EP4261042A1 - Printing head comprising a maintenance circuit and coating installation - Google Patents

Abstract

The invention relates to a print head (1) for applying a coating product to an object to be coated, the print head comprising a body (10) in which several nozzles (11) are arranged, comprising each an ejection orifice (112) and an outlet channel (111) opening into an ejection zone (2) of the coating product through the ejection orifice (112), as well as a supply circuit (12) in coating product connected to the nozzle (11). The print head further comprises a maintenance circuit (13), intended to convey a maintenance fluid and extending inside the body (10) up 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

TECHNICAL FIELD OF THE INVENTION

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

The present invention relates more particularly to a print head for applying a coating product to an object to be coated and to a coating installation comprising the print head.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

The personalization of decorations and coverings affixed to objects is becoming more and more frequent. This is for example the case in the automobile industry for vehicle body coverings. In this case, these may be monochrome, two-tone or multi-chrome paint type coatings. In addition, the production of patterns with a specific geometry proves interesting for other markets, in particular to visually differentiate two products according to their purpose or their manufacture. In this context, the coatings industry has recently explored solutions that involve “printing” paint using print heads, rather than spraying it using sprayers.

The paints used to produce coatings by printing have viscosities of the order of 50 to 200 millipascal-second (mPas) and contain pigment particles whose dimensions are of the order of micrometers. To apply these paints, a print head equipped with several nozzles is usually used. The print head is, for example, mounted on the arm of a multi-axis robot. Each nozzle includes an outlet channel opening onto the outside through an ejection orifice of small diameter, typically of the order of 100 µm to 200 µm, i.e. much smaller than the dimensions of a sprayer outlet orifice (generally greater at 800 µm).

Given the small diameter of the nozzle ejection orifices, there is a risk of the nozzles being blocked by paint residue. Nozzle cleaning operations are therefore carried out between printing phases to avoid clogging of the nozzles and maintain good print quality.

Furthermore, for reasons of economy and practicality, the same print head is generally used to apply paints of different colors. This involves cleaning each nozzle during a paint change.

The patent application EP3725421A1 describes an installation for applying a coating product comprising a print head provided with a set of nozzles and a nozzle cleaning station. The cleaning station includes a plurality of injectors intended to simultaneously clean several nozzles, by injecting a cleaning fluid into the outlet channels of the nozzles, through their ejection ports.

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

In order to maximize printing time, and therefore production rate, it would be advantageous to mount the cleaning station with the print head on the arm of the multi-axis robot. The document cleaning station EP3725421A1 is, however, too bulky to be able to be loaded with the print head and to be compatible with the short printing distance, that is to say the distance between the nozzles and the object to be coated.

It is also known to US5877788A to clean the nozzles of a print head with a fluid conveyed through channels common to all the nozzle ejection orifices. The ejection ports located near the outlet of the channels are cleaned before and with cleaner fluid than the channels located far from this outlet. Cleaning of the nozzle ejection zones is therefore not uniform.

SUMMARY OF THE INVENTION

There is therefore a need to be able to clean different nozzles of a print head in a homogeneous manner when the print head is in position for printing, that is to say in the vicinity of the object to be coated.

• plusieurs buses comprenant chacune un orifice d'éjection et un canal de sortie débouchant dans une zone d'éjection du produit de revêtement par l'orifice d'éjection ;
• un circuit d'alimentation en produit de revêtement relié à la buse ;

la tête d'impression comprenant, en outre, un circuit de maintenance destiné à véhiculer un fluide de maintenance, le circuit de maintenance s'étendant à l'intérieur du corps jusqu'à la zone d'éjection de la buse et comprenant un premier canal interne débouchant dans la zone d'éjection d'au moins une buse. Conformément à l'invention, le circuit de maintenance comprend une pluralité de premiers canaux internes, chaque premier canal interne débouchant dans la zone d'éjection d'une seule buse associée au premier canal interne, le nombre de premiers canaux internes étant égal au nombre de buses.According to a first aspect of the invention, we tend to satisfy this need 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 comprising a maintenance circuit intended to convey a maintenance fluid, the maintenance circuit extending inside the body up to the ejection zone of the nozzle 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.

The maintenance circuit makes it possible to route the maintenance fluid into the ejection zone of each nozzle or, on the contrary, to evacuate the maintenance fluid from the ejection zone, and therefore to clean the ejection orifices of the nozzles, in an individualized and homogeneous manner. The maintenance circuit thus offers a cleaning solution which is integrated into the print head and which is not bulky like the solutions of the prior art and which is more effective. Cleaning can thus be accomplished when the print head is in position for printing.

