Spraying process for coating a substrate

Abstract

In a spraying process for coating a substrate with a substance atomised in a stream of gas, a spray head is used to generate a stream of gas that acts upon the substrate. The substance is present in a syringe-like application container equipped with an application tip. The application tip of the application container containing the substance is introduced into the stream of gas outside the spray head at a distance therefrom and transversely with respect to the main direction of flow of the stream of gas, and the substance is introduced from the application container into the stream of gas at that location.

Claims

1. A spraying process for coating a substrate with a substance atomised in a stream of gas, wherein a spray head is used to generate a stream of gas that acts upon the substrate, and wherein the substance is present in an application container equipped with an application tip and, without contact with the spray head, is introduced from the application container into the stream of gas and thereby atomised, wherein the application tip of the application container containing the substance is introduced into the stream of gas outside the spray head at a distance therefrom and transversely with respect to a main direction of flow of the stream of gas, and the substance is introduced into the stream of gas at that distance, wherein a disposable syringe or a disposable pipette is used as the application container.

2. The spraying process according to claim 1, wherein the application container with the application tip is selected from a set of different application containers having different application tips.

3. The spraying process according to claim 1, wherein the application tip of the application container is arranged at a distance of 0.01-5 cm from an axial main nozzle of the spray head, measured in the main direction of flow of the stream of gas.

4. The spraying process according to claim 1, wherein a spray head is used which has two oppositely located horn air nozzles which generate two inwardly directed horn gas streams, and the application tip of the application container is arranged in a region of intersection of the two horn gas streams.

5. The spraying process according to claim 1, wherein the substrate, while being acted upon by the atomised substance, is moved in one or two dimensions transversely with respect to the main direction of flow of the stream of gas.

6. The spraying process according to claim 1, wherein, while the substrate is being acted upon by the atomised substance, the spray head and the application container with the application tip are moved in one or two dimensions transversely with respect to the main direction of flow of the stream of gas.

7. The spraying process according to claim 1, wherein the spray head is operated at a pressure of 1-10 bar and a gas throughput of 100-10001/min.

8. The spraying process according to claim 1, wherein the application tips of more than one application container are introduced simultaneously or sequentially into the stream of gas, and different substances to be sprayed that are contained in the application containers are delivered into the stream of gas and atomised either in succession or simultaneously.

9. A spray device for carrying out the spraying process according to claim 1, comprising a spray head for generating a stream of gas that acts upon the substrate; an application container equipped with an application tip for holding a substance to be atomised in the stream of gas; and a robot for picking up the application container from a storage container and for introducing the application tip into the stream of gas, wherein the application container is a disposable syringe or disposable pipette.

10. The spray device according to claim 9, further comprising a discharger configured to discharge the substance contained in the application container from the application container into the stream of gas generated by the spray head.

11. The spray device according to claim 9, wherein the robot is configured to remove a partly or fully emptied application container from the stream of gas.

12. The spray device according to claim 9, wherein the spray device is configured to adjust the distance between the spray head and the application tip and/or the distance between the application tip and the substrate automatically or manually.

13. The spray device according to claim 9, wherein the spray device is configured for sequential or simultaneous introduction of application tips of two or more application containers into the stream of gas.

14. The spray device according to claim 9, wherein the application tip is straight and an outlet opening of the application tip opens into the stream of gas at a right-angle, so that the substance to be applied is introducible into the stream of gas at a right-angle to the main direction of flow thereof.

15. The spray device according to claim 9, wherein the application tip is straight and has at least one lateral outlet opening through which the substance to be applied is introducible into the stream of gas.

16. The spray device according to claim 9, wherein the application tip is bent at an angle and an outlet opening of the application tip opens in the direction of the stream of gas, so that the substance to be applied is introducible into the stream of gas parallel to the main direction of flow thereof.

17. The spray device according to claim 9, wherein the robot is configured to move the spray head together with the application container in at least one dimension transversely with respect to the main direction of flow of the stream of gas.

18. The spray device according to claim 9, further comprising a second robot for holding a substrate and for moving the substrate in at least one direction transversely with respect to the main direction of flow of the stream of gas.

19. The spray device according to claim 9, further comprising an electronic controller for the robot, for a second robot for holding a substrate, for a discharger for discharging the substance contained in the application container from the application container, and/or for supplying gas to the spray head, the controller being programmed to autonomously control workflows necessary for carrying out the spraying process.

