Air-tight longitudinal sealing seam for thin films

Abstract

The present invention relates to techniques for producing a sealing seam which air-tightly joins together two film sides, in particular two film sides of a film in the formation of a film tube (3), comprising the following steps: · carrying out a pre-sealing process, wherein at least one of the two film sides is heated in a pre-sealing process and wherein, in the heated state of the at least one film side, both film sides are brought into contact with one another, wherein a pre-sealing seam (32) is formed which joins the two film sides together; · carrying out a final sealing process, wherein the pre-sealing seam (32) is supplied at a transport speed to a pressing means (52), wherein, in terms of the process, the pressing means (52) is arranged downstream of the pre-sealing process, in particular as close as structurally possible, and wherein the pressing means (52) applies force to at least one of the two film sides along the pre-sealing seam (32) substantially perpendicularly to the transport direction (25), as a result of which the pre-sealing seam (32) is made into a final sealing seam (54) which is substantially impermeable to air.

Description

[0001] Airtight longitudinal seal for thin films

[0002] The present invention relates to an airtight longitudinal seal in thin films, such as those used in the food industry for enclosing food, especially cheese. It is important that airtight seals can be created to prevent a food, for example, from reacting with oxygen and thereby losing its desired properties. In addition to food, this can of course also apply to other products that can be enclosed in such a thin film. Furthermore, the invention relates to techniques for producing such an airtight longitudinal seal.

[0003] The following solutions for producing a sealing seam, in particular a longitudinal seam, are known from the state of the art:

[0004] US Pat. No. 5,112,632 by Schreiber describes an apparatus and method for producing an airtight package for a slice of food. An airtight longitudinal seam is created between two film sides by passing both film sides through a heated, wave-shaped tube arrangement, with the waves of the tube arrangement alternately applying pressure to each side of the film against the other film. Disadvantageously, the film is exposed to high mechanical stress, particularly friction, during this process, which can damage the film and, in particular, prevents the film from falling below a certain thickness. Schreiber uses a so-called V-tube for this.

[0005] DE 198 04 221 A1 describes the creation of a longitudinal seam using a low-friction, particularly contactless, process. Two film sides, particularly an O-shaped film tube, are blown onto one side using hot air nozzles, thereby forming a sealed seam between the two film sides along an elongated blowing line. A disadvantage is that the longitudinal seam created in this way is not airtight. The invention is therefore based on the object of specifying techniques that make it possible to produce an at least largely airtight sealed seam in films with as little friction as possible. The disadvantages of the prior art mentioned above are intended to be at least partially eliminated by the techniques presented here.

[0006] The features of the various aspects of the invention or the various embodiments described below can be combined with one another, unless this is explicitly excluded or technically mandatory.

[0007] According to the invention, a method is provided for producing a sealing seam that hermetically connects two film sides, in particular two film sides of a film in the form of a film tube. This method can be used in particular in the packaging of foodstuffs, particularly preferably in the context of cheese packaging. The method comprises the following steps:

[0008] • Carrying out a pre-sealing process, wherein at least one of the two film sides is heated in a pre-sealing process and wherein both film sides are brought into contact with one another in the heated state of at least one film side, wherein a pre-sealing seam is formed which connects both film sides to one another; o In this case, the pre-sealing seam produced still has a certain air permeability. The air permeability is particularly undesirable since it is so high that a food product cannot be sealed airtight if the film is further processed into packaging for the food in a later process. By heating the film, a sealing layer of the film is activated so that the two film sides stick together and adhere to one another at least to a certain extent without the rest of the film being “melted”.The temperature at which the sealing layer is activated is therefore preferably lower than the temperature that would cause structural damage to the remaining layers of the film. The pre-sealing process can, in principle, be implemented using various techniques, as long as this process involves feeding the film in a heated state to the final sealing process described below. In principle, this also includes the possibility of reheating a film with an already cooled pre-sealing seam. A pre-sealing process using a hot air bar is preferred, and will be described in more detail below.

[0009] • Carrying out a final seal, wherein the pre-sealing seam is fed to a pressure means at a transport speed, wherein the pressure means is arranged downstream of the pre-sealing process in terms of process technology, in particular as close as structurally possible, and wherein the pressure means applies force to at least one of the two film sides along the pre-sealing seam essentially perpendicular to the transport direction, whereby the pre-sealing seam is formed into a final seal seam which is essentially impermeable to air. o In particular, the transport speed at which the pre-sealing seam on the film is fed to the pressure means corresponds to the transport speed of the film in upstream and / or downstream processing processes of the film, so that the film is neither built up too much nor stretched too much.However, it may be intended to transport the film in downstream processes at a slightly higher transport speed, since increased tension in the film can lead to a higher sealing pressure of the pressure means; o the closer the pressure means is arranged behind the pre-sealing process in terms of process technology, the less the pre-sealing seam cools down and the more effectively the pressure means can create an airtight final seal; however, it is still the case that the temperature of the pre-sealing seam, when it reaches the final sealing device, is at least slightly lower than in the pre-sealing device; o the force of the pressure means preferably acts perpendicular to the local flat surface that the film forms in the area of ​​the pre-sealing seam.If the pre-sealing seam is created in an embodiment in which the film is designed as a film tube, it cannot, of course, be said that the "entire film" has a film plane. Therefore, in this context, we refer to a "local flat surface in the area of ​​the pre-sealing seam"; o In the case of a film tube, this creates, in particular, a continuous longitudinal seam into which a product, in particular cheese, can be inserted and which is then transformed into individual portions by a final transverse seal;

[0010] The repeated processing of the pre-sealing seam according to the invention has the technical effect of transforming a non-airtight pre-sealing seam into an airtight final seal. A particular advantage of the invention is that the resulting airtight final seal allows the production of airtight inner packaging for packaging food, especially cheese, allowing alternative outer packaging materials such as paper to be used, or even eliminating the need for outer packaging altogether. Furthermore, it is possible to dispense with the need to place the airtight inner packaging in a gassed (CO2 atmosphere) "tight" outer packaging, thus preventing any reaction of the food with the ambient air.

