Printing method with improved ink transfer in a printing machine and printing machine implementing said printing method

Abstract

Printing method with improved ink transfer comprising the steps of: identifying, on a digital prepress information, at least one monochrome image as an opaque base coat, a transparent varnish coat, and / or a metallic image, configuring some of the printing units (10) of a printing machine as lithographic printing units with a rubber sleeve (40) on a first cylinder (11) and lithographic plates (41) on a second cylinder (12); and configuring at least one of the printing units (10) as a non-lithographic printing unit with improved ink transfer by including a relief plate (42) or a relief cylindrical sleeve (43) surrounding one of the first and second cylinders (11, 12) adapted to print one of the monochrome images identified as an opaque base coat and / or as a transparent varnish coat and / or as a metallic image, and by including the rubber sleeve (40) surrounding the other of the first and second cylinders (11, 12). A corresponding printing machine for printing according to the aforementioned method is also provided.

Description

Technical field

[0001] The present invention is directed towards a method for improving the ink transfer in a printing machine and towards the printing machine implementing this method.

[0002] The ink transfer is the amount of ink which can be applied by the printing machine to the printed substrate, which directly affects the opacity of the image printed, and its ability to cover previously printed images or the color of a colored substrate or its ability to make opaque a transparent substrate.Background of the Invention

[0003] A web printing machine is a known printing machine in which the substrate to be printed is a continuous web of laminar material continuously conveyed through the machine by guiding cylinders and in which several printing units successively print images. Ink drying units can be also included between the printing units or downstream the succession of printing units.

[0004] In one particular type of printing machines, the printing units are all distributed along a conveyance path conveying a web of laminar material, the printing units printing said portion of the web of laminar material. This is particularly relevant when the web of laminar material is made of a stretchable material such plastic.

[0005] The offset printing is a known printing technique according to which the image to be printed is defined in a lithographic plate, where the image to be printed is defined by hydrophobic regions of the surface of the lithographic plate, and where the regions of the lithographic plate devoid of image to be printed are hydrophilic, so that when water is provided to the lithographic plate, said water is retained on the hydrophilic regions, preventing the adhesion thereto of a non-polar ink, for example oil-based ink, or ultraviolet or electron-beam curable ink. Therefore, when non-polar ink is feed to the lithographic plate, said a non-polar ink is repelled by the water, which is a polar liquid, and is only adhered to the hydrophobic regions of the lithographic plate devoid of water.

[0006] The ink on the hydrophobic regions is then transferred to a blanket cylinder surrounded by rubber sleeve, o rubber-like sleeve, which transfers the ink to the web of laminar material to be printed.

[0007] Offset printing is very ink efficient, because the ink can be efficiently distributed to obtain the desired image to be printed, but said ink produce a limited transfer and a reduced opacity of the printed image.

[0008] If an improved ink transfer is required, to produce more opaque images, the amount of water feed to the lithographic plate shall be increased to increase also the amount of ink feed to the lithographic plate, but it tends to produce emulsion, and increases the water transferred to the web of laminar material, which can affect the ink transfer of subsequent printing units. Also, the maximum amount of water and of ink which can be retained on the surface of the lithographic plate is limited, so improvement above certain threshold is not possible.

[0009] Also, the lithographic plates are aluminum plates which, when are attached surrounding one support cylinder of the printing unit, produce a gap, preventing the impression of a continuous gap-less image.

[0010] Another problem of the lithographic plates is the toning, caused by small impurities on the regions of the lithographic plate where no printing is intended, said impurities transferring an ink dot on said regions.

[0011] The present invention solves those and other problems of the offset printing machines, improving the ink transfer.Description of the Invention

[0012] The present invention concerns to a printing method with improved ink transfer in a printing machine, as described in claim 1.

[0013] The printing machine in which the invention is implemented is a printing machine comprising several printing units successively arranged along a conveyance path conveying a web of laminar material to be printed, each printing unit comprising a first cylinder in contact with the conveyance path, a second cylinder in contact with the first cylinder, inking cylinders arranged to transfer a selected quantity of ink from an ink supply to the second cylinder, and watering cylinders arranged to transfer a selected quantity of water from a water supply to the second cylinder.

[0014] The inking cylinders comprise several successive cylinders parallel and adjacent to each other forming a train of cylinders, one initial inking cylinder collecting ink from an ink supply, intermediate cylinders transferring said ink and one final inking cylinder delivering a controlled amount of ink, with a controlled thickness over the surface of the final inking cylinder, to the second cylinder of the printing unit. Relative position between the inking cylinders can be precisely controlled to adjust the ink transferred from the initial inking cylinder to the final inking cylinder.

