EP2734371A1

EP2734371A1 - Print head for an ink jet printer

Info

Publication number: EP2734371A1
Application number: EP12735287.0A
Authority: EP
Inventors: Franz Obertegger
Original assignee: Durst Phototechnik AG
Current assignee: Durst Phototechnik AG
Priority date: 2011-07-22
Filing date: 2012-07-11
Publication date: 2014-05-28
Anticipated expiration: 2032-07-11
Also published as: CN103826858A; EP2734371B1; US20150360472A1; JP2014520689A; WO2013013983A1; US20140192117A1; CN103826858B; PL2734371T3; ES2553749T3; JP6133857B2; ES2553749T7; US9994029B2; EP2734371B3; US9751313B2; US20170297340A1

Abstract

The invention relates to a print head for an ink jet printer, wherein the print head comprises at least one ink supply channel and at least one nozzle having a nozzle channel and an inflow opening, and ink can be pressed from the ink supply channel through the inflow opening into the nozzle channel and ejected therefrom, wherein the nozzle is arranged in a stationary manner on a side wall of the ink supply channel and in the ink supply channel a ram is provided, which can be moved back and forth between a reversal point (U1) that has a minimal distance from the inflow opening of the nozzle and a reversal point (U2) that has a maximal distance from the inflow opening of the nozzle, wherein first means limit the movement of a ram end face to a movement between the reversal points (U1, U2) and second external means are provided for applying a negative pressure relative to the ambient air pressure to the ink in the ink supply channel.

Description

Printhead for an inkjet printer

The present invention relates to a printhead for an ink jet printer, the printhead having at least one ink supply channel and at least one nozzle with nozzle channel and inflow opening, whereby ink can be forced out of the ink supply channel into and out of the nozzle channel through the inflow opening Nozzle is fixedly disposed on a side wall of the ink supply channel and the at least one nozzle is associated with a tappet with lying in the ink supply channel tappet front side, the inflow opening opposite, the printhead comprises first means for moving the tappet front side in the ink supply channel between a Furthermore, the invention relates to a method for carrying out printing processes with the following Sc. The reversal point is at a distance from the inflow opening of the nozzle and is at a maximum distance from the inflow opening of the nozzle hritten:

Providing a printhead with ink supply channel, plunger and nozzle with nozzle channel and inflow opening which forms the connection of the nozzle channel to the ink supply channel,

- Fill the ink supply channel with ink

A printhead for an ink-jet printer of the invention comprises an ink supply channel and at least one nozzle, the nozzle being associated with a movable plunger for effecting ink ejection from the ink supply channel.

At this point, some terms used in this document should be defined in advance: The term "rest position" is understood in the present context that a closure body occupies a position dependent on the printing process in the ink supply channel of a printhead, which leads to that no Ink comes out of the print head corresponding to the printing of a substrate does not take place.

The term "working position" is to be understood in the context that a closure body occupies a printing-dependent position in the ink supply channel, which allows the printing of a substrate with ink. The term "means" is to be understood in the context that contextually both the singular and the plural of the term may be meant.

The term "pigments" is to be understood in the context that they are particles in the ink having solid properties that are not soluble.

The term "ink channel" is to be understood as synonymous with the term "ink supply channel" in the context.

The ink jet printing technique is a widely used printing technique for printing on substrates. The printheads of inkjet printing devices typically include at least one ink supply channel and at least one nozzle for ejecting the ink from the ink supply channel.

In piezo inkjet printers, at least one piezoelectric element is deformed by applying an electrical voltage to such an extent that the deformation creates a pressure wave in the ink chamber or the ink channel, which causes an ejection of an ink drop through the nozzle.

A printhead of the type mentioned is known for example from WO2008 / 044069 A. In the known device, nozzles formed in the form of narrow strips with a passage for ink are vibrated to cause drop ejection from the nozzle.

In other known printheads, which allow the printing of ink with a high viscosity, the ink is often applied to the drop ejection and opened a valve for a short time to let a drop through. However, such systems have the disadvantage that problems can arise with the use of inks with large pigment sizes with the tightness of the valves and prevention of sedimentation in the region of the valve seat is very difficult to realize.

Conventional printheads, which include an ink supply channel and at least one nozzle, wherein each nozzle is associated with a closure body, comprise means which open a nozzle during the printing operation. In the rest position, the nozzle is sealingly closed by the closure body, so that leakage of the pressurized ink from the ink supply channel is prevented. In a job The plunger is lifted from the nozzle so that ink can flow into the nozzle and be expelled from the ink supply channel.

Such a printhead is disclosed in document EP0445137B1. The document describes a print head for an inkjet printer with an ink chamber connected to an ink pressure source, in which a plurality of, each closing a nozzle closure body are arranged, which are each connected to a pull rod and the closure body with a drive device in the ink chamber up and down to be moved. In the rest position of the closure body completely closes the ink jet. If the closure body is moved from the rest position to a working position, it is lifted or withdrawn by the nozzle. The ink is permanently pressurized in the ink chamber, so that only upon retraction of the closure body, the ink can be ejected from the ink supply channel through the nozzle. As soon as the closure body has returned to its normal position, the ink jet nozzle is closed.

