Pressure-Sensitive Adhesive Sheet Hardness Curability
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Solution Overview
Problem
Active energy-ray curable pressure-sensitive adhesive (PSA) sheets experience a decrease in hardness due to the inclusion of a curable component, leading to issues with processing and shape retention, as the curable component typically has a lower molecular weight than the base polymer.
Innovation Solution
Incorporating a resin A with a glass transition temperature of 0° C. or higher and a weight average molecular weight of 3000 or higher, selected from urethane, epoxy, or acrylic resins, into the PSA layer, which reduces the decrease in hardness and imparts curability with active energy rays, while maintaining suitable cohesion and adhesive properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If an active energy ray-curable component is included in the PSA to impart curability, then the PSA layer can be cured by active energy rays, but the hardness (tensile modulus) of the PSA layer decreases due to the lower molecular weight of the curable component
Solution Approach 1:
The patent changes the molecular weight parameter of the curable component from conventional low molecular weight to high molecular weight (Mw≥3000), and sets the glass transition temperature parameter to 0°C or higher. This parameter transformation allows the curable component to maintain high hardness before curing while still being curable by active energy rays, resolving the contradiction between curability and hardness maintenance.
2Adaptability or versatility
If a curable component with lower molecular weight is used to ensure curability, then the PSA can be cured effectively, but the ease of processing and handling deteriorates due to softening
Solution Approach 1:
By transforming the molecular weight parameter to high molecular weight (Mw≥3000) and setting Tg≥0°C, the patent maintains the PSA layer in a solid state at room temperature with sufficient hardness for easy processing and handling, while still enabling effective curing by active energy rays. This resolves the contradiction between curability and ease of operation.
3Strength
If the hardness of the PSA layer is increased to improve shape retention, then shape retention improves, but the ease of application deteriorates due to excessive rigidity
Solution Approach 1:
The patent creates a dynamic state where the PSA layer maintains high hardness (Mw≥3000, Tg≥0°C) for good shape retention during storage and handling, but becomes soft and conformable during application through the curable component's response to active energy rays and environmental conditions. This dynamic property resolution allows both shape retention and ease of application to be achieved.
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 use of resin A in the PSA layer enhances the tensile modulus by 1.1 times or more after curing, improves ease of processing and handling, and maintains desirable adhesive properties, ensuring effective shape retention and ease of application.
Implementation Method 1
active energy ray-curable PSA layer... curability by active energy rays... after curing by active energy rays
Data Source
AI summary
Provided is a PSA sheet having an active energy ray-curable PSA layer that is less susceptible to reduction of hardness to the curable component. The PSA sheet provided comprises an active energy ray-curable PSA layer. The PSA forming the PSA layer comprises a base polymer and a resin A. The resin A is an active energy ray-curable resin having a glans transition temperature of 0° C. or higher by DSC analysis.