EP1556219B1 - Guiding elements for a printing unit - Google Patents

Abstract

A folding element for a printing press, or sheet handler, has the folding guide (03) with a microporous surface to generate an air cushion and thereby prevent mechanical contact between the guide and the sheets. The pore size is less than 500 microns and the pores are evenly distributed over the surface of the guide. Air is blown through the porous surface from inside the hollow guide.

Description

The invention relates to printing units with guide elements according to the preamble of claim 1 or 2.

From the DE 93 11 113 U1 a printing unit with two web guiding elements is known, which are arranged in an inlet and an outlet region of a printing unit in such a way that a web can be guided without contact by the printing site when the printing site is stopped. The web guide elements are designed as rotatably mounted in side walls rollers.

By the US 37 44 693 A In one exemplary embodiment, a turner bar is disclosed, wherein a tube wall segment of porous, air-permeable material together with a base body forms a closed pressure chamber. The porous segment forms a wall of the chamber and load carrying over its width - without load-bearing pad - executed. In a second example, a segment having through holes is arranged instead of the porous segment.

The US 54 23 468 A shows a guide element, which has a bore-containing inner body and an outer body made of porous, air-permeable material. The holes in the inner body are provided only in the expected wrap.

The EP 0 705 785 A2 deals with the transport and the deflection of band-shaped material, in particular in the form of z. B. footage. In one embodiment, compressed air flows through the pores of a porous wall with mean pore diameters of 7 to 10 microns and in another embodiment through a microbores of 350 microns large openings wall.

The invention has for its object to provide printing units with vanes for the flying printing form change.

The object is achieved by the features of claim 1 or 2.

The achievable with the invention advantages are, in particular, a reliable and accurate working web guide of a printing unit is created. By means of a micro-openings created air cushion a high degree of homogeneity over the length of the air cushion is created at the same time low losses. In contrast to rollers - especially at varying speeds - no inertia to overcome.

By means of air outlet openings with diameters in the millimeter range can be selectively applied to the material forces (momentum of the beam), by means of which it is employed by the component in question, or to another component, while by a distribution of micro holes with high hole density, a broad support and priority the effect of a trained air cushion comes into play. Previously used holes were in cross section, for example, 1 to 3 mm, whereas for the micro-openings, the cross-section is smaller by at least one order of magnitude. This results in significantly different effects. For example, the distance between the surface carrying the openings and the web can be reduced, the volume flow of fluid can be lowered considerably and, as a result, leakage losses that occur outside the effective range with the web can be significantly reduced.

In contrast to components with openings or holes of opening cross sections in the range of millimeters and a hole spacing of several millimeters, a much more homogeneous surface structure is advantageously created in the formation of micro-openings on the surface. Under micro-openings here are understood openings on the surface of the component, which have a diameter less than or equal to 500 microns, advantageously less than or equal to 300 microns, in particular less than or equal to 150 microns. A "hole density" for the surface provided with the micro-openings is at least one micro-opening per 5 mm ² (= 0.20 / mm ² ), advantageously at least one micro-opening per 3.6 mm ² (= 0.28 / mm ² ).

As a result of the formation of the openings as microapertures, the air cushion is made uniform and the volumetric flow exiting per unit area is reduced in such a way that a leakage current can be reasonably small even in regions which are not looped around by the web.

The microapertures can advantageously be designed as open pores on the surface of a porous, in particular microporous, air-permeable material or else as openings of through holes of small cross-section which extend outwardly through the wall of a supply chamber. In another embodiment, the micro-openings are designed as openings through continuous microbores.

In order to achieve a uniform distribution of air emerging at the surface of the material in the case of the use of microporous material without simultaneously requiring high layer thicknesses of the material with high flow resistance, it is expedient that the guide element has a solid, air-permeable carrier on which the microporous material is applied as a layer. Such a carrier can be acted upon with compressed air, which flows out of the carrier through the microporous layer and thus forms an air cushion on the surface of the component.

This support, in turn, may be porous with better air permeability than that of the microporous material; but it can also be formed from a cavity enclosing, provided with air passage openings flat material or molded material. Combinations of these alternatives are also possible.

