Lens-type retroreflective sheeting

• US 5,984,479 A
• Filed: 08/25/1997
• Issued: 11/16/1999
• Est. Priority Date: 09/30/1994
• Status: Expired due to Fees

• Current Assignee: Nippon Carbide Kogyo Kabushiki Kaisha (Nippon Carbide Industries Company Incorporated)
• Original Assignee: Nippon Carbide Kogyo Kabushiki Kaisha (Nippon Carbide Industries Company Incorporated)
• Inventors: Tanaka, Osamu, Takeda, Makoto, Ochi, Katsura
• Primary Examiner(s): Phan, James
• Application Number:
  US08/917,286
• Time in Patent Office: 813 Days
• Field of Search: 359/534-542, 359/900, 359/513-514
• US Class Current: 359/539
• CPC Class Codes: G02B 5/128 transparent spheres being embedded in matrix

Abstract

The present invention discloses lens-type retroreflective sheeting excellent in appearance and having constant thickness and desired retroreflective performance, wherein the transparent microspheres in the retroreflective layer are composed of transparent microspherical lenses (A) having a refractive index of 1.8 or more and transparent microspherical fillers (B) having a refractive index different by at least 5% from the refractive index of the lenses (A).

Claims

1. Lens-type retroreflective sheeting having a retroreflective layer comprising a resin layer and a substantial monolayer of transparent microspheres partially embedded in the resin layer wherein the transparent microspheres in the retroreflective layer comprise transparent microspherical lenses (A) having a refractive index of at least 1.8 and transparent microspherical fillers (B) having a refractive index different by at least 5% from the refractive index of the lenses (A);

and a light reflective layer located substantially at the focal point of the transparent microspherical lenses.

2. The retroreflective sheeting according to claim 1 wherein the refractive index of the transparent microspherical fillers (B) is different by at least 10% from the refractive index of the transparent microspherical lenses (A).

3. The retroreflective sheeting according to claim 2 wherein the refractive index of the transparent microspherical fillers (B) is different by at least 15% from the refractive index of the transparent microspherical lenses (A).

4. The retroreflective sheeting according to claim 1 wherein the refractive index of the transparent microspherical fillers (B) is lower than the refractive index of the transparent microspherical lenses (A).

5. The retroreflective sheeting according to claim 1 wherein the transparent microspherical fillers (B) are composed of soda-lime glass.

6. The retroreflective sheeting according to claim 1 wherein the transparent microspherical lenses (A) have an average particle size within the range of 20 to 120 μ

m.

7. The retroreflective sheeting according to claim 1 wherein the transparent microspherical fillers (B) have an average particle size which is within the range of 1/2 to 3/2 of the average particle size of the transparent microspherical lenses (A).

8. The retroreflective sheeting according to claim 7 wherein the average particle size of the transparent parent microspherical fillers (B) is within the range of 2/3 to 4/3 of the average particle size of the transparent microspherical lenses (A).

9. The retroreflective sheeting according to claim 1 wherein the transparent microspherical lenses (A) and the transparent microspherical fillers (B) are present in the retroreflective layer at a total packing ratio which is within the range of 60 to 90%.

10. The retroreflective sheeting according to claim 9 wherein the total packing ratio of the transparent microspherical lenses (A) and the transparent microspherical fillers (B) in the retroreflective layer is within the range of 65 to 85%.

11. The retroreflective sheeting according to claim 1 wherein the ratio (B)/(A) in number of the content of the transparent microspherical fillers (B) to the content of the transparent microspherical lenses (A) is within the range of 1/10 to 5/1.

12. The retroreflective sheeting according to claim 11 wherein the ratio (B)/(A) in number of the content of the transparent microspherical fillers (B) to the content of the transparent microspherical lenses (A) is within the range of 1/5 to 9/2.

13. The retroreflective sheeting according to claim 1 wherein the transparent microspherical lenses (A) are composed of BaO--TiO₂ glass or lead oxide glass.

14. The retroreflective sheeting according to claim 1 which is open lens-type retroreflective sheeting.

15. The retroreflective sheeting according to claim 14 wherein the refractive index of the transparent microspherical lenses (A) is within the range of 1.8 to 2.0.

16. The retroreflective sheeting according to claim 1 which is enclosed lens-type retroreflective sheeting.

17. The retroreflective sheeting according to claim 16 wherein the refractive index of the transparent microspherical lenses (A) is within the range of 2.0 to 2.9.

