Optically Variable Laser Marking on Plastic Security Articles
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Solution Overview
Problem
Laser-inscribed security features on materials like plastics often lack visual impact and can be easily reproduced, as they typically result in black or grey coloration that is difficult to distinguish from conventional printed features.
Innovation Solution
A two-step laser inscription process is employed, using low power and low speed followed by high power and high speed irradiation, creating an optically variable appearance that changes with viewing angles without requiring additional components or equipment, and can be applied to materials not typically absorbent to laser radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional laser inscription is used on plastics material, then the material is marked with black or grey coloration, but the visual impact is poor and can be easily reproduced by photocopying
Solution Approach 1:
The patent applies parameter changes by varying laser power levels (low and high) and marking speeds (low and high) during the inscription process. This creates regions with different optical properties that interact to produce an optically variable appearance, transforming the static black/grey marking into a dynamic visual feature that changes with viewing angle.
Solution Approach 2:
The patent employs periodic action through the two-step laser inscription process, where the laser is applied in sequential passes with different parameters. The first pass creates a baseline marking, and the second pass modifies specific regions, creating a periodic pattern of optical variation that enhances both visual impact and security.
2Productivity
If laser power and marking speed are increased to improve productivity, then marking efficiency increases, but the optically variable appearance cannot be achieved
Solution Approach 1:
The patent segments the laser marking process into two distinct passes: a first pass at low power and low speed to establish baseline marking, and a second pass at high power and high speed to create the optically variable regions. This segmentation allows each pass to optimize for its specific function while achieving the overall goal of both productivity and optical variability.
Solution Approach 2:
The patent applies partial action by having the second laser pass overlap only partially with the first pass. The overlapping regions receive both low and high power irradiation, creating the optically variable effect, while non-overlapping regions receive only high power irradiation. This partial overlap strategy efficiently creates the desired visual effect without requiring excessive marking time.
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 process enhances the visual impact and security of the markings by making them difficult to reproduce, as the optically variable effect is inherent to the laser marking itself, appearing bright at some angles and dark at others, and can be applied to materials like PET that are usually transparent to laser wavelengths.
Implementation Method 1
using a laser to irradiate a first region of the security article, the laser being operated at a low power level and low marking speed; and using a laser to irradiate a second region of the security article
Implementation Method 2
the overlapping portions of the regions are marked and exhibit an optically variable appearance... its appearance (e.g. colour and/or brightness) differs depending on the angle of view
Data Source
Figure 1(a)~2
Figure 3(a)~3(b)
Figure 4(a)~4(c)
AI summary
A method is disclosed for manufacturing a security feature on a security article. The security article comprises a first layer of plastics material, and the method comprises, in any order: using a laser to irradiate a first region of the security article, the laser being operated at a low power level and low speed; and using a laser to irradiate a second region of the security article, the second region at least partially overlapping the first, the laser being operated at a higher power level and higher speed. In this way, the overlapping portions of the regions are marked and exhibit an optically variable appearance. Also disclosed is a security article comprising a first layer of plastics material exhibiting a laser marking of which at least a portion has an optically variable appearance.