EP3829782B1 - Device and method for processing shear-sensitive coating compounds - Google Patents

Description

The invention is based on a device for processing shear-sensitive coating materials, the device having a transfer roller and a doctor blade which are spaced apart from one another to form a coating gap.

The device also has an outlet nozzle for metering a coating composition. Such a device is from EP 1 117 488 B1 known. A similar device is also described in DE 3717882 A1 or EP2727652 .

The devices and methods known from the prior art are used, for example, in the coating of aqueous dispersions, for example for the production of PSA products. Among these devices and methods, the gravure roller method and the doctor blade method are particularly noteworthy. What these methods have in common is that the storage and sometimes also the pre-metering of the coating mass in some areas of the device is realized with very small distances between two walls of the device, for example in the area of the outlet nozzle, which leads to considerable shear stress on the dispersions. For this purpose, for example, side limiters are used for sealing, or simply the so-called squeegee as a scraper in a gravure roll coating machine.

As a result, very small gaps of a few µm are formed, which lead to impermissibly high shear rates during the coating process of shear-sensitive coating materials and thus to agglomeration of the coating material. The latter is undesirable.

It is therefore the object of the invention to propose a device and a method for processing shear-sensitive coating materials in which agglomerates in the coating materials are at least largely avoided.

This object is achieved by a device having the features of claim 1.

The independent claim 10 relates to a corresponding method. Advantageous embodiments are the subject matter of the dependent claims.

Accordingly, in a device for processing shear-sensitive coating materials, it is provided that the outlet nozzle faces a lower gap opening of the coating gap with its nozzle opening. The device has a compulsory conveying system via which a coating mass is metered into the coating gap. The result of this is that the coating composition is exposed to the lowest possible shear rate and long dwell times of the coating composition in the coating machine are avoided.

Provision can be made for the device to have a flushing device with a seal-free chamber system. The flushing device can be set up to ensure a homogeneous distribution of the coating mass over the width of the transfer roller. The forced conveying system can be set up to meter the coating mass directly into the coating gap under a slight excess pressure compared to atmospheric pressure. In particular, the coating composition can be flushed directly into the coating gap. If the chamber system of the flushing device is designed without seals, it can be avoided that the coating composition is exposed to high pressures in the region of the coating gap, which can lead to agglomeration of the coating composition. In the present case, seal-free or side-limiter-free means that the flushing device, for example a flushing chamber which has the outlet nozzle, is arranged in a fluidically permeable manner relative to the transfer roller. For this purpose, the flushing chamber and in particular the outlet nozzle can be arranged at a distance from the transfer roller. A gap formed between the flushing device and the transfer roller can be dimensioned such that excess coating mass can flow out of the coating gap via the gap between the flushing device and the transfer roller due to a geodetic pressure difference.

By dosing the coating mass into the coating gap via a lower gap opening of the coating gap, the production of smooth, defect-free layers on continuously flat substrates is achieved, in particular in the case of self-adhesive PSA applications and in the processing of paints. In particular, aqueous acrylate dispersions with shear-sensitive behavior can be coated with the devices and methods according to the invention without agglomerates.

Due to the dosage via a lower gap opening directly into the coating gap, a uniform residence time of the coating masses in the Coating gap reached and thus prevents overaging of the coating composition. In this respect, too, the formation of agglomerates in the coating composition is prevented.

According to the invention, the transfer roller and the doctor blade are arranged next to one another, so that the coating gap is permeable in the vertical direction. The squeegee can preferably be a comma squeegee.

The nozzle opening is located in front of the lower gap opening without contact, with the coating composition being flushed into the coating gap under pressure. The non-contact positioning of the nozzle opening in front of the lower gap opening ensures that the coating mass in the coating gap is exposed solely to atmospheric pressure and is therefore not subjected to compression and shearing stress, which could lead to the formation of agglomerates.

The outlet nozzle is an outlet of a priming chamber located below the coating gap, the priming chamber preferably further having an inlet for coating composition.

