Airtight longitudinal sealing seams for thin films

Abstract

The present invention relates to a technique for forming a sealing seam that hermetically joins two film surfaces, particularly two film surfaces of a film in the formation of a film tube (3), and comprises the following steps: performing a pre-sealing process, in which at least one of the two film surfaces is heated in the pre-sealing process, and while at least one of the film surfaces is heated, both film surfaces are brought into contact with each other to form a pre-sealing seam (32) that joins the two film surfaces to each other; and performing a final sealing process, in which the pre-sealing seam (32) is fed to a pressing means (52) at a conveying speed, the pressing means (52) being arranged downstream of the pre-sealing process in terms of the process, in particular as close as possible structurally possible, and the pressing means (52) applies a force along the pre-sealing seam (32) to at least one of the two film surfaces substantially perpendicular to the conveying direction (25), so that the pre-sealing seam (32) becomes a final sealing seam (54) that is substantially airtight.

Description

[Technical Field]

[0001] The present invention relates to an airtight longitudinal sealing seam for thin films, such as those used in the food industry to enclose food products, especially cheese. The key here is to be able to form an airtight seam, thus preventing, for example, the food product from reacting with oxygen and losing its desired properties. In addition to food products, this can of course also be applied to other products that can be placed in such thin films. The present invention also relates to a technique for forming such an airtight longitudinal sealing seam. [Background technology]

[0002] The following solutions for forming hermetic seams, especially longitudinal seams, are known from the prior art: U.S. Pat. No. 5,112,632 to Schreiber describes an apparatus and method for producing hermetic packaging for food slices. The hermetic longitudinal seam is formed between two film surfaces by passing a heated, corrugated tubular arrangement over both film surfaces, with the tubular arrangement's waves applying pressure alternately to each side of the film. Unfortunately, during this process, the film is subjected to high mechanical stresses, especially friction, which can damage the film and prevent it from dropping below a certain thickness. Schreiber uses a so-called V-tube for this purpose.

[0003] DE 19804221 A1 describes the production of longitudinal seams using a low-friction, particularly non-contact, method in which two sides of a film, particularly an O-shaped film tube, are blown onto one side using a hot air nozzle, thereby forming a sealed seam between the two sides of the film along an elongated blowing line. The drawback is that the longitudinal seam formed in this way is not airtight. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention is therefore based on the object of providing a technique that allows for the formation of at least approximately airtight sealing seams on films with as little friction as possible. The disadvantages of the prior art mentioned at the outset are at least partially overcome by the technique presented here. [Means for solving the problem]

[0005] The features of the various aspects of the invention or of the various exemplary embodiments described below can be combined with one another unless expressly excluded or unless it is necessarily technically impossible.

[0006] According to the present invention, a method for forming a hermetically sealed seam that hermetically joins two film surfaces, particularly two film surfaces of a film in the form of a film tube, is specified. This method can be used in particular for packaging food products, particularly preferably cheese. The method comprises the following steps: A step of performing a pre-sealing process, in which at least one of the two film surfaces is heated in the pre-sealing process, and in the heated state of at least one film surface, both film surfaces are brought into contact with each other, forming a pre-sealing seam that joins the two film surfaces to each other. The pre-sealing seam still has a certain degree of air permeability. High air permeability is particularly undesirable because it prevents the film from airtightly sealing the food product when it is further processed into food product packaging in a later process. Heating the film activates the sealing layer of the film, causing the two surfaces of the film to stick together and bond to each other, at least to a certain extent, without "melting" the remaining portions of the film. Therefore, the temperature at which the sealing layer is activated is 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 realized by various techniques, as long as it involves feeding a heated film 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. Preferably, a pre-sealing process using hot air bars is used, which is described in more detail below. a step of carrying out a final sealing process, in which the pre-sealing seam is fed to a pressing means at the conveying speed, the pressing means being arranged downstream of the pre-sealing process in terms of the process, in particular as close as possible structurally possible, and the pressing means applying a force along the pre-sealing seam to at least one of the two film surfaces substantially perpendicular to the conveying direction, so that the pre-sealing seam becomes a final sealing seam that is substantially air-tight. In particular, the conveying speed at which the pre-sealing seam on the film is fed to the pressing means corresponds to the conveying speed of the film in the processing steps upstream and / or downstream of the film, so that the film is not over-structured or over-stretched. However, the film may need to be conveyed at a slightly faster conveying speed in downstream processes, since an increased tension in the film may lead to a higher sealing pressure in the pressing means. Regarding the process, the further downstream the pressing means is positioned in the pre-sealing process, the less the pre-sealing seam will be cooled and the more effectively the pressing means can form an airtight final sealing seam; however, the temperature of the pre-sealing seam when it reaches the final sealing device may still be at least slightly lower than the temperature in the pre-sealing device. Preferably, the force of the pressing means acts perpendicular to the local flat surface formed by the film in the region of the pre-sealing seam. The pre-sealing seam is formed in the exemplary embodiment in which the film is formed as a film tube, but of course it cannot be said that the "entire film" has a film plane. This is why the term "local flat surface in the region of the pre-sealing seam" is used in this context. In the case of a film tube, this forms a continuous longitudinal seam into which the product, in particular cheese, can be inserted and which is then transformed into individual sections by final lateral sealing.

[0007] The repeated processing of the pre-sealed seam according to the present invention has the technical effect of forming an airtight final sealed seam from a non-airtight pre-sealed seam. A particular advantage of the present invention is that the resulting tight final sealed seam allows for the production of a tight inner package for packaging food products, particularly cheese, so that an alternative outer packaging material, such as paper, can be used, or the outer package can be eliminated entirely. Furthermore, the sealed inner package does not need to be placed within a fumigated (CO atmosphere) "tight" outer package, thus preventing the food product from reacting with the ambient air.

[0008] A tight package, in particular one having at least one longitudinal seam and two conventional transverse sealing seams, is also called a tight disk. Such a tight package is also called a first package or inner package when it is repackaged in an outer package, also called a second package or outer package. For example, in cheese production, several cheese slices, each individually wrapped in an inner package (a so-called IWS), are repackaged together in a larger outer package.

