Patent Publication Number: US-2022219444-A1

Title: Printing device for a coupling machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national phase of International Application No. PCT/IB2020/054731 filed May 19, 2020 which designated the U.S. and claims priority to IT Patent Application No. 102019000007024 filed May 20, 2019, the entire contents of each of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a printing device for printing on a sheet of material, in particular a movable-type printing device to be used in associated with a laminating machine. 
     Description of the Related Art 
     Flexographic printing machines used to print single layer or laminated sheet materials of various types, prevalently used in the industrial packaging and paper converting sector, are well known. 
     One type of widely used flexographic printing machine generally comprises a central drum around which a plurality of independent printing units are arranged. 
     The material to be printed in the form of a continuous film is unwound from a first reel, guided in contact with at least one portion of the surface of the drum and is rewound onto a second reel. In the segment in which it is in contact with the drum, the film passes through one or more printing units which, in general, carry out partial printing on the surface of the film. In general, each printing unit is associated with a given colour so that the sum of several partial one-color prints carried out in sequence on the film by the various printing units gives rise to the final graphics of the print. 
     Another type of flexographic printing machine comprises a plurality of independent printing units arranged consecutively one after another along a path that extends horizontally, vertically or in a horseshoe. 
     In this case, each printing unit comprises a counter-pressure roller that performs the function of supporting and contacting the film like the central drum of the first type described. 
     These known machines are generally somewhat complex, cumbersome and costly. Moreover, preparing and setting up the machine for a new printing process requires a considerable amount of time. Therefore, these flexographic machines are used profitably to carry out complex printing processes, using several colours and for large production batches. 
     Films printed with these machines can be used directly as end product or can be used as semi-finished product to produce multi-layer films laminated by means of laminating machines. 
     Especially in the packaging sector, a company that produces multi-layer films consisting of two or more layers of laminated film, in addition to the process of laminating and joining of the films, must also carry out partial printing or “reprinting” on at least one of said films, for example to complete parts of the graphics or to insert writing or information in given areas of the film. 
     For printing operations of this type, typically simple, one-color and on surfaces of limited size, the use of a flexographic printing machine is not justified in relation to costs (whether for the possible purchase by the company or for third party printing) and times, required to set up and prepare the machine. 
     For this reason, in cases such as the one described above, movable-type printing devices, also called “printing trolleys” can be used; these can be temporarily installed in a laminating machine in order to share some components normally involved in the laminating process such as unwinders, winders, guide rollers, etc. to carry out a printing process on a film. 
     These known printing trolleys generally comprise a blade chamber to contain the printing ink, an Anilox roller that rotates in contact with said blade chamber, a cliché roller that rotates in contact with the Anilox roller and a counter-pressure roller that rotates in contact with the cliché roller. The print medium (film) is passed between the cliché roller and the counter-pressure roller. The Anilox roller picks up a quantity of ink from the blade chamber, which remains trapped in the cells made on its surface, and transfers it to the cliché roller, which in turn, prints the film. 
     As the size of the print in the direction of unwinding of the film depends on the outer diameter of the printing cliché, the device must be configured to accommodate cliché rollers that have sleeves, and related printing cliché s, of different diameters. Moreover, both it and the other rollers are mounted on the structure of the trolley by means of sliding guides that allow them to be moved to adapt their position to the diameter of the cliché and, at the same time, to be held and maintained in contact with one another. 
     In a known type of printing trolley, manufactured and marketed by the applicant, the rotating motion to the rollers is imparted by a motor connected to all the rollers by means of a gear train connected to one end of the rollers. 
     Although this solution is simple, sturdy and reliable, it has some problems. In fact, as the transmission ratio between the various rollers is predetermined, all the gears of the system must be replaced each time the diameter of the printing cliché changes. 
     This implies an evident loss of time to prepare the device, as well as costs linked to the procurement and storage of the multiple gears. 
     Moreover, indirect transmission, i.e. through one or more transmission members, of motion to the rollers can cause, due to inevitable backlash and tolerances that, although minimum, are always present, vibrations that produce a deterioration in the print quality. For this reason, to minimize vibrations the rotation speed of the rollers is often limited, lengthening printing times. 
     SUMMARY OF THE INVENTION 
     In this context, the object of the present invention is to provide a flexographic printing device to be used in association with a laminating machine that overcomes the problems of the prior art set forth above. 
     In particular, an object of the present invention is to provide a printing device that is more efficient and less complicated to handle and adjust, with respect to those of the prior art. 
     Another object of the present invention is to provide a compact and light movable-type printing device, to facilitate the installation and subsequent removal operations in a laminating machine. 
