Method and device for heating a film, and associated thermoforming system

Abstract

The invention relates to a method (100) for heating a thermoplastic film (2). The method (100) comprises: S1: fixing the film (2) on a heating surface (3) by means of a fixing device (4), wherein the heating surface (3) and the fixing device (4) are arranged on opposite sides of the film (2) such that a first region (5) is formed on a side of the film (2) opposite the heating surface (3) and a second region (6) is formed between the film (2) and the heating surface (3); S3: heating the fixed film (2) until a target temperature is reached; S4: generating a pressure difference between the first region (5) and the second region (6) in such a way that the pressure p1 in the first region (5) is lower at least in regions than the pressure p2 in the second region (6); and S5: removing the heated film (2) from the heating surface (3). The invention also relates to a device (1) for heating a thermoplastic film (2), to a thermoforming system (200), to the use of the thermoforming system (200), and to a method (300) for producing a moulded part (17).

Description

[0001] Method and apparatus for heating a film and associated thermoforming system

[0002] The invention relates to a method and a device for heating a thermoplastic film. Furthermore, the invention relates to an associated thermoforming machine, the use of a thermoforming machine, and a method for producing a molded part.

[0003] Blister packs are opaque packaging made from a plastic film using a thermoforming process. In this process, a thermoplastic film is formed into the desired shape using a mold, sometimes with the aid of compressed air or vacuum.

[0004] Before the film is inserted into the forming tool, it is heated to a temperature suitable for subsequent thermal forming. For this purpose, a heating device can be positioned against one side of the film. During heating, the film is pressed onto or fixed to the heating device using a clamping or tensioning frame. This ensures good heat transfer and targeted heating through preferably direct contact between the film and the heating device's surface. Once heating is complete, the heating device is moved away from the film, allowing the heated film to be conveyed to the forming tool.

[0005] The inventors of the present invention have found that this movement of the heating device can lead to undesirable plastic deformation and / or stretching of the heated film, which adversely affects subsequent shaping and causes quality problems. Investigations by the inventors revealed that the cause of this is the localized adhesion of the heated film to the surface of the heating device, which, during further transport of the film, can, for example, cause wrinkling and lead to a local, unpredictable change in the material thickness or film thickness.

[0006] Against this background, the object of the invention is to provide possibilities by which the disadvantages described above can be reduced or even completely eliminated.

[0007] This problem is solved by the subject matter of the independent claims. The dependent claims relate to embodiments of these solutions according to the invention.

[0008] A basic idea of ​​the invention is to improve the removal of the film from the heating surface and thereby avoid, as far as possible, the aforementioned problems associated with the undesirable adhesion of the film to the heating surface.

[0009] A first aspect of the invention relates to a method for heating a thermoplastic film, i.e., a film comprising or consisting of a thermoplastic polymer. A thermoplastic polymer is understood to be a material consisting mainly of macromolecules that can be reversibly deformed within a specific temperature range. In this context, a film is understood to be a sheet-like structure, preferably a homogeneous sheet-like structure, whose thickness is very small compared to its lateral dimensions. The thickness can be, for example, in the pm or mm range. For example, the thickness can be between 50 pm and 1000 pm. Consequently, a film has two opposite sides, the distance between which is determined by the thickness of the film. The opposite sides can be referred to, for example, as the top and bottom or front and back.

[0010] The film can contain materials other than thermoplastic, such as metals, fibers, or non-thermoplastic materials. Preferred thermoplastic materials include polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyethylene (PE), polyamide (PA), polyetheretherketone (PEEK), and polylactic acid (PLA). Preferably, the film can be supplied as a continuous material, e.g., from a roll. In this case, the term "film" refers to a section of the film used in the proposed process. The film, or a section thereof, can be transported to the heating surface using suitable conveying equipment.

[0011] Advantageously, thermoplastic materials can be heated by targeted heat input to enable forming. For example, forming can be carried out according to the thermoforming process described in the introduction. Furthermore, products made of thermoplastic materials can be welded, which, among other things, allows for sealing.

[0012] The proposed procedure has several procedural steps that can be carried out in the order described below, but also in a different chronological order or overlapping in time.

[0013] In a first process step, the thermoplastic film is fixed to a heating surface of a heating device; that is, the film is brought into at least partial direct contact with the heating surface and attached to it. This fixing is achieved using a fixing device that preferably covers at least some or all sections of the film. The fixing device is positioned on the side of the film opposite the heating surface. In other words, the film is located between the heating surface and the fixing device.

[0014] The described arrangement of the film, heating surface, and fixing device creates two regions: a first region on the side of the film opposite the heating surface and a second region located between the film and the heating surface. The first region can, for example, be positioned between the film and the fixing device. With full-surface contact between the film and the heating surface, the volume of the second region can initially be almost zero. The heating surface may have openings, such as channels and / or bores, and / or surface roughness, so that while the volume of the second region can be almost zero, it is never actually zero. During the separation of the heating surface from the film, or vice versa, the volume of the second region increases accordingly.

[0015] Optionally, the film can be drawn onto the heating surface by negative pressure (i.e., reducing the pressure in the second area compared to the ambient pressure) or pressed onto the heating surface by positive pressure (i.e., increasing the pressure in the area surrounding the second area). This can achieve improved fixation of the film to the heating surface.

[0016] The fixing device can be designed, for example, as a clamping frame or tensioning frame, so that the film is clamped or stretched between the fixing device and the heating surface. The clamping frame can also be used to fix the film to the heating surface, for example, to create a vacuum between the film and the heater.