In one embodiment of the print head, the maintenance circuit further comprises a plurality of second internal channels, each second internal channel being associated with a first internal channel and opening into the ejection zone of the only associated nozzle to the first internal channel. This embodiment combines practicality (numerous maintenance operations possible) and cleaning performance.

According to a development of this embodiment, each second internal channel is located opposite the first associated internal channel with respect to the ejection orifice of the nozzle in the ejection zone from which this second channel opens. This arrangement of the first and second internal channels improves cleaning of the ejection port and facilitates the flow of maintenance fluid.

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

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

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 nozzles) through several first openings.

According to another development compatible with the previous one, the maintenance circuit further comprises a second storage chamber for the maintenance fluid, the second storage chamber communicating with the ejection zone of the nozzle or several nozzles (preferably all the nozzles) through one or more second openings.

• le premier canal interne est dirigé vers l'orifice d'éjection de la buse ;
• la tête d'impression comprend une face d'éjection dans laquelle est aménagé l'orifice d'éjection de la buse ;
• le premier canal interne est agencé de sorte que le fluide de maintenance circule en contact avec la face d'éjection ;
• le premier canal interne est orienté parallèlement à la face d'éjection ;
• le premier canal interne est incliné par rapport à la face d'éjection en direction de l'orifice d'éjection de la buse ;
• le premier canal interne est aménagé dans une plaque disposée sur la face d'éjection de la tête d'impression ;
• le premier canal interne comprend une extrémité ouverte sur la zone d'éjection et située à une distance inférieure ou égale à 1 mm de l'orifice d'éjection de la buse ;
• le circuit de maintenance comprend une première chambre de stockage du fluide de maintenance, la première chambre de stockage communiquant avec la zone d'éjection de chaque buse par l'un des premier canaux interne, dont la longueur est comprise entre 0,5 mm et 10 mm ;
• le circuit de maintenance comprend en outre une première chambre de stockage du fluide de maintenance, le premier canal interne reliant la première chambre de stockage du fluide de maintenance à la zone d'éjection de la buse ;
• les premiers canaux internes ou les premières ouvertures s'étendent à travers une paroi interne du corps qui sépare la première chambre de stockage et les zones d'éjection des buses ;
• les premiers canaux internes sont ménagés dans une plaque de maintenance externe disposée sur une face d'éjection du corps, dans laquelle sont ménagés les orifices d'éjection des buses ;
• le premier canal interne s'étend à travers une paroi interne séparant la première chambre de stockage du fluide de maintenance et la zone d'éjection de la buse ;
• les premiers canaux internes ont une section de dimensions caractéristiques inférieures ou égales à 0,5 mm, de préférence inférieures ou égales à 0,25 mm
• le deuxième canal interne est dirigé vers l'orifice d'éjection de la buse ;
• le deuxième canal interne est agencé de sorte que le fluide de maintenance circule en contact avec la face d'éjection ;
• le deuxième canal interne est orienté parallèlement à la face d'éjection ;
• le deuxième canal interne est incliné par rapport à la face d'éjection en direction de l'orifice d'éjection de la buse ;
• le deuxième canal interne est aménagé dans une plaque disposée sur la face d'éjection de la tête d'impression ;
• le deuxième canal interne comprend une extrémité ouverte sur la zone d'éjection et située à une distance inférieure ou égale à 1 mm de l'orifice d'éjection de la buse ;
• le circuit de maintenance comprend en outre une deuxième chambre de stockage du fluide de maintenance, le deuxième canal interne reliant la deuxième chambre de stockage à la zone d'éjection de la buse ; et
• le deuxième canal interne s'étend à travers une paroi interne séparant la deuxième chambre de stockage du fluide de maintenance et la zone d'éjection de la buse ;
• le deuxième canal interne s'étend en outre partiellement dans la deuxième chambre de stockage du fluide de maintenance ;
• le circuit d'alimentation en produit de revêtement comprend une chambre de stockage du produit de revêtement et une pluralité de canaux de distribution reliant la chambre de stockage du produit de revêtement aux buses.

In addition to the characteristics which have just been mentioned in the preceding paragraphs, the print head according to the first aspect of the invention may have one or several complementary characteristics among the following, considered individually or in all technically possible combinations:

