U.S. patent application number 09/577301 was filed with the patent office on 2001-11-15 for conformable cube corner retroreflective sheeting.
Invention is credited to Bacon, Chester A. JR., Benson, Gerald M..
Application Number | 20010040731 09/577301 |
Document ID | / |
Family ID | 27385417 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010040731 |
Kind Code |
A1 |
Bacon, Chester A. JR. ; et
al. |
November 15, 2001 |
Conformable cube corner retroreflective sheeting
Abstract
Conformable cube corner retroreflective sheetings comprising a
plurality of discrete cube corner segments which are conformably
bonded together, each cube corner segment comprising a plastic body
portion having a substantially planar front major surface and at
least one minute cube corner retroreflective element projecting
rearwardly from the body portion and defining a cube corner point
side of the cube corner segment. The peripheries of the cube corner
segments can be defined by a plurality of separations extending
from the cube corner point sides to the front major surfaces, the
separations being disposed between adjacent cube corner segments.
Adjacent cube corner segments are conformably bonded together in
the sense that they are either: (1) separated by a gap of less than
about 1 millimeter and bonded together through a conformable
carrier layer; or (2) separated by a gap which is substantially
filled with a conformable resin that bonds the side walls of
adjacent cube corner segments together. Alternatively, a
conformable cube corner retroreflective sheeting can comprise a
plurality of connecting bridges disposed between adjacent cube
corner segments, the connecting bridges being at least one of
fractured and frangible, and spanning grooves which extend
vertically from the cube corner point sides toward the front major
surfaces and terminate at the connecting bridges. Also, methods for
making such conformable sheetings.
Inventors: |
Bacon, Chester A. JR.;
(Oakdale, MN) ; Benson, Gerald M.; (Woodbury,
MN) |
Correspondence
Address: |
Office of Intellectual Property Counsel
3M Innovative Properties Company
PO Box 33427
St Paul
MN
55133-3427
US
|
Family ID: |
27385417 |
Appl. No.: |
09/577301 |
Filed: |
May 24, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09577301 |
May 24, 2000 |
|
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09270365 |
Mar 16, 1999 |
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Current U.S.
Class: |
359/530 |
Current CPC
Class: |
Y10S 359/90 20130101;
Y10T 428/24521 20150115; B29C 39/148 20130101; G02B 5/124
20130101 |
Class at
Publication: |
359/530 |
International
Class: |
G02B 005/124 |
Claims
What is claimed is:
1. A conformable cube corner retroreflective sheeting comprising a
plurality of discrete cube corner segments which are conformably
bonded together, each cube corner segment comprising a plastic body
portion having a substantially planar front major surface and side
walls and comprising at least one minute cube corner
retroreflective element projecting rearwardly from said body
portion and defining a cube corner point side of said cube corner
segment.
2. The sheeting of claim 1 wherein substantially all of the cube
corner retroreflective elements located closest to said side walls
are intact and capable of retroreflecting light.
3. The sheeting of claim 1 wherein the peripheries of said cube
corner segments are defined by a plurality of separations extending
from said cube corner point sides to said front major surfaces, the
separations being disposed between adjacent cube corner
segments.
4. The sheeting of claim 3 wherein said cube corner segments are
defined by a pattern of said separations.
5. The sheeting of claim 4 wherein said pattern comprises a
plurality of contiguous polygons selected from the group consisting
of parallelograms, triangles, and hexagons.
6. The sheeting of claim 1 wherein adjacent cube corner segments
are separated by a gap of less than about 1 millimeter and
conformably bonded together through a conformable carrier
layer.
7. The sheeting of claim 6 wherein said conformable carrier layer
is bonded to said front major surfaces of said body portions.
8. The sheeting of claim 7 wherein said conformable carrier layer
comprises a continuous, transparent film and is bonded to said
front major surfaces through a transparent adhesive.
9. The sheeting of claim 1 further comprising a specularly
reflective coating on said cube corner point sides of said cube
corner segments.
10. The sheeting of claim 9 further comprising an adhesive on said
specularly reflective coating.
11. The sheeting of claim 1 wherein said cube corner segments are
conformably bonded together through a conformable resin which bonds
the side walls of adjacent cube corner segments together.
12. The sheeting of claim 11 wherein the separation between
adjacent cube corner segments ranges between about 0.5 and about 3
millimeters.
13. The sheeting of claim 11 further comprising a back sealing film
disposed adjacent said cube corner retroreflective elements and
bonded to said cube corner segments through said conformable
resin.
14. The sheeting of claim 11 wherein a continuous, transparent film
is bonded to said front major surfaces through said conformable
resin, said conformable resin being transparent.
15. The sheeting of claim 1 further comprising septa which extend
rearwardly into sealing contact with a conformable back sealing
film, said septa defining hermetically sealed cells or pockets in
said sheeting.
