Printing head comprising a maintenance circuit and coating installation

Abstract

The invention relates to a print head (1) for applying a coating product to an object to be coated. The print head comprises a body (10) in which several nozzles (11) are arranged, each nozzle having an ejection orifice (112) and an outlet channel (111) opening into an ejection zone (2) for the coating product through the ejection orifice (112), as well as a coating product supply circuit (12) connected to the nozzle (11). The print head further comprises a maintenance circuit (13) for conveying a maintenance fluid and extending inside the body (10) to the ejection zone (2) of the nozzle (11). The maintenance circuit comprises several internal channels (131), each opening into the ejection zone of a single nozzle associated with the first internal channel. The number of first channels (131) is equal to the number of nozzles (11).

Description

DOMAINE TECHNIQUE DE L'INVENTION

[0001] The technical field of the invention is that of the application by printing of a coating product onto an object to be coated.

[0002] The present invention relates more particularly to a print head for applying a coating product to an object to be coated and a coating installation comprising the print head. ARRIERE-PLAN TECHNOLOGIQUE DE L'INVENTION

[0003] The customization of decorations and coatings applied to objects is becoming increasingly common. This is the case, for example, in the automotive industry for vehicle body coatings. These coatings can be monochrome, two-tone, or multi-tone paint finishes. Furthermore, creating patterns with specific geometries is proving advantageous for other markets, particularly for visually differentiating two products based on their intended use or manufacturing process. In this context, the coating industry has recently explored solutions involving "printing" paint using printheads, rather than spraying it with spray guns.

[0004] The paints used for printing coatings have viscosities ranging from 50 to 200 millipascal-seconds (mPas) and contain pigment particles with dimensions on the order of micrometers. To apply these paints, a print head equipped with multiple nozzles is generally used. The print head is, for example, mounted on the arm of a multi-axis robot. Each nozzle includes an output channel opening to the outside through a small-diameter ejection orifice, typically on the order of 100 µm to 200 µm, which is significantly smaller than the dimensions of a spray gun orifice (generally greater than 800 µm).

[0005] Due to the small diameter of the nozzle ejection orifices, there is a risk of nozzle clogging by paint residue. Therefore, nozzle cleaning operations are performed between printing phases to prevent clogging and maintain good print quality.

[0006] Furthermore, for reasons of economy and practicality, the same print head is generally used to apply different colored paints. This means that each nozzle must be cleaned when changing paints.

[0007] Patent application EP3725421A1 describes a coating product application system comprising a print head equipped with a set of nozzles and a nozzle cleaning station. The cleaning station includes a plurality of injectors designed to simultaneously clean several nozzles by injecting a cleaning fluid into the nozzle outlet channels through their ejection ports.

[0008] When it is necessary to clean the nozzles, for example in anticipation of a change of paint color, the print head is moved by the multi-axis robot to be positioned above the cleaning station.

[0009] To maximize printing time, and therefore production rate, it would be advantageous to mount the cleaning station with the print head on the multi-axis robot arm. However, the cleaning station for document EP3725421A1 is too bulky to be mounted with the print head and to be compatible with the short printing distance, i.e., the distance between the nozzles and the object to be coated.

[0010] It is also known that US5877788A cleans the nozzles of a print head with a fluid delivered through channels common to all the nozzle ejection ports. Ejection ports located near the channel openings are cleaned earlier and with a cleaner fluid than channels located further from these openings. Therefore, the cleaning of the nozzle ejection areas is not uniform. RESUME DE L'INVENTION

[0011] Therefore, there is a need to be able to clean different nozzles of a print head in a homogeneous way when the print head is in position for printing, i.e. in the vicinity of the object to be coated.

[0012] According to a first aspect of the invention, this need is met by providing a print head for applying a coating product to an object to be coated, the print head comprising a body in which are arranged: several nozzles each comprising an ejection orifice and an outlet channel opening into an ejection zone of the coating product through the ejection orifice; a coating product supply circuit connected to the nozzle; The print head further comprises a maintenance circuit for conveying a maintenance fluid, the maintenance circuit extending inside the body to the nozzle ejection zone and comprising a first internal channel opening into the ejection zone of at least one nozzle. According to the invention, the maintenance circuit comprises a plurality of first internal channels, each first internal channel opening into the ejection zone of a single nozzle associated with the first internal channel, the number of first internal channels being equal to the number of nozzles.

[0013] The maintenance circuit allows for the delivery of maintenance fluid to the ejection zone of each nozzle, or conversely, the removal of maintenance fluid from the ejection zone, thus cleaning the nozzle ejection orifices individually and uniformly. The maintenance circuit therefore offers a cleaning solution that is integrated into the printhead, is less bulky than prior art solutions, and is more efficient. Cleaning can thus be performed while the printhead is in the printing position.

[0014] In one embodiment of the print head, the maintenance circuit further includes a plurality of secondary internal channels, each secondary internal channel being associated with a primary internal channel and opening into the ejection zone of the single nozzle associated with the primary internal channel. This embodiment combines practicality (numerous possible maintenance operations) and cleaning performance.

[0015] According to one development of this embodiment, each second internal channel is located opposite the associated first internal channel with respect to the nozzle's ejection orifice, into the ejection zone of which this second channel opens. This arrangement of the first and second internal channels improves the cleaning of the ejection orifice and facilitates the flow of the maintenance fluid.

[0016] According to another development consistent with the previous one, each first internal channel and associated second internal channel are oriented in the same direction. This arrangement further facilitates the flow of the maintenance fluid.

[0017] In another embodiment, the maintenance circuit includes a first storage chamber for the maintenance fluid, the first storage chamber communicating with the nozzle ejection zone through a first opening.

[0018] According to a development of this third embodiment, the print head comprises a plurality of nozzles connected to the supply circuit, each nozzle comprising an ejection orifice and an outlet channel opening into an ejection zone, and the first maintenance fluid storage chamber communicates with the ejection zone of several nozzles (preferably all of the nozzles) through several first openings.

