SLOT DIE, COATING ARRANGEMENT COMPRISING SUCH A SLOT DIE, AND CLEANING DEVICE FOR SUCH A SLOT DIE

Abstract

 The present invention relates to a slot die, preferably a wide-slot die, configured and intended to be operated in an environment with negative pressure. The present invention further relates to a coating arrangement comprising a slot die and a cleaning device for a slot die. Preferably both, the coating arrangement as well as the cleaning device, comprise a slot die configured and intended to be operated in an environment with negative pressure.

Description

[0001] The present invention relates to a slot die, preferably a wide-slot die, a coating arrangement comprising such a slot die, and a cleaning device for such a slot die.

[0002] A slot die, including the slot die according to the present invention, can be distinguished from other dies or nozzles by the specific dimensions of its slot, the slot having a slot length being at least 100 times, preferably up to 500 times, longer than its slot width, wherein a width of the slot is usually smaller than 2 mm, preferably smaller than 1 mm, more preferably smaller than 0,5 mm, even more preferably smaller than 0,2 mm. Typically, a slot die is used for coating processes during which a coating medium is transferred to a surface, for example, of a rolled sheet or a film web, preferably in a contactless manner, i.e. without contact between slot die and surface. As a slot die allows a high accuracy and an increased production speed by applying thin and broad layers compared to conventional round nozzles applying medium in a meandering manner, it can be used for applications calling for an evenly spread of medium over a surface.

[0003] Conventional slot dies are known, for example, from US 3,940,221 A or EP 0 367 022 A2. These slot dies are intended to be operated under atmospheric pressure. However, an operation under atmospheric pressure bears the risk of imperfections, such as non-coated areas, due to air entrapped in the coating medium. If the coating surface is transparent or the coating is adjacent to a transparent part, e.g. in the case of the coating of display screens, even slight imperfections can lead to unsaleable products.

[0004] A known method to remove air from a medium is the application of a vacuum. In connection with the coating of a surface, the vacuum is typically applied to an already coated medium as an air intake into the coating medium usually takes place during the application thereof. Thus, conventionally, an already coated surface is placed in a vacuum chamber before it will be further processed. It is to be understood that the term "vacuum" refers to any pressure lower than the ambient pressure during the application of the coating. Accordingly, the part having the coated surface has to be transferred to a vacuum chamber and afterwards the pressure therein has to be reduced. The steps of transferring said part and reducing the pressure require a relatively long time and are therefore disadvantageously under the aspect of achieving a cost- and time-efficient process.

[0005] In view of the above circumstances, it is an object of the present invention to provide an enhanced coating process.

[0006] For this purpose, the slot die, preferably a wide-slot die, according to the present invention is configured and intended to be operated in an environment with negative pressure. This allows reducing the risk of entrapped air in the coated medium and the time needed for the coating process.

[0007] The closure mechanism can minimize or even prevent an undesired flowing out of coating medium out of the slot of the die. Or in other words, the closure mechanism can be able to keep coating medium inside the slot of the die in a surrounding with negative pressure regardless of whether a coating process is running or not. By using the slot die in a surrounding with negative pressure, the risk of air entrapped in the coating medium can be significantly reduced. Further, the step of transferring a part having an already coated surface into a vacuum chamber is no longer necessary so that the time needed for the coating process is also reduced.

[0008] Typically, a negative pressure for degassing coatings applied by a slot die is in a range of 1 to 50 mbar. Depending on an operating mode, the slot die or only a part of it including the slot of the die can be arranged in the surrounding with negative pressure.

[0009] An actuation mechanism for the feed of the coating medium or/and for stopping said feed can be a pump, especially a gear pump.

[0010] According to one embodiment, the slot die can comprise a first slot die part and a second slot die part located opposite to the first slot die part, the first slot die part and the second slot die part therebetween forming a slot of the die. The slot die may further comprise a coating medium supply system configured and intended to provide a feed of coating medium to the slot of the die and can include a coating medium reservoir and a coating medium channel connecting the coating medium reservoir with the slot of the die. The coating medium can be a liquid or paste like medium. Furthermore, the slot die can comprise a closure mechanism configured and intended to reduce the amount of coating medium flowing out of the slot of the die after the feed of coating medium has been stopped.

