EP3756890B1 - Method and device for measuring ink viscosity in pad printing - Google Patents

Description

TECHNICAL AREA

The present invention relates to a method and a device for measuring ink viscosity in pad printing.

STATE OF THE ART

With pad printing, the print quality that can be seen on the printed object is largely dependent on correct adjustment and, even more important, control of the viscosity of the printing ink. The printing ink is usually adjusted to the desired viscosity with a thinner before printing begins. The viscosity of the printing ink can be checked using a measuring device before the printing of usually a large number of objects is started.

However, during the printing of a variety of objects, a part of the diluent substance cannot be prevented from evaporating over time. With open ink systems, evaporation is naturally the fastest, but even with closed systems, the thinner will evaporate over time due to the movement of the ink pot on the cliché. The problem with rotary pad printing machines is that the low-viscosity 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 and, in particular, transferred to the object to be printed. As a direct result, the print quality is reduced and rejects are produced.

In order to counteract the continuous evaporation of the thinner during the printing process, the printing ink 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, the humidity, any air movements, the printing speed, etc. In addition, the viscosity is strongly dependent on the color temperature. For this reason, the evaporation rate can hardly be precisely predicted in practice and is also usually subject to fluctuations. Accordingly, the ink viscosity must be checked at regular intervals during a printing process and the supply of the thinning substance must be adjusted.

For example, spatulas with a printed or embossed measurement scale are known in the prior art for checking the paint viscosity. These spatulas are dipped into the printing ink in order to measure the speed at which the printing ink flows off with the help of the scale after they have been pulled out, and thereby draw conclusions about the viscosity.

With a viscometer in the form of a flow cup, the colored liquid is filled into a cup that runs conically at the bottom into a hole with a precisely known diameter. The viscosity of the liquid can be determined based on the volume of the cup, the diameter of the nozzle and the measured time it takes for the liquid to flow out.

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

Rotational viscometers are known in the prior art, 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. Although such rotary viscometers enable the viscosity to be determined precisely, they are only intended for use outside of the pad printing machine. Such measuring devices are therefore unsuitable for continuous or regular measurements during the printing process.

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

In the EP 1 780 012 A1 a relatively complicated system is proposed in which the printing ink is fed continuously to the ink pot via a feed line. This means that the viscosity can be checked outside of the ink cup during the printing process. However, the additional expenditure on equipment is considerable. In addition, the system is unsuitable, for example, for pad printing machines in which the ink pot rotates during the printing process.

Furthermore, the DE 41 16 989 A1 a supply device for wetting the roller of a sheet-fed printing machine or strip material printing machine with varnish. A flow cup fitted with measuring electrodes is used to measure the viscosity of the paint.

PRESENTATION OF THE INVENTION

It is therefore an object of the present invention to specify a method for pad printing which, by means of simple handling and equipment, allows the ink viscosity to be reliably measured. A method as specified in claim 1 is proposed to solve this problem. In addition, claim 11 specifies a device for carrying out this method. Other embodiments are set out 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 in Schritt b.) bestimmten Zeitverlauf.

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

1. a.) set an ink received in an ink container in motion;
2. b.) 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; as well as
3. c.) determining a measure for the viscosity of the printing ink based on the time profile determined in step b.).

By setting the printing ink in the ink container in motion and determining the movement of the printing ink in the ink container over time by measuring a local level of the printing ink in the ink container, a measure of 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.), i.e. setting the printing ink in the ink container in motion, can be implemented very easily, for example by simply pushing or moving the ink container. If the ink container is an ink pot of a pad printing machine with a closed ink system, the ink pot movement that is present anyway between two print image transfers can be used directly, for example.

The measurement of the local level, ie 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, for example, can be used for this purpose.

