Apparatus and Method for Processing Shear Sensitive Coating Compositions

Abstract

The invention relates to a device for processing shear-sensitive coating compounds, with a transfer roller and a doctor blade, in particular a comma doctor blade, which are spaced apart from one another to form a coating nip, the device further having an outlet nozzle for dosing a coating compound, the outlet nozzle facing a lower nip opening of the coating nip with its nozzle opening, wherein the device comprises a forced conveying system via which a coating compound is dosed into the coating nip, the transfer roller and the doctor blade being arranged next to each other, so that the coating nip is permeable in the vertical direction (z), wherein the coating nip is between 30 and 400 m and the outlet nozzle is an outlet of a rinsing chamber arranged below the coating nip. A corresponding method is also described.

Claims

1. A method for processing shear-sensitive coating compounds, comprising: providing a rotationally driven transfer roller and a doctor blade, wherein the transfer roller and the doctor blade are arranged next to each other such that a coating nip formed by the transfer roller and the blade is permeable in a vertical direction (z); and dosing a coating compound, using an outlet nozzle and a forced conveying system, into the coating nip, wherein a nozzle opening of the outlet nozzle is mounted contact-free in front of a lower nip opening of the coating nip.

2. The method of claim 1, wherein the transfer roller and the doctor blade are spaced apart from each other to form the coating nip.

3. The method of claim 2, wherein the coating nip is between 30 and 400 m.

4. The method of claim 1, wherein the coating compound is flushed in the vertical direction (z) from below into the coating nip.

5. The method of claim 4, wherein the coating compound is flushed into the coating nip without lateral limiter, allowing excess coating compound to flow off.

6. The method of claim 1, wherein a discharge gap is formed between a boundary wall of the outlet nozzle on an outer side of boundary wall facing the transfer roller and the transfer roller.

7. The method of claim 1, wherein the outlet nozzle is an outlet of a rinsing chamber.

8. The method of claim 7, further comprising: collecting coating compound flowing outside of the rinsing chamber into a collecting trough and pumping the collected coating compound back into the rinsing chamber.

9. The method of claim 8, further comprising: transporting the collected coating compound from the collecting trough via an outlet to a coating compound storage tank and pumping the coating compound from the storage tank to the rinsing chamber, using a pump.

10. The method of claim 9, wherein the pump is an eccentric screw pump.

11. The method of claim 9, wherein the pump is arranged in a the storage tank.

12. The method of claim 8, wherein the rinsing chamber is arranged above the collecting trough.

13. The method of claim 7, wherein the rinsing chamber on an outer side facing the transfer roller has a recess free discharge contour for the coating compound.

14. The method of claim 7, wherein the rinsing chamber is sealed against the doctor blade 2.

Description

[0032] Further details of the invention are explained using the figures below. Here shows:

[0033] FIG. 1 shows a state-of-the-art device;

[0034] FIG. 2 shows a schematic cross-sectional view of an exemplary embodiment of a device according to the invention;

[0035] FIG. 3 a schematic cross-sectional view of another exemplary embodiment of a device according to the invention;

[0036] FIG. 4 a schematic cross-sectional view of a detailed representation of the injection area; and

[0037] FIG. 5 shows a perspective view of the back of the flushing device.

[0038] FIG. 1 shows an exemplary device for processing coating compounds 100 such as dispersions, e.g. adhesives, as known from the state of the art. Here, a mating roller 17, a transfer roller 1 and an outlet nozzle 4 for dosing a coating compound 100 are arranged one above the other in the vertical direction z, with the outlet nozzle 4 with its nozzle opening 5 facing a lowest position of the transfer roller 1 and arranged directly adjacent to it and thus sealing against it. In particular, the outlet nozzle 4 is sealed off from the environment of the device by means of the blades 2 arranged on opposite sides of the outlet nozzle 4 in the direction of rotation of the transfer roller 1. In this process, the coating compound 100 is applied to the circumference of the transfer roller via the outlet nozzle 4 with the aid of an overpressure relative to atmospheric pressure and is brought to a desired coating thickness with the aid of the opposite blades 2, whereby the coating compound 100 is subjected to high shear rates, which leads to agglomerates in the coating compound 100.

[0039] The device shown has the disadvantage that for effective application of the coating compound 100 on the transfer roller 1, the coating compound 100 must be dosed under a comparatively high pressure onto the transfer roller 1, which leads to the formation of the mentioned agglomerates in the coating compound 100, which impairs the quality of the coating on the transfer roller 1 and thus also reduces the quality of the coating compound layer produced on the material web 200.

