Non-iridescent film with polymeric particles in primer layer

Abstract

This invention relates to an optically clear film of predominantly thermoplastic polyester base layer and a carbodiimide-crosslinked, polyester and polymethylmethacrylate blend primer layer. The base layer preferably has a particle-free core layer and outer layers containing nonpolyester, organic and/or inorganic particles. The primer layer is preferably applied to the base layer from solution that is organic solvent-free. The primer layer and base layer composite can be laminated with a protective layer of primarily acrylic polymer to form a solar control film. Functional additives, such as UV light blockers, can be present in various layers of the solar control film. Polymethylmethacrylate in the primer, especially in combination with crosslinking by the carbodiimide, provides the acrylic coated polyester base solar control film with notably reduced iridescence. Adhesion between the acrylic layer applied from organic solvent solutions and the polyester layers is durable in moist and warm service conditions.

What is claimed is: 
     
         1 . A composite film comprising
 (a) a core layer of substantially particle-free and optically clear polyester,   (b) a first outer layer in direct contact with one side of the core layer,   (c) an optically clear primer layer in direct contact with a side of the first outer layer opposite the core layer, and   (d) optionally, a second outer layer in direct contact with a side of the core layer opposite the first outer layer,
 in which each outer layer is optically clear, is independently about 0.1 μm-5 μm thick and independently comprises inorganic particles dispersed uniformly in a polyester matrix, 
 and in which the primer layer comprises an iridescence reducing agent selected from the group consisting of inversely synthesized aliphatic polyurethane particles and polymethylmethacrylate particles uniformly dispersed in a matrix of polyester crosslinked by a carbodiimide crosslinking agent. 
   
     
     
         2 . The composite film of  claim 1  in which the iridescence reducing agent is polymethylmethacrylate particles. 
     
     
         3 . The composite film of  claim 2  in which both of the first outer layer and the second outer layer are present. 
     
     
         4 . The composite of  claim 2  which further comprises an optically clear protective layer in direct contact with a side of the primer layer opposite the first outer layer. 
     
     
         5 . The composite of  claim 4  in which the protective layer comprises greater than 50 wt. % of an acrylic polymer. 
     
     
         6 . The composite of  claim 5  in which the protective layer is a devolatized residue of a solution of the acrylic polymer dissolved in an organic solvent from which solution the organic solvent has been substantially removed. 
     
     
         7 . The composite of  claim 6  in which the protective layer comprises a trace amount of the organic solvent. 
     
     
         8 . The composite of  claim 7  in which the organic solvent is methyl ethyl ketone. 
     
     
         9 . The composite of  claim 6  in which the polymethylmethacrylate particles are present in the primer layer at a concentration such that the composite exhibits haze of at most about 3%. 
     
     
         10 . The composite of  claim 9  in which thickness of the primer layer is about 0.03-0.15 μm. 
     
     
         11 . The composite of  claim 4  which is substantially non-iridescent under fluorescent illumination. 
     
     
         12 . The composite of  claim 2  in which the polymethylmethacrylate particles are microspheres of diameter in the range of about 1 μm-10 μm. 
     
     
         13 . The composite of  claim 12  in which polymethylmethacrylate particles are solid microspheres. 
     
     
         14 . The composite of  claim 12  in which polymethylmethacrylate particles have a particle size distribution defining a median particle size and the particle size distribution is narrow such that at least 80 wt. % of the particles have a diameter within a range from about +4 μm to −4 μm of the median particle size. 
     
     
         15 . A method of making an optically clear non-iridescent composite film comprising the steps of
 (A) providing a mixture comprising an iridescence reducing agent selected from the group consisting of inversely synthesized aliphatic polyurethane particles and polymethylmethacrylate particles and polyester binder particles of a polyester resin having a softening point lower than 100° C. uniformly dispersed in a predominantly aqueous medium comprising carbodiimide crosslinking agent dissolved in water,   (B) providing a base layer comprising a core layer of polyester film of thickness in the range of about 1-500 μm and optionally comprising about 0.1 to 2 wt % of a UV light absorber composition,   (C) depositing a wet coating of the mixture onto one side of the base layer,   (D) heating the base layer and wet coating effectively to (i) soften the polyester binder, (ii) evaporate substantially all volatile components of the predominantly aqueous medium, and (iii), and activate the crosslinking agent, thereby creating an optically clear film of solidified primer layer in contact with the one side of the base layer,
 in which the wet coating on the base layer is present in an amount effective to produce a thickness of the solidified primer layer in the range of about 0.03-0.15 μm. 
   
     
     
         16 . The method of  claim 15  in which the iridescence reducing agent is polymethylmethacrylate particles. 
     
     
         17 . The method of  claim 16  in which the polymethylmethacrylate particles are present in the primer layer at a concentration effective to make the optically clear non-iridescent composite film have a haze value of at most about 3%. 
     
     
         18 . The method of  claim 16  in which the step of providing the base layer further comprises the step of providing a first outer layer about 0.1-5 μm thick and comprising inorganic particles uniformly dispersed in a polyester matrix, in which the first outer layer is in direct contact with a side of the core layer opposite the one side of the base layer bearing the primer layer, such that the core layer and the first outer layer collectively define the base layer. 
     
     
         19 . The method of  claim 18  in which the step of providing the base layer further comprises the step of providing a second outer layer about 0.1-5 μm thick and optionally comprising inorganic particles uniformly dispersed in a polyester matrix, in which the second outer layer is in direct contact with a side of the core layer opposite the first outer layer, such that the core layer, first outer layer and second outer layer collectively define the base layer. 
     
     
         20 . The method of  claim 18  which further comprises the steps of
 (E) providing a solution comprising acrylic polymer, a cure initiator, and an amount of organic solvent effective to dissolve the acrylic polymer, 
 (F) placing a uniformly thick solvent-wet coating of the solution onto a side of the primer layer opposite the base layer, 
 (G) heating solvent-wet coating effectively to evaporate substantially all volatile components of the organic solvent, thereby creating an optically clear film having a protective layer of solidified acrylic polymer in contact with the primer layer,
 in which acrylic polymer comprises greater than 50 wt. % of the primer layer. 
 
 
     
     
         21 . The method of  claim 19  in which the protective layer is effective to make the optically clear non-iridescent composite film have a haze value of at most about 3%. 
     
     
         22 . The method of  claim 16  in which the polymethylmethacrylate particles are microspheres of diameter in the range of about 1 μm to about 10 μm and in which polymethylmethacrylate particles have a particle size distribution defining a median particle size and the particle size distribution is narrow such that at least 80 wt. % of the particles have a diameter within a range from about +4 μm to −4 μm of the median particle size.