[0017] In a further process step, the fixed film is heated, at least in certain areas, until a target temperature is reached. The term "at least in certain areas" here also includes heating the entire film. It may also be possible to heat areas of the film only to a temperature below the target temperature, or not at all, to influence the wall thickness distribution, for example, if such areas are not to be stretched. To heat the film, energy is transferred from the heating surface and introduced into the film, causing a temperature increase. The target temperature can be, for example, a softening temperature, such as the Vicat softening temperature, or a glass transition temperature of the film's plastic material, or a temperature that is above the softening or glass transition temperature but below the melting temperature.

[0018] Once the target temperature is reached, a pressure difference is created between the first and second compartments. The pressure in the first compartment is, at least in some areas, lower than the pressure in the second compartment. Since both the first and second compartments are filled with a gas, preferably air, the pressure difference refers to the corresponding gas and air pressures in the first and second compartments, respectively.

[0019] The pressure differential can be created by decreasing the pressure in the first area and / or increasing the pressure in the second area. For example, the pressure in the first area can be decreased relative to the ambient pressure, i.e., a negative pressure can be created, and / or the pressure in the second area can be increased relative to the ambient pressure, i.e., a positive pressure can be created. The resulting pressure differential prevents unwanted adhesion of the heated film to the heating surface when it is subsequently removed, by counteracting the adhesive force. For example, the pressure differential can cause the film to adhere to the fixing device, at least temporarily. The disadvantages described earlier, such as wrinkling or changes in material thickness, can thus be reduced or even completely avoided.The pressure difference can preferably be generated before the heated film is removed from the heating surface and maintained during the removal of the film.

[0020] Removing the film from the heating surface can be achieved, for example, by moving the heating element and / or the clamping frame away from the film. The heated film can then be transported further, for example to a forming tool.

[0021] Alternatively, the heating device can also be integrated into the mold. In this case, the heated film is first drawn to the heating surface by negative pressure and / or pressed to the heating surface by positive pressure, before a further pressure difference is created and the heated film is removed from the heating surface and formed into the mold.

[0022] According to various embodiments, the process can involve increasing the pressure in the first area to a pressure that is at least equal to the ambient pressure after the heated film has been removed from the heating surface.

[0023] In other words, pressure equalization with the environment can occur in the first area, or an overpressure can be created compared to the ambient pressure.

[0024] This allows any film that may be adhering to the fixing device to be removed more easily, thus reducing damage or impairment of the molded part quality. The previously generated pressure differential can therefore be reversed to facilitate easier removal of the film from the fixing device as well.

[0025] According to further design variants, it can be provided that the pressure difference is generated by actively changing the pressure in the first and / or second area.

[0026] Active pressure modification means that the pressure conditions are specifically influenced through additional measures. This can be achieved, for example, with a vacuum pump acting on the first area and / or a booster pump acting on the second area.

[0027] Actively generating the pressure differential has the advantage that the pressure conditions can be adjusted precisely, quickly, and according to demand. For example, the pressures prevailing in the first and / or second zone can be controlled and, if necessary, regulated by a control unit. According to other design variations, the pressure differential can be generated by passively changing the pressure in the first and / or second zone.

[0028] Passive pressure change means that the pressure conditions change without any additional measures being taken, but simply due to temperature changes, for example.

[0029] Passive pressure reduction in the first area can occur, for example, through cooling of the gas present in the first area, e.g., air. If the second area cools down less, e.g., because the heating surface continuously emits heat, a pressure difference results.

[0030] Another way to passively reduce pressure in the first region is to increase its volume, for example, by having the film initially adhere to the heating surface and move along with it. In both cases, passive pressure reduction requires a sealed first region.

[0031] Passive generation of the pressure difference has the advantage that no additional components, such as a vacuum pump and / or a pressure pump along with their associated control system, are required.

[0032] According to further embodiment variants, a pressure difference of at least 0.1 bar, preferably a pressure difference between 0.4 bar and 1 bar, can be generated.

[0033] In other words, after heating the film and before removing the film from the heating surface or at the same time as removing the film, the pressure in the first area can be at least 0.1 bar, preferably between 0.4 bar and 1 bar, lower than the pressure in the second area.

[0034] A pressure difference in the aforementioned range has the advantage that, on the one hand, unwanted adhesion of the film to the heating surface can be reliably avoided, and on the other hand, the film is not damaged by the application of the pressure difference.

[0035] According to further embodiment variants, the method can provide for the creation of different pressure differences in areas of the heated film.

[0036] In other words, it is possible to define and generate the pressure difference locally or in specific areas. For example, a higher pressure difference can be generated in areas where increased adhesion of the film to the heating surface is expected than in areas where adhesion is less likely or occurs with lower adhesive force. For instance, a higher pressure difference can be generated in the center of the film than at its edges.

[0037] The varying pressure differential across different areas advantageously prevents deformation of the film due to pressure. Furthermore, the required pressure differential can be generated more quickly, allowing the heating of a film according to the proposed method to be carried out efficiently in a continuous process with no or only minimal time delay.

[0038] Depending on the design, different areas of the film can be heated until different target temperatures are reached.

[0039] In other words, different areas of the film can be heated to different temperatures. The specific areas and their corresponding temperatures can be defined, for example, based on the mold contour and the desired properties of the molded part, such as material distribution, which are to be achieved during subsequent forming.

[0040] This can contribute to improved material utilization and thus lower material consumption as well as lower energy consumption for heating the film, especially in the production of packaging.

[0041] According to further embodiment variants, the method can, after fixing the film to the heating surface and before heating the fixed film, involve a reduction of the pressure in the second area such that the pressure in the second area is at least partially lower than the pressure in the first area.

[0042] For example, the pressure in the second area can be reduced to a level below ambient pressure. This allows for particularly good contact between the heating surface and the film, enabling the film to be heated quickly and with low energy consumption.