In order to achieve uniform air distribution, it is also desirable that the thickness of the layer be at least equal to the spacing of adjacent openings of the carrier.

In the case of the use of microbores, a design is advantageous, wherein the Web-facing and the micro-openings having side of the guide element is formed as one or more inserts in a carrier. The insert can be releasably and possibly changeable connected with the carrier in training. Thus, it is possible to clean and / or exchange inserts of different types of microperforations for adaptation to different materials and web widths.

Embodiments of the invention are illustrated in the drawings and will be described in more detail below.

Fig. 1

eine schematische Darstellung mehrerer von einer Bahn durchlaufener Druckwerke;

Fig. 2

einen Schnitt durch eine erste Ausführung eines Leitelements;

Fig. 3

einen Schnitt durch eine zweite Ausführung eines Leitelements;

Fig. 4

einen Schnitt durch eine dritte Ausführung eines Leitelements;

Fig. 5

einen Schnitt durch eine vierte Ausführung eines Leitelements;

Fig. 6

einen Schnitt durch eine fünfte Ausführung eines Leitelements;

Fig. 7

einen Schnitt durch eine sechste Ausführung eines Leitelements;

Fig. 8

einen Schnitt durch eine siebte Ausführung eines Leitelements;

Fig. 9

einen Schnitt durch eine achte Ausführung eines Leitelements.

Show it:

Fig. 1

a schematic representation of several traversed by a web printing units;

Fig. 2

a section through a first embodiment of a guide element;

Fig. 3

a section through a second embodiment of a guide element;

Fig. 4

a section through a third embodiment of a guide element;

Fig. 5

a section through a fourth embodiment of a guide element;

Fig. 6

a section through a fifth embodiment of a guide element;

Fig. 7

a section through a sixth embodiment of a guide element;

Fig. 8

a section through a seventh embodiment of a guide element;

Fig. 9

a section through an eighth embodiment of a guide element.

Fig. 1 shows a schematic section through three of a web 02, z. B. web 02 or substrate web 02, in particular paper web 02, successively passed printing units 05, z. B. printing 05 for perfecting, especially offset printing 05 for perfecting. The printing units 05 can also in other ways, for. B. as a three-cylinder offset printing units 05, as a direct or flexographic printing, as a printing unit for the high pressure or gravure or be different from each other. For example, has at least one of the printing units 05 designed for perfecting printing 05 at least in the outlet area (in Fig. 1 in the entry and exit area) of its printing nip 10, a guide element 01, in particular Bahnleitelement 01 to redirect the freshly printed, not yet dried web 02 at the output of the printing unit 05, for example, to supply them to the printing nip 10 of the subsequent printing unit 05 in the correct orientation.

A following on the first printing unit 05 printing unit 05, has in the inlet and outlet region of the printing nip 10 each have a Bahnleitelement 01 in order to perform an already printed web 02 contactlessly through the nip 10 at abolished pressure point. This printing unit 05 is operable as an imprinting unit 05 or as a printing unit 05 for the flying printing form change in alternation with a second such printing unit 05. In an operating situation, the web 02 is printed by one of the printing units 05 while it passes through the other of these printing units 05 without contact. In the other operating situation, the opposite occurs. The two web guiding elements 01 are z. B. spatially arranged so that the web 02 in the region of the printing gap 10 is substantially perpendicular to a connecting plane of the two cylinders forming the pressure point. Of at least two printing units 05 is imprinted the one printing unit 05 employed and printed on the web 02, while the other is parked and traversed by the web 02 without contact. Preferably, the printing press has five printing units 05, wherein in one operating mode the five printing units is passed without contact, while the web 02 is printed by the other four printing units 05 four-color (eg, both sides). In the other second operating situation, the previously contactless printing unit 05 is set in printing mode while one of the four previously printing printing units 05 is passed through without contact. At least the two contactless to be traversed by pressure units 05 each have in the inlet and outlet region of the pressure nip 10 described below guide elements 01.

