EP3102413A1

EP3102413A1 - Printing unit for a flexographic printing press

Info

Publication number: EP3102413A1
Application number: EP15702151.0A
Authority: EP
Inventors: Guntmar M. LUDIN
Original assignee: CONPRINTA & Co KG GmbH
Current assignee: CONPRINTA & Co KG GmbH
Priority date: 2014-02-05
Filing date: 2015-01-16
Publication date: 2016-12-14
Also published as: WO2015117807A1; DE102014101432B3

Abstract

The invention relates to a printing unit for a flexographic printing press, said printing unit comprising - a plate cylinder (12) for supporting a printing plate (18) fastened to a printing plate support (16) in the form of a flexible continuous belt, - a tensioning cylinder (14) for tensioning the printing plate support (16) between the plate cylinder (12) and the tensioning cylinder (14), said tensioning cylinder being arranged such that it is parallel to the plate cylinder (12) and can be displaced perpendicularly thereto. The invention is characterized in that the plate cylinder (12) is hollow, its surface is provided with openings and its inner chamber is connected to a controllable compressed air source.

Description

Printing unit for a flexographic printing machine

description

Field of the invention

The invention relates to a printing unit for a flexographic printing press, comprising

- A plate cylinder for supporting one on a flexible endless belt

trained clichés fixed clichés,

- One arranged parallel to the plate cylinder and perpendicular to this

movable clamping cylinder for clamping the plate carrier between the

Plate cylinder and the clamping cylinder.

State of the art

Such printing units for flexographic printing machines are known from EP 0 308 367 A1. According to the so-called belt principle flexographic printing machines are the

Professional known for a long time. They include a support cylinder, usually referred to as a plate cylinder, for supporting a plate carrier wrapping around it. The trained as a belt cliché carrier consists of a flexible but tensile film material, has a length that is significantly larger than the circumference of

Plate cylinder is, and is connected at its ends to an endless belt or connected in the final assembled state. On the cliché carrier the actual flexo printing cliché, a relief made of an elastic material, is fixed. Parallel to the plate cylinder, a clamping cylinder is arranged, which also in the final assembled state of the

Envelope carrier is entwined and whose distance from the plate cylinder is variable in order to clamp plate carriers of different lengths between clamping and plate cylinder can. Further elements of typical flexographic printing machines are an impression cylinder and a dyeing roller. The impression cylinder is substantially parallel to the

Plate cylinder arranged, with its distance to this is variable to form a defined pressure gap. Through the nip, a web-shaped substrate is guided and pressed during the printing process between the plate cylinder and the impression cylinder against the cliché, so that color can be transferred from the cliché to the substrate. The dyeing roller is used for coloring the plate and is also arranged at a variable distance to the plate cylinder substantially parallel to this. The dyeing roller is connected to a paint reservoir so that its surface wets with ink during operation of the printing unit and this is transferred to the latter during the rolling of the dyeing roller on the cliché. The special one

Design of counter-pressure cylinder and dyeing roller is not relevant to the present invention.

To operate the printing unit, the plate cylinder is set in rotational motion. Both in the pressed and in the spaced state of the impression cylinder, this leads to a transport movement of the plate carrier. This is frictional entrainment, wherein the frictional forces between the surface of the plate cylinder and the inside of the plate carrier depend on a number of factors. On the one hand, the structural nature of both surfaces plays an important role. At the same time, the weight of the plate carrier together with the cliché and the tensioning force set on the clamping cylinder influence the resulting friction. Next also affects the contact pressure of the impression cylinder. Finally, the current speed of rotation of the plate cylinder plays a role. Some of these factors are constant in time, while others change with cylinder and cliché life. In particular, experience teaches that "new" plate carriers have significantly greater friction with the plate cylinder surface than those with already substantial tool life.

From US 3 851 582 A a conventional, i. not working on the belt principle, known printing press. In this printing machine, the printing material after the printing process via a pulley, out of the compressed air emerges, out.

As a result, the friction between the deflection roller and the substrate is minimized. In addition, an improved drying of the ink on the substrate be achieved after the actual printing and in this way the quality of the entire print can be improved.

