WEB-FED PRINTING MACHINE

Abstract

A printing machine for printing on a web includes a first roller and a second roller between which the web forms a loop. A trough for pneumatically guiding the loop equidistantly to the major part of the length of curvature of the trough is provided between the first roller and the second roller.

Claims

1. A printing machine for printing on a web, the printing machine comprising: a first roller; a second roller and between said first and second rollers the web forms a loop; and a trough for pneumatically guiding the loop equidistantly relative to a major part of a length of curvature of said trough and said trough disposed between said first roller and said second roller.

2. The printing machine according to claim 1, wherein said trough has suction openings and blower openings formed therein for guiding the loop in a contact-free way.

3. The printing machine according to claim 2, wherein said suction openings are grooves extending to be either parallel to a travelling direction of the web or at an angle relative to the travelling direction.

4. The printing machine according to claim 2, wherein said blower openings form nozzle rows that are disposed to alternate with said suction openings.

5. The printing machine according to claim 1, further comprising a support roller; and wherein said trough is disposed on an outer side of the loop and said support roller that is out of contact with the web during a trouble-free printing operation is disposed on an inner side of the loop.

6. The printing machine according to claim 5, wherein an inner circumferential surface of said trough and an outer circumferential surface of said support roller are parallel to one another.

7. The printing machine according to claim 2, further comprising a format adjustment device for adjusting said suction openings to a respective width of the web.

8. The printing machine according to claim 2, wherein said blower openings are throttle nozzles that throttle air flow by means of a filter insert or a channel maze.

9. The printing machine according to claim 1, wherein said first roller and/or said second roller is a cooling roller through which a cooling fluid flows to cool the web.

10. The printing machine according to claim 1, further comprising a drying or pinning device; further comprising at least one downstream inkjet print head; and wherein said first roller, said second roller and said trough are disposed between said drying or pinning device and said at least one downstream inkjet print head along a transport path of the web.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0020] FIG. 1 is an illustration of a digital printing machine with a trough for guiding a web of printing material according to the invention;

[0021] FIG. 2 is a perspective view of he guide trough together with a support roller;

[0022] FIG. 3 is an illustration of a nozzle surface of the guide trough; and

[0023] FIG. 4 is an illustration of a modified nozzle surface.

DETAILED DESCRIPTION OF THE INVENTION

[0024] In FIGS. 1 to 4, mutually corresponding components and elements have the same reference symbol.

[0025] Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown an illustration of a digital printing machine through which a web B of printing material passing in a direction of travel R. Firstly a coating device 10 embodied as an inkjet print head applies a base coat or primer to the web B. The next step is to dry the applied base coat/primer by means of a pinning device 8. Finally one or more inkjet print heads 9 print an image onto the base coat/primer.

[0026] A first roller 1 and a second roller 2 are disposed between a pinning device 8 and an inkjet print head 9 along a web B and a trough 3 and a support roller 6 are disposed between the two rollers 1, 2. The web B forms a noose or loop S between the two rollers 1, 2. The trough 3 is disposed on the same side of the web B as the rollers 1, 2, namely on the back side of the web B, i.e. the side that has not been coated by a coating device 10. On the opposite side, namely on the front side of the web B, i.e. the side that has been coated by the web B, there is the support roller 6.

[0027] During a printing operation, the trough 3 acts to keep the loop S stable, ensuring that the web B wraps around each one of the rollers 1, 2 over a maximized circumferential angle. As a consequence, the area of contact between the web B and the roller 1 or 2 is large and thus the transfer of heat from the web B to the respective roller 1 or 2 is maximized accordingly.

[0028] When the web B is treated by the pinning device 8, the web B is heated. This is an undesired side effect that cannot be avoided. The heating of the web B would affect the print quality of the web B when it is printed by the ink jet print head 9 if no countermeasures were taken. Without countermeasures, longitudinal creases that would be visible in the image printed by the inkjet print head 9 would occur in the web B.

