UV-LED Photocuring with Dichroic Reflectors for Magnetic Particle Orientation
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Solution Overview
Problem
Existing methods for producing magnetically induced visual effects in coatings with orientable magnetic particles are not suitable for industrial printing speeds, as they often result in mechanical issues, premature drying, and thermal effects that disrupt particle orientation and cause registration problems, especially in sheet-fed processes.
Innovation Solution
A device comprising a printing unit, orientation means, and a photocuring unit that limits thermal radiation to prevent heating of the magnetic field generating elements and substrate, ensuring the magnetic particles remain oriented and the coating is partially or fully cured without thermal distortion, using a UV-LED lamp or other radiation sources with dichroic reflectors to direct UV wavelengths effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If thermal radiation energy is used for curing the coating composition, then the curing process is effective, but the magnetic field generating elements and substrate are heated causing thermal distortion and disrupting particle orientation
Solution Approach 1:
The patent applies dichroic reflectors that selectively reflect UV wavelengths while allowing other wavelengths to pass through or be absorbed. This creates a localized UV field for curing without heating the magnetic field generating elements, as the thermal radiation at other wavelengths does not contribute to the curing process but would cause heating. The reflectors are positioned to direct UV energy precisely where needed while protecting sensitive components from thermal effects.
Solution Approach 2:
The dichroic reflectors act as an intermediary between the radiation source and the coating composition. They selectively transmit UV radiation needed for curing while blocking or redirecting thermal radiation that would cause heating. This intermediary component enables the separation of the curing function from the heating effect, allowing effective curing without thermal distortion of the magnetic particles or substrate.
2Manufacturing precision
If the coating is cured quickly to preserve particle orientation, then the orientation is maintained, but industrial printing speeds cannot be achieved
Solution Approach 1:
The patent employs a continuous UV-LED irradiation system that cures the coating composition as it passes through the printing apparatus. The UV-LED lamps are positioned to provide continuous curing along the printing path, allowing the coating to be cured progressively without interrupting the printing process. This continuous action enables both high printing speeds and complete curing to preserve particle orientation.
Solution Approach 2:
The patent uses UV-LED technology which emits UV radiation at specific wavelengths optimized for photopolymerization. By changing the spectral parameters of the radiation source to match the absorption characteristics of the coating's photoinitiators, the curing efficiency is dramatically increased. This allows rapid curing at industrial printing speeds while maintaining particle orientation, as the UV-LEDs provide high energy density at the required wavelengths without excessive heat generation.
3Productivity
If high energy radiation is used for curing, then the curing speed increases, but thermal radiation heats the substrate and causes misalignment
Solution Approach 1:
The dichroic reflectors create a localized UV radiation field that concentrates curing energy precisely on the coating composition while allowing thermal radiation to pass through or be directed away from the substrate. This spatial and spectral localization enables high-speed curing without heating the substrate, as the UV energy is confined to the coating layer where it is needed for curing.
Solution Approach 2:
The patent replaces traditional thermal curing methods with UV-LED photopolymerization. Instead of using heat (thermal energy) to cure the coating, UV radiation (electromagnetic energy) is used to initiate photopolymerization reactions. This substitution eliminates the thermal heating problem while maintaining effective curing, as the UV-LEDs provide high energy density for rapid curing without the thermal side effects of conventional heating methods.
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 solution allows for precise orientation and curing of magnetic particles at industrial printing speeds, reducing mechanical and thermal issues, maintaining image sharpness and preventing misalignment, while keeping the magnetic field effects stable and preserving the visual effects intended.
Implementation Method 1
The orientation means comprises at least one magnetic field generating element for orienting the magnetic particles in the coating composition of the printed image
Implementation Method 2
The photocuring unit comprises a radiation source arranged with respect to the orientation means so as to irradiate the image printed on the first side of the substrate to at least partially cure the coating composition
Data Source
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AI summary
The invention relates to a device, system and method for producing magnetically induced visual effects in coatings, particularly security or decorative features, containing orientable magnetic particles. The device comprises a printing unit, an orientation means, a substrate-guiding system and a photocuring unit. The printing unit is arranged to print with the coating composition an image on a first side of a substrate. The orientation means comprises a magnetic field generating element for orienting the magnetic particles in the coating composition of the printed image. The substrate-guiding system is arranged to bring and hold the substrate in contact with the orientation means. The photocuring unit irradiates the image printed on the substrate to at least partially cure the coating composition of the image while the substrate is still in contact with the orientation means. The photocuring unit is configured such that its emission of thermal radiation energy is such limited as to not heat the orientation means to an average temperature T1 exceeding 100°C.