The flushing chamber can have a recess-free drainage contour for the coating composition on an outside facing the transfer roller. The coating composition that is dosed, in particular flushed, into the coating gap from below and is not applied to the transfer roller can run off via the depression-free drainage contour on the outside of the flushing chamber.

The rinsing chamber can be arranged above a collecting trough, from which the coating mass flowing off into the collecting trough via the outside of the rinsing chamber is pumped back into the rinsing chamber.

The coating compound can be pumped from the collection pan into the flushing chamber via a pump of the compulsory conveying system, preferably an eccentric screw pump, with the pump preferably being arranged in a coating compound reservoir.

Between a boundary wall of the outlet nozzle on an outside of the boundary wall facing the transfer roller and the transfer roller, a drainage gap for excess coating material to flow off can be formed. As a result, excess coating mass can flow off via the drainage gap due to a geodetic pressure difference.

In addition, a gap seal can be formed on the outside of the boundary wall facing the transfer roller. Due to the gap seal, a slight overpressure can be built up between the nozzle outlet area and the transfer roller in order to enable flushing of the transfer roller over the entire surface and to prevent the coating compound from flowing out of the flushing area.

In particular, the gap seal can be at a distance of 0.01 mm to 0.5 mm, preferably 0.1 mm to 0.2 mm, from the transfer roller.

The gap seal can be part of a nozzle tip, which forms the outlet nozzle on its side opposite the gap seal. On the squeegee side, the nozzle tip can have a surface that forms the outlet nozzle. On the transfer roller side, the nozzle tip can have the discharge gap and the gap seal arranged underneath. The nozzle tip can be fixed to the top of the flushing chamber by means of a mounting plate. The nozzle tip can be clamped to the flushing chamber by means of the fastening plate and/or screwed to it. The nozzle tip can be designed in one piece. The nozzle tip can be made of natural or synthetic rubber.

The nozzle tip can be designed to be horizontally adjustable in order to be able to set the pressure ratio between the nozzle opening and the gap seal.

Furthermore, the components of the flushing device that face the squeegee can be sealed off from the squeegee and the components of the flushing device that face the transfer roller can be designed without contact with the transfer roller. The flushing device can in particular comprise the flushing chamber and the nozzle tip, with the flushing chamber having the coating material inlet on the squeegee side, a coating material reservoir and one tapering towards the outlet nozzle area can include. On the transfer roller side, the flushing chamber has an outside through which excess coating composition can run off.

The device can also have a counter-roller which is set up to press a material web against the transfer roller. The coating composition can be a flowable material, preferably a dispersion, for example an adhesive.

The transfer roller can be a chrome-coated steel roller. The backing roll may have a shell of ethylene propylene diene monomer rubber (EPDM) with a Shore A hardness of 65. The coating composition can be, for example, a dispersion with a viscosity of 1,200 mPa·s and a solids content of 58.7%. The rotational speed of the transfer roller can be, for example, 20 to 80 m/min. be. The coating gap can be 50 μm, for example. The aforementioned numerical values are merely examples and are not intended to limit the subject matter of the invention to corresponding embodiments.

• Bereitstellen einer rotativ angetriebenen Übertragwalze und einer Rakel, vorzugsweise einer Kommarakel, die unter Ausbildung eines Beschichtungsspalts zueinander beabstandet sind; und
• Dosieren einer Beschichtungsmasse mit einem Zwangsfördersystem in den Beschichtungsspalt. Die Düsenöffnung wird einer unteren Spaltöffnung des Beschichtungsspalts berührungsfrei vorgelagert und die Beschichtungsmasse in den Beschichtungsspalt gespült.

According to another aspect of the invention, a method for processing shear-sensitive coating compositions is proposed that has the steps:

• providing a rotationally driven transfer roller and a doctor blade, preferably a comma blade, which are spaced apart from one another to form a coating gap; and
• Dosing of a coating compound into the coating gap with a forced conveying system. The nozzle opening is placed in front of a lower gap opening of the coating gap without contact and the coating mass is flushed into the coating gap.

