Surface-Treated Steel Sheet With Zr-Ti Coating for Chromium-Free Adhesion
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Solution Overview
Problem
Existing surface-treated steel sheets used in containers lack sufficient paint secondary adhesion in wet environments and maintain the original bright appearance while avoiding the use of hexavalent chromium.
Innovation Solution
A surface-treated steel sheet with a Sn plating layer and a coating layer containing Zr oxide and Ti oxide, controlled water contact angle, and limited adsorption of K, Na, Mg, and Ca, produced under specific conditions including cathodic electrolysis and water washing with low conductivity water.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If chromating treatment is performed to improve paint adhesion and sulfide staining resistance, then adhesion and corrosion resistance are improved, but environmental harm increases due to hexavalent chromium use
Solution Approach 1:
The invention extracts and eliminates hexavalent chromium from the chromating treatment process while retaining the essential functionality of forming a protective surface layer. The patent uses alternative compounds (such as zirconium, titanium, or manganese-based compounds) to form a coating layer that provides both paint adhesion and sulfide staining resistance without the environmental harm of hexavalent chromium.
Solution Approach 2:
The alternative coating layer is designed to perform multiple functions simultaneously: it provides paint adhesion, sulfide staining resistance, and environmental safety. The coating layer serves as a universal solution that replaces the multiple roles previously fulfilled by hexavalent chromium-based treatments.
2Object-affected harmful factors
If zirconium compound coating is applied to avoid hexavalent chromium, then environmental safety is improved, but paint secondary adhesion in wet environments becomes insufficient
Solution Approach 1:
The invention optimizes specific parameters of the coating layer including thickness (0.1-5.0 mg/m²), composition ratios, and surface properties to achieve both environmental safety and adequate paint secondary adhesion. By carefully controlling these parameters, the alternative coating layer can function effectively in wet environments without requiring hexavalent chromium.
3Object-affected harmful factors
If trivalent chromium is used to form surface treatment layer, then hexavalent chromium is avoided, but appearance quality deteriorates due to loss of metallic luster
Solution Approach 1:
The invention uses alternative compounds (zirconium, titanium, manganese) that can be applied as thin coating layers to achieve the desired protective and aesthetic functions without the appearance degradation associated with trivalent chromium treatments.
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 steel sheet achieves excellent sulfide staining resistance, paint secondary adhesion, and maintains a bright appearance without hexavalent chromium, suitable for use in containers.
Implementation Method 1
a metal Cr layer and an Cr oxide layer are formed on the surface of the steel sheet by cathodic electrolysis in an electrolytic solution containing a hexavalent chromium compound
Implementation Method 2
a total atomic ratio of K, Na, Mg, and Ca adsorbed on the surface of the steel sheet to all elements is 5.0% or less
Data Source
AI summary
A surface-treated steel sheet that can be produced without the use of hexavalent chromium and that combines excellent sulfide staining resistance, paint secondary adhesion, and appearance is provided. A surface-treated steel sheet having, on at least one surface of a steel sheet, a Sn plating layer and a coating layer disposed on the Sn plating layer and containing at least one of Zr oxide or Ti oxide, wherein a water contact angle is 50° or less, and a total atomic ratio of K, Na, Mg, and Ca adsorbed on a surface of the steel sheet to all elements is 5.0 % or less.