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) as lithographic printing units with a lithographic plates (41) on a second cylinder (12) and with an elastomeric sleeve (40) on a first cylinder (11); 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 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 elastomeric sleeve (40) surrounding the other of the first and second cylinders (11, 12).

Description

[0001] PRINTING METHOD WITH IMPROVED INK TRANSFER IN A PRINTING MACHINE AND PRINTING MACHINE IMPLEMENTING SAID PRINTING METHOD

[0002] Technical field

[0003] The present invention is directed towards a method for improving the ink transfer in a printing machine and towards the printing machine which allows the implementation of this method.

[0004] 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.

[0005] Background of the Invention

[0006] 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.

[0007] 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.

[0008] 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 nonpolar 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.

[0009] The ink on the hydrophobic regions is then transferred to a blanket cylinder surrounded by elastomeric sleeve, which transfers the ink to the web of laminar material to be printed.

[0010] 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. 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.

[0011] 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.

[0012] 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.

[0013] Documents US20040079246A1 and US20060107852A1 both describe a printing machine including several printing units in succession, where at least one of the printing units can be configured to be either a flexographic printing unit or a non-flexographic printing unit. In both documents the printing unit includes one separated ink supply and ink cylinders for feeding the printing unit with flexographic ink, and one separated ink supply and ink cylinders for feeding the printing unit with non-flexographic ink. This makes the solution more complicated and expensive, and too bulky to fit in printing units arranged around a central drum.

[0014] The present invention solves those and other problems of the offset printing machines, improving the ink transfer.

[0015] Description of the Invention

[0016] The present invention concerns to a printing method with improved ink transfer in a printing machine, as described in claim 1.

[0017] The printing machine in which the invention is implemented is a printing machine comprising several printing units successively arranged around a central drum, along a conveyance path conveying a web of laminar material to be printed.

[0018] Each printing unit comprises 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. According to the above, all the printing units are arranged around said central drum, with the corresponding first cylinders being in contact with the web of laminar material supported on said central drum.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] Optionally the inking cylinders include multiple inking cylinders in contact with the second cylinder.

[0023] 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.

[0024] In any case, all the printing units have the same ink supply, the same inking cylinders, the same water supply and the same watering cylinders (30).

[0025] The proposed method comprises, in a manner already known, defining before executing a printing job, in a digital prepress information, several monochrome images to be printed overlapped in a selected order defining a polychrome image to be printed during the printing job.

[0026] Some of the printing units are configured, before executing the printing job, as lithographic printing units by including a lithographic plate surrounding the second cylinder and adapted to print one of the monochrome images, by including a elastomeric sleeve surrounding the first cylinder as a blanket cylinder to transfer said monochrome image to be printed to the web of laminar material, and by feeding the ink supply and the inking cylinders of each lithographic printing unit with lithographic ink.

[0027] It will be understood that the lithographic ink is an ink specially adapted to the lithographic printing process.

[0028] The elastomeric sleeve can be a continuous gap-less cylinder or a plate curved as a cylinder defining a gap.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] Also, the elastomeric sleeve may have a variable diameter, preferably coincident with the diameter of the lithographic plate. The elastomeric sleeve is also easily insertable and extractable from the first cylinder and can also be attached around a support sleeve interposed between the elastomeric sleeve and the first cylinder, which can be easily inserted and attached to, or detached and extracted from, the first cylinder.

[0033] 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.

[0034] The present invention further proposes, in a manner not known in the available state of the art, the following steps of the method, implemented before the execution of the printing job: 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 , by including the elastomeric sleeve surrounding the other of the first and second cylinders; by deactivating the transfer of water from the watering cylinders to the second cylinders and by feeding the ink supply and the inking cylinders of each non-lithographic printing unit, which are identical to the ink supply and the inking cylinders of the lithographic printing unit, with non-lithographic ink selected among opaque ink, transparent varnish or ink with metallic flakes.

[0035] Once the lithographic and non-lithographic printing units have been configured, the printing job can be carried out.

[0036] It will be understood that the non-lithographic ink is an ink adapted to the non-lithographic printing process. Said non-lithographic ink is an opaque ink with an improved opacity, or a transparent ink which actuates as a varnish, or an ink with metallic flakes to provide the print with a metallic appearance.

[0037] According to the above, to configure one printing unit as a flexographic printing unit, a lithographic printing plate has to be included around the second cylinder, an elastomeric sleeve has to be included around the first cylinder and the ink supply and the inking cylinders have to be feed with lithographic ink, while maintaining active the transfer of water from the water supply and the watering cylinders to the second cylinder.