20. The spray device according to claim 19, wherein the electronic controller is programmed so that it iteratively optimises parameters and the workflows necessary for carrying out the spraying process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described in greater detail below with reference to exemplary embodiments shown in the drawings, wherein:

(2) FIG. 1a-1d—are a diagrammatic representation of an exemplary embodiment of the spraying process according to the invention,

(3) FIG. 2a-2d—are a side view, a plan view, a front view and a sectional view of a spray head suitable for the spraying process according to the invention,

(4) FIG. 3—is a diagrammatic side view of an exemplary embodiment of the spray device according to the invention in the non-operating state,

(5) FIG. 4—is a plan view of the spray device of FIG. 3 in a state in which it is ready for the spraying operation,

(6) FIG. 5—is a side view analogous to FIG. 3 of the spray device during a spraying operation,

(7) FIG. 6—is a diagram illustrating the movement of a substrate relative to the spray head,

(8) FIG. 7a-b—are diagrams showing two possible forms of application tips and

(9) FIG. 8—shows the spray device in an exemplary embodiment that has been slightly modified in comparison with the exemplary embodiment according to FIG. 5.

DETAILED DESCRIPTION

(10) The following observations apply in respect of the description which follows: where, for the purpose of clarity of the drawings, reference signs are included in a Figure but are not mentioned in the directly associated part of the description, reference should be made to the explanation of those reference signs in the preceding or subsequent parts of the description. Conversely, to avoid overcomplication of the drawings, reference signs that are less relevant for immediate understanding are not included in all Figures. In that case, reference should be made to the other Figures.

(11) Hereinbelow the invention is described purely by way of example in connection with the spray application of a liquid paint formulation to a substrate. It will be understood, however, that the process according to the invention and the corresponding device according to the invention are in principle also suitable for the spray application of substances other than paint formulations or adhesives and adhesive formulations, provided the substances in question are suitable for atomisation or nebulisation (aerosol formation) in a stream of air or, more generally, gas. As well as liquid substances, in principle substances in powder form also come into consideration for spray application.

(12) Compressed air is normally used for atomisation or nebulisation of the substance, but it is also possible to use any other gas or gaseous mixture for that purpose. For the sake of simplicity the following explanation is confined to a paint formulation as the substance being applied and (compressed) air as the gaseous mixture used for the nebulisation or atomisation of the substance.

(13) FIGS. 1a-1d show the typical steps of the spraying process according to the invention.

(14) A substance to be applied here in the example a liquid paint formulation F is held in readiness in a storage container V (FIG. 1a). A desired (relatively small) amount of the paint formulation F is drawn up from the storage container V into an application container 10 (FIG. 1b). The application container 10 is syringe-like and has a chamber 11, a plunger 12 axially displaceable therein, a plunger rod 13 and an application tip 14. In practice, a commercially available disposable syringe or a (plunger) pipette is advantageously used as application container 10. The application tip 14 is advantageously configured as a commercially available metering needle or cannula.

(15) Those two preparative steps just described can also take place outside the actual spraying process, with a desired number of application containers 10 being provided that have different contents or the same contents, as the case may be.

(16) For the spraying process, a spray head 20 is used to generate a substantially conical stream of air (or generally a stream of gas) L, the spray head 20 being arranged in front of and at a distance from a (flat) substrate S to be sprayed so that the stream of air L acts upon the substrate S (FIG. 1c). During operation, the spray head 20 is connected to a compressed air source (not shown) via a supply line 21. The pressure of the compressed air is, for example, 3-4 bar; the air throughflow rate is, for example, 200-600 l/min.

(17) The application tip 14 of the application container 10 is introduced laterally into the stream of air L generated by the spray head 20, that is to say transversely with respect to the main direction of flow of the stream of air L, so that the free end (the outlet opening) of the application tip 14 is located approximately centrally (axially) in the stream of air L at a relatively small axial distance ds (FIG. 2d) from the spray head 20.

(18) By axial displacement of the plunger 12 in the chamber 11 of the application container 10, paint formulation F is introduced from the application container 10 into the stream of air L, where it is atomised. The spray mist consisting of the mixture of air and extremely small paint droplets is indicated by FN in FIG. 1d. The spray mist FN acts upon the substrate S and produces a patch of coating FS thereon.

(19) The outlet opening of the application tip 14 of the application container 10 must be sufficiently small to deliver very fine droplets of the paint formulation F into the stream of air L. The distance ds of the application tip 14 from the spray head 20, or rather the main nozzle 24 thereof, is only a few millimetres, typically about 0.01-5 cm. The application tip 14 can be straight, as shown as 14a in FIG. 7a, and project into the stream of air L at a right-angle, so that the outlet opening of the tip is likewise located at a right-angle to the stream of air, or, as shown in FIG. 7b, is in the form of a curved application tip 14b in which the front portion of the tip is bent over so that the outlet opening of the tip lies parallel to the stream of air. Alternatively, the application tip can also be provided with one or more lateral outlet openings. It is also possible for the outlet opening of the application tip to open into the stream of air at angles other than a right-angle or parallel to the main direction of flow of the stream of air L.

