Rub-to-Metal Primer with Blocked Isocyanate Crosslinking
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Solution Overview
Problem
Conventional rubber-to-metal bonding systems face issues with time-consuming application processes, evaporation of cross-linkers leading to mould fouling and health hazards, limited pre-bake resistance, red rust formation, poor adhesion on zinc phosphate surfaces, and reduced aging resistance, especially due to the instability of chlorinated polyethylene at high temperatures and the soft, waxy nature of nitroso compounds.
Innovation Solution
A curable composition comprising hydroxyl-group containing resins, nitroso-containing compounds, blocked isocyanates, and crystallization germs, which provides excellent adhesion, pre-bake performance, steam resistance, and scratch resistance by crosslinking and crystallizing to form a durable, stable primer coating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high amount of nitroso compound is used as crosslinker to ensure scratch resistance, then scratch resistance is improved, but the coating becomes tacky and waxy with poor adhesion
Solution Approach 1:
A blocked isocyanate is introduced as an intermediary substance that reacts with the nitroso compound to form a crosslinked network. This mediator enables the nitroso compound to provide scratch resistance through crosslinking without remaining as free soft/waxy material that would cause tackiness and poor adhesion. The blocked isocyanate controls the reaction timing and spatial distribution of crosslinking.
Solution Approach 2:
The chemical state of the isocyanate is changed from active to blocked form, allowing it to remain stable during application and only activate under specific conditions (heat, moisture). This parameter change enables controlled crosslinking after application, transforming the coating from a tacky state to a rigid, adherent state without compromising scratch resistance.
2Ease of manufacture
If chlorinated polyethylene is used as film former, then film formation is improved, but HCl is released at high temperatures causing corrosion and red rust
Solution Approach 1:
The harmful chlorine element is extracted from the film former molecule by replacing chlorinated polyethylene with a non-chlorinated alternative. This extraction eliminates the source of HCl release while maintaining the essential film-forming functionality through other polymer mechanisms.
Solution Approach 2:
The thermal stability issue of chlorinated polyethylene is addressed by selecting a different polymer that inherently provides thermal stability without HCl release. The new film former converts the potential harm (thermal degradation) into a benefit (thermal stability) by choosing materials that maintain integrity at vulcanization temperatures.
3Reliability
If two coat systems are used for rubber to metal bonding, then adhesion performance is improved, but application process becomes time-consuming
Solution Approach 1:
The functions of multiple coating layers are merged into a single multi-functional coating layer. This single layer simultaneously provides adhesion promotion, crosslinking capability, and film formation properties that were previously distributed across two separate coats, thereby reducing application time while maintaining adhesion performance.
Solution Approach 2:
The curable composition is designed to perform multiple functions within a single coating system: it acts as an adhesion promoter, a crosslinking agent, and a film former. This multi-functionality eliminates the need for separate coating steps while ensuring comprehensive performance in adhesion and durability.
4Strength
If nitroso compound is used as crosslinker, then crosslinking capability is improved, but evaporation during vulcanization leads to mould fouling and health issues
Solution Approach 1:
The blocked isocyanate serves as an intermediary that reacts with the nitroso compound to form crosslinks. This intermediary approach allows the nitroso compound to fulfill its crosslinking function while being consumed in the reaction, preventing free nitroso compound from evaporating during vulcanization and causing mould fouling or health issues.
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 composition significantly improves adhesion and aging resistance, offering a scratch-resistant and durable bond between rubber and metal substrates, preventing adhesion failure and corrosion, while allowing for easy transportation and storage of coated substrates.
Implementation Method 1
the hydroxyl-group containing resin, especially phenoxy/epoxy systems, which are crosslinked by the blocked isocyanates
Implementation Method 2
at least one crystallization germ suitable as primer or coating for rubber to substrate bonding, which provides a scratch resistant primer surface
Data Source
AI summary
The subject matter is a new composition comprising at least one hydroxyl-group containing resin, at least one nitroso-containing compound or at least one nitroso precursor compound, at least one blocked isocyanate and at least one crystallization germ suitable as primer or coating for rubber to substrate bonding, which provides a scratch resistant surface, when applied, and excellent adhesion and steam resistance for rubber to substrate bonds. These compositions can especially be used as one coat systems.