Dual Cure Coating Composition for Thermoforming
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Solution Overview
Problem
Radiation curing of thick pigmented systems and 3D shaped substrates is challenging due to light penetration issues, and existing coatings face cracking problems during thermoforming due to high crosslinking density, which affects their stretchability and adhesion.
Innovation Solution
A dual cure coating composition that combines radiation and thermal curing mechanisms, using hydroxyl functional urethane (meth)acrylate compounds with specific molecular weights and hydroxyl values, along with isocyanate functional compounds, to achieve high adhesion and resistance while allowing for post-forming without cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If radiation curing is used to achieve high crosslinking density and good surface properties, then coating performance is improved, but light penetration is blocked by pigments making deep curing difficult
Solution Approach 1:
The patent combines radiation curing (UV/actinic) and thermal curing mechanisms in a dual-cure coating composition. The coating contains both photopolymerizable groups (acrylate/methacrylate) and thermally curable groups (isocyanate-hydroxyl reactive groups), allowing simultaneous or sequential activation by both radiation and heat to achieve complete curing throughout thick pigmented coatings where light penetration is limited
Solution Approach 2:
The coating composition uses a composite chemical system with multiple curable functional groups: hydroxyl-functional urethane (meth)acrylate compounds providing both photopolymerization capability and thermal crosslinking capability through isocyanate reaction. This composite material structure enables the coating to respond to both radiation and thermal energy for comprehensive curing
2Strength
If high crosslinking density is achieved for good surface properties, then coating strength is improved, but the coating becomes prone to cracking during thermoforming
Solution Approach 1:
The patent controls the molecular weight and hydroxyl value parameters of the urethane (meth)acrylate compound to optimize the balance between crosslinking density and flexibility. By selecting specific ranges of these parameters, the coating achieves sufficient crosslinking for strength while maintaining adequate elongation capability for thermoforming operations without cracking
3Productivity
If radiation curing is used for fast curing, then productivity is improved, but shadow areas on 3D substrates remain uncured
Solution Approach 1:
The dual-cure mechanism combines radiation curing for rapid surface and accessible area curing with thermal curing that can penetrate and cure shadow areas on 3D substrates. The thermal component activates the isocyanate-hydroxyl crosslinking reaction in regions where UV light cannot reach, ensuring complete and uniform curing throughout the entire coating
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 provides coatings with excellent stain resistance, high elongation without cracking, and strong adhesion to polymeric substrates, suitable for thermoforming and other applications requiring block-resistant and post-formable films.
Implementation Method 1
Radical polymerization is generally obtained through application of light radiation (typically UV light) often with help of a photoinitiator thereby the common designation of 'radiation curable compositions'
Implementation Method 2
In addition to photopolymerization, they can also rely on a curing mechanism independent of irradiation, for example a crosslinking reaction of polyisocyanates with polyols
Data Source
AI summary
The present invention provides a radiation curable composition comprising a hydroxyl functional urethane (meth)acrylate compound (A) having an hydroxyl value between 10 and 80 mg KOH/g and which is the reaction product of a hydroxyl functional (meth)acrylate compound (A1) obtained from the reaction a or b: a.at least one diepoxy functional compound (A11a) with a (meth)acrylate compound (A11b) comprising at least one (meth)acrylate group and one carboxylic acid functional group or b.a carboxylic acid functional compound (A12a) comprising two carboxylic acid groups with an epoxy (meth)acrylate compound (A12b) comprising one glycidyl group and at least one (meth)acrylate group, with a diisocyanate functional compound (A3), and optionally a compound (A2) different of compound (A1) comprising two hydroxyl groups. Such composition is useful for example for dual curable compositions or for thick pigmented systems.