     These objects and other objects are achieved by a movable-type flexographic printing device, adapted to be used in association with a laminating machine, in accordance with one or more of the appended claims. 
     According to the invention the printing device comprises at least:
         a support structure that includes at least one pair of shoulders mounted on a trolley frame;   a blade chamber with a tank for containing printing ink;   an Anilox roller the surface of which is facing the tank of the blade chamber so that, rotating, a quantity of ink remains adhering thereto;   a print roller that holds a printing cliché adapted to rotate in contact with the Anilox roller so that a layer of ink is deposited onto the surface of said cliché; and   a counter-pressure roller that can rotate in contact with the print roller.       

     The trolley support structure facilitates movement of the device on the ground so that it can be temporarily positioned inside a laminating machine to perform printing operations. Said support structure generally comprises wheels or other equivalent rolling means. 
     The Anilox roller and the print roller are each supported by a pair of supports that can slide with respect to the shoulders of the support structure along a direction substantially orthogonal to the axis of said rollers and, preferably, substantially horizontal. 
     According to an aspect of the invention, the printing device also comprises at least one first motor for rotating the Anilox roller, at least one second motor for rotating the print roller and possibly a third motor for rotating the counter-pressure roller. 
     Said third motor can be mounted on the printing device or, preferably, it is designed to connect said counter-pressure roller to a motor mounted on the laminating machine by means of a belt. 
     The rollers of the device are therefore motorized independently from one another. The rotation speed of each roller is therefore managed and controlled by a control unit, integrated in, or external to, the device. As a function of the diameter of the printing cliché, the control unit calculates the rotation speed of each roller for correct operation of the device and drives the related motor accordingly. 
     In this way, during the operations to replace the sleeve of the cliché roller with one of a different diameter, it is not necessary to act on or disassemble parts of the other rollers. This operation is therefore faster and more practical to carry out with respect to known devices. 
     According to another aspect of the invention, the print roller comprises a cliché-holder cylinder supported at the ends by two shafts, where at least one first shaft is stably mounted on a respective sliding support and can be coupled to the cliché-holder cylinder. The second shaft is instead preferably in one piece with the cylinder. The second motor that operates the print roller is connected to the first shaft. 
     In this way, when the cliché-holder sleeve must be removed to replace the printing cliché, or possibly also said sleeve, it is possible to easily remove the cliché-holder cylinder from the printing device, while leaving the first shaft and all the parts connected to or associated with it (motor, sensors, supports, etc.) fixed on the device. 
     According to an aspect of the invention, the second motor that operates the print roller can comprise a ring rotor fitted directly onto the first shaft and a ring stator, which wraps around the rotor, mounted fixed on the sliding support. 
     Typically, the rotor has permanent magnets while the stator houses the windings of conductive material. 
     This configuration of the device has more than one advantage. In fact, the direct coupling of the motor to the shaft, i.e., without the interposition of transmission members, such as pulleys and belts, gears or the like, makes it possible to eliminate backlash that occurs in the direction of rotation, obtaining precise phase synchronism between the motor and the print roller and, consequently, the corresponding cliché. 
     Moreover, positioning of the motor aligned with the shaft makes the device more compact, leaving space around the shaft of the print roller for the positioning of other parts. 
     Further, this configuration makes it possible to mount the motor in a point of the shaft distal from its end, leaving this latter free and accessible. As better described below, this facilitates the connection of a source of compressed air to supply air inside the print cylinder. 
     In fact, said print cylinder typically has an internal cavity that can be supplied with pressurized air, which can be ejected from holes produced on the wall of the cylinder in order to create an air cushion between the surface of the cylinder and that of the sleeve and thereby facilitate sliding thereof during the mounting or removal operations. 
     For this purpose, according to an aspect of the invention, a passage can be made in the first shaft of the print roller, which extends parallel to its axis. A first end of said passage ends at the free end of said shaft while a second end, opposite the first end, communicates with the cavity of the cylinder. 
     As stated above, the mounting configuration of the second motor of the print roller allows the connection of a line for conveying air to the passage in the shaft, directly at said free end, for example by means of a common axial connector of rotary type. This solution reduces the constructional complexity of known systems with aligned motor where the air can be fed into the shaft through a radial opening that requires a particular rotary seal system that must be fitted on the shaft. 
     According to another aspect of the invention, the print roller can be mounted on its sliding supports so as to be able to translate axially, i.e., in a direction parallel to its axis. 