At least the two web-guiding elements 01 of the printing unit 05 or printing unit 05 and / or at least the web-guiding element 01 arranged in the outlet area of the printing gap 10 are or will act as a non-contact web-guiding element 01, in particular as an air-pervaded rod 01, as described below Way trained.

The lateral surface of the guide element 01 has openings 03, z. B. micro-openings 03, through which in operation from an internal cavity 04, z. B. a chamber 04, in particular pressure chamber 04, under overpressure against the environment fluid standing, z. As a liquid, a gas or a mixture, in particular air, flows. In the figures, a corresponding supply of compressed air into the cavity 04 is not shown.

The guide element 01 has, at least on the side cooperating with the web 02 or on the web 02 side facing its surface on the micro-openings 03. However, it can also have the openings 03 on other sides facing the web 02, or at least on its longitudinal section cooperating with the web 02 entirely made of a material comprising the microapertures 03.

This simplest version without preferential direction for the arrangement of the openings 03 is made possible by the formation of the openings 03 as micro-openings 03, since hereby created a thinner but more homogeneous air cushion, at the same time a required or resulting volume flow and thus a leakage current on the "open" side is significantly reduced. The high resistance of the micro-apertures 03, in contrast to large-cross-section apertures, causes "not capping" a range of apertures to result in a sort of short-circuit current. In the total resistance of the falling over the openings 03 partial resistance receives an increased weight.

In a first embodiment ( Fig. 2 to 6 ) are the micro-openings 03 as open pores on the surface of a porous, especially microporous, air-permeable material 06, z. B. of an open-pore sintered material 06, in particular of sintered metal formed. The pores of the air-permeable porous material 06 have a mean diameter (average size) of less than 150 microns, z. B. 5 to 60 microns, in particular 10 to 30 microns. The material 06 is formed with an irregular, amorphous structure.

Material selection, dimensioning and pressurization are selected such that 1 - 20 standard cubic meters per m ² , in particular 2 to 15 standard cubic meters per m ² , emerge from the air outlet surface of the sintered material per hour. Particularly advantageous is the air outlet of 3 to 7 standard cubic meters per m ² .

Advantageously, the sintered surface from the cavity 04 out with an overpressure of at least 1 bar, in particular more than 4 bar, applied. Particularly advantageous is an application of the sintering surface with an overpressure of 5 to 7 bar.

If the cavity 04 of the guide element 01, at least on their longitudinal section cooperating with the web 02, formed essentially solely from a body of porous material 06 enclosing the cavity 04 (ie without further load-bearing layers), then this z. B. tubular body substantially self-supporting with a wall thickness of greater than or equal to 2 mm, in particular greater than or equal to 3 mm, designed ( Fig. 2 ). Possibly. can run in the cavity 04, a carrier on which the body can be selectively or partially supported, but which is not the entire surface in operative contact with the body. Such a body of porous material 06 can, as in Fig. 3 represented, also be formed shell-shaped.

In order to achieve a uniform distribution of exiting air at the surface of the microporous material 06, without simultaneously requiring high layer thicknesses of the material 06 with correspondingly increased flow resistance, it is expedient in an advantageous embodiment that the guide elements 01 a solid, at least partially air-permeable support 07, on which the microporous material 06 is applied as layer 06 ( Fig. 4 . 5 and 6 ). Such a carrier 07 can be acted upon with compressed air, which flows out of the carrier 07 through the microporous layer 06 and thus forms an air cushion on the surface of the guide element 01. In a particularly advantageous embodiment, the porous material 06 is thus not designed as a carrying solid body (with or without frame construction), but as a coating 06 on a bushings 08 or through holes 08 having, in particular metallic, carrier material. In contrast to, for example, "self-supporting" layers, "non-bearing" layer 06 is understood to mean a structure, the layer 06 being supported over a plurality of supporting points of the carrier 07 over its entire layer length and entire layer width. The carrier 07 has z. B. on its acting together with the layer 06 width and length each have a plurality of non-contiguous passages 08. This embodiment is distinctly different from a design in which a porous material 06 extending over the entire width cooperating with the web 02 is designed to be self-supporting over this distance, is supported on a frame or carrier only in one end region, and therefore one must have appropriate strength.

