High-Solids Coating Composition Using Silane-Modified Isocyanate
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Solution Overview
Problem
Coating compositions for automotive refinish require high solids content and low solvent content to maintain flow and topcoat holdout while ensuring effective curing and good surface properties, but existing technologies face challenges in achieving these conditions without compromising optical quality or increasing viscosity.
Innovation Solution
Development of coating compositions based on aprotic solvents, including oligomeric and/or polymeric hydroxyl-containing compounds and isocyanate-group-containing compounds with silane groups, specifically using uretdione groups and linear aliphatic diisocyanates to create high-solids solutions with improved surface properties and curing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the nonvolatile fraction is increased to reduce solvent content, then environmental compliance and solids content are improved, but viscosity increases and fluidity deteriorates
Solution Approach 1:
The invention changes the chemical composition parameters by introducing silane-modified isocyanate compounds with specific molecular structures that have lower inherent viscosity. This allows increasing the nonvolatile fraction from 60% to over 70% while maintaining acceptable fluidity through molecular-level parameter optimization rather than macroscopic formulation adjustments
Solution Approach 2:
The invention creates a composite coating system combining hydroxyl-containing polymers with silane-modified isocyanate crosslinkers. This composite approach allows the system to achieve high solids content while the silane groups provide chain flexibility that counteracts viscosity increase, maintaining workability despite high nonvolatile fraction
2Quantity of substance
If the nonvolatile fraction is increased to reduce solvent content, then environmental compliance is improved, but flow properties deteriorate
Solution Approach 1:
The invention modifies the molecular parameters of the isocyanate component by incorporating silane groups that alter the polymer chain conformation and intermolecular interactions. This parameter change enables high nonvolatile fraction while maintaining smooth flow characteristics and preventing defects like orange peel or runs during application
3Ease of operation
If the viscosity is reduced by lowering curing agent viscosity, then fluidity is improved, but physical film formation deteriorates
Solution Approach 1:
The invention uses a composite curing agent system where silane-modified isocyanates provide both low viscosity for good fluidity and reactive silane groups that ensure reliable physical film formation through condensation crosslinking. The silane functionality compensates for any film formation issues that might arise from lower viscosity curing agents
4Reliability
If the reaction time is extended to improve curing, then cure completeness is improved, but productivity decreases
Solution Approach 1:
The invention changes the chemical reactivity parameters by introducing silane groups that enable dual-crosslinking mechanisms (isocyanate-polyol and silane-condensation). This parameter change accelerates overall cure kinetics, achieving complete curing faster than conventional systems, thus improving both cure completeness and productivity simultaneously
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 coating compositions achieve effective curing, high acid resistance, and excellent surface properties, including low long-wave measurement values, while maintaining good flow and topcoat holdout, even at high film thicknesses, and are environmentally friendly with easy reproducibility.
Implementation Method 1
The compound (B) used in these coating compositions and containing isocyanate groups and silane groups
Implementation Method 2
coating compositions which, in addition to hydroxyl-containing binders (A), comprise compounds (B) with isocyanate groups as crosslinkers
Implementation Method 3
coating compositions which, in addition to hydroxyl-containing binders (A), comprise compounds (B) with isocyanate groups as crosslinkers
Implementation Method 4
a reduction in the solvent fraction, in other words an increase in the nonvolatile fraction, of the coating compositions
Data Source
AI summary
Disclosed is a coating composition based on aprotic solvents and comprising at least one hydroxyl-containing compound (A) and at least one compound (B) having isocyanate groups and having at least one silane group of the formula (I)—X—Si—R″xG3-x (I)withG=identical or different hydrolyzable groups,R′=hydrogen, alkyl or cycloalkyl,X=organic radical,R″=alkyl, cycloalkyl, aryl or aralkyl,x=0 to 2,and characterized in that(i) the compound (B) containing isocyanate groups and silane groups comprises uretdione groups, and(ii) the compound (B) has been prepared from a linear aliphatic diisocyanate.The present invention additionally provides multistage coating methods using these coating compositions, and the use of the coating compositions as clearcoat, and application of the coating method for automotive refinish and/or for the coating of plastics substrates.