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

Measuring paint viscosity may refer to measuring an absolute viscosity value. However, the measurement of the paint viscosity preferably only means the measurement of a relative viscosity value, ie the measure determined in step e.) is a relative measure. It is therefore preferably a question of determining 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 not moved during the determination of the time course of the movement in step b.). The point in time for starting the time course determination in step b.) is also preferably chosen such that the printing ink lowers 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 that it is measured at the same point in each case, 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 already sufficient, for example. The measurement of the local level in step b.) is therefore preferably carried out exactly twice, with a predetermined time interval lying between the two measurements. As a result, the measurement can be carried out in a particularly simple manner. According to this particular In a preferred embodiment, the determination of the time course in step b.) thus comprises at least the following sub-steps:

• b1.) measuring a first local level of the printing ink in the ink container;
• b2.) Waiting for a time interval; as well as
• b3.) measuring a second local level of the printing ink in the ink container,
• wherein the measure of the viscosity in step e.) is determined based on the first local level and the second local level.

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

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

In order to achieve a particularly meaningful measurement, the local water level is preferably determined in a decentralized manner 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 cup (or the cliché surface) and the surface of the printing ink at a specific point in the ink cup. However, the local water level can just as well, and is even preferred here, 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 refers less to the distance between the ink surface and the floor on which the printing ink lies, but rather to the measuring point as a whole in a broader sense. 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. By the term "local level" it is meant that the level is measured at a specific location. 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 important to measure a change in the local level of the printing ink over a specific time.

In order to determine the measure for the viscosity in step c.), the difference between the mentioned first level and the second level is preferably calculated. The measure for the viscosity is then preferably determined on the basis of this calculated difference. The calculated difference itself can even be used as a measure of the viscosity of the printing ink.

Instead of waiting between two measurements for a predetermined time interval, however, a first level can also be measured and then the time interval can be determined until the local level of the printing ink has lowered to a second predetermined level. The time interval lying 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 it is also possible to determine a time course of the movement of the printing ink in the ink container by measuring a local water level according to step b.) in order to then be able to determine a measure of the viscosity of the printing ink based on this in step c.).

The ink container can be an ink tray of a pad printing machine with an open ink system or an ink tray of a rotary pad printing machine. With such an open system, the evaporation rate of the diluent 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 is then generally in contact with a cliché in such a way that the printing ink contained in the ink container contacts the cliché. The ink is then preferably by means of a relative movement of the cliché to Paint container set in motion. As during the printing process, the cliché preferably moves while the ink container remains stationary.

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

When determining the quantity 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 safe, since the degrees of freedom of the system are restricted.

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

According to a development of the invention, the paint container has a delimited partial area. The local water level is then preferably measured within this sub-area. 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 be designed in particular as a riser pipe. By providing a delimited partial area, the measuring method becomes independent of the size, ie the diameter, of the paint container. By inserting the insert, the paint viscosity can be measured in the same way for paint containers of different sizes and manner and without adjusting presets.

In another development of the invention, the paint container has a surface 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 determined precisely, even at low 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.

• dieses Druckbildes auf ein zu bedruckendes Objekt sowie ausserdem aufweisend
• 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 ink viscosity in pad printing using the method specified above, the device being a pad printing machine with a cliché and a printing pad for recording a printed image from the cliché and for subsequent transfer

• this printed image on an object to be printed and also having
• an ink reservoir for containing an ink;
• a measuring device for measuring a local level of the printing ink in the ink container; as well as
• an evaluation unit which is designed to determine a measure of the viscosity of the printing ink based on a time profile of the local water level measured by the measuring device.

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

The device preferably has a supply device for supplying a thinner substance to the printing ink held in the paint container, with the evaluation unit preferably being designed to determine, based on the measure of the viscosity, a quantity and/or concentration of the thinner substance which is added to the printing ink by means of the supply device will be added. The device is preferably designed to automatically based on the viscosity measurement control thinner injection.

The ink container is advantageously designed to rest against the cliché in such a way that the printing ink contained 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 for explanation only and are not to be interpreted as restrictive. In the drawings show:

1

a perspective view of a device according to a first embodiment for carrying out the inventive method;

Figure 2a

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

Figure 2b

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

Figure 3a

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

Figure 3b

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

Figure 4a

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

Figure 4b

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

figure 5

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

6

a perspective view of the insert part of the device figure 5 , as well as

7

a perspective view of a variant of an insert.

