FR3044259A1 - INK JET PRINTING METHOD, INK JET PRINTING MACHINE, AND ANTI-DRYING DEVICE - Google Patents

Abstract

The present invention relates to an inkjet printing method on plate elements (12) in an inkjet printing machine (10) comprising a vacuum transport device (13) and at least one head printing (14). According to the invention, the position of openings (21) in the vacuum transport (13) is measured during a preliminary calibration phase and then, during a printing phase, ink is projected by the print head (14) through openings (21) whose position has been measured during the calibration phase. The invention also relates to an inkjet printing machine and an anti-drying device for an ink jet printing machine, for implementing the preceded according to the invention. The invention is particularly suitable for printing on large plate elements, and prevents the ink from drying in the nozzles of the printing heads, and thus avoids machine downtime.

Description

Ink jet printing process, ink jet printing machine and anti-drying device. FIELD OF THE INVENTION The invention relates to the field of digital inkjet printing, and more particularly to inkjet printing on sheet or plate substrates, by using the technology known as drop on demand within inkjet printing machines including vacuum transport. 2. Prior Art

Inkjet printing machines are known. These machines use for example a so-called continuous flow technology, or a so-called drop-on-demand technology. These machines use printheads with a number of nozzles through which the ink is projected. One of the technical constraints of so-called drop-on-demand inkjet printing technology is the discontinuous character of the inkjet. Indeed, the ink passes through a given nozzle only when it is necessary to print a droplet on a substrate. But if the nozzle is not traversed sufficiently regularly, the ink dries in the nozzle and closes. The nozzle can no longer be used for printing and requires cleaning. To avoid stopping the machine, make sure that each nozzle is filled with ink evenly enough so that the ink does not dry out.

Technologies have been developed for inkjet printing when the substrate is a web, especially a web of paper.

On the other hand, when the substrate is a relatively large rigid sheet or sheet material (greater than A3), for example a flat or corrugated cardboard sheet used to manufacture a package, vacuum transport devices are used to transport the substrates. inside the machine and keep them flat under the print heads. Such devices generally comprise a belt or strips having openings through which a vacuum effect is applied to the surface of the transported substrates. The ejection of a droplet through a nozzle outside the substrate may dirty the transport device, which in turn may soil the underside of the substrates it carries.

Document US Pat. No. 5,717,446 has proposed a solution to this problem for paper sheets of reduced dimensions (typically A4), by using a vacuum transport device comprising a carpet traversed by oblong holes regularly arranged and having a particular angle by relative to the movement of the carpet. According to this disclosure, the particular geometry of the holes on the surface of the carpet makes it possible to determine whether a hole is below any given nozzle by means of a single fixed sensor. It is then sufficient to regularly project droplets through the nozzles to prevent the ink from drying and closes, projecting if necessary droplets through the holes of the carpet. An ink collection device is also provided under the carpet.

This solution therefore requires the use of a mat having openings whose shape and location must be very precise. However, the manufacture of such a carpet is expensive, and the positioning of this carpet within the machine is complex. In addition, it is extremely complicated or impossible to maintain a constant geometry of the carpet throughout intensive industrial use, especially for large substrates (greater than A3). 3. OBJECTIVES OF THE INVENTION The invention aims in particular to overcome all or part of these disadvantages of the prior art.

More specifically, an object of the invention is to provide an ink jet printing method in a printing machine comprising a vacuum transport device. 4. Summary of the invention

All or some of these objectives, as well as others which will appear more clearly later, are achieved by the invention by means of an inkjet printing process on plate elements in a machine. ink jet printing apparatus comprising a vacuum transport device and at least one printhead, wherein the position of openings in the vacuum transport is measured during a preliminary calibration phase, and then, when an ink jet printing phase, ink is projected by the print head through apertures whose position has been measured during the calibration phase.

Thus, the method begins by acquiring a knowledge of the geometry of the surface of the vacuum transport device and makes it possible to regularly use all the nozzles of the printing heads, and thus to prevent the ink from clogging the nozzles while drying. .

Advantageously, the shape of the openings is also measured during the calibration phase. Thus the knowledge of the geometry of the surface is more precise and allows more quickly to project ink through a nozzle if necessary.

In a particular embodiment, the position of openings near the lateral edges of the vacuum transport is measured during the calibration phase. Thus the knowledge of the geometry of the surface of the vacuum transport device is focused on the areas where the nozzles are less frequently used, corresponding to the nozzles used to print on the substrates of maximum width.