In the in Fig. 4 . 5 and 6 In the exemplary embodiment illustrated, the carrier material essentially absorbs the weight, shear, torsional, bending and / or shear forces of the component, which is why a corresponding wall thickness (eg greater than 3 mm, in particular greater than 5 mm) of the carrier 07 and / or a suitably stiffened construction is selected. The z. B. the cavity 04 to 06 layer limiting, or by appropriate shaping (eg., In Fig. 4 tubular) forming the cavity 04 carrier 07 has on the side coated with the porous material a plurality of openings 09 for supplying the compressed air into the porous material 06. Also in the openings 09 of the carrier 07 may be in the region of the walls z. T. porous material are.

The guide element 01, as in the Fig. 4 . 5 and 6 shown, the carrier 07 also referred to as the main body 07 with the hollow or interior 04, z. B. a tubular support 07 ( Fig. 4 ), which in its wall radially up to the lateral surface has a plurality of through openings 09. The carrier 07 can in principle be designed with any hollow profile, but advantageously with an annular profile. Through the cavity 04 and the openings 09 a fluid, for. B. gas, blown, which z. B. by a compressor, not shown, under a pressure P is greater than the ambient pressure. The lateral surface of the carrier 07 has, at least in the section provided with openings 09, the layer 06 of the porous material, which also covers the openings 09 and extends continuously over the area acting together with the web 02, ie a continuous surface at least in the of the Formed web 02 for wrapping area.

In another embodiment ( FIGS. 5 and 6 ), the cavity 04 is not formed by a tube designed as an annular carrier 07, but in a different geometry. Advantageously, the support 07 has a part-circular wall 15 or wall 15 (in particular with a fixed radius or radius of curvature R07 or R15 with respect to a fixed center M07), which on its open side, for example by a Cover 20 is completed. This part-circular wall 15 with cover 20 may be made in one piece or several pieces but connected to each other. In Fig. 5 the pitch circle angle γ of the openings 09 having wall 15 is selected to about 180 °. With this measure, for example, a certain width b01 of the guide element 01-for example, a maximum width prescribed for space reasons-achieves the greatest possible effective area. With a desired or predetermined width b01, the radius R15 for the pitch circle (or the pipe as the raw material) is selected on the basis of the required deflection (deflection angle α of the change in direction of the track 02) and a corresponding pitch circle is taken. A deflection is thus as "soft" and is supported on the available space in the widest possible range by the air cushion.

In the presentation of the Fig. 6 is a pitch angle γ smaller than 180 °, z. B. between 10 ° and 150 °, in particular between, here about 90 °. In a preferred embodiment for use in the region of the printing gap before and / or behind the printing unit 05, the pitch circle angle γ is selected to be 10 ° to 45 °, in particular between 15 ° to 35 °. The width b01 is selected, for example, to be 30 to 150 mm, in particular 50 to 110 mm. The radius of curvature R15 is for the wall 15, for example between 120 and 150 mm, in particular between 140 and 200 mm. The layer can be like in Fig. 5 be extended to the frontal cover 20 or only cover the openings 09 receiving, curved wall 15. The layer 06 may also be flattened in its outgoing region, forming a smooth transition.

With the mentioned measure, a width b01 of the guide element 01 or width b07 of the carrier 07 - for example a maximum width prescribed for space reasons - achieves the largest possible area of the air cushioning which is effective as a support. In the case of a desired or predetermined width b01, based on the required deflection (by way of example as the deflection angle α of the change in direction of the web 02 in FIG Fig. 1 shown in first printing unit 05) the radius R07 for the pitch circle (or the tube as raw material) selected and taken from a corresponding pitch circle. A deflection is thus as "soft" and is supported on the available space in the widest possible range by the air cushion.

