Method for Printing A Substrate

Abstract

A method for printing on a substrate, wherein the substrate is printed upon with a plate-based printing process, i.e., an offset printing process, and with a plateless printing process, i.e., an inkjet printing process, inline with the plate-based printing process. In accordance with the invention, the printing resolution of the plateless printing process is determined depending on a printing speed of the plate-based printing process.

Description

The invention is directed to a method for printing on a substrate according to the preamble of claim 1.

Inkjet printing units which do not use printing plates are increasingly used in printing plate-based printing presses, mainly printing presses working on the principle of offset printing, e.g., in web-fed rotary offset printing presses and sheet-fed printing presses. These plateless inkjet printing units are used particularly for individualizing printed products produced by offset printing, e.g., with barcodes, numbering or other markings. Inkjet printing units of this kind have at least one inkjet printing head which can be designed to work on the principles of a continuous inkjet, drop-on-demand inkjet, thermal inkjet, bubble inkjet, or any other inkjet principle.

Since the maximum printing speed of inkjet printing units is appreciably less than the maximum printing speed of offset printing units, there are difficulties involved in inline printing on a substrate by offset printing and inkjet printing.

To increase the achievable printing speed of inkjet printing units, it is known in practice to use inkjet printing units having a plurality of inkjet printing heads, namely, a plurality of inkjet printing heads transverse to the transporting direction of the substrate or transverse to the printing direction on the one hand and a plurality of inkjet printing heads in the transporting direction of the substrate or in the printing direction on the other hand, the plurality of inkjet printing heads being arranged next to one another in the shape of an array or matrix.

Although the printing speed of inkjet printing processes can be increased in this way, it has not been possible thus far in a web-fed rotary offset printing press designed, e.g., as a newspaper printing press operating at printing speeds for plate-based offset printing of up to 15 m/s to print on a substrate inline with a plateless inkjet printing process due to the fact that the maximum printing speed which it has been possible to realize thus far for inkjet printing processes is 5 m/s. Consequently, when printing on a substrate with a plate-based printing process and, inline with the latter, with a plateless inkjet printing process, the print image applied by means of the inkjet printing process is subject to distortion. Therefore, there is a need for a method for printing on a substrate by means of which the substrate can be printed upon at high printing speeds of more than 5 m/s inline or simultaneously with a plate-based printing process and a plateless inkjet printing process, specifically without the risk that a print image to be applied by means of the inkjet printing process is subject to distortion. A similar problem occurs, for example, when laser printing is used as a plateless printing method.

Therefore, it is the object of the present invention to provide a novel method for printing on a substrate. This object is met by a method according to claim 1. According to the invention, a printing resolution of the plateless printing process is determined depending on a printing speed of the plate-based printing process. Within the meaning of the present invention, the printing resolution of the plateless printing process, particularly of the inkjet printing process, is determined depending on the printing speed of the plate-based printing process, particularly of the offset printing process. The higher the printing speed of the plate-based printing process compared to the maximum printing speed of the plateless printing process at which printing can be carried out at maximum printing resolution, the lower the printing resolution of the plateless printing process.

In this way, it is possible to operate the plateless printing process at a higher printing speed than the maximum printing speed for which it is specified without the risk of distortion of the print image to be applied by means of the plateless printing process.

A printing resolution of the plateless printing process considered transverse to the transporting direction of the substrate is preferably independent of the printing speed of the plate-based printing process; however, a printing resolution of the plateless printing process considered in the transporting direction of the substrate is determined depending on the printing speed of the plate-based printing process.

Preferred further developments of the invention are indicated in the subclaims and the subsequent description. Embodiment examples of the invention are described more fully with reference to the drawings. The drawings show:

FIG. 1 a first schematic view illustrating the method according to the invention for printing on a substrate; and

FIG. 2 a second schematic view illustrating the method according to the invention for printing on a substrate.