In one embodiment, during the printing phase of the ink is projected through vacuum transport openings located between the side edge of a plate member and the side edge of the vacuum transport. Thus, ink is projected into the nozzles lying outside the width of the substrate, which makes it possible to prevent the ink from drying in these nozzles.

Optionally, the positions of all openings of the vacuum transport are measured during the calibration phase. Thus, ink can be projected through any nozzle if necessary.

In a particular embodiment, during the printing phase of the ink is projected through openings in the gap between the trailing edge of a first plate member and the leading edge of a second element in plate. Thus the regular use of all the nozzles is possible without imposing the presence of a zone of waste front or near the rear edge of the plate element. The invention also relates to an inkjet printing machine, comprising a vacuum transport device for transporting plate elements and a print head for inkjet printing on the plate elements, comprising also an opening detection device in the vacuum transport device and a control device capable of measuring the position of openings in the vacuum transport device and able to control the projection of ink through openings passing under the printhead. Thus the inkjet printing machine allows the implementation of the printing method according to the invention, and reduce the risk of clogging of the nozzles due to the drying of the ink.

Advantageously, the detection device is movable transversely, and the control device is able to control the displacement of the detection device to measure the position of openings or to detect the passage of openings. Thus, the detection device can measure the geometry of all or part of the surface of the vacuum transport device during a preliminary phase, and then possibly be used to perform a detection function during a printing phase.

In a particular embodiment, the control device stores the duration of non-use of each of the nozzles of the print head and controls the projection of ink by a nozzle through an opening when the duration of unused nozzle is greater than a threshold. Thus all nozzles are used regularly and the risk of clogging is reduced to a minimum, without too much ink being projected through the openings.

Preferably, the vacuum transport device comprises openings of substantially circular or oval shape. Thus the transport device is inexpensive to manufacture. The invention also relates to an anti-drying device for an inkjet printing machine comprising a vacuum transport device for transporting plate elements and a print head for ink jet printing on plate elements; said anti-drying device comprising a detection device adapted to detect openings in the vacuum transport device, and a control device capable of measuring the position of openings in the vacuum transport device and able to control the projection of ink through openings passing under the print head. Thus, the device enables an ink jet printing machine to be adapted in order to be able to implement the printing method according to the invention. 5. List of Figures Other features and advantages of the invention will appear more clearly on reading the following description of a particular embodiment, given as a simple illustrative and nonlimiting example, and the accompanying drawings, among which :

Fig. 1 schematically shows an inkjet printing machine according to the invention;

Fig. 2 represents a printing station of a printing machine according to the invention;

Fig. 3 represents an example of theoretical arrangement of openings on the surface of the carpet of a vacuum transport device;

Fig. 4 shows an example of a realistic arrangement of openings on the surface of the carpet of a vacuum transport device;

Fig. 5 schematically represents an additional imaginary image created in accordance with an embodiment of the invention. 6. embodiment

In connection with FIGS. 1 to Fig. 5, various embodiments according to the invention.

Shown schematically in FIG. 1 a printing machine 10 implementing the ink jet printing method according to the invention. Conventionally, a stack of plate elements is arranged in an insertion station 11. In the insertion station 11, the plate elements 12 are deposited one after the other on a transport device 13. Numerous types of introduction stations have been described which make it possible, for example, to pick up the plate element situated on the top of a substantially horizontal stack, or the element at the base of such a stack. , or even using inclined batteries, or even a manual introduction. All types of introduction station can be used for the implementation of the invention.

Fig. 1 represents a succession of four plate elements 12, carried by the transport device 13. The transport device 13 shown is a carpet through which there are numerous openings for applying a vacuum effect to the plate elements 12. the belt 13 is a vacuum box (not shown in Fig. 1), in which a vacuum is created to produce the vacuum effect.

The plate elements 12 are held by the vacuum effect on the transport device 13 which moves them under one or more inkjet printing heads 14. The machine shown in FIG. 1 has four printhead bars 14, but the invention relates to inkjet printing machines having any number of printhead bars 14.

In the example of printing machine shown in FIG. 1, a control device 16 conventionally controls the different functions of the machine according to data received by sensors. For example, an optional sensor 17 makes it possible to detect the leading edge of a plate element 12 enabling the control device 16 to control the transport device 13 and the various printing bars 14 to print the desired digital image at the same time. surface of the substrate 12. Fig. 2 illustrates an example of printing bar 14, comprising four printheads mounted in staggered rows, and an example of vacuum transport comprising a mat 13 having many openings 21 for applying to the lower surface of a substrate plate or sheet 12 a vacuum effect generated by a vacuum box 22. The optional sensor 17 is also shown schematically FIG. 2.

