HARDENING CHAMBER FOR PRINTED MATTER

Abstract

A curing chamber for curing and drying a flat printing product printed with at least one UV-curing pigment, comprising a first chamber wall including a cooling surface or is a cooling surface, a second chamber wall which is opposite the first chamber wall, wherein at least one UV lamp directed onto the cooling surface is arranged on or in the second chamber wall, third and fourth chamber walls which are arranged opposite one another between the first and the second chamber walls and which each comprise an introductory slot or removal slot and/or form an appropriate slot to the first chamber wall, fifth and sixth side walls arranged opposite one another and arranged between the first and the second chamber walls, wherein a gas inlet or a gas outlet is arranged in the vicinity of the third and fourth chamber walls, and the gas inlet is an inert gas inlet.

Claims

1. A curing chamber for curing and drying a flat printed product printed with at least one UV-curing pigment, comprising a first chamber wall which comprises a cooling surface or is a cooling surface, a second chamber wall which is opposite the first chamber wall, wherein at least one UV lamp directed onto the cooling surface is arranged on or in the second chamber wall, third and fourth chamber walls which are arranged opposite one another between the first and the second chamber walls and which each comprise an introductory slot or removal slot and/or form an appropriate slot to the first chamber wall, fifth and sixth side walls arranged opposite one another and arranged between the first and the second chamber walls, wherein a gas inlet or a gas outlet is arranged on or in the vicinity of the third and fourth chamber walls, wherein the gas inlet is an inert gas inlet.

2. The curing chamber according to claim 1, characterized in that the gas inlet is placed on or in the vicinity of a chamber boundary which is opposite a direction of transport like the gas outlet.

3. The curing chamber according to claim 1, characterized in that the inert gas supply comprises or is at least one Ar, Ne, He and/or Xe, CO.sub.2 but especially a nitrogen supply (N.sub.2).

4. The curing chamber according to claim 1, characterized in that the gas inlet is placed on or in the vicinity of a front chamber wall relative to a transport direction (T).

5. The curing chamber according to claim 1, characterized in that the cooling surface is the surface of a rotatable cooling roller.

6. The curing chamber according to claim 1, characterized in that the gas inlet comprises at least one flat jet or an appropriate linear jet arrangement with an alignment to the transport plane which is parallel to the longitudinal dimension of the jet opening or jet arrangement, and with an outlet plane (IG) of the inert gas which is directed parallel to or at an acute angle to the transport plane, in particular to the cooling surface.

7. The curing chamber according to claim 1, characterized in that the UV lamp emits light in a range between 200 nm and 450 nm or between 365 nm and 405 nm.

8. The curing chamber according to claim 1, characterized in that the UV lamp is arranged parallel to the cooling surface and at a distance of 5 mm to 50 mm, or of 10 mm to 40 mm.

9. The curing chamber according to claim 1, characterized in that the curing chamber comprises two or more UV lamps which are arranged offset with respect to the transport direction and/or staggered from one another laterally.

10. The curing chamber according to claim 1, characterized in that the UV lamp comprises or is an LED lamp or an LED array.

11. The curing chamber according to claim 1, characterized in that the curing chamber comprises means for pressing the printed product onto the cooling surface and/or means for guiding the printed product on the cooling surface.

12. A printer with at least one printing device for applying a UV-curing ink to a printing web, said printing device having at least one UV ink reservoir or a UV ink supply, characterized in that said printer comprises a curing chamber according to claim 1 which is arranged downstream from the printing device.

13. The printer according to claim 12, characterized in that it comprises means for pressing the printed product onto the cooling surface.

14. The printer according to claim 12, characterized in that the pressing means comprises at least one spring-loaded roller.

15. The printer according to claim 13, characterized in that the printing device comprises at least one inkjet printing head.

16. The printer according to claim 15, characterized in that the printing device comprises two, three, four or more inkjet printing heads with a different ink.

17. The printer according to claim 16, characterized in that a fixing station is arranged between at least two printing heads with different inks and/or between the last printing head and the curing chamber.

18. The printer according to claim 13, characterized in that the printer comprises a supply roll for receiving a printing material web and/or comprises a receiving roll for receiving the printed product.

19. The printer according to claim 13, characterized in that the printer is designed as a module of an in-line printing system with a continuous printing web.

