Aqueous Upconverting Inkjet Inks for Security
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Solution Overview
Problem
Existing aqueous-based upconverting inks for inkjet printers are unstable and expensive, making them unsuitable for widespread use, while ultraviolet inks are easily replicable by counterfeiters due to their widespread availability and ease of use.
Innovation Solution
A stable and cost-effective aqueous upconverting pigment dispersion is developed, using β-NaYF4 crystals doped with Er, Yb, or Tm, combined with dispersants and humectants, which is milled to achieve a stable particle size for use in inkjet printers, enhancing the ink's stability and usability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If aqueous-based upconverting inks are formulated using conventional methods, then the ink can be used in inkjet printers, but the ink exhibits poor stability and high cost
Solution Approach 1:
A dispersant is introduced as an intermediary substance to mediate between the hydrophobic upconverting pigment particles and the aqueous ink medium. The dispersant contains hydrophilic groups that interact with water and hydrophobic groups that interact with the pigment particles, enabling stable dispersion of the pigment in the aqueous medium without requiring complex formulation adjustments
Solution Approach 2:
The ink formulation uses a composite approach by combining upconverting pigment particles with a dispersant system that has both hydrophilic and hydrophobic components. This composite structure allows the hydrophobic pigment to be stably dispersed in the hydrophilic aqueous medium, resolving the incompatibility between the pigment and the ink vehicle
2Reliability
If upconverting pigment particles are dispersed in water-based systems, then the ink becomes cost-effective and stable, but the particles tend to aggregate and precipitate
Solution Approach 1:
The dispersant acts as a mediator that prevents direct interaction between water molecules and hydrophobic pigment surfaces. By forming a protective interface layer, the dispersant eliminates the aggregation tendency and maintains long-term suspension stability of the pigment particles in the aqueous medium
Solution Approach 2:
The surface properties of the pigment particles are effectively modified by the adsorption of dispersant molecules. This changes the interfacial parameters between the solid pigment and liquid medium, transforming the system from one where particles aggregate to one where particles remain stably suspended through steric or electrostatic repulsion
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 solution provides a stable and affordable aqueous-based upconverting ink that can be used in inkjet printers, effectively converting infrared light to visible light, offering enhanced security features that are less susceptible to counterfeiting.
Implementation Method 1
upconverting inks convert light in the infrared spectrum to light in the visible spectrum. For example, these upconverting inks may fluoresce at a wavelength of about 500 nm (600 THz, which is in the visible light spectrum) when illuminated by light having a wavelength of about 900 nm (331 THz, which is in the infrared spectrum)
Implementation Method 2
The upconverting pigment is a water-insoluble powder and needs to be dispersed in the aqueous system in order to be used for inkjet printing. However, the selected dispersant used increases the stability of the upconverting pigment particles in the water based system
Data Source
AI summary
An upconverting pigment dispersion includes an upconverting pigment, such as a β-NaYF4 crystal doped with at least one of Erbium, Ytterbium or Thulium. The upconverting pigment dispersion is aqueous. Upconverting inkjet ink is made by mixing the crystals with a polymer dispersant and water and milling the mixture until the crystal particles are between 50 nanometers and 200 nanometers. Deionized water, a colorant and a humectant are added to the milled mixture.