Deep drawing device, packaging machine with a deep drawing device and method for operating the deep drawing device

Description

[0001] The invention relates to a thermoforming device with the features according to the preamble of claim 1 and a packaging machine for producing filled bags with such a thermoforming device, as well as a method for operating the thermoforming device.

[0002] In a common design (e.g., US 2021 / 276754 A1), packaging units are often produced by first thermoforming films. A product is filled into the resulting cavities, and then sealed with a top film. This creates a double-layered film strip in which portions of the product are separated. These portions are then separated in a cutting station.

[0003] Naturally, when manufacturing such packaging units, it must be ensured that the film can withstand external stresses so that the packaged product is adequately protected. If, during the manufacturing process, it was discovered that the film had torn or thinned to such an extent that it leaked, the film thickness was previously increased. Adjustments to the forming process parameters, such as the preheating temperature or the preheating of the film, can also be made. This can prevent defects in the film packaging. However, using a thicker film can lead to increased environmental impact. Furthermore, the necessary adjustments also result in higher production costs.

[0004] Another disadvantage of packaging machines known from the prior art arises particularly when using water-soluble films. Water-soluble films, such as PVOH films, are well known from the prior art and are used especially in the packaging of detergents, for example, for dishwashers or washing machines. The packaging units are placed in the machine and surrounded by water. As soon as the film dissolves, the detergent is released. Using a thicker film, in turn, increases the dissolution time of the packaging unit. Furthermore, extremely irregular and non-reproducible dissolution times of the packaging units have been observed.

[0005] Consequently, the object of the invention is to provide a deep-drawing device that enables the reliable, environmentally friendly and at the same time cost-effective production of filled foil bags.

[0006] This problem is solved by a deep-drawing device with the features of claim 1.

[0007] Another objective of the invention is to provide a packaging machine that enables the reliable, environmentally friendly and cost-effective production of filled foil bags.

[0008] This further problem is solved by a packaging machine with the features of claim 11.

[0009] Another object of the invention is to provide a method for deep drawing film for the production of film packaging, which enables a process-reliable, environmentally friendly and at the same time inexpensive production of filled film bags.

[0010] The further problem is solved by a method with the features of claim 12.

[0011] The invention is based on the finding that the irregular dissolution times of water-soluble films are at least largely attributable to uneven film thickness. Furthermore, it was determined that this uneven film thickness arises during the deep drawing process. Plastic films exhibit heterogeneous material properties, which in turn affect the deformation properties of the plastic. For example, plastic films exhibit locally varying moduli of elasticity and locally varying strain rate dependencies. It has now been recognized that these locally varying material properties of the plastic film lead to locally varying thinning. Furthermore, local thinning is also attributable to the stretching of the film, which is essentially dependent on the tool geometry.

[0012] It has been found that reducing the thermoforming speed homogenizes the thinning of the plastic film. Furthermore, it is assumed that the structure of the plastic film can align better at the supramolecular level with a reduced strain rate, thereby homogenizing the material properties during thermoforming. Therefore, the thermoforming device according to the invention includes a mold vacuum device by means of which the pressure applied to the die cavity can be continuously adjusted during thermoforming. This also allows the thermoforming speed to be adjusted.

[0013] For this purpose, the inventive deep-drawing device for deep-drawing film is provided, comprising an arrangement of several die plates which can be driven in a circular path by a conveyor, wherein each die plate has at least one die shape, and with at least one forming vacuum device, wherein the forming vacuum device comprises at least one vacuum source for providing a vacuum, and wherein the at least one vacuum source can be connected to the at least one die shape of each die plate via a vacuum channel, wherein the forming vacuum device comprises at least one switching unit associated with the vacuum source, wherein the switching unit comprises a valve functionally arranged between the vacuum source and the at least one die shape, and wherein the switching unit is configured in a first embodiment as follows:that the pressure applied to the at least one die shape is continuously adjustable by the switching unit and that, in a second variant, the switching unit comprises a vacuum tank functionally arranged between the valve and the at least one die shape.