20. A method for printing a printing material web wherein the printing material web is first printed in a printing device with a UV-curing ink and is subsequently cured in a curing chamber according to claim 1 under inert gas.

21. The method according to claim 20, characterized in that the inert gas is Ar or also Ne, He, Xe or CO.sub.2, but in particular nitrogen.

22. The method according to claim 20, characterized in that the method is carried out in a printer with at least one printing device for applying a UV-curing ink to a printing web, said printing device having at least one UV ink reservoir or a UV ink supply, characterized in that said printer comprises a curing chamber, characterized in that it comprises means for pressing the printed product onto the cooling surface, characterized in that the pressing means comprises at least one spring-loaded roller, characterized in that the printing device comprises at least one inkjet printing head, characterized in that the printing device comprises two, three, four or more inkjet printing heads with a different ink, characterized in that a fixing station is arranged between at least two printing heads with different inks and/or between the last printing head and the curing chamber, characterized in that the printer comprises a supply roll for receiving a printing material web and/or comprises a receiving roll for receiving the printed product, and characterized in that the printer is designed as a module of an in-line printing system with a continuous printing web.

23. The method according to claim 20, characterized in that the method is an endless printing method and that the printed product is printed at a through speed of 5 to 300 m/min or 7 to 60 m/min and is cured.

24. The method according to claim 23, characterized in that a power of 1 to 40 W/cm.sup.2, or between 2 to 20 W/cm.sup.2 is introduced onto the surface of the printed product guided onto or on the cooling surface.

25. The method according to claim 20, characterized in that the printing material web comprises a film or an endless film.

26. The method according to claim 25, characterized in that the film is a plastic film, a paper-based film, a label film or an aluminum foil.

27. The method according to claim 25, characterized in that the film or endless film has a thickness of 0.5 m to 600 m, in particular between 10 m to 300 m.

28. The method according to claim 20, characterized in that the UV-curing ink comprises an acrylate base with a content of pigment(s) and/or clear lacquer, radical photoinitiators, dispersant(s) and optionally other additives, wherein at least two radical photoinitiators of the Norrish type 1 and at least one radically curable monomer in the form of a polyfunctional alkoxylated and/or polyalkoxylated acrylate monomer comprising one or more di- and/or triacrylates are contained, wherein the molar ratio of all acrylates to all initiators is about 5:1 to 19:1, especially about 7:1 to 15:1.

29. The method according to claim 28, characterized in that the UV-curing ink contains an adhesion promotor in the form of an isocyanate in a concentration of 0.1 wt % to 20 wt % or 0.5 wt % to 2.5 wt %.

Description

DESCRIPTION OF THE FIGURES

[0032] The invention is described in the following by way of example using figures. The same reference numbers in different figures have the same meaning. All drawings are schematic and cannot serve for a direct derivation of relationships of magnitudes or of dimensions.

[0033] FIG. 1 A curing chamber according to the invention

[0034] FIG. 2 Another curing chamber according to the invention

[0035] FIG. 3 A printer with a curing chamber

[0036] FIG. 4 Course of polymerization with/without inert gas

[0037] The embodiment of a curing chamber according to the invention shown in FIG. 1 comprises a cooling roller 5 which substantially forms the first lower chamber wall at the same time. In the following, like the concept below already previously used inside the curing chamber regarding an area extending from the plane of the printing product 9 in the direction of the cooling surface 5 or of the first chamber wall, the concept above concerns an area extending from the plane of the printing product in the direction of the UV lamps 11, 11 and of the second chamber wall 2. A diode array 11 which is formed substantially in a (partially) circular manner in parallel above the cooling roller and composed of five segments is located in the second, opposing upper chamber wall 2, which array irradiates onto the printed surface 10 of the printing product 9 resting on the cooling surface of a cooling roller 5 which is, e.g., water-cooled. The printing product 9 is guided or entrained from or on the cooling roller 5 rotating in the transport direction about the axis 5 (according to the arrow T on the ends of the printed product which are cut off for the sake of the representation. Laterally limiting surfaces 6, e.g., of the sidewalls corresponding to a fifth and a sixth chamber wall, shown here only in a smaller partial area of the drum circumference as is necessary for the sealing of the chamber can be sealed against the rotating roller 5 by a dynamic seal 18, e.g., a labyrinth seal or brushes. The side surfaces 6 can be attached on the third and fourth lateral chamber walls, which are not shown in detail here, or can be components of the corresponding sidewalls. Additional upper and lower surfaces 7 can facilitate the entrance of the printed product into the introductory slot 21 of the curing chamber 1. The contact pressure of the printed product, e.g., of the sheet or of a label sheet on the cooling surface 5 can be increased by adjustment means which are not shown here for the roller 5. In addition, several contact pressure rollers or contact pressure cylinders 8 which are elastically positioned against the printed surface 9 of the exiting print web are provided as contact pressure means. The latter as well as upper and lower guide surfaces can be mounted either directly on the chamber 1, 1 or separately on the associated printer 23.

