EQUIPMENT FOR PRINTING MOVING SHEETS

Abstract

A suction device for printing moving sheets, characterized in that it comprises an elongated hollow body (6) with an interior space (11) that communicates with the outside through a tubular junction (7) and through through holes (9) that open onto a lower horizontal surface (S) that is configured to adhere to it by the suction effect at least one sheet (L, L') in longitudinal motion along the entire length of the elongated hollow body (6) below it: wherein the tubular junction (7) is connected to a compressed air device to generate a degree of vacuum within the interior space (11) of the elongated hollow body (6); and wherein the lower horizontal surface (S) of the elongated hollow body (6) forms part of a lower wall (8) traversed by the through holes (9).

Description

EQUIPMENT FOR PRINTING MOVING SHEETS Object of the invention The present invention relates to equipment for printing moving sheets that allows printing with optimal quality on a die-cut sheet in motion before a box is formed with said die-cut sheet, i.e., when it is still a flat sheet body that is moved by means of a conveyor device towards the assembly area of ​​the respective box. The invention is preferably applicable to cardboard sheets, which receive printing on their underside from below; where the cardboard sheets are transported after printing to a box forming station, where there are automatic assembly or mounting mechanisms for the respective box. Background of the invention Currently, different transport and positioning systems are known for printing loose cardboard sheets (blanks), or other materials, before forming cardboard boxes, so that what poses a real challenge is maintaining the stability of each cardboard sheet so that an inkjet print head has precision when printing the corresponding graphics on the cardboard sheet with quality. US Patent No. 10752023B2 describes a vacuum conveyor belt system with air channels and a vacuum table. This system is suitable when the cardboard sheet is not perfectly flat; the vacuum effect of the conveyor belt "suctions" the cardboard sheet against the conveyor belt to ensure a constant distance to the print head. Its drawbacks include its ineffectiveness for high-speed printing and its complex and expensive structure, as it is designed to print cardboard sheets on their top surface. The patent with publication number US12122171 (Multi-wall Printing) protects a device that prints patterns that cross the crease lines (fold lines where the different parts of the box will be folded), allowing a logo or legend to be seen continuously on several contiguous outer faces of the box once assembled. Single-pass printing technologies are also well-known. Unlike home printers where the printhead moves from side to side, industrial cardboard systems use single-pass technology. Other techniques and integration with the process allow printing on a paper roll (liner) before gluing it to the corrugated material that will form the cardboard. Description of the invention In order to achieve the objectives and avoid the drawbacks mentioned in the previous sections, the invention proposes equipment for printing moving sheets comprising in principle a suction device, a printing head and at least one sheet transport device. The suction device comprises an elongated hollow body with an interior chamber-like space that communicates with the outside through a tubular connection and through through holes that lead to a lower horizontal surface configured to adhere to it by the suction effect of the longitudinally moving sheets along the entire length of the elongated hollow body below it; where said sheets remain in contact with said lower horizontal surface during their longitudinal movement. The tubular junction is connected to a compressed air device to generate a degree of vacuum within the interior space of the elongated hollow body; and where the lower horizontal surface of the elongated hollow body forms part of a lower wall traversed by through holes. Extreme areas of the lower horizontal surface of the lower wall of the elongated hollow body comprise two inclined planes that converge downwards and towards the center of the elongated hollow body. The suction device includes a regulating valve fixed to the elongated hollow body; where said valve is configured to be able to regulate the degree of vacuum within the interior space of the elongated hollow body. Following the above description, the equipment for printing on moving sheets includes a suction device in combination with a print head and at least one sheet carrier device. The sheets are dragged substantially in a horizontal plane, held by lateral portions of the sheets and complemented by cantilevered main portions. These cantilevered main portions of the sheets are configured to receive a print pattern from the print head. The suction device is located above the conveyor device and also above the sheets; where below the conveyor device and the sheets is located the print head, which is configured to print the print configuration when a printable area of ​​the main cantilevered portion of the respective sheet is located in a vertically facing position with a central part of the suction device. It should be noted that the simplicity of the suction device allows it to be seamlessly integrated into most sheet conveyors. With the printing equipment of the invention, the low quality printing generated by the oscillating movements of the main cantilevered portions of the sheets during the dragging and transport process is eliminated, oscillating movements that prevent the distance between the printing head and the respective sheet to be printed from remaining constant and with stable mobility. In contrast, with the characteristic suction device of the invention, the main cantilevered portions of the sheets are kept stable and in constant contact with the lower horizontal surface of the elongated hollow body that forms part of the suction device. In another embodiment of the invention, the equipment of the invention is also configured to be able to print a continuous sheet to perform successive printing configurations on it before making cuts on it to obtain the respective sheets to then be able to assemble the corresponding boxes. Next, to facilitate a better understanding of this descriptive report and forming an integral part thereof, a series of figures are included in which, for illustrative and non-limiting purposes, the object of the invention has been represented. Brief description of the figures Figure 1.- Shows a perspective view of the equipment for printing moving sheets, the object of the invention. Figure 2 shows another perspective view of the sheet printing equipment seen from below. The equipment is configured to print individual sheets to form individual boxes. Figure 3.- Shows a longitudinal section view of the equipment for printing moving sheets. Figure 4.- Shows a cross-sectional view of the equipment for printing moving sheets. Figure 5.