Electrowetting Moisture Applicator for Inkjet Substrate Curl Control
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Solution Overview
Problem
Inkjet printing systems face the issue of substrate curling due to the absorption and subsequent drying of aqueous inks, leading to shrinkage and unevenness, which affects the flatness and desirability of printed substrates.
Innovation Solution
A moisture applicator with hydrophobic and hydrophilic tile segments, controlled by an electrical switching network, is integrated into the printing system to selectively apply moisture to the substrates, counteracting curling by adjusting the hydrophilicity of the segments based on ink coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If aqueous ink is applied to the substrate and then dried, then the ink image is formed on the substrate, but the substrate curls due to shrinkage from moisture loss
Solution Approach 1:
The moisture applicator applies moisture to the substrate in advance (after printing but before final drying) to counteract the shrinkage and curling that would otherwise occur during the drying process. This preliminary anti-action prevents the harmful curling effect before it fully manifests.
Solution Approach 2:
The system changes the moisture content parameter of the substrate by applying controlled amounts of moisture through the moisture applicator. This parameter change compensates for the moisture loss during drying and prevents the dimensional changes that cause curling.
2Reliability
If the substrate is dried to remove ink solvents, then the ink image is set, but the substrate shrinks and becomes uneven
Solution Approach 1:
The moisture applicator performs a preliminary action of adding moisture back to the substrate after the ink has been printed and initially dried. This preliminary moisture restoration prevents the dimensional instability that would otherwise occur during complete drying.
Solution Approach 2:
The system converts the harmful effect of moisture loss (which causes shrinkage and unevenness) into a benefit by deliberately controlling the moisture content through the moisture applicator. The moisture that would otherwise be lost is now controlled to maintain dimensional stability while still allowing the ink to set.
3Manufacturing precision
If moisture is applied to the substrate to reduce curling, then substrate flatness is improved, but the drying process becomes more complex
Solution Approach 1:
The moisture applicator acts as an intermediary device between the printing and drying processes. It applies moisture in a controlled manner without requiring complex modifications to the drying system itself, thereby improving flatness while maintaining relatively simple drying system architecture.
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
The solution effectively reduces substrate curling by managing moisture distribution, maintaining substrate flatness and original size, even after drying, without significant increases in drying complexity or temperature.
Implementation Method 1
each tile segment being configured to be hydrophobic when not electrically biased and to be hydrophilic when electrically biased
Data Source
AI summary
An aqueous ink printer includes a moisture applicator that applies moisture to a side of a substrate that is opposite a side that bears or will bear an ink image. The moisture applicator includes a switching network that is configured to independently and selectively bias the tile segments electrically. The tile segments contiguously cover a surface of the roller. As the switching network is operated to electrically bias the tile segments using data corresponding to the ink image, they transition from being hydrophobic to hydrophilic so the electrically-biased hydrophilic tile segments attract moisture from water in a trough or from water vapor produced by an ultrasonic transducer in the trough. The moisture is carried by the electrically-biased tile segments to the substrate at areas where the amount of ink in a portion of the substrate on the other side of the substrate exceeds a predetermined ink coverage threshold.