In an advantageous embodiment, the design of the guide element 01 takes place in such a way that the pitch circle angle γ of the wall 15 is formed from the deflection angle α desired for the web run to γ = α + δ, where δ represents an addition for safe running and running of the web 02 and Z. B. between 0 ° and 50 °, in particular from 10 ° to 30 ° is selected. The radius of curvature R07 is then selected so that, taking into account the addition δ, the desired width b01 or b07 is maintained. The radius of curvature R15 (or R07) is then chosen to be R 15 ( or R 07) = b 01 / ( a * sin (γ / 2)). An optionally formed by the layer thickness supernatant can be neglected in the small thicknesses. With optimal use of space so a large effective area is created taking into account a security.

At required deflection angles α of, for example, 120 °, for reasons of simplification, a semicircular profile or even a full circle may be advantageous. In this case, openings 09 and / or layer 06 may include the full 360 ° angle, or only a partial circle.

In principle, other deviating from pitch circles profiles for the interacting with the web 02 area of the guide element 01 (or its curved wall 15) are conceivable, for example as a section of an ellipse, parabola or hyperbola. In this case, the curve shape of the deflection with respect to a "soft" deflection can be optimized. However, the pitch circle shape has advantages in terms of standardization, material consumption and simplified manufacturing.

Compared to an embodiment of a guide element 01, wherein the porous material 06 not largely supported by an opening 09 having carrier 07 or main body 07, but is supported for example only bridge-like on a frame-like support in edge regions, the formation of a circular, teilkreis-, elliptical, parabolic or hyperbolic body 07 directly below the Layer in terms of manufacturing, dimensional stability, cost and handling great advantages. For this embodiment, for example, at least half of the surface 02 of the layer 06 acting together with the web 02 is underlaid by the carrier 07 or its curved wall 15 and / or openings 09 or free cross sections have a diameter or a maximum inside width of 10 mm, in particular of less than or equal to 5 mm.

For the examples carried out with carrier 07, the porous material 06 outside the feedthrough 08 has a layer thickness which is less than 1 mm. Particularly advantageous is a layer thickness between 0.05 mm and 0.3 mm. A proportion of open area in the area of the effective outer surface of the porous material, here referred to as opening degree, is between 3% and 30%, preferably between 10% and 25%. In order to achieve a uniform air distribution, it is also desirable that the thickness of the layer at least equal to the distance of adjacent openings 09 of the carrier 07.

The wall thickness of the carrier 07 is - at least in the layer 06 having region - greater than 3 mm, in particular greater than 5 mm, executed.

The optionally configured with a hollow profile carrier 07 may in turn also made of porous material, but with a better air permeability -. B. a larger pore size - be designed as the microporous material of the layer 06. In this case, the openings 09 of the carrier 07 are formed by open pores in the region of the surface, and the passages 08 are formed by the randomly formed via the porosity inside the channels. However, the carrier 07 may also be made of any, the cavity 04 enclosing, provided with bushings 08 Be formed flat material or molded material. Combinations of these alternatives are also possible.

In a second embodiment ( Fig. 7 to 9 ) are the micro-openings 03 as openings through holes 11, in particular microbores 11 executed, which is characterized by a z. B. as a pressure chamber 04 formed cavity 04 delimiting wall 12, z. B. chamber wall 12, extend outward. The holes 11 have z. B. a diameter (at least in the region of the openings 03) of less than or equal to 500 .mu.m, advantageously less than or equal to 300 .mu.m, in particular between 60 and 150 .mu.m. The opening degree is z. From 3% to 25%, especially from 5% to 15%. A hole density is at least 1 / (5 mm ² ), in particular at least 1 / mm ² up to 4 / mm ² . The wall 12 thus has, at least in one of the web 02 opposite region, a microperforation. Advantageously, the microperforation extends over the region which interacts with the web 02; However, it can - as in the first embodiment, the bushings 08 and layer 06 - extend to the full extent of 360 °, as the losses are kept within limits as mentioned.

In a second example for the execution of the guide element 01 with microbores 11 (FIG. Fig. 8 ) is the chamber wall 12 on the web 02 side facing a curved wall 14 and a curved wall portion 14 - comparable to the FIGS. 5 and 6 described wall 15 - on, which has the microbores 11. That to the angles α, γ, δ and the widths b01 and b07 (here b01 and b12, respectively) and the radius R15 (here R14) to FIGS. 5 and 6 said, as well as the procedure and selection of the radii of curvature is to be transferred in the same way to the present example.

