DE102013021552A1 - Applying water or solvent based hydraulic fluid i.e. ink on printing substrate e.g. sheet to form multi colored image, by applying fluid on intermediate carrier or substrate by inkjet heads, heating and evaporating water or solvent content - Google Patents

Abstract

Applying hydraulic fluid on a printing substrate, comprises applying a water-based or solvent-based hydraulic fluid either on an intermediate carrier (2) or directly to the printing substrate using one or more inkjet heads (16a-e), and heating the hydraulic fluid and evaporating amount of water or solvent content in the hydraulic fluid, where wet air arising under inkjet heads and solvent-containing air arising in close proximity to the inkjet heads are replaced by dry air. An independent claim is included for a device for carrying out the above method, comprising a squeegee (30a-e), by which flow of the wet air or solvent-containing air is interrupted to the intermediate carrier or the printing substrate.

Description

The present invention relates to a method for applying printing fluid to a printing material having the features of the preamble of claim 1.

Various methods and devices for the so-called indirect inkjet are known from the prior art. In this case, a plurality of inkjet inks or inks are applied by means of successive inkjet printheads on a rotating intermediate carrier according to the printed image, d. H. aufgejettet. From this intermediate carrier, z. As a transfer belt or a transfer cylinder, the inks or the multi-color print image on the substrate, z. B. a paper sheet or a paper web transferred. The paint is thus not directly, but indirectly over the surface of a transfer device to the substrate. This surface must therefore be so designed or treated that the necessary color transfer is possible, d. H. she must accept the color and the - if necessary treated, z. B. hardened - can give paint again.

In the US 2008/0166495 A1 is z. B. discloses such a machine for indirect inkjet printing. This comprises a central circulating transfer belt as an intermediate for the inks, which are jetted by four printheads on the tape. Before the ink application, a coating liquid is applied to the tape by means of a separate applicator. After ink application, the ink on the belt is exposed to radiation from a radiation source and thereby dried. Subsequently, the transfer of the dried inks or the printed image takes place in a heated printing nip on a substrate web, on which the ink. finally heat treated again. The tape is cleaned by a cleaning device before re-inking.

From the US 7661809 B2 For example, a similar machine is known which, however, has a central transfer cylinder instead of a belt and prints with water-based inks.

When printing with water-based inks in the indirect inkjet printing process, considerable amounts of water must be evaporated within a short time in order to dry the printing liquid so that the unvaporized residue in the printing nip can be transferred to the printing substrate or the paper. As a rule, this is a polymer which carries the dye or the pigments dispersed therein or adhering thereto. These amounts of energy are supplied by heat, infrared radiation, etc. and strongly heat the surface of the intermediate carrier. The inkjet head, however, or its nozzle openings have only a very small distance of typically 1 mm to the surface of the "hot" subcarrier. As a result, the moisture of the evaporating water portion of the ink deposits on the cooler inkjet head, adversely affects the jet performance of the nozzles, or causes water stains in the inkjet image as the condensate drips onto the subcarrier belt.

This condensation problem is hard to get a grip on. Although you could try the inkjet heads operate at a higher temperature to prevent condensation of water vapor from the ink. However, this in turn requires the formulation of higher-boiling inks or the addition of higher-boiling solvents, which must be removed in the subsequent drying process by additional measures from the subcarrier.

Even with direct inkjet printing, there is the problem that the ink mist or the amount of water in the ink is deposited on the printheads. In the EP 2436519 an inkjet printer is described in which before, behind or even between the individual printheads cooled areas are provided, where the moisture should deliberately precipitate, so they do not get on the inkjet heads. However, this method is not particularly effective, especially with high throughput inkjet printers. Furthermore, it is from the JP 2005-212323 (A) for large format inkjet printers known to remove the resulting ink mist by a directed to the underside of the printhead blower. However, this measure alone can not reliably prevent the condensation of solvent or water vapor at the print head.

From the JP 6064159 (A) It is known to suck and condense the solvent in a solvent-based inked encapsulated indirect inkjet printer to prevent it from leaking to the outside. However, the problem of condensation of solvent on the inkjet head is not addressed there.

