Radical-Curable Coating Composition for Crack-Free Thermal Embossing
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Solution Overview
Problem
Radiation-curable coatings fail to maintain surface quality during thermal processes like lamination or embossing, often leading to delamination, cracking, or formation of defects.
Innovation Solution
A radical-curable coating composition comprising specific oligomers, reactive diluents, photo-initiators, and thermal initiators, with controlled molar ratios and concentrations, allowing for photo-curing followed by thermal curing, ensuring flexibility and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If UV radiation curing is used to achieve fast drying and surface hardness, then the coating dries quickly and provides initial protection, but the coating becomes too rigid and cracks or delaminates during subsequent heat treatment
Solution Approach 1:
The curing process is divided into two distinct stages: first UV radiation curing to achieve rapid drying and surface hardness, then thermal curing to restore flexibility and prevent cracking. This segmentation allows each curing method to perform its optimal function without the drawbacks of using either method alone for the complete curing process.
Solution Approach 2:
UV radiation curing is applied as a preliminary action to quickly dry the coating and provide initial surface hardness before the substrate undergoes heat treatment. This preliminary curing enables the coating to withstand handling and initial processing, while the subsequent thermal curing step completes the process by eliminating brittleness and preventing cracks during high-temperature operations.
2Shape
If high temperature heat treatment is applied to achieve lamination or embossing, then the desired surface structure is obtained, but the UV-cured coating cracks or delaminates due to excessive rigidity
Solution Approach 1:
The curing process is divided into two distinct stages: first UV radiation curing to achieve rapid drying and surface hardness, then thermal curing to restore flexibility and prevent cracking. This segmentation allows each curing method to perform its optimal function without the drawbacks of using either method alone for the complete curing process.
Solution Approach 2:
The curing parameters are changed from UV radiation (wavelength, intensity) to thermal energy (temperature, time). By adjusting the curing parameters from cold UV radiation to hot thermal treatment, the coating transitions from a rigid state to a flexible state, enabling it to withstand the mechanical stresses of lamination and embossing without cracking or delaminating.
3Object-affected harmful factors
If 100% solids content coating is used to eliminate volatile compounds, then environmental friendliness is improved, but the coating thickness reduction during curing is minimized, making it harder to maintain flexibility during subsequent processing
Solution Approach 1:
The curing process is divided into two distinct stages: first UV radiation curing to achieve rapid drying and surface hardness, then thermal curing to restore flexibility and prevent cracking. This segmentation allows each curing method to perform its optimal function without the drawbacks of using either method alone for the complete curing process.
Solution Approach 2:
The coating system uses a composite curing mechanism combining UV radiation curing and thermal curing. This composite approach leverages the advantages of both curing methods: UV curing provides rapid drying with minimal volatile emission, while thermal curing adds flexibility and prevents cracking during subsequent high-temperature processing.
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 composition maintains surface quality and flexibility during thermal treatments, enabling embossing without cracking and providing stain resistance, allowing handling and storage before achieving a hard, scratch-resistant finish.
Implementation Method 1
radical-curable coating compositions polymerizable by e-beam or by ultraviolet radiation (UV). In general the cross-linking mechanism involves the use of actinic sources or ultraviolet radiation lamps (UV)
Implementation Method 2
One or more thermal initiators, wherein the acrylate functionalities of the acrylate reactive diluents (C) and the methacrylate functionalities of the methacrylate reactive diluents (B) are present in a molar ratio of the acrylate functionalities to the methacrylate functionalities of at least 0.2
Data Source
AI summary
The present invention is directed to a radical-curable coating composition comprising(A) One or more oligomers selected from the group consisting of urethane (meth)acrylates, (meth)acrylated epoxidized triglycerides and any mixture thereof, wherein said oligomers have a molar mass equal to or higher than 800 g/mol and lower than 4500 g/mol,(B) One or more methacrylate reactive diluents having a molar mass lower than 800 g/mol, wherein said methacrylate reactive diluents have an average methacrylate functionality higher than 2,(C) One or more acrylate reactive diluents having a molar mass lower than 800 g/mol, wherein said acrylate reactive diluents have an average acrylate functionality higher than 2,(D) One or more photo-initiators, and(E) One or more thermal initiators,wherein the acrylate functionalities of the acrylate reactive diluents (C) and the methacrylate functionalities of the methacrylate reactive diluents (B) are present in a molar ratio of the acrylate functionalities to the methacrylate functionalities of at least 0.2,wherein the amount of oligomers (A) is higher than 20 wt. % and lower than 90 wt. % and the amount of reactive diluents (B) and (C) is higher than 10 wt. % and lower than 80 wt. %, based on the total amount of (A), (B) and (C), andwherein the total amount of (A), (B) and (C) is at least 25 wt. % of the radical-curable coating composition.