Retroreflective articles having microcubes, and tools and methods for forming microcubes

Abstract

A method for tooling a pattern of retroreflective microcubes, which pattern can be subdivided into smaller increments within which there are straight line tooling paths, none of which pass through an otherwise solid part of the incremental pattern. The tooling paths within the various increments need not be parallel to a common plane. Various adaptions of the method enable the tooling of a number of specific microcube shapes and for modifying such optical properties of the microcubes as entrance angularity, incidence angularity, orientation angularity, observation angularity, percent active aperture and retroreflectance. Specific techniques govern the pre-selection of cube parameters such as cube axis cant, cube apex decentration, and cube boundary proportions, which parameters can be adjusted independently of each other. Designs tooled by the method can have 100% active aperture at near zero degrees entrance angle. The method involves providing a plurality of plates of micro thickness, each plate having at least one end comprised of a material that can be tooled with polished surfaces by means of an appropriate tool, tooling on said end of each plate an increment of the pattern, and assembling the plates together in various ways to form a master. Retroreflective articles made by means of this technique are expected to provide superior performance when used in pavement markers, highway signs and other applications.

1. An article comprising an array of microcubes, at least one of said microcubes being non-hexagonal, such that for every plane in space there are two adjacent microcubes for which at the place of the adjacency none of the face edges is parallel to that plane, said at least one microcube having a projected area of less than 1 mm 2 , said at least one microcube being canted edge-more-parallel. 
     
     
       2. The article of  claim 1  wherein said array is retroreflective. 
     
     
       3. The article of  claim 2  wherein said article comprises retroreflective sheeting. 
     
     
       4. The article of  claim 3  wherein at least one microcube of said array has a projected area of about 1 mm 2  or less. 
     
     
       5. The article of  claim 4  wherein at least one microcube of said array has a projected area of about 0.35 mm 2  or less. 
     
     
       6. The article of  claim 5  wherein at least one microcube of said array has a projected area of about 0.04-0.12 mm 2 . 
     
     
       7. The article of  claim 3  wherein said sheeting comprises a polymer resin. 
     
     
       8. The article of  claim 7  wherein said polymer resin is selected from the group consisting of acrylic, polycarbonate, vinyl, polyester, and polyethylene. 
     
     
       9. The article of  claim 7  wherein said microcubes are formed by embossing. 
     
     
       10. The article of  claim 7  wherein said microcubes are formed by casting. 
     
     
       11. The article of  claim 3  wherein said sheeting is transilluminated. 
     
     
       12. The article of  claim 1  in which at least one microcube of said array is canted. 
     
     
       13. The article of  claim 12  in which at least one microcube in said array is edge-more-parallel. 
     
     
       14. The article of  claim 13  wherein retroreflectance in the plane of symmetry of the microcubes of said array is substantially constant and is greater than about 50% for all entrance angles less than about 30°. 
     
     
       15. The article of  claim 12  in which not all the cube axes in said array are parallel to each other. 
     
     
       16. The article of  claim 15  in which some adjacent cubes are alternately face-more-parallel and edge-more-parallel. 
     
     
       17. The article of  claim 12  in which said array is a retroreflective part of a pavement marker. 
     
     
       18. The article of  claim 1  wherein said article is a master for use in the production of a tool for making a retroreflective article. 
     
     
       19. The article of  claim 1  wherein said article is an electroform for use in the production of a tool for making a retroreflective article. 
     
     
       20. The article of  claim 1  wherein said microcubes of said array are of unequal sizes. 
     
     
       21. An article comprising an array of microcubes, at least one of said microcubes being non-hexagonal such that for every plane in space there are two adjacent microcubes for which at the place of the adjacency none of the face edges is parallel to that plane, said at least one microcube having a projected area of less than  1  mm 2 , in which array at least one said microcubes is canted, said array being formed of a material having a refractive index n, and the cant of at least one microcube in said array does not exceed about tan −1 √{square root over (2)}−sin −1 (1/n). 
     
     
       22. An article comprising an array of rectangular microcubes, at least some of which have no dihedral face-edges collinear with any dihedral faces-edges of any adjacent microcubes, at least one of said rectangular microcubes having a projected area of less than 1 mm 2 , said at least one microcube being canted edge-more-parallel. 
     
     
       23. A pavement marker for establishing on a finished roadway surface a marking visible from an oncoming vehicle, said pavement marker comprising a base member adapted to be mounted on the finished roadway surface, and a retroreflective signal means, said retroreflective signal means comprising an array of microcubes of  claim 22 . 
     
     
       24. The pavement marker of  claim 23  wherein the retroreflective signal means front surface is sloped about 30°-40° with respect to the road surface and comprises an array of canted rectangular microcubes, the cube axis cant being in the range of about −5° to −13°. 
     
     
       25. The pavement marker of  claim 24  having horizontal entrance angularity up to at least about 30°. 
     
     
       26. An article comprising an array of microcubes in which every region of three by three microcubes is nonrulable and in which at least one microcube in a said region of three by three microcubes is rectangular, said at least microcube having a projected area of less than 1 mm 2 , said at least one microcube being canted edge-more-parallel. 
     
