The present invention relates to digital commercial or industrial printing system utilizing printheads to eject dot matrix patterns of drops of UV curable ink upon a web of print media to form images and text. More particularly the present invention relates to a “PIN” unit emitting radiation at a power level to partially cure ink between two printheads using an advantageous power level versus transport speed.
A rapid change is occurring in the commercial and industrial printing marketplace with an expanded use of digital printing presses to replace their analog counterparts. Digital printing presses have an advantage of lower “set-up” costs in that a change to a print pattern is accomplished with a file change. This improves the economics of “short run” printing and reducing a need to print large inventories of a given design.
One common form of digital printing press is a web press based upon inkjet printing of radiation curable inks. In this embodiment a roll of media is unwound and then passed through a paper path defined by a series of rollers. A part of the paper path is a print zone within which inkjet printheads eject a dot matrix pattern of fluid drops on a surface of the media thereby forming images and/or text on the media surface.
An important factor with radiation curable inks is a tendency to flow between depositing the inks and providing a radiation cure of the inks. Another factor is a tendency of inks having different primary colors to intermix. A certain amount of flow and intermixing can be desirable but there is an optimal level in order to maximize resultant image quality.
To control flow and intermixing PIN units can be used to “pin down” the ink to a certain extent to reduce flow and mixing. The effect of these units has been found to change with the transport speed of the print unit in unexpected ways.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
Within the print zone 8 the media is transported in a direction X through the print zone. The printheads 10 each at least a portion of the print media along a transverse or cross-web direction Y. Each printhead 10 ejects droplets upon the media along a vertical axis Z.
Arranged in the print zone along the transport direction V are a series of modules or units 11 including printheads 10, PIN units 14, and a curing unit 16. Only two printheads 10 and one PIN unit 14 is shown for simplicity but it is to be understood that any number of such units may be used. Each of the modules spans at least a portion of the print zone in transverse direction Y (cross-web direction).
The arrangement of the modules 11 relative to the transport direction V is important. A first printhead 10-1 is up-web of the remaining modules 11. First printhead 10-1 emits a dot matrix pattern of UV-curable ink onto media 6 in a first color (preferably a primary color).
Immediately down-web of printhead 10-1 is PIN unit 14. PIN unit 14 emits a wavelength of light with a power sufficient to partially cure the UV-curable ink from printhead 10-1. The power of the PIN unit 14 needs to be sufficient to reduce or eliminate a flow of UV ink just emitted by printhead 10-1. In one embodiment PIN unit is an array of LED's emitting blue or UV light.
Immediately down-web from PIN unit 14 is second printhead 10-2 that emits a second (preferably primary) color. Down-web from printhead 10-2 is a cure unit that emits UV light for providing a complete cure of the UV-curable inks. In one embodiment the cure unit 16 is UV arc lamp. In another embodiment the cure unit 16 is an array of LED's. An important aspect of the arrangement of printing system 2 is that a PIN unit is arranged between two printheads with respect to the media transport direction V.
Coupled to each of the modules 11 is a controller 18. Controller 18 may be a single controller or it may include multiple controllers 18. However it is to be understood that multiple controllers 18 can be coordinated to operate cooperatively based on the state of and operation of printing system 2.
Controller 18 is configured to independently control the radiative power output of PIN units 14 and cure lamp 16. When PIN units 14 and/or cure unit 16 are arrays of LED's then the radiative power can be controlled for example via PWM (pulse width modulation), or other suitable means. When cure unit 16 is a mercury lamp then the power output may be controlled for example by a shutter, or other suitable means.
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The power level and transport speed can be adjusted to achieve a desired amount flow and intermixing can of the inks to achieve the desired image quality.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
This application claims priority to U.S. Provisional Patent Application Ser. No. 61/893,773 filed Oct. 21, 2013. The entire disclosure of the above application is incorporated herein by reference.
Number | Date | Country | |
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61893773 | Oct 2013 | US |