Thin Polarizing Plate with Dual Adhesive Layers
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Solution Overview
Problem
The challenge is to create a polarizing plate with a thin polarizer of less than 20 μm thickness that maintains a good appearance by minimizing minor irregularities on its surface, which occur when using active energy ray curing adhesive for bonding protective films.
Innovation Solution
A polarizing plate configuration with a pressure sensitive adhesive layer, where a first protective film is bonded to one surface of the polarizer using an active energy ray curing adhesive, and a second protective film is bonded to the other surface using a water-soluble adhesive, ensuring moisture permeability and surface treatment to prevent irregularities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the thickness of the polarizer is reduced to 20 μm or smaller, then the overall thickness of the polarizing plate is reduced, but minor irregularities occur on the surface of the polarizing plate
Solution Approach 1:
The patent segments the adhesive bonding system into two distinct adhesive layers with different properties: a first adhesive layer (water-soluble adhesive) and a second adhesive layer (active energy ray curing adhesive). This segmentation allows each adhesive layer to perform its specific function optimally, with the water-soluble adhesive providing initial bonding and the curing adhesive providing final bonding while minimizing shrinkage effects on thin polarizers.
Solution Approach 2:
The patent applies different adhesive properties to different regions of the bonding interface. The first adhesive layer is positioned closer to the polarizer surface while the second adhesive layer is positioned farther away, creating a gradient of adhesive properties that localizes the shrinkage compensation effect away from the thin polarizer surface, thus preventing surface irregularities.
2Strength
If an active energy ray curing adhesive is used to bond protective films to a thin polarizer, then bonding strength is improved, but shrinkage effects cause minor irregularities on the polarizing plate surface
Solution Approach 1:
The water-soluble adhesive layer is applied first as a preliminary bonding layer before the active energy ray curing adhesive is applied. This preliminary action provides initial bonding strength and creates a buffer layer that mitigates the shrinkage effects of the curing adhesive, preventing direct transmission of shrinkage stresses to the thin polarizer surface.
Solution Approach 2:
The water-soluble adhesive layer acts as an intermediary between the active energy ray curing adhesive and the thin polarizer. This intermediary layer absorbs and distributes the shrinkage stresses from the curing adhesive, preventing direct contact with the polarizer surface and thus eliminating surface irregularities while maintaining bonding strength.
3Adaptability or versatility
If a water-soluble adhesive is used to bond protective films, then moisture permeability requirements are relaxed, but the adhesive layer requires a drying step that takes relatively long time
Solution Approach 1:
The bonding process is segmented into two sequential adhesive applications: first the water-soluble adhesive is applied and allowed to form a preliminary bond, then the active energy ray curing adhesive is applied and cured. This segmentation allows the water-soluble adhesive to provide initial bonding without requiring complete drying, as the curing adhesive is applied on top and the entire structure is cured together, eliminating the need for a separate drying step.
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 configuration effectively suppresses minor irregularities on the polarizing plate's surface, maintaining a good appearance even with thin polarizers, and enhances bonding stability by mitigating the shrinkage effects of the active energy ray curing adhesive.
Implementation Method 1
an active energy ray curing adhesive being interposed, and thereafter, curing the adhesive layer
Implementation Method 2
a second adhesive layer formed from a water-soluble adhesive being interposed
Implementation Method 3
high moisture permeability is required in the protective film
Data Source
AI summary
There is provided a polarizing plate, including: a polarizing layer having a thickness not greater than 20 μm; a first protective film stacked on one surface of the polarizing layer, with a first adhesive layer formed from an active energy ray curing adhesive being interposed; and a second protective film stacked on the other surface of the polarizing layer, with a second adhesive layer formed from a water-soluble adhesive being interposed. There are also provided a polarizing plate with a pressure sensitive adhesive layer, a substrate having a polarizing plate bonded thereto, a liquid crystal display device, and an organic electroluminescence display device, all of which include the polarizing plate. Preferably, at least one of the first protective film and the second protective film has a moisture permeability not higher than 1000 g/m2/24 hr.