COMPENSATION OF THERMAL DEFORMATION ON SONOTRODES

Description

[0001] The present invention relates to a sonotrode for an ultrasonic welding device having a lower section of length u and an upper section of length o, wherein the upper section and the lower section are arranged next to one another on a longitudinal axis of the sonotrode and the total length of the sonotrode in the direction of the longitudinal axis is u + o, wherein the lower section has a sealing surface oriented perpendicular to the longitudinal axis, wherein the sealing surface is intended to come into contact with a material to be processed.

[0002] Ultrasonic welding has long been an established process for joining thermoplastics using a form-fit or material-fit connection. Applications range from the automotive and electrical industries to the packaging, medical, and hygiene industries.

[0003] Typical ultrasonic welding devices consist of an ultrasonic generator, a converter, possibly an amplitude transformer, and a welding tool, the sonotrode. The ultrasonic generator generates a high voltage at the desired ultrasonic frequency from an applied mains voltage. The electrical oscillation of the ultrasonic generator is then converted into a mechanical longitudinal oscillation in the converter using the inverse piezoelectric effect and transmitted to the amplitude transformer or the welding tool. With the help of the amplitude transformer, which may be arranged between the converter and the welding tool, the amplitude of the mechanical oscillation can be increased or decreased. In addition, the amplitude transformer can also serve to mount the oscillating structure consisting of the converter, amplitude transformer, and welding tool.Finally, the sonotrode, as the actual, active welding tool, transmits the mechanical vibration to the components to be joined. The sonotrode has a sealing surface through which the sonotrode comes into contact with the material being processed.

[0004] The mechanical vibrations at frequencies in the ultrasonic range generate frictional heat in the plastic being joined, stimulating the molecules within the plastic to move. As a result, the plastic softens and begins to melt, allowing the components to be joined to bond together when a certain pressure is applied to them over a certain period of time. The components are then firmly bonded at the molecular level.

[0005] The properties of the welded joint produced in terms of strength, tightness, and visual appearance depend on various factors during ultrasonic welding. For example, the frequency and amplitude of the vibration used during welding play a role, while the duration and applied welding force also influence the final weld result. Furthermore, the welding result also depends on the geometric or spatial shape of the welding tool. The shape of the welding tool is therefore selected in advance to achieve a specific welding result, for example, with regard to its visual appearance. An example of this can be found in WO 2012 / 107522 A1, which discloses, among other things, a device for producing a transverse sealing seam.

[0006] Different geometries for welding tools are described, for example, in "The design of ultrasonic resonators with wide output cross-sections" by P. Derks (Technische Hogeschool Eindhoven, https: / / doi.org / 10.6100 / IR34306).

[0007] However, the shape of the welding tool, i.e., the sonotrode, can also change during the welding process. During the welding process, temperature differences occur within the sonotrode, leading to uneven thermal expansion of the sonotrode material. This results in partially convex sealing surfaces, which, depending on the material being welded, significantly influences the welding result. In particular, this severely limits the homogeneous welding of very thin material layers, such as nonwovens used in the medical industry or in hygiene products. During production, fluctuations in the results occur both in the strength of the joint and in the visual appearance of the welded joint.This is due to the fact that, when welding very thin material layers, the distance between the welding tool and a counter-tool, between which the material layers are arranged, must be chosen to be correspondingly small in order to achieve a weld. If this distance is, for example, only in the range of a few micrometers, the deformation of the sealing surface of the sonotrode, which is also only in the range of a few micrometers, leads to a significant local change in the distance between the welding tool and counter-tool. Thus, in some areas, too little pressure is applied to the materials to be joined, while in others, too much pressure is applied.

[0008] To solve or minimize this problem, it is known from the prior art to grind the sealing surfaces that come into contact with the material to be processed to a concave shape. The concave indentation in the sealing surface is then eliminated by the convex thermal expansion of the sonotrode material, thus achieving a flat sealing surface and thus a homogeneous weld during operation of an ultrasonic welding device.

[0009] The disadvantage of this solution is that the deformation is only ideally compensated at a very specific operating point of the ultrasonic welding device. When the ultrasonic welding device is started from a cold state or when the tool heats up more than originally planned, this optimal operating point is not reached, and thus a homogeneous weld is not achieved.

