Automotive Clearcoat Scratch Resistance via Silane Optimization
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Solution Overview
Problem
Current coating compositions for automotive clearcoats face challenges in achieving high scratch resistance, particularly long-term scratch resistance, while maintaining good Erichsen cupping values and antistonechip properties, often requiring high silane levels that can be costly and environmentally problematic.
Innovation Solution
The development of coating compositions comprising hydroxyl-containing polyacrylates or polymethacrylates with a glass transition temperature below 10°C, combined with isocyanate-containing compounds featuring specific silane structural units, which allow for improved scratch resistance and Erichsen cupping without excessive silane content, enabling production of clearcoats with high scratch resistance and good antistonechip properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high fractions of bisalkoxysilaneamines are used to improve scratch resistance, then scratch resistance is improved, but weathering stability deteriorates
Solution Approach 1:
The invention changes the chemical composition parameters by using specific ratios of monoalkoxysilylamine (2-50 mol%) and bisalkoxysilylamine (50-78 mol%) instead of high fractions of bisalkoxysilaneamines alone. This parameter optimization resolves the contradiction by achieving high scratch resistance through the synergistic combination of both silane types while maintaining weathering stability through controlled proportions and specific chemical structures.
Solution Approach 2:
The invention creates a composite crosslinking system combining monoalkoxysilylamine and bisalkoxysilylamine components with hydroxyl-containing polyacrylate/polymethacrylate polyols. This composite material approach allows the system to achieve both high scratch resistance (from the crosslinked network) and good weathering stability (from the balanced composition and silane structure), resolving the contradiction between these two properties.
2Strength
If high levels of silane are used to achieve very high scratch resistance, then scratch resistance is improved, but cost and environmental impact increase
Solution Approach 1:
The invention optimizes the silane content parameter by achieving very high scratch resistance with lower overall silane levels through the specific combination of monoalkoxysilylamine (2-50 mol%) and bisalkoxysilylamine (50-78 mol%). This parameter change reduces the total quantity of silane required while maintaining or improving scratch resistance performance, thereby reducing cost and environmental impact.
Solution Approach 2:
The invention applies local quality by using specific structural units (I) and (II) with particular R, R′, X, and n values to create regions of high crosslinking efficiency. This allows concentrated scratch resistance enhancement in critical areas of the coating without requiring high overall silane content throughout the entire formulation, thus reducing total silane quantity while maintaining high scratch resistance.
3Strength
If coatings with high scratch resistance are produced, then scratch resistance is improved, but Erichsen cupping values decrease
Solution Approach 1:
The invention changes the compositional parameters by using hydroxyl-containing polyacrylate/polymethacrylate polyols with specific glass transition temperatures and combining them with optimized ratios of monoalkoxysilylamine and bisalkoxysilylamine. This parameter optimization achieves a balance where the crosslinked network provides high scratch resistance while the polymer matrix maintains adequate ductility and flexibility for good Erichsen cupping values.
Solution Approach 2:
The invention creates a composite coating system combining organic polymer matrices (hydroxyl-containing polyacrylate/polymethacrylate) with silane crosslinking agents (monoalkoxysilylamine and bisalkoxysilylamine). This composite structure allows the organic phase to provide ductility and flexibility (good Erichsen cupping) while the silane crosslinked network provides scratch resistance, resolving the contradiction between these two properties.
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 solution provides clearcoats with enhanced scratch resistance, including long-term scratch resistance, and improved Erichsen cupping values, while reducing the need for high silane levels, thus being economically and environmentally more favorable.
Implementation Method 1
thermally curable coating compositions based on aprotic solvents, comprising hydroxyl-containing polyacrylate polyols and/or hydroxyl-containing polymethacrylate polyols and compounds (B) containing isocyanate groups and silane groups
Implementation Method 2
compounds (B) containing isocyanate groups and silane groups
Data Source
AI summary
The present invention relates to coating compositions comprising(A) at least one hydroxyl-containing polyacrylate and/or at least one hydroxyl-containing polymethacrylate and(B) at least one compound containing isocyanate groups and having at least one structural unit (I) of the formula (I)—NR—(X—SiR″x(OR′)3-x) (I),and having at least one structural unit (II) of the formula (II)—N(X—SiR″x(OR′)3-x)n(X′—SiR″y(OR′)3-y)m (II),where(i) (A) has a glass transition temperature of less than 10° C.,(ii) (B) contains more than 10 to more than 90 mol %, of at least one structural unit of the formula (I) and 10 to less than 90 mol % of at least one structural (II), based on the entirety of the structural units (I) and (II), and(iii) 10 to 60 mol % of the isocyanate groups of the diisocyanate and/or polyisocyanate parent structure of (I) and (II).The invention provides multistage coating processes using these coating compositions.