[0009] In a preferred embodiment, the pressing means protrudes into a conveying plane in the conveying direction of the pre-sealing seam, so that the pre-sealing seam extends around the pressing means, whereby a force is applied to at least one side of the pre-sealing seam, wherein the conveying plane is a local conveying plane formed in the area of ​​the pre-sealing seam.

[0010] This has the technical effect that, simply due to the preferred, structurally simple arrangement of the pressure means, pressure, also known as sealing pressure, acts on the pre-sealed seam. This passive pressure application method is very low-maintenance and generally subject to very small fluctuations, which can be crucial to the success of the process, especially when using thin films. Generally, this sealing pressure results from the interaction of the external design of the pressure means, the extent to which the pressure means protrudes into the film's conveying plane, and film tension. However, to change the sealing pressure, it is best to change the pressure means, e.g., how far the pressure means protrudes into the conveying plane. A simple adjusting screw or a technically automated unit can be used to adjust the distance the pressure means protrudes into the conveying plane.

[0011] Preferably, the pressing means is designed as a roller.

[0012] This ensures, in a technically advantageous manner, that a very uniform force is applied radially from the center of the roller to the pre-sealing seam. Particularly with thin films, it is important to avoid peaks in the force application to prevent damage to the film. The rounded contour of the roller ensures this in a particularly advantageous manner when the pre-sealing seam extends at least partially along the circumference of the roller.

[0013] 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.

[0014] The advantage of passive rollers is that they do not need to be driven by a separate motor synchronized with the transport speed, but are automatically brought to the correct speed by friction with the film. This is particularly advantageous when the film transport speed exhibits fluctuations to which an external motor has difficulty responding or can only respond with a certain delay. It is particularly advantageous to mount passive rollers on very low-friction ball or roller bearings. In this way, the tangential friction forces on the film, especially on the pre-sealing seam, can be advantageously significantly reduced.

[0015] In a preferred embodiment, the roller has a smooth outer surface and / or has, at least on its outer surface, a material with a high heat storage capacity, such as stainless steel.

[0016] A smooth surface also has the advantage of minimizing pressure peaks that could cause damage to the film. If the outer surface is made at least in part of a material with a high heat storage coefficient, the roller can become hot during the process, which improves the final sealing process. The roller can receive heat from the heated pre-sealing seam and / or from being located near the pre-sealing device. For example, if the pre-sealing seam is formed using a hot air nozzle, this heat is radiated to the roller due to its proximity to the hot air nozzle, heating the roller in addition to the sealing seam. In a further embodiment, the roller can be connected to a separate heat source that transfers energy to the roller.

[0017] Preferably, a counter pressure is achieved on the opposite side of the pressing means by applying a force to the fluid. This counter pressure has the technical effect that the sealing pressure of the pressing means can effectively act on the pre-sealing seam and not "go anywhere." This also provides the technical effect that the counter pressure can be generated very gently and with as little friction as possible to protect the film, which is particularly necessary for thin films. The fluid is preferably air, since air provides a kind of substantially frictionless counter pressure cushion in a very special way. Other fluids, such as water or oil, are less flexible than air, but can still be used in principle. When packaging food products in the film, the use of a food-safe fluid is particularly recommended.

[0018] Preferably, the fluid is supplied at a predetermined pressure and / or a predetermined temperature to a point opposite the pressing means. In embodiments using air as the fluid, the air can be sprayed at a predetermined pressure and / or a predetermined temperature, in particular using a nozzle, onto the side of the pre-sealing seam opposite the roller. The other fluids mentioned above can also be supplied to the roller using a nozzle on the side opposite the pre-sealing seam. Another advantage of using air as the fluid is that the air does not have to be collected and / or disposed of. When oil is used as the fluid, a higher and more consistent pressure can be generated.

[0019] In particular, it may be envisaged to supply the heated fluid to the side of the pre-sealing seam opposite the roller, which also has an advantageous effect on the final sealing seam.

[0020] Any temperature-related characteristics that have a beneficial effect on the final sealed seam can have the consequence of changing the parameters, for example, by using a lower indentation depth T1, the mechanical stress on the film can be further reduced, and as a result, it may be possible to use an even thinner film.

[0021] Alternatively, a further roller can be used to generate counter pressure on the opposite side of the pressing means. In this case, the film with the pre-sealing seam is fed through a two-roller arrangement, at least one of which can be heated. The gap between the two rollers through which the film is fed is particularly smaller than the film's thickness, so that a sealing pressure can be generated. Compared to the variant without a second roller, this alternative advantageously generates significantly more pressure on the pre-sealing seam, which may be advantageous for some films that require a higher sealing pressure. This is particularly likely with thicker films, for example, above 25 μm.

[0022] In a preferred embodiment, the pre-seal seam in the pre-sealing process is formed by blowing hot air onto the film.

[0023] This activates at least one sealing layer of the film, allowing the two film surfaces to adhere to each other to form a pre-sealed seam. Blowing hot air onto at least one of the film surfaces is particularly low-friction and gentle on the film. This method is particularly suitable for thin films. Blowing can be achieved, for example, by at least one hot air bar with multiple outlet nozzles from which heated air flows. Preferably, only one of the overlapping film surfaces is blown by the hot air bar. Blowing also ensures that one film surface applies a consistent amount of pressure to the other, allowing the pre-sealed seam to be formed.

[0024] Preferably, the pre-sealing process is characterized in that the heating of at least one film surface and the contact of the two film surfaces are achieved by blowing heated air onto at least one film surface. Advantageously, at least one film surface has a sealing layer that can be activated by heating without melting the remaining film at the activation temperature. The activated sealing layer has adhesive properties for joining the two film surfaces.

