EP1902843A1 - Method and device for creating ink drops with variable drop volume - Google Patents

Abstract

The method involves combining freely selectable ink droplets (11, 12), following in succession, with each other during projecting the droplets by a discharge nozzle (6) up to a striking spot on a print substrate. The ink droplets are individually and/or selectively advanced or retarded into an electrode arrangement (50) by electrical fields caused in a direction of projection of the ink droplets. The ink droplets are combined to a common drop, and form a droplet group. An independent claim is also included for a method for creating ink-droplets with a continuously operating ink-jet printer.

Description

The invention relates to a method and a device for producing drops of ink with variable drop volume, in particular in a continuous ink jet printer. The invention further relates to a printing device with such a device.

Continuous inkjet printers have been used industrially for many years to label a variety of products. The working principle of this inkjet printer works so that an ink to be printed from a reservoir via pumps with positive pressure is conveyed into a located in the actual print head pressure chamber, which has a nozzle, in particular on the side facing the material to be printed.

The nozzle can in this case have an opening diameter in the range of 30μ to 200μm. From the nozzle, the ink jet now emerges initially as a continuous ink jet, which is impractical for a label, since the characters generated in this way should be composed of individual dots or individual drops of ink in this type of labeling. In order to decompose the ink jet into individual similar, in particular equal sized ink drops, a modulation element is attached to the pressure chamber, which Pressure fluctuations generated in the ink jet emerging from the printhead, so that this ink jet breaks up after exiting the nozzle, in particular after a short time and at a defined distance, in individual, in particular equal-sized ink droplets.

The size of the ink droplets depends, inter alia, on the applied modulation frequency, the nozzle diameter and the pressure generated by the pump, and can be set within the limits set by the combination of said parameters for the system. A variation of the droplet size of successive ink droplets is not possible.

Shortly before the tearing off of the ink drops from the leaked ink jet, the ink droplets are each provided with an individual electrical charge, the height of the charge depending on the desired impact position on the product to be labeled. To ensure electrical charging, the ink has a low electrical conductivity. During the charging process, the ink droplet has not yet broken off from the ink jet emanating from the nozzle of the ink jet printer, so that due to electrical influence free charge carriers in the ink are moved towards or away from the charging electrode, depending on the polarity and magnitude of an external charging voltage Ink chamber and thus the ink reservoir, for example, electrically held at ground potential. The charging electrode has no mechanical contact with the ink jet.

If the ink droplet now tears off the ink jet while it is in the field region of the charging electrode, then the electrical charges migrated through the influence in the droplets remain in the drop volume and this appears to be electrically charged even after the demolition. Becomes For example, when the charging electrode is charged positively, as the ink jet enters the electric field of the charging electrode, the negative free carriers in the ink migrate into the field, whereas the positively charged free carriers in the ink are forced out of the electric field. As a result, a charge separation takes place immediately prior to the demolition of the droplet at the leading edge of the ink jet, and the charge imbalance thus created in the tearing droplet is retained and the droplet leaves the field region of the charging electrode negatively charged in this example. Since the ink droplet tears off due to the design and principle during the influence of the charging voltage on the droplet remains as described on the detached ink droplet, an amount of charge whose size is at a constant electrical conductivity of the ink according to the level of the applied charging voltage, so that in a change in the Charging voltage thus the amount of charge on each drop can be changed.

On their first rectilinear flight, the electrically charged ink drops subsequently enter the electrostatic field of a deflection device, e.g. of a plate capacitor, and are more or less deflected from their rectilinear trajectory, depending on their individual charge, and fly on leaving the electrostatic field at a certain angle dependent on their charge to their original trajectory.

With this principle, different impact positions can be selected on a surface to be labeled with individual ink droplets, which in this embodiment takes place only in a deflection direction. To hide individual drops from the typeface or when not to be printed, the ink drops receive a certain fixed charge or remain uncharged, so that after exiting the electrostatic field of the Condenser plate in a collecting tube from where they are pumped back via a pump system in the ink tank. This causes the unprinted ink to circulate, resulting in the designation of continuous ink jet printers.

A disadvantage of the described embodiment is that due to the system-related generation of the ink droplets they always have the same size within narrow tolerances, so that a generated with these drops typeface always has the same size pressure point sizes.