- Shows a view similar to that shown in Figure 2, where in this case the equipment is configured to print a single continuous sheet to perform successive prints on it, before making successive cuts to obtain the respective sheets for the boxes. Description of an example of embodiment of the invention Considering the numbering adopted in the figures, the equipment for printing moving sheets L comprises a suction device 1 that is located above a conveyor device T that is configured to transport the sheets L in a substantially horizontal plane; where the sheets L can be made of cardboard or any other material. Below the conveyor device T is located a print head 2 which is configured to print a print configuration C onto a lower face of the sheet L when a printable area of ​​the sheet L is located in a position facing vertically with a central part of the suction device 1. As shown more clearly in Figure 4, the L sheets to be printed are dragged and transported at all times by the transport device T, which holds them by lateral portions of the L sheets, so that other main portions of the L sheets are cantilevered. It is precisely these cantilevered main portions on which each of the prints of the printing configuration C is made. The conveyor device T is conventional and comprises at least one lower closed-loop conveyor belt 3 in combination with at least one second upper conveyor belt 4 that is located above the lower conveyor belt 3. In the embodiment shown in Figure 4, the printing equipment comprises two conveyor devices T, one on each side of the assembly formed by the suction device 1 and the print head 2; where on one of the two sides the conveyor device T comprises double conveyor belts 3, 4. The L sheets are held by their lateral portions between at least one of the two lower conveyor belts 3 and one of the two upper conveyor belts 4 of one of the two conveyor devices T. All the conveyor belts 3, 4 are coupled on pairs of end wheels 5; where at least one of them transmits its rotary motion to each of said conveyor belts 3, 4 to thus drag the succession of L sheets. In this situation, when said sheets L reach the suction device 1, their main cantilevered portions are perfectly positioned on a horizontal plane, adhering to a lower horizontal surface S of the suction device 1 by being held against said lower horizontal surface S due to the vacuum effect generated by the suction device 1. The plane of the main cantilevered portion of each sheet L, when attached to the lower horizontal surface S of the suction device 1, is a coplanar plane with the plane in which the side portion of the respective sheet L is held between the conveyor belts 3, 4 of the conveyor device T. The suction device 1 comprises an elongated hollow body 6 to which a tubular junction 7 is connected, communicating with an interior space 11 of said elongated hollow body 6; wherein said tubular junction 7 is connected to a compressed air device to generate a degree of vacuum within said interior space 11 of the elongated hollow body 6. The lower horizontal surface S of the suction device 1 forms part of a lower wall 8, which in turn forms part of the elongated hollow body 6; wherein said lower wall 8 is pierced by a set of through holes 9 that connect the interior space 11 of the elongated hollow body 6 with the exterior; said through holes 9 opening into the lower horizontal surface S. With this described arrangement of the suction device 1, when the compressed air device is activated, a degree of vacuum is generated in the interior space 11 of the elongated hollow body 6, causing the main cantilevered portions of the sheets L dragged by the conveyor device T to come into contact with the lower horizontal surface S of the elongated hollow body 6, so that during this contact the dragging of the sheets L is kept stable, maintaining a constant distance between each sheet L and the print head 2. When each of the L sheets is positioned in correspondence with the central part of the suction device 1, the print head 2 is activated, projecting its fluid (ink) onto the lower face of the L sheet, printing the C print configuration on said L sheet; all this while maintaining the drag and mobility of the L sheets with total stability and obviously keeping the distance between the L sheet and the print head 2 constant. During the dragging of the L sheets, their main cantilevered portions may have tilting mobility up and down; where when said main cantilevered portions come into contact with the lower horizontal surface S of the suction device 1, then said mobility disappears completely, maintaining said contact with adhesion thanks to the constant suction or vacuum effect generated by the suction device 1, which always tends to absorb the L sheet through the through holes 9 of the elongated hollow body 6 that forms part of the suction device 1. The C print configuration to be printed on the L sheets are usually quality seals, barcodes, QR codes, simple texts, or any other print motifs. The new suction device 1 consists of the elongated hollow body 6 equipped with the tubular connection 7 which constitutes an air suction inlet at a first end of the elongated hollow body 6. It is also possible to include at least one valve 10 located at a second end (opposite to the first end) of the elongated hollow body 6. This valve 10 is intended to regulate the degree of vacuum (depression / vacuum) within the interior space 11 of the elongated hollow body 6. Optionally, additional valves 10 can be included on the elongated body 6 to allow for sectioning the degree of vacuum within the interior space 11 of the elongated hollow body 6. Furthermore, with the addition of these valves 10, very precise vacuum regulation is achieved. These additional valves 10 are mounted on an upper wall 12, opposite the lower wall 8 of the elongated hollow body 6. On the other hand, it should be noted that extreme areas of the lower horizontal surface S of the lower wall 8 of the elongated hollow body 6 comprise two inclined planes 8a that facilitate the movement of the sheets L along the lower part without obstruction when they are pulled by the transport device T; where said inclined planes 8a converge towards the print head 2; and where said inclined planes 8a could also be two curved planes. As previously mentioned, the print head 2 is located below the respective sheet L, once it has been sucked in by the corresponding suction zones with the lower horizontal surface S of the suction device 1; where the central zone of said lower horizontal surface S coincides with the vertical of the print head 2. The cardboard sheets L are moved at high speed, dragged by the conveyor device T, until each sheet L adheres to an initial area of ​​the lower horizontal surface S of the suction device 1; where said sheet L continues to advance to the central area or part of the suction device 1, maintaining the adhesion of the sheet L, so that printing occurs on the cardboard sheet L when it is perfectly adhered to said central part of the suction device 1 at a constant and calculated distance with respect to said print head 2. As shown in Figure 5, the equipment of the invention is also configured to be able to print a continuous sheet L (coupled on an endless roll reel) to perform successive printing configurations C on it before making cuts on it L to obtain the respective sheets to then be able to assemble the corresponding cardboard boxes. On the other hand, the invention is applicable to cardboard sheets, but also to sheets made of other materials, such as metal, plastic, paper; and in general any other material; it should also be noted that the invention is applicable to independent L sheets and to a continuous L sheet, as referred to above. It should also be noted that the invention can be applied to any substrate that needs to be printed, and which moves, vibrates, bends, etc. during transport. Furthermore, although the invention originates from printing from the bottom up, it is also possible to print in any direction or sense of space: from top to bottom or at any angle.

