EP3756890A1 - Method and device for measuring ink viscosity in pad printing - Google Patents

Abstract

A method and a device for measuring the ink viscosity in pad printing are specified. A printing ink (3) held in an ink container (2) is set in motion and, by means of a measuring device (5), a time curve of the movement of the printing ink (3) in the ink container (2) is measured by measuring a local level (hl, h2) of the printing ink (3) in the paint container (2). Based on the time curve determined in this way, an evaluation unit is used to determine a measure for the viscosity of the printing ink (3).

Description

TECHNICAL AREA

The present invention relates to a method and a device, in particular a pad printing machine, for measuring the ink viscosity during pad printing.

STATE OF THE ART

With pad printing, the print quality that can be determined on the printed object is essentially dependent on a correct setting and, more importantly, control of the viscosity of the printing ink. The printing ink is usually adjusted to the desired viscosity with a thinner before printing begins. Using a measuring device, the viscosity of the printing ink can be checked before the printing of usually a large number of objects is started.

While printing on a large number of objects, however, it cannot be prevented that some of the thinner substance evaporates over time. Evaporation is naturally the fastest with open ink systems, but even with closed systems the thinner evaporates over time as the ink pot moves on the cliché. There is also the problem with rotary pad printing machines that the thin liquid thinner evaporates over time. As a result, the printing ink becomes more viscous and can no longer be absorbed equally well by the printing pad from the cliché and, in particular, transferred to the object to be printed. As a direct consequence, the print quality is reduced and rejects occur.

In order to counteract the continuous evaporation of the thinner during the printing process, thinner is added to the printing ink continuously or at regular intervals in most pad printing machines. However, the evaporation rate depends on a wide variety of influences, such as the choice of printing ink, air humidity, any air movements, printing speed, etc. Furthermore, the viscosity is strongly dependent on the color temperature. For this reason, the rate of evaporation can hardly be predicted precisely in practice and is also usually subject to fluctuations. Accordingly, the ink viscosity must be checked at regular intervals during the printing process and the supply of the thinner must be adjusted.

For checking the viscosity of the paint, for example spatulas with a printed or embossed measuring scale are known in the prior art. These spatulas are immersed in the printing ink in order to measure the flow rate of the printing ink after the subsequent pulling out with the help of the scale and thereby to infer the viscosity.

In the case of a viscometer in the form of a flow cup, the color liquid is filled into a cup that runs out conically at the bottom into a hole with a precisely known diameter. The viscosity of the liquid can be determined on the basis of the volume of the cup, the nozzle diameter and the measured time for the liquid to drain.

The measuring methods with spatula and flow cup are easy to carry out and very inexpensive with regard to the measuring instrument, but unsuitable for precise viscosity determinations. Such methods are at most suitable for setting the color viscosity before the start of the printing process, since during printing it is less the initial viscosity than the constancy of the color viscosity that is important. Before the printing process, the pad printing machine usually has to be adapted to the existing conditions, such as the printing pad used, printing speed, printing ink, etc., by means of its setting parameters anyway. In most applications it is sufficient if the ink viscosity is in a certain range. However, in order to be able to guarantee consistent print quality and an uninterrupted printing process, it is important that the ink viscosity is maintained throughout Printing process remains unchanged as possible.

In the prior art, rotary viscometers are known in which a rod-shaped element is dipped into the printing ink from above and is rotated there by means of a motor. Such a measuring device is known, for example, under the name TampoVisco from Tampoprint® AG, Germany. Rotary viscometers of this type enable the viscosity to be determined precisely, but are only intended for use outside the pad printing machine. Such measuring devices are therefore unsuitable for continuous or regular measurements during the printing process.

Rotational viscometers, such as the Viscomat from microPrint LC GmbH, Switzerland, are also known, in which a rotary element is arranged in the ink pot. By turning the rotary element, the ink viscosity can be measured directly in the ink pot without having to remove it from the pad printing machine. However, the disadvantage is, on the one hand, the more complex handling when inserting the ink pot into the pad printing machine and, on the other hand, the need to clean the rotary element after it has been used.

In the EP 1 780 012 B1 a relatively complicated system is proposed in which the printing ink is continuously fed to the ink pot via a feed line. The viscosity control can thus be carried out outside the ink pot during the printing process. However, the additional outlay on equipment is considerable. In addition, the system is unsuitable for pad printing machines, for example, in which the ink pot rotates during the printing process.

DISCLOSURE OF THE INVENTION

It is therefore an object of the present invention to provide a method for pad printing which allows a reliable measurement of the ink viscosity by means of simple handling and apparatus. A method as specified in claim 1 is proposed to solve this problem. In addition, an apparatus for performing this method is specified in claim 11. Other embodiments are given in the dependent claims.