[0015] The watering cylinders have similar configuration than the inking cylinders but transferring water from a water source to the second cylinder, also controlling the thickness and distribution of the water.

[0016] Optionally, the final inking cylinder and the final watering cylinder can be the same cylinder, shared between the inking cylinders and the watering cylinders, collecting, and transferring both water and ink to the second cylinder.

[0017] Optionally the inking cylinders include multiple inking cylinders in contact with the second cylinder.

[0018] The first cylinder, second cylinder and all the inking cylinders and watering cylinders are parallel to each other. Each printing unit further include adjustment devices to regulate radial position of the cylinders and the pression on the contact point therebetween, and also the lateral position at least of the first and / or second cylinders.

[0019] In a preferred embodiment, the conveyance path is defined around a central drum, all the printing units being arranged around said central drum, with the corresponding first cylinders being adapted to contact with the web of laminar material supported on said central drum.

[0020] The proposed method comprises, in a manner already known, defining, in a digital prepress information, several monochrome images to be printed overlapped in a selected order defining a polychrome image to be printed, and configuring some of the printing units as lithographic printing units by including a lithographic plate surrounding the second cylinder and adapted to print one of the monochrome images, and by including a rubber sleeve, or a rubber-like sleeve, surrounding the first cylinder as a blanket cylinder to transfer said monochrome image to be printed to the web of laminar material.

[0021] The rubber or rubber-like sleeve can be a continuous gap-less cylinder or a plate curved as a cylinder defining a gap.

[0022] In a lithographic plate the image to be printed is defined by hydrophobic regions of the surface of the lithographic plate, and the regions of the lithographic plate devoid of image to be printed are hydrophilic, so that when water is provided to the lithographic plate, said water is retained on the hydrophilic regions, preventing the adhesion of a non-polar ink thereto. Therefore, when a non-polar ink is feed to the lithographic plate, said ink is repelled by the water, which is a polar liquid, and is only adhered to the hydrophobic regions of the lithographic plate devoid of water.

[0023] Said lithographic plate is a planographic plate (devoid of relief), which is curved surrounding the second cylinder and attached thereto, typically by a mechanical attachment.

[0024] Preferably, the lithographic plate is attached around a support sleeve, which diameters determines the length of the image to be printed. As described above, such support sleeve can be easily inserted and attached to, or detached and extracted from, the second cylinder allowing for an easy and fast change in the image to be printed and in the format of the image to be printed.

[0025] Also, the rubber sleeve, or the rubber-like sleeve, may have a variable diameter, preferably coincident with the diameter of the lithographic plate. The rubber sleeve or the rubber-like sleeve is also easily insertable and extractable from the first cylinder and can also be attached around a support sleeve interposed between the rubber or rubber-like sleeve and the first cylinder, which can be easily inserted and attached to, or detached and extracted from, the first cylinder.

[0026] The watering cylinders provide water to the lithographic plate surrounding the second cylinder, and the inking cylinders provide ink to the lithographic plate also feed with water, said ink being adhered only on the hydrophobic regions of the lithographic plate devoid of water constitutive of the image to be printed.

[0027] The present invention further proposes, in a manner not known in the available state of the art, the following steps of the method: identifying, on the digital prepress information, at least one of said monochrome images as one selected among: an opaque base coat to be overprinted with at least most of the other monochrome images, a transparent varnish coat, and / or a metallic image to be printed with ink with metallic flakes; configuring at least one of the printing units as a non-lithographic printing unit with improved ink transfer by including a relief plate, or relief cylindrical sleeve surrounding one of the first and second cylinders adapted to print one of the monochrome images identified as an opaque base coat and / or as a transparent varnish coat and / or as a metallic image, and by including the rubber sleeve, or the rubber-like sleeve, surrounding the other of the first and second cylinders; the lithographic printing units and the non-lithographic printing units being arranged along the conveyance path, or around the central drum when exists, in the selected order defined in the digital prepress information; and deactivate the transfer of water from the watering cylinders to the second cylinders of the non-lithographic printing units.

[0028] A relief plate is a plate where the image to be printed is defined by raised or embossed regions thereof, the depressed regions, located between the raised regions, defining the regions devoid of image to be printed. The relief plate is made of elastic material so that the raised or embossed regions are squeezeable when pressed against another cylinder, ensuring a complete contact of the raised or embossed regions and a proper transfer of ink, improving the collection of ink and the delivery of ink, therefore improving the ink transfer on the printed image.

