Curable Hot-Melt Ink Gloss Control via Thermal Cycling
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Solution Overview
Problem
Existing UV curable hot-melt ink printing processes typically produce images with a matte gloss appearance, and there is a need for higher gloss levels, particularly for applications like photographs where a more reflective and smooth finish is desired.
Innovation Solution
A method and apparatus that utilize a curable hot-melt ink comprising radiation curable compounds and a meltable hot-melt agent, which reversibly liquefies and thickens upon heating and cooling, allowing for controlled ink spreading and gloss enhancement through post-application heating before curing, using infrared radiation, and subsequent UV curing for mechanical durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the ink is allowed to cool down to thicken for controlling droplet spreading, then the droplet spreading is controlled, but the gloss level becomes low (matte appearance)
Solution Approach 1:
The ink is pre-heated before application to maintain it in a fluid state during ejection, ensuring precise droplet placement. After application, the ink is allowed to cool and thicken for spreading control, then pre-heated again before curing to restore gloss. This preliminary heating action resolves the contradiction by preparing the ink in different states at different stages of the process.
Solution Approach 2:
The ink undergoes periodic temperature changes: heated to fluid state for application, cooled to thickened state for spreading control, then heated again to restore gloss before curing. This periodic heating and cooling cycle allows the ink to alternately exhibit thickened and glossy properties, resolving the contradiction between spreading control and gloss level.
2Illumination intensity
If the ink is heated to increase gloss level, then the gloss level increases, but the droplet spreading control is disturbed
Solution Approach 1:
Heating to increase gloss is performed as a preliminary action after the ink has already been applied and thickened for spreading control. By heating after application rather than during application, the ink's spreading is already controlled, and the heating solely serves to restore gloss before curing.
Solution Approach 2:
The periodic heating cycle applies heat at specific stages: initially to maintain fluidity during ejection, then allows cooling for thickening and spreading control, and finally applies heat again to restore gloss before curing. This timing-specific periodic action ensures that heating for gloss does not interfere with spreading control.
3Ease of operation
If the ink is kept in fluid state for easy application, then the application is easy, but the droplet spreading cannot be controlled
Solution Approach 1:
The ink is preliminarily heated to a fluid state before application, making ejection and application easy. After application, the ink is allowed to cool and thicken, providing spreading control. This preliminary heating followed by cooling resolves the contradiction by having the ink in fluid state only during application, then transitioning to thickened state for control.
Solution Approach 2:
The temperature parameter is changed to control the ink's physical state: heated to high temperature for fluidity and easy application, then cooled to lower temperature for thickening and spreading control. This parameter change (temperature) allows the ink to transition between states, resolving the contradiction between ease of application and spreading control.
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 method achieves a higher gloss level and maintains it after curing, ensuring a mechanically robust and visually appealing image with controlled spreading and reduced phase separation, while maintaining the ink's mechanical durability.
Implementation Method 1
The hot-melt agent may be a meltable component, such as a organic crystalline component. The meltable component is such that the carrier composition is enabled to reversibly liquefy upon heating.
Implementation Method 2
In an embodiment, the thickener induces solidification of the carrier upon cooling of the ink to a temperature below an application temperature.
Implementation Method 3
In an embodiment heating of the ink may be carried out by providing infrared radiation to the ink.
Implementation Method 4
In a next step curing of these ink droplets is carried out by irradiating the ink droplets with UV light in order to provide a mechanically robust image.
Data Source
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Figure 3A~3B
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AI summary
In a method for applying a curable hot-melt ink the ink is applied in a fluid state on a medium, in particular a recording medium or an intermediate transfer member, on which the ink cools, thereby thickening. Then, the applied ink is at least partly heated such that the viscosity of at least a part of the ink decreases. Thereafter, the ink is cured. The method is suitable for providing a high gloss image and/or for improving an ink transfer from the intermediate transfer member to a recording medium and/or for improving an adhesion of the ink on the recording medium.