It is therefore the object of the present invention to provide a method which is also suitable in particular for indirect inkjet printing with water-based or solvent-based printing fluids, with which the problems described above can be avoided or at least mitigated by, for example, the extent of condensation of water or solvent on the inkjet heads is significantly reduced.

This object is achieved by a method having the features of claim 1. A suitable device is in Claim 7 specified. Advantageous developments of this invention will become apparent from the accompanying dependent claims and from the following description and the accompanying drawings.

According to the invention, therefore, a completely different approach is taken and instead the moist or solvent-containing air is replaced by dry air immediately before the respective inkjet printheads.

In this case, the moist or solvent-containing air which is produced when the conditioner or the ink reaches the hot surface of the intermediate carrier or the printing substrate expediently is sucked out there and immediately afterwards replaced by dry air blown onto the surface. Here, the use of a doctor blade is expedient, which prevents a drag flow of moist air formed by the moving subcarrier belt and passes to the inkjet print head following in the direction of movement. This squeegee can be either a mechanical squeegee, which is placed at a very short distance contactless in the manner of a shoe over the entire width of an inkjet print head in front of this, or even an air knife by dry air before the next inkjet print head so on Intermediate carrier is inflated so that no moist air enters the space between the bottom of the printhead and the top of the intermediate carrier belt or in the case of direct inkjet, the printing substrate.

In the case of a mechanical squeegee, the underside of the doctor blade can be formed as a so-called labyrinth seal, which prevents a laminar drag flow of moist air forms under the doctor blade.

All this helps to prevent the condensation of moisture or solvents on the inkjet heads in the beginning.

Hereinafter, the invention will be described in more detail with reference to FIGS 1 - 3 of the accompanying drawings. The 1 shows the embodiment of an apparatus for the indirect inkjet with the method of the invention can be carried out in a schematic view, the 2 shows the environment of the inkjet heads 16a and 16b on 1 in greater detail on an enlarged scale, the 2a shows the lower part of the squeegee 30a out 2 on an enlarged scale, the 2 B is a schematic view of the squeegee 30a with the air duct located behind it 53 in the direction of movement of the tape 2 and the 3 shows an embodiment of a device for drying the under the Inkjetköpfen 16 resulting moist air.

The device described in the figure 1 for four-color printing in the indirect inkjet printing process comprises a circulating belt 2 which is around two cylinders 3 and 4 as well as a guide surface 5 is guided. At least one of the two cylinders is powered by an engine 6 powered and in turn drives the tape. The guide surface serves to stabilize the run of the band 2 in the area of the print job.

The substrate is in the form of individual sheets of a plant stack 7 to a delivery pile 8th transported. The transport is over as lines 9 and 10 simplified illustrated bow guides (in fact, it can be one or more transport cylinder) and by means of the sheet transport cylinder 11 . 12 and 13 , The latter have gripper systems 42 for the printing material sheets 43 on. Every single sheet 43 goes through a pressure gap 44 between the cylinders 13 and an employed on this press roll 14 , The drive of this sheet transport system via at least one motor 15 ,

Adjacent to the strand of the band 2 are several inkjet printheads 16a to 16d in the direction of movement of the tape 2 arranged one behind the other, for. B. Printheads for the common colors cyan, magenta, yellow and black. Each printhead makes drops with a water-based ink 45 , which are jetted on the tape and create there color dots. In this way, multicolored rasterized printed images can be created. However, it can also be provided that the color drops of a color run at least in places into one another and therefore form closed color areas. Since the printheads are arranged consecutively in the direction of the tape, the different color dots come to lie partly on each other. It can be provided that the printheads 16a to 16d a device 16e for post-treatment, z. B. for painting or paint application, is arranged downstream.