The present invention is directed to a method for printing on a substrate, wherein the substrate is printed on by a plate-based printing process and, inline with the plate-based printing process, by a plateless inkjet printing process. The plate-based printing process is preferably an offset printing process. The method according to the invention is preferably used in web-fed rotary offset printing presses such as, e.g., in newspaper printing presses, in order to print on a web-shaped substrate by means of the inkjet printing process inline with the offset printing within the web-fed rotary offset printing press.

Within the meaning of the invention, for inline printing on a substrate with a plate-based printing process and simultaneously with a plateless inkjet printing process, a printing resolution of the inkjet printing process is determined depending on a printing speed of the plate-based printing process, particularly of the offset printing process. The printing resolution is preferably determined in such a way that a printing resolution of the inkjet printing process transverse to the transporting direction of the substrate is independent of the printing speed of the plate-based printing process, but a printing resolution of the inkjet printing process in the transporting direction of the substrate is dependent on the printing speed of the plate-based printing process,

This will be described in detail in the following with reference to FIGS. 1 and 2. FIG. 1 is a schematic visualization of a resolution which can be achieved by means of a conventional inkjet printing process, wherein the resolution considered transverse to transporting direction of the substrate (arrow 10) and considered in the transporting direction of the substrate (arrow 11) is identical. Accordingly, considered transverse to the transporting direction of the substrate, the distance x between dots which can be printed by means of the inkjet printing process corresponds to the distance y between the same dots considered in the transporting direction of the substrate.

Typically, the resolution of an inkjet printing process is 240×240 dpi or 300×300 dpi. With a printing resolution of this kind which is identical considered transverse to the transporting direction of the substrate and in the transporting direction of the substrate, printing can be carried out, for example, in the manner of character A according to FIG. 1.

When the printing speed of the plate-based printing process, particularly of the offset printing process, is less than or equal to a maximum printing speed of the inkjet printing process at which printing can be carried out at the maximum inkjet printing resolution, the printing resolution of the inkjet printing process in the transporting direction of the substrate and transverse to the transporting direction of the substrate corresponds to the maximum printing resolution of the inkjet printing process.

On the other hand, when the printing speed of the plate-based printing process, particularly of the offset printing process, is greater than the maximum printing speed of the plateless inkjet printing process at which printing can be carried out at maximum inkjet printing resolution, the selected printing resolution of the inkjet printing process considered in the transporting direction of the substrate is lower than the maximum printing resolution of the inkjet printing process.

When the printing speed of the plate-based printing process is greater than the maximum printing speed of the plateless inkjet printing process, the printing resolution of the inkjet printing process in the transporting direction of the substrate is determined according to the following formula:

${\mathrm{DA}}_{\mathrm{inkjet}}={\mathrm{DA}}_{\mathrm{inkjet}}^{\max }*\frac{v_{\mathrm{inkjet}}^{\max }}{v_{\mathrm{offset}}},$

where DA_inkjet is the printing resolution of the inkjet printing process in the transporting direction of the substrate, DA_inkjet^max is the maximum printing resolution of the inkjet printing process, v_inkjet^max is the maximum printing speed of the inkjet printing process at which printing can be carried out at maximum printing resolution DA_inkjet^max, and v_offset is the printing speed of the plate-based printing process.

Accordingly, it follows from the above formula that the printing resolution of the inkjet printing process in the transporting direction of the substrate depends on the transporting speed of the plate-based printing process, particularly of the offset printing process, namely in such a way that the printing resolution of the inkjet printing process is reciprocally or inversely proportional to the printing speed of the plate-based printing process.

In a concrete embodiment example, it is assumed that the maximum printing resolution of the inkjet printing process at a maximum printing speed of the inkjet printing process of 5 m/s is 300×300 dpi. When a substrate is to be operated with an inkjet printing process of this kind inline with a plate-based offset printing process operating at a printing speed of 15 m/s, the printing resolution of the inkjet printing process is 300 dpi transverse to the transporting direction of the substrate and 100 dpi in the transporting direction of the substrate so that the total resolution is 300×100 dpi.

