Equipment for applying coating agents and method for cleaning the equipment

Abstract

To provide a facility for applying a coating agent having a printing nozzle that can be easily cleaned.SOLUTION: A facility for applying a coating agent includes one set 10 of printing nozzles 12. Each of the printing nozzles has an outlet channel 126 extending in a downstream direction to a discharge orifice 127 for the coating agent. The facility further includes a cleaning station 30 for at least one nozzle among the one set of printing nozzles. The station has at least one cleaning fluid injector 38 in outlet channels of the printing nozzles via the discharge orifice.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an installation for applying a coating agent comprising a set of nozzles each having an outlet channel extending downstream to a discharge orifice for the coating agent.

[0002] The demand for customizing the decoration of objects is on the rise. For example, dual-tone coatings for car bodies are on the rise. Furthermore, the generation of patterns with specific shapes is of potential interest for certain markets. In this context, the coatings industry has been exploring ways to "print" paint using printheads rather than spraying it using a sprayer in recent years. [Background technology]

[0003] Current printheads are designed to operate with very low viscosity inks, especially below 20 millipascal seconds (mPas), containing very small particles on the submicron scale. To apply coatings such as paints using printing techniques, it is usually necessary to use print nozzles with paint ejection orifices having a small diameter of about 150-200 micrometers (μm), much smaller than the diameter of the exit orifices of sprayers, which are generally larger than 800 μm. In the field of ink printing, the color of the applied layer of ink results from a combination of four base colors, namely cyan, magenta, yellow and black. However, in the field of paints, the color of the applied layer is determined by the pigments dispersed in the paint. Summary of the Invention [Problem to be solved by the invention]

[0004] For reasons of economy and practicality, the same applicator is generally used with multiple nozzles for applying paints of different colors, and in this case, each nozzle must be cleaned when changing the coating material, i.e., when changing colors.

[0005] When applying paint using printing techniques, due to the small dimensions of the nozzle outlet orifices, the known technique of circulating a cleaning fluid after each application at the nozzles is unable to effectively clean the outlet channel of each nozzle, in particular the cleaning agent discharge orifice, which can lead to clogging of the nozzles, which can lead to mixing of paints used successively at one set of nozzles.

[0006] Furthermore, individual cleaning of nozzles is known from WO2018 / 108568, but the technique is time-consuming and difficult to apply in practice.

[0007] More specifically, the invention addresses the above mentioned drawbacks by proposing a new installation for applying coating agents, which has a printing nozzle and which can be easily cleaned. [Means for solving the problem]

[0008] The invention therefore relates to an installation for applying a coating agent, comprising a set of printing nozzles, each of which has an outlet channel extending in a downstream direction to an outlet orifice for the coating agent, and according to the invention, the installation further comprises a number of injectors arranged to simultaneously clean all nozzles of the set of printing nozzles or a number of nozzles in a row of nozzles by injecting a cleaning fluid into the outlet channel through the outlet orifice of the set of printing nozzles or the row of nozzles.

[0009] According to the invention, a simultaneous cleaning of the downstream parts of several printing nozzles, i.e. the outlet ducts and the discharge orifices, is carried out in a direction opposite to the normal flow direction of the coating agent at each nozzle, which is the flow direction of the coating agent during application. This cleaning is particularly effective and time-saving in the case of a matrix nozzle configuration, since it can be carried out simultaneously for a large number of nozzles of a set of printing nozzles, for example for all nozzles of a row of nozzles.

[0010] According to optional and advantageous aspects of the invention, such equipment may include one or more of the following features in any technically permissible combination:

[0011] The cleaning station has one or more sealing gaskets that isolate the ejection orifices of the print nozzles from the outside world when a set of print nozzles is mounted in the cleaning station.

[0012] One or more sealing gaskets individually isolate the ejection orifices from the outside when a set of print nozzles is mounted in the cleaning station.

[0013] The cleaning station includes a member for cleaning a front surface of at least one, and preferably each, print nozzle.

[0014] Nozzles of the set of print nozzles protrude from a front face of the assembly. The cleaning station includes a plurality of housings. The housings at least partially receive the print nozzles when a front face of the set of nozzles faces or is positioned against a top or side face of the cleaning station. The housings extend to the top or side face of the cleaning station, and a cleaning fluid injector is provided in communication with the housings.

