Heterogeneous Coating Boundary Control for Foldable Displays

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Solution Overview

Problem

Foldable displays face challenges in achieving flexibility, durability, and refractive visibility due to the step difference at the boundary between different types of coating solutions, which affects the application of hard coating layers on foldable displays.

Innovation Solution

A method of manufacturing a heterogeneous coating solution bonded coating layer using a slot die coater, where the difference in capillary number between rigid and flexible coating solutions is controlled to minimize the step difference at the boundary, using specific compositions and ratios of organic and inorganic compounds, photoinitiators, and diluents, and applying these solutions to respective regions on a substrate.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If the hard coating layer is made thick to increase surface hardness, then the hardness and strength of the coating film are improved, but the coating layer becomes wrinkled, curled, cracked, or separated due to shrinkage

Engineering Contradiction:

ImprovehardnessVSAvoidsurface smoothness

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The coating layer is divided into multiple regions with different material compositions (rigid coating solution and flexible coating solution). The rigid coating provides hardness while the flexible coating accommodates deformation, preventing the wrinkling and cracking that occurs in uniformly thick hard coatings.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the coating layer are assigned different properties: the rigid coating solution is applied to specific regions where hardness is needed, while the flexible coating solution is applied to regions that require flexibility to prevent cracking during folding. This local differentiation allows the coating to maintain both hardness and surface smoothness.

Inventive Principle:

Principle #3Local quality

2Adaptability or versatility

If different types of materials are used to create a flexible material layer for folded portions, then flexibility is improved, but refractive visibility deteriorates due to the difference in refractive index at the boundary between materials

Engineering Contradiction:

ImproveflexibilityVSAvoidrefractive visibility

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The refractive indices of the rigid and flexible coating solutions are carefully controlled to be within 0.05 of each other. This parameter matching ensures that light passes through the boundary between different material regions without significant refraction, maintaining visual clarity while allowing the heterogeneous structure to provide the needed flexibility.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If a step difference is formed at the boundary between different types of coating solutions, then the coating process is simplified, but refractive visibility deteriorates

Engineering Contradiction:

Improvecoating process simplicityVSAvoidrefractive visibility

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The viscosity and surface tension of the rigid and flexible coating solutions are adjusted so that their capillary numbers are within 10% of each other during discharge. This parameter control ensures that the coating solutions flow and bond smoothly at the boundary without forming significant step differences, maintaining both ease of manufacture and refractive visibility.

Inventive Principle:

Principle #35Parameter changes

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 method improves refractive visibility and simultaneously enhances the flexibility and durability of the cover window, maintaining transmittance and preventing cracking even after 50,000 bends at a radius of curvature of 10 mm or less.

Implementation Method 1

a difference in capillary number between the rigid coating solution and the flexible coating solution is controlled

Methodology Applied

Scientific EffectCapillary number: Capillary Action

Implementation Method 2

adjacent heterogeneous coatings bonded along boundaries thereof

Methodology Applied

Scientific EffectBonding: Adhesive

Data Source

PatentUS11130703B2Method of manufacturing a bendable substrate coated with a coating layer of adjacent heterogeneous coatings bonded along boundaries thereof useful for foldable displays

Publication Date: 2021.09.28 KOREA INSTITUTE OF INDUSTRIAL TECHNOLOGY

AI summary

Disclosed herein are a method of manufacturing a heterogeneous coating solution bonded coating layer, and a coating layer and a cover window produced thereby. More particularly, there are provided a method of manufacturing a heterogeneous coating solution bonded coating layer, in which a step difference at the boundary between different types of coating solutions is controllable by controlling a difference in capillary number during discharge of the different types of coating solutions using a slot die coater, and a coating layer and a cover window produced thereby. Therefore, the method of manufacturing a heterogeneous coating solution bonded coating layer can produce a cover window that is excellent in all the properties including durability, optical characteristics, and flexibility.