In flexographic printing presses, in particular, the friction between

Plate cylinder surface and inside of the plate carrier is a sensitive in terms of print quality size. The transport speed of the plate carrier must match the transport speed of the substrate very exactly. During the printing process, significant flexing forces occur on the elastic

Cliché material on. Among other things, this results in that the transport speed of the disk carrier deviates from the rotational speed of the plate cylinder. Too much friction between plate cylinder and plate carrier would not allow a sufficiently large speed difference; a too small friction, however, would allow too much slippage. The experienced worker at the printing press is able, by slight variations of the connection of the ends of the

Cliché carrier to create a "crown" of the plate carrier and adjust in this way, the resulting friction between plate carrier and plate cylinder situation adapted.This basically a great individual experience is required.

In practice, any such intervention means shutdown of the printing unit, an opening of the plate carrier endless belt and a new, modified connection of its ends. Then the printing unit must be started up again and the success of the measure checked. This is always associated with considerable loss of time and pressure.

Taking into account that typical flexo printing machines for multi-color printing have a number of printing units connected in series, it is easy to see that this procedure is associated with considerable costs. In addition, the use is actually more advantageous, standardized cliché closures under the described

Conditions not possible.

task

It is the object of the present invention to provide a printing unit for flexographic printing machines which is suitable for the use of standardized cliché fastener closures. Presentation of the invention

This object is achieved in conjunction with the features of the preamble of claim 1, characterized in that the plate cylinder is hollow, its surface with

Provided breakthroughs and its interior is connected to a controllable source of compressed air.

As a result, the sensitive parameter of the friction between the surface of the plate cylinder and the inside of the plate carrier of a controller or

- Preferably - a control accessible, this control or regulation can take place during the current printing operation. Namely, by means of the compressed air source, the interior of the plate cylinder can be subjected to an overpressure, which leads to an escape of air from the openings in the plate cylinder surface. In this way, air can pass between the plate cylinder surface and the inside of the plate carrier to a defined extent. The amount of air is dependent on the size and number of breakthroughs and the applied pressure in the interior of the plate cylinder. It is therefore very accurately adjustable within wide limits. Note that this approach is completely counterproductive to conventional approaches in printing press technology. Usually, one endeavors to completely dissipate any air that is sucked in, for example by the transport movement of the plate carrier between these and the plate cylinder, or even completely prevent such a suction. By way of example, reference may be made here to DE 43 41 262 A1, which discloses a hollow plate cylinder with Luftabführperforationen - but for the flexographic printing machine according to the sleeve principle. The use of an overpressure in a hollow, perforated plate cylinder is known from DE 36 33 155 A1, which, however, also refers solely to a flexographic printing press according to the sleeve principle and the application of the overpressure as a measure for widening the plate cylinder fully and tightly looping around

Cliché carrier disclosed solely for the purpose of its assembly.

Typically, in Flexodruckmaschinen after the belt principle on both sides axially marginal of the plate cylinder depending on an independently driven pin wheel with a plurality of equidistantly distributed over its circumference, radially aligned

Guiding pins arranged. These guide pins correspond with both sides marginal rows of holes in the cliché carrier. In the final assembly state, the guide pins pass through the holes in the plate carrier in the contact area between the plate cylinder and the plate carrier. This can be low managers between the

Guide pins and the hole edges are transmitted. They are usually not sufficient to generate the transport movement of the plate carrier. This is rather, as explained above, caused by the frictional force between the disk carrier and plate cylinder. Optimally, a Flexod jerk works so that the

Guide pins are concentric and force-free in each of them interspersed holes are positioned. Since, as explained above, plate cylinders and plate carriers typically have different speeds, it is understood that the pin wheels must be drivable independently of the plate cylinder. The printing unit according to the invention preferably also has such pin wheels, which are known in principle from the prior art.