[0015] The print nozzles have exit orifices that are flush with the front faces of the set of print nozzles. The cleaning station has a top or side face with which the cleaning fluid injectors communicate. When the front faces of the set of print nozzles are positioned against the top or side face of the cleaning station, the print nozzles have exit orifices that are aligned with the injectors of the cleaning station, respectively.

[0016] The cleaning station has a body with a cleaning fluid circulation channel therein, and an injector is mounted in the body downstream of the channel.

[0017] The system further includes a multi-axis robot that moves the set of print nozzles between a spray position, where the set of print nozzles is oriented toward the object to be coated, and a cleaning position, where the set of print nozzles contacts a cleaning station.

[0018] Each printing nozzle has a printhead with an outlet orifice having an inner diameter of 50 to 300 μm, preferably 100 to 200 μm, and more preferably around 150 μm.

[0019] The ratio of the inner diameter of the nozzle's outlet orifice to the diameter of the injector is 0.03 to 0.5, preferably 0.05 to 0.2.

[0020] The print nozzles of the set of print nozzles are arranged in at least one row, and the injectors of the cleaning station are provided in the same number of rows, and a spacing between two adjacent injectors in a row of injectors is equal to a spacing between two adjacent print nozzles in the row of print nozzles.

[0021] The set of nozzles includes a first bleed valve, and the cleaning station includes a second bleed valve, each of which allows cleaning fluid to be drained after use.

[0022] According to a second aspect, the invention relates to a method for cleaning a set of printing nozzles of said installation, i.e. an installation for applying a coating agent, each printing nozzle having an outlet channel extending in a downstream direction to an outlet orifice for the coating agent. According to the invention, the method comprises at least one step consisting of a) injecting a cleaning fluid into the outlet channels of several printing nozzles simultaneously through the outlet orifices.

[0023] This method provides the same advantages as the apparatus of the present invention.

[0024] Advantageously, the method of the invention comprises at least one additional step consisting of b) directing a flow of cleaning fluid towards a front surface of each print nozzle where its ejection orifice is located.

[0025] According to another advantageous aspect, the method comprises, before step a), and if necessary before step b), at least the steps of: y) moving the set of printing nozzles from a spray position in which the set of printing nozzles are oriented towards the object to be coated to a pre-cleaning position in which the set of printing nozzles face the cleaning station; and z) closely positioning the set of printing nozzles relative to the cleaning station such that the ejection orifices of the printing nozzles are aligned with cleaning fluid injectors in the cleaning station.

[0026] According to another advantageous aspect of the invention, the method includes the additional step of c) injecting a cleaning fluid into a printing nozzle that is part of the set of printing nozzles, from the supply duct through the outlet channel towards the discharge orifice.

[0027] The invention can be understood in more detail and other advantages will become more apparent from the following description of three exemplary embodiments of an installation and a method according to its principles, given with reference to the attached drawings, in which: [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is a schematic diagram of an installation according to the invention. [Diagram 2] FIG. 2 is a partial cross-sectional view of a cleaning station and a set of nozzles provided in the installation of FIG. [Diagram 3] FIG. 3 is an enlarged view of a portion III in FIG. [Figure 4] FIG. 4 is a view similar to FIG. 3, showing an installation according to a second embodiment of the invention. [Diagram 5] FIG. 5 is a view similar to FIG. 1, showing an installation according to a third embodiment of the invention. [Figure 6] FIG. 6 is a view similar to FIG. 3 and shows the installation of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] 1 to 3 is provided for applying paint to an object O that is movable by a conveyor 2. The object O is suspended from the conveyor 2 by a hook 4.

[0030] In the illustrated example, the object O is a flat panel of the kind used worldwide, although in variants the object may include an automobile body part or an entire automobile body moving on a stop-and-go or continuous forward conveyor.

[0031] Equipment I has a set of nozzles 10 attached to the end of an arm 22 of a multi-axis robot 20 located near a conveyor 2 .

[0032] In FIG. 1, the perspective is exaggerated and a known robot 20 is shown small.

[0033] The nozzle set 10 has eight nozzles 12 arranged in a row, each protruding from a front face 14 of the nozzle set, which when the nozzles 12 are used to apply paint is oriented towards an object O to be painted.

[0034] As can be seen in Figure 2, each printhead 13 with its nozzles 12 has a control member 132, for example of the piezoelectric type, and a rod 134. Each nozzle 12 has a needle 122 that is controlled by the control member 132 of the printhead 13 to which the nozzle belongs. The needle is attached to the control member 132 via a rod 134.

