Multilayer Embossing Lacquer for Security Paper
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Solution Overview
Problem
Conventional multilayer systems for security elements, such as security papers and documents, face challenges in achieving optimal flexibility, metallizability, and releasability due to the need for thick embossable layers, which compromise durability and adhesion, and often result in brittleness and poor corrosion resistance.
Innovation Solution
A method involving a multilayer embossing lacquer applied without complete intermediate drying, allowing for embossing and subsequent full hardening, where each layer is optimized for specific properties like release, flexibility, and scratch resistance, with diffusion-driven mixing at interfaces enhancing adhesion, and allowing embossing across multiple layers to avoid thickness limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thick embossable layer is used to compensate for tool irregularities, then embossing quality is improved, but flexibility and metallizability deteriorate
Solution Approach 1:
The coating is divided into multiple functional layers: a first layer providing flexibility and metallizability, a second embossable layer compensating for tool irregularities, and optionally a third layer for additional protection. This segmentation allows each layer to optimize its specific function without compromising overall performance.
Solution Approach 2:
The patent uses composite multilayer coating structures combining different material properties. The first layer may contain flexible polymers and metallization promoters, while the second layer provides embossing compensation, creating a composite system that achieves both flexibility and embossing quality simultaneously.
2Reliability
If a thick embossable layer is used to ensure adhesion, then interlayer adhesion is improved, but flexibility and release properties deteriorate
Solution Approach 1:
Adhesion is achieved through multiple thin layers with graded properties rather than a single thick layer. The first layer provides strong substrate adhesion, while the second layer provides embossing compensation, distributing the adhesion function across layers to maintain flexibility.
Solution Approach 2:
The patent optimizes layer thickness parameters and material composition parameters to achieve sufficient adhesion with thin layers. By controlling crosslinking density and surface energy parameters, strong adhesion is obtained without requiring thick layers that would compromise flexibility.
3Adaptability or versatility
If multiple layers are applied successively with intermediate curing, then each layer can be optimized, but production time and complexity increase
Solution Approach 1:
The patent combines multiple coating applications and curing steps into integrated processes. Multiple layers can be applied in sequence with minimal drying time between layers, and curing can be performed continuously, merging what would traditionally be separate discrete operations into a streamlined production process.
4Adaptability or versatility
If a highly flexible lacquer formulation is used, then flexibility is improved, but metallizability and release properties deteriorate
Solution Approach 1:
Flexibility is concentrated in the first layer which is specifically formulated with flexible polymers, while subsequent layers are optimized for metallizability and embossing. This segmentation allows the flexible layer to provide flexibility without interfering with the manufacturing properties of other layers.
Solution Approach 2:
Different regions of the coating system have different local properties: the first layer has high flexibility and metallizability, the second layer has high embossability. Each layer is locally optimized for its specific function, allowing the overall system to achieve properties that would be contradictory in a single uniform layer.
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 approach results in improved mechanical resistance, sweat resistance, and interlayer adhesion, enabling the production of security elements with enhanced durability and flexibility without compromising overprintability, and allows for a single-step curing process, reducing costs and time.
Implementation Method 1
diffusion-driven mixing at interfaces enhancing adhesion
Implementation Method 2
curing the coating. In this context, the term 'optically variable structure' encompasses not only holograms but also hologram-like diffraction structures
Data Source
Figure 1~3
AI summary
The invention relates to a method for producing a security element for a security paper, a document comprising a substrate (10), wherein the substrate (10) is at least partially provided with a coating (11) comprising at least two layers (1, 2). The method comprises the steps of applying a first layer (1) to the substrate (10), applying at least one second layer (2) to the first layer (1), wherein the first layer (1) is not fully cured before the application of the second layer (2), embossing at least one layer of the coating (11), and curing the coating (11).