[0019] According to another development compatible with the previous one, the maintenance circuit further includes a second storage chamber for the maintenance fluid, the second storage chamber communicating with the ejection area of ​​the nozzle or several nozzles (preferably all the nozzles) by one or more second openings.

[0020] In addition to the characteristics mentioned in the preceding paragraphs, the print head according to the first aspect of the invention may have one or more additional characteristics from among the following, considered individually or in all technically possible combinations: The first internal channel is directed towards the nozzle ejection orifice; the print head includes an ejection face in which the nozzle ejection orifice is provided; the first internal channel is arranged so that the maintenance fluid circulates in contact with the ejection face; the first internal channel is oriented parallel to the ejection face; the first internal channel is inclined relative to the ejection face in the direction of the nozzle ejection orifice; the first internal channel is provided in a plate disposed on the ejection face of the print head; the first internal channel includes an end open to the ejection area and located at a distance less than or equal to 1 mm from the nozzle ejection orifice;The maintenance circuit includes a first storage chamber for the maintenance fluid, the first storage chamber communicating with the ejection zone of each nozzle by one of the first internal channels, the length of which is between 0.5 mm and 10 mm; the maintenance circuit further includes a first storage chamber for the maintenance fluid, the first internal channel connecting the first storage chamber of the maintenance fluid to the ejection zone of the nozzle; the first internal channels or the first openings extend through an internal wall of the body which separates the first storage chamber and the ejection zones of the nozzles; the first internal channels are provided in an external maintenance plate disposed on an ejection face of the body, in which the ejection orifices of the nozzles are provided;The first internal channel extends through an internal wall separating the first maintenance fluid storage chamber and the nozzle ejection area; the first internal channels have a cross-section with characteristic dimensions less than or equal to 0.5 mm, preferably less than or equal to 0.25 mm; the second internal channel is directed towards the nozzle ejection orifice; the second internal channel is arranged so that the maintenance fluid circulates in contact with the ejection face; the second internal channel is oriented parallel to the ejection face; the second internal channel is inclined relative to the ejection face in the direction of the nozzle ejection orifice; the second internal channel is arranged in a plate disposed on the ejection face of the print head; the second internal channel includes an end open to the ejection area and located at a distance less than or equal to 1 mm from the nozzle ejection orifice;The maintenance circuit further comprises a second maintenance fluid storage chamber, a second internal channel connecting the second storage chamber to the nozzle ejection zone; and the second internal channel extends through an internal wall separating the second maintenance fluid storage chamber and the nozzle ejection zone; the second internal channel further extends partially into the second maintenance fluid storage chamber; the coating product supply circuit comprises a coating product storage chamber and a plurality of distribution channels connecting the coating product storage chamber to the nozzles.

[0021] A second aspect of the invention relates to a coating installation comprising: a print head according to the first aspect of the invention; a maintenance fluid injection circuit connected to at least one inlet of the print head; a maintenance fluid suction circuit connected to at least one outlet of the print head.

[0022] Advantageously, the suction circuit includes: a vacuum generator; a first suction valve connected on one side to the vacuum generator and on the other side to a first output of the print head; and a second suction valve connected on one side to the vacuum generator and on the other side to a second output of the print head.

[0023] In one embodiment, the first output of the print head is confused with a first input-output of the maintenance circuit and the second output of the print head is confused with a supply input of the supply circuit.

[0024] In one embodiment, the first output of the print head is coincided with a first input-output of the maintenance circuit and the second output of the print head is coincided with a second input-output of the maintenance circuit.

[0025] Advantageously, the injection circuit includes: a first pressurized tank containing a cleaning fluid; a second pressurized tank containing a wetting liquid; a first injection valve connected on one side to the first and second pressurized tanks and on the other side to a first inlet of the print head; a second injection valve connected on one side to the first and second pressurized tanks and on the other side to a second inlet of the print head.

[0026] In one embodiment, the first input of the print head is confused with a first input-output of the maintenance circuit and the second input of the print head is confused with a supply input of the supply circuit.

[0027] In one embodiment, the first input of the print head is coincided with a first input-output of the maintenance circuit and the second input of the print head is coincided with a second input-output of the maintenance circuit. BREVE DESCRIPTION DES FIGURES

[0028] Other features and advantages of the invention will become clear from the description given below, which is by way of example and not limitation, with reference to the accompanying figures, including: THE figures 1A et 1B represent a first embodiment of a print head according to the first aspect of the invention; the figure 2 represents on a larger scale a nozzle of the print head of the figures 1A-1B and a maintenance channel associated with this nozzle; the figure 3 represents a second embodiment of a print head according to the first aspect of the invention; the figure 4 represents on a larger scale a nozzle of the print head of the figure 3 and two maintenance channels associated with this nozzle; the figure 5 represents a third embodiment of a print head according to the first aspect of the invention; the figure 6 schematically represents a first embodiment of a coating installation according to the second aspect of the invention; and the figure 7 schematically represents a second embodiment of a coating installation according to the second aspect of the invention.

[0029] For clarity, identical or similar elements are identified by identical reference symbols across all figures. DESCRIPTION DETAILLEE

[0030] THE figures 1A et 1B are partial three-dimensional views of a print head 1 according to a first embodiment. The view of the figure 1A results from a cross-section of the print head 1 along a transverse plane and along a first longitudinal plane. The partial view of the figure 1B This results from a cross-section of the print head 1 along a second longitudinal plane parallel to the first longitudinal plane. These figures therefore show internal elements of the print head 1.

[0031] The print head 1 comprises a body 10 and a plurality of nozzles 11 located inside the body 10. Preferably, the nozzles 11 are arranged in one or more rows. For the sake of simplicity, only one row of nozzles 11 is shown in the figure 1A (the first longitudinal section plane passing through said row of nozzles). The number of nozzles in each row can be between 2 and 500.