• the first internal channel is directed towards the ejection port of the nozzle;
• the print head comprises an ejection face in which the ejection orifice of the nozzle is arranged;
• 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 towards the ejection port of the nozzle;
• the first internal channel is arranged in a plate placed on the ejection face of the print head;
• the first internal channel comprises an end open to the ejection zone and located at a distance less than or equal to 1 mm from the ejection orifice of the nozzle;
• the maintenance circuit comprises a first storage chamber for the maintenance fluid, the first storage chamber communicating with the ejection zone of each nozzle via one of the first internal channels, the length of which is between 0.5 mm and 10mm;
• the maintenance circuit further comprises a first maintenance fluid storage chamber, the first internal channel connecting the first maintenance fluid storage chamber to the nozzle ejection zone;
• the first internal channels or the first openings extend through an internal wall of the body which separates the first storage chamber and the nozzle ejection zones;
• the first internal channels are provided in an external maintenance plate arranged 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 zone;
• the first internal channels have a section of 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 ejection port of the nozzle;
• 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 towards the ejection orifice of the nozzle;
• the second internal channel is arranged in a plate placed on the ejection face of the print head;
• the second internal channel comprises an end open to the ejection zone and located at a distance less than or equal to 1 mm from the ejection orifice of the nozzle;
• the maintenance circuit further comprises a second storage chamber for the maintenance fluid, the 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.

• une tête d'impression selon le premier aspect de l'invention ;
• un circuit d'injection du fluide de maintenance relié à au moins une entrée de la tête d'impression ;
• un circuit d'aspiration du fluide de maintenance relié à au moins une sortie de la tête d'impression.

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 output of the print head.

• un générateur de vide ;
• une première vanne d'aspiration reliée d'une part au générateur de vide et d'autre part à une première sortie de la tête d'impression ; et
• une deuxième vanne d'aspiration reliée d'une part au générateur de vide et d'autre part à une deuxième sortie de la tête d'impression.

Advantageously, the suction circuit comprises:

• a vacuum generator;
• a first suction valve connected on the one hand to the vacuum generator and on the other hand to a first outlet of the print head; And
• a second suction valve connected on the one hand to the vacuum generator and on the other hand to a second outlet of the print head.

In one embodiment, the first output of the print head is combined with a first input-output of the maintenance circuit and the second output of the print head is combined with a supply input of the power supply circuit .

In a variant embodiment, the first output of the print head is combined with a first input-output of the maintenance circuit and the second output of the print head is combined with a second input-output of the maintenance circuit.

• un premier réservoir pressurisé contenant un fluide de nettoyage ;
• un deuxième réservoir pressurisé contenant un liquide de mouillage ;
• une première vanne d'injection reliée d'une part aux premier et deuxième réservoirs pressurisés et d'autre part à une première entrée de la tête d'impression ;
• une deuxième vanne d'injection reliée d'une part aux premier et deuxième réservoirs pressurisés et d'autre part à une deuxième entrée de la tête d'impression.

Advantageously, the injection circuit comprises:

• a first pressurized tank containing a cleaning fluid;
• a second pressurized tank containing a wetting liquid;
• a first injection valve connected on the one hand to the first and second pressurized tanks and on the other hand to a first inlet of the print head;
• a second injection valve connected on the one hand to the first and second pressurized tanks and on the other hand to a second inlet of the print head.

In one embodiment, the first input of the print head is combined with a first input-output of the maintenance circuit and the second input of the print head is combined with a supply input of the power supply circuit .

In a variant embodiment, the first input of the print head is combined with a first input-output of the maintenance circuit and the second input of the print head is combined with a second input-output of the maintenance circuit.

BRIEF DESCRIPTION OF THE FIGURES

• les figures 1A et 1B représentent un premier mode de réalisation d'une tête d'impression selon le premier aspect de l'invention ;
• la figure 2 représente à plus grande échelle une buse de la tête d'impression des figures 1A-1B et un canal de maintenance associé à cette buse ;
• la figure 3 représente un deuxième mode de réalisation d'une tête d'impression selon le premier aspect de l'invention ;
• la figure 4 représente à plus grande échelle une buse de la tête d'impression de la figure 3 et deux canaux de maintenance associés à cette buse ;
• la figure 5 représente un troisième mode de réalisation d'une tête d'impression selon le premier aspect de l'invention ;
• la figure 6 représente schématiquement un premier mode de réalisation d'une installation de revêtement selon le deuxième aspect de l'invention ; et
• la figure 7 représente schématiquement un deuxième mode de réalisation d'une installation de revêtement selon le deuxième aspect de l'invention.

Other characteristics and advantages of the invention will emerge clearly from the description given below, for information only and in no way limiting, with reference to the appended figures, among which:

• THE Figures 1A and 1B represent a first embodiment of a print head according to the first aspect of the invention;
• there 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;
• there Figure 3 represents a second embodiment of a print head according to the first aspect of the invention;
• there 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;
• there figure 5 represents a third embodiment of a print head according to the first aspect of the invention;
• there Figure 6 schematically represents a first embodiment of a coating installation according to the second aspect of the invention; And
• there Figure 7 schematically represents a second embodiment of a coating installation according to the second aspect of the invention.

For greater clarity, identical or similar elements are identified by identical reference signs throughout the figures.