In contrast, it is known in the art to use dots of varying sizes to produce gray gradations and color gradients in printed images so as to allow the viewer's eye a visual impression of grayscale or color gradients. Thus, for example, in all printing processes which use a printing form, the individual printing dots in the production of the printing form can be made to vary in size according to the original, which leads to pressure points of different sizes.

It is also known to realize inkjet printers of the drop-on-demand type (DOD) differently sized pressure points by a different number of small drops of the same size on the surface of the material to be printed is superimposed during printing to a common larger pressure point.

A disadvantage of the known methods is that, on the one hand, they do not allow variability of the print data within the printing process, since they work in the form of printing forms or, in the case of the DOD method, have only a small working distance of the print heads to the surface to be printed, in particular in the marking area. There DOD printers always have a plurality of nozzles in a printhead, moreover, in these printheads only inks can be used, which either have no or very slow drying properties or radiation-curable inks, otherwise the ink in individual nozzles, not during a particular print image or rarely used, dry, causing this nozzle to fail.

Although the use of radiation-curable inks solves this problem, but requires the additional use of downstream curing facilities a significantly higher equipment costs and significantly higher costs. Due to the small working distance mentioned above, it is also not possible to characterize a structured surface, for example, with high writing quality, since the trajectories of the ejected ink drops become so unstable after a short distance that a desired impact position is no longer reliably hit, and thus one of several Ink drops composite pressure point can no longer be printed as a closed pressure point with defined shape.

The use of the above-mentioned inks is mandatory in these systems because such DOD systems operate with a plurality of individual nozzles which are driven as needed. It is normal that a single nozzle according to the type of image to be printed for a long period of time is rarely or rarely driven, which would lead to the use of a fast-drying ink such as a solvent-containing ink that the ink dries in this nozzle and the nozzle opening clogged.

If this nozzle is needed later, it is no longer available and it is a cleaning, often also a manual cleaning of the printhead required. In contrast, the continuously working Inkjet printers print inks that have an extremely short drying time because the solvents used in these inks evaporate very quickly.

By continuously ejecting ink from the nozzle in this type of inkjet printer, the nozzle can not clog and the process can not be interrupted. So far, however, it has not been possible with continuous ink jet printers of this type optionally to produce ink drops of different sizes even within a typeface.

The invention described herein relates to a method and apparatus which may preferably be used with this type of continuous ink jet printer described above. However, the invention may also be used with any other type of device that is capable of producing successive ink droplets of substantially the same size and / or electrical charge and in particular the same distance from one another in a trajectory.

The object of the invention is to provide a method and a device by which it is possible, in particular by means of a continuous ink jet printer, to apply a freely programmable marking on any surfaces, wherein the label may include pressure points of either different size, preferably each be generated by only one drop of ink with either different drop volume.

This object is achieved by a method in which a freely selectable number of successive ink droplets in flight are combined during flight, in particular during flight from an outlet nozzle of the droplets producing ink jet print head to the impact location on a substrate. The problem is solved by a device that eg in a continuous ink jet printer can be used, in which a freely selectable number of successive ink droplets in flight are unified during flight, especially during flight from an outlet nozzle of the droplets generating ink jet print head to the impact location on a substrate.

Thus, it is essential to the invention that differently sized ink droplets are not originally produced, which implies complicated devices, but that initially with a device, such as e.g. the above-described continuous ink jet printhead or any other ink drop generating device, ink drops of substantially and preferably within narrow tolerances of the same size are generated. Thus, it is possible to resort to existing and established techniques for the generation of these drops of ink, which fly in an original trajectory successively and in particular with equidistant spacing, unless individual drops are suppressed or hidden.

The core idea of the invention is to optionally obtain drops of different sizes or drops with optionally different drop volumes by combining an optional number of successive drops of ink into one drop. Thus, if each of the original individual drops has a volume of V, then the common drop of n drops has a volume of n x V.

The union of individual drops between the place of production, such as after a pressure chamber of an ink jet print head and the location of impact on a substrate can be anywhere during the entire flight time, eg before the individual original drops are deflected or after the original drops have been deflected.

According to the invention, the size of a pressure point on a surface to be marked is determined by the number of ink droplets combined to form a common droplet. It is possible in this way, for example, in a multi-line marking a product to write the respective lines with different sized pressure points or to write within a single print line characters or only individual pressure points with a different pressure point size, such as special effects, highlights or gradients especially at rounded edges of logos or special characters better represent.