1. a.) eine in einem Farbbehälter aufgenommene Druckfarbe in Bewegung versetzen;
2. b.) Bestimmen eines Zeitverlaufs der Bewegung der Druckfarbe im Farbbehälter mittels Messung eines lokalen Pegelstandes der Druckfarbe im Farbbehälter; sowie
3. c.) Ermitteln eines Masses für die Viskosität der Druckfarbe basierend auf dem bestimmten Zeitverlauf.

The present invention thus provides a method for measuring the ink viscosity in pad printing, comprising at least the following steps

1. a.) set a printing ink received in an ink container in motion;
2. b.) determining a time course of the movement of the printing ink in the ink tank by measuring a local level of the printing ink in the ink tank; such as
3. c.) Determining a measure for the viscosity of the printing ink based on the determined time course.

Steps a.) To c.) Are preferably carried out in the order given.

By setting the printing ink in motion in the ink container and determining a time course of the movement of the printing ink in the ink container by measuring a local level of the printing ink in the ink container, a measure for the ink viscosity can be determined in a very simple manner. The behavior of the liquid is thus examined during a time interval after the liquid has previously been set in motion. The process principle is therefore similar to that of the flow cup.

Step a.), That is, to set the printing ink contained in the ink container in motion, can be implemented very easily, e.g. the paint container is simply pushed or moved. If the ink container is an ink pot of a pad printing machine with a closed ink system, for example, the already existing ink pot movement between two print image transfers can be used directly.

The measurement of the local water level, that is to say a height of the printing ink at a specific point in the ink container, can also be carried out in a very simple manner and preferably even without contact. For example, an optical measurement method based on a laser beam can be used for this purpose.

The measurement of the ink viscosity with the method according to the invention is preferably carried out during the printing process or during a brief interruption of the printing process if the ink container is arranged in the pad printing machine as intended for printing. However, it is also conceivable to use the specified measuring method to determine the ink viscosity outside the pad printing machine, for example to set and / or determine the ink viscosity before the start of the printing process.

Measuring paint viscosity can refer to measuring an absolute viscosity value. By measuring the paint viscosity, however, it is preferred to mean only measuring a relative viscosity value, that is to say the measure determined in step e.) Is a relative measure. It is therefore preferable to determine whether and how the viscosity of the printing ink has changed in comparison to an earlier point in time, in particular at the point in time at the beginning of the printing process.

The paint container is preferably immobile during the determination of the time course of the movement in step b.). The point in time to start the time course determination in step b.) Is also preferably selected such that the printing ink sinks during the determination due to the gravitational force from the point where the local water level is measured towards a state of rest. The measured local water level, provided it is measured at the same point, is therefore usually reduced.

Steps a.) To c.) Are preferably carried out at regular time intervals, for example every half hour.

• b1.) Messen eines ersten lokalen Pegelstandes der Druckfarbe im Farbbehälter;
• b2.) Warten während eines Zeitintervalls; sowie
• b3.) Messen eines zweiten lokalen Pegelstandes der Druckfarbe im Farbbehälter,

wobei das Mass für die Viskosität in Schritt e.) basierend auf dem ersten lokalen Pegelstand und dem zweiten lokalen Pegelstand ermittelt wird.The measurement of the local water level in step b.) Can be carried out continuously or at regular intervals during a certain time interval. In order to determine a time course of the movement of the printing ink, two measurements spaced apart in time are sufficient, for example. The measurement of the local level in step b.) Is therefore preferably carried out exactly twice, with a predetermined time interval between the two measurements. The measurement can thereby be carried out in a particularly simple manner. According to this in particular In the preferred embodiment, the determination of the course of time in step b.) thus comprises at least the following substeps:

• b1.) measuring a first local level of the printing ink in the ink tank;
• b2.) waiting for a time interval; such as
• b3.) measuring a second local level of the printing ink in the ink tank,

wherein the measure for the viscosity in step e.) is determined based on the first local level and the second local level.

The first and second local water levels generally each relate to the level of the printing ink at a specific point in the ink container. The two heights are advantageously, but not absolutely necessary, determined in steps b1.) And b2.) At the same point on the paint container.

If steps a.) To c.) Are repeated, e.g. are carried out at regular time intervals, the waiting time defined in step b2.) by the time interval specified there remains advantageously constant. The time interval specified in step b2.) Is advantageously less than one second, even more advantageously even less than half a second.

In order to achieve a particularly meaningful measurement, the local water level is preferably determined decentrally in each case in the paint container, in particular in an edge region of the paint container. The local water level can relate to the distance between the bottom of the ink container (or the cliché surface) and the surface of the printing ink at a specific point in the ink container. Just as well and even preferred here, however, the local level can relate to the distance between the surface of the printing ink and a fixed point arranged above it. The fixed point arranged above the surface of the printing ink can be defined by the arrangement of a measuring device, in particular an optical measuring device.

