EP1022137B2 - Digital ink dosing - Google Patents

Abstract

An inking unit for a printing machine includes one or more distributor drums, ink transfer rollers, ink application rollers, an ink reservoir for printing ink and an ink metering device having at least one electrically controllable valve for metering the printing ink. In accordance with the invention, there are provided a high-pressure pumping device for supplying the ink metering device with printing ink at a predetermined high pressure from the ink reservoir, and a heating device for heating the printing ink to a predetermined temperature above room temperature. Moreover, the at least one valve of the ink metering device has a short reaction time and a flow rate with a low dependence upon viscosity. The invention also relates to a method for supplying printing ink to a printing machine.

Description

The invention relates to an offset printing machine according to the preamble of claim 1 and a method for supplying the offset printing press with printing ink.

Such an offset printing machine is off DE2951651 known. In addition, a conventional inking unit for an offset printing machine in Fig. 7 shown. The inking unit includes an ink fountain 122 as a reservoir for ink 124, a Farbduktor 126, a color lifter 128 and a roller assembly, in this example four distribution cylinders 130a to 130d, four inking rollers 132, which roll on a plate cylinder 134 of the printing press, and a number of ink transfer rollers 136 contains. The need for ink 124 is adjusted in zones depending on the printed image by pressing a resilient knife (color knife) more or less strongly against the ink fountain roller 126 and thus changing the amount of ink passing through the gap between the ink knife and the ink fountain roller 126 , The regulation of the printing ink 124 over the entire width of the ink ductor 126 is effected by a change in the color removal strip, which is removed by the ink lifter 128 in a rhythmic pendulum movement of the ink fountain roller 126. The subsequent arrangement of hard and soft rolls of different diameters, the ink 124 is repeatedly distributed, split and triturated by an axial movement of the distribution cylinder 130a to 130d, before being applied by means of the inking rollers 132 on the plate cylinder 134.

The arrangement described allows only a relatively inaccurate ink dosage, which is still deteriorated by wear in Farbdosierbereich, so that it takes a large number of rollers to achieve the required low ink layer thickness. The ink supply is difficult to reproduce. Assemblies such as ink fountain, ink ductor and ink lifter require a relatively large amount of space and must be cleaned regularly. In order to automate the color dosing, which is normally done manually, one needs in addition to the elements described above electrical actuators and controls. Furthermore, one needs a squeegee device to remove excess ink. Known methods for solving these problems are e.g. the use of color cartridges, which eliminates only the manual ink feed, or the use of low-wear materials for the Farbdosierbereich, which solves the problems described only partially.

The journal Zeitungstechnik, July / August 1996, p. 30, shows an inking unit in which the ink is applied to a specially formed ink film roll by means of a digital ink pumping system which includes a gear pump and pulse length controlled solenoid valves. Although the ink metering is more accurate than in ink fountain systems, you still need a doctor blade device for scraping off excess paint.

The invention has for its object to provide an inking unit that allows extremely accurate color metering, which is simple and compact and can be derived by simple design changes of a conventional inking unit.

This object is solved by the characterizing part of claims 1 and 7.

The offset printing machine according to the invention enables the use of a standard offset ink which has a dynamic viscosity of more than 10 Pa s at room temperature and low shear rate, e.g. 50 to 70 Pa s. By supplying the printing ink to the at least one valve under a pressure in the range of about 10 to 100 bar and thereby heating to a temperature in the range of about 40 to 70 ° C, the viscosity decreases so far that in conjunction with a sufficiently short reaction time the valve is a high-precision color dosing is possible. By choosing the valve design as a ball element can be taken to ensure that the passage rate of the valve depends as little as possible on the viscosity, so that the desired color dose is virtually unaffected by any inhomogeneities of the ink or by temperature fluctuations.

The at least one valve is preferably a valve with piezoelectric actuators as adjusting elements, a so-called piezoelectric valve. Such a valve, as for example in the DE-A-4 220 177 has response times on the order of microseconds. Thus, it can be opened and closed many times faster than conventional solenoid valves, which have response times of several milliseconds. This allows a very fine dosing of the ink, preferably by pulse length controlled full opening and closing of the valve or alternatively by controlling the flow rate of a valve whose degree of opening is controlled by a fast control loop.