Thus, in accordance with the invention, any drop generators in a first step, e.g. In a known manner, ink droplets of the same size are generated at a certain following frequency, in particular by pumping an ink from an ink tank by means of a pump into a pressure chamber at one end of which there is a nozzle. A modulation element attached to the pressure chamber modulates the pressure in the pressure chamber such that the ink jet emerging from the nozzle breaks up into individual ink droplets of substantially the same size, in particular after a defined short distance.

A charging device mounted directly in front of the nozzle (in the direction of the jet after the nozzle) acts by influencing any emerging ink droplet with an electrostatic charge as described above. According to the invention, the exiting ink droplets, in particular ink droplets of a droplet train or a droplet group from which a common, larger ink droplet is to be formed in a subsequent step, can be provided with a constant charge which is at least substantially the same for all droplets.

In order to combine a desired number of individual original drops, it can be provided according to the invention that the ink droplets are accelerated or retarded individually and / or optionally by means of an electric field acting essentially in the direction of flight of the drops, in particular in an electrode arrangement. Essential for this is that all individual ink droplets to be combined initially have the same velocity in one direction. This may be the original direction or a deflected direction. Because the drops to be united pass through an electric field whose field lines run at least substantially parallel to the direction of flight, the drops can be individually accelerated or also decelerated depending on the strength and direction of the electric field. The drops of a group of drops which pass through such an electric field can then combine if a different electric field acts on different drops of the drop group.

A device for generating such an electric field may e.g. are formed by an electrode arrangement, in particular with at least two electrodes arranged one after the other in the direction of flight of the drops. These can be arranged such that the surface normals of the electrodes are arranged at least substantially parallel to the direction of flight of the ink droplets.

The electrodes may be formed as plate electrodes of substantially any shape having a recess through which the drops fly substantially perpendicular to the plate surface.

It may be provided that the droplets of a group of droplets fly through an electrode arrangement by means of an adjustable voltage are respectively accelerated or retarded to a different extent between the electrodes of the electrode arrangement, so that the drops flying ahead in the drop group are delayed and the trailing drops are accelerated. Thus, the trailing in the droplet group drops catch the preceding flying drops and the drops can connect to a common drop of larger volume. This can be done in such a way that the drops of the drop group unite in a further flight to form a common drop only after leaving the electrode arrangement, in particular shortly after the electrode arrangement.

The arrangement of a device for uniting the ink droplets can be carried out with respect to a previously described inkjet printer both in front of a deflector for the ink drops and afterwards. An arrangement in front of a deflection device has the advantage that the electrode arrangement can be aligned exactly perpendicular to the original direction of flight.

In a deflector arrangement, the ink drops or groups of ink drops may have many different directions. An electrode arrangement of two or more parallel electrodes can therefore be arranged only for an excellent direction exactly perpendicular to the direction. For the remaining possible direction, this alignment may only be substantially correct.

However, it can be provided according to the invention to adapt the electrodes of the electrode arrangement to the at least one deflection of the droplets such that for each direction of the ink droplets after the at least one deflection directions, the surface normals of the electrodes, in particular at the entry of the droplets in the electrode assembly and the direction of the Ink drops are parallel to each other. For this purpose, the electrodes can be designed, for example bent around a center.

In a further preferred embodiment, it may be provided that the electrodes of the electrode arrangement have a distance from each other which is less than or equal to the mean distance of the ink droplets traversing them. This ensures that only one drop of ink from an ink droplet group, which is to be combined, is arranged between the electrodes, and thus the electric field also acts only on this one ink droplet. Each individual ink drop can thus experience a different field strength and field direction if a change of the field takes place temporally between two consecutive drops.

In an arrangement of an apparatus for uniting a desired number of ink droplets with a deflector for the originally generated droplets, the original droplets along their flight after production may first pass into a deflector which may be configured to cause each droplet of ink to move with the droplet synchronously mitlaufendes, individual electric transverse field variable strength and duration can be assigned, so that the ink droplets can each learn different deflection angle. In this way it is also possible to generate already mentioned drop trains / drop groups, consisting for example of n individual drops, whose individual drops all or only a certain number of them are deflected in the same spatial direction. Thus, a drop group having a desired number of drops may be deflected from the original direction in a desired direction.

