Trivalent Chromium Nitrate Post-Treatment for E-Coat Adhesion
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Solution Overview
Problem
Existing methods for treating metal-based surfaces, particularly before electrocoating, fail to adequately enhance corrosion, detergent, and chemical resistance, leading to unsatisfactory appearance and durability of the electrocoated layers.
Innovation Solution
An acidic aqueous composition comprising trivalent chromium ions from trivalent chromium nitrate salt and hexafluorozirconate ions is used to treat zirconium-pretreated metal-based surfaces, providing a post-treatment for subsequent electrocoating that improves corrosion, detergent, and chemical resistance, as well as adhesion bonding properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acidic aqueous compositions containing trivalent chromium salts (sulphate or chloride) are used for post-treating metal-based surfaces, then the treatment process can be completed, but the corrosion resistance, detergent resistance, and appearance of the electrocoated layers become unsatisfactory
Solution Approach 1:
The invention changes the chemical parameters of the treatment composition by specifying trivalent chromium nitrate salt as the chromium source instead of conventional sulphate or chloride salts. This parameter change in the composition chemistry results in improved corrosion resistance and e-coat durability while maintaining satisfactory appearance, resolving the contradiction between reliability and ease of manufacture.
2Strength
If the surface is treated with conventional solutions prior to e-coat application, then the treatment process is completed, but the adhesion bonding properties and detergent resistance are insufficient
Solution Approach 1:
The invention uses a composite chemical system combining trivalent chromium nitrate salt with hexafluorozirconate in a controlled acidic aqueous solution. This composite composition creates a synergistic effect that simultaneously improves adhesion bonding properties and detergent/chemical resistance, resolving the contradiction between strength and reliability.
3Manufacturing precision
If existing treatment methods are used, then the substrate can be treated, but the e-coat coverage uniformity and optical quality are unsatisfactory
Solution Approach 1:
The invention modifies the chemical composition parameters by using trivalent chromium nitrate salt instead of conventional chromium salts, and controls the pH within a specific range (2.5-4.5). These parameter changes result in improved surface preparation that enhances e-coat coverage uniformity and optical quality, resolving the contradiction between manufacturing precision and illumination intensity.
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 process significantly enhances e-coat coverage and uniformity, improves detergent resistance, and ensures a corrosion-resistant, optically flawless surface with improved adhesion of the electrocoated layers.
Implementation Method 1
an acidic aqueous composition comprising a) trivalent chromium ions; b) hexafluorozirconate ions
Implementation Method 2
treating of zirconium-pretreated metal-based substrate surfaces with the composition
Implementation Method 3
subsequent electrocoating of the treated surfaces
Data Source
AI summary
The present invention relates to an acidic aqueous composition for treating of zirconium-pretreated metal-based substrate surfaces such as steel metals or aluminium surfaces, a process for treating the substrate surfaces with the composition and the use of the composition as post-treatment of zirconium-pretreated metal-based substrate surfaces for subsequent electrocoating of the surfaces to increase corrosion resistance of said metal-based surfaces prior to electro-coating (e-coat) applications and increases detergent and chemical resistance of treated surfaces used in the white goods industry. The acidic aqueous composition comprises trivalent chromium ions; and hexafluorozirconate ions; characterized in that the source of trivalent chromium ions is a trivalent chromium nitrate salt.