[0011] Sealed packages, which in particular have at least one longitudinal seal and, conventionally, two transverse seals, are also referred to as sealed slices. Such sealed packages are also referred to as primary packaging or inner packaging if they are further packaged in an outer package, also known as secondary packaging or secondary packaging. For example, in cheese production, several cheese slices, each individually packaged in an inner package (so-called IWS), are then packed together in a larger outer package.

[0012] In a preferred embodiment, the pressure means extends into a transport plane of the pre-sealing seam's transport direction, causing the pre-sealing seam to encircle the pressure means, thereby applying force to at least one side of the pre-sealing seam. The transport plane is the local transport plane that forms in the area of ​​the pre-sealing seam.

[0013] This has the technical effect that the preferred structurally simple arrangement of the pressure device alone exerts pressure, also known as sealing pressure, on the pre-sealed seam. This type of passive application of pressure requires very little maintenance and is generally subject to only very small fluctuations, which can be essential for the success of the process, especially with thin films. This sealing pressure generally results from an interaction between the external design of the pressure device, how far this pressure device extends into the transport plane of the film, and the film tension. In order to change the sealing pressure, however, it is most expedient to make changes to the pressure device, for example how far the pressure device extends into the transport plane. The distance the pressure device extends into the transport plane can be adjusted using a simple adjusting screw or a technically automated unit.

[0014] Preferably, the pressure means is designed as a roller.

[0015] This technically advantageously ensures a very even radial application of force from the center of the roll to the pre-sealing seam. Especially with thin films, it is important to avoid peaks in the application of force to prevent damage to the film. The round outer shape of the roll ensures this particularly advantageously when the pre-sealing seam runs at least partially along the outer circumference of the roll.

[0016] In a preferred embodiment, the roller is designed as a passive roller which can be driven by friction with the film, in particular by friction with the pre-sealing seam.

[0017] The advantage of a passive roller is that it does not need to be driven by an additional motor in synchronization with the transport speed, but is automatically brought to the correct rotational speed through friction with the film. This is particularly advantageous when the transport speed of the film fluctuates, to which an external motor can only react with difficulty or with a certain delay. It is particularly advantageous to mount the passive roller on a very low-friction ball or roller bearing. In this way, the tangential friction force on the film, and in particular on the pre-sealed seam, can be significantly reduced.

[0018] In a preferred embodiment, the roller has a smooth outer surface and / or at least on the outer surface a material with a high heat storage capacity, such as stainless steel.

[0019] The smooth surface also has the advantage of minimizing pressure peaks that can cause damage to the film. If the outer surface is at least partially made of a material with a high heat storage coefficient, the roll can also assume a higher temperature during the process, which improves the final sealing. The roll can be heated either by the heated pre-sealing seam or by being positioned close to the pre-sealing device. If the pre-sealing seam is created using hot air nozzles, for example, this heat is radiated onto the roll by positioning the roll close to the hot air nozzles, heating it in addition to the sealing seam. In another embodiment, the roll can also be connected to another heat source that transfers energy to the roll.

[0020] Preferably, a counterpressure is achieved on the opposite side of the pressure medium by applying force to a fluid. This counterpressure has the technical effect that the sealing pressure of the pressure medium can act effectively on the pre-sealed seam and does not run into empty space. This also has the technical effect that the counterpressure can be generated very gently and with as little friction as possible in order to protect the film, which is particularly necessary for thin films. The fluid is preferably air, as air in a very special way provides a kind of quasi-friction-free counterpressure cushion. Other fluids, such as water or oils, are less flexible than air, but can in principle still be used. If food is to be wrapped in the film, it is particularly recommended to use food-safe fluids.

[0021] Preferably, the fluids are supplied to a location opposite the pressure means at a defined pressure and / or a defined temperature. In the embodiment using air as the fluid, the air can be blown at the defined pressure and / or temperature, particularly using nozzles, onto the opposite side of the pre-sealing seam to the roll. The other aforementioned fluids can also be supplied to the opposite side of the pre-sealing seam to the roll using nozzles. A further advantage of using air as the fluid is that the air does not have to be collected and / or disposed of again. Using oil as the fluid allows a higher and more uniform pressure to be generated.

[0022] In particular, it may be provided to supply the fluid in a heated state to the side of the pre-sealing seam opposite the roll. This also has a beneficial effect on the final sealing seam. All temperature-related characteristics that may have a beneficial effect on the final sealing seam can result in the parameters being varied—for example, using a smaller indentation depth T1—so that the mechanical stress on the film can be further reduced, potentially making it possible to use even thinner films.

[0023] Alternatively, it is possible to generate the counterpressure on the opposite side of the pressure means using an additional roller. In this case, the film with the pre-sealing seam is fed through an arrangement of two rollers, at least one of which can be heated. The gap between the two rollers, through which the film is fed, is then particularly smaller than the film thickness, so that the sealing pressure can be generated. Advantageous compared to the variant without the second roller, this alternative can, in principle, generate significantly more pressure on the pre-sealing seam, which can be advantageous for some films that require a higher sealing pressure. This is particularly the case the thicker the film, for example, over 25 μm.

[0024] In a preferred embodiment, the pre-sealing seam of the pre-sealing process is created by blowing hot air onto the film.

[0025] This activates at least one sealing layer of the film and the two sides of the film can stick together in such a way that the pre-sealing seam is formed. Blowing hot air onto at least one of the sides of the film is particularly low-friction and gentle on the film. This process is particularly suitable for thin films. The blowing can be achieved, for example, by at least one hot air bar which comprises a plurality of outlet nozzles from which heated air flows. The superimposed sides of the film are preferably only blown from one side by the hot air bar. The blowing also ensures that one side of the film exerts a certain amount of pressure on the other side of the film so that the pre-sealing seam can form.Preferably, the pre-sealing process is characterized in particular by heating at least one film side and bringing the two film sides into contact by blowing heated air onto at least one film side. At least one film side expediently has a sealing layer that is activated by heating without the remaining film melting at the activation temperature. The activated sealing layer has adhesive properties for bonding the two film sides.

[0026] The pre-sealing process, which can also be referred to as the first sealing process, is preferably characterized by the contactless welding of overlapping films using hot air, creating a first seal, in particular a first longitudinal seal. The first seal is also referred to as the pre-sealing seam because it does not yet have the desired final airtight properties.