FIG. 2 shows a reduced printing resolution for the inkjet printing process. In this case, the distance x between printing dots remains unchanged considered transverse to the transporting direction (arrow 10) of the substrate, but the distance y* between the printing dots is increased considered in the transporting direction (arrow 11) of the substrate. The character A is accordingly printed with fewer dots considered in the transporting direction of the substrate.

According to a first variant of the invention, the printing resolution of the inkjet printing process is determined once depending on the maximum printing speed of the plate-based printing process, particularly of the offset printing process, so that the printing resolution of the inkjet printing process is constant and is accordingly independent from the actual printing speed of the plate-based offset printing process.

Accordingly, a uniform appearance of the print image to be printed by means of the inkjet printing process can be realized over the entire speed range of the plate-based offset printing process.

In order to optimize the printing quality of the inkjet printing process, the printing resolution of the inkjet printing process can also be determined depending on the actual printing speed of the plate-based offset printing process so that the printing resolution of the inkjet printing process can accordingly be varied; namely, it depends on the actual printing speed of the plate-based offset printing process at the current time.

With the printing process according to the invention, it is possible to print on a substrate with a high printing quality in offset printing and inline in inkjet printing even at printing speeds above a permissible printing speed for inkjet printing processes.

The invention can also be employed when using another plateless printing process, e.g., laser printing, inline with the plate-based printing process.

Claims

1.-8. (canceled)

9. A method for printing on a substrate, determining a first printing resolution of a plateless printing process based on a printing speed of a plate-based printing process inline with the plateless printing process; andprinting on the substrate with the plate-based printing process and the plateless printing process at the determined printing speed of the plate-based printing process.

10. The method according to claim 9, wherein a second printing resolution of the plateless printing process transverse to the transporting direction of the substrate is independent from the printing speed of the plate-based printing process.

11. The method according to claim 9, wherein the first printing resolution of the plateless printing process is in a transporting direction of the substrate.

12. The method according to claim 10, wherein the first printing resolution of the plateless printing process in a transporting direction of the substrate.

13. The method according to claim 11, wherein the first printing resolution of the plateless printing process in the transporting direction of the substrate is determined such that when the printing speed of the plate-based printing process is less than or equal to a maximum printing speed of the plateless printing process at which printing can be performed at a maximum printing resolution, the first printing resolution of the plateless printing process in the transporting direction of the substrate corresponds to the maximum printing resolution of the plateless printing process.

14. The method according to claim 11, wherein the first printing resolution of the plateless printing process in the transporting direction of the substrate is determined such that when the printing speed of the plate-based printing process is greater than a maximum printing speed of the plateless printing process at which printing can be performed at a maximum printing resolution, the first printing resolution of the plateless printing process in the transporting direction of the substrate is lower than the maximum printing resolution of the plateless printing process.

15. The method according to claim 13, wherein the first printing resolution of the plateless printing process in the transporting direction of the substrate is determined such that when the printing speed of the plate-based printing process is greater than the maximum printing speed of the plateless printing process at which printing can be performed at the maximum printing resolution, the first printing resolution of the plateless printing process in the transporting direction of the substrate is lower than the maximum printing resolution of the plateless printing process.

16. The method according to claim 15, wherein when the printing speed of the plate-based printing process is greater than a maximum printing speed of the plateless printing process at which printing can be performed at maximum printing resolution, the printing resolution of the plateless printing process in the transporting direction of the substrate is determined in accordance with the following relationship:

17. The method according to claim 9, wherein the first printing resolution of the plateless printing process is determined depending on a maximum printing speed of the plate-based printing process so that the first printing resolution of the plateless printing process is constant and is independent from an actual printing speed of the plate-based printing process.

18. The method according to claim 9, wherein the first printing resolution of the plateless printing process is determined depending on an actual printing speed of the plate-based printing process so that the first printing resolution of the plateless printing process is variable.

19. The method according to claim 9, wherein the plate-based printing process is an offset printing process and the plateless printing process is an ink jet printing process.