In the context of this document, the word “level” therefore does not denote the distance between the color surface and the floor on which the printing ink is placed, but rather, in a broader sense, the measuring point as a whole. Accordingly, the word "level" is the level of the surface of the printing ink at the measuring point, based on the Direction of gravity, meant. The expression "local water level" means that the water level is measured at a specific point. A local water level measured at another point at the same time is usually different as long as the printing ink is still in motion.

When determining the course of time in step b.), It is therefore particularly a matter of measuring a change in the local level of the printing ink during a certain time.

To determine the measure for the viscosity in step c.), The difference between the mentioned first height and the second height is preferably calculated. Based on this calculated difference, the measure for the viscosity is then preferably determined. The calculated difference can even be used as such as a measure of the viscosity of the printing ink.

Instead of waiting between two measurements during a predetermined time interval, a first level can also be measured and then the time interval can be determined until the local level of the printing ink has decreased to a second predetermined level. The time interval between two measurements does not necessarily have to be a predetermined time interval, but can also be a time interval to be determined. In this way, too, it is possible to determine a time course of the movement of the printing ink in the ink container by measuring a local water level in accordance with step b.) In order to then be able to determine a measure for the viscosity of the printing ink based on this in step c.).

The ink container can be an ink pan of a pad printing machine with an open ink system or an ink pan of a rotary pad printing machine. In such an open system, the evaporation rate of the diluting liquid is particularly high. In a particularly preferred embodiment, however, the ink container is an ink pot of a pad printing machine with a closed ink system. The ink container then usually rests against a cliché in such a way that the printing ink accommodated in the ink container contacts the cliché. The printing ink is then preferably by means of a relative movement of the cliché to the Paint container set in motion. The cliché preferably moves, as it does during the printing process, while the ink container remains stationary.

In a particularly preferred embodiment, an amount and / or concentration of a diluent substance that is to be added to the printing ink is determined based on the measure for the viscosity determined in step c.). The measure of the viscosity of the printing ink can be shown on a display, for example, so that the operating personnel can control the amount of thinner liquid supplied and, if necessary, adjust it based thereon. However, the amount and / or concentration of the diluent to be added is advantageously displayed directly or, even more advantageously, the injection of the diluent is automatically regulated by the pad printing machine based on the viscosity measure determined in step c.).

When determining the amount and / or concentration of the diluent substance, a quantity value and / or a concentration value is preferably selected from a limited number of predetermined quantity values and / or concentration values. This makes the regulation particularly simple and reliable, since the degrees of freedom of the system are restricted.

The measure for the viscosity determined in step c.) Can, for example, be compared with a target value in order to adjust the supply of the diluent based on a deviation determined in the process.

According to a development of the invention, the paint container has a delimited partial area. The measurement of the local water level is then preferably carried out within this sub-range. The partial area can be partially or completely separated from the rest of the interior of the paint container, for example by means of a wall. The wall for separating the partial area is preferably formed by an insert part. The insert part can in particular be designed as a riser pipe. By providing a delimited sub-area, the measuring method is independent of the size, ie the diameter, of the paint container. By inserting the insert, the measure of the paint viscosity can be determined in the same way for paint containers of different sizes and way and without adjusting the default settings.

In another development of the invention, there is a surface in the paint container that extends obliquely relative to the direction of gravity. The local level is then measured directly in the area of this inclined surface. In this way, the viscosity can still be precisely determined even at low fill levels. The obliquely extending surface is advantageously arranged at an angle of 30 ° to 60 °, in particular approximately 45 °, relative to the direction of gravity.

• einen Farbbehälter zur Aufnahme einer Druckfarbe;
• eine Messeinrichtung zum Messen eines lokalen Pegelstandes der Druckfarbe im Farbbehälter; sowie
• eine Auswerteeinheit, welche dazu ausgebildet ist, ein Mass für die Viskosität der Druckfarbe zu ermitteln basierend auf einem Zeitverlauf des durch die Messeinrichtung gemessenen lokalen Pegelstandes.

The present invention also relates to a device for measuring the ink viscosity during pad printing, in particular by means of the method specified above

• an ink container for holding a printing ink;
• a measuring device for measuring a local level of the printing ink in the ink tank; such as
• an evaluation unit which is designed to determine a measure for the viscosity of the printing ink based on a time curve of the local level measured by the measuring device.

The device also preferably has an insert part, in particular a riser pipe, arranged inside the ink container, the measuring device being designed to measure the local level of the printing ink within this insert part.

The device preferably has a supply device for supplying a diluent substance to the printing ink received in the ink container, the evaluation unit preferably being designed to determine, based on the measure of the viscosity, an amount and / or concentration of the diluent substance, which by means of the supply device to the printing ink will be added. The device is thus preferably designed to automatically regulate the thinner injection based on the viscosity measurement.