[0035] The paint to be applied flows through channels 16 in the body 11 of a pair of nozzles 10 and circulates in the direction of arrow F2 in FIG.

[0036] According to one aspect of the invention shown in Figure 2, a set of nozzles 10 is provided with a supply valve 102, a bleed valve 104 and a recirculation valve 106. A bleed valve 304 is provided to control the discharge of cleaning fluid to a collector (not shown) after use of the circulating wash. In this view, the valves 102, 104 and 106 are shown on the outside of the body 11. In practice, these valves are integral with the body and therefore are not shown in Figure 1.

[0037] Reference numeral 121 denotes a portion of the nozzle 12 that protrudes from the surface 14 .

[0038] Located within a portion 121 of the nozzle 12 is a seat 125 against which a nozzle needle 122 is selectively supported and controlled by an element 132.

[0039] An outlet channel 126 is provided in each nozzle 12 downstream of the needle 122. The outlet channel 126 is located opposite the needle 122 and extends outwardly through an outlet orifice 127. The outlet orifice 127 is disposed in a front face 128 of the nozzle 12, more specifically, in the front face 128 of a portion 121 of the nozzle 12.

[0040] In a variant, nozzles 12 having different structures may be used, as long as they have an outlet channel 126 and an exit orifice 127, which are advantageously identical to each other.

[0041] The installation I also includes a cleaning station 30. The cleaning station 30 is supplied with a cleaning fluid via a hose 40. The hose 40 is connected to the station 30 via a coupling 42 that constitutes the downstream end of the hose 40.

[0042] The cleaning station 30 is located in the booth where the paint is applied, in an area reachable by the multi-axis robot 20 .

[0043] The cleaning station 30 has a body 31. Eight housings 32 are arranged in a row in the body 31. Each housing 32 is configured to partially or entirely receive a portion 121 of the nozzle 12.

[0044] Each housing 32 has a groove 322 at the interface between the bottom 326 and the annular wall 328. Disposed within groove 322 is a sealing gasket 34. Sealing gasket 34 is preferably an O-ring type gasket and is formed from an elastomer.

[0045] The body 31 is provided with channels 36 through which the cleaning fluid is supplied from a hose 40 to each of the housings 32. More specifically, a set of channels 36 communicate with each housing 32 respectively via injectors 38. Advantageously, the injectors 38 are channels with a diameter d38 smaller than the diameter of the channels 36. This allows for an even distribution of the flow rate of the cleaning fluid towards the injectors 38 by providing a gradual head loss in the flow path of the fluid in the channels 36, thereby preventing the creation of specific flow paths.

[0046] According to one aspect of the invention shown in Figure 2, the cleaning station 30 is provided with a supply valve 302 and a bleed valve 304. The bleed valve 304 is provided to control the discharge of cleaning fluid to a collector (not shown) after use in circulating cleaning. In this view, the valves 302, 304 are shown on the outside of the body 31. In practice, these valves are integral with the body and therefore are not shown in Figure 1.

[0047] The cleaning fluid flowing through the hose 40, the channel 36 and the injector 38 may be a cleaning fluid that is solvent or water-soluble, or that contains a gas, particularly air or a mixture of liquid and gas, that affects the properties of the paint applied using the nozzle 12.

[0048] Each housing 32 extends to the upper surface 33 of the station 30 via a bevel 324 that serves to guide the portions 121 as they are inserted together into the housings 32, as will be described below.

[0049] During application of paint to an object O, the set of nozzles 10 is directed at one of the objects and coating material is supplied to the nozzles 12 through the channel 16. The supply valve 102 and the recirculation valve 106 are open and the bleed valve 104 is closed. Each needle 122 is individually controlled by a component 132 associated with the printhead 13 to selectively move away from the corresponding seat 125. This allows control of whether or not paint is supplied to the outlet channel 126 of each nozzle 12. In this case, paint flows in the direction of the arrow F3 in FIG. 2 and is discharged from the corresponding nozzle 12 through the discharge orifice 127 towards the object O to be coated.

[0050] Thus, arrow F3 indicates the normal flow direction of paint being applied to object O.

[0051] During the application phase, if the nozzles 12 need to be cleaned, for example to change the color of the paint, a set of nozzles 10 are moved above the cleaning station 30 by the multi-axis robot 20 and placed in a pre-position by positioning the front surface 14 above and parallel to the upper surface 33, as shown by arrow F4 in FIG. 1.