[0027] In particular, the hot air for sealing the film during the pre-sealing process can be generated from conventional compressed air, which is heated to a temperature of approximately 170-300° Celsius by suitable heating devices and fed to the film tube via nozzles. The temperature and / or quantity of the supplied hot air can be regulated and quickly adapted to the required conditions.

[0028] A pre-sealing device for the pre-sealing process preferably comprises a housing with at least one air inlet for the compressed air. The compressed air can branch into a series of distribution channels within the housing. The air can then be fed from the distribution channels to at least one heating device via overflow channels. The air heated there is in turn fed via overflow channels to an outlet channel and applied to the film tube via nozzles. The pre-sealing device, i.e., in particular, the outlet nozzles for the hot air, are arranged at a defined distance from the film tube and do not touch it.

[0029] A key advantage of the hot-air pre-sealing process is that thinner films can be used to produce the film tube, as there is no "destructive" contact between the film and the sealing device. This results in significant cost savings in the film material. In principle, the thinner the film, the faster the heating can take place.

[0030] A further advantage is that various parameters of the sealing system, such as temperature, pressure of the incoming cold compressed air, and flow rate of the compressed air, can be adjusted over a wide range without requiring any other structural changes to the rest of the system. Non-contact pre-welding allows the speed of the film tube to be increased.

[0031] However, if only the pre-sealing process is used, a tight seal cannot be created, which is a disadvantage. Another highlight of the invention is the special combination, even in this process sequence, of the pre-sealing process and the final seal. Both processes, considered individually, are not capable of creating a tight seal. A preferred concept of the invention is to combine these two processes to create a tight seal. This concept is also inventive in that, for reasons of efficiency, it would be obvious to optimize a single process instead of combining the pre-sealing process and the final seal.

[0032] Preferably, the two film sides form an O-shaped film tube, with one side of the film, also referred to as the inner side, resting on the other side of the film, also referred to as the outer side. Accordingly, the sealing layer can be provided variably on the inner and / or outer side of the film. If the sealing layer is provided on the outer side of the film, contact between the sealing layer and the food inside the film tube is minimized. This can be advantageous if the sealing layer has components that are not food-safe. Furthermore, the use of an O-shaped film tube is advantageous because it is always under a certain amount of tension. In addition, less material is required for the O-shaped film tube than for the V-shaped film tube. With the V-shaped film tube, the opening tabs of the inner packaging are generated from both film sides (inside to inside).

[0033] The film may preferably have a thickness of less than 30 pm.

[0034] This has the advantage that less film material needs to be used, which saves costs and is also environmentally friendly. It is surprising that a film with a thickness of less than 30 μm can be used to produce packaging that has at least the final seal seam with the airtight properties described above. This is possible thanks to the final sealing process described above and, in particular, by combining the final sealing process with the pre-sealing process of the pre-sealing device. These processes are both very gentle on the material, allowing the use of such thin films. In particular, the thinner the film, the better the one-sided blowing of hot air onto the film works.

[0035] The final seal seam is also called the longitudinal seal seam because it is essentially formed parallel to the transport direction of the film. If a single film was previously folded over itself either to form a V-shaped tube or, preferably, an O-shaped tube, the film is already sealed at this fold point. Typically, the longitudinal seal seam is parallel to the fold. In the transport direction, the tubular bag is then only open at the top and bottom. A product, in particular a foodstuff, most preferably cheese, can be filled through these openings. To ensure that the tubular bag encloses the product, foodstuff or cheese, in particular in an airtight manner, a transverse seal is carried out perpendicular to the transport direction in a subsequent process step.It is known from the prior art how to implement an airtight transverse seal and how, after the transverse seal, the product tube can be severed along the cross-sectional areas, creating an overall airtight film package. This packaging is also referred to as the inner packaging or primary packaging. Since this packaging is made of film, it can also be referred to as the inner film packaging or primary film packaging.

[0036] According to a second aspect of the invention, a device for producing an airtight seal seam that connects two film sides, in particular two film sides of a film in the form of a film tube, is specified. The device is particularly designed to carry out the method described above. The airtight seal seam is in particular a longitudinal seal seam. The device for producing the airtight seal seam comprises:

[0037] • a pre-sealing device configured to carry out a pre-sealing process, wherein at least one of the two film sides is heated in a pre-sealing process by a heating means of the pre-sealing device, and wherein both film sides are brought into contact with one another in the heated state of at least one film side, wherein a pre-sealing seam is formed which connects both film sides to one another. o the pre-sealing device is configured in particular so that the film can be guided through the pre-sealing device. For this purpose, the pre-sealing device can additionally comprise guide means. o the heating means can also be designed in particular to bring the two film sides into contact with one another.In one embodiment, the heating means, as described above, is designed as a hot air bar with a plurality of nozzles through which hot air flows in such a way that at least one side of the film is directly heated and is subjected to a force by the air pressure and pressed onto the other side of the film.

[0038] • a closing device arranged behind the pre-sealing device in terms of process technology and configured to carry out a final seal; the closing device has a pressure means which is arranged such that the pre-sealing seam can be fed to the pressure means at a transport speed and such that at least one of the two heated film sides can be subjected to force along the pre-sealing seam essentially perpendicular to the transport direction by means of the pressure means.

[0039] The advantages of the device for producing an airtight seal are essentially analogous to those described in connection with the method explained above.

[0040] According to a third aspect of the invention, a device for producing an airtight film package is specified, comprising the above-described device for producing an airtight seal, in particular an airtight longitudinal seal, and, in terms of process technology, a transverse sealing device downstream thereof. A film tube having at least one airtight longitudinal seal leaves the device for producing an airtight film package and is fed to the transverse sealing device. The transverse sealing device is configured to provide two transverse seals transversely to the transport direction of the film tube and to separate the film tube into individual airtight packages.In particular, an inlet device can be provided between the final sealing device, which creates an airtight longitudinal seam, and the transverse sealing device to introduce products, especially food products, into the still-open film tube. The film preferably has a thickness of less than 30 μm.

