EP1476311B1 - Digital printing method and printing device having a cup-shaped printing carrier - Google Patents

Abstract

In a method and device to print a carrier material, a print carrier is provided with depressions on a surface. On the surface, a fluid layer is applied such that the depressions are filled with fluid. In a structuring process, ink-attracting and ink-repelling regions are generated so that the fluid in the depressions is removed in the ink-attracting regions not removed in the ink-repelling regions. Ink that adheres in the ink-attracting regions and which does not adhere in the ink-repelling regions is applied on the surface. The ink applied on the surface of the print carrier is transferred to the carrier material.

Description

The invention relates to a method and a device for printing on a carrier material, in which a print carrier has a multiplicity of depressions on its surface. Such a print carrier is known for example from gravure printing.

Digital printing methods have become known in which structuring into ink-attracting and ink-repelling areas is carried out by digitally controlled energy sources, for example lasers. Before re-structuring the same surface of the print carrier, the respective surface must be precisely cleaned. For this purpose, appropriate cleaning stations are required, which increase the hardware cost.

For example, from US-A-5,067,404 a digitally operating printing method is known in which a fountain solution is applied to the surface of the print carrier. The dampening solution is vaporized by selective application of radiant energy in image areas. The anhydrous areas later form the ink-bearing areas, which are led past a development unit and colored by means of a paint vapor. After transfer printing, the ink residues must be completely removed from the surface of the print substrate in order to re-apply a dampening solution and to restructure it.

Furthermore, US Pat. No. 6,295,928 (corresponding to WO 98/32608) discloses a method in which an ice film is applied to the surface of a print carrier and this is structured using local thermal energy, wherein, for example, a digitally controlled laser system is used. After transfer printing, the ice layer must and the ink residues are removed to allow for restructuring with new print images.

DE-A-101 32 204 (not prepublished) by the same Applicant describes a CTP (computer-to-press) method, wherein multiple structuring processes can be carried out on the same surface of the print carrier. Structuring into ink-receptive and ink-repellent areas is done using digitally controlled systems, such as laser systems. The ink-attracting areas are later colored with color. Before a new structuring process, the surface of the print carrier is cleaned.

Cleaning devices that can be used for digital printing methods are known e.g. in DE-A-100 63 987 of the same Applicant. For cleaning, the surface of the print substrate is treated with cleaning liquid, whereby further measures, such as the use of ultrasonic energy, may be added.

WO 01/02170 A of the same applicant discloses a method and a printing device for printing on a carrier material and for cleaning a printing roller. The print carrier contains a multitude of depressions in which ink can be absorbed. This color in the depressions is subjected to thermal energy in a structuring process, whereby color-printing areas and areas which do not give off color are produced. Using a complex cleaning station, the surface of the print substrate is completely cleaned before re-structuring.

DE 102 08 250 A1 (not prepublished) describes a printing method in which the surface of a print carrier is wetted with a dampening solution. With the help of energy, the dampening solution is removed at image locations, the surface is inked and the ink is applied to an intermediate carrier, e.g. a blanket tape, transferred. From there, the paint is transferred to a substrate. Between two printing cycles, the surface of the print carrier is cleaned in each case.

As a further prior art reference is made to DE 195 03 951 C2 and EP 0 711 671 A1.

The document EP-A-0 730 953 describes a device for printing on a carrier material in which a print carrier has on its surface a plurality of wells (recesses). An applicator transfers a liquid to a print carrier. With the aid of a pixel transfer device, the liquid is removed in ink-attracting areas and the ink is not removed in ink-repellent areas. After transfer printing, the wells are not completely emptied, so that the surface of the print carrier is cleaned in each case between two successive printing cycles.

Document EP-A-0 101 266 relates to a printing method and apparatus in which a thin hydrophobic layer is disposed over a substantially hydrophilic printing surface, whereby a latent image is formed by patterning to form hydrophilic and hydrophobic regions. These areas are colored with the help of an aqueous or an oily colored liquid and prepared for further printing.

It is an object of the invention to provide a printing method and a printing device that allows or that different printed images are generated on the same surface of the print carrier, wherein the cleaning effort is minimized.

This object is achieved by a method according to claim 1 for printing a substrate, in which a print carrier on its surface has a plurality of wells on the surface of the print carrier, a thin, homogeneous liquid layer is applied, so that all wells fill with liquid in inking and ink repelling areas are produced in a patterning process, wherein in ink-attracting areas the liquid in the recesses is removed and in ink-repellent areas, the liquid is not removed, is applied to the surface of ink, which adheres in ink-attracting areas on the surface of the print carrier and in ink repellent Not adhered to areas, and in which the ink applied to the surface of the print carrier is transferred in the further course directly to the substrate, and in which on the same surface of the print substrate again a liquid layer is applied and the printing process is continued.