18. The retroreflective sheeting according to claim 1 which is encapsulated lens-type retroreflective sheeting.

19. The retroreflective sheeting according to claim 18 wherein the refractive index of the transparent microspherical lenses (A) is within the range of 1.8 to 2.0.

20. Lens-type retroreflective sheeting comprising a transparent resin layer, a substantial monolayer of transparent microspheres partially embedded in one surface of the resin layer, wherein said substantial monolayer comprises a blend of transparent microspherical lenses (A) having a refractive index of at least 1.8 and transparent microspherical fillers (B) having a refractive index which differs by at least 5% from the refractive index of the microspherical lenses (A), and a light reflective layer underlying the embedded portions of the transparent microspheres.

21. A lens-type retroreflective sheeting comprising a resin substrate having partially embedded therein substantially a monolayer of transparent microspheres and a thin reflective metallic layer for reflecting light passing through the transparent microspheres back towards the microspheres in the direction of the source of the light;

wherein the transparent microspheres in said monolayer comprise transparent microspherical lenses (A) having a refractive index of at least 1.8 and transparent microspherical fillers (B) whose refractive index differs by at least 5% from the refractive index of the lenses (A) and which do not substantially contribute to the retroreflective performance of the retroreflective sheeting, whereby the mixing ratio of fillers (B) to lenses (A) controls the retroreflective performance of the retroreflective sheeting.

22. The retroreflective sheeting of claim 21 wherein the total packing ratio of transparent microspheres in said substantial monolayer is in the range of 60 to 90%.

23. The retroreflective sheeting of claim 22 wherein the average particle size of the transparent microspherical lenses (A) and the average particle size of transparent microspherical fillers (B) are substantially the same.

24. In an encapsulated lens-type retroreflective sheeting having a support layer, a substantial monolayer of transparent microspheres partially embedded in one surface of the support layer, a light reflective layer coating on the portion of the transparent microspheres which are embedded in the one surface of the support layer, a transparent surface protective film facing in spaced relationship to the one surface of the support layer, and the protective film being bonded to the one surface of the support layer via a series of continuous bonding lines to thereby form a plurality of sealed, small compartment cells, each of the sealed cells containing therein a substantial monolayer of transparent microspheres, the non-embedded portions of which are exposed to the atmosphere within the sealed cell,

the improvement comprising,

as the transparent microspheres a blend of transparent microspherical lenses (A) having a refractive index of at least 1.8 and transparent microspherical filler (B) having a refractive index which differs by at least 5% from the refractive index of the microspherical lenses (A).

25. The lens-type retroreflective sheeting of claim 24 wherein the average particle size of the microspherical fillers (B) is within the range of 1/2 to 3/2 of the average particle size of the microspherical lenses (A) and wherein the total packing ratio of the lenses (A) and fillers (B) in the substantial monolayer is from about 60% to about 90% and wherein the mixing number ratio of the fillers (B) to lenses (A) is within the range of from about 1/10 to about 5/1.

26. A method for controlling the retroreflective performance of lens-type retroreflective sheeting in which a substantial monolayer of transparent microspheres are partially embedded in a resin layer and a light reflective layer is provided substantially at the focal point of the transparent microspheres, said method comprising

selecting a total packing ratio of the transparent microspheres to provide a desired appearance of the retroreflective sheeting,

determining a mixing ratio between transparent microspherical lenses (A) having a refractive index of at least 1.8 and which contribute to retroreflective performance of the retroreflective sheeting and transparent microspherical fillers (B) which do not substantially contribute to the retroreflective performance, and which have a refractive index different by at least 5% from the refractive index of lenses (A), to provide a desired retroreflective performance for the lens-type retroreflective sheeting when a mixture of the lenses (A) and fillers (B) at said mixing ratio is used to form the substantial monolayer of transparent microspheres, and

forming the substantial monolayer of transparent microspheres from a mixture of lenses (A) and fillers (B) at the determined mixing ratio and at the selected total packing ratio.

27. The method of claim 26 which further comprises selecting the transparent microspherical lenses (A) and transparent microspherical fillers (B) wherein the refractive index of fillers (B) is different by at least 15% from the refractive index of lenses (A);

and further wherein the average particle size of the lenses (A) is within the range of about 40 to 100 μ

m and wherein the average particle size of the fillers (B) is within the range of 2/3 to 4/3 of the average particle size of lenses (A).

28. The method of claim 26 which further comprises selecting a total packing ratio of lenses (A) and fillers (B) in the substantial monolayer of the retroreflective layer in the range of 65% to 85% and selecting the mixing weight ratio of fillers (B) to lenses (A) in the range of from 1/5 to 9/2.