In the remainder of the disclosure, the term print head 14 will be used to designate a print head or a printhead bar, each bar having one or more printheads aligned or staggered, of to produce a continuous impression.

The operation of a printing machine described so far is conventional and does not require a detailed description.

Fig. 3 represents an exemplary theoretical surface of the carpet of the vacuum transport device 13, said belt moving in the direction of the arrow. In this example, the carpet surface has openings 21 regularly arranged in a 60 ° pattern. All openings have exactly the same shape, and the carpet is perfectly positioned so that the observation of a light beam or laser 23 would at any time to define the position of all the openings 21 on the surface of the vacuum transport 13 Fig. 4 represents an example of the real surface of the carpet of a vacuum transport device 13 corresponding to the theoretical example shown in FIG. 3, and illustrates that the shape and arrangement of the openings 21 are not constant or regular. Fig. 4 also illustrates the fact that the observation of a light or laser beam absolutely makes it impossible to deduce the position of all the openings 21, in particular those located under the print heads 14.

According to the invention, the printing machine comprises an aperture detection device 24 diagrammatically represented as Fg. 2.

Thus, an ink jet printing method according to the invention comprises a preliminary calibration phase during which the position of openings 21 in the vacuum transport device 13 is measured.

This preliminary calibration phase makes it possible to precisely measure the geometry of the surface of the transport device 13, or of certain parts of this surface.

According to the invention, the printing method also comprises an ink jet printing phase during which ink is projected through openings 21 whose position has been measured during the preliminary phase. calibration.

Thus, an ink jet printing method according to the invention begins by acquiring the geometry of the surface of the vacuum transport device, in particular the position of the openings 21, then uses this data to project ink to through openings 21 whose position has been previously measured. Thus, it is ensured that all the nozzles are regularly traversed by ink to avoid the risk of obstruction of a nozzle in which the ink has dried.

According to one embodiment, the position of the openings 21 near the lateral edges of the vacuum conveying device 13 is measured. Indeed, the problem of drying the ink in the nozzles of the print head 14 arises in particular for the nozzles which are outside the passage of substrates 12 whose width is less than the maximum printing width. For nozzles located in a more central part, it is most often possible to print on a waste zone corresponding to the front edge or the rear edge of the substrate 12.

According to an alternative embodiment, the position of all the openings 21 present on the surface of the vacuum transport device is measured during the preliminary calibration phase. This embodiment makes it possible in particular to project ink through the central nozzles when openings 21 present on the surface of the vacuum transport device 14 are visible between the rear edge of a substrate 12 and the front edge of the next substrate.

Advantageously, the shape of the openings 21 is also measured during the preliminary calibration phase. This gives a better knowledge of the geometry of the surface of the vacuum transport 13, which offers more possibilities to project ink through openings 21 when necessary. The invention also relates to an inkjet printing machine comprising a vacuum transport device 13 for transporting plate elements 12 and a print head 14 for inkjet printing on the plate elements. Transported by the vacuum transport device 13. According to the invention, such an inkjet printing machine comprises a detection device 24 of openings 21 in the vacuum transport device 13, and a control device 16 adapted to measure the position of openings 21 in the vacuum transport device 13 and adapted to control the ink projection through openings 21 passing under the print head 14.

The detection device 24 openings can take any number of forms such as for example a point sensor, a linear sensor or a two-dimensional sensor. Regardless of the shape of the opening detection device 24, the control device 16 is adapted to be able to measure the position of the openings 21. The control device 16 may be a computer such as a microprocessor or a microprocessor. microcontroller. Many associations of an opening detection device 24 and a control device 16 capable of measuring the position of the openings 21 are conceivable by the person skilled in the art to implement the invention.

Preferably, the detection device 24 is movable transversely, and the control device 16 is able to control the displacement of the detection device 24 to measure the position of openings 21 or to detect the passage of openings 21. of a preliminary calibration phase, the control device 16 can control the displacement of the detection device 24 of openings 21. By simultaneously advancing the belt 13 or by reproducing this operation with several positions of the belt 13, the control device 16 measures the position of the openings 21, possibly after several rotations of the belt 13.

The control device 16 may optionally move the detection device 24 also during the printing phase, for example so that it detects the passage of openings near the edge of the belt 13 or to detect the presence of openings 21 between the rear edge of a plate member 12 and the front edge of the next substrate 12. Such detections can indeed make it possible to synchronize the various mechanisms (for example the transport device and / or the printing device) of the printing machine 10 or to verify the good positioning of the substrate 12 on the vacuum transport device 13. The aperture detection device 24 may optionally replace the front edge detection sensor 17.

