Cobalt-Free Rubber Composition for Steel Cord Adhesion

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Solution Overview

Problem

Sulfur-crosslinkable rubber mixtures for metallic reinforcements, particularly for brass-plated steel cords, face challenges due to the use of cobalt-based adhesive systems, which can lead to undesirable aging and health and environmental concerns, as well as rising cobalt prices, necessitating a cobalt-free alternative that maintains adhesion and durability.

Innovation Solution

A sulfur-crosslinkable rubber mixture essentially free of cobalt, utilizing 0.5 to 3 phr of sulfenimide accelerators and 0.25 to 5 phr of adhesion stabilizers like sodium hexamethylene-1,6-bisthiosulfate dihydrate, along with zinc oxide and methylene acceptor-donor pairs, to enhance adhesion and durability without cobalt.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If cobalt-based bonding systems are used to improve adhesion, then adhesion between steel cord and rubber is enhanced, but undesirable aging processes occur and health/environmental concerns arise

Engineering Contradiction:

ImproveadhesionVSAvoidaging resistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The invention extracts and removes cobalt compounds from the rubber compound formulation, replacing them with alternative adhesion promoters and stabilizers that do not cause oxidative aging, thereby eliminating the harmful effects while maintaining adhesion functionality

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention uses alternative adhesion promoters and stabilizers that are less expensive and environmentally friendly compared to cobalt compounds, providing a sustainable replacement that does not require expensive cobalt sourcing and processing

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Productivity

If cobalt salts are used as vulcanization accelerators, then vulcanization speed is improved, but oxidation catalysis occurs leading to reduced durability

Engineering Contradiction:

Improvevulcanization speedVSAvoiddurability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The invention removes cobalt salts from the vulcanization system and replaces them with alternative accelerators that do not possess strong oxidation catalysis activity, thereby maintaining vulcanization efficiency while preventing premature aging and durability loss

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention introduces alternative adhesion promoters and stabilizers that act as intermediaries to facilitate vulcanization and adhesion processes without the harmful oxidation catalysis effect of cobalt salts, mediating between the need for fast vulcanization and long-term durability

Inventive Principle:

Principle #24Intermediary (Mediator)

3Stability of the object's composition

If cobalt compounds are used to prevent zinc oxide and copper sulfide layer formation, then adhesion stability is improved, but health and environmental hazards increase

Engineering Contradiction:

Improveadhesion stabilityVSAvoidhealth and environmental hazards

Core Design Contradiction:

Stability of the object's compositionVSObject-affected harmful factors

Solution Approach 1:

The invention extracts cobalt compounds from the formulation and replaces them with environmentally benign alternatives that provide the same protective function against zinc oxide and copper sulfide layer formation without posing health or environmental hazards

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention uses alternative substances that convert the harmful cobalt-based protection mechanism into a beneficial, environmentally friendly adhesion stabilization system that achieves the same protective effect without the associated health and environmental risks

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 cobalt-free rubber mixture achieves improved adhesion and durability, especially at elevated temperatures, with enhanced resistance to oxidative aging, maintaining rubber-metal adhesion and extending the service life of rubberized reinforcement layers.

Implementation Method 1

sulfur-crosslinkable rubberizing compound

Methodology Applied

Scientific EffectVulcanization: Chemical Bonding

Implementation Method 2

sulfenimide accelerator

Methodology Applied

Scientific EffectCatalysis: Catalysis

Implementation Method 3

adhesion stabilizer acting after vulcanization... enhanced resistance to oxidative aging

Methodology Applied

Scientific EffectOxidation inhibition: Oxidation

Data Source

PatentEP4144787A1Sulphur-crosslinkable rubber composition and pneumatic vehicle tyre

Publication Date: 2023.03.08 CONTINENTAL REIFEN DEUTSCHLAND GMBH

AI summary

The invention relates to a sulfur-crosslinkable, essentially cobalt-free rubber compound for metallic reinforcing elements, containing 0.5 to 3 phr (parts by weight, based on 100 parts by weight of the total rubbers in the compound) of at least one sulfenimide accelerator and 0.25 to 5 phr of at least one adhesion stabilizer acting after vulcanization. The invention further relates to a vehicle tire comprising at least one such sulfur-crosslinked rubber compound.