The coating composition can be flushed into the coating gap in the vertical direction from below (upward).

The coating compound can be flushed into the coating gap without a side limiter, so that excess coating compound can flow off.

The coating composition can be metered into the coating gap via an outlet nozzle, with a drainage gap being formed between a boundary wall of the outlet nozzle on an outside of the boundary wall facing the transfer roller and the transfer roller, so that excess coating composition flows out via the drainage gap due to the geodetic pressure difference.

The coating composition can be metered into the coating gap via an outlet nozzle, the outlet nozzle being an outlet of a rinsing chamber and coating composition flowing off into a collection trough on the outside of the rinsing chamber being pumped back into the rinsing chamber.

Figur 1

eine Vorrichtung gemäß dem Stand der Technik;

Figur 2

in schematischer Querschnittsansicht eine beispielhafte Ausführungsform einer erfindungsgemäßen Vorrichtung;

Figur 3

in schematischer Querschnittsansicht eine weitere beispielhafte Ausführungsform einer erfindungsgemäßen Vorrichtung

Figur 4

in schematischer Querschnittsansicht eine Detaildarstellung des Anspülbereichs; und

Figur 5

in perspektivischer Darstellung eine rückwärtige Ansicht der Anspülvorrichtung.

Further details of the invention are explained with reference to the figures below. It shows:

figure 1

a prior art device;

figure 2

in a schematic cross-sectional view an exemplary embodiment of a device according to the invention;

figure 3

in a schematic cross-sectional view a further exemplary embodiment of a device according to the invention

figure 4

in a schematic cross-sectional view, a detailed representation of the flushing area; and

figure 5

a rear view of the flushing device in a perspective representation.

figure 1 shows an exemplary device for processing coating materials 100 such as dispersions, for example adhesives, as is known from the prior art. A counter-roller 17, a transfer roller 1 and an outlet nozzle 4 for metering a coating composition 100 are arranged one above the other in the vertical direction z, with the outlet nozzle 4 facing a lowermost position of the transfer roller 1 with its nozzle opening 5 and directly adjoining it and thus opposite this is arranged sealingly. In particular, the outlet nozzle 4 is sealed off from the area surrounding the device by the doctor blades 2 arranged on opposite sides of the outlet nozzle 4 in the direction of rotation of the transfer roller 1 . The coating composition 100 is applied to the circumference of the transfer roller with the help of an overpressure compared to atmospheric pressure via the outlet nozzle 4 and brought to a desired coating thickness with the help of the opposing doctor blades 2, with the coating composition 100 being exposed to high shear rates, which leads to agglomerates in the coating composition 100 leads.

The device shown has the disadvantage that for effective application of the coating composition 100 to the transfer roller 1, the coating composition 100 must be metered onto the transfer roller 1 under a comparatively high pressure, which results in the formation of the agglomerates mentioned in the coating composition 100, including the Quality of the coating of the transfer roller 1 suffers and thus the quality of the layer of coating mass produced on the material web 200 is reduced.

To solve this problem, a device can be used as shown in figure 2 is shown. Here, the device has a transfer roller 1 and a doctor blade 2, which is designed as a comma blade. The transfer roller 1 and the doctor blade 2 are arranged horizontally next to one another, forming a coating gap 3 . The coating gap 3 can have a minimum gap width of 50 μm, for example. Due to the horizontal arrangement of the transfer roller 1 and the squeegee 2, a passage direction of the coating gap 3 extends essentially in the vertical direction z. For the realization of the invention, however, it is not essential that the transfer roller 1 and the squeegee 2 are arranged exactly horizontally next to one another. Rather, it is important that the resulting coating gap 3 between the transfer roller 1 and doctor blade 2 has a vertical component in its direction of extension. In any case, however, it should be avoided that the transfer roller 1 and doctor blade 2 are arranged one above the other in the vertical direction, as is the case in the devices known from the prior art according to FIG figure 1 is provided.

