DE102009043518A1 - Inkjet printer for printing e.g. photo on e.g. thin label paper, has calendar unit arranged upstream to inkjet print head in production flow direction, and printing substrate printed by inkjet print head without interrupting production - Google Patents

Abstract

The printer has an inkjet print head (1) and a calendar unit including a calendar roller (2) and a counter-printing roller (3), where a calendar gap is formed between the calendar roller and the counter-printing roller. The calendar unit is arranged upstream to the inkjet print head in a production flow direction. A printing substrate (4) is placed in the calendar gap and directly printed by the inkjet print head without interrupting production. Sensors are arranged before and/or after the calendar unit, and detect a position of the printing substrate on conveyor belts (6-8). An independent claim is also included for a method for producing a printing product.

Description

The invention relates to an inkjet printer, a method of pretreatment of the printing medium (printing substrate) prior to inkjet printing and printed products, which were prepared by this method.

Inkjet printing is today technically sophisticated and is used in many applications, such as graphic printing or photo printing.

The ink jet printing unit consists of a large number of adjacent and possibly successively arranged printheads, wherein each printhead can again have a large number of individual nozzles from which the ink or the coating material is sprayed onto the printing material. Inkjet printers can be based on the valve technology (Valve technique). Such a printing system consists essentially of an ink system in which the ink or the coating material is kept under low pressure, an electronic control and a print head, which is usually connected via flexible lines with the other parts. The ink or paint is transported from the ink system to the printhead where it supplies the nozzle (s). These nozzles are again equipped with simple valves that can be opened and closed. When a drop is needed, the electronics opens the valve and the ink is squeezed out under pressure.

The other group of inkjet printers is based on impulse technology. There are two different types of technology: piezo technology and bubble jet technology.

In piezo technology, the ink or coating material is introduced into the nozzle under low pressure so that the ink or coating material is retained only by the surface tension in the nozzle. If a drop is needed, voltage is applied to a piezocrystal in the nozzle. As a result, the crystal bends or deforms, reduces the volume of the cavity and a drop is thrown out of the nozzle. The piezo crystal then returns to its original shape. The surface tension forces more ink or coating material from the ink supply to replenish the nozzle.

In bubble jet technology, an electrical voltage is applied to two poles. As a result of the resistance between the poles is so much heat that a vapor bubble is generated. As the bubble expands, it hurls an ink drop from the nozzle. When the voltage is no longer applied to the poles, the bubble collapses. Due to the surface tension, the nozzle fills again with ink or coating material.

The three technologies valve ink jet printing, piezo ink jet printing and bubble jet are subsumed within the meaning of the invention by the term ink jet printing or inkjet. The terms inkjet and inkjet are alternatively used within this specification and describe the same thing. Likewise, the terms ink, printing ink and ink are used equivalently in the context of ink jet printing. The term "inkjet device" or "inkjet printing device" is understood to mean the entire machine, consisting of the printing material guide, calendering, ink jet print head or drying and drying.

Sheet-fed sheetfed inkjet printers are well known. In most cases, the substrates are transported by vacuum belts through the print zone. The EP 1 097 821 B1 describes such a printer in which the transport of the substrate is carried out with a vacuum belt. Other embodiments of such transport systems are in the DE 101 08 931 A1 and in the EP 1 967 374 A1 disclosed.

In ink-jet printing, however, there is the challenge of trying to apply the smallest possible drops of ink to the substrate. The drop volume of modern inkjet printing systems is a few picoliters, since the resolution and the applied volume of ink are correlated in a certain way. Ink systems are also known in the market which apply varnishes to preprinted sheets for finishing, for example, to produce glossy effects selectively at selected locations. Such a method for inkjet finishing is in US Pat. No. 7,451,698 B2 explained.

In ink-jet color printing, there is a risk that the drops will run. For this reason, typical inkjet papers are provided with a Topcoating that gives the paper on the one hand a good smoothness and gives the reception and thus quick drying. A generic representative of such a printing material coating is inter alia in the EP 1 826 020 B1 disclosed.

One of the future trends in the printing industry, however, are hybrid printing systems in which different printing processes are combined in different sequential steps. For example, it makes economic sense if large static image content in a mass printing process, such as the Offset printing, are printed and then variable print contents are printed with an inkjet printer. Such, also economically successful combination of a static printing process (here web offset) with a variable printing process (ink jet printing) is among other things from the DE 10 20 2007 046 772 A1 known.