[0032] The print head 1 is designed for applying a coating product to an object to be coated, for example, a car body. It preferably operates using drop-on-demand (DOD) technology. Each nozzle 11 is then configured to deposit the coating product drop by drop. To achieve this, each nozzle 11 can be equipped with a valve that is controlled to open or close, respectively, to allow or prevent the flow of the coating product through the nozzle 11. The valves of the nozzles 11 are, for example, pneumatic valves, each comprising a controllable diaphragm. Such a valve is pneumatically actuated (for example, with compressed air). The valves of the nozzles 11 can also be solenoid-type valves.

[0033] Alternatively, the print head is a continuous jet print head, meaning it has permanently open circuits. The nozzles 11 are then valve-free.

[0034] The coating product used as an example below is paint, but it could also be a primer, a varnish, or a more viscous product such as glue or sealant.

[0035] There figure 2 is a larger scale cross-sectional view of a portion A of the print head 1, portion A being located around a nozzle 11 (cf. Fig.1A It will be described jointly with the figures 1A et 1B .

[0036] Each nozzle 11 comprises an outlet channel 111 and an ejection orifice 112. The outlet channel 111 opens outside the body 10 through the ejection orifice 112, into a paint ejection zone 2. Each nozzle 11 is thus associated with an ejection zone 2 that extends from the outlet channel 111 of the nozzle 11.

[0037] The outlet channel 111 and the ejection orifice 112 of the nozzles 11 are provided in the body 10 of the print head 1. More specifically, the ejection orifice 112 is provided in an ejection face 100 of the body 10. The ejection orifice 112 has a diameter that can be from 100 µm to 500 µm, for example, 150 µm. The ejection face 100 partially delimits the ejection zones 2. The ejection axis z of each nozzle 11, defined as the axis of the ejection orifice 112, is preferably oriented perpendicular to the ejection face 100.

[0038] The print head 1 further comprises two internal fluidic circuits, i.e. arranged inside the body 10: a supply circuit 12 connected to the nozzles 11 and intended to convey the paint; a maintenance circuit 13 intended to convey a maintenance fluid.

[0039] The supply circuit 12 is responsible for supplying paint to the nozzles 11. It includes a supply inlet 121 and extends inside the body 10 from the supply inlet 121 to the nozzles 11. The supply inlet 121 is an inlet orifice through which the paint enters the print head 1. The supply circuit 12 may also include a purge or recirculation outlet 122 (see diagram). Fig.1B The purge outlet 122 is an outlet through which paint can be discharged from the print head 1 (and conveyed to recovery and processing collectors or to the supply tanks). The purge outlet 122 is used to purge the supply circuit 12, for example, when changing paint colors. The supply circuit 12 can also be primed, i.e., filled with paint before a printing phase, by circulating paint from the supply inlet 121 to the purge outlet 122 (but not through the nozzles 11). The supply inlet 121 and the purge outlet 122 are located in an outer wall of the body 10.

[0040] As depicted on the figures 1A-1B The supply circuit 12 may further include a storage chamber 123 (of the paint) connected to the supply inlet 121 and a plurality of distribution channels 124 (of the paint) connecting the storage chamber 123 to the nozzles 11. Advantageously, the storage chamber 123 is further connected to the purge outlet 122. Two elements of the same fluidic circuit (or two elements belonging to two different fluidic circuits) are considered to be connected when they are in fluidic communication.

[0041] Each distribution channel 124 can connect the storage chamber 123 to one or more nozzles 11, for example, two consecutive nozzles in the row. Preferably, the number of distribution channels 124 is equal to the number of nozzles 11, and each distribution channel 124 serves a single nozzle 11.

[0042] The storage chamber 123 and the distribution channels 124 are arranged in the body 10. The supply inlet 121 and the purge outlet 122 can open directly into the storage chamber 123 or be connected to the storage chamber 123 by conduits called inlet and outlet respectively.

[0043] The maintenance circuit 13 extends inside the body 10 to the ejection zone 2 of at least some of the nozzles 11, preferably all of the nozzles 11. It is configured to convey the maintenance fluid to the ejection zone 2 of at least some of the nozzles 11 and / or to evacuate the maintenance fluid from the ejection zone 2 of at least some of the nozzles 11 (preferably all of the nozzles 11).

[0044] In this first embodiment, the maintenance circuit 13 comprises several first internal channels 131, referred to as maintenance channels. Each first internal channel 131 is associated with one or more nozzles 11. Each first internal channel 131 opens into the ejection zone 2 of the nozzle(s) associated with the first internal channel 131.

[0045] The maintenance circuit 13 is advantageously configured so that the maintenance fluid can be brought into each ejection zone 2 or evacuated from each ejection zone 2 by at least one first internal channel 131. All the nozzles 11 of the print head 1 can thus be serviced.

[0046] Advantageously, the number of first internal channels 131 is equal to the number of nozzles 11, and each first internal channel 131 opens into the ejection zone 2 of a single nozzle 11 (in other words, each first internal channel 131 is associated with a single nozzle 11). Maintenance is thus performed in the same way and with the best level of performance for all nozzles.

[0047] In addition to the first internal channels 131, the maintenance circuit 13 includes a first storage chamber 132 for the maintenance fluid and a first inlet / outlet 133. An inlet / outlet here refers to an orifice for the inlet and / or outlet of the maintenance fluid in the print head 1. The first inlet / outlet 133 can open directly into the first storage chamber 132 or be connected to the first storage chamber 132 by a conduit. It is located in an external wall of the body 10. The first storage chamber 132 (also called the first distribution chamber for the maintenance fluid) is connected to the ejection zones 2 by the first internal channels 131.

[0048] Thus, the maintenance circuit 13 extends here from the first inlet-outlet 133 to the ejection zones 2 of the nozzles 11.

