Printing process and perfector for perfecting both sides of sheets

Abstract

Printing method for double-sided printing of sheets (32a, 32b, 32c) in a perfector (31), wherein the respective sheet (32a, 32b, 32c) is during its passage through the perfector (31) - in a first step is transported on a first cylinder (13) of the perfector (31), wherein the first cylinder (13) is tempered to a first temperature (T13), and is printed on a first sheet side (33), - in a second step, the perfector (31) is turned by means of a turning device (5) and - in a third step is transported on a second cylinder (16) of the perfector (31), wherein the second cylinder (16) is a component of a printing unit (6) for offset printing, which is subordinate to the turning device (5) in the sheet transport direction (15), and is tempered to a second temperature (T16) different from the first temperature (T13), and is printed on a second sheet side (34).

Description

[0001] The present invention relates to a printing method for double-sided printing of sheets and a perfector for double-sided printing on sheets.

[0002] When printing on the reverse side in perfectors, there is a risk of ink being deposited from the already printed front side onto the impression cylinder.

[0003] To counter this danger, DE 19716424 A1 proposes coating the counter-pressure cylinder after the turning device with a silicone rubber layer. Additionally, the cylinder can be cooled to a temperature below 28 °C. A cooling system for a cooling medium can be arranged inside the cylinder for this purpose. The silicone rubber layer acts as a color-repellent layer, and the cooling serves to enhance this color-repellent effect.

[0004] Further state of the art is provided by DE 19 2008 001 309 B4, which describes a method and a device for controlling a printing press.

[0005] Another problem that occurs in the printing process is the insufficient drying of the sheets.

[0006] One could try to accelerate the drying of the printing ink by means of a treatment agent that includes an infrared absorber, as described in US 7,913,622 B2.

[0007] With reference to this problem of insufficient drying, DE 102007056899 A1 describes a printing press in which sheets are heated in a coating unit before a perfecting unit. The sheets are heated to a temperature above that of the printing units of the press by contact with a heated impression cylinder of the coating unit. To heat the impression cylinder, a heated fluid can be flowed through it.

[0008] Another problem encountered when printing with perfectors is an insufficient gloss level on the front side of the sheets. No satisfactory solution has yet been found for this problem.

[0009] The invention is based on the objective of providing a printing process with which a high degree of gloss can be achieved on the front side of the print. Furthermore, it is an objective to provide a printing press suitable for carrying out this printing process.

[0010] This problem is solved by a printing method having the features of claim 1 and by a printing machine having the features of claim 8.

[0011] The printing method according to the invention for double-sided printing of sheets in a perfector comprises the following process steps: In a first process step, the respective sheet is transported on a first cylinder of the perfector during its passage through the perfector, the first cylinder being heated to a first temperature. In the first process step, the respective sheet is printed on a first side. In a second process step, the respective sheet is turned over by means of a turning device of the perfector during its passage through the perfector. In a third process step, the respective sheet is transported on a second cylinder of the perfector during its passage through the perfector, the second cylinder being heated to a second temperature different from the first. In the third process step, the respective sheet is printed on a second side.In this case, the second cylinder is a component of an offset printing unit, which is located downstream of the turning device in the sheet transport direction.

[0012] This method allows for a particularly high gloss level to be achieved on the first side of the sheet.

[0013] In a further development of the inventive method, a counter-pressure cylinder is used as the first cylinder.

[0014] In a further development, the first cylinder is a component of a paint shop, which is located upstream of the turning device in the direction of arc transport.

[0015] In a further development process, in the first step the respective sheet is printed in several offset printing units one after the other, which are arranged upstream of the turning device in the sheet transport direction.

[0016] In a further development, the first cylinder is heated to the first temperature, and this first temperature is higher than the temperature of the counter-pressure cylinders of the perfector. Preferably, these counter-pressure cylinders are untempered, i.e., neither heated nor cooled, counter-pressure cylinders of the perfector.

[0017] In a further development process, a counter-pressure cylinder is used as the second cylinder.

[0018] In a further development, the second cylinder is cooled to a second temperature, and this second temperature is lower than the temperature of the counter-pressure cylinders of the perfector. Preferably, these counter-pressure cylinders are those previously mentioned counter-pressure cylinders that are not temperature-controlled, i.e., neither heated nor cooled.

