Surface-Treated Steel Sheet Coating for Wet Paint Adhesion

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Solution Overview

Problem

Conventional surface-treated steel sheets without hexavalent chromium suffer from insufficient paint secondary adhesion in wet environments and loss of metallic luster, failing to meet the requirements for sulfide staining resistance and appearance in actual can conditions.

Innovation Solution

A surface-treated steel sheet with a Ni-containing 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 through specific surface conditioning and water washing processes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a surface-treated steel sheet is produced without hexavalent chromium to meet environmental regulations, then environmental compliance is improved, but paint secondary adhesion in wet environments and appearance (metallic luster) deteriorate

Engineering Contradiction:

Improveenvironmental complianceVSAvoidpaint secondary adhesion

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent changes the chemical composition parameters of the coating layer by specifying precise ratios of Zr, Ti, and other metal oxides, along with controlling the water contact angle and adsorbed ion concentrations, to achieve both environmental compliance and excellent paint adhesion without hexavalent chromium

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses a composite coating layer containing multiple metal oxides (Zr oxide, Ti oxide, and other metal oxides) that work synergistically to provide corrosion resistance, paint adhesion, and environmental compliance, replacing the single-component hexavalent chromium system

Inventive Principle:

Principle #40Composite materials

2Object-affected harmful factors

If a surface-treated steel sheet is produced without hexavalent chromium to meet environmental regulations, then environmental compliance is improved, but appearance (metallic luster) deteriorates

Engineering Contradiction:

Improveenvironmental complianceVSAvoidmetallic luster

Core Design Contradiction:

Object-affected harmful factorsVSIllumination intensity

Solution Approach 1:

The patent controls the water contact angle within a specific range (5° to 75°) and adjusts the composition ratios of metal oxides in the coating layer to maintain the bright metallic luster appearance while using environmentally friendly materials instead of hexavalent chromium

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If a zirconium compound coating is applied to replace chromating treatment, then hexavalent chromium usage is eliminated, but paint secondary adhesion in wet environments becomes insufficient

Engineering Contradiction:

Improvehexavalent chromium eliminationVSAvoidpaint secondary adhesion in wet environments

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent enhances the simple zirconium compound coating by adding titanium oxide and other metal oxides to create a composite coating layer that provides synergistic effects, improving paint secondary adhesion in wet environments while maintaining hexavalent chromium elimination

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent optimizes the water contact angle and controls the concentrations of adsorbed ions (K, Na, Mg, Ca) to specific ranges to enhance the hydrophilicity and surface properties of the coating, thereby improving paint adhesion in wet conditions

Inventive Principle:

Principle #35Parameter changes

4Object-affected harmful factors

If trivalent chromium is used to form a surface treatment layer without hexavalent chromium, then environmental compliance is improved, but appearance (metallic luster) is lost

Engineering Contradiction:

Improvehexavalent chromium eliminationVSAvoidmetallic luster

Core Design Contradiction:

Object-affected harmful factorsVSIllumination intensity

Solution Approach 1:

The patent controls the water contact angle within a specific range (5° to 75°) and optimizes the metal oxide composition ratios to restore and maintain the bright metallic luster appearance that was lost in conventional trivalent chromium treatments, while remaining environmentally compliant

Inventive Principle:

Principle #35Parameter changes

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

excellent sulfide staining resistance

Methodology Applied

Scientific EffectChemical resistance:

Implementation Method 2

adhesion to the paint layer in wet environments

Methodology Applied

Scientific EffectAdhesion: Adhesive

Data Source

PatentEP4617401A1Surface-treated steel sheet and method for producing same

Publication Date: 2025.09.17 JFE STEEL CORP

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 Ni-containing layer and a coating layer disposed on the Ni-containing 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.