[0014] The first version of the switching unit allows for continuous pressure adjustment at the die during the thermoforming process. The second version, with its vacuum tank positioned downstream of the valve, achieves a significantly slower pressure build-up at the die. Both versions share the common feature of allowing the pressure profile at the die to be adjusted so that the film can be thermoformed at a reduced speed. The switching unit adjusts the pressure profile to form the film with a reduced stretch rate, resulting in uniform thinning. This eliminates the need for thicker film to prevent material failure. In this way, packaging units can be manufactured in an environmentally friendly and cost-effective manner.By selectively and uniformly thinning the films during thermoforming, the dissolution time of the films, especially the PVOH films, in water can be set reliably and reproducibly.

[0015] It is preferably provided that the switching unit includes a control device, wherein the valve is controlled by the control device via a pulsed signal sequence. A pulsed signal sequence can be generated, for example, in the form of pulse width modulation and / or frequency modulation. With such control of the valve, it can also be designed as a discrete switching valve, in particular as a discrete switching directional control valve. Such a discrete switching directional control valve has only two switching positions, namely an open position and a closed position. When the valve is switched to the open position, a flow connection is enabled, i.e., the flow cross-section of the valve is at its maximum. When the valve is switched to a closed position, the flow connection is prevented, i.e., the flow cross-section of the valve is at its minimum.By controlling the valve with the pulsed signal sequence, an effective switching position, i.e., a kind of average switching position, is established through the rapid switching of the valve's switching positions. The flow rate of the medium, and thus also the pressure in the die, can be adjusted via the effective switching position. The signal sequence comprises several operating pulses, whereby the effective switching position of the valve can be continuously adjusted by varying the duration of the operating pulses and / or by varying the frequency of the signal sequence, which is particularly advantageous.

[0016] It is advantageous for the valve to be designed as a continuous valve. A continuous valve is characterized by continuously variable switching positions. Therefore, the flow cross-section of the continuous valve, and thus also the pressure at the die, can be continuously varied. For this purpose, it is not necessary to control the continuous valve in a pulsed manner. However, in an advantageous embodiment of the deep-drawing device, it can also be provided that the continuous valve is controlled in a pulsed manner via the control unit.

[0017] In a preferred embodiment, the continuous valve is a pressure valve, a throttle valve, or a flow control valve. Particularly preferably, the continuous valve is a directional control valve. The directional control valve is most preferably designed as a proportional valve. Alternatively, the directional control valve can also be designed as a control valve or a servo valve.

[0018] It is specifically intended that the forming vacuum device includes a vacuum tank associated with the first variant of the switching unit. In one embodiment of the deep-drawing device, the vacuum tank can be functionally arranged between the vacuum source and the valve. The vacuum source thus creates a negative pressure in the vacuum tank, which is applied to the die mold via the valve during the deep-drawing of the film. In such a functional arrangement of the vacuum tank, its primary function is to store a vacuum.

[0019] In an alternative embodiment of the deep-drawing device, the vacuum tank associated with the first variant of the switching unit is preferably arranged functionally between the valve and the at least one die. To apply a vacuum to the die, a flow connection between the vacuum source and the die must be opened via the valve. To provide sufficient vacuum at the die, a corresponding negative pressure must also be generated in the vacuum tank. The vacuum tank thus forms an additional volume alongside the die, slowing down the generation of the vacuum at the die. Furthermore, the vacuum tank smooths out the irregular pressure profile at the die, which results from pulsed control of the valve by the control unit.

