Polyvinyl Acetal Resin Composition for Touch Panel Laminates
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Solution Overview
Problem
Polyvinyl acetal resin compositions used in extrusion molding for touch panels experience a significant reduction in storage modulus at high temperatures, leading to the formation of minute gels and non-uniform molded articles, which affects their thermal stability and adhesion properties.
Innovation Solution
A polyvinyl acetal resin composition containing a hydrogen abstraction type photoradical polymerization initiator and a monomer or oligomer with a radical polymerizable double bond, which remains stable during extrusion molding and is activated by light to crosslink the polyvinyl acetal, maintaining high storage modulus even at elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If polyvinyl acetal is crosslinked using boric acid during extrusion molding to maintain high storage modulus at high temperature, then thermal stability is improved, but the resin composition reacts at high temperature to form minute gels and fails to provide uniform molded articles
Solution Approach 1:
The patent applies preliminary action by pre-mixing the polyvinyl acetal resin with the photoradical polymerization initiator and monomer before extrusion molding, but designing the system so that crosslinking does not occur during molding. The crosslinking is then activated afterward by light irradiation, achieving the desired thermal stability without compromising molding uniformity. This separates the preparation phase from the activation phase, allowing uniform molding first and crosslinking later.
Solution Approach 2:
The patent changes the activation parameter of the crosslinking system from thermal activation (boric acid) to photochemical activation (photoradical polymerization initiator). This parameter change allows the crosslinking to be controlled by light irradiation after molding rather than occurring thermally during extrusion, thus maintaining both molding uniformity and achieving high-temperature storage modulus through subsequent crosslinking.
2Strength
If polyvinyl acetal resin composition is designed to crosslink at high temperature during extrusion molding, then high storage modulus at elevated temperature is achieved, but thermal stability deteriorates due to reaction and gel formation
Solution Approach 1:
The patent prepares the resin composition with all necessary crosslinking components (photoradical polymerization initiator and monomer) in advance, but designs the system so that crosslinking is postponed until after molding via light irradiation. This preliminary preparation without immediate reaction achieves both thermal stability during processing and high storage modulus after crosslinking.
Solution Approach 2:
The patent replaces the thermal activation mechanism (heat-induced crosslinking with boric acid) with a photochemical activation mechanism (light-induced photoradical polymerization). This substitution eliminates unwanted thermal reactions during extrusion molding while enabling controlled crosslinking afterward, thus maintaining thermal stability and achieving high storage modulus.
3Strength
If photoradical polymerization initiator is activated during extrusion molding, then crosslinking occurs and high storage modulus is achieved, but the initiator must be stable at normal extrusion temperature to prevent premature reaction
Solution Approach 1:
The patent changes the activation parameter of the photoradical polymerization initiator from thermal sensitivity to light sensitivity. By selecting initiators that are stable at extrusion temperatures (100-220°C) but can be activated by light irradiation, the system achieves reliable stability during processing while enabling crosslinking afterward to obtain high storage modulus.
Solution Approach 2:
The patent applies local quality by making the photoradical polymerization initiator have different stability characteristics at different conditions: thermally stable during extrusion molding but photochemically active under light irradiation. This localized property differentiation allows the initiator to remain stable during processing in one condition (heat) while being activatable in another condition (light) to achieve crosslinking and high storage modulus.
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 enables the production of a laminate with improved thermal stability and adhesion properties, preventing foaming in high temperature and humidity environments and ensuring effective scattering prevention of glass fragments, while maintaining moldability and followability to steps.
Implementation Method 1
the photoradical polymerization initiator is activated by irradiation with light to generate radicals, and the radicals abstract hydrogen atoms of C-H in the polyvinyl acetal to cause crosslinking via the monomer or oligomer having a radical polymerizable double bond
Data Source
Figure 1
AI summary
The present invention aims to provide a polyvinyl acetal resin composition that is excellent in thermal stability and moldable by an extrusion method and can exhibit a high storage modulus even under high temperature, an adhesive sheet prepared from the polyvinyl acetal resin composition, an interlayer filling material for a touch panel prepared from the polyvinyl acetal resin composition, and a laminate produced using the interlayer filling material for a touch panel. The present invention relates to a polyvinyl acetal resin composition containing: a polyvinyl acetal; a photoradical polymerization initiator; and a monomer or oligomer having a radical polymerizable double bond.