In a particularly preferred embodiment, the device is a pad printing machine with a cliché and a printing pad for Recording a print image from the cliché and then transferring this print image to an object to be printed. The ink container is advantageously designed to rest against the cliché in such a way that the printing ink received in the ink container contacts the cliché.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1

eine perspektivische Ansicht einer Vorrichtung gemäss einer ersten Ausführungsform zum Durchführen des erfindungsgemässen Verfahrens;

Fig. 2a

eine perspektivische Ansicht mit aufgeschnittenem Farbtopf der Vorrichtung der Fig. 1, beim Bestimmen einer ersten Höhe der Druckfarbe;

Fig. 2b

eine zentrale Schnittansicht der Vorrichtung der Fig. 1, zum selben Zeitpunkt wie in der Fig. 2a;

Fig. 3a

eine perspektivische Ansicht mit aufgeschnittenem Farbtopf der Vorrichtung der Fig. 1, zu einem Zeitpunkt kurz nach dem Bestimmen der ersten Höhe der Druckfarbe;

Fig. 3b

eine zentrale Schnittansicht der Vorrichtung der Fig. 1, zum selben Zeitpunkt wie in der Fig. 3a;

Fig. 4a

eine perspektivische Ansicht mit aufgeschnittenem Farbtopf der Vorrichtung der Fig. 1, beim Bestimmen einer zweiten Höhe der Druckfarbe;

Fig. 4b

eine zentrale Schnittansicht der Vorrichtung der Fig. 1, zum selben Zeitpunkt wie in der Fig. 4a;

Fig. 5

eine perspektivische Ansicht einer Vorrichtung gemäss einer zweiten Ausführungsform zum Durchführen des erfindungsgemässen Verfahrens, mit einem Einsatzteil;

Fig. 6

eine perspektivische Ansicht des Einsatzteils der Vorrichtung der Fig. 5; sowie

Fig. 7

eine perspektivische Ansicht einer Variante eines Einsatzteils.

Preferred embodiments of the invention are described below with reference to the drawings, which are only used for explanation and are not to be interpreted as restrictive. In the drawings show:

Fig. 1

a perspective view of a device according to a first embodiment for performing the method according to the invention;

Fig. 2a

a perspective view with a cut-open paint pot of the device of Fig. 1 , in determining a first height of the ink;

Figure 2b

a central sectional view of the device of FIG Fig. 1 , at the same time as in the Fig. 2a ;

Fig. 3a

a perspective view with a cut-open paint pot of the device of Fig. 1 , at a point in time shortly after determining the first height of the ink;

Figure 3b

a central sectional view of the device of FIG Fig. 1 , at the same time as in the Fig. 3a ;

Figure 4a

a perspective view with a cut-open paint pot of the device of Fig. 1 , in determining a second height of the ink;

Figure 4b

a central sectional view of the device of FIG Fig. 1 , at the same time as in the Figure 4a ;

Fig. 5

a perspective view of a device according to a second embodiment for performing the method according to the invention, with an insert part;

Fig. 6

a perspective view of the insert part of the device of FIG Fig. 5 ; such as

Fig. 7

a perspective view of a variant of an insert part.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the Figures 1 to 7 Elements with an identical or similar function in different embodiments are each provided with the same reference symbols. Locations and directions such as “up”, “down”, “up”, “down” etc. refer in the following and throughout the present document to the direction of gravity when the paint container is properly inserted into the respective device.

In the Figure 1 a first embodiment of a device according to the invention for measuring the ink viscosity in pad printing is shown. The device shown here is a pad printing machine, of which only a part is shown. In particular, a cliché plate 1 and an ink pot 2 are shown. The pad printing machine also has a printing pad for receiving a print image from the cliché plate 1 and then transferring this print image to an object to be printed. The object to be printed is generally held in a print item holder, which, like the printing pad, is not shown in the figures. However, the person skilled in the art is sufficiently familiar with the basic structure and mode of operation of pad printing machines.

The ones in the Figure 1 pad printing machine, which is partially shown, has a closed ink system with an ink pot 2 which is essentially closed to the outside. The paint pot 2 has an upper cover wall 21, from the outer edge of which a circumferential side wall 20 extends downward. A squeegee edge 25 is attached all the way around the lower edge of the side wall 20. Towards the bottom, the paint pot 2 is open, that is to say without a bottom. A printing ink 3 is received in the interior of the ink pot (see e.g. Figures 2a and 2b ).

The ink cup 2 is pressed down onto the cliché plate 1 by means of a pressing device 4. The squeegee edge 25 is thereby pressed onto the cliché plate 1 in a sealing manner and ensures that during the printing process when the cliché plate 1 is moved, the printing ink 3 does not emerge from the ink drop 2, but only remains in a known manner within the depressions provided in the cliché plate 1 and forming the print motif. Nevertheless, it cannot be prevented that thin liquid thinner liquid, which is mixed with the printing ink 3, gradually emerges from the ink pot 2.

