Inkjet Printing on Pre-Printed Substrates with Wetting Mismatch
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Solution Overview
Problem
Inkjet printing on pre-printed substrates, particularly those with offset or flexographic ink, results in differential ink spread causing visible image quality defects due to differences in surface wetting properties.
Innovation Solution
A method involving a printing machine with both a first printing unit and an inkjet unit, where contiguous inkjet dots are printed at locations with similar surface wetting properties, and additional steps such as raster image data adjustment, coating application, and specific inkjet printing strategies are employed to minimize ink spread variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If inkjet printing is performed on pre-printed substrate areas with offset or flexographic ink, then variable information and special visual effects can be achieved, but differential ink spread occurs causing visible image quality defects
Solution Approach 1:
The patent applies local quality by classifying the substrate surface into different wetting property zones (first wetting property areas with offset/flexographic ink and second wetting property areas without ink) and printing inkjet dots only on areas with matching wetting properties. This ensures that inkjet ink is applied locally to areas where it will spread predictably, preventing the differential spread that causes image defects while still allowing variable information to be overlaid on the static background.
2Area of stationary object
If inkjet dots are printed on areas with different surface wetting properties, then complete coverage can be achieved, but ink spread varies causing image quality defects
Solution Approach 1:
The patent changes the parameter of surface wetting property matching by selecting dot locations based on the wetting property of the underlying area. Instead of printing inkjet dots on all areas regardless of wetting properties, the system modifies the printing parameters to print only on areas with the second wetting property (no pre-printed ink) or specifically matched wetting properties, thereby ensuring consistent ink spread behavior across all printed areas.
3Adaptability or versatility
If raster image areas are used for inkjet overprinting, then combined printing functionality is achieved, but differential spread occurs on heterogeneous surfaces
Solution Approach 1:
The patent addresses the heterogeneous surface problem by applying local quality principles: it identifies and classifies different areas of the raster image based on their wetting properties, then applies inkjet printing only to areas with compatible wetting characteristics. This local matching approach eliminates the harmful differential spread effect while preserving the ability to perform combined offset/flexographic and inkjet printing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method effectively prevents and corrects differential ink spread, ensuring consistent image quality by ensuring all inkjet dots are printed on areas with matching surface wetting properties, thereby improving the appearance of the final printed product.
Implementation Method 1
an inkjet printing unit is provided. The substrate is moved through the printing machine. A raster image consisting or formed of image dots is printed on the substrate at a first moment using at least the first printing unit. At least one contiguous area of inkjet dots in the raster image is printed at a second moment after the first moment using the inkjet printing unit
Implementation Method 2
A difference in spread characteristics of ink for inkjet printing on certain papers, notably gloss papers, and pre-printed offset ink has been observed. A differential spread of ink on a heterogeneous surface can cause serious, in particular visible image quality defects
Data Source
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AI summary
A method of printing an image on a substrate in a printing machine comprising at least a first printing unit and an inkjet printing unit is described. The substrate is moved through the printing machine. A raster image consisting of image dots is printed on the substrate at a first moment using at least the first printing unit (34). At least one contiguous area of inkjet dots in the raster image is printed at a second moment after the first moment using the inkjet printing unit (38), whereby substantially all inkjet dots forming the contiguous area are printed at dot locations having similar surface wetting properties.