Polarized glass (specifically, polarized lenses) is typically manufactured using a lamination process, not by altering the glass itself. Here's a breakdown of the method:
The Lamination Process Explained
Polarized lenses are constructed using a multi-layered approach:
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Polarizing Film Creation: The core of polarized lenses is a thin polarizing film. This is often made from polyvinyl alcohol (PVA). The PVA is stretched and then treated with iodine or dichroic dyes. This process aligns the molecules, creating a filter that only allows light vibrating in a specific direction to pass through.
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Lamination: The polarizing film is incredibly fragile. Therefore, it's laminated between layers of a more durable and optically clear material. Common laminating materials include:
- CR-39 (a polymer known for its optical clarity and scratch resistance)
- Polyurethane (another durable polymer option)
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Applying Heat and Pressure: The lamination process involves applying heat and pressure to bond the polarizing film securely between the protective polymer layers.
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Lens Shaping and Curvature: Once laminated, the flat lens blank is subjected to heat and pressure to mold it into the desired lens curvature (e.g., for sunglasses or prescription eyewear).
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Surface Treatments: Additional coatings, such as scratch-resistant or anti-reflective coatings, may be applied to the lens surface for improved performance and durability.
Summary of Key Steps
| Step | Description | Materials Involved |
|---|---|---|
| 1. Film Creation | Stretching and treating PVA film to align molecules for polarization. | Polyvinyl Alcohol (PVA), Iodine or Dichroic Dyes |
| 2. Lamination | Encapsulating the PVA film between protective polymer layers. | Polarizing Film, CR-39 or Polyurethane |
| 3. Bonding | Applying heat and pressure to bond the layers together. | Heat, Pressure |
| 4. Shaping | Molding the flat lens blank into the desired curvature. | Heat, Pressure, Lens Molds |
| 5. Coating | Applying surface treatments for enhanced performance. | Scratch-resistant or Anti-reflective coatings |
It's important to remember that the polarization effect comes from the specifically treated film embedded within the lens structure, not from manipulating the glass (or polymer) material directly. This lamination technique allows for the creation of durable and effective polarized lenses.