[0029] The countermeasure is to cool the web B by means of one of the rollers 1, 2 or preferably both of them, which are embodied as cooling rollers for this purpose. A coolant such as water flows through the rollers 1, 2, causing the temperature of the web B to be reduced down to a value at which longitudinal creases no longer occur and there is no detrimental effect on the downstream inkjet print as a consequence.

[0030] FIG. 2 shows that the trough 3 has a length of curvature L. In the present case of a trough 3 ideally shaped like a circular arc, the length L is a length of a circular arc. In a trouble-free printing operation, a gap of a width or distance a is present between the running web B and the web-facing nozzle surface of the trough 3. This width a is constant along almost the entire length of curvature L. Due to pneumatic peculiarities in the two end sections of the length of curvature L, namely in the entry region and the exit region of the web B, the distance a may be different, for instance smaller than in the main section of the length of curvature L between the two end sections.

[0031] FIG. 3 is a top view of the web-facing nozzle surface of the trough 3, showing the trough 3 as an individual part in an unwound state. The guide surface or nozzle surface of the trough 3 has a one-dimensional curvature and the center of curvature is the geometric axis of rotation of the support roller 6. Thus the inner circumferential surface or guide surface of the trough 3 is concentric with the outer circumferential surface of the support roller 6 (cf. FIG. 2).

[0032] Suction openings 4 and blower openings 5 are formed in the guide or nozzle surface. A format adjustment device 7 connects the suction openings 4 to a vacuum source (not shown in any detail) and the blower openings 5 to a compressed-air source (not shown in any detail).

[0033] The blower openings 5 are embodied as throttle nozzles and arranged in rows that are parallel to the direction of travel of the web B. The suction openings 4 are embodied as grooves that likewise extend in parallel with the direction of travel R. As viewed in a direction transverse to the direction of travel R, the suction openings 4 and the blower openings 5 are arranged in an alternating way.

[0034] As an alternative to the pattern shown in FIG. 3, there may be several rows of throttle nozzles between two suction grooves and/or there may be several suction grooves between two rows of throttle nozzles.

[0035] The format adjustment device 7, which is only schematically shown in the drawing, may deactivate those suction openings 4 and/or blower openings 5 that are outside the format width of the web B and are not covered by the latter.

[0036] The vacuum source and the compressed-air source may be set to balance the force of the vacuum applied to the suction openings 4 and the force of the blown air emitted by the blower openings 5 in such a way that the web B, which is simultaneously subjected to suction by the suction openings 4 and carried on an air cushion by the blower openings 5, floatingly passes between the trough 3 and the support roller 6, contacting neither as long as the printing operation remains trouble-free.

[0037] The web B may contact the support roller 6 and wrap around the latter during a disturbance in the printing operation or during an intentional or unintentional disruption of the printing operation. If the web B continues to run during a disturbance or interruption of the printing operation, the web B may drive the support roller 6 that it is wrapped around by circumferential surface friction. In this respect, the support roller 6 may not have a drive of its own and may co-run with the web B.

[0038] In a trouble-free printing operation, the image printed by the coating device, which has not yet been completely dried or cured by the pinning device 8, is guaranteed to be protected against damage because the printed image does not get into contact with the support roller 6. The trough 3, which guides the web B without contact, ensures that the web is guided in a very gentle way.

[0039] FIG. 4 illustrates a modification that differs from the example illustrated in FIG. 3 only in as much as the grooves (suction openings 4) and the throttle nozzle rows (blower openings 5) extend at an angle, preferably an acute angle, relative to the direction of travel R of the web B.

[0040] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: [0041] 1 first roller [0042] 2 second roller [0043] 3 trough [0044] 4 suction opening [0045] 5 blower opening [0046] 6 support roller [0047] 7 format adjustment device [0048] 8 pinning device [0049] 9 ink jet print head [0050] 10 coating device [0051] a distance [0052] B web [0053] L length of curvature [0054] R running direction [0055] S loop