Transparent Adhesive Sheet Wavelength Conversion for Shadow Curing
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Solution Overview
Problem
The challenge in bonding image display device constituent members with photocurable adhesives is the difficulty in achieving stable curing, especially in areas with limited UV light reach, leading to issues like uneven thickness, reduced transparency, and potential adhesive overflow or corrosion.
Innovation Solution
A transparent adhesive sheet composed of a thermoplastic resin, crosslinking agent, photopolymerization initiator reacting with light between 380-430 nm, and a wavelength conversion agent that emits light between 380-550 nm, allowing for photo-crosslinking even in shadowed areas, with absorbance and thickness adjusted to ensure complete curing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a liquid UV-curable adhesive is used to fill the gap between image display device constituent members, then the bonding can be achieved, but unevenness in thickness easily occurs and productivity decreases due to complicated adjusting or setting conditions
Solution Approach 1:
The patent uses a photocurable adhesive sheet instead of liquid adhesive, which maintains a sheet shape in its normal state. This sheet form provides inherent thickness uniformity and eliminates the need for complicated adjusting or setting conditions required for liquid adhesive application, thereby improving productivity while maintaining bonding quality.
2Reliability
If phosphor is mixed in the adhesive resin composition to enable curing in shadow parts, then curing in concealed sections improves, but transparency of the adhesive resin composition decreases and thickness becomes too thick for light to reach deep parts
Solution Approach 1:
The patent introduces a wavelength conversion agent as an intermediary substance that converts UV light to visible light. This agent is mixed into the adhesive sheet at a controlled concentration (0.01-5 wt%), allowing it to emit visible light in shadowed areas to enable photopolymerization, while the controlled concentration prevents excessive opacity that would block light from reaching deep parts of the adhesive.
Solution Approach 2:
The patent carefully controls the concentration of the wavelength conversion agent within a specific range (0.01-5 wt%) to balance two opposing requirements: enough concentration to enable visible light emission for curing in shadow areas, but low enough concentration to maintain sufficient transparency for light penetration to deep parts of the adhesive sheet.
3Ease of operation
If the adhesive sheet has sufficient thickness to maintain sheet shape, then handling and application improve, but UV light cannot reach deep parts for complete curing
Solution Approach 1:
The wavelength conversion agent acts as a mediator that transforms UV light into visible light with longer wavelength. Since visible light penetrates deeper into the adhesive sheet than UV light, this enables complete curing even in thicker sheets that maintain their shape for easy handling and application.
Solution Approach 2:
The patent utilizes a wavelength dimension transformation by introducing the wavelength conversion agent that converts UV light to visible light. This dimensional change in light wavelength allows the light to penetrate deeper into the adhesive sheet, enabling complete curing throughout the thickness while maintaining sufficient sheet thickness for handling.
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 adhesive sheet ensures thorough curing of the adhesive, preventing issues like overflow and corrosion, while maintaining transparency and flexibility, thus enhancing the bonding process and product stability.
Implementation Method 1
a photopolymerization initiator that reacts with light having a wavelength of at least 380 to 430 nm
Implementation Method 2
a wavelength conversion agent that is excited by light having a wavelength shorter than 380 nm and that emits light having a wavelength of 380 to 550 nm
Data Source
AI summary
A photocurable adhesive sheet that can be photocured even if there are places such as print-concealed sections that are difficult for light to reach, and even if the adhesive sheet has a certain degree of thickness, the entire sheet can be cured. A transparent adhesive sheet formed from an adhesive composition containing: (A) a thermoplastic resin; (B) a crosslinking agent; (C) a photopolymerization initiator that reacts with light having a wavelength of at least 380 to 430 nm; and (D) a wavelength conversion agent that is excited by light having a wavelength shorter than 380 nm and that emits light having a wavelength of 380 to 550 nm. The transparent adhesive sheet is characterized by the adhesive sheet absorbance X at a wavelength of 390 nm and the adhesive sheet thickness Y satisfying relational formula (1):0.5≤X/Y≤12. Formula (1):