[0020] The inventive method for deep drawing film for the production of film packaging with a packaging machine according to the invention comprises the following steps: A film is fed into at least one die plate, with a starting pressure being applied in the die at the beginning of the thermoforming process. This starting pressure is in the range of 1.0 bar to 0.8 bar. During the thermoforming process, the switching unit of the mold vacuum device generates a pressure profile at the die, in which the pressure at the die is reduced from the starting pressure to a minimum final pressure within a certain time interval. This causes the film to be thermoformed into the die plate. The final pressure is in the range of 0.05 bar to 0.5 bar, preferably in the range of 0.1 bar to 0.4 bar, and more preferably in the range of 0.15 bar to 0.35 bar. The time interval between the starting pressure and the final pressure is at least 0.5 s, preferably at least 0.75 s, particularly preferably at least 1.0 s, advantageously at least 1.25 s, and most advantageously at least 1.5s.

[0021] Preferably, the time interval between the start and end pressure is no greater than 2.0 s, preferably no greater than 1.75 s, and preferably no greater than 1.5 s. These limits represent typical cycle times for a corresponding packaging machine.

[0022] The relatively slow generation of the vacuum at the die allows the film to be deep-drawn at such a low speed that it thins uniformly. This prevents tears or other damage to the film, ensuring reliable, environmentally friendly, and cost-effective production of packaging units. Fig. 1 in a side view shows a packaging machine designed according to the invention with a continuously rotating conveyor and with cyclically moving forming, filling and sealing stations, Fig. 2 in a schematic representation shows an embodiment of the forming vacuum device with a discretely switching valve and vacuum tank connected with a die plate and Fig. 3 in a schematic representation shows an embodiment of the forming vacuum device with a continuously switching valve and die plate.

[0023] Fig. 1 Figure 1 shows a side view of a section of a packaging machine 1 according to the invention for producing filled bags. The packaging machine 1 comprises a machine frame 8, a forming station 4, a filling station 5, and a sealing station 6. A film 2 is fed into the packaging machine 1 and deep-drawn in the forming station 4, so that cavities are formed in the film 2. In the present embodiment, the film is formed as a continuous web. It may also be advantageous to feed individual sheets of film into the packaging machine.

[0024] The cavities are filled with a product in filling station 5. A cover film 3 is then fed in and sealed onto film 2 in sealing station 6, thus closing the filled cavities. In a cutting station (not shown), the film unit thus formed is separated into film bags. In this exemplary embodiment, film 2 and cover film 3 are water-soluble films, specifically PVOH films, between which, for example, a detergent or cleaning agent is packaged. Filled film bags produced in this way are placed, for example, in a dishwasher. There, the film material dissolves upon contact with water and releases the detergent. The same principle applies to the use of such a film bag in a washing machine.

[0025] The packaging machine 1 comprises a stationary machine frame 8 and a preferably continuously driven conveyor 7. The conveyor 7 can be a conveyor belt or the like and, in the preferred embodiment, is formed by articulated and chain-like connected elements on which several die plates 9, 9' are mounted. The latter are preferably driven continuously and rotating around the machine frame 8 together with the conveyor 7, moving along an upper horizontal track in the direction of arrow 30 for the actual bag-making process and, after appropriate deflection, are then returned in the lower area of ​​the machine frame 8 in the direction of arrow 31. The film 2, preferably an endless film web, is also preferably fed continuously and placed from above onto the conveyor 7 with the die plates 9, 9'.Between filling station 5 and sealing station 6, the top film 3 is subsequently fed in, preferably continuously, and placed from above onto the top surface of film 2. In the placed state, film 2 and the top film 3 are moved synchronously and preferably continuously with the conveyor 7, as indicated by arrow 30.

[0026] The film feed station 2 and the top film feed station 3 are fixed in position relative to the machine frame 8, as are the water application stations (not shown) for supporting the sealing process and for perforating or trimming the films. It is also possible for the stations to be at least partially attached to the machine frame 8. In the preferred embodiment of the packaging machine 1, the movement of the conveyor 7 is continuous. In such an embodiment of the packaging machine 1, the processes described here also operate continuously. To enable continuous movement, the forming station 4, the filling station 5, and the sealing station 6 are not fixed in position relative to the machine frame 8, but rather move synchronously with the conveyor 7 over a specific distance in segments.Meanwhile, in forming station 4, the film 2 is deep-drawn; in filling station 5, the product to be packaged is filled into the deep-drawn cavities; and in sealing station 6, the top film 3 is sealed onto the lower film 2 in the area of ​​the sealing ridges of the cavity. After completion of each process, forming station 4, filling station 5, and sealing station 6 are cyclically returned to their starting positions, where a new cycle of the respective process then begins.