DETAILED DESCRIPTION

THE Figures 1A and 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 section of the print head 1 along a transverse plane and along a first longitudinal plane. The partial view of the Figure 1B results from a section of the print head 1 along a second longitudinal plane parallel to the first longitudinal plane. These figures therefore show interior elements of the print head 1.

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 simplification, a single row of nozzles 11 is shown on the Figure 1A (the first longitudinal section plane passing through said row of nozzles). The number of nozzles 11 in each row can be between 2 and 500.

The print head 1 is intended for applying a coating product to an object to be coated, for example a motor vehicle body. It preferably works using drop on demand (or DOD) technology. Each nozzle 11 is then configured to deposit the coating product drop by drop. To do this, each nozzle 11 can be equipped with a valve which 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 pneumovalves each comprising a controllable membrane. Such a valve is controlled pneumatically (e.g. with compressed air). The valves of the nozzles 11 can also be solenoid type valves.

Alternatively, the print head is a continuous jet print head, that is to say it has permanently open circuits. The nozzles 11 are then devoid of valves.

The coating product taken as an example below is paint, but it can also be a primer, a varnish or a more viscous product such as a glue or putty.

There figure 2 is a sectional view on a larger scale of a portion A of the print head 1, the portion A being located around a nozzle 11 (cf. Fig.1A ). It will be described in conjunction with the Figures 1A and 1B .

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 an ejection zone 2 of the paint. Each nozzle 11 is thus associated with an ejection zone 2 which extends in the extension of the outlet channel 111 of the nozzle 11.

The outlet channel 111 and the ejection orifice 112 of the nozzles 11 are arranged in the body 10 of the print head 1. More particularly, the ejection orifice 112 is arranged in an ejection face 100 of the body 10. The ejection orifice 112 has a diameter which can be between 100 µm to 500 µm, for example equal to 150 µm. The ejection face 100 partly 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 face ejection 100.

• un circuit d'alimentation 12 relié aux buses 11 et destiné à véhiculer la peinture ;
• un circuit de maintenance 13 destiné à véhiculer un fluide de maintenance.

The print head 1 further comprises two internal fluid circuits, that is to say 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.

The function of the supply circuit 12 is to supply the nozzles 11 with paint. It includes a so-called 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 can also include a so-called purge or recirculation outlet 122 (cf. Fig.1B ). Purge outlet 122 is an outlet through which paint can be discharged from the print head 1 (and conveyed to recovery and processing manifolds or to the supply tanks). The purge outlet 122 is used to purge the circuit power supply 12, for example when changing paint shade. The supply circuit 12 can also be primed, that is to say filled with paint before a printing phase, by circulating the 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 arranged in an exterior wall of the body 10.

As shown on the figures 1A-1B , the supply circuit 12 may further comprise 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 also 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 communication fluidics.

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.

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 so-called inlet and outlet conduits respectively.

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

In this first embodiment, the maintenance circuit 13 comprises several first internal channels 131, called 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.

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 through at least a first internal channel 131. All the nozzles 11 of the head printing 1 can be maintained in this way.

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 accomplished in the same way and with the best level of performance for all nozzles.

In addition to the first internal channels 131, the maintenance circuit 13 comprises a first storage chamber 132 for the maintenance fluid and a first inlet-outlet 133. An inlet-outlet designates here an inlet and/or outlet orifice for the maintenance fluid. maintenance 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 arranged in an external wall of the body 10. The first storage chamber 132 (also called first maintenance fluid distribution chamber) is connected to the ejection zones 2 by the first internal channels 131.

Thus, the maintenance circuit 13 extends here from the first input-output 133 to the ejection zones 2 of the nozzles 11.

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 can also extend partially into the first storage chamber 132 , as shown in the Figure 1A .

• une opération de nettoyage (ou rinçage) d'une partie au moins des buses 11 et d'une partie au moins du circuit d'alimentation 12 au moyen d'un fluide de nettoyage ; et
• une opération de mouillage d'une partie au moins des buses 11 au moyen d'un liquide non volatil.

The maintenance circuit 13 makes it possible to carry out maintenance operations on the print head 1. In this first embodiment, the possible maintenance operations are:

• a cleaning (or rinsing) operation of 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.

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

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

The cleaning fluid can be brought into the ejection zone 2 of the nozzles 11 thanks to the first internal channels 131 of the maintenance circuit 13, then be evacuated in passing 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 direction of flow of the paint, also called normal flow direction. Conversely, the cleaning fluid can be brought into the ejection zone 2 by passing through the nozzles 11 thanks to the supply circuit 12, then be evacuated from the ejection zone 2 by 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 may be a liquid (volatile or not), a gas (e.g. air) or a mixture of liquid and gas. The cleaning liquid advantageously comprises a solvent (in order to “dissolve” the dry paint residue), preferably the same as that used in the composition of the paint.