However, in the context of the present invention, these have an additional significance in addition to their known task as guide elements. Thus, in an advantageous development of the invention, it is provided that the compressed air source is coupled to a control unit, which is further coupled to a sensor device for detecting a measured variable relating to at least one of the pin wheels, wherein the

Control of the compressed air source as a function of a measuring signal of

Sensor device takes place. This development is based on the recognition that the pin wheels can serve as indicators for the correctness of the machine run. With suitable sensors, pin wheel-dependent parameters can be determined, from which the quality of the current operating setting of the printing unit can be determined and, if necessary, corrections, namely by appropriate activation or control change of the compressed air source, i. As a result, corrections of the friction between plate cylinder and plate carrier, be made. Conveniently, a loop is established, i. The sensor system conveniently detects a pin wheel-dependent parameter which itself is (indirectly) changed by a change in the pressure source control.

For the specific design of the sensors, different approaches can be pursued in each case alternatively or additionally. For example, it can be provided that the sensor device comprises a torque sensor, by means of which a torque acting on at least one of the pinwheels can be measured. Be the pinwheels, like it would be required in synchronism of printing material and plate carrier, synchronized with the transport speed of the printing material driven, would a

Expressing velocity mismatching of the plate carrier in a tangential force action between the guide pins and edges of the holes they penetrate in the plate carrier. This would become one acting on the entire pinwheel

Torque lead, which detected by means of the torque sensor and to the

Control unit would be transmitted. With appropriate adjustment of

Compressed air control, i. Adjustment of friction between plate cylinder and

Cliché carrier, the torque would be reduced again and disappear at optimum setting. However, an undesired lateral movement of the plate carrier could not be detected with such a sensor system.

Another approach therefore provides that the sensor device comprises a force sensor, by means of which a tangential and / or axial force acting on the guide pins can be measured. Such a sensor would be guide pin based and would sense forces acting on individual (some or all) guide pins. In particular, in addition to the tangential forces also detected by the torque sensor, it is also possible to detect axial forces which arise due to a lateral displacement of the plate carrier. This misalignment parameter can also be corrected by correcting the friction between the plate cylinder and the plate carrier. However, such a force sensor is quite complicated and complicated in terms of their integration into the intended

Control loop.

According to a further approach, it is therefore provided that the sensor device comprises an image detector directed onto the end face of the pin wheel and synchronized with its rotational speed. By means of such a sensor, a "standing picture" of the relative positioning of the guide pins to those of you

penetrated holes produced in the plate carrier and transmitted to the control unit for evaluation. A transmission to a visual display unit for the control of a worker is possible. The generated image data can be evaluated, in particular, to determine whether the relative position of the guide pin and hole deviates from the optimal, concentric alignment and, if so, in which direction

Deviation occurs. This can be simultaneously misalignments in axial as well as in Detect tangential direction and combat by appropriate countermeasures in the control of the compressed air source.

The term of the control of the compressed air source is to be understood here wide and not only describes the setting of a predetermined overpressure in the plate cylinder interior. For example, it is also possible, as provided in an advantageous embodiment of the invention, that the number and / or size of the openings in the

Surface of the plate cylinder is variable. This measure also allows the amount of air introduced between the plate cylinder surface and the inner surface of the plate carrier to vary. Technically feasible such a measure, for example, by movement of sliding elements in the interior of the plate cylinder with which some or all breakthroughs in the plate cylinder surface are completely or partially covered.

The use of ionized air has proved to be particularly effective with regard to the correction of the friction between plate cylinder and plate carrier. In a preferred embodiment of the invention, therefore, an ionization source for at least partial ionization of at least that portion of the air from the compressed air source, which traverses the openings in the surface of the plate cylinder, is provided. The ionization source may be part of the compressed air source, arranged in the interior of the plate cylinder or provided in the region of the openings in the plate cylinder surface.

Preferred embodiments are subject of the dependent claims.

Further features and advantages of the invention will become apparent from the following specific description and the drawings. Brief description of the drawings In the drawings:

Figure 1: a schematic sectional view through an inventive

Printing,

Figure 2: a schematic sectional view of the plate cylinder of

printing unit according to the invention,

FIG. 3 shows a schematic perspective view of a plate cylinder and a plate carrier of a printing unit according to the invention,

FIG. 4: a schematic representation of exemplary hole / guide pin

Constellations.