[0041] The device according to the invention for producing an airtight film packaging makes it possible, to our knowledge, for the first time to provide airtight film packaging, so-called IWS, with extremely thin films, so that resources and the environment are efficiently conserved and the products, in particular foodstuffs, are nevertheless hermetically sealed inside the film packaging.

[0042] According to a fourth aspect of the invention, an airtight seal seam is provided, obtainable by the method described above. The airtight seal seam corresponds to the final seal seam, so both terms are equivalent.

[0043] This sealing seam can advantageously be used to produce an airtight film packaging, in particular for foodstuffs such as cheese.

[0044] According to a further aspect of the invention, an airtight film packaging, in particular for food products, is provided, which has at least the above-described airtight seal seam produced by the method according to the invention, in particular as an airtight longitudinal seal seam. Preferably, the packaging has two additional transverse seals.

[0045] Surprisingly, to our knowledge, this is the first airtight film packaging with a longitudinal seal created by this process, especially for films thinner than 30 μm. The film packaging according to the invention is therefore particularly suitable for food products that should not have contact with the ambient air and is also extremely environmentally friendly and resource-saving, as extremely thin films can be used for the first time.

[0046] According to a further aspect of the invention, a combination packaging comprising an air-permeable outer packaging - also referred to as outer packaging - and the above-described airtight film packaging - also referred to as inner packaging - is specified for the storage of air-sensitive foodstuffs.

[0047] Surprisingly, to our knowledge, this is the first communication packaging whose outer packaging can consist of an air-permeable material, such as paper, and an inner packaging, particularly with a film thinner than 30 μm. Conventionally, the outer packaging had to be airtight and additionally gassed to prevent the food inside the inner packaging from reacting with air, especially ambient air.

[0048] The innovative combination packaging not only makes it possible to save film on the inner packaging, but also to completely eliminate film on the outer packaging. The outer packaging therefore only needs to be suitable for holding several individual slices together. Typically, several individual slices of processed cheese, such as 10, are contained in a single outer packaging, making it easier to offer and sell.

[0049] The airtight film packaging described above is also referred to as airtight individual film packaging, especially individual film packaging for food. Such individual film packaging is also known in the trade as an IWS slice (IWS = individual wrapped slice).

[0050] To put it another way: The tight individual film packaging offers the advantage that foodstuffs, in particular, which are contained inside the tight individual film packaging do not react with the ambient air and thus do not suffer any adverse changes in their properties. This advantageously allows the tight individual film packaging to be used as inner packaging surrounded by outer packaging that no longer has to be airtight, and the space between the outer and inner packaging no longer has to be fumigated with carbon dioxide as was traditionally the case, in particular to prevent the food from reacting with the oxygen in the air. To prevent the carbon dioxide from escaping from the space between the inner and outer packaging, the outer packaging was traditionally formed by a tight outer packaging made of a plastic film with a barrier.Thanks to the invention, the outer packaging can now be made at least largely of paper, which is a major environmental advantage, as it efficiently reduces the amount of film used. This type of outer packaging is significantly more sustainable and is also increasingly in demand and required by politicians and customers.

[0051] The outer packaging can also be made of plastic, although this no longer requires fumigation. This outer packaging—whether film or paper—is preferably opaque to prevent the food from reacting with light.

[0052] According to a further aspect of the invention, the combination packaging already described above can also be additionally or alternatively configured as follows: Combination packaging comprising an inner airtight film packaging, in particular comprising at least the inventive airtight seal seam described above, and an outer packaging as described above surrounding the inner airtight film packaging, wherein the space between the outer packaging and the inner packaging is ungassed. The term "ungassed" is to be understood here that a gas such as carbon dioxide is not introduced into the space, as is conventionally the case, thus preventing a reaction of a foodstuff, in particular the cheese, with the ambient air. If, for example, normal ambient air is present in the space, this state is considered "ungassed" within the scope of this invention.In particular, the outer packaging is at least essentially opaque, i.e. impermeable to light.

[0053] This makes it possible, in particular, for cheese slices made from a mix of an airtight film-based inner packaging and an outer paper-based outer packaging, i.e. the outer packaging, to be offered to a customer in a store.

[0054] To illustrate this, consider the following numerical example: The paper content of the total packaging can make up between 20-80%, preferably between 25-75%, and particularly preferably between 30-65%. Compared to conventional packaging, this results in less packaging material, which saves CO2 during packaging production. For example, the outer packaging can be a tubular paper bag with a weight of 2.00 g per end-user unit, and the film-based inner packaging can, for example, be a PP / EVA film with a film thickness of 23 μm or preferably less.

[0055] Further advantageous features of the present invention are defined in the patent claims.

[0056] In the following, preferred embodiments of the present invention are explained with reference to the accompanying figures:

[0057] Fig. 1 : shows a side section of a pre-sealing device for producing a film tube with a pre-sealing seam;

[0058] Fig. 2: shows a front view of the sealing device with a view of the outlet nozzles.

[0059] Fig. 3: illustrates a cross-section of a final sealing device; Fig. 4: illustrates another embodiment of the final sealing device;

[0060] Fig. 5: shows schematically an overall process for producing a tight film packaging;

[0061] Fig. 6: shows in detail a cross-sealing device of the overall process according to Fig. 5;

[0062] Fig. 7 shows a tight inner film package having at least one airtight sealing seam according to the invention;

[0063] Fig. 8 shows a section through a combination packaging;

[0064] Fig. 9 shows a plan view of the airtight sealing seam according to the invention;

[0065] Fig. 10 shows a plan view of another sealing seam produced by another prior art method;

[0066] Fig. 11 shows a plan view of another sealing seam produced according to another prior art method;

[0067] Numerous features of the present invention are explained in detail below using preferred embodiments. The present disclosure is not limited to the specifically mentioned feature combinations. Rather, the features mentioned here can be combined in any desired way to form embodiments of the invention, unless expressly excluded below.

[0068] A special feature of the process is the combination of pre-sealing using hot air and final sealing using a passive roller. This ensures extremely low frictional forces and / or mechanical stress on the film, allowing the film to be made very thin, resulting in a significant reduction in film material and thus significant environmental protection. Especially with pre-sealing using hot air, the sealing layer on at least one side of the film is heated more efficiently the thinner the film.

