Dual-Cure Conformal Coating Viscosity and Curing Balance
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Solution Overview
Problem
Dual-cure polyurethane resins used as conformal coatings face challenges with high viscosity, which affects their ability to evenly coat contoured surfaces, and reducing viscosity with reactive diluents compromises the moisture cure mechanism, leading to insufficient hardness and solvent resistance in shadow areas.
Innovation Solution
A one-component composition comprising at least 40% isocyanate-functional urethane (meth)acrylate and 10-30% polyisocyanate with allophanate and/or uretdione groups, achieving a viscosity of less than 800 mPa.s and maintaining an isocyanate content greater than 5%, allowing for effective curing by both actinic radiation and atmospheric moisture while maintaining hardness and solvent resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dual-cure polyurethane resins are used to ensure adequate curing in shadow areas, then the coating achieves sufficient hardness and solvent resistance, but the viscosity becomes too high for good flowability on contoured surfaces
Solution Approach 1:
The patent modifies the chemical composition parameters of the resin system by incorporating specific ratios of polyisocyanate (10-30 wt%), isocyanate-functional urethane (meth)acrylate (40-95 wt%), and reactive diluent (5-40 wt%). This parameter optimization achieves a balanced viscosity range (200-800 cP) that maintains both flowability for contoured surface application and sufficient isocyanate content (>5 wt%) for effective moisture curing in shadow areas.
2Ease of operation
If reactive diluent is added to reduce viscosity, then the coating flows better on contoured surfaces, but the isocyanate content decreases and moisture cure mechanism becomes ineffective
Solution Approach 1:
The patent establishes optimized concentration ranges for each component to balance viscosity reduction with isocyanate content maintenance. Specifically, the reactive diluent is limited to 5-40 wt% while polyisocyanate is maintained at 10-30 wt%, ensuring the final formulation achieves both adequate flowability and sufficient isocyanate content (>5 wt%) for effective moisture curing.
Solution Approach 2:
The patent creates a composite resin system combining multiple functional components: polyisocyanate for moisture cure, isocyanate-functional urethane (meth)acrylate for UV cure and additional isocyanate content, and reactive diluent for viscosity control. This composite approach allows the system to simultaneously achieve good flowability and effective dual-cure mechanism.
3Reliability
If high isocyanate content is maintained for effective moisture curing, then shadow areas achieve sufficient hardness, but the viscosity increases and flowability decreases
Solution Approach 1:
The patent formulates a composite system where isocyanate-functional urethane (meth)acrylate serves dual purposes: providing isocyanate groups for moisture curing in shadow areas and containing polymerizable double bonds for UV curing. This composite structure allows the resin to maintain adequate isocyanate content (>5 wt%) for hardness while the overall formulation viscosity is controlled through balanced component ratios.
Solution Approach 2:
The patent optimizes the weight percentage parameters of each component to achieve a viscosity range (200-800 cP) that permits both adequate isocyanate content for moisture curing and sufficient flowability for application. The specific parameter ranges established ensure that hardness in shadow areas and flowability are simultaneously achieved.
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 ensures sufficient hardness and solvent resistance, especially in shadow areas, by balancing viscosity and isocyanate content, enabling effective curing on contoured surfaces without compromising flowability or curing efficiency.
Implementation Method 1
The atmospheric moisture reacts with free isocyanate groups in the dual cure resin forming an amine group(s). The amine groups react with other isocyanate groups to form a polyurea.
Implementation Method 2
The amine groups react with other isocyanate groups to form a polyurea.
Implementation Method 3
coatings may be cured relatively quickly by exposure to a radiation source, typically UV light
Data Source
AI summary
Disclosed are one-component compositions that include: (1) an isocyanate-functional urethane acrylate and (2) a polyisocyanate containing allophanate and/or uretdione groups, wherein the one-component composition has a viscosity of less than or equal to about 800mPa.s and an isocyanate content of greater than about 5% by weight, based on the weight of the one-component composition. Also disclosed are circuit boards and electronic components that are coated with such compositions.