[0010] To achieve the most reproducible processing result possible, strong air cooling of the sonotrode is often used as an alternative or in addition to this solution to minimize excessive heating or deformation. It is also known to equip the sonotrode with cooling channels near the sealing surface to keep the sonotrode temperature as constant as possible. However, even this method cannot guarantee a homogeneous weld of very thin materials.

[0011] The present invention is therefore based on the object of providing a sonotrode for an ultrasonic welding device with which even very thin material layers can be welded together with high quality.

[0012] According to the invention, this object is achieved by a sonotrode according to claim 1.

[0013] Dividing a lower section of the sonotrode reduces the effect of thermal expansion, preventing the sealing surface, which is divided into several sealing surface sections by the slots, from becoming curved. In other words, all sealing surface sections lie in one plane, come into contact with the material to be welded simultaneously, and exert the same pressure on the material. This allows even very thin material layers to be welded together, where a convex curvature of the sealing surface would lead to an unsatisfactory welding result.

[0014] In one embodiment, the sonotrode is designed such that u > 0.25 o, preferably 0.8 o < u < 1.5 o, and particularly preferably 0.95 o < u < 1.1 o. Ideally, the length o of the upper section essentially corresponds to the length u of the lower section.

[0015] If in this case the total length o + u of the sonotrode in the direction of the longitudinal axis corresponds to a wavelength λ with which the sonotrode is excited during an ultrasonic welding process, this results in the boundary between the upper section and the lower section running in the region of a vibration node of the excitation vibration. The arrangement of the boundary between the slotted lower section and the upper section in a vibration node has the advantage that this is an area with low stress and strain. This not only reduces stresses between the individual segments, but also minimizes the influence of the segments on the overall vibration behavior of the sonotrode. Thus, the slots in the lower section have almost no influence on the vibration transmitted to the material.

[0016] The slots according to the invention in the lower section of the sonotrode thus minimize the thermal deformation of the sealing surface and, at the same time, do not significantly influence the vibration behavior of the sonotrode, so that the welding result is optimized overall.

[0017] In a further embodiment, the sealing surface is delimited by two substantially parallel, opposite side surfaces of the sonotrode and the slot encloses an angle of < 90° and preferably an angle between 80° and 87° with the two side surfaces of the sonotrode in the region of the sealing surface.

[0018] The arrangement of the slots at an angle to the side surfaces of the sonotrode, which are arranged perpendicular to the feed direction of the material during the welding process, means that a uniform welding result can be achieved across the entire width of the sonotrode. The width of the sonotrode is understood to be the extent of the sonotrode that comes into contact with the material to be processed during a welding process and thus corresponds to the width of the material that is processed simultaneously during a welding process. If the slots were arranged perpendicular to the side surfaces, i.e. parallel to the feed direction, this would result in the sealing surface having areas in which no welding takes place. This would impair the tightness and the visual impression of the resulting weld.However, by arranging the slots at an angle to the side surfaces, welding occurs across the entire width of the sonotrode.

[0019] In this embodiment, the entire slot does not necessarily have to be arranged at an angle. It is sufficient if only a lower part of the slot, which adjoins the sealing surface, is arranged at an angle. This design offers the advantage of being easier to manufacture.

[0020] According to the invention, the slot has two supporting walls, wherein a distance between the supporting walls tapers towards the sealing surface, wherein the taper is preferably step-shaped, wherein particularly preferably the distance at the sealing surface is less than or equal to 1 mm, preferably less than or equal to 0.5 mm and particularly preferably less than or equal to 0.3 mm.

[0021] The tapering of the slots towards the sealing surface offers the advantage that, in terms of area, only the smallest possible area of ​​the sealing surface is interrupted by the slots. This minimizes the impact of the slots on the welding result, apart from compensating for thermal expansion.

[0022] In a further embodiment, the slot has a widening at an end facing away from the sealing surface, wherein the sealing surface is preferably delimited by two substantially parallel, opposite side surfaces of the sonotrode and wherein the widening is circular when viewed in a plane of the two opposite side surfaces of the lower section.