[0049] Each first internal channel 131 extends through an internal wall separating the first storage chamber 132 and the ejection zones 2 of the nozzles 11. Each first internal channel 131 may further extend partially into the first storage chamber 132, as illustrated in the figure 1A .

[0050] Maintenance circuit 13 allows for maintenance operations to be performed on the print head 1. In this first embodiment, the possible maintenance operations are: an operation of cleaning (or rinsing) at least part of the nozzles 11 and at least part of the supply circuit 12 using a cleaning fluid; and an operation of wetting at least part of the nozzles 11 using a non-volatile liquid. Thus, the nature of the maintenance fluid varies depending on the desired maintenance operation.

[0051] These operations are described in more detail in the preferential case of simultaneous maintenance of all the nozzles 11 of the print head 1.

[0052] The operation of cleaning the nozzles 11 and at least part of the supply circuit 12 consists of removing paint residues located in the nozzles 11 (typically in the outlet channel 111 and the ejection orifice 112) and in the supply circuit 12.

[0053] The cleaning fluid can be brought into the ejection zone 2 of the nozzles 11 via the first internal channels 131 of the maintenance circuit 13, and then evacuated through the nozzles 11 and the supply circuit 12 (cf. Fig.2 The cleaning fluid then flows through the nozzles 11 in the opposite direction to the paint flow, also known as the normal flow direction. Conversely, the cleaning fluid can be supplied to the ejection zone 2 by passing through the nozzles 11 via the supply circuit 12, and then discharged from the ejection zone 2 through the first internal channels 131 of the maintenance circuit 13. The cleaning fluid then flows through the nozzles 11 in the normal flow direction. The cleaning fluid can be a liquid (volatile or inert), a gas (e.g., air), or a mixture of liquid and gas. Advantageously, the cleaning fluid includes a solvent (to dissolve dried paint residue), preferably the same solvent used in the paint composition.

[0054] Such an operation can be performed to unclog blocked nozzles 11 and restore optimal operation (in particular, ensuring repeatable droplet trajectories). It can also be performed between two printing phases of the object, during a paint color change, or after a prolonged shutdown of the print head. The supply circuit 12 is advantageously purged before this operation.

[0055] A nozzle wetting operation 11 consists of forming a film of non-volatile liquid at the ejection orifice 112 of the nozzles 11, in order to prevent the paint from drying during a prolonged pause in printing and clogging the nozzles 11. The non-volatile liquid, also called wetting liquid or stopping liquid, can be brought to the ejection orifice 112 of the nozzles 11 through the first internal channels 131 at the end of a printing phase, and then discharged before the start of the next printing phase, either through the supply circuit 12 or through the first internal channels 131. Alternatively, the wetting liquid can be brought to the ejection orifice 112 of the nozzles 11 through the supply circuit 12, and then discharged through the supply circuit 12 or through the first internal channels 131.

[0056] Thus, the maintenance circuit 13 carries only one or more maintenance fluids (cleaning fluid and / or wetting fluid), unlike the supply circuit 12 which can receive paint and maintenance fluids.

[0057] The maintenance fluid is drawn out of the ejection zone 2 of the nozzles 11. The first internal channels 131 – or the nozzles 11 and the supply circuit 12 – are thus subjected to a vacuum. The vacuum is preferably between 0.1 bar and 0.8 bar, for example, 0.5 bar. The maintenance fluid is injected into the print head 1 under a pressure that can be between 0.1 bar and 1 bar.

[0058] The pressure and vacuum values ​​depend on the type of operation required and the properties of the maintenance fluid. For example, for a cleaning operation, it is advantageous to circulate the fluid rapidly through the ejection zone, thus requiring high pressure / vacuum values. For a nozzle wetting operation, the wetting fluid is introduced slowly into the ejection zone to form the wet film that will seal the nozzle.

[0059] The first storage chamber 132 is preferably arranged to guarantee identical pressure / vacuum along the print head 1 and thus ensure identical operation for all nozzles 11.

[0060] Thanks to the first internal channels 131 opening into the ejection zone 2 of the nozzles 11, maintenance operations can be carried out without external discharge when the print head 11 is in the printing position, i.e., in the immediate vicinity of the object to be coated. This eliminates the need for a collection tray.

[0061] With reference to the figure 2 A first internal channel 131 can be arranged so that the maintenance fluid flows in contact with the ejection face 100. This allows the face to be cleaned and freed of paint residue between the end of the first internal channel 131 and the ejection orifice 112 of the associated nozzle(s) 11. The first internal channel 131 preferably includes a wall forming a flat surface with the ejection face 100, as illustrated. For example, it is oriented parallel to the ejection face 100.

[0062] In another configuration, not represented by the figures, the first internal channel 131 is inclined relative to the ejection face 100 in the direction of the ejection orifice 112 of the nozzle(s) associated with the first internal channel 131.

[0063] The first internal channel 131 opens into the ejection zone 2 at a distance d from the z-axis of the ejection orifice 112 which is advantageously less than or equal to 1 mm, for example equal to 0.25 mm. A small distance d between the end of the first internal channel 131 and the ejection orifice 112 improves the cleaning or wetting of the ejection orifice (by limiting the dispersion of the fluid jet) and facilitates the suction of the maintenance fluid.

[0064] The first internal channel 131 preferably has a cross-section with characteristic dimensions less than or equal to 0.5 mm, preferably less than or equal to 0.25 mm. This cross-section is for example round (diameter less than or equal to 0.5 mm) or rectangular (height and width less than or equal to 0.5 mm).

[0065] The length of the first internal channel 131 can be between 0.5 mm and 10 mm. Such a length allows the maintenance fluid to be properly "guided" to the ejection zone 2.

[0066] Preferably, all the first internal channels 131 of the maintenance circuit 13 have the same configuration and dimensions. In other words, they are identical.

