DE102016214721A1 - Inkjet printing machine with at least two inkjet printheads - Google Patents

Abstract

An ink jet printing machine according to the invention comprising at least two ink jet printheads (11, 12, 13, 14), wherein a first printhead (11) comprises a first water based ink (11 ') and a second printhead (12) is different from the first water-based ink (12 ') on a substrate (2), eg A sheet of paper, printed, and with a dryer (20), which acts on the printed inks (11 ', 12') with electromagnetic radiation (25), is characterized in that the dryer (20) at least one of a laser different LED radiator (21), which acts on the first and the second ink (11 ', 12')) with the same narrow-band radiation (25) in the wavelength range between 350 nm and 405 nm. The cost effective invention allows to achieve a good drying result while preventing drying damage to the substrate and the inks.

Description

The present invention relates to an ink-jet printing machine with at least two ink-jet printheads having the features of the preamble of claim 1. Furthermore, the present invention relates to a method for drying water-based inks on a substrate having the features of claim 7.

The invention lies in the technical field of the graphic arts industry and in particular in the field of inkjet printing (inkjet). In the known DOD ink-jet printing method (drop-on-demand), a printed image is produced on a substrate or a printing material by a printhead correspondingly producing the finest ink droplets to the image to be printed and transferring them contactlessly onto the printing substrate. The substrate can be made of paper, cardboard, plastic or metal and be curved or web-shaped.

The invention also relates to the technical field of drying printing fluids on substrates, in particular of water-based inks on paper or cardboard. The drying is achieved by applying the electromagnetic radiation to the fluid. The fluid is heated and its solvent evaporated. For example, the use of infrared or IR radiation is known.

In known ink-jet Fujifilm, Japan, where water-based inks are being printed, the dryers are usually spaced far from the printheads. This is necessary because the drying is achieved by a combination of hot air and heat radiation. If the location of the drying were too close to the printheads, the printing process could be disturbed by air turbulence and, moreover, the heat to dry the inks on the nozzle surface of the printheads could lead to the drying of ink. A more compact design would be desirable.

Hot air drying and heat radiation not only heats the ink but also the substrate, which in the worst case can cause the unprinted areas to become too dry while the printed areas remain too wet. In the latter then there is the problem that the so-called paper coating of the substrate can be destroyed and this can lead to a corrugation of the substrate. Drying the ink at too long a time to apply the ink may also cause water from the ink to penetrate too much into the substrate, significantly disturbing the structure of the substrate, such as its fiber structure or coating. This can also cause the substrate to become wavy. The waves of the substrate is not reversible and leads to the further disadvantage that a printing of the back of the substrate is not or only possible with inferior quality. An effective prevention of these problems would be desirable.

From the DE 103 16 471 A1 is a method for drying a printing ink on a substrate known which uses laser light sources. In this case, offset printing inks are exposed to laser light, whereby the color pigments of the offset printing ink absorb the radiation. The document calls for the color yellow (yellow) a wavelength range of 400 ± 100 nanometers and thus ultraviolet radiation.

Also the JP 2007/245374 (A) discloses drying in the UV range. Here, in the inkjet process applied fluids are exposed to radiation from LEDs. It is mentioned that color pigments absorb the radiation, but details of UV radiation, for example their wavelength, are lacking.

In view of the cited prior art and the problems indicated, it is an object of the present invention to provide a prior art improved ink jet printing machine which is inexpensive and achieves good drying results while minimizing drying damage to the substrate and to the substrate Pressure fluid, in particular the ink can be prevented. In particular, a wave of the substrate and a burning of the substrate or the ink to be prevented. It is also an object of the present invention to provide a corresponding method.

Inventive solutions of this object are given with an ink jet printing machine having the features of claim 1 and a method of drying with the features of claim 7.

An ink jet printing machine according to the invention comprising at least two (or four, CMYK, or seven, CMYKOGV) ink jet printheads, wherein a first printhead has a first water-based ink and a second printhead has a second, non-aqueous second water-based ink on a substrate, e.g. a paper sheet, printed, and with a dryer, which acts on the printed inks with electromagnetic radiation, characterized in that the dryer at least one, different from a laser LED spotlight (or an LED spotlight row or an LED spotlight Field), which applies the same narrow-band radiation to the first and second inks in the wavelength range between 350 nanometers and 405 nanometers.