[0038] The third chamber wall, which is the front one regarding the transport direction T, is formed here by the inert gas inlet 3 which conducts the inert gas, especially cooling gas, e.g. nitrogen, flowing in through the gas line 14 by flow conduction means such as flow conduction sheets 16, 16 in the inlet 3, 3 and/or by the geometry of the jets 12 at an acute angle or parallel to the surface 9 of the printing product. The direction of flow of the cooling gas can form a so-called cooling gas curtain with a cooling plane or inert gas plane IG (vertical to the viewing plane) parallel to or an at acute angle to the transport plane or the cooling surface. Gas inlet 3 comprises two longitudinal jets 12, 12 or jet rows 12, 12 which are arranged in an appropriate linear manner with different flow directions and inlet lines according to the arrows. The first jet or jet row 12 produces a flow curtain directed in the transport plane in the chamber 1. On the other hand, the second jet or jet row 12 produces outside of the chamber 1 a flow curtain directed counter to the transport direction, which reduces the oxygen component already before the introductory slot 3 and therefore inflowing leakage gas has a lesser oxygen content already between the sheet and the third chamber wall or inlet 3.

[0039] The fourth chamber wall, the rear one regarding the transport direction T, is formed here by the gas outlet 4 through which the blown-in inert gas is removed by suction and conducted into the gas removal line 15. As FIG. 1 shows, the outlet 4 can also comprises two outlet openings 13, 13, in particular outlet slots or opening rows arranged in an appropriate linear manner of which the one 13 is arranged in the chamber and the other one 13 is arranged outside of the chamber, here in the direct vicinity of the discharge slot 22. This can prevent an undesired inflow of air through the discharge slot 22 on the one hand by the inert gas flowing with an excess pressure out of the chamber and the additional outer chamber suction removal 13, and on the other hand also without additional seals. A static seal 19 can also be attached between gas outlet 4, 4 or the fourth chamber wall and the second chamber wall 2 such as between gas inlet 3, 3 or the third chamber wall 3 and the second chamber wall 2 as well as between all other elements forming a partial area of a chamber wall. Furthermore, an oxygen sensor 17 can be arranged in the chamber 1, 1 in order, e.g., to display a too high concentration of oxygen, e.g., in order to turn off the printer or to elevate the influence of gas by a process control.

[0040] The curing chamber 1 shown in FIG. 2 is constructed similarly to the one shown in FIG. 2; however, a cooling gas inlet is constructed here as a so-called air sword with a compressor 20 which comprises only a longitudinal jet or jet arrangement 12 which generates an air curtain symbolized by an arrow in the inert gas plane IG represented by dotted lines which curtain is deflected by the printing product resting on the cooling surface in the transport direction T and is spun more in the chamber, as is indicated by 3 arrows. An inert gas turbulence shown by two arrows counter to the transport direction T and formed by a concave inlet surface 12 formed after the jet 12 in or on the 3d chamber wall is simultaneously formed which additionally prevents the penetration of air into the curing chamber. In distinction to the embodiment shown in FIG. 1, two individual LED irradiators are shown which are arranged in series relative to the transport direction T. Furthermore, the cooling gas is removed by suction here only by outlet openings 13 directed into the chamber 1, wherein the discharge slot 22 is sealed by a brush 19 against atmosphere.

