DE102023114852A1 - Ultrasonic machining process for joining layers and ultrasonic machining device - Google Patents

Abstract

The present invention relates to an ultrasonic processing method for connecting layers of a compressible material or an ultrasonic processing device for carrying out the method, wherein at least three layers of one material or different materials arranged on top of one another, namely an outer layer, an inner layer and a middle layer, wherein at least one of the at least three layers comprises a compressible material, and a sonotrode which can be excited with an ultrasonic vibration are provided, wherein the sealing surface of the sonotrode is brought into contact with the outer layer and the sonotrode is moved in the direction of the inner layer with a feed force so that the layers arranged on top of one another are pressed together by the feed force, wherein the feed force and/or an oscillation amplitude of the ultrasonic vibration is selected such that the outer layer is connected to the at least one middle layer which adjoins the outer layer, but not all of the at least three layers lying on top of one another are connected to one another.

Description

The present invention relates to an ultrasonic processing method for joining layers of a compressible material and to an ultrasonic processing device for carrying out the method.

Compression is the reduction in volume and thus an increase in density of a body when it is compressed from one or more directions, i.e. when a force is exerted on the body. In general, any solid body can therefore be considered compressible, provided that a sufficiently high pressure is exerted on the solid body.

However, compressible materials in the sense of the present invention are understood to mean in particular materials whose volume and thus their density can be easily changed by compressing the material. These include, for example, loose structures made of fibers or threads such as cotton wool or spongy materials that are characterized by a high air content and thus have a low compression modulus < 0.01 GPa.

Ultrasonic processing methods are increasingly being used to process these compressible materials, for example to produce hygiene products such as diapers or tampons. To do this, an ultrasonic vibration is introduced into the material using a sonotrode, which causes the material to be heated locally. The heating changes the composition of the components of the material, such as fibers or threads, so that, for example, individual layers of a material can be connected to one another or the material can be shaped into a specific form.

In the described manufacturing and processing methods using ultrasound, the compressible materials are typically fed to the processing device in the form of rolled-up material webs or rolled up into an intermediate or final product. Different material webs can also be fed to the processing device at the same time or connected to one another for feeding. If the processing process is interrupted, for example because materials or tools have to be replaced, the material web must be secured against further unrolling. For this purpose, the only known method from the relevant state of the art is to seal the still rolled-up material web with an adhesive tape or other adhesive.

However, this represents an additional step in the processing process, which requires a lot of personnel and a corresponding preparation time. In addition, the use of an adhesive tape leads to additional material costs and reduces the sustainability of the processing process or the manufactured product. The adhesives used are undesirable, especially in hygiene products.

Sealing rolled up material webs is also necessary in the production of toilet paper rolls, for example. In this technical area, the rolls are currently sealed using thermal sealing. However, transferring this technology to ultrasonic processing methods would require an additional tool in the ultrasonic processing device. Furthermore, thermal sealing is associated with high energy costs and impairs the quality of the product and the process stability.

This disadvantage of thermal sealing can also be found, for example, in the production of tampons and other absorbent, multi-layered hygiene products that need to be shaped into a specific form.

The present invention is therefore based on the object of providing an ultrasonic processing method for joining layers of a compressible material or a corresponding device with which the layers can be joined without additional adhesives or additional tools for thermal sealing.

1. a. Bereitstellen von zumindest drei aufeinander angeordneten Schichten eines Materials oder verschiedener Materialien, nämlich einer äußeren Schicht, einer inneren Schicht und zumindest einer zwischen der äußeren Schicht und der inneren Schicht angeordneten mittleren Schicht, wobei zumindest eine der zumindest drei Schichten ein kompressibles Material aufweist,
2. b. Bereitstellen einer Sonotrode mit einer Siegelfläche, wobei die Sonotrode dafür vorgesehen ist, mit einer Ultraschallschwingung in Resonanz gebracht zu werden,
3. c. Inkontaktbringen der Siegelfläche mit der äußeren Schicht und Bewegen der Sonotrode in Richtung der inneren Schicht mit einer Zustellkraft, sodass die aufeinander angeordneten Schichten durch die Zustellkraft zusammengedrückt werden,
4. d. Anregen der Sonotrode mit der Ultraschallschwingung,

wobei die Zustellkraft und/oder eine Schwingungsamplitude der Ultraschallschwingung derart gewählt wird, dass die äußere Schicht mit der zumindest einen mittleren Schicht, die an die äußere Schicht angrenzt, verbunden wird, aber nicht alle der zumindest drei aufeinanderliegenden Schichten miteinander verbunden werden.The object underlying the invention is achieved by an ultrasonic processing method of the type mentioned above, wherein the method comprises the following steps:

