Ultra-flexible retroreflective cube corner composite sheetings and methods of manufacture

• US 5,691,846 A
• Filed: 06/07/1995
• Issued: 11/25/1997
• Est. Priority Date: 10/20/1993
• Status: Expired due to Term

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Company
• Inventors: Smith, Kenneth L., Benson, Olester Jr., Shusta, Jeanine M., Bacon, Chester A. Jr., Lightle, Vera L., Nestegard, Susan K., Frey, Cheryl M.
• Primary Examiner(s): Phan, James
• Application Number:
  US08/472,444
• Time in Patent Office: 902 Days
• Field of Search: 359/529-550, 359/515-524, 359/900, 264/1.1, 264/1.9, 264/166, 264/212-214, 264/216, 156/230-232, 156/242-243, 156/245, 428/167, 428/172, 428/161
• US Class Current: 359/530
• CPC Class Codes: B29C 2059/023 Microembossing
• CPC Class Codes: B29C 39/148 characterised by the shape of the surface
• CPC Class Codes: B29C 59/046 for layered or coated substantially flat surfaces
• CPC Class Codes: G02B 5/124 plural reflecting elements forming part of a unitary plate or sheet
• CPC Class Codes: Y10S 359/90 Methods
• CPC Class Codes: Y10T 428/24612 Composite web or sheet

Abstract

A method for manufacturing flexible cube corner retroreflective sheeting comprising the steps of:

a) providing a tool having a molding surface;

b) applying to the molding surface a volume of a flowable resin composition;

c) contacting the resin composition with a first major surface of an overlay film;

d) minimizing excess resin composition;

e) curing the resin composition to form a sheeting comprising an array of cube corner elements bonded to the overlay film;

f) removing the sheeting from the tool; and

g) applying mechanical stress to the sheeting so as to cause a fractured separation of substantially each individual cube corner element from surrounding cube corner elements. Also, flexible retroreflective sheetings comprising: a) a two dimensional array of substantially independent cube corner elements, the array comprising a first polymeric material, and b) an overlay film having two major surfaces and comprising of a second polymeric material, the array being bonded to the first major surface of the overlay film. Also safety devices incorporating such sheetings.

Claims

1. A method of manufacturing microstructured composite sheeting comprising the steps of:

a) providing a tool having a molding surface with a plurality of cavities opening thereon suitable for forming desired microstructures;

b) applying to said molding surface a volume of a flowable curable resin composition suitable for forming desired microstructure elements;

c) contacting said resin composition with a first major surface of a transparent overlay film having first and second major surfaces; and

d) minimizing excess resin composition extending above said cavitites and tool;

then e) curing said resin composition while in contact with said overlay film to form a sheeting comprising an array of microstructure elements bonded to said overlay film;

then

f) removing said sheeting from said tool; and

g) applying mechanical stress to said sheeting so as to cause a fractured separation of substantially each individual microstructure element from surrounding microstructure elements;

wherein said resin composition and said overlay film are such that said resin composition penetrates said overlay film when contacted thereto such that after said curing said array of cube corner elements are bonded to said overlay film through as interpenetrating network between the material of said microstructure elements and the material of said overlay film.

2. The method of claim 1 wherein said microstructure elements are cube corner elements and wherein said curable resin composition is suitable for forming cube corner elements.

3. The method of claim 1 wherein said curing comprises exposing said resin composition at least one curing treatments selected from the following:

actinic radiation from a radiation source, an electron beam, and chemical curing agent.

4. The method of claim 1 further comprising the step of subjecting said resin to a secondary curing treatment.

5. The method of claim 1 further comprising the step of subjecting said sheeting to a heat treatment after said applying mechanical stress.

6. The method of claim 1 wherein said overlay film has an elastic modulus less than about 13×

10⁸ pascals.

7. The method of claim 1 wherein the elastic modulus of said microstructure elements is at least 1.0×

10⁷ pascals more than the elastic modulus of said overlay film.

8. The method of claim 1 wherein said overlay film is light transmissive.

9. The method of claim 1 wherein said overlay film is selected from the group consisting of the following:

ionomeric ethylene copolymers, plasticized vinyl halide polymers, acid-functional ethylene copolymers,

aliphatic polyurethanes, aromatic polyurethanes, other light transmissive elastomer, and combinations thereof.

10. The method of claim 1 wherein said resin composition shrinks when cured.

11. The method of claim 1 wherein said resin composition shrinks by at least 5 percent by volume when cured.

12. The method of claim 1 wherein said resin composition shrinks be between about 5 and about 20 percent by volume when cured.

13. The method of claim 1 wherein said microstructure elements, after curing, have an elastic modulus greater than about 25×

10⁸ pascals.

14. The method of claim 1 wherein said microstructure elements have an elastic modulus of at least about 2.0×

10⁸ pascals.

15. The method of claim 1 wherein said microstructure elements, comprise a material selected from the group consisting of the following:

monofunctional, difunctional, and polyfunctional acrylates.

