Pyrazole-Blocked Polyisocyanate for Low-Temperature Urethane Coatings
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Solution Overview
Problem
Current blocked polyisocyanates used in one-component urethane coating compositions require high curing temperatures, leading to energy inefficiency and poor coating film appearance and hardness, while existing solutions for low-temperature curability either result in unsmooth film surfaces or insufficient hardness.
Innovation Solution
A blocked polyisocyanate derived from an aliphatic diisocyanate and polyol, with specific conditions for isocyanate group number, trimer concentration, and polyol content, blocked using a pyrazole compound, achieving low-temperature curability, high film hardness, and improved appearance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a pyrazole compound is used as a blocking agent to achieve low-temperature curability, then the curing temperature is reduced, but unsmoothness is formed on the surface of the coating film resulting in poor appearance
Solution Approach 1:
The patent modifies the chemical structure parameters of the pyrazole compound by introducing specific substituents (alkyl groups at positions 3 and 5) to change the blocking characteristics. This structural parameter change enables the blocking agent to facilitate low-temperature curing while maintaining smooth coating film surface, resolving the contradiction between curing temperature reduction and appearance quality.
Solution Approach 2:
The patent creates a composite blocking system by combining the specifically structured pyrazole compound with polyisocyanate having controlled molecular weight and functional group distribution. This composite approach allows the blocking agent to effectively reduce curing temperature while the polyisocyanate structure ensures proper film formation and surface smoothness.
2Temperature
If the number of isocyanate functional groups is increased to improve low-temperature curability, then the curing temperature is reduced, but the hardness of the cured coating film becomes insufficient
Solution Approach 1:
The patent optimizes the average number of isocyanate groups parameter to a specific range (2-10) rather than simply increasing it. This parameter optimization, combined with controlling the polyol content (5-40 mass%), achieves low-temperature curability while maintaining adequate crosslinking density for proper coating film hardness.
Solution Approach 2:
The patent creates local quality differentiation by having different regions of the polyisocyanate molecule with varying isocyanate group densities. The controlled trimer concentration (10-50 mass%) provides localized crosslinking zones that contribute to hardness while the overall structure enables low-temperature reactivity.
3Manufacturing precision
If a high temperature is used for curing to achieve good coating film appearance and hardness, then the coating quality is improved, but energy consumption increases and carbon dioxide generation increases
Solution Approach 1:
The patent changes the chemical reactivity parameters of the blocked polyisocyanate by selecting specific polyol types and ratios, enabling the curing reaction to proceed efficiently at lower temperatures. This parameter modification reduces the thermal energy input required while maintaining the crosslinking efficiency needed for high-quality coating films.
Solution Approach 2:
The patent substitutes thermal energy input (mechanical/physical approach) with chemically optimized reactivity (chemical approach). By designing the blocked polyisocyanate with enhanced low-temperature reactivity through specific molecular structure, the system achieves effective curing at reduced temperatures, replacing the need for high thermal energy input.
4Strength
If a high temperature is used for curing, then adequate coating film hardness is achieved, but the curing process becomes energy inefficient
Solution Approach 1:
The patent modifies the reaction kinetics parameters of the blocked polyisocyanate system by optimizing the blocking agent structure and polyol composition. This enables the curing reaction to achieve adequate hardness at lower temperatures by enhancing the chemical reactivity and crosslinking efficiency under reduced thermal conditions.
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 provides a coating film with excellent low-temperature curability, high hardness, and improved weatherability, reducing energy consumption and enhancing the coating's appearance and durability.
Implementation Method 1
isocyanate groups of a polyisocyanate which is derived from an aliphatic diisocyanate and a polyol and satisfies all of the following conditions 1)-5) are mainly blocked with a pyrazole compound
Data Source
AI summary
Disclosed is a block polyisocyanate obtained by blocking at least a part of isocyanate groups of a polyisocyanate, which is derived from an aliphatic diisocyanate and a polyol and satisfies all of the conditions (1)-(5) shown below, with a pyrazole compound. (1) Average number of isocyanate groups: 3.0-20 (2) Diisocyanate monomer trimer concentration: 10-50% by mass (3) Isocyanate group concentration: 5-22% by mass (4) Polyol content concentration: 5-40% by mass (5) Diisocyanate monomer concentration: 3% by mass or less.