Another printhead is disclosed in document EP0787587B1. The document describes a closure body, which is formed from a piston with an axially associated closure pin T-shaped. The closure body is located within a cylindrical chamber, wherein the outer diameter of the cylindrical piston corresponds approximately to the inner diameter of the chamber, so that the piston is sealingly moved up and down along the chamber wall. The piston separates the chamber into two regions, with a region at the bottom having a faceplate containing a downhole nozzle for ejecting ink droplets. This area comprises the ink and forms the ink chamber which is connected to an ink pressure source. In the other chamber is a spring which presses against the closure body. Due to the design, in the rest position, the locking pin extends into the borehole of the nozzle and closes it, whereby an ink film is present between the front plate and the piston. When an overpressure is built up in the ink chamber, the pressure causes the piston, and thus the locking pin, to be withdrawn from the borehole from the rest position to a working position against the return force of a spring, whereupon the pressurized ink flows into the borehole and out of the nozzle can be ejected. If the overpressure is reduced, the lock pin is brought back into the rest position and moves back into the Borehole, whereby the remaining ink in the nozzle is displaced and the wellbore is closed.

The conventional printheads for performing printing processes with a closure body are designed by their functional and characteristic structure for carrying out printing processes with relatively low printing frequencies, which is reflected in the relatively slow printing processes.

In carrying out a printing step, the closure body is brought from the rest position to a working position, wherein the pressurized ink from the ink channel exits through the nozzle. The ink flow is stopped by the closure body impinges on the nozzle, on the nozzle or on the inner wall of the ink chamber and the inlet opening of the nozzle sealingly closes. In order to be able to cleanly separate an ink droplet from the residual ink, the closure body must close the inflow opening of the nozzle completely or sealingly, wherein a collision of the closure body with the nozzle and / or the inner wall of the ink chamber is unavoidable. If the inlet opening of the nozzle is not completely closed with the closure body in a rest position, ink can continuously emerge from the ink channel through the nozzle in the form of an ink jet.

The more drops are required per unit time for the generation of a desired motif or structural printing motif, the higher the corresponding printing frequency of the printing steps to be performed.

It goes without saying that the feasibility of printing steps with a relatively high printing frequency is limited by periodically occurring collisions of the closure body with the nozzle and / or the inner wall of the ink chamber, since the collisions in a short time a material failure of the closure body and / or cause the nozzle, which is associated with a short life of the print head. The stability of the printing process is reduced in conventional printheads increasingly the higher the print frequency is selected, since the probability of material failure in the closure body and / or increases at the nozzle accordingly. In other conventional printheads, such as in the EP0787587B1, a hard collision of a T-shaped closure body with the nozzle and / or inner wall of the ink chamber can be at least partially avoided, since an ink film at least a portion or part of the closure body separates from the nozzle. If the closure body is moved from a working position into the rest position, the closure pin of the closure body extends into the channel of the nozzle in the rest position and closes it, but the ink or ink film, which is no longer displaceable in the ink chamber, owing to design and process reasons in one of the end face of the closure body piston opposite portion radially outward beyond the closure body piston outer edge beyond can not escape because the closure body piston is sealingly moved up and down on the chamber wall, so still a collision of the closure body with the Ink film is done. A collision with the ink film is somewhat gentler than collision with a solid, since, as known, a liquid has a greater compressibility than a solid, so that the life can be at least partially increased. However, a material failure can not be ruled out, but can only be delayed in terms of time. In the case of the abovementioned embodiment of the printhead, the following also applies, namely, the higher the printing frequency and thus the collision frequency, the higher the probability of a material failure. If pigments are contained in the ink, material failure is more likely to occur. It is an object of the invention to provide a printing method and apparatus which enable the feasibility of printing steps at a higher frequency than conventional printing methods.

This object is achieved with a printing device of the type mentioned in the present invention in that the first means limit the movement of a plunger end to move between the reversal points and second means are provided for applying the ink in the ink supply channel with a negative pressure relative to the ambient air pressure. During the printing process, ie at least during the time intervals in which should not be printed or ink is to be ejected from the ink channel, the ink supply channel is at least in the region of the inflow opening of the nozzle with a negative pressure relative to the ambient pressure applied. The negative pressure prevents ink from inadvertently leaking from the ink channel. In this way, can be dispensed with a closure body. For ejecting the ink, a plunger provided in the ink channel is used, the end face of which is moved toward the nozzle channel, whereby ink is pressed through and out of the nozzle channel, preferably during the entire printing process, a plunger / nozzle spacing is maintained, ie a At a turning point, the tappet end face has a distance from the inflow opening of greater than zero and the inflow opening of the nozzle remains permanently open during the entire printing process. The plunger according to the invention therefore does not assume the function of a closure body. With the printhead according to the invention it is possible to use inks which are in a wide viscosity range and / or include the pigments.

This is particularly because the plunger does not have to function as a closure body and the ink and / or pigments sliding between the plunger end side and the inlet opening of the nozzle channel do not interfere.

The above-mentioned inks can be used with the inventive printhead for structural printing. By the term "structural pressure" is meant in this case the application of three-dimensional shapes, lines, structures etc. on at least one surface with smooth and / or rough areas, e.g. a wood structure on an MDF / HDF board or tray, Braille writing, or simulation of a lettering etc.

Preferably, the nozzle is fixedly arranged on a side wall of the ink supply channel and there is a plunger which is reciprocated in the ink supply channel between two opposite of the nozzle reversal points, provided.

The functional and characteristic structure and printing method of the printing device according to the invention is characterized in particular by the fact that means, preferably ex- provided means that generate a negative pressure in the ink supply channel, so that a nozzle can remain open during the entire printing process without unintentional leakage of ink can take place. According to a preferred embodiment, a plunger is moved back and forth between two reversal points (U1) and (U2) opposite the nozzle, wherein the plunger / nozzle distance is greater than zero, so that at no time during the printing process, ie before and / or during and / or after the ejection of ink periodically occurring collisions of the plunger with the nozzle. This ensures that you can print with the inventive printhead with higher print frequencies than in conventional printing process.