[0011] According to a feature of the invention, the closure mechanism can include at least one closing element which can be arranged within the coating medium channel and can be transferable between at least two positions, namely a closing position, in which the at least one closing element closes the coating medium channel and a supply position, in which the coating medium channel allows a feed of coating medium. Due to the arrangement of the at least one closing element within the coating medium channel, it can be located spaced apart from the slot of the die. This has the advantage that the closing element, regardless of its position, has no influence on the width of the slot of the die, which, in turn, has a great effect on the shape, such as the thickness, of the coated medium.

[0012] For example, the at least one closing element can be located between a coating medium channel main section and a coating medium channel end section. The coating medium main section can provide a flow connection between the reservoir and the at least one closing element, and the coating medium end section can provide a flow connection between the at least one closing element and the slot of the die. Such a location of the at least one closing element is of advantage when at least a portion of the coating medium channel end section has a minimal cross-sectional diameter providing sufficient capillary forces to keep a coating medium a certain time, e.g. a few seconds. This could enable the slot die to be transferred from one surface to be coated to another one, without the risk of an undesirably flowing out of coating medium out of the slot of the die. Further, the coating medium channel end section has advantageously a minimal length, preferably 10 mm or shorter. Or in other words, the closing mechanism could be arranged close to the slot of the die. In this way said risk of undesirably flowing out of coating medium out of the slot of the die can be further reduced. Moreover, the amount of coating medium, which in the worst case can undesirably flow out of the slot of the die, is limited to the amount of coating medium included in the, preferably very short, coating medium channel end section.

[0013] In order to provide a homogenous feed of coating medium over the whole length of the slot of the die, the coating medium channel main section can include several coating medium tubes. The coating medium tubes can preferably be evenly distributed over a longitudinal region of the first and/or second slot die parts being adjacent to the slot of the die. Of course, the at least one closing element can be configured and intended to close all of said tubes, advantageously to commonly close all of said tubes.

[0014] In order to provide a fast transfer of the at least one closing element between the closing position and the supply position, the at least one closing element can be actuated by a pneumatic cylinder or an electric motor.

[0015] While in a basic embodiment of the present invention, the at least one closing element is transferable between the closing and supply positions, in a more sophisticated embodiment, the at least one closing element can additionally be transferred into one or more intermediate positions, in which the at least one closing element is divided into a plurality of regions, some of which allow the coating medium to pass the coating medium channel, preferably allow a flow connection between the coating medium channel main section and the coating medium channel end section, while others do not. The intermediate positions may allow to use the slot die for coating surfaces having surface portions to be coated as well as surface portions not to be coated. For example, in one of the intermediate positions the closing element can close a central region of the coating medium channel and can allow the coating medium to pass edge regions thereof at the same time.

[0016] In general, the thickness of a layer of coating medium applied to a surface to be coated is determined by the amount of coating medium leaving the slot and the relative velocity between said surface to be coated and the slot die. The amount of coating medium leaving the slot is determined by the width of the slot and the pressure expelling the coating medium from the slot, which in turn is determined by the amount of coating medium supplied per unit of time by a pump, preferably an extruder or positive displacement pump, and coating medium properties, such as viscosity, density and surface tension. Thus, a change of one of these parameters can affect the thickness of the coating medium layer. In this context, the transfer of the closing element into one of the one or more intermediate positions may result in a variation of the expelling pressure, if the supply velocity isn't adapted to the respective length of the slot. In order to avoid or make explicit use of such variations, the slot die may further comprise a control device. The control device can be configured and intended to adapt the feed of the coating medium or/and the relative velocity between said surface and the slot die to a respective dimension of the slot of the die.

[0017] The applicability of the slot die for various coating processes can be further increased, when the slot die is provided with different slot widths. For example, a slot width can be defined by a spacer element mounted between the first and second slot die parts. The spacer element can be demountable and replaceable so that the slot die can be equipped with spacer elements having a varying thickness. This allows the slot die to be used for coating mediums having various properties. For example, the spacer element can define a slot die width of at least 150 µm, preferably of at least 200 µm, or more preferably of at least 500 µm. However, the slot of the die can also have a width up to 1 mm, or preferably up to 2 mm. The spacer element can be provided as metal sheet, but can also comprise a polymer material, such as Teflon®.

[0018] Furthermore, the spacer element can also be provided with one or more protrusions, which protrude in the coating medium channel end section and close regions thereof. Thus, the one or more protrusions can be used to reduce the slot length or/and to divide the slot of the die into two or more regions. In other words, the spacer element can be used for an adaption of the regions, in which coating medium is not allowed to flow out of the slot of the die. Such an adaption enables the slot die to be employed for coating surfaces having a section not to be coated or varying in their dimensions.