[0023] Such a widening offers the advantage of reducing tension that may build up between the segments due to the vibration of the sonotrode and thermal deformation.

[0024] In a further embodiment, a further widening is additionally arranged in the area of ​​the stepped tapering of the slot. This further widening preferably has a circular cross-section, like the widening at the end of the slot facing away from the sealing surface, in a plane of the two opposite side surfaces of the sonotrode. This arrangement also counteracts tension between the individual segments.

[0025] In a further embodiment, the sealing surface is delimited by two substantially parallel, opposite side surfaces and by a front and a rear surface of the sonotrode, wherein a width of the lower section between the front and the rear surface corresponds substantially to a width of the upper section between the front and the rear surface.

[0026] In other words, in this embodiment, at least one dimension of the upper and lower sections is selected such that it is substantially identical for the lower and upper sections. Since the lengths u and o of the upper and lower sections are preferably also substantially identical in the direction of the longitudinal axis, the dimensions of the upper and lower sections essentially coincide with each other in two dimensions.

[0027] In one embodiment, the extension in a third dimension between the essentially parallel, opposing side surfaces is smaller in the lower section than in the upper section. In other words, the sonotrode tapers in the lower section toward the sealing surface.

[0028] In a further embodiment, the extension of the sonotrode in the lower section is smaller than in the upper section, both between the front and rear surfaces and between the essentially parallel, opposite side surfaces. In this embodiment, the sonotrode tapers in two dimensions toward the sealing surface.

[0029] In a further embodiment, the number of slots and thus the width of the individual segments is selected such that the convex thermal deformation of the sonotrode in the region of the sealing surface is less than 3 µm, preferably less than 2 µm. The deformation is measured in a direction parallel to the longitudinal axis between the edge of the sealing surface and the extension of the sonotrode in the center of the sealing surface.

[0030] In a further embodiment, the lower section has a plurality of slots, each slot having two slot walls, wherein a width of the segments between two adjacent slot walls of two adjacent slots is at most (u+o) / 3, preferably (u+o) / 4 and particularly preferably (u+o) / 6.

[0031] It is understood that even in an embodiment with only one slot, the width of the segments between a slot wall and the front or rear surface of the sonotrode can also be at most (u+o) / 3, preferably (u+o) / 4 and particularly preferably (u+o) / 6.

[0032] The number of slots thus depends on the total width of the sonotrode between the front and rear surfaces of the sonotrode and the length u of the lower section and the length o of the upper section. Since the lengths u and o of the upper and lower sections are preferably selected depending on the wavelength with which the sonotrode is excited, the number of slots depends on the total width of the sonotrode and the wavelength of the exciting ultrasonic vibration.

[0033] The number of slots affects the overall vibration behavior of the sonotrode. The number of slots must therefore be selected so that, on the one hand, sufficient compensation for thermal deformation is achieved, while, on the other hand, the vibration behavior of the sonotrode itself is affected as little as possible.

[0034] In a further embodiment, the sealing surface is delimited by two substantially parallel, opposite side surfaces and by a front and a rear surface of the sonotrode, wherein the front surface is arranged at least on the sealing surface at an angle of < 90° to the two opposite side surfaces, wherein preferably also the rear surface is arranged at least on the sealing surface at an angle of < 90° to the two opposite side surfaces.

[0035] The arrangement of the front and preferably also the rear surface at an angle of < 90° to the two opposite side surfaces offers the advantage that several of the sonotrodes according to the invention can be arranged next to one another in order to increase the processing width of an ultrasonic welding device without interrupting the weld seam in the direction of the processing width. The angular arrangement of the front and rear surfaces is therefore based on the same considerations as the angular arrangement of the slots in the lower section of the sonotrode. In particular, it is not necessary here for the entire front or rear surface to extend at a specific angle to the two opposite side surfaces. Rather, only the arrangement of the front and rear surfaces in the region of the sealing surface is important.Areas of the front and rear surfaces that do not directly adjoin the sealing surface can also be arranged at any other angle to the two opposite side surfaces.