[0069] Below, we will therefore first list exemplary specifications of the film that are particularly well suited for the process.

[0070] The film should have a thickness between 10 and 30 μm, preferably less than 25 μm, in particular less than or equal to 23 μm, or particularly preferably less than or equal to 21 μm, most preferably between 15 and 20 μm. The current technical limit for films is 12 μm or 10 μm for OPET film (OPET = biaxially oriented polyester: rigid OPET with sealing wax on both sides) or for the thinnest possible OPP film (OPP = biaxially oriented polypropylene: OPP with sealing material) with a sealing layer on both sides—polymers or sealing wax.

[0071] The film is preferably constructed from 2 to 30 layers. At least one outer layer is a sealing layer comprising polymers or sealing wax. If sealing layers are provided on both sides of the film, the film comprises 3-30 layers. The middle layer(s) are made of PP, OPP, or OPET. PP layers consist of a blend or layers of different PP types. PP films are extruded polypropylene films. "Cast PP" (with a sealing layer on both sides) is particularly frequently used in the food industry due to several preferred properties.

[0072] The final seal differs from the pre-seal seam in that the former is wider. Differences can also be seen in the tearing behavior depending on the film type: With the final seal, the sealing layer is essentially completely peeled off the carrier layer, which is visually detectable. This means that an adhesion failure can occur between the sealing layer and carrier layer. The airtightness of the inner packaging, in particular the sealing seams, is measured using a method with hydrogen as a tracer gas under overpressure in the package. The maximum concentration of escaping hydrogen along at least one sealing seam on the outside must not exceed a maximum concentration of 10 ppm, preferably even a concentration of less than 7 ppm, more preferably less than 5 ppm, and most preferably less than 3 ppm. This measurement method is used to define and demonstrate airtightness.This limit value must be achieved by at least 80%, preferably 85%, particularly 90%, and most preferably 99% of the products measured.

[0073] In general, sealing depends on the three factors of time, pressure, and temperature. In principle, the films used for the process according to the invention can seal at temperatures as low as 100°C. Preferably, the films are heated to a temperature between 170°C and 300°C for the pre-sealing process. Particularly if a final sealing process is also planned, it may be advantageous to heat the film to over 200°C. However, it is also possible to use lower temperatures by appropriately varying the three factors of time, pressure, and temperature.

[0074] Fig. 1 shows a side section of a pre-sealing device 9 for producing a film tube with a pre-sealing seam 32:

[0075] A film 1, in particular a flat film web 1, which is preferably made of plastic, is unwound from a spool (not shown) and continuously passes to a forming device consisting of a forming shoulder, by means of which the flat film web is formed into a film tube 3 which is open on the longitudinal side and has overlapping film edges and is transported further on a cylindrical forming tube 4 in the transport direction 25 at a transport speed. The forming shoulder 2 and the forming tube 4 are held in a holder 5. The forming tube 4 extends further in the transport direction 25 into an area of ​​the pre-sealing device 9, which is fastened to a machine housing by a suspension 6. The suspension 6 is mounted in a pivot bearing 7 so as to be rotatable about a vertical axis, wherein the suspension 6 can be locked by a fastening screw 11 which is part of a pivot arm 10 fastened to the holder 5.This firmly connects the suspension 6 to the bracket 5 to prevent unintentional pivoting.

[0076] The housing 14 of the actual pre-sealing device 9 is connected to the suspension 6 via a mounting arm 8. Various adjustment devices are provided to align the housing 14 relative to the forming tube 4. A stop adjustment 12 is provided, which is supported on the machine housing and by means of which the distance between the housing 14 of the sealing device and the forming tube 4 can be adjusted. Furthermore, an inclination adjustment 13 is provided, by means of which the inclination of the housing 14 relative to the axis of the forming tube 4 can be adjusted. This allows a uniform distance between the housing 14 of the pre-sealing device 9 and the forming tube 4 to be set over the length of the forming tube.

[0077] The housing 14 of the pre-sealing device 9 has at least one air inlet 15, wherein the incoming compressed air is distributed by means of tree-like branching distribution channels 16 within the housing 14 and is spatially distributed via overflow channels 19 to a heating device. The heating device comprises, for example, a first heating cartridge 17, to which a second heating cartridge 18 is connected. The heating cartridges 17, 18 are approximately tubular and have at least one electrically heatable heating coil, which heats the compressed air flowing into the inner volume of the heating cartridge. The heated hot air leaves the heating cartridge 18 via overflow channels 20 and reaches an outlet channel 21, which is arranged longitudinally parallel to the forming tube 4. As shown in Fig.2, the outlet channel 21 has a plurality of outlet nozzles 22 on the side facing the forming tube 4, through which the hot air exits and impinges on the film tube 3 guided along the forming tube 4. The film tube 3 is aligned on the forming tube 4 such that the overlapping film edges lie opposite the outlet nozzles 22 and are continuously welded together to form a pre-sealing seam 32 by the escaping hot air in a pre-sealing process. The pre-sealing seam 32 created in this way, however, still has increased air permeability. It is important that the pre-sealing device 9 "does not touch" the surface of the film tube, but rather that the welding takes place without contact.

[0078] A temperature sensor 23 is arranged in the area of ​​the outlet duct 21, by means of which the temperature of the hot air in the outlet duct 21 is measured. Depending on the measured temperature, the heating power of the heating cartridges 17, 18 is regulated, thus achieving a constant hot air temperature corresponding to the preset value.

[0079] The amount of air can also be measured using a measuring device and controlled by means of a control system.

[0080] The required electrical and electronic components for the sealing device are advantageously located in a separate housing 24, which facilitates access and maintenance of the electrical components.

[0081] However, this pre-sealing process can be carried out in particular as a preparatory step in order to seal the produced pre-sealing seam 32 in a second sealing process, i.e. a final sealing, in an airtight manner to form a final sealing seam 54.