[0027] As in Fig. 1 The forming station 4 is shown to be formed by a deep-drawing device 12. The deep-drawing device 12 can be designed to hold only a single die plate 9, 9' and to deep-draw the film 2 there in one cycle. In the illustrated embodiment, the deep-drawing device 12 is designed to simultaneously hold several, here two successive, die plates 9, 9'.

[0028] As in Fig. 2 As shown, a single die plate 9, 9' has at least one die form 10, and in particular several die forms 10, on its upper surface. In the present, preferred embodiment, four die forms are provided on each die plate 9. Each die form 10 is provided with at least one capillary bore 11, and preferably several capillary bores 11. The capillary bores 11 are part of a vacuum channel 26, through which the die cavities 10 are connected to a vacuum source 21.

[0029] Fig. 2 shows a forming vacuum station 20, which is part of the deep drawing device 12 ( Fig. 1 The forming vacuum station 20 comprises a vacuum source 21, a switching unit 22, and a vacuum channel 26. The vacuum source 21 is preferably designed as a vacuum pump. The vacuum source 21 is connected to the die 10 of the die plate 9 via the vacuum channel 26. The switching unit 22 comprises a valve 23. The valve 23 is functionally arranged between the vacuum source 21 and the die cavity 10. In its open position, the valve 23 enables the flow connection between the vacuum source 21 and the die cavity 10, thereby creating a vacuum or negative pressure at the die cavity 10. The film 2 is deep-drawn into the die cavity 10 by means of the vacuum at the die cavity 10. During deep drawing, the foil 2 is held clamped against the matrix plate 9, 9' by a pressure plate 13, 13' resting on the matrix plate 9, 9'.In the closed position of valve 23, valve 23 blocks the flow connection between the vacuum source 21 and the die cavity 10. This reduces the vacuum applied to the die cavity 10.

[0030] As in Fig. 2 As shown, the valve 23 is designed as a discrete switching valve. The valve 23 has only one open position with a maximum flow cross-section and one fully closed position. Thus, the valve 23 has only one open position with a maximum flow cross-section and one fully closed position. The valve 23 is designed as a directional control valve, in particular as a 3 / 2-way valve. The valve 23 is preferably switched via a control device 24 of the forming vacuum device 20.

[0031] As in Fig. 2 As shown, the mold vacuum device 20 includes a vacuum tank 25. The vacuum tank 25 is functionally arranged between the valve 23 and the die 10. When a vacuum is generated at the die 10, the vacuum tank 25 increases the time required to establish the final pressure at the die 10. This is due to the additional volume of the vacuum tank, which must be vacuumed in addition to the die 10.

[0032] The slowed pressure reduction at the die cavity for deep drawing the film 2, achieved by means of the vacuum tank 25, is intended to prevent the vacuum from being applied abruptly and the resulting high forming speed from damaging the film 2. Consequently, the film 2 is fed to the die plate 9, 9' in a first step. The film 2 is then clamped between the die plate 9, 9' and the pressure plate 13, 13'. At the start of the deep drawing process, a starting pressure is applied to the die 10. This starting pressure is preferably in the range of 1.0 bar to 0.8 bar. Particularly preferably, the starting pressure corresponds to the ambient atmospheric pressure, i.e., approximately 1 bar. During the deep drawing process, a pressure profile is generated at the die 10 by the switching unit 22 of the forming vacuum device 20. In this process, the pressure is reduced from the initial pressure to a minimum final pressure within a certain period of time.The time span therefore corresponds to the duration required to reduce the pressure in the matrix shape 10 from the starting pressure to the final pressure.

