Two-Pass Adhesive Dispensing for Electro-Optical Encapsulation
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Solution Overview
Problem
Existing methods for encapsulating electro-optical devices with optical films recessed from the edge of a substrate, such as liquid crystal screens, face mechanical stresses due to adhesive shrinkage, leading to deformation, delamination, and bubble formation, which degrade the product's quality and reliability.
Innovation Solution
A two-pass adhesive dispensing method where a first layer of non-crosslinked glue is applied to fill the height difference between the substrate and the optical film, followed by a second layer to bond the protective slab, minimizing cumulative adhesive shrinkage and mechanical stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single layer of adhesive glue is used to bond the protective slab, then the encapsulation process is simple, but the adhesive shrinkage causes mechanical stresses that deform the optical film and create bubbles
Solution Approach 1:
The single layer of adhesive is segmented into two distinct layers: a first layer applied to the substrate that fills the height difference and is partially cured, and a second layer applied to the protective slab. This segmentation allows each layer to perform its specific function - the first layer compensates for topography while the second layer provides final bonding - thereby reducing cumulative shrinkage stress and preventing optical film deformation
Solution Approach 2:
The first layer of adhesive is applied and partially cured before the second layer is applied. This preliminary action allows the first layer to establish the proper height compensation and initial bonding, creating a stable foundation that reduces the shrinkage burden on the second layer, thus preventing mechanical stresses that would deform the optical film
2Length of stationary object
If multiple layers of adhesive glue are used to fill the height difference, then the height compensation is sufficient, but the cumulative shrinkage increases mechanical stresses and causes delamination
Solution Approach 1:
The adhesive system is segmented into two functionally distinct layers with different thicknesses and curing states. The first layer has greater thickness to fill the height difference and is partially cured to provide initial stability. The second layer is thinner and fully cured to provide final bonding. This segmentation distributes the shrinkage stress across layers with different mechanical properties, preventing delamination at the bonding interface
Solution Approach 2:
The invention changes the curing parameter of the adhesive by applying a partial cure to the first layer before applying the second layer. This parameter change allows the first layer to maintain some flexibility for stress absorption while the second layer provides rigid final bonding, thereby reducing cumulative shrinkage effects and preventing interface delamination
3Ease of manufacture
If hot rolling is used to laminate the protective slab, then the adhesive creeps to fill gaps completely, but sophisticated equipment and vacuum chambers are required
Solution Approach 1:
The invention replaces the complex mechanical hot rolling and vacuum lamination system with a simpler dispensing and curing system. The adhesive is dispensed in controlled layers and cured through UV or thermal treatment, eliminating the need for sophisticated rolling equipment and vacuum chambers while achieving uniform adhesive distribution through controlled dispensing parameters
4Ease of operation
If dispensing with non-crosslinked glue is used, then the process can be done at ambient temperature, but the shrinkage upon cross-linking creates critical mechanical stresses
Solution Approach 1:
The adhesive application is segmented into two stages with different curing states. The first layer is partially cured to provide initial structural support and height compensation. The second layer is fully cured to provide final bonding. This segmentation distributes the shrinkage stress from cross-linking across two separate events rather than one large shrinkage event, preventing critical mechanical stresses that would deform the optical film
Solution Approach 2:
The first layer of adhesive is applied and partially cured before the second layer is applied and fully cured. This preliminary partial curing action provides initial structural stability and height compensation, allowing the second layer to be applied without experiencing the full cumulative shrinkage stress, thereby protecting the optical film from deformation
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
This approach significantly reduces adhesive shrinkage and mechanical stresses, enhancing the cosmetic quality and environmental resistance of the encapsulated electro-optical device.
Implementation Method 1
the cross-linking, or polymerization, of the adhesive, which is done conventionally under UV or temperature, introduces a shrinkage of material, in all directions, and therefore in particular in thickness
Implementation Method 2
This material shrinkage may be of the order of 10%. Given the small thicknesses involved (relative to the dimensions of the front face surface) and the difference in path between the optical film and the substrate on which the optical film is bonded, the shrinkage of the adhesive material in thickness is critical
Data Source
Figure 1~2
Figure 3~5
AI summary
A method for protecting the outer surface of an electro-optical device, which has at least one optical film 4 bonded to a recessed area on a transparent substrate 2, comprises encapsulating the optical element between the substrate 2 and a transparent plate 6 having substantially the same dimensions as the substrate 2. The method includes bonding the plate, which is achieved by applying a non-crosslinked adhesive in two passes: a first pass to compensate for the step size difference ep between the substrate and the optical element, and a second pass to bond the protective plate 6. The respective adhesive shrinkage in each pass is applied to smaller thicknesses. Ultimately, the cumulative shrinkage is limited, and the product quality is improved.