The pressing device 4 has a piston rod 40 which projects vertically downward and which extends into a depression 26 arranged centrally in the top wall 21. A hexagonal head 41 is attached to the lower, free end of the piston rod 40. The hexagonal head 41 engages in an engagement structure which is designed to be complementary thereto and which is formed by the recess 26. During the printing process, on the one hand, a constant pressure is exerted on the ink pot 2 by the piston rod 40, in order to ensure that the ink pot 2 is sealed against the cliché plate 1. On the other hand, the ink pot 2 is also rotated continuously during the printing process by means of the piston rod 40 in order to achieve the most uniform possible wear of the squeegee edge 25 and the cliché plate 1. This rotation is made possible by the engagement of the hexagonal head 41 in the recess 26 which is shaped complementarily thereto.

The pressing device 4 has operating elements 42 which are used to set the contact pressure, the rotational speed and for various other functions. In principle, the pressing device 4 and the paint pot 2 are in accordance with the information in FIG CH 688 545 A5 formed, the entire content of which is hereby included.

To fill in the printing ink 3, the top wall 21 of the ink pot 2 has a filling opening 24 which is arranged in an outer radial area of the top wall 21 in the immediate vicinity of the side wall 20.

In order to counteract the volatilization of the diluting liquid during the printing process, the device has a feed device for injecting diluting liquid with an injection hose 6. The injection hose 6 protrudes from down to the top wall 21 and opens just above an annular groove 22 formed in the top wall 21 concentric to the recess 26. During injection, the thinner liquid runs from the injection hose 6 into the annular groove 22 and via an inlet opening 23 provided within the annular groove 22 into the interior of the Paint cup 2. Due to the annular groove 22, injection through the injection hose 6 is possible regardless of the rotational position of the paint cup 2.

The following is based on the Figures 2a to 4b the method according to the invention for measuring the ink viscosity by means of the device shown, which here, as mentioned, is a pad printing machine.

In a first method step, the printing ink 3 received in the ink pot 2 is set in motion. This can be done, for example, by pushing the paint pot 2, that is to say slightly moving it. For this purpose, however, the movement of the cliché plate 1 relative to the ink pot 2, which is taking place anyway, is used when re-inking during the usual printing process. By moving the cliché plate 1 relative to the ink pot 2, the printing ink 3 lying on the cliché plate 1 is set in motion within the ink pot 2, so that its surface corresponds to the Figures 2a and 2b shown oblique position.

The movement of the cliché plate 1 is then stopped in order to carry out two measurements of a local water level, that is to say two height measurements of the printing ink 2. The movement of the paint pot 2, that is to say in particular its rotational movement, is also advantageously stopped.

The local level measurement of the printing ink 3 is carried out with the aid of a laser measuring device 5 which, by means of a laser beam 50, measures the distance to the surface of the printing ink 3 through the open filling opening 24. The local level or fill level of the printing ink 3 in the area of the filling opening 24 is thus measured. For this purpose, the laser measuring device 5 is advantageously arranged directly above the filling opening 24.

The time of the measurement of a first water level or a first height h1 (see Fig. 2 B ) is preferably carried out when the height of the printing ink 3 in the area directly below the filling opening 24 is at its maximum. This is usually the case immediately after the movement of the cliché plate 1 (or the ink pot 2) has stopped.

Strictly speaking, the laser measuring device 5 does not use the Figure 2b The height h1 shown is measured, but the distance between the surface of the printing ink 3 and the laser measuring device 5. However, since the distance between the laser measuring device 5 and the cliché plate 1 is known and usually constant, the conversion of the distance measured by the laser measuring device 5 to the height h1 is something for a person skilled in the art trivial task. Since, as will be explained below, the subsequent determination of a measure for the viscosity is only about the difference between two measured water levels, the conversion to the actual height h1 or h2 is as shown in the Figures 2b and 4b not even necessary here. Due to the trivial possibility of conversion, however, in the context of this document, measurement of the first height h1 or the second height h2 by means of the laser beam 50 is used.

As the next method step after measuring the first height h1 or the first local water level, there is a wait during a time interval until the printing ink 3 has moved back within the ink pot 2 in the direction of a rest position. The surface of the printing ink 3 gradually sinks in the area of the filling opening 24, as is the case in FIG Figures 3a and 3b is shown. The speed at which the printing ink 3 moves back in the direction of its rest position is directly dependent on the viscosity.