[0025] The pre-sealing process, which may also be called the first sealing process, is preferably characterized in that the overlapping films are welded together without contact using hot air, resulting in the formation of a first sealing seam, in particular a first longitudinal sealing seam, which is also called a pre-sealing seam because it does not yet have the desired final properties in terms of gas tightness.

[0026] In particular, the hot air for sealing the film in the pre-sealing process can be generated from ordinary compressed air, which is heated to a temperature of approximately 170-300°C by a suitable heating device and fed to the film tube through a nozzle. The temperature and / or amount of the hot air supplied can be regulated and quickly adjusted to suit the required conditions.

[0027] The pre-sealing device for the pre-sealing process preferably includes a housing having at least one air inlet for compressed air, which can be branched into a series of distribution channels within the housing, from which the air can be supplied via an overflow channel to at least one heating device, where the heated air is supplied via the overflow channel to an outlet channel and applied to the film tube via a nozzle.

[0028] The pre-sealing device, i.e. the outlet nozzle especially for hot air, is located at a certain distance from the film tube and does not come into contact with the film tube.

[0029] A substantial advantage of the hot air pre-sealing process is that thinner films can be used to produce the film tube because there is no "destructive" contact between the film and the sealing equipment. This results in significant cost savings in film material. As a general rule, the thinner the film, the faster heating can occur.

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

[0031] However, if only the pre-sealing process is used, it is impossible to form a tightly sealed seam. Therefore, a further feature of the present invention, also in terms of the process sequence, is the special combination of the pre-sealing process and the final sealing process. Neither process by itself is capable of forming a tightly sealed seam. The preferred idea of ​​the present invention is to combine these two processes to form a tightly sealed seam. This idea is also inventive in that it is obvious that instead of combining the pre-sealing process and the final sealing process for efficiency reasons, a single process is optimized.

[0032] Preferably, the two film surfaces form an O-film tube, with one surface of the film, also referred to as the inside, resting on the other surface of the film, also referred to as the outside.

[0033] Therefore, the sealing layer can be variably applied to the inside and / or outside of the film. If the sealing layer is applied to the outside of the film, contact between the sealing layer and the food product inside the film tube is minimized. This can be advantageous, especially when the sealing layer contains ingredients that are not food-safe. The use of O-film tubes is also advantageous because they are always under constant tension. Furthermore, O-film tubes require less material than V-tube types. In V-tube types, the opening flaps of the inner package are generated from both sides of the film (from inside to inside).

[0034] The film may preferably have a thickness of less than 30 μm.

[0035] This has the advantage of requiring less film material, which reduces costs and protects the environment. Surprisingly, a film less than 30 μm thick can be used to form a package with the above-described final sealing seam, which has at least airtight properties. This is made possible by the above-described final sealing process, particularly by combining the final sealing process with the pre-sealing process of the pre-sealing device. Both of these processes are very gentle on the material, allowing the use of such thin films. In particular, the thinner the film, the better the one-sided application of hot air to the film.

[0036] The final sealing seam is also called a longitudinal sealing seam, since it is substantially parallel to the film's conveying direction. When a single film is pre-folded over itself in the process to form a V-tube or, preferably, an O-tube, the film is already sealed at this folding point. Typically, the longitudinal sealing seam is parallel to the fold. In this case, the tubular bag is open only at the top and bottom in the conveying direction. A product, particularly a food product, particularly preferably cheese, can be filled through these openings. To ensure that the tubular bag hermetically seals the product, food product, or cheese, a transverse seal is formed transversely to the conveying direction in a subsequent process step. It is known from the prior art how to form an airtight transverse seal and how, after the transverse seal, the product tube can be separated along the cross-section, thereby forming an airtight film package as a whole. Hereinafter, this package will also be called an inner package or a first package. Since this package is made of film, it can also be called an inner film package or a first film package.

[0037] According to a second aspect of the present invention, an apparatus for forming a hermetically sealed seam joining two film surfaces, in particular two film surfaces of a film in the form of a film tube, is specified. In particular, the apparatus is configured to carry out the method described above. The hermetically sealed longitudinal seam is in particular a longitudinal sealed seam. The apparatus for forming the hermetically sealed seam comprises: A pre-sealing device configured to perform a pre-sealing process, wherein at least one of two film surfaces is heated by a heating means of the pre-sealing device in the pre-sealing process, and in the heated state of at least one film surface, both film surfaces are brought into contact with each other, forming a pre-sealing seam that joins the two film surfaces to each other. The pre-sealing device is especially designed so that the film can be guided through the pre-sealing device. For this purpose, the pre-sealing device may also have guide means. The heating means can also be designed in particular to bring two film surfaces into contact with each other. In one embodiment, the heating means is designed as a hot air bar with several nozzles through which hot air flows, so that at least one surface of the film is directly heated and subjected to an air pressure force, which presses it against the other film surface, as described above. A final device arranged downstream of the pre-sealing device in the process and configured to perform the final sealing process, the final device having a pressing means arranged such that the pre-sealing seam can be fed to the pressing means at a conveying speed and that at least one of the two heated film surfaces can be subjected by the pressing means to a force substantially perpendicular to the conveying direction along the pre-sealing seam.

[0038] The advantages of the apparatus for forming the hermetically sealed seam are generally similar to those described in connection with the method above.

[0039] According to a third aspect of the present invention, an apparatus for forming airtight film packaging is provided, comprising the above-described apparatus for forming an airtight sealing seam, particularly an airtight longitudinal sealing seam, and a transverse sealing device downstream thereof in the process. A film tube having at least one airtight longitudinal sealing seam exits the apparatus for forming the airtight film packaging and is fed to the transverse sealing device. The transverse sealing device is configured to provide two transverse seals transverse to the conveying direction of the film tube, separating the film tube into individual airtight packages. In particular, an impact device can be provided between the final sealing device that forms the airtight longitudinal seam and the transverse sealing device for introducing a product, particularly a food product, into the still-open film tube. Preferably, the film has a thickness of less than 30 μm.