The device according to the invention makes it possible in an advantageous manner to achieve good drying results and at the same time to prevent damage due to drying on the substrate and on the pressurized fluid. In addition, it is inexpensive to produce and operate. According to the invention, the use of expensive laser emitters or laser radiation is dispensed with. As a result, the disadvantage can be avoided that special, matched to the laser wavelength absorber must be provided in the colors. Such special absorbers can have a negative effect on the color of the color and thereby lead to noticeable disturbances of the printed image. Instead, the invention uses different, less expensive LED emitters from a laser. In particular, IR lasers operating at wavelengths longer than that of the visible spectrum are used, but (non-laser) LED emitters operating at shorter wavelengths than the visible spectrum, preferably in the UV range.

According to the invention, such a radiator is used not only to dry an ink but at least to dry (preferably simultaneously and preferably at the same drying location within the machine) two inks. Or vice versa: for the drying of two or more inks, only one dryer is required according to the invention. This measure is also associated with cost savings in an advantageous manner.

The narrow-band wavelength range which can be used according to the invention is between 350 nanometers and 405 nanometers. In this UV range, in the case of the chromatic colors (CMY), there is an absorption by the color pigments present. Extensive measurements with different inks (chromatic colors CMY and black ink K) in the wavelength range between 300 nanometers and 800 nanometers have revealed that in this limited UV range alone by the existing color pigments sufficient absorption and thus sufficient for the physical drying Coupling of heat into the ink via the UV radiation is possible. At the same time can be effectively prevented by the relatively narrow spectrum of UV radiation that the radiation heats the substrate material or water in the substrate. In the investigations, it was also revealed that no substantial absorption by the water or the material of the substrate takes place in the limited UV range. Unprinted areas are thus not heated.

Advantageous and therefore preferred developments of the invention will become apparent from the dependent claims and from the description and the accompanying drawings.

A preferred embodiment of the invention may be characterized in that the dryer comprises a plurality of LED emitters, wherein at least two LED emitters emit the same radiation, that is, substantially the same wavelength. Particularly preferred is the use of identical LED emitters, since this can reduce the cost of production for the printing press according to the invention. The plurality of radiators may also be provided as a so-called array (one or preferably two-dimensional). Such an array can in turn be modularly constructed of emitter units. Preferably, all radiators of the dryer generate UV radiation between 350 nanometers and 405 nanometers. Preference is given to two to six consecutively arranged, (with respect to the substrate format) page width, modular LED arrays. Each of these arrays preferably irradiates a page-wide strip of an extent of 40 mm to 120 mm in the printing-material transport direction. The individual modules are (transversely to the transport direction) preferably about 20 mm to 30 mm wide. A separate control of the modules also allows format adaptation.

A preferred embodiment of the invention may be distinguished by the fact that the first ink comprises a first pigment and the second ink comprises a second pigment different from the first. The inks may thus have different colors, e.g. C, M, Y or K. It has surprisingly been found in the context of the above-mentioned multiplicity of printing tests that in the limited wavelength range also different inks, and in particular multicolour CMY, with different pigments each have an absorption of UV radiation which is sufficient for the required drying. Have radiation. In addition, the inks and their pigments absorb the radiation in the limited wavelength range approximately equally. On additional and expensive absorber in the inks can therefore be dispensed with in an advantageous manner.

A preferred embodiment of the invention can be characterized in that between the printhead and the dryer a shield, e.g. a shielding plate is arranged, which prevents water vapor (evaporated solvent of the ink due to drying) and / or drying radiation from reaching the print head. In this way, an increased cleaning effort or damage to the print head can be prevented.