Such an operation can be carried out to unclog clogged nozzles 11 and restore optimal operation (in particular guaranteeing repeatable drop trajectories). It can also be accomplished between two phases of printing the object, during a change of paint shade, or after a prolonged shutdown of the print head. The supply circuit 12 is advantageously purged before this operation.

A wetting operation of the nozzles 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 stoppage of printing and obstruct 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 via the first internal channels 131 at the end of a printing phase, then evacuated before the next printing phase begins, either by the supply circuit 12 or by the first internal channels 131. Alternatively, the dampening liquid can be brought to the orifice ejection 112 of the nozzles 11 by the supply circuit 12, then evacuated by the supply circuit 12 or by the first internal channels 131.

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

The maintenance fluid is sucked in to be evacuated from 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 depression is preferably between 0.1 bar and 0.8 bar, for example equal to 0.5 bar. The maintenance fluid is injected into the print head 1 under a pressure which can be between 0.1 bar and 1 bar.

The pressure and vacuum values depend on the type of operation desired and the properties of the maintenance fluid. For example, for a cleaning operation, it It is advantageous to circulate the fluid quickly in the ejection zone and therefore to have high pressure/vacuum values. For a nozzle wetting operation, the wetting liquid is slowly brought into the ejection zone in order to form the wet film which will seal the nozzle.

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 the nozzles 11.

Thanks to the first internal channels 131 opening into the ejection zone 2 of the nozzles 11, maintenance operations can be accomplished without external flow, when the print head 11 is in position for printing, that is to say say in the immediate vicinity of the object to be coated. It then becomes possible to do without a recycling bin.

In reference to the figure 2 , a first internal channel 131 can be arranged so that the maintenance fluid flows into contact with the ejection face 100. This can thus be cleaned and freed of paint residues 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 comprises a wall forming a flat surface with the ejection face 100, as illustrated. It is for example oriented parallel to the ejection face 100.

In another configuration, not shown in the figures, the first internal channel 131 is inclined relative to the ejection face 100 towards the ejection orifice 112 of the associated nozzle(s). ) to the first internal channel 131.

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 cleaning or wetting of the ejection orifice (by limiting the dispersion of the fluid jet) and facilitates suction of the maintenance fluid.

The first internal channel 131 preferably has a section with characteristic dimensions less than or equal to 0.5 mm, preferably less than or equal to 0.25 mm. This 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 first internal channel 131 can be between 0.5 mm and 10 mm. Such a length makes it possible to properly “guide” the maintenance fluid to ejection zone 2.

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

The first internal channels 131 are advantageously arranged in a plate (or layer) 101 called external maintenance plate and arranged on the ejection face 100. This external maintenance plate 101 is very thin, for example between 0, 1 mm and 1 mm, and therefore does not significantly increase the size of the print head 1.

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

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

In this second embodiment, the maintenance circuit 13 comprises, 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.

Like the first internal channels 131, the second internal channels 135 serve to convey the maintenance fluid to the ejection zones 2 or to evacuate the maintenance fluid from the ejection zones 2.

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).

The maintenance circuit 13 further comprises a second storage (or distribution) chamber 136 of the maintenance fluid and a second inlet-outlet 137 connected to the second storage chamber 136. The second inlet-outlet 137 can be arranged in a external wall of the body 10 and open directly into the second storage chamber 136 or be connected to the second storage chamber 136 by a conduit. The second storage chamber 136 is preferably arranged to guarantee identical pressure/vacuum along the print head 1 and thus ensure identical operation for all the nozzles 11.

The maintenance circuit 13 extends here from the first input-output 133 to the ejection zones 2 of the nozzles 11 and from the ejection zones 2 to the second input-output 137.

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. nozzles 11. Each second internal channel 135 can further extend partially into the second storage chamber 136, as is illustrated in the Figure 3 .

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

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 into 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.

Alternatively, the second internal channel 135 can be inclined relative to the ejection face 100 towards the ejection orifice 112.

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 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 port 112.

The second internal channel 135 preferably has a section with characteristic dimensions less than or equal to 0.5 mm, preferably less than or equal to 0.25 mm. This 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 can be between 0.5 mm and 10 mm.

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.

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

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

• une opération de nettoyage d'une partie au moins des buses 11 et d'une partie au moins du circuit d'alimentation 12 au moyen d'un fluide de nettoyage ; et
• une opération de mouillage d'une partie au moins des buses 11 au moyen d'un liquide non volatil ; et
• une opération de nettoyage de la face d'éjection 100 et de l'orifice d'éjection d'une partie au moins des buses 11 au moyen d'un fluide de nettoyage.

