Dual-Stage UV Curing for Ink Layers
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Solution Overview
Problem
Existing energy-curable inkjet printing systems face challenges in reducing heat generation and oxygen presence at the ink surface during curing, leading to limited depth penetration and potential yellowing of the ink, especially when using UV LEDs, which complicates achieving both surface and depth curing effectively without expensive inks or complex photo-initiators.
Innovation Solution
A method involving a dual radiation approach, where a first radiation dose in the spectral range of 320-445 nm is followed by a second dose in the range of 200-319 nm, with a controlled ratio, to penetrate deeper into the ink layer, reduce surface oxygen, and enhance curing efficiency, using UV-LEDs for the first dose and mercury discharge lamps for the second, while maintaining ambient air conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If UV-LEDs are used for curing, then heat generation is reduced and lifetime is extended, but curing depth is limited and surface oxygen inhibition persists
Solution Approach 1:
The curing process is segmented into two distinct spectral stages: first UVA/UVV (320-445 nm) for deep penetration and bulk curing, then UVB/UVC (200-319 nm) for surface curing. This segmentation allows each wavelength range to address specific curing needs without the limitations of using a single light source type.
Solution Approach 2:
The invention changes the spectral parameter of the curing light by sequentially applying different wavelength ranges. The first dose uses longer wavelengths (320-445 nm) for deep penetration, then switches to shorter wavelengths (200-319 nm) for surface curing, thereby optimizing both curing depth and surface quality without yellowing.
2Manufacturing precision
If mercury bulbs are used, then curing depth is improved, but heat generation and infrared radiation increase
Solution Approach 1:
The invention extracts the beneficial UV curing wavelengths from the mercury bulb spectrum while eliminating the harmful infrared heat radiation. By using LEDs for UVA/UVV and selective mercury discharge for UVB/UVC, the system achieves deep curing without the excessive heat generation of traditional mercury bulbs.
Solution Approach 2:
The invention substitutes the thermal-mechanical curing approach of mercury bulbs with a controlled dual-stage photonic approach. Instead of relying on high-temperature infrared radiation, the system uses precisely controlled UV wavelength sequences to achieve curing without excessive heat.
3Manufacturing precision
If nitrogen blanket or temporary foils are used to reduce oxygen, then surface curing is improved, but device complexity and space requirements increase
Solution Approach 1:
The system uses the ink formulation itself (with appropriate photoinitiators) to generate the chemical environment needed for surface curing. The sequential wavelength application creates conditions where surface curing occurs effectively without requiring external nitrogen blankets or temporary foiling mechanisms.
4Object-affected harmful factors
If complex photo-initiators are used to prevent yellowing, then yellowing is reduced, but ink cost increases
Solution Approach 1:
The system performs preliminary bulk curing with UVA/UVV wavelengths before applying UVB/UVC for surface curing. This sequence ensures that the bulk ink is already cured and cross-linked before the shorter wavelengths act on the surface, preventing yellowing without requiring expensive complex photo-initiators.
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 allows for full curing of the ink layer with reduced heat generation, minimal ozone production, and less yellowing, suitable for various substrates, including heat-sensitive ones, without the need for additional components or complex ink formulations, ensuring both surface and depth curing are achieved efficiently.
Implementation Method 1
UV radiation is categorized based on the emitted wavelength... Photoinitiators distributed throughout the ink are able to capture the UV photons emitted by the bulbs. The photoinitiators decompose into free radicals when exposed to light, which promotes cross-linking at the surface of the ink layer and within the bulk of the ink layer.
Implementation Method 2
The photoinitiators decompose into free radicals when exposed to light... which promotes cross-linking at the surface of the ink layer and within the bulk of the ink layer.
Implementation Method 3
This method allows for full curing of the ink layer with reduced heat generation, minimal ozone production, and less yellowing
Data Source
AI summary
A method for curing of an actinic light sensitive ink or toner layer on a substrate includes irradiating the actinic light sensitive ink or toner layer with a first radiation dose D1 in a first spectral range between 320 nm and 445 nm, followed by a second radiation dose D2 in a second spectral range between 200 nm and 319 nm. The ratio D1/D2 of the first radiation dose and the second radiation dose is between 0.25 and 500, more preferably between 0.25 and 200, even more preferably between 0.50 and 100.