By means of a downstream electrode arrangement whose electric field is aligned substantially along the direction of flight, are now synchronous to the drops that they fly through, in particular the group of drops, slows down the advancing drops by means of the electric field and accelerates the trailing drops with an electric field of opposite polarity so that all the drops of a group of drops, in particular after a short distance after the electrode arrangement, unite in flight. Depending on the number of drops contained in a drop train, this results in pressure drops with 1, 2, 3, ... initial drop volumes.

The electrode arrangement for merging ink droplets can also be arranged in front of a deflection device. Then, first an association of the drops and then a distraction of the volume-enlarged drops. This can be done with the same deflection device as described above. The deflecting electric field then acts on each of the combined drops.

Figur 1:

Den schematischen Aufbau eines kontinuierlich arbeitenden Tintenstrahldruckers gemäß Stand der Technik;

Figur 2:

Eine schematische Darstellung einer erfindungsgemäßen Ausführung eines kontinuierlich arbeitenden Tintenstrahldruckers zur Erzeugung variabler Tropfengrößen;

Figur 3:

Eine schematische perspektivische Darstellung einer erfindungsgemäßen Ausführung der Elektrodenanordnung zur Geschwindigkeitsmodulation der abgelenkten Tropfen;

Figur 4a, 4b:

Eine schematische Darstellung des Spannungsverlaufes bezogen auf die in Figur 2 gezeigten erfindungsgemäßen Ausführung zur Modulation der Geschwindigkeit bei unmittelbar einander nachfolgenden Tropfenzügen;

Figur 5a, 5b:

Eine schematische Darstellung des Spannungsverlaufes bezogen auf die in Figur 2 gezeigten erfindungsgemäßen Ausführung zur Modulation der Geschwindigkeit bei Lücken zwischen den einander nachfolgenden Tropfenzügen;

Figur 6:

Eine Druckvorrichtung, bei der eine Elektrodenanordnung zur Vereinigung von Tropfen vor einer Ablenkeinrichtung angeordnet ist;

Figur 7:

Beispiel der Verläufe der Spannungen zwischen den zwei Elektroden einer Elektrodenanordnung gemäß Figur 6 zur Vereinigung der Tropfen.

The prior art and embodiments of the invention show the following figures. Show it:

FIG. 1:

The schematic structure of a continuous ink jet printer according to the prior art;

FIG. 2:

A schematic representation of an embodiment according to the invention of a continuous ink jet printer for generating variable drop sizes;

FIG. 3:

A schematic perspective view of an embodiment of the invention the electrode arrangement for speed modulation of the deflected drops;

FIGS. 4a, 4b:

A schematic representation of the voltage curve with respect to the embodiment of the invention shown in Figure 2 for Modulation of the velocity in immediately successive drops;

FIGS. 5a, 5b:

A schematic representation of the voltage curve with respect to the embodiment according to the invention shown in Figure 2 for the modulation of the velocity at gaps between the successive drip trains;

FIG. 6:

A printing apparatus in which an electrode assembly for combining drops is disposed in front of a deflector;

FIG. 7:

Example of the courses of the voltages between the two electrodes of an electrode arrangement according to FIG. 6 for uniting the drops.

FIG. 1 shows by way of example a printhead of a known conventional continuous ink jet printer for comparison with the invention. The ink 1 is first pumped from a reservoir 2 by means of a pump 3 via leads 4a into the pressure chamber 5, at one end of which a nozzle 6 is introduced. By means of additionally mounted on the pressure chamber modulation means 7, the pressure in the pressure chamber 5 is modulated so that the emerging from the nozzle 6 ink jet 9 breaks shortly after its exit into individual ink droplets 11 of substantially the same size. Shortly before breaking up, the individual ink droplets 11 are provided with an individual electrical charge via a charging electrode 8.

Along their trajectory 100, the ink drops 11 now enter an electric field 21, which is formed by means of the electrodes 20a and 20b of the plate capacitor 20. Depending on the amount of charge and the polarity of the charges on the ink drops 11 and the polarity and strength of the electric field 21 in the field space of the plate capacitor 20, the individual ink droplets are deflected in different spatial directions 103, 104 shown by way of example.