[0029] Also, because no ink can reach the depressed regions, the amount of ink can be increased without increasing the amount of water, which can be no water at all, for example by completely detaching the final watering cylinder from the second cylinder by increasing their distance. This also improve the resulting ink transfer on the printed image.

[0030] Said relief plate is curved and attached to the first or second cylinder, typically by adhesives. Optionally the relief plate is adhered to a sleeve, the first or second cylinder being inserted in said sleeve interposed between the relief plate and the cylinder.

[0031] A relief cylindrical sleeve has the same features than the relief plate but on the external surface of a cylindrical sleeve. The first or second cylinder, or an interposed sleeve, will be inserted in the relief cylindrical sleeve, which internal diameter will match with the external diameter of the element inserted therein.

[0032] The use of a relief cylindrical sleeve allows printing a continuous gap-less image when the rubber, or rubber-like sleeve, is a continuous gap-less cylinder.

[0033] According to the above, in a first embodiment the relief plate or the relief cylindrical sleeve surrounds the second cylinder and the rubber sleeve, or a rubber-like sleeve, surrounds the first cylinder as a blanket cylinder for transferring the image to be printed from the relief plate or the relief cylindrical sleeve to the web of laminar material. This configuration is exactly the same configuration of one of the lithographic printing units but substituting the lithographic plate devoid of relief by a relief plate or by a relief cylindrical sleeve.

[0034] In this manner a lithographic printing unit of an existing offset printing machine can be easily and inexpensively adapted to become a non-lithographic printing unit to increase the ink transfer obtained from said particular non-lithographic printing unit, or from several printing units, while the rest of the printing units remain with the original configuration as lithographic printing units.

[0035] According to a second embodiment of the present invention, the relief plate or the relief cylindrical sleeve surrounds the first cylinder and the rubber sleeve, or the rubber-like sleeve, surrounds the second cylinder to transfer ink from the inking cylinders to the relief plate or relief cylindrical sleeve. In this case, the cylinder surrounded by rubber sleeve, or rubber-like sleeve, does not transfer the ink, distributed according to the image to be printed, to the web of laminar material where it is printed, but transfer all the ink provided by the inking cylinders to the cylinder carrying the plate, which in this case is the first cylinder, which only collects therefrom the required ink on the raised or embossed surfaces.

[0036] In this case, to adapt one of the lithographic printing units to become one non-lithographic printing unit according to this second embodiment, the order of the cylinders carrying the rubber sleeve and carrying the plate has to be inverted. This can be easily and inexpensively made since in the regular offset printing machines those cylinders are easily extractable and replaceable to adapt the printing machine to different printing jobs and / or to different sizes of the image to be printed.

[0037] The watering cylinders of each non-lithographic printing unit are configured to transfer no water to the second cylinder.

[0038] Optionally, in the digital prepress information, each monochrome image is associated with color information, and each lithographic printing unit is feed with ink of a color corresponding with the color information of the monochrome image printed with said lithographic printing unit. Each non-lithographic printing unit will be also feed with opaque ink, transparent varnish or ink with metallic flakes corresponding with the color information of the monochrome image printed with said non-lithographic printing unit.

[0039] Diameters of first and second cylinders can be modified, typically by inserting a sleeve therearound, to adapt the printing unit to the size of the image to be printed. An adjusting device modifies the distance between the center of the cylinders of the printing unit, and between the center of the first cylinder and the web of laminar material, to adapt the printing unit to the modified diameter.

[0040] Each of the first and second cylinders can be supported in cantilever, allowing for an axial insertion and extraction of a sleeve through the end thereof in cantilever, allowing for a fast and easy sleeve exchange.

[0041] The axial insertion and extraction are produced in an axial direction concentric with the center of the respective first or second cylinder.

[0042] Preferably, the relief plate or the relief sleeve is attached around a support sleeve, which diameters determines the length of the image to be printed. As described above, such support sleeve can be easily inserted and attached to, or detached and extracted from, the first or second cylinder allowing for an easy and fast change in the image to be printed and in the format of the image to be printed.

[0043] Also, the rubber sleeve, or the rubber-like sleeve, may have a variable diameter, preferably coincident with the diameter of the relief plate or sleeve. The rubber sleeve or the rubber-like sleeve is also easily insertable and extractable from the first or second cylinder and can also be attached around a support sleeve interposed between the rubber or rubber-like sleeve and the first or second cylinder, which can be easily inserted and attached to, or detached and extracted from, the first or second cylinder.

