Cationic Electrodeposition Coating with Bismuth Catalyst Stability
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Solution Overview
Problem
Existing cationic electrodeposition coating compositions face challenges with the need for an alternative to organotin compounds as curing catalysts, deterioration of edge part rust prevention properties due to film flow during heating and curing, and issues with storage stability and aggregation.
Innovation Solution
A method involving the preparation of a resin emulsion with an aminated resin and blocked isocyanate curing agent, and a pigment dispersion paste using a bismuth-metal oxide mixture liquid with specific metal oxides, monohydroxycarboxylic acids, and polyvalent acids to enhance edge part rust prevention and storage stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bismuth compound is dispersed in a pigment dispersion paste, then it can be used as a curing catalyst, but the catalytic activity is reduced and the coating film cannot be sufficiently cured
Solution Approach 1:
The patent uses a carboxylic acid as an intermediary substance to dissolve the bismuth compound before incorporating it into the coating composition. This intermediary step ensures the bismuth compound is in a soluble form that maintains high catalytic activity while being compatible with the coating system, thereby resolving the contradiction between dispersibility and catalytic effectiveness
Solution Approach 2:
The patent changes the physical-chemical parameters of the bismuth compound by dissolving it in a carboxylic acid medium, transforming it from an insoluble dispersed state to a soluble molecular state. This parameter change maintains the bismuth's catalytic activity while enabling its effective incorporation into the coating composition
2Reliability
If a bismuth compound is added to the cationic electrodeposition coating composition, then it can serve as a curing catalyst, but the storage stability deteriorates and aggregation occurs
Solution Approach 1:
The carboxylic acid acts as a stabilizing intermediary that complexes with the bismuth compound, preventing its aggregation during storage. This intermediary complex maintains the bismuth in a stable, soluble form that does not precipitate or aggregate, thereby resolving the contradiction between catalytic function and storage stability
Solution Approach 2:
The patent creates a composite system where the bismuth compound is combined with a carboxylic acid to form a stable complex. This composite material approach ensures both the catalytic activity of bismuth and the storage stability of the coating composition are maintained simultaneously
3Reliability
If a large amount of acid is used to dissolve bismuth, then the catalytic activity is improved, but the conductivity increases and electrodeposition coating workability deteriorates
Solution Approach 1:
The patent optimizes the concentration parameters of the carboxylic acid and bismuth compound to achieve the minimum effective amount needed for high catalytic activity. By precisely controlling these parameters, the system maintains excellent catalytic performance while keeping the conductivity increase minimal, thus preserving electrodeposition coating workability
Solution Approach 2:
The patent uses a controlled, partial amount of carboxylic acid rather than excessive acidification. This partial action approach provides sufficient catalytic activity through the bismuth-carboxylic acid complex while avoiding the harmful effects of high acid concentration on conductivity and coating workability
4Reliability
If the film flow is suppressed to improve edge part rust prevention, then the film thickness at edge part is secured, but the leveling property of flat parts is impaired
Solution Approach 1:
The patent achieves different functional outcomes in different regions of the coating: edge parts benefit from reduced flow and maintained thickness for rust prevention, while flat parts maintain their natural leveling. This local differentiation of quality is achieved through the optimized bismuth compound system that provides sufficient catalytic activity without excessive film flow, allowing each region to exhibit its desired property
Solution Approach 2:
The patent modifies the rheological parameters of the coating through the bismuth compound system to achieve optimal flow characteristics. The parameter changes result in reduced excessive flow that would harm edge coverage, while maintaining sufficient flow for flat surface leveling, thereby resolving the contradiction between edge protection and overall smoothness
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 method results in a cationic electrodeposition coating composition with improved storage stability, coatability, and superior edge part rust prevention and film appearance.
Implementation Method 1
bismuth compound as a curing catalyst
Implementation Method 2
cationic electrodeposition coating composition
Data Source
AI summary
An object of the present invention is to provide a preparation method for improving the edge part rust prevention property in the preparation of a cationic electrodeposition coating composition containing a bismuth compound as a curing catalyst. The present invention provides a method for preparing a cationic electrodeposition coating composition, including a step of preparing a resin emulsion (i) containing an aminated resin (A) and a blocked isocyanate curing agent (B), a step of preparing a pigment dispersion paste (ii) containing a bismuth-metal oxide mixture liquid (C) containing a bismuth compound (c1), a metal oxide (c2), a monohydroxycarboxylic acid (c3) having 3 to 5 carbon atoms in total and a solvent; a pigment dispersion resin (D); a polyvalent acid (E); and a pigment (F), and a step of mixing the resin emulsion (i) and the pigment dispersion paste (ii).