     
       27. An article comprising an array of microcubes, at least one of said microcubes being rectangular such that for every plane in space there are two adjacent microcubes for which at the place of the adjacency none of the face edges is parallel to that plane, said at least one microcube having a projected area of less than  1  mm 2   , in which array at least one of said microcubes is canted, said array being formed of a material having a refractive index n, and the cant of at least one microcube in said array does not exceed about tan   −1  √{square root over (   2   )}− sin   −1  (   1 /n ). 
     
     
       28. The article of  claim 27  in which a plurality of microcubes in said array are male microcubes and said array of microcubes is nonrulable. 
     
     
       29. The article of  claim 27  in which a plurality of said microcubes of said array have a projected area of about  0 . 35  mm 2    or less.   
     
     
       30. The article of  claim 27  in which a plurality of said microcubes of said array have a projected area of  0 . 12  mm 2    or less.   
     
     
       31. The article of  claim 27  in which the article comprises retroreflective sheeting. 
     
     
       32. The article of  claim 27  in which one or more microcubes within said array have substantially  100 %  active aperture for incidence angles of about zero degrees.   
     
     
       33. The article of  claim 27  in which said array comprises at least three consecutive rows of said microcubes. 
     
     
       34. The article of  claim 27  in which said array of microcubes comprises rows of said microcubes in which each row of microcubes is a replica of a structure that has been ruled on the end of a microthick plate. 
     
     
       35. The article of  claim 27  in which said array comprises rows of rectangular microcubes, in which each row is a replica of a structure that has been ruled on the end of a microthick plate by a bevel face formed along the end of the plate and a plurality of v- grooves substantially perpendicular to the bevel face.   
     
     
       36. The article of  claim 35  in which adjacent rows of said microcubes correspond to adjacent plates oriented  180 ° to each other. 
     
     
       37. The article of  claim 35  in which said array comprises microcubes present as opposed paired microcubes, and in which said array comprises pairs of rows of rectangular microcubes in which each pair of rows is a replica of a structure that has been ruled on the end of a microthick plate by a v- groove extending along the center of the plate end, with opposed pairs of v - grooves extending substantially perpendicular to the center v   -   groove.   
     
     
       38. The article of  claim 27  in which said array comprises an array of male microcubes for which every three by three subarray of said microcubes is nonrulable. 
     
     
       39. The article of  claim 38  in which the article comprises retroreflective sheeting. 
     
     
       40. The article of  claim 39  in which one or more microcubes within said array have substantially  100 %  active aperture for incidence angles of about zero degrees.   
     
     
       41. The article of  claim 40  in which a plurality of said microcubes of said array have a projected area of about  0 . 35  mm 2    or less.   
     
     
       42. The article of  claim 40  in which a plurality of said microcubes of said array have a projected area of  0 . 12  mm 2    or less.   
     
     
       43. The article of  claim 38  in which said array comprises at least three consecutive rows of said microcubes. 
     
     
       44. The article of  claim 38  in which said array of microcubes comprises rows of said microcubes in which each row of microcubes is a replica of a structure that has been ruled on the end of a microthick plate. 
     
     
       45. The article of  claim 44  in which said array comprises rows of rectangular microcubes in which each row is a replica of a structure that has been ruled on the end of a microthick plate by a bevel face formed along the end of the plate and a plurality of v- grooves substantially perpendicular to the bevel face.   
     
     
       46. The article of  claim 45  in which adjacent rows of said microcubes correspond to adjacent plates oriented  180 ° to each other. 
     
     
       47. The article of  claim 44  in which said array comprises microcubes present as opposed paired microcubes, and in which said array comprises pairs of rows of rectangular microcubes in which each pair of rows is a replica of a structure that has been ruled on the end of a microthick plate by a v- groove extending along the center of the plate end, with opposed pairs of v - grooves extending substantially perpendicular to the center v   -   groove.   
     
     
       48. The article of  claim 38  in which said array of male microcubes comprises at least three consecutive rows of said microcubes in which each row of microcubes is a replica of a structure that has been ruled on the end of a microthick plate having a thickness of less than  1  mm. 
     
     
       49. The article of  claim 34  in which the microthick plate has a thickness of ( a )-( b ):
 ( a )  less than  1  mm, or      ( b )    0 . 012  inch  (   0 . 305  mm )  or less.     
     
     
       50. The article according to  claim 44  in which the microthick plate has a thickness of ( a )-( b ):
 ( a )  less than  1  mm, or      ( b )    0 . 012  inch  (   0 . 305  mm )  or less.     
     
     
       51. The article of  claim 48  in which the microthick plate has a thickness of  0 . 012  inch (   0 . 305  mm )  or less.   
     
     
       52. The article of  claim 27  in which a plurality of said microcubes are male microcubes at least some of which have no dihedral face edges collinear with any dihedral face edges of any adjacent microcubes.