Method for avoiding start-up waste in a printing press printing metal sheets in an offset printing process

Abstract

The invention relates to a method for avoiding start-up waste in a printing press printing metal sheets in an offset printing process, wherein printing ink is transported in the direction of the respective metal sheet to be printed on an ink transport path arranged in a printing unit of the printing press by means of a rotating blanket cylinder, wherein a rider roller not arranged in the ink transport path and a doctor blade device permanently attached to the rider roller are positioned against the rotating blanket cylinder in a first operating state and are positioned away from this blanket cylinder in a second operating state, wherein when the printing press starts up, printing ink is applied to the blanket cylinder and the rider roller together with its doctor blade device are positioned against the blanket cylinder before the printing ink applied to the blanket cylinder is further transported to the respective metal sheet,wherein a time for the detachment of the rider roller together with its doctor blade device from the rotating blanket cylinder is set by a control device and / or wherein the rider roller together with its doctor blade device are detached from the blanket cylinder transporting the printing ink after a period set or at least adjustable by the control device, wherein a transport of the metal sheets is set in such a way that these metal sheets reach a printing nip formed by the blanket cylinder and an impression cylinder only after the rider roller together with its doctor blade device has been detached from the blanket cylinder, so that the application of the printing ink to the metal sheet in question only begins thereafter.

Description

[0001] The invention relates to a method for avoiding start-up waste in a printing press printing sheet metal in an offset printing process according to claim 1.

[0002] DE 10 2017 207 050 A1 discloses a metal printing machine with a sheet feeder, through which metal sheets can be removed from a stack of sheets and fed to the transport path leading through the metal printing machine on the inlet side, with at least one printing unit arranged in the transport path, through which the metal sheets can be printed according to an offset printing process, and with a stack delivery, at which the printed metal sheets can be delivered to a stack in at least one stacking space, wherein the printing unit has a printing cylinder designed as a form cylinder, a printing cylinder designed as a transfer cylinder and a printing cylinder forming a printing point with the transfer cylinder.

[0003] DE 10 2019 102 762 A1 relates to a method for setting a color profile in a sheetfed offset printing press, in which pre-printed waste sheets and unprinted good sheets are used during a changeover after a job change of the sheetfed offset printing press in question.

[0004] The invention is based on the objective of creating a method for avoiding start-up waste in a printing press printing sheet metal using an offset printing process.

[0005] The problem is solved according to the invention by the features of claim 1. The dependent claims relate to advantageous embodiments and / or further developments of the solution found.

[0006] The advantages achievable with the invention consist in particular of the fact that start-up waste in a printing press printing sheet metal in an offset printing process is avoided or at least significantly reduced. Further advantages will become apparent from the following description.

[0007] An embodiment of the invention is shown in the drawings and is described in more detail below.

[0008] They show: Fig. 1 a printing unit of a printing press printing sheet metal plates in an offset printing process in a first operating state; Fig. 2 the printing mechanism of this printing press in a second operating state.

[0009] Fig. Figure 1 represents, in a highly simplified example, a printing unit for metal sheets 01 in an offset printing press. The metal sheets 01 to be printed are fed sequentially, lying down in a transport direction T, to the printing unit of the printing press by means of a transport device 02, e.g., a conveyor belt or a chain conveyor, and guided through a printing gap 13 formed by a blanket cylinder 03 and an impression cylinder 04. An alternative design of the transport device 02 consists of a conveying device with grippers, which conveys the metal sheets 01 to be printed to the printing gap 13 in a gripper closure. At least during printing operation of the printing press, a plate cylinder 06 is engaged with the blanket cylinder 03.An ink transport path in the printing unit of the printing press carries printing ink taken from an ink reservoir 12 (not specified in detail) via the plate cylinder 06 and the blanket cylinder 03 to the respective metal plate 01 to be printed. The ink reservoir 12 works, for example, in conjunction with a roller inking unit and applies printing ink to the plate cylinder 06 by means of at least one inking roller.

