Tinplate Strip Passivation With Chromium-Free Homogeneous Oxide Layers

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Solution Overview

Problem

Existing methods for passivating tinplate surfaces using dichromate or chromic acid solutions are harmful and result in non-homogeneous oxide layers, leading to variations in corrosion resistance and adhesion, especially when exposed to sulfur-containing substances.

Innovation Solution

A method involving cathodic removal of pre-existing oxide layers followed by anodic re-oxidation in a sodium carbonate solution, followed by application of a chromium-free post-treatment agent, ensuring a homogeneous tin oxide layer consisting mainly of SnO, which is then stabilized with a post-treatment agent.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If dichromate or chromic acid solution is used for passivation, then corrosion resistance and adhesion are improved, but harmful Cr6+ chemicals are introduced and environmental safety deteriorates

Engineering Contradiction:

Improvecorrosion resistanceVSAvoidharmful Cr6+ chemicals

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The invention changes the chemical composition parameters of the passivation solution by replacing Cr6+ containing dichromate or chromic acid solutions with a chromium-free electrolyte solution containing zinc salts and ammonium salts, thereby eliminating harmful chemicals while maintaining passivation functionality

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention uses readily available, inexpensive zinc salts and ammonium salts as substitutes for expensive and hazardous chromium-based chemicals, providing an economical and environmentally friendly alternative that can be easily disposed of or regenerated

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Reliability

If anodic oxidation is applied to form tin oxide layer, then corrosion resistance is improved, but oxide layer homogeneity across strip width deteriorates

Engineering Contradiction:

Improvecorrosion resistanceVSAvoidoxide layer homogeneity

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The invention replaces the mechanical/electrochemical anodic oxidation process with an electrochemical reduction process using a cathodic treatment, where electrons are supplied to reduce tin ions to metallic tin, creating a homogeneous surface layer across the entire strip width

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The invention achieves homogeneous distribution of the treated layer across the strip width by using a cathodic electrolyte treatment where the electrolyte uniformly contacts the entire surface, ensuring consistent composition and properties throughout the passivated layer

Inventive Principle:

Principle #33Homogeneity

3Productivity

If pre-existing oxide layer is not removed, then processing time is reduced, but adhesion of organic coatings deteriorates

Engineering Contradiction:

Improveprocessing speedVSAvoidadhesion of organic coatings

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The invention performs a preliminary cathodic treatment step before the main passivation process to completely remove pre-existing oxide layers and prepare a fresh, homogeneous tin surface, ensuring optimal adhesion properties for subsequent organic coatings

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The invention applies a preliminary cathodic reduction treatment to counteract and remove the detrimental effects of pre-existing oxide layers, preventing adhesion problems before they occur by creating a clean, reactive tin surface

Inventive Principle:

Principle #9Preliminary anti-action

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

Achieves consistent corrosion resistance and adhesion across the tinplate width, preventing sulfur staining and improving organic coating adhesion, while eliminating the use of harmful chemicals.

Implementation Method 1

the tinplate is led into the electrolyte solution as a cathode for cathodically removing the pre-existing oxide and producing a bare and pure tin surface

Methodology Applied

Scientific EffectElectrochemical reduction: Reduction

Implementation Method 2

the tinplate is led into the electrolyte solution as an anode for depositing a fresh and homogeneous tin oxide layer onto the bare and pure tin surface

Methodology Applied

Scientific EffectAnodic oxidation: Oxidation

Implementation Method 3

Tin is deposited as a whitish coating having a slight metallic lustre

Methodology Applied

Scientific EffectElectrodeposition: Electrodeposition

Data Source

PatentUS12359337B2Method for passivating a tinplate strip and apparatus for producing said passivated tinplate strip

Publication Date: 2025.07.15 TATA STEEL IJMUIDEN BV

AI summary

A method for passivating a tinplate strip after electrodepositing the tin layer or tin layers, or after an optional flow-melting of the electrodeposited tin layer or tin layers, and an apparatus for producing the passivated tinplate strip.