The device has an outlet nozzle 4 for dosing the coating mass 100 , which nozzle opening 5 faces a lower gap opening 6 of the coating gap 3 . The coating composition 100 is metered into the coating gap 3 from below via a compulsory conveying system 7 of the device.

In particular, the nozzle opening 5 is positioned in front of the lower gap opening 6 without touching it, so that the nozzle opening 5 is in connection with the surroundings of the device, and therefore with atmospheric pressure. A slight excess pressure of the coating composition 100 is already sufficient to flush the coating composition 100 through the nozzle opening 5 into the coating gap 3 . The nozzle opening 5 can in particular be aligned in the vertical direction, so that the pressure with which the coating compound 100 is provided via the nozzle opening is adjusted in such a way that the coating gap is effectively wetted with the coating compound 100 . Any further pressurization of the coating composition 100 is not necessary and should be avoided in order to avoid the formation of agglomerates in the coating composition 100 .

The outlet nozzle 4 is formed at an upper end of a flushing chamber 8 which is arranged below the coating gap 3 . The coating mass 100 is conducted via an inlet 9 into a forced conveying system 7 which has a pump 13 . In order to achieve the lowest possible compression of the coating composition 100 within the pump 13, the pump 13 is preferably an eccentric screw pump.

On its outside and facing the transfer roller 1, the flushing chamber 8 has a drainage contour 11 without any depressions, via which excess coating composition can flow off unhindered. In order to encourage the excess coating composition to flow off via the depression-free drainage contour 11 of the flushing chamber 8 , the flushing chamber 8 can be sealed off from the squeegee 2 .

The flushing chamber 8 is arranged above a collecting trough 12 in which the excess coating material 100, which flows back out of the coating gap 3 via the run-off contour 11 of the flushing chamber 8, is collected.

As in figure 3 is shown, it can be provided that the coating composition 100 flowing out via the outside 10 of the rinsing chamber 8 into the collecting trough 12 is pumped back into the rinsing chamber 8 . Flushing the coating gap 3 "from below" promotes a short dwell time of the coating composition in the coating gap 3 and thus good preservation of the dispersive properties of the coating composition 100. Since the coating composition 100 remains in constant motion and is only exposed to comparatively low overpressures compared to atmospheric pressure, the formation of agglomerates is effectively suppressed. The coating composition 100 can be transported from the collecting trough 12 via an outlet 18 into a coating composition storage container 14 and from there it can be fed back to the flushing chamber 8 via the inlet 9 . The pump 13 for transporting the coating composition 100 from the storage container 14 into the flushing chamber 8 can be arranged in the coating composition storage container 14 .

The transfer roller 1 can be a chrome-coated steel roller, for example. The counter-roller can have a cover made of EPDM rubber with a hardness of 65 Shore A. The web of material 200 to which the layer of coating composition 100 is applied can be, for example, a web of siliconized paper. The gap between doctor blade 2 and transfer roller 1 can be between 30 and 400 μm, for example. The rotational speed of the transfer roller 1 can be, for example, 5 to 80 m/min. be. The coating composition layer 100 applied to the material web 200 can have a basis weight of, for example, 30 g/m ² to 200 g/m ² . The material data and numerical values mentioned are merely examples and are not intended to limit the subject matter of the invention to corresponding embodiments.

figure 4 shows an embodiment of the invention, which is shown in side view and illustrates the flushing area with transfer roller 1, comma blade 2 and a flushing device arranged in the middle between them. The arrow on transfer roller 1 indicates its direction of rotation. The flushing device has in particular a nozzle 19 which initially has an inlet 9 below the coating gap 3 through which coating material is fed through a distributor plate 23 into the flushing chamber 8 . The coating composition is fed into the inlet from the side, ie parallel to the axial directions of the rollers. Feeding preferably takes place from both sides in the area of the end faces of the transfer roller 1 and the comma blade 2 respectively. The mass is distributed first on the sheet metal and then evenly across the width via the large flushing chamber 8. The pressure in the flushing chamber 8 corresponds approximately to the pump pressure the pump 13. The coating mass is then conveyed in the direction of the coating gap 3 and moves along the tapering contour of the flushing chamber 8 in the direction of the outlet nozzle 4, which passes through the squeegee 2 on one side and through the horizontally adjustable inner side of the Nozzle tip 20 is formed. The flushing chamber 8 is sealed towards the squeegee 2 by a flexible seal 23, so that there is no overflow at this point. The converging gap between squeegee 2 and flushing device generates an increase in the speed of the mass. The speed of the surface speed of the transfer roller 1 approaches. The arrows drawn in clarify the direction of movement of the coating composition. The dashed horizontal arrow indicates the direction of adjustment of the flushing device.

