Spherodized fluorescent beads for improved roadway pavement marker visibility

• US 5,516,227 A
• Filed: 07/07/1994
• Issued: 05/14/1996
• Est. Priority Date: 07/07/1994
• Status: Expired due to Fees

• Current Assignee: Alion Science and Technology Corporation, IIT Research Institute (Alion Science & Technology Corp.), ITT Research Institute
• Original Assignee: IIT Research Institute (Alion Science & Technology Corp.)
• Inventors: Bartholomew, Craig S., Kozak, Edward M.
• Primary Examiner(s): Novosad, Stephen J.
• Assistant Examiner(s): O'Connor, Pamela A.
• Application Number:
  US08/271,450
• Time in Patent Office: 677 Days
• Field of Search: 404/12, 404/14, 428/402, 428/406, 428/407, 428/328
• US Class Current: 404/9
• CPC Class Codes: C09D 5/004 Reflecting paints; Signal paints
• CPC Class Codes: E01F 9/524 Reflecting elements specially adapted for incorporation in or application to road surface markings
• CPC Class Codes: G09F 13/0472 Traffic signs
• CPC Class Codes: G09F 13/16 Signs formed of or incorporating reflecting elements or surfaces, e.g. warning signs having triangular or other geometrical shape
• CPC Class Codes: G09F 13/22 electroluminescent electroluminescent light sources per se H05B33/00
• CPC Class Codes: G09F 2013/227 Electroluminescent displays for vehicles
• CPC Class Codes: Y10T 428/24612 Composite web or sheet
• CPC Class Codes: Y10T 428/2857 including metal or compound thereof or natural rubber

Abstract

Retroreflective glass or plastic beads have fluorescent properties when irradiated with ultraviolet light and are emplaced in signs in patterns indicative of alphanumeric characters, or embedded in a hot melt comprising road stripes or embedded in the road asphalt or aggregate during construction of the road, to provide effectively bright and clear indications of signs or the extent and direction of the road. The glass beads comprise spherodized soda lime, borosilicate, phosphosilicate or aluminosilicate glasses with low levels of rare-earth dopants mixed therein, such as compounds containing one of the rare earths, or lanthanides. The plastic beads may have fluorescent materials mixed therein, typically organic pigments or dyes based on coumarin and rhodamine or the like.

Claims

1. An optically transparent bead for enhancing the brightness of road markings and signs, having a substantially spherical shape for substantially retroreflecting incident light of optical wavelengths, and comprising a glass;

and an oxide dopant of at least one of the lanthanide series of the elements at an effective concentration to activate substantial fluorescence in the glass under illumination with ultraviolet light.

2. An optically transparent bead according to claim 1, wherein said glass bead with lanthanide oxide dopant is substantially free of tint under illumination with optical wavelengths.

3. An optically transparent bead according to claim 1, wherein the lanthanide element of said lanthanide oxide dopant is in a trivalent state.

4. An optically transparent bead according to claim 3, comprising at least one of the set of La₂ O₃, Ce₂ O₃, Eu₂ O₃, Gd₂ O₃, or Tb₂ O₃.

5. An optically transparent bead according to claim 4, comprising a coating of material having high reflectivity at visible wavelengths, substantially covering approximately a hemisphere of said bead.

6. An optically transparent bead according to claim 4, wherein said bead has a refractive index relative to air greater than 1.6.

7. An optically transparent bead according to claim 4, comprising approximately 30% to approximately 80% of one of the set of SiO₂ and B₂ O₃ ;

approximately 1% to approximately 35% of one of the set of La₂ O₃ and Gd₂ O₃ ;

approximately 5% to approximately 45% Al₂ O₃ ; and

about 0.5% to about 30% of one of the set of Tb₂ O₃ and Ce₂ O₃, where percentages are percentages-by-weight.

8. An optically transparent bead according to claim 1, comprising about 76% SiO₂ ;

about 2% Al₂ O₃ ;

about 15% B₂ O₃ ;

about 6% Na₂ O;

about 0.20% to about 0.95% Eu₂ O₃ ; and

about 0.01% to about 0.05% CeO₂, where percentages are percentages-by-weight.

9. An optically transparent bead according to claim 1, comprising a coating of material having high reflectivity at visible wavelengths, substantially covering approximately a hemisphere of said bead.

10. An optically transparent bead according to claim 1, wherein said bead has a refractive index relative to air greater than 1.6.