[0043] Another aspect of the invention relates to a device for heating a thermoplastic film. The proposed device may, for example, be suitable for carrying out the method described above. Therefore, the above explanations of the proposed method also serve to describe the device. The advantages of the method and its various embodiments are correspondingly linked to the device.

[0044] The device includes a heating element with a heating surface. The heating element can be stationary or movable. For example, movement of the entire heating element or at least the heating surface can be enabled vertically, i.e., perpendicular to the sides of the film or the transport direction of the film, and / or translationally, i.e., in and against the transport direction of the film.

[0045] The heating device can, for example, comprise a planar support substrate with a front and a back, made of an electrically non-conductive ceramic material, and on whose front side at least one heating conductor is arranged. A planar support substrate is understood to be a plate-shaped element, i.e., an element whose thickness is small compared to its dimensions in the other two spatial directions, regardless of whether the support substrate is flat, curved, or arched. The heating surface of the heating device can be formed partially or completely by the front side of the support substrate.

[0046] In one embodiment, a support substrate can contain exactly one heating circuit, which can be produced, for example, using a thin-film coating process with metal or a thick-film printing process with conductive paste or conductive ceramic slurry. In other words, the heating surface can be formed using ceramic thick-film technology.

[0047] Alternatively, two or more heating circuits can be arranged on a single substrate. It is advantageous to provide that the heating elements can be controlled individually. It is particularly advantageous that each individual heating circuit can be controlled separately from all other heating circuits, even those located on the same substrate, with regard to its heating power or target temperature. This allows the device to heat different areas of the film to different target temperatures or to apply a temperature profile to the film.

[0048] The at least one heating conductor can be electrically contacted from the back of the substrate through the substrate. To contact the heating conductor(s) located on the front of the substrate from the back, the substrate can, for example, have so-called VIAs (Vertical Interconnect Accesses, a term for perpendicular vias between the layers of an integrated circuit or printed circuit board). These are electrical conductors that extend through the substrate in the thickness direction between the front and back sides. For example, the substrate can have small holes in the form of through-holes whose outer surfaces are coated with or filled with electrically conductive material.

[0049] Furthermore, the device includes a fixing device for securing the film to the heating surface, which, as already mentioned, can be designed as a clamping frame or tensioning frame. The fixing device can be fixed or movable. For example, movement of the fixing device can be vertical, i.e., perpendicular to the sides of the film or the transport direction of the film, and / or translational, i.e., in and against the transport direction of the film.

[0050] Furthermore, the device includes means for generating a pressure difference between a first area, located on the side of the film opposite the heating surface, and a second area, located between the film and the heating surface. The first area can, for example, be located between the film and the fixing device. The pressure difference is generated such that the pressure in the first area is, at least in some areas, lower than the pressure in the second area.

[0051] The pressure difference can be created by decreasing the pressure in the first area and / or increasing the pressure in the second area. For example, the pressure in the first area can be decreased compared to the ambient pressure, i.e., creating a negative pressure, and / or the pressure in the second area can be increased compared to the ambient pressure, i.e., creating a positive pressure. To create the positive pressure in the second area, a perforated or porous heating surface can be used, through which, for example, air is pumped into the second area to increase the pressure.

[0052] The means for generating the pressure difference can be configured, for example, as explained below. Furthermore, the means can include pumps for increasing or decreasing the pressure of a medium present in the first or second area, e.g., air.

[0053] The possibility of creating the pressure difference described above reduces or prevents unwanted adhesion of the foil to the heating surface, so that the disadvantages described in the introduction are either not present or are less pronounced.

[0054] According to various embodiments, the means for creating the pressure difference can comprise a sealed chamber, preferably a gas-tight, in particular an airtight sealed chamber.

[0055] The chamber can preferably be closed and sealed. For example, the chamber can be designed like a protective bell. The fixing device can be integrated into the chamber, meaning the chamber and fixing device can form a single component.

[0056] The inner volume of the chamber can form the first area, so that by sealing the chamber a desired pressure in the first area, in particular a negative pressure compared to the ambient pressure, can be set quickly and easily, either actively or passively.

[0057] According to further design variants, the means for creating the pressure difference can include at least one perforated and / or porous area.

[0058] In this context, the term "perforated" refers to a surface with intentionally introduced holes, whereby the number, shape, size, and regularity of the holes can be varied. In contrast, the term "porous" refers to a surface that is naturally or due to manufacturing processes permeable to gases and therefore has pores.

[0059] For example, the perforated and / or porous area can be arranged in a plate, preferably a sealed plate, in particular a gas-tight or airtight sealed plate. The fixing device can be integrated into the plate, i.e., the plate and fixing device can form a single component.

[0060] For example, the perforated and / or porous area can be positioned centrally with respect to the dimensions of the panel. This allows the perforated and / or porous area to also be positioned centrally above the film.

[0061] In the case of a perforated and / or porous area, only the holes of the perforation or the pores are gas-permeable, particularly permeable to air. This means that an initial pressure differential can be generated in the perforated and / or porous area compared to the non-perforated or non-porous area. This advantageously allows for improved, targeted detachment of the film from the heating surface in specific areas, for example, in areas where increased adhesion of the film would be expected without applying the pressure differential, such as in a central area of ​​the film.

[0062] In addition to the option of providing a single perforated and / or porous area, several perforated and / or porous areas arranged separately from one another can also be provided. For example, the panel can have several perforated and / or porous areas arranged separately from one another. Separate from one another means that there is an area without perforation or a non-porous area between two perforated and / or porous areas.

[0063] Multiple perforated and / or porous areas offer the advantage of creating locally varying pressure differentials, enabling precise control of the peeling process. Optionally, a seal can be positioned between the individual perforated and / or porous areas to create a gas-tight seal between them. This allows for even more precise control of the peeling process.