[0019] In this aspect it is further advantageous, if the length of the slot of the die allowing coating medium to leave the slot of the die can be adapted during the coating process. Therefore, the slot die can further comprise a slot length adjusting element configured and intended to adjust the length of the slot of the slot die. The slot length adjusting element can be a slider located a one or both sides of the slot die and can be adjustable between a maximal slot length position and a minimal slot length position. Further, each position between said maximal and minimal slot length position can be adjustable. Preferably, said adjustment can be conducted during operation of the slot die. The slot length adjusting element can be actuated by a linear step motor or/and a rack and pinion assembly.

[0020] The latter of the above mentioned measures are intended to enable the slot die to be used for applications where a surface to be coated can vary in its width or/and length. However, there are also surfaces varying not only in its width or/and length, but also in its height. It is therefore advantageous for the slot die to be adapted for coating surfaces having an undulated, a curved, a wavy, a concave, a convex, or/and a tilted shape. Such an adaption can be that slot defining edges of the first and second slot die parts extending parallel to each other define a plane, all surface points of outer surfaces of the first and the second slot die parts being spaced apart from said plane. A slot having said slot defining edges can be tilted according to the shape of the surface to be coated without the risk that a surface of the first and second parts contacts the surface to be coated. For example, the mentioned conditions and advantages can be achieved, if at least one of the first and the second slot die parts taper in the direction of the slot of the die and thus form together a slot die with a pointed end. It is further possible that the first and second slot die parts form an angle between their outer surfaces smaller than or equal to 160°, preferably smaller than or equal to 120°, more preferably smaller than or equal to 60°, but preferably equal to or greater than 15°.

[0021] According to another feature of the invention, the closure mechanism and the coating medium supply system are located in the first slot die part. The second slot die part can be free of the closure mechanism and the coating supply system. It is however conceivable that a surface portion of the second slot die part facing the first slot die part can contribute to forming the coating medium channel end section. Such a location is advantageous as an adjustment of a slot width is not influenced by the closure mechanism and the coating medium supply system, as it would be the case when they are arranged between the first and second slot die parts.

[0022] In order to provide a simple cleanability of the slot die, the surfaces of the first and second slot die parts being opposite to each other can be substantially plan surfaces, excluding portions forming the slot of the die as well as connecting members.

[0023] In a further embodiment of the invention, it may be conceivable that the at least one closing element can be a rotatable shaft including one or more through holes, which in the supply position overlap with both, the coating medium channel main section and the coating medium channel end section, and in the closing position are free of overlap with at least one of said coating medium channel main and coating medium channel end sections. A minimal cross-sectional dimension of each through hole can be smaller than or equal to 0.1 mm. The at least one closing element as a rotatable shaft has the advantage that a rotation of the shaft, for example of only a few degrees, is sufficient to transfer the at least one closing element between said supply and closing positions. Of course, the rotatable shaft can also be transferred into the one or more intermediate positions.

[0024] The one or more through holes in the rotatable shaft can be oriented in a parallel manner. It is also possible that each through hole of a first set of one or more through holes has a first orientation and a second set of one or more through holes has a second orientation. The first orientation can differ from the second orientation. It is further possible that a set of one or more through holes has two inlets and one outlet. Each inlet can overlap with the coating medium channel main section and the one outlet can overlap with the coating medium channel end section. Furthermore, an inlet and/or an outlet of the one or more through holes can have the shape of a funnel. The rotation angle of the rotatable shaft can define which of the one or more through holes provide a flow connection between the coating medium channel main section and the coating medium channel end section.

[0025] In order to prevent coating medium from flowing around the rotatable shaft, the circumferential surface of the rotatable shaft can be sealingly engaged with at least one of the first and second slot die parts. Further, the outermost side surfaces of the rotatable shaft can also be sealingly engaged with a respective surface of the first or/and second slot die parts.