1. a. Providing at least three layers of one material or different materials arranged on top of one another, namely an outer layer, an inner layer and at least one middle layer arranged between the outer layer and the inner layer, wherein at least one of the at least three layers comprises a compressible material,
2. b. Providing a sonotrode with a sealing surface, wherein the sonotrode is intended to be brought into resonance with an ultrasonic vibration,
3. c. Bringing the sealing surface into contact with the outer layer and moving the sonotrode towards the inner layer with a feed force so that the superimposed ten layers are compressed by the delivery force,
4. d. Stimulating the sonotrode with the ultrasonic vibration,

wherein the feed force and/or an oscillation amplitude of the ultrasonic oscillation is selected such that the outer layer is connected to the at least one middle layer which adjoins the outer layer, but not all of the at least three superimposed layers are connected to one another.

The method according to the invention offers the advantage that the processing of compressible materials, for example for closing a rolled-up material web or for producing a tampon, is automated and manual use or additional energy-intensive tools are no longer necessary. This also eliminates the previous need for additional consumables such as adhesive tape or additional tools.

Preferably, only the outer layer and the middle layer immediately adjacent to the outer layer are bonded together so that the underlying layers are not affected by the ultrasonic processing.

It is understood that in one embodiment, the layers arranged on top of one another are provided by rolling up a web of material. Alternatively or additionally, the layers arranged on top of one another can also be formed by folding a web of material.

In a further embodiment, the layers arranged on top of one another can also be provided by different compressible or non-compressible materials. A layer can also consist of several sub-layers, which are preferably already connected to one another.

In one embodiment of the method, a multilayer material is therefore provided with a compressible layer and a film-like layer, wherein the film-like layer protrudes beyond the compressible layer in at least one direction and the multilayer material is rolled up such that the compressible layer provides the inner layer and the film-like layer provides the middle layer and the outer layer in the region of an overlap.

To produce a tampon, for example, multi-layered material webs made up of different materials are fed to the processing device, rolled up and pressed into a specific shape, e.g. a tampon shape. To prevent the layers from coming apart again, the top layers of the rolled-up material web are bonded together using ultrasound. This offers the advantage that neither health-endangering adhesives are used nor is an additional tool required for thermal sealing. The surface of the tampon is less affected by ultrasonic processing than by thermal sealing and is therefore more comfortable to wear.

The materials arranged on top of each other can be the same or different materials, with at least one of the material layers comprising a compressible material. The materials of one layer can consist of a mixture of thermoplastic and non-thermoplastic fibers, or one of the layers can consist of thermoplastic material while another layer consists of non-thermoplastic material. Multi-layer composite materials are used in tampon production, which consist, for example, of a thermoplastic outer film and inner, compressible cotton layers. If these composite materials are rolled up, the outer thermoplastic film encloses the inner, compressible cotton layers.

In particular, the compressible material exerts a restoring force on the sonotrode that counteracts the feed force. In one embodiment, the compressible material is selected such that the restoring force provides a counterforce required to connect the layers. The compressible material therefore applies sufficient force to the sonotrode on its own, which is sufficient to connect the outer layer to the adjacent middle layer.

In a further preferred embodiment, the method is therefore carried out without an additional counter tool as an energy director. In the context of the present invention, an energy director is understood to mean components of the ultrasonic processing device or of the material to be processed that focus the ultrasonic energy to be introduced or introduced into the material on a defined joining area between the outer and middle layers. This energy focusing means that the heat development is greatest in the defined joining area. A stable connection is achieved with the lowest possible energy consumption. For example, a sonotrode that introduces the ultrasonic vibration into the material in a targeted manner is an energy director. In particular, the sonotrode can have certain shapes for this purpose.

