Dual orientation retroreflective sheeting

• US 5,706,132 A
• Filed: 01/19/1996
• Issued: 01/06/1998
• Est. Priority Date: 01/19/1996
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Inventors: Frey, Cheryl, Smith, Kenneth L., Benson, Gerald M., Kelliher, John C., Nestegard, Susan K., Lasch, James E., Szczech, Theodore J.
• Primary Examiner(s): Phan, James
• Application Number:
  US08/587,719
• Time in Patent Office: 718 Days
• Field of Search: 359/529-533
• US Class Current: 359/529
• 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 said base surface, said structured surface comprising a plurality of zones of cube corner elements, including:

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

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

and wherein said retroreflective sheeting exhibits substantially similar retroreflective performance in response to light incident on said sheeting across a range of entrance angles in said first plane and said second plane.

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

said array of cube corner elements in said first zone is oriented such that said first plane lies substantially perpendicular to first edge of said sheeting.

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

said array of cube corner elements in second zone is oriented such that said second plane lies substantially parallel to the first edge of said sheeting.

4. Retroreflective sheeting in accordance with claim 3, wherein:

said second zone extends substantially parallel with said first zone.

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

said first zone measures between about 3 millimeters and 25 millimeters in width.

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

said second zone measures between about 3 millimeters and 25 millimeters in width.

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

said 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 said base surface.

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

said 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 said base surface.

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

said sheeting exhibits a coefficient of retroreflection of at least 16 candelas/lux/m² in response to light incident on the surface of said sheeting in said 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

said sheeting exhibits a coefficient of retroreflection of 16 candelas/lux/m² in response to light incident on the surface of said sheeting in said 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.

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

said sheeting exhibits a coefficient of retroreflection at least of about 30 candelas/lux/m² in response to light incident on the surface of said sheeting in said 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

said sheeting exhibits a coefficient of retroreflection of at least about 30 candelas/lux/m² in response to light incident on the surface of said sheeting in said 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.

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

said sheeting exhibits a coefficient of retroreflection of at least 90 candelas/lux/m² in response to light incident on the surface of said sheeting in said 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

said sheeting exhibits a coefficient of retroreflection of 90 candelas/lux/m² in response to light incident on the surface of said sheeting in said 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.

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

said sheeting exhibits a coefficient of retroreflection of at least about 150 candelas/lux/m² in response to light incident on the surface of said sheeting in said 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

said sheeting exhibits a coefficient of retroreflection of at least about 150 candelas/lux/m² in response to light incident on the surface of said sheeting in said 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.

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

portions of said structured surface are coated with a specularly reflective substance.

14. Retroreflective sheeting in accordance with claim 1, further comprising:

a sealing medium disposed adjacent said structured surface.

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

said sealing medium is bonded to said substrate by a network of intersecting bonds to define a plurality of cells within which retroreflective elements are hermetically sealed.

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

said sealing medium maintains an air interface with said structured surface such that said cube corner elements retroreflect according to the principles of total internal reflection.

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

said 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

said cube corner elements comprise a light transmissible polymeric material having an elastic modulus greater than 16×

10⁸ pascals.

18. Retroreflective sheeting in accordance with claim 17, 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.

19. Retroreflective sheeting in accordance with claim 18, wherein the land layer has a thickness in the range of 1 to 100 micrometers.

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

10⁸ pascals.

21. Retroreflective sheeting in accordance with claim 17, wherein the body layer has a thickness of approximately 20 to 1,000 micrometers.

22. Retroreflective sheeting in accordance with claim 17, wherein the body layer has a thickness in the range of 50 to 250 micrometers.

23. Retroreflective sheeting in accordance with claim 17, wherein the body portion includes a land layer that comprises the same polymeric material as the cube-corner elements.

24. Retroreflective sheeting in accordance with claim 17, wherein the body layer contains a light transmissible polymeric material having an elastic modulus less than 5×

10⁸ pascals.

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 articles 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 1, wherein:

said substrate comprises an overlay film comprising a first polymeric material and having two major surfaces; and

said cube corner elements comprise a second polymeric material and are bonded to the first major surface of said overlay film with a fractured land, said cube corner elements being substantially independent.

30. Retroreflective sheeting in accordance with claim 29, wherein:

the material of said microstructure elements and the material of said overlay film form an interpenetrating network.

31. Retroreflective sheeting in accordance with claim 29, wherein:

said land has a thickness of less than about 10 percent of the average height of said microstructure elements of said array.

32. Retroreflective sheeting in accordance with claim 29, wherein:

said land has a thickness of less than about 1 percent of the average height of said microstructure elements of said array.

33. Retroreflective sheeting in accordance with claim 29, further comprising:

a sealing layer adhered to said overlay film through openings between individual microstructure elements.

34. Retroreflective sheeting in accordance with claim 29, further comprising:

a reflective layer on said cube corner elements.

35. Retroreflective sheeting in accordance with claim 29, further comprising:

a sealing film adhered to the cube corner side of said sheeting in an interconnecting network so as form cells in which cube corner elements are encapsulated.

36. An article comprising a sheeting of claim 29 bonded thereto wherein said sealing film acts as the bonding.

37. An article comprising a sheeting of claim 29 attached thereto.

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

said sheeting exhibits a retroreflectance which is five percent of the maximum retroreflectance in response to light incident on the surface of said sheeting in said 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

said sheeting exhibits a retroreflectance which is five percent of the maximum retroreflectance in response to light incident on the surface of said sheeting in said 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.

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

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

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

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

a first zone comprising an array of cube corner elements comprising a material having a refractive index of between 1.46 and 1.60, the optical axes of said cube corner elements canted between 7 and 15 degrees from a position perpendicular to said base surface to define a first primary plane of improved retroreflective performance at increased entrance angles; and

a second zone comprising an array of cube corner elements comprising a material having a refractive index of between 1.46 and 1.60, the optical axes of said cube corner elements canted between 7 and 15 degrees from a position perpendicular to said base surface to define a second primary plane of improved retroreflective performance at increased entrance angles, said second plane being perpendicular to said first plane;

and wherein said retroreflective sheeting exhibits substantially similar retroreflective performance in response to light incident on said sheeting across a range of entrance angles in said first plane and said second plane.

41. Retroreflective sheeting in accordance with claim 40, wherein:

said 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 said base surface.

42. Retroreflective sheeting in accordance with claim 40, wherein:

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

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

43. Retroreflective sheeting in accordance with claim 40, wherein:

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

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

44. Retroreflective sheeting in accordance with claim 40, wherein:

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

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

45. Retroreflective sheeting in accordance with claim 40, wherein:

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

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