[0040] Therefore, to the best of the inventors' knowledge, the device according to the invention for producing airtight film packaging makes it possible for the first time to provide airtight film packaging with an extremely thin film, so-called IWS, in such a way that resources and the environment are efficiently conserved and yet products, in particular foodstuffs, are hermetically sealed inside the film packaging.

[0041] According to a fourth aspect of the invention, a hermetically sealed seam obtained by the above-mentioned method is specified. The hermetically sealed seam corresponds to the final sealed seam, so that both terms are equivalent.

[0042] Advantageously, this sealing seam can be used to produce airtight film packaging, especially for food products such as cheese.

[0043] According to a further aspect of the invention, there is provided an airtight film packaging, in particular for food products, having at least the above-mentioned airtight sealing seam, the airtight film packaging produced by the method according to the invention being specified in particular as an airtight longitudinal sealing seam. The packaging preferably has two further transverse seals.

[0044] Surprisingly, to our knowledge, this is the first airtight film packaging with a longitudinal sealing seam formed by this method, especially for films thinner than 30 μm. The film packaging according to the present invention is therefore particularly suitable for food products that should not come into contact with the ambient air, and at the same time, is extremely environmentally friendly and resource-saving, since extremely thin films can be used for the first time.

[0045] According to a further aspect of the present invention, a combination package consisting of an air-permeable outer package (also referred to as outer package) and the above-mentioned airtight film package (also referred to as inner package) is specified for the storage of air-sensitive food products.

[0046] Surprisingly, to our knowledge, this is the first communication package whose outer packaging is made of an air-permeable material such as paper, while the inner packaging can have a film thinner than 30 μm. Previously, the outer packaging had to be airtight and even fumigated to prevent the food product inside the inner packaging from reacting with air, especially ambient air.

[0047] Innovative combination packaging not only allows for the saving of film in the inner packaging, but also makes it possible to completely eliminate the need for film in the outer packaging. Thus, the outer packaging only needs to be suitable for holding several individual slices together. Typically, several individual slices of processed cheese, for example, 10, are contained in a single outer packaging, which allows for better presentation and sale.

[0048] The airtight film packaging mentioned above is also called tight individual film packaging, especially for food products. This type of individual film packaging is also known as IWS slices (IWS = Individual Wrapped Slices).

[0049] In other words, this tight individual film packaging offers the advantage, inter alia, that the food product contained inside the tight individual film packaging does not react with the ambient air and therefore does not undergo any adverse changes in its properties.

[0050] This advantageously allows the use of tight individual film packages as inner packaging surrounded by an outer packaging that no longer needs to be airtight, eliminating the need to fumigate the intermediate space between the outer and inner packaging, particularly with carbon dioxide, to prevent the food product from reacting with oxygen in the air, as previously required. To prevent carbon dioxide from leaking from the intermediate space between the inner and outer packaging, the outer packaging was previously formed by a tight outer packaging made of a plastic film with a barrier. According to the present invention, the outer packaging can be made, in particular, at least predominantly, from paper, which is a major advantage from an environmental point of view, as it allows for efficient film reduction. This type of outer packaging is much more sustainable and is increasingly in demand and required by politicians and customers.

[0051] The outer packaging can also be made of plastic, but this no longer needs to be fumigated. Preferably, this outer packaging, whether film or paper, is opaque to prevent the food product from reacting with light.

[0052] According to a further aspect of the present invention, the combination packaging already described above can additionally or alternatively be designed as follows: a combination packaging including an inner airtight film packaging, in particular at least the airtight sealing seam of the present invention described above, and an outer packaging surrounding the inner airtight film packaging, wherein the intermediate space between the outer packaging and the inner packaging is non-fumigated. Here, the term "non-fumigated" means that, as in the conventional case, no extra gas such as carbon dioxide is introduced into the intermediate space, thereby preventing a reaction between the food product, i.e., cheese, and the ambient air. For example, if normal ambient air is present in the intermediate space, this state is considered "non-fumigated" in the context of the present invention. In particular, the outer packaging is at least substantially opaque, i.e., impermeable to light.

[0053] This makes it possible, in particular, to offer cheese slices to customers in a store from a mixture of an airtight film-based inner packaging and an outer paper-based outer packaging, i.e. from the outer packaging.

[0054] The following numerical example illustrates this: The proportion of paper in the overall packaging can be between 20 and 80%, preferably between 25 and 75%, and particularly preferably between 30 and 65%. Compared to conventional packaging, this reduces packaging material and saves CO2 in the production of the packaging. For example, the outer packaging can be formed by a paper tubular bag with a weight of 2.00 g / end-user unit, and the film-based inner packaging can be a film made of PP / EVA material, for example, with a film thickness of 23 μm or preferably less.

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

[0056] Preferred exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0057] [Figure 1] 1 shows a side cross-sectional view of a pre-sealing device for producing a film tube having a pre-sealing seam. [Figure 2] FIG. 1 shows a front view of the sealing device looking at the outlet nozzle. [Figure 3] 1 shows a cross-sectional view of a final sealing device. [Figure 4] 10 shows a further exemplary embodiment of a final sealing device. [Figure 5] 1 shows a schematic representation of the overall process for producing a tight film packaging. [Figure 6] The transverse sealing device for the entire process according to FIG. 5 is shown in detail. [Figure 7] 1 shows a tight inner film wrap having at least one hermetically sealed seam according to the present invention. [Figure 8] 1 shows a cross-sectional view of a combination package. [Figure 9] 1 shows a top view of an airtight sealed seam according to the present invention. [Figure 10] 1 shows a top view of another sealed seam manufactured using a method different from the prior art. [Figure 11] 1 shows a top view of a further sealed seam produced using a further method of the prior art; DETAILED DESCRIPTION OF THE INVENTION

[0058] Many features of the present invention are described in detail below with reference to preferred embodiments. The disclosure is not limited to the combination of features specifically mentioned. Rather, the features mentioned herein can be combined as desired to form embodiments in accordance with the present invention, unless expressly excluded below.