In methods known from the prior art, a counter tool, for example in the form of a roller, is arranged opposite the sonotrode, so that the material to be processed is arranged in a gap between the sonotrode and the counter tool and the counter tool, as a second energy director, also concentrates the ultrasonic energy in the joining area.

According to the invention, however, the compressible material itself acts as a second energy director to concentrate the ultrasonic energy in the joining area between the outer and middle layers. By eliminating a counter tool in the true sense, the costs of the processing method can be significantly reduced. It goes without saying that any holding or positioning devices that serve to hold or position the layers arranged on top of one another do not represent a counter tool in the sense of an energy director, since the ultrasonic energy introduced into the material is not focused on the joining area by these mechanical components. Such holding or positioning devices serve exclusively to hold or position the materials to be processed, but do not themselves contribute to the ultrasonic processing.

In a further embodiment, the connection created in step d. between the outer layer and the at least one middle layer is a point-like or linear connection. The point-like or linear, i.e. non-flat, connection ensures that, for example, the material web is prevented from unrolling on its own, but the compressible material itself is processed as little as possible. In particular, the connection between the outer layer and the adjacent middle layer is designed to be detachable, so that the material web can be easily opened when ultrasonic processing is resumed. It goes without saying that the point-like connection is not limited to circular connection points, but also includes other geometric shapes such as triangles, rectangles, etc.

In one embodiment, the ultrasonic vibration with which the sonotrode is excited in step d. has a frequency of at least 20 kHz and at most 35 kHz. At these frequencies, it is ensured that the material is sufficiently processed, but at the same time the material's structure is not unnecessarily impaired.

In a further embodiment, the ultrasonic vibration with which the sonotrode is excited in step d. has an amplitude of at least 5 µm, preferably of at least 10 µm and particularly preferably of at least 15 µm. The amplitude of the ultrasonic vibration is understood to be a maximum amplitude that is defined between the rest position of the sonotrode and the maximum expansion of the sonotrode. The choice of the vibration amplitude ensures that the compressible material is compressed sufficiently in addition to the feed force and thus the counterforce of the material for connecting the layers is increased, so that ultimately the connection stability is increased.

In a further embodiment, the sonotrode rotates about a rotation axis during step f., wherein the rotation axis is aligned perpendicular to a direction of the feed force. A rotating sonotrode can simultaneously be used as a material guide roller for the compressible material.

In one embodiment, the sealing surface is tailored to the compressible material to be processed. Depending on the material, the sealing surface is smooth or structured in one embodiment. In the case of a structured sealing surface, the sealing surface preferably has at least one slot and/or point-like elevations and/or a honeycomb structure. The structured sealing surface enables targeted energy input into the compressible material. The slot in particular provides a flow channel for the melt that is created when the material is heated, so that the melt is directed in a targeted manner along the material surface.

In particular, in one embodiment, the slot is preferably not oriented in a feed direction in which the layers of the compressible material arranged on top of one another are moved relative to the sonotrode.

In a further embodiment, the sealing surface of the sonotrode is curved, preferably concavely curved. This increases the contact area and the contact time between the sonotrode and the outer layer of the material and improves the connection stability.

The object underlying the invention is also achieved by an ultrasonic processing device for a method according to one of the aforementioned embodiments, wherein the ultrasonic processing device has a generator, a converter and a sonotrode, wherein the generator is set up and connected to the converter in such a way that an ultrasonic frequency can be generated by the generator and transmitted to the converter, wherein the converter is set up and connected to the sonotrode in such a way that that the converter can convert the ultrasonic frequency generated by the generator into a mechanical ultrasonic vibration and transmit it to the sonotrode, wherein the sonotrode has a sealing surface which is intended to come into contact with an outer layer of a multi-layer, compressible material and to exert a delivery force on the compressible material.

In particular, in one embodiment, the multilayer, compressible material is a rolled-up material web that acts as a counter-tool during operation of the ultrasonic processing device and provides a counterforce to the feed force required for bonding the outer layer to a middle layer adjacent to the outer layer.