The plunger, in a preferred embodiment, is non-sealingly disposed in the ink supply channel on an ink channel wall, i. it does not form a closure body at any time, with an end face of the tappet being moved towards the inlet opening from a starting point for discharging the ink. An end face of the plunger is moved toward the inflow opening only up to a first reversal point (Ul), this first reversal point (Ul) being spaced from the inflow opening, so that even at the first reversal point (Ul) there is no closure of the ink supply channel comes. When the plunger end is moved toward the inlet opening for ejecting the ink from a starting point, the ink is pressed from a stagnation area between the end face of the plunger and the side of the side wall opposite the plunger front side toward the inlet opening of the nozzle, at the same time ink inside the ink supply channel to the outside, ie can flow beyond the ram outer edge. The term "ram face" and "face" in the context are synonymous to understand. As a tappet end face in the invention is not necessarily meant a contiguous surface, but it may also be two or more surfaces meant.

The inventive printing method has shown that the life of the printhead is increased, since the plunger collisions are avoided with the underlying under the plunger face liquid or liquid film and / or the nozzle and / or the inner wall of the ink supply channel. By the invention, compared to a conventional printhead, which includes a plunger, a higher process stability is achieved, because of design and process reasons, the probability of material failure of the plunger and / or the nozzle is greatly reduced.

The inventive printhead for an ink jet printer comprises at least one ink supply channel and at least one nozzle with nozzle channel and inflow opening, whereby ink can be forced out of the ink supply channel into the nozzle channel and ejected from the ink supply channel through the inflow opening, the nozzle being stationary on a side wall the ink supply channel is arranged and the at least one nozzle is associated with a tappet with located in the ink supply channel ram face opposite the inlet opening, wherein the print head comprises first means for moving a plunger front side in the ink supply channel between a minimum distance from the inlet opening of the nozzle reversal point (Ul) and one of the Ein-flow opening of the nozzle maximally spaced reversal point (U2), wherein the first means limit the movement of a plunger front side to a movement between the reversal points (U1, U2) and two Ite means for applying the ink in the ink supply channel are provided with a negative pressure relative to the ambient air pressure. Third means for pumping the ink through the ink supply channel may be provided to prevent sedimentation of the ink in the ink supply channel.

The means for moving a plunger comprise in a preferred embodiment at least one actuator, wherein the at least one actuator can move the plunger between two reversal points. In another preferred embodiment of the present invention, the means for moving a plunger may comprise at least one actuator and at least one spring. However, other conventional means for moving the plunger can also be used.

The preferred external means for charging the ink in the ink supply channel with a negative pressure relative to the ambient air pressure may be, for example, conventional vacuum pumps with which it is possible to generate a corresponding back pressure to the ambient air pressure and the geodetic pressure of the ink in the nozzle channel To prevent leakage of the ink from the ink supply channel. The ink pressure must be adjusted in combination with the capillary so that no air is sucked through the nozzle channel in the ink supply channel and that no ink from the nozzle channel unintentionally emerges. The ink pressure is by definition the sum of the circulation pressure and the meniscus negative pressure.

The external means may be conventional pumps such as e.g. be a circulation pump or a circulation pump. With the means, the ink is pumped through the ink supply channel, preferably permanently. In a preferred embodiment of the present invention, the distance between a plunger end face and the inlet opening is greater than zero at the minimally spaced reversal point (U1).

In order to ensure optimum productivity of a printhead according to the invention, several nozzles may be present in the ink supply channel, each nozzle being associated with a plunger.

In another preferred embodiment of the invention, at least in the case of the at least one nozzle, no side wall is formed integrally with the nozzle and an end face of the at least one nozzle surrounding the inflow surface is flush with an inner surface of a side wall in contact with the ink formed of the ink supply channel.

The abovementioned object can also be achieved with a method of the type mentioned in the introduction by subjecting the ink at least during the time intervals in which the ink supply channel is subjected to a negative pressure relative to the ambient air pressure at least in the region of the inlet opening of the nozzle whereby a leakage of the ink from the nozzle channel is prevented even without closure body and that for ejecting the ink, an end face of the plunger is moved from a starting point to the inlet opening.

The inventive printing method for performing printing processes includes a plurality of steps, wherein in a first step, a print head with ink supply channel, plunger and nozzle with nozzle channel and inflow opening, the connection of the nozzle channel is provided to the ink supply channel, is provided and in a second step, the ink supply channel is filled with ink, wherein the ink is at least during the time intervals in which not to be printed in the ink supply channel at least in the region of the inlet opening of the nozzle is subjected to a negative pressure, whereby an outflow the ink is prevented from the nozzle channel even without closure body and wherein for ejecting the ink, an end face of the plunger is moved from a starting point to the inlet opening.

In the printing method, in a preferred embodiment, an end face of the plunger is moved toward the inflow opening only up to a first reversal point (U1), this first reversal point (U1) being spaced from the inflow opening, so that it is spaced even at the first reversal point (U1 ) does not come to a closure of the ink supply channel. After reaching the reversal point (Ul), the end face of the plunger is moved away from the inflow opening to a second reversal point (U2), which forms the starting point for the subsequent printing cycle.

The position of the starting point and the subsequent reversal point (UI) is selected so that the ram stroke ejects a predetermined amount of ink and thus drop size.