[0040] To solve this problem, a device as shown in FIG. 2 can be used. This device has a transfer roller 1 and a doctor blade 2, which is designed as a comma doctor. The transfer roller 1 and the doctor blade 2 are arranged horizontally next to each other forming a coating nip 3. The coating nip 3 can have a minimum nip width of 50 m, for example. Due to the horizontal arrangement of the transfer roller 1 and the doctor blade 2, a passage direction of the coating nip 3 extends essentially in vertical direction z. For the realization of the invention, however, it is not essential that the transfer roller 1 and the doctor blade 2 are arranged exactly horizontally next to each other. It is rather important that the resulting coating nip 3 between transfer roller 1 and doctor blade 2 has a vertical component in its direction of extension. In any case, however, it must be avoided that transfer roller 1 and doctor blade 2 are arranged vertically one above the other, as is the case with the state of the art devices shown in FIG. 1.

[0041] The device has an outlet nozzle 4 for dosing the coating compound 100, which with its nozzle opening 5 faces a lower nip opening 6 of the coating nip 3. The coating compound 100 is dosed from below into the coating nip 3 via a forced conveying system 7 of the device. In particular, the nozzle opening 5 is positioned in front of the lower nip opening 6 without contact, so that the nozzle opening 5 is in contact with the environment of the device, i.e. with atmospheric pressure. Even a slight overpressure of the coating compound 100 is sufficient to flush the coating compound 100 via the nozzle opening 5 into the coating nip 3. In particular, the nozzle opening 5 can be aligned in vertical direction so that the pressure at which the coating compound 100 is supplied via the nozzle opening is adjusted in such a way that effective wetting of the coating nip with the coating compound 100 is achieved. Pressurization of the coating compound 100 beyond this is not necessary and should be avoided in order to prevent the formation of agglomerates in the coating compound 100.

[0042] The outlet nozzle 4 is located at the upper end of a rinsing chamber 8, which is located below the coating nip 3. Via an inlet 9, the coating compound 100 is fed into a forced feed system 7, which has a pump 13. In order to achieve the lowest possible compression of the coating compound 100 within the pump 13, the pump 13 is preferably an eccentric screw pump.

[0043] On its outside and facing the transfer roller 1, the rinsing chamber 8 has a recess free drain contour 11, over which excess coating compound can flow off unhindered. In order to facilitate the flow of the excess coating compound over the recess free drain contour 11 of the rinsing chamber 8, it may be provided that the rinsing chamber 8 is sealed against the doctor blade 2.

[0044] The rinsing chamber 8 is arranged above a collecting trough 12 in which the excess coating compound 100, which flows back from the coating nip 3 via the drain contour 11 of the rinsing chamber 8, is collected.

[0045] As shown in FIG. 3, it can be provided that the coating compound 100 flowing out of the outside 10 of the rinsing chamber 8 into the collecting trough 12 is pumped back into the rinsing chamber 8. Flushing the coating nip 3 from below favors a short residence time of the coating compound in the coating nip 3 and thus good preservation of the dispersive properties of the coating compound 100. Since the coating compound 100 remains in constant motion and is exposed to only comparatively slight overpressures relative to atmospheric pressure, the formation of agglomerates is effectively suppressed. The coating compound 100 can be transported from the collecting trough 12 via an outlet 18 to a coating compound storage tank 14 and from there via the inlet 9 back to the rinsing chamber 8. The pump 13 for transporting the coating compound 100 from the storage tank 14 to the rinsing chamber 8 can be located in the coating compound storage tank 14.

[0046] The transfer roller 1 can, for example, be a chrome-coated steel roller. The mating roller can have a jacket of EPDM rubber with a hardness of 65 Shore A. The material web 200 on which the coating compound layer 100 is applied can, for example, be a web of siliconized paper. The gap between doctor blade 2 and transfer roller 1 can be between 30 and 400 m, for example. The circulation speed of transfer roller 1 can be 5 to 80 m/min. The coating compound layer 100 applied to the material web 200 can have a basis weight of, for example, 30 g/m.sup.2 to 200 g/m.sup.2. The material data and numerical values mentioned are only exemplary and are not intended to limit the subject matter of the invention to corresponding embodiments.

