WIDE SLOT DIE AND METHOD FOR OPERATING A WIDE SLOT DIE

Abstract

The present disclosure relates to a wide slot die for applying a fluid provided with particles, having a die body. The die body comprises a die interior chamber for receiving the fluid provided with particles. The fluid provided with the particles can be discharged via a die gap, which is bounded by two walls, onto a substrate which is in motion relative to the wide slot die in a transport direction. A vibration device is mechanically coupled to the die body in order to vibrate the die gap and the fluid located in the die interior chamber and provided with the particles. The vibration device is adapted to excite the die body with an upper limit frequency of at most 1 kHz.

Claims

1. A wide slot die for applying a fluid provided with particles, which comprises: a die body defining a die interior chamber configured to receive a fluid provided with particles a die gap defined by two walls, wherein a fluid provided with particles can be discharged from the die interior chamber onto a substrate which is in motion relative to the wide slot die in a transport direction, and; a vibration device which is mechanically coupled to the die body in order to vibrate the die gap and the fluid located in the die interior chamber and provided with the particles, wherein the vibration device is adapted to excite the die body with an upper limit frequency of 1 kHz.

2. The wide slot die according to claim 1, wherein the vibration device is adapted to excite the die body with a lower limit frequency of at least 1 Hz.

3. The wide slot die according to claim 1, wherein the mechanical amplitude of the vibration device in relation to the nominal diameter of the particles contained in the fluid is greater than or equal to 0.1.

4. The wide slot die according to claim 1, wherein the mechanical amplitude of the vibration device is at most 5 mm.

5. The wide slot die according to claim 1, wherein the mechanical amplitude of the vibration device acts in a transverse direction of the die body corresponding to the transport direction.

6. The wide slot die according to claim 1, wherein the mechanical amplitude of the vibration device acts in a height direction of the die body.

7. The wide slot die according to claim 1, wherein the fluid provided with particles is structurally viscous.

8. The wide slot die according to claim 1, wherein the die gap has a width of between 10 mm and 5 m in a width direction extending transversely to the transport direction.

9. The wide slot die according to claim 1, wherein the die gap has a slot width between 10 μm and 2.5 mm.

10. The wide slot die according to claim 1, further comprising a fastening device mechanically fixed to the die body via damper elements.

11. A method of operating a wide slot die for applying a fluid provided with particles, comprising: providing a wide slot die having a die body, wherein the die body defines a die interior chamber configured to receive a fluid provided with particles, a die gap defined by two walls, wherein a fluid provided with particles can be discharged onto a substrate in motion relative to the wide slot die in a transport direction, and having a vibration device which is mechanically coupled to the die body in order to vibrate the die gap; and actuating the vibration device such that the die body is excited with an upper limit frequency of at most 1 kHz.

12. The method according to claim 11, wherein the vibration device is actuated such that the die body is excited with a lower limit frequency of at least 1 Hz.

13. The method according to claim 11, wherein the mechanical amplitude of the vibration device is set to be greater than or equal to 0.1 in relation to the nominal diameter of a fluid provided with particles.

14. The method according to claim 13, wherein the mechanical amplitude of the vibration device is set to be at most 5 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 shows a cross-section through a wide slot die according to the present disclosure, which is mounted on a fastening device;

[0033] FIG. 2 shows a side view of the wide slot die of FIG. 1;

[0034] FIG. 3 shows a cross-section along line III-III through the wide slot die of FIG. 2, wherein a vibration device is mechanically coupled to the wide slot die; and

[0035] FIG. 4 shows a partial cross-section through the fastening device of the wide slot die of FIG. 2.

