Patent ID: 12214373

FIG.1shows an exemplary device for processing coating compounds100such as dispersions, e.g. adhesives, as known from the state of the art. Here, a mating roller17, a transfer roller1and an outlet nozzle4for dosing a coating compound100are arranged one above the other in the vertical direction z, with the outlet nozzle4with its nozzle opening5facing a lowest position of the transfer roller1and arranged directly adjacent to it and thus sealing against it. In particular, the outlet nozzle4is sealed off from the environment of the device by means of the blades2arranged on opposite sides of the outlet nozzle4in the direction of rotation of the transfer roller1. In this process, the coating compound100is applied to the circumference of the transfer roller via the outlet nozzle4with the aid of an overpressure relative to atmospheric pressure and is brought to a desired coating thickness with the aid of the opposite blades2, whereby the coating compound100is subjected to high shear rates, which leads to agglomerates in the coating compound100.

The device shown has the disadvantage that for effective application of the coating compound100on the transfer roller1, the coating compound100must be dosed under a comparatively high pressure onto the transfer roller1, which leads to the formation of the mentioned agglomerates in the coating compound100, which impairs the quality of the coating on the transfer roller1and thus also reduces the quality of the coating compound layer produced on the material web200.

To solve this problem, a device as shown inFIG.2can be used. This device has a transfer roller1and a doctor blade2, which is designed as a comma doctor. The transfer roller1and the doctor blade2are arranged horizontally next to each other forming a coating nip3. The coating nip3can have a minimum nip width of 50 μm, for example. Due to the horizontal arrangement of the transfer roller1and the doctor blade2, a passage direction of the coating nip3extends essentially in vertical direction z. For the realization of the invention, however, it is not essential that the transfer roller1and the doctor blade2are arranged exactly horizontally next to each other. It is rather important that the resulting coating nip3between transfer roller1and doctor blade2has a vertical component in its direction of extension. In any case, however, it must be avoided that transfer roller1and doctor blade2are arranged vertically one above the other, as is the case with the state of the art devices shown inFIG.1.

The device has an outlet nozzle4for dosing the coating compound100, which with its nozzle opening5faces a lower nip opening6of the coating nip3. The coating compound100is dosed from below into the coating nip3via a forced conveying system7of the device. In particular, the nozzle opening5is positioned in front of the lower nip opening6without contact, so that the nozzle opening5is in contact with the environment of the device, i.e. with atmospheric pressure. Even a slight overpressure of the coating compound100is sufficient to flush the coating compound100via the nozzle opening5into the coating nip3. In particular, the nozzle opening5can be aligned in vertical direction so that the pressure at which the coating compound100is supplied via the nozzle opening is adjusted in such a way that effective wetting of the coating nip with the coating compound100is achieved. Pressurization of the coating compound100beyond this is not necessary and should be avoided in order to prevent the formation of agglomerates in the coating compound100.

The outlet nozzle4is located at the upper end of a rinsing chamber8, which is located below the coating nip3. Via an inlet9, the coating compound100is fed into a forced feed system7, which has a pump13. In order to achieve the lowest possible compression of the coating compound100within the pump13, the pump13is preferably an eccentric screw pump.

On its outside and facing the transfer roller1, the rinsing chamber8has a recess free drain contour11, 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 contour11of the rinsing chamber8, it may be provided that the rinsing chamber8is sealed against the doctor blade2.

The rinsing chamber8is arranged above a collecting trough12in which the excess coating compound100, which flows back from the coating nip3via the drain contour11of the rinsing chamber8, is collected.

As shown inFIG.3, it can be provided that the coating compound100flowing out of the outside10of the rinsing chamber8into the collecting trough12is pumped back into the rinsing chamber8. Flushing the coating nip3“from below” favors a short residence time of the coating compound in the coating nip3and thus good preservation of the dispersive properties of the coating compound100. Since the coating compound100remains in constant motion and is exposed to only comparatively slight overpressures relative to atmospheric pressure, the formation of agglomerates is effectively suppressed. The coating compound100can be transported from the collecting trough12via an outlet18to a coating compound storage tank14and from there via the inlet9back to the rinsing chamber8. The pump13for transporting the coating compound100from the storage tank14to the rinsing chamber8can be located in the coating compound storage tank14.