Color dosing by means of piezoelectric actuators is known per se in the technology of inkjet printers. Ink-jet printers normally spray low viscosity paint directly onto paper, and in one of the known techniques, ink is metered by briefly compressing a small volume of ink by a piezoelectric actuator, spraying a droplet of ink onto a pixel. In contrast, relatively high-viscosity offset printing ink can be used in the invention, and the compressed and heated ink is already under a sufficiently high pressure for spraying paint, so that it only needs to be metered by means of the piezo-valve.

The valve design for a viscosity-independent ink dosage as possible is a valve with a spherical closure element, which faces a spherical recessed valve seat, in which an opening with a substantially smaller diameter than the spherical closure element is formed. A nozzle downstream of the valve determines the volume flow. In this case, this nozzle may have a very short flow channel, whereby the mode of action corresponds to a diaphragm.

In a preferred embodiment, the paint metering device includes a series of nozzles directed at the surface of one of the distribution cylinders. The distribution cylinder moves in the machine cycle along its longitudinal axis back and forth, so that the ink is rubbed laterally. In the case of pulse-length-controlled opening and closing of the at least one valve, care must be taken that the ink spraying does not occur synchronously with the machine cycle or the rubbing motion, which would result in an inhomogeneous color profile. A homogenization of the applied ink layer can be achieved, for example, by the fact that the time of ink application is offset in time with each Reiberhub or each Reiberdrehung something, such as by temporal modulation of the valve control pulses.

The invention is suitable both for conventional offset printing presses (sheetfed and web presses) with ink zones and for zoneless inking units. In one embodiment, for inking zones, a valve is provided for each inking zone, the outlet of which is connected to one or more nozzles located in that inking zone. The more nozzles per color zone are present, the smoother the thickness of the applied color layer. If sprayed with variable timing on a distribution cylinder, as described above, can be achieved with a single nozzle per color zone, a sufficiently uniform color distribution. On the other hand, when using many nozzles side by side also be sprayed on another high-speed roller as a distribution cylinder.

The color reservoir may e.g. a color cartridge, which is located in a pressure vessel and which is connected via a pressure line with the at least one valve. The ink is pressurized by pressurizing the interior of the pressure vessel. The required pressure can be easily generated by means of a pressure booster from the available in a printing operation compressed air. An alternative to ink supply by cartridges is a loose package supply, e.g. the paint supply via the drum, which is known in the art, and which does not require a cartridge change.

As mentioned, the inking unit according to the invention allows such a precise and uniform ink metering that one manages with significantly fewer ink rollers than before. In addition, conventional components such as ink fountain and ductor can be saved. For the remaining part of the inking you need no special components, but it can be conventional components, especially conventional ink rollers are used. As a result, a conventional inking unit can be easily converted to an inking unit according to the invention.

The high-precision ink metering according to the invention makes it possible to dispense the printing ink without excess according to its requirements in the printing press, so that it is possible to dispense with any doctoring device. If you still work with a certain excess of color and accordingly a squeegee device used, the abzurakelnde amount of ink can be much lower.

Fig. 1

eine Prinzipskizze eines Piezo-Ventils,

Fig. 2

einen Schnitt entlang einer Linie II-II in Fig. 1, der außerdem mehrere nebeneinander angeordnete Piezo-Ventile in einer Art Ventilleiste zeigt,

Fig. 3

einen Reibzylinder, der durch die Piezo-Ventile von Fig. 2 mit Druckfarbe versorgt wird,

Fig. 4

Bauteile einer Farbversorgung für ein Piezoventil oder mehrere Piezo-Ventile, die eine Ventilleiste bilden,

Fig. 5

eine Ansicht ähnlich wie in Fig. 2 und Fig. 3, die ein Piezo-Ventil mit einer vorgeschalteten Mehrfachdüse zeigt,

Fig. 6

mögliche Anordnungen von Piezo-Ventilen in einem Farbwerk, und

Fig. 7

ein konventionelles Farbwerk für eine Offsetdruckmaschine.