[0052] The set of nozzles 10 is then securely supported in the cleaning station 30 by inserting a portion 121 of the nozzles 12 into the housing 32 in the direction of the arrow F5 in FIG.

[0053] The portion 121 and orifice 32 are shaped such that after movement along arrow F5, the discharge orifice 127 of each nozzle 12 is aligned with the injector 38 of station 30.

[0054] The duct 36 can then be supplied with cleaning fluid by activating the booster pump or other supply means of the hose 40. The supply valve 302 is then open and the bleed valve 304 is closed. The cleaning fluid thus flows from each injector 38 through the discharge orifice 127 in the direction of the arrow F6 in FIG. 3, i.e. in the direction opposite to the normal flow direction of the paint in the nozzle during application as indicated by the arrow F3, into the outlet channel 126 of the nozzle 12, the portion 121 of which is arranged in the housing 32.

[0055] Thus, the nozzles 12 engaged in the housing 32 are simultaneously cleaned. The cleaning fluid entering each outlet duct 126 raises the seat 125 and needle 122 of the nozzles, which are also cleaned. The bleed valve 104 is open and the supply valve 102 and recirculation valve 106 are closed, allowing flow in the opposite direction in the nozzles 12.

[0056] Reference numeral 123 denotes a joining edge between a front surface 128 of the nozzle 12 and a peripheral surface 129 of the portion 121. In a configuration during injection of cleaning fluid into the outlet channels 126 through each discharge orifice 127 of the plurality of nozzles 12, the joining edge 123 abuts the corresponding seal 34, thus isolating the front surface 128 from the outside. Each discharge orifice 127 and each front surface 128 are therefore individually isolated from the outside by the seal 34.

[0057] As a result, the flow of cleaning fluid leaving the injector 38 is distributed against the front face 128 of the corresponding nozzle 12, cleaning said front face. The injector 38 thus constitutes a cleaning member for the inner part of the nozzle 12 formed by the needle 122, the seat 125 and the channel 126, and a cleaning member for the front face 128 of the nozzle.

[0058] 4 to 6, the same reference numerals are used for components similar to those in the first embodiment. The following mainly describes the differences between the first embodiment and the second and third embodiments.

[0059] 4, O-ring 34 is disposed within groove 32 at the bottom 326 of housing 32 rather than at the junction between the side and bottom of housing 32. Seal 34 fluidly isolates a smaller portion of front surface 128 of nozzle 12, portion 121 of which is disposed within housing 32.

[0060] In a third embodiment shown in Figures 5 and 6, the set of nozzles 10 comprises nozzles 12. The nozzles 12 are arranged in three rows, each row including eight nozzles 12. The front faces 128 of the nozzles 12 are flush with the front face 14 of the set of nozzles 10. Thus, the exit orifices 127 of the nozzles 12 are located at the front face 14.

[0061] 5, a cutaway shows only one nozzle 12. Each nozzle 12 is provided in a printhead (not shown), which in the first embodiment is in the form of a printhead 13.

[0062] The cleaning station 30 is also supplied via a hose 40 and a downstream hose connection 42. The cleaning station 30 has 24 injectors 38. The injectors 38 are arranged in three rows, each row containing eight injectors.

[0063] The multiple injectors 38 are provided directly on the upper surface 33 of the main body 31 of the station 30. That is, in this embodiment, no housing like the housing 32 in the first and second embodiments is provided.

[0064] The outlet orifice 382 of each injector 38 provided in the upper surface 33 is surrounded by a groove 332 provided in the upper surface 33 of the body 31. An O-ring 34 is placed in the groove 332. The depth of the groove 332 and the toroidal diameter of the seal 34 are selected so that, when placed in the groove 332, the O-ring 34 protrudes from the groove 382 over a height h34 of 0.1 to 0.5 mm. Thus, if cleaning of the nozzles 12 is required after the paint application stage, the set of nozzles 10 is moved in the direction of the arrow F4 in FIG. 5 to be placed in a pre-cleaning position with the front surface 34 facing the upper surface 33 of the cleaning station 30. The set of nozzles 10 is then moved in the direction of the arrow F5 in FIG. 5 to be closely supported by the seals 34.

[0065] Again, each discharge orifice 17 and each front face 128 are isolated from the outside by a seal 34, respectively.

