Surface-Treated Steel Sheet for BPA-Free Paint Corrosion Resistance
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Solution Overview
Problem
Conventional surface-treated steel sheets exhibit poor corrosion resistance at BPA-free painted worked parts and are unable to maintain adhesion with BPA-free paint, despite having excellent adhesion and corrosion resistance with epoxy-based paint, making it difficult to replace epoxy-based paint without using hexavalent chromium.
Innovation Solution
A surface-treated steel sheet with a chromium-containing layer that includes linear regions where elements smaller in atomic number than chromium are concentrated, formed by contacting the steel sheet with an aqueous solution containing sulfate ions and undergoing cathodic electrolysis treatment in a trivalent chromium ion solution, controlling the number and structure of these regions to enhance corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If hexavalent chromium treatment is used to form a chromium oxide layer, then adhesion to organic resin coating is improved, but environmental harm increases due to restrictions on hexavalent chromium use
Solution Approach 1:
The patent creates a composite chromium-containing layer that combines chromium with other elements (C, N, O, and optionally B, Si, P, S) to form a multi-component surface treatment layer. This composite structure achieves the desired adhesion and corrosion resistance properties while avoiding hexavalent chromium
2Object-affected harmful factors
If conventional electrolysis treatment with trivalent chromium is used, then hexavalent chromium use is avoided, but corrosion resistance at BPA-free painted worked parts deteriorates
Solution Approach 1:
The patent creates local compositional variations within the chromium-containing layer by concentrating light elements (C, N, O) in specific regions, forming a non-uniform structure that provides localized adhesion and corrosion resistance properties necessary for BPA-free paint applications
3Object-affected harmful factors
If BPA-free polyester-based paint is used instead of epoxy-based paint, then health safety is improved, but adhesion to the steel sheet deteriorates
Solution Approach 1:
The chromium-containing layer acts as an intermediary between the steel sheet and the BPA-free polyester-based paint. By optimizing the composition of this intermediate layer (controlling C, N, O concentrations), the patent enables effective adhesion between the paint and steel sheet without requiring BPA-containing epoxy paint
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 corrosion resistance at BPA-free painted worked parts without using hexavalent chromium, suitable for use in containers and other applications.
Implementation Method 1
subjecting the steel sheet to cathodic electrolysis treatment in an electrolytic solution containing 0.05 mol/L or more of trivalent chromium ions
Implementation Method 2
a chromium-containing layer disposed on a surface of the steel sheet on at least one side
Data Source
AI summary
Provided is a surface-treated steel sheet that can be produced without using hexavalent chromium and has excellent corrosion resistance at BPA-free painted worked part. A surface-treated steel sheet comprises: a steel sheet; and a chromium-containing layer disposed on a surface of the steel sheet on at least one side, wherein when the chromium-containing layer is observed from a surface direction, linear regions in which an element smaller in atomic number than chromium is concentrated are present, and the number of the linear regions is 5.0 or more per 100 nm.