[0033] The final pressure is preferably in the range of 0.05 bar to 0.5 bar, more preferably in the range of 0.1 bar to 0.4 bar, and more preferably in the range of 0.15 bar to 0.35 bar. A final pressure of approximately 0.3 bar is particularly preferred. The applied vacuum deep-draws the film 2 into the die 10. The time interval between the initial pressure and the final pressure advantageously corresponds to the maximum process time required at another station of the packaging machine 1, for example, the filling station 5 or the sealing station 6. The time interval between the initial pressure and the final pressure is at least 0.5 s, preferably at least 0.75 s, particularly preferably at least 1.0 s, advantageously at least 1.25 s, and most advantageously at least 1.5 s. The time interval is preferably not greater than 2 s, more preferably not greater than 1.75 s, and most preferably not greater than 1.5 s.

[0034] Preferably, the valve 23 of the forming vacuum device 20 is controlled by the control device 24 with a pulsed signal sequence. Consequently, the valve switches back and forth between the closed and open positions according to the signal sequence. The resulting average switching position corresponds to an effective switching position. The effective switching position can be set by pulse width modulation and / or frequency modulation of the operating pulses of the signal sequence. Thus, the pressure at the die 10 can be continuously adjusted.

[0035] The switching unit 22 after Fig. 2 In a first variant, the switching unit 22 is therefore designed such that only two discretely switchable switching positions are provided as effective switching positions of the switching valve 23. Pulse width modulation and / or frequency modulation of the operating pulses of the signal sequence does not occur. In this first variant of the switching unit 22, a vacuum tank 25 downstream of the switching valve 23 is absolutely necessary to achieve a slower pressure build-up at the die 10.

[0036] The switching unit 22 after Fig. 2 In a second variant, the valve is designed such that the pressure applied to at least one die 10 can be continuously adjusted by the switching unit 22. For this purpose, the switching valve 23 is controlled by the control device 24 using a pulsed signal sequence. The ability to continuously adjust the effective switching position also allows the effective flow cross-section of the valve to be adjusted. By adjusting the effective flow cross-section of the valve, the pressure at the die 10 can also be continuously adjusted. In this second variant, the vacuum tank 25 is not strictly necessary to slow down the pressure reduction or the increase in vacuum. Of course, it is also possible to design the valve 23 to be continuously adjustable and to additionally provide a vacuum tank 25 downstream of the valve.In this variant, a further effect is that the pulsed control of valve 23 is smoothed by the vacuum tank 25. Optionally, a vacuum tank can also be connected upstream of valve 23.

[0037] Fig. 3 Figure 20 shows another embodiment of the forming vacuum device 20. The valve 23 of the forming vacuum device 20 is designed as a continuous valve. Accordingly, the switching position of the valve 23 is continuously adjustable. Thus, the flow cross-section in the valve 23, and therefore the pressure at the die 10, is also continuously adjustable via the valve 23. Furthermore, the forming vacuum device 20 preferably includes the control unit 24, which actuates the valve 23. The valve 23 can therefore be adjusted as desired even during the deep-drawing process, thereby allowing the pressure profile at the die 10 to be adapted. Pulsed actuation of the valve is not required. However, in an alternative embodiment, it may also be advantageous for the valve 23, designed as a continuous valve, to be pulsed via the control unit 24. Of course, the embodiment of the forming vacuum device 20 can also be adapted according to Figure 24. Fig. 3in a preferred embodiment shall be provided with a vacuum tank 25.

[0038] In a preferred embodiment, the continuous valve is configured as a pressure valve, a throttle valve, or a flow control valve. In a particularly preferred embodiment, the continuous valve is a directional control valve, wherein the directional control valve is specifically configured as a proportional valve, a control valve, or a servo valve.

[0039] The pressure profile on the matrix shape 10 between the initial pressure and the final pressure preferably corresponds to a continuous, decreasing function over the entire time period. The pressure profile on the matrix shape 10 between the initial pressure and the final pressure preferably corresponds approximately to a decreasing exponential function over the entire time period.

