Aqueous Radiation-Curable Polyurethane Coatings for Pigmented Systems
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Solution Overview
Problem
Aqueous radiation-curable polyurethane dispersions face limitations in achieving high chemical resistance and hardness in pigmented coatings due to low reactivity and sensitivity to UV light or electron beams, which hinder efficient curing and result in coatings with poor scratch resistance and the need for coalescing solvents that pose safety and environmental concerns.
Innovation Solution
Aqueous radiation-curable composition comprising high and low molecular weight ethylenically unsaturated polyurethanes, with specific reactants and process conditions to enhance chain extension and film formation, reducing the need for coalescing solvents and improving curing efficiency and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high molecular weight ethylenically unsaturated polyurethane is used to provide mechanical strength and chemical resistance, then the coating shows good mechanical and chemical resistance, but the minimum film formation temperature increases and coalescing solvents are required
Solution Approach 1:
The patent changes the molecular weight parameter by using a blend of high molecular weight polyurethane (A) and low molecular weight polyurethane (B), where polyurethane (B) has a weight average molecular weight of less than 100,000 g/mol. This parameter change allows the coating to achieve both good chemical resistance and low minimum film formation temperature without requiring coalescing solvents.
2Productivity
If low molecular weight ethylenically unsaturated polyurethane is used to reduce minimum film formation temperature and eliminate coalescing solvents, then the coating shows higher reactivity and better chemical resistance, but deep curing in pigmented coatings is inefficient
Solution Approach 1:
The patent creates a composite polyurethane system by combining high molecular weight polyurethane (A) with low molecular weight polyurethane (B) in specific ratios. This composite approach leverages the high reactivity of low molecular weight polyurethane while the high molecular weight polyurethane ensures deep curing efficiency in pigmented coatings, achieving both improved productivity and reliability.
3Strength
If high molecular weight polyurethane is used to ensure mechanical strength, then the coating shows high end hardness and scratch resistance after curing, but the reactivity decreases and chemical resistance is limited
Solution Approach 1:
The patent employs a composite polyurethane formulation where high molecular weight polyurethane (A) provides the mechanical strength and hardness, while low molecular weight polyurethane (B) contributes high reactivity. The synergistic combination allows the coating to achieve both high hardness and high reactivity, overcoming the limitation of using high molecular weight polyurethane alone.
4Manufacturing precision
If coalescing solvents are used to achieve film formation, then the coating shows uniform defect-free film, but safety and environmental issues arise due to elimination of solvents upon application
Solution Approach 1:
The patent extracts and eliminates the need for coalescing solvents by using a blend of high and low molecular weight polyurethanes that can form uniform films without them. The low molecular weight polyurethane component enables film formation without requiring external coalescing solvents, thereby removing the harmful factor while maintaining film uniformity.
Solution Approach 2:
The polyurethane blend system is self-sufficient for film formation, with the low molecular weight polyurethane component providing the necessary film-forming capability without requiring external coalescing solvents. This self-service mechanism eliminates the harmful solvents while achieving the desired film uniformity.
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 achieves high chemical resistance, mechanical strength, and flexibility in coatings, allowing for deep curing in pigmented systems without the use of coalescing agents, resulting in superior scratch resistance and reduced environmental impact.
Implementation Method 1
carbon-carbon double bonds which under the influence of irradiation and/or a (photo)initiator can undergo radical polymerization
Implementation Method 2
at least one active hydrogen-containing chain extender (Avii) capable to react with isocyanate groups and provide chain extension
Data Source
AI summary
The invention relates to radiation-curable aqueous composition comprising a high molecular weight ethylenically unsaturated polyurethane obtained from the reaction of a polyisocyanate, at least one hydrophilic compound which is capable to render the polyurethane prepolymer dispersible in aqueous medium, an ethylenically unsaturated compound containing at least two reactive groups capable to react with isocyanate groups and an active hydrogen containing chain extender and a low molecular weight ethylenically unsaturated polyurethane end-capped with an ethylenically unsaturated compound containing essentially one reactive group capable to react with isocyanate groups.