[0064] At least one of the perforated and / or porous areas, but also several perforated and / or porous areas or all perforated and / or porous areas, can be circular. Alternatively, other geometries are possible, whereby the areas can also have different geometries, e.g. adapted to the geometry of the film to be heated.

[0065] This has the advantage that areas with more perforations and / or higher porosity can generate different peel forces under the same pressure. Consequently, the peeling process can be controlled more precisely.

[0066] According to further embodiment variants, by means of the means for forming the pressure difference between the first area and the second area, a pressure difference can be formed such that the pressure p2 in the second area is at least partially lower than the pressure pi in the first area.

[0067] For example, the heating surface can be perforated and / or porous, so that applying a vacuum presses the film onto the heating surface. This creates particularly good contact between the heating surface and the film, allowing the film to be heated quickly and with low energy consumption.

[0068] Optionally, the heating surface can be surrounded by a seal to promote the formation of a vacuum between the film and the heating surface.

[0069] According to further design variants, the heating device can be integrated into a mold.

[0070] This has the advantage that heating and forming can take place in a single tool. Transporting the heated film from the heating unit to the forming tool is therefore unnecessary. This has the advantage of preventing the heated film from cooling during transport and allows for a more compact thermoforming system.

[0071] According to further embodiments, the device can have a control unit designed and configured to generate and output control signals, wherein the control signals cause the pressure difference to be generated.

[0072] The control unit can be implemented in hardware and / or software and can be physically designed as one or more parts.

[0073] For example, the control signals can activate or deactivate a vacuum pump acting on the first area and / or a pressure booster pump acting on the second area.

[0074] For this purpose, the pump(s) can be connected to the control unit via a signal communication system. Optionally, one or more pressure sensors can be provided to determine the pressure in the first and / or second zone. By outputting sensor signals from the pressure sensor(s) to the control unit, the control unit can receive and process these signals. This allows the pump(s) to be activated or deactivated in response to the processed sensor signals, based on instructions or code programmed into the control unit, according to one or more routines. Pressure regulation in the first and / or second zone, or pressure differential control, can also be implemented in this way.

[0075] According to further design variants, the heating surface can have a non-stick coating.

[0076] The non-stick coating can, for example, consist of polytetrafluoroethylene, be a coating made of polytetrafluoroethylene, or be a ceramic coating. Such a non-stick coating can further help prevent the film from sticking. Another aspect of the invention relates to a thermoforming machine.

[0077] The proposed thermoforming machine incorporates one of the previously described devices for heating the thermoplastic film. Therefore, the above explanations of the device also serve to describe the thermoforming machine. The advantages of the device and its various design options are inherent in the thermoforming machine.

[0078] In addition to the device for heating the film, the thermoforming system has other tools, devices and equipment, such as a transport device for transporting the film from a film reservoir, e.g. a film roll, to various processing stations, such as the device for heating the film.

[0079] Other processing stations could include, for example:

[0080] - a forming tool, designed and set up for forming the heated film, the forming tool comprising, for example, a forming bowl and a forming tool lid; and

[0081] - a sealing tool, designed and equipped for sealing the shaped film, the sealing tool comprising, for example, a sealing plate.

[0082] Another aspect of the invention relates to the use of a thermoforming machine as described above for the production of packaging. Therefore, the above explanations of the thermoforming machine also serve to describe its use. The advantages of the thermoforming machine are correspondingly linked to its use.

[0083] In particular, packaging can be made with a plastic film, such as plastic packaging, but also cardboard or paper packaging with a plastic film, e.g. as a laminate.

[0084] Another aspect of the invention relates to a method for producing a molded part, e.g., a package, using the proposed thermoforming system. The method comprises the following steps: transporting a film to the device for heating the film, heating the film using one of the methods for heating a film described above, transporting the heated film to a forming tool, and forming the heated film into a molded part.

[0085] Optionally, the process can include transporting the molded part to a sealing tool and sealing it as a further step. Between the forming and closing / sealing steps, the molded part can optionally be filled, for example, if it is packaging such as a blister or tray, or part of packaging such as an insert. The above explanations of the thermoforming system and the film heating process also serve to describe the packaging manufacturing process. This process combines the advantages of both the thermoforming system and the film heating process.

[0086] The invention is explained below with reference to exemplary embodiments. The accompanying drawings show:

[0087] Fig. 1 shows an exemplary device for heating a foil;

[0088] Fig. 2a shows an exemplary means of creating the pressure difference;

[0089] Fig. 2b shows another exemplary means of forming the pressure difference;

[0090] Fig. 2c shows another exemplary means of forming the pressure difference;

[0091] Fig. 3 shows the device of Fig. 1 during the heating of the foil;

[0092] Fig. 4 shows the device of Fig. 1 shortly before the removal of the heating surface;

[0093] Fig. 5 shows the device of Fig. 1 during the removal of the heating surface;

[0094] Fig. 6 shows the device of Fig. 1 when released from the fixing device;

[0095] Fig. 7 Diagrams illustrating the pressure profiles in the first and second areas

[0096] (above) and the corresponding position of the heating surface (below);

[0097] Fig. 8 shows an exemplary thermoforming machine;

[0098] Fig. 9 shows a flowchart of an exemplary method for heating a film; and

[0099] Fig. 10 shows a flowchart of an exemplary process for producing a

[0100] Packaging.

[0101] The figures are not necessarily detailed or to scale and may be enlarged or reduced to provide a better overview. Therefore, the functional details disclosed here are not to be understood as limiting, but merely as an illustrative basis to guide those skilled in this field of technology in using the present invention in a variety of ways.

