Retroreflective sheet with enhanced brightness
AssigneeMinnesota Mining and Manufacturing Company
InventorWallace K. Bingham
Life of this patent
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Abstract
Retroreflective construction comprising a monolayer of microspheres with associated dielectric mirrors which are hemispherically surrounded by tangentially-oriented, preferably contour-conforming, reflective pigment nacreous flakes. The dielectric mirrors and reflective nacreous pigment flakes cooperate additively substantially without interfering with each other to provide a high brightness retroreflective sheet. The novel sheets retain much of their reflectivity after several launderings or drycleanings and, in some embodiments, can be made very flexible, making them well-suited for use as reflective fabrics.
Claims18
A retroreflective sheet comprising:
- (A) a monolayer of transparent microspheres having a refractive index n.sub.2 ;
- and
- (B) transparent specular reflectors associated with said microspheres in optical connection therewith, said specular reflectors comprising a transparent layer of refractive index n.sub.1, the faces of said layer being in contact with materials of refractive index n.sub.2 and n.sub.3, wherein n.sub.2 and n.sub.3 are both at least 0.1 either higher or lower than n.sub.1, said transparent layer having an optical thickness corresponding to an odd numbered multiple of about one quarter wavelength of light in the wavelength range of about 3,800 to 10,000 angstroms;
- partially embedded in
- (C) a base layer comprising a substantially transparent binder material and reflective nacreous pigment flakes which are arranged about the embedded portion of said microspheres and said specular reflectors in approximately tangential orientation thereto.
Dependencies are inferred from the claim text.