Another wide field of application for the combination of a static with a variable printing process lies in the refinement of a printed product, such as in the US Pat. No. 7,451,698 B2 disclosed. Nowadays, the so-called spot painting (partial image painting) is based on the paint application with flexo plates. Flexo plates are very expensive and usually require a day from exposure to assembly in the press. This gives the printer the flexibility to quickly respond to production changes. A flexible, digitally controlled coating application system, such as with an inkjet printer, offers cost and flexibility advantages.

However, the combination of a static printing process with an inkjet printing process leads to the fact that no special, suitable for inkjet printing or suitable substrates can be used. The large number of possible substrates thus rises sharply, from a thin label paper to a waste paper carton. In the publication of the Swiss printing UGRA research institute in St. Gallen, Switzerland "Roughness as a negligible influence of print quality", UGRA Mitteilungen 2004 , the authors write: "If one imagines the surface of paper and cardboard products to be greatly enlarged, this is roughly comparable to a mountain landscape. The topography of the surfaces (surface design) is characterized by valleys and "mountain peaks * of different depths or high. Depending on the surface structure of a paper, these values may be between 0.4 μm and 10 μm. [...] A good printing result can only be achieved if the layer thickness of the printing ink is not substantially thinner than the surface roughness of the paper surface. In the case of insufficient smoothness of the paper, this could only be compensated for by an increased consumption of printing ink, with an increased risk of kickback and puncturing. "

What applies to a great extent for conventional printing applies even more to inkjet printing. The small amount of drops in a very rough paper leads to print quality and gloss losses. The negative effect of paper roughness in the application of paints by the ink-jet process for finishing pre-printed products is even more pronounced since, in addition to the topography of the paper, the topography of the pre-printed ink is additionally added. In order to achieve a high gloss effect, this surface topography must be filled as completely as possible in order to achieve a very flat paint film with a high gloss. However, the high order quantities lead to high paint costs, reduced production speeds and insufficient order to undesirable and disturbing gloss differences on the sheet. In addition, the high order quantity usually causes a lower print resolution, d. H. fine details are displayed worse.

The object of the invention is therefore to provide a device and a method which makes it possible to work with a lower printing ink or paint (coating material) order or with a constant printing inks or paint (coating material) order a higher To achieve printing or paint quality.

This is achieved by the characterizing claims of the apparatus of claim 1 and the characterizing claims of the method of claim 15 and the printed products made by the process 16 - 19 , Meaningful developments emerge from the respective subclaims.

In 1 a first schematic embodiment of the inventive ink jet device is set forth. The sheet or sheet is substantially horizontal by means of the transport devices ( 6 . 7 . 8th ). The transport devices ( 6 . 7 . 8th ) consist of one or more circumferential bands. The conveyor belts may be, for example, perforated belts or a mesh belt, which make it possible to fix the sheet or the sheet on the upper run of the circulating belt. The fixation may, for example, by vacuum pass by a vacuum is built up below the upper run of the circulating belt, which acts through the openings of the belt on the substrate.

Prior to ink-jet printing or ink-jet coating with one or more inkjet printheads ( 1 ) essential to the invention, the sheet or the sheet is calendered under the action of pressure and optionally heat. The calendering takes place in a calendering plant consisting of a shiny metal roller ( 2 ), preferably with a low surface roughness, and a counterpressure roller ( 3 ), preferably with a polymer or rubber coating. In the calendering nip between the metal roller ( 2 ) and the counterpressure roller ( 3 ) the substrate (sheet, sheet) is introduced. The calendering pressure in the calendering nip leads to a surface smoothing of the printing substrate and the possibly preprinted printed image. The resulting surface smoothing causes the pressure point is better, ie the pressure point is less in the substrate, the gloss of the ink jet printing or the ink jet coating increases and overall a better printing or paint result is achieved with less ink or coating material use. The lower ink or coating material use leads to material savings and thus to cost reduction, but also to a higher productivity, since less ink or varnish must be applied. In addition, the required drying energy can be reduced due to the lower layer thicknesses of the ink jet application. The calendering prior to the inkjet printing therefore offers economic and qualitative advantages in ink-jet printing or in the inkjet coating.