[0059] A special feature of the method is in particular the combination of pre-sealing with hot air and final sealing with passive rollers, which results in extremely low frictional forces and / or mechanical stresses on the film, allowing the film to be very thin, thus considerably reducing film material and thus providing strong environmental protection. In particular, when pre-sealing with hot air, the thinner the film, the more efficiently the sealing layer on at least one film surface is heated.

[0060] Thus, examples of film specifications that are particularly well suited for this method are listed below.

[0061] The film should have a thickness of 10 to 30 μm, preferably less than 25 μm, in particular not more than 23 μm, or particularly preferably not more than 21 μm, most preferably 15 to 20 μm. Currently, the technical limit for films is 12 μm or 10 μm for OPET films (OPET = biaxially oriented polyester: rigid OPET with sealing lacquer on both sides) or the thinnest possible OPP films (OPP = biaxially oriented polypropylene: OPP with sealing material) with a sealing layer on both sides, i.e. polymer or sealing lacquer.

[0062] The film preferably consists of 2 to 30 layers. At least one outer layer is a sealing layer comprising a polymer or sealing lacquer. If a sealing layer is provided on both sides of the film, the film contains 3 to 30 layers. One or more intermediate layers are made of PP, OPP or OPET. The PP layer consists of a mixture or layers of different PP types. The PP film is an extruded polypropylene film. In particular, "cast PP" (with sealing layers on both sides) is often used in the food industry due to its favorable properties.

[0063] The final sealed seam differs from the pre-sealed seam in that it is wider than the pre-sealed seam. Depending on the type of film, differences can also be observed in terms of tear behavior. At the final sealed seam, the sealing layer is substantially completely peeled off from the carrier layer, which is visually evident. This means that adhesive failure can occur between the sealing layer and the carrier layer.

[0064] The tightness of the inner packaging, especially the sealing seams, is measured using a method that uses hydrogen as a tracer gas under overpressure inside the packaging. The maximum concentration of hydrogen leaking along at least one outer sealing seam must not exceed a maximum concentration of 10 ppm, preferably less than 7 ppm, particularly preferably less than 5 ppm, and very particularly preferably less than 3 ppm. This measurement method is used to define and verify the tightness. This limit must be achieved by at least 80%, preferably 85%, particularly 90%, and particularly preferably 99% of the products measured.

[0065] Generally, sealing depends on three factors: time, pressure, and temperature. In principle, the film used in the method according to the present invention can be sealed already at a temperature of about 100°C. Preferably, the film is heated to a temperature of 170°C to 300°C for the pre-sealing process. In particular, if a final sealing process is also planned, it may be desirable to heat the film to above 200°C. However, it is also possible to use lower temperatures by appropriately changing the three factors: time, pressure, and temperature.

[0066] 1 shows a side cross-sectional view of a pre-sealing device 9 for producing a film tube with a pre-sealing seam 32, in which a film 1, in particular a flat film web 1, preferably made of plastic, is unwound from a reel (not shown) and passes continuously through a forming device consisting of forming shoulders, through which the flat film web is formed into a film tube 3 with open longitudinal sides and overlapping film edges, and which is further conveyed on a cylindrical forming tube 4 in a conveying direction 25 at a conveying speed. The forming shoulders 2 and the forming tube 4 are held in holders 5.

[0067] The forming tube 4 extends further in the conveying direction 25 in the region of a pre-sealing device 9 which is mounted on a suspension 6 on the machine housing. The suspension 6 is mounted rotatably about a vertical axis in a swivel bearing 7, the suspension 6 being lockable by means of a fixing screw 11 which is part of a swivel arm 10 attached to the holder 5. This firmly connects the suspension 6 to the holder 5 and prevents it from pivoting unintentionally.

[0068] The housing 14 of the actual pre-sealing device 9 is connected to the suspension 6 via a fixed arm 8. Various adjustment devices are provided to enable the orientation of the housing 14 relative to the forming tube 4 to be carried out. There is a stop adjustment 12 supported on the machine housing, by means of which the distance between the sealing device housing 14 and the forming tube 4 can be adjusted. Furthermore, there is provided an inclination adjustment 13, by means of which the inclination of the housing 14 relative to the axis of the forming tube 4 can be adjusted. This allows the distance between the housing 14 of the pre-sealing device 9 and the forming tube 4 to be set uniformly over the length of the forming tube.

[0069] The housing 14 of the pre-sealing device 9 has at least one air inlet 15. The incoming compressed air is distributed within the housing 14 by a tree-shaped distribution channel 16 and then spatially distributed via an overflow channel 19 to the heating device. The heating device, for example, comprises a first heating cartridge 17 connected to a second heating cartridge 18. The heating cartridges 17, 18 are generally tubular in shape and contain at least one electrically heatable heating coil that heats the compressed air entering the interior volume of the heating cartridge. The heated hot air leaves the heating cartridge 18 via an overflow channel 20 and reaches an outlet channel 21, which is arranged longitudinally parallel to the forming tube 4.

[0070] 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 hot air emerges and impinges on the film tube 3 guided along the forming tube 4. The film tube 3 is oriented on the forming tube 4 with the overlapping film edges facing the outlet nozzles 22 and is continuously welded by the emerging hot air in the pre-sealing process to form a pre-seal seam 32. However, the pre-seal seam 32 thus formed still exhibits increased air permeability. It is essentially important that the pre-sealing device 9 does not "touch" the surface of the film tube, but the sealing is performed without contact.

[0071] A temperature sensor 23 is arranged in the area of ​​the outlet channel 21, which measures the temperature of the hot air in the outlet channel 21. Depending on the measured temperature, the heating power of the heating cartridges 17, 18 is regulated so that a constant hot air temperature corresponding to a preset value is achieved.

[0072] Similarly, the amount of air can be measured by a measuring device and controlled by regulations.

[0073] The electrical and electronic components required for the sealing device are advantageously located in a separate housing 24, which allows easy access and maintenance of the electrical components.

