Solvent-Free Acrylic Adhesive Viscosity Control
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Solution Overview
Problem
Solvent-free acrylic adhesives face issues with viscosity rise during heating, leading to reduced thermal stability and applicability, especially when used in thick applications, and they often suffer from haze under moist-heat environments due to residual impurities like acrylic acid from hydroxy group-containing monomers.
Innovation Solution
A solvent-free acrylic resin composition with a reduced acid value and a specific range of hydroxy group-containing monomer content, combined with a carbodiimide compound, to suppress viscosity rise and enhance thermal stability, step followability, and moist-heat haze resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a solvent-free acrylic adhesive is heated for application, then the adhesive becomes more fluid and easier to apply, but the viscosity rises due to crosslinking reactions, reducing applicability
Solution Approach 1:
The patent removes carboxyl groups through preliminary treatment during the polymerization process by controlling the ratio of acrylic acid to hydroxy group-containing monomer and using specific catalysts. This preliminary removal of harmful groups prevents subsequent crosslinking reactions that would cause viscosity rise during heating and application, thereby maintaining good applicability throughout the adhesive's service life
Solution Approach 2:
The patent precisely controls the acid value parameter within a specific range (0.001-0.5 mgKOH/g) by adjusting the ratio of acrylic acid to hydroxy group-containing monomer during polymerization. This parameter control prevents excessive crosslinking reactions during heating, maintaining the adhesive's fluidity and applicability while still providing sufficient thermal stability
2Strength
If the adhesive layer is made thick to provide sufficient impact-absorbing performance, then the impact resistance is improved, but application dripping occurs and solvent volatilization is incomplete
Solution Approach 1:
The patent changes the fundamental parameter of the adhesive system from solvent-based to solvent-free, eliminating the solvent volatilization issue that plagues thick solvent-type adhesive applications. The controlled acid value and specific monomer composition enable the adhesive to maintain proper rheology during thick application, preventing dripping while ensuring complete curing without solvent-related defects
Solution Approach 2:
The patent utilizes the phase transition properties of the solvent-free acrylic resin, which transitions from a solid or highly viscous state at room temperature to a more fluid state during heating, then stabilizes in the final cured state. This controlled phase behavior enables thick application without dripping, as the adhesive remains stable until properly heated and applied
3Productivity
If acrylic acid is present as a residual monomer to facilitate polymerization, then the polymerization reaction is enhanced, but crosslinking occurs during heating, increasing molecular weight and reducing applicability
Solution Approach 1:
The patent optimizes the concentration parameter of acrylic acid by controlling its ratio to hydroxy group-containing monomer within specific ranges, and by controlling the acid value to 0.001-0.5 mgKOH/g. This parameter optimization balances polymerization efficiency with thermal stability, ensuring sufficient reaction while preventing excessive crosslinking during subsequent heating processes
Solution Approach 2:
The patent converts the potentially harmful effect of acrylic acid residual monomer into a beneficial outcome by carefully controlling its quantity and reactivity. The small controlled amount of acrylic acid facilitates complete polymerization of the main monomer mixture, while the limited quantity prevents excessive crosslinking during heating, thus converting a potential defect into a useful polymerization promoter
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 composition achieves excellent thermal stability, allowing for thick applications and improved corrosion resistance and haze resistance, making it suitable for use in touch panels and image display apparatuses.
Implementation Method 1
a carboxyl group is introduced into the acrylic resin by the presence of, for example, acrylic acid remaining in a trace amount in a residual monomer or a residual catalyst at the time of the production of the adhesive
Data Source
AI summary
A solvent-free acrylic resin composition includes an acrylic resin (A), wherein the acrylic resin (A) contains 5 wt. % to 60 wt. % of a structural moiety derived from a hydroxy group-containing monomer (a1), and an acid value in the resin composition is from 0.001 mgKOH/g to 0.3 mgKOH/g. The solvent-free acrylic resin composition is suppressed in viscosity rise due to heating, and is hence excellent in thermal stability; the composition can be thickly applied when used as an adhesive; and the composition can provide an adhesive excellent in step followability, corrosion resistance, and moist-heat haze resistance.