(20) In order to apply a homogeneous paint layer to the entire area of the substrate S to be sprayed, the substrate S, for example as shown in the diagram in FIG. 6, is moved in one or two directions (horizontally and/or vertically) in its own plane. This can also be advantageous if a coating is to be applied to an area of the substrate S that is larger than can immediately be acted upon by the spray mist FN. A possible travel path of the substrate S is indicated by 65 in FIG. 6. The axial distance between the substrate S and the spray head 20 remains constant, but in an advantageous implementation could also be adjusted during a spraying operation or between a plurality of spraying operations. As an alternative to the movement of the substrate S, it is also possible for the spray head 20 together with the application tip 14 of the application container 10 to be moved in one or two dimensions transversely with respect to the direction of flow of the spray mist FN.

(21) A commercially available spray head can be used as spray head 20. An example of a suitable spray head 20 is shown in FIGS. 2a-2d in a drawing showing three views (FIGS. 2a-c) and a sectional view (FIG. 2d).

(22) The spray head 20 has a housing 22, at one end of which there is arranged an inlet 23 for the connection of the compressed air supply line 21 (FIG. 1c). At the other end of the housing there are arranged an axial main nozzle 24 and two diametrically opposite horn air nozzles (or, generally, horn gas nozzles) 25. The axial main nozzle 24 and the two horn air nozzles 25 are in communicating connection with the inlet 23 via ducts 26 and 27, respectively, provided in the housing 22. The main nozzle 24 and the two horn air nozzles 25 together generate the afore-mentioned, substantially conical air jet L which, as a result of the inwardly directed, advantageously adjustable horn air streams (or, generally, horn gas streams) generated by the two horn air nozzles 25, can be varied in shape between a wide jet and a round jet.

(23) It would also be possible to use as spray head 20 a commercially available spray head having (a) feed opening(s) for the substance to be sprayed, in which case, however, its feed opening(s) for substance to be sprayed would be inactive or closed, that is to say the spray head would serve only for generating the stream of gas.

(24) FIGS. 3-5 show an exemplary embodiment of a complete spray device which is suitable for carrying out the spraying process according to the invention fully automatically.

(25) The spray device is constructed on a base plate 1. On the base plate 1 there are arranged a first multi-axis robot 30, a holder 40 for the spray head 20, a holder 50 for an application container 10, a second multi-axis robot 60 and a spray chamber 70. Also located on the base plate 1 are a magazine 81 for a supply of application containers 10, a waste container 82 for empty or discarded application containers 10 and a collecting container 90 for receiving finished sprayed substrates S.

(26) The first (multi-axis) robot 30 constructed on a mounting frame 31 comprises as main element a multi-axis robot arm 32, on the foremost end of which there is arranged a gripping mechanism 33 for taking hold of an application container 10. The holder 40 is essentially a pedestal. The spray head 20 is mounted at its upper end. The spray head is (during operation of the device) connected to a compressed air source (not shown) via the supply line 21. The holder 50 is likewise essentially a pedestal, at the upper end of which there are arranged a receiving device 51 and a guide 52 (FIG. 4) for an application container 10. On the holder 50 there is also arranged a drive device 53 for the plunger 12 of an inserted application container 10 (FIG. 4). This drive device can be an advancing drive, as known, for example, from fully automatic pipetting systems. The plunger 12, the plunger rod 13 and the drive device 53 together form discharge means for discharging the substance located in the application container 10 into the stream of gas L.

(27) The second multi-axis robot 60, which is likewise constructed on a mounting frame 61, comprises as main element a robot arm 62 which, similarly to an XY table, can be moved vertically (perpendicular to the base plate 1) and horizontally (perpendicular to the plane of the drawing). At the free end of the robot arm 62 there is arranged a holding device 63 for a substrate S to be coated. The holding device 63 can be, for example, in the form of a vacuum holding device which (during operation) is connected to a vacuum source or source of reduced pressure (not shown) via a line 64.

(28) The spray chamber 70 forms an extractor for stray spray mist, i.e. spray mist bypassing the substrate, which is advantageously provided with a filter and is connected to a suction device (not shown) via a suction tube 71.

(29) The relative arrangement of the described components of the spray device can be seen clearly from FIG. 3 (side view) and FIG. 4 (view from above).