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. Statements of location and direction such as "up", "down", "upwards", "downwards" etc. refer below and throughout the present document to the direction of gravity when the paint container is inserted as intended in 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 is a pad printing machine, but only part of it is shown. In particular, a cliché plate 1 and an ink cup 2 are shown. The pad printing machine also has a printing pad for receiving a printed image from the cliché plate 1 and for subsequently transferring this printed image to an object to be printed. The object to be printed is generally held in a print holder, which, like the printing pad, is not shown in the figures. However, the basic structure and the mode of operation of pad printing machines are well known to those skilled in the art.

The one in the figure 1 So partially shown pad printing machine has a closed ink system with an ink cup 2, which is closed to the outside substantially. The paint pot 2 has an upper top wall 21, from the outer edge of which a peripheral side wall 20 extends downwards. A squeegee edge 25 is attached circumferentially to the lower edge of the side wall 20 . The paint pot 2 is open at the bottom, ie bottomless. A printing ink 3 is accommodated inside the ink pot (see, for example, Figures 2a and 2b ).

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

The pressing device 4 has a piston rod 40 which protrudes vertically downwards and which extends into a recess 26 arranged centrally in the top wall 21 . At the lower, free end of the piston rod 40, a hexagonal head 41 is attached. The hexagonal head 41 engages in an engagement structure which is designed to complement it and is formed by the recess 26 . During the printing process, the piston rod 40 on the one hand exerts a constant pressure on the ink cup 2 in order to ensure that the ink cup 2 is sealed off from the cliché plate 1 . On the other hand, the ink cup 2 is also rotated continuously during the printing process by means of the piston rod 40 in order to achieve wear of the squeegee edge 25 and the cliché plate 1 that is as uniform as possible. This rotation is made possible by the engagement of the hexagon head 41 in the complementary shaped recess 26 thereto.

The pressing device 4 has operating elements 42 which are used to adjust the contact pressure, the rotational speed and for various other functions. Basically, the pressing device 4 and the ink pot 2 according to the information in the CH 688 545 A5 educated.

For filling 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 thinner liquid during the printing process, the device has a feed device for injecting thinner liquid with an injection hose 6 . The injection hose 6 protrudes from down to the top wall 21 and opens out just above an annular groove 22 formed in the top wall 21 concentrically with the recess 26. During injection, the diluting 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 pot 2. Due to the annular groove 22, injection through the injection hose 6 is possible regardless of the rotational position of the paint pot 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 is a pad printing machine, is explained.

In a first method step, the ink 3 contained in the ink pot 2 is set in motion. This can be done, for example, by pushing the paint pot 2, ie slightly moving it. However, the movement of cliché plate 1 relative to ink cup 2, which occurs anyway, is preferably utilized for this purpose during 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 is in the Figures 2a and 2b shown oblique position occupies.

The movement of cliché plate 1 is then stopped in order to carry out two measurements of a local water level, ie two height measurements of printing ink 2. The movement of the paint pot 2, ie 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 measures the distance to the surface of the printing ink 3 through the open filling opening 24 by means of a laser beam 50 . The local level or filling 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 vertically above the filling opening 24 .

The time of the measurement of a first water level or a first height h1 (see figure 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 is not used in the Figure 2b shown height h1 is measured, but rather 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 is usually constant, the conversion of the distance measured by the laser measuring device 5 to the height h1 is a task for the person skilled in the art is a 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 must be carried out in accordance with the illustrations in the figures 2b and 4b not even necessary here. Due to the trivial possibility of conversion, however, this document refers to measuring the first height h1 or the second height h2 by means of the laser beam 50 .

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

After the time interval mentioned has elapsed, a local water level is measured 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 this way is smaller than the first height h1, since the printing ink 3 has meanwhile approached its resting position and the local filling level in the region of the filling opening 24 has reduced accordingly.