[0036] In a further embodiment, the upper section of the sonotrode has at least one gap, wherein the gap is not arranged in extension of the slot of the lower section and / or wherein the gap has a gap width that is greater than a distance of the slot walls of the slot.

[0037] The advantage of creating gaps in the upper section of the sonotrode is that the vibration behavior of the sonotrode and its expansion are kept stable during ultrasonic vibration excitation in the direction of the machining width. When a sonotrode is excited with ultrasonic vibration, the sonotrode also expands in a direction perpendicular to the material feed direction, i.e., in the machining width. This effect is already clearly evident when the width of the sonotrode exceeds one-third of the excitation wavelength of the ultrasonic vibration.

[0038] Since these gaps, unlike the slots in the lower section, are not intended to compensate for thermal deformation, but rather only for deformation due to ultrasonic vibration, the gaps can be shaped differently, for example, wider, and arranged independently of the slots. In particular, there is no connection between the slots in the lower section and the gaps in the upper section.

[0039] In a further embodiment, a holder for holding the sonotrode in an ultrasonic welding device is provided, wherein the holder is arranged on the segments of the lower section of the sonotrode.

[0040] Mounting the sonotrode on the segments of the lower section offers the advantage that the vibration behavior of the sonotrode is essentially unaffected by the mount. If the mount is positioned in an area where the vibration amplitude is lowest, the position of the sonotrode requires little readjustment to maintain a constant distance between the sonotrode and the material to be machined.

[0041] When the holder is arranged on the segments in the lower section, the effect of thermal deformation is also reduced, as there is less sonotrode material between the holder and the material to be machined, which can expand thermally. Furthermore, thermal expansion is compensated for by the slots in the lower section, so that readjustment of the sonotrode's position relative to the material to be machined can be achieved within a significantly smaller range or, depending on the application, may not be necessary at all.

[0042] The problem underlying the invention is further solved by a method for ultrasonic processing of a material, the method comprising the following steps: a) providing a sonotrode according to any one of claims 1-10, b) providing a counter-tool having a sealing surface, c) arranging the material between the sealing surface of the sonotrode and the sealing surface of the counter-tool, d) exciting the sonotrode with an ultrasonic oscillation having the wavelength λ, e) transmitting the ultrasonic oscillation to the material.

[0043] In a further embodiment of the method according to the invention, the wavelength λ is: 0,8 u + o < λ < 1,2 u + o and preferably 0,9 u + o < λ < 1,1 u + o .

[0044] Preferably, the total length u + o of the sonotrode along its longitudinal axis essentially corresponds to the wavelength λ at which the sonotrode is excited. In this case, it is also referred to as a λ-sonotrode.

[0045] In one embodiment, in particular, 0.4 λ < u < 0.6 λ and preferably λ / 2 = u. In other words, the extension of the slots in one direction of the longitudinal axis corresponds to half the wavelength. This also has advantages for the vibration behavior of the sonotrode, since the slots end at a vibration node of the ultrasonic vibration. In this case, the slots have virtually no influence on the vibration behavior of the sonotrode and merely compensate for the thermal deformation of the sonotrode.

[0046] In a further embodiment of the method according to the invention, during step e) the material is moved between the sealing surface of the sonotrode and the sealing surface of the counter tool at a feed rate v > 0 m / s.

[0047] By matching the feed speed to the ultrasonic welding process, a welding process is created that can process tubular and web-like materials in either intermittent or continuous operation. The material to be processed is continuously fed through the welding tool and, depending on the feed speed and the timing or design of the welding tool, is processed with ultrasound at specific points or continuously. Similar processes are used, for example, in the packaging industry, where a tubular material into which a product is filled is welded and severed at specific intervals in order to package the product individually. Other areas of application include, for example, the processing of web-like nonwovens, which are mainly processed in a continuous process in the hygiene industry.

