Method for producing a sealing seam in packaging materials with layer breaks

Abstract

The present invention relates to a method for producing a transverse sealing seam in sheet-shaped or tubular packaging materials.

Description

[0001] The present invention relates to a method for producing a sealed seam in packaging materials with layer gaps. For example, in vertical flow-wrap packaging machines, a tube is formed from a material web, and the two side edges of the material web are joined together with a longitudinal seal. The tube thus produced is then divided into several sealed tubular bags using transverse seals.

[0002] This requires the tubular bag, which has already been sealed with a longitudinal seal, to be sealed. Due to the presence of the longitudinal seal, the number of material web layers arranged between the corresponding sealing tools is not constant across the width of the sealing surface.

[0003] As in Fig. As shown schematically in Figure 1, this typically results in a 2-4-2 layer structure. This means that while only two layers of material lie on top of each other in the outer areas of the transversely sealed tubular bag, four layers of material lie on top of each other in the area of ​​the longitudinal seal. This means that at the point where the longitudinal seal is folded over, there are twice as many layers of material as in the remaining area of ​​the seal.

[0004] There are other applications where different numbers of layers need to be welded together. For example, side-gusseted bags have a 4-2-4 layer structure. However, 2-3-2 layer structures, 2-4 layer structures, and 4-2-4-2-4 layer structures are also known.

[0005] Sealed seams are often produced using ultrasonic welding. The area to be welded is positioned between an ultrasonic sonotrode and a corresponding counter-tool. Ultrasonic sonotrodes are familiar from manufacturing technology, for example, in the ultrasonic welding of plastics.

[0006] Ultrasound is a mechanical vibration above the audible threshold. The frequency range begins at around 20 kHz and extends up to frequencies of 1 GHz. Such ultrasonic frequencies are often generated from electrical energy using piezoelectric sound transducers (converters). This mechanical vibration energy is applied to the workpiece or the material to be processed via the sonotrode, which is connected to the converter and, if necessary, via an amplitude transformation piece (booster). The surface of the sonotrode intended to come into contact with the material to be processed is also referred to as the sealing surface. Likewise, the surface of the counter tool intended to come into contact with the material to be processed is also referred to as the sealing surface. In the following, the sealing surface of the sonotrode is referred to as the first sealing surface and the sealing surface of the counter tool as the second sealing surface.

[0007] Since the sonotrode is usually pressed against the counter tool with a constant force, also known as the welding force, this leads to high surface pressure in areas with more layers of material than in other areas. This leads to premature melting in areas with more layers, which in turn causes unwanted overwelding of the thermoplastic material. This can lead to defects, leaks, and an undefined melt flow, which in the best case scenario only has a negative visual impact on the sealed seam. Furthermore, leaks can occur in areas with fewer layers, as a large portion of the available energy is transferred to the area with more layers.

[0008] It is therefore already known to use a process in which the sonotrode or counter-tool has a recess in the area where more layers are arranged. During the welding process, the longitudinal seam resting on the tubular bag is guided in the area of ​​the recess. This eliminates the higher surface pressure and the relatively high energy input in the four-layer area.

[0009] However, this process has the disadvantage that the sonotrode or anvil must be specially adapted, i.e. both the material web thickness and the width of the longitudinal seal seam must be known and the corresponding sonotrode or counter tool can then only be used for materials of the same thickness and the same longitudinal seal seam width. If, for example, the width of the longitudinal seal seam is changed, this welding device can no longer be used; instead, a new sonotrode or a new anvil with the appropriate recess must be manufactured. In addition, precise film web guidance in the packaging machine is essential. With thin, very flexible packaging materials, this can only be achieved satisfactorily in isolated cases. It is also known to use multiple seal seams, whereby not every seal seam runs completely transversely across the bag.

[0010] DE 10 2011 004 002 A1 therefore proposes that the sonotrode or counter-tool have a gap through which the longitudinal sealing seam is guided, so that only areas with the same number of layers can actually be welded. This process is quite complex and requires precise material guidance. Furthermore, it can only be used for longitudinal sealing seams designed as fin seams.

[0011] Based on the described prior art, it is therefore the object of the present invention to provide a method which at least reduces the disadvantages described.