[0026] In yet another embodiment of the present invention, it may be conceivable that the at least one closing element is a rotatable shaft having at least one groove in the circumferential surface, which in the supply position overlap with both, the coating medium channel main section and the coating medium channel end section, and in the closing position is free of overlap with at least one of said coating medium channel main and coating medium channel end sections. The profile of the at least one groove in the circumferential surface can determine the regions in the longitudinal extension of the rotatable shaft at which a flow connection between the coating medium channel main section and the coating medium channel end section is provided. This allows an adjustment of the regions in the longitudinal extension of the slot of the die at which coating medium is allowed to pass the coating medium channel end section. The rotatable shaft can also be provided with a groove having a predefined profile, for example a triangle profile, when viewed in a not rolled status. In this way, the coating medium is not allowed to pass the coating medium channel end section at some regions of the slot of the die, for example outside the triangular groove, whereas other regions allow the passage thereof. Further, by varying the rotation angle of the rotatable shaft, the profile defining the regions at which coating medium is allowed to pass the fluid channel end section, can be changed. Furthermore, the slot die can be equipped with different rotatable shafts having different groove profiles. All of said measures enable a broad applicability of the slot die.

[0027] In yet another embodiment of the present invention, it may be conceivable that the at least one closing element is a plunger. The plunger can comprise an elastic material, such as rubber, suitable to close the coating medium channel in the closing position. The employment of the plunger as the at least one closing element has the advantage that the manufacturing of a plunger is simpler compared to a rotatable shaft as described above.

[0028] The plunger can be formed out of two or more plungers which are adjacently arranged in said coating medium channel in a direction being substantially parallel to the longitudinal extension of the slot of the die. Preferably, the two or more plungers can be actuated separately and independently so that each plunger is transferable between the closing position and the supply position.

[0029] Depending on the overall geometry of the coating medium channel and the used one or more plunger, it may be beneficial, if the coating medium supply system further includes a volume compensation element configured and intended to compensate the volume occupied by a one or more rods of the one or more plungers. The volume compensation element can be transferable between a first position and a second position. The first position can be associated with the supply position of the at least one closing element and the second position can be associated with the closing position of the at least one closing element. The volume compensation element can displace an amount of coating medium contained in the coating medium channel, which can be substantially equal to an amount of coating medium, which the plunger displaces during a transfer of its position. It can therefore prevent that, during the transfer of the at least one plunger from the supply position to the closing position, coating medium undesirably leaves the slot of the die.

[0030] According to a second aspect, the invention relates to a coating arrangement comprising a slot die, preferably a slot die as discussed above, and further comprising a distance control device, said distance control device including at least one distance sensor configured and intended to detect a distance of the slot of the slot die to a surface to be coated and at least one actuator configured and intended to control a distance between the slot of the slot die and the surface to be coated.

[0031] The coating arrangement is equally suitable to achieve the above mentioned object of the invention.

[0032] Further, by employing the coating arrangement non-planar surfaces can be coated in a reproducible manner. A non-planar surface can be, for example, an undulated surface, a curved surface, or a wavy surface, a concave surface, a convex surface, or/and a tilted surface.

[0033] The coating arrangement can comprise means, which enable a rotation of the slot of the die around an axis of rotation being parallel to a longitudinal extension of the slot of the die so that an angle between a plane defined by pointed ends of the slot of the die and a plane defined by a portion of the surface to be coated being adjacent to the slot of the die can be varied.

[0034] Both, the distance control device and the means enabling a rotation, enhance the coating of non-planar surfaces by providing a defined position of the slot of the die in relation to the surface to be coated.

[0035] The at least one distance sensor of the distance control device can comprise two distance rollers protruding from the slot of the die. Due to a predefined distance between the slot of the die and the two distance rollers, the two distance rollers can be able to sense the distance to a surface to be coated by contacting said surface and can control said distance at the same time as long as a force acting perpendicular to said surface ensures a contact between the two distance rollers and said surface. Such a force can be gravity or/and an external applied force, for example, by an actuator of the slot die.

[0036] In order to vary the distance between the slot of the die and the surface to be coated, the distance control device can comprise a plurality of distance rollers varying in their diameters. Alternatively, the distance rollers can be mounted on the slot die in, for example, a high adjustable manner, so that said distance can be varied during a coating process is running.

[0037] The employment of the at least two distance rollers is a mechanical simple and cost-efficient method to reduce an influence of a non-planar surface to be coated on the coating process.

[0038] It is also possible that the distance control element comprises a distance sensor for measuring the distance between the slot of the die and the surface to be coated. The distance sensor can be in contact with said surface.

[0039] It is further possible that the distance control element comprises an optical distance sensor for measuring the distance between the slot of the die and the surface to be coated. The optical sensor has not to be not in contact with the surface to be coated. Such a non-contact solution can be of advantage, when the surface to be coated is made of a pressure-sensitive material.