[0082] Fig. 3 illustrates a cross-section of a final sealing device 50. The preferred final sealing device 50 and, in particular, a preferred pressure means 52 in the form of a passive roller 52, mounted, in particular, on a ball bearing 53 or roller bearing 53, are described below. The final sealing device 50 converts the pre-sealing seam 32 into an airtight final sealing seam 54.

[0083] The roll 52 has an outer diameter d1 of 16 mm and is made of stainless steel, at least on its smooth outer surface 52a. Stainless steel has the properties of being rust-proof and heating up during the final sealing process, which leads to a beneficial result for the final sealing seam 54. Another possible material for the roll can be ceramic. The width of the roll 52, i.e. the contact surface on the film 1, should be at least as wide as the pre-sealing seam 32, so that pressure is exerted by the roll 52 on every point of the pre-sealing seam 32. For example, the roll 52 has a width of 5 mm for this purpose. Tests must show whether an even narrower width would advantageously increase the pressure on the pre-sealing seam 32. The same applies to alternative diameters.

[0084] The roller 52 is a passively driven roller 52 that rotates on a ball bearing, thereby advantageously minimizing friction in the transport direction of the film 1. Theoretically, an actively driven roller, e.g., by an external motor, would be able to drive the rotational speed of the roller "even better" in synchronization with the transport speed of the film 1, which could theoretically reduce friction in the transport direction of the film 1 even further.In practice, however, it has surprisingly been shown that this theoretically better solution actually generates higher friction, particularly friction peaks, in the transport direction of the film 1, since the transport speed of the film varies to an extent that cannot be immediately compensated for in practice via a feedback loop. As a result, the roller 52 with the external drive would, for example, be operated at a "rigid" predetermined rotational speed different from the transport speed of the film 1, resulting in strong friction in the transport direction. Surprisingly, the passive roller 52 therefore delivers better results in terms of protecting the film 1. The variation in the transport speed of the film can arise in particular from slippage in upstream or downstream processes.

[0085] The roller 52 is arranged such that it has an indentation depth T1 of 0.2-0.5 mm with respect to the plane of the film 1, in particular the local plane of the pre-sealing seam 9. This can be understood geometrically as follows: the film 1, in particular the pre-sealing seam 9 and the final seam 54 created by the roller 52, run in a transport plane, wherein the roller 52 locally presses the pre-sealing seam 32 out of the plane with the penetration depth T1 and the film 1 is preferably guided back into the original transport plane as in front of the roller 52 after passing the roll 52. The roller 52 can press rigidly onto the pre-sealing seam 32. The indentation depth T1 has the effect that the pre-sealing seam 32 has to travel a longer distance around the outer circumference of the roll 52, whereby the sealing pressure of the final seal is generated. The greater T1, the greater the sealing pressure.Other parameters that influence the sealing pressure include the tension of film 1 and the transport speed. The higher the values ​​of these parameters, the greater the sealing pressure.

[0086] Another aspect that can influence the indentation depth T1 is the distance of the roller 52 around the forming tube 4. The forming tube 4 has a significant influence on where the film 1, in particular the transport plane of the film 1, runs. The distance of the roller to this forming tube 4 can fluctuate slightly due to various external influences, so that the indentation depth T1 also changes. Preferably, a sensor system is provided which directly measures the distance of the roller 52 to the forming tube 4 and / or the indentation depth T1. If the indentation depth T1 deviates from a previously defined target value, a corresponding notification signal is generated by the sensor system so that the position of the roller 52 can be changed either manually, for example using adjusting screws, or automatically by a servo motor such that the target value for the indentation depth T1 is set.

[0087] The fact that the film runs close to the forming tube 4 also has the following advantage: Particularly in cheese production, but also for other hot food products, it can be provided that a heated cheese mass is introduced into the film tube 3 after the final sealing. The heated cheese mass can be guided, for example in a transport tube, inside the forming tube 4 to a point after the final sealing. This has the effect that the forming tube is also heated by the heated cheese mass - up to a temperature of approximately 80 °C - which in turn results in heat transfer to the film 1 and has a beneficial effect on both the pre-sealing seam 32 and the final sealing seam 54.

[0088] To prevent the temperature of the pre-sealing seam 32 from cooling down too much after the pre-sealing device 9, the closing device 50, in particular the roller 52, is arranged as close as possible to the pre-sealing device 9. For example, the distance d2 between the pre-sealing device 9 and the final sealing device 50 is provided between 9 and 15 mm. In this way, it is possible for the temperature of the pre-sealing seam 32 to be between 100 and 150 °C when brought into contact with the roller 52.

[0089] It is particularly advantageous for the quality of the final sealing seam 54 if a counterpressure is generated on the opposite side of the passive roller 52. Fig. 3 shows a fluid pressure generation unit 60 which is designed to introduce a fluid under pressure into a fluid channel 62 in the direction of the arrow, wherein the fluid channel 62 is introduced into a housing 64 and the fluid is guided in the direction of the passive roller 52 so that the fluid hits the pre-sealing seam 32 on the side opposite the passive roller 52. In this case, nozzles 66 are provided, in particular at the outlet of the fluid from the housing 64, which nozzles increase the pressure of the fluid as it exits. In Fig. 3, normal air is used as the fluid. The housing 64 can also have a pocket-like recess 68 so that the passive roller 52 can be brought as close as possible to the outlet openings of the nozzles 66.

[0090] Fig. 4 illustrates a further embodiment of the final sealing device 50 in which the counterpressure is generated by a second roller 72, in particular a passive second roller 72, which is arranged opposite the first passive roller 52. The second roller 72 can in particular be structurally identical to the first roller 52. Fig. 4 shows that the film 1 with the pre-sealing seam 32 is passed through a gap 74 between the first roller 52 and the second roller 72. The gap 74 between the two rollers 52, 72 is narrower than the pre-sealing seam 32, so that pressure can be generated on the heated pre-sealing seam 32, creating the air-tight final sealing seam 54. By changing the dimensions of the gap 74, a variable sealing pressure can be flexibly set.The two-roller design is particularly advantageous for thicker films where higher friction is not critical and where higher pressure is required. To improve the sealing result, it is possible to heat both rollers 52, 72.