A preferred embodiment of the invention may be characterized in that the dryer has a surface in which a plurality of LED radiators and a plurality of air nozzles, in particular blowing nozzles and / or suction nozzles, are arranged. Such a design is characterized by a high compactness and therefore requires little space in the machine. In addition, such an integrated design can be easily cleaned and maintained. However, a great advantage results from the fact that a (quasi-) homogeneous radiation field and at the same time a tuyere field integrated into the homogeneous radiation field can be realized. The supplied and preferably dry and heated blowing air serves to remove vaporized solvent from the ink. In addition to the blowing nozzles provided for this purpose, suction nozzles (in the field or at its edges) may also be provided. The tuyeres can also form a (quasi-) homogeneous field which overlaps with the (quasi) homogeneous field of LEDs. The printed and dried sheet is thus (quasi) homogeneously exposed to the UV radiation and the evaporated solvent, in particular water, is guided (quasi) homogeneously away from the printed substrate.

A preferred development of the invention may be distinguished by the fact that the dryer is arranged downstream of the last print head. The distance from dryer to print head is preferably chosen as small as possible, so that the drying time is also as close to the time of printing. Undesired (deep) penetration of water from the ink into the substrate can be effectively prevented in this way.

A process according to the invention for drying water-based inks on a printing substrate is a process in which at least two inks, which comprise different pigments, are exposed to the same narrow-band radiation (preferably at the same drying location and preferably at the same drying time), the radiation being in the wavelength range between 350 nanometers and 450 nanometers.

The method according to the invention also leads to the same advantages as described above with reference to the device according to the invention.

A preferred embodiment of the invention may be distinguished by the fact that the pigments absorb the radiation (or at least a portion of the radiation sufficient for a physical drying).

A preferred development of the invention can be distinguished by the fact that the inks, apart from the pigments, do not comprise any absorbers which absorb a significant portion of the radiation. In this way, inks can be produced and processed inexpensively, and it is also possible to prevent the color locations of the inks from being appreciably changed by additional absorbers.

A preferred embodiment of the invention may be distinguished in that the inks each comprise at least one absorber which is different from the respective pigments and which absorbs a substantial portion of the radiation, the ink being a colorless ink or a white ink is magenta or a purple ink. It is preferred to dispense entirely with additional absorbers, but it may be necessary or at least helpful in certain ink colors ("transparent", white, magenta, violet) to use an absorber. When printing with e.g. seven colors (K CMY OGV) may e.g. be advantageous to provide only for the inks magenta M and / or violet V absorber, black K, cyan C and yellow Y, as well as orange O and green G without additional absorber use. Opaque white and colorless lacquer, if used, would however be equipped with absorbers if necessary.

A preferred development of the invention can be characterized in that the absorption initiates a physical drying of the two inks, wherein there is a heating of the two inks and evaporation of water from the two inks. Although UV radiation is used in the present invention, the drying of the inks is not chemical, i. by polymerization, but physically, i. by evaporation of the solvent.

A preferred embodiment of the invention may be distinguished by the fact that the radiation lies in the (narrower, or more limited) wavelength range between 375 nanometers and 405 nanometers. This part of the radiation has proven to be particularly favorable in the context of extensive pressure tests.

A preferred embodiment of the method according to the invention can be characterized in that the irradiance is in the range of 12 W / cm ² to 50 W / cm ² , preferably in the range of 20 W / cm ² to 25 W / cm ² . It has been determined in extensive experiments that the surface power density for irradiating the water-based inks must not be too high in order not to dry the inks too quickly. However, for a certain time, about 0.1 s to 0.5 s, the ink layer should be heated sufficiently and remain hot so that the water can evaporate well and sufficiently. The preferred area power density is about 25 W / cm ² , which is a value that can be achieved with available high power UV LED spotlights.

A preferred embodiment of the invention may be characterized in that the Energy input in the range of 1 J / cm ² to 10 J / cm ² , preferably in the range of 2.5 J / cm ² to 4.5 J / cm ² .

The invention and its advantageous developments are described below with reference to the accompanying drawings with reference to preferred embodiments, in the drawings, corresponding elements are each provided with the same reference numerals.

1 : schematic side view of a preferred embodiment of a printing press according to the invention in carrying out the method according to the invention;

2 : schematic plan view of a dryer of a preferred embodiment of a printing press according to the invention; and

3 : schematic plan view of an alternative dryer of a preferred embodiment of a printing press according to the invention

1 shows a printing machine according to the invention 1 , in which a sheet-shaped substrate 2 by means of a cylinder 3 and its gripper 4 in a transport direction 5 is moved. The substrate or the substrate can be made of paper, cardboard, plastic film, metal foil or metal sheet. Alternatively, the printing material can also be web-shaped. The substrate may also be permanently curved, eg an object surface.