[0038] Contrary, to configure one printing unit as a non-flexographic printing unit, a relief plate or a relief cylindrical sleeve has to be included around either the first of the second cylinder, the elastomeric sleeve has to be included around the other of the first and second cylinders, and the ink supply and the inking cylinders have to be feed with non-lithographic ink, while maintaining deactivated the transfer of water from the water supply and the watering cylinders to the second cylinder.

[0039] 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.

[0040] 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 improves the resulting ink transfer on the printed image.

[0041] 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.

[0042] 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.

[0043] The use of a relief cylindrical sleeve allows printing a continuous gap-less image when the elastomeric sleeve is a continuous gap-less cylinder.

[0044] According to the above, in a first embodiment the relief plate or the relief cylindrical sleeve surrounds the second cylinder and the elastomeric 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.

[0045] 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.

[0046] According to a second embodiment of the present invention, the relief plate or the relief cylindrical sleeve surrounds the first cylinder and the elastomeric 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 elastomeric 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.

[0047] 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 elastomeric 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.

[0048] The watering cylinders of each non-lithographic printing unit are configured to transfer no water to the second cylinder.

[0049] Optionally, the proposed method further comprises, before the printing job, 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 or on top thereof when the laminar material is transparent, a transparent varnish coat, and / or a metallic image to be printed with ink with metallic flakes, and adapting the relief plate, or relief cylindrical sleeve, of each non-lithographic printing unit to print one of said monochrome images identified as an opaque base coat, as a transparent varnish coat and / or as a metallic image.

[0050] Optionally, the method further comprises arranging the lithographic printing units and the non- lithographic printing units in the selected order, defined in the digital prepress information, along the conveyance path.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] The axial insertion and extraction are produced in an axial direction concentric with the center of the respective first or second cylinder. 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.

[0055] Also, the elastomeric sleeve may have a variable diameter, preferably coincident with the diameter of the relief plate or sleeve. The elastomeric 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 elastomeric 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.

[0056] According to a second aspect, the present invention is also directed towards a printing machine, which allows the printing method described above, as described in claim 15.

[0057] The proposed printing machine comprises: several printing units successively arranged around a central drum 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 elastomeric sleeve surrounding the first cylinder as a blanket cylinder to transfer said monochrome image to be printed to the web of laminar material, and with the corresponding ink supply and inking cylinders (20) feed with lithographic ink; 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 and including the elastomeric sleeve surrounding the other of the first and second cylinders; the watering cylinders of each non-lithographic printing unit being detached from the second cylinders and / or the water supply of each non-lithographic printing unit being deactivated; and with the corresponding ink supply and inking cylinders, which are identical to the feed supply and inking cylinders of the lithographic printing units, feed with non-lithographic ink. Preferably, the lithographic printing units and the non-lithographic printing units are arranged along the conveyance path in the selected order defined in the digital prepress information.

[0058] 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.

[0059] Alternatively, the method can further comprise replacing one elastomeric sleeve from one first cylinder by one relief plate or relief sleeve, and replacing one lithographic sleeve, from one second cylinder, by one elastomeric sleeve or by the elastomeric sleeve extracted from the first cylinder, transforming one lithographic printing unit into one non-lithographic printing unit.

[0060] 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 elastomeric sleeve can also be extracted from, and / or inserted to, the first or second cylinder together with a support sleeve around which the elastomeric sleeve is attached.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] Brief description of the Figures 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:

[0066] 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;

[0067] Fig. 2 shows a perspective view of one printing unit devoid of the inking cylinders and watering cylinders;

[0068] 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 elastomeric sleeve surrounding the first cylinder;

[0069] 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 elastomeric sleeve surrounding the first cylinder;

[0070] Fig. 5 shows a zoomed view of one printing unit of Fig. 1 configured as one non-lithographic printing unit, with elastomeric sleeve surrounding the second cylinder and with a relief plate or a relief cylindrical sleeve surrounding the first cylinder.

[0071] Detailed Description of the Invention and of particular embodiments

[0072] 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 defines, on its perimeter, the conveyance path.

[0073] 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.

[0074] 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.

[0075] 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. In this example, the ink supply comprises an ink tray constantly feed with ink to maintain certain level, or a doctor blade defining an enclosed chamber containing the ink with one opening applied against the surface of one inking cylinder. An initial inking cylinder of the inking cylinders is partially submerged in said ink of the ink tray or of the doctor blade, 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] Some of the printing units 10 of the printing machine are configured as lithographic printing units by including a lithographic plate 41 surrounding the second cylinder 12, and a elastomeric sleeve 40 surrounding the first cylinder 11 , and by feeding the ink supply and the inking cylinders 20 of each lithographic printing unit with lithographic ink. This arrangement can be seen on Fig. 3.