[0040] For the purpose to achieve a coating arrangement having a slot die, which can be adapted to a non-planar surface, the coating arrangement could further comprise a bearing arrangement allowing a movement of the slot of the die in three axial directions. It is also possible that the slot die is elastically supported, for example by a spring, to move according to a z-profile of the surface to be coated.

[0041] According to a third aspect, the invention relates to a cleaning device for a slot die, configured and intended to be operated in an environment with negative pressure, preferably a slot die as discussed above, comprising a cleaning surface and an actuator, wherein the actuator is configured to reciprocate the cleaning surface in the length direction of the slot die, wherein during reciprocating movement the cleaning surface is in contact with end portions of first and second slot die parts forming the slot of the die. In particular, cleaning of the slot die is necessary for applications operating in a surrounding with negative pressure, since there is a risk that coating medium leaves the slot die caused by the negative pressure. Residuals at the slot of the die will lead to imperfections at a subsequent coating process.

[0042] The coating arrangement is therefore equally suitable to achieve the above mentioned object of the invention.

[0043] Preferably, the slot die is transferable between a working position, in which the slot die can be moved in three axial directions, and a cleaning position, in which the slot die is in a fixed position.

[0044] The cleaning device can be brought in contact with the slot die, if the slot die is in the fixed position. The cleaning device can comprise a cleaning head movable substantially parallel to the longitudinal extension of the slot of the die. Preferably, the cleaning head is in contact with end portions of first and second slot die parts forming the slot of the die. The cleaning head can include wiper lips sliding intended and configured to slide along said end portions. Additionally or alternatively, the cleaning head can include nozzles providing an air flow to the slot of the die. It is also possible that the cleaning head includes means intended and configured to clean the end portions via ultrasonic, for example an ultrasonic cleaning device.

[0045] Further advantages and features of the present invention will become even clearer from the following description of embodiments of the invention with reference to the accompanying figures, wherein:

Figure 1a

presents a schematic cross-sectional view transversal to a longitudinal extension of a slot of a die of a first embodiment of a slot die according to the invention;

Figure 1b

presents a schematic cross-sectional view transversal to a longitudinal extension of a slot of a die of a second embodiment of a slot die according to the invention;

Figure 1c

presents a schematic cross-sectional view transversal to a longitudinal extension of a slot of a die of a third embodiment of a slot die according to the invention;

Figure 2a

presents schematic cross-sectional views in a longitudinal extension of a slot of a die of the first embodiment presented in figure 1a;

Figure 2b

presents schematic cross-sectional views in a longitudinal extension of a slot of a die of the first embodiment presented in figure 1 b;

Figure 3a to 3c

present respective cross-sectional views of different through holes of a rotational shaft presented in figures 1a and 2a;

Figure 4a and 4b

present respective rolled-up profiles of a rotating surface of a rotational shaft presented in figure 1 c;

Figure 5

presents a front view of a slot die according to the invention comprising a slot length adjusting element;

Figure 6

presents a side view of a coating arrangement according to the invention;

Figures 7a and 7b

present a perspective view of a cleaning device for a slot die according to the invention; and

Figure 7c

presents a front view of a slot die according to an embodiment of the invention in a working position illustrated with solid lines and in a fixed position illustrated with dashed lines.

[0046] A slot die, preferably a wide-slot die, according to preferred embodiments of the present invention is denoted by reference sign 10 in the Figures. The slot die can comprises a first slot die part 12 and a second slot die part 14 located opposite to the first slot die part 12. The first and second slot die parts 12, 14 can form together a slot of the die 16 between them. A width 18 of the slot of the die 16 can be defined by a spacer element 20 mounted between the first and second slot die parts 12, 14, as shown in Figures 1 a and c.

[0047] Figures 1 and 2 present an example of a coating medium supply system 22 of the slot die 10, which can be configured and intended to provide a feed of coating medium to the slot of the die 16 and can include a coating medium reservoir not shown and a coating medium channel 24-26 connecting the coating medium reservoir with the slot of the die 16 as well as a closure mechanism 28', 38'. The closure mechanism 28', 38' can be configured and intended to reduce the amount of coating medium flowing out of the slot of the die 16 after the feed of coating medium has been stopped. The closure mechanism 28', 38' can include at least one closing element 28, 34, 38, which can be arranged in the coating medium channel 24-26. The at least one closing element 28, 34, 38 can be located between a coating medium channel main section 24 and a coating medium channel end section 26. Further, the coating medium channel 24-26 can also include a coating medium distribution channel 25, which can be configured and intended to ensure an even distribution of the coating medium over a whole length 17 of the slot of the die 16. In this context, the coating medium main section can also include several coating medium tubes 27, as it can be seen in figures 2a and b. The several coating medium tubes 27 can be distributed over a longitudinal region of the first and second slot die parts.