[0067] The first internal channels 131 are advantageously arranged in a plate (or layer) 101 called the external maintenance plate and disposed on the ejection face 100. This external maintenance plate 101 is of very low thickness, for example between 0.1 mm and 1 mm, and therefore does not significantly increase the size of the print head 1.

[0068] There figure 3 is a partial three-dimensional view of a print head 1 according to a second embodiment. It results from a cross-section of the print head 1 along a transverse plane.

[0069] The print head 1 according to the second embodiment ( Fig.3 ) differs from print head 1 according to the first embodiment ( Figs.1A-1B ) essentially in the arrangement of the maintenance circuit 13.

[0070] In this second embodiment, the maintenance circuit 13 includes, in addition to the first internal channels 131, second internal channels 135. Each second internal channel 135 is associated with a first internal channel 131 and opens into the ejection zone 2 of the nozzle(s) 11 associated with said first internal channel 131.

[0071] Like the first internal channels 131, the second internal channels 135 are used to convey the maintenance fluid to the ejection zones 2 or to evacuate the maintenance fluid from the ejection zones 2.

[0072] Advantageously, the number of second internal channels 135 is equal to the number of nozzles 11 and each second internal channel 135 opens into the ejection zone 2 of a single nozzle 11 (in other words, each second internal channel 135 is associated with a single nozzle 11).

[0073] The maintenance circuit 13 further includes a second storage (or distribution) chamber 136 for the maintenance fluid and a second inlet / outlet 137 connected to the second storage chamber 136. The second inlet / outlet 137 may be located in an external wall of the body 10 and open directly into the second storage chamber 136, or it may be connected to the second storage chamber 136 by a conduit. The second storage chamber 136 is preferably arranged to ensure identical pressure / vacuum along the print head 1, thus ensuring identical operation for all nozzles 11.

[0074] The maintenance circuit 13 extends here from the first inlet-outlet 133 to the ejection zones 2 of the nozzles 11 and from the ejection zones 2 to the second inlet-outlet 137.

[0075] The second internal channels 135 connect the second storage chamber 136 to the ejection zones 2 of the nozzles 11. Each second internal channel 135 extends through an internal wall separating the second storage chamber 136 and the ejection zones 2 of the nozzles 11. Each second internal channel 135 may also extend partially into the second storage chamber 136, as illustrated in the figure 3 .

[0076] There figure 4 is a larger scale cross-sectional view of a portion B of the print head 1, portion B being located around a nozzle 11 (cf. Fig.3 ). This figure shows a preferential arrangement of a first internal channel 131 and an associated second internal channel 135.

[0077] The second internal channel 135 is located opposite the first internal channel 131 associated with the ejection orifice 112 of the nozzle 11. It can be arranged so that the maintenance fluid flows in contact with the ejection face 100, as described previously in relation to the first internal channel 131 ( figure 2 ). In this configuration, the first internal channel 131 and the second internal channel 135 are advantageously oriented in the same direction.

[0078] Alternatively, the second internal channel 135 can be inclined relative to the ejection face 100 in the direction of the ejection orifice 112.

[0079] The second internal channel 135 opens into the ejection zone 2 at a distance d' from the z-axis of the ejection orifice 112 which is advantageously less than or equal to 1 mm, for example equal to 0.25 mm. The distance d' between the end of the second internal channel 135 and the z-axis of the ejection orifice 112 is preferably equal to the distance d between the end of the first internal channel 131 and the z-axis of the ejection orifice 112.

[0080] The second internal channel 135 preferably has a cross-section with characteristic dimensions less than or equal to 0.5 mm, preferably less than or equal to 0.25 mm. This cross-section is, for example, round (diameter less than or equal to 0.5 mm) or rectangular (height and width less than or equal to 0.5 mm). The length of the second internal channel 135 may be between 0.5 mm and 10 mm.

[0081] The first internal channel 131 and the second internal channel 135 can be arranged symmetrically with respect to the ejection orifice 112 of the nozzle 11.

[0082] Preferably, all the second internal channels 135 of the maintenance circuit 13 have the same configuration and the same dimensions. They are therefore identical.

[0083] The second internal channels 135 are advantageously arranged in the same external maintenance plate 101 as the first internal channels 131.

[0084] The possible maintenance operations with print head 1 according to the second embodiment are: an operation of cleaning at least part of the nozzles 11 and at least part of the supply circuit 12 using a cleaning fluid; and an operation of wetting at least part of the nozzles 11 using a non-volatile liquid; and an operation of cleaning the ejection face 100 and the ejection orifice of at least part of the nozzles 11 using a cleaning fluid.

[0085] The cleaning operation of at least part of the nozzles 11 and at least part of the supply circuit 12, and the wetting operation, have been described previously. The second internal channels 135 can perform the same function as the first internal channels 131 (i.e., suction or injection of the maintenance fluid). For example, they can be used to drain the maintenance fluid from the ejection zones 2 after it has circulated through the supply circuit 12 and the nozzles 11. Alternatively, the second internal channels 135 can perform a different function from that of the first internal channels 131. For example, they can be used to suction the wetting fluid after the first internal channels 131 have supplied it to the ejection zones 2.

[0086] The cleaning operation of the ejection face 100 and the nozzle ejection orifice 11 involves conveying the cleaning fluid to the ejection zones 2 through the first internal channels 131 and expelling the cleaning fluid through the second internal channels 135, or vice versa. Thus, during this operation, the cleaning fluid circulates only in the maintenance circuit 13 (between the first and second inlet / outlet ports 133, 137) and in the ejection zones 2, in contact with the ejection face 100.

[0087] Since the first internal channel 131 and the second internal channel 135 are located on either side of the ejection zone 2 (and preferably located opposite each other), a more thorough cleaning of the ejection face 100 can be achieved.