The invention will be explained in more detail by means of embodiments with reference to the drawings. In the drawing show:

Fig. 1

a schematic diagram of a piezo valve,

Fig. 2

a section along a line II-II in Fig. 1 which also shows a plurality of juxtaposed piezo valves in a kind of valve strip,

Fig. 3

a distribution cylinder passing through the piezo valves of Fig. 2 supplied with printing ink,

Fig. 4

Components of a paint supply for a piezo valve or a plurality of piezo valves, which form a valve strip,

Fig. 5

a view similar to in Fig. 2 and Fig. 3 showing a piezo valve with an upstream multiple nozzle,

Fig. 6

possible arrangements of piezo valves in an inking unit, and

Fig. 7

a conventional inking unit for an offset printing machine.

A piezo valve 2, which in Fig. 1 is shown in longitudinal section, contains a base body 4 with an L-shaped cross-section. On the shorter leg of the Base 4 are based on two piezoelectric translators 6, each consisting of a stack piezoceramic plates. The piezoelectric translators 6 extend parallel to the longer leg of the main body 4 to a tapered operating lever 8. The blunt end of the actuating lever 8 is connected by means of a screw 10 which extends between the two piezoelectric translators 6 and parallel to the shorter leg screwed to the base body 4, whereby the two piezoelectric translators 6 are firmly biased between the shorter leg of the base body 4 and the actuating lever 8.

Transversely through the pointed end of the actuating lever 8, an actuating rod 12 which is fixed by pressing voltage on the actuating lever 8 extends. The actuating rod 12 extends through a matching bore in the longer leg of the base body 4 into a channel 14 formed therein. At its end projecting into the channel 14, the actuating rod 12 carries a valve ball 16. On the side facing away from the actuating rod 12 side of the valve ball 16 contains the main body has a nozzle 18 with an opening 20 which has a smaller diameter than the valve ball 16. When closed, the valve ball 16 closes the opening 20, and when the valve ball 16 is raised, the channel 14 communicates via the narrow opening 20 with the outside.

The channel 14 carries a printing ink which is heated to about 40 to 70 ° C and under a pressure of e.g. 40 bar stands. The ink is a standard offset ink having a viscosity of e.g. 50 to 70 Pa s at room temperature, which is greatly reduced by the heating. This and the relatively high pressure make it possible to finely dose the ink by means of the piezo-valve 2 and subsequently to spray it from one or more nozzles.

This in Fig. 1 shown piezoelectric valve 2 operates as follows. If opposite polarity electrical voltages are applied to the two piezoelectric translators 6, one of the two piezoelectric translators 6 expands a little, while the other shortens a little. As a result, the operating lever 8 tilts in the direction of the longer leg of the main body 4 or away, depending on the applied voltage. The elongation or shortening of the individual piezoelectric translators 6 is indeed very small, but at the tip of the actuating lever 8 is achieved but a stroke in the order of a few hundred micrometers. Accordingly, the valve ball 16 is moved, and depending on the position of the valve ball 16, the opening 20 in the nozzle 18 is either closed or kept more or less open.

Preferably, the passage rate of the piezo-valve 2 is controlled by being alternately fully closed and fully opened, the length of electrical control pulses, during which the valve ball 16 assumes a defined open position, is changed. This means defined that the valve 2 opens sufficiently wide, so that the flow resistance at the outlet opening 20 is significantly greater than the remaining flow resistance at the sealing seat. The outlet opening 20 is designed according to a diaphragm 18, that is, that the nozzle channel is designed short against its diameter. An aperture 18 is characterized in that the flow rate is independent of viscosity. If the pressure in the device is kept constant, the flow is exclusively time-dependent.

In order to dose as independent of viscosity as possible, it is also important that the transitions between the states (open / closed) are very short. With the piezo actuators 6 used, the required steep opening and closing edges can be achieved.

In addition to the valve construction (ball valve with downstream nozzle), steep flanks are advantageous in the opening or closing of the nozzle 18 by the valve ball 16. This advantage is largely fulfilled by the fast reaction time of the piezoelectric translators 6.

Fig. 2 shows an arrangement of a plurality of piezo-valves 2 according to section II Fig. 1 side by side. The piezo valves 2 have a common main body 4 and are supplied via a common channel 14 with ink.