16. The method of claim 1 wherein said microstructure elements are substantially transparent.

17. A microstructured composite sheeting comprising:

(a) a two dimensional array of cured microstructure elements, said array comprising a first polymeric material, and (b) an overlay film having two major surfaces and comprising a second polymeric material, said array being bonded to the first major surface of said overlay film with a fractured land and wherein the material of said microstructure elements and the material of said overlay film form an interpenetrating network, said microstructure elements being substantially independent from adjacent microstructure elements, said microstructure elements having been cured while in contact with said overlay film.

18. A microstructured composite sheeting comprising:

(a) a two dimensional array of cured microstructure elements, said microstructure elements being substantially independent from adjacent microstructure elements, said array comprising a first polymeric material, and (b) an overlay film having two major surfaces and comprising a second polymeric material, said array being bonded to the first major surface of said overlay film wherein said array of microstructure elements was cured in situ on said overlay film and wherein the material of said microstructure elements and the material of said overlay film form an interpenetrating network.

19. The sheeting of claim 18 wherein at least some of said microstructure elements were in connection with adjacent microstructure elements through a land after said curing in situ, said land having been fractured such that said microstructure elements are substantially independent.

20. The sheeting of claim 19 wherein said land has a thickness of less than about 10 percent of the average height of said microstructure elements of said array.

21. The sheeting of claim 19 wherein said land has a thickness of less than about 1 percent of the average height of said microstructure elements of said array.

22. The sheeting of claim 18 wherein said microstructure elements are cube corner elements and wherein said composite is a retroreflective sheeting.

23. The sheeting of claim 22 wherein the elastic modulus of said cube corner elements is at least 1.0×

10⁷ pascals more than the elastic modulus of said overlay film.

24. The sheeting of claim 22 wherein said cube corner elements have an elastic modulus of at least about 2.0×

10⁸ pascals.

25. The sheeting of claim 22 wherein said cube corner elements have an elastic modulus of at least about 25×

10⁸ pascals.

26. The sheeting of claim 22 wherein said sheeting has a coefficient of retroreflectivity greater than about 50 candelas per lux per square meter, measured at an entrance angle of -4°

and an observation angle of 0.2°

.

27. The sheeting of claim 26 wherein said sheeting has a coefficient of retroreflectivity greater than about 250 candelas per lux per square meter.

28. The sheeting of claim 26 wherein said sheeting has a coefficient of retroreflectivity greater than about 500 candelas per lux per square meter.

29. The sheeting of claim 22 having a coefficient of retroreflectivity greater than about 50 candelas per lux per square meter, measured at an entrance angle of -4°

and an observation angle of 0.2°

, when said sheeting has been elongated to 110 percent of its original length.

30. The sheeting of claim 22 having a coefficient of retroreflectivity, measured at an entrance angle of -4°

and an observation angle of 0.2°

, after being stretched to at least 110 percent of its original length that is at least 30 percent of it initial coefficient of retroreflectivity.

31. The sheeting of claim 22 having a coefficient of retroreflectivity, measured at an entrance angle of -4°

and an observation angle of 0.2°

, after being stretched to at least 110 percent of its original length that is at least 50 percent of it initial coefficient of retroreflectivity.

32. The sheeting of claim 22 having a retroreflective brightness greater than about 75 percent of its initial retroreflective brightness after being stretched 10 percent in one dimension and allowed to relax.

33. The sheeting of claim 22 having a coefficient of retroreflectivity of at least 50 candela/lux/meter², measured at an entrance angle of -10°

and an observation angle of 0.15°

when elongated to 150 percent of its original length over a radius of curvature of about 150 millimeters.

34. The sheeting of claim 22 having a retroreflective brightness of greater than about 50 percent of its initial brightness after being laundered for twenty five home laundering cycles.

35. The sheeting of claim 34 having a retroreflective brightness of greater than about 75 percent of its initial brightness after being laundered for twenty five home laundering cycles.

36. The sheeting of claim 22 having a retroreflective brightness of greater than about 50 percent of its initial brightness after 1000 hours of accelerated UV weathering.

37. The sheeting of claim 22 having a retroreflective brightness of greater than about 50 percent of its initial brightness after 170 hours at 82°

C.

38. The sheeting of claim 22 having a retroreflective brightness of greater than about 50 percent of its initial brightness after 48 hours in a temperature and humidity cycling chamber.

39. The sheeting of claim 22 further comprising a reflective layer on said cube corner elements.

40. The sheeting of claim 22 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.

41. An article comprising a sheeting of claim 40 bonded thereto wherein said sealing film acts as the bonding.

42. The sheeting of claim 18 wherein said first polymeric material shrunk while curing.

43. The sheeting of claim 18 wherein said overlay film has an elastic modulus of less than about 13×

10⁸ pascals.

44. The sheeting of claim 18 wherein said first polymeric material is a thermoset material or a thermoplastic material.

45. The sheeting of claim 18 wherein said overlay film is an elastomeric film.

46. The sheeting of claim 18 wherein said overlay film is extensible and has substantially no tendency to recover.

47. The sheeting of claim 18 further comprising a sealing layer adhered to said overlay film through openings between individual microstructure elements.

48. An article of personally comprising a sheeting of claim 18 attached thereto.