• 1 zeigt eine schematische Darstellung einer Ausführungsform der erfindungsgemäßen Ultraschallbearbeitungsvorrichtung.
• 2a schematische Darstellung eines Ausgangsmaterials für eine Ausführungsform des erfindungsgemäßen Verfahrens.
• 2b schematische Darstellung der in 1 gezeigten Ausführungsform der Ultraschallbearbeitungsvorrichtung zur Bearbeitung des Materials nach 2a.

Further advantages, features and possible applications of the present invention will become clear from the following description of a preferred embodiment and the associated figure. Identical components are provided with the same reference numerals.

• 1 shows a schematic representation of an embodiment of the ultrasonic processing device according to the invention.
• 2a schematic representation of a starting material for an embodiment of the process according to the invention.
• 2b schematic representation of the 1 shown embodiment of the ultrasonic processing device for processing the material according to 2a .

The in 1 The ultrasonic processing device 1 shown serves to carry out the ultrasonic processing method according to the invention. To carry out the method, a rolled-up web of a compressible material 6 is provided, which consists of several layers, namely an outer layer 6a, an inner layer 6c and several middle layers in between. A middle layer 6b is directly adjacent to the outer layer 6a.

In order to prevent the rolled-up material web from unrolling accidentally, the outer layer 6a is connected to the adjacent middle layer 6b using the ultrasonic processing device 1. For this purpose, the ultrasonic processing device has a generator 2 for generating an ultrasonic frequency, which is passed on to a converter 3. The converter 3 converts the ultrasonic frequency into a mechanical ultrasonic vibration and thus excites the sonotrode 4, the sealing surface 5 of which is in contact with the outer layer 6a after the sonotrode 4 has been pressed onto the compressible material 6 with a feed force, so that it is compressed.

The sonotrode 4 moves due to the ultrasonic vibration with vibration amplitudes of 25 µm in the 1 shown oscillation direction 100 towards or away from the material, whereby a locally limited heating of the compressible material 6 occurs and the outer layer 6a is connected to the adjacent middle layer 6b.

The feed force and the vibration amplitude of the sonotrode 4 are selected such that a counterforce, which is counteracted by the compressible material 6 of the sonotrode 4, is sufficient to create a connection between the outer layer 6a and the adjacent middle layer 6b. An additional counter tool is not required. The rolled-up material web made of the compressible material 6 acts as a second energy director, which focuses the ultrasonic energy on a joining area between the outer layer 6a and the middle layer 6b.

In order to introduce the vibration energy into the compressible material 6 in a targeted manner, the sealing surface 5 of the sonotrode 4 has a slot 7. The slot 7 serves to guide the melt in a targeted manner in order to improve the connection stability between the outer layer 6a and the adjacent middle layer 6b.

With the ultrasonic processing method according to the invention or the associated device, it is possible to seal a rolled-up material web of a compressible material 6 without using additional adhesives or sealing tools.

In the 2a and 2b a second possible application of the ultrasonic processing device 1 according to the invention is shown. In this embodiment, the three layers 6a, 6b, 6c arranged on top of one another partially comprise different materials.

The starting material 6 is, as in 2a shown, a multilayer composite material is used which has a cotton-like layer 6c and a film-like layer arranged thereon, the length of which is at least slightly greater than a length of the cotton-like layer.

To produce a tampon, this composite material is rolled up to form several layers 6a, 6b, 6c arranged one on top of the other, with the inner layer 6c being formed from the cotton-like layer surrounded by the film-like layer. Due to the greater length The film-like layer is rolled up and the film-like layer overlaps, so that the film-like layer forms an outer layer 6b and a middle layer 6b, which are connected to one another using the ultrasonic processing device 1 according to the invention. This prevents the rolled-up starting material from coming loose.

list of reference symbols

1

ultrasonic processing device

2

generator

3

converter

4

sonotrode

5

sealing surface

6

compressible material

6a

outer layer

6b

middle layer

6c

inner layer

7

slot

Claims (14)

