One-way imaging optical window film

A one-way imaging optical film comprising a transparent polymer substrate having coatings thereon defining an image area and a surround area,

• the coating defining the image area comprising a first layer of chromium deposited on the substrate and having a thickness in the order of about 0.7 nm, a layer of indium tin oxide deposited on said first layer of chromium and having a thickness in the order of about 60 nm, and a second layer of chromium deposited on said layer of indium tin oxide and having a thickness in the order of about 1 to 3 nm,
• the coating defining the surround area comprising the same three layers as the coating defining the image area and a second layer of indium tin oxide deposited on said second layer of chromium and having a thickness in the order of about 30-110 nm, and a third layer of chromium deposited on said second layer of indium tin oxide and having a thickness in the order of about 0.18 to 1.0 nm,
• the coatings, in the visible light spectrum, having similar values of light transmittance and similar values of reverse reflectance when the film is viewed from the substrate side thereof and different values of reflectance when viewed from the coated side thereof,
• the image area being visually distinct from the surround area when the film is viewed from the coated side thereof and being virtually non-discernible when the film is viewed from the substrate side thereof,
• said coatings at 550 nm having a visible light transmittance of at least about 25 percent and a reflectance value differential of at least about 5 percent.

A process of making one-way imaging optical film comprising the steps of

• providing a transparent substrate,
• depositing a first layer of metal onto the substrate,
• depositing a first layer of dielectric onto the first layer of metal,
• depositing a second layer of metal onto the first layer of dielectric,
• applying a mask of an image onto part of the surface area of said second layer of metal,
• depositing a second layer of dielectric onto the mask and the surface area of the second layer of metal not covered by the mask,
• depositing a third layer of metal onto the second layer of dielectric, and
• removing the mask to define an image area comprised of the substrate, the first layer of metal, the first layer of dielectric and the second layer of metal, and a surround area comprised of the substrate, the first layer of metal, the first layer of dielectric, the second layer of metal, the second layer of dielectric, and the third layer of metal,
• the layers of metal and dielectric being selected and being deposited at respective thicknesses, such that the image area and the surround area have in the visible light spectrum similar values of light transmittance and similar values of reverse reflectance when the film is viewed from the substrate side thereof, and different values of reflectance when the film is viewed from the coated side thereof,
• the image area being visually distinct from the surround area when the film is viewed from the coated side thereof and being virtually non-discernible when the film is viewed from the substrate side thereof,
• the layers of metal and dielectric further being selected and being deposited at respective thicknesses, such that the image area and the surround area have, at 550 nm, a visible light transmittance of at least about 5 percent.