Claims

1. Suction device for printing moving sheets, characterized in that it comprises an elongated hollow body (6) with an interior space (11) that communicates with the outside through a tubular junction (7) and through through holes (9) that open onto a lower horizontal surface (S) that is configured to adhere to it by the suction effect at least one sheet (L, L') in longitudinal motion along the entire length of the elongated hollow body (6) below it: wherein the tubular junction (7) is connected to a compressed air device to generate a degree of vacuum within the interior space (11) of the elongated hollow body (6);and wherein the lower horizontal surface (S) of the elongated hollow body (6) forms part of a lower wall (8) through which the through holes (9) pass.

2. A suction device for printing moving sheets, according to claim 1, characterized in that end areas of the lower horizontal surface (S) of the lower wall (8) of the elongated hollow body (6) comprise two inclined planes (8a) that converge downwards and towards the center of the elongated hollow body (6).

3. A suction device for printing moving sheets, according to any one of the preceding claims, characterized in that it includes at least one regulating valve (10) fixed at one end of the elongated hollow body (6);wherein said valve (10) is configured to regulate the degree of vacuum within the interior space (11) of the elongated hollow body (6).

4. Suction device for printing moving sheets, according to claim 3, characterized in that it includes additional regulating valves (10') on the elongated body (6), which are configured to segment the degree of vacuum within the interior space (11) of the elongated hollow body (6);wherein said additional valves (10') are mounted on an upper wall (12) of the elongated hollow body (6).

5. Equipment for printing moving sheets, according to any one of the preceding claims, wherein the equipment includes the suction device (1) in combination with a print head (2) and at least one conveyor device (T) for at least one sheet (L, L') that is dragged in a horizontal plane by holding it by a lateral portion of said sheet (L, L') complemented by a main cantilever portion of said sheet (L, L'), which is configured to print on said main cantilever portion at least one print configuration (C) with the print head (2); characterized in that the suction device (1) is located above the conveyor device (T) and above the sheets (L);where below the conveyor device (T) and the sheets (L) is located the print head (2) which is configured to print the print configuration (C) when a printable area of ​​the main cantilevered portion of the sheet (L, L') is located in a position facing vertically with a central part of the suction device (1).;