[0088] The print head 1, according to the second embodiment, thus allows for an additional maintenance operation. The pressure and vacuum values ​​are similar to those indicated previously. Implementation is easier because maintenance is completely independent of the power supply (elimination of valves in the circuit).

[0089] In another embodiment of the print head 1, not shown in the figures, the maintenance circuit 13 includes a single first internal channel 121 opening into the ejection zone 2 of several nozzles 11, and preferably of all the nozzles 11.

[0090] A maintenance circuit 13 comprising several first internal channels 131, however, offers better performance (in terms of nozzle cleaning, for example) than a maintenance circuit 1 with a single first internal channel common to several nozzles. This is because the maintenance fluid can thus be delivered to or discharged from the nozzle ejection zone 2 more precisely. Furthermore, increasing the number of first internal channels 131 allows their size to be reduced, thereby increasing the velocity of the maintenance fluid flowing within them.

[0091] Similarly, the maintenance circuit 13 may include (in addition to the first internal channel(s) 131) only one second internal channel 135 opening the ejection zone 2 of several nozzles 11, and preferably of all the nozzles 11.

[0092] There figure 5 represents a third embodiment, in which the print head maintenance circuit 13 is devoid of first internal channels 131 and second channels 135. The first storage chamber 132 communicates with the ejection zone 2 of at least part of the nozzles 11 by one or more first openings 138.

[0093] Preferably, the first storage chamber 132 communicates with the ejection zone 2 of each of the nozzles 11 through a single first opening 138. The number of first openings 138 is then equal to the number of nozzles 11.

[0094] The first openings 138 are made in the wall of the body 10 which separates the first storage chamber 132 and the ejection zones 2. They result from the intersection between the first storage chamber 132 and the ejection zones 2 (here in the form of straight cylinders, in the extension of the outlet channels 111 of the nozzles 11).

[0095] In addition, the second storage chamber 136 communicates with the ejection zone 2 of at least some of the nozzles 11 by one or more second openings 139. Preferably, the second storage chamber 136 communicates with the ejection zone 2 of each of the nozzles 11 by a single second opening 139. The number of second openings 139 is then equal to the number of nozzles 11.

[0096] The second openings 139 are made in the wall of the body 10 which separates the second storage chamber 136 and the ejection zones 2. They result from the intersection between the second storage chamber 136 and the ejection zones 2.

[0097] Thus, a nozzle 11 and a first opening 138 can be associated with each second opening 139. Each second opening 139 is advantageously located opposite the associated first opening 138 with respect to the ejection orifice 112 of the associated nozzle 11. In other words, the first opening 138, the second opening 139, and the end of the ejection orifice 112 are aligned. This arrangement improves the cleaning and wetting of the ejection orifice 111 of the nozzle 11. Furthermore, the first and second openings 138-139 are advantageously arranged so that the maintenance fluid flows in contact with the ejection face 100.

[0098] Compared to the first and second embodiments ( Figs.1A-1B , 2 And Figs.3-4 ), the first and second openings 138-139 can be considered as (first and second) internal channels of zero length.

[0099] Print head 1 of the figure 5 works in the same way as the print head of the figure 3 the other elements, not mentioned, being otherwise identical.

[0100] According to a variant of this third embodiment, the maintenance circuit lacks a second storage chamber 136. The print head then operates in the same way as print head 1 of the figures 1A-1B .

[0101] Finally, in another embodiment, the print head comprises only a single nozzle 11, a first internal channel 131 opening into the ejection zone 2 of the nozzle 11 (as described in relation to the figure 2 ) or a first opening 138 and, advantageously, a second internal channel 132 opening into the ejection zone 2 of the nozzle 11 (as described in relation to the figure 4 ) or a second opening 139. The supply circuit 12 then comprises only one distribution channel 124 connecting the storage chamber 123 to the nozzle 11.

[0102] An installation for applying (or printing) a coating product onto an object to be coated will now be described in relation to the figures 6 And 7 . There figure 6 shows a fluidic diagram of a coating installation 3 according to a first embodiment, comprising the printing head 1 of the figures 1A-1B (or a variant of the third embodiment). The figure 7 shows a fluidic diagram of a coating installation 3 according to a second embodiment, comprising the print head 1 of the figure 3 (or of the figure 5 ).

[0103] Common to both embodiments, the coating installation 3 comprises (in addition to the print head 1): an injection circuit 31 connected to (at least) one inlet of the print head 1 and configured to inject the maintenance fluid into the print head 1; a suction circuit 32 connected to (at least) one outlet of the print head 1 and configured to suction the maintenance fluid from the print head 1; and a coating product supply circuit 33 (e.g. paint) connected to the supply inlet 121 of the supply circuit 12 of the print head 1.

[0104] The coating product supply circuit 33 may include at least one coating product reservoir 331 and at least one filling valve 332 connected on one side to the coating product reservoir 331 and on the other side to the supply inlet 121 of the supply circuit 12.

[0105] The injection circuit 31 (also called the maintenance fluid supply circuit) includes at least one pressurized reservoir 311 containing maintenance fluid and at least one injection valve 312 connected on one side to the pressurized reservoir 311 and on the other side to the inlet of the print head 1. "Pressurized" means that the pressure inside the reservoir is higher than atmospheric pressure. The injection circuit 31 may also include means for regulating the maintenance fluid pressure. These regulating means may be located between the pressurized reservoir 311 and the injection valve 312. They include, for example, a variable flow valve 313. Alternatively, the pressure may be regulated at the pressurized reservoir 311 or even further upstream (compressed air source, pump, etc.).The injection circuit 31 then advantageously includes a two-way valve 313 disposed between the pressurized reservoir 311 and the injection valve 312.