[0047] FIG. 4 shows an embodiment of the invention, which is shown in side view and illustrates the spraying area with transfer roller 1, comma doctor blade 2 and a spraying device arranged centrally in between. The arrow on the transfer roller 1 indicates its direction of rotation. In particular, the flushing device has a nozzle 19, which has an inlet 9 below the coating nip 3, through which coating compound is fed through a distributor plate 23 into the rinsing chamber 8. The coating compound is fed into the inlet at the side, i.e. parallel to the axial directions of the rollers. Preferably, the coating compound is fed from both sides in the area of the front sides of the transfer roller 1 and the doctor blade 2. The distributor plate 23 has several spaced openings perpendicular to the image plane through which the coating compound enters the rinsing chamber 8. The coating compound is first distributed evenly across the width of the sheet and then via the large rinsing chamber 8. The pressure in the rinsing chamber 8 corresponds approximately to the pump pressure of the pump 13. The coating compound is then conveyed in the direction of the coating nip 3 and moves along the tapering contour of the rinsing chamber 8 in the direction of the outlet nozzle 4, which is formed on one side by the doctor blade 2 and on the other side by the horizontally adjustable inner side of the nozzle tip 20. The spray chamber 8 is sealed towards the doctor blade 2 by a flexible gasket 23 so that no overflow occurs at this point. The converging gap between doctor blade 2 and the flushing device produces an increase in the speed of the compound. This causes the speed to approach the surface speed of the transfer roller 1. The arrows in the diagram illustrate the direction of movement of the coating compound. The dotted horizontal arrow indicates the direction of movement of the spraying device.

[0048] The nip pressure between the doctor blade 2 and transfer roller 1 must be lower than in the discharge nip 16 between the nozzle tip 20 and the transfer roller 1. As a result, the mass moves with increasing speed into the coating nip 3. The differential speed of the mass to the surface of the transfer roller 1 is so low that the mass is not subject to shear and thus not to a change in viscosity. This results in a uniform coating appearance. In the area of the nip seal 21, the theoretically high flow velocity generates a resistance that settles at the total pressure of the purge area. It must be ensured that the nip seal 21 does not touch the transfer roller 1, but is positioned at a distance of 0.1 mm to 0.2 mm from it. The gap between the nip seal 21 and the transfer roller 1 is therefore very small, so that the speed in this area would have to be very high to allow the downward flow to pass. The transfer roller 1, which rotates in the direction of the discharge gap 16, reduces the leakage, i.e. the coating compound that runs over discharge gap 16 and nip seal 21 in the direction of the outside 10 is reduced by counter-rotating movement of transfer roller 1.

[0049] FIG. 5 shows a perspective view of the back of the spraying device. The nozzle tip 20 is located on the top side, which initially has a boundary wall 15 in the downward direction, which forms the discharge gap 16 together with the transfer roller 1. Below this, the gap is tapered to 0.1-0.2 mm by the nip seal. Coating compound that overcomes the nip seal 21 runs over the drain contour 11 of the outside 10 of the flushing device back into the collecting trough 12. Side walls laterally delimit the flushing device, which each have seals 24, which comprise a front part 24a, which faces the transfer roller 1, and a rear part 24b, which faces the rinsing chamber 8 and the comma blade 2 respectively. The washing chamber 8 is only sealed over the rear section 24b towards the doctor blade 2. The front section 24a of the seal 24, on the other hand, is stepped over the rear section 24b so that the front section 24a has no contact with the transfer roller 1 and is leaky. Overflowing coating compound is returned to the mass container via the collecting trough 12.

[0050] The features of the invention disclosed in the above description, in the drawings as well as in the claims can be essential for the realization of the invention either individually or in any combination.

LIST OF REFERENCE SIGNS

[0051] 1 Transfer roller [0052] 2 Doctor blade [0053] 3 Coating nip [0054] 4 Outlet nozzle [0055] 5 Nozzle opening [0056] 6 Nip opening [0057] 7 Forced conveying system [0058] 8 Rinsing chamber [0059] 9 Inlet [0060] 10 Outside [0061] 11 Drain contour [0062] 12 Collecting trough [0063] 13 Pump [0064] 14 Coating compound storage tank [0065] 15 Boundary wall [0066] 16 Discharge gap [0067] 17 Mating roller [0068] 18 Outlet [0069] 19 Nozzle [0070] 20 Nozzle tip [0071] 21 Nip seal [0072] 22 Distributor plate [0073] 23 flexible gasket [0074] 24a lateral seal front part [0075] 24b lateral seal rear part [0076] 100 Coating compound [0077] 200 Material web [0078] z Vertical direction