In a preferred embodiment, in the printing process in the step in which the plunger front side is moved to eject the ink from the starting point to the inflow opening, the ink starts from a stagnation area between the end face of the plunger and the opposite side of the plunger face Side wall with nozzle in the direction of the inlet opening of the nozzle pressed, at the same time ink within the ink supply channel to the outside, that can flow out beyond the plunger outer edge, wherein in this preferred printing method, the distance from the plunger outer edge to a side wall of the ink supply channel in a direction vertical to the nozzle axis must be greater than zero. As a result of the movement of the plunger, a relatively strong flow of the ink constantly prevails in the area of the inlet opening of the nozzle, so that sedimentation of the ink can be prevented very efficiently in this area. When the end face of the plunger is moved toward the inflow port from a starting point, there is a volume and pressure change in the nozzle near area, which causes ejection of ink from the ink supply passage. The ink is pumped in the process according to the invention through the ink supply channel, preferably permanently.

A stagnation region is that region between the plunger end side and the region of the side wall with nozzle which is opposite the plunger end side. In that stagnation area, as a result of the movement of the plunger, which is moved from a starting point to the inlet opening of the nozzle, the ink experiences the highest pressure, so that the ink is pressed from this stagnation area in the direction of the inlet opening of the nozzle, at the same time Ink within the ink supply channel to the outside, ie can flow beyond the ram outer edge. If according to a preferred embodiment of the invention, the plunger is cylindrical and the nozzle also, the stagnation region is referred to in an ideal case for simplicity as stagnation radius.

In the printing method according to the invention, the nozzle remains open during the entire printing process, so that the plunger does not close the inlet opening of the nozzle and does not touch the nozzle and / or the inner wall of the ink supply channel.

In the printing method, in a step (a), the plunger front side is moved by means of a reversal point (U2) opposite to the inlet opening of the nozzle in a stroke movement in the direction of the inlet opening of the nozzle to a reversal point (U1) opposite to the nozzle a volume and pressure change in the nozzle near area occurs, which causes an ejection of ink from the nozzle. In a step (b), the plunger end is moved by means of a reversal point (Ul) in a stroke movement in the opposite direction of the inflow opening of the nozzle to a reversal point (U2), wherein the steps (a) and (b) take place successively and Reversal point (U2) forms the starting point for the subsequent printing cycle, during the entire printing process, the plunger / nozzle distance is greater than zero. The reversal point (Ul) always has a smaller nozzle / plunger distance than the reversal point (U2). In particular, it should be emphasized that the printing method with the printing device is a drop on demand (DOD) printing technique in which ink drops are ejected from a nozzle only when actually needed Ink in the ink channel and nozzles is prevented because the inventive printhead, according to a preferred embodiment, is provided with external means for pumping the ink through the ink channel which pumps the ink through the ink supply channel, preferably permanently printing processes with the print head is characterized in a preferred embodiment in that the plunger in the ink supply channel between two inflow of the nozzle opposite reversal points, a reversal point (Ul) and a reversal point (U2), is moved, preferably at no time during the Printing, ie before and / or it does not touch or close the nozzle and / or a side wall of the ink supply channel during and / or after the ejection of ink, the plunger.

The solution according to the invention enables in a simple manner a mechanically very stable arrangement of the nozzles and a very efficient prevention of sedimentation of the ink even when using inks with large pigments. It should be noted at this point that the term stationary in the present context should be understood to mean that the position of the nozzle does not change during operation relative to the ink channel. However, for purposes of maintenance and replacement, the nozzle may be removed from the ink channel, such as the nozzle may be threaded into the ink channel, for example. Moreover, by using a tappet cooperating with the nozzle, it is possible to dispense with the arrangement of a valve, which is opened after the generation of an overpressure in the ink channel.

Sedimentation at the nozzles can also be very well prevented by having an inlet opening having the end face of the nozzle is flush with an inner, in contact with the ink surface of the side wall of the ink supply channel. Ink ejection and self-cleaning of the nozzle are facilitated by having a longitudinal central axis of the at least one nozzle normal to the surface of the ink supply channel. A particularly preferred embodiment of the invention is that the inflow opening of the nozzle is arranged in a region of the side wall opposite the plunger, which is delimited by a cylindrical boundary surface forming in the ink when the plunger moves. This embodiment of the invention is characterized in that a pumping chamber, that is to say that region in which a volume change occurs when the ink is ejected or aspirated, can be realized, in which only the two cover surfaces (end face of the plunger and the end face of the nozzle) are formed as a solid and the lateral surfaces are formed by the ink liquid. As a result, the sedimentation and agglomeration of the ink in the pumping chamber as well as the maintenance effort can be significantly reduced.

According to an advantageous embodiment of the invention, it may be provided that a front side opposite portion of the plunger is fixedly connected to a movable push rod, which is acted upon by a force acting in the direction of the nozzle restoring force. This embodiment of the invention makes it possible to initiate a movement of the plunger in the direction of the nozzle in a simple manner for expelling ink. The restoring force may, for example, be caused by a coil spring which is compressed by the nozzle when the plunger is retracted. The force required to retract the plunger can be generated by means such as an actuator, for example an electromechanical actuator, in particular an electromagnet, a pneumatic or another suitable actuator. For this purpose, the push rod may be connected to the actuator, which generates a force acting against the restoring force. When using an electromechanical actuator can be moved in a de-energized state of the actuator, the plunger by the spring against the nozzle. Of course, it is also conceivable that spring and actuator are reversed in the embodiment just described. Also, the use of a second actuator instead of the spring would be possible.