[0010] A rider roller 07 not arranged in the ink transport path and a doctor blade device 08 permanently attached to the rider roller 07 is attached to the rotating rubber blanket cylinder 03 in a first operating state ( Fig. 1) and in a second operating state, this rubber blanket cylinder 03 is switched off ( Fig.2) The doctor blade assembly 08 has a doctor blade 09 that is attached to, or at least adjustable to, the rider roller 07. The rider roller 07 can, for example, absorb excess printing ink from the blanket cylinder 03 or supply additional printing ink to the blanket cylinder 03 from the ink reservoir 12 if this is necessary to achieve optimal inking. The doctor blade 09 of the doctor blade assembly 08 wipes the printing ink absorbed by the rider roller 07 from this rider roller 07.

[0011] The metal sheets 01 to be printed are typically rectangular in format with dimensions, for example, between 500 mm x 650 mm and 1,000 mm x 1,200 mm, and each has a thickness, for example, between 0.1 mm and 1.0 mm, preferably between 0.14 mm and 0.5 mm. Depending on its format and material—whether tin-plated steel, tin-free steel, or aluminum—each of these metal sheets 01 can have a mass, for example, from 0.5 kilograms to 5 kilograms or more. Particularly in the production of metal packaging, i.e., in metal packaging printing, metal sheets 01 of this type are printed and / or varnished industrially in mass production at a production rate of several thousand metal sheets 01 per hour, for example, at least 3,000 metal sheets 01 per hour, using a printing press of the aforementioned type.

[0012] To avoid start-up waste in a printing press printing sheet 01 in an offset printing process, a method is proposed in which printing ink is transported towards the sheet 01 to be printed by means of the rotating blanket cylinder 03 on the ink transport path arranged in a printing unit of the printing press, wherein a rider roller 07 not arranged in the ink transport path and a doctor blade device 08 permanently attached to the rider roller 07 are attached to the rotating blanket cylinder 03 in a first operating state and are detached from this blanket cylinder 03 in a second operating state.wherein, at the start of production and thus when the printing press starts up, printing ink is applied to the blanket cylinder 03 and the rider roller 07 together with its doctor blade 08 is positioned at the blanket cylinder 03 before the printing ink applied to the blanket cylinder 03 is transported to the relevant metal sheet 01, wherein a time for switching off the rider roller 07 together with its doctor blade 08 from the rotating blanket cylinder 03 is set by a control device 11, which is in particular programmable, and / or wherein the rider roller 07 together with its doctor blade 08 is switched off from the ink-transporting blanket cylinder 03 after a duration set or at least adjustable by such a control device 11, wherein a transport of the metal sheets 01 is set in such a way thatthat these metal sheets 01 reach the printing gap 13 formed by the blanket cylinder 03 and the impression cylinder 04 only after the rider roller 07, including its doctor blade assembly 08, has been disengaged from the blanket cylinder 03, so that the application of the printing ink to the respective metal sheet 01 only begins after the rider roller 07, including its doctor blade assembly 08, has been disengaged from the blanket cylinder 03. Printing of the metal sheets 01 thus only begins after stable conditions have been established in the printing unit with regard to the printing ink actually required for the current production run. For example, it can be provided that the control unit 11 sends a control signal to the transport unit 02, which transports the metal sheets 01 to the printing unit, and that this transport unit 02 is only activated after the rider roller 07, including its doctor blade assembly 08, has been disengaged from the blanket cylinder 03.

[0013] In a preferred embodiment, the timing for disengaging the rider roller 07, including its doctor blade assembly 08, from the rotating blanket cylinder 03, or the corresponding duration for this disengagement of the rider roller 07, including its doctor blade assembly 08, from the rotating blanket cylinder 03, are set by the control unit 11 as a function of an adjustable number of revolutions of the blanket cylinder 03, wherein this number of revolutions of the blanket cylinder 03 can be selected in a range, for example, between 20 and 70, preferably at about 50. The number of revolutions of the blanket cylinder 03 can be made dependent on whether the printing press is operating at full speed. B. whether after an interruption in the transport of the sheet metal plates 01, restarts (e.g. 20 revolutions of the rubber blanket cylinder 03), or whether a new production run is currently starting (e.g. 50 revolutions of the rubber blanket cylinder 03), or whether the printing press is currently operating in setup mode (e.g.70 revolutions of the rubber blanket cylinder 03).