Ultrasonic processing method for joining layers (6a, 6b) of a compressible material (6) with the steps: a. Providing at least three layers (6a, 6b, 6c) of a material (6) or different materials (6) arranged on top of one another, namely an outer layer (6a), an inner layer (6c) and at least one middle layer (6b) arranged between the outer layer (6a) and the inner layer (6c), wherein at least one of the at least three layers comprises a compressible material, b. Providing a sonotrode (4) with a sealing surface (5), wherein the sonotrode (4) is intended to be brought into resonance with an ultrasonic vibration, c. Bringing the sealing surface (5) into contact with the outer layer (6c) and moving the sonotrode (4) in the direction of the inner layer (6c) with a feed force so that the layers (6a, 6b, 6c) arranged on top of one another are pressed together by the feed force, d. Exciting the sonotrode (4) with the ultrasonic vibration, wherein the feed force and/or an oscillation amplitude of the ultrasonic vibration is selected such that the outer layer (6a) is connected to the at least one middle layer (6b) which adjoins the outer layer (6c), but not all of the at least three layers (6a, 6b, 6c) lying on top of one another are connected to one another. Method according to the preceding claim, wherein the layers arranged on top of one another are provided by rolling up a web of material (6). Method according to one of the preceding claims, wherein in step a. a multilayer material (6) with a compressible layer and a film-like layer is provided, wherein the film-like layer protrudes beyond the compressible layer in at least one direction and the multilayer material (6) is rolled up such that the compressible layer provides the inner layer (6c) and the film-like layer in the region of an overlap provides the middle layer (6b) and the outer layer (6a). Method according to one of the preceding claims, wherein the compressible material (6) exerts a restoring force on the sonotrode (4) which counteracts the feed force, wherein the compressible material (6) is selected such that the compressible material (6) provides a counterforce required for connecting the layers (6a, 6b) through the restoring force. Method according to one of the preceding claims, wherein the method is carried out without an additional counter tool as an energy director. Method according to one of the preceding claims, wherein the connection produced in step d. between the outer layer (6a) and the at least one middle layer (6b) is a point-like or linear connection. Method according to one of the preceding claims, wherein the ultrasonic vibration with which the sonotrode (4) is excited in step d. has an amplitude of at least 5 µm, preferably of at least 10 µm and particularly preferably of at least 15 µm. Method according to one of the preceding claims, wherein the sonotrode (4) rotates about a rotation axis during step d., wherein the rotation axis is aligned perpendicular to a direction of the feed force. Method according to one of the preceding claims, wherein the sealing surface (5) of the sonotrode (4) is smooth or structured, wherein the structured sealing surface (5) preferably has at least one slot and/or point-like elevations and/or a honeycomb structure. procedure according to claim 9 , wherein the layers of the compressible material (6) arranged on top of one another are arranged in a feed direction relative to the Sonotrode can be moved, whereby the slot is preferably not oriented in the feed direction. Method according to one of the preceding claims, wherein the sealing surface (5) of the sonotrode (4) is curved, preferably concavely curved. A tampon produced by a process according to any one of the preceding claims. Ultrasonic processing device (1) for a method according to one of the preceding claims, wherein the ultrasonic processing device (1) has a generator (2), a converter (3) and a sonotrode (4), wherein the generator (2) is set up and connected to the converter (3) in such a way that an ultrasonic frequency can be generated by the generator (2) and transmitted to the converter (3), wherein the converter (3) is set up and connected to the sonotrode (4) in such a way that the ultrasonic frequency generated by the generator (2) can be converted into a mechanical ultrasonic vibration by the converter (3) and transmitted to the sonotrode (4), wherein the sonotrode (4) has a sealing surface (5) which is intended to come into contact with an outer layer (6a) of a multi-layer, compressible material (6) and to exert a feed force on the compressible material (6). Ultrasonic processing device (1) according to claim 13 , wherein the multi-layer, compressible material (6) is a rolled-up material web which acts as a counter-tool during operation of the ultrasonic processing device (1) and provides a counterforce to the feed force required for connecting the outer layer (6a) to a middle layer (6b) adjacent to the outer layer (6a).

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