Also adjacent to the band 2 is a device 17 for strip treatment, z. B. for plasma treatment arranged. By means of the plasma or a corona discharge, the strip surface can be cleaned and added to a surface state defined for the application of liquid media with respect to the surface energy. Furthermore, it is adjacent to the band 2 a device 18 intended for applying conditioner. The conditioner causes the belt surface to accept the ink, the ink on the belt does not undesirably spread or bead, the ink adheres to the belt during belt transport, and the ink in the nip 44 on the substrate 44 can be transferred. The conditioner is like the ink also for the most part from water in which certain additives, eg. B. salts are dissolved, the tape 2 give the desired surface property.

The on the tape 2 applied ink 46 is by a hot air jet of a hot air dryer 19 at least partially dried by evaporating water and / or solvent from the ink. The hot air is supplied via a feeder 20 supplied and the steam resulting from the drying is via a in a housing 21 integrated air extraction 22 dissipated.

For further treatment is another dryer 23 , Preferably, an infrared dryer, provided, which the already dried ink, the conditioner 47 and / or the band 2 heated immediately before and / or in the region of the pressure nip. By this mention and the concomitant influence on the adhesion of the ink on the tape and the printing material sheet 44 It is achieved that the dried ink and thus the printed image substantially completely detached from the tape and deposited on the substrate. Optionally, another, the pressure nip 44 downstream dryer 24 be provided, which further heats the transferred print image and thereby finally dries and / or hardens by radiation.

Since it is beneficial for the overall process, the on the tape 2 jetted ink 46 to maintain at or above a certain temperature level and to provide sufficient heat energy in the belt 2 can enter optional heating devices 25 . 26 . 27 and or 28 be provided, which is the cylinder 3 and 4 to temper from inside or outside. Likewise, the press roll 14 be heated.

However, the measures described also have the consequence that the band 2 heats up during printing or is already hot when it is under the device 18 and the printheads 16a -D walks by.

A device 29 , z. As a camera, to inspect the image is also adjacent to the tape 2 arranged. With it can be determined via an image acquisition and evaluation, whether that on the tape 2 generated print image meets the quality requirements or z. B. has undesirable errors. The resulting knowledge can be used to improve the printing process, eg. B. the order of the conditioner 47 , the order of the ink drops 45 and / or the performance of the dryer 19 adapt or regulate.

Optionally, in the field of sheet feeding or removal devices 31 and 32 for inspecting the bow and / or a device 33 for the pretreatment of the bow, z. B. by a primer application, and / or a device 34 for the aftertreatment of the sheet, z. B. by further drying, provided.

A device 35 for cleaning the tape 2 is located adjacent to the belt and is used to remove any possible debris from the belt. These may be due to residues of the primer, the printing substrate, the conditioner and / or the dried ink. The cleaning device may comprise a cleaning roller engageable with the belt and a cleaning fluid supply.

The in the facility 1 intended for consumption liquids are provided in respective storage containers: reservoir 36 for cleaning fluid, reservoir 37 for conditioning fluid, reservoir 38 for multiple inks, and storage tanks 39 for primer fluid. The containers and the associated application devices are connected via supply lines, not shown.

A device 40 , z. As a central computer, to control the device 1 controls the individual components of the device, in particular the printheads 16a to 16d and the dryers 19 and 23 , The control device is preferably with all components 6 . 15 to 20 . 22 to 39 and 41 via data lines not shown in connection. component 41 is a device for changing the tape 2 , which allows you to swap the existing band for a new one as the band quality decreases.

In the movement area of the band 2 in front of the respective inkjet printheads 16a to 16e are five each extending over the width of a printhead doctor 30a to 30e arranged. These squeegees are essentially made of sheet metal and have as the more detailed representation of the 2 emerges from the tape 2 facing end of a "shoe-soled" section 51 , where the "shoe sole" as in 2a shown with several transverse to the direction of the tape 2 extending channels may be provided to improve in this way the sealing effect of the doctor blade underside against the tape top.

The airspace in front of the squeegees 30a -E stands with the air suction 22 in connection, from the steam-laden moist air from the hood 21 enclosed area of the printing device is sucked. This extraction can be done by additional fans 55 between the backs of the inkjet heads 16 and the front sides of the squeegees 30a -E be supported.