DETAILED DESCRIPTION

[0036] FIG. 1 shows a wide slot die 1 according to the present disclosure for applying a fluid provided with particles onto a substrate 20, which is arranged below wide slot die 1. The distance between substrate 20 and wide slot die 1, as well as the components of wide slot die 1, are not shown to scale for drawing reasons. The fluid is hereinafter referred to as the coating fluid. Next to wide slot die 1, a coordinate system is shown in which q denotes a transverse direction, h denotes a height direction, and b denotes a width direction of wide slot die 1. The transverse direction q extends in a direction corresponding to a transport direction TR of substrate 20. The width direction b extends in a plane defined by the transverse and width directions transverse to the transport direction TR.

[0037] The coating fluid contains one or more different liquids, e.g. one or more solvents, and one or more particulate solids. Concentration, size, density and shape of particles in the coating fluid are selected according to a present application. Commonly encountered cases of application are shown at the end of the description.

[0038] Wide slot die 1 comprises a die body 2 which, for example, is formed from two die halves 3, 4. A die interior chamber 6 is formed between die halves 3, 4, which in the cross-sectional view shown is only exemplarily in the shape of a circle. A die foil 5 of predetermined thickness is arranged between die halves 3, 4. This defines the slot width of a die gap 7 in the lower region of die body 2 between opposing walls 7a, 7b of respective die halves 3, 4 and, together with die halves 3, 4, encloses the fluid located in die interior chamber 6. Die foil 5 has a recess for die interior chamber 6 and die gap 7 corresponding to the required coating width in the width direction b. The slot width of die gap 7 thus corresponds to the thickness of die foil 5. In the case of application, the slot width is selected such that the wide slot die essentially allows the desired uniform distribution by means of sufficient pressure drop of the die gap. However, the minimum die gap width is limited by the particles present in the fluid. In this case, the slot width is always at least slightly larger than the particle size of the particles contained in the coating fluid. Preferably, die gap 7 has a slot width of between 10 μm and 2.5 mm.

[0039] The coating fluid located in die interior chamber 6, which is conveyed via one or more inlets not explicitly shown, can be discharged through a die gap opening 7L onto a substrate 20 moving relative to wide slot die 1 in transport direction TR. Substrate 20 is a flat substrate, for example a foil made of plastic, aluminum or paper or another material to be coated. The distance between substrate 20 and a die lip 9 facing the side of substrate 20 to be coated can be between a few micrometers and a few centimeters.

[0040] Die gap 7 can have a width of between 10 mm and 5 m in the width direction b, depending on the selected application.

[0041] The selection of die gap 7, essentially the gap length (i.e., the length required by the fluid from the inner chamber to the exit) and the gap width, depends on the coating fluid and the desired process and operating conditions. The coating fluid is applied at the exit point between two die lips 9 and substrate 20. For a selected operating point, a uniform distribution caused predominantly by the viscous forces can thus be achieved with a wide slot die. A large part of the resulting pressure drop is caused by the fluid flowing through die gap 7, which leads to large pressure forces from inside to the die body. This pressure drop is specifically adjusted to achieve a uniform distribution, but is technically limited by the elasticity values of the materials of the die body. Excessively high viscosities can thus lead to a deflection of the die gap and subsequently result in an influence on the uniform distribution.

[0042] Die body 2 is mechanically connected to a fastening device 10. Fastening device 10 comprises a first retaining element 11 and a second retaining element 12. First retaining element 11 has a retaining extension 11F. Second retaining element 12 has an engagement extension 12F corresponding thereto. Second retaining element 12 is mechanically connected to die half 4, for example. The second retaining element with die body 2 attached thereto can be brought into engagement with first retaining element 11 by engagement extension 12F. First and second retaining elements 11, 12 are mechanically connected to each other by a fixing element 13 which clamps engagement extension 12F and retaining extension 11F. The illustrated retainer is thus only exemplarily designed as a so-called dovetail. Which retainer is actually selected is not specified in more detail.

[0043] In order to prevent a transmission of vibrations from second retaining element 12 to first retaining element 11 by a vibration device 16 described in more detail below, a damper element 14 is provided between first retaining element 11 and second retaining element 12, and a damper element 15 is provided between second retaining element 12 and fixing element 13.

