Radiation-Curable Adhesive Sheet Conformity and Warping Control
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Solution Overview
Problem
Existing methods for producing thick adhesive sheets struggle with conforming to three-dimensional surface topographies and preventing air pocket formation, leading to inadequate adhesion and potential warping issues in applications like touch panels and image display modules.
Innovation Solution
A method involving a radiation-curable adhesive sheet precursor, comprising a polymer/monomer mixture with partially polymerized (meth)acrylic monomers and radiation reactive sites, is used. This precursor is irradiated with specific wavelengths of radiation to control polymerization and crosslinking, allowing for conformability and high adhesion without solvent-induced air pockets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thick adhesive sheet is used to conform to large three-dimensional surface topographies, then conformity to surface topography is improved, but air bubbles are prone to form in the adhesive sheet during production
Solution Approach 1:
The patent changes the physical-chemical parameters of the adhesive composition by incorporating specific viscosity modifiers and curing agents that allow the adhesive to maintain appropriate flow characteristics at thick sections while preventing bubble entrapment during application and curing processes
Solution Approach 2:
The patent uses a composite adhesive formulation combining multiple polymers with different viscosities and curing mechanisms, creating a multi-phase system that provides both the thickness needed for surface conformity and the bubble-release properties required for reliability
2Manufacturing precision
If the adhesive sheet thickness is increased to conform to three-dimensional surface topography, then conformity is improved, but warping and color patches occur in sensitive adherends like LCDs
Solution Approach 1:
The patent applies different adhesive formulations or thicknesses in different regions of the adhesive sheet, using thinner sections where warping sensitivity is high and thicker sections where surface conformity is critical, thereby locally optimizing performance for each region's specific requirements
Solution Approach 2:
The patent modifies the adhesive's viscoelastic parameters and curing characteristics to reduce internal stresses during bonding, preventing warping and color patches in sensitive adherends while maintaining sufficient thickness for surface topography conformity
3Strength
If a pressure-sensitive adhesive sheet is used instead of solvent-based adhesive, then adhesion strength and reapplicability are improved, but conforming to three-dimensional surface topography becomes difficult
Solution Approach 1:
The patent designs the pressure-sensitive adhesive with dynamic viscoelastic properties that allow it to be soft and compliant during application for conforming to surface topography, then transitions to a rigid state after curing to provide strong adhesion strength, effectively adapting its mechanical properties to different stages of the bonding process
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 method produces a thick, highly transparent adhesive sheet with satisfactory fluidity and adhesion before curing, and high hardness after curing, effectively conforming to large topographies and preventing warping, thus enhancing the reliability of surface-protecting layers on complex surfaces.
Implementation Method 1
irradiating the precursor with radiation of a wavelength greater than the first wavelength to polymerize the radiation-curable adhesive sheet precursor
Implementation Method 2
irradiating the polymerized adhesive sheet with radiation of a wavelength of the first wavelength or less to crosslink the polymerized adhesive sheet
Data Source
AI summary
Problem: To provide a method for producing a laminate comprising a thick, highly transparent cured adhesive sheet exhibiting flow characteristics accompanied by satisfactory fluidity and satisfactory initial adhesion to an adherend before irradiation, and satisfactory hardness (in particular, a high storage modulus) after irradiation. Solution: A method for producing a laminate comprising a first substrate, a second substrate, and a cured adhesive sheet disposed therebetween, the method comprising steps of: forming into a sheet a radiation-curable adhesive sheet precursor comprising a polymer/monomer mixture comprising a partially polymerized (meth) acrylic monomer, a monomer having radiation reactive sites activated by short-wavelength radiation of a first wavelength or less, and a photoinitiator for initiating polymerization of the polymer/monomer mixture and the radiation reactive site-possessing monomer via radiation of a wavelength greater than the first wavelength; irradiating the precursor with radiation of a wavelength greater than the specific wavelength to polymerize the radiation-curable adhesive sheet precursor, forming a radiation-curable adhesive sheet; disposing the radiation-curable adhesive sheet adjacent to at least one surface of the first substrate; disposing the second substrate adjacent to a radiation-curable adhesive sheet; applying heat and/or pressure to the radiation-curable adhesive sheet; and irradiating the radiation-curable adhesive sheet with radiation comprising short-wavelength radiation of a first wavelength or less to obtain a cured adhesive sheet.