[0091] Fig. 5 shows schematically an overall process for producing a tight film packaging;

[0092] In a first step, the film 1 is fed to the pre-sealing device 9 as described above, whereby the pre-sealing seam 32 is formed. The film 1 with the pre-sealing seam 32 is then fed to the final sealing device 50, whereby the airtight final sealing seam 54 is created. Since the film 1 is typically designed as a film tube that is still open at the top and bottom in the transport direction 25, an introduction device 80 can be provided in a next step, which introduces a product, in particular a foodstuff such as cheese, into one of the open ends of the film tube 3. In a next step, the film tube 3 must still be sealed at the top and bottom in the transport direction 25, transversely to the transport direction, in particular airtight. This is carried out by means of a transverse sealing device 100, which is described in detail below.

[0093] Fig. 6 shows in detail the transverse sealing device 100 of the overall process according to Fig. 5.

[0094] The film tube 3 is guided along a tube conveyor by guide means (not shown). It can be filled with a product, in particular a processed cheese mass, whereby the product packaged in the film tube 3 is separated into individually packaged slices. At the end of the process, individually packaged products, in particular cheese slices of a specific size, are produced. In the present embodiment, each package can be provided with an image 14 centered precisely on the package, which includes product information in text form.

[0095] Each image 114 has a repeat mark 105, which is detected by a sensor 106. At a defined distance from the repeat mark 105, a displacement region 102 is defined, at which a displacement tool 108 is positioned to displace the product, in particular the processed cheese, from the displacement region 102. When the sensor 106 detects the repeat mark 105, the displacement region 102 is located at a location x' at time t' of detection. Due to the constant conveying speed v of the hose 3, a displacement time t" can then be calculated at which the displacement region 102 is located at a location x" along the conveying path, at which displacement then occurs via the displacement rollers 112 of a displacement tool 108.In this process, displacement surfaces 113 on the displacement rollers 112 are moved toward each other by rotation and squeeze the film tube 3 there, whereby the product, in particular the processed cheese, is displaced out of the displacement area 102. The tube 3 is then sealed by a transverse sealing tool 107 with transverse sealing rollers 107a using transverse sealing surfaces in the region of the displacement area 2. This creates the tight film packaging 104 for the product, in particular the cheese.

[0096] The sealed areas can then be cut later, for example by a device as described in WO 2008 / 119633 A1, the disclosure of which is hereby explicitly incorporated into the application.

[0097] Ultimately, this results in the individual, tight, particularly inner, film packages 104a.

[0098] Fig. 7 shows a sealed, particularly inner, film package 104a, which has at least one above-described airtight seal 54 on one side of the film package 104a. The film package 104a is also airtight along its other sides, so that a food product, such as a cheese product 116, can be contained airtight in the film package 104a.

[0099] Fig. 8 shows a section through a combination package 120. The combination package 120 has an outer package 122 that encloses the airtight inner film package 104a, with the cheese product 116 in turn enclosed by the inner film package 104a. A space 124 is formed between the outer package 122 and the airtight inner film package 104a, which space is not exposed to gas and therefore essentially contains only ambient air.

[0100] Fig. 9 shows a plan view of a photograph of the airtight sealing seam 54 according to the invention under a microscope, wherein the outward-facing surface of at least one film side can be seen. The sealing seam 54 does not fill the entire area of ​​the photograph, but in the vertical direction the central vertical region 150, which therefore corresponds to the width 150 of the sealing seam 54, and in the horizontal direction up to the circular peripheral boundaries of the photograph. The sealing seam 54 can have a width of 0.5 mm to 1.5 mm in the vertical direction. This width is thicker than in conventional sealing seams from the prior art, since the gentle and low-friction production of the sealing seam 54 means that a certain increased width is advantageous in order to ensure airtightness.

[0101] The entire sealing process of the airtight seal seam 54, as described above, takes place with as little friction and as evenly as possible, which results in the fusion bond of the seal seam 54 between the two film sides being very homogeneous and the surfaces of the two film sides along the seal seam 54, in particular also the surface of the film side that rests on the roll 52, being very homogeneous and uniformly smooth. The surface of the film sides is therefore essentially free of traces of abrasion or other mechanical stress. The seal seam is thus evenly fused; more than 25%, preferably more than 50% of the area of ​​the seal seam 54 is homogeneous 155. Smaller inhomogeneities 160, in particular in the fusion layer of the seal seam 54 between the two film sides, are in particular point-shaped and have no preferred direction, in particular no tail in the transport direction 25.These small inhomogeneities can have a diameter of 1 -5 pm.

[0102] The surfaces are, as already described above, essentially smooth. In concrete terms, this can mean that the surfaces of the films along the sealing seam 54 have indentations which correspond to a maximum of 25%, preferably a maximum of 10%, particularly preferably a maximum of 5% of the film thickness. If the film has a thickness of 20 μm, then mechanical stresses, for example from the roller 52, have at most led to indentations with a depth of a maximum of 10 μm, a maximum of 5 μm, or particularly preferably a maximum of 2 μm. The film is therefore virtually undamaged and it is even possible to use even thinner films. This is how a structure of the sealing seam 54 according to the invention could be described. Fig. 10 shows a plan view of another sealing seam produced according to a different method from the prior art, and Fig.Figure 11 shows a plan view of another sealing seam produced according to another prior art method. Since the two films according to Figures 10 and 11 differ from the sealing seam 54 according to the invention in many structural features, Figures 10 and 11 will be described together.

[0103] The differences from the photograph in Fig. 9, i.e., the sealing seam 54 according to the invention, are immediately apparent. The width 165 of the sealing seam 170 of the other method and the width 165 of the sealing seam 175 of the further method are each less than 0.5 mm. Strong mechanical pressure is exerted on at least one surface of the film when creating the sealing seams 170, 175, resulting in severe surface damage 180, so that the film has depressions along the sealing seam that may correspond to the thickness of the film. These sealing seams 170, 175 do not have homogeneous regions. In addition, many damages have a tail in the transport direction 25, which results from the fact that the film was subjected to mechanical force at the transport speed in the transport direction 25.

