Sn-Plated Steel Sheet Coating for Yellowing Resistance
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Solution Overview
Problem
Sn-based plated steel sheets without chromate treatment suffer from inadequate yellowing resistance, coating film adhesiveness, and sulfurization blackening resistance due to the growth of tin oxide over time.
Innovation Solution
A Sn-based plated steel sheet with a coating layer containing zirconium oxide and manganese oxide, where the manganese oxide is thicker on the surface and the zirconium oxide is positioned deeper, forming a barrier to suppress tin oxide growth and improve adhesiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If chromate treatment is used to improve yellowing resistance and coating film adhesiveness, then the external appearance stability and coating adhesion are improved, but environmental safety and human health safety deteriorate due to hexavalent chromium content
Solution Approach 1:
The invention extracts and removes the harmful chromate treatment step from the plating process while maintaining the desired functional outcomes through alternative treatments that do not involve hexavalent chromium
Solution Approach 2:
The invention changes the chemical composition parameters of the coating layer by specifying precise ranges of Zn (3-11 mass%), Al (0.03-0.3 mass%), and Si (0.03-0.3 mass%), replacing the traditional chromate-based protection mechanism with a controlled metallic coating composition that provides equivalent or superior performance without toxic substances
2Object-affected harmful factors
If Sn-based plated steel sheet without chromate treatment is used to improve environmental safety, then yellowing resistance, coating film adhesiveness, and sulfurization blackening resistance deteriorate due to tin oxide growth
Solution Approach 1:
The invention creates a composite coating layer structure containing multiple elements (Zn, Al, Si, and optionally Ti, Ni, Co, Cu, In) that work synergistically to prevent tin oxide growth and maintain coating adhesion, replacing the single-chromate protection mechanism with a multi-element protective system
Solution Approach 2:
The coating layer acts as an intermediary barrier between the Sn-based plating layer and the external environment, preventing direct oxidation of tin while providing a stable surface for coating adhesion without requiring chromate treatment
3Object-affected harmful factors
If Sn-based plated steel sheet without chromate treatment is used to improve environmental safety, then external appearance stability deteriorates due to tin oxide growth
Solution Approach 1:
The invention converts the inherent reactivity of tin (which causes oxidation and yellowing) into a benefit by using controlled alternative plating compositions that form protective layers, turning the vulnerability of Sn into an opportunity for environmentally safe protection
4Reliability
If chromate treatment is used to improve sulfurization blackening resistance, then the resistance to sulfurization is improved, but environmental safety deteriorates due to hexavalent chromium
Solution Approach 1:
The invention extracts the sulfurization blackening resistance function from the chromate treatment and implements it through the controlled composition of the coating layer itself, eliminating the need for hexavalent chromium while maintaining the protective function
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 solution significantly enhances yellowing resistance, coating film adhesiveness, and sulfurization blackening resistance without the need for chromate treatment, making it suitable for applications like food and beverage cans.
Implementation Method 1
the prevention of yellowing of an external appearance owing to the suppression of oxidation of the surface of the Sn-based plating layer
Implementation Method 2
The Sn-based plated steel sheet is mainly manufactured by an electroplating method
Implementation Method 3
After plating or after being given beautiful metallic luster by the heating and melting treatment after plating
Data Source
AI summary
To provide a Sn-based plated steel sheet excellent in yellowing resistance, coating film adhesiveness, and sulfurization blackening resistance without performing the conventional chromate treatment.A Sn-based plated steel sheet of the present invention includes: a steel sheet; a Sn-based plating layer located on at least one surface of the steel sheet; and a coating layer located on the Sn-based plating layer, wherein: the Sn-based plating layer contains 0.10 to 15.00 g/m2 of Sn per side in terms of metal Sn; the coating layer contains a Zr oxide and a Mn oxide; a content of the Zr oxide is 0.20 to 50.00 mg/m2 per side in terms of metal Zr; a content of the Mn oxide in terms of metal Mn is 0.01 to 0.50 times on a mass basis relative to the content of the Zr oxide in terms of metal Zr; and a depth position A where an element concentration of Mn is maximum is located on a side closer to a surface of the coating layer than a depth position B where an element concentration of Zr is maximum, and a distance in a depth direction between the depth position A and the depth position B is 2 nm or more in an element analysis in the depth direction by XPS.