The line load in the calendering nip between the rolls 2 and 3 can be chosen between 2 and 12 tons. As a rule, one roller of the calendering unit is fixedly mounted while the corresponding roller is pivoted against the fixed roller of the calendering unit. For the purposes of the invention, the metal roller ( 2 ) against the counterpressure roller ( 3 ) of the calendering unit or vice versa the counter-pressure roller ( 3 ) against the metal roller ( 2 ). The contact pressure can be achieved by a pneumatic, adjustable device. However, all other methods of force delivery are conceivable. At least the metal roller / calendering roller ( 2 ) of the calendering unit can be heated. In this case, temperatures between 30 ° and 80 ° Celsius, in special cases and with a suitable temperature up to 120 ° Celsius can be selected. The temperature should be monitored and regulated. The temperature of the calendering roll ( 2 ) can be done by the calender roll ( 2 ) is flowed through by a heated fluid. The fluid can be, for example, water or oil. The calendering roll ( 2 ) can also be heated indirectly by induction or heat radiation. Alternatively, a heating by a within the calender roll ( 2 ) located electrical heating. In a first version, the inkjet printing device has at least one alignment station ( 11 or 12 ), which aligns the substrate (sheet, sheet) at least laterally. The lateral alignment can be done by a stop against the substrate (sheet, sheet) is guided laterally and aligns with this. In addition, a leading edge alignment in the alignment can be done by the substrate (sheet, bow) preferably aligned with clocked retractable front stops. Alignment stations can be arranged in front of the calendering station (alignment station 11 ) and / or after the calendering station (alignment station 12 ). In a purely lateral orientation, the inkjet printing device has at least one sensor which provides a trigger signal for the drive device of the inkjet printheads (not shown).

In a second embodiment, the position of the printing material (sheet) is detected on the conveyor belt by a suitable sensor or sensors laterally and in the transport direction and passed these signals to a controller that makes corrections to the print head drive by image shifts that the print image within narrow limits always printed correctly on the substrate (sheet, sheet). Suitable sensors for this purpose are CCD cameras, CCD line, laser measuring method or any other suitable, sufficiently accurate measuring method.

The print image of the ink jet printer after the ink jet printing by a drying or hardening device ( 5 ) dried or hardened. The drying device ( 11 ) may be an infrared and / or convection dryer, or a UV dryer (UV lamp, UV LED). For the purposes of the invention, combination dryers consisting of different dryers with different curing and drying principles are also conceivable.

The feeding of the printing material ( 4 ) can be done by the substrate ( 4 ) in a de-stacking device with a suction head ( 9 ) or another suitable device from a stack ( 10 ) and supplied to the ink jet printing apparatus. Alternatively, the ink jet printing device can also be supplied directly from an upstream machine, for example a digital printing machine, in a production flow stream with printing material. In this case, the destacking device is eliminated.

The substrates ( 4 ) may be pre-printed in a different printing process when supplied to the ink-jet printing apparatus. Alternatively, the printing substrate may also be non-printed substrates if an exclusive ink-jet printing is desired.

Due to the calendering of the printing material according to the invention prior to inkjet printing, this can be more economical and more productive due to the lower required layer thickness, at the same time increasing the print quality. In the case of a gloss coating with inkjet printing higher and reproducible gloss levels are achieved because the substrate and print image topography is leveled to a certain extent. Calendering in the context of ink jet printing therefore brings considerable economic and qualitative advantages.

LIST OF REFERENCE NUMBERS

1

Inkjet printhead / ink jet printheads

2

Calender roll / metal roll

3

Backing roll

4

substrate

5

Dryers (UV and / or IR and / or convection)

6

conveyor belt

7

conveyor belt

8th

conveyor belt

9

unstacking

10

stack

11

aligning

12

aligning

13

position sensor

14

controller

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1097821 B1 [0008]
• DE 10108931 A1 [0008]
• EP 1967374 A1 [0008]
• US 7451698 B2 [0009, 0012]
• EP 1826020 B1 [0010]
• DE 10202007046772 A1 [0011]

Cited non-patent literature

• Research institute UGRA in St. Gallen, Switzerland "Roughness as a negligible influence of print quality", UGRA Mitteilungen 2004 [0013]

Claims (18)

