A SYSTEM COMPRISING A SINGLE-CAVITITY THERMOFORMING DIE AND A HEATING DEVICE AND A THERMOFORMING DEVICE

Description

[0001] The present invention relates to a device for heating packaging films, in particular for heating packaging films in the context of deep-drawing processes.

[0002] The packaging and distribution of consumer goods are subject to constantly changing demands. In the area of detergents and cleaning agents, for example, there has been a focus for some time on convenient dosing for the consumer and simplifying the steps required to carry out a washing or cleaning process. Pre-portioned detergents and cleaning agents, such as foil pouches with one or more compartments for solid or liquid detergents or cleaning agents, offer a technical solution.

[0003] A relevant trend for the production of these film bags is the miniaturization of these bags. In addition to increased consumer acceptance due to easier handling, this development is driven by sustainability considerations, for example, with regard to the amount of packaging used.

[0004] The film bags described above are manufactured using multi-stage processes during which water-soluble film materials are formed into cavities, for example, through the action of heat and negative pressure, filled, and then sealed. While heating the film increases its plasticity, the force resulting from the negative pressure applied to the heated film causes it to stretch and plastically deform. In this heating device, the film is not stretched homogeneously across its surface; rather, areas of high stretch, for example, in the edge area of the cavity, alternate with areas of lower stretch. A film material with a homogeneous film thickness is thus transformed into a deformed film in the shape of a receptacle with a heterogeneous film thickness distribution. This heterogeneous film thickness distribution becomes more pronounced the more the original film material is deformed.The degree of deformation generally increases, for example, with the number of receiving chambers formed in the receiving container or their depth.

[0005] Among other factors, both the film thickness distribution and the absolute film thickness determine the haptic, optical, and mechanical properties of the film pouch. Film pouches with large differences in film thickness are often perceived as less appealing. Film pouches with a low minimum film thickness deform more easily under their own weight than corresponding film pouches with a higher film thickness and appear flabby. These film pouches withstand mechanical stress to a lesser extent and detach too quickly when exposed to water. The latter two properties are not only relevant for film pouches in the areas of production, transport, and storage, but also have a particular impact on product safety, for example in the event of accidental oral ingestion.

[0006] The European patent application EP 3 738 751 A1 describes a process for producing compact multi-chamber thermoformed bags with a reduced seal seam width.

[0007] Multi-chamber thermoformed bags with specific geometry and methods for their production are described in the patent applications US 2018 / 0282672 A1 and EP 1 375 637 A1.

[0008] Applications US 2022 / 0081656 A1, DE 20 19 295 A1, and EP 0 055 082 A2 relate to deep-drawing processes in which the deep-drawing sheet is heated unevenly before its deformation. DE 20 19 295 A1 and EP 0 055 082 A2 disclose systems according to the preamble of claim 1.

[0009] A heating device suitable for generating a temperature profile on a film web is the subject of European patent EP 3 078 478 B1.

[0010] To increase the homogeneity of the wall thickness in deep-drawing processes, the international application WO 2019 / 206448 A1 proposes a deep-drawing process in which a flat film is exposed to a temperature profile.

[0011] With the same objective, European patent application EP2298536 A2 and international patent application WO 2020 / 152044 A1 propose heating devices using heating devices with heterogeneous temperature distribution.

[0012] However, these previously described solutions require complex equipment and are only suitable to a limited extent for high throughputs. Furthermore, setting up and converting corresponding thermoforming lines is costly.

[0013] Against this technical background, the application was based on the object of providing a heating device for the production of portion units, which enables the efficient production of portion units with maximum stability and an appealing appearance and feel with minimal equipment expenditure and minimal use of film materials used for packaging.

[0014] A first subject matter of the application is a system comprising a deep-drawing die with a cavity and a heating device which is set up to heat a packaging film in a deep-drawing process, in the course of which the heated packaging film is formed into the cavity of a deep-drawing die, wherein the surface area of the heating device which is brought into contact with the film section to be formed into the cavity has at least one depression whose opening area is 40 to 95% of the opening area of the cavity, characterized in that the surface area of the heating device surrounding the depression is flat and is enclosed by a circumferential border with a height of 0.5 to 2 mm.

[0015] The heating device according to the invention enables, for example, the efficient production of detergent portion units. Due to the uniform thickness of the water-soluble film, these detergent portion units are characterized by high mechanical stability with minimal packaging material usage and an appealing feel and appearance.

