Radiation Curable Polyurethane Coatings with Controlled Flow
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Solution Overview
Problem
Water-based polymer systems for coating applications face challenges in achieving a balance between optical properties, chemical resistance, and mechanical properties, particularly in controlling polymer flow during and after film formation, which can lead to defects and sensitivity issues.
Innovation Solution
Aqueous radiation-curable composition comprising ethylenically unsaturated polyurethanes with specific molecular weights and reactive groups, characterized by a high steady-state creep viscosity, allowing for controlled polymer flow and improved adhesion and optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high molecular weight polymers with high glass transition temperature are used for water-based coating, then the coating provides good chemical and mechanical resistance, but the polymer flow during film formation is insufficient leading to low to medium gloss and difficulty in achieving very high gloss coating with good mirror effect
Solution Approach 1:
The patent applies parameter changes by carefully adjusting the glass transition temperature (Tg) to a specific range (0°C to 20°C) and molecular weight (10,000 to 50,000 g/mol) of the polyurethane dispersion. This optimization enables the polymer to achieve sufficient flow during film formation for high gloss and mirror effect, while maintaining adequate chemical and mechanical resistance after curing. The specific parameter ranges resolve the contradiction between flowability and resistance.
2Manufacturing precision
If polymer flow is increased during film formation to achieve very high gloss coating with good mirror effect, then the optical properties are improved, but the polymer accumulates in thick layers around spray guns or on filters creating defects and cleaning problems
Solution Approach 1:
The patent optimizes the polymer flow characteristics by controlling the Tg and molecular weight parameters, achieving a balance where sufficient flow occurs during the intended film formation process without excessive accumulation on machine parts. The controlled flow reduces defects and cleaning requirements while maintaining high gloss appearance.
Solution Approach 2:
The patent utilizes the dynamic nature of polymer flow during the coating process, where the polymer exhibits appropriate flow behavior during application and film formation, then stabilizes after curing. This dynamic control allows high gloss appearance without excessive polymer migration to machine parts.
3Ease of operation
If the dry coating before cure is made less tacky to reduce sensitivity to dust pick-up and finger prints, then the handling ease is improved, but the adhesion properties may be compromised
Solution Approach 1:
The patent optimizes the Tg and composition parameters of the polyurethane dispersion to achieve a balanced surface characteristic where the coating has reduced tackiness for easier handling and reduced sensitivity to dust and fingerprints, while maintaining adequate adhesion properties through the specific polymer structure and composition.
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 a good balance of optical properties, chemical resistance, and mechanical resistance, reducing defects and sensitivity, while maintaining high gloss and hiding power, suitable for applications like wood and plastic coatings.
Implementation Method 1
radiation curable aqueous compositions based on ethylenically unsaturated polyurethanes
Data Source
AI summary
Provided in the invention is an aqueous radiation curable composition (I) comprising : - at least one ethylenically unsaturated polyurethane (A) obtained from the reaction of at least one polyisocyanate compound (Ai); at least one ethylenically unsaturated compound (Aii) containing at least one reactive group capable to react with isocyanate groups; at least one hydrophilic compound (Aiii) containing at least one reactive group capable to react with isocyanate groups and at least one other group which is capable to render the polyurethane polymer dispersible in aqueous medium as such or after the formation of a salt; optionally, at least one polyol (Aiv); optionally, at least one further compound (Av) different from the polyol (Aiv) and comprising at least one reactive group capable to react with isocyanate groups; and optionally, at least one reactive electrophilic compound (Avi); said ethylenically unsaturated polyurethane (A) preferably being characterized by a molecular weight that is above 1,000 Daltons; - at least one ethylenically unsaturated polyurethane (B), different from the polyurethane (A), obtained from the reaction of at least one polyisocyanate compound (Bi); at least one ethylenically unsaturated compound (Bii) containing at least one reactive group capable to react with isocyanate groups; optionally, at least one polyol (Biv); optionally, at least one further compound (Bv) different from the polyol (Biv) and comprising at least one reactive group capable to react with isocyanate groups; and optionally, at least one reactive electrophilic compound (Bvi); said ethylenically unsaturated polyurethane (B) preferably being characterized by a molecular weight that is below 10,000 Daltons; and optionally, at least one ethylenically unsaturated compound (C) different from (A) and (B); wherein the radiation curable composition (I) in dry form has a steady-state creep viscosity η30, expressed as the apparent viscosity after a deformation time of 30 minutes with a load σ0 = 50 Pa at 23°C, that is above 1.103 Pa.s, more preferably above 1.104 Pa.s. Compositions (I) of the invention are characterized by a n improved creep viscosity r|3oand provide polymer materials with a good flow and mirror effect. In general these materials are less sensitive to dust pick-up and fingerprints. Further provided in the invention is a one-vessel solvent free process for preparing such materials.