Optically Clear Adhesive Sheet for Display Devices
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Solution Overview
Problem
The presence of an air gap between optical members in display devices with touchscreens causes interfacial reflection, leading to deteriorated visibility, and existing optically clear adhesive (OCA) sheets struggle with adhesive performance and flexibility, especially when bonding a display panel to a touchscreen with a thick bezel.
Innovation Solution
An optically clear adhesive sheet formed from a thermosetting polyurethane composition with specific shear storage modulus and loss tangent ranges, along with a tackifier and plasticizer, is developed to enhance adhesive strength and flexibility, reducing delay bubble generation and achieving stable bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If acrylic resin composition is used for OCA sheet, then adhesive strength is improved, but metal corrosion occurs due to acrylic acid remaining or acid components generated through hydrolysis
Solution Approach 1:
The patent changes the chemical composition parameters by using a polyurethane-based adhesive instead of acrylic resin, and by controlling the molecular weight distribution (weight average molecular weight 10,000-1,000,000, number average molecular weight 1,000-100,000) and functional group content (isocyanate group content 0.1-10 mmol/g) to achieve both adhesive strength and corrosion resistance
Solution Approach 2:
The patent creates a composite adhesive system combining polyurethane polymer with specific functional groups (isocyanate, hydroxyl, carboxyl) and crosslinking agents to form a multi-component system that provides both bonding strength and chemical stability against metal corrosion
2Strength
If UV-curing resin composition is used for OCA sheet, then adhesive strength is improved, but thick OCA sheet cannot be obtained due to free radical consumption in outer layer
Solution Approach 1:
The patent replaces the UV-curing mechanism (photochemical) with a moisture-curing or heat-curing polyurethane system, eliminating the free radical consumption problem in thick sections by using a different curing chemistry that progresses uniformly through the material thickness
Solution Approach 2:
The patent changes the curing mechanism parameters by using polyurethane chemistry with controlled molecular weight and functional group content, allowing thick sections (without specification limit) to cure uniformly without the outer-layer free radical depletion issue inherent in UV-curing systems
3Adaptability or versatility
If silicone-based resin composition is used for OCA sheet, then flexibility is improved, but adhesive strength decreases allowing air to enter gap between optical members
Solution Approach 1:
The patent creates a composite polyurethane system combining flexibility-providing segments (polyether or polyester polyol) with adhesive-strength-providing segments (isocyanate groups, hydroxyl groups, carboxyl groups) to achieve both flexibility and strong adhesion that prevents air entrapment
4Illumination intensity
If OCA sheet thickness is increased to reduce interfacial reflection, then visibility is improved, but adhesive performance and flexibility deteriorate
Solution Approach 1:
The patent changes the adhesive composition parameters (polyurethane base, molecular weight distribution, functional group content) to maintain strong adhesive performance and flexibility even in thick sections, allowing visibility improvement through increased thickness without sacrificing bonding performance
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 effectively reduces delay bubble generation, ensures stable bonding, and maintains optical clarity and flexibility, improving the visibility and reliability of display devices by conforming to uneven surfaces and maintaining adhesive strength.
Implementation Method 1
An optically clear adhesive sheet formed of a cured product of a thermosetting polyurethane composition
Implementation Method 2
having a shear storage modulus (G′) at 85° C. of 4.5×10³ to 5.0×10⁴ Pa, a loss tangent (tan δ) at 85° C. of 0.3 to 0.97
Data Source
AI summary
The present invention provides an optically clear adhesive sheet with reduced delay bubble generation using a thermosetting polyurethane composition that has excellent flexibility and is capable of giving a thick film. The optically clear adhesive sheet of the present invention is an optically clear adhesive sheet formed of a cured product of a thermosetting polyurethane composition, the optically clear adhesive sheet having a shear storage modulus (G′) at 85° C. of 4.5×103 to 5.0×104 Pa, a loss tangent (tan δ) at 85° C. of 0.3 to 0.97, and a thickness of 50 to 2000 μm. The optically clear adhesive sheet preferably has an adhesive strength measured by a 180° peel test of 2 N/25 mm or more.