[0104] List of reference symbols:

[0105] 1 film strip, film

[0106] 2 forming shoulders

[0107] 3 film tube (open)

[0108] 4 shaped pipe

[0109] 5 Bracket (for forming shoulder and forming tube)

[0110] 6 Suspension (for sealing device)

[0111] 7 swivel bearings

[0112] 8 Mounting arm

[0113] 9 Pre-sealing device

[0114] 10 Swivel arm (on bracket)

[0115] 11 Fixing screw

[0116] 12 Stop adjustment

[0117] 13 Tilt adjustment

[0118] 14 Housing of the sealing device

[0119] 15 Hot air inlet

[0120] 16 distribution channels

[0121] 17 Heating cartridge

[0122] 18 heating cartridge

[0123] 19 transfer channels

[0124] 20 transfer channels

[0125] 21 Exhaust channel

[0126] 22 outlet nozzles

[0127] 23 Temperature sensor

[0128] 24 housings (for electrical systems)

[0129] 25 Transport direction

[0130] 32 Pre-sealing seam

[0131] 50 Final sealing device 52 Pressure medium, passive roller

[0132] 52a Outer surface roller

[0133] 53 ball bearings

[0134] 54 Final seal seam; airtight seal seam

[0135] 60 Fluid pressure generation unit

[0136] 62 fluid channel

[0137] 64 fluid channel housing

[0138] 66 nozzles

[0139] 68 pocket-like recess of the housing 64

[0140] 72 second role

[0141] 80 filling device

[0142] T1 Indentation depth d1 Outer diameter of the roll 52 d2 Distance between the pre-sealing device 9 and the

[0143] Final sealing device 50

[0144] 100 cross sealing device

[0145] 102 Displacement area

[0146] 104 tight foil packaging

[0147] 104a single sealed film packaging (IWS)

[0148] 105 Repeat mark

[0149] 106 Sensor

[0150] 107 Cross sealing tool

[0151] 107a Cross sealing rollers

[0152] 107b Transverse sealing surfaces

[0153] 108 Displacement tool

[0154] 112 displacement rollers

[0155] 113 displacement surfaces

[0156] 114 Image

[0157] 116 Cheese product 120 Combination packaging

[0158] 122 outer packaging

[0159] 124 space

[0160] 150 central vertical area, width 155 homogeneous

[0161] 160 smaller inhomogeneities

[0162] 170 Sealing seam other process

[0163] 175 Sealing seam further process

[0164] 180 surface damages

[0165] 190 Tail

Claims

Patent claims Method for producing a sealing seam which connects two film sides, in particular two film sides of a film in the form of a film tube (3), in an airtight manner, comprising the following steps: • Carrying out a pre-sealing process, wherein at least one of the two film sides is heated in a pre-sealing process and wherein both film sides are brought into contact with one another in the heated state of the at least one film side, wherein a pre-sealing seam (32) is formed which connects both film sides to one another; • Carrying out a final seal, wherein the pre-sealing seam (32) is fed to a pressure means (52) at a transport speed, wherein the pressure means (52) is arranged downstream of the pre-sealing process in terms of process technology, in particular as close as structurally possible, and wherein the pressure means (52) applies force to at least one of the two film sides along the pre-sealing seam (32) essentially perpendicular to the transport direction (25), as a result of which the pre-sealing seam (32) is formed into a final seal seam (54) which is essentially impermeable to air. Method according to claim 1, characterized in that the pressure means (52) projects into a transport plane of the transport direction (25) of the pre-sealing seam (32), as a result of which the pre-sealing seam (32) runs around the pressure means (52) and the force is applied to one side of the pre-sealing seam (32) in this way. Method according to one of claims 1 to 2, characterized in that the pressure means (52) is designed as a roller (52). Method according to claim 3, characterized in that the roller is designed as a passive roller (52) which can be driven by friction with the film (1), in particular by friction with the pre-sealed seam (32). Method according to one of claims 3 to 4, characterized in that the roller (52) has a smooth outer surface (52a) and / or at least on the outer surface a material with a high heat storage capacity, such as stainless steel. Method according to one of claims 1 to 5, characterized in that a counterpressure on the opposite side of the pressure means (52) is achieved by applying force from a fluid. Method according to one of claims 1 to 5, characterized in that a counterpressure on the opposite side of the pressure means (52) is generated by a further roller (72).Method according to one of claims 1 to 7, characterized in that the pre-sealing seam (32) of the pre-sealing process is produced by blowing hot air onto the film (1).

9. Method according to one of claims 1-8, characterized in that the two film sides form a 0-film tube (3), wherein one side of the film rests on the other side of the film.

10. The method according to any one of claims 1-9, wherein the film has a thickness of less than 30 pm.

11. Device for producing a sealing seam which connects two film sides, in particular two film sides of a film in the form of a film tube, in an airtight manner, comprising: • a pre-sealing device (9) configured to carry out a pre-sealing process, wherein at least one of the two film sides is heated in a pre-sealing process by a heating means of the pre-sealing device (9) and wherein both film sides are brought into contact with one another in the heated state of the at least one film side, wherein a pre-sealing seam (32) is formed which connects both film sides to one another • a final sealing device (50) arranged behind the pre-sealing device (9) in terms of process technology and configured to carry out a final seal; the final sealing device has a pressure means (52) which is arranged in such a way that the pre-sealing seam (32) can be fed to the pressure means (52) at a transport speed and that at least one of the two heated film sides along the pre-sealing seam (32) is substantially perpendicular to the Transport direction can be subjected to force by means of the pressure means (52). Airtight sealing seam (54) obtainable by the method according to claim 1. Airtight film packaging (104), in particular for foodstuffs, comprising at least the airtight sealing seam according to claim 12, which seals a film tube (3) along one side and two airtight transverse seals. Combination packaging comprising an inner airtight film packaging according to claim 13 and an outer packaging surrounding the inner airtight film packaging (104), wherein a space between the outer packaging and the inner packaging is not gas-exposed.Combination packaging for foodstuffs comprising an inner airtight film packaging (104) and an outer packaging (122) surrounding the inner airtight film packaging (104), wherein an intermediate space (124) between the outer packaging and the inner packaging is not gas-filled, wherein the inner airtight film packaging has a smooth, homogeneous longitudinal sealing seam (54).

Images