Laser Curing of Magnetic Flakes for High-Speed Security Printing
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Solution Overview
Problem
Existing methods for producing optically variable devices with magnetic pigments are not suitable for high-speed printing processes and often fail to create noticeable security features, as they rely on bulky UV lamps that cannot selectively cure flakes in a binder within adjacent regions on a moving substrate.
Innovation Solution
A high-speed system using a laser to selectively cure magnetically aligned flakes in a UV curable binder on a moving substrate, where the laser beam is directed across the substrate in a manner that aligns and fixes the flakes in specific patterns, allowing for the creation of distinct visible regions with different alignments, and a second magnetic field is used to realign and cure remaining flakes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If bulky UV lamps are used to cure magnetically aligned flakes, then the flakes can be cured in the binder, but the system cannot operate at high speed and cannot selectively cure adjacent regions
Solution Approach 1:
The patent replaces the mechanical UV lamp curing system with a laser-based curing system. The laser beam can be precisely directed and scanned across the substrate, enabling selective curing of specific regions containing magnetically aligned flakes. This substitution allows for high-speed operation because the laser can quickly move between regions and cure only where needed, rather than requiring a bulky UV lamp to illuminate and cure entire areas sequentially.
Solution Approach 2:
The laser curing system enables local quality by allowing different regions of the substrate to be cured selectively. The laser beam can be directed to cure specific adjacent regions with magnetically aligned flakes while leaving other regions uncured or differently cured. This creates distinct visible regions with different alignments and optical properties, enhancing the security feature visibility and allowing for complex multi-region designs in a single high-speed printing pass.
2Illumination intensity
If magnetic pigments are used to create optically variable features, then color-shifting effects are achieved, but the features are not noticeable under uniform fluorescent lighting
Solution Approach 1:
The patent applies local quality by creating distinct regions with different magnetic flake alignments through selective laser curing. Some regions are cured with flakes aligned in one orientation while adjacent regions have flakes aligned differently or remain uncured. This creates visible contrast between regions under various lighting conditions, including uniform fluorescent lighting, making the security features noticeable without requiring specific lighting angles or intensities.
Solution Approach 2:
The patent utilizes color changes through the magnetic flakes' optical properties. The magnetically aligned flakes in different regions reflect and refract light differently based on their alignment, creating color-shifting effects and visual contrast between cured and uncured regions. This enhances the visibility of security features under various lighting conditions by creating inherent optical differences in the printed regions themselves.
3Productivity
If the substrate moves at high speed through the curing station, then productivity increases, but the magnetic alignment of flakes cannot be maintained
Solution Approach 1:
The patent applies preliminary action by first applying the magnetic field to align the flakes in the binder before the laser curing process. The magnetic flakes are oriented in the desired pattern while the binder is still in a liquid state and the substrate is moving at high speed. Once the alignment is achieved, the laser immediately cures the binder in place, freezing the flake positions. This sequence of preliminary alignment followed by immediate curing maintains flake alignment stability even at high processing speeds.
Solution Approach 2:
The patent replaces the traditional sequential process (align then cure with UV lamp) with a synchronized laser curing system. The laser beam can be precisely controlled to cure regions immediately after magnetic alignment, maintaining the alignment stability. The laser's rapid response time and precise positioning capability allow the system to operate at high substrate speeds while maintaining flake alignment, unlike bulky UV lamps that require longer exposure times and cannot keep up with high-speed production.
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
Enables high-speed inline printing and painting with reoriented magnetic flakes, producing noticeable optically variable security features by selectively curing specific regions of the substrate, maintaining alignment and preventing disorientation, thus enhancing the visibility of security features on financial documents and other products.
Implementation Method 1
irradiating with one or more laser beams in one or more sub-regions of the first region of aligned flakes so as to cure the binder
Implementation Method 2
applying a magnetic or electric field so as to orient at least some of the flakes within the coating
Data Source
AI summary
A scanning laser having a wavelength compatible with a coating binder so as to cure it as the laser scans and irradiates the coating on a moving web. A system and method for curing flakes by providing a scanning laser which scans across a moving coated substrate in a magnetic field allows images to be formed as magnetically aligned flakes are cured into a fixed position. The images have regions of cured aligned flakes. The scanning laser cures the magnetically aligned flakes within it region it irradiates. Alternatively an array of lasers can be used wherein individual lasers can be switched on and off to fix irradiated coating as a moving web is moved at a high speed.