[0012] This object is achieved by a method for producing a transverse sealing seam in web-, sheet- or tubular packaging materials with the following steps: A) Providing a sonotrode with a first sealing surface, B) Providing a counter tool with a second sealing surface, C) Providing a sealing section of web-, sheet- or tubular packaging material by folding a layer of a web-, sheet- or tubular packaging material in such a way that a sealing section is formed which has an n-layer subsection and an m-layer subsection, where n≠m, D) Positioning the sealing section and the sonotrode and the counter tool such that the sealing section is positioned between the first and second sealing surfaces and touches both the first and second sealing surfaces and E) Exciting an oscillation of the sonotrode such that a reference point on the first sealing surface experiences an in-plane oscillation movement.

[0013] While it is known from the prior art to impart a longitudinal oscillation to the first sealing surface, i.e. an oscillation which ensures that the distance between the first and second sealing surface becomes larger and smaller in rapid succession (out-of-plane oscillation), according to the invention an in-plane oscillation is now provided, i.e. an oscillation tangential to the first sealing surface.

[0014] In other words, in out-of-plane vibration, the vibration is transmitted in the direction of the surface normal of the sealing surface, while in in-plane vibration, the vibration is transmitted perpendicular to the surface normal of the sealing surface.

[0015] Typically, the vibration is transmitted to the sonotrode via a converter. The converter uses piezo elements to generate a longitudinal vibration, which is coupled into the sonotrode via one end face. If the opposite end face is used as the sealing surface, the vibration is coupled out in the direction of the surface normal to the end face (out-of-plane vibration). If, however, the outer surface of the sonotrode at the end facing the opposite side is used as the sealing surface, the sealing plane that couples the sound out is oriented parallel to the direction of the longitudinal vibration (in-plane vibration).

[0016] This means that the areas with a larger number of layers and thus greater thickness are not subjected to as much mechanical stress. Furthermore, in-plane motion is suitable for transferring energy to the desired position via interfacial friction, whereas in longitudinal ultrasonic welding, intramolecular friction, due to damping within the material, essentially dominates the desired heating process.

[0017] The use of in-plane oscillation to bond materials is known from the paper packaging industry. However, there is no melting of the materials involved. Nor are materials bonded with layer discontinuities.

[0018] In a preferred embodiment, the web-, sheet-, or tubular packaging material is made of a thermoplastic material or has at least one thermoplastic layer. With such thermoplastic materials, or materials with a thermoplastic layer, melting of the material is mandatory at the interface between the layers to be joined.

[0019] In practice, n = 2 and m > 2, although other embodiments are conceivable. As already mentioned at the beginning, the sealing section can also have more than two subsections with different numbers of layers.

[0020] A reference point is any point on the first sealing surface. At least this reference point undergoes the described oscillating motion in step E). Other points on the sealing surface may experience different oscillating motions or even no motion at all.

[0021] However, in a preferred embodiment, not just a reference point on the first sealing surface undergoes the described oscillating motion, but the entire sealing surface. This allows for greater interfacial friction energy to be introduced into the materials to be joined. The first and / or second sealing surface can be flat. However, for some embodiments, they can also be curved. It is also possible for the first sealing surface to be flat and the second sealing surface to be curved, or for the second sealing surface to be flat and the first sealing surface to be curved.

[0022] In a further preferred embodiment, in step E) the reference point undergoes an in-plane oscillation movement with an oscillation amplitude A t and an out-of-plane oscillation motion with an oscillation amplitude A SIt is thus also possible to apply a combination of an in-plane and an out-of-plane oscillation. However, it is particularly preferred if the in-plane oscillation is greater than the out-of-plane oscillation. Particularly preferred embodiments provide an oscillation amplitude of the in-plane oscillation that is at least five times, and preferably at least 20 times, greater than the out-of-plane oscillation amplitude.

[0023] In fact, ideally, no out-of-plane oscillation is applied at all. In practice, however, this cannot always be completely prevented, so small out-of-plane oscillation amplitudes must be tolerated. According to the invention, however, a significant portion of the energy required to melt the materials to be joined is introduced via the in-plane oscillation.

[0024] With this type of vibration transmission, it is essential that the superimposed material layers to be welded are moved relative to each other. Therefore, it is advantageous if the first sealing surface and / or the second sealing surface have a structure to increase the friction between the sealing surfaces and the material layers. The structure can be achieved, for example, by means of grooves, ribbing, or a waffle or pyramid structure.

[0025] In a further preferred embodiment, during step E), the counter-tool is also excited to oscillate, preferably in such a way that a reference point or even the entire second sealing surface undergoes an in-plane oscillation. Essentially, the counter-tool in this embodiment represents a second sonotrode. The oscillation frequencies of the sonotrode and the counter-tool differ in a preferred embodiment.

