transition area 83. Due to the heat, the tensile strength Rm of the lid film 8 at the warmest section 83a of the transition area 83 is approximately 12 to 16 N / mm². 2 reduced. In Fig. 2c the tensile stress σ reached the tensile strength Rm of the lid film 8 in the warmest section 83a of the transition area 83; consequently, the lid film 8 was separated there. A seal is formed between the sealing area 82 of the lid film 8 and the packaging tray 7 after the separation process.

Claims

[1] Method for sealing a lid film (8) to a packaging tray (7) using a sealing station (2), wherein the sealing station (2) has a tool upper part (3) and a tool lower part (4) and wherein a sealing frame (5) with a heated sealing surface (5b) is arranged on the tool upper part (3), the method comprising the following steps: Clamping of at least one clamping area (81) of the cover film (8) between the upper tool part (3) and the lower tool part (4), Heating a sealing area (82) of the lid film (8) by means of the heated sealing surface (5b) such that a transition area (83) of the lid film (8) located between the clamping area (81) and the sealing area (82) receives a temperature gradient increasing towards the sealing area (82), Sealing the sealing area (82) of the lid film (8) to the packaging tray (7) on a packaging tray receptacle (6), and Generating a tensile stress (σ) in the transition area (83) of the lid foil (8), characterized by Separation of the lid film (8) at a warmest section (83a) of the transition area (83) if the tensile stress (σ) corresponds to at least one tensile strength (Rm) of the lid film (8). [2] Method according to claim 1, characterized by , that the sealing frame (5) is moved relative to the lower part of the tool (4) to generate the tensile stress (σ) in the transition area (83) of the lid film (8). [3] Method according to claim 1 or 2, characterized by , that the sealing frame (5) and the packaging tray holder (6) together with the sealing area (82) of the lid film (8) and the packaging tray (7) are moved relative to the tool base (4) to generate the tensile stress (σ) in the transition area (83) of the lid film (8) when the sealing area (82) of the lid film (8) and the packaging tray (7) are clamped. [4] Method according to any of the preceding claims, characterized by , that the temperature gradient at the transition area (83) is generated without contact via the sealing frame (5). [5] Method according to any of the preceding claims, characterized by , that the transition area (83) of the lid film (8) is near or adjacent to the sealing area (82). [6] Method according to any of the preceding claims, characterized by , that the lid film (8) is separated while the sealing area (82) of the lid film (8) and the packaging tray (7) are clamped. [7] Method according to any of the preceding claims, characterized by , that the separation of the lid film (8) takes place before or during the sealing of the lid film (8) to the packaging tray (7). [8] Method according to any of the preceding claims, characterized by , that the interior of the packaging tray (7) is evacuated and / or fumigated before sealing. [9] Method according to any of the preceding claims, characterized by , that the tensile stress (σ) is constant over the entire transition area (83). [10] Sealing station (2) for sealing a lid film (8) to a packaging tray (7) which is designed to carry out the method according to one of the preceding claims. [11] Packaging machine (1), preferably tray sealing machine, comprising a sealing station (2) for sealing a lid film (8) to a packaging tray (7), which is designed to carry out the method according to one of claims 1 to 9.

Images