As smartphones fold like pages, smartwatch bands integrate curved screens, and automotive dashboards stretch into seamless arcs, flexible electronics have moved from concept to daily reality. Yet every bend, press, or drop subjects delicate internal components to severe mechanical and environmental stress: OLED organic layers are vulnerable to moisture and oxygen, ultra-thin glass is prone to fracture, and flexible circuits fatigue under repeated deformation.

In this demanding landscape, high-performance silicone rubber has emerged as an indispensable “invisible support” in flexible display systems—serving simultaneously as a flexible encapsulant against water/oxygen ingress and as a dynamic stress buffer during bending, quietly ensuring the reliability of our “foldable future.”

I. Core Vulnerabilities of Flexible Displays

OLED Sensitivity to Moisture/Oxygen:

Water vapor transmission rate (WVTR) must be <10⁻⁶ g/m²·day; otherwise, dark spots proliferate rapidly.

Ultra-Thin Glass (UTG) Fragility:

Thickness of only 30–100 μm offers poor impact resistance.

Thermal & Mechanical Mismatch:

Multi-layer stacks with differing coefficients of thermal expansion (CTE) lead to delamination or cracking under repeated flexing.

Hinge Stress Concentration:

At bend radii <5 mm, local strain can exceed 1%, accelerating material fatigue.

Traditional rigid encapsulation (e.g., glass cover + epoxy) fails under dynamic flexing—necessitating soft, adaptive materials like silicone rubber.

II. Silicone Rubber’s Dual Roles

1. Organic Layer in Thin-Film Encapsulation (TFE)

Flexible OLEDs use alternating inorganic/organic multilayers:

Inorganic layers (Al₂O₃, SiNₓ): Provide high barrier performance but are brittle.

Organic interlayers (often UV-curable silicone or acrylate):

Planarize surface defects;

Absorb mechanical stress to prevent inorganic layer cracking;

Typical thickness: 1–3 μm, with >95% optical transmittance.

Silicone Advantages:

CTE (～300 ppm/°C) closely matches organic emissive layers, minimizing thermal stress.

Low elastic modulus (1–3 GPa) ensures minimal strain transfer during bending.

UV-curable formulations enable compatibility with roll-to-roll (R2R) manufacturing.

Leading manufacturers like Samsung Display and BOE already deploy silicone-based organic layers in premium foldable displays.

2. Optical Clear Resin (OCR) for Buffering & Bonding

Between UTG cover and OLED panel, transparent liquid silicone OCR is applied:

Refractive index ≈1.43, matching glass to reduce reflection;

Shore hardness 40A–60A absorbs impact energy during drops;

Allows controlled micro-sliding during folding, preventing shear-induced failure.

Unlike solid OCA films, liquid silicone OCR fills micron-scale gaps, improving lamination yield and optical clarity.

3. Hinge Zone Protection

The folding axis is a critical failure point—prone to “crease lines” or “bright streaks.”

High-flow liquid silicone rubber (LSR) is locally dispensed to:

Encapsulate flexible circuits and FPCs, mitigating metal fatigue;

Deliver IPX8-level waterproofing and dust exclusion;

Maintain transparency for in-line visual inspection.

Devices like the Huawei Mate X series and Xiaomi MIX Fold employ custom-engineered silicone sealing solutions in their hinge mechanisms.

III. Performance Requirements vs. Silicone Solutions

表格

Property Requirement Silicone-Based Solution

Transmittance     >92% (400–700 nm)    High-purity, filler-free, low-yellowing formulation

Moisture Barrier   WVTR <10⁻⁴ g/m²·day (as organic layer)     Used in hybrid TFE stacks with inorganic layers

Fold Endurance   >200,000 cycles @ R=3 mm     Low hysteresis, high elastic recovery

Adhesion Strength     0.5–1.0 N/mm (repairable) Plasma activation + silane-based primers

Yellowing Resistance  ΔYI <3 after 500h UV  Hindered amine light stabilizers (HALS)

⚠️ Note: Pure silicone rubber has a relatively high intrinsic WVTR (～10⁻³ g·mm/m²·day) and cannot serve as a standalone barrier—it must function within a multilayer encapsulation system.

IV. Emerging Innovations

Self-Healing Encapsulation:

Incorporation of Diels-Alder reversible covalent bonds enables microcrack repair upon mild heating.

Thermally Conductive OCR:

Boron nitride (BN) or alumina fillers enhance heat dissipation from OLEDs, extending operational lifetime.

Integrated Touch Functionality:

Embedding transparent conductive networks (e.g., silver nanowires) directly into silicone layers for capacitive sensing.

Bio-Based Siloxanes:

Sustainable monomers derived from renewable feedstocks align with ESG goals and reduce carbon footprint.

V. Industry Standards & Supply Chain

Key Material Suppliers:

Dow (Dow Silicones), Shin-Etsu, Henkel, DYNA (De Yuen)

Critical Reliability Tests:

MIT Folding Test: 200,000+ cycles at R = 1–5 mm

Environmental Aging: 85°C/85% RH for 500 hours—no delamination or dark spot growth

Conclusion

Behind every smooth unfolding arc of a foldable screen lies the silent resilience of silicone rubber—the “flexible skeleton” of modern displays. It emits no light, yet safeguards the brilliance of billions of pixels; it makes no sound, yet endures hundreds of thousands of bends without complaint.

This transparent, silicon-based material bridges the paradox of flexibility and durability—offering molecular-level elasticity and macro-level reliability. In the delicate balance between rigidity and pliancy, it constructs an invisible yet vital shield, ensuring that the promise of foldable electronics isn’t just about being able to fold, but about folding without failing.

Because true innovation isn’t measured in curvature alone—but in the quiet confidence that every crease will hold, every pixel will shine, and every fold will last.



Antibacterial silicone rubber-Precipitated