Blocked Phosphoric Acid Catalyst for Low-Temperature Coating Crosslinking
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Solution Overview
Problem
Existing coating compositions for automotive finishes lack sufficient weathering stability, scratch resistance, and retention of gloss after scratches, especially under UV radiation in wet/dry cycles, and require high curing temperatures, which is problematic for refinishing where low-temperature curing is necessary to avoid damaging temperature-sensitive parts.
Innovation Solution
The use of bicyclic amines, such as diazabicyclooctane, to block phosphoric acid catalysts, allowing for complete crosslinking at low temperatures through the reaction of isocyanate groups with hydroxyl-containing compounds and hydrolyzable silane groups, resulting in coatings with high acid resistance and scratchproofing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional coating compositions are used to achieve scratch resistance, then scratch resistance is improved, but weathering stability deteriorates under UV radiation in wet/dry cycles
Solution Approach 1:
The patent employs a composite coating system combining silane-modified polyesters with specific catalysts (phosphoric acid compounds blocked with amines having pKb 3-4) to achieve both scratch resistance and weathering stability. The composite nature of the coating, integrating silane crosslinking with controlled catalysis, resolves the contradiction by providing a synergistic effect where silane groups contribute to hardness and scratch resistance while the blocked catalyst system ensures stable curing without compromising weathering performance.
Solution Approach 2:
The patent modifies the chemical parameters of the coating composition by using silane-modified polyesters with specific hydroxyl numbers and incorporating blocked phosphoric acid catalysts with controlled pKb values (3-4). This parameter optimization allows the coating to achieve high scratch resistance through silane crosslinking while maintaining weathering stability by controlling the curing kinetics and avoiding excessive acidity that would compromise UV resistance.
2Stability of the object's composition
If high curing temperatures are used to achieve complete crosslinking, then crosslinking completeness is improved, but damage to temperature-sensitive parts occurs
Solution Approach 1:
The patent changes the temperature parameter by introducing blocked phosphoric acid catalysts that are activated at lower temperatures. The blocked catalyst system (phosphoric acid compounds blocked with amines having pKb 3-4) allows the crosslinking reaction to proceed effectively at reduced temperatures, achieving complete crosslinking without subjecting temperature-sensitive parts to damaging high heat exposure.
Solution Approach 2:
The blocked phosphoric acid catalyst acts as an intermediary that mediates the crosslinking reaction at lower temperatures. The blocking group temporarily deactivates the catalyst, preventing premature reaction, and then releases controlled amounts of active catalyst at lower temperatures to facilitate complete crosslinking without requiring high thermal energy that would damage sensitive components.
3Productivity
If conventional catalysts are used for crosslinking, then crosslinking speed is improved, but aftercrosslinking increases causing stress cracks
Solution Approach 1:
The blocked phosphoric acid catalyst serves as an intermediary that controls the timing and rate of crosslinking. The blocking mechanism prevents premature catalyst activity, ensuring that crosslinking occurs at the appropriate stage with controlled speed. This eliminates excessive aftercrosslinking that would cause stress cracks, while still achieving complete crosslinking through the gradual release of active catalyst.
Solution Approach 2:
The blocked catalyst system implements periodic action by controlling catalyst activation in stages. The blocking group prevents initial catalyst activity, then allows controlled activation during the curing process, and prevents further excessive activity that would cause aftercrosslinking. This periodic control of catalytic activity optimizes crosslinking speed while preventing stress crack formation.
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 coatings exhibit outstanding resistance to cracking under UV radiation and wet/dry cycling, maintaining high scratch resistance and gloss retention without stress cracks, even in film thicknesses over 40 μm, suitable for automotive OEM finishing and refinishing.
Implementation Method 1
the catalyst (C) is a phosphoric acid compound, more particularly phosphoric acid or phosphonic acid, which is blocked with an amine having a pKb 3 and a boiling point >100° C.
Implementation Method 2
one or more constituents (A) and/or (B) and/or at least one further constituent of the coating composition contain hydrolyzable silane groups
Data Source
AI summary
The present invention relates to a coating composition comprising(d) at least one binder (A) having reactive groups,(e) at least one crosslinking agent (B) which is able to react, with crosslinking with the reactive groups of the binder (A),andat least one catalyst (C) for the crosslinking of silane groups, one or more constituents (A) and/or (B) and/or at least one further constituent of the coating composition containing hydrolyzable silane groups, wherein the catalyst (C) is a phosphoric acid compound, more particularly phosphoric acid or phosphonic acid, which is blocked with an amine having a pKb≧3 and a boiling point >100° C.