[0048] In one preferred embodiment, the closure mechanism 28', 38' and the coating medium supply system 22 can be located in the first slot die part 12, as it is exemplarily shown in Figures 1 a and c. However, a surface portion of the second slot die part 14 facing the first slot die part 12 can contribute to forming the coating medium channel end section 26.

[0049] In the embodiments presented in figure 1, the at least one closing element 28, 34, 38 is in a supply position, in which the coating medium channel 24-26 allows a flow of coating medium from the reservoir to the slot of the die. However, the at least one closing element 28, 34, 38 can also be transferred into a closing position, in which the at least one closing element closes the coating medium channel 24-26.

[0050] In the embodiment illustrated in Figures 1a and 2a, the at least one closing element 28 may be a rotatable shaft 28 including one or more through holes 30. As presented, the one or more through holes 30 can overlap with both, the coating medium channel main section 24 and the coating medium channel end section 26 in the supply position. In the closing position not shown the one or more through holes can be free of overlap with at least one of said coating medium channel main and coating medium channel end sections 24, 26. The rotatable shaft 28 can be transferred from the supply position to the closing position by rotating it in one of directions denoted by reference sign 32. Additionally a sealingly engagement between the at least one closing element 28 and the first slot die part 12 might be of importance in order to prevent coating medium from flowing around the rotatable shaft 28.

[0051] In the embodiment illustrated in Figures 1c, the at least one closing element 34 may be a rotatable shaft 34 having at least one groove 35 in its circumferential surface. Figure 1c presents the at least one closing element 34 in the supply position, in which the groove 35 can overlap with both, the coating medium channel main section 24 and the coating medium channel end section 26. In the closing position not shown the groove 35 can be free of overlap with at least one of said coating medium channel main and coating medium channel end sections 24, 26. The rotatable shaft 34 can be transferred from the supply position to the closing position by rotating it in one of the directions denoted by reference sign 36. A portion of the rotatable shaft being free of a groove could be in a sealingly engagement with the first slot die part 12 in order to prevent coating medium from flowing around the rotatable shaft 34 at said portion.

[0052] It should be stated that the slot die 10 presented in Figure 2a can also be equipped with a rotatable shaft 34 having grooves 35 as presented in Figure 1c instead of the presented rotatable shaft 28 including one or more though holes 30.

[0053] In the embodiment illustrated in Figures 1b and 2b, the at least one closing element 38 may be a plunger 38. The plunger 38 can be transferred from the supply position to the closing position by moving it in a direction denoted by reference sign 40. As it can be seen in Figure 2b, the coating medium supply system 22 can further include a volume compensation element 42 presented as volume compensation plunger 42. The volume compensation element 42 can be moved in the direction denoted by reference sign 44 so that the volume occupied by a rod 39 of the plunger 38 can be compensated in order to control the coating medium feed in the coating medium channel 24-26. This means, during the transfer of the plunger 38 in the supply position, the volume displaced by the rod 39 of the plunger 38 can decrease, and during the transfer of the volume compensation element 42 in a first position, the volume occupied by the volume compensation element 42 can increase. And, vice versa, during the transfer of the plunger 38 in the closing position, the volume displaced by the rod 39 of the plunger 38 can increase, and during the transfer of the volume compensation element 42 in a second position, the volume occupied by the volume compensation element 42 can decrease. Thus, coordinated movements of both, the plunger and the volume compensation element 42, can on the one hand side prevent that coating medium unwantedly leaves the slot of the die 16 and on the other hand that the pressure conditions inside the coating medium channel 24-26 are substantially stable during a coating process.

