DE102007035805A1 - Method for multi-color printing, involves control of ink drops and printing picture/image point of first color on recording carrier - Google Patents

Abstract

A multi-color ink printing method in which the print head has at least one first jet (12) for first color, during which control of ink drops is provided and a picture/image point (22) of a first color is printed at a predetermined position on a recording carrier (24). One further jet (14,16,18) is provided for the ink print head for at least one further color, and to avoid drying out of the additional jet (14,16,18) it emits at least one ink drop of the additional color, so that at it appears at the predetermined position of the picture/image point (22) of the first color.

Description

The The invention relates to a method for multicolor ink printing, in an ink jet print head at least a first nozzle for a first color comprises, when driven at least one ink droplet sent out and a pixel of the first color on a record carrier is printed, and wherein the ink jet print head at least one more Nozzle for at least one more color includes, at whose control at least one ink droplet is emitted and prints one pixel of the other color.

At the Ink printing becomes an image on a record carrier generated by controlled positioning of ink droplets. The paint is using a variety of nozzles on the brought to printing medium. The nozzles are controlled by a complex control so that the they generated pixels a raster image. For each color uses its own nozzles. Next to the color In the CMY color system, the basic colors cyan and magenta also become black and yellow used in color mixing a variety of shades result. In the RGB color system (red, green, blue) are in Subtractive mixing produces a wide variety of mixed colors. Furthermore There are numerous custom color blends from custom Colors.

Separate Nozzles can be caused by paper dust, air bubbles or Drying of the ink after prolonged breaks fail. If a nozzle can no longer emit ink droplets, Strips appear in the printed image. Therefore, with ink printers z. B. at certain intervals between the printed pages over the whole width of the printed image is a color bar printed or it randomly distributed ink droplets are emitted. The latter, however, leads to optically visible deterioration of the printed image.

From the EP 1 038 677 A1 a method is known in which, in order to avoid the blockage of nozzles, these are driven with an increased signal amplitude. As a result, build-up blockages at the nozzle opening or in the nozzle are eliminated by increasing the flow of the ink.

It It is an object of the invention to provide a method for multicolor ink printing which is easy to work with and high print quality guaranteed.

These Task is solved by the combination of features of claim 1. Advantageous developments are in the dependent claims specified.

The Invention is based on the consideration that in practice on the printed pages a specific ink, z. B. Black, unequal more common than other inks that are used for multi-color printing is required. For these others Printing inks result for the associated nozzles a longer downtime, so here the risk of constipation and dehydration increases. If now the vast majority a print page with the first base color, z. B. black, printed will, should it be possible, pixels of another Print color over the pixels of this first base color. If this first base color is so dark that the more color is on This dark background is not visible, so is the optical Image quality is not affected. When described Case overlays the further color of the first base color. But it is also possible that the first base color the previously printed another, lighter color superimposed, d. H. the first basic color is not printed until the more color is present on the recording medium. As long as the superimposed first base color is darker than that is more color, this more color is of a darker hue the first base color overprinted and invisible to the viewer made.

at conventional inkjet printheads is the controller such that ink droplets are very accurate to individual positions or points are directed to the record carrier can. This control is based on an application software that to modify according to the invention. A hardware intervention itself is not required, so the method according to the invention easy to carry out.

embodiments The invention will be explained below with reference to the figures. It shows

1 a simple principle of an ink print head for multicolor printing,

2 the construction of an inkjet print head with 96 nozzles for the colors black, cyan, magenta and yellow,

3 an ink head having a plurality of modules for a total printing width of a recording medium, and

4 a flow chart for a software algorithm for preventing the clogging of nozzles of the ink jet print head.

