Ultraviolet Curable Composition for Flexible Display Coatings
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Solution Overview
Problem
Ultraviolet curable compositions used for surface coatings on flexible displays and touch panels suffer from inadequate flexibility and hardness, leading to issues like whitening and damage when flexed.
Innovation Solution
Incorporating an alkylene diol with 1 to 5 carbon atoms having two or more polymerizable unsaturated groups and a photopolymerization initiator with an absorption peak between 320 to 460 nm into the urethane resin, which reacts with a polyisocyanate to form a coating film with improved elongation and surface hardness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If an aqueous polyurethane dispersion is used for surface coating, then adhesion to substrate is improved, but flexibility and hardness of coating film deteriorate
Solution Approach 1:
The patent uses a composite polyol system combining polyester polyol and polyether polyol in specific ratios (60-90 wt% polyester, 10-40 wt% polyether) to achieve both flexibility and hardness. This composite material approach allows the coating film to exhibit both good adhesion and mechanical properties simultaneously.
Solution Approach 2:
The patent optimizes the molecular weight of the polyol within a specific range (1,000-10,000 g/mol) and controls the NCO/OH ratio (0.95-1.05) to achieve the desired balance between flexibility and hardness. By adjusting these parameters, the coating film properties can be tuned to meet both adhesion and mechanical strength requirements.
2Productivity
If conventional photopolymerization initiators are used, then curing speed is improved, but yellowing of coating film occurs
Solution Approach 1:
The patent employs a photopolymerization initiator that operates effectively at lower UV intensities and shorter exposure times, enabling rapid curing without the harmful side effects of conventional initiators. This allows for quick curing while preventing yellowing, making the process both efficient and visually stable.
Solution Approach 2:
The patent selects a photopolymerization initiator with specific absorption characteristics that matches the UV LED wavelength (365 nm), optimizing the curing efficiency while avoiding the yellowing issue associated with conventional initiators. This parameter optimization enables fast curing without compromising color stability.
3Stability of the object's composition
If the coating film is made softer to improve flexibility, then elongation is improved, but surface hardness deteriorates
Solution Approach 1:
The patent creates a composite polymer network through the reaction of polyester polyol and polyether polyol with polyisocyanate, forming a crosslinked structure that inherently provides both flexibility and hardness. The synergistic interaction between the two polyol components enables the coating film to achieve elongation of 50% or more while maintaining surface hardness of 2H or higher.
Solution Approach 2:
The patent introduces polymerizable unsaturated groups into specific portions of the polyol molecules, creating localized crosslinking sites within the coating film. This allows different regions of the polymer network to have different properties: some regions provide flexibility through the polyether segments, while others provide hardness through the crosslinked polyester regions.
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 resulting coating film exhibits excellent elongation and surface hardness, making it suitable for use on substrates like ABS resin, PC resin, and PET resin, and can be effectively cured using an LED lamp without yellowing.
Implementation Method 1
a photopolymerization initiator (C) having an absorption peak at a wavelength in the range of from 320 to 460 nm
Data Source
AI summary
The present invention provides an ultraviolet curable composition including: an urethane resin having a polymerizable unsaturated group, which is obtained by reacting a polyol and a polyisocyanate with each other, wherein the polyol contains an alkylene diol having two or more polymerizable unsaturated groups, which is represented by general formula (1), or an oxyalkylene diol having two or more polymerizable unsaturated groups, which is represented by general formula (2); an aqueous medium; and a photopolymerization initiator having an absorption peak at a wavelength in the range of from 320 to 460 nm. The ultraviolet curable composition is satisfactorily cured even when using an LED lamp as a light source, and can form a cured coating film having both elongation and surface hardness. HO-R1-OH (1) HO-R1O-R2-OR3-OH (2)