The transfer roller1can, 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 web200on which the coating compound layer100is applied can, for example, be a web of siliconized paper. The gap between doctor blade2and transfer roller1can be between 30 and 400 μm, for example. The circulation speed of transfer roller1can be 5 to 80 m/min. The coating compound layer100applied to the material web200can have a basis weight of, for example, 30 g/m2 to 200 g/m2. 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.

FIG.4shows an embodiment of the invention, which is shown in side view and illustrates the spraying area with transfer roller1, comma doctor blade2and a spraying device arranged centrally in between. The arrow on the transfer roller1indicates its direction of rotation. In particular, the flushing device has a nozzle19, which has an inlet9below the coating nip3, through which coating compound is fed through a distributor plate23into the rinsing chamber8. 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 roller1and the doctor blade2. The distributor plate23has several spaced openings perpendicular to the image plane through which the coating compound enters the rinsing chamber8. The coating compound is first distributed evenly across the width of the sheet and then via the large rinsing chamber8. The pressure in the rinsing chamber8corresponds approximately to the pump pressure of the pump13. The coating compound is then conveyed in the direction of the coating nip3and moves along the tapering contour of the rinsing chamber8in the direction of the outlet nozzle4, which is formed on one side by the doctor blade2and on the other side by the horizontally adjustable inner side of the nozzle tip20. The spray chamber8is sealed towards the doctor blade2by a flexible gasket23so that no overflow occurs at this point. The converging gap between doctor blade2and the flushing device produces an increase in the speed of the compound. This causes the speed to approach the surface speed of the transfer roller1. 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.

The nip pressure between the doctor blade2and transfer roller1must be lower than in the discharge nip16between the nozzle tip20and the transfer roller1. As a result, the mass moves with increasing speed into the coating nip3. The differential speed of the mass to the surface of the transfer roller1is 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 seal21, 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 seal21does not touch the transfer roller1, but is positioned at a distance of 0.1 mm to 0.2 mm from it. The gap between the nip seal21and the transfer roller1is 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 roller1, which rotates in the direction of the discharge gap16, reduces the leakage, i.e. the coating compound that runs over discharge gap16and nip seal21in the direction of the outside10is reduced by counter-rotating movement of transfer roller1.

FIG.5shows a perspective view of the back of the spraying device. The nozzle tip20is located on the top side, which initially has a boundary wall15in the downward direction, which forms the discharge gap16together with the transfer roller1. Below this, the gap is tapered to 0.1-0.2 mm by the nip seal. Coating compound that overcomes the nip seal21runs over the drain contour11of the outside10of the flushing device back into the collecting trough12. Side walls laterally delimit the flushing device, which each have seals24, which comprise a front part24a, which faces the transfer roller1, and a rear part24b, which faces the rinsing chamber8and the comma blade2respectively. The washing chamber8is only sealed over the rear section24btowards the doctor blade2. The front section24aof the seal24, on the other hand, is stepped over the rear section24bso that the front section24ahas no contact with the transfer roller1and is leaky. Overflowing coating compound is returned to the mass container via the collecting trough12.

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

1Transfer roller2Doctor blade3Coating nip4Outlet nozzle5Nozzle opening6Nip opening7Forced conveying system8Rinsing chamber9Inlet10Outside11Drain contour12Collecting trough13Pump14Coating compound storage tank15Boundary wall16Discharge gap17Mating roller18Outlet19Nozzle20Nozzle tip21Nip seal22Distributor plate23flexible gasket24alateral seal front part24blateral seal rear part100Coating compound200Material webz Vertical direction