Patent NZ-711765-A (NZ)
Title: Method of preparing photochromic-dichroic films having reduced optical distortion
Inventor: PARK DAVID
IPC: B29C48/49
Filed: 2014-03-05
Abstract: It is known to form films that include one or more photochromic-dichroic compounds. Such photochromic-dichroic films can be used to form optical articles having photochromic and dichroic properties, such as by lamination or in-mold film injection methods. The formation of such photochromic-dichroic films is often and undesirably accompanied by the introduction of optical distortion into the photochromic-dichroic film. The optical distortion can result in the photochromic-dichroic film having undesirable properties, such as uneven shading, uneven linear polarization properties, and observable visual distortions when objects and/or direct light sources and/or indirect light sources are viewed through the film. Disclosed herein is a method of preparing a photochromic-dichroic film that exhibits reduced or minimal optical distortion. The method includes: forming a first molten thermoplastic composition comprising a first thermoplastic polymer and a photochromic-dichroic compound; forming a second molten thermoplastic composition comprising a second thermoplastic polymer; and forming a third molten thermoplastic composition comprising a third thermoplastic polymer. The method further comprises, introducing the first molten thermoplastic composition, the second molten thermoplastic composition, and the third molten thermoplastic composition into a die having a terminal slot. A molten extrudate is removed from the terminal slot of the die. The molten extrudate comprises: (i) a first molten layer comprising the first molten thermoplastic composition; (ii) a second molten layer comprising the second molten thermoplastic composition; and (iii) a third molten layer comprising the third molten thermoplastic composition. The first molten layer, of the molten extrudate, is interposed between the second molten layer and the third molten layer. The method further comprises cooling the molten extrudate to form a multilayer film comprising a first layer formed from the first molten layer, a second layer formed from the second molten layer, and a third layer formed from the third molten layer. The first layer, of the multilayer film, is interposed between the second layer and the third layer. The method additionally comprises removing, from the first layer, the second layer and the third layer, and retaining the first layer. The retained first layer, which comprises the photochromic-dichroic compound(s), defines the photochromic-dichroic film. Prior to removing, from the first layer, the second layer and the third layer, the second layer defines a first exterior surface of the multilayer film, and the third layer defines a second exterior surface of the multilayer film. The method further comprises forming microgrooves in at least one of the first exterior surface and the second exterior surface of said multilayer film, collecting the multilayer film on a collection roll thereby forming a wound roll, and optionally storing said wound roll, wherein the collecting and the optional storing steps are performed prior to removing, from the first layer, the second layer and the third layer, and further wherein the micro-grooves are dimensioned to allow gas to escape from between overlapping layers of the multilayer film residing on the wound roll. The film with reduced or minimal optical distortion is provided at least in part, and in summary, by: forming a molten extrudate that includes a first molten layer containing a photochromic dichroic compound that is interposed between a second molten layer and a third molten layer; cooling the molten extrudate; removing, from the first layer, the second and third layers; and retaining the first layer.