[0102] In the examples described below, reference is made to the accompanying drawings, which form part of the examples and in which specific embodiments of the invention are shown for illustrative purposes. In this respect, directional terminology such as "top," "bottom," "front," "back," "anterior," "rear," etc., is used with reference to the orientation of the described figure(s). Since components of embodiments can be positioned in a number of different orientations, the directional terminology serves for illustrative purposes and is in no way limiting. It is understood that other embodiments may be used and structural or logical modifications may be made without deviating from the scope of protection of the present invention.It is understood that the features of the various exemplary embodiments described herein can be combined with one another, unless specifically stated otherwise. The following detailed description is therefore not to be interpreted in a limiting sense, and the scope of protection of the present invention is defined by the appended claims.

[0103] In the figures, identical or similar elements are provided with identical reference symbols where appropriate.

[0104] Fig. 1 shows an embodiment of a device 1 for heating a film 2. The device 1 has a heating element 9 with a heating surface 3. Optionally, the heating surface 3 can be provided with a polytetrafluoroethylene coating or a ceramic coating as a non-stick coating (not shown). Several heating conductors (not shown) are arranged on the heating surface 3 so that areas of the heating surface 3 can be heated to different temperatures. For example, a higher target temperature can be set for a central area 7 of the film 2 than for peripheral areas 8 of the film 2. However, the invention is not limited to such differently temperature-controlled surfaces. The heating surface 3 is surrounded by a seal 20, which can, for example, be designed as a sealing cord.

[0105] The film 2 is designed as a continuous substrate and can be transported along a transport direction 26 (see Figure 8). In the exemplary embodiment, the film 2 consists of a thermoplastic material.

[0106] The device 1 also includes a fixing device 4 for fixing the film 2 to be heated to the heating surface 3. Furthermore, the device 1 comprises means 10 for creating a pressure difference between a first region 5, located on a side of the film 2 opposite the heating surface, and a second region 6, located between the film 2 and the heating surface 3. The pressure difference can be configured such that the pressure π in the first region 5 is at least partially lower than the pressure p2 in the second region 6. A pressure difference can also be configured such that the pressure p2 in the second region 6 is at least partially lower than the pressure π in the first region 5. Depending on the process step, one or the other pressure difference is set, as will be explained below.

[0107] The means 10 for generating the pressure difference can be configured differently, for example as shown in Fig. 2. Fig. 2a shows a sealed chamber 11 with a rectangular base in a top view, which can be arranged over the film 2 or over the area of ​​the film 2 to be heated, similar to a protective bell. The chamber 11 has a seal at the contact points with the film 2, so that an overpressure or underpressure can be set in the chamber 11, e.g., relative to the ambient pressure or the pressure p2 in the second area 6. The pressure can be set passively, e.g., by reducing the temperature in the first area 5 and / or by changing the volume of the first area.

[0108] 5 increases in volume. Such an increase in volume can result, for example, from the fact that the film 2 adheres slightly to the heating surface 3 as the heating surface 3 moves downwards, i.e., away from the film 2, and the volume of the first area 5 increases due to the elasticity of the film 2. Subsequently, the film 2 detaches from the heating surface due to the negative pressure in the first area 5. Consequently, the required pressure difference can be passively generated by means of the sealed chamber 11.

[0109] Fig. 2b shows an alternative embodiment of the means 10 for generating the pressure differential in the form of a rectangular plate 13 with circumferentially bounded sides and a perforated and / or porous area 12, which is circular and arranged centrally with respect to the plate. Fig. 2c shows another alternative embodiment of the means 10 for generating the pressure differential in the form of a circumferentially bounded plate 13 with several circular perforated and / or porous areas 12, which are spaced apart from one another and evenly distributed over the surface of the plate 13. As with chamber 11, the lateral boundaries of the plate 13 allow a protective dome to form over the area of ​​the film 2 to be heated. As with the sealed chamber 13, the circumferential lateral boundaries of chamber 11 can also be provided with a seal.

[0110] The perforated and / or porous areas 12 enable the active formation of a pressure difference, in particular a negative pressure in the first area 5, by removing gas or air from the first area 5 by means of a pressure pump 27 (see Figure 8).

[0111] The dimensions of chamber 11 and plates 13 are adapted to the dimensions of film 2 in such a way that the area of ​​film 2 to be heated is covered by chamber 11 and plates 13, respectively.

[0112] The means 10 for generating the pressure difference are at least partially integrated into the fixing device 4, in that the lateral boundaries of the chamber 11 or plate 13 can fix the film 2 in a manner similar to a clamping frame. The fixing device 4 and the sealed chamber 11 or the plates 13 therefore form a single or combined component.

[0113] The means 10 for generating the pressure difference can therefore include a pressure pump 27, by means of which the pressure in the first or second area 5, 6 can be actively adjusted. A single pressure pump 27 can be used for adjusting the pressure in both the first and second areas 5, 6.

[0114] 6 can be used, or each of the areas 5 and 6 can be assigned a separate pressure pump.

[0115] Furthermore, the device 1 includes a control unit 15 (see Figure 8) designed and configured to generate and output control signals 16a, b, c, d, e. Control signal 16a is output to the pressure pump 27, which is connected to the control unit 15 via a signal transmission system. Control signal 16a activates or deactivates the pressure pump 27, thereby actively changing the pressure in the first or second section 5, 6 and consequently generating the desired pressure differential. It should be noted that actively changing the pressure is not strictly necessary, but can be advantageous in certain applications.

[0116] The control signal 16b is output to the heating device 9, which is connected to the control unit 15 via a signal communication. The control signal 16b causes the heating surface 3 to move perpendicular to the transport direction 26 of the film 2, either towards or away from the film 2. Optionally, the control signal 16b can also activate or deactivate the heating surface 3 and, if necessary, set different temperatures on the heating surface 3.

[0117] The control signal 16c is output to the fixing device 4, which is connected to the control unit 15 via a signal transmission system. The control signal 16c causes the fixing device 4 to move perpendicular to the transport direction 26 of the film 2, either towards or away from the film 2.