[0074] However, this pre-sealing process can be carried out particularly as a preparatory step for a second, i.e., final, sealing process, in which the formed pre-sealing seam 32 is sealed in an airtight manner to form the final sealing seam 54.

[0075] FIG. 3 shows a cross-sectional view of a final sealing device 50, and a preferred final sealing device 50, in particular a preferred pressing means 52 in the form of a passive roller 52 mounted on a ball bearing 53 or roller bearing 53, will be described below, which final sealing device 50 transforms the pre-sealing seam 32 into an airtight final sealing seam 54.

[0076] The roller 52 has an outer diameter d1 of 16 mm and at least the smooth outer surface 52a is made of stainless steel. Stainless steel material is rust-resistant and has the property of being heated during the final sealing process, which advantageously results in a final sealed seam 54. Another possible material for the roller may be ceramic. The width of the roller 52, i.e., its contact surface on the film 1, should be at least as wide as the pre-sealed seam 32 so that pressure is applied by the roller 52 at each point on the pre-sealed seam 32. For example, the roller 52 has a width of 5 mm. Testing should show whether a narrower width advantageously increases the pressure on the pre-sealed seam 32. The same applies to alternative diameters.

[0077] The roller 52 is a passively driven roller 52 that rotates on ball bearings, which advantageously minimizes friction in the film 1 transport direction. In theory, a roller actively driven, for example by an external motor, could drive the roller's rotation speed in "even better" synchronization with the film 1 transport speed, which could theoretically further reduce friction in the film 1 transport direction. However, in practice, it was surprisingly found that this theoretically better solution actually generates higher friction in the film 1 transport direction, especially friction peaks, because the film transport speed varies to an extent that cannot be immediately compensated for via a feedback loop. As a result, the externally driven roller 52 operates, for example, at a "strict" predetermined rotation speed that differs from the film 1 transport speed, resulting in strong friction in the transport direction. Surprisingly, the passive roller 52 provides better results in terms of protecting the film 1. Fluctuations in the film transport speed can be caused, in particular, by slippage in upstream or downstream processes.

[0078] The roller 52 is positioned to have a penetration depth T1 of 0.2 to 0.5 mm relative to the plane of the film 1, particularly the local plane of the pre-sealing seam 9. Geometrically, this should be understood as follows: the film 1, particularly the pre-sealing seam 9, and the final seam 54 formed by the roller 52 extend in the conveying plane; the roller 52 locally presses the pre-sealing seam 32 out of the plane at the penetration depth T1; and the film 1 is preferably guided back into the original conveying plane after passing the roller 52, as it was before the roller 52. The roller 52 can firmly press the pre-sealing seam 32. The penetration depth T1 means that the pre-sealing seam 32 must travel a longer distance around the circumference of the roller 52, which generates the sealing pressure of the final sealing process. The greater the T1, the greater the sealing pressure. Other parameters that affect the sealing pressure are, for example, the tension of the film 1 and the conveying speed. The higher the values ​​of these parameters, the greater the sealing pressure.

[0079] A further aspect that can influence the indentation depth T1 is the distance of the rollers 52 around the forming tube 4. The forming tube 4 has a decisive influence on where the film 1, and in particular the conveying surface of the film 1, runs. The distance between the rollers and this forming tube 4 can fluctuate slightly due to various external influences, resulting in a change in the indentation depth T1. Preferably, a sensor system is provided that directly measures the distance between the rollers 52 and the forming tube 4 and / or the indentation depth T1. If the indentation depth T1 deviates from a predefined target value, a corresponding notification signal is generated by the sensor system, so that the position of the rollers 52 can be changed, for example manually using an adjustment screw or automatically using an actuator, thereby setting the target value for the indentation depth T1.

[0080] The fact that the film extends close to the forming tube 4 also has the following advantage: in particular in cheese production, but also for other hot foodstuffs, it can be intended that a heated cheese mass be introduced into the film tube 3 after the final sealing process. Here, for example, a heated cheese mass in a conveying tube can be guided inside the forming tube 4 up to a point after the final sealing process. This has the effect that the forming tube is heated by the heated cheese mass to a temperature of about 80° C., which in turn results in heat transfer to the film 1, having a beneficial effect on both the pre-sealing seam 32 and the final sealing seam 54.

[0081] To ensure that the temperature of the pre-sealing seam 32 is not cooled excessively after the pre-sealing device 9, the final sealing device 50, i.e., the rollers 52 in particular, is positioned as far downstream as possible from the pre-sealing device 9 in terms of the process. For example, the distance d2 between the pre-sealing device 9 and the final sealing device 50 is 9 to 15 mm. In this way, it is possible to bring the temperature of the pre-sealing seam 32 to 100 to 150°C when it comes into contact with the rollers 52.

[0082] The generation of counterpressure on the opposite side of the passive roller 52 is particularly beneficial for the quality of the final sealed seam 54. FIG. 3 shows a fluid pressure generating unit 60 designed to introduce fluid under pressure into a fluid channel 62 along the arrow. The fluid channel 62 is inserted into a housing 64, and the fluid is guided toward the passive roller 52, so that the fluid contacts the pre-sealed seam 32 on the opposite side of the passive roller 52. Here, a nozzle 66 is provided, which increases the fluid pressure as the fluid exits the housing 64. In FIG. 3, ordinary air is used as the fluid. The housing 64 can also have a pocket-like recess 68 to allow the passive roller 52 to be as close as possible to the outlet opening of the nozzle 66.

[0083] FIG. 4 shows a further exemplary embodiment of the final sealing device 50, in which counterpressure is generated by a second roller 72, particularly a passive roller 72, positioned opposite the first passive roller 52. In particular, the second roller 72 may have the same structure as the first roller 52. FIG. 4 shows that the film 1 with the pre-sealing seam 32 is fed 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 applied to the heated pre-sealing seam 32 to form a final sealing seam 54 that is impermeable to air. By changing the dimensions of the gap 74, variable sealing pressures can be flexibly set. The exemplary embodiment with two rollers is particularly advantageous for thicker films, for which higher friction is not important and which require higher pressures. To improve the sealing results, both rollers 52, 72 can be heated.