The valve bar of Fig. 2 is placed lengthwise close to the surface of a rubbing cylinder 38, as shown Fig. 2 along with Fig. 3 can be seen. As in connection with Fig. 4 will be described in more detail, inject the nozzles 18 of the piezo-valves 2 in operation small Farbkleckse 74 on the rotating distribution cylinder 38. The distribution cylinder 38 moves in operation along its axis, so that the Farbkleckse 74 distributed in the form of serpentine lines on the distribution cylinder 38 become.

To roll out the scattered ink blobs 74 on the dispensing cylinder 38 into a continuous color film, only a few more rollers are needed, as will be described below.

In the arrangement of Fig. 3 For example, a piezo-valve 2 is provided for each color zone, so that the ink can be finely dosed depending on the current needs in the respective color zone.

Fig. 4 shows the components of a paint supply for a schematically illustrated piezo-valve 34, which in this example includes a single nozzle 36 which is directed to the surface of a rubbing cylinder 38 of the inking unit. An embodiment of a multi-nozzle piezoelectric valve will be described below.

The distribution cylinder 38 reciprocates in its axial direction by about 35 mm as it rotates, as indicated by arrows. With the nozzle 36 is thus achieved an axial portion 40 on the distribution cylinder 38, which is slightly wider than the width of a color zone of 32 mm. For the other color zones is respectively another piezo-valve 34 is provided (in Fig. 4 Not shown). In the Fig. 4 shown ink supply supplies not only the one shown piezoelectric valve 34, but all the piezo valves 34 that are needed for the printing width of the printing press, such as a valve bar as in Fig. 2 shown.

A pressure booster 42 receives via a pressure line 44 compressed air of about 6 to 8 bar, as it is available to operate a printing press, and generates compressed air with about 40 bar, which is fed via a further pressure line 46 to a pressure vessel 48. The pressure vessel 48 includes a base 50 through which the pressure line 46 and a Farbauslaßleitung 52 extend, and a pressure-tight screw-bell 53. Within the pressure vessel 48 is a paint cartridge 54 which is connected to the Farbauslaßleitung 52. The ink cartridge 54 is open at its top or closed with a movable plunger, so that the pressure within the pressure vessel 48 drives the ink from the ink cartridge 54 in the Farbauslaßleitung 52. The level of ink within the ink cartridge 54 is monitored by a level sensor 56 which is connected by a cable to a sensor electronics 58 which provides a warning signal to a central printing machine controller, not shown, as the contents of the ink cartridge 54 tend toward the end.

Instead of the pressurized ink cartridge 54 as in Fig. 4 , which must be changed from time to time, alternatively, a continuous ink supply from a loose container such as a drum by means of a drum pump can be used. Suitable drum pumps are commercially available in various forms.

The operating pressure air of the printing machine is also supplied to a tank 60 containing a cleaning liquid to pressurize the cleaning liquid. Instead of the tank 60, alternatively, a cartridge with cleaning liquid which is pressurized may be used. An outlet conduit of the tank 60 may be selectively connected to a conduit 63 or an outlet 64 via a three-way cock 62. An inlet line 66 of the piezo-valve 34 can be connected via a further three-way valve 68 selectively with the Farbauslaßleitung 52 or 63 with the line piece. In the printing operation, the three-way valve 68 is in the illustrated position, in which the inlet line 66 of the piezo-valve 34 is connected to the paint outlet 52. For cleaning the three-way valves 62 and 68 are adjusted so that the cleaning liquid can flow through the piezo-valve 34 and through the valve bar.

The required for color change cleaning of the piezo-valve 34 and the piezo valves 94 can be used in an advantageous manner also to make the spraying of the ink rollers with cleaning liquid. Thus, there is a possibility that the previously required spraying device for washing liquid for cleaning the inking deleted. The corresponding advantages are that with simultaneous use of the piezo-valve 34 for the metering of ink and washing liquid less cost and less space is required or is.