[0106] Advantageously, the injection circuit 31 includes: a first pressurized tank 311a containing the cleaning fluid; a second pressurized tank 311b containing the wetting liquid; a first injection valve 312a connected on one side to the first and second pressurized tanks 311a-311b and on the other side to a first inlet of the print head 1; a second injection valve 312b connected on one side to the first and second pressurized tanks 311a-311b and on the other side to a second inlet of the print head 1 (distinct from the first inlet).

[0107] The means for regulating the maintenance fluid pressure may then include a variable flow valve 313 coupled to each of the first and second pressurized tanks 311a-311b. The first and second injection valves 312a-312b are preferably two-way valves (of the pneumatic, solenoid type, etc.).

[0108] The suction circuit 32 includes a vacuum generator 321 (venturi effect system or vacuum pump) and at least one suction valve 322 connected on one side to the vacuum generator 321 and on the other side to the outlet of the print head 1. In addition, the suction circuit 32 advantageously includes a recovery volume 323, connected to the vacuum generator 321 and intended to recover the suctioned maintenance fluid.

[0109] Advantageously, the suction circuit 32 includes: a first suction valve 322a connected on one side to the vacuum generator 321 and on the other side to a first outlet of the print head 1; and a second suction valve 322b connected on one side to the vacuum generator 321 and on the other side to a second outlet of the print head 1 (distinct from the first outlet).

[0110] The first and second suction valves 322a-322b are preferably two-way valves (pneumatic, solenoid type, etc.). Typically, the vacuum generator 321 can be a venturi effect system comprising an ejector, a compressed air buffer volume, a pressure gauge, and means for adjusting the vacuum generated by the vacuum generator 321. Alternatively, the vacuum generator 321 can include a vacuum pump located above the recovery volume 323.

[0111] In the first embodiment ( Fig.6 ), the first injection valve 312a is connected to the first inlet-outlet 133 of the maintenance circuit 13 and the second injection valve 312b is connected to the supply inlet 121 of the supply circuit 12 (or to the purge outlet 122 of the supply circuit 12, not shown in the figure 6 ).

[0112] Furthermore, the first suction valve 322a is connected to the first inlet-outlet 133 of the maintenance circuit 13, and the second suction valve 322b is connected to the supply inlet 121 of the supply circuit 12 (or to the purge outlet 122 of the supply circuit 12, not shown in the diagram). figure 6 ).

[0113] In other words, the first output of print head 1 and the second input of print head 1 are confused with the first input-output 133 of the maintenance circuit 13. The second output of print head 1 and the first input of print head 1 are confused with the supply input 121 of the supply circuit 12.

[0114] In the second embodiment ( Fig.7 ), the first injection valve 312a is connected to the first inlet-outlet 133 of the maintenance circuit 13 and the second injection valve 312b is connected to the second inlet-outlet 137 of the maintenance circuit 13.

[0115] Furthermore, the first suction valve 322a is connected to the first inlet-outlet 133 of the maintenance circuit 13 and the second suction valve 322b is connected to the second inlet-outlet 137 of the maintenance circuit 13.

[0116] In other words, the first output of print head 1 and the second input of print head 1 are coincident with the first input-output 133 of the maintenance circuit 13. The second output of print head 1 and the first input of print head 1 are coincident with the second input-output 137 of the maintenance circuit 13.

[0117] The two injection valves 312a-312b and the two suction valves 322a-322b enable the multitude of maintenance operations described previously to be performed.

[0118] The first injection valve 312a and the first suction valve 322a are advantageously controlled in opposite phases. In other words, when one is open, the other is closed, and vice versa. The second injection valve 312b and the second suction valve 322b are also advantageously controlled in opposite phases.

[0119] Advantageously, the first injection valve 312a is open only when the second suction valve 322b is open, and the second injection valve 312b is open only when the first suction valve 322a is open. Thus, the injection of the maintenance fluid always occurs simultaneously with the suction.

[0120] According to a particular cleaning method, the first suction valve 322a (respectively the second suction valve 322b) is permanently open (continuous suction) and the second injection valve 312b (respectively the first injection valve 312a) is intermittently opened, so as to produce pulsations of cleaning fluid.

[0121] The two injection valves 312a-312b and the two suction valves 322a-322b allow the cleaning fluid to circulate in both directions inside the print head 1, thus improving cleaning operations. For example, in the embodiment of the figure 6 , the cleaning fluid can first be injected through the first inlet-outlet 133 and drawn through the supply inlet 121, then injected through the supply inlet 121 and drawn through the first inlet-outlet 133 (or in the reverse order).

[0122] According to one alternative embodiment, the installation of coating 3 of the figure 7It further includes a third suction valve connected on one side to the vacuum generator 321 and on the other side to the supply inlet 121, as well as a third injection valve connected on one side to the first and second pressurized tanks 311a-311b and on the other side to the supply inlet 121. This variant of the embodiment allows cleaning (in both directions) of the nozzles 11 and at least part of the supply circuit 12. For example, the cleaning fluid can be injected through the supply inlet 121 and drawn out through the first inlet-outlet 133 and the second inlet-outlet 137 (or vice versa).

[0123] The body 10 of the print head 1 (containing the nozzles 11, the power supply circuit 12 and the maintenance circuit 13) can be manufactured in various ways. Examples include diffusion welding or brazing of metal sheets, selective laser sintering of metal powder, micromolding and fabrication techniques for silicon microelectromechanical systems (MEMS).

[0124] The body can also be made up of machined elements assembled by gluing or screwing, with a gasket being installed between the different components to ensure sealing.

[0125] A manufacturing process for the body 10 of the print head 1 may include the following steps: the supply of a plurality of plates, in which are arranged all or part of the components (channels, chambers, conduits, inlet and / or outlet ports...) of the nozzles 11, the supply circuit 12 and the maintenance circuit 13; and the assembly of the plates together, for example by means of a welding, brazing or gluing technique.

