Optically Clear Adhesive Sheet for Display Devices
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Solution Overview
Problem
Optically clear adhesive (OCA) sheets used in display devices with touchscreens face issues such as air gaps causing interfacial reflection, low adhesive strength, and susceptibility to air bubbles due to outgassing and poor wettability, especially at high temperatures and humidity levels.
Innovation Solution
A heat-curable polyurethane composition using a polyolefin-based polyol and acyclic or alicyclic polyisocyanates with a specific mole ratio, combined with a tackifier and plasticizer, to create an optically clear adhesive sheet that prevents air bubbles and maintains a stable bonded interface even at high temperatures and humidity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a thick OCA sheet is used to eliminate air gaps and improve visibility, then display screen visibility is improved, but the sheet becomes difficult to conform to uneven surfaces and may trap air bubbles
Solution Approach 1:
The patent modifies the chemical composition parameters of the adhesive, specifically using polyols with specific molecular weights (500-5000) and isocyanate group densities, along with adding lubricants and plasticizers, to achieve optimal balance between thickness and conformability without sacrificing either visibility or adaptability to uneven surfaces
2Illumination intensity
If silicone resin is used for OCA sheets to achieve optical clarity, then transparency is improved, but adhesive strength decreases allowing air to enter gaps
Solution Approach 1:
The patent creates a composite adhesive system combining polyurethane base resin with specific polyols (containing hydroxyl groups), isocyanates, lubricants, and plasticizers in controlled ratios to achieve both optical clarity and high adhesive strength that prevents air infiltration while maintaining transparency
3Strength
If acrylic resin is used for OCA sheets to achieve good adhesion, then adhesive strength is improved, but acid components corrode metals in optical members
Solution Approach 1:
The patent fundamentally changes the chemical composition by using polyol-isocyanate polyurethane systems instead of acrylic resins, eliminating carboxylic acid groups entirely while maintaining adhesive strength through urethane bond formation, thus preventing metal corrosion without sacrificing adhesion performance
4Speed
If UV-curing acrylic resin is used for OCA sheets to achieve rapid curing, then curing speed is improved, but thick sheets remain uncured due to radical consumption in outer layers
Solution Approach 1:
The patent replaces the UV photopolymerization mechanism with thermal polyurethane curing through isocyanate-hydroxyl condensation reactions, eliminating the depth limitation of UV penetration while maintaining efficient curing through controlled thermal processing and catalyst systems
5Adaptability or versatility
If the OCA sheet has high flexibility to conform to uneven surfaces, then adaptability is improved, but adhesive strength may decrease allowing air gaps to form
Solution Approach 1:
The patent optimizes the molecular weight and structural parameters of polyols (500-5000 range) and controls isocyanate group density to create a polyurethane system with inherent flexibility from chain mobility while maintaining strong adhesion through extensive crosslinking, achieving simultaneous high flexibility and adhesive strength
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 solution provides excellent environmental resistance, flexibility, and adhesive strength, preventing air bubbles and maintaining optical clarity, making it suitable for thick films on uneven surfaces and improving display device visibility.
Implementation Method 1
a cured product of a heat-curable polyurethane composition, the heat-curable polyurethane composition containing a polyol component (A) and a polyisocyanate component (B)
Data Source
Figure 1~2
Figure 3~4(b)
AI summary
The present invention provides an optically clear adhesive sheet using a heat-curable polyurethane composition, wherein the optically clear adhesive sheet can, when bonded to an adherend such as a glass plate, prevent the occurrence of air bubbles even at high temperature and normal humidity and maintain a stable bonded interface. The optically clear adhesive sheet of the present invention is an optically clear adhesive sheet containing: a cured product of a heat-curable polyurethane composition, the heat-curable polyurethane composition containing a polyol component and a polyisocyanate component, the polyol component having an olefin skeleton, the polyisocyanate component containing an acyclic aliphatic polyisocyanate and/or an alicyclic polyisocyanate.