[0084] 5 shows a schematic representation of the overall process for producing a tight film package, in which, in a first step, the film 1 is fed to a pre-sealing device 9 as described above, resulting in the formation of a pre-sealing seam 32. The film 1 with the pre-sealing seam 32 is then fed to a final sealing device 50, which forms an airtight final sealing seam 54. Since the film 1 is typically designed as a film tube that remains open at the top and bottom in the conveying direction 25, in a next step a filling device 80 can be provided, which introduces a product, in particular a foodstuff such as cheese, into one of the open ends of the film tube 3.

[0085] In the next step, the film tube 3 must still be sealed, particularly airtight, at the top and bottom transversely to the conveying direction 25 in the conveying direction 25. This is carried out by a transverse sealing device 100, which will be described in detail below.

[0086] FIG. 6 shows in detail the transverse sealing device 100 for the entire process according to FIG.

[0087] The film tube 3 is guided along a tube conveying path by guide means (not shown). This film tube 3 can be filled with a product, in particular a processed cheese mass, and the product packaged in the film tube 3 is separated into individually packaged slices. In this way, individually packaged products, in particular cheese slices of a consistent size, are obtained. In this exemplary embodiment, each package can be provided with an image 114, which is precisely located in the center of the package and contains product information in text form.

[0088] Each image 114 has a repeat mark 105 that is recognized by a sensor 106. A displacement area 102 is defined at a predetermined distance from the repeat mark 105, and a displacement tool 108 is positioned to displace the product, particularly the process cheese, from the displacement area 102. When the sensor 106 detects the repeat mark 105, the displacement area 102 is at position x' at the time of detection t'. Based on a constant conveying speed v of the tube 3, a displacement time t" can be calculated. At displacement time t", the displacement area 102 is positioned at position x" along the conveying path, and displacement is performed by displacement rollers 112 of the displacement tool 108. In this process, displacement surfaces 113 on the displacement rollers 112 are moved toward each other by rotation, squeezing the film tube 3 there, so that the product, particularly the process cheese, is displaced from the displacement area 102.

[0089] The tube 3 is then sealed in the region of the displacement area 2 by a transverse sealing tool 107 with transverse sealing rollers 107a by means of transverse sealing surfaces, thereby forming a tight film packaging 104 for the product, in particular cheese.

[0090] The sealed area can then be cut, for example, by an apparatus such as that described in WO 2008 / 119633, the disclosure of which is hereby expressly incorporated into the present application.

[0091] Ultimately, this results in individual tight, particularly inner film wraps 104a.

[0092] 7 shows a tight, particularly inner, film package 104a having at least one airtight sealing seam 54 described above on one side of the film package 104a. The film package 104a is also airtight along the other side, allowing a food product, such as a cheese product 116, to be airtightly contained within the film package 104a.

[0093] 8 shows a cross-sectional view of combination package 120. Combination package 120 has an outer package 122 enclosing an airtight inner film package 104a, with cheese product 116 enclosed by inner film package 104a. An intermediate space 124 is formed between outer package 122 and airtight inner film package 104a, which is unfumed and therefore contains substantially only ambient air.

[0094] FIG. 9 shows a top view of a photograph of an airtight sealing seam 54 according to the present invention under a microscope, showing the outer-facing surface of at least one film surface. The sealing seam 54 does not fill the entire area of ​​the photograph, but fills a central vertical region 150 vertically, corresponding to the width 150 of the sealing seam 54, and horizontally, up to the circular perimeter boundary of the photograph. The sealing seam 54 may have a width of 0.5 to 1.5 mm vertically. This width is thicker than conventional sealing seams from the prior art, because the gentle, low-friction formation of the sealing seam 54 means that a certain increased width is advantageous to ensure airtightness.

[0095] As described above, the entire sealing process of the airtight sealing seam 54 proceeds as smoothly and uniformly as possible. This means that the fusion of the sealing seam 54 between the two film surfaces is very uniform, and the surfaces of the two film surfaces along the sealing seam 54, particularly the surface of the film surface in contact with the roller 52, are also very uniform and uniformly smooth. Therefore, the surfaces of the film surfaces are substantially free of wear marks or other mechanical stress marks. Therefore, the sealing seam is uniformly fused, and more than 25%, preferably more than 50%, of the area of ​​the sealing seam 54 is uniformly formed (155). Smaller non-uniformities 160 in the fused layer of the sealing seam 54 between the two film surfaces are particularly spot-like, have no preferred direction, and do not have tails, particularly in the conveying direction 25. These small non-uniformities can have a diameter of 1 to 5 μm.

[0096] As already mentioned above, the surface is substantially smooth. Specifically, this can mean that the surface of the film has depressions along the sealing seam 54, corresponding to a thickness of at most 25%, preferably at most 10%, and particularly preferably at most 5% of the film thickness. Thus, if the film has a thickness of 20 μm, the mechanical stress from the roller 52, for example, will result in depressions having a depth of at most 10 μm, at most 5 μm, or particularly preferably at most 2 μm. Therefore, the film is substantially undamaged, and even thinner films can be used. The structure of the sealing seam 54 according to the present invention can be described in this way.

[0097] Figure 10 shows a top view of a further sealing seam made according to another method of the prior art, and Figure 11 shows a top view of a further sealing seam made according to another method of the prior art. Figures 10 and 11 will be described together because the two films according to Figures 10 and 11 also differ in many structural features from the sealing seam 54 according to the present invention.