The printing press 1 includes a first station 10 , which may also be referred to as a printer or a printing unit. This includes a first printhead 11 , a second printhead 12 , another, third printhead 13 and another, fourth printhead 14 , All printheads are controlled by a controller 15 controlled such that these together a (preferably multi-colored) printed image on the substrate 2 produce. The printheads 11 to 14 are formed as ink-jet printheads and eject each ink 11 ' . 12 ' . 13 ' and 14 ' , eg in the order KCMY. It contains the first ink 11 ' a first pigment, the second ink 12 a second pigment 12 ' and so on. The inks ejected from the printheads are water-based inks, that is to say, inks which are primarily built up on the solvent water and have to be heated for drying.

Furthermore, the printing press includes 1 a second station 20 , which can be referred to as a dryer or drying plant. This station in turn includes a first LED spotlight 21 , another, second LED spotlight 22 , another, third LED spotlight 23 and another, fourth LED spotlight 24 , The dryer has at least the first LED emitter 21 on, the other LED spotlights 22 to 24 are optional. The LED emitter (s) apply electromagnetic radiation to the printed inks 25 , The radiation is narrow-band radiation in the wavelength range between 350 nanometers and 405 nanometers. The radiation is from the pigments 11 ' . 12 ' . 13 ' and 14 ' absorbs and results in heating of the ink 11 . 12 . 13 and 14 or the water contained therein. The latter vaporizes and the inks dry.

Furthermore, the second station includes 20 blowing devices 26 and suction devices 27 , By means of the blowing devices blowing air is in the range of drying (drying location) between the radiators and the substrate 2 blown and by means of the suction devices, the supplied air together with water or water vapor 27 ' sucked off again. The water vapor is generated by the irradiation of the LED radiation 25 on the printed inks 11 . 12 . 13 and 14 from which the solvent evaporates water. The LED emitter (s) are controlled by a control device 28 controlled such that on the substrate 2 applied inks are dried sufficiently in the drying area. Sufficient drying can already be present when the inks have dried to the extent that a stacking of printed substrate sheets or if further processing in a post-processing machine is possible.

Between the first station 10 and the second station 20 can be a shield 29 be provided. The shield prevents water or water vapor and / or radiation 25 from the area of the second station 20 in the area of the first station 10 arrives. Both the water vapor and the radiation, could lead to disturbances or even damage to the printheads.

The first station 10 and the second station 20 may also include respective housings enclosing the printheads or dryer and the cylinder 3 are open.

In the 2 is the second station 20 shown in plan view, wherein a substrate 2 below the LED spotlight 21 to 24 is recognizable. Between the LED spotlights are blowing devices and suction devices 26 respectively. 27 arranged such that an air flow between the LED radiators and the printing material through (at the place of drying over) is passed and the water vapor formed during drying 27 ' effectively dissipates from this area. The facilities 26 and 27 are preferably formed as slit nozzles.

An alternative embodiment of the second station 20 or of the dryer is in the plan view of 3 shown. The dryer 20 has an area 20 ' on, in which a field 30 is arranged by LED spotlights. In addition, in the area 20 also a number or a field of blowing devices 26 , in particular round nozzles, arranged. The area 20 ' is from suction devices 27 surround. According to this embodiment, surface irradiation and surface blowing of the inks to be dried is possible. In this case, the water vapor laxative air flows outwards and is there via the suction devices 27 dissipated. Alternatively, it is also possible in the area 20 ' in addition to the blowing devices 26 also a number or a field of suction devices 27 provided.