According to a variant of the invention it can be provided that the push rod at least in sections in a hollow shaft parallel to a longitudinal center line the hollow shaft is movably guided, wherein between the guide rod and the hollow shaft, a radially encircling seal can be provided. By means of this embodiment of the invention, the flow resistance in the ink channel can be substantially reduced, since the hollow shaft, which is also referred to below as the guide shaft, can be designed to be very slim, without impairing the guide function for the push rod. The seal between the push rod and the guide shaft prevents ink from entering the guide shaft.

In order to reduce the flow resistance in the nozzle and to increase the efficiency, it can be provided that the inflow opening of the nozzle is conical, in the form of a funnel tapering in the direction of an outlet opening. A particularly favorable development of this embodiment provides that the outlet opening of the nozzle is cylindrical. In order to prevent a complete emptying of the nozzle during an aspiration of ink caused by a lifting movement of the plunger air into the pumping chamber, the nozzle may have a length in the flow direction which is a multiple, but at least twice, a maximum Diameter of the nozzle is. The life of the nozzle and the plunger can be increased by the fact that the nozzle made of ceramic, hard metal or surface-treated steel are made and / or the end face of the plunger is at least partially formed of ceramic, hard metal or surface-treated steel. The invention together with further advantages will be explained in more detail with reference to some non-limiting embodiments, which are illustrated in the drawings.

In these, in each case in a highly schematically simplified representation: FIG. 1 shows a partial section through a print head;

Fig. 2 shows a part of the print head of Fig. 1 in more detail;

Fig. 3 is a formed between an end face of a plunger and a nozzle

Pumping chamber; Fig. 4 is a principle of operation of an imaginary pumping chamber and

Fig. 5 is a theoretically calculated pressure distribution under the end face of a plunger.

By way of introduction, it should be noted that in the differently described embodiments identical parts are provided with the same reference numerals or identical component designations, wherein the disclosures contained in the entire description can be mutatis mutandis transferred to like parts with the same reference numerals or identical component names. Also, the location information chosen in the description, such as top, bottom, side, etc. related to the immediately described and illustrated figure and are to be transferred to the new situation mutatis mutandis when a change in position.

The figures are described below overarching.

Referring to Figs. 1 and 2, an ink jet printer head 1 according to the present invention has at least one ink supply passage 2 and at least one nozzle 3 for ejecting the ink from the ink supply passage 2.

A plurality of ink ducts arranged parallel to one another and extending in length may be provided in the print head 1, in which, as shown in FIG. 1, nozzles 3 and movable plungers 6 are arranged at regular intervals. The ink channels, nozzles 3 and plunger 6 are in this case formed or arranged like the ink channel 2, nozzle 3 and plunger 6 described below. The ink channel 2 serves to supply ink to the nozzle 3. The ink can flow continuously through the ink channel 2 to avoid sedimentation of the ink. The pressure drop in the ink channel 2 is favorably very low, which can be achieved by the largest possible cross section of the ink channel.

The nozzle 3 is fixedly arranged on a side wall 4 of the ink supply passage 2, and in the ink supply passage 2 is a reversing point opposite to two of the inflow port of the nozzle, a reciprocating point (U1) and a reversing point (U2) reciprocating pestle 6 provided. The nozzle 3 can be arranged interchangeably on the side wall 4, for example, the nozzle 3 can be inserted into the side wall 4 of the ink cartridge. be screwed supply channels 2. In order to be able to withstand abrasive pigments of the ink, the nozzle 3 can be made of ceramic, hard metal, glass, etc.

An end face 7 of the nozzle 3 having the inflow opening 5 may be flush with an inner surface 8 of the side wall 4 of the ink supply channel 2 in contact with the ink. Due to the flush design of the nozzles 3 at their inner end faces 7 with the inner wall of the ink channel 2, the flow of ink is disturbed as little as possible and avoid sedimentation. A longitudinal central axis a of the nozzle 3 can in this case run normal to the surface 8 of the ink supply channel 2.

A front side 9 of the plunger 6 opposite portion of the plunger 6 can be firmly connected to a force acting in the direction of the nozzle 3 restoring force, movable push rod 10 connected. The plunger 6 can be withdrawn from the nozzle by means of an actuator. As an actuator for actuating the plunger, an electromechanical actuator, for example in the form of an associated with the push rod 10 armature 11, which cooperates with a coil 12 which may be wound around a core 13, may be provided. The plunger 6 can be pulled upwards by the armature 11 of the tension magnet. In this case, a provided in Fig. 1 with the reference numeral 14 spring is tensioned, which pushes the plunger 6 back down in a de-energized state of the actuator. When the plunger 6 approaches the nozzle 3 or when the armature 11 approaches the core 13, a strong damping caused by radial film flow, and prevents the hard impact of the plunger 6 and the armature 11 on the between the plunger and the nozzle or the inner wall of the ink supply channel present ink or ink film and thus increases the life of the plunger 6 and the actuator. Instead of the tension magnet, other types of drive for the plunger are conceivable, for example in the form of a pneumatic or piezo actuator.

The push rod 10 may be at least partially movable in a hollow shaft 15 parallel to a longitudinal center line of the guide shaft or hollow shaft 15, wherein between the guide rod 10 and the hollow shaft 15, a radially encircling seal 16 may be provided. As can be seen from FIGS. 1 and 2, the guide shaft 15 can project from the nozzle wall 3 opposite the boundary wall 17 of the ink channel 2 into the ink channel 2. By sealing the transition between the guide shaft 15 and the plunger 6, the ink can be prevented from entering the guide shaft 15. The guide shaft 15 may be made slender so as to cause as little as possible flow resistance in the ink channel. It is particularly favorable in this case if the guide shaft or hollow shaft 15 has a smooth and / or rounded surface. The guide shaft or hollow shaft 15 may, for example, have a circular, elliptical or similar cross-section.