[0014] Preferably, it can also be provided that the respective contact pressure with which the rider roller 07, together with its doctor blade assembly 08, is positioned against the blanket cylinder 03 and / or with which the doctor blade 09 is positioned against the rider roller 07, is set, for example, by the control unit 11. This adjustment of the contact pressure can be pneumatically operated or, for example, via Schmitz rings mounted on the blanket cylinder 03. The excess printing ink removed from the blanket cylinder 03 by the rider roller 07 is preferably discharged via the doctor blade assembly 08 and, if necessary, returned to the ink reservoir 12.

[0015] One advantage of the proposed solution is that metal sheets (01) are always inked with the correct amount of ink, thus preventing waste, especially during press start-up. Since metal sheets (01) are relatively expensive compared to paper sheets, the proposed solution offers a significant economic benefit. Disposal of incorrectly inked metal sheets (01) is also eliminated or at least considerably reduced. Furthermore, this waste reduction eliminates the need to remove defective metal sheets (01) from the production flow. Given the relatively large number of these sheets, this also reduces the workload for the press operators, as this removal is typically done manually. In practice, it has been shown that without this proposed solution, up to 50 metal sheets (01) can be wasted during press start-up. Reference symbol list 01 Sheet metal panel 02 Transport equipment 03 Rubber blanket cylinders 04 Counterpressure cylinder 05 - 06 plate cylinders 07 Rider roller 08 Squeegee attachment 09 Squeegee blade 10 - 11 Control unit 12 color reservoirs 13 Pressure gap T Transport direction

Claims

[1] A method for avoiding start-up waste in a printing press printing on metal sheets (01) in an offset printing process, wherein ink is transported towards the metal sheet (01) to be printed by means of a rotating blanket cylinder (03) on an ink transport path arranged in a printing unit of the printing press, wherein a rider roller (07) not arranged in the ink transport path and a doctor blade device (08) permanently attached to the rider roller (07) are attached to the rotating blanket cylinder (03) in a first operating state and are detached from this blanket cylinder (03) in a second operating state,wherein, when the printing press starts up, printing ink is applied to the blanket cylinder (03) and the rider roller (07) together with its doctor blade assembly (08) is positioned against the blanket cylinder (03) before the printing ink applied to the blanket cylinder (03) is transported to the relevant metal sheet (01), wherein a time for switching off the rider roller (07) together with its doctor blade assembly (08) from the rotating blanket cylinder (03) is set by a control device (11) and / or wherein the rider roller (07) together with its doctor blade assembly (08) is switched off from the ink-transporting blanket cylinder (03) after a duration set or at least adjustable by the control device (11), wherein a transport of the metal sheets (01) is set in such a way thatthat these metal sheets (01) reach a printing gap (13) formed by the blanket cylinder (03) and a counter-pressure cylinder (04) in the printing unit of the printing press only after the rider roller (07) together with its doctor blade assembly (08) has been stopped by the blanket cylinder (03), so that the application of the printing ink to the respective metal sheet (01) only begins after the rider roller (07) together with its doctor blade assembly (08) has been stopped by the blanket cylinder (03). [2] Method according to claim 1, characterized by , that the time for switching off the rider roller (07) together with its doctor blade assembly (08) from the blanket cylinder (03) and / or the duration for switching the rider roller (07) together with its doctor blade assembly (08) on to the blanket cylinder (03) are set by the control unit (11) depending on an adjustable number of revolutions of the blanket cylinder (03). [3] Method according to claim 1 or 2, characterized by, that a contact pressure is set with which the rider roller (07) together with its doctor blade device (08) is positioned against the rubber blanket cylinder (03). [4] Method according to claim 1 or 2 or 3, characterized by , that the contact pressure with which the doctor blade (09) is applied to the rider roller (07) is set by the control device (11). [5] Method according to claim 1 or 2 or 3 or 4, characterized by , that the printing ink taken from the rubber blanket cylinder (03) by means of the rider roller (07) is carried away via the doctor blade device (08). [6] Method according to claim 1 or 2 or 3 or 4 or 5, characterized by , that the control device (11) sends a control signal to a transport device (02) that transports the sheet metal panels (01) to the printing unit. [7] Method according to claim 1 or 2 or 3 or 4 or 5 or 6, characterized by, that sheet metal panels (01) with a mass of at least 0.5 kg each are printed in the printing press.

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