Multilayer Hard Coating Film for Polyimide Substrates
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Solution Overview
Problem
Existing hard coating films for polymer films face challenges in achieving a balance between high surface hardness for scratch resistance and flexibility, often resulting in reduced flexibility when surface hardness is increased, and vice versa, leading to issues like curling and cracking.
Innovation Solution
A multilayer hard coating film structure is introduced, comprising a highly bendable layer with Vickers hardness of 40 or less and a high-hardness layer with Vickers hardness of 55 or more, stacked on a transparent polyimide substrate, achieving a Vickers hardness of 20 to 65 for the film, which provides excellent scratch resistance and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If surface hardness is increased to improve scratch resistance, then abrasion resistance is improved, but flexibility is reduced
Solution Approach 1:
The coating layer is divided into multiple layers with different hardness values. The lower layer has lower hardness (Hv 30-50) to maintain flexibility and prevent cracking, while the upper layer has higher hardness (Hv 50-70) to provide scratch resistance. This segmentation allows each layer to perform its specific function without compromising the overall performance of the coating film.
Solution Approach 2:
The patent uses a composite coating structure combining materials with different mechanical properties. The lower layer uses a softer material that provides flexibility and adhesion to the substrate, while the upper layer uses a harder material that provides wear resistance. This composite approach enables the coating to simultaneously achieve both flexibility and hardness, resolving the technical contradiction between these two properties.
2Strength
If surface hardness is increased, then scratch resistance is improved, but curling and cracking occur due to shrinkage
Solution Approach 1:
The coating is segmented into two layers where the lower layer acts as a buffer zone that absorbs shrinkage stress. This lower layer with moderate hardness (Hv 30-50) prevents the transmission of stress to the substrate, thereby preventing curling and cracking while maintaining good adhesion. The upper layer can then be made harder (Hv 50-70) for scratch resistance without causing adhesion problems.
Solution Approach 2:
The lower layer serves as a cushioning layer that absorbs the shrinkage stress generated during coating formation and curing. By placing this compliant layer between the substrate and the hard upper coating layer, the system pre-compensates for the shrinkage forces that would otherwise cause curling, cracking, or delamination, ensuring long-term reliability of the coating.
3Adaptability or versatility
If flexibility is increased by decreasing hardness, then bendability is improved, but abrasion resistance is deteriorated
Solution Approach 1:
The coating structure is segmented into a flexible lower layer and a hard upper layer. The lower layer (Hv 30-50) provides the necessary flexibility and bendability, allowing the coated substrate to be bent without cracking the coating. The upper layer (Hv 50-70) provides the abrasion resistance needed for durable surfaces. This segmentation enables both flexibility and wear resistance to coexist in the same coating system.
Data Source
AI summary
The present invention relates to a hard coating film having a multilayer-structure and, specifically, to a hard coating film having a multilayer-structure, which has a low Vickers hardness (Hv) value while having an excellent scratch resistance together with flexibility.