[0098] The difference from the photograph in Figure 9, i.e., the sealing seam 54 according to the present invention, is immediately apparent. The width 165 of the sealing seam 170 according to the alternative method and the width 165 of the sealing seam 175 according to the further method are each less than 0.5 mm. When the sealing seams 170, 175 are formed, strong mechanical pressure is applied to at least one surface of the film, resulting in severe surface damage 180, such that the film has a depression along the sealing seam that may correspond to the thickness of the film. These sealing seams 170, 175 do not have a homogeneous region. Furthermore, many of the damages have tails in the conveying direction 25, which are caused by mechanical forces applied to the film in the conveying direction 25 at the conveying speed. [Explanation of symbols]

[0099] 1 Film web, film 2 Molded shoulder 3 Film tube (open) 4. Formed tube 5 Holder (for forming shoulder, for forming tube) 6. Suspension (for sealing devices) 7 Slewing bearing 8 Fixed Arm 9 Pre-sealing device 10 Swivel arm (on holder) 11 Fixing screw 12 Stop adjustment part 13 Tilt adjustment part 14 Sealing device housing 15 Hot air inlet 16 Distribution Channels 17 Heating Cartridge 18 Heating Cartridges 19. Overflow Channel 20. Overflow Channel 21 Exit Channel 22 outlet nozzle 23 Temperature Sensor 24 Housing (for electrical components) 25 Conveying direction 32 pre-sealed seams 50 Final sealing device 52 Pressing means, passive roller 52a Outer surface of roller 53 Ball bearings 54 Final sealed seam, airtight sealed seam 60 Fluid pressure generating unit 62 fluid channels 64 Fluid channel housing 66 nozzles 68 Pocket-like recess of housing 64 72 Second Roller 80 Filling equipment T1 indentation depth d1 Outer diameter of roller 52 d2: Distance between the pre-sealing device 9 and the final sealing device 50 100 Lateral sealing device 102 Displacement Area 104 Tight film packaging 104a Individual Dense Film Wrap (IWS) 105 Repeat Mark 106 Sensors 107 Lateral Sealing Tool 107a Lateral sealing roller 107b Lateral sealing surface 108 Displacement Tool 112 Displacement roller 113 Displacement Surface 114 images 116 Cheese Products 120 combination packaging 122 Outer packaging 124 Intermediate Space 150 center vertical area, width 155 homogeneous Inhomogeneity less than 160 170 Alternative Sealing Methods 175 Further Methods of Sealing Seams 180 Surface damage 190 tail

Claims

1. A method for forming a hermetically sealed seam hermetically joining two film surfaces, in particular two film surfaces of a film in the formation of a film tube (3), comprising: - performing a pre-sealing process, in which at least one of the two film surfaces is heated in a pre-sealing process, and in the heated state of the at least one film surface, both film surfaces are brought into contact with each other, forming a pre-sealing seam (32) joining the two film surfaces together; - carrying out a final sealing process, in which the pre-sealing seam (32) is fed at a conveying speed to a pressing means (52), with respect to which the pressing means (52) is arranged downstream of the pre-sealing process, in particular as close as possible structurally possible, and which applies a force along the pre-sealing seam (32) to at least one of the two film surfaces substantially perpendicular to the conveying direction (25), so that the pre-sealing seam (32) becomes a final sealing seam (54), which is substantially air-tight; A method comprising:

2. 2. The method according to claim 1, wherein the pressing means (52) protrude into a conveying plane of the pre-sealing seam (32) in the conveying direction (25), so that the pre-sealing seam (32) extends around the pressing means (52), whereby the force is applied to one side of the pre-sealing seam (32).

3. 3. Method according to claim 1 or 2, characterized in that the pressing means (52) are designed as rollers (52).

4. 4. The method according to claim 3, characterized in that the roller is designed as a passive roller (52) that can be driven by friction with the film (1), in particular by friction with the pre-sealing seam (32).

5. 5. The method according to claim 3 or 4, characterized in that the roller (52) has a smooth outer surface (52a) and / or has, at least on said outer surface, a material with a high heat storage capacity, such as stainless steel.

6. 6. A method according to any one of claims 1 to 5, characterized in that the counter pressure on the opposite side of the pressing means (52) is achieved by applying a force to a fluid.

7. 6. A method according to any one of claims 1 to 5, characterized in that a counter pressure is generated on the opposite side of the pressing means (52) by a further roller (72).

8. 8. The method according to any one of claims 1 to 7, characterized in that the pre-sealing seam (32) of the pre-sealing process is formed by blowing hot air onto the film (1).

9. 9. A method according to any one of claims 1 to 8, characterized in that the two film surfaces form a film tube (3), one surface of the film resting on the other surface of the film.

10. 10. The method of claim 1, wherein the film has a thickness of less than 30 μm.

11. 1. An apparatus for forming a hermetically sealed seam that hermetically joins two film surfaces, particularly two film surfaces of a film in the formation of a film tube, comprising: a pre-sealing device (9) configured to perform a pre-sealing process, wherein at least one of the two film surfaces is heated in the pre-sealing process by a heating means of the pre-sealing device (9), and in the heated state of the at least one film surface, both film surfaces are brought into contact with each other, forming a pre-sealing seam (32) joining the two film surfaces together; a final sealing device (50) arranged downstream of the pre-sealing device (9) for said process and adapted to carry out a final sealing process, the final sealing device comprising a pressing means (52) arranged so that the pre-sealing seam (32) can be fed to the pressing means (52) at a conveying speed and so that at least one of the two heated film surfaces can be subjected by the pressing means (52) to a force substantially perpendicular to the conveying direction along the pre-sealing seam (32), An apparatus comprising:

12. A hermetically sealed seam (54) obtained by the method of claim 1.

13. 13. An airtight film packaging (104), in particular for foodstuffs, comprising at least an airtight sealing seam according to claim 12 sealing a film tube (3) along one side and two airtight transverse seals.

14. A combination package comprising an inner airtight film package according to claim 13 and an outer package surrounding the inner airtight film package (104), wherein an intermediate space between the outer package and the inner package is non-fumigated.

15. A combination package for food products, comprising an inner airtight film package (104) and an outer package (122) surrounding the inner airtight film package (104), wherein an intermediate space (124) between the outer package and the inner package is non-fumigated, and the inner airtight film package has a smooth, uniform longitudinal sealed seam (54).

Images