[0041] FIG. 3 shows by way of example in a greatly simplified manner a universally useable UV-DOD (drop on demand) label printer 23 with a curing chamber 1, 1 according to the invention which is mounted in a frame 44 supported on leveling feet 45 on which the input/output unit 43 for the operator is also located. Therefore, printing web rolls 25 to 600 mm in diameter can be processed.

[0042] The individual components of the printer 23, which are already known in part from the prior art, are described in the following substantially along a partially optional flow path of the printing web 25 (web) or of the printing product 9, i.e. of the printed printing web. The printing web 25 is drawn from the printing web roll 25 by the or via the inlet-side printing web guide 29 at first past the station 26 for measuring the thickness of the printing web via the input splicing table 27 and the input-side dancer rollers 28. The measuring of the layer thickness for the automatic cutting off of an erroneous printing web, e.g., for determining any folds, bubbles or wrinkles on the labels can take place by deflection or pressure on two oppositely positioned rollers. The printing web guide 29, on which a measuring device which is not shown in detail for the detection of the webpage can also be provided, is followed by three optional modules: a cleaning station 30 for the cleaning, e.g., by a counter-roller with an adhesive surface, a corona station 31 for pretreating the printing web 25 with a corona discharge, and a printing web heating 32 whose temperature can be adjusted by the input/output unit 43. A label image sensor and/or printing position sensor 34 is located directly in front of the printing device 33 in order to make possible the most exact printer result. This can take place, e.g., by a 4-point measuring of a preprinted position or the like.

[0043] The printing device 34 comprises four to ten printing heads with different colors, wherein 1 to 10 printing heads can be used per color, wherein UV inkjet printing heads 35, 35 for only two colors with a fixing station 36 arranged between them are shown by way of example. The fixing station can be provided between two printing heads or between two printing head rows with a different color in order to make possible printing the colors over even at high printing speeds without them running into each other (bleeding). Even an arrangement between the printing station or the last printing head or the last printing head row and the curing chamber is possible to achieve a temporary fixing, e.g., in order to fix the uppermost color layer. Such a printing device usually comprises, in as far as it is intended to be universally used, printing heads for the colors white, CMYK, full colors, transparent lacquer and the corresponding fixing stations between them. The fixing station 36 can also harden the ink printed by the first printing head by a UV lamp but is operated in this case at a lower W/cm.sup.2 performance than the UV lamp(s) of the following curing station according to the invention. The curing station can be constructed, for example, with a plane cooling surface or analogously to the curing chambers 1, 1 shown in FIGS. 1 and 2 with a cooling roller or from an appropriate mixture of different feature combinations according to the invention.

[0044] Subsequently, an optional control system 37 for the automatic testing of the print quality can also be provided in front of the output dancer rollers 38 and/or in front of an output-side splicing table 29 which comprises, analogously to the input-side splicing table 27, two printing web holders 39 and an adhesive roller holder 39. After having run through the printing product guide 40, the printing product 9 runs over a traction control 41 in order to properly adjust and control the traction tension present on the printing product before the printed web is wound up on the printing product roll 42.

[0045] FIG. 4 shows results of a comparison test of a curing chamber according to the invention which is operated with nitrogen and the results from a conventional operation with compressed air. The so-called SOZ (safe operating zone) performance of the UV lamps per cm.sup.2 of the irradiated surface was determined (y axis) at different run-through speeds (x axis) in which a reliable thorough curing was able to be determined after a passage of an irradiated, cylindrical plane with a length of, for example, 8 to 20 cm. The corresponding numerical values are listed in table 1. The SOZ performance corresponds to the performance which brings about such a thorough curing (complete polymerization) at the corresponding speed and which prevents the production of splashing, e.g., on the back side of a rolled-up sheet. It is clear here that for the curing under an atmosphere of nitrogen a performance (SOZ.sub.N2) can be adjusted at almost all through speeds which corresponds at the most to 50% of the performance (SOZ.sub.Air) necessary under cooling air, which is important for the rapid curing without damage of printed, temperature-sensitive plastic sheets.

[0046] The inflow surface of the jet for nitrogen was 0.2 mm300 mm in the present instance.