[0083] The final watering cylinder transfers 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.

[0084] Then the lithographic plate 41 transfers the ink from the hydrophobic surfaces to the elastomeric 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.

[0085] In order to print monochrome images with an improved ink transfer, at least one of the printing units 10 is 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 , by including the elastomeric sleeve 40 surrounding the other of the first and second cylinders 11 , 12, by deactivating the transfer of water from the watering cylinders 30 to the second cylinders and by feeding the ink supply and the inking cylinders 20 of each non-lithographic printing unit, which are identical to the ink supply and the inking cylinders 20 of the lithographic printing unit, with non-lithographic ink selected among opaque ink, transparent varnish or ink with metallic flakes.

[0086] The opaque base coat is an image to be printed with opaque ink, or with ink opaquer than the lithographic inks printed with the lithographic printing units, offering an opaque background to enhance the other colors overlapped thereon.

[0087] 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, or alternatively, when the web material is transparent, the opaque base coat can be printed the last covering at least most of the other monochrome images previously printed.

[0088] Commonly, the opaque base coat is the first or the last monochrome image to be printed.

[0089] 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.

[0090] 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. As stated 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] Then the relief plate 42 or the relief cylindrical sleeve 43 transfers the ink from the raised or embossed surfaces to the elastomeric 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.

[0099] 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. The method further proposes, before executing the printing job, 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 or on top thereof when the laminar material is transparent, a transparent varnish coat, and / or a metallic image to be printed with ink with metallic flakes, and adapting the relief plate 42, or relief cylindrical sleeve 43, of each non-lithographic printing unit to print one of said monochrome images identified as an opaque base coat, as a transparent varnish coat and / or as a metallic image.

[0100] The method can further comprise arranging the lithographic printing units and the non- lithographic printing units in the selected order, defined in the digital prepress information, along the conveyance path.

[0101] 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 non- lithographic ink corresponding with the color information of the monochrome image to be printed with said non-lithographic printing unit.

[0102] According to one embodiment, at least the first printing unit of the succession of printing units along the conveyance path, is configured as the non-lithographic printing unit and successive printing units along the conveyance path are configured as the lithographic printing units. In this case, preferably the monochrome images printed by the non-lithographic printing units are at least partially cured or pinned by a curing unit before the printing additional monochrome images on top thereof by the lithographic printing units.

[0103] According to another alternative or additional embodiment, at least the last printing unit of the succession of printing units along the conveyance path is configured as the non-lithographic printing unit and preceding printing units along the conveyance path are configured as the lithographic printing units. In this case, the monochrome images printed by the lithographic printing units are preferably at least partially cured or pinned by a curing unit before the printing additional monochrome images on top thereof by the non-lithographic printing units.

[0104] A final curing unit can be included downstream the central drum to provide a final drying or curing of the printed images. According to the above, the non-lithographic ink can be at least partially cured or pinned before the printing of additional monochrome images on top thereof with lithographic ink, of vice versa, for example using UV light, infrared light, hot air, heat or a combination thereof.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] Alternatively, the configuration of the non-lithographic printing unit may comprise substituting the elastomeric sleeve 40 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 elastomeric sleeve 40 transforming the lithographic printing unit into a non- lithographic printing unit.

[0112] According to this arrangement, the final inking cylinder transfers ink to the elastomeric sleeve 40. Then, the elastomeric 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.

[0113] 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 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.

[0114] By changing the diameter of the first and second cylinders, changes the longitude of its perimeter, which determines the longitude of the monochrome image to be printed on the laminar web substrate in the direction of the conveyance path.

[0115] 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.

[0116] 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.

[0117] The present invention is also directed at a printing machine for printing with improved ink transfer.

[0118] The proposed printing machine comprises several printing units 10 successively arranged around a central drum 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, and a control unit containing the digital prepress information.

[0119] Some of the printing units 10 of the printing machine are lithographic printing units including a lithographic plate 41 surrounding the second cylinder and adapted to print one of the monochrome images, and including a elastomeric sleeve 40 surrounding the first cylinder 11 as a blanket cylinder to transfer said monochrome image to be printed to the web of laminar material; and with the corresponding ink supply and inking cylinders 20 feed with lithographic ink.

[0120] 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 and including the elastomeric sleeve 40 surrounding the other of the first and second cylinders 11 , 12.

[0121] The watering cylinders 30 of each non-lithographic printing unit are detached from the second cylinders and / or the water supply of each non-lithographic printing unit is deactivated.

[0122] Also, the corresponding ink supply and inking cylinders 20 of each non-lithographic printing unit, which are identical to the feed supply and inking cylinders 20 of the lithographic printing units, are feed with non-lithographic ink.

