DE4128590A1 - Multi-nozzle transfer of printing ink using pneumatic jets - electronically controlling timing of valve operations blowing ink out of individual nozzles of linear array - Google Patents

Abstract

The printhead (10) has, e.g. seven, nozzles (11) spaced 10 mm apart and supplied with ink from an easily replaceable plastics material bottle (12) which feeds a common ink chamber (13). The ink fills a cylindro-conical space (15) around each nozzle body (16) and is ejected through the opening (14) by the jet of air delivered by the individual two-position two-port magnetic valve (20). An electronic control operates the valves to produce a 5 x 7 dot matrix character or continuous stripe. USE/ADVANTAGE - For application of characters, symbols or bar codes, drying time is shortened and sharpness of imprint is improved.

Description

The invention relates to a method for applying Print color on an object using multiple colors spray nozzles for generating a print image and one Printhead for marking devices with several paint spray nozzles, which can be individually controlled and which can be controlled via one Line printing ink is supplied.

Signers working according to the DOD (Drop On Demand) process devices are used to apply characters, symbols or barcodes on packages and other items. Such DOD marking devices usually consist of them  ben or sixteen in a row one above the other Paint spray nozzles that electronically with short pulses like this can be controlled that they on passing objects spray on individual drops of paint, then the total is a typeface in a 7 × 5 or 16 × 10 matrix result depending on the number of paint spray nozzles.

According to a generally known design, the colors spray nozzles supplied with paint via separate lines, which are opened and closed via solenoid valves will.

From DE-A-33 02 617 is a paint spray head for signing devices known in which the paint spray nozzles directly with communicating with an ink chamber and by closure body are locked, which are arranged in the color chamber are not. The closure body is controlled by Springs and flexible pull nipples made by strong electro magnets are withdrawn.

A paint spray nozzle is known from US-A-43 83 264, with a piezo element on the one behind the nozzle opening located chamber exerts a short pressure pulse, so that a single drop of ink from the paint spray nozzle is delivered. New ink is made by capillary action sucked into a reservoir.

In these known methods for producing ink or ink drop is the drying time of the writing or the other printed symbol for a very long time and the printing or writing speed is thereby limits that in addition to the intended drop So-called satellites emerge, which in particular at higher speeds the cleanliness of the print affect.

The invention as set out in claims 1 and 7 solves the problem, the drying time of the writing or  to shorten the writing symbol and the cleanliness of the To improve pressure.

Because of the process taking place in the method according to the invention Atomizing the ink creates droplets with a Diameters in the range from 5 to 30 µm. As a result of the ge ring diameter of these droplets arises as a whole a very large surface area and a very small one Color amount to create full-coverage dots. This results in the much shorter one Drying time on the object to be printed, against over the conventional methods, in which by means of a Nozzle opening from 100 to 300 µm a single inks drop is generated.

Even in applications where a quick drying Printing ink is required can be in the inventive Process using water-based inks that, because of the fine atomization also the evaporation is increased by a factor of 100 or more.

There is no fear that the paint will dry out relatively large nozzle openings can be used and / or the supply of the printing ink by a cleaner supply needle in the paint spray nozzle can be kept clear. It is therefore also possible to use printing inks with a very high Glue content can be used. So it can be both thin and pasty printing inks and even printing colors of almost powdery consistency can be processed.

The color density of each printed dot is weak controllable to bold in very fine gradation. The shape of each The point does not have to be circular, but can also be ring be like or elongated, depending on the geometry of the Paint spray nozzle. In particular nozzle geometries that are ring-shaped Generating points are particularly interesting because little dye application still gives the impression of a full one Point can be generated. Through continuous control  of the printhead can even create continuous lines the.

If the printing ink is circulated, pigmented ones can also be used Printing inks or multi-component inks are used.

Due to the design of the Er specified in claim 4 with a single printhead, a complete, Color spectrum printed on three or more colors will.

The control of the application of the printing ink takes place by that the gas stream serving as the carrier medium and / or the Zu management of the printing ink is controlled. When together The letters are set from individual points Control by short impulses. With every impulse there is created at a point on the moving object.

In the first possibility of control mentioned the gas flow through a fast switching solenoid valve or piezo valve intermittently through a paint spray nozzle directs. There he takes the ink with him and transports it the gas-ink mixture on the surface of the be printing object. The printing ink becomes a all paint spray nozzles are drawn together. At this embodiment has the advantage that with relatively uncritical control elements for the control the gas flow, e.g. B. the air flow can be worked and not insensitive Ven to ink tiles are needed. After exiting the paint spray nozzle can also introduce a calming section before then the air-ink mixture over a further nozzle is finally expelled. As a result the possibility, e.g. B. the height of the nozzle row of relative large-area nozzle facilities on a small writing merge height.