After the mentioned time interval has elapsed, a measurement of a local water level is carried out again. For this purpose, the height of the printing ink 3 is measured by means of the laser measuring device 5 through the filling opening 24 (see FIG Figures 4a and 4b ). The second height h2 measured in the process is smaller than the first height h1, since the printing ink 3 has meanwhile approached its rest position and the local filling level in the area of the filling opening 24 has accordingly reduced.

The difference between the first measured height h1 and the second measured height If the time interval between the measurements is known, h2 can be used directly as a measure of the viscosity of the printing ink 3. The difference and the measure for the viscosity are preferably calculated or determined automatically by an evaluation unit of the device, not shown in the figures.

As soon as the second height h2 has been measured, the printing process can be continued. The printing process only has to be interrupted for a few seconds, if at all.

The determined measure for the ink viscosity can now be used by the evaluation unit to automatically, that is, without the help of human operating personnel, to determine an amount and / or concentration of a diluent that is to be added to the printing ink. The diluting substance, usually a diluting liquid, can then also be added automatically to the printing ink 3 during the printing process via the injection hose 6 and the inlet opening 23. Due to the rotational movement of the ink pot 2, but also due to the movement of the cliché plate 1 relative to the ink pot 2, the thinner substance is mixed very quickly with the printing ink 3.

In order to find the correct rotational position of the ink pot 2 for measuring the height of the printing ink 3 by means of the laser beam 50, the ink pot can simply be rotated further until the laser beam 50 falls through the filling opening 23 onto the printing ink 3 and that of the laser measuring device 5 fails the determined measuring distance is therefore suddenly increased. Alternatively or additionally, one or more markings, e.g. in the form of local elevations or depressions, so that the correct rotational position of the paint pot 2 can be found more quickly.

In order to achieve the correct rotational position of the ink pot 2 for measuring the local level of the printing ink 3 even faster and more reliably, one or more magnets 27 can also be attached to the outside of the side wall 20 (see FIG Figures 1 to 4b ). The desired rotational position can then be set quickly and easily by means of an inductive sensor 7.

The setting of the correct rotational position of the ink pot 2 is preferably carried out while the printing process is still running, before the actual viscosity measurement is started.

In tests it was found that the printing ink 3 tends to form a bubble within the filling opening 24, as a result of which the measurement with the laser beam 50 is impaired. In order to ensure a reliable measurement, compressed air is therefore preferably briefly blown into the filling opening 24 immediately before the measurement in order to remove any bubbles that may be present there.

In the Figure 5 a further preferred embodiment of a device according to the invention for measuring the ink viscosity during pad printing is shown. The embodiment of the Figure 5 differs from that of the Figure 1 that an insert in the form of a riser pipe 8 is arranged in the area of the filling opening 24.

The riser pipe 8 is according to Figure 6 formed with an upper cylindrical section and a lower section, in which the cylinder shape is formed only over a partial area of the circumference and is open over the remaining, larger partial area. As a result, the riser pipe 8 has a curved wall extending downward on one side from the upper cylindrical section. At the lower free end of this wall, an inclined surface 80 is attached, which extends radially from the inside upwards towards the wall. When it is inserted into the paint pot 2 through the filling opening 24, the riser pipe 8 comes to rest on the cliché plate 1. The inclined surface 80 is then located at the very bottom in the ink pot 2. Due to the inclined surface 80, viscosity measurements using the specified method are still reliably possible even if the total level of the printing ink 3 in the ink pot 2 has decreased significantly.

A variant of a riser pipe 8 'is in Figure 7 shown. The riser pipe 8 ′ has an overall hollow cylindrical shape with a longitudinal slot 81 that is open at the bottom. Due to the longitudinal slot 81, the water level inside the riser pipe 8 'when the printing ink 3 is stationary essentially corresponds to the local water level in the immediate vicinity Area around the riser pipe 8 '. When the printing ink 3 is moving, the level inside the riser pipe 8 'is essentially independent of the diameter of the ink pot 2 and can therefore also deviate from the local level in the immediate area around the riser pipe 8'. The riser pipe 8 ′ thus has the considerable advantage that the viscosity measurement is largely independent of the diameter of the paint pot 2. The reason is that the printing ink 3, after it has been set in motion, behaves in the same way within the riser pipe 8 ', essentially regardless of the size of the ink pot. The viscosity measurement is then particularly similar to the measurement with a flow cup.

Of course, the advantages of the riser pipe 8 can also be combined with those of the riser pipe 8 ', that is to say the riser pipe 8' can additionally have an inclined surface in its lower area.

In order to prevent evaporation of the diluent liquid through the filling opening 24, the filling opening can be closed and only opened during the level measurements by means of the laser measuring device 5, preferably automatically. It is basically also conceivable that the laser measuring device 5 is attached directly to the top wall 21 of the paint pot 2 and an opening provided in the top wall 21 is closed by the laser measuring device 5 itself.

