Cationic Electrodeposition Coating Bismuth Catalyst Stability
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Solution Overview
Problem
Cationic electrodeposition coating compositions using bismuth compounds face issues with catalyst activity, storage stability, and coating appearance due to the limitations of organic tin compounds and the inadequacies of bismuth compounds like bismuth oxide or bismuth hydroxide, which require high acid usage and lead to coagulation and electroconductivity problems.
Innovation Solution
A method involving the preparation of a cationic electrodeposition coating composition by dissolving a bismuth compound in an organic acid and mixing it with an aminated resin and blocked isocyanate curing agent, along with an amine-modified epoxy resin, to create a stable and curable coating composition without the need for aqueous solutions of low solubility bismuth compounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a bismuth compound such as bismuth oxide or bismuth hydroxide is used as the curing catalyst, then the environmental compliance is improved by replacing organic tin compounds, but the catalyst activity is insufficient and the coating film cannot be sufficiently cured
Solution Approach 1:
The patent introduces a carboxylic acid as an intermediary substance that reacts with the bismuth compound to form a soluble complex. This carboxylic acid mediator enables the poorly soluble bismuth compound to dissolve and exert its catalytic function effectively, resolving the contradiction between environmental compliance and catalyst activity
Solution Approach 2:
The patent changes the solubility parameter of the bismuth compound by reacting it with carboxylic acid to form a soluble complex. This parameter change transforms the bismuth compound from an insoluble state to a soluble state, enabling it to function as an effective catalyst while maintaining environmental compliance
2Quantity of substance
If a bismuth compound is dispersed in a pigment dispersion paste, then the catalyst is incorporated into the coating composition, but the storage stability deteriorates and coagulation occurs during storage
Solution Approach 1:
The carboxylic acid acts as a mediator that forms a soluble complex with the bismuth compound, preventing direct interaction between the bismuth compound and the pigment dispersion paste that would cause coagulation. This intermediary complex maintains storage stability while incorporating the catalyst
Solution Approach 2:
The patent performs preliminary reaction between the bismuth compound and carboxylic acid to form a soluble complex before incorporating it into the pigment dispersion paste. This preliminary action prevents subsequent coagulation and maintains storage stability
3Reliability
If a large amount of acid is used to dissolve bismuth in advance, then the catalyst activity is improved, but the electroconductivity increases and electrodeposition coating workability deteriorates
Solution Approach 1:
The carboxylic acid serves as a mediator that enables bismuth dissolution at lower acid concentrations. The intermediary complex formation allows effective catalyst activity without requiring large amounts of acid, thus maintaining electrodeposition coating workability
Solution Approach 2:
The patent changes the chemical state of bismuth from insoluble to soluble through complex formation with carboxylic acid. This parameter change enables effective catalyst activity at lower acid concentrations, preserving electrodeposition coating workability
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 coating composition with improved stability, curability, and appearance, while eliminating the use of organic tin compounds and maintaining excellent dispersion stability and corrosion resistance.
Implementation Method 1
dissolving a bismuth compound in an organic acid
Implementation Method 2
neutralizing the mixture using a neutralizing acid to obtain resin emulsion
Implementation Method 3
cationic electrodeposition coating composition
Data Source
AI summary
The objective of the present invention is to provide a method for preparing a cationic electrodeposition coating composition that contains a bismuth compound and exhibits excellent coating material stability, curability, coating film appearance and the like. The present invention provides a method for preparing a cationic electrodeposition coating composition, which comprises a step for mixing a resin emulsion (i) and a pigment-dispersed paste, and wherein: the resin emulsion (i) contains an aminated resin (A) and a blocked isocyanate curing agent (B); the pigment-dispersed paste contains a bismuth mixture (C) that is obtained by mixing a bismuth compound (c1) and an organic acid (c2) in advance, a pigment-dispersed resin (D), an amine-modified epoxy resin emulsion (ii) that contains an amine-modified epoxy resin (E), and a pigment (F); the pigment-dispersed resin (D) has a hydroxyl number of 20-120 mgKOH/g; and the amine-modified epoxy resin (E) has a hydroxyl number of 150-650 mgKOH/g.