After the second possibility mentioned, the gas flows con  continuous, d. H. the gas flow is e.g. B. by another Solenoid valve for all paint spray nozzles together shortly before Start of printing switched on and switched off after printing. The control of the printing process takes place through the delivery the printing ink via an injector in the gas flow, the specified amounts of the printing ink in the gas stream gives. For example, the ink can be pumped or otherwise Conveyor to be pressurized and the line opened and closed to the injector by means of a valve be so that predetermined amounts of ink in the Airflow. Abge in a time unit given amount of color, the z. B. control over the pump pressure bar, the color intensity of the pressure points can be controlled will. About the opening time of the feed valve can Dot size can be controlled, the dot size up to a solid line is expandable.

By two or more injectors, each one by one Supply valves can be controlled, the use of two Component printing inks enables. This allows a che mixing curing and drying can be achieved. Also are Color mixtures within the entire color spectrum one injector for each of the three primary colors (blue, yellow and red) possible. Such mixtures can be used as outside Mixtures are generated when the injectors are in the off sit step nozzle and are flowed around by the gas stream. However, the mixing nozzle can also be followed by a calming pipe are switched, which then ent only the outlet nozzle holds.

For the implementation and control of the injectors there are different options. Via a dosing pump a short pump for each color point to be generated hub executes, the ink can be in via the injector the gas flow can be initiated. It is for each color spray nozzle of the nozzle block need its own dosing pump does. It can also be a common pump for all colors spray nozzles are provided, which the printing ink under pressure  sets and the individual nozzles via fast-switching Ven tile supplied with the printing ink. Here is the too additional possibility of using a bypass orderly pump z. B. quickly segregating pigments pumping inks containing and thus a To prevent settling of the pigments.

The valves can have needle valves integrated in the injector be controlled by an external magnet will. In general, however, it may be more convenient fast 2/2-way solenoid valves in the supply line of the Arrange printing ink because of the larger nozzles openings are then not as easy as integrated Block the needle valves. This is a particular risk for pigment inks.

Finally, a piezo or magneto can also be used as an injector strict actuator used on a paint chamber presses, thereby injecting a drop into the gas stream. Such a drop can also be generated electrostatically will.

Embodiments of the invention are described below hand of the drawing explained. It shows

Figure 1 shows in schematic form a 7-nozzle print head with a common ink chamber and separate pressure air supply line for each paint spray nozzle.

FIG. 2 shows a single color spray nozzle of the print head according to FIG. 1;

Fig. 3 shows a 7-nozzle print head with injector and inte grated needle valve for each spray nozzle for controlling the supply of the printing ink;

FIG. 4 shows a single color spray nozzle of the print head according to FIG. 3;

Fig. 5 is a 7düsigen print head for the three primary colors;

Fig. 6 is a paint spray nozzle for the print head of Fig. 5;

FIG. 7 shows magnified a spray head with a cap for the concentration of the gas jet;

Fig. 8 in enlargement a paint spray head with a swirl body;

Fig. 9 shows a spray head with electro-static focus tion of the gas jet;

Fig. 10 shows a print head with quadrupoles for focusing and

Fig. 11 shows a print head according to Fig. 1 with a nozzle attachment.

In the embodiment of the invention according to FIGS. 1 and 2, the print head 10 has seven ink spray nozzles 11 at a distance of z. B. 10 mm. Printing ink is automatically fed from a storage container 12 , which can be a quickly replaceable plastic bag, into a common ink chamber 13 . The paint chamber 13 has for each paint spray nozzle 11 a cylindrical, forward to a nozzle opening 14 of z. B. 2 mm diameter tapering cavity 15 . All cavities 15 within a print head 10 are connected to one another. In each cavity 15 a nozzle body 16 is arranged centrally, in the front end of a fine nozzle bore 17 of z. B. 0.6 mm is provided. Between the front end of each nozzle body 16 and the nozzle opening 14 be concerned there is an annular gap 18 of z. B. 0.5 mm width.

Each nozzle body 16 is connected via a hose 19 with an electrically controllable 2/2-way solenoid valve 20 and with an air pressure source of e.g. B. 1 to 2 bar connected. By means of control electronics, the solenoid valve 20 is opened in a pulse-like manner so that an air jet emerges briefly from the nozzle bore 17 . This entrains ink from the cavity 15 surrounding the nozzle body 16 , so that a small ink cloud emerges from the ink spray nozzle 11 .