The squeegee 30a -E can be heated to prevent moisture from condensing on them and the band passing underneath 2 drips.

Immediately behind the squeegees 30a -E, again seen in the direction of movement of the tape 2 , the extracted moist air is replaced by dry air, by a blower 52 through a separate channel system 53 blown in, which is in the area of the printheads 16a -E according to the dimensions of the squeegees 30a -E widened, like that in the 2 B outlined. This dry air now enters the area between the underside of the print heads instead of the moist air, as shown by the arrows 16a -E and the surface of the tape 2 , The dry air can be warm air, which can absorb a correspondingly higher amount of moisture and thus absorb the evaporating moisture from the water-based ink when the ink drops 45 on the hot surface of the tape 2 incident. The so charged with moisture air is then again in front of the next direction of movement squeegee z. B. 34b sucked off and can not at the following printhead z. B. 16b knock down. Instead, in front of this printhead, dry air is also returned via the piping system 53 on the surface of the tape 2 inflated.

The dry air can be removed from an air handling unit, not shown here, which is placed next to the printing device. However, it is also possible to generate the dry air by removing the air from the air 22 blown moist air like in the 3 represented by a capacitor 60 is passed, in which the air is cooled, so that the moisture condenses out there. The waste heat of the compressor 61 who is the condenser 60 operates, in turn, in a heat exchanger 62 be used to reheat the dried air and thus improve their ability to absorb moisture. After passing through the heat exchanger 62 Then the dried and reheated exhaust air through the blower 52 and the pipe system 53 the inkjet printheads 16 fed.

By at the bottom of the printheads 16a -E air flowing past, however, become the ink drops 45 in the direction of movement of the tape 2 distracted and the stronger, the smaller the droplets are. As a result, an inhomogeneous print image results from the mispositioning of these smaller drops. This effect is all the more pronounced the farther the printheads from the surface of the tape 2 are arranged away, ie the longer the trajectory of the droplets 45 is. This effect is counteracted by the fact that the deflection of the droplets, depending on the droplet size, is already taken into account in the raster image processor, by means of which the image data with which the print heads are generated 16a -E are controlled. This happens in the way that the printheads 16a -E are instructed to jet smaller droplets earlier than their geometric position.

This measure is set a limit that a minimum distance to the previous drop, by the formation of the control electronics for the printheads 16a -E is predetermined, can not be fallen below. However, it is also possible to jettify the predecessor drops a little earlier if this is possible from the printed image. This can be taken into account in the raster image processor by optimizing the finished ribbed print image nozzle-wise with regard to the optimal locations of incidence of the ink droplets 45 on the surface of the tape 2 with the aim of homogenizing the printed image.

The inventive method is carried out as a whole in several process steps as follows. It becomes an intermediary 2 , in particular the band shown or alternatively a cylinder provided. It becomes a water-based conditioner in a reservoir 37 provided and by a device 18 on the surface of the intermediate carrier 2 applied. Preferably, the conditioner is passed through the device 18 sprayed on and wets the surface of the subcarrier 2 at least in the print image areas completely and forms there a release layer. In the storage containers 38 One or more differently colored inks are provided in the colors cyan, magenta, yellow and black, and with the print heads 16a to 16d in the form of drops 45 on the wetted surface of the intermediate carrier 2 applied according to the printed image. With the hot air dryer 19 and / or with the infrared dryer 23 is the applied pressure fluid on the rotating intermediate carrier 2 heated while the solvent components of the hydraulic fluid, usually also water, expelled or vaporized.

Subsequently, the dried ink existing print image in the nip 44 on the printing substrate 43 transfer. These are essentially the polymers and dyes that were dissolved in the ink and after drying form a thin, plastic film extending from the surface of the belt 2 detached and on the fibers of the printing substrate 43 tacking.

Condensation of the water components of the conditioner and inks is prevented by immediately removing the evaporating moisture from the belt 2 is sucked off and replaced by dry air.

