Blocked Polyisocyanate Coating for Low-Temperature One-Component Curing
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Solution Overview
Problem
Conventional polyurethane resin coatings require separate storage and mixing of polyol and polyisocyanate components, leading to gelation issues and limited application in automated coating processes, and high-temperature baking is necessary for blocked polyisocyanates using traditional blocking agents, which is energetically disadvantageous and limits substrate applicability.
Innovation Solution
A blocked polyisocyanate composition using a pyrazole-based blocking agent that allows for curing at temperatures below 100°C, incorporating an organic acid salt and a polyisocyanate derived from aliphatic or alicyclic diisocyanates, enabling a one-component coating composition with improved curability at low temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a blocked polyisocyanate obtained using traditional blocking agents (phenol or methylethylketoxime) is used, then the coating material can be stored and handled conveniently, but a baking procedure at high temperature (140°C or more) is needed which is energetically disadvantageous and limits substrate applicability
Solution Approach 1:
The patent changes the chemical structure of the blocking agent from traditional phenol or methylethylketoxime to a pyrazole-based compound. This parameter change in the blocking agent's molecular structure enables the blocked polyisocyanate to dissociate and cure at lower temperatures (below 100°C), resolving the contradiction between ease of operation and high temperature requirement.
2Reliability
If a two-component composition (polyol and polyisocyanate) is used, then excellent abrasion resistance, chemical resistance and contamination resistance are achieved, but separate storage and mixing are required which is extremely inconvenient and causes gelation issues
Solution Approach 1:
The patent merges the polyol and polyisocyanate components into a single one-component system by pre-reacting the polyisocyanate with the blocking agent to form a blocked polyisocyanate. This combining eliminates the need for separate storage and mixing operations, preventing gelation issues while maintaining the protective properties of the coating.
Solution Approach 2:
The blocking agent acts as an intermediary that temporarily deactivates the polyisocyanate's reactivity, allowing it to be stored and handled as a stable one-component system. Upon heating, the blocking agent dissociates, releasing the active isocyanate groups to react with the polyol and form the cross-linked coating structure.
3Reliability
If an isocyanate-containing coating material is used, then excellent weather resistance is achieved, but the coating device and coating tank require sufficient washing which significantly deteriorates operating efficiency
Solution Approach 1:
The blocking agent creates an inert chemical environment by temporarily blocking the reactive isocyanate groups. This allows the coating material to be stored and handled without active isocyanate groups that would react with water or require extensive washing, thereby improving operating efficiency while maintaining weather resistance through the aliphatic or alicyclic diisocyanate structure.
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 composition facilitates low-temperature curing, enhancing operational efficiency and expanding substrate applicability by eliminating the need for high-temperature baking and separate component handling.
Implementation Method 1
a blocked polyisocyanate formed by blocking all active isocyanate groups by a blocking agent. The blocked polyisocyanate does not react with polyols at ordinary temperature.
Implementation Method 2
the blocking agent dissociates by heating, and active isocyanate groups regenerate and react with polyols, thereby causing a cross-linking reaction
Implementation Method 3
a blocked polyisocyanate composition in which a pyrazole-based compound is used as a blocking agent that can form a cross-linked coating film at a baking temperature of 140°C or lower
Data Source
AI summary
This block polyisocyanate composition has excellent curability at a low temperature when formed as a coating film, and comprises: a block polyisocyanate derived from a polyisocyanate and a block agent; at least one organic acid and/or inorganic acid (A); and at least one metal and/or quaternary ammonium cation (X), wherein the mass ratio X/A of X to A is 0.01-5.0, the content of X is 0.001-20 mass% with respect to the total mass of the block polyisocyanate composition, and the block agent includes a compound having a heterocyclic ring containing at least one nitrogen atom.