[0066] The cleaning fluid is then fed to the injector 38, which circulates the cleaning fluid in the direction of arrow F6 in Figure 6, through the outlet orifice 127 and through the inside of the outlet channels 126 of the nozzle 12 to the seat and needle of the nozzle. The placement of the seal 34 also allows for the front face 128 of the nozzle 12 to be cleaned.

[0067] In the second and third embodiments, like the first embodiment, a supply valve, a bleed valve and a recirculation valve (not shown) are provided.

[0068] In practice, regardless of the embodiment, the diameter d38 of the injector 38 is adapted to the diameter d126 of the outlet channel 126 and to the diameter d127 of the discharge orifice 127. The diameters d126 and d127 may be of the same size. For example, these diameters are between 50 μm and 300 μm, preferably between 100 μm and 200 μm, and even more preferably 150 μm. In this case, the diameter d38 of the injector 38 is between 0.5 mm and 2 mm, preferably around 1 mm. Advantageously, regardless of the embodiment, the ratio d126 / d38 and / or the ratio d127 / d38 is between 0.03 and 0.5, preferably between 0.05 and 0.2.

[0069] The invention has been described in the context of a paint being the coating material applied by means of the nozzle 12. However, other coating materials may also be applied in the installation of the invention, such as in particular a primer or a varnish.

[0070] The invention has been described with respect to a set of nozzles 10 docking from above into the cleaning station 30. In a variant, said docking may be from the side of the cleaning station, in which case the openings 382 of the injectors 38 or the housings 32 are located on the side of the body 31 rather than on the top surface 33 of the body.

[0071] Regardless of the embodiment, the cleaning station 30 may be manufactured by 3D printing with adjustable distribution and placement of the channels 36 and injectors 38 within the cleaning station body without the use of molds with slide valves or complex machining lines, although the cleaning station may also be manufactured by casting and / or machining.

[0072] The number of rows of print nozzles 12 is selected to be one or more depending on the size of the surface to be coated of each object O. Accordingly, the number of rows of injectors 38 is also selected to be one or more.

[0073] Reference e12 denotes the spacing between two print nozzles 12 in a row of print nozzles, and reference e38 denotes the spacing between two injectors 38 in a row of injectors. Regardless of the embodiment, the spacings e12 and e38 are selected such that the nozzles and injectors are matched for the purposes of coordinating with each other.

[0074] According to an advantageous aspect of the invention applicable to all embodiments, to further improve the cleaning of the printing nozzles 12, before or after the injection of the cleaning fluid into the outlet channel 126 via the discharge orifice 127 in the direction of the arrow F6, a cleaning fluid may be injected into each printing nozzle in the normal flow direction of the coating material, i.e. from the supply channel 16 through the outlet channel 126 towards the discharge orifice 127 in the direction of the arrow F3 in Fig. 2. In this case, it is assumed that the cleaning fluid is injected into the channel 16 upstream of the supply valve 102, while the supply valve 102, the bleed valve 104 and the bleed valve 304 are in an open state, and the recirculation valve 106 and the supply valve 302 are in a closed state. When this optional aspect of the invention is implemented, the cleaning of the injection nozzle 12 is performed in both directions, i.e. in the direction of the arrow F6, when the valves 302, 104 are open and the remaining valves are closed, and continuously in the direction of the arrow F3, when the valves 102, 104, 304 are open and the remaining valves are closed.

[0075] Regardless of the embodiment, the addition of a bleed valve 104, 304 allows cleaning fluid to be collected to clean one or more nozzles 12 after use without contaminating the coating or unused cleaning fluid.

[0076] The present invention has been shown and described with all nozzles 12 in a set of nozzles 10 being cleaned simultaneously. However, this is not required. Nozzles may be cleaned in groups, for example row by row in the case of a set of nozzles 10 having multiple rows. In this case, the distribution of injectors 38 in the cleaning station 30 is coordinated with the distribution of seals 34 and channels 36.

[0077] The above embodiments and modifications may be combined to form new embodiments of the present invention.