The invention has been described above with reference to a device for indirect inkjet printing. However, it is also possible to use the described measures in direct inkjet printing process to avoid the described problem of condensation of moisture or solvents on the inkjet heads.

LIST OF REFERENCE NUMBERS

1

Facility

2

tape

3

Cylinder for tape guide

4

Cylinder for tape guide

5

Guide surface for tape guide

6

Motor for the tape guide

7

system stack

8th

delivery pile

9

bowing

10

bowing

11

Cylinder for sheet transport

12

Cylinder for sheet transport

13

Cylinder for sheet transport

14

press roll

15

Motor for sheet transport

16a-d

printheads

16e

Device for post-treatment, z. B. painting or embossing

17

Device for strip treatment, z. Eg plasma

18

Device for applying conditioner

19

Hot air dryer

20

Hot air supply

21

casing

22

air extraction

23

Dryer, z. B. IR dryer

24

Dryer, z. B. IR dryer

25

Heater inside

26

Heater outside

27

Heater inside

28

Heater outside

29

Device for inspection of the image

30a-e

doctor

31

Device for inspecting the bow

32

Device for inspecting the printed image

33

Apparatus for pretreatment of the sheet, z. B. Primer order

34

Apparatus for post-treatment of the sheet, z. B. drying

35

Device for cleaning the belt

36

Reservoir for cleaning fluid

37

Reservoir for conditioning fluid

38

Reservoir for hydraulic fluid, z. For example, ink

39

Storage container for primer liquid

40

Device for controlling the device

41

Device for changing the band

42

gripper systems

43

bow

44

nip

45

Ink drops / pressure liquid

46

printing ink

47

conditioner

51

Section of the squeegee 30a

52

fan

53

Line system for dry air

55

Fan

60

capacitor

61

compressor

62

heat exchangers

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

• US 2008/0166495 A1 [0003]
• US 7661809 B2 [0004]
• EP 2436519 [0007]
• JP 2005-212323 A [0007]
• JP 6064159 A [0008]

Claims (10)

Method for applying printing fluid to a printing substrate, wherein - a water-based or solvent-based printing fluid ( 45 ) with one or more inkjet heads either only on an intermediate carrier ( 2 ) or applied directly to a printing substrate, - the printing fluid ( 45 ) is heated and at least the proportion of water or solvent content is evaporated in the printing fluid, characterized in that - the inkjet heads ( 16a -E) produced moist or solvent-containing air in the immediate vicinity of the individual inkjet heads ( 16a -E) is replaced by dry air. A method according to claim 1, characterized in that in the direction of movement of the intermediate carrier ( 2 ) or printing substrate flowing moist or solvent-containing air flow through doctor blade ( 30a -E) from the surface of the intermediate carrier ( 2 ) or the print substrate is removed before it reaches the next inkjet head. A method according to claim 1, characterized in that the moist air is dried and then the printheads ( 16a -E) is returned. A method according to claim 2, characterized in that the doctoring of the moist or solvent-containing air by a mechanical squeegee ( 30a -E) or an air knife made of dry air. A method according to claim 4, characterized in that the squeegee and / or the dry air are heated. A method according to claim 2, characterized in that the of the air flow under the inkjet heads depending on the volume of the ink drops ( 45 ) differently sized deflection of the ink drops ( 45 ) is compensated in the pre-press and / or in the generation of the control data for the inkjet heads. Device for carrying out the method according to one of claims 1 to 6, characterized by a mechanical squeegee or air knife of dry air, of which the flow of moist and / or solvent-containing air over the intermediate carrier ( 2 ) or the printing substrate is interrupted. Apparatus according to claim 7, wherein the mechanical squeegee in the manner of a shoe ( 51 ) is trained. Device according to claim 8, wherein the underside of the shoe ( 51 ) is provided with a labyrinth seal. Device according to one of claims 7 to 9, characterized by a capacitor ( 60 ) for cooling the moist air and / or a heat exchanger ( 62 ) for reheating the of the capacitor ( 60 ) dried air.

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