The difference between the first measured height h1 and the second measured height h2 can be used directly as a measure of the viscosity of the printing ink 3 if the time interval between the measurements is known. The difference and the measure of the viscosity are preferably calculated or determined automatically by an evaluation unit of the device, which is 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 measure determined for the ink viscosity can now be used by the evaluation unit to automatically, ie without the help of human operating personnel, determine a quantity and/or concentration of a diluent substance which is to be added to the printing ink. The diluting substance, usually a diluting liquid, can then likewise be automatically added 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 thinning substance is mixed with the printing ink 3 very quickly.

In order to find the correct rotational position of the ink cup 2 for measuring the height of the printing ink 3 using the laser beam 50, the ink cup can simply be rotated further until the laser beam 50 falls through the filling opening 23 onto the printing ink 3 and the laser measuring device 5 emits determined measuring distance suddenly increased. Alternatively or additionally, one or more markings, e.g. in the form of local elevations or depressions, can also be provided for this purpose on the upper side of the top wall 21, 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 more quickly and 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 correct rotational position of the ink cup 2 is preferably set while the printing process is still running, before the actual viscosity measurement is started.

It was found in experiments 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 blown into the filling opening 24 for a short time immediately before the measurement in order to eliminate any bubbles present there.

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

The riser 8 is according to the figure 6 shaped with an upper cylindrical section and a lower section in which the cylindrical shape is only formed over a portion of the circumference and is open over the remaining, larger portion. As a result, the riser pipe 8 has a curved wall which extends downward on one side from the upper cylindrical section. Attached to the lower free end of this wall is an inclined surface 80 which extends radially from the inside upwards towards the wall. When inserted into the ink pot 2 through the filling opening 24, the riser pipe 8 comes to rest on the cliché plate 1. The sloping surface 80 is then located at the very bottom in the ink cup 2. Due to the sloping surface 80, viscosity measurements can still be carried out reliably using the specified method even when the total filling level of the printing ink 3 in the ink cup 2 has been greatly reduced.

A variant of a riser 8 'is in the figure 7 shown. The riser pipe 8' has an overall hollow-cylindrical shape with a longitudinal slot 81 open towards the bottom. Because of the longitudinal slit 81, the water level inside the riser pipe 8' when the printing ink 3 is not moving essentially corresponds to the local water level in the immediate vicinity Area around the riser 8 'around. When the printing ink 3 is in motion, however, the level within 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 brings the significant 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 essentially the same within the riser pipe 8', independently of the ink cup size. The viscosity measurement is then particularly similar to 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', ie the riser pipe 8' can also have an inclined surface in its lower region.

In order to prevent diluting liquid from evaporating 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. In principle, it is also conceivable for the laser measuring device 5 to be attached directly to the top wall 21 of the paint pot 2 and for an opening provided in the top wall 21 to be 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 locate the filling opening 24, a marking in the form of a local elevation is attached to the upper side of the cover wall 21, which is arranged directly in front of the filling opening 24 in the direction of rotation of the paint can 2. The procedure is carried out as follows and in the order given:

1. 1. The pad printing machine is in auto mode and is printing. One every 30 minutes Viscosity measurement according to the following steps 2. to 5a. carried out.
2. 2. Find filler opening 24 (machine runs/prints normally)
   • 2a. Rotating 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 into step 2c.),
   • 2c. Turn the ink cup further by a certain angular range, so that the laser beam 50 strikes the printing ink 3 centrally through the filling opening 24
3. 3. Measuring 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 about 1 second)
   • 3a. Measurement of the first height h1 after cliché plate 1 has stopped moving,
   • 3b. Measurement of the time and/or the time course of the local water level until the color level has fallen below the height h1 by a certain value (e.g. 1mm),
4. 4. Evaluate (machine runs/prints normally)
   • 4a. This measured time or this measured time profile characterizes the time profile 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 profile with a target time or a target time profile,
5. 5. Injecting thinner liquid, taking into account any deviation of the measured time or the measured time profile from the target time or the target time profile (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 diluent injection.