[0016] The surface area of the heating device surrounding the recess is preferably flat. Particularly preferred materials for manufacturing the surface of the heating device are ceramic or metal, especially aluminum.

[0017] Preferred heating devices have a metallic surface, in particular a metallic surface comprising aluminum. Due to their thermally conductive properties, metallic heating device surfaces are preferred which consist of at least 70 wt. %, preferably at least 90 wt. %, particularly preferably at least 98 wt. %, and in particular entirely of aluminum.

[0018] The flat surface areas of the heating device can be structured to control heat transfer or to prevent adhesion. Surfaces structured in this way have, for example, visible or noticeable unevenness such as grooves. The structural elements naturally differ from the depressions in terms of their depth and width. In preferred structured surface areas, the maximum depth of the structural elements is less than 0.5 mm, preferably less than 0.2 mm and in particular less than 0.1 mm. The maximum depth corresponds to the maximum length of a line segment orthogonal to the opening surface between a point on the opening surface and a point on the bottom surface of the structural element.

[0019] Preferred heating devices have a circumferential border. The border encloses the flat surface area and the depression(s) formed in this surface area. Preferably, the border encloses at least four, preferably at least eight, and in particular at least sixteen depressions.

[0020] The border is used to space a film placed over the heating device from the heated surface. Contact between the film and the surface of the heating device only occurs through the application of targeted force, for example by applying a vacuum between the heating device surface and the film. As a result, the contact times between the heated surface and the film can be precisely controlled, even at high process speeds. Since the described spacing effect is less pronounced with a low border height, while the effect of the vacuum used is reduced with a high border height, the height of the border is 0.5 to 2 mm, particularly preferably 0.8 to 1.2 mm. A border height of 1 mm is particularly preferred.

[0021] In summary, the subject matter of the claim is characterized in that the surface area of the heating device surrounding the recess is flat and is enclosed by a peripheral border with a height of 0.5 to 2 mm, preferably 0.8 to 1.2 mm.

[0022] With regard to the desired homogeneous film expansion, it has proven advantageous if the opening area of the at least one depression is smaller than the opening area of the cavity. In preferred methods, the opening area of the at least one depression is 50 to 90% and in particular 60 to 80% of the opening area of the cavity.

[0023] To achieve homogeneous film expansion, it is also advantageous to replicate the outline of the opening surface of the recess to the outline of the opening surface of the cavity. A replica is the two-dimensional shape of the opening surface of a recess that resembles the two-dimensional shape of the opening surface of the cavity, for example, with regard to the number of corners present.

[0024] It is particularly preferred if the outline of the opening area of the depression is obtained from the outline of the opening area of the cavity by a reduction, wherein reduction factors of 0.4 to 0.95, preferably of 0.5 to 0.9 and in particular of 0.6 to 0.8 are preferably used.

[0025] Preferred recesses have an opening area with a maximum diameter of 10 to 40 mm, preferably 20 to 35 mm. The maximum depth of preferred recesses is 0.5 to 7 mm, preferably 0.8 to 4 mm. The maximum depth corresponds to the maximum length of a line orthogonal to the opening area between a point on the opening area and a point on the bottom surface of the recess.

[0026] The depressions can have different spatial shapes. Preferred depressions have at most one further edge in addition to the edge of the opening surface. It is further preferred if the depressions do not have any side surfaces orthogonal to the opening surface. Rather, depressions are preferred which are delimited exclusively by their opening surface and a base surface directly adjacent to the opening surface. Particularly preferred depressions have, for example, a hemispherical, compressed hemispherical, elongated hemispherical, or compressed and elongated hemispherical spatial shape. The base surface can be flattened, for example in the form of a region plane-parallel to the opening surface.

[0027] Preferred depressions are characterized by a bottom surface that slopes continuously from its edge to its lowest point. Of course, the depression may have more than one lowest point. For example, as described above, the depression may have a bottom surface that is partially plane-parallel to the opening surface. In such an embodiment, the bottom surface has a continuous slope between the edge of the depression and the edge of the plane-parallel region of the bottom surface.

[0028] The gradient can be linear or non-linear. Both the absolute gradient and its relative gradient have proven to be relevant for the film thickness homogeneity achieved. Preferred depressions have a bottom surface that slopes continuously from their edge to their deepest point, the gradient of which is linear for at least 10%, preferably 30%, of the shortest distance from the edge to the deepest point. Process variants that use depressions that have a bottom surface that slopes continuously from their edge to their deepest point, the gradient of which is linear for 10 to 90%, preferably 30 to 80%, of the shortest distance from the edge to the deepest point have proven advantageous.