LIST OF REFERENCE NUMBERS

1

 press

2

 substrate

3

 cylinder

4

 grab

5

 transport direction

10

 first station / printer

11

 first printhead

11 '

 first ink, first pigment

12

 second printhead

12 '

 second ink, second pigment

13

 another (third) printhead

13 '

 another (third) ink, third pigment

14

 another (fourth) printhead

14 '

 another (fourth) ink, fourth pigment

15

 first control device

20

 second station / dryer

20 '

 area

21

 first LED spotlight

22

 further (second) LED spotlight

23

 another (third) LED spotlight

24

 another (fourth) LED spotlight

25

 LED radiation

26

 blowing devices

27

 suction devices

27 '

 Water / steam

28

 second control device

29

 shielding

30

 LED field with LED spotlights

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

• DE 10316471 A1 [0006]
• JP 2007/245374 A [0007]

Claims (14)

Inkjet printing machine with at least two inkjet printheads ( 11 . 12 . 13 . 14 ), wherein a first print head ( 11 ) a first water-based ink ( 11 ' ) and a second printhead ( 12 ) a second water-based ink other than the first ( 12 ' ) on a substrate ( 2 ) and with a dryer ( 20 ), which prints the printed inks ( 11 ' . 12 ' ) with electromagnetic radiation ( 25 ), characterized in that the dryer ( 20 ) at least one, different from a laser LED spotlight ( 21 ) comprising the first and second inks ( 11 ' . 12 ' )) with the same narrow-band radiation ( 25 ) is applied in the wavelength range between 350 nm and 405 nm. Ink jet printing machine according to claim 1, characterized in that the dryer ( 20 ) a variety of LED spotlights ( 21 . 22 . 23 . 24 ), wherein at least two LED spotlights ( 21 . 22 . 23 . 24 ) the same radiation ( 25 ), ie essentially the same wavelength, emit. Ink-jet printing machine according to one of the preceding claims, characterized in that the first ink ( 11 ' ) a first pigment ( 11 ' ) and the second ink ( 12 ' ) a second different pigment from the first ( 12 ' ). Ink-jet printing machine according to one of the preceding claims, characterized in that between the print head ( 11 . 12 ) and the dryer ( 20 ) a shield ( 28 ), which prevents water vapor and / or radiation to the print head ( 11 . 12 ). Ink jet printing machine according to one of the preceding claims, characterized in that the dryer ( 20 ) an area ( 20 ' ), in which a plurality of LED emitters ( 30 ) and a plurality of air nozzles, in particular blowing nozzles 26 and / or suction nozzles 27 , are arranged. Ink jet printing machine according to one of the preceding claims, characterized in that the dryer ( 20 ) the last print head ( 14 ) is subordinate directly. Process for drying water-based inks on a printing substrate, wherein at least two inks ( 11 ' . 12 ' ), which differ from each other pigments ( 11 ' . 12 ' ), with the same narrowband radiation ( 25 ), the radiation ( 25 ) in the wavelength range between 350 nm and 405 nm is located. Process according to claim 7, characterized in that the pigments ( 11 ' . 12 ' ) the radiation ( 25 ) absorb. Method according to claim 8, characterized in that the inks ( 11 ' . 12 ' ) except the pigments ( 11 ' . 12 ' ) do not comprise absorbers containing a substantial proportion of the radiation ( 25 ) absorb. Method according to claim 7, characterized in that the inks ( 11 ' . 12 ' ) at least one of the respective pigments ( 11 ' . 12 ' ) comprise various absorbers, which absorb a substantial portion of the radiation ( 25 ), whereby the ink ( 11 ' . 12 ' ) is a colorless ink, a white ink, a magenta or a violet-colored ink. Method according to one of claims 7 to 10, characterized in that the absorption of a physical drying of the two inks ( 11 ' . 12 ' ), causing the two inks ( 11 ' . 12 ' ) and evaporation of water ( 15 ) from the two inks ( 11 ' . 12 ' ) comes. Method according to one of claims 7 to 11, characterized in that the radiation ( 25 ) is in the wavelength range between 375 nm and 405 nm. Method according to one of claims 7 to 12, characterized in that irradiance in the range of 12 W / cm ² to 50 W / cm ² , preferably in the range of 20 W / cm ² to 25 W / cm ² . Method according to one of claims 7 to 13, characterized in that the energy input in the range of 1 J / cm ² to 10 J / cm ² , preferably in the range of 2.5 J / cm ² to 4.5 J / cm ² ,

Images