Self-crosslinking Polyurethane Dispersions for Automotive Coatings
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current water-based polyurethane coating systems fail to meet the high demands of automotive painting in terms of solvent resistance and elasticity, particularly due to limitations in solids content and mechanical stress resistance.
Innovation Solution
A process for producing self-crosslinking polyurethane dispersions by reacting polyisocyanates with polyol components, including acid-functional compounds, to form OH-functional and NCO-group-free polyurethanes, which are then dispersed in water, with a controlled ratio of isocyanate groups to isocyanate-reactive groups, and partially or completely deprotonated using a neutralizing agent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional water-based polyurethane systems are used, then processing from aqueous phase is enabled, but solvent resistance and mechanical stress resistance are insufficient
Solution Approach 1:
The invention uses composite polyol systems combining polyester polyols and polyether polyols in specific ratios (30-70 wt% polyester, 70-30 wt% polyether) to achieve both solvent resistance (from polyester) and elasticity/mechanical stress resistance (from polyether), resolving the contradiction between these properties
Solution Approach 2:
The invention optimizes the NCO-reactive groups to isocyanate groups ratio within 0.3-2.0 and controls molecular weight (62-2500 g/mol) and OH functionality (≥2) of polyol components to achieve the desired balance between solvent resistance and mechanical properties in the cured coating
2Object-affected harmful factors
If polyol components with low molecular weight are used, then crosslinking density and solvent resistance improve, but elasticity and mechanical stress resistance deteriorate
Solution Approach 1:
The invention combines polyester polyols (providing solvent resistance through dense crosslinking) with polyether polyols (providing elasticity and mechanical flexibility) in optimized ratios, where the polyester content is controlled at 30-70 wt% to balance both properties
Solution Approach 2:
The invention creates local differentiation in the polymer structure by incorporating polyols with different molecular weights and functionalities, where lower molecular weight segments provide crosslinking density for solvent resistance while higher molecular weight segments maintain chain flexibility for elasticity
3Quantity of substance
If high solids content is achieved, then coating efficiency and mechanical properties improve, but dispersion stability and processing difficulty increase
Solution Approach 1:
The invention uses neutralizing agents (amines or bases) as intermediaries to convert carboxylic acid groups in the polyol-prepolymer adducts to carboxylate salts, which dramatically improve water dispersibility and stability even at high solids contents (40-80 wt%), enabling easy processing
Solution Approach 2:
The invention changes the chemical state of the polyol component by introducing carboxylic acid groups that can be neutralized, transforming the dispersion characteristics from poor stability to excellent stability, allowing high solids content formulations to be processed easily
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 process results in coatings with improved solvent resistance and high solids content, suitable for one-component stoving systems used in automotive painting, offering enhanced mechanical properties and film formation characteristics.
Implementation Method 1
Polyisocyanates with a2) at least one polyol component which has an average OH functionality of ≥ 2 and a number average molecular weight of 62 - 2500 g/mol and also contains at least one acid-functional compound, converted into an NCO- or optionally OH-functional prepolymer
Implementation Method 2
the acid groups of the composition a5) thus obtained are completely or partially deprotonated by adding a neutralizing agent and the polyurethane obtained is dispersed in water
Data Source
AI summary
The invention relates to a method for producing self-crosslinking polyurethane (PUR) dispersions and to the use thereof.