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

Since the rotational position can be directly and correctly set using the inductive sensor 7, step 2c can be carried out in this case. 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 without any problems with an open color system or with a rotary 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 using a laser beam, any other measuring method could also be used. For example, a capacitive sensor could be attached to the paint can to measure a local level at the rim of the paint can. Also, while preferred, the first and second heights of the ink need not both be measured at the same location.

REFERENCE LIST

1 cliche plate 41 hex head 42 controls 2 paint pot 20 Side wall 5 laser measuring device 21 top wall 50 laser beam 22 ring groove 23 intake port 6 injection hose 24 filling hole 25 squeegee edge 7 Inductive sensor 26 deepening 27 magnet 8, 8' riser 80 bevel 3 ink 81 longitudinal slit 4 pressing device h1 First height 40 piston rod h2 second height

Claims (14)

1. Method for measuring the ink viscosity in pad printing, comprising the steps of

   a.) setting a printing ink (3) accommodated in an ink container (2) in motion;

   b.) determining a time characteristic of the movement of the printing ink (3) in the ink container (2) by means of measuring a local level (h1, h2) of the printing ink (3) in the ink container (2); and

   c.) determining a measure for the viscosity of the printing ink (3) based on the time characteristic determined in step b.).
2. Method according to claim 2, wherein determining the time characteristic of the movement in step b.) includes

   b1.) measuring a first local level (h1) of the printing ink (3) in the ink container (2);

   b2.) waiting during a time interval; and

   b3.) measuring a second local 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).
3. Method according to claim 1 or 2, wherein the ink container (2) bears against a cliché (1) in such a way that the printing ink (3) accommodated in the ink container (2) contacts the cliché (1), and wherein the printing ink (3) is set in motion by means of a relative movement of the cliché (1) with respect to the ink container (2).
4. Method according to one of the preceding claims, wherein the local level (h1, h2) is measured without contact, in particular by means of a laser beam (50).
5. Method according to one of the preceding claims, wherein, based on the determined measure for the viscosity, an amount and/or concentration of a diluent substance is determined which is to be added to the printing ink (3).
6. Method according to claim 5, wherein for determining the amount and/or concentration of the diluent substance, an amount value and/or a concentration value is selected from a limited number of predetermined amount values and/or concentration values.
7. Method according to one of the preceding claims, wherein the measurement of the local level (h1, h2) is carried out in an edge region of the ink container (2).
8. Method according to one of the preceding claims, wherein steps a.) to c.) are carried out at regular time intervals.
9. Method according to one of the preceding claims, wherein the ink container (2) has a delimited partial region (8, 8'), and wherein the measurement of the local level (h1, h2) is carried out within this partial region (8, 8').
10. Method according to one of the preceding claims, wherein a surface (80) extending obliquely relative to the direction of gravity is present in the ink container (2), and wherein the measurement of the local level (h1, h2) is carried out directly in the region of this oblique surface (80).
11. Device for measuring the ink viscosity in pad printing by means of a method according to one of the preceding claims, wherein the device is a pad printing machine with a cliché (1) and a printing pad for receiving a printed image from the cliché (1) and for subsequently transferring this printed image to an object to be printed, and further comprising

    an ink container (2) for receiving 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); and

    an evaluation unit which is designed to determine a measure for the viscosity of the printing ink (3) based on a time characteristic of the local level (h1, h2) measured by the measuring device (5).
12. Device according to claim 11, further comprising an insert part (8, 8') arranged inside the ink container (2), wherein the measuring device (5) is designed for measuring the local level (h1, h2) of the printing ink (3) inside this insert part (8, 8').
13. Device according to claim 11 or 12, further comprising a supply device (6) for supplying a diluting substance to the printing ink (3) accommodated in the ink container (2), wherein the evaluation unit is preferably designed to determine, based on the determined measure for the viscosity, an amount and/or concentration of the diluting substance which is added to the printing ink (3) by means of the supply device (6).
14. Device according to one of claims 11 to 13, wherein the ink container (2) is designed to abut 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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