Inkjet printing device for printing or coating sheet-form substrates ( 4 ), in which at least in the area of the Tintenstrahldruckopfs ( 1 ) or the inkjet printheads ( 1 ) the substrate ( 4 ) approximately horizontally under the ink jet printhead (s) ( 1 ) is passed through, and the substrate ( 4 ) on a circulating belt or circulating belts ( 6 ), characterized in that, in the direction of production flow, the ink jet print head ( 1 ) or the inkjet printheads ( 1 ) a calendering unit, consisting of a calendering roller ( 2 ) and a counterpressure roller ( 3 ), which together form a calendering nip, is arranged upstream, the printing substrate ( 4 ) is calendered in the calendering nip under the influence of pressure and optionally heat, and then by the inkjet printhead ( 1 ) or the inkjet printheads ( 1 ) is printed immediately without production interruption, Ink jet printing apparatus according to claim 1, characterized in that the line load in the calendering nip can be set between 2 and 20 tons, preferably between 2 and 12 tons, Ink jet printing device according to claim 1 and 2, characterized in that a roller of the calendering unit, consisting of a calendering roller ( 2 ) and a counterpressure roller ( 3 ), is fixedly mounted and the corresponding roller is swung against the fixed roller for the purpose of pressure build-up, Ink-jet printing device according to claim 1 and 2, characterized in that in the calendering roll ( 3 ), which acts against the substrate surface to be treated, is a tempered roller with a metallic surface, Inkjet printing device according to claim 4, characterized in that the surface temperature of the calendering roll ( 3 ) between 20 ° C and 120 ° Celsius, preferably between 20 ° C and 80 ° Celsius, Inkjet printing device according to claim 4 and 5, characterized in that the temperature of the calender roll ( 3 ) by a tempered fluid, for example water or oil, takes place, which flows through the roll body, Inkjet printing device according to claim 4 and 5, characterized in that the temperature of the calender roll ( 3 ) is carried out indirectly by induction or irradiation by heat radiation, Inkjet printing device according to claim 4 and 5, characterized in that the temperature of the calender roll ( 3 ) by a in the calender roll ( 3 ) located electric heating, Inkjet printing device according to claim 1 and at least one further of claims 2-8, characterized in that before and / or after the calendering station an alignment station ( 11 and or 12 ) is arranged, which the printing material ( 4 ) to at least laterally aligned by the substrate ( 4 ) is guided against a lateral stop or is pulled pneumatically against a lateral stop, Ink jet printing device according to claim 9, characterized in that in addition to the lateral alignment, an alignment at the leading edge takes place at stops which during the alignment process in the conveying plane of the printing material ( 4 protrude and after alignment below the conveying level of the substrate it ( 4 ) sunk or swung away, Inkjet printing device according to claim 1 and at least one further of claims 2-8, characterized in that before and / or after the calendering unit one or more sensors ( 13 ), which determine the position of the printing substrate ( 4 ) on the conveyor belt ( 6 and or 8th ), the signals are forwarded to a controller and there are determined position correction values, which are passed to the control of the ink jet head or the ink jet heads for correcting the drive signals, Inkjet printing device according to claim 1 and at least one further of claims 2-8, characterized in that the printing substrate ( 4 ) from a destacking device ( 9 ) from a stack ( 10 ) and supplied to the ink jet printing apparatus, Inkjet printing device according to claim 1 and at least one further of claims 2-8, characterized in that the printing substrate ( 4 ) is supplied from an upstream printing device directly, "inline", in a printing operation without interruption of production of the inkjet printing device, Process for the production of a printed product, characterized in that a printing material is calendered under the influence of pressure with a line load of more than 2 tons and the effect of heat and subsequently printed and / or painted in an ink-jet printing process, Method according to claim 14, characterized in that the printing substrate is previously printed in a printing method deviating from the ink-jet printing, subsequently calendered and then printed and / or painted in the ink-jet printing method, Printed product produced by the process according to claim 14 and 15, characterized in that the printing material was first printed in a digital toner printing process, for example in the xerographic process, then fed directly or via intermediate stack of the inkjet printing device, wherein in this the printed sheet (printed substrate) first calendered and then printed by ink jet printing and / or painted, Printed product produced by the method according to claim 14 and 15, characterized in that the substrate was first printed in the offset printing process, for example in sheetfed offset printing, then directly or via intermediate stack of inkjet printing device is supplied, in which the sheet (printed substrate) first calendered and subsequently imprinted and / or painted in the inkjet printing process, Printed product produced by the method according to claim 14, characterized in that the printing material of the inkjet printing device is supplied, in which the printing material first calendered and then printed in the ink jet printing process and / or painted.

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