The possible maintenance operations with the 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 by means of a cleaning fluid.

The operation of cleaning 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 evacuate the maintenance fluid from the ejection zones 2 after it has circulated in the supply circuit 12 and the nozzles 11. Alternatively, the second internal channels 135 can fulfill a function different from that of the first internal channels 131. For example, they can be used to suck up the wetting liquid while the first internal channels 131 were used to bring it to the ejection zones 2.

The cleaning operation of the ejection face 100 and the ejection orifice of the nozzles 11 comprises the conveying of the cleaning fluid to the ejection zones 2 via the first internal channels 131 and the evacuation of 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 input-outputs 133, 137) and in the ejection zones 2, in contact with the ejection face 100 .

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), cleaning more thrust from the ejection face 100 can be obtained.

The print head 1 according to the second embodiment thus makes it possible to carry out an additional maintenance operation. The pressure and depression values are similar to those indicated previously. Implementation is easier because maintenance is completely unrelated to the power supply (removal of valves in the circuit).

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

A maintenance circuit 13 comprising several first internal channels 131, however, has better performance (in terms of cleaning the nozzles for example) than a maintenance circuit 1 with a single first internal channel common to several nozzles. In fact, the maintenance fluid can thus be conveyed to the ejection zone 2 of the nozzles or evacuated from the ejection zone 2 of the nozzles in a more precise manner. Multiplying the number of first internal channels 131 also makes it possible to reduce their size and therefore to increase the speed of the maintenance fluid which circulates inside.

Similarly, the maintenance circuit 13 may only comprise (in addition to the first internal channel(s) 131) a single second internal channel 135 opening out to the ejection zone 2 of several nozzles 11, and preferably of all the nozzles. 11.

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

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.

The first openings 138 are arranged in the wall of the body 10 which separates the first storage chamber 132 and the ejection zones 2. They result from the overlap 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).

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

The second openings 139 are arranged in the wall of the body 10 which separates the second storage chamber 136 and the ejection zones 2. They result from the overlap between the second storage chamber 136 and the ejection zones 2.

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 first opening 138 associated with respect to the ejection orifice 112 of the nozzle 11 associated. In other words, the first opening 138, the second opening 139 and the end of the ejection port 112 are aligned. This arrangement improves the cleaning and wetting of the ejection orifice 111 of the nozzle 11. In addition, the first and second openings 138-139 are advantageously arranged so that the maintenance fluid flows into contact with the face of ejection 100.

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

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.

According to a variant of this third embodiment, the maintenance circuit does not have a second storage chamber 136. The print head then operates in the same way as the print head 1 of the figures 1A-1B .

Finally, in another embodiment, the print head comprises only one 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 a single distribution channel 124 connecting the storage chamber 123 to the nozzle 11.

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

• un circuit d'injection 31 relié à (au moins) une entrée de la tête d'impression 1 et configuré pour injecter le fluide de maintenance dans la tête d'impression 1 ;
• un circuit d'aspiration 32 relié à (au moins) une sortie de la tête d'impression 1 et configuré pour aspirer le fluide de maintenance de la tête d'impression 1 ; et
• un circuit d'approvisionnement 33 en produit de revêtement (ex. peinture) reliée à l'entrée d'approvisionnement 121 du circuit d'alimentation 12 de la tête d'impression 1.

In a manner common to these two embodiments, the coating installation 3 comprises (in addition to the print head 1):

• an injection circuit 31 connected to (at least) one input 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 suck up the maintenance fluid from the print head 1; And
• a supply circuit 33 for coating product (e.g. paint) connected to the supply inlet 121 of the supply circuit 12 of the print head 1.

The coating product supply circuit 33 may comprise at least one coating product tank 331 and at least one so-called filling valve 332 connected on the one hand to the coating product tank 331 and on the other hand to the supply inlet 121 of the power supply circuit 12.

The injection circuit 31 (also called maintenance fluid supply circuit) comprises at least one pressurized tank 311 containing maintenance fluid and at least one so-called injection valve 312 connected on the one hand to the pressurized tank 311 and on the other hand at the inlet of the print head 1. By “pressurized” means that the pressure inside the tank is higher than atmospheric pressure. The injection circuit 31 may also include means for adjusting the maintenance fluid pressure. These adjustment means can be arranged between the pressurized tank 311 and the injection valve 312. They include for example a variable flow valve 313. Alternatively, the pressure adjustment can be carried out at the level of the pressurized tank 311 or even more upstream (compressed air source, pump, etc.). The injection circuit 31 then advantageously comprises a two-way valve 313 disposed between the pressurized tank 311 and the injection valve 312.

