Radiation-Curable Coatings with Thiol-Acrylate Chemistry
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Solution Overview
Problem
Radiation-curable coatings face issues with oxygen inhibition during curing, leading to incomplete polymerization in shadow regions and requiring inert gas environments, and existing systems have high VOC levels and limited storage stability, with adhesion issues and slow curing at low temperatures.
Innovation Solution
The development of coating compositions comprising α-(1′-hydroxyalkyl)acrylates, thiols, reactive diluents, catalysts, and photoinitiators, which allow for curing at low temperatures and provide high adhesion and storage stability, enabling use as paints, sealants, and adhesives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If radiation curing is used to achieve fast curing speed, then curing speed is improved, but oxygen inhibition prevents complete polymerization in shadow regions and requires inert gas environments
Solution Approach 1:
The patent combines two different curing mechanisms: radiation curing (photopolymerization) and chemical curing (thiol-acrylate addition reaction). The coating composition contains both photoinitiators for UV/visible light curing and thiol groups that enable oxygen-independent chemical crosslinking. This merging allows the coating to cure rapidly under radiation while the thiol-acrylate reaction continues in shadow regions and provides oxygen inhibition resistance, eliminating the need for inert gas environments.
Solution Approach 2:
The invention uses a composite coating system containing multiple functional components: acrylate monomers/oligomers, thiol compounds, photoinitiators, and optional catalysts. This composite formulation integrates the advantages of different curing mechanisms - the speed of photopolymerization with the reliability of chemical crosslinking that proceeds independently of oxygen and light penetration, achieving both fast curing and complete polymerization throughout the coating thickness.
2Reliability
If two-component epoxy resin systems are used to achieve oxygen resistance, then oxygen resistance is improved, but toxic amines are required and reaction is slow at low temperatures
Solution Approach 1:
The patent changes the chemical parameters of the curing system by using thiol compounds (with S-H groups) instead of toxic amine curing agents. The thiol-acrylate addition reaction proceeds at lower temperatures and with different kinetics compared to epoxy-amine systems. Optional catalysts can further accelerate the reaction, enabling effective curing at low temperatures without requiring toxic substances, while maintaining oxygen resistance through the chemical crosslinking mechanism.
3Strength
If thiol and acrylate are mixed for immediate reaction, then adhesion is improved, but storage life is limited due to ongoing reaction
Solution Approach 1:
The patent performs preliminary action by pre-synthesizing α-(1′-hydroxyalkyl)acrylate groups through the reaction of acrylates with carbonyl compounds (aldehydes or ketones) before application. This preliminary chemical modification creates reactive groups that will subsequently react with thiol compounds during curing, ensuring strong adhesion. The pre-formed hydroxyalkylacrylate structures remain stable during storage but react efficiently with thiols when cured, separating the storage stability requirement from the adhesion mechanism.
4Speed
If high functionality thiol compounds are used to accelerate polymerization, then curing speed is improved, but stabilization becomes more difficult
Solution Approach 1:
The patent introduces dynamic control of the thiol-acrylate reaction through optional catalysts that can be activated at specific stages. The system allows the reaction to proceed slowly during storage (maintaining stability) and then accelerates rapidly during curing when catalysts are activated or conditions change. This dynamic behavior enables the use of high functionality thiol compounds for fast curing while maintaining system stability during storage through controlled reaction kinetics.
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 coating compositions cure effectively at low temperatures, offer high adhesion, and have improved storage stability, addressing the limitations of existing radiation-curable coatings by allowing curing in the presence of oxygen and reducing VOC levels.
Implementation Method 1
Coatings obtainable by radiation curing have been known for a long time... with the aid of a photoinitiator, to induce radicals
Implementation Method 2
the reacting of radiation-curable acrylates with compounds containing thiol groups... the copolymerization of acrylates with thiols
Implementation Method 3
optionally at least one catalyst (E2) which is able to accelerate the addition of thiol groups onto acrylate groups
Data Source
AI summary
The invention relates to coatings which can be obtained by adding mercapto groups to acrylates and/or by a radiation curing process, said coatings having good properties, to methods for producing same, and to the use thereof.