Dual orientation retroreflective sheeting

• US 5,936,770 A
• Filed: 07/02/1997
• Issued: 08/10/1999
• Est. Priority Date: 01/19/1996
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Smith, Kenneth L., Benson, Gerald M., Kelliher, John C., Nestegard, Susan K., Frey, Cheryl M., Lasch, James E., Szczech, Theodore J.
• Primary Examiner(s): Phan, James
• Application Number:
  US08/887,006
• Time in Patent Office: 769 Days
• Field of Search: 359/529, 359/530
• US Class Current: 359/530
• CPC Class Codes: G02B 5/124 plural reflecting elements forming part of a unitary plate or sheet

Abstract

A cube corner retroreflective sheeting construction comprising alternating zones of cube corner element arrays disposed at approximately ninety degrees orientations to provide exactly two principal plane of improved retroreflective performance in response to light incident on the sheeting at high entrance angles is disclosed. According to one embodiment the sheeting includes a body layer which has an elastic modulus less than 7×10⁸ pascals and cube corner elements formed from a material which has an elastic modulus greater than 16×10⁸ pascals. According to a second embodiment the sheeting includes an overlay film having two major surfaces and comprising a first polymeric material and a plurality of arrays of substantially independent cube corner elements bonded to a major surface of the overlay film having a minimal, fractured land.

Claims

1. A retroreflective sheeting comprising a substrate having a base surface and a structured surface opposite the base surface, the structured surface comprising a plurality of zones of cube corner elements, including:

a first zone comprising an array of cube corner elements, the optical axes of the cube corner elements canted to define a first primary plane of improved retroreflective performance at increased entrance angles, the first primary plane extending substantially parallel with a longitudinal edge of the sheeting; and

a second zone comprising an array of cube corner elements, the optical axes of the cube corner elements canted to define a second primary plane of improved retroreflective performance at increased entrance angles, the second primary plane being perpendicular to the first primary plane.

2. Retroreflective sheeting in accordance with claim 1, wherein the array of cube corner elements in the first zone is oriented such that the first primary plane lies substantially perpendicular to a second edge of the sheeting.

3. Retroreflective sheeting in accordance with claim 1, wherein the array of cube corner elements in the second zone is oriented such that the second primary plane lies substantially parallel to a second edge of the sheeting.

4. Retroreflective sheeting in accordance with claim 1, wherein the cube corner elements comprise truncated cube corner elements.

5. Retroreflective sheeting in accordance with claim 1, wherein the cube corner elements comprise full cube corner elements.

6. Retroreflective sheeting in accordance with claim 1, wherein the second zone extends substantially parallel with the first zone.

7. Retroreflective sheeting in accordance with claim 1, wherein the first zone measures between about 3 millimeters and 25 millimeters in width.

8. Retroreflective sheeting in accordance with claim 1, wherein the second zone measures between about 3 millimeters and 25 millimeters in width.

9. Retroreflective sheeting in accordance with claim 1, wherein the cube corner elements comprise a material having a refractive index of between 1.46 and 1.60 and the optical axes of opposing cube corner elements are canted between 7 and 15 degrees from a position perpendicular to the base surface.

10. Retroreflective sheeting in accordance with claim 1, wherein the cube corner elements comprise a material having a refractive index of about 1.5 and the optical axes of opposing cube corner elements are canted between 8 and 9.736 degrees from a position perpendicular to the base surface.

11. Retroreflective sheeting in accordance with claim 1, wherein:

the sheeting comprises a coefficient of retroreflection of at least 16 candelas/lux/m² in response to light incident on the surface of the sheeting in the first primary plane at an entrance angle of about 60 degrees, measured at a 0.33 degree observation angle and a 90 degree presentation angle; and

the sheeting comprises a coefficient of retroreflection of at least 16 candelas/lux/m² in response to light incident on the surface of the sheeting in the second primary plane at an entrance angle of about 60 degrees measured at a 0.33 degree observation angle and a 90 degree presentation angle.

