Bismuth-Based Aqueous Coating Eliminates Phosphating
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Solution Overview
Problem
Conventional coating processes in the automotive industry require a phosphating step that is resource-intensive and generates waste, posing environmental and economic challenges, while existing electrophoretic coating compositions using aminopolycarboxylic acids suffer from bath stability issues and pollution concerns.
Innovation Solution
An aqueous coating composition with a pH range of 4.0 to 6.5, containing at least 130 ppm bismuth, including 30 ppm dissolved and optionally 100 ppm undissolved bismuth, along with a bidentate complexing agent, which allows for direct electrophoretic coating of electrically conductive substrates without the need for a phosphating pretreatment, enhancing corrosion protection and reducing environmental impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a phosphating pretreatment step is used, then corrosion protection is achieved, but process complexity and waste generation increase
Solution Approach 1:
The invention combines the functions of phosphating pretreatment and electrophoretic coating into a single integrated process. The coating composition contains bismuth compounds that perform both the corrosion protection function of phosphating and the coating function, eliminating the need for separate pretreatment tanks and process steps while maintaining effective corrosion protection.
Solution Approach 2:
The coating composition is designed to be multi-functional, serving both as a pretreatment agent (replacing phosphating) and as the electrophoretic coating material. This universal composition eliminates the need for separate pretreatment and coating steps, reducing process complexity while maintaining corrosion protection efficacy.
2Reliability
If a phosphating pretreatment step is used, then corrosion protection is achieved, but waste sludge production and environmental pollution increase
Solution Approach 1:
The invention eliminates the generation of harmful waste sludge by replacing the phosphating process with an electrophoretic coating process that does not produce insoluble phosphate sludge. The bismuth-based coating composition allows for cleaner waste streams that can be more easily treated and recycled, reducing environmental pollution while maintaining corrosion protection.
3Reliability
If aminopolycarboxylic acids are used in electrophoretic coating compositions, then bismuth complexing is achieved, but bath stability and environmental compatibility worsen
Solution Approach 1:
The invention replaces persistent aminopolycarboxylic acids with alternative bismuth complexing agents that form sufficient complexes for electrophoretic deposition but do not accumulate in the bath over time. These alternative agents may be consumed or transformed during the process, preventing long-term bath instability and environmental contamination while maintaining effective bismuth complexing during the coating operation.
4Reliability
If aminopolycarboxylic acids are used in electrophoretic coating compositions, then bismuth complexing is achieved, but wastewater treatment and environmental pollution worsen
Solution Approach 1:
The invention replaces environmentally harmful aminopolycarboxylic acids with alternative complexing agents that are less harmful to the environment. The alternative agents still achieve effective bismuth complexing for electrophoretic deposition but do not mobilize heavy metals in natural waters or cause pollution in wastewater treatment plants, thus converting a harmful process into a beneficial or neutral one.
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
This approach enables a more economical and ecological coating process by eliminating the phosphating step, maintaining effective corrosion protection, and avoiding the use of environmentally harmful compounds, thereby improving bath stability and reducing waste generation.
Implementation Method 1
for at least partially coating an electrically conductive substrate with an electrophoretic coating
Implementation Method 2
at least one at least bidentate complexing agent (A5), where (A5) is a compound of the general formula (1) suitable for complexing Bi
Data Source
AI summary
The present invention relates to an aqueous coating composition (A) with pH in the range from 4.0 to 6.5 comprising at least one binder (A1) amenable to cathodic deposition, a total quantity of at least 130 ppm of Bi, in relation to the total weight of (A), whereof at least 30 ppm of Bi are present in a form (A3) dissolved in (A) and optionally at least 100 ppm of Bi are present in a form (A4) not dissolved in (A), and at least one at least bidentate complexing agent (A5) suitable for the complexing of Bi, where (A5) is a compound of the general formula (1) or an anion of said compound, for the at least partial coating of an electrically conductive substrate with an electrodeposition coating, a process for producing (A), the use of (A) for the least partial coating of an electrically conductive substrate with an electrodeposition coating, a corresponding coating process, an at least partially coated substrate obtainable by said process, and a process for establishing and/or maintaining the concentration of the component (A3) and/or optionally (A4) in the coating composition (A) during the coating process.