(30) The spray device further comprises an electronic controller 100 which actuates the two multi-axis robots 30 and 60, the drive device 53 for advancing the plunger 12 of the application container, as well as the necessary valves (vacuum, spray head control). The controller 100 need not necessarily be arranged on the base plate 1, but can also be realised, for example, by an appropriately connected external computer. The controller 100 can also be configured so that, by means of adjusting means (not shown herein), it adjusts the distance between the application tip of the application container and the spray head and optionally also the distance between the application tip of the application container and the substrate, either as a result of a manual command or automatically on the basis of, for example, an analysis of the spray pattern on the substrate.

(31) FIG. 3 shows the spray device in the non-operating configuration. The magazine 81 holds a number of pre-filled application containers 10. A substrate S to be sprayed is held in place on the holding device 63 of the second multi-axis robot 60.

(32) The mode of operation of the spray device is as follows, all the workflows being initiated and controlled by the controller 100:

(33) In response to the start command of the controller 100, the arm 32 of the first multi-axis robot 30 is moved over the magazine 81 and with its gripping mechanism 33 picks up an application container 10 held in readiness therein. The application container 10 is then moved by the multi-axis robot 30 to the storage container V and the tip of the application container is dipped into the paint formulation F. Here a desired (relatively small) amount of the paint formulation F is sucked into the application container 10 by withdrawal of the plunger 13 (see FIG. 1b). The arm 32 of the multi-axis robot 30 then moves over the holder 50 and travels with the application container 10 into the receiving device 51 and guide 52 of the holder (FIG. 4). As described in connection with FIGS. 1c and 1d, the tip 14 of the application container 10 is located in front of the spray head 20 and at an axial distance therefrom essentially approximately in the centre of the stream of air L generated by the spray head 20. Advantageously the distance between the spray head 20 and the application tip 14 can be altered automatically during the spraying operation or manually between individual spraying operations in such a way that the spray pattern (affects patch of coating FS) can be adjusted in respect of size and paint mist density.

(34) Once the spray head 20 has been activated and the said stream of air is stable, the drive device 53 on the holder 50 displaces the plunger 12 of the application container 10, the paint formulation F located in the application container 10 gradually being introduced from the latter into the stream of air L and, by its atomisation, forming a paint formulation mist FN which in turn acts upon the substrate S (FIG. 5). The movement of the plunger 12 of the application container 10 can alternatively also be effected by the first multi-axis robot 30 by means of its gripping mechanism 33. The speed with which the paint formulation F is delivered into the stream of air L, and/or the stream of air itself (amount of air, air speed), can be varied in order to alter the spray pattern.

(35) If necessary, during the spraying operation the substrate S can be moved up and down as well as back and forth by means of the second multi-axis robot 60, as shown in the diagram in FIG. 6. Advantageously, the distance between the application tip 14 and the substrate S can be altered during the spraying operation or manually between individual spraying operations in such a way that the spray pattern (affects patch of coating FS) can be adjusted in respect of size and spray mist density.

(36) After the end of the spraying operation, the application container 10 is thrown into the waste container 82 by means of the first multi-axis robot 30. The finished sprayed substrate S is then deposited in the collecting container 90. This too can be effected, for example, by means of the first multi-axis robot 30 insofar as it is equipped with suitable mechanisms for taking hold of the substrate.

(37) If necessary, the described workflows are repeated with a fresh substrate and a fresh application container.

(38) As shown in FIG. 8, a further advantageous embodiment of the spray device according to the invention has, instead of the first and second robots, a single multi-function robot 130 which assumes the functions of those two robots: the multi-function robot 130 picks up, for example, the application container 10 with the application tip 14 and fixes them in a spraying tool 120, which is stored on a parking station 110, can be picked up by the multi-function robot and has an inbuilt spray head 20 and an application container holder 51 including the drive 53 (the latter two components not being shown in FIG. 8 for clarity of the drawing), then picks up that spraying tool 120 and, during the spraying operation, moves it along a substrate S which is fixedly mounted on a substrate holder 66 (see also FIG. 6).

(39) In a further embodiment, not shown in the drawings, the spray device is configured to introduce the application tips 14 of more than one application container 10 simultaneously or sequentially into the stream of air L of the spray head 20. This enables a plurality of different paint formulations F to be sprayed either immediately one after the other or even simultaneously, thus allowing intermixing of the different paint mists FN. This is an advantage, for example, for the application of two-component systems, but it would in that way also be possible for a solvent or some other auxiliary substance to be added to the spray mist in addition to the paint formulation F, for example in order to compensate for the evaporation of the solvents contained in the paint formulation at high ambient temperatures.