[0123] Since all the printing units of the proposed printing machine have the same ink supply, inking cylinders, water supply and watering cylinders, any printing unit can be easily adapted to work as a lithographic printing unit or as a non-lithographic printing unit, merely adapting the first and second cylinders, providing lithographic or non-lithographic ink and activating or deactivating the transfer of water towards the second cylinder.

[0124] Optionally, the lithographic printing units and the non-lithographic printing units are arranged along the conveyance path in the selected order defined in the digital prepress information.

[0125] The non-lithographic printing unit is preferably at least the first and / or at least the last printing unit, and curing units are included between the non-lithographic printing units and the lithographic printing units to provide at least a partial curing or pinning.

[0126] Preferably, curing units are included between each pair of successive printing units.

Claims

CLAIMS1. Printing method with improved ink transfer in a printing machine comprising several printing units (10) successively arranged around a central drum 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 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, before executing a printing job: defining, in a digital prepress information, several monochrome images to be printed overlapped in a selected order defining a polychrome image to be printed in the printing job; 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, by including a elastomeric sleeve (40) surrounding the first cylinder (11) as a blanket cylinder to transfer said monochrome image to be printed to the web of laminar material; and by feeding the ink supply and the inking cylinders (20) of each lithographic printing unit with lithographic ink; characterized in that the method further comprises, before executing the printing job: 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 and by including the elastomeric sleeve (40) surrounding the other of the first and second cylinders (11 , 12); by deactivating the transfer of water from the watering cylinders (30) to the second cylinders and by feeding the ink supply and the inking cylinders (20) of each non- lithographic printing unit, which are identical to the ink supply and the inking cylinders (20) of the lithographic printing unit, with non-lithographic ink selected among opaque ink, transparent varnish or ink with metallic flakes.

2. The method according to claim 1 wherein the method further comprises, before the printing job: 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 or on top thereof when the laminar material is transparent, a transparent varnish coat, and / or a metallic image to be printed with ink with metallic flakes, andadapting the relief plate (42), or relief cylindrical sleeve (43), of each non-lithographic printing unit to print one of said monochrome images identified as an opaque base coat, as a transparent varnish coat and / or as a metallic image.

3. The method according to claim 1 or 2 wherein the method further comprises arranging the lithographic printing units and the non-lithographic printing units in the selected order, defined in the digital prepress information, along the conveyance path.

4. The method according to claim 1 , 2 or 3 wherein, in the digital prepress information, each monochrome image is associated with color information, and wherein each lithographic printing unit is feed with lithographic 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 non-lithographic ink corresponding with the color information of the monochrome image printed with said non-lithographic printing unit.

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 web of laminar material, 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 onelithographic 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 elastomeric sleeve (40) 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 elastomeric sleeve (40) 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), 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. The method according to any preceding claim wherein at least the first printing unit of the succession of printing units along the conveyance path, is configured as the non-lithographic printing unit and successive printing units along the conveyance path are configured as the lithographic printing units; wherein the monochrome images printed by the non-lithographic printing units are at least partially cured or pinned by a curing unit before the printing additional monochrome images on top thereof by the lithographic printing units; and / or at least the last printing unit of the succession of printing units along the conveyance path, is configured as the non-lithographic printing unit and preceding printing units along the conveyance path are configured as the lithographic printing units; wherein the monochrome images printed by the lithographic printing units are at least partially cured or pinned by a curingunit before the printing additional monochrome images on top thereof by the non-lithographic printing units.

15. A printing machine for printing with improved ink transfer, the printing machine comprising: several printing units (10) successively arranged around a central drum 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 elastomeric sleeve (40) surrounding the first cylinder (11) as a blanket cylinder to transfer said monochrome image to be printed to the web of laminar material; and with the corresponding ink supply and inking cylinders (20) feed with lithographic ink; 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 and including the elastomeric sleeve (40) surrounding the other of the first and second cylinders (11 , 12); the watering cylinders (30) of each non-lithographic printing unit being detached from the second cylinders and / or the water supply of each non-lithographic printing unit being deactivated; and with the corresponding ink supply and inking cylinders (20), which are identical to the feed supply and inking cylinders (20) of the lithographic printing units, feed with non-lithographic ink.

16. The printing machine according to claim 15 wherein the lithographic printing units and the non-lithographic printing units are arranged along the conveyance path in the selected order defined in the digital prepress information.

17. The printing machine according to claim 15 or 16 wherein the non-lithographic printing unit is at least the first and / or at least the last printing unit, and wherein curing units are included between the non-lithographic printing units and the lithographic printing units.

Images