The total number of possible deflection angles depends only on the control of the charging electrode and is not limited in principle. The individual plates 20a and 20b of the plate capacitor 20 may be inclined relative to each other, as shown in Figure 1. However, it is also possible to use plates arranged parallel to one another without restriction of generality.

The polarity and strength of the electric field 21 is expediently kept substantially constant in this embodiment, since a change in the field strength to a plurality of drops, which are located in the field space of the plate capacitor at this time, simultaneously affects and thus an influence of a single drop is impossible.

After leaving the field space 21 of the plate capacitor 20, no more electrostatic force acts on the ink drops 11 and they maintain their new trajectories 103, 104 at. This results in a fan-shaped array of trajectories. For example, ink drops 11, which have not been charged or only slightly charged because they must be discarded from the typeface, experience no or only a slight deflection in the electrostatic field 21 of the plate capacitor 20 and strike into an opening 19 of a catch tube 18 for ink return. The ink thus collected is returned to the ink container 2 through leads 4b and returned to the ink circuit.

FIG. 2 shows a schematic representation of an arrangement according to the invention for generating and deflecting droplets of variable drops of ink droplets continuous inkjet printer. The drop formation itself takes place here in the manner described above according to FIG. 1.

However, the generation can also be done in any other way, essential to the invention is the type of drop combination during the flight. The ink 1 is also first pumped from a reservoir 2 by means of a pump 3 via leads 4a into the pressure chamber 5, at one end of a nozzle 6 is introduced. The pressure in the pressure chamber 5 is also modulated by means of modulation devices 7 likewise mounted on the pressure chamber, so that the ink jet 9 emerging from the nozzle 6 breaks open at a short distance after its exit into individual ink droplets 11 of essentially the same size. Shortly before breaking up, the individual ink drops 11 are each provided with a same electrical charge via a charging electrode 8, in contrast to the known embodiment.

Along their trajectory 100, the ink drops 11 now enter a variable electric field 44, which is formed by means of the electrodes 40a and 40b or E0 and E1 to En of the electrode arrangement 40. The electrode assembly 40 consists of a number of individual electrodes E0 and E1 to En, which are arranged transversely to the trajectories 100 of the ink droplets 11 so that their respective distances from each other corresponds to the distance between successive ink droplets.

A deflection voltage UO, U1 to Un at the electrodes E0 and E1 can then be switched via a suitable electronic circuit to the subsequent electrode E2, then to E3, etc. to En, so that there is an electric field in the direction of movement of the ink droplets.

When this happens according to the flying speed of the ink drops, each ink drop experiences an individual electrostatic deflection. By As the intensity and duration of the electric field applied to each ink drop vary, so different deflection angles for the ink drops can be produced. For example, ink drops to be discarded from the typeface experience no distraction in that the electric field accompanying them disappears.

According to the invention, it is thus possible to divert groups of ink droplets 12 in certain directions, which consist of a plurality of individual drops. Each single drop of a drop group thus preferably had the same electric field in the deflection device.

In this case, according to the invention, the maximum number of drops in a drop group can be defined according to a specification in a superordinate electronic control, which corresponds to the number of different drop sizes produced according to the invention. If, for example, a maximum number of 8 drops is determined per drop group, then 8 differently sized ink drops can be produced, which leads to the state of non-printing to 9 gray levels. With this specification, the electrode assemblies 40 each leave a certain number of successive ink drops of a drop group 12 in a deflection direction, wherein the number of ink droplets present in each drop group may be different as described.

The droplet groups thus produced subsequently pass into the electrode arrangement 50, comprising the electrodes 50a, 50b or Ek1 and Ek2, which each have openings 51a and 51b. The arrangement of the electrodes 50a and 50b is such that the electric field established between them by applying an electrical voltage essentially points in the direction of flight of the ink droplets. The structure and arrangement of the electrodes 50a and 50b is further, such that the ink drops fly through the openings 51a and 51b of the electrodes 50a and 50b.

Furthermore, the spacing of the electrodes 50a and 50b is selected such that only one single ink droplet is always present in the intermediate space between the electrodes 50a and 50b. If an electric voltage Uk is now applied to the electrodes Ek1 and Ek2, an electric field builds up in the space between the electrodes Ek1 and Ek2 which, depending on its strength and polarity, either accelerates or decelerates an ink droplet located in this field space.