[0019] The perfector according to the invention for printing on both sides of a sheet comprises at least one first unit for printing, varnishing, or drying a first side of the sheet, wherein the first unit has a first cylinder for sheet transport. Furthermore, the perfector comprises at least one second unit for printing a second side of the sheet, wherein the second unit has a second cylinder for sheet transport. The perfector also comprises at least one temperature control device for temperature-controlled the first cylinder to a first temperature and the second cylinder to a second temperature that differs from the first temperature.

[0020] Accordingly, there may be a first temperature control device for temperature control of the first cylinder and a second temperature control device for temperature control of the second cylinder, and there may also be a common temperature control device for temperature control of both the first cylinder and the second cylinder.

[0021] Further constructively and functionally advantageous developments result from the following description of an exemplary embodiment and the associated drawing.

[0022] The single figure in the drawing shows a sheet-fed printing press in a series configuration with several units arranged one behind the other. The sheet-fed printing press is a Perfektor 31 and includes a perfecting unit 5 for turning the sheets in the perfector 31's perfector 31's perfector 31's perfector 31. The perfecting unit 5 can be switched from a mode for perfector 31 to a mode for perfector 31 only, in which the sheets pass through the perfecting unit 5 without being turned. Viewed in the sheet transport direction 15, upstream of the perfecting unit 5, are a sheet feeder (not shown in the drawing), printing units 1, 2, a coating unit 3, and a drying unit 4, arranged in that order. Viewed in the sheet transport direction 15, downstream of the perfecting unit 5 are printing units 6, 7, 8, and 9, a coating unit 10, and a sheet delivery unit (not shown in the drawing), arranged in that order. The printing units 1, 2, 6 to 9 are flat or...Lithographic offset printing units. The coating units 3 and 10 are used to apply a protective varnish or clear varnish or a similar coating liquid to the respective offset printed image.

[0023] The printing units 1, 2, 6 to 9 and the coating units 3, 10 each comprise a sheet-transporting cylinder 11, 12, 13, 16, 17, 18, 19 and 20, which is an impression cylinder. The drying unit 4 also comprises a sheet-transporting cylinder 14. Further cylinders for transporting the sheets are arranged between the impression cylinders and in the perfecting unit 5. Each of the cylinders 11 to 14 and 16 to 20 is assigned a temperature control unit 21, 22, 23, 24, 26, 27, 28, 29 and 30, by means of which a temperature control fluid is circulated through the respective cylinder. The temperature control devices 21 to 24, 26 to 30 can also be grouped together to form a common temperature control device for the cylinders 11 to 14 before the reversing device 5 and a common temperature control device for the cylinders 16 to 20 after the reversing device 5 or in a similar form.The reference symbols “32a”, “32b” and “32c” represent one and the same arc in different positions during its passage through the perfector 31.

[0024] The printing process for the sheet is as follows: First, the sheet's front side (front side) 33 is printed with an offset imprint in printing units 1 and 2. Then, the front side 33 is varnished in the coating unit 3 to apply a glossy, protective layer to the offset imprints. The coating unit 3 is the last printing or varnishing unit before the perfecting unit 5. During varnishing, the sheet 32a rests on the rotating cylinder 13, which is heated to a temperature T13 by the temperature control unit 23. The temperature T13 of cylinder 13 is at least 10 K and at most 30 K above the temperature T11 = T12 = T14 = T17 = T18 = T19 = T20 of cylinders 11, 12, 14, 17 to 20, which can be approximately 30 °C.After varnishing, the printed image on the first sheet side 33 is dried in the drying unit 4 using hot or warm air and / or infrared radiation, and the sheet is transported through the cylinder 14.

[0025] The arc 32b then passes through the turning device 5 and is turned in it.

[0026] The turned sheet 32c is then printed on its second side (reverse side) 34 in printing units 6 to 9 using offset printing. During printing in unit 6, the sheet 32c is transported on cylinder 16, which is cooled to a temperature T16 by the temperature control unit 26. The temperature T16 of cylinder 16 is at least 10 K and at most 20 K lower than the common temperature T11 = T12 = T14 = T17 = T18 = T19 = T20 of cylinders 11, 12, 14, 17 to 20, which can be approximately 30 °C.