[0054] Generally, the at least one closing element 28, 34, 38 can be divided into a plurality of regions adjacently arranged and separately transferable between the closing and supply positions so that the at least one closing element 28, 34, 38 is in an intermediate position. This means, in such an intermediate position some of said plurality of regions of the at least one closing element 28, 34, 38 can allow the coating medium to pass the coating medium channel 24-26, preferably allow a flow connection between the coating medium channel main section 24 and the coating medium channel end section 26, whereas others of said plurality of regions of the at least one closing element 28, 34, 38 do not. For example, the rotatable shaft 28, 34 can be divided into a plurality of rotatable shafts adjacently arranged and individually rotatable. In case of the plunger 38 as the at least one closing element, the plunger 38 can be divided into a plurality of plungers, each of which can be moved in the direction denoted by reference sign 40, as shown in figure 2b.

[0055] Further, each of the rotatable shafts 28, 34 can be transferred in one or more intermediate positions by changing its rotation angle by rotating it in a respective one of the directions denoted by reference signs 32, 36. For example, the one or more through holes 30 can have different orientations, so that depending on the rotation angle of the rotatable shaft 28 coating medium is allowed to pass some of the one or more through holes 30, but others not. Possible arrangements of the one or more through holes 30 are presented in Figure 3, wherein Figure 3a is a cross-sectional view of a through hole 30 allowing a passage of coating medium from the coating medium channel main section 24 to the coating medium channel end section 26 only at one rotation angle of the rotational shaft 28, whereas the through holes 30 presented in Figures 3b and c allow a passage of coating medium at two different rotation angles of the rotational shaft 28. One rotational shaft can include one kind of through holes 30 but can also include different kinds of through holes, which can be arranged in any desired sequence along a longitudinal extension of the rotatable shaft 28.

[0056] The at least one groove 35 of the rotational shaft 34 can have a profile at its circumferential surface allowing a transfer of the rotational shaft 34 into one of the one or more intermediate positions. Such profiles are exemplarily shown in rolled-up states in Figures 4a and b. The profile presented in figure 4a has a groove 35 in a shape of a triangle. This means, depending on the rotation angle of the rotational shaft 34, some regions of the rotational shaft 34 close the coating medium channel 24-26 and others can allow a passage of the coating medium. An exemplarily profile allowing the coating medium to pass the coating medium channel only in one rotation angle is shown in Figure 4b. One rotational shaft can include one kind of profile but also different kinds of profiles, which can be arranged in any desired manner.

[0057] In the specific embodiment, schematically shown in figure 5, the slot die 10 can comprise a slot length adjusting element 46. The slot length adjusting element 46 can be located at one longitudinal side of the slot of the die 16 or at both longitudinal sides thereof. The slot length adjusting tool 46 can be moved in directions denoted by reference sign 48, which can be coincide with the longitudinal extension of the slot of the die 16, wherein a movement in the inward direction decreases the length 17 of the slot of the die 16.

[0058] Again, with reference to figures 1 a to c, the first or/and the second slot die parts 12, 14 can have a tapered shape and may have a pointed end, when viewed in a cross-sectional view transversal to the longitudinal extension of the slot of the die 16. Each of the first and the second slot die parts 12, 14 can have a respective slot defining edge 50. Preferably, the slot defining edges 50 extending parallel to each other define a plane. All surface points of outer surfaces 52 of the first and the second slot die parts 12, 14 can be spaced apart from said plane. It is further possible that the first and second slot die parts 12, 14 form an angle 53 between their outer surfaces 52, which is smaller than or equal to 160°, preferably smaller than or equal to 120°, more preferably smaller than or equal to 60°, but preferably greater than or equal to 15°.

[0059] Figure 6 illustrates a coating arrangement 54 comprising a slot die 10, and a distance control device 56. The distance control device 56 can comprises a pair of distance rollers 56, one of which is visible in figure 6. The distance control device 56 includes at least one distance sensor 58 detecting a distance 60 of the slot of the slot die 16 to a surface to be coated 62 and at least one actuator, which can be a force acting perpendicular to said surface 62 and ensuring a contact between the distance sensor 58 and said surface 62. Such a force can be gravity or/and an external applied force, for example, by an actuator of the slot die 10, as exemplarily shown in figure 6 by an arrow denoted by reference sign 64.

[0060] The coating arrangement 54 can further comprise a bearing arrangement 66, as it can be seen in figures 5 and 7c. The bearing arrangement 66 may be configured and intended to allow a tilting of the slot die 10 and preferably to allow a movement of the slot die 10 in a vertical direction 68. In other words, the bearing arrangement 66 allows an adaption of the alignment of the slot of the die 16 according to the sensed profile of the surface to be coated 62.