Detailed description of preferred embodiments

Like reference numerals in the figures indicate like or analogous elements.

Figure 1 shows a highly schematic representation of a sectional view through a

The printing unit 10 comprises a plate cylinder 12 and a relative to this movable in the direction of distance clamping cylinder 14th

Plate cylinder 12 and clamping cylinder 14 are wrapped together by a formed as an endless belt, flexible plate carrier 16, which carries on its outer side designed as a relief of elastic material flexographic printing plate 18. By

Setting the distance between the plate cylinder 12 and clamping cylinder 14, the plate carrier 16 can be clamped so that the friction of its inner surface on the surface of the plate cylinder 12 is approximately in a predetermined range. A high-precision adjustment of this friction is not possible only by distance adjustment between plate cylinder 12 and clamping cylinder 14. Due to said friction, a rotation in which the plate cylinder 12 is displaced leads to a corresponding one

Transport movement of the cliché carrier. In Figure 1 above the plate cylinder 12, a counter-pressure cylinder 20 is arranged, of a web of a printing material 22, typically paper, metal or

Plastic film, is entwined. The distance between the plate cylinder 12 and the impression cylinder 20 is variable, so that there is a pressure gap 24 of predetermined width between the two cylinders 12, 20. The printing gap 24 is so wide that in it the cliché 18 is pressed with a predetermined contact force against the substrate 22, so that located on the cliché ink is transferred to the substrate 22. The cliché carrier 16 or the cliché 18 and the printing material 22 move with the correct setting with the same transport speed. This may differ from the rotational speed of the plate cylinder 12 due to the slippage between the plate carrier 16 and the plate cylinder 12.

In Figure 1 right of the plate cylinder 12, a coloring roller 26 is shown, which is in communication with a paint reservoir 28. Also, the distance between the plate cylinder 12 and the coloring roller 26 is adjustable. In printing operation, the dyeing roller 26 rotates and is wetted by ink from the ink reservoir 28 on its surface. By rolling on the cliché 18, the color is transferred to this and the cliché 18 so dyed.

As roughly indicated in FIG. 1, the plate cylinder 12 is hollow and has a perforated surface. This is shown more clearly in FIG. The interior of the hollow plate cylinder 12 is connected to a compressed air source, not shown, which ensures that in the interior of the plate cylinder 12, a pressure P1 prevails, which is higher than the external pressure PO. The pressure difference ΔΡ = Ρ1 -PO can be set by appropriate control of the compressed air source. By the pressure difference ΔΡ an air flow through the openings 121 of the plate cylinder surface is effected. In that angular range in which the plate cylinder 12 is wrapped by the plate carrier 16, this leads to an entry of air between the plate carrier 16 and the plate cylinder 12, whereby the friction between the two surfaces is reduced depending on the set pressure difference .DELTA.Ρ. Accordingly, the slippage of the plate carrier 16 with respect to the plate cylinder 12 can be adjusted with high precision, so that in particular an exact equality of speed between plate carrier 16 and substrate 22 can be achieved. Figure 3 shows a highly schematic, perspective view of the plate cylinder 12 with its perforated by the openings 121 surface. A connection to the compressed air source, not shown, can be made via hollow axle journal 122.

Laterally of the plate cylinder 12, two pin wheels 30 are arranged, which carry a plurality of radially aligned, equidistant, conical pins 301 on their front side. In Figure 3, the pin wheels 30 are spaced in the manner of an exploded view from

Plate cylinder 12 shown. In the final assembly state, however, they form an axial extension of the plate cylinder 12, but are independent of this rotatable and in particular driven independently of him. The cliché carrier 16, of which only a portion is shown in FIG. 3, has at its lateral outer edges a row of holes of equidistantly arranged perforations 161. The rows of holes correspond in distance and size of their perforations 161 with the guide pins 301 of the sprocket wheels 30. In the final assembly state, the guide pins 301 enforce the perforations 181 in that angular range in which the plate cylinder 12 is wrapped by the plate carrier 16. Upon contact of the guide pins 301 with the edges of the perforations 161 results in a low power transmission in the axial and / or tangential direction, which causes a guide of the plate carrier 16. However, the drive force for generating the transport movement of the disc carrier 16 is, as explained above, caused by the friction between the disc carrier 16 and plate cylinder 12.

