Polyurethane Coating with Zinc and Bismuth Catalysts
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Solution Overview
Problem
Existing coating material compositions for multicoat paint systems face challenges in achieving good scratch resistance, chemical resistance, and low thermal yellowing, especially when cured at low temperatures, while also requiring easy production and environmental sustainability.
Innovation Solution
The development of coating material compositions comprising polyhydroxyl group-containing components, isocyanate groups with hydrolyzable silane groups, phosphorus- and nitrogen-containing catalysts, and specific catalysts for hydroxyl and isocyanate group reactions, which allow for crosslinking at low temperatures and improved properties such as hardness, scratch resistance, and reduced thermal yellowing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If polyisocyanate crosslinkers with hydrolyzable silane groups are used for low-temperature curing (≤90°C), then scratch resistance and assembly strength are improved, but chemical resistance (especially toward sodium hydroxide) and hardness immediately after curing deteriorate
Solution Approach 1:
The invention changes the chemical composition parameters by introducing specific catalysts (zinc carboxylate and bismuth carboxylate) and reaction accelerators (aromatic carboxylic acids) to modify the crosslinking reaction kinetics, enabling simultaneous achievement of good scratch resistance and chemical resistance at low curing temperatures
Solution Approach 2:
The invention uses a composite catalyst system combining zinc carboxylate, bismuth carboxylate, and aromatic carboxylic acid reaction accelerators to achieve synergistic effects that resolve the contradiction between scratch resistance and chemical resistance
2Strength
If polyisocyanate crosslinkers with hydrolyzable silane groups are used for low-temperature curing (≤90°C), then assembly strength is improved, but thermal yellowing increases
Solution Approach 1:
The invention changes the chemical composition by selecting specific catalysts (zinc carboxylate and bismuth carboxylate) and reaction accelerators (aromatic carboxylic acids) that enable low-temperature crosslinking with minimal thermal yellowing, optimizing the balance between assembly strength and color stability
3Temperature
If conventional catalysts (e.g., DABCO-blocked bis(2-ethylhexyl) phosphate) are used for silane crosslinking, then low-temperature curing is achieved, but yellowing tendency increases at elevated temperatures (60-100°C)
Solution Approach 1:
The invention replaces conventional DABCO-blocked phosphate catalysts with zinc carboxylate and bismuth carboxylate catalysts combined with aromatic carboxylic acid reaction accelerators, changing the chemical parameters to achieve low-temperature curing with reduced yellowing tendency
Solution Approach 2:
The invention uses zinc carboxylate and bismuth carboxylate catalysts that are effective at low concentrations and do not exhibit the thermal yellowing problems of conventional organic catalysts, providing a more stable long-term solution
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 compositions exhibit excellent packing resistance, assembly strength, hardness, scratch resistance, and chemical resistance, with low thermal yellowing, while enabling low-temperature crosslinking and easy, reproducible production without environmental issues.
Implementation Method 1
at least one phosphorus- and nitrogen-containing catalyst (D) for the crosslinking of silane groups
Implementation Method 2
component (B) having on average at least one isocyanate group and having an average of at least one hydrolyzable silane group
Implementation Method 3
at least one catalyst (Z) for the reaction of the hydroxyl groups with the isocyanate groups
Implementation Method 4
simultaneous crosslinking via the silane groups and the OH/NCO reaction
Data Source
AI summary
Disclosed herein is a coating material compositions containing (A) a polyhydroxyl group-containing component, (B) a component (B) having on average at least one isocyanate group and having on average at least one of: at least one hydrolyzable silane group of the formula (I): —NR—(X—SiR″x(OR′)3-x), and at least one hydrolyzable silane group of the formula (II): —N(X—SiR″x(OR′)3-x)n(X′—SiR″y(OR′)3-y)m, (D) a phosphorus and nitrogencontaining catalyst, and a catalyst (Z), wherein: the catalyst (Z) is selected from zinc and bismuth carboxylates, of aluminum, zirconium, titanium and/or boron chelates and/or of inorganic, tin-containing catalysts, and mixtures thereof; and the coating material composition comprises at least one reaction accelerator (R) which is selected from the group of inorganic acids and/or of organic acids and/or of partial esters of the inorganic acids and/or of partial esters of the organic acids. Processes for producing multicoat paint systems, and coatings obtained from the coating material compositions are also disclosed.