Method of casting a microstructure sheet having an array of prism elements using a reusable polycarbonate mold

A method for forming a microstructure from a polymeric reusable mold wherein said microstructure has prism elements having a base side and a facet side, comprising the steps of:

• a) forming a first mold having a positive prism array pattern;
• b) forming a second mold of polycarbonate material in said first mold, said second mold comprising a negative prism array pattern;
• c) removing the second mold from the first mold;
• d) coating the negative prism array pattern on the second mold with a protective surface layer that is opaque to radiation;
• e) forming a positive prism array structure over said protective surface layer by curing of a plastic material on said second mold;
• f) removing said structure from said second mold to form a retroreflective structure while said protective layer adheres to said second mold;
• and
• g) reusing said second mold to form additional retroreflective structures.

A method for casting a retroreflective sheet, comprising the steps of:

• a) providing an embossing mold having a facet side with an array of positive prism elements and a base side;
• b) molding a polycarbonate material on the facet side of said embossing mold to form a polycarbonate mold having a facet side comprising an array of negative prism elements;
• c) removing the formed polycarbonate mold;
• d) applying a coating to the facet side of said polycarbonate mold to form a protective layer;
• e) casting the retroreflective sheet on said protective layer of said polycarbonate mold by
• i) applying a plastic compound,
• ii) laminating a carrying film over said plastic compound, and
• iii) curing said plastic compound and said carrying film to form the retroreflective sheet having a facet side and window side;
• and
• f) removing said casted retroreflective sheet.

A method for forming arrays of cube-corner microprism elements from polycarbonate reusable molds wherein said microprism elements have a base side and a facet side, comprising the steps of:

• a) forming a first master mold having a positive cube-corner microprism array pattern;
• b) forming a continuous belt mold in said first mold, said continuous belt mold being formed of polycarbonate material comprising a negative cube-corner microprism array pattern, to thereby allow the continuous formation of additional retroreflective structures;
• c) removing the continuous belt mold from the first mold;
• d) forming a positive cube-corner microprism array structure on said continuous belt mold layer by curing a plastic material applied to said array structure;
• e) removing said structure from said continuous belt mold to form a retroreflective structure;
• and
• f) reusing said continuous belt mold to form additional retroreflective structures.