[0048] Further advantages, features, and possible applications of the present invention will become clear from the following description of various embodiments of the invention and the accompanying figures. Identical elements are designated by the same reference numerals. Figure 1 shows a three-dimensional, schematic representation of an embodiment of the sonotrode according to the invention. Figure 2a shows a plan view of the sealing surface of the Figure 1 shown embodiment. Figure 2b shows an enlargement of the marked area in Figure 2a . Figure 3a shows a side view of a side surface of the Figure 1 shown embodiment. Figure 3b shows an enlargement of the Figure 3a marked area. Figure 4 shows another side view of the front surface of the Figure 1shown embodiment. Figure 5 shows a three-dimensional, schematic representation of another embodiment of the sonotrode according to the invention. Figure 6 shows a schematic representation of an embodiment of the sonotrode according to the invention in an ultrasonic welding device.

[0049] The Figure 1 The embodiment shown of the sonotrode 1 according to the invention for an ultrasonic welding device can be divided into a lower section 10 of length u and an upper section 20 of length o. The upper section 20 and the lower section 10 are arranged side by side on a longitudinal axis 100 of the sonotrode 1. The total length of the sonotrode 1 in the direction of the longitudinal axis 100 is u + o. In addition, the length u of the lower section 10 corresponds to the length o of the upper section 20. Furthermore, a width 19 of the lower section 10 corresponds to a width 29 of the upper section 20.

[0050] Out of Figure 4It can be seen that the front surface 13 tapers towards the sealing surface 11. An extension of the sonotrode 1 in the upper section 20 and in an upper region of the lower section 10 in a plane of the front surface 13 is therefore greater than an extension of a lower region of the lower section 10, which adjoins the sealing surface 11. The rear surface 14 is designed in the same way as the front surface 13.

[0051] Furthermore, the lower section 10 has a sealing surface 11 aligned perpendicular to the longitudinal axis 100, which in Figure 2a The sealing surface 11 is intended to come into contact with a material 40 to be processed (see Figure 6 ). The width 19 corresponds to the width over which ultrasonic processing of the material 40 takes place with the sonotrode 1 according to the invention.

[0052] The lower section 10 of the sonotrode 1 has three slots 15, wherein the slot 15 extends from the sealing surface 11 to one side of the lower section 10 opposite the sealing surface 11. The slot 15 has two slot walls which are spaced apart from each other at a distance 17 (see Figure 2b ).

[0053] Out of Figure 3b It is also evident that the slot 15 tapers towards the sealing surface 11, with the tapering occurring in a step-like manner. In the region of the step-like taper, a widened portion 18' is arranged, which has a circular cross-section in a plane of the side surface 12. The distance between the slot walls in the region 15' of the slot 15, which is arranged between the widened portion 18' and the sealing surface 11, is also significantly smaller than a distance 17 between the slot walls of the slot 15 above the widened portion 18'.

[0054] In addition to the widening 18' in the area of ​​the stepped taper, the slot 15 has a further widening 18, which is arranged at an end of the slot 15 facing away from the sealing surface 11. Viewed in a plane of the side surface 12, the widening 18 also has a circular cross-section (see Figure 3a ).

[0055] The widenings 18, 18' prevent or at least reduce stresses that could develop between the segments 10' during operation of the sonotrode 1 in an ultrasonic welding device due to vibrations and thermal expansion of the sonotrode material.

[0056] In the Figures 2a and 2bIt is also shown that the slots 15 in the area of ​​the sealing surface 11 form an angle 16 of 81° with the side surface 12 of the sonotrode 1. The side surfaces 12, 12' run parallel to each other, are arranged opposite each other and delimit the sealing surface 11 of the sonotrode 1. As in Figure 3a The slots 15 are shown arranged only in a small area 15' of a few millimeters from the sealing surface 11 in the direction of the longitudinal axis 100 at this angle 16 to the side surface 12. In the adjoining area in the direction of the longitudinal axis 100, the slots 15 are arranged perpendicular to the two side surfaces 12, 12'.

[0057] In addition, the Figure 2aIt can be seen that a front surface 13 and a rear surface 14 of the sonotrode 1, which delimit the sealing surface 11 in addition to the side surfaces 12, 12', are also arranged at an angle of < 90° to the side surfaces 12. This allows the sonotrode 1 according to the invention to be connected to additional sonotrodes in order to increase the processing width of an ultrasonic welding device.