[0044] According to a second aspect, the present invention is also directed towards a printing machine for printing with improved ink transfer, according to the method described in this application, as described in claim 13.

[0045] The proposed printing machine comprises: several printing units successively arranged along a conveyance path conveying a web of laminar material to be printed, each printing unit comprising a first cylinder in contact with the conveyance path, a second cylinder in contact with the first cylinder, inking cylinders arranged to transfer a selected quantity of ink from an ink supply to the second cylinder, and watering cylinders arranged to transfer a selected quantity of water from a water supply to the second cylinder; a control unit containing the digital prepress information; some of the printing units being lithographic printing units including a lithographic plate surrounding the second cylinder and adapted to print one of the monochrome images, and including a rubber sleeve, or a rubber-like sleeve, surrounding the first cylinder as a blanket cylinder to transfer said monochrome image to be printed to the web of laminar material; at least one of the printing units is a non-lithographic printing unit with improved ink transfer including a relief plate, or relief cylindrical sleeve surrounding one of the first and second cylinders adapted to print one of the monochrome images identified as an opaque base coat and / or as a transparent varnish coat and / or as a metallic image, and including the rubber sleeve, or the rubber-like sleeve, surrounding the other of the first and second cylinders; the lithographic printing units and the non-lithographic printing units being arranged along the conveyance path in the selected order defined in the digital prepress information.

[0046] The proposed method can further comprise replacing one lithographic sleeve, from one second cylinder, by one relief plate or relief sleeve, transforming one lithographic printing unit into one non-lithographic printing unit.

[0047] Alternatively, the method can further comprise replacing one rubber or rubber-like sleeve from one first cylinder by one relief plate or relief sleeve, and replacing one lithographic sleeve, from one second cylinder, by one rubber or rubber-like sleeve or by the rubber or rubber-like sleeve extracted from the first cylinder, transforming one lithographic printing unit into one non-lithographic printing unit.

[0048] The lithographic plate can be extracted from the second cylinder together with a support sleeve around which the lithographic plate is attached. Also, the relief plate or the relief sleeve is inserted to the first or second cylinder together with a support sleeve around which the relief plate or the relief sleeve is attached. The rubber or rubber-like sleeve can also be extracted from, and / or inserted to, the first or second cylinder together with a support sleeve around which the rubber or rubber-like sleeve is attached.

[0049] Said support sleeve provides a support to avoid deformations during the manipulation of the different elements, and also allows for adapting the outer diameter to the length of the image to be printed.

[0050] The replacement is preferably produced by releasing one distal end of the first and / or second cylinder, maintaining said first and / or second cylinder supported in cantilever from one proximal end, extracting the elements to be replaced through the distal end of the first and / or second cylinder in an axial direction, inserting the elements to be replaced through the distal end of the first and / or second cylinder, providing support to the distal end of the first and / or second cylinders.

[0051] Preferably, before the replacing, the distance between the first and second cylinders with other components of the printing machine is increased by the adjusting device to avoid any contact between the elements to be replaced and other components or cylinders different to the first or second cylinder on which the element to be replaced is supported.

[0052] After the replacement, the adjusting device will adjust the distance between the first and second cylinders and other components of the machine to adapt the machine to the diameter of the replaced elements, to ensure a proper impression.Brief description of the Figures

[0053] The foregoing and other advantages and features will be more fully understood from the following detailed description of an embodiment with reference to the accompanying drawings, to be taken in an illustrative and non-limitative manner, in which: Fig. 1 shows a schematic diagram of an offset printing machine, where the inking cylinders and the watering cylinders have been shown in a simplified manner; Fig. 2 shows a perspective view of one printing unit devoid of the inking cylinders and watering cylinders; Fig. 3 shows a zoomed view of one printing unit of Fig. 1 configured as one lithographic printing unit, with a lithographic plate surrounding the second cylinder and with a rubber sleeve surrounding the first cylinder; Fig. 4 shows a zoomed view of one printing unit of Fig. 1 configured as one non-lithographic printing unit, with a relief plate or a relief cylindrical sleeve surrounding the second cylinder and with a rubber sleeve surrounding the first cylinder; Fig. 5 shows a zoomed view of one printing unit of Fig. 1 configured as one non-lithographic printing unit, with rubber sleeve surrounding the second cylinder and with a relief plate or a relief cylindrical sleeve surrounding the first cylinder. Detailed Description of the Invention and of particular embodiments

[0054] According to one embodiment of the present invention, shown in Fig. 1, the offset printing machine comprises several conveyance cylinders, including one central drum 1 surrounded by six printing units 10. Any other number of printing units are also possible, such four, eight or ten for example. The central drum define, on its perimeter, the conveyance path.