In an embodiment according to Fig. 9 the wall 14 having the microbores 11 is designed as an insert 14 or as a plurality of inserts 14 arranged next to one another in the axial direction in a carrier 16. The use can be fixed or be detachably connected or exchangeable with the carrier 16. The latter is advantageous in terms of cleaning or exchanging inserts 14 of different types of microperforations for adaptation to different materials (mass and / or surface structure) and web widths. In the variant of this embodiment with substantially full arranged inserts 14 and / or micro-openings 03 such inserts 14 may be arranged, for example, on a running in the cavity 04 support 16. However, an embodiment is advantageous, wherein, as shown, the insert 09 comprising the openings 09 is formed merely by means of an angular segment with a curvature, in particular adapted to the web run.

For the formation of the curved surface of the insert 14 and the inserts 14 is again to the angles α, γ, δ and the widths b01 and b07 (here b01 and b12) and the radius R15 (here R14) to FIGS. 5 and 6 as well as the procedure and selection of the radii of curvature in the same way to the present example. However, if necessary, a projection required for the connection between the application width and the carrier width is to be taken into account. The curvature may, for example, be enforced by an intended excess width of the insert 14 relative to the support 16 (or its attachment means) as resulting bending.

The releasable connection can be realized as shown for example by the ends of the insert 14 receiving grooves 17 in the carrier 16. In addition or instead, however, a connection can be made by screwing or by bracing.

One of the flow resistance influencing wall thickness of the bores 11 containing chamber wall 12 (or wall 14 or insert 14) can for all the examples at 0.2 to 3.0 mm, advantageously at 0.2 to 1.5 mm, in particular from 0.3 to 0.8 mm. In the interior of the guide element 01, in particular in the cavity 04, can in particular at the smaller of the wall thicknesses mentioned a reinforcing construction, not shown, for example, extending in the longitudinal direction of the guide element 01 carrier, in particular metal support, be arranged on which the chamber wall 12, the wall 14 or the insert 14 at least partially or supported selectively. This can be done for example by mutually spaced apart in the axial direction ribs.

For the execution of the micro-openings 03 as openings 03 of holes 11 z. B. an overpressure in the chamber 04 of 0.5 to 2 bar, in particular from 0.5 to 1.0 bar of advantage.

The bores 11 may be cylindrical, funnel-shaped or else of a special shape (for example in the form of a Laval nozzle).

The microperforation, d. H. the bores 11 are preferably produced by drilling by means of accelerated particles (eg liquid such as water jet, ions or elementary particles) or by means of electromagnetic radiation of high energy density (eg light by means of a laser beam). Particularly advantageous is the production by means of electron beam.

The web 02 facing side of the holes 11 having wall 12 (14), z. As a stainless steel formed wall 12 (14), in a preferred embodiment, a dirt and / or color-repellent finish. It has a not shown, the openings 03 and holes 11 not covering coating -. As nickel or advantageous chromium - on which z. B. is additionally processed - z. B. structuring with micro ribs or a lotus flower effect structuring or preferably highly polished).

LIST OF REFERENCE NUMBERS

01

Guide element, web guide element, rod

02

Web, material web, substrate web, paper web

03

Opening, micro opening

04

Cavity, interior, chamber, pressure chamber

05

Printing unit, printing unit, offset printing unit

06

microporous material, sintered material, layer, microporous

07

Carrier, inner body, basic body

08

Feedthrough, passage opening

09

opening

10

nip

11

Bore, micro bore

12

Wall, chamber wall

13

supply

14

Wall, curved, wall section, insert

15

Wall, wall, curved

16

carrier

17

groove

18

-

19

-

20

cover

b01

width

b07

width

M07

Focus

R07

radius

R14

radius

R15

Radius, radius of curvature

α

deflection

γ

Pitch angle

Claims (40)