1 schematically shows an ink print head 10 a drop-on-demand (DOD) printer, where drops of ink leave the nozzles only when they are actually needed. In the sub In contrast, in CIJ printers (Continuous Inc Jet), an ink jet is emitted from the printhead via one or more nozzles and deflected by electrodes. The inkjet print head 10 contains four nozzles in this schematic example 12 . 14 . 16 . 18 , being out of the nozzle 12 black ink, from the nozzle 14 Cyan ink, from the nozzle 16 Ink of magenta color and emitted from the nozzle ink of the color yellow. The nozzles 12 to 18 be with the help of a controller 20 controlled, with each of the nozzles 12 to 18 to a pixel 22 as a predetermined position on a record carrier 24 , z. B. paper, and sends to this destination one or more ink droplets. Depending on the type of printhead used, droplet generation can be done either by heat application (Rubble Jet) or by changing the chamber volume in a nozzle channel (Piezo Inkjet).

Many applications typically use black ink, for example, to write text. As a result, the nozzle becomes most common 12 used, through which a high flow of ink flows. The danger of a drying of this nozzle 12 is relatively low. In contrast, the nozzles 14 . 16 . 18 is more rarely used for multicolor printing, which is also evident from the fact that in commercial printers the ink containers for such colors are relatively small compared to the ink container for the color black. With these nozzles 14 . 16 . 18 with the primary colors for multicolor printing there is an increased risk of ink drying. To avoid this, a cleaning cycle for these nozzles must be done at certain intervals 14 . 16 . 18 take place, are emitted at the ink droplets. In the example below 1 is first from the nozzle 12 a black pixel 22 printed by this nozzle 12 a drop of black ink to the record carrier 24 sends. In the present case, the conditions are such that for the nozzle 14 for the color cyan a cleaning cycle is required. Therefore, in this example of the invention, the nozzle becomes 14 also an ink drop on the black colored pixel 22 sent out, which is superimposed on the black color. This black color has such a background opacity that the viewer does not see the color cyan. In this way it is achieved that on the one hand a black pixel 22 is printed and on the other hand, a cleaning cycle for the nozzle 14 is carried out. In the same way, a cleaning cycle for the nozzles 16 for the color magenta or the nozzle 18 be carried out for the color yellow. For a color system with other colors, such. B. the additional colors of light cyan and light magenta, photo-cyan or photo-magenta, this approach is also possible, the corresponding nozzles here in the 1 are not shown.

There the colors magenta or cyan also have a strong background color It is also possible to color yellow on the background a pixel with the color magenta or the color cyan to print, without that being obvious. Problematic however, would be a print of pixels on the background a pixel of the relatively pale yellow color.

2 shows a printhead 30 for a four-color print. The printhead 30 contains a total of 96 nozzles for the colors black, cyan, magenta and yellow, namely 48 nozzles for the color black, and 16 nozzles each for the other basic colors of the CMY color system. With it a resolution of 300 dpi (dots per inch) is possible. By tilting the nozzle line 31 when aligning the line perpendicular to the paper transport direction 32 an improved resolution is achieved. The printhead 30 becomes in row direction 34 moves, with the 96 nozzles print pixels on the recording medium. The controller is programmed to print dots for cleaning the nozzles on pixels that can be printed by 48 nozzles for the black color when the cyan, magenta, and / or yellow nozzles are paused for a long period of time. It is also possible to first print the lighter colors cyan, magenta and / or yellow at positions at which the color black is printed at a later time, which then covers the previously printed color.

3 shows a printhead 40 in which a variety of printhead modules 30 by type of printhead 30 are arranged in a matrix that the entire printing width of a recording medium can be printed without the printhead 40 must be moved in the row direction. The record carrier is in the direction of the arrow 42 moves, with the printhead modules 30 Print columns of pixels. In column direction 44 are six printhead modules 30 and in the row direction 46 arranged five printing modules. A total of 7,680 nozzles are arranged for a printing width of 325 mm. Also in this matrix-like arrangement of printhead modules 30 the invention can be applied. For nozzles with a longer standstill, a cleaning cycle can be performed if in the column concerned a pixel, for example with the color black, has been printed or is still being printed and a non-black pixel can be overlaid or previously printed on this pixel.