For washing operations which are then required when a color change takes place at the same time, the cleaning of the piezo-valves 34 automatically results in spraying of the rubbing cylinder 38 with washing liquid. About this distribution cylinder 38 then takes place the distribution of the washing liquid in the whole inking unit. In order to keep the additional consumption of printing ink low during washing operations which take place when no color change is associated therewith, the attachment of the three-way valve 68 close to the piezo valve 34 is advantageous. In other cases, a previous sucking back of the ink from the line system 14, 66 in the ink cartridge 54 or a corresponding reservoir. Thereafter, the cleaning of the piezo-valve 34 and then the entire inking begins.

The inlet line 66 of the piezo-valve 34 passes through a schematically illustrated preheating device 70, which heats the pressurized ink from the ink cartridge 54 to a temperature of up to 65 ° C. The piezo valve 34 includes a heater, not shown, which keeps it at the same temperature so that the ink does not cool therein.

The piezo-valve 34 is driven by a valve control unit 72 connected to the central printing machine control by means of square pulses which open the piezo-valve 34 for the duration of each pulse while it is closed in the remaining time. The short reaction time of the piezo-valve 34 allows the pulses to follow each other very rapidly, e.g. with a frequency of 3 kHz, and the ink accordingly distributed finely applied to the distribution cylinder 38.

Since the switch-on time of the individual rectangular pulses is very short, the nozzle 36 of the piezo valve 34 injects tiny splashes of paint 74 onto the rotating distributor cylinder 38, as in FIG Fig. 4 indicated schematically, while a long rectangular pulse generates a more or less long line on the distribution cylinder 38. Because of the axial movement of the friction cylinder 38, the ink spots 74 are distributed not only in the radial direction but also in the axial direction on the distribution cylinder 38.

If the piezoelectric valve 34 is actuated synchronously with the machine cycle, the pattern of the ink spots 74 applied to the dispensing cylinder 38 is repeated after one or more revolutions, which would result in an uneven color profile. Therefore, it is advantageous if the color output is offset in time relative to the machine cycle by a suitable software control several times during a Reibzylinderumdrehung, for example by a temporal modulation of the pulse train before and back, whereby a zonal equalization of the applied ink can be achieved. Another option for the most uniform application of paint is to squirt the amount of ink needed per ink roller revolution in many small splashes of color instead of a few large. In this way, it is possible to achieve a very uniform application of ink on the distribution cylinder 38 with only one nozzle 36 per ink zone. Such equalization of ink application may also be useful in the case of using a multiple nozzle per piezo valve 34, but with a sufficiently large number of nozzles, one may also come without targeted variation of the timing with respect to the machine cycle.

The amount of ink applied to the dispensing cylinder is adjusted by adjusting the duration of the rectangular pulses during which the piezo valve 34 is open and the nozzle 36 injects ink onto the dispensing cylinder 38. Alternatively, one can regulate the piezo-valve 34 so that it assumes the current need for opening position at any time. With the pulse-length-controlled ink feed described above, however, it is particularly easy to achieve a very precisely defined and precisely reproducible ink dosage over a very large metering range of minimum to maximum ink quantity.

Fig. 5 is a FIGS. 2 and 3 similar view of a piezoelectric valve 2, which does not inject the ink directly on the distribution cylinder 38, but has a distribution attachment 116, which may be, for example, a one-piece or multi-part plastic injection molded part. The distributor attachment 116 includes a channel 118 in the form of an inverted "T" whose central part is connected to the opening 20 in the nozzle 18 of the piezo-valve 2 and whose transverse part contains four nozzles 120 arranged in a row. The multiple nozzle formed thereby allows a single piezo valve 2 to sweep the distribution cylinder 38 across the width of a full inking zone with finely divided ink, as indicated by the ink spots 74. In the case of a zoneless inking unit with or without squeegee device, such a multi-nozzle can even extend over the entire printing width, so that you can make do with a single piezo valve.

Fig. 6 shows an inking unit that works from a conventional inking unit as in Fig. 7 is derived by the color box 122, the ink fountain roller 126 and the ink lifter 128 have been removed. In a first embodiment example, a piezo valve 94 or a corresponding valve strip with a plurality of piezo valves 94 are arranged so that the distribution on the distribution cylinder 130a. In a second embodiment also omitted in Fig. 6 dash-dotted drawn parts, and the piezo valves 94 are not disposed on the distribution cylinder 130a, but on the distribution cylinder 130b. With a correspondingly fine dosage, even more rolls can be saved by, for example, spraying onto the distribution cylinder 130c or any other location, as a result of which the inking unit advantageously shortens and becomes a so-called short inking unit.