According to the invention, all depressions, which generally have a cup shape, are filled with liquid, for example water. In the subsequent patterning process, which is generally digitally controlled, the liquid in the recesses is removed in ink-receptive areas, for example by evaporation. In the ink-repellent areas, the liquid is still present in the depressions. The entire usable surface of the print carrier is then inked with ink that is repelled by the liquid, but is taken up by the wells without liquid. The carrier material, for example paper, now comes directly into contact with the surface. The color from the wells is completely transferred to the substrate. After transfer, all wells are empty and contain no ink residues. Consequently, the thin, homogeneous liquid layer can be applied again immediately in the next work step, and a renewed structuring into ink-repelling and ink-attracting regions takes place. It is therefore dispensed cleaning between two printing cycles, whereby a corresponding cleaning station can be omitted. As a result, the hardware cost for implementing the method is reduced. It may be possible that cleaning in a simplified form is required after longer time intervals. In general, however, such cleaning is not necessary between two successive printing cycles, but only after a large number of printing cycles and then only in a simplified form of cleaning, so that even then the cleaning effort is reduced. As a result, high printing speeds can be achieved by applying a digital printing method.

According to a further aspect of the invention, a printing device according to claim 12 is provided. In the dependent claims to the method or the printing device further features for advantageous embodiments are defined.

An embodiment of the invention will be explained below with reference to FIG.

In this figure 1, a printing device is shown, through which the described method for printing a substrate can be realized. A print carrier 10, also referred to as a forme cylinder, has a surface structure which is shown enlarged in the image detail 12. The surface structure contains planar grid-like arranged cups 14, for example in a grid of 300 to about 2500 dpi ( d ots p er i nch), preferably 600 to 1200 dpi. Using these cups, corresponding pixels can be printed. The well depth is 0.1 to 50 microns, preferably 5 to 20 microns.

Around the circumference of the cylindrical print carrier 10 around a dampening unit 16, an image forming device 18, an inking unit 20 and an impression cylinder 22 is arranged, also called "impression roller". The carrier material 24 is performed between the cylindrical print carrier 10 and the impression cylinder 22. It passes through a drying station 26 for drying.

When rotating the printing medium 10 in the direction of arrow P1 occurs at the dampening unit 16, the application of a thin, homogeneous liquid layer, so that all wells 14 with liquid, preferably water, fill. The fountain solution is applied, for example, by rolling, However, alternatively, the order can be made by spraying or steaming.

Preferably, excess dampening solution is removed with a doctor blade (not shown) downstream of the dampening unit 16. The fountain solution is selectively evaporated by a digital imaging device 18 to produce ink-attracting and ink-repelling regions. In the ink-attracting areas, the liquid in the cups 14 is removed; in the ink-repellent areas, the dampening solution is not removed. The image generating device 18 may be, for example, a digitally controlled laser or another controlled energy source. By the inking unit 10 10 color is applied to the surface of the print carrier, which adheres in the ink-attracting areas on the surface of the print carrier 10 and does not adhere in the ink-repellent areas. When using a water-containing fountain solution, the color is generally oily. Excess paint is removed by a the inking unit 20 downstream doctor blade (not shown).

Subsequently, the printing ink is directly transferred to the carrier material 24. The transfer to an elastic intermediate carrier, as described in the patent US-A-5,295,928, deleted. The color transfer is effected by adhesion forces. By appropriate design of the ink in its viscosity and crosslinking, as is well known, and by suitable design of the cup shape to achieve a very good emptying of the wells 14. Water-based inks, as used in the known gravure printing process, are the use of To prefer printing media with a relatively large well depth and their problem of complete emptying.

The substrate is then passed through a drying station 26 which dries the paint.

Preferably, as mentioned, a dampening solution containing water is used. Wetting-promoting substances may then be added to the dampening solution, for example surfactants. Alternatively, silicone-repellent liquids can also be used in order to be able to process silicone-containing printing inks.

An electrostatic field can be applied in the region of the transfer printing point in order to support the emptying of the ink from the cups 14 in the surface of the print carrier 10.

As mentioned, no cleaning station is arranged between the transfer printing and the renewed dampening application. The wells 14 are completely emptied. After a renewed dampening application, structuring into ink-attracting and ink-repelling areas can take place either according to the previous printed image or according to a new printed image. In this way, printed images of smaller and larger print runs can be printed with the same print carrier with high flexibility. Because of the elimination of the cleaning process, which may be required only in a simplified form and in much larger time intervals, an increased printing speed compared to the previous digital printing method can be achieved.