The gap pressure between comma blade 2 and transfer roller 1 must be lower than in the discharge gap 16 between the nozzle tip 20 and the transfer roller 1. As a result, the mass moves with increasing speed into the coating gap 3. The speed difference between the mass and the surface of the transfer roller 1 is so low , that the mass is not subject to shearing and thus no change in viscosity. This results in an even coating pattern. In the area of the gap seal 21, the theoretically high flow rate generates a resistance that levels off at the overall pressure of the flushing area. It should be noted that the gap seal 21 does not touch the transfer roller 1, but is at a distance of 0.1 mm to 0.2 mm from it. The gap between the gap seal 21 and the transfer roller 1 is therefore very small, so that the speed in this area would have to be very high in order to allow the volumetric flow flowing downwards to pass. The transfer roller 1 rotating in the direction of the discharge gap 16 reduces the leakage, that is, the coating mass that runs over the discharge gap 16 and gap seal 21 in the direction of the outside 10 is reduced by the transfer roller 1 moving in the opposite direction.

figure 5 shows a rear view of the flushing device in a perspective representation. The nozzle tip 20 is arranged on the upper side and initially has a boundary wall 15 in the downward direction, which together with the transfer roller 1 forms the discharge gap 16 . Below this, it tapers to 0.1-0.2 mm due to the gap seal. Coating compound, which overcomes the gap seal 21, runs back into the collection pan 12 via the drainage contour 11 of the outside 10 of the flushing device. Side walls delimit the flushing device at the sides, 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 flushing chamber 8 and the comma blade 2, respectively. The flushing chamber 8 is in each case sealed off from the comma hook 2 only via the rear section 24b. The front part 24a of the seal 24, on the other hand, is stepped over the rear part 24b, so that the front part 24a is designed without contact with the transfer roller 1 and has leakage. Coating compound that has spilled over is returned to the compound container via the collecting pan 12 .

Reference list:

1

transfer roller

2

squeegee

3

coating gap

4

outlet nozzle

5

nozzle opening

6

stomata

7

Forced Conveyor System

8th

flushing chamber

9

inlet

10

outside

11

drainage contour

12

collection tray

13

pump

14

Coating compound storage tank

15

boundary wall

16

drainage gap

17

counter roll

18

Sequence

19

jet

20

nozzle tip

21

gap seal

22

spreader plate

23

flexible seal

24a

side seal front part

24b

side seal rear part

100

coating mass

200

web of material

e.g

vertical direction

Claims (18)