[0026] In a preferred embodiment, the first and second sealing surfaces are flat and aligned parallel to each other. In principle, however, the first and second sealing surfaces could also each be cylindrical, with the sonotrode, for example, having a cylindrical section whose outer surface forms the first sealing surface, and the counter-tool having a hollow-cylindrical section whose inner surface forms the second sealing surface. Alternatively, the counter-tool could be cylindrical and the sonotrode could have a hollow-cylindrical section.

[0027] In a further preferred embodiment, it is provided that during step E) a sealing force is exerted on the sealing section with the first sealing surface and / or with the second sealing surface.

[0028] This can increase the interfacial friction.

[0029] In a preferred embodiment, a composite film is used as the web-, sheet-, or tubular packaging material, which has at least one sealing layer, which preferably consists of a thermoplastic material, and a carrier layer, wherein in step E) the vibration amplitude and / or the sealing force is dimensioned such that superimposed sealing layers are welded together.

[0030] Further advantages, features, and possible applications will become clear from the following description of a preferred embodiment and the accompanying figures. They show: Fig. 1 a schematic representation of a 2-4-2 layer structure, Fig. 2 a schematic representation: Welding of a tubular bag with an out-of-plane oscillation and Fig. 3 a schematic representation: welding of a tubular bag with an in-plane oscillation.

[0031] In Fig. Figure 2 shows a schematic representation of the welding process known from the prior art using out-of-plane oscillations. Fig. A known layered structure is positioned between a sonotrode 1 and a counter-tool 2. The sonotrode 1 oscillates in the direction of the double arrow, i.e., the distance between the sonotrode 1 and counter-tool 2 alternately increases and decreases. The sealing surfaces of the sonotrode 1 and counter-tool 2, i.e., the surfaces that come into contact with the layered structure, are smooth.

[0032] In Fig. 3 schematically shows an embodiment of the method according to the invention. Fig.1 known layer structure is positioned between a sonotrode 1 and a counter tool 2. The sonotrode 1 oscillates in the direction of the double arrow, i.e. the distance between the sonotrode 1 and counter tool 2 remains the same until a displacement of the sealing layer occurs due to plasticization and applied sealing force. The sealing surfaces of the sonotrode 1 and counter tool 2, i.e. the surfaces that come into contact with the layer structure, have a structure. The layer facing the sealing surface of the counter tool 2 is held by the counter tool or its possible movement is at least slowed down. The layer facing the sealing surface of the sonotrode 1 moves with the in-plane oscillation of the sonotrode, so that the layers are moved relative to one another tangentially to the sealing surface. List of reference symbols 1 sonotrode 2 counter tools QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2011 004 002 A1

[0010]

Claims

[1] Method for producing a transverse sealing seam in web-shaped, sheet-shaped or tubular packaging materials, comprising the steps: A) Providing a sonotrode with a first sealing surface, B) Providing a counter tool with a second sealing surface, C) Providing a sealing section of web-, sheet- or tubular packaging material by folding a layer of a web-, sheet- or tubular packaging material in such a way that a sealing section is formed which has an n-layer subsection and an m-layer subsection, where n≠m, D) Positioning the sealing section and the sonotrode and the counter tool such that the sealing section is positioned between the first and second sealing surfaces and touches both the first and second sealing surfaces, E) Exciting an oscillation of the sonotrode such that a reference point on the first sealing surface experiences an in-plane oscillation movement. [2] Method according to claim 1, characterized by that in step E) the first sealing surface undergoes an in-plane oscillating movement. [3] Method according to one of the preceding claims, characterized by that in step E) the reference point has an in-plane oscillation movement with an oscillation amplitude A t and an out-of-plane oscillation motion with an oscillation amplitude A s preferably A t > A s , especially preferred A t > 5 × A s and preferably A t > 20 × A s is. [4] Method according to one of the preceding claims, characterized by that the first sealing surface and / or the second sealing surface have a structure. [5] Method according to one of the preceding claims, characterized bythat during step E) the counter tool is excited to oscillate, which is preferably such that a reference point on the second sealing surface experiences an in-plane oscillating movement. [6] Method according to one of the preceding claims, characterized by that during step E) a sealing force is exerted on the sealing section with the first sealing surface and / or with the second sealing surface. [7] Method according to one of the preceding claims, characterized bythat a material which is made of a thermoplastic material or has at least one thermoplastic layer is used as the web-, sheet- or tubular packaging material, wherein preferably a composite film is used which has at least one sealing layer and a carrier layer, wherein in step E) the vibration amplitude and / or the sealing force is dimensioned such that superimposed sealing layers are welded together.

Images