Optically Clear Adhesive Refractive Index Matching
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Solution Overview
Problem
Existing adhesives used in optical applications face challenges in matching the refractive index of optical substrates, leading to light refraction and clarity issues, and hot melt processing struggles to replicate solvent-based adhesive properties, particularly in achieving high visible light transmission and low haze.
Innovation Solution
The development of adhesive compositions comprising a first elastomeric polymer and a low molecular weight polymeric additive that form an acid-base interaction, allowing for increased refractive index without altering the elastomeric copolymer, and enabling both solvent-based and hot melt processing methods to produce optically clear adhesives with high refractive indices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If traditional adhesives are used in optical applications, then adhesive properties such as tack and peel strength are maintained, but light refraction occurs and optical clarity is compromised due to mismatched refractive index
Solution Approach 1:
The patent changes the refractive index parameter of the adhesive by incorporating low molecular weight polymeric additives with high refractive indices (such as aromatic compounds) into the elastomeric polymer matrix. This adjustment allows the adhesive's refractive index to match optical substrates, eliminating light refraction while preserving adhesive properties like tack and peel strength.
Solution Approach 2:
The patent creates a composite adhesive system combining an elastomeric polymer base with low molecular weight polymeric additives. This composite structure enables the adhesive to simultaneously exhibit optical clarity (by matching refractive index) and adhesive functionality (through the elastomeric polymer), resolving the contradiction between optical performance and adhesive performance.
2Productivity
If hot melt processing is used to prepare adhesives, then processing efficiency is improved, but achieving high visible light transmission and low haze is difficult compared to solvent-based methods
Solution Approach 1:
The patent adjusts the molecular weight and chemical structure parameters of the polymeric additives to enable effective dispersion and homogeneous distribution during hot melt processing. By selecting low molecular weight additives with appropriate functional groups, the adhesive achieves both processing efficiency through hot melt application and optimal optical properties including high visible light transmission and low haze.
Solution Approach 2:
The patent ensures uniform distribution of the low molecular weight polymeric additives throughout the elastomeric polymer matrix during hot melt processing. This homogeneous local distribution prevents light scattering and haze formation, allowing hot melt processed adhesives to achieve optical clarity comparable to or better than solvent-based methods while maintaining processing efficiency.
3Object-affected harmful factors
If the refractive index of the adhesive is increased to match optical substrates, then optical clarity is improved, but adhesive properties may be compromised
Solution Approach 1:
The patent designs a composite adhesive where the elastomeric polymer provides adhesive strength (tack, peel adhesion, shear strength) while the low molecular weight polymeric additives provide high refractive index for optical clarity. This functional separation in the composite material allows both optical properties and adhesive properties to be optimized independently, resolving the contradiction between increasing refractive index and maintaining adhesive strength.
Solution Approach 2:
The patent carefully selects and optimizes the concentration, molecular weight, and chemical structure parameters of the polymeric additives to achieve the desired refractive index without adversely affecting adhesive properties. By controlling these parameters, the adhesive maintains its tack and bonding strength while achieving the necessary optical clarity for optical applications.
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 effectively raises the refractive index of adhesives to match optical substrates, maintaining adhesive properties like peel strength and tack, while achieving high visible light transmission and low haze, thus addressing the limitations of traditional adhesives in optical clarity and processing methods.
Implementation Method 1
The first elastomeric polymer and the low molecular weight polymeric additive form an acid-base interaction, meaning that if the first elastomeric polymer has a plurality of acidic functional groups, then the low molecular weight polymeric additive has a plurality of basic functional groups. Conversely, if the first elastomeric polymer has a plurality of basic functional groups, then the low molecular weight polymeric additive has a plurality of acidic functional groups.
Data Source
AI summary
Optically clear adhesive compositions contain an elastomeric polymer and a low molecular weight polymeric additive. The elastomeric polymer and the low molecular weight polymeric additive form an acid-base interaction. The refractive index of the adhesive composition is higher than the refractive index of the elastomeric polymer. The adhesive composition may also contain additional domains of liquids, polymers, additives or particles that have a higher refractive index than the elastomeric polymer.