The present invention relates generally to durable articles. More particularly, the present invention relates to increasing the durability of a microstructured bearing article such as, for example, a brightness enhancing film, an optical lighting film or a reflective element.
Microstructure bearing articles, such as, brightness enhancing films, optical turning films or reflective elements, are made in a variety of forms. One such form includes a series of alternating tips and grooves. One example of such a form is brightness enhancing film, which has a regular repeating pattern of symmetrical tips and grooves. Other examples include patterns in which the tips and grooves are not symmetrical and in which the size, orientation, or distance between the tips and grooves is not uniform.
One drawback of current brightness enhancing films and optical lighting films, and the like, is that the tips of the microstructure are susceptible to mechanical damage. For example, light scraping with a fingernail or a hard, relatively sharp edge can cause the tips of the microstructure to break or fracture. Conditions sufficient to break the tips of prior art microstructures are experienced during normal handling of brightness enhancing films, such as, in the manufacturing of liquid crystal displays for laptop computers.
When microstructure peaks are broken, the reflective and refractive properties of the affected peaks are reduced and the transmitted light scattered to virtually all forward angles. Hence, when the brightness enhancing film is in a display, and the display is viewed straight on, scratches in the brightness enhancing film are less bright than the surrounding, undamaged area of the film. However, when the display is viewed at an angle near or greater than the “cutoff” angle, the angle at which the image on the display is no longer viewable, the scratches look substantially brighter than the surrounding, undamaged area of the film. In both situations, the scratches are very objectionable from a cosmetic standpoint, and brightness enhancing film with more than a very few, minor scratches is unacceptable for use in a liquid crystal display.