In the plunger end face 9, a ceramic part or a part of a different material than those of the plunger material may be inserted to obtain a longer life of the end face 9 in the presence of abrasive pigments. As can be seen from FIG. 3, the inflow opening 5 of the nozzle 3 can be conical, in the form of a funnel tapering in the direction of an outlet opening 18. The outlet opening 18 of the nozzle 3 can be cylindrical in this case. In addition, the nozzle 3 may have a length L which is a multiple, but at least twice, of a maximum diameter d of the nozzle 3.

Preferably, the inflow opening 5 of the nozzle 3 is arranged in a region of the side wall 4 opposite the plunger 6, which is located within a pumping chamber 19 and delimits it in one direction. The existing and necessary in each inkjet printhead pumping action, which is illustrated by an imaginary pumping chamber 19 and can be formed from a cylindrical space portion which by the diameter dl of the plunger end face 9 and the distance al plunger end face to inner Nozzle end face or to the end face of the inflow opening 5 is limited. However, this space does not necessarily have to be cylindrical.

The pumping chamber 19 is the space in which a volume change takes place. The pumping chamber 19 has, as in the only illustrative of the principle of action of a Pumping serving Fig. 4 shown, always two openings 20 and 21, one for the inlet and one for the outlet. During the refill cycle, the plunger 6 moves upward and ink flows into the space of the pumping chamber 19 through the inlet 20 and the outlet opening 21. During the ejection cycle, the plunger 6 moves downward and ink flows through the inlet 21 and outlet opening 20 from the space of the pumping chamber 19th

For the printhead 1 to be able to eject a drop, more ink has to flow out through the outlet opening 21 of the pumping chamber than flows back into the ink channel 2 through the inlet opening of the pumping chamber 20. For the suction of ink into the pumping chamber 19, the reverse condition applies. In Fig. 4, this is graphically illustrated, wherein the direction of movement of the plunger 6 and the flow directions of the ink when sucking in or expelling the ink from the pumping chamber 19 in Fig. 4 are indicated by arrows. By different thickness arrows, the different amounts of incoming or outflowing ink to be indicated.

When the plunger 6 moves, ink is displaced or sucked out of the pumping chamber 19. The plunger movement simultaneously causes a change in volume and pressure in the pumping chamber 19. In this case, as can be seen from FIG. 5, a pressure profile is formed along the plunger radius r.

Where this pressure curve has its maximum or minimum, arises according to FIG. 3, a cylindrical boundary surface 22 with the so-called stagnation radius rs. Outside this limiting surface 22, the ink flows into or out of the ink channel, within this limiting surface 22, the ink flows out of the nozzle or into the nozzle, depending on the direction of movement of the plunger 6. The stagnation radius rs depends on the direction of movement and speed of the plunger 6, from the distance al of the plunger 6 to the nozzle and the pressure at the radius r and the radius ri from. This results in the ink volumes flowing in both directions during the up and down movement of the plunger 6.

The inflow opening 5 of the nozzle 3 can be arranged directly at the outlet opening 21 of the pumping chamber 19. In this embodiment, the inflow opening 5 of the nozzle 3 is disposed in a region of the side wall 4 opposite the plunger 6, which is at Movement of the plunger 6 by the associated pressure curve in the ink within the ink forming boundary surface 22 is limited.

Fig. 5 shows a theoretically calculated radius-dependent pressure curve under the plunger 6. The stagnation radius rs is where the pressure has the maximum value.

In commercially available inkjet printheads, the length L in the flow direction is usually designed so that the ink volume in the nozzle approximately corresponds to the drop volume. Since the nozzle diameter in a printhead for structure printers must be greater than in commercial inkjet printheads to achieve the required drop volume of the capillary pressure is much smaller and it is sucked during the refill cycle more ink through the nozzle 3 in the pumping chamber 19 back. For this reason, the length of the nozzle L may be substantially increased, so that the nozzle during the refill cycle can not be completely emptied and air in the pumping chamber 19 reached.

The length L of the nozzle consists of the lengths for the cylindrical part 11 and for the conical part 12. For the sake of order, it should finally be pointed out that for a better understanding of the construction of the device according to the invention, these or their constituents are partly not to scale and / or enlarged and / or reduced in size.

For the sake of order, it should finally be pointed out that, for a better understanding of the structure of the device according to the invention, these or their components have been shown partly in an inaccurate manner and / or enlarged and / or reduced in size.

In a preferred embodiment of the present invention, a plurality of ink supply channels 6 in a printhead are aligned parallel to each other in length, in each of which a plurality of nozzles 3 with nozzle channel and inflow opening 5 are preferably arranged at equal intervals on the ink supply channel wall. First means 23, such as at least one actuator or at least one actuator and at least one spring are provided for the movement of a tappet end face 9 or of the tappet 6 which limit the tappet end face 9 to a movement between the reversal points (U1, U2). Second external means, like a vacuum pump, which is arranged, for example, in an intermediate ink tank, which is connected to the printhead via at least one ink supply line, and which pump is arranged in the air space above a liquid level, is provided for pressurizing the ink in the ink supply channel 2 with a negative pressure relative to the ambient air pressure , Third external means, such as a recirculation pump, is provided, for example, in an intermediate ink tank which preferably pumps the ink permanently through the at least one ink supply conduit and ink supply channels of the printhead.