LIST OF REFERENCE NUMBERS

10

print carrier

12

image area

14

wells

16

dampening

18

Imaging device

20

inking

22

Impression cylinder

24

support material

26

drying station

P1

direction of rotation

Claims (20)

1. Method for printing a carrier material (24),
   in which a print carrier (10) has a plurality of depressions (14) on its surface,
   on the surface of the print carrier (10), a thin, homogenous fluid layer is applied, such that all depressions (14) fill with fluid,
   in a structuring process, ink-attracting and ink-repelling regions are generated, wherein the fluid in the depressions (14) is removed in ink-attracting regions and the fluid is not removed in ink-repelling regions,
   ink that adheres in ink-attracting regions on the surface of the print carrier (10) and does not adhere in ink-repelling regions is applied on the surface,
   the ink applied on the surface of the print carrier (10) is, in the further course, directly transferred to the carrier material (24), wherein the ink from the depressions (14) is completely transferred onto the carrier material (24) so that after the transfer-printing all depressions (14) are empty and without any ink residues,
   and in that a fluid layer is reapplied on the same surface of the print carrier (10) and the print process is continued,
   wherein a plurality of print cycles follow one another without the surface of the print carrier (10) being cleaned.
2. Method according to claim 1, in which the depressions (14) form a cup structure with a cup depth in the range of 0.1 to 50 µm, preferably in the range of 5 to 20 µm.
3. Method according to claim 1 or 2, in which the cups (14) are arranged in a grid of 300 to 2500 dpi, preferably 600 to 1200 dpi, on the usable surface of the print carrier (10).
4. Method according to any of the preceding claims, in which the fluid comprises water.
5. Method according to claim 4, in which wetting-aiding substances, preferably surfactants, are added to the water-containing fluid.
6. Method according to any of the preceding claims 1 to 3, in which the fluid comprises silicone-repelling substances and the ink comprises silicone-containing substances.
7. Method according to any of the preceding claims, in which excess fluid is removed by a scraper after the application of the fluid.
8. Method according to any of the preceding claims, in which excess ink is removed with the aid of a scraper after the application of the ink.
9. Method according to any of the preceding claims, in which, in the region of the transfer printing location, an electrostatic field is effective that supports the emptying of the ink from the depressions (14) in the surface of the print carrier (10).
10. Method according to any of the preceding claims, in which the printed carrier material (24) is dried.
11. Method according to any of the preceding claims, in that the print carrier (10) is cylindrical or plate-shaped.
12. Device for printing a carrier material (24),
    in which a print carrier (10) has a plurality of depressions (14) on its surface,
    a dampening system (16) is provided by which on the surface of the print carrier (10), a thin, homogenous fluid layer is applied, such that all depressions (14) fill with fluid,
    means are provided via which,
    in a structuring process, ink-attracting and ink-repelling regions are generated, wherein the fluid in the depressions (14) is removed in ink-attracting regions and the fluid is not removed in ink-repelling regions,
    ink that adheres in ink-attracting regions on the surface of the print carrier (10) and does not adhere in ink-repelling regions is applied to the surface,
    the ink applied on the surface of the print carrier (10) is, in the further course, directly transferred to the carrier material (24), wherein the ink from the depressions (14) is completely transferred onto the carrier material (24) so that after the transfer-printing all depressions (14) are empty and without any ink residues,
    and via which a fluid layer is reapplied on the same surface of the print carrier (10) and the print process is continued,
    and in which between the transfer printing and the renewed application of the a dampening solution, no cleaning station is arranged,
    wherein a plurality of print cycles follow one another without the surface of the print carrier (10) being cleaned.
13. Device according to claim 12, in which the depressions (14) form a cup structure with a cup depth in the range of 0.1 to 50 µm, preferably in the range of 5 to 20 µm.
14. Device according to claim 12 or 13, in which the cups (14) are arranged in a grid of 300 to 2500 dpi, preferably 600 to 1200 dpi, on the usable surface of the print carrier (10).
15. Device according to any of the preceding claims, in which the fluid comprises water.
16. Device according to claim 15, in which wetting-aiding substances, preferably surfactants, are added to the water-containing fluid.
17. Device according to any of the preceding claims 12 to 13, in which the fluid comprises silicone-repelling substances and the ink comprises silicone-containing substances.
18. Device according to any of the preceding claims, in which, in the region of the transfer printing location, an electrostatic field is effective that supports the emptying of the ink from the depressions (14) in the surface of the print carrier (10).
19. Device according to any of the preceding claims, in which means are provided by which the printed carrier material (24) is dried.
20. Device according to any of the preceding claims, in which the print carrier (10) is cylindrical or plate-shaped.

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