Due to the fact that only a single ink drop is located in the intermediate space, the force thus generated acts only on this ink droplet. It is thus possible, by varying the strength and / or the polarity of the applied voltage Uk, to accelerate or decelerate successive ink droplets to different extents.

In order to combine the individual ink droplets of a pot group to form a common ink droplet, it is provided according to the invention to decelerate the advancing ink droplets of a droplet group and accelerate the subsequent ink droplets so that all the ink droplets in a group after a short distance to the electrode assembly 50 in the common center of gravity Pool drop group in flight. This ensures that the differently sized ink droplets 101 produced in this way have substantially the same distance from one another and thus result in a typeface which contains differently sized pressure points 201 on a substrate 200 after the impact of the ink droplets 101 and the distance between the pressure points is regular is.

FIG. 3 shows schematically in a perspective view the deflection device 40 and the downstream electrode arrangement 50 as well as some exemplary deflection directions 103, 104 and 105 of the ink droplets as well as droplet groups shown schematically. The shape of the electrodes 50a and 50b may be different, for example rectangular, round, oval or another form adapted to the respective system.

The same applies to the openings 51a and 51b, which can preferably be designed such that the most homogeneous possible electric field distribution results in the space traversed by the ink droplets between the electrodes 50a and 50b.

It is also possible to design the electrode arrangement 50 in the direction of flight of the ink droplets in a cylindrical, spherical-cap-shaped or generally concave manner, so that regardless of the deflection angle of the respective ink droplets, they always traverse the gap between the electrodes 50a and 50b exactly along the electric field lines.

FIGS. 4a, 4b and 5a, 5b schematically show the relationship of the voltage Uk to the respective ink drops 11 of the respective drop group 12. In this case, FIG. 4a shows by way of example a sawtooth pattern of the voltage Uk from a positive voltage + Uk to a negative voltage -Uk , wherein each portion 13a, 13b, 13c of a sawtooth-shaped voltage interval 13 acts only on the ink droplets shown above in the drawing, which passes through the electrode assembly 50 at this time. Thus, only the field strength determined for this drop acts on each drop, as a result of which the drop is more or less decelerated or accelerated.

FIG. 4b shows, by way of example, another way of driving the electrodes 50a and 50b with a step-like voltage curve, so that each ink drop 11 when flying through the field space a different but constant field strength according to the voltage acting at this time in the respective section 13a, 13b, 13c, the voltage interval 13 experiences. It is expedient to keep the sums of the accelerating and decelerating voltages constant, particularly preferably equal to zero. In this case, the accelerating or decelerating voltages may also assume different values in terms of magnitude, which may be advantageous in particular when uneven-ink droplets are combined to form a common ink droplet.

It may also be advantageous to superimpose a correction voltage on the variable acceleration or braking voltage of each group of drops in such a way that position deviations that can occur between odd and even drop volumes are compensated for in the labeling plane.

It may be expedient to deflect one or more drops of ink into the catching tube between the respective groups of drops in order to realize, for example, the voltage jump between successive drop groups from -Uk to + Uk shown in FIGS. 4a and 4b in a technically simpler manner. The missing ink drops at these locations are marked 11 b in FIGS. 5a and 5b. It is further shown in FIGS. 4a, 4b, 5a, 5b that within a drop group not all ink drops need to be present, depending on the desired size of the resulting ink drop 101. These missing ink droplets are denoted by 11a. It should also be noted that each of the illustrated drop groups may have a different deflection angle.

In another embodiment, as shown in FIG. 6, it is provided to carry out the combination of the individual ink droplets of a droplet group in front of the deflection unit formed by the electrode arrangement 40 by means of the electrode arrangement 50, so that differently sized ink droplets corresponding to the desired impact position on a printing substrate are produced in the deflection unit 40 be articulated. In this case, the acceleration or deceleration of the drops for the drops to be combined takes place in the manner described, whereas the voltage Uk for the drops to be blanked out becomes zero, as shown in FIGS. 7a and 7b.

