Waterborne UV Coating Viscosity Stability via pH Control
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Solution Overview
Problem
UV-curable, water-based coating compositions often exhibit poor pH and viscosity stability under alkaline conditions, leading to an undesired increase in viscosity over time due to hydrolysis of multi-functional (meth)acrylates present in these compositions.
Innovation Solution
A waterborne coating composition comprising a carrier fluid, an acid functional polymer, a neutralizing agent with a monofunctional tertiary amine having a pKa of no more than 9.5, and a hydrophobic multi-functional ethylenically unsaturated compound, which is cured using ultraviolet or electron beam radiation, maintaining viscosity stability for at least 28 days at elevated temperatures when neutralized to a pH of 7 to 9.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If UV-curable water-based coating compositions are used to achieve fast curing speed, then the curing rate is improved, but the viscosity stability under alkaline conditions deteriorates due to hydrolysis of multi-functional (meth)acrylates
Solution Approach 1:
The patent changes the pH parameter by using a buffered system that maintains pH between 7 and 9, preventing the alkaline hydrolysis that causes viscosity increase. This parameter control allows the coating to remain stable while still achieving fast UV curing
Solution Approach 2:
The patent introduces a buffer system as an intermediary that mediates between the alkaline conditions needed for application and the stability requirements. The buffer acts as a chemical mediator that maintains pH stability and prevents hydrolysis of the acrylate groups
2Reliability
If multi-functional (meth)acrylates are used in UV-curable water-based coatings to enable crosslinking, then the curing performance is improved, but the pH and viscosity stability under alkaline conditions deteriorates
Solution Approach 1:
The patent controls the pH parameter within a specific range (7-9) using a buffered system, which prevents the alkaline hydrolysis that would otherwise occur with multi-functional (meth)acrylates. This allows the coating to maintain both curing performance and stability
Solution Approach 2:
The patent creates a composite coating composition that combines UV-curable (meth)acrylate monomers with a buffered water-based system. This composite formulation allows the hydrophobic (meth)acrylates to provide crosslinking functionality while the buffered aqueous phase maintains pH stability and prevents hydrolysis
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 composition remains viscosity stable under alkaline conditions, with a viscosity increase of no more than 50% after 28 days at 49°C, ensuring consistent performance and application on heat-sensitive substrates.
Implementation Method 1
the radiation curable coating composition is cured when exposed to ultraviolet radiation or electron beam radiation
Implementation Method 2
a neutralizing agent comprising predominantly a monofunctional tertiary amine having a pK a of no more than 9.5... the neutralizing agent is present in an amount sufficient to neutralize the coating composition to a pH within the range of 7 to 9
Data Source
AI summary
Disclosed are waterborne, radiation-curable coating compositions. These coating compositions include a water-dispersible polymer and a hydrophobic multi-functional ethylenically unsaturated compound. The compositions are characterized by being viscosity stable at elevated temperatures and alkaline conditions.