This guide is tailored for chemical engineers specializing
in ink formulation, providing insights into how industry experts measure and
evaluate these characteristics. Understanding these parameters and the methodologies used will help you make informed decisions when comparing
different products.
1. Lightfastness
Definition: Lightfastness refers to the resistance of pigments to fading or degradation when exposed to visible light and UV
radiation over an extended period.
Measurement:
Equipment Used: Xenon arc lamps, Fadeometers, and
Weatherometers are commonly used to simulate natural sunlight and UV exposure.
Procedure: Pigment samples or printed swatches are exposed
to controlled light sources, and their color change is monitored over time
using spectrophotometers.
Trustworthiness: Highly reliable, as the equipment
replicates a wide range of environmental conditions.
Measurement Location: This characteristic is typically
measured on printed swatches.
Best Practices: Ensure uniform exposure conditions and use
standardized test durations to enable consistent comparisons.
2. UV Absorption / Emission (Intensity)
Definition: This characteristic refers to the wavelength
range that pigments can effectively absorb and their absorption strength or
intensity.
Measurement:
Equipment Used: UV-Vis spectrophotometers and fluorometers.
Procedure: Pigment powders are dissolved in a suitable
solvent, and the absorption spectra are recorded. Emission spectra are measured
by exciting the pigment with a UV light source and recording the emitted light.
Trustworthiness: Spectrophotometers and fluorometers provide
precise and reproducible data.
Measurement Location: Measured on pigment powders in solution.
Best Practices: Use solvents that do not interact with the
pigments and calibrate the equipment regularly to maintain accuracy.
3. Photo-stability
Definition: Photo-stability measures the resistance of
pigments to degradation or changes caused by light exposure, including both
visible and ultraviolet radiation. It includes not only the retention of color but also resistance to photochemical degradation, molecular breakdown, loss of
functional properties, or changes in physical properties.
Measurement:
Equipment Used: Similar to lightfastness equipment – Xenon
arc lamps and Weatherometers.
Procedure: Both pigment powders and printed swatches can be exposed to light, with subsequent analysis of color retention and chemical
structure using techniques like HPLC (High-Performance Liquid Chromatography) and FTIR (Fourier Transform Infrared Spectroscopy).
Trustworthiness: Reliable with thorough testing protocols.
Measurement Location: Can be measured on both pigment
powders and printed swatches.
Best Practices: Conduct long-term studies and use multiple
analytical techniques to get a comprehensive understanding of photo-stability.
4. Chemical Resistance
Definition: This measures the resistance of pigments to
various solvents, oils, or chemicals, ensuring they maintain their integrity
and performance.
Measurement:
Equipment Used: Chemical resistance testing chambers,
solvent immersion baths, and mechanical stirrers.
Procedure: Pigment powders or printed swatches are exposed
to various chemicals. The integrity and performance of the pigments are assessed through visual inspection, weight loss measurements, and
spectrophotometric analysis.
Trustworthiness: High, with standardized test methods like
ASTM and ISO guidelines.
Measurement Location: Typically measured on printed
swatches.
Best Practices: Use a broad range of chemicals relevant to
the end-use application and adhere to standardized protocols for consistent
results.
5. Heat Resistance
Definition: Heat resistance measures the thermal stability
of pigments to maintain their performance under elevated temperatures.
Measurement:
Equipment Used: Thermogravimetric analyzers (TGA) and differential scanning calorimetry (DSC).
Procedure: Pigment powders are subjected to controlled
heating, and their weight loss and thermal transitions are recorded.
Trustworthiness: Very reliable, providing detailed
information on thermal stability.
Measurement Location: Measured on pigment powders.
Best Practices: Conduct both isothermal and dynamic heating
tests to cover a range of possible thermal conditions.
Conclusion
Understanding the characteristics of high-quality organic UV pigments and how they are measured can significantly enhance your formulation processes. By utilizing the appropriate equipment and following best practices, you can ensure that your security inks meet the highest standards of performance and durability.
