FAST HOMOGENOUS COATING PROCESS

Abstract

The present invention is directed to a process for the production of exhaust catalysts. In particular, the process describes a way of coating a substrate in a manner which finally leads to reduced coating times.

Claims

1. Process for homogenously coating substrates for the production of exhaust gas purification catalysts, particularly for motor vehicles, which are cylindrical substrates and each have two end faces, a circumferential surface and an axial length L and are traversed from the first end face to the second end face by a multiplicity of channels, with liquid coating media, against the force of gravity, wherein the introduction of the liquid coating medium into the substrate from below is controlled in such a way that the coating speed from part of the axial length towards the end of the substrate is being reduced compared to the speed at the initial introduction of the liquid coating medium into the substrate, and wherein the coating height in the coating chamber is checked by conductivity sensors before the liquid coating medium enters the substrate, and the coating speed at the beginning of the introduction of the liquid coating medium is above or equal to 0.1 m/s, and the reduction in coating speed is started not before half of the substrate is already wetted with the liquid coating medium.

2. Process according to claim 1, wherein the coating speed at the initial introduction of the liquid coating medium into the substrate is at least twice the magnitude compared to the coating speed shortly before the liquid coating medium emerges at the top of the substrate.

3. Process according to claim 2, wherein the coating speed at a point of 95% of the substrate is taken as the coating speed shortly before the liquid coating medium emerges at the top of the substrate.

4. Process according to claim 1, wherein the coating height in the coating chamber is checked by conductivity sensors before the liquid coating medium enters the substrate.

5. Process according to claim 1, wherein the liquid coating medium emerging at the top of the substrate is monitored by a visual sensor.

6. Process according to claim 1, wherein the substrate is fixed to the coating station by inflatable seals both at the lower end as well as at the upper end face.

7. Process according claim 1, wherein the viscosity of the liquid coating medium is between 2-200 mPa*s.

8. Process according to claim 1, wherein a device is used, which has a cylinder filled with a liquid and having a piston, wherein the liquid-filled cylinder communicates with a tank, in the interior of which a displacement body is arranged in such a way that, when the piston is moved, the displacement body is moved proportionally by the liquid, and the tank communicates with the coating device for the substrate, wherein the displacement body acts on the liquid coating medium, with the result that a proportional change in the level of liquid coating medium in the coating device is brought about.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1: [0030] 1 substrate [0031] 2 unit for fixing the substrate [0032] 3 coating device [0033] 4 sensors for monitoring the filling level in the coating device [0034] 5 sensor for monitoring the emergence of coating slurry at the top of the substrate [0035] 6 central processing unit [0036] 7 flow of liquid coating medium [0037] 10 inflatable seals

[0038] FIG. 2: [0039] 100 actuator [0040] 101 piston [0041] 102 cylinder [0042] 103 fluid [0043] 104 line section [0044] 111 displacement body [0045] 112 tank [0046] 113 liquid coating medium [0047] 114 filling flow direction [0048] 124 sensor for monitoring the displacement body [0049] 125 central processing unit

DETAILED DESCRIPTION OF THE DRAWINGS:

[0050] FIG. 1 shows an arrangement of the invention for coating a substrate (1). The liquid coating medium is filled through line sections (7) into the coating apparatus (3), wherein the coating apparatus (3) is provided with the substrate (1) and with sensors (4) for accurately determining the first level of the liquid coating medium in the device (3). The values determined by the sensors (4) are transmitted to a central processing unit (6) which, for its part, controls at least the further pumping or suction of the coating slurry based on the above-mentioned analysis.

[0051] After the filling of the coating apparatus (3) with coating medium up to the first level (level of sensors 4) in the filling flow direction (7) has been performed, and after the liquid coating medium emerges at the top of the substrate (1), which is monitored by sensor (5), the coating slurry can be sucked out in the return flow direction, leading to a storage tank for excess coating medium and for holding it ready for further use. All the control commands required for this purpose are preferably likewise output by the central processing unit (6).

[0052] FIG. 2 shows an arrangement of the invention for coating substrates, which has a piston (101), actuated by an actuator (100), in a cylinder (102), which is filled with liquid (103) and, through a connection (104) of the cylinder (102) to the displacement body (111), allows the actuation of the displacement body (111) in the tank (112), which is filled with liquid coating medium (113) and has a line sections (114) connected to the coating unit. Sensors (124) are used to monitor the displacement volume of the coating medium (113) and the state of the displacement body (111) in the tank (112).

[0053] The values determined by the sensors (124) are also transmitted to a central processing unit (125) which, for its part, controls the actuator (100) and hence the piston (101).

[0054] All the control commands required for the purpose of coating the substrate and based on the signals stemming from (4), (5) and (124) are preferably likewise output by the central processing unit (125 [FIG. 2], 6 [FIG. 1]).

[0055] The finished substrates, which are suitable for the production of exhaust gas catalysts for motor vehicles, have a particularly uniform coating on or in its wall sections, which is at least characterized in that the homogeneity of the coating along the longitudinal channel axis is superior compared to coating with lower but therefore constant speed. It has been detected that the high speed of coating in fact serves for more homogeneity in at least the gradient in amount of catalytic species and/or amount of washcoat per unit catalyst (in g/L). The present invention achieves this result in a very easy but nevertheless surprisingly effective manner. In that a special coating speed profile is applied a very fast coating method can be employed which surprisingly still furnishes advantageously coated substrates. This greatly helps to shorten the cycle time (time needed to coat one body) but on the other hand also serves to have less coated monoliths falling out of specification. Hence, this invention allows to greatly improve the economy of a process for coating exhaust catalysts. This was not made obvious from the prior art teaching at the date of this invention.

EXAMPLES

[0056] A 2.5 l substrate with a diameter of 143.8 mm is coated according to the process described in DE102010007499A1. Compared is a normal coating process to a fast coating according to the invention. The washcoat is stopped when the overflow sensor signals the end of the introduction of coating medium.

TABLE-US-00001 Setting of station test fast speed coating 2000 ml/s acceleration 3000 ml/s.sup.2 normal speed coating  600 ml/s deceleration 3000 ml/s.sup.2

TABLE-US-00002 Normal coating mode Total coating coating time stop time (deceleration) time (s) (s) (s) 4.17 0.20 4.37

TABLE-US-00003 New fast coating mode coating time Deceleration coating time Total fast 80% between fast slow remaining stop time coating of volume and slow volume (deceleration) time (s) (s) (s) (s) (s) 1 0.47 0.29 0.20 1.96

[0057] The conditions given are comparable to real coating processes. It can be seen that a large amount of time per piece can be saved by application of the new coating strategy. The quality of the coating with fast coating process is considerably better than with the normal coating process (600 ml/s) due to the fact that the monolith substrate used is not able to absorb water fast enough when introducing the liquid coating medium to substantially change the viscosity of the coating medium while still being introduced into the part.