Three-Stage UV Ink Curing to Reduce Packaging Migration
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Solution Overview
Problem
Existing methods for curing UV-curable inks often result in insufficient cross-linking, leading to the migration of low molecular weight ink components into packaging products, which can be hazardous, and require costly inert gas environments for complete curing.
Innovation Solution
A three-step curing process involving pre-curing under ambient air, intermediate curing under inert gas or oxygen-reduced air, and post-curing under ambient air, eliminating the need for inert gas in all but the intermediate step, thereby reducing migration and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If UV curing is performed under inert gas to prevent migration of low molecular weight ink components, then migration is reduced, but installation space and costs increase
Solution Approach 1:
The curing process is divided into three distinct stages: pre-curing under ambient air, intermediate curing under inert gas, and post-curing under ambient air. This segmentation allows the system to use inert gas only for the intermediate stage where it is most critical for preventing migration, while avoiding the need for inert gas throughout the entire process, thereby reducing installation space and operational costs.
Solution Approach 2:
The pre-curing stage performed under ambient air before the intermediate curing stage serves to partially polymerize the ink and reduce its reactivity. This preliminary action reduces the overall curing time and UV energy required in subsequent stages, making the use of inert gas more efficient and reducing the total installation space needed for the curing system.
2Object-affected harmful factors
If ink is formulated with higher molecular weight to reduce migration, then migration is reduced, but ink viscosity increases and printing problems occur
Solution Approach 1:
The invention changes the chemical environment parameters during curing by introducing inert gas in the intermediate stage. This parameter change (atmospheric composition) allows the ink to cure sufficiently without requiring higher molecular weight formulations, thereby maintaining good flow properties and printability while preventing migration of low molecular weight components.
3Object-affected harmful factors
If complete UV curing is performed to prevent migration, then migration is prevented, but curing time and energy consumption increase
Solution Approach 1:
By segmenting the curing process into three stages with different atmospheric conditions, the system achieves complete curing more efficiently. The pre-curing stage under ambient air quickly establishes a polymer network, the intermediate stage under inert gas prevents migration without requiring extended curing time, and the post-curing stage under ambient air completes the polymerization. This segmentation reduces total curing time compared to a single-stage approach.
Solution Approach 2:
The alternating atmosphere conditions (ambient air - inert gas - ambient air) create a periodic curing action that enhances efficiency. Each stage builds upon the previous one, with the inert gas stage being brief and targeted, thereby reducing overall energy consumption and curing time while ensuring complete polymerization and migration prevention.
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 effectively hardens UV-curable inks, reducing unwanted migration of low molecular weight components and improving print quality while minimizing installation space and costs.
Implementation Method 1
The curing of UV-curable inks can be carried out in several steps, for example, first a so-called pinning (pre-curing) and then a final curing
Implementation Method 2
the ink is further cured by means of at least one second UV lamp of a UV dryer not under ambient air, but under inert gas, under inert gas-enriched air or under oxygen-reduced air
Data Source
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AI summary
A method according to the invention for curing ink on a substrate, wherein at least one UV-curable ink is applied in the form of drops to a substrate (2) and is exposed to UV radiation by means of at least one first UV lamp (5) and thereby pre-cured, is characterized in that the ink is further cured by means of at least one second UV lamp (11, 11a, 11b) of a UV dryer (10) under inert gas, under inert gas-enriched air or under oxygen-reduced air, and that the ink is subsequently post-cured by means of at least one third UV lamp (21, 21a, 21b, 31, 31a, 31b) of a further UV dryer (20, 30). The invention makes it possible to sufficiently harden UV-curable inks, so that unwanted migration of low molecular weight ink components is reduced or avoided.