     This axial movement is useful and necessary to carry out the calibration operations of the print position in transverse direction with respect to the direction of movement of the print medium or film. Typically, said axial, or transverse, movement, has a total amplitude ranging from 5 mm to 30 mm and more preferably from 10 mm to 20 mm. In general, this movement is a movement away from a neutral central position and can thus be quantified from ±2.5 mm to ±15 mm, preferably from ±5 mm to ±10 mm from said neutral position. 
     According to this variant, the printing device further comprises a position adjustment system adapted to control the movement of said print roller in said direction of axial translation. 
     According to a possible embodiment, said position adjustment system comprises a motor, preferably electric, connected to a control member movable along a direction parallel to the axis of the print roller. 
     Typically, a transmission system, for example comprising belts and pulleys, recirculating ball screws, gears or a combination of two or more different systems from those cited or other equivalent systems, is interposed between the motor and control member. 
     The control member engages an insert in one piece with the first shaft of the print roller, preferably made with it, to move it along the aforesaid axial direction. 
     Said insert, for example, is disc or annular shaped and projects radially from the surface of the shaft. The control member is cradle or jaw shaped and has a seat in which at least one part of the insert is housed. 
     This configuration marginally influences the axial dimensions of the shaft, as the moving member and the jaw can have a width, in axial direction, of a few millimetres. This is particularly advantageous as the printing device of the present invention must be able to be housed inside a laminating machine, more precisely between its shoulders, in place of a conventional glue spreading trolley. 
     The jaw preferably comprises contact elements that remain substantially in contact with respective opposite faces of the insert. These contact elements allow the axial position of the shaft to remain stable during operation of the device, and control of the movement of said shaft along the axial direction. Said contact elements are preferably rolling means, such as wheels, bearings or the like, mounted in the seat of the jaw. 
     In this way it is possible to hold said contact elements pressed against the insert to eliminate, or minimize, axial backlash of the shaft and ensure the stability of the axial position during operation, without causing premature wear of the parts in contact and without affecting the rotation of the print cylinder. 
     According to another aspect of the invention, the second motor that operates the print roller is equipped with a rotor whose active part has a length, i.e. an extension in the axial direction, greater than that of the stator. Therefore, according to a preferred variant, the section of the rotor that houses the permanent magnets has an extension greater than that of the section of the stator occupied by the windings that generate the magnetic field. Typically, the extension of the rotor is greater than that of the stator by a length at least equal to, or preferably greater than, the axial movement of said rotor with respect to the stator. 
     In this way the magnetic field of the motor is not influenced by the axial movement of said print roller, and consequently of the rotor, delivering the rated torque. 
     According to another aspect of the invention the sliding supports are connected to the respective shoulders of the device, each by means of a pair of sliding guides. In this way the structure is stiffer, thus ensuring greater positioning precision of the rollers. According to a preferred variant, each shoulder is provided with a pair of guides on which the supports of the Anilox roller, of the respective blade chamber, and of the print roller, slide. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the present invention will be more apparent from the description of a preferred but not exclusive example of embodiment of an apparatus for producing a multi-layer film, as illustrated in the accompanying figures, wherein: 
         FIGS. 1 a  and 1 b    are two perspective views of the printing device according to the present invention; 
         FIG. 2  is a view of the device according to the invention, sectioned along a vertical plane orthogonal to the axes of the rollers; 
         FIGS. 3 a  and 3 b    are two side views, respectively from opposite sides, of the device according to the present invention; 
         FIGS. 4 a  and 4 b    are two side views, respectively of opposite sides, of the device of  FIGS. 3 a  and 3 b    partially disassembled; 
         FIG. 5  is a view of the device according to the invention, sectioned along a vertical plane passing through the axis of rotation of the print roller; 
         FIG. 6  is a detail view of the print roller, sectioned along a vertical plane passing through its axis of rotation; 
         FIG. 7  is a schematic side view of a laminating machine equipped with the printing device according to the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the accompanying  FIGS. 1 a  and 1 b   , the number  1  indicates as a whole a printing device of the type adapted to be used preferably, but not exclusively, in association with a laminating machine  100  or the like, as illustrated in  FIG. 7 . 
     The device essentially comprises a support structure  10  with a pair of shoulders  10   a ,  10   b  supported by a trolley frame  11  equipped with wheels  12 . A blade  13 , an Anilox roller  14 , a print roller  30  and a counter-pressure roller  15  are mounted on the shoulders  10   a ,  10   b.    
     In the variant illustrated, the counter-pressure roller  15  is mounted to be able to rotate about its axis Xp directly on the shoulders  10   a ,  10   b . The counter-pressure roller is rotated by a motor, by means of a belt transmission, not illustrated in the figures. The position of the counter-pressure roller with respect to the shoulders  10   a ,  10   b  is therefore substantially fixed. 