[0029] It is preferred if the depression has a bottom surface which slopes continuously from its edge to its deepest point, the gradient of which changes at least at one point over the shortest distance from the edge to the deepest point.

[0030] Preferably, the depression has a bottom surface which slopes continuously from its edge to its lowest point, the gradient of which on the shortest distance from the edge to the lowest point is 10 to 50%, preferably 15 to 40%, over the entire distance.

[0031] The volume of preferred wells is 1 to 8 ml, preferably 1 to 6 ml.

[0032] The ratio of the maximum depth of the depression to the maximum depth of the cavity is preferably 2:3 to 1:5, particularly preferably 1:2 to 1:4. A corresponding ratio has proven advantageous both with regard to the homogeneity of the film thickness distribution and with regard to process control.

[0033] The heating device according to the invention is particularly suitable for producing portion units with complex geometries or for portion units with more than one receiving chamber.

[0034] The surface of the heating device is preferably flat between two adjacent recesses belonging to a portion unit. The minimum distance between two such adjacent recesses is preferably 0.5 to 4 mm, preferably 1 to 3 mm. The recesses may differ in their maximum depth.

[0035] In a preferred embodiment, the two, three, or four receiving chambers, and consequently also the recesses associated with the receiving chambers, are arranged in the heating device to at least partially enclose one another. Preferred heating devices have two, preferably at least three, and in particular at least four recesses, one of which forms a center point around which the remaining recesses are arranged rotationally symmetrically.

[0036] As stated above, the heating device preferably has a metallic surface. This preferably metallic surface, in turn, has recesses that enable the efficient production of portion units with maximum stability and an appealing appearance and feel, with minimal equipment expenditure and minimal use of film materials used for packaging.

[0037] These advantageous properties of the method according to the invention can be enhanced by at least partially coating the surface of the heating device. It is particularly advantageous if the surface of the heating device is at least partially coated in the region of the depression. Such a coating, like the depressions in the surface, influences the film thickness distribution of the produced receptacles. In this context, it has proven advantageous to fully coat the surface of the heating device in the region of the depression(s).

[0038] The coating may extend to the surface of the heating device in the region of the depression(s) and the edge region surrounding the depression.

[0039] The coating of the heater surface in the region of the recesses necessarily leads to at least partial filling of the recess volume. In variants of the method according to the invention, the at least one recess is filled to at least 60 vol.%, preferably to at least 80 vol.%, and in particular completely with a coating material.

[0040] The coating may cover 5 to 80%, preferably 10 to 70% and especially 20 to 50% of the surface area of the heater which is brought into contact with the film.

[0041] Suitable coating materials include metals and polymers, especially rubber and silicone. Silicone coatings are particularly preferred due to their heat resistance and moldability.

[0042] Preferred coating agents have a lower thermal conductivity and / or a lower heat transfer coefficient than the heater surface.

[0043] The thickness of the coating is preferably 100 to 4000 µm, particularly preferably 200 to 2000 µm.

[0044] Any coatings can be bonded to the base surface in a variety of ways. Adhesive bonds are suitable for creating a permanent and temporally stable bond between the heater surface and the coating agent. Clamp or plug connections, on the other hand, are preferably used in cases where rapid replacement of the coating agent is desired, for example, due to wear or to change the process parameters.

[0045] To reduce the process time and ensure reproducible contact between a packaging film and the surface of the heating device, the film is preferably brought into contact with the heating device by means of a negative pressure. Furthermore, it is preferable to maintain contact between the film and the heating device by maintaining a negative pressure.

[0046] To support the uniform development of a negative pressure between the heating device and the water-soluble film, the surface of the heating device preferably has holes through which gas located between the heating device and the film can be removed. These holes are preferably located 60%, preferably 90%, especially 95%, and most preferably completely outside the recesses.

[0047] For reasons of process efficiency, it is preferred if the heating device has at least four, preferably at least sixteen and in particular sixty-four recesses.

[0048] A further subject of the present application is a deep-drawing device comprising the described system.

[0049] To increase process efficiency and film thickness homogeneity, it has proven advantageous for the deep-drawing device to comprise a deep-drawing die arranged below the heating device. The distance between the surface of the heating device and the surface of the deep-drawing die is preferably less than 10 mm, preferably less than 5 mm, in particular 0.1 to 2 mm, and particularly preferably 0.2 to 1 mm.