It is obvious that the control device 16 can control the ink projection through openings 21 passing under the print head 14 in a very large number of different ways, depending on the type of control device used and its integration into the printing machine 10.

For example, if the printing machine is from the outset designed to implement a printing method according to the invention, the control device 16 may be the main computer of the machine 10, as shown in FIG. 1. In this case, the control device 16 advantageously stores the duration of non-use of each of the nozzles of the print head 14 and controls the ink jet through a nozzle through an opening 21 when the duration of the unused nozzle is greater than a predefined threshold. The invention also relates to an anti-drying device comprising a control device 16 and a detection device 24 as described above. This anti-drying device is intended to be installed on an ink jet printing machine according to the prior art, comprising a vacuum transport device 13 and a print head 14 for ink jet printing on inkjet printing machines. plate elements 12 according to the prior art, in order to modify it and make it suitable for implementing a printing method according to the invention.

In a preferred embodiment of the invention, the control device 16 creates an additional imaginary image composed only of points corresponding to droplets projected through apertures 21. An example of a fictitious image 24 is shown in FIG. . 5 for an arrangement of openings 21 corresponding to FIG. 3 and FIG. 4. By superimposing this additional imaginary image 24 on the image to be printed on the substrate 12, the printing machine 10 in accordance with the printing will simultaneously print an image on the substrate 12 and project ink through nozzles so that they are not blocked.

The frequency of projection of ink droplets through the openings 21 and the volume of these droplets do not justify the presence of a particular system for collecting or discharging ink in the vacuum transport 13, the quantity of ink droplets. ink being fully compatible with the usual frequency of cleaning vacuum transport devices.

Naturally, the printing method according to the invention and the printing machines for their implementation allow the use of conventional vacuum transport devices 13, inexpensive to manufacture, in particular vacuum transport devices 13 having openings 21. of substantially circular or oval shape.

Claims (11)

A method of ink jet printing on plate elements (12) in an inkjet printing machine (10) comprising a vacuum transport device (13) and at least one printhead (14), characterized in that during a preliminary calibration phase, the opening position (21) in the vacuum transport (13) is measured; during an ink jet printing phase, ink is projected by the print head (14) through openings (21) whose position has been measured during the calibration phase . 2. Ink jet printing method according to claim 1, characterized in that during the calibration phase is also measured the shape of the openings (21). 3. An ink jet printing method according to claim 1 or 2, characterized in that during the calibration phase is measured the position of openings (21) near the side edges of the vacuum transport (13). Ink-jet printing method according to one of the preceding claims, characterized in that during the printing phase, ink is projected through vacuum transport openings located between the lateral edge. a plate member and the side edge of the vacuum transport (13). Ink-jet printing method according to one of the preceding claims, characterized in that the positions of all the openings of the vacuum transport (13) are measured during the calibration phase. The ink jet printing method according to claim 5, characterized in that during the printing phase the ink is projected through apertures in the gap between the trailing edge of an ink jet. first plate member (12) and the leading edge of a second plate member (12). An ink jet printing machine (10), comprising a vacuum transport device (13) for transporting plate elements (12), a print head (14) for jet printing ink on the plate elements (12), characterized in that it comprises A device (24) for detecting openings (21) in the vacuum transport device (13), A control device (16) able to measure the position of openings (21) in the vacuum transport device (13) and adapted to control the ink projection through openings (21) passing under the print head (14). An inkjet printing machine (10) according to claim 7, characterized in that the detection device (24) is transversely movable, the control device being (16) able to control the movement of the device of the device. detection (24) for measuring the position of openings (21) or for detecting the passage of openings (21). An inkjet printing machine (10) according to claim 7 or 8, characterized in that the control device (16) stores the duration of non-use of each of the nozzles of the print head (14). ) and controls the jet of ink through a nozzle through an opening (21) when the duration of nonuse of the nozzle considered is greater than a threshold. Inkjet printing machine (10) according to one of claims 7 to 9, characterized in that the vacuum transport device (13) has openings (21) of substantially circular or oval shape. An anti-drying device for an inkjet printing machine (10) having a vacuum transport device (13) for transporting plate elements (12) and a print head (14) for ink jet printing on the plate elements (12), characterized in that said anti-drying device comprises a detection device (24) able to detect openings (21) in the vacuum transport device (13), A control device (16) capable of measuring the position of openings (21) in the vacuum transport device (13) and adapted to control the ink projection through openings (21) passing under the head of printing (14).