N-oxyl Radical Light Stabilizer for Thermal Dye Image Stability
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Solution Overview
Problem
Current heat transferable dye donor elements do not provide sufficient image stability, particularly for cyan dye images, due to susceptibility to light fade and retransfer, and existing light stabilizers may have environmental concerns or inadequate stability.
Innovation Solution
A heat transferable dye donor element incorporating a polymeric support coated with a heat transferable material containing an N-oxyl radical derived from a hindered amine as a light stabilizer, which migrates to the dye receiver element, reducing light fade and eliminating the need for UV absorbing materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional light stabilizers (nickel complexes or alkoxy-substituted aromatic stabilizers) are used in thermal dye donor elements, then some level of light stability is achieved, but environmental harm is caused or adequate light stability is not provided for all dyes
Solution Approach 1:
The patent replaces persistent environmental contaminants (nickel complexes) with readily biodegradable hindered amine light stabilizers (HALS) that have molecular weights of 600 or less. These HALS compounds are designed to be effective at lower concentrations and are environmentally benign, eliminating the harmful effects of heavy metal stabilizers while maintaining adequate light stability for cyan and other dyes.
Solution Approach 2:
The invention changes the molecular weight parameter of light stabilizers to 600 or less, which enables these stabilizers to migrate effectively from the donor element to the receiver element during thermal transfer. This parameter change also allows the stabilizers to be incorporated into the dye layer without causing environmental harm, while still providing adequate light stability.
2Reliability
If UV absorbing compounds are incorporated in the protective overcoat to provide improved light stability, then light fade is reduced, but production costs increase and environmental impact worsens
Solution Approach 1:
The patent extracts the light stabilizing function from the protective overcoat layer and relocates it to the dye layer through the use of migratory HALS compounds. This eliminates the need for UV absorbing compounds in the overcoat, reducing material costs and environmental impact while maintaining light stability through the HALS that migrate with the dye during thermal transfer.
3Reliability
If light stabilizers are incorporated within the receiver element through thermal extrusion at 250°C or higher, then image stability is improved, but only stabilizers with very high thermal stabilities can be used
Solution Approach 1:
The patent applies light stabilizers to the donor element before the thermal transfer process, allowing the stabilizers to be incorporated into the dye layer along with the dye itself during the transfer. This preliminary action eliminates the need for high-temperature thermal extrusion of stabilizers into the receiver element, enabling the use of HALS with molecular weights of 600 or less that would decompose at extrusion temperatures.
Solution Approach 2:
The donor element acts as an intermediary carrier that transports both the dye and the light stabilizer from the manufacturing stage to the receiver element. The stabilizer is incorporated into the donor element's dye layer, migrates during thermal transfer, and ends up in the receiver element's image layer, bypassing the need for high-temperature extrusion processing.
4Manufacturing precision
If colorants remain at the surface of the receiver element to allow for image formation, then image quality is achieved, but susceptibility to retransfer and discoloration increases
Solution Approach 1:
The HALS compounds incorporated in the dye layer provide self-service light protection directly where the dye resides on the receiver element surface. The stabilizers migrate with the dye during thermal transfer and remain co-located in the image layer, providing localized protection without requiring a separate protective overcoat layer, thus maintaining image quality while improving stability.
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 N-oxyl radical light stabilizer effectively enhances the light stability of transferred dye images, particularly for cyan dyes, while reducing production costs and environmental impact by minimizing the use of UV absorbing compounds.
Implementation Method 1
heat transferable material comprising a heat transferable dye and an N-oxyl radical as a light stabilizer
Implementation Method 2
which N-oxyl radical... migrates to the dye receiver element
Implementation Method 3
N-oxyl radical... provides improved dye image stability... reducing light fade
Implementation Method 4
The light stabilizers must be incorporated within the receiver element in such a manner that they will react with the colorants
Data Source
AI summary
A heat transferable dye donor element includes a heat transferable dye and an N-oxyl radical light stabilizer that is derived from a hindered amine. The N-oxyl radical has the following formula,wherein R1, R2, R5, and R6 are each independently selected from a straight or branched C1-C6 alkyl, and R3 and R4 are each independently selected from H, OH, OR, COOH, or COOR, wherein R is a straight or branched C1-C6 alkyl or alkene, and has a molecular weight of 600 or less. The dye donor element includes a heat transferable material that can be in one or more sections or patches including heat transferable dye patches. The heat transferable material provides better dye image stability when applied to a thermal receiver element.