The measuring method according to the invention is explained below using a specific example:

example

1. 1. Die Tampondruckmaschine ist im Autobetrieb und druckt. Alle 30 min wird eine Viskositäts-Messung gemäss den nachfolgenden Schritten 2. bis 5a. durchgeführt.
2. 2. Einfüllöffnung 24 suchen (Maschine läuft/druckt normal)
   • 2a. Drehen des Farbtopfs 2 bis die Lasermesseinrichtung 5 aufgrund der Markierung einen minimalen Messabstand detektiert,
   • 2b. Stoppen der Drehung des Farbtopfs 2 (der Schritt 2b. kann auch entfallen, d.h. der Schritt 2a. kann direkt in den Schritt 2c. übergehen),
   • 2c. Den Farbtopf um einen gewissen Winkelbereich weiterdrehen, so dass der Laserstrahl 50 zentral durch die Einfüllöffnung 24 hindurch auf die Druckfarbe 3 fällt
3. 3. Messen des ersten lokalen Pegelstandes bzw. der ersten Höhe h1 und des zweiten lokalen Pegelstandes bzw. der zweiten Höhe h2 gemäss den nachfolgenden Schritten 3a. und 3b. (Maschine stoppt ca. 1 Sekunde lang)
   • 3a. Messung der ersten Höhe h1, nachdem die Klischeeplatte 1 ihre Bewegung gestoppt hat,
   • 3b. Messen der Zeit und/oder des Zeitverlaufs des lokalen Pegelstandes bis das Farbniveau um einen bestimmten Wert unter die Höhe h1 abgefallen ist (zB. 1mm),
4. 4. Auswerten (Maschine läuft/druckt normal)
   • 4a. Diese gemessene Zeit bzw. dieser gemessene Zeitverlauf charakterisiert den Zeitverlauf der Bewegung der Druckfarbe 3 und stellt deshalb ein Mass für die Viskosität dar,
   • 4.b Vergleich der gemessenen Zeit bzw. des gemessenen Zeitverlaufs mit einer Sollzeit bzw. einem Sollzeitverlauf,
5. 5. Einspritzen von Verdünnerflüssigkeit unter Berücksichtigung einer allfälligen Abweichung der gemessenen Zeit bzw. des gemessenen Zeitverlaufs von der Sollzeit bzw. vom Sollzeitverlauf (Maschine läuft/druckt normal),
   5.a Falls erforderlich wird die Einspritzmenge erhöht oder verringert, indem z.B. die Zykluszeit der Verdünnereinspritzung verkürzt bzw. verlängert wird.

In this example, the inductive sensor 7 is not used. To find the filling opening 24, a marking in the form of a local elevation is attached to the top of the top wall 21, which is arranged immediately in front of the filling opening 24 in the direction of rotation of the paint pot 2. The procedure is carried out as follows and in the order given:

1. 1. The pad printing machine is in auto operation and is printing. Every 30 minutes a Viscosity measurement according to the following steps 2. to 5a. carried out.
2. 2. Find filling opening 24 (machine runs / prints normally)
   • 2a. Rotate the paint pot 2 until the laser measuring device 5 detects a minimum measuring distance based on the marking,
   • 2 B. Stopping the rotation of the paint pot 2 (step 2b. Can also be omitted, ie step 2a. Can go directly to step 2c.),
   • 2c. Turn the ink pot further through a certain angular range so that the laser beam 50 falls centrally through the filling opening 24 onto the printing ink 3
3. 3. Measure the first local water level or the first height h1 and the second local water level or the second height h2 according to the following steps 3a. and 3b. (Machine stops for approx. 1 second)
   • 3a. Measurement of the first height h1 after the cliché plate 1 has stopped moving,
   • 3b. Measuring the time and / or the time course of the local water level until the color level has fallen by a certain value below the height h1 (e.g. 1mm),
4. 4. Evaluate (machine runs / prints normally)
   • 4a. This measured time or this measured time course characterizes the time course of the movement of the printing ink 3 and therefore represents a measure of the viscosity,
   • 4.b comparison of the measured time or the measured time course with a target time or a target time course,
5. 5. Injection of thinner liquid, taking into account any deviation of the measured time or the measured time course from the target time or from the target time course (machine runs / prints normally),
   5.a If necessary, the injection quantity is increased or decreased, for example by shortening or lengthening the cycle time of the thinner injection.

Alternatively, in the above step 2, instead of an applied marking, the inductive sensor 7 can also be used to adjust the rotational position of the paint pot 2 in order to carry out the viscosity measurement by means of the laser measuring device 50. The Step 2a. of the example procedure would then simply be replaced by the following step:
2a. Rotate the paint pot 2 until the inductive sensor 7 detects the magnet 27,

Since the rotational position can be set directly and correctly with the aid of the inductive sensor 7, step 2c. omitted.