12. Retroreflective sheeting in accordance with claim 1, wherein:

the sheeting comprises a coefficient of retroreflection at least of about 30 candelas/lux/m² in response to light incident on the surface of the sheeting in the first primary plane at an entrance angle of about 60 degrees, measured at a 0.33 degree observation angle and a 90 degree presentation angle; and

the sheeting comprises a coefficient of retroreflection of at least about 30 candelas/lux/m² in response to light incident on the surface of the sheeting in the second primary plane at an entrance angle of about 60 degrees measured at a 0.33 degree observation angle and a 90 degree presentation angle.

13. Retroreflective sheeting in accordance with claim 1, wherein:

the sheeting comprises a coefficient of retroreflection of at least 90 candelas/lux/m² in response to light incident on the surface of the sheeting in the first primary plane at an entrance angle of about 40 degrees, measured at a 0.33 degree observation angle and a 90 degree presentation angle; and

the sheeting comprises a coefficient of retroreflection of at least 90 candelas/lux/m² in response to light incident on the surface of the sheeting in the second primary plane at an entrance angle of about 40 degrees measured at a 0.33 degree observation angle and a 90 degree presentation angle.

14. Retroreflective sheeting in accordance with claim 1, wherein:

the sheeting comprises a coefficient of retroreflection of at least about 150 candelas/lux/m² in response to light incident on the surface of the sheeting in the first primary plane at an entrance angle of about 40 degrees, measured at a 0.33 degree observation angle and a 90 degree presentation angle; and

the sheeting comprises a coefficient of retroreflection of at least about 150 candelas/lux/m² in response to light incident on the surface of the sheeting in the second primary plane at an entrance angle of about 40 degrees measured at a 0.33 degree observation angle and a 90 degree presentation angle.

15. Retroreflective sheeting in accordance with claim 1, wherein portions of the structured surface are coated with a specularly reflective substance.

16. Retroreflective sheeting in accordance with claim 1 further comprising a sealing medium disposed adjacent the structured surface.

17. Retroreflective sheeting in accordance with claim 16 wherein the sealing medium is bonded to the substrate by a network of intersecting bonds to define a plurality of cells within which retroreflective elements are hermetically sealed.

18. Retroreflective sheeting in accordance with claim 16 wherein the sealing medium maintains an air interface with the structured surface such that the cube corner elements retroreflect according to the principles of total internal reflection.

19. Retroreflective sheeting in accordance with claim 1 wherein the substrate comprises a body portion that includes a body layer which contains a light transmissible polymeric material having an elastic modulus less than 7×

10⁸ pascals and the cube corner elements comprise a light transmissible polymeric material having an elastic modulus greater than 16×

10⁸ pascals.

20. Retroreflective sheeting in accordance with claim 19 wherein the body portion includes a land layer that has a thickness in the range of 0 to 150 micrometers and is comprised of a light transmissible polymeric material having an elastic modulus greater than 16×

10⁸ pascals.

21. Retroreflective sheeting in accordance with claim 20 wherein the land layer has a thickness in the range of 1 to 100 micrometers.

22. Retroreflective sheeting in accordance with claim 20 wherein the cube-corner elements and land layer comprise a polymer(s) that has an elastic modulus greater than 18×

10⁸ pascals.

23. Retroreflective sheeting in accordance with claim 19 wherein the body layer has a thickness of approximately 20 to 1,000 micrometers.

24. Retroreflective sheeting in accordance with claim 19 wherein the body layer has a thickness in the range of 50 to 250 micrometers.

25. Retroreflective sheeting in accordance with claim 1 wherein the cube-corner elements have a height in the range of about 60 to 180 micrometers.

26. Retroreflective sheeting in accordance with claim 1 wherein the cube-corner elements comprise a polymeric material having an elastic modulus of greater than 18×

10⁸ pascals.

27. Retroreflective sheeting in accordance with claim 1 wherein the cube-corner elements comprise a light transmissible polymeric material having a elastic modulus greater than 20×

10⁸ pascals.

28. Retroreflective sheeting in accordance with claim 1 wherein the cube-corner elements contain poly(carbonate), poly(methylmethacrylate), poly(ethyleneterephthalate), or a crosslinked acrylate.

29. Retroreflective sheeting in accordance with claim 19 wherein the body portion includes a land layer that comprises the same polymeric material as the cube-corner elements.