     The Anilox roller  14  is instead supported at its ends, so that it can rotate about its axis Xa, by a pair of first supports  16   a ,  16   b . The blade chamber  13  is preferably also mounted on the first supports  16   a ,  16   b.    
     Said blade chamber  13  defines a compartment  17  that acts as tank for containing printing ink. The compartment  17  has at least one slot shaped opening  17   a , facing the Anilox roller  14 , which places the surface thereof in communication with the ink in the compartment  17 . 
     Said opening  17   a  is delimited transversely by at least one blade  18 , preferably by a pair of blades  18 . The Anilox roller  14  is arranged so as to rotate substantially in contact with said blades  18 , which have the function of distributing the ink uniformly in the micro cavities or cells made on its surface. The blade chamber  13  is preferably movingly mounted on the first supports  16   a ,  16   b  so that it can be moved away from or toward the Anilox roller  14 . 
     The Anilox roller  14  is rotated by a first motor  19 , preferably of brushless type, through a transmission comprising a belt  20 , a first pulley connected to the first motor  19 , not visible in the figures, and a second pulley  21  connected to the Anilox roller  14 . 
     The first supports  16   a ,  16   b , are mounted sliding on the shoulders  10   a ,  10   b  along a direction substantially horizontal and perpendicular to the axis Xa of the Anilox roller  14 . More in detail, said supports  16   a ,  16   b  are each provided with at least two, and preferably at least three, slides  22   a ,  22   b  sliding on respective guides  23   a ,  23   b  fixed to the shoulders  10   a ,  10   b.    
     The movement of the first supports  16   a ,  16   b  is controlled by a pair of motors  24 , each acting on one of the supports by means of a transmission. In the variant illustrated, said transmission comprises a first pulley  25  connected to the shaft of the motor  24 , a belt  26 , a second pulley  27  and a recirculating ball screw  28 , moved by the second pulley  27 , which engages a nut mounted on the support  16   a ,  16   b.    
     The print roller  30  is interposed between the Anilox roller  14  and the counter-pressure roller  15 . In a similar manner to the Anilox roller  14 , the print roller is also supported at the ends by a pair of second supports  31   a ,  31   b  mounted sliding on the shoulders  10   a ,  10   b . In the variant illustrated, each support is provided with at least two, and preferably at least three, slides  29   a ,  29   b  that slide on the same guides  23   b ,  23   b  as the first supports  16   a ,  16   b.    
     The print roller  30  comprises a cliché-holder cylinder  32  (hereinafter also simply “cylinder  32 ”), preferably hollow inside, with two end shafts  33 ,  40 . One of said shafts, defined here as second shaft  33 , is in one piece with the cliché-holder cylinder  32 . The other shaft, defined as first shaft  40 , can instead be coupled to the cylinder  32 . 
     This construction solution allows the first shaft to be shaped in the most convenient way and at the same time makes it possible to connect/fix certain components thereto, during assembly of the machinery, before it is coupled to the rest of the cylinder. 
     More in detail, the cylinder  32  comprises a coupling portion  32   a  with a seat  32   b  adapted to accommodate an end portion of  42  of the first shaft. Coupling between the parts typically takes place by means of a shrink disc or other systems by means of which said parts, shaft  40  and cylinder  32 , become one piece both in rotation and axially ( FIGS. 5 and 6 ). 
     The print roller  30 , and more precisely its shafts  33 ,  40 , are mounted on the respective supports  31   a ,  31   b  by means of flanges  34   a ,  34   b  that allow said print roller  30  both to rotate around its axis Xs and to translate along said axis for a travel of a few millimetres, typically from 10 mm to 20 mm. 
     To allow the axial movement of the shafts  33 ,  40 , said flanges are preferably equipped with rolling means, such as radial roller bearings. 
     This movement is managed by a position adjustment system comprising a motor  35  which, by means of a transmission  36 , operates a control member  37  movable along a direction parallel to the axis Xs of the print roller  30 . 
     According to a preferred variant, the transmission  36  comprises a pulley  36   b , connected to the motor  35  by means of a belt  36   a , which rotates a shaft  36   c  arranged with its axis parallel to the axis Xs. Said shaft  36   c  comprises a threaded portion  36   c ′ that engages a lead screw  36   d  in one piece with a slider  36   e  sliding along the axis of the shaft  36   c . Said threaded portion  36   c ′ of the shaft  36   c  and the lead screw  36   d  are preferably of recirculating ball type. 