Claims (18)

Method for producing variable-drop-volume ink drops, in particular in a continuous ink-jet printer, characterized in that an arbitrary number of successive ink drops (11, 12) are combined during the flight, in particular during the flight from an outlet nozzle ( 6) of a drop (11,12) generating ink jet print head (5,6,7) to the point of impact on a substrate. A method according to claim 1, characterized in that the ink drops (11,12), in particular which are ejected from a common nozzle (6) of an ink print head (5,6,7), have a substantially same size. Method according to one of the preceding claims, characterized in that the ink droplets (11, 12), in particular produced by the ink jet print head (5, 6, 7), each have a substantially equal electrical charge. Method according to one of the preceding claims, characterized in that the ink drops (11,12) by means of an essentially in the direction of flight of the drops (11,12) acting electric field, in particular in an electrode assembly (50), individually and / or optionally accelerated or be delayed. Method according to one of the preceding claims, characterized in that the number of drops (11, 12) which are combined to form a common drop (101), in particular before entry into the electrode assembly (50), a drop group (12) form and the number of drops (11,12) of the drop group (12) is arbitrary. Method according to Claim 5, characterized in that the drops (11, 12) of a drop group (12) accelerate at different speeds when passing through an electrode arrangement (50) by means of an adjustable voltage between the electrodes (50a, 50b) of the electrode arrangement (50) be delayed, so that in the drop group (12) advancing drops delayed and the trailing drops are accelerated. Method according to one of the preceding claims, characterized in that the drops of the drop group (12) after leaving the electrode assembly (50) in flight to a common drop (101) unite. Method according to one of the preceding claims, characterized in that for the combination of the drops (11,12) of a drop group (12) the voltage between two electrodes (50a, 50b) of the electrode assembly (50) during the passage through the drop group (12) the sign changes. Method according to one of the preceding claims, characterized in that the ink droplets (11, 12) are produced by means of a common drop-generating device (5, 6, 7), in particular with an ink-jet print head (5, 6, 7), and after being generated along a move common trajectory (100). Apparatus for producing variable drop volume ink droplets, in particular for use with a continuous ink jet printer, characterized in that a freely selectable number of successive ink drops (11, 12) can be combined with one another during the flight, in particular during the flight from an outlet nozzle (6) of a droplet-producing ink jet print head (5, 6, 7) to the place of impact on a printing material. Apparatus according to claim 10, characterized in that it comprises an electrode arrangement (50), by means of which an essentially in the direction of flight of the drops (11,12) acting in its strength changeable electric field can be generated, by means of which the ink drops (11,12) individually and / or optionally can be accelerated and / or delayed, in particular in such a way that the preceding drops of a drop group (12) are delayed and the trailing drops of a drop group (12) are accelerated. Apparatus according to claim 11, characterized in that it comprises at least two electrodes (50a, 50b), which are arranged one behind the other in the direction of flight of the ink drops (11,12) such that the surface normals of the electrodes (50a, 50b) at least substantially parallel to Flight direction (100, 103, 104) of the ink droplets (11,12) are arranged. Device according to one of claims 10 to 12, characterized in that the electrodes (50a, 50b) of the electrode assembly (50) at a distance from each other, the is less than or equal to the average distance of the ink droplets (11, 12) traversing them. Device according to one of claims 10 to 13, characterized in that the number of drops (11,12), which are combined into a common drop (101) before entering the electrode assembly (50) form a drop group (12) and the Number of drops of the drop group (12) is arbitrary. Device according to one of claims 10 to 14, characterized in that through them the speed of the drops (11,12), in particular the speed of each drop of a drop group (12) is changeable such that the drops (11,12), in particular After leaving the electrode assembly (50), the drops of a drop group (12) merge in flight to form a common drop (101). Device according to one of Claims 10 to 15, characterized in that the electrodes (50a, 50b) of the electrode arrangement (50) are adapted to at least one deflection device (40) of the drops (11, 12) such that for each direction (103, 104) the ink droplet (11,12) after the at least one deflection direction (40) the surface normal of the electrodes and the direction (103, 104) of the ink droplets (11,12) are parallel to each other. A printing apparatus comprising an ink jet print head for producing successive substantially equal sized ink drops having substantially equal electrical charge and a deflection device for deflecting individual or groups of ink droplets therefrom original direction, characterized in that it comprises a device according to one of claims 10 to 16. Printing device according to claim 17, characterized in that the device is arranged according to one of claims 10 to 16 before or after a deflection device (40).

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