Thus, it can be seen that for practical use, an inking unit can be produced with much fewer moving parts than a conventional inking unit, which also enables a uniform and extremely precise inking. As a result, it is furthermore possible to dispense the printing ink without excess and thus to dispense with a squeegee device, as required in conventional offset inking units for sheetfed or web presses. Since there is no mechanical wear in the ink metering area, the ink dosage is very well reproducible. Furthermore, the cleaning of the inking unit is facilitated.

LIST OF REFERENCE NUMBERS

2

Piezo valve

4

body

6

piezoelectric translator / stack actuator

8th

actuating rod

10

screw

12

actuating rod

14

channel

16

valve ball

18

Nozzle / orifice

20

opening

34

Piezo valve

36

jet

38

distribution cylinder

40

Section on the distribution cylinder

42

Pressure intensifier

44

pressure line

46

pressure line

48

pressure vessel

50

base

52

Farbauslaßleitung

53

Bell jar

54

ink cartridge

56

level sensor

58

sensor electronics

60

Tank with cleaning fluid

62

Three-way valve

63

line section

64

outlet

66

inlet line

68

Three-way valve

70

preheater

72

Valve control unit

74

Farbkleckse

94

Piezo valve / valve strip

116

distribution of intent

118

channel

120

jet

122

paintbox

124

printing ink

126

ink fountain roller

128

color Heber

130a-d

distribution cylinder

132

Inking rollers

134

plate cylinder

136

Ink transfer rollers

Claims (9)

1. Offset printing machine with an inking unit including one or more distributor rollers (38, 130a-d), ink transfer rollers (136), ink application rollers (132), an ink reservoir for printing ink and an ink metering device with at least one electrically controllable valve for metering the printing ink,
   as well as a high-pressure pumping device (42) for supplying the ink metering device with printing ink from the ink reservoir (54) at a predetermined high pressure,
   characterized by
   the fact that a heating device (70) for heating the printing ink to a predetermined temperature above room temperature is present,
   that the at least one valve (2; 34; 94) of the ink metering device has a short reaction time and a flow rate with a low dependence on viscosity, and
   that the at least one valve (2; 34; 94) includes a spherical closing element (16) located opposite a valve seat (18) which has a spherical depression and in which an opening (20) is formed whose diameter is essentially smaller than that of the spherical closing element.
2. Offset printing machine according to claim 1,
   characterized in
   that the at least one valve (2; 34, 94) includes piezoelectric actuators (6).
3. Offset printing press according to one of the preceding claims,
   characterized in
   that, at room temperature and a low shear rate, the printing ink has a dynamic viscosity of more than 10 Pa s, that the pressure generated by the pumping device is in the region of approximately 10 to 100 bar, and that the temperature of the printing ink heated by the heating device (70) is in the region of about 40 to 70°C.
4. Offset printing machine according to one of the preceding claims,
   characterized in
   that the ink metering device includes a row of nozzles (18; 36; 120) directed to the surface of one of the distributor rollers (38; 130).
5. Offset printing machine according to Claim 4,
   characterized in
   that for each ink zone, a valve (2; 34; 94) is provided, the outlet of which is connected to one or more nozzles (18; 36; 120) located in the respective ink zone.
6. Offset printing machine according to one of the preceding claims,
   characterized in
   that the ink reservoir either is an ink cartridge (54) or is formed by a bulk container.
7. Method of supplying printing ink to an offset printing machine according to claims 1-6,
   characterized in
   that the printing ink is metered without excess as it is required in the printing machine.
8. Method according to Claim 7,
   characterized in
   that the reaction time of the at least one valve (2; 34; 94) is in the order of magnitude of microseconds and that the ink is metered by opening and closing the at least one valve (2; 34; 94) under pulse-length control.
9. Method according to Claim 7,
   characterized in
   that the printing ink is sprayed onto a distributor roller (38; 130) of the printing machine out of synchronism with the machine cycle by temporally offsetting the application of ink with respect to the machine cycle at each distributor stroke or each distributor revolution.

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