[0118] The following section explains in more detail the mode of operation of the device 1 with reference to Figures 1 and 3 to 7, which is independent of the specific design of the means 10 for generating the pressure difference.

[0119] Figure 1 shows the device 1 in an initial state before the heating of the film 2, which was previously transported such that the area of ​​the film 2 to be heated is arranged above and parallel to the heating surface 3. The fixing device 4 is already in loose contact with the film 2.

[0120] Next, the heating surface 3 is moved upwards towards the film 2 until contact is made. The film 2 is fixed to the heating surface 3 by means of the fixing device 4, or rather, the film 2 is clamped between the fixing device 4 and the heating surface 3. By activating the pressure pump 27 acting on the second area 6, the air pressure p2 in the second area 6 between the film 2 and the heating surface 3 is reduced by removing air from the second area 6 through holes in the heating surface 3, as indicated by the arrows in Figure 3. For example, the pressure P2 can be reduced by at least 0.8 bar compared to the ambient pressure, which simultaneously corresponds to the pressure pi in the first area 5, as shown in Figure 3. The pressure pi, however, remains unaffected.This ensures the best possible contact between the film 2 and the heating surface 3, allowing the film 2 to be heated quickly and energy-efficiently until a target temperature or different target temperatures are reached. Fig. 4 shows the device 1 shortly before venting, i.e., shortly before the heating surface 3 is moved away from the film 2. In the second area 6, a negative pressure of at least 0.8 bar (p2 < -0.8 bar) is maintained relative to the ambient pressure. However, the air pressure pi in the first area 5 is now also reduced relative to the ambient pressure by activating the pressure pump 27 acting on the first area 5. The negative pressure in the first area 5 relative to the ambient pressure can be at least 0.4 bar (pi < -0.4 bar). The pressure pi in the first area 5 can initially be higher than the pressure p2 in the second area 6.

[0121] Fig. 5 shows the device 1 during the removal of the heating surface 3 from the film 2 by moving the heating surface 3 downwards, perpendicular to the transport direction 26 of the film 2. For this purpose, the pressure p2 in the second area 6 is increased back to ambient pressure while the pressure pump 27 is simultaneously deactivated, i.e., pressure equalization with the ambient pressure takes place. Consequently, a negative pressure exists only in the first area 5. This negative pressure causes the film 2 to adhere to the fixing device 4 while the heating surface 3 is moved away from the film 2. Undesirable wrinkling and changes in material thickness due to adhesion of the film 2 to the heating surface 3 can thus be avoided.

[0122] Fig. 6 shows the device 1 during the removal of the fixing device 4 from the film 2. After the heating surface 3 has been removed from the film 2, the pressure pi in the first area 5 is also increased back to ambient pressure while the pressure pump 27 is simultaneously deactivated; that is, pressure equalization with the ambient pressure takes place. This causes the film 2 to detach from the fixing device 4, so that the heated film 2 can be transported to one or more further processing stations. Subsequently, a new area of ​​the film 2 can be positioned over the heating surface 3 for heating, as shown in Fig. 1.

[0123] Figure 7 shows the corresponding pressure profiles over time in the first and second regions 5, 6 (top) and the corresponding position of the heating surface 3 (bottom). The position of the heating surface 3 varies between bottom, i.e., away from the film 2, as shown, for example, in Figures 1, 5, and 6, and top, i.e., in contact with the film, as shown, for example, in Figures 3 and 4. The negative pressure can vary between on and off for the first region pi (solid line) and the second region p2 (dashed line). "On" means that negative pressure is applied, i.e., the pressure is reduced relative to the ambient pressure. "Off" means that no negative pressure is applied, i.e., the pressure equals the ambient pressure.

[0124] Initially, the heating surface 3 is in the lower position, i.e., away from the foil 2. There is no negative pressure in either the first area 5 or the second area 6.

[0125] When the heating surface 3 is brought into contact with the film 2 (position "top"), the pressure p2 in the second area 6 is also reduced to ensure good contact between the film 2 and the heating surface 3. The pressure pi in the first area 5, however, remains unchanged.

[0126] The foil 3 is then heated by heat transfer from the heating surface 3 (area A “heating” in Fig. 7).

[0127] Upon reaching the target temperature, i.e., the completion of the heating of the film 2, a negative pressure is also created in the first area 5, while the position of the heating surface 3 and the pressure in the second area 6 remain unchanged (area B “just before ventilation” in Fig. 7).

[0128] Subsequently, for venting (area C “Ventilation” in Fig. 7), i.e., for removing the heating surface 3 from the film 2, the pressure p2 in the second area 6 is first increased back to ambient pressure. These pressure conditions cause the film 2 to detach from the heating surface 3 and, at the same time, to adhere to the fixing device 4. After venting, i.e., when the heating surface 3 has returned to its lower position, the pressure pi in the first area 5 is also increased again, so that the film 2 is released and can be transported further.

[0129] It should be noted that the time sequences shown in Fig. 7 are to be regarded as exemplary and can be varied and flexibly adjusted to each other as required, e.g. depending on the specific film material, the film thickness, the desired target temperature, etc.

[0130] Fig. 8 shows an embodiment of a thermoforming machine 20 with a device 1 for heating the film 2. The device 1 can, for example, be configured as described above with reference to Figures 1 to 7. The thermoforming machine 1 has several processing stations, which are completed starting from the film roll 21 of the bottom film along the transport direction of the film 2 to the finished packaging 17, as explained in more detail below.

[0131] The film 2 to be heated forms the bottom film of the packaging 17 and is initially located as a continuous substrate on the film roll 21 of the bottom film. From there, the film 2 is transported along the transport direction 26 by means of transport devices 25, which can be designed, for example, as at least partially driven transport rollers, from left to right in the illustration of Fig. 8.