In a preferred embodiment of the printing method, the ink in the ink supply channel 2 is subjected to a negative pressure in the range of greater than zero to preferably 5 mbar relative to the ambient pressure with a nozzle internal diameter of 300 μιη at the outlet opening of the nozzle. However, it is also possible, for example, for other negative pressures to be used, wherein the ink pressure must not be chosen to be smaller than the capillary pressure, so as to ensure that no air is sucked through the nozzle into the ink supply channel. Under the term "negative pressure in the range greater than zero to preferably 5 mbar relative to the ambient air pressure", a pressure is meant which is smaller in the range of greater than zero to 5 mbar than the ambient air pressure.

The ink delivery rate per unit time "X" pumped by the ink supply channel, in one preferred embodiment, is greater than the sum of the amount of ink that can be maximally expelled through all nozzles during the printing operation, by a particular factor adapted to the system The rule is that the ink pressure in combination with the capillary pressure must be set so that no air is sucked through the nozzle channel in the ink supply channel and that no ink from the nozzle channel unintentionally leaks.

The plunger 6 is arranged non-sealingly in the ink supply channel 2 on an ink channel wall, wherein a distance from the plunger outer edge to a side wall of the ink supply channel in a direction vertical to the nozzle axis is preferably greater than 1 mm and more preferably greater than 3 mm. In a preferred embodiment of the printhead device, the plunger 6 has an outer diameter preferably between 3.0 to 5.0 mm. The nozzle 3 in this case has an inner diameter preferably between 200 to 350 μιη. In a preferred embodiment of the printing method, the change of direction at the reversal point (Ul) has a frequency preferably up to 1.1 kHz and more preferably up to 1.0 kHz. If the ram outer diameter is chosen smaller, you can print at much higher frequencies. In the printing method, the plunger / nozzle distance at the reversal point (Ul) is greater than zero and preferably adhered to 100 μιη and the plunger / nozzle spacing at the reversal point (U2) greater than 250 μιη and preferably adhered to 400 μιη.

The method is used in the printing of inks of different viscosity, wherein it is preferred that the ink has a viscosity η of η = 50-100 mPsec and / or the ink for printing pigments having a pigment size of up to 10 μιη wherein the ink preferably has a pigment size of up to 5 μm. Inks with a low or higher viscosity than the stated viscosity η of η = 50-100 mPas and / or with larger pigment sizes than 10 μm may in principle also be used, as long as optimum pressure stability can be ensured.

If inks are used in a printing process with pigments having a particle size "g", it goes without saying that one should choose at least one plunger / nozzle spacing at a reversal point at least greater than the corresponding particle size "g", to avoid collisions of the plunger with the possibly present on the nozzle surface pigments.

When the plunger end face 9 is moved toward the inflow opening from a starting point, a change in volume and pressure occurs in a portion of the inflow port of the nozzle, and a certain amount of ink and thus droplet size are ejected from the nozzle. A main drop is ejected from the nozzle, but depending on the printing process, more or less undesirable small droplets, so-called satellites, are ejected with the main drop with the main drop. In other embodiments of the present invention, multiple printheads may be mounted in a staggered or any other arrangement and arranged such that in the printing process at least one nozzle of a printhead overlaps at least one nozzle of another printhead in at least one direction and / or the nozzles of a nozzle row of a printhead are shifted from one another by a certain nozzle spacing with respect to the nozzles of a nozzle row of another printhead.

If the nozzles are shifted from each other, higher drop densities and thus higher image resolutions can be achieved.

In another embodiment of the present invention, in which the print heads are moved in a subscanning direction Y and main printing direction X in the printing process, the nozzle rows of the printheads can be set parallel to each other and obliquely at an angle with respect to a subscanning direction Y, thereby spacing the nozzle the individual nozzles of a print head in a main printing direction X has a nozzle pitch Y, so that one can print in the main scanning direction X with a higher resolution than with the native resolution of a print head. The present invention is not to be limited to the embodiments of the printhead device in the example and the drawings.

REFERENCE NUMBERS

printhead

Ink supply channel

jet

Side wall

inflow

tappet

Front side of the nozzle

surface

Tappet front side or front side

pushrod

1 magnet armature

Kitchen sink

core

feather

5 hollow shaft

6 sealing

7 boundary wall

8 outlet opening of the nozzle

9 pumping chamber

0 inlet opening

1 outlet opening

2 boundary surface

Claims

Patent claims

A printhead (1) for an ink jet printer, the printhead (1) having at least one ink supply passage (2) and at least one nozzle (3) with nozzle passage and one flow port (5), the ink flow through the inflow port (5) The nozzle (3) is fixedly arranged on a side wall (4) of the ink supply channel (2) and the at least one nozzle (3) has a plunger (6) with in the ink supply channel (2) in the nozzle channel Ink supply channel (2) lying ram face (9) which is the inlet opening (5) spaced opposite, associated, wherein the print head (1) comprises first means for moving the plunger end face (9) in the ink supply channel (2) between one of the inlet opening (5) the nozzle (3) minimally spaced reversal point (Ul) and one of the inflow opening (5) of the nozzle (3) maximally spaced reversal point (U2), characterized in that the first means di e limiting movement of a plunger end face (9) to movement between the reversal points (U1, U2) and second means for pressurizing the ink in the ink supply channel (2) with a negative pressure relative to ambient air pressure.

2. Printhead according to claim 1, characterized in that at the minimum spaced reversal point (Ul), the distance between a plunger front side (9) and the inlet-flow opening (5) is greater than zero.