1. A printing unit (05) with one respective guiding element provided in the inlet region and in the outlet region of a printing gap (10) formed by two cylinders, wherein the guiding elements are arranged in such a way for the use of the printing unit (05) with an imprinter function that in one operating situation a web (02) is printed in the printing gap (10), and in another operating situation with the printing point thrown off it is guided without contact through the thrown-off printing gap (10) by way of the guiding element (01), characterized in that at least the guiding element (01) has a plurality of openings (03) in its external face in the outlet region for the issue of a fluid under pressure, the openings (03) are in the form of micro-openings (03) with a diameter of less than 500 µm, the micro-openings (03) are in the form of outwardly directed openings (03) of micro-bores (11) in a wall (12) bounding the guiding element (01) towards the outside, and a hole density, i.e. a number of openings (03) per unit of area, amounts to at least 0·2 / mm² for the area provided with the micro-openings (03).
2. A printing unit (05) with one respective guiding element provided in the inlet region and in the outlet region of a printing gap (10) formed by two cylinders, wherein the guiding elements are arranged in such a way for the use of the printing unit (05) with an imprinter function that in one operating situation a web (02) is printed in the printing gap (10), and in another operating situation with the printing point thrown off it is guided without contact through the thrown-off printing gap (10) by way of the guiding element (01), characterized in that at least the guiding element (01) is constructed in the outlet region in the form of a rod which is flushed with air flowing around it and which has micro-porous, air-permeable material (06), and the micro-porous material (06) is constructed in the form of a coating (06) on a support (07) which is load-bearing but fluid-permeable at least in part.
3. A printing unit according to Claim 1 or 2, characterized in that the guiding element (01) is constructed in the form of a circular profile.
4. A printing unit according to Claim 1 or 2, characterized in that the guiding element (01) is constructed in the form of a profile in the form of a half shell.
5. A printing unit according to Claim 1 or 2, characterized in that the guiding element (01) is constructed on the side facing the web (02) with a profile substantially in the form of a circular segment.
6. A printing unit according to Claim 2, characterized in that on its external face the material (06) has a plurality of micro-openings (03) for the exit of a fluid under pressure, the micro-openings (03) having a diameter of less than 500 µm.
7. A printing unit according to Claim 6, characterized in that the micro-openings (03) are in the form of open pores of a porous material (06) through which the fluid flows.
8. A printing unit according to Claim 2 or 7, characterized in that the pores of the fluid-permeable porous material (06) have an average diameter of from 5 to 50 µm, and in particular from 10 to 30 µm.
9. A printing unit according to Claim 2 or 7, characterized in that the porous material (06) is in the form of an open-pored sintered material (06), and in particular in the form of a sintered metal.
10. A printing unit according to Claim 2, characterized in that on its side facing the layer (06) the support (07) has at least one support face joined to the layer (06) and a plurality of openings (09) for the supply of the fluid into the layer (06).
11. A printing unit according to Claim 2, characterized in that in the region of the support face the layer (06) has a thickness of less than 1 mm, and in particular from 0·05 mm to 0·3 mm.
12. A printing unit according to Claim 2, characterized in that on its width and length co-operating with the layer (06) the support (07) has a plurality of passages (08), in particular not connected, in each case.
13. A printing unit according to Claim 2, characterized in that the support (07) is constructed in the form of a support tube (07) with a hollow profile, and in particular with an annular profile.
14. A printing unit according to Claim 2, characterized in that a wall (15) of the support (07) carrying the layer (06) has in profile substantially a curvature based upon the course of the web.
15. A printing unit according to Claim 2, characterized in that a wall (15) of the support (07) carrying the layer (06) is constructed in the form of a curved wall (15) with a profile substantially in the form of a circular segment.
16. A printing unit according to Claim 2, 14 or 15, characterized in that a wall thickness of the support (07) or at least of the wall (15) carrying the layer (06) is larger than 3 mm, and in particular larger than 5 mm.
