Coating processing of PC lenses

The coating process for PC lenses (polycarbonate lenses) aims to enhance their optical performance, durability, and functionality, primarily encompassing the following key steps and technologies:

1. Pretreatment (Cleaning and Activation)

Ultrasonic Cleaning: Removes contaminants such as grease and dust from the lens surface.

Plasma Treatment: Enhances coating adhesion by bombarding the surface with plasma.

Chemical Treatment: Further cleans and activates the surface using solvents or acidic or alkaline solutions.

2. Base Coating Process

Primer Coating

Purpose: Fills minor irregularities on the PC surface and improves the adhesion of subsequent coatings.

Method: Spin coating, dip coating, or spray coating. Commonly used materials are silane or polyurethane primers.

Curing: UV curing or thermal curing (60–80°C).

Hard Coating

Purpose: Improves scratch resistance (PC is inherently soft).

Materials: Silicon dioxide (SiO₂), silicone resin, or acrylate.

Process: Dip coating or spray coating followed by UV curing (high-intensity ultraviolet light irradiation).

3. Functional Coating Process

Anti-Reflective Coating (AR Coating)

Purpose: Reduces reflection and increases light transmittance (e.g., multilayers of metal oxides such as MgF₂ and SiO₂).

Process: Vacuum evaporation (physical vapor deposition (PVD)) or magnetron sputtering, requiring multiple layers (each layer thickness is 1/4 the wavelength of light).

Anti-fouling and Water-Repellent Coating (Hydrophobic/Oleophobic Coating)

Purpose: Anti-fingerprint, easy to clean.

Material: Fluorosilanes (e.g., perfluoropolyether).

Process: Spray coating or vacuum deposition, often combined with AR coating.

Anti-Blue Light Coating

Purpose: Absorbs or reflects harmful blue light (wavelength 400–450nm).

Material: Metal oxides or organic dyes.

Process: Coated simultaneously with AR coating or applied separately.

Anti-Static Coating

Purpose: Prevents dust absorption.

Materials: Conductive polymer or metal-doped coating.

4. Curing Technology

UV curing: Suitable for organic coatings (such as hard coatings), fast and efficient (curing in seconds).

Thermal curing: Used for some high-temperature stable coatings (such as certain primers).

Electron beam curing: Used in a few high-precision applications.

5. Post-Processing and Testing

Annealing: Eliminates internal stress and improves coating stability.

Quality Testing:

Adhesion testing (Bicester method).

Abrasion resistance testing (Taber abraser).

Optical performance testing (spectrophotometer for transmittance and reflectance).

Key Challenges and Innovation Directions

Adhesion Issues: PC surface is hydrophobic, requiring plasma treatment or primer optimization.

High-temperature resistance: PC has a low melting point (approximately 145°C), requiring a low-temperature curing process.

Environmentally friendly processes: Water-based coatings replace solvent-based coatings to reduce VOC emissions.

Nanotechnology: For example, the sol-gel method can be used to produce nanoscale hard coatings.

Typical Applications

Eyeglass lenses: AR + hard coating + hydrophobic composite coating.

Automotive headlight covers: Weather-resistant hard coating.

Electronic screen protectors: Anti-glare + antistatic coating.

The following is a detailed analysis of the PC lens hardening process:

1. The core principle of the hardening process

Base treatment: Clean the lens surface through chemical or physical methods to remove grease and impurities and enhance the adhesion of the hardening layer.

Hard coating: Coat the lens surface with a high-hardness material (such as silicone resin) and form a wear-resistant layer through curing.

Curing technology: UV curing or thermal curing is commonly used to make the coating tightly bonded to the PC substrate.

2. Main hardening methods

(1) Dip Coating

Process: Immerse the lens in the hardening liquid → Pull at a constant speed to control the thickness → UV/thermal curing.

Advantages: Uniform coating, suitable for mass production.

Key points: Hardening liquid formula (including nano-silica and other ingredients) and curing conditions (UV intensity, temperature).

(2) Spin Coating

Process: Fix the lens on a rotating table, add the hardening liquid → High-speed rotation and evenly spin → Curing.

Advantages: Controllable thickness, suitable for high-precision requirements.

Disadvantages: Large amount of material waste.

(3) Vacuum coating method

Technology: SiO₂ and other inorganic hard films are deposited on the surface through PVD (physical vapor deposition).

Features: Extremely high hardness (close to glass), but high cost and requires special equipment.

(4) Plasma treatment

Function: Cleans the surface and activates molecules through plasma to improve coating adhesion.

Application: Often used as a pretreatment or in combination with the dipping method.

3. Materials for hard coating

Silicone resin: The mainstream choice, forming a cross-linked network through UV curing.

Nanocomposite materials: Such as nano-SiO₂ and Al₂O₃ dispersed in the resin, significantly improving hardness.

Polyurethane acrylate: Good flexibility and strong impact resistance.

4. Key process parameters

Curing conditions: UV wavelength (usually 365nm), energy (500-1000mJ/cm²), temperature (60-80℃).

Coating Thickness: Generally 2-5μm. Thicker coatings are prone to cracking, while thinner coatings may result in insufficient wear resistance.

Environmental Control: Dust-free room (ISO Class 7 or higher), humidity 40-60%.

5. Quality Inspection Standards

Abrasion Resistance: Taber Abrasion Test (CS-10 grinding wheel, 500g load, haze change ≤5% after 1000 cycles).

Adhesion: Grid Knife Test (ASTM D3359, 4B or higher).

Hardness: Pencil Hardness Test (≥3H is acceptable).

Weather Resistance: UV Aging Test (no cracking or yellowing after 500 hours).

6. Common Problems and Solutions

Coating Delamination: Optimize surface treatment (such as plasma activation) or adjust curing parameters.

Surface Orange Peel: Caused by excessive viscosity of the hardening solution or uneven spin coating speed; adjust the formulation or process.

Air Bubbles: Vacuum degassing or reduce the pull/spin speed.