Aqueous Polymer Dispersion with TEMPO for UV-Durable Coatings
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Solution Overview
Problem
Existing aqueous polymer dispersions used in exterior coatings lack sufficient durability, as inorganic pigments like TiO2, when exposed to sunlight, can adversely affect coating longevity, and current photo-stabilizers and photo-antioxidants contribute to VOC emissions when dissolved in organic solvents.
Innovation Solution
An aqueous polymer dispersion comprising 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and/or its derivatives combined with a specific emulsion polymer containing ethylenically unsaturated ionic, photosensitive, and nonionic monomers, which provides improved durability through enhanced gloss retention after prolonged UV exposure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If inorganic pigments like TiO2 are used in exterior coatings, then coating opacity and coverage are improved, but coating durability deteriorates due to photo-induced damages from sunlight exposure
Solution Approach 1:
The patent introduces photo-stabilizers and photo-antioxidants as intermediary substances that mediate between the inorganic pigment and sunlight. These additives absorb or scavenge harmful UV radiation and free radicals, protecting the pigment and coating matrix from photo-induced degradation while maintaining the pigment's opacity-enhancing function.
Solution Approach 2:
The patent creates a composite coating system combining inorganic pigments with organic photo-stabilizing additives. This composite approach allows the inorganic pigment to provide opacity while the organic additives provide UV protection, achieving both high coverage and improved durability simultaneously.
2Reliability
If photo-stabilizers are added to coatings to improve durability, then coating durability is improved, but VOC emissions increase due to dissolution in organic solvents
Solution Approach 1:
The patent replaces the traditional organic solvent-based dissolution method with an aqueous dispersion system. Instead of dissolving photo-stabilizers in organic solvents (which releases VOCs), the photo-stabilizers are dispersed in water, eliminating VOC emissions while maintaining the photo-stabilizing function and improving coating durability.
3Object-generated harmful factors
If conventional aqueous polymer dispersions are used in exterior coatings, then VOC emissions are reduced, but coating durability remains insufficient after prolonged UV exposure
Solution Approach 1:
The patent modifies the chemical composition parameters of the aqueous polymer dispersion by incorporating specific photo-stabilizing additives (TEMPO derivatives and other photo-active compounds) into the polymer matrix. This parameter change enables the aqueous system to provide both low VOC emissions and enhanced UV resistance, achieving superior durability compared to conventional aqueous dispersions.
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 described aqueous polymer dispersion achieves higher 60° gloss retention after 1650 hours of QUV testing, significantly outperforming incumbent formulations, with coatings demonstrating improved durability and reduced VOC emissions.
Implementation Method 1
They protect coatings against photo-induced damages by absorbing the harmful actinic solar radiation and transforming the absorbed radiation energy into less harmful thermal energy via a photophysical process involving ground state and excited state molecules.
Implementation Method 2
the emulsion polymer comprises as polymerized units... (b) from 5% to 90% by weight of a photosensitive monomer
Data Source
AI summary
An aqueous polymer dispersion and an aqueous coating composition comprising the aqueous polymer dispersion that provides coatings with improved durability.