[0132] The first processing station is the device 1 for heating the film 2, for which further details are provided in the preceding descriptions. After heating, the heated film 2 is transferred to the forming tool 14, which in the exemplary embodiment comprises a forming tray 24 and a forming tool lid 23. Optionally, the forming tool 14 can also be integrated into the device 1 for heating the film 2, thus eliminating the need to transport the heated film 2 from the device 1 to the forming tool 14. In the forming tool 24, the heated film 24 is pressed into the forming tray 24 by closing the forming tray 24 and the forming tool lid 23, so that the heated film 2 assumes the shape of the forming tray 24 and a corresponding molded part 18 is formed. The molded part 18 is then transported to a sealing tool 19. In the sealing tool 19, the molded part 18 is sealed with a top film which is supplied from a film roll 22 of the top film.After sealing, individual packages can be separated from each other using a cutting tool 28, so that the individual packages 17 are released.

[0133] The control unit 15 of the device 1 can simultaneously be used to control other tools of the thermoforming machine 200. In other words, a common control system can be provided. In addition to the control signals 16a, 16b and 16c already described, the control unit 15 can generate and output further control signals 16d, 16e.

[0134] The control signal 16d is output to the forming tool 14, e.g., the forming shell 24 and / or the forming tool cover 23, which is in a signal-technical communication link with the control unit 15. The control signal 16d causes the forming tool 14 to move such that the heated film 2 is brought into the shape of the desired molded part 18. For example, the forming shell 24 and / or the forming tool cover 23 can move perpendicular to the transport direction 26 of the film 2, either towards or away from the film 2.

[0135] The control signal 16e is output to the sealing tool 19, which is connected to the control unit 15 via a signal transmission system. The control signal 16e causes the molded part 18 to be sealed to the top film, for example by selectively welding the top film to the molded part. For example, the sealing tool 19 can move perpendicular to the transport direction 26 of the film 2 and apply the temperature required for sealing to the sealing or welding area, resulting in a material-bonded connection between the molded part and the top film.

[0136] With reference to Fig. 9, an exemplary method 100 for heating a film 2 is explained in more detail below. Method 100 can be carried out, for example, using the device 1 described above with reference to Figures 1 to 7 or the thermoforming machine 200 described with reference to Figure 8. Therefore, reference is also made to the explanations of Figures 1 to 8.

[0137] After the start of process 100, in step S1 the film 2 is fixed to the heating surface 3 by means of the fixing device 4. Here, the heating surface 3 and the fixing device 4 are arranged on opposite sides of the film 2, so that a first area 5 is formed on one side of the film 2 opposite the heating surface 3 and a second area 6 is formed between the film 2 and the heating surface 3.

[0138] In step S2, the pressure p2 in the second area 6 is reduced such that the pressure p2 in the second area 6 is at least partially lower than the pressure pi in the first area 5. This ensures good contact between film 2 and the heating surface 3. In step S3, the fixed film 2 is heated until the target temperature is reached.

[0139] In step S4, a pressure difference is created between the first area 5 and the second area 6 such that the pressure pi in the first area 5 is at least partially lower than the pressure p2 in the second area 6.

[0140] In step S5, the heated foil 2 is then removed from the heating surface 3.

[0141] Finally, in step S6, the pressure pi in the first area 5 is increased to a pressure that is at least equal to the ambient pressure. The film 2, now heated and no longer adhering to either the heating surface 3 or the fixing device 4, can now be transported further, for example to the forming tool 14.

[0142] With reference to Fig. 10, an exemplary method 300 for manufacturing a package 17 is explained in more detail below. Method 300 can, for example, be carried out using the thermoforming machine 200 described above with reference to Figure 8. Therefore, reference is also made to the explanations in Figure 8.

[0143] In step S10, the film 2 is first transported to a device 1 for heating the film 2. This device 1 can, for example, be designed like the device 1 described above with reference to Figures 1 to 7.

[0144] In step S11, the foil 2 is heated, whereby, for example, the method 100 described above with reference to Figure 9 can be used.

[0145] In step S12, the heated film 2 is transported to a forming tool 14 and then formed into a molded part 18 in step S13.

[0146] The molded part 18 is then transported to a sealing tool 19 and sealed in step S15.

[0147] The expression "and / or" used here, when used in a series of two or more elements, means that each of the listed elements can be used alone, or any combination of two or more of the listed elements can be used. For example, when referring to the first and / or second area, the first area alone, the second area alone, or the first area and the second area in combination may be meant. (List of references)

[0148] 1 Device

[0149] Slide 2

[0150] 3 Heating surface

[0151] 4 Fixing device

[0152] 5 first area

[0153] 6 second area

[0154] 7 middle area

[0155] 8 Edge area

[0156] 9 Heating system

[0157] 10 means of creating a pressure difference

[0158] 11 sealed chambers

[0159] 12 perforated and / or porous area

[0160] 13 plate

[0161] 14 Forming tool

[0162] 15 Control unit

[0163] 16a,b,c,d,e Control signal

[0164] 17 Packaging

[0165] 18 Molded part

[0166] 19 Sealing tools

[0167] 20 Seal

[0168] 21 roll of foil for the bottom foil

[0169] 22 rolls of top film

[0170] 23 Mold lids

[0171] 24 mold trays

[0172] 25 T transport equipment

[0173] 26 Transport direction

[0174] 27 Pressure pump

[0175] 28 cutting tools

[0176] 100 methods for heating a foil

[0177] 200 thermoforming machines

[0178] 300 methods for manufacturing packaging

[0179] Pi pressure in the first area p2 pressure in the second area

[0180] A. Heating B. Shortly before ventilation

[0181] C Ventilate

[0182] 51 Fixing the thermoplastic film to a heating surface using a fixing device

[0183] 52 Reducing the pressure p2 in the second area

[0184] 53 Heating the fixed film until a target temperature is reached

[0185] 54. Generating a pressure difference between the first area and the second area such that the pressure p1 in the first area is at least partially lower than the pressure p2 in the second area.

