Chain Extended Polyurethane Dispersion for Hardness Flexibility Balance
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Solution Overview
Problem
Radiation curable polyurethane coatings face a challenge in achieving a balance between high cross-link density for hardness and resistance, and flexibility, especially for substrates like wood that require tolerance to expansion and contraction, without compromising chemical resistance or becoming brittle.
Innovation Solution
The development of chain extended polyurethane dispersions with specific polyol compositions and reaction ratios, including the use of soft linear polyols with small block lengths, acryloyl groups, and urea groups, to create coatings with improved balance of cross-link density and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If crosslink density is increased to improve hardness and resistance, then hardness and resistance are improved, but flexibility is rapidly lost
Solution Approach 1:
The patent applies parameter changes by carefully controlling the NCO to OH ratio (1.05-1.30) and the concentration of polymeric polyol (5-30 phr) to achieve an optimal crosslink density that provides both hardness and flexibility. This quantitative parameter optimization resolves the contradiction by finding the precise balance point where sufficient crosslinking provides resistance without creating excessive brittleness.
Solution Approach 2:
The patent creates a composite polyurethane system combining hard urethane/urea domains (providing hardness and resistance) with softer polyol segments (providing flexibility). The specific composition including polymeric polyol, chain extenders, and isocyanates creates a multi-phase structure that simultaneously delivers both hardness and flexibility, resolving the contradiction through material composition design.
2Ease of operation
If concentration of polymeric polyol is increased to improve flexibility, then flexibility is improved, but resistance to staining is significantly lowered
Solution Approach 1:
The patent resolves this contradiction through precise parameter control, limiting polymeric polyol concentration to 5-30 phr and NCO to OH ratio to 1.05-1.30. This optimized parameter range provides sufficient flexibility while maintaining adequate crosslink density for stain resistance, avoiding the trade-off that would otherwise exist.
Solution Approach 2:
The patent creates local quality differentiation within the coating structure, where hard crosslinked domains provide stain resistance while softer polyol-rich regions provide flexibility. This spatial differentiation of properties allows the coating to simultaneously achieve both flexibility and stain resistance without one property compromising the other.
3Strength
If number of radiation curable groups is increased to improve hardness and crosslinking, then hardness and chemical resistance are improved, but coating becomes more rigid and less flexible
Solution Approach 1:
The patent applies parameter changes by optimizing the concentration of radiation curable groups through controlled addition of (meth)acrylate compounds and by regulating the overall crosslink density via NCO to OH ratio. This quantitative control ensures sufficient chemical resistance while preventing excessive rigidity, resolving the contradiction through precise compositional tuning.
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 resulting coatings exhibit high resistance levels while maintaining flexibility, preventing brittleness and stress whitening, suitable for applications like resilient flooring that requires handling and storage on rolls at low temperatures.
Implementation Method 1
Radiation curable polyurethane dispersions (PUDs) are widely used to produce materials (such as coatings, inks, adhesives and/or composites) that are subsequently cured by radiation
Implementation Method 2
polyurethanes that have domains of hard urethane and urea moieties that are strongly bound together via hydrogen bounds
Data Source
AI summary
The present invention relates to a radiation curable aqueous coating composition comprising a dispersion of a chain extended polyurethane which dispersion comprises (a) a polyurethane-urea polymer comprising (i) acryloyl groups present in an amount of at least 2.0 mmol per g of the polyurethane-urea polymer; and (ii) urea groups present in an amount of at least 0.35 milli-equivalents (meq) per g of the polyurethane-urea polymer; (b) optionally a multifunctional ethylenically unsaturated compound unreactive towards isocyanates, in an amount, where present, of up to 40% by weight of components (a) and (b); and (c) a neutralizing agent; where the polyurethane-urea polymer (component (a)) is obtained by (I) the reaction of at least the following polyurethane precursors: at least one polyisocyanate (a1), two or more polyols (a2) and at least one isocyanate reactive compound (a3) to obtain a polyurethane prepolymer, where the isocyanate and hydroxy groups on the polymer precursors (a1), (a2) and (a3) are present in a respective mole ratio (NCO to OH) of at least 1.35, and (II) by reacting the polyurethane prepolymer with an active hydrogen chain extending compound and optionally with water to obtain the polyurethane-urea polymer (a), where (a1) the amount of polyisocyanates (a1) is from 10 to 80% by weight; (a2) the two or more polyols being an Anionic Polyol A, a Polyether Polyol B and optionally a High MW NCO-Reactive Polyol C and optionally a Low MW NCO-Reactive Polyol D; (a3) the isocyanate reactive compounds are compounds having an average of less than 1.2 groups reactive towards isocyanate and an average of at least one acryloyl group, the compounds being other than (a2A), (a2B), (a2C) and (a2D) and where the amount of isocyanate reactive compound is from 5 to 60% by weight; where the weight % of components (a1), (a2A), (a2B), (a2C), (a2D), (a3) and (b) are calculated based on the total of components (a) and (b) being 100%.