[0050] Furthermore, for reasons of process efficiency, it is preferred to arrange the heating device and the deep-drawing die in such a way that the cavity of the deep-drawing die, into which a partial area of the heated packaging film is formed, is located opposite the opening surface of that recess of the heating device which this partial area of the packaging film covers when heated by the heating device. Examples

[0051] A water-soluble polyvinyl alcohol film (88 µm thick) was heated using various heating devices and subsequently formed into a droplet-shaped receiving chamber by applying negative pressure. The heating plate temperature was 120°C in each case. With the exception of the heating device, the process parameters used in the experiments were identical.

[0052] The following two heating devices were used: Heating device 1: completely flat heating plate (aluminium) Heating device 2: heating plate (aluminium) with a recess (maximum depth 1 mm) whose outline is modeled on the drop-shaped receiving chamber with a reduction factor of 0.8

[0053] Following the deep-drawing process, the film thickness in the receiving chambers was determined using optical methods (film thickness analyzer) along a cross-section orthogonal to the longitudinal axis of the droplet. The film thickness was measured at nine equidistant measuring points along the cross-section.

[0054] Film thickness ([µm]) 1 2 3 4 5 6 7 8 9 Heating device 1 34,6 29,6 27,1 24,4 25,9 24,7 24,1 27,1 33,3 Heating device 2 36,6 34,1 32,0 35,0 35,0 34,6 25,9 33,7 43,8

[0055] The receiving chambers obtained using the recessed heating plate are characterized by a higher film thickness despite the identical starting film. Portion units obtained by filling them with a liquid detergent and subsequently sealing them with a second water-soluble film exhibited improved mechanical stability.

Claims

1. A system comprising a thermoforming die having a cavity and a heating device which is arranged to heat a packaging film in a thermoforming process in the course of which the heated packaging film is moulded into the cavity of a thermoforming die, wherein the surface area of the heating device which is brought into contact with the film portion to be moulded into the cavity has at least one depression, the opening area of which is 40 to 95% of the opening area of the cavity, characterised in that the surface area of the heating device surrounding the depression is flat, which is enclosed by a peripheral border with a height of 0.5 to 2 mm.

2. System according to claim 1, wherein the surface area of the heating device surrounding the recess is flat, which is enclosed by a circumferential border with a height of 0.8 to 1.2 mm.

3. System according to one of the preceding claims, wherein the contour of the opening surface of the recess is modelled on the contour of the opening surface of the cavity.

4. System according to one of the preceding claims, wherein the outline of the opening surface of the recess is obtained from the outline of the opening surface of the cavity by a reduction factor of 0.4 to 0.95, preferably of 0.5 to 0.9 and in particular of 0.6 to 0.8.

5. System according to any one of the preceding claims, wherein the cavity has a hemispherical, compressed hemispherical, stretched hemispherical or compressed and stretched hemispherical spatial shape.

6. System according to any one of the preceding claims, wherein the recess has a continuously sloping bottom surface from its edge to its deepest point.

7. System according to any one of the preceding claims, wherein the well has a volume of from 1 to 8 ml, preferably from 1 to 6 ml.

8. System according to any one of the preceding claims, wherein the heating device comprises at least two wells which differ with respect to their maximum depth.

9. System according to any one of the preceding claims, wherein the heating device comprises at least two, preferably at least three and in particular at least four recesses which enclose each other at least partially.

10. System according to one of the preceding claims, wherein the heating device comprises at least two, preferably at least three and in particular at least four recesses, of which one recess forms a centre around which the remaining recesses are arranged rotationally symmetrically.

11. System according to one of the preceding claims, wherein the surface of the heating device is at least partially coated.

12. System according to one of the preceding claims, wherein the surface of the heating device is fully coated in the region of the recess(es).

13. A thermoforming device comprising system according to any one of the preceding claims.

14. A thermoforming device according to claim 13, wherein the thermoforming device comprises a deep drawing die arranged below the heating device.

15. The thermoforming device according to any one of claims 13 or 14, wherein the deep drawing device comprises a deep drawing die and the distance between the surface of the heating device and the surface of the deep drawing die is less than 10 mm, preferably less than 5 mm and in particular between 0.1 and 2 mm, more preferably between 0.2 and 1 mm.