Transparent Adhesive Sheet for Display Stepped Portions
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Solution Overview
Problem
Image display devices with stepped portions face challenges in maintaining thickness reduction and design diversification while minimizing distortion and optical property degradation due to the limitations of existing adhesive methods, particularly when forming masking portions in colors other than black.
Innovation Solution
A transparent double-sided adhesive sheet with a photocuring-type adhesive composition is used, where the gel fraction is adjusted to be higher at flat surface portions and lower at stepped portions, ensuring the adhesive sheet's thickness remains 250 µm or less, thereby relieving distortion and maintaining optical quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a liquid adhesive resin composition containing UV-curable resin is filled in the gap and then illuminated with UV light to cure it, then the adhesive bonding is achieved, but the operation becomes cumbersome, productivity is poor, and curing is difficult at locations that UV light has difficulty reaching
Solution Approach 1:
The patent replaces the liquid filling and UV curing process with a solid adhesive sheet that can be directly applied and pressed into place. This mechanical application method eliminates the cumbersome liquid handling, improves productivity through faster application, and ensures uniform adhesive distribution without UV light penetration issues.
Solution Approach 2:
The patent changes the adhesive from a liquid state requiring UV curing to a solid sheet state that bonds through pressure and temperature. This parameter change in the adhesive's physical state eliminates the need for UV light exposure and associated curing complexities, streamlining the bonding process.
2Reliability
If the thickness of the masking portion is increased to improve masking ability for colors other than black, then the masking effectiveness is improved, but the adhesive sheet experiences large stress at the contact portion, generating distortion and negatively affecting optical properties
Solution Approach 1:
The patent creates a stepped structure in the adhesive sheet where the thickness varies by location: thicker at the masking portion to provide sufficient masking ability, and thinner at the contact portion to reduce stress and prevent distortion. This local variation in thickness allows the adhesive to simultaneously achieve both masking effectiveness and optical quality.
3Length of stationary object
If the thickness of the adhesive sheet is reduced to support thinner device designs, then the device thickness is decreased, but the adhesive sheet's ability to follow large printed steps is compromised
Solution Approach 1:
The adhesive sheet features localized thickness variation with a thicker region at the masking portion and a thinner region at the contact portion. This allows the overall device thickness to be reduced while the thicker masking portion maintains the ability to follow and fill large printed steps effectively.
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 distortion at stepped portions and enhances optical properties in image display devices with stepped surfaces, supporting the trend of thinner, more diverse designs in devices like mobile phones and TVs.
Implementation Method 1
a transparent double-sided adhesive sheet for image display device formed from a photocuring-type adhesive composition is filled in between the constitutive members for display device
Data Source
Figure 1~2(b)
AI summary
A novel transparent double-sided adhesive sheet for image display device is provided, that, under the constraint of holding down the thickness of the adhesive sheet to 250 µm or less, can relieve a distortion arising within the adhesive sheet after laminating even if a member has a stepped portion of 50 µm to 100 µm in height on the laminating surface. Proposed is a transparent double-sided adhesive sheet for image display device which is used for the purpose of laminating an image display device constitutive member having on a laminating surface a stepped portion of 50 µm to 100 µm in height and a flat surface portion, and another image display device constitutive member, wherein a thickness of the maximum thickness portion of the adhesive sheet is 250 µm or less, and a gel fraction (a) at a position in contact with a stepped portion after laminating is 10% or greater and smaller than a gel fraction (b) at a position in contact with a flat surface portion.