[0044] In each of FIG. 2 to FIG. 4, which illustrate different details of wide slot die 1 of FIG. 1, vibration device 16 is shown which is mechanically coupled to die body 2. Vibration device 16, which is operated by compressed air, hydraulically or electrically, for example, is arranged on a side of die body 2 facing away from die gap 7. The mechanical attachment can be made, for example, by means of screws and the like.

[0045] Vibration device 16 is adapted to cause die body 2 and thus die gap 7 and the coating fluid in die interior chamber 6 to vibrate. Vibration device 16 is designed such that the mechanical amplitude is generated primarily in the transverse direction q and the height direction h of die body 2. Alternatively or additionally, a mechanical amplitude can also be generated by the vibration device in the width direction b of die body 2. Preferably, vibration device 16 is adapted and operated such that the mechanical amplitude acts both in the transverse direction q and in the height direction h.

[0046] The mechanical amplitude of vibration device 16 is greater than or equal to 0.1 in relation to the nominal diameter of the particles contained in the fluid. Preferably, the mechanical amplitude of vibration device 16 is at most 5 mm. In the case of particle size distributions, the amplitude can be determined by the largest particle diameter. However, this does not exclude the selection of smaller amplitudes corresponding to the particle size distribution range from the application of the process principle, since an excitation of particle fractions can equally serve the purpose. In this case, the vibration device is operated at a frequency in a range between 1 Hz and 1 kHz. The optimum frequency and the exact mechanical deflection of an application depend on a plurality of parameters. The shape and material of wide slot die 1, the shape of die interior chamber 6 and die gap 7, the coating fluid and its flow all play a role. The application point at die gap opening 7L and the two die lips 9 are typically wetted with the coating fluid during coating. In interaction with the relative velocity of substrate 20, this creates a fluid contingent upstream of the die gap that is enclosed by the contact with die lip 9 and is also excited, and thus, also determines the process.

[0047] Vibration device 16 introduces kinetic energy into die body 2 and the coating fluid by means of mechanical amplitudes. This allows to stabilize the fluid by means of the additional momentum exchange and to homogenize it in connection with the flow. Furthermore, agglomerates of particles contained in the coating fluid can be broken up and sedimentation zones in die interior chamber 6 can be avoided. Likewise, the buildup of particle agglomerates can be avoided by the kinetic energy introduced. By means of vibration device 16, it is thus possible to increase the kinetic energy components without significantly influencing the process stability of the coating process.

[0048] FIG. 3 and FIG. 4 each show different partial cross-sections through wide slot die 1 of FIG. 2. While FIG. 3 shows a cross-section through die body 2 (with die gap 7 not explicitly shown in this illustration), FIG. 4 shows a partial cross-section through fastening device 10, with die body 2 shown uncut.

[0049] The process-technical basis of the uniform full-surface application of the coating fluid by means of wide slot die 1 is the pressure drop generated in die gap 7. The pressure drop is essentially created by die gap 7, the connection of die interior chamber 6 with die gap opening 7L and the exit point of the coating fluid from die gap opening 7L. The pressure drop for a sufficient uniform distribution on substrate 20 can be achieved by selecting die foil 5 whose thickness is equivalent to the slot width of the exit gap, i.e., die gap opening 7L. Substantially, the pressure drop is limited by the mechanical deflection of wide slot die 1 due to pressure forces.

[0050] The achievement of a sufficiently large pressure drop, and thus, a good transverse distribution or uniformity of the layer to be produced on the substrate 20 results from the relationship between the desired application speed, the material properties of the coating fluid and, to a decisive extent, the die gap parameters. By using vibration unit 16, the particle size can be selected larger in relation to the die gap. It is thus possible to select smaller gap thicknesses for a coating fluid with particles. A wide slot die thus allows a wider range of practicable wet film thicknesses. The use of the vibration unit also results in an influence on the stability of the homogeneity of the coating fluid, which increases the range of achievable processing speeds. The vibrations have a homogenizing influence on the creation and the characteristic of the boundary layer in the die gap, which is advantageous in connection with the process stability and manufacturing accuracy of the die gap of the wide slot die. The homogeneity of the wet film on the substrate can thus be optimized in width and length by the introduced mechanical vibrations in addition to the influence of the pressure drop.