[0055] A continuous web of laminar material is feed to the outer perimeter of the central drum 1 through an entrance nip and is extracted through an exit nip. The continuous web of laminar material is guided and conveyed in a conveyance direction by conveyance cylinders.

[0056] Each printing unit 10 comprises one first cylinder 11 in contact with the web of laminar material supported on the central drum 1, and one second cylinder 12 in contact with the first cylinder 11. Each printing unit 10 further comprises several inking cylinders 20 arranged to transfer a selected quantity of ink from an ink supply to the second cylinder 12, and several watering cylinders 30 arranged to transfer a selected quantity of water from a water supply to the second cylinder 12.

[0057] In this example, the ink supply comprises an ink tray constantly feed with ink to maintain certain level. An initial inking cylinder of the inking cylinders is partially submerged in said ink of the ink tray collecting ink on its surface. Typically, a blade applied against the surface of the initial inking cylinder removes excess ink leaving only the desired amount of ink.

[0058] Then the ink is transferred from the initial inking cylinder to the subsequent cylinders of the train of inking cylinders until reaches the final inking cylinder of the train of inking cylinders, which is in contact with the second cylinder 12. One or more of the inking cylinders can have variable position to modify the amount of ink to be transferred. This can be done also to adapt different superficial speeds in the roller train.

[0059] In the figures the inking cylinders are three cylinders, but it is only a schematic view and the inking cylinders can be any number of cylinders.

[0060] The water supply can be also a water tray constantly feed with water to maintain certain level, but alternatively the desired amount of water is sprayed onto an initial watering cylinder of the train of watering cylinders through nozzles.

[0061] Then the water is transferred from the initial watering cylinder to the subsequent cylinders of the train of watering cylinders until reaches the final watering cylinder of the train of watering cylinders, which is in contact with the second cylinder 12.

[0062] The proposed printing method with improved ink transfer comprises defining, in a digital prepress information typically stored in a control device of the printing machine, several monochrome images to be printed overlapped in a selected order defining a polychrome image to be printed.

[0063] Each monochrome image is intended to be printed with a single color. When all the monochrome images are printed overlapped in the selected order, a polychrome image is obtained.

[0064] Some of the printing units 10 of the printing machine are configured as lithographic printing units including a lithographic plate 41 surrounding the second cylinder 12, and a rubber sleeve 40, or a rubber-like sleeve, surrounding the first cylinder 11. This arrangement can be seen of Fig. 3.

[0065] The final watering cylinder transfer a controlled amount of water to the surface of the lithographic plate 41, which collects the water only on the hydrophilic regions thereof. Then the final inking cylinder transfers ink to the lithographic plate 41, which collects ink only on the hydrophobic regions devoid of water of its surface, corresponding with the image to be printed by said printing unit 10.

[0066] Then the lithographic plate 41 transfers the ink from the hydrophobic surfaces to the rubber sleeve 40 surrounding the first cylinder 11, which transfers the ink defining the images to be printed to the web of laminar material supported on the central drum 1 completing the printing.

[0067] The method further proposes identifying, on the digital prepress information, at least one of said monochrome images as one selected among: an opaque base coat to be overprinted with at least most of the other monochrome images, a transparent varnish coat, and / or a metallic image to be printed with ink with metallic flakes.

[0068] The opaque base coat is an image to be printed with opaque ink, or with ink opaquer than the inks used in the other printing units, offering an opaque base covering the color or the transparency of the web of laminar material. At least most of the other monochrome images will be printed overlapped to said opaque base coat, so that those other monochrome images can be printed with a less opaque ink.

[0069] Commonly, the opaque base coat is the first monochrome image to be printed.

[0070] Typically, the opaque base coat is the monochrome image with a larger colored surface area of the polychrome image to be printed and is commonly, but not exclusively, printed in color white or black. Also, the opaque base coat is typically devoid of small details, for example details smaller than 2mm, such small letters or detailed figurative motives.

[0071] The transparent varnish coat is an image of the printed with transparent varnish, offering protection to at least some regions of the printed image. Typically, the transparent varnish coat covers all the printed surface of the polychrome image, and therefore commonly is the last, or one of the last, monochrome images to be printed.

[0072] As states above, the metallic image is an image to be printed with ink with metallic flakes, offering a metallic appearance, such a gold, silver or copper appearance.

