Laser Window Production in Banknote Security Threads
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Solution Overview
Problem
Existing security documents, such as banknotes, lack the ability to produce windows for security threads with complex shapes and 'islands of paper' that can enhance forgery protection, as conventional methods restrict design freedom and cannot create paper islands within window threads.
Innovation Solution
A method involving a laser beam that removes specific areas of a substrate to create windows up to a reflector layer, allowing for attractive and register-accurate effects, and enabling the production of complex window shapes with 'islands of paper' by directing the laser onto the front side of a substrate with a security element, ensuring the security element remains embedded and visible.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If windows for security threads are produced by applying watermarks to the paper wire during paper production, then the security threads can be embedded in the paper, but the shape of the windows is already defined and cannot be subsequently changed, restricting design freedom
Solution Approach 1:
The window production process is segmented into two independent stages: (1) watermark application during paper production to create the basic window structure, and (2) subsequent laser processing to modify the window shape and create complex designs including islands of paper. This segmentation allows each stage to optimize for its specific function, achieving both manufacturing ease and design freedom.
Solution Approach 2:
The watermark is applied in advance during paper production to establish the initial window structure and security thread embedding. This preliminary action prepares the substrate for subsequent laser processing, enabling complex shape modifications without compromising the embedded security thread's integrity or connection to the substrate.
2Adaptability or versatility
If conventional watermark methods are used to create windows, then security threads can be embedded, but islands of paper cannot be left within the windows
Solution Approach 1:
The conventional mechanical watermarking process is supplemented with laser processing, which uses optical energy to precisely remove or retain paper in specific areas. This substitution enables the creation of islands of paper and complex window shapes that cannot be achieved with mechanical watermarking alone, while maintaining precise control over the final window geometry.
3Manufacturing precision
If laser radiation is used to remove paper from the front side up to the reflector coating, then attractive and register-accurate effects can be created, but the process requires precise control
Solution Approach 1:
The reflector coating serves as an intermediary layer that reflects laser radiation back through the paper being processed. This reflection mechanism enables precise control of the laser ablation depth, ensuring that paper removal stops exactly at the desired location without penetrating through the substrate, thereby achieving high register accuracy while managing the complexity of the laser processing system.
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 enhances forgery protection by allowing flexible design of window threads and creating tactile 'islands of paper' that are securely connected to the substrate, providing additional security features and attractive visual effects.
Implementation Method 1
a laser beam is directed onto the front side of the substrate, wherein the laser beam removes at least a first partial area of the substrate, which is located between the front side of the substrate and the reflector layer
Implementation Method 2
a reflector layer that reflects laser beams is at least partially introduced into the substrate or applied to the back of the substrate
Data Source
Figure 1~3
Figure 4~5
Figure 6a~7c
AI summary
The invention relates to a method for producing a security document, in particular a banknote, wherein a paper substrate is first provided, having a front side and a back side opposite the front side. In a region of the substrate, a security element consisting of at least one reflective layer that reflects laser beams is at least partially embedded in the substrate or applied to the back side of the substrate. According to the invention, a laser beam (5) is directed onto the front side of the substrate (1), wherein the laser beam (5) removes at least a first partial region of the substrate (1) located between the front side of the substrate and the reflective layer (2), so that at least one window is formed on the front side of the security element (4) extending to the reflective coating (2).The laser beam (5) thus exposes at least part of the front of the safety element (4), so that the safety element (4) becomes visible through the window.