Iron-Doped Brass Steel Cord Rubberization for Cobalt-Free Tire Adhesion
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Solution Overview
Problem
Existing sulfur-curable rubber compounds for steel cords in pneumatic vehicle tires rely on cobalt-based bonding systems, which are harmful to health and the environment, and their removal leads to undesirable changes in compound properties, particularly extended vulcanization times and reduced adhesion over time.
Innovation Solution
A sulfur-crosslinkable, cobalt-free rubber compound using sulfenimide and sulfenamide accelerators, such as N-tert-butyl-2-benzothiazolesulfenimide (TBSI) and N,N'-dibenzyl-2-benzothiazolesulfenamide (DBBS), along with iron-doped brass coatings, to achieve optimal vulcanization times and improved adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cobalt-based bonding systems are used in sulfur-curable rubber compounds for steel cords, then adhesion under stress in humid and hot environments is improved, but health and environmental harm increases and material cost increases
Solution Approach 1:
The patent removes cobalt-based bonding systems from the rubber compound formulation, extracting the harmful element while maintaining the adhesive function through alternative chemistry. The cobalt salt is completely eliminated from the compound, and adhesion is achieved through a different mechanism involving sulfenimide/sulfenamide accelerators and iron-doped brass coating.
Solution Approach 2:
The patent replaces expensive cobalt salts with a more economical accelerator system based on sulfenimide and sulfenamide compounds. This substitution reduces material cost while achieving the required adhesion performance through the synergistic interaction of the accelerator system with the iron-containing brass coating.
2Object-affected harmful factors
If cobalt compounds are removed from rubber compounds, then health and environmental harm is reduced, but vulcanization times become significantly longer
Solution Approach 1:
The patent changes the chemical parameters of the vulcanization system by introducing sulfenimide and sulfenamide accelerators in specific proportions (0.5-3 phr of sulfenimide and/or 0.5-3 phr of sulfenamide based on dibenzylamine). This parameter change enables rapid vulcanization without cobalt, achieving t90 times comparable to or better than cobalt-containing systems.
Solution Approach 2:
The patent creates a composite adhesion system combining the rubber compound with iron-doped brass coating on the steel cord. The iron particles (10-1000 nm) in the brass coating work synergistically with the sulfenimide/sulfenamide accelerators to achieve rapid vulcanization and strong adhesion without cobalt.
3Productivity
If larger amounts of vulcanization accelerator are used to counteract extended vulcanization times, then vulcanization speed is improved, but initial crosslinking proceeds too quickly preventing sufficient adhesive layer formation
Solution Approach 1:
The patent uses a balanced combination of sulfenimide and sulfenamide accelerators in controlled amounts (0.5-3 phr each) rather than excessive accelerator loading. This partial action approach provides sufficient vulcanization speed while maintaining the adhesive function, avoiding the problem of overly rapid initial crosslinking that would prevent proper adhesive layer formation.
Solution Approach 2:
The patent creates a dynamic vulcanization system where the sulfenimide and sulfenamide accelerators work in sequence or synergy to provide both rapid initial crosslinking and sustained adhesive layer formation. The iron-doped brass coating also contributes dynamically to the adhesion process, ensuring continuous bond development during vulcanization.
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 provides a balance between initial and final crosslinking times, ensuring good adhesion even after aging, while being environmentally friendly and cost-effective, with improved processability and durability.
Implementation Method 1
a sulfur-crosslinkable, essentially cobalt-free rubberizing mixture
Implementation Method 2
vulcanization times become significantly longer
Implementation Method 3
The adhesion of steel cords to a rubber matrix is achieved via brass (on the steel) and sulfur (from the rubber compound)
Data Source
AI summary
The invention relates to a metallic strength member rubberized with a sulfur-crosslinkable, substantially cobalt-free rubberization mixture, wherein the metallic strength member is a steel cord containing one or more filaments, wherein the filaments comprise a filament-like steel substrate and a coating partially or completely covering the filament-like steel substrate, wherein the coating comprises brass consisting of copper and zinc, and wherein the coating is enriched with iron which is present in the brass in the form of particles having a size between 10 and 10 000 nm. To optimize vulcanization times, the rubberization mixture contains 0.5 to 3 phr of at least one sulfenimide accelerator and/or at least one sulfenamide accelerator based on dibenzylamine.