[0073] In order to print such monochrome images identified as opaque base coat, as a transparent varnish and / or as a metallic image, at least one of the printing units 10 are configured as a non-lithographic printing unit with improved ink transfer. This is achieved by including a relief plate 42, or relief cylindrical sleeve 43 surrounding one of the first and second cylinders 11, 12 adapted to print one of the monochrome images identified as an opaque base coat and / or as a transparent varnish coat and / or as a metallic image, and by including the rubber sleeve 40, or the rubber-like sleeve, surrounding the other of the first and second cylinders 11, 12.

[0074] The printing using non-lithographic printing units allow for an improved ink transfer, allowing printing of thicker layers of ink, achieving a better coverage, higher opacity, reduced toning, and also better application of special inks such the inks with metallic flakes.

[0075] The lithographic printing units and the non-lithographic printing units are arranged along the conveyance path, or around the central drum when exists, in the selected order defined in the digital prepress information, in order to obtain the intended polychrome image.

[0076] The method further comprises deactivate the transfer of water from the watering cylinders 30 to the second cylinders of the non-lithographic printing units, because the printing with non-lithographic printing unit does not require the application of water.

[0077] Preferably, the deactivation of the transfer of water is achieved by creating a separation between the watering cylinders 30 and the second cylinder of the non-lithographic printing units.

[0078] Each printing unit 10 is intended to print with one ink of one color, therefore all the printing units shall be coordinated to print the corresponding images at a register.

[0079] The relief plate 42 and the relief cylindrical sleeve 43 are made of flexible material and include raised and / or embossed regions on its surface defining the image to be printed.

[0080] The final inking cylinder transfers ink to the relief plate 42 or to the relief cylindrical sleeve 43, which collects ink only on the raised or embossed regions, corresponding with the image to be printed.

[0081] Then the relief plate 42 or the relief cylindrical sleeve 43 transfers the ink from the raised or embossed surfaces to the rubber sleeve 40 surrounding the first cylinder 11, which transfers the ink defining the images to be printed to the web of laminar material conveyed along the conveyance path, for example supported on the central drum 1, completing the printing.

[0082] By substituting the lithographic plate 41 by a relief plate 42 or by a relief cylindrical sleeve 43, the amount of ink transferred can be increased without requiring supply of water at all. Also, the viscosity or density of the ink can be adjusted beyond the parameters acceptable for the printing using the lithographic plate, printing with more viscose or dense ink than the ink usable with the lithographic printing units, resulting in an improvement on the resulting ink transfer when overlapped to other printed images and when printed on a transparent or colored substrate.

[0083] Optionally, in the digital prepress information, each monochrome image can be associated with color information, and each lithographic printing unit can be feed with ink of a color corresponding with the color information of the monochrome image to be printed with said lithographic printing unit. Equally, each non-lithographic printing unit can be feed with opaque ink, transparent varnish or ink with metallic flakes corresponding with the color information of the monochrome image to be printed with said non-lithographic printing unit.

[0084] The opaque base coat can be at least partially cured or pinned before the printing of additional monochrome images on top thereof, for example using UV light, infrared light, hot air, heat or a combination thereof.

[0085] According to an embodiment, each cylinder of the inking cylinders 20 contacting with the second cylinder 12 can be adjusted by moving each end thereof independently with micrometric precision to adjust the distance and pressure between the adjusted cylinder of the inking cylinders 20 and the second cylinder in contact therewith to achieve an optimal printing.

[0086] Similarly, each cylinder of the watering cylinders 30 contacting with the second cylinder 12 can be also adjusted by moving each end thereof independently with micrometric precision to adjust the distance and pressure between the adjusted cylinder of the watering cylinders 30 and the second cylinder in contact therewith to achieve an optimal printing.

[0087] It is also proposed that each first and second cylinder can be adjusted by moving each end thereof independently with micrometric precision to adjust the distance and pressure between first and second cylinders and between second cylinder and conveyance path to achieve an optimal printing.

[0088] Such adjustments will be made considering the polychrome printed image obtained, the adjustments being made manually, after a manual inspection of the printed image, or automatically after obtaining images of the printed image through a camera, processing said images by the control device to automatically detect printing errors such unevenness of the colors or insufficient coverage and calculate required adjustments to solve the detected errors, typically using a stored information of previous printing jobs.

[0089] Optionally, the adjusted position of the first and second cylinder of the printing units to achieve an optimal printing are stored in the digital prepress information. When the printing machine is not printing, the first and second cylinders can be moved to a spaced position in which are separated to each other and from the conveyance path to avoid deformations, and when a printing job has to be performed those cylinders are moved to the adjusted position stored in the digital prepress information.