As explained in the general part of the description, a preferred development of the invention provides a sensor system related to the guide pins 301. FIG. 4 serves to illustrate such a sensor system. In subfigure (a) the spatial relation of the

Guiding pins 301 are shown to the enforced perforations 161 of the disc carrier with perfect machine setting. The cliché carrier 16 moves exactly at the speed of the pin wheels 30, which are synchronized with the speed of the printing material 22. The plate cylinder 12 may rotate at a slightly different speed. Essential for the quality of the printing process, however, is the exact movement of the cliché, which is indicated by the concentric relation of guide pins 301 to perforations 161.

Partial figure (b) shows a speed mismatch. Here are the

Guide pins 301 not concentric, but positioned tangentially offset to the perforations 161. In sub-figure (c), however, is a mismatch in the axial direction shown. Both types of mismatch, which can usually occur simultaneously, can be corrected by targeted change in the friction between the plate cylinder 12 and plate carrier 16. This is accomplished, according to the invention, by a corresponding change in the compressed air source control, which may also include a variation in the size and / or position of some or all of the plate cylinder perforations 121.

The spatial relationships of guide pins 301 and shown in FIG

Perforations 161 can be measured in different ways, for example by image detection, measuring the force on the guide pins 301 or measuring a resulting torque on the sprockets 30. Corresponding sensors are not shown separately in the figures.

Of course, the embodiments discussed in the specific description and shown in the figures represent only illustrative embodiments of the present invention. A broad range of possible variations will be apparent to those skilled in the art in light of the disclosure herein.

LIST OF REFERENCE NUMBERS

10 printing units

12 plate cylinders

121 perforation in 12th

122 journals of 12 14 clamping cylinders

16 cliché carriers

161 perforation in 16

18 cliché

20 impression cylinders

22 substrate

24 pressure gap

26 dyeing roller

28 color reservoir

30 pinwheel

301 guide pin

Claims

claims

1 . Printing unit for a flexographic printing machine, comprising

- A plate cylinder (12) for supporting one on a flexible

Endless belt trained cliché carrier (16) fixed clichés (18),

a clamping cylinder (14) arranged parallel to the plate cylinder (12) and movable perpendicular thereto, for clamping the plate carrier (16) between the plate cylinder (12) and the clamping cylinder (14),

characterized,

that the plate cylinder (12) is hollow, its surface provided with openings and its interior is connected to a controllable compressed air source.

2. Printing unit according to claim 1,

characterized,

that on both sides axially marginally of the plate cylinder (12) each one independently of this driven pin wheel (30) with a plurality of equidistantly distributed over its circumference, radially aligned guide pins (301) is arranged.

3. Printing unit according to claim 2,

characterized,

the compressed-air source is coupled to a control unit which is further coupled to a sensor device for detecting a measured variable relating to at least one of the pin wheels (30), the control of the compressed-air source being dependent on a measuring signal of the sensor device.

4. Printing unit according to claim 3,

characterized,

in that the sensor device comprises a torque sensor by means of which a torque acting on at least one of the pinwheels (30) can be measured. Printing unit according to one of claims 3 to 4,

characterized,

in that the sensor device comprises a force sensor by means of which a tangential and / or axial force acting on the guide pins (301) can be measured.

Printing unit according to one of claims 3 to 5,

characterized,

the sensor device comprises an image detector directed onto the end face of a pin wheel (30) and synchronized with its rotational speed.

Printing unit according to one of the preceding claims,

characterized,

the number and / or size of the apertures (121) in the surface of the plate cylinder (12) is variable.

Printing unit according to one of the preceding claims,

marked by

an ionization source for the at least partial ionization of at least that portion of the air from the compressed air source which traverses the openings (121) in the surface of the plate cylinder (12).