[0047] In order not to have to consider the thermal sensitivity of plastic sheets, the test was carried out on aluminum sheets b=260 mm, d=20 m which had been preprinted with Ascepte Extra Black, a black, UV-curing acrylate ink with several Norrish I photoinitiators with the surface covered. Compressed air and nitrogen were blown at a preliminary pressure of 6 bar via an air sword at the input of a chamber constructed analogously to FIG. 2 with two LED lamps offset in series as an air curtain or nitrogen curtain at an angle of 45 in the transport direction onto the printed surface of the sheet passing through, as a result of which, in combination with a suction removal, an excess pressure of 0.1-20 mbar was adjusted in the chamber. The diameter of the cooling cylinder was 84 mm, width 380 mm and the irradiated circumference has a length in the transport direction of ca. 122 mm at a looping angle of ca. 167. Basically, quite differently dimensioned cooling rollers are possible for such a use; however, cooling rollers with a diameter of 60 mm to 200 mm are advantageous based on the sheet thickness and the inertia forces which can still be readily controlled up to 200 mm. As regards the roller width, it is normally in accordance with the widest printing web to be printed. Refer for the rest to the above indications. A cotton rod (Q-tips) was pressed on and drawn over the printed surface directly after having passed the curing chamber, wherein the SOZ-UV performance was determined as the lowest performance at which no more color was transferred onto the small cotton rod. The performance was increased in Watt steps of 1.6 Watt/cm.sup.2, if necessary up to the maximum value of 16 Watts/cm.sup.2.

TABLE-US-00001 TABLE 1 V.sub.web [m/min] 10 20 30 40 50 60 SOZ.sub.Air [W/cm.sup.2] 4.8 5.0 8.0 9.6 11.2 >16 SOZ.sub.N2 [W/cm.sup.2] <1.6 <1.6 3.2 4.8 6.4 8.7

[0048] Analogous tests were also carried out with Ar and Ne as inert gases. The SOZ-UV performance was also able to be distinctly lowered with this compared to an air cooling; however, not quite to the same extent as with nitrogen.

[0049] Even though the present invention was described as above using different embodiments with partially different features, it is noted here that even other combinations which are not cited here, in particular embodiments with features which were cited only in conjunction with another embodiment, are also considered as being disclosed in accordance with the invention in as far as such a combination was not recognized at the start as illogical to a person skilled in the art.

LIST OF REFERENCE NUMERALS

[0050] 1, 1 curing chamber [0051] 2 2.sup.nd chamber wall [0052] 3, 3 IG outlet, air sword in/as the 3.sup.d chamber wall [0053] 3 3.sup.d chamber wall [0054] 4, 4 IG outlet, air sword in/as the 4.sup.th chamber wall [0055] 5 cooling surface, 1.sup.st chamber wall [0056] 5 cooling roller [0057] 5 cooling roller axis [0058] 6 side surface, section of the side surface of the 5.sup.th/6.sup.th chamber wall [0059] 7 guide means, upper/lower guide surface for printing product [0060] 8 contact pressure means, contact pressure roller for printing product [0061] 9 printing product [0062] 10 printed surface of the printing product [0063] 11 LED lamp, LED array [0064] 11 LED lamp, LED irradiator [0065] 12, 12, 12 jet [0066] 12 inlet surface [0067] 13, 13, 13 IG outlet opening [0068] 14 IG supply line [0069] 15 IG removal line [0070] 16, 16 flow guidance means in IG inlet [0071] 17 oxygen probe [0072] 18 dynamic seal, e.g. labyrinth, brush [0073] 19 static seal [0074] 20 compressor [0075] 21 inlet slot [0076] 22 outlet slot [0077] 23 printer [0078] 24 printing device [0079] 25 printing web [0080] 26 thickness measuring of the printing web [0081] 27 inlet dancer rollers [0082] 28 splicing table (inlet) [0083] 29 printing web guide [0084] 30 printing web cleaning station (opt.) [0085] 31 corona station (opt.) [0086] 32 printing web heating (opt.) [0087] 33 label edge &/or printing position sensor [0088] 34 printing device [0089] 35, 35 inkjet printing head [0090] 36 fixing station [0091] 37 optical testing device (opt.) [0092] 38 outlet dancer rollers [0093] 39 splicing table (outlet) [0094] 40 printing product guide [0095] 41 winding-up traction control [0096] 42 printing product roll [0097] 43 inlet/outlet unit [0098] 44 frame [0099] 45 frame foot