[0090] According to an embodiment, the configuration of the non-lithographic printing unit comprises substituting the lithographic plate 41 of at least one lithographic printing unit by the relief plate 42 or the relief cylindrical sleeve 43, transforming the lithographic printing unit into a non-lithographic printing unit.

[0091] Alternatively, the configuration of the non-lithographic printing unit may comprise substituting the rubber sleeve 40, or the rubber-like sleeve of the first cylinder of the at least one lithographic printing unit by the relief plate 42 or the relief cylindrical sleeve 43 of the at least one non-lithographic printing unit and substituting the lithographic plate 41 of the second cylinder of said at least one lithographic printing unit by the rubber sleeve 40, or the rubber-like sleeve, transforming the lithographic printing unit into a non-lithographic printing unit.

[0092] According to this arrangement, the final inking cylinder transfers ink to the rubber sleeve 40. Then, the rubber sleeve 40 transfers the ink to the raised or embossed surfaces of the relief plate 42 or of the relief cylindrical sleeve 43, corresponding with the image to be printed, which later transfers the ink to the web of laminar material supported on the conveyance path completing the printing.

[0093] The method can further comprise modifying the diameter of the first and second cylinders of all the printing units to a diameter adapted to support the lithographic plates 41 and the relief plates 42 or the relief cylindrical sleeves 43 with a perimeter coincident with the longitude of the corresponding monochrome images to be printed, and adjusting the distance between the centers of the first cylinder, of the second cylinder, of the cylinders of the inking cylinders in contact with the second cylinder, and of the cylinders of the watering cylinders in contact with the second cylinder of all the printing units, and also between the center of the second cylinder and the conveyance path, to ensure the adequate contact and pressure between the contacting cylinders.

[0094] Optionally, the modification of the diameter can be achieved by adding or substituting a first cylindrical sleeve integrated in each first cylinder and a second cylindrical sleeve integrated in each second cylinder.

[0095] According to this embodiment, each first and second cylinder may comprise a central shaft surrounded by a first or a second sleeve. Substituting the sleeve, the diameter of the first and second cylinders can be adapted to the different longitude of the monochrome images to be printed in different printing jobs.

Claims

1. Printing method with improved ink transfer in a printing machine comprising several printing units (10) successively arranged along a conveyance path of a web of laminar material to be printed, each printing unit (10) comprising a first cylinder (11) in contact with the conveyance path of the web of laminar material, a second cylinder (12) in contact with the first cylinder (11), inking cylinders (20) arranged to transfer a selected quantity of ink from an ink supply to the second cylinder (12), and watering cylinders (30) arranged to transfer a selected quantity of water from a water supply to the second cylinder (12); the method comprising: defining, in a digital prepress information, several monochrome images to be printed overlapped in a selected order defining a polychrome image to be printed; configuring some of the printing units (10) as lithographic printing units by including a lithographic plate (41) surrounding the second cylinder and adapted to print one of the monochrome images, and by including a rubber sleeve (40), or a rubber-like sleeve, surrounding the first cylinder (11) as a blanket cylinder to transfer said monochrome image to be printed to the web of laminar material; characterized in that the method further comprises: identifying, on the digital prepress information, at least one of said monochrome images as one selected among: an opaque base coat to be overprinted with at least most of the other monochrome images, a transparent varnish coat, and / or a metallic image to be printed with ink with metallic flakes; configuring at least one of the printing units (10) as a non-lithographic printing unit with improved ink transfer by including a relief plate (42), or relief cylindrical sleeve (43) surrounding one of the first and second cylinders (11, 12) adapted to print one of the monochrome images identified as an opaque base coat and / or as a transparent varnish coat and / or as a metallic image, and by including the rubber sleeve (40), or the rubber-like sleeve, surrounding the other of the first and second cylinders (11, 12); the lithographic printing units and the non-lithographic printing units being arranged along the conveyance path in the selected order defined in the digital prepress information; and deactivate the transfer of water from the watering cylinders (30) to the second cylinders of the non-lithographic printing units.

2. The method according to claim 1 wherein, in the digital prepress information, each monochrome image is associated with color information, and wherein each lithographic printing unit is feed with ink of a color corresponding with the color information of the monochrome image printed with said lithographic printing unit, and each non-lithographic printing unit is feed with opaque ink, transparent varnish or ink with metallic flakes corresponding with the color information of the monochrome image printed with said non-lithographic printing unit.

3. The method according to claim 1 or 2 wherein the base coat is at least partially cured or pinned before the printing of additional monochrome images on top thereof.

