Malonic Acid Ester Blocked Polyisocyanate for Low-Temperature Curing
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Solution Overview
Problem
Conventional polyurethane resin coating materials using polyisocyanate require separate storage and mixing of components, leading to gelation issues and limited application in automated coating processes, and high-temperature baking is necessary, which restricts their use in substrates with low heat resistance.
Innovation Solution
A blocked polyisocyanate composition using a malonic acid ester as a blocking agent, allowing for storage stability and curability at low temperatures (80-85°C), with a resin composition that includes a blocked polyisocyanate derived from diisocyanate and an active hydrogen compound, enhancing hardness and strength of the coating film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a blocked polyisocyanate using conventional blocking agents (phenol, methylethylketoxime) is used, then storage stability is improved, but baking temperature must be 140°C or more which limits application to substrates with high heat resistance
Solution Approach 1:
The patent changes the chemical structure of the blocking agent from conventional phenol or methylethylketoxime to a specific malonic acid ester compound with particular molecular weight and functional group characteristics. This parameter change in the blocking agent structure enables dissociation at lower temperatures (80-90°C) while maintaining storage stability, thereby resolving the contradiction between storage stability and baking temperature requirement
Solution Approach 2:
The patent creates a composite blocked polyisocyanate system by combining polyisocyanate with a specifically designed malonic acid ester blocking agent that has both ester groups and hydroxyl groups. This composite structure allows the blocking agent to provide both storage stability through blocking and low-temperature curability through controlled dissociation, simultaneously addressing both requirements
2Temperature
If a blocked polyisocyanate that can be cured at low temperature (90°C) is used, then baking temperature is reduced, but dispersibility in polyvalent polyol and storage stability are insufficient
Solution Approach 1:
The patent precisely controls the molecular weight (60-5,000) and functional group count (1.6-2.4) of the malonic acid ester blocking agent to achieve optimal balance between storage stability and low-temperature curability. This parameter optimization ensures the blocking agent remains stable during storage but dissociates effectively at 80-90°C to enable curing
3Strength
If conventional two-component polyurethane resin coating material is used, then abrasion resistance and chemical resistance are excellent, but separate storage and mixing are required which reduces ease of operation
Solution Approach 1:
The patent merges the polyisocyanate and blocking agent into a single blocked polyisocyanate component that can be stored and applied separately from polyol without gelation. The blocking agent prevents premature reaction, allowing the coating material to be stored as a stable single component while maintaining the ability to form cross-linked polyurethane structures with excellent abrasion and chemical resistance after application and curing
4Reliability
If polyisocyanate is mixed with polyol to form coating material, then curability is achieved, but gelation occurs quickly which reduces productivity
Solution Approach 1:
The blocking agent performs a preliminary blocking action on the polyisocyanate groups before application, preventing premature reaction with polyol or moisture. This preliminary blocking allows the coating material to be stored and handled without gelation, while still enabling complete curing after application when the blocking agent dissociates at curing temperature (80-90°C), thus maintaining both curability and productivity
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 provides favorable storage stability and excellent curability at low temperatures, resulting in a coating film with improved hardness and strength, suitable for applications requiring low-temperature curing.
Implementation Method 1
a blocked polyisocyanate derived from a polyisocyanate and a blocking agent containing a malonic acid ester
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
active isocyanate groups regenerate and react with polyols, thereby causing a cross-linking reaction
Implementation Method 4
exhibits excellent curability at a low temperature of about 80° C. or 85° C.
Data Source
AI summary
This blocked polyisocyanate composition contains a block polyisocyanate derived from one or more diisocyanates, an active hydrogen compound, and a blocking agent containing a malonic acid ester. The active hydrogen compound has a number-average molecular weight of 60 to 5,000 and an average of 1.6 to 2.4 functional groups.