[0058] The slots 15 divide the lower section 10 of the sonotrode 1 into several adjacent segments 10' in a direction perpendicular to the longitudinal axis 100. The arrangement of the slots 15 in the lower section 10 of the sonotrode 1 reduces thermal deformation of the sealing surface 11, so that a more homogeneous welding result is achieved across the width 19 of the lower section 10.

[0059] In addition, two gaps 21 with a gap width 27 are arranged in the upper section 20 (see Figure 3a). The gaps 21 serve to minimize expansion of the sonotrode 1 in the width 29 of the upper section 20 during operation of the sonotrode 1 in an ultrasonic welding device.

[0060] As in the Figures 1 and 3 As shown, the gaps 21 are independent of the slots 15, i.e. they are not arranged in extension of these or on a common line and also have a larger gap width 27, since the gaps 21 compensate for a different deformation effect of the sonotrode 1 than the slots 15

[0061] Ultimately, the Figures 1-4 shown embodiment has holders 30 which are arranged in a region of the segments 10' of the lower section 10.

[0062] The Figure 5 The embodiment of the sonotrode 1 according to the invention shown differs from that shown in the Figures 1-4shown embodiment in that the holders 30 are not arranged in the lower section 10, but in the upper section 20.

[0063] In Figure 6 is the Figure 5 The embodiment of the sonotrode 1 shown in FIG. 1 is schematically illustrated in an ultrasonic welding device. A material 40 to be processed is arranged between the sonotrode 1 and a counter-tool 50. The material 40 moves at a feed rate v > 0 m / s in a feed direction 101 between the sonotrode 1 and the counter-tool 50.

[0064] During operation of the ultrasonic welding device, the sonotrode 1 is excited by an ultrasonic vibration with a wavelength of λ, and this ultrasonic vibration is transmitted via the sealing surface 11 to the material 40. The ultrasonic vibration presses the material 40 against a sealing surface 51 of the counter-tool 50, so that the material 40 is ultrasonically processed by the transmitted ultrasonic vibrations. The material 40 can, for example, be several layers of nonwoven fabric that are to be bonded together. When the sonotrode 1 impacts the nonwoven fabric 40, the fabric begins to melt due to the frictional heat generated and bonds with an underlying layer of material.

[0065] The total length o + u of the sonotrode 1 is selected so that it essentially corresponds to the wavelength λ of the exciting ultrasonic vibration. Furthermore, the length of the slots 15, i.e., the length u of the lower section 10, corresponds to half the wavelength λ.

[0066] The selection of these dimensions ensures that the slots 15 optimally compensate for the thermal deformation of the sealing surface 11, while at the same time not significantly affecting the vibration behavior of the sonotrode 1. Thus, even very thin material layers 40 can be homogeneously welded together or generally processed with ultrasound using the sonotrode 1 according to the invention. List of reference symbols

[0067] 1 Sonotrode 10 Lower section 10 Segments 11 Sealing surface of the sonotrode 12, 12 Parallel, opposite side surfaces 13 Front surface 14 Rear surface 15 Slot 15 Partial section of the slot arranged towards the sealing surface 16 Angle 17 Distance between the slot walls 18, 18 Widening 19 Width of the lower section 20 Upper section 21 Gap 27 Gap width 29 Width of the upper section 30 Holder 40 Material 50 Counter tool 51 Sealing surface of the counter tool 100 Longitudinal axis 101 Feed direction

Claims

1. A sonotrode (1) for an ultrasonic welding apparatus, having a lower portion (10) of length u and an upper portion (20) of length o, the upper portion (20) and the lower portion (10) being arranged adjacent to each other on a longitudinal axis (100) of the sonotrode (1), and the total length of the sonotrode (1) in the direction of the longitudinal axis (100) being u + o, the lower portion (10) having a sealing surface (11) oriented perpendicular to the longitudinal axis (100), the sealing surface (11) is intended to come into contact with a material (40) to be processed, wherein the lower portion (10) has a slot (15), wherein the slot (15) extends from the sealing surface (11) to a side of the lower portion (10) opposing the sealing surface (11), such that the lower portion (10) of the sonotrode (1) is divided into a plurality of segments (10') which lie adjacent to each other in a direction perpendicular to the longitudinal axis (100), the slot (15) having two slot walls, characterized in that a spacing (17) between the slot walls tapers in the direction of the sealing surface (11).

