Curable Silicone Composition for Low-Yellowing Optical Adhesion
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Solution Overview
Problem
Existing curable silicone compositions face challenges in achieving high adhesive strength to substrates with hard coat layers, such as polarizing plates, while maintaining transparency and avoiding yellowing, especially under high temperature conditions, and require improved curing mechanisms that do not rely on UV light penetration.
Innovation Solution
A curable silicone composition comprising specific components (A, B, C, and D) that include organopolysiloxanes with alkenyl groups, organohydrogenpolysiloxanes, and a platinum group metal catalyst activated by light, with controlled ratios of silicon-bonded hydrogen atoms and platinum atoms, ensuring effective adhesion and minimal yellowing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If an ultraviolet light curable composition is used, then curing can be achieved at low temperatures, but portions where ultraviolet light does not penetrate are not properly cured
Solution Approach 1:
The patent introduces a photo-initiator as an intermediary substance that absorbs ultraviolet light and converts it into chemical energy to activate the curing reaction. This mediator enables the curing process to proceed even in areas where direct UV light penetration is limited, as the photo-initiator distributes the activation throughout the composition.
Solution Approach 2:
The patent replaces the direct mechanical/physical UV light curing mechanism with a chemical initiation mechanism. Instead of relying solely on UV light penetration to drive polymerization, the system uses photo-initiators that convert UV energy into chemical reactions that can propagate through the material more effectively.
2Reliability
If a large amount of platinum catalyst is used to achieve curing with ultraviolet light, then curing can proceed, but yellowing occurs over time
Solution Approach 1:
The patent optimizes the concentration of platinum catalyst to a specific range that is sufficient to enable curing but low enough to minimize yellowing. By precisely controlling the catalyst amount and using photo-initiators that operate efficiently at lower catalyst concentrations, the system achieves curing while reducing the harmful yellowing effect.
Solution Approach 2:
The patent employs photo-initiators with short activation lifetimes that convert UV energy rapidly and then decompose into harmless byproducts. These short-living photo-active components replace the need for large amounts of persistent platinum catalyst, reducing both cost and long-term yellowing while maintaining effective curing.
3Strength
If conventional ultraviolet light curable composition is used on polarizing plates with hard coat layers, then adhesion is attempted, but poor adhesion occurs due to curing inhibition
Solution Approach 1:
The patent uses photo-initiators with specific absorption characteristics that are tailored to penetrate through the hard coat layer on polarizing plates. By selecting photo-initiators with appropriate wavelength absorption profiles, the system achieves localized activation through the coating, enabling curing and adhesion where conventional UV compositions fail.
Solution Approach 2:
The patent creates a composite curing system combining multiple photo-initiators with different activation characteristics and silicon-based precursors. This composite approach allows the composition to overcome the hard coat layer barrier, achieving both curing through the coating and strong adhesion to the polarizing plate surface.
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 exhibits high adhesive strength to glass and polarizing plates with hard coat layers, maintains transparency, and minimizes yellowing even under high temperatures, suitable for optical displays and touch panels.
Implementation Method 1
a platinum group metal catalyst activated by light having a wavelength of 200 to 500 nm
Implementation Method 2
an organohydrogenpolysiloxane having at least three silicon-bonded hydrogen atoms per molecule
Data Source
AI summary
Provided is a curable silicone composition which is ultraviolet light delay curable, transparent, shows little yellowing even under high temperature conditions, and which can show high adhesive strength even to substrates that show reduced adhesive strength/difficulty in adhesion, such as certain polarizing plates, and uses thereof. The composition contains: (A) an organopolysiloxane having an alkenyl group; (B) (b1) a linear polysiloxane having SiH at terminals of the molecular chain, and (b2) a polysiloxane having three or more silicon bonded hydrogen atoms; (C) one or more types of compounds selected from (c1) compounds having two or more alkoxysilyl groups in one molecule, and (c2) organic compounds having an alkoxysilyl group and an epoxy group in one molecule; and (D) a photoactive platinum group metal catalyst. The composition has a SiH/Vi ratio of 1 or more and a platinum content in component (D) of 15 ppm or less, calculated as solid fractions, as well as uses thereof.