1. An apparatus for processing shear-sensitive coating compounds (100), comprising a transfer roller (1) and a doctor blade (2), which are spaced apart from one another to form a coating nip (3), the apparatus further comprising an outlet nozzle (4) for dosing a coating compound (100), the outlet nozzle (4) facing with its nozzle opening (5) a lower nip opening (6) of the coating nip (3), wherein the device comprises a forced conveying system (7) via which a coating compound (100) is dosed into the coating nip (3), the transfer roller (1) and the doctor blade (2) being arranged next to each other, so that the coating nip (3) is permeable in the vertical direction (z), wherein the coating nip (3) is between 30 µm and 400 µm and the outlet nozzle (4) is an outlet of a rinsing chamber (8) arranged below the coating nip (3).
2. The apparatus of claim 1 wherein the doctor blade (2) is a comma doctor blade.
3. The apparatus according to claim 1 or 2, in which the nozzle opening (5) is mounted in front of the lower nip opening (6) without contact, the coating compound (100) being flushed into the coating nip (3).
4. The apparatus according to one of the preceding claims, in which the rinsing chamber (8) continues to have an inlet (9) for coating compound (100).
5. The apparatus according to claim 4, in which the rinsing chamber (8) on an outer side (10) facing the transfer roller (1) has a recess free discharge contour (11) for coating compound (100).
6. The apparatus according to claim 1, in which the rinsing chamber (8) is arranged above a collecting trough (12) from which coating compound (100) flowing off via the outside (10) of the rinsing chamber (8) into the collecting trough (12) is pumped back into the rinsing chamber (8).
7. The apparatus according to claim 6, in which the coating compound (100) is pumped out of the collecting trough (12) into the rinsing chamber (8) via a pump (13) of the forced conveying system (7), preferably an eccentric screw pump, the pump (13) preferably being arranged in a coating compound storage container (14).
8. The apparatus according to one of the preceding claims, in which a discharge gap (16) for the discharge of excess coating compound (100) is formed between a boundary wall (15) of the outlet nozzle (4) on an outer side (10) of the boundary wall (15) facing the transfer roller (1) and the transfer roller (1).
9. The apparatus according to claim 8, wherein a nip seal (21) is formed on the outer side (10) of the boundary wall (15) facing the transfer roller (1).
10. The apparatus according to claim 9, wherein the nip seal (21) has a distance of 0.01 mm to 0.5 mm, preferably 0.1 mm to 0.2 mm, from the transfer roller (1).
11. The apparatus according to one of claims 9 or 10, wherein the nip seal (21) is part of a nozzle tip (20) which forms the outlet nozzle (4) on its side opposite the nip seal (21).
12. The apparatus according to claim 11, wherein the nozzle tip (20) is horizontally adjustable to adjust the pressure ratio between the nozzle orifice (5) and the nip seal (21).
13. The apparatus according to one of the preceding claims, wherein the components of the flushing device (8) facing the doctor blade (2) are sealed towards the doctor blade (2) and the components of the flushing device (8) facing the transfer roller (1) are designed to be contactless towards the transfer roller (1).
14. The apparatus according to one of the preceding claims, which has a mating roller (17) which is set up to press a material web (200) against the transfer roller (1), the coating compound (100) being a flowable material, preferably a dispersion and particularly preferably an adhesive.
15. A method for processing shear-sensitive coating compounds (100), the method comprising the steps

    - providing a rotationally driven transfer roller (1) and a doctor blade (2), which are arranged next to each other so that the coating nip (3) is permeable in vertical direction (z), wherein the transfer roller (1) and the doctor blade (2) are spaced apart from each other to form a coating nip (3) which is between 30 and 400 µm;

    - dosing a coating compound (100) with an outlet nozzle (4) and a forced conveying system (7) into the coating nip (3), wherein the nozzle opening (5) of the outlet nozzle (4) is mounted contact-free in front of a lower nip opening (6) of the coating nip (3) and the coating compound (100) is flushed in vertical direction (z) from below into the coating nip (3).
16. The method according to claim 15, in which the coating compound (100) is flushed into the coating nip (3) without lateral limiter so that excess coating compound (100) can flow off.
17. The method according to claim 15 or 16, in which the coating compound (100) is dosed into the coating nip (3) via an outlet nozzle (4), wherein a discharge gap (16) is formed between a boundary wall (15) of the outlet nozzle (4) on an outer side (10) of the boundary wall (15) facing the transfer roller (1) and the transfer roller (1), so that excess coating compound (100) flows off via the discharge gap (16) due to a geodetic pressure difference.
18. The method according to one of claims 15 to 16, in which the coating compound (100) is dosed into the coating nip (3) via an outlet nozzle (4), the outlet nozzle (4) being an outlet of a rinsing chamber (8) and coating compound (100) flowing off into a collecting trough (12) via the outside (10) of the rinsing chamber (8) being pumped back into the rinsing chamber (8).

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