2. The sonotrode (1) according to the preceding claim, wherein u > 0,25o, preferably 0,8o < u < 1,5o, and particularly preferably 0,95o < u < 1,1o.

3. The sonotrode (1) according to any of the preceding claims, wherein the sealing surface (11) is bordered by two opposing side surfaces (12, 12') of the sonotrode (1) which extend essentially parallel to each other, and the slot (15) in the region of the sealing surface (11) forming an angle (16) of < 90°, and preferably an angle (16) of between 80° and 87°, with each of the two side surfaces (12, 12') of the sonotrode (1).

4. The sonotrode (1) according to any of the preceding claims, wherein the tapering is stepped, wherein said spacing (17) preferably is less than or equal to 1 mm, preferably less than or equal to 0.5 mm, and particularly preferably less than or equal to 0.3 mm.

5. The sonotrode (1) according to any of the preceding claims, wherein the slot (15) has a widening (18) on an end facing away from the sealing surface (11), the sealing surface (11) preferably being bordered by two opposing side surfaces (12, 12') of the sonotrode (1), which extend essentially parallel to each other, and wherein the widening (18) is circular when viewed on a plane of the two opposing side surfaces (12, 12').

6. The sonotrode (1) according to any of the preceding claims, wherein the sealing surface (11) is bordered by two opposing side surfaces (12, 12') which are essentially parallel to each other, and bordered by a front surface (13) and a rear surface (14) of the sonotrode (1), wherein a width (19) of the lower portion (10) between the front surface (13) and the rear surface (14) essentially corresponds to a width (29) of the upper portion (20) between the front surface (13) and the rear surface (14).

7. The sonotrode (1) according to any of the preceding claims, wherein the lower portion (10) has a plurality of slots (15), each slot (15) having two slot walls, a width of the segments between two adjacent slot walls of two adjacent slots (15) being at most (u+o) / 3, preferably (u+o) / 4, and more preferably (u+o) / 6.

8. The sonotrode (1) according to any of the preceding claims, wherein the sealing surface (11) is bordered by two opposing side surfaces (12, 12') which extend essentially parallel to one another, and bordered by a front surface (13) and a rear surface (14) of the sonotrode (1), wherein the front surface (13) is arranged, at least on the sealing surface (11), at an angle of less than 90° to the two opposing side surfaces (12, 12'), wherein preferably the rear surface (14) is also arranged, at least on the sealing surface (11), at an angle smaller than 90° to the two opposing side surfaces (12, 12').

9. The sonotrode (1) according to any of the preceding claims, wherein the upper portion (20) of the sonotrode (1) has at least one gap (21), wherein the gap (21) is not arranged along an extension of the slot (15) of the lower portion (10), and / or wherein the gap (21) has a gap width (27) that is larger than a spacing (17) of the slot walls of the slot (15).

10. The sonotrode (1) according to any of the preceding claims, wherein a support (30) is provided for holding the sonotrode (1) in an ultrasonic welding apparatus, the support (30) being arranged on the segments (10') of the lower portion (10) of the sonotrode (1).

11. A method for ultrasonic processing of a material (40) comprising the following steps: a) providing a sonotrode (1) according to any of claims 1 to 10, b) providing a counter-tool (50) having a sealing surface (51), c) arranging the material between the sealing surface (11) of the sonotrode (1) and the sealing surface (51) of the counter-tool (50), d) exciting the sonotrode (1) with an ultrasonic oscillation of wavelength λ, e) transferring the ultrasonic vibration to the material (40).

12. The method according to claim 11, wherein the following applies to wavelength λ 0,8(u + o) < λ < 1,2(u + o) and preferably 0,9(u + o) < λ < 1,1(u + o).

13. The method according to claim 12, wherein 0,4λ < u < 0,6λ, and preferably λ / 2 = u.

14. The method according to one of claims 11 to 13 wherein, during step e) the material (40) is passed at a feed rate of v > 0 m / s in a feed direction (101) between the sealing surface (11) of the sonotrode (1) and the sealing surface (51) of the counter-tool (50).