Claims

1. An apparatus for applying a coating agent, comprising: a set of printing nozzles; each of said printing nozzles having an outlet channel extending downstream to an outlet orifice for a coating material; The apparatus further comprises a washing station; the cleaning station comprises a plurality of injectors; the plurality of injectors are arranged to simultaneously clean all nozzles of the set of printing nozzles or a plurality of nozzles in the row of nozzles by injecting cleaning fluid into the outlet channel through an exit orifice of the set or row of nozzles; the cleaning station includes a cleaning member for cleaning a front surface of at least one print nozzle; The ratio of the inner diameter of the outlet orifice of the nozzle to the diameter of the injector is between 0.03 and 0.

5.

2. 2. The apparatus of claim 1, wherein the cleaning station comprises one or more sealing gaskets that isolate the ejection orifices of the set of printing nozzles from the outside when the set of printing nozzles is disposed in the cleaning station.

3. 3. The apparatus of claim 2, wherein the sealing gasket individually isolates the ejection orifices from the outside when the set of printing nozzles is disposed in the cleaning station.

4. 4. The facility according to claim 1, wherein the cleaning member is for cleaning each of the printing nozzles.

5. the nozzles of the set of print nozzles protruding from a front surface of the set of print nozzles; The cleaning station comprises a plurality of housings; the plurality of housings at least partially receive the printing nozzles when the front faces of the set of nozzles face or are disposed against a top or side surface of the cleaning station; the housing extends to the top or side of the cleaning station; The apparatus of any one of claims 1 to 4, further comprising a cleaning fluid injector extending to the housing.

6. the ejection orifice of the print nozzle is flush with a front surface of the set of print nozzles; the cleaning station having a top or side surface with a cleaning fluid injector in communication therewith; 5. The apparatus of claim 1, wherein when the front faces of the set of printing nozzles are positioned against the top or side face of the cleaning station, the ejection orifices of the printing nozzles are aligned with the injectors of the cleaning station, respectively.

7. The cleaning station has a body having a cleaning fluid circulation channel therein; 7. The installation according to claim 1, wherein the injector is provided in the body downstream of the channel.

8. The apparatus further comprises a multi-axis robot; 8. The apparatus of claim 1, wherein the multi-axis robot moves the set of printing nozzles between a spray position, in which the set of printing nozzles is oriented towards an object to be coated, and a cleaning position, in which the set of printing nozzles contacts the cleaning station.

9. An installation according to any one of the preceding claims, characterized in that each printing nozzle comprises a printhead, the ejection orifice having an inner diameter of 50 to 300 μm.

10. The apparatus according to claim 9, characterized in that the inner diameter of the orifice is 100 to 200 μm.

11. 11. The installation according to claim 10, characterized in that the inner diameter of the orifice is 150 μm.

12. The installation according to any one of claims 1 to 11, characterized in that the ratio is between 0.05 and 0.

2.

13. the print nozzles in the set of print nozzles are arranged in at least one row, and the injectors of the cleaning station are provided in a number of rows equal to the number of rows of the print nozzles; 13. An arrangement according to any of the preceding claims, characterized in that the spacing between two adjacent injectors in a row of injectors is equal to the spacing between two adjacent print nozzles in a row of print nozzles.

14. a first bleed valve is provided in the set of nozzles; 14. The installation according to any one of claims 1 to 13, characterized in that the washing station is provided with a second bleed valve, each of the first and second bleed valves allowing the drainage of washing fluid after use.

15. 1. A method for cleaning a set of print nozzles in an installation for applying a coating agent, comprising the steps of: each of said printing nozzles having an outlet channel extending downstream to an outlet orifice for a coating material; The method comprises: a) using an installation according to any one of claims 1 to 14 for simultaneously injecting a cleaning fluid into the outlet channel through the exit orifices of all nozzles of the set of printing nozzles or of a plurality of printing nozzles of a row of nozzles.

16. 16. The method of claim 15, further comprising the step of: b) directing a flow of cleaning fluid at a front face of the printing nozzle where the ejection orifice is located.

17. y) moving the set of printing nozzles from a spray position in which the set of printing nozzles is oriented at an object to be coated to a pre-clean position in which the set of printing nozzles faces a cleaning station; z) closely distributing the set of printing nozzles relative to the cleaning station such that the ejection orifices of the printing nozzles are aligned with cleaning fluid injectors in the cleaning station; 17. The method according to claim 15 or 16, characterized in that it comprises at least the step consisting of: before step a) and, if necessary, before step b).

18. 18. The method of claim 15, further comprising the step of: c) injecting a cleaning fluid into a print nozzle that is part of the set of print nozzles from a supply duct through the outlet channel towards the discharge orifice.

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