[0061] A cleaning device 70 for a slot die 10 comprising a cleaning surface 72 and an actuator not shown is presented in figures 7a and b. The actuator of the cleaning device 70 is configured to reciprocate the cleaning surface 72 in length directions denoted by reference sign 74 being parallel to the longitudinal extension of the slot of the die 16, wherein during reciprocating movement in said directions 74 the cleaning surface 72 is in contact with end portions of first and second slot die parts 12, 14 forming the slot of the die 16.

[0062] During a cleaning process of said end portions, the slot die 10 is in a fixed position, presented in figure 7c with dashed lines, whereas the solid lines show the slot die in an operation position. The actuator is configured and intended to bring the cleaning surface in contact with the end portions of the first and second slot die parts 12, 14 when the slot die 10 is in the fixed position. Therefore, the actuator can be moved along a direction denoted in figure 7a by reference sign 76.

Claims

1. Slot die, preferably a wide-slot die, configured and intended to be operated in an environment with negative pressure.

2. Slot die according to claim 1,
characterized in that the slot die comprises:

- a first slot die part and a second slot die part located opposite to the first slot die part, the first slot die part and the second slot die part therebetween forming a slot of the die,

- a coating medium supply system configured and intended to provide a feed of coating medium to the slot of the die and including a coating medium reservoir and a coating medium channel connecting the coating medium reservoir with the slot of the die, the coating medium being a liquid or paste like medium, and

- a closure mechanism configured and intended to reduce the amount of coating medium flowing out of the slot of the die after the feed of coating medium has been stopped.

3. Slot die according to one of the claims 1 or 2,
characterized in that the closure mechanism includes at least one closing element which is arranged within the coating medium channel and is transferable between at least two positions, namely a closing position, in which the at least one closing element closes the coating medium channel and a supply position, in which the coating medium channel allows a feed of medium.

4. Slot die according to claim 3,
characterized in that the at least one closing element is located between a coating medium channel main section and a coating medium channel end section.

5. Slot die according to any of the preceding claims,
characterized in that a width of the slot of the die is defined by a spacer element mounted between the first and second slot die parts.

6. Slot die according to any of the preceding claims,
characterized in that the slot die further comprises a slot length adjusting element configured and intended to adjust the length of the slot of the slot die.

7. Slot die according to any of the preceding claims,
characterized in that slot defining edges of the first and second slot die parts extending parallel to each other define a plane, all surface points of outer surfaces of the first and the second slot die parts being spaced apart from said plane.

8. Slot die according to any of the preceding claims,
characterized in that the closure mechanism and the coating medium supply system are located in the first slot die part.

9. Slot die according to any of the claims 3 to 8,
characterized in that the at least one closing element is a rotatable shaft including one or more through holes, which in the supply position overlap with both, the coating medium channel main section and the coating medium channel end section, and in the closing position are free of overlap with at least one of said coating medium channel main and coating medium channel end sections.

10. Slot die according to claim 9,
characterized in that the circumferential surface of the rotatable shaft is sealingly engaged with at least one of the first and second slot die parts.

11. Slot die according to any of the claims 3 to 8,
characterized in that the at least one closing element is a rotatable shaft having at least one groove in the circumferential surface, which in the supply position overlap with both, the coating medium channel main section and the coating medium channel end section, and in the closing position is free of overlap with at least one of said coating medium channel main and coating medium channel end sections.

12. Slot die according to one of the claims 3 to 8,
characterized in that the at least one closing element is a plunger.

13. Slot die according to claim 12,
characterized in that the coating medium supply system further includes a volume compensation element configured and intended to compensate the volume occupied by a rod of the plunger, wherein the volume compensation element is transferable between a first position and a second position, the first position being associated with the supply position of the at least one closing element and the second position being associated with the supply position of the at least one closing element.

14. Coating arrangement comprising a slot die, preferably a slot die according to claim 1 and optionally according to any of the preceding claims, and further comprising a distance control device, said distance control device including at least one distance sensor configured and intended to detect a distance of the slot of the slot die to a surface to be coated and at least one actuator configured and intended to control a distance between the slot of the slot die and the surface to be coated.

15. Cleaning device for a slot die, preferably according claim 1 and optionally according to any of the preceding claims, comprising a cleaning surface and an actuator, wherein the actuator is configured to reciprocate the cleaning surface in the length direction of the slot die, wherein during reciprocating movement the cleaning surface is in contact with end portions of first and second slot die parts forming the slot of the die.

Drawing