Surface Protective Film with Polyurethane Roughness for Touch Pen Writing
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Solution Overview
Problem
Electronic devices with glass or polycarbonate substrates provide a poor writing sensation when using a touch pen due to their high hardness, lacking the tactile experience of writing on paper.
Innovation Solution
A surface protective film with a polyurethane protective layer having specific roughness and hardness characteristics, combined with an adhesive layer, is applied to the substrate, enhancing the writing sensation by mimicking the feel of paper.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a transparent substrate made of glass or polycarbonate is used, then optical transparency and hardness are improved, but the writing sensation with a touch pen deteriorates
Solution Approach 1:
The invention uses a composite material approach by creating a multi-layer protective film structure. The protective layer is made from a composite system comprising a polyol (with specific hydroxyl value range), isocyanate, and curing agent, forming a polyurethane-based coating. This composite material system allows the surface to achieve both adequate hardness for protection and controlled roughness (Ra: 0.2-0.6 μm, Rz: 1.0-3.0 μm) for paper-like writing sensation, resolving the contradiction between hardness and writing comfort.
Solution Approach 2:
The invention applies parameter changes by precisely controlling the surface roughness parameters (arithmetic average roughness Ra and maximum height Rz) of the protective layer. By adjusting the formulation ratios of polyol, isocyanate, and curing agent, along with curing conditions, the surface morphology is optimized to achieve Ra of 0.2-0.6 μm and Rz of 1.0-3.0 μm. This parameter optimization provides a writing sensation similar to paper while maintaining the underlying substrate's hardness and transparency.
2Illumination intensity
If a smooth protective layer is applied, then optical transparency is improved, but the writing sensation deteriorates
Solution Approach 1:
The invention optimizes the surface roughness parameters within specific ranges (Ra: 0.2-0.6 μm, Rz: 1.0-3.0 μm) to achieve a balance between transparency and writing sensation. This controlled roughness creates light scattering that mimics paper texture while maintaining sufficient optical clarity for display visibility. The parameter optimization ensures that the surface provides tactile feedback similar to paper without completely compromising transparency.
Solution Approach 2:
The protective layer exhibits local quality differentiation where the bulk material maintains high transparency for optical performance, while the surface layer develops controlled roughness for tactile feedback. This gradient structure allows the interior to remain smooth and transparent for light transmission, while the exterior surface achieves the desired roughness characteristics for paper-like writing sensation.
3Ease of operation
If a rough surface is created, then writing sensation is improved, but scratch resistance deteriorates
Solution Approach 1:
The protective layer uses a composite polyurethane system formed from polyol, isocyanate, and curing agent that provides both surface roughness and structural integrity. The crosslinked network structure of the cured polyurethane maintains high scratch resistance and self-healing properties, while the surface morphology is controlled to provide paper-like writing sensation. The composite structure ensures that surface roughness does not compromise overall mechanical strength.
Solution Approach 2:
The protective film exhibits local quality differentiation where the surface layer has controlled roughness for writing sensation, while the bulk material maintains high density and crosslinking for scratch resistance. The roughness is confined to the top surface layer (Ra: 0.2-0.6 μm), while the underlying structure remains robust and cohesive, providing both tactile feedback and mechanical protection against scratches and impacts.
4Ease of operation
If a polyurethane protective layer with specific roughness is applied, then writing sensation is improved, but manufacturing precision requirements increase
Solution Approach 1:
The invention establishes specific parameter ranges (Ra: 0.2-0.6 μm, Rz: 1.0-3.0 μm) that can be consistently achieved through controlled formulation and curing processes. By defining these parameter windows, the patent makes the manufacturing process more predictable and controllable. The use of standard materials (polyol, isocyanate, curing agent) with controlled ratios, along with standardized curing conditions, enables reproducible surface roughness within the target range, reducing manufacturing variability.
Solution Approach 2:
The invention utilizes a curing process where the polyurethane system undergoes chemical transformation from liquid precursors to a solid, crosslinked network. This curing process naturally develops the desired surface roughness characteristics through controlled phase separation and network formation. The process recovers and stabilizes the surface morphology during curing, ensuring consistent roughness parameters without requiring additional post-processing steps, thereby simplifying manufacturing precision requirements.
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 surface protective film provides a writing sensation similar to that of paper with a touch pen, while maintaining optical transparency, non-coloring properties, and weather resistance, and offering excellent scratch resistance and self-repairability.
Implementation Method 1
a protective layer made of a polyurethane on the outermost surface thereof, wherein the protective layer has an arithmetic average roughness (Ra) of 0.3 μm or more and 0.6 μm or less and a maximum height (Rz) of 1.5 μm or more and 3.5 μm or less
Data Source
AI summary
There is provided a surface protective film having an excellent writing sensation when a touch pen is used. A surface protective film has a protective layer made of a polyurethane on the outermost surface, and the protective layer has an arithmetic average roughness (Ra) of 0.3 μm or more and 0.6 μm or less, and a maximum height (Rz) of 1.5 μm or more and 3.5 μm or less.