05468540 is referenced by 42 patents and cites 34 patents.

A retroreflective article comprising a transparent base sheet having first and second broad faces, the second face being substantially planar and the first face having an array of substantially hemi-spheroidal microlenses thereon, the microlenses being wider and shorter than portions of true spheres, the shape of the microlenses and thickness of the base sheet being such that collimated light substantially orthogonally incident to the array is focused approximately at the second face, wherein the second face has a coating of a nacreous pigment composition thereon. The article can include an optional layer of adhesive over the reflective layer to permit the article to be adhered to a document as a tamper-indicating, authenticating, and protective overlay. Special images can be formed within the article to enhance the security provided thereby. Also, a method for making such base sheets, and a method for making a forming master.

Title
Retroreflective article comprising a transparent base sheet and nacreous pigment coating, method for making such a base sheet, and method for making a forming master
Application Number
613136
Publication Number
5468540
Application Date
July 29, 1993
Publication Date
November 21, 1995
Inventor
Shih Lai Lu
Woodbury
MN, US
Agent
Robert H Jordan
Walter N Kirn
Gary L Griswold
Assignee
Minnesota Mining and Manufacturing Company
MN, US
IPC
B32B 3/00
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