Viscoelastic Layer for OLED Encapsulation Bubble Resistance
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Solution Overview
Problem
Conventional organic light emitting display (OLED) encapsulation structures are vulnerable to external impacts and suffer from visually recognizable bubbles due to low heat-resistance adhesive layers, which can deform under high temperature and humidity, leading to reduced productivity and reliability.
Innovation Solution
Incorporating a viscoelastic layer with an elastic portion of 30% or more, defined by a specific stress relaxation modulus test, made from materials like acryl resin, olefin resin, or synthetic rubber, to enhance the encapsulation structure's resistance to temperature and humidity-induced bubble formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional adhesive layer with low heat-resistance is used to bond the encapsulation film, then the manufacturing process is simple and cost-effective, but the adhesive layer deforms under high temperature and humidity, causing visually recognizable bubbles that reduce productivity and reliability
Solution Approach 1:
The patent changes the key parameter of the adhesive layer from conventional low heat-resistance materials to viscoelastic materials with specific thermal and mechanical properties. The viscoelastic layer maintains its structural integrity at high temperatures (resisting deformation up to 150°C or higher) while providing the necessary bonding function, thereby preventing bubble formation without compromising manufacturing efficiency
Solution Approach 2:
The patent employs a composite encapsulation structure where the viscoelastic layer is integrated between the encapsulation film and the OLED structure. This composite approach combines the protective function of the encapsulation film with the thermal stability and shock absorption properties of the viscoelastic material, creating a system that resists bubble formation under high temperature and humidity conditions
2Strength
If the encapsulation film is bonded using a conventional adhesive layer, then the device structure is simple, but the adhesive layer has low heat-resistance and deforms under external impacts and thermal stress, leading to bubble formation
Solution Approach 1:
The patent modifies the thermal and mechanical parameters of the bonding layer by introducing viscoelastic materials with specific glass transition temperatures and elastic portions. These material parameter changes enable the layer to maintain strength and flexibility under thermal stress, preventing deformation and bubble formation while keeping the overall device structure relatively simple
Solution Approach 2:
The viscoelastic layer serves as an intermediary between the encapsulation film and the OLED structure, absorbing thermal expansion differences and mechanical shocks. This intermediary layer protects the bonded interface from stress concentration, preventing bubble formation without requiring complex multi-layer structures
3Strength
If a rigid encapsulation structure is used to prevent external impacts, then structural strength is improved, but the structure becomes vulnerable to bubble formation under thermal stress and reduces flexibility for flexible displays
Solution Approach 1:
The patent employs a flexible viscoelastic layer that can deform elastically under external impacts and thermal stress, then return to its original state. This flexible bonding layer maintains the integrity of the encapsulation structure while allowing the overall device to be bent or flexed, enabling both impact resistance and flexibility for flexible display applications
Solution Approach 2:
The viscoelastic layer introduces dynamic response characteristics to the encapsulation structure, allowing it to adapt to varying mechanical and thermal conditions. The material's time-dependent viscoelastic properties enable it to dissipate impact energy through controlled deformation while maintaining structural integrity, providing both strength and adaptability
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 viscoelastic layer significantly reduces the occurrence of visually recognizable bubbles, improving the reliability and productivity of OLED apparatuses by maintaining structural integrity under high temperature and humidity conditions.
Implementation Method 1
an elastic portion of the viscoelastic layer is about 30% or more, defined by: Elastic portion (Ep) (%) = (σ/σ 0 ) × 100, wherein σ 0 is an initial stress generated when a strain of about 50% is applied to the viscoelastic layer and σ is a final stress measured after the strain is continuously applied thereto for about 180 seconds
Implementation Method 2
a viscoelastic layer on the organic light emitting element, wherein an elastic portion of the viscoelastic layer is about 30% or more
Data Source
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AI summary
Disclosed is an organic light emitting display (OLED) apparatus that includes a substrate; an organic light emitting element on the substrate, the organic light emitting element including a first electrode, an organic light emitting layer and a second electrode; a viscoelastic layer on the organic light emitting element, wherein an elastic portion of the viscoelastic layer is about 30% or more, the elastic portion being defined by <Equation 1> : Elastic portion (Ep) (%) = (σ/σ0) × 100, wherein σ0 is an initial stress generated when a strain of about 50% is applied to the viscoelastic layer and σ is a final stress measured after the strain is continuously applied thereto for about 180 seconds, with the initial stress σ0 and the final stress σ being measured at about 80°C through a relaxation modulus test.