• un premier réservoir pressurisé 311a contenant le fluide de nettoyage ;
• un deuxième réservoir pressurisé 311b contenant le liquide de mouillage ;
• une première vanne d'injection 312a reliée d'une part aux premier et deuxième réservoirs pressurisés 311a-311b et d'autre part à une première entrée de la tête d'impression 1 ;
• une deuxième vanne d'injection 312b reliée d'une part aux premier et deuxième réservoirs pressurisés 311a-311b et d'autre part à une deuxième entrée de la tête d'impression 1 (distincte de la première entrée).

Advantageously, the injection circuit 31 comprises:

• 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 the one hand to the first and second pressurized tanks 311a-311b and on the other hand to a first inlet of the print head 1;
• a second injection valve 312b connected on the one hand to the first and second pressurized tanks 311a-311b and on the other hand to a second inlet of the print head 1 (separate from the first inlet).

The means for adjusting the maintenance fluid pressure can then comprise 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 pneumovalve, solenoid, etc. type).

The suction circuit 32 comprises a vacuum generator 321 (venturi effect system or vacuum pump) and at least one so-called suction valve 322 connected on the one hand to the vacuum generator 321 and on the other hand to the outlet of the print head 1. In addition, the suction circuit 32 advantageously comprises a recovery volume 323, connected to the vacuum generator 321 and intended to recover the vacuumed maintenance fluid.

• une première vanne d'aspiration 322a reliée d'une part au générateur de vide 321 et d'autre part à une première sortie de la tête d'impression 1 ; et
• une deuxième vanne d'aspiration 322b reliée d'une part au générateur de vide 321 et d'autre part à deuxième sortie de la tête d'impression 1 (distincte de la première sortie).

Advantageously, the suction circuit 32 comprises:

• a first suction valve 322a connected on the one hand to the vacuum generator 321 and on the other hand to a first outlet of the print head 1; And
• a second suction valve 322b connected on the one hand to the vacuum generator 321 and on the other hand to the second outlet of the print head 1 (separate from the first outlet).

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

In the first embodiment ( Fig.6 ), the first injection valve 312a is connected to the first input-output 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 on the Figure 6 ).

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 at the purge outlet 122 of the supply circuit 12, not shown on the Figure 6 ).

In other words, the first output of the print head 1 and the second input of the print head 1 are combined with the first input-output 133 of the maintenance circuit 13. The second output of the print head 1 and the first input of the print head 1 coincides with the supply input 121 of the power supply circuit 12.

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.

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.

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

The two injection valves 312a-312b and the two suction valves 322a-322b make it possible to carry out the multitude of maintenance operations described above.

The first injection valve 312a and the first suction valve 322a are advantageously controlled in phase opposition. 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 phase opposition.

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 takes place at the same time as the suction.

According to a particular cleaning mode, 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 opened intermittently, so as to produce pulsations of cleaning fluid.

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 be sucked in through the supply inlet 121, then be injected through the supply inlet 121 and be sucked in through the first inlet-outlet 133 (or in reverse order).

According to a variant embodiment, the coating installation 3 of the Figure 7 further comprises a third suction valve connected on the one hand to the vacuum generator 321 and on the other hand to the supply inlet 121, as well as a third injection valve connected on the one hand to the first and second pressurized tanks 311a-311b and on the other hand at the supply inlet 121. This alternative embodiment makes it possible to clean (in the two directions) 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 be sucked in through the first inlet-outlet 133 and the second inlet -output 137 (or vice versa).

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 different ways. As an example, we can cite diffusion welding or brazing of metal sheets, selective laser sintering of metal powder, micro-molding and manufacturing techniques for microelectromechanical systems (MEMS) in silicon.

The body can also be composed of machined elements assembled by gluing or screwing, a seal can be installed between the different components to ensure sealing.

• la fourniture d'une pluralité de plaques, dans lesquelles sont aménagées tout ou partie des composants (canaux, chambres, conduits, orifices d'entrée et/ou de sortie...) des buses 11, du circuit d'alimentation 12 et du circuit de maintenance 13 ; et
• l'assemblage des plaques entre elles, par exemple grâce à une technique de soudage, brasage ou collage.

A method of manufacturing the body 10 of the print head 1 may comprise the following steps:

• the supply of a plurality of plates, in which all or part of the components (channels, chambers, conduits, inlet and/or outlet orifices, etc.) of the nozzles 11, of the supply circuit 12 and of the maintenance circuit 13; And
• the assembly of the plates together, for example using a welding, brazing or bonding technique.

The plates are preferably made of metal, for example stainless steel. They are machined to form the different parts of the nozzles 11, the supply circuit 12 and the maintenance circuit 13, for example by chemical cutting, laser cutting or electroerosion by sinking (also called EDM, for “electrical discharge machining” in English). The plates (also called “strata”) preferably have a thickness of between 10 µm to 1000 µm.