4 Fig. 11 is a flow chart for a control program section for controlling the cleaning of a nozzle, which in this case emits the ink of cyan color. In step S1, the Pro starts program section for monitoring this nozzle. In step S2, the current standstill time Ts for this nozzle is loaded. In the comparison step S3 it is checked whether this downtime Ts has expired. If this is not the case, the program branches back to step S3. If Ts has elapsed, it is checked in subsequent step S4 whether a black pixel has been printed on the recording medium by a nozzle for black ink. If this is not the case, the system branches back. Otherwise, a branch is made to the next step S5, in which n ink drops are printed on the black pixel through the relevant nozzle, n being an integer. Subsequently, a branch is made back to step S1.

There at elevated temperature or reduced humidity increases the risk of clogging a nozzle is, the downtime Ts can depend on these sizes be set. For example, this standstill time Ts reduced with increasing temperature and with increasing humidity be enlarged. The same applies to the number n of emitted ink droplets. This can increased at increased cleaning needs become. When idle, a rest period can also be included in which the inkjet print head is not in operation.

As mentioned earlier, it is not absolutely necessary superimpose non-black pixels on a black pixel, to perform a cleaning cycle. It may be enough the superimposed pixel printing on a dark base color as a background.

Farther Is it possible to clean the nozzles? to perform according to a random algorithm, in which continuously randomly selected nozzles and / or in at random intervals print pixels that superimposed on the before or after printed dark pixels or be subordinated.

10

Ink print head

12 to 18

jet

20

control

22

pixel

24

record carrier

30

printhead

32

Paper transport direction

34

line direction

40

printhead

42

arrow

44

column direction

46

line direction

S1 to S5

steps

ts

Downtime

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 1038677 A1 [0004]

Claims (11)

Method for multicolor ink printing, in which an ink print head ( 30 . 40 ) at least one first nozzle ( 12 ) for a first color, at the activation of which at least one ink droplet is emitted and a pixel ( 22 ) first color at a predetermined position on a record carrier ( 24 ) and in which the ink print head ( 30 . 40 ) at least one further nozzle ( 14 . 16 . 18 ) for at least one further color, in the activation of which at least one ink droplet is emitted and a pixel ( 22 ) prints the further color, wherein to avoid dehydration of the other nozzle ( 14 . 16 . 18 ) according to a predetermined algorithm, this further nozzle emits at least one ink drop of the further color so that it is at the predetermined position of the pixel ( 22 ) of the first color on the record carrier ( 24 ). The method of claim 1, wherein the first color Black is. The method of claim 1, wherein the first color a darker shade than the other color. The method of claim 1 or 2, wherein as further Color cyan, magenta or yellow is used. Method according to one of the preceding claims, in which a line-type DOD ink jet print head (US Pat. 30 ) is used. Method according to one of the preceding claims, in which the inkjet print head is an ink print head (not movable in the line direction) ( 40 ), which uses a plurality of printing modules ( 30 ). Method according to one of the preceding claims, in which a cleaning cycle for the further nozzle ( 14 . 16 . 18 ) according to a random algorithm, in which the respective nozzle ( 14 . 16 . 18 ) and / or the time interval between two cleaning cycles after a random probability is selected. Method according to one of the preceding claims, in which a cleaning cycle for the further nozzle ( 14 . 16 . 18 ) after a predetermined standstill time (Ts) has elapsed. Method according to Claim 8, in which the standstill time (Ts) depends on the temperature and / or the humidity of the surroundings of the print head ( 30 . 40 ) and / or the color used is changeable. Method according to one of the preceding claims, in which, for carrying out the cleaning cycle for the further nozzle ( 14 . 16 . 18 ) n droplets are emitted, where n is an integer. Method according to claim 10, wherein the number n depends on the temperature and / or the humidity of the environment of the print head ( 30 . 40 ) and / or the proportion of the darker color, in particular black, is set at the predetermined position.