The control electronics work in a known manner such that the seven superimposed paint spray nozzles 11 are actuated so that characters or symbols were formed in a 5 × 7 matrix on the object to be printed. Full lines can also be drawn by opening the solenoid valves 20 for a longer period.

About the amount of pressure with which air is supplied via the solenoid valve 20 of the paint spray nozzle 11 , the exit speed of the ink cloud can be changed. This means that good print quality can still be achieved even with quickly moving objects.

In printing inks of high viscosity, in which the entrainment effect of the emerging from the nozzle opening 14 air jet is insufficient more, between the reservoir 12 and the print head 10 additionally Dosiereinreichung, z. B. a pump and a solenoid valve can be interposed or the reservoir can be designed as a double-walled plastic bag, in which the outer envelope can be pressurized by compressed air and thereby the printing ink of the inner bag is squeezed out under pressure.

In the embodiment shown in FIGS. 3 and 4, the print head 10 is constructed similarly to the game in Ausführungsbei of FIGS. 1 and 2. The supply of compressed air and the ink is reversed. Compressed air from z. B. 1 to 2 bar is passed via a solenoid valve 21 into the interconnected cavities 15 and flows from there through the nozzle openings 14 . The solenoid valve 21 opens shortly before the start of writing and the compressed air flows out continuously during the entire writing process. Printing ink is from a reservoir 12 via a Pum pe 22 with a pressure of z. B. 0.3 to 1 bar in a color chamber 23 , which is in connection with all nozzle bodies 16 in United. The nozzle body 16 are here as needle valves with openings of z. B. 1 mm. The needles 24 of the needle valves are actuated electrically, but can also be actuated by small pneumatic cylinders. When the control electronics opens the needle valves, certain amounts of the printing ink are injected into the air stream flowing out of the nozzle openings 14 and atomized therein. Just as in the embodiment of FIGS. 1 and 2, a cloud of printing ink is therefore generated, which is reflected as a dot on the moving object.

FIGS. 5 and 6 show an embodiment with a full-color print head 10 which by means of mixture of the three primary colors yellow, blue and red filters the full color spectrum ago and he can thus attest fonts with different colors. The print head 10 in turn consists of seven identical paint spray nozzles 11 at a distance of z. B. 10 mm. A paint spray nozzle 11 is shown in section in FIG. 6. Each paint spray nozzle 11 has a central channel 30 . Around this concentric ring channels 31 , 32 and 33 are arranged, which converge towards the nozzle opening 14 (z. B. 3 mm diameter). The outer channel 33 is for a solenoid valve 20 of the compressed air. B. 1 to 2 bar supplied. The central channel 30 and the two inner ring channels 31 and 32 are supplied with different printing inks via solenoid valves 21 a, 21 b and 21 c. The pressure (for example 0 to 1 bar) is generated here by electrically controllable pumps 22 a, 22 b and 22 c, the amount of printing inks to be dispensed being controlled by the pump pressure. The opening time of the solenoid valves 21 a, 21 b and 21 c again determines the longitudinal dimension of the point generated or the line length. For one point the opening time is z. B. 0.3 to 1 ms. The line for the yellow ink also includes a return line 34 with a throttle 35 , so that the pump 22 c at the same time circulates the yellow dye and thus a pigmented dye can be used for the yellow ink. The circulation prevents the pigments from settling. Instead of different color printing inks, multi-component printing inks can also be processed with the printing head 10 shown in FIG. 6. The individual components are separately injected into the air flow and mix and react with one another outside of the paint spray nozzle. This ensures a very short drying time.

All printheads of the previous embodiments can be used to generate smaller point sizes directions are provided that shape the air jet or focus.

In Fig. 7, a conically tapering cap 36 is placed on the nozzle opening 14 , in which external air is sucked in through lateral air inlet holes 37 , which further bundles the emerging air jet with the ink atomized therein.

In Fig. 8, a nozzle opening is shown, in which the gas jet is initially rotated by swirl body 38 arranged within the paint spray nozzle in order to achieve better atomization of the printing ink. However, the centrifugal force that becomes effective means that the gas jet strives apart faster and thus a larger scattering angle for the ink cloud. This is generally not desirable, since then there are large differences in the diameter of the printing dots even with small changes in the distance between the print head and the object to be printed. This is prevented in the paint spray head of FIG. 8 by an additional control air nozzle 39 , which is arranged in a ring around the nozzle opening 14 . The outlet opening of the control air nozzle 39 tapers, so that the control air has a focusing effect.