[0051] It has been found that an optimum application of the coating fluid onto substrate 20 can be achieved by setting the frequency of the flow not in the ultrasonic range but well below it, preferably with an upper limit at 1 kHz. The set frequency, in particular in conjunction with a suitably selected mechanical amplitude, enables an introduction of kinetic energy into die body 2. This allows an improvement of the momentum exchange in the coating fluid, and thus, has a homogenizing and stabilizing effect in interaction with the flow. This behavior allows to reduce sedimentation zones and/or to break up particle agglomerates with the support of the shear forces of the flow or to prevent their formation for entry into die gap 7.

[0052] The die described above can be used in a wide range of different applications. Preferably, the wide slot die is adapted to all process and operating conditions as far as possible. The following applications are possible, for example:

Battery Production

[0053] Using reel-to-reel equipment with integrated drying, slurry is coated on thin copper and aluminum foils with thicknesses of about 100 μm. The copper/aluminum foil forming the substrate is passed over a roller. The wide slot die is positioned against the roller by means of an applicator, e.g. in the so-called 9 o'clock position, wherein the wide slot die is positioned horizontally and centrally on the coating roller. The distance is approximately twice the wet film thickness, which places high demands on the concentricity of the roller, the tolerances of the die lip and the substrate. Battery slurries comprising water or solvent, carbon particles of various particle size ranges, binding agents, viscosity modifiers and active materials for the battery function are applied. The solid mass fractions of the fluids are typically in the range of 30% to 60%. Production speeds are approximately 10 m to 100 m per minute (web speed).

Epoxy Resin UV Coating Application

[0054] Substrates referred to as sheets are coated using a coating table. The die is mounted vertically in an applicator with a downward discharge of the coating fluid. Robot arms can also be used to move the wide slot die. Substrate materials are plastic foils or glass. Wet film thicknesses are in the range of 10 μm. The coating media contain resins, in some cases volatile organic solvents, and more often particulate fractions, e.g. optical functional coatings. The processing is sequential, wherein a drying occurs through the thin layers without a dryer, for example in the case of a UV coating by means of a UV lamp. Production speeds are in the range of 0.01 to 5 m/min of relative speed of the die to the substrate. The requirements for application tolerances are very high in some cases.

Curtain Application

[0055] In addition to methods in which the wide slot die is coating directly very close to the substrate, there is the option of operating the wide slot die at a high mass flow rate so that a curtain is formed at the exit opening. This curtain is a uniform thin falling film of liquid. The curtain falls onto the substrate, which is moved through the curtain. Distances of more than 10 cm are possible. Characteristics of the method are the fast substrate speed enabled by the curtain formation and good traverse distribution properties. Wet film thicknesses in the range of 50 μm and more are possible. The formation and the stability of a curtain are determined by the fluid parameters.

LIST OF REFERENCE SIGNS

[0056] 1 wide slot die [0057] 2 die body [0058] 3 die half [0059] 4 die half [0060] 5 die foil (foil) [0061] 6 die interior chamber [0062] 7 die gap [0063] 7a wall (inner wall of gap) [0064] 7b wall (inner wall of gap) [0065] 7L die gap opening [0066] 9 die lip [0067] 10 fastening device [0068] 11 first retaining element [0069] 11F retaining extension [0070] 12 second retaining element [0071] 12F engagement extension [0072] 13 fixing element [0073] 14 damper element [0074] 15 damper element [0075] 16 vibration device [0076] 20 substrate [0077] TR transport direction [0078] b width direction [0079] q transverse direction [0080] h height direction