Core-Shell Security Pigment Resists Solvent Attack
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Solution Overview
Problem
Existing security pigments face challenges in protecting embedded luminescent or absorber dyes from chemical attacks, solvent migration, and environmental influences due to their porous structure, which affects their stability and longevity in applications like printing.
Innovation Solution
A core-shell particle structure is developed, where a porous polyurethane or polyurea core is coated with a dense melamine-formaldehyde resin shell, enhancing protection against solvents, acids, bases, and redox-active substances, and improving the stability of the embedded feature substances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a porous polyurethane core is used to embed feature substances, then the ease of manufacture and dispersion of feature substances is improved, but the protection against solvent attack and chemical migration deteriorates
Solution Approach 1:
The security pigment is divided into a core-shell structure with a porous polyurethane core for easy feature substance embedding and a dense polyacrylonitrile shell for solvent protection. This segmentation allows each component to fulfill its specific function optimally.
Solution Approach 2:
A dense polyacrylonitrile shell is formed around the porous polyurethane core to create a protective barrier. The shell acts as a flexible protective film that prevents solvent penetration while maintaining the structural integrity of the core.
2Reliability
If a dense shell is formed to protect against chemical attacks, then the protection against solvent migration is improved, but the manufacturing complexity increases
Solution Approach 1:
The protective shell formation is merged with the core particle synthesis process. The polyacrylonitrile shell is formed in situ around the polyurethane core during the same manufacturing process, eliminating the need for separate coating steps and reducing overall manufacturing complexity.
Solution Approach 2:
A composite core-shell structure is created combining porous polyurethane and dense polyacrylonitrile materials. This composite structure provides superior chemical resistance while maintaining manufacturability through a unified synthesis process.
3Ease of operation
If a porous structure is used for easy feature substance incorporation, then the ease of operation is improved, but the stability against environmental influences deteriorates
Solution Approach 1:
The pigment structure is segmented into a porous core for easy feature substance incorporation and a dense shell for environmental stability. This allows the core to remain accessible for manufacturing while the shell provides the necessary protective barrier.
Solution Approach 2:
Different regions of the pigment particle are given different properties: the core is porous to facilitate feature substance embedding and dispersion, while the shell is dense to provide environmental stability. Each region has optimized local quality for its specific function.
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 core-shell particle design significantly enhances the chemical resistance and stability of the security pigments, maintaining over 80% of their original luminescence or absorption intensity even after exposure to aggressive solvents and chemicals, ensuring high-level protection and longevity in printing applications.
Implementation Method 1
the condensation polymer of the outer shell is formed by an acidic condensation reaction
Implementation Method 2
the pigment is protected against migration and bleed-out. The advantage of the particles according to the invention is, among other things, that the condensation polymer of the outer shell is formed by an acidic condensation reaction, thereby creating a dense, low-porosity shell. This outer shell optimally protects the inner, porous, but easily produced polyurethane core from attack by solvents, weak acids and bases, or redox-active substances.
Data Source
AI summary
The invention relates to a security pigment comprising core-shell particles that have an organic addition polymer-based core, an organic condensation polymer-based shell, and a distinctive substance that is finely distributed or dissolved in the core, the addition polymer being a three-dimensionally cross-linked thermosetting material.