Of course, the invention described here is not limited to the embodiments mentioned and a large number of modifications are possible. Thus, the method according to the invention can also be used with an open ink system or with a rotary pad printing machine without any problems. The device according to the invention does not even have to be a pad printing machine. It could also be a device which is only used to set and / or control the ink viscosity before the printing process, before the printing ink is filled into the ink pot 2 or this is inserted into a pad printing machine. The rotation of the ink pot 2 during the printing process is not mandatory. Furthermore, the measuring method can be used largely independently of whether the cliché or the ink pot is moved during the printing process. Instead of measuring the local level of the printing ink by means of a laser beam, any other measurement method could also be used. For example, a capacitive sensor could be attached to the paint pot in order to measure a local level at the edge of the paint pot. In addition, although this is preferred, the first and the second height of the printing ink do not necessarily have to both be measured at the same point. A large number of further modifications are conceivable REFERENCE LIST 1 Cliché plate 41 Hexagon head 42 Controls 2 Paint pot 20th Side wall 5 Laser measuring device 21st Top wall 50 laser beam 22nd Ring groove 23 Inlet opening 6th Injection hose 24 Filling opening 25th Squeegee edge 7th Inductive sensor 26th deepening 27 magnet 8, 8 ' Riser pipe 80 Bevel 3 Printing ink 81 Longitudinal slot 4th Pressing device h1 First height 40 Piston rod h2 Second height

Claims (14)

A method for measuring ink viscosity in pad printing, comprising the steps a.) set in motion a printing ink (3) held in an ink container (2); b.) determining a time course of the movement of the printing ink (3) in the ink container (2) by measuring a local level (hl, h2) of the printing ink (3) in the ink container (2); such as c.) Determining a measure for the viscosity of the printing ink (3) based on the time course determined in step b.). Method according to claim 2, wherein determining the time course of the movement in step b.) Comprises b1.) measuring a first local level (h1) of the printing ink (3) in the ink container (2); b2.) waiting for a time interval; such as b3.) measuring a second local water level (h2) of the printing ink (3) in the ink container (2), and wherein the measure for the viscosity in step e.) is determined based on the first local level (h1) and the second local level (h2). Method according to claim 1 or 2, wherein the ink container (2) rests against a cliché (1) in such a way that the printing ink (3) received in the ink container (2) contacts the cliché (1), and wherein the printing ink (3) is Relative movement of the cliché (1) to the ink container (2) is set in motion. Method according to one of the preceding claims, wherein the local water level (hl, h2) is measured without contact, in particular by means of a laser beam (50). Method according to one of the preceding claims, an amount and / or concentration of a diluent substance which is to be added to the printing ink (3) is determined based on the determined measure for the viscosity. Method according to claim 5, wherein, in order to determine the amount and / or concentration of the diluent substance, a quantity value and / or a concentration value is selected from a limited number of predetermined quantity values and / or concentration values. Method according to one of the preceding claims, wherein the measurement of the local water level (hl, h2) is carried out in an edge region of the paint container (2). Method according to one of the preceding claims, wherein steps a.) To c.) Are carried out at regular time intervals. Method according to one of the preceding claims, wherein the paint container (2) has a delimited sub-area (8, 8 '), and wherein the measurement of the local water level (h1, h2) is carried out within this sub-area (8, 8'). Method according to one of the preceding claims, wherein the paint container (2) has a surface (80) extending obliquely relative to the direction of gravity, and wherein the measurement of the local water level (hl, h2) is carried out directly in the area of this oblique surface (80) . Having a device for measuring the ink viscosity during pad printing, in particular by means of a method according to one of the preceding claims an ink container (2) for holding a printing ink (3); a measuring device (5) for measuring a local level (h1, h2) of the printing ink (3) in the ink container (2); such as an evaluation unit which is designed to determine a measure for the viscosity of the printing ink (3) based on a time curve of the local level (h1, h2) measured by the measuring device (5). Apparatus according to claim 11, further comprising an insert part (8, 8 ') arranged inside the ink container (2), the measuring device (5) for measuring the local level (hl, h2) of the printing ink (3) within this insert part (8, 8 ') is formed. Apparatus according to claim 11 or 12, additionally having a feed device (6) for feeding a diluent substance to the printing ink (3) received in the ink container (2), the evaluation unit preferably being designed to determine an amount and based on the determined measure for the viscosity / or to determine the concentration of the diluent which is added to the printing ink (3) by means of the feed device (6). Device according to one of Claims 11 to 13, which is a pad printing machine with a cliché (1) and a printing pad for receiving a print image from the cliché (1) and for the subsequent transfer of this print image to an object to be printed, and wherein the The ink container (2) is designed to rest against the cliché (1) in such a way that the printing ink (3) accommodated in the ink container (2) contacts the cliché (1).

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