A focusing effect is achieved in the ink spray nozzle shown in FIG. 9 in that the printing ink is set to a positive potential and thus positively charged droplets are formed during atomization. These droplets can then be focused in free flight by means of a ring 40 which is arranged in front of the paint spray nozzle and is at a high positive potential and acts like a field lens for the paint droplets. Such a field lens can be realized in a particularly advantageous manner by so-called quadrupoles, which act as cylindrical lenses. At least two quadrupoles are connected in series in order to focus the droplets first through the first quadrupole in the Y direction and then through the second quadrupole in the Z direction.

Such an electrostatic focusing simplifies the construction of the printhead, as shown in FIG. 10. There is the additional advantage that both the air inlet and the ink supply and the nozzle itself can have a relatively large cross section, so that there is no risk of clogging.

The print head 10 shown in Fig. 10 has seven to a distance of about 2 mm superimposed paint spray nozzles 11. The diameter of the nozzle openings 14 is in the order of 1 mm and opens into an electrostatic collimation channel 41 of 10 to 20 mm in length and about 1.5 mm in diameter (the illustration of FIG. 10 is not to scale). The inner surfaces of the collimation channels 41 are protected against electrical flashover by a Teflon® coating. The atomization takes place as an internal mixture in a nozzle tube 42 , into which the gas jet tangentially shoots into the axially supplied printing ink. Conversely, there is also the possibility of introducing the printing ink tangentially into the axial gas flow. The gas or air supply is in turn controlled jointly for all paint spray nozzles 11 via a solenoid valve, while the ink supply can be controlled individually for each paint spray nozzle 11 via fast solenoid valves. The air pressure is in the range of 1 to 2 bar and the printing ink is supplied at a pressure in the range of 0.5 to 1 bar. With a print head of FIG. 10 is very small fonts with well-collimated points can be produced. By tilting the print head and delaying the activation of the paint spray nozzles, the font size can be reduced again in accordance with the cosine of the angle of the tilt to the direction of movement of the object to be printed.

FIG. 11 shows a print head 10 similar to that of FIG. 1. In order to reduce the typeface, a nozzle attachment 43 is arranged in front of the print head 10 , in which the nozzle openings 14 are continued in channels 44 . The channels of the individual spray nozzles 11 run towards each other so that at the front of the nozzle attachment 43 the distance between the individual channels 44 is only about half the distance between the nozzle openings 14 in the print head 10 .

Claims (10)

1. A method for applying printing ink to an object was by means of several spray nozzles ( 11 ) for generating a print image, characterized in that the printing ink is atomized in a gas stream and is transported to the object by the gas stream. 2. The method according to claim 1, characterized in that that the ink is carried away by the gas flow and will generate the gas stream according to that the print pattern is controlled. 3. The method according to claim 1, characterized in that the gas flow is continuous and the pressure color according to the print pattern to be created is injected into the gas stream. 4. The method according to claim 3, characterized in that several different inks or the individual components of a multi-component printing color to be injected into the gas stream. 5. The method according to any one of claims 1 to 4, characterized characterized in that the gas flow through external air or Control air directed towards the center of the gas flow is focused. 6. The method according to any one of claims 1 to 4, characterized in that the ink droplets are electrically charged and the gas jet is focused by a arranged in front of the paint spray nozzle, high electrical potential ring ( 40 ) or by one or more quadrupoles. 7. printhead ( 10 ) for performing the method according to claim 1 with a plurality of spray nozzles ( 11 ) which can be controlled individually and with a line for supplying printing ink to each spray nozzle ( 11 ), characterized by a nozzle which is supplied with compressed gas and generates a gas jet, the emerging gas jet atomizes the printing ink and carries it to the object to be printed. 8. printhead ( 10 ) according to claim 7 for performing the method according to claim 2, characterized in that a nozzle body ( 16 ) in a ge filled with printing ink cavity ( 15 ) of the printhead ( 10 ) is arranged and generates the gas jet which by a nozzle opening ( 14 ) emerges from the print head ( 10 ), an annular gap ( 18 ) being formed between the nozzle opening ( 14 ) and the nozzle body ( 16 ), through which printing ink is sucked in and entrained by the gas jet. 9. printhead ( 10 ) according to claim 7 for performing the method according to claim 3, characterized in that the nozzle body ( 16 ) are designed as needle valves for the supply of printing ink to the cavity ( 15 ), the compressed gas is supplied, which is a gas current emerges from the nozzle opening ( 14 ), printing ink being injected through the needle valves ( 16 ) into the gas jet in accordance with the printing pattern to be generated. 10. printhead ( 10 ) according to claim 9, characterized in that each nozzle body ( 16 ) has a central channel ( 30 ) and one or more annularly arranged channels ( 31 , 32 ) for feeding several printing inks or the individual components of a multi-component printing ink has and an outer ring channel ( 33 ) is used to generate the gas flow.