[0186] 55. Removing the heated film from the heating surface

[0187] 56. Increase the pressure p1 in the first area to a pressure that is at least equal to the ambient pressure.

[0188] 510 Transporting the thermoplastic film to a device for heating the film

[0189] 511 Heating the foil

[0190] 512 Transporting the heated film to a forming tool

[0191] 513 Forming the heated foil into a molded part

[0192] 514 Transporting the molded part to a sealing tool

[0193] S15 Sealing the molded part

Claims

Patent claims 1. Method (100) for heating a thermoplastic film (2), comprising the method (100): S1: Fixing the thermoplastic film (2) to a heating surface (3) by means of a fixing device (4), wherein the heating surface (3) and the fixing device (4) are arranged on opposite sides of the film (2), so that a first area (5) is formed on a side of the film (2) opposite the heating surface (3) and a second area (6) is formed between the film (2) and the heating surface (3), S3: at least partial heating of the fixed film (2) until a target temperature is reached, S4: Generating a pressure difference between the first area (5) and the second area (6) such that the pressure pi in the first area (5) is at least partially lower than the pressure p2 in the second area (6), and S5: Remove the heated film (2) from the heating surface (3).

2. Method (100) according to claim 1, comprising: S6: after removing the heated film (2) from the heating surface (3), increase the pressure pi in the first area (5) to a pressure that is at least equal to the ambient pressure.

3. Method (100) according to one of the preceding claims, wherein the pressure difference is generated by actively changing the pressure pi, p2 in the first and / or second area (5,6).

4. Method (100) according to one of the preceding claims, wherein the pressure difference is generated by passively changing the pressure pi, p2 in the first and / or second region (5,6).

5. Method (100) according to one of the preceding claims, wherein a pressure difference of at least 0.1 bar, preferably a pressure difference between 0.4 bar and 1 bar, is generated.

6. Method (100) according to one of the preceding claims, wherein a vacuum is generated to create the pressure difference in the first area (5).

7. Method (100) according to one of the preceding claims, wherein an overpressure is generated to create the pressure difference in the second area (6).

8. Method (100) according to one of the preceding claims, wherein a different pressure difference is generated in areas of the heated film (2).

9. Method (100) according to claim 8, wherein in a central area (7) of the film (2) a higher pressure difference than is generated in the edge areas (8) of the film (2).

10. Method (100) according to one of the preceding claims, wherein areas of the film (2) are heated until different target temperatures are reached.

11. Method (100) according to any one of the preceding claims, comprising: S2: after fixing the film (2) on the heating surface (3) and before heating the fixed film (2), reduce the pressure p2 in the second area (6) such that the pressure P2 in the second area (6) is at least partially lower than the pressure pi in the first area (5).

12. Device (1) for heating a thermoplastic film (2), the device (1) comprising: a heating device (9) with a heating surface (3), a fixing device (4) for fixing the film (2) on the heating surface (3), and Means (10) for forming a pressure difference between a first area (5) located on a side of the film opposite the heating surface (3) and a second area (6) located between the film (2) and the heating surface (3) such that the pressure pi in the first area (5) is at least partially lower than the pressure p2 in the second area (6).

13. Device (1) according to claim 12, wherein the means (10) for forming the pressure difference comprise a sealed chamber (11).

14. Device (1) according to claim 12 or 13, wherein the means (10) for forming the pressure difference comprise at least one perforated and / or porous area (12).

15. Device (1) according to claim 14, wherein the means (10) for forming the pressure difference have several separate perforated and / or porous areas (12).

16. Device (1) according to claim 14 or 15, wherein the at least one perforated and / or porous area (12) is arranged in a plate (13).

17. Device (1) according to claim 16, wherein the perforated and / or porous area (12) is arranged centrally with respect to the plate (13).

18. Device (1) according to one of claims 14 to 17, wherein at least one of the perforated and / or porous areas (12) is circular.

19. Device (1) according to one of claims 12 to 18, wherein the means (10) for forming the pressure difference are at least partially integrated into the fixing device (4).

20. Device according to one of claims 12 to 19, wherein by means of the means (10) for Forming the pressure difference between the first area (5) and the second area (6) such that the pressure p2 in the second area (6) is at least partially lower than the pressure pi in the first area (5).

21. Device (1) according to one of claims 12 to 20, wherein the heating device (9) is integrated into a forming tool (14).

22. Device (1) according to one of claims 12 to 21, wherein the means (10) for forming the pressure difference comprise a pressure pump (27).

23. Device (1) according to one of claims 10 to 20, comprising: a control unit (15), designed and configured to generate and output control signals (16) that cause the pressure difference to be formed.

24. Device (1) according to one of claims 12 to 23, wherein the heating surface (3) has a non-stick coating.

25. Thermoforming system (200) with a device (1) according to one of claims 12 to 24.

26. Use of a thermoforming machine (200) according to claim 25 for the production of molded parts (18).

27. Method (300) for producing a molded part (18) using a thermoforming machine (200) according to claim 22, comprising the method (300): S10: Transporting a thermoplastic film (2) to a device (1) according to one of claims 12 to 24, S11 : Heating the film (2) by means of a method (100) according to one of claims 1 to 11 , S12: Transporting the heated film (2) to a forming tool (14) and S13: Shaping the heated foil (2) into a molded part (18).

28. Method (300) according to claim 27, comprising the method (300): S14: Transporting the molded part (18) to a sealing tool (19) and S15: Sealing the molded part (18).

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