Isocyanate Hardener for Coating Drying Speed and Reactivity
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Solution Overview
Problem
Current high-tech coating compositions for the automobile and aeronautics industries face challenges in accelerating drying speed while maintaining isocyanate reactivity, leading to issues like plasticization, degradation, and appearance defects due to unreacted isocyanate functions.
Innovation Solution
A compound with isocyanate functionality greater than 2, resulting from the reaction of a (poly)isocyanate with specific cycloaliphatic, aromatic, or heterocyclic compounds, which includes labile hydrogen-containing functions, enhancing drying speed without compromising reactivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If cycloaliphatic polyisocyanates (IPDI-based) are added to accelerate physical drying, then drying speed is improved, but isocyanate reactivity is significantly reduced
Solution Approach 1:
The invention segments the polyisocyanate hardener into two distinct components: a first polyisocyanate with high isocyanate function reactivity (aliphatic structure) and a second polyisocyanate with lower reactivity but high functionality (cycloaliphatic structure like IPDI). This segmentation allows each component to fulfill its specific role - the first ensures rapid crosslinking and the second accelerates physical drying, resolving the contradiction between drying speed and reactivity.
Solution Approach 2:
The invention changes the parameters of the polyisocyanate system by controlling the functionality distribution - the first polyisocyanate has functionality of 2-3 while the second has functionality of 3-6. By adjusting these functionality parameters and their proportions, the system achieves both rapid initial reaction (from the lower functionality component) and accelerated drying (from the higher functionality component), resolving the reactivity-drying speed contradiction.
2Ease of operation
If unreacted isocyanate functions remain in the coating, then plasticization occurs during polishing, but this leads to degradation and appearance defects
Solution Approach 1:
The invention applies preliminary action by ensuring that the high-reactivity first polyisocyanate rapidly reacts with the polyol during the initial crosslinking phase, forming a stable polyurethane network before the lower-reactivity second polyisocyanate completes its reaction. This preliminary rapid crosslinking locks in the coating structure, preventing subsequent plasticization and degradation during polishing operations.
Solution Approach 2:
The invention maintains continuity of useful action through the two-component system where the first polyisocyanate initiates continuous crosslinking and the second polyisocyanate continues the reaction process. This continuous crosslinking action ensures complete consumption of isocyanate functions without leaving unreacted portions that would cause plasticization, while maintaining consistent coating quality throughout the process.
3Productivity
If rapid drying is achieved, then productivity increases, but unreacted isocyanates react with water to cause whitish spots
Solution Approach 1:
The invention segments the crosslinking process into two phases using two different polyisocyanates. The first polyisocyanate with high reactivity provides rapid initial crosslinking that quickly forms the coating structure, enabling fast turnover. The second polyisocyanate with higher functionality ensures complete reaction of all isocyanate groups, preventing residual isocyanates from reacting with atmospheric moisture and causing whitish spots, thus maintaining coating appearance quality.
Solution Approach 2:
The invention creates a composite hardener system combining two polyisocyanates with complementary properties. The composite system leverages the high reactivity of the first polyisocyanate for rapid drying and the high functionality of the second polyisocyanate for complete reaction, achieving both high productivity and defect-free coating appearance through synergistic material combination.
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 accelerates drying while maintaining good isocyanate reactivity, reducing defects and improving the overall performance of the coating by optimizing the crosslinking process.
Implementation Method 1
the reaction of a (poly)isocyanate with an average functionality greater than 2 with at least one compound X comprising: at least one function B(H) n in which: n is a number equal to 1 or 2, H is a labile hydrogen
Implementation Method 2
there is a chemical phenomenon which is the formation of a polyurethane network and which is essentially the consequence of the creation of covalent urethane bonds by chemical reaction between the hardener and the polyol
Implementation Method 3
too rapid exposure of these coatings to humid conditions leads to the appearance of whitish spots due to the reaction with water of the unreacted isocyanate functions
Data Source
AI summary
The compound of the invention, having an average isocyanate functionality of greater than 2, results from the reaction of a (poly)isocyanate having an average functionality of greater than 2, with the compound X comprising a function B(H)n or B'(H)n' where n is equal to 1 or 2, n' is equal to 1, 2 or 3, H is a labile hydrogen and B denotes O, S, N, N being a primary or secondary nitrogen, -C(=O)-O, -C(=O)-N, or else the groups O=P(O)2; O=P(O)OR1; O=P(O)3; O=P(O)2 OR1; O=P(O)-OR1, R1 denoting an alkyl or aralkyl radical, and B' denotes -SiR2R3R4, R2, R3 and R4 representing oxygen, an alkyl radical bearing a function that is reacted with the (poly)isocyanate, or an aralkyl, aryl, -O-alkyl or -O-aralkyl radical, X being, in addition, a cycloaliphatic, aromatic or heterocyclic compound or a particle of a crosslinked polymer; and with the proviso that, when B denotes a secondary nitrogen and X is a cycloaliphatic compound, X is then a compound having at least two rings; the reaction being carried out with a compound X/[compound X + (poly)isocyanate] weight ratio of at most 50%. The invention also relates to a composition of the hardener type which comprises at least one compound of the above type. The compound or the composition of the invention can be used in the preparation of a coating of the paint or varnish type.