[0027] For example, cylinder 13, which participates in the front printing process, is heated to 55 °C, while cylinder 16, which participates in the back printing process, is simultaneously cooled to 15 °C. The temperature difference between the heated cylinder 13 and the cooled cylinder 16 is at least 20 K and at most 50 K. The printing unit 6 is the first printing or coating unit after the perfecting unit 5. Unit 6 follows directly after the perfecting unit 5.

[0028] Afterwards, the reverse side printed image on sheet 32c is coated in the coating unit 10 to provide the printed image on the second sheet side 34 with a gloss and protective layer.

[0029] Various modifications to the operating and printing process are possible: During a modification, not only cylinder 13 of the coating unit 3, but also cylinders 11 and 12 of the printing units 1 and 2, and / or cylinder 14 of the drying unit 4, are heated to a temperature of approximately 40 to 60 °C. Accordingly, the sheet-transporting cylinder of at least one of the units 1 to 4 upstream of the turning unit 5 in the sheet transport direction 15, or of several of these units 1 to 4, or of all units 1 to 4, is heated to the aforementioned increased operating temperature.

[0030] In a further modification, which may be provided independently of or together with the modification explained above, not only cylinder 16 of the printing unit 6, but also cylinders 17, 18, 19 of the printing units 7 to 9 and / or cylinder 20 of the coating unit 10 are cooled to a temperature of approximately 10 to 20 °C. Reference symbol list 1, 2 Printing work 3 Paint shop 4 Drying plant 5 Reversing device 6 to 9 printed matter 10 Paint shop 11 to 14 cylinders 15 Bow transport direction 16 to 20 cylinders 21 to 24 temperature control unit 25 . / . 26 to 30 temperature control unit 31 Perfector 32a, 32b, 32c arch 33 first page of the sheet 34 second page of the sheet T11 to T20 temperature

Claims

[1] Printing method for double-sided printing of sheets (32a, 32b, 32c) in a perfector (31), wherein the respective sheet (32a, 32b, 32c) during its passage through the perfector (31) - in a first step, it is transported on a first cylinder (13) of the perfector (31), the first cylinder (13) being heated to a first temperature (T13), and printing is carried out on a first sheet side (33), - in a second step, it is turned by means of a turning device (5) of the perfector (31) and - in a third step, it is transported on a second cylinder (16) of the perfector (31), the second cylinder (16) being a component of a printing unit (6) for offset printing, which is arranged downstream of the turning device (5) in the sheet transport direction (15), and is tempered to a second temperature (T16) different from the first temperature (T13), and is printed on a second sheet side (34). [2] Printing method according to claim 1, wherein an impression cylinder is used as the first cylinder (13). [3] Printing method according to claim 1 or 2, wherein the first cylinder (13) is a component of a coating unit (3) which is arranged upstream of the turning device (5) in the sheet transport direction (15). [4] Printing method according to one of claims 1 to 3, wherein in the first step the respective sheet (32a, 32b, 32c) is printed successively in several printing units (1, 2) for offset printing, which are arranged upstream of the turning device (5) in the sheet transport direction (15). [5] Printing method according to one of claims 1 to 4, wherein the first cylinder (13) is heated to the first temperature (T13) and this is higher than a temperature (T11, T12) of counter-pressure cylinders (11, 12) of the perfector (31). [6] Printing method according to one of claims 1 to 5, wherein an impression cylinder is used as the second cylinder (16). [7] Printing method according to one of claims 1 to 6, wherein the second cylinder (16) is cooled to the second temperature (16) and this is lower than a temperature (T17, T18, T19) of impression cylinders (17, 18, 19) of the perfector (31). [8] Perfector (31) for perfecting and reverse printing on sheets (32a, 32b, 32c) - for carrying out the printing method according to one of claims 1 to 7 - comprising - at least one first unit (3) for printing, varnishing or drying a first sheet side (33), wherein the first unit (3) has a first cylinder (13) for sheet transport, - at least one second unit (6) for printing, varnishing or drying a second sheet side (34), wherein the second unit (6) has a second cylinder (16) for sheet transport, and - at least one tempering device (23, 26) for tempering the first cylinder (13) to a first temperature (T13) and the second cylinder (16) to a second temperature (T16) which is different from the first temperature (T13).

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