30. Retroreflective sheeting in accordance with claim 19 wherein the body layer contains a light transmissible polymeric material having an elastic modulus less than 5×

10⁸ pascals.

31. Retroreflective sheeting in accordance with claim 1 wherein the substrate comprises an overlay film comprising a first polymeric material and having two major surfaces and the cube corner elements comprise a second polymeric material and are bonded to the first major surface of the overlay film with a fractured land, the cube corner elements being substantially independent.

32. Retroreflective sheeting in accordance with claim 31 wherein the material of the cube corner elements and the material of the overlay film form an interpenetrating network.

33. Retroreflective sheeting in accordance with claim 31 wherein the land has a thickness of less than about 10 percent of the average height of the cube corner elements of the array.

34. Retroreflective sheeting in accordance with claim 31 wherein the land has a thickness of less than about 1 percent of the average height of the cube corner elements of the array.

35. Retroreflective sheeting in accordance with claim 31 further comprising a sealing layer adhered to the overlay film through openings between individual cube corner elements.

36. Retroreflective sheeting in accordance with claim 31 further comprising a reflective layer on the cube corner elements.

37. Retroreflective sheeting in accordance with claim 31 further comprising a sealing film adhered to the cube corner side of the sheeting in an interconnecting network so as form cells in which cube corner elements are encapsulated.

38. An article comprising a sheeting of claim 31 wherein the sealing film acts as the bonding.

39. An article comprising a sheeting of claim 31 attached thereto.

40. Retroreflective sheeting in accordance with claim 1 wherein:

the sheeting comprises a retroreflectance which is approximately five percent of the maximum retroreflectance in response to light incident on the surface of the sheeting in the first primary plane at an entrance angle of about 60 degrees, measured at a 0.33 degree observation angle and a 90 degree presentation angle; and

the sheeting comprises a retroreflectance which is approximately five percent of the maximum retroreflectance in response to light incident on the surface of the sheeting in the second primary plane at an entrance angle of about 60 degrees measured at a 0.33 degree observation angle and a 90 degree presentation angle.

42. Retroreflective sheeting in accordance with claim 5 wherein the full cube corner elements comprise a height of about 10 micrometers to about 500 micrometers.

43. Retroreflective sheeting in accordance with claim 5 wherein the full cube corner elements comprise a height of about 25 micrometers to about 250 micrometers.

44. The sheeting of claim 1, wherein:

the retroreflective sheeting comprises substantially similar retroreflective performance in response to light incident on the sheeting across a range of entrance angles in the first primary plane and the second primary plane.

41. Retroreflective sheeting in accordance with claim I wherein:

the sheeting comprises a retroreflectance which is approximately 30 percent of the maximum retroreflectance in response to light incident on the surface of the sheeting in the first primary plane at an entrance angle of about 40 degrees, measured at a 0.33 degree observation angle and a 90 degree presentation angle; and

the sheeting comprises a retroreflectance which is approximately 30 percent of the maximum retroreflectance in response to light incident on the surface of the sheeting in the second primary plane at an entrance angle of about 40 degrees measured at a 0.33 degree observation angle and a 90 degree presentation angle.

45. A retroreflective sheeting comprising a substrate having a base surface and a structured surface opposite the base surface, the structured surface comprising:

a first array of cube corner elements;

a second array of cube corner elements optically opposing the cube corner elements of the first array, the optical axes of the cube corner elements in the first and second arrays canted to define a first primary plane of improved retroreflective performance at increased entrance angles, the first primary plane extending substantially parallel with a longitudinal edge of the sheeting;

a third array of cube corner elements; and

a fourth array of cube corner elements optically opposing the cube corner elements of the third array, the optical axes of the cube corner elements in the third and fourth arrays canted to define a second primary plane of improved retroreflective performance at increased entrance angles, the second primary plane being perpendicular to the first primary plane.

46. Retroreflective sheeting in accordance with claim 45 wherein the cube corner elements comprise full cube corner elements.

47. Retroreflective sheeting according to claim 45 wherein the first array is physically off-set from the second array.

48. The sheeting of claim 45, wherein:

the retroreflective sheeting comprises substantially similar retroreflective performance in response to light incident on the sheeting across a range of entrance angles in the first primary plane and the second primary plane.