     The slider  36   e  preferably has a hollow cylindrical shape and is slidingly coupled to a cylindrical support  36   f  fixed in one piece to one of the sliding supports  31   a ,  31   b  of the print roller  30 , in particular to the support  31   a  in the example in the figures. 
     The slider  36   e  is in turn connected to the control member  37 . 
     Said control member  37  is adapted to engage an insert  43  in one piece with, and which projects radially from, the first shaft  40  of the print roller  30 . In a preferred variant, said insert  43  is disc shaped, preferably substantially cylindrical. Said insert  43  can be in one piece with the first shaft  40  or made in it, as in the example illustrated. 
     The moving member  37  is preferably in the shape of a cradle, a jaw or the like that at least partly surrounds the insert  43 . For example, the moving member can comprise a body with a circular shaped sector in which a housing  37   a  to accommodate the insert  43  is made. Rotation of the motor  35  in one direction or the other causes the movement of the slider  36   e , which drives the control member  37  in a direction parallel to the axis Xs which, in turn, rests on the insert  43  to move the first shaft  40  and the rest of the print roller  30  along the axis Xs. 
     The moving member  37  is preferably provided with contact elements  37   b  in the form of a wheel, which remain substantially in contact with the outer surfaces of the insert  43 , allowing it to rotate freely. 
     The longitudinal movement of the print roller, or of the supports  31   a ,  31   b , is controlled by a pair of motors  38 , each acting on one of the supports by means of a transmission. Said transmission, similarly to the Anilox roller  14 , comprises a first pulley  38   a  connected to the shaft of the motor  38 , a belt  38   b , a second pulley  38   c  and a recirculating ball screw  39 , moved by the second pulley  38   c , which engages the nut, not shown in the figure, mounted on the supports  31   a ,  31   b.    
     According to a preferred variant, the first shaft  40  has an internal passage  45  passing through it completely from a first free end  41  to the opposite end  42 , i.e., the end connected to the cliché-holder cylinder  32 . 
     Said passage  45  allows the internal cavity  32   c  of the cliché-holder cylinder to communicate with a source of compressed air. Advantageously, said source of air can be connected by means of a connector  44  fixed to the end of the passage  45  that ends on the free end  42  of the first shaft. As mentioned above, the air introduced into the cavity  32   c  of the cliché-holder cylinder  32  flows out through holes that pass through the surface of the cylinder, not visible in the figures, to create an air cushion that facilitates sliding of the cliché-holder sleeve. 
     The print roller  30  is rotated by an electric motor, indicated as a whole with  50 . In accordance with a preferred embodiment of the invention, said motor  50  comprises a ring rotor  51  fitted directly onto the first shaft  41  and a ring stator  52 , in one piece with the sliding support  31   a  of the print roller  30 , arranged around the rotor  51 . The motor is preferably a permanent magnet motor, with the permanent magnets  51   b  held by the rotor  51 . Instead, the stator  52  holds the windings  52   a  of the motor. Typically, the motor  50  is a torque motor. In fact, this type of motor can be fitted directly onto the first shaft  40  without the need for transmission members or connection elements, with the aforementioned advantages in relation to precision of movement and absence of vibrations. In addition to this, positioning of the motor in an area at a distance from the end of the shaft, allows, as in the case of the invention, this end  41  to be uncovered and made accessible, for connection of the source of air as described above. 
     Moreover, this type of motor makes it possible to limit the overall axial dimensions and, consequently, the length of the first shaft  40  that extends laterally from the shoulders  10   a ,  10   b  of the device. 
     The stator  52  is fixed to the sliding support  31   a  by means of a flange  53 , which preferably also acts as a cover for the control member  37  that controls the axial translation movement of the first shaft  40 . 
     The rotor  51  is mechanically released from the stator  52  and from the support flange  53  so as to be able to move along its rotation axis, coincident with the axis Xs, driven by the first shaft  40 . 
       FIG. 7  illustrates a laminating machine  100  in which the printing device according to the invention is installed. Typically, the printing device is positioned in the area of the laminating machine that is usually occupied by the glue spreading unit (not illustrated) when the machine operates to laminate layers of film. In fact, when it is necessary to carry out reprinting on the film, laminated or to be laminated, this spreading unit can be temporarily removed and the printing device  1  positioned in its place. 
     In this way it is possible to make use of components already present on the laminating machine, such as winders and unwinders, guide rollers, tensioners, motors, sensors, etc. 
     The invention has been described purely for non-limiting illustrative purposes, according to some preferred embodiments. The person skilled in the art may find many other embodiments and variants, all falling within the scope of protection of the appended claims.