3. Printhead according to claim 1 and 2, characterized in that a plunger - outer edge to a side wall (4) of the ink supply channel (2) in a direction vertical to the nozzle axis greater zero, more preferably greater than 1mm and more preferably greater than 3 mm.

4. Printhead according to one of the preceding claims, characterized in that a plurality of nozzles (3) are present and each nozzle (3) is assigned a plunger (6).

5. Printhead according to one of the preceding claims, characterized in that at least in the case of at least one nozzle (3) no side wall (4) together with the nozzle (3) is made in one piece and the inflow opening (5) surrounding the end face (7) at least one nozzle (3) flush with an inner, in contact with the ink standing surface (8) of a side wall (4) of the ink supply channel (2) is formed.

6. Printhead according to one of the preceding claims, characterized in that a longitudinal central axis (a) of the at least one nozzle (3) normal to the surface (8) of the

Ink supply channel (2) runs.

7. Print head according to one of claims 1 to 6, characterized in that the inflow opening (5) of the nozzle in a the plunger (6) opposite region of the side wall (4) is arranged by a movement of the plunger in the Ink forming cylindrical boundary surface is limited.

8. Printhead according to claim 7, characterized in that one of an end face (9) of the plunger (6) opposite section of the plunger (6) fixed with an acted upon in the direction of the nozzle (3) restoring force, movable push rod (10 ) connected is.

9. Printhead according to claim 8, characterized in that the push rod (10) at least in sections in a hollow shaft (15) parallel to a longitudinal middle line of the hollow shaft (15) is movably guided, wherein between the guide rod (10) and the hollow shaft (15) a radially encircling seal (16) is provided.

10. Printhead according to one of the preceding claims, characterized in that, the inflow opening (5) of the nozzle (3) is conical, in the form of a tapering in the direction of an outlet opening (18) funnel is formed.

11. Print head according to claim 10, characterized in that the outlet opening (18) of the nozzle (3) is cylindrical.

12. Printhead according to one of the preceding claims, characterized in that the nozzle (3) has a length (L) which is a multiple, but at least twice, a maximum diameter (d) of the nozzle.

13. Printhead according to one of the preceding claims, characterized in that the nozzle (3) are made of ceramic, hard metal or surface-treated steel and / or the end face of the plunger is at least partially formed of ceramic, hard metal or surface-treated steel.

14. Printhead according to one of the preceding claims, characterized in that the plunger (6) has an outer diameter preferably between 3.0 to 5.0 mm.

15. Printhead according to one of the preceding claims, characterized in that a nozzle has an inner diameter preferably between 200 to 350 μιη.

16. A method for performing printing processes comprising the steps of: - Providing a print head with ink supply channel (2), plunger (6) and nozzle (3) with nozzle channel and inlet opening (5) which forms the connection of the nozzle channel to the ink supply channel (2) .

Filling of the ink supply channel (2) with ink, characterized in that the ink at least during the time intervals in which should not be printed, the ink supply channel (2) at least in the region of the inflow opening (5) of the nozzle (3) is subjected to a negative pressure relative to the ambient air pressure whereby a leakage of the ink from the nozzle channel is prevented even without closure body and that for ejecting the ink, an end face (9) of the plunger (6), starting from a starting point to the inflow opening (5) is moved.

17. The method according to claim 16, characterized in that an end face (9) of the plunger (6) only to a first reversal point (Ul) on the inflow opening (5) is moved, said first reversal point (Ul) of the inflow opening (5 ), so that even at the first turning point (Ul), there is no closure of the ink supply passage (2).

18. The method according to claim 17, characterized in that after reaching the

Turning point (Ul) one end face (9) of the plunger (6) from the inflow opening (5) to a second reversal point (U2) is moved away, which forms the starting point for the subsequent printing cycle.

19. The method according to claim 18, characterized in that the position of the starting point and the subsequent turning point (Ul) is selected so that the ram stroke ejects a predetermined amount of ink and thus drop size.

20. The method according to claim 16 to 19, characterized in that in the step in which the plunger end face (9) for ejecting the ink from a starting point to the inflow opening (5) is moved, the ink starting from a stagnation region between the end face (9) the ram (6) and the region of the side wall (4) opposite the tappet end face (9) is pressed with nozzle (3) in the direction of the inflow opening (5) of the nozzle (3), at the same time ink within the ink supply channel (2) Outside, ie can flow beyond the ram outer edge.

21. The method according to claim 16 to 20, characterized in that the ink is pumped through the ink supply channel (2), preferably permanently.

22. The method according to claim 17 to 21, characterized in that a change of direction of the plunger (6) at the reversal point (Ul) has a frequency preferably up to 1.1 kHz and more preferably up to 1.0 kHz.

23. The method according to claim 17 to 22, characterized in that the plunger / nozzle spacing at the reversal point (Ul) is greater than zero and preferably maintained to 100 μιη.

24. Printing method according to claim 17 to 23, characterized in that the tappet / nozzle distance at the reversal point (U2) is greater than 250 and preferably up to 400.

25. Use of a method according to claim 16 to 24 for printing with inks of different viscosity wherein it is preferred that the viscosity η of η = 50 - has 100 mPas sec and / or for printing with inks, the pigments having a pigment size of up to 10 μιη have, wherein the pigment size preferably up to 5 μιη include.

26. The method according to claim 16 to 25, characterized in that with the

Printhead three-dimensional shapes, lines, structures are applied to at least one surface with smooth and / or rough areas.