N-oxyl Radical Stabilizer for Heat Transferable Overcoat
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Solution Overview
Problem
Current heat transferable protective overcoats for images suffer from issues of light fade and iridescence, and existing solutions either compromise on gloss or are costly due to the need for UV absorbing materials and refractive index mismatch with dye receiving layers.
Innovation Solution
A heat transferable donor element coated with a polymeric binder and an N-oxyl radical light stabilizer derived from a hindered amine, which migrates to the receiver, reducing light fade and iridescence while maintaining high gloss and reducing the need for UV absorbing materials, and is manufactured at a lower cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If UV absorbing materials are used in protective overcoats, then light stability is improved, but manufacturing cost increases and the overcoat thickness must be increased which affects gloss
Solution Approach 1:
The patent extracts the UV absorption function from the protective overcoat layer and places it in a separate donor layer. This allows the overcoat to be thinner and maintain gloss while the donor layer provides UV protection, resolving the contradiction between light stability and gloss/thickness constraints.
Solution Approach 2:
The protective system is segmented into two functional layers: a donor layer containing UV absorbers and a separate protective overcoat layer. This segmentation allows each layer to be optimized independently - the donor for UV protection and the overcoat for gloss and durability, eliminating the need for thick UV-absorbing overcoats.
2Reliability
If UV absorbing materials are incorporated in the protective overcoat, then image stability is improved, but the thickness of the overcoat must be increased which causes iridescence
Solution Approach 1:
The UV absorption function is extracted from the protective overcoat and placed in the donor layer. This allows the overcoat to remain thin and avoid iridescence while still providing UV protection through the donor layer, resolving the contradiction between image stability and iridescence.
Solution Approach 2:
The system segments UV protection and protective coating functions into separate layers. The donor layer provides UV absorption without contributing to overcoat thickness, while the protective overcoat provides durability and gloss without the iridescence associated with thick UV-absorbing coatings.
3Object-affected harmful factors
If the protective overcoat is made thinner to reduce iridescence, then optical quality is improved, but light stability decreases
Solution Approach 1:
The UV absorption capability is extracted from the protective overcoat and placed in the donor layer. This enables the overcoat to be thin and free from iridescence while the donor layer compensates by providing the necessary UV protection, thus maintaining light stability without the iridescence problem.
4Object-affected harmful factors
If refractive index matching materials are used, then optical properties are improved, but material selection and manufacturing complexity increase
Solution Approach 1:
The system segments optical optimization from material formulation complexity. By separating the UV absorption function (donor layer) from the protective coating function (overcoat), the overcoat can be formulated with simple refractive index matching materials without the complexity of combining multiple functional requirements in a single 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
The solution effectively reduces light fade and iridescence, enhances gloss, and lowers production costs by eliminating the need for UV absorbing materials, while ensuring refractive index matching for improved optical properties.
Implementation Method 1
The most common approach is to filter out UV radiation since it is known that UV radiation is detrimental to the underlying colorants
Implementation Method 2
a light stabilizer that is an N-oxyl radical that is derived from a hindered amine
Implementation Method 3
Heat can be used to drive the colorants deeper into the receiver
Implementation Method 4
a heat transferable donor element comprising a polymeric support, the support having at least one portion thereof coated with a heat transferable material
Implementation Method 5
Application of a protective overcoat on these types of prints, as well as silver halide prints, is also known, and effectively reduces retransfer and discoloration by adding a protective polymeric layer over the image
Implementation Method 6
U.S. Pat. No. 5,387,573 discloses a protective overcoat including particles in an amount of up to about 75% of the thickness of the heat transferable protective overcoat. Although the particles reduce the iridescence problems
Data Source
AI summary
A heat transferable material includes a heat transferable polymeric binder and a light stabilizer that is an N-oxyl radical derived from a hindered amine, the N-oxyl radical having 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 having a molecular weight of 600 or less, is described. The heat transferable material can be in one or more sections or patches on a thermal donor element to provide a protective overcoat material. Optionally, a patch in the donor element can also include a dye. The heat transferable material provides better image stability and improved iridescence when applied to a thermal, inkjet, electophotographic, or silver halide receiver.