[0126] The plates are preferably made of metal, for example stainless steel. They are machined to form the various parts of the nozzles 11, the supply circuit 12, and the maintenance circuit 13, for example by chemical etching, laser cutting, or electrical discharge machining (EDM). The plates (also called "layers") preferably have a thickness between 10 µm and 1000 µm.

[0127] In a preferred implementation of the manufacturing process, the metal plates are assembled by diffusion welding. The assembly step then includes the following operations: the contacting of the plates so as to form a stack; the pressure stressing of the stack, for example between 300 bar and 500 bar; and the annealing (or heat treatment) of the pressure-stressed stack, in order to diffuse (or migrate) the atoms of the metal at the interfaces between the plates.

[0128] Annealing is preferably carried out at a temperature between 0.6Tf and 0.8Tf, where Tf is the melting point of the metal. The annealing time can be between 1 and 3 hours.

[0129] The surfaces of the plates that are brought into contact preferably have a low surface roughness, typically less than 0.5 µm. This roughness value is expressed as a root mean square value.

[0130] Such a manufacturing process is precise, simple, and quick to implement (and therefore inexpensive). Furthermore, when diffusion welding is used, the resulting body 10 is robust, as it is ultimately formed from a single piece (it has a monolithic appearance). Diffusion welding is also advantageous because it does not require any additional material (adhesive, filler metal, etc.) at the interfaces between the metal plates.

[0131] The membranes of the pneumovannes belonging to the nozzles 11 (in the case of a DOD head) are advantageously formed after manufacturing the body 10.

Claims

1. A print head (1) for applying a coating product to an object to be coated, the print head comprising a body (10) wherein are fitted out: - a plurality of nozzles (11) each comprising an ejection hole (112) and an outlet channel (111) opening into an ejection zone (2) of the coating product through the ejection hole (112); - a feeder circuit (12) for the coating product, connected to the nozzle (11); the print head further comprising a maintenance circuit (13) for conveying a maintenance fluid, the maintenance circuit (13) extending inside the body (10) to the ejection zone (2) of the nozzle (11), and comprising a first internal channel (131); (138) opening into the ejection zone (2) of at least one nozzle (11), characterized in that the maintenance circuit (13) comprises a plurality of first internal channels (131; 138), each first internal channel (131; 138) opening into the ejection zone (2) of only one nozzle (11) associated with the first internal channel (131; 138), the number of first internal channels (131; 138) being equal to the number of nozzles (11).

2. The print head (1) according to claim 1, wherein the maintenance circuit (13) comprises a plurality of second internal channels (135), each second internal channel (135) being associated with a first internal channel (131) and opening into the ejection zone (2) of the only one nozzle (11) associated with the first internal channel (131).

3. The print head (1) according to claim 2, wherein each second internal channel (135) is situated opposite the associated first internal channel (131) with respect to the ejection hole (112) of the nozzle (11) in the ejection zone from which the second channel (135) opens.

4. The print head (1) according to one of claims 2 and 3, wherein each associated first inner channel (131) and second inner channel (135) are oriented along the same direction.

5. The print head (1) according to any of claims 1 to 4, comprising an ejection face (100) wherein the ejection hole (112) of the nozzle (11) is fitted and wherein the first internal channel (131) is arranged so that maintenance fluid flows in contact with the ejection face (100).

6. The print head (1) according to any of claims 1 to 4, comprising an ejection face (100) wherein the ejection hole (112) of the nozzle (11) is fitted and wherein the first internal channel (131) is arranged in a plate (101) placed over the ejection face (100) of the print head (1).

7. The print head (1) according to one of claims 1 to 6, wherein the first internal channel (131) comprises an end open to the ejection zone (2) and situated at a distance (d) less than or equal to 1 mm from the ejection hole (112) of the nozzle (11).

8. The print head (1) according to one of claims 1 to 7, wherein the maintenance circuit (13) comprises a first storage chamber for the maintenance fluid (132), the first storage chamber (132) communicating with the ejection zone (2) of each nozzle (11) through one of the first internal channels (131), the length of which is comprised between 0.5 mm and 10 mm.

9. The print head (1) according to one of claims 1 to 7, wherein the maintenance circuit (13) comprises a first storage chamber (132) for the maintenance fluid, the first storage chamber (132) communicating with the ejection zones (2) of each nozzle through a first opening (138).

10. The print head (1) according to one of claims 8 and 9, wherein the first internal channels (131) or the first openings (138) extend through an internal wall of the body (10) which separates the first storage chamber (132) and the ejection zones (2) from the nozzles (11).

11. The print head (1) according to one of claims 1 to 10, wherein the first internal channels (131) are provided in an external maintenance plate (101) placed over an ejection face (100) of the body (10), wherein the ejection holes (112) of the nozzles (11) are provided.

12. The print head (1) according to one of claims 1 to 11, wherein the first internal channels (131) have a cross-section with characteristic dimensions less or equal to 0.5 mm, preferentially less than or equal to 0.25 mm.

13. A coating installation (3) comprising: - a print head (1) according to any of claims 1 to 12; - an injection circuit (31) for the maintenance fluid, connected to at least one inlet of the print head (1); - a suction circuit (32) for the maintenance fluid, connected to at least one outlet of the print head (1).

14. The coating installation (3) according to claim 13, wherein the suction circuit (32) comprises: - a vacuum generator (321); - a first suction valve (322a) connected to the vacuum generator (321) and to a first outlet of the print head (1); and - a second suction valve (322b) connected to the vacuum generator (321) and to a second outlet of the print head (1).

15. The coating installation (3) according to one of claims 13 or 14, wherein the injection circuit (33) comprises: - a first pressurized tank (311a) containing a cleaning fluid; - a second pressurized tank (311b) containing a wetting liquid; - a first injection valve (312a) connected to the first and second pressurized tanks (311a-311b) and to a first inlet of the print head (1); - a second injection valve (312b) connected to the first and second pressurized tanks (311 a-311b) and to a second inlet of the print head (1).

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