• la mise en contact des plaques de manière à former un empilement ;
• la contrainte en pression de l'empilement, par exemple entre 300 bar et 500 bar ; et
• le recuit (ou traitement thermique) de l'empilement contraint en pression, afin de faire diffuser (ou migrer) les atomes du métal aux interfaces entre les plaques.

In a preferred mode of implementation of the manufacturing process, the metal plates are assembled by diffusion welding. The assembly step then includes the following operations:

• bringing the plates into contact so as to form a stack;
• the pressure stress of the stack, for example between 300 bar and 500 bar; And
• annealing (or heat treatment) of the pressure-stressed stack, in order to diffuse (or migrate) the metal atoms at the interfaces between the plates.

Annealing is preferably accomplished at a temperature between 0.6.T _f and 0.8.T _f , where T _f is the melting temperature of the metal. The duration of the annealing can be between 1 hour and 3 hours.

The surfaces of the plates which 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.

Such a manufacturing process is precise, simple and quick to implement (and therefore inexpensive). Furthermore, when the diffusion welding technique is used, the body 10 obtained is robust, because it is ultimately formed in one piece (it has a monolithic appearance). The diffusion welding technique is also advantageous in that it does not require additional material (glue, filler metal, etc.) at the interfaces between the metal plates.

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

Claims (15)

Print head (1) for applying a coating product to an object to be coated, the print head comprising a body (10) in which are arranged: - several nozzles (11) each comprising an ejection orifice (112) and an outlet channel (111) opening into an ejection zone (2) of the coating product through the ejection orifice (112); - a coating product supply circuit (12) connected to the nozzle (11); the print head further comprising a maintenance circuit (13) intended to convey a maintenance fluid, the maintenance circuit (13) extending inside the body (10) up to the zone d ejection (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 a single 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). Print head (1) according to claim 1, in which 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 single nozzle (11) associated with the first internal channel (131). Print head (1) according to claim 2, in which each second internal channel (135) is located opposite the first internal channel (131) associated with respect to the ejection orifice (112) of the nozzle (11) in the ejection zone from which this second channel (135) opens. Print head (1) according to one of claims 2 and 3, in which each first internal channel (131) and second associated internal channel (135) are oriented in the same direction. Print head (1) according to any one of claims 1 to 4, comprising an ejection face (100) in which the ejection orifice (112) of the nozzle (11) is arranged and in which the first internal channel (131) is arranged so that the maintenance fluid circulates in contact with the ejection face (100). Print head (1) according to any one of claims 1 to 4, comprising an ejection face (100) in which the ejection orifice (112) of the nozzle (11) is arranged and in which the first internal channel (131) is arranged in a plate (101) arranged on the ejection face (100) of the print head (1). Print head (1) according to one of claims 1 to 6, in which the first internal channel (131) comprises an end open to the ejection zone (2) and located at a distance (d) less than or equal to 1 mm from the ejection port (112) of the nozzle (11). Print head (1) according to one of claims 1 to 7, in which the maintenance circuit (13) comprises a first storage chamber (132) of the maintenance fluid, 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 between 0.5 mm and 10 mm. Print head (1) according to one of claims 1 to 7, in which the maintenance circuit (13) comprises a first storage chamber (132) of the maintenance fluid, the first storage chamber (132) communicating with the ejection zones (2) of each nozzle through a first opening (138). Print head (1) according to one of claims 8 and 9, in which 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) of the nozzles (11). Print head (1) according to one of claims 1 to 10, in which the first internal channels (131) are provided in an external maintenance plate (101) arranged on an ejection face (100) of the body ( 10), in which the ejection orifices (112) of the nozzles (11) are provided. Print head (1) according to one of claims 1 to 11, in which the first internal channels (131) have a section of characteristic dimensions less than or equal to 0.5 mm, preferably less than or equal to 0.25 mm. Coating installation (3) comprising: - a print head (1) according to any one of claims 1 to 12; - an injection circuit (31) of 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). Coating installation (3) according to claim 13, in which the suction circuit (32) comprises: - a vacuum generator (321); - a first suction valve (322a) connected on the one hand to the vacuum generator (321) and on the other hand to a first outlet of the print head (1); And - a second suction valve (322b) connected on the one hand to the vacuum generator (321) and on the other hand to a second outlet of the print head (1). Coating installation (3) according to one of claims 13 and 14, in which 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 on the one hand to the first and second pressurized tanks (311a-311b) and on the other hand to a first inlet of the print head (1); - a second injection valve (312b) connected on the one hand to the first and second pressurized tanks (311a-311b) and on the other hand to a second inlet of the print head (1).

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