17. A printing unit according to Claim 2 or 7, characterized in that a degree of opening on the outwardly directed surface of the porous material (06) is between 3 % and 30 %, and preferably between 10 % and 25 %.
18. A printing unit according to Claim 1, characterized in that a diameter of the openings (03) is smaller than or equal to 300 µm, and in particular between 60 and 150 µm.
19. A printing unit according to Claim 1, characterized in that a thickness of the wall (12) is from 0·2 to 3·0 mm.
20. A printing unit according to Claim 1 or 6, characterized in that the choice of material, dimensioning and pressure stressing are selected in such a way that from 1 to 20 standard cubic metres emerge from the air-outlet face of the sintered material per hour onto a square metre of the external face comprising the openings (03).
21. A printing unit according to Claim 1 or 6, characterized in that the choice of material, dimensioning and pressure stressing are selected in such a way that from 2 to 15, and in particular from 3 to 7, standard cubic metres of air emerge per hour onto a square metre of the external face comprising the openings (03).
22. A printing unit according to Claim 2 or 7, characterized in that the porous material (06) is acted upon from the inside with at least 1 bar of over-pressure.
23. A printing unit according to Claim 2 or 7, characterized in that the porous material (06) is acted upon from the inside with more than 4 bar, and in particular with more than from 5 to 7 bar, of over-pressure with the fluid.
24. A printing unit according to Claim 1 or 6, characterized in that a supply line for supplying the fluid to the guiding element (01) has an internal cross-section of less than 100 mm², and in particular between 10 and 60 mm².
25. A printing unit according to Claim 1 or 6, characterized in that the external diameter of the guiding element (01) amounts to from 60 to 100 mm.
26. A printing unit according to Claim 1 or 6, characterized in that the guiding element (01) has a length of more than 1,200 mm.
27. A printing unit according to Claim 1 or 6, characterized in that the fluid under pressure is in the form of compressed air.
28. A printing unit according to Claim 1, characterized in that the part of the guiding element (01) provided with the micro-openings (03) is constructed in the form of a releasable insert (14) on a support (16).
29. A printing unit according to Claim 1 or 28, characterized in that a region of the wall (12) provided with the micro-bores (11) or the insert (14) has in profile substantially a curvature based upon the course of the web.
30. A printing unit according to Claim 1 or 28, characterized in that a region of the wall (12) of the support (07) provided with the micro-bores (11) or the insert (14) is constructed in the form of a curved wall (15) with a profile substantially in the form of a circular segment.
31. A printing unit according to Claim 5, 15 or 30, characterized in that a partial angle (γ) of the segment is selected to be from 10° to 45°, and in particular between 15° to 35°.
32. A printing unit according to Claim 5, 15 or 30, characterized in that a width (b01) of the guiding element (01) in the region of the segment is from 30 to 150 mm, and in particular from 50 to 110 mm.
33. A printing unit according to Claim 1 or 2, characterized in that the said first printing unit is designed so as to be capable of being operated alternately with a second printing unit (05) in such a way that in a first manner of operation the first printing unit (05) is set on so as to print the web (02), whereas the web (02) is guided through the second printing unit (05) without contact, and in a second manner of operation the first printing unit (05) is set off and has the web (02) running through it without contact, whereas the second one is set on and the web (02) is printed.
34. A printing unit according to Claim 1 or 2, characterized in that the web (02) is guided through five printing units (05).
35. A printing unit according to Claim 33 or 34, characterized in that at least the two printing units (05) to be traversed without contact in a selective manner have guiding elements (01) in the inlet region and the outlet region of their printing gap (10) in each case.
36. A printing unit according to Claim 1, characterized in that the bores (11) are produced by means of accelerated particles.
37. A printing unit according to Claim 36, characterized in that the bores 811) [sic] are produced by boring by means of an electron beam.
38. A printing unit according to Claim 1, characterized in that at least one wall portion of the guiding element (01) comprising the bores (11) has a dirt- and/or ink-repelling conditioning on its surface.
39. A printing unit according to Claim 38, characterized in that the conditioning is produced by chromium as a coating.
40. A printing unit according to Claim 39, characterized in that the surface is made high-gloss polished.

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