4. The method according to claim 1, 2 or 3 wherein the conveyance path is defined around a central drum.

5. The method according to any preceding claim wherein each cylinder of the inking cylinders (20) contacting with the second cylinder (12) is adjusted by moving each end thereof independently with micrometric precision to adjust the distance and pressure between the adjusted cylinder of the inking cylinders (20) and the second cylinder in contact therewith to achieve an optimal printing.

6. The method according to any preceding claim wherein each cylinder of the watering cylinders (30) contacting with the second cylinder (12) is adjusted by moving each end thereof independently with micrometric precision to adjust the distance and pressure between the adjusted cylinder of the watering cylinders (30) and the second cylinder in contact therewith to achieve an optimal printing.

7. The method according to any preceding claim wherein each first and second cylinder is adjusted by moving each end thereof independently with micrometric precision to adjust the distance and pressure between first and second cylinders and between second cylinder and the conveyance path to achieve an optimal printing.

8. The method according to claim 7 wherein the adjusted position of the first and second cylinder of the printing units are stored in the digital prepress information, when the printing machine is not printing, the first and second cylinders are moved to a spaced position in which are separated to each other and from the conveyance path, and when a printing job has to be performed are moved to the adjusted position stored in the digital prepress information.

9. The method according to any preceding claim wherein the configuration of the non-lithographic printing unit comprises substituting the lithographic plate (41) of at least one lithographic printing unit by the relief plate (42) or the relief cylindrical sleeve (43), transforming the lithographic printing unit into a non-lithographic printing unit.

10. The method according to any preceding claim wherein the configuration of the non-lithographic printing unit comprises substituting the rubber sleeve (40), or the rubber-like sleeve of the first cylinder of the at least one lithographic printing unit by the relief plate (42) or the relief cylindrical sleeve (43) of the at least one non-lithographic printing unit and substituting the lithographic plate (41) of the second cylinder of said at least one lithographic printing unit by the rubber sleeve (40), or the rubber-like sleeve, transforming the lithographic printing unit into a non-lithographic printing unit.

11. The method according to any preceding claim wherein the method further comprises modifying the diameter of the first and second cylinders of all the printing units to a diameter adapted to support the lithographic plates (41) and the relief plates (42) or the relief cylindrical sleeves (43) with a perimeter coincident with the longitude of the corresponding monochrome images to be printed, and adjusting the distance between the centers of the first cylinder, of the second cylinder, of the cylinders of the inking cylinders in contact with the second cylinder, and of the cylinders of the watering cylinders in contact with the second cylinder of all the printing units and between the center of the first cylinder and the conveyance path to ensure the adequate contact and pressure between the contacting cylinders.

12. The method according to claim 11 wherein the modification of the diameter is achieved by adding or substituting a first cylindrical sleeve integrated in each first cylinder and a second cylindrical sleeve integrated in each second cylinder.

13. The method according to any preceding claim wherein the deactivation of the transfer of water is achieved by creating a separation between the watering cylinders (30) and the second cylinder of the non-lithographic printing units.

14. A printing machine for printing with improved ink transfer, according to the method described in any of the preceding claims, the printing machine comprising: several printing units (10) successively arranged along a conveyance path conveying a web of laminar material to be printed, each printing unit (10) comprising a first cylinder (11) in contact with the conveyance path, a second cylinder (12) in contact with the first cylinder (11), inking cylinders (20) arranged to transfer a selected quantity of ink from an ink supply to the second cylinder (12), and watering cylinders (30) arranged to transfer a selected quantity of water from a water supply to the second cylinder (12); a control unit containing the digital prepress information; some of the printing units (10) being lithographic printing units including a lithographic plate (41) surrounding the second cylinder and adapted to print one of the monochrome images, and including a rubber sleeve (40), or a rubber-like sleeve, surrounding the first cylinder (11) as a blanket cylinder to transfer said monochrome image to be printed to the web of laminar material; at least one of the printing units (10) is a non-lithographic printing unit with improved ink transfer including a relief plate (42), or relief cylindrical sleeve (43) surrounding one of the first and second cylinders (11, 12) adapted to print one of the monochrome images identified as an opaque base coat and / or as a transparent varnish coat and / or as a metallic image, and including the rubber sleeve (40), or the rubber-like sleeve, surrounding the other of the first and second cylinders (11, 12); the lithographic printing units and the non-lithographic printing units being arranged along the conveyance path in the selected order defined in the digital prepress information.

15. The printing machine according to claim 14 wherein the conveyance path is defined around a central drum.

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