Claims

1. Thermoforming device for thermoforming a film, comprising: an arrangement of multiple die plates (9, 9') which is drivable by a conveyor (7) on a circulating path, wherein each die plate (9, 9') has at least one mould (10), and having at least one moulding-vacuum device (20), wherein the moulding-vacuum device (20) comprises at least one vacuum source (21) for providing a vacuum, and wherein the at least one vacuum source (21) can be connected via a vacuum channel (26) to the at least one mould (10) of each die plate (9, 9'), characterized in that the moulding-vacuum device (20) comprises at least one switching unit (22) assigned to the vacuum source (21), wherein the switching unit (22) comprises a valve (23) arranged in functional terms between the vacuum source (21) and the at least one mould (10), and wherein the switching unit (22) in a first variant is designed in such a way that the pressure prevailing in the at least one mould (10) can be continuously adjusted by the switching unit (22) and in that the switching unit (22) in a second variant comprises a vacuum tank (25) arranged in functional terms between the valve (23) and the at least one mould (10).

2. Thermoforming device according to Claim 1, characterized in that the switching unit (22) has a control device (24), wherein the control device is designed in such a way that the valve (23) can be actuated by the control device (24) via a pulsed signal sequence.

3. Thermoforming device according to Claim 2, characterized in that the control device is designed in such a way that the signal sequence comprises multiple operating pulses, wherein an effective switching position of the valve (23) can be continuously adjusted by varying the signal duration of the operating pulses and / or by varying the frequency of the signal sequence.

4. Thermoforming device according to one of Claims 1 to 3, characterized in that the valve (23) is in the form of a continuous valve.

5. Thermoforming device according to Claim 4, characterized in that the continuous valve is a pressure valve, a throttle valve or a flow regulating valve.

6. Thermoforming device according to Claim 4, characterized in that the continuous valve is a directional control valve, wherein the directional control valve is in particular in the form of a proportional valve, a regulating valve or a servo valve.

7. Thermoforming device according to Claim 2 or 3, characterized in that the valve (23) is in the form of a discrete directional control valve.

8. Thermoforming device according to one of Claims 1 to 7, characterized in that the moulding-vacuum device (20) has a vacuum tank (25) associated with the first variant of the switching unit (22).

9. Thermoforming device according to Claim 8, characterized in that the vacuum tank (25) is arranged in functional terms between the vacuum source (21) and the valve (23).

10. Thermoforming device according to Claim 8, characterized in that the vacuum tank (25) is arranged in functional terms between the valve (23) and the at least one mould (10).

11. Packaging machine for producing film packaging, having a thermoforming device (12) according to one of Claims 1 to 10.

12. Method for thermoforming a film for producing film packaging by a packaging machine according to Claim 11, wherein a film (2) is fed to at least one die plate (9, 9'), wherein, at the start of the thermoforming operation, an initial pressure prevails in the mould (10), wherein the initial pressure ranges from 1.0 bar to 0.8 bar, wherein, during the thermoforming process, the switching unit (22) of the moulding-vacuum device (20) generates a pressure profile in the mould (10) in which the pressure in the mould (10) is reduced from the initial pressure to a minimum final pressure within a period of time, as a result of which the film (2) is drawn into the mould (10) of the die plate (9, 9'), and wherein the final pressure ranges from 0.05 bar to 0.5 bar, preferably ranges from 0.1 bar to 0.4 bar, preferably ranges from 0.15 bar to 0.35 bar, and wherein the period of time between the initial pressure and the final pressure is at least 0.5 s, preferably at least 0.75 s, particularly preferably at least 1.0 s, advantageously at least 1.25 s, particularly advantageously at least 1.5 s.

13. Method according to Claim 12, characterized in that the period of time between the initial pressure and the final pressure is no more than 2.0 s, preferably no more than 1.75 s, preferably no more than 1.5 s.