16. A method for making a conformable cube corner retroreflective
sheeting, comprising: a) providing a tool having a molding surface
which comprises a plurality of raised protrusions and
retroreflective element-forming cavities adapted for molding a cube
corner retroreflective sheeting comprising a plurality of cube
corner segments, each cube corner segment comprising a plastic body
portion having a substantially planar front major surface and side
walls and at least one cube corner retroreflective element
projecting rearwardly therefrom and defining a cube corner point
side of said cube corner segment, the peripheries of said cube
corner segments being defined by a plurality of separations
extending from said cube corner point sides of said cube corner
segments to said front major surfaces of said cube corner segments;
b) depositing a hardenable molding material on the molding surface
of the tool, the molding material being sufficient in amount and
fluidity to essentially completely fill the cavities; c) applying a
conformable carrier layer to the molding material on the molding
surface under sufficient pressure to effect intimate surface
contact between the carrier layer, the raised protrusions of the
tool, and the molding material; d) effecting substantial
solidification of the molding material and bonding of the molding
material to the carrier layer to form said conformable sheeting;
and e) removing said conformable sheeting from the molding
surface.
17. The method of claim 16 wherein said protrusions form a pattern
of said separations in said conformable sheeting.
18. The method of claim 17 wherein said pattern comprises a
plurality of contiguous polygons selected from the group consisting
of parallelograms, triangles, and hexagons.
19. The method of claim 16 wherein said conformable carrier layer
is laminated to said front major surfaces.
20. The method of claim 16 wherein said conformable carrier layer
comprises a continuous, transparent film.
21. The method of claim 16 further comprising coating said cube
corner point sides of said cube corner segments with a specularly
reflective coating.
22. The method of claim 21 further comprising applying an adhesive
onto said specularly reflective coating.
23. A method for making a conformable cube corner retroreflective
sheeting, comprising: a) providing a tool having a molding surface
which comprises a plurality of raised protrusions and
retroreflective element-forming cavities adapted for molding a cube
corner retroreflective sheeting comprising a plurality of cube
corner segments, each cube corner segment comprising a plastic body
portion having a substantially planar front major surface and side
walls and at least one cube corner retroreflective element
projecting rearwardly therefrom and defining a cube corner point
side of said cube corner segment, the peripheries of said cube
corner segments being defined by a plurality of separations
extending from said cube corner point sides of said cube corner
segments to said front major surfaces of said cube corner segments;
b) placing a thermoplastic sheet on said tool; c) heating the resin
of said sheet to a temperature at least as high as its softening
temperature; d) pressing said sheet onto the molding surface of
said tool to thereby form a plurality of said cube corner segments;
e) conformably bonding the cube corner segments together with a
conformable carrier layer to form said conformable sheeting; and f)
removing said conformable sheeting from said tool.
24. The method of claim 23 wherein said protrusions form a pattern
of said separations in said conformable sheeting.
25. The method of claim 24 wherein said pattern comprises a
plurality of contiguous polygons selected from the group consisting
of parallelograms, triangles, and hexagons.
26. The method of claim 23 wherein said conformable carrier layer
is laminated to said front major surfaces.
27. The method of claim 26 wherein said conformable carrier layer
comprises a continuous, transparent film.
28. The method of claim 23 further comprising coating said cube
corner point sides of said cube corner segments with a specularly
reflective coating.
29. The method of claim 28 further comprising applying an adhesive
onto said specularly reflective coating.
30. A method for making a conformable cube corner retroreflective
sheeting, comprising: a) providing an initial cube corner
retroreflective sheeting comprising a plastic body portion having a
substantially planar front major surface and a multiplicity of
minute cube corner retroreflective elements projecting rearwardly
from said body portion and defining a cube corner point side of
said initial sheeting; b) dividing said body portion into a
plurality of discrete cube corner segments, each cube corner
segment comprising a plastic body portion having a substantially
planar front major surface and side walls and at least one of said
cube corner retroreflective elements projecting rearwardly
therefrom and defining a cube corner point side of said cube corner
segment, wherein the peripheries of said cube corner segments are
defined by a plurality of separations extending from said cube
corner point sides of said cube corner segments to said front major
surfaces of said cube corner segments; and c) conformably bonding
said cube corner segments together to form said conformable
sheeting.
31. The method of claim 30 wherein the body portion dividing step
is carried out such that substantially all of the cube corner
retroreflective elements located closest to said side walls remain
intact and capable of retroreflecting light.
32. The method of claim 30 wherein said cube corner segments are
defined by a pattern of said separations.
33. The method of claim 32 wherein said pattern comprises a
plurality of contiguous polygons selected from the group consisting
of parallelograms, triangles, and hexagons.
34. The method of claim 30 wherein adjacent cube corner segments
are conformably bonded together through a conformable carrier layer
such that they are separated by a gap having a width of less than
about 1 millimeter.
35. The method of claim 34 wherein said conformable carrier layer
is bonded to said cube corner point sides of said cube corner
segments.
36. The method of claim 34 wherein said conformable carrier layer
is bonded to said front major surfaces of said cube corner
segments.
37. The method of claim 30 further comprising substantially filling
said separations with a conformable resin so that said conformable
resin contacts the side walls of adjacent cube corner segments, and
effecting substantial solidification of said conformable resin so
that it conformably bonds said cube corner segments together.
38. The method of claim 37 wherein said resin filling step
comprises coating said conformable resin onto said front major
surfaces of said cube corner segments after the body portion
dividing step and permitting said conformable resin to flow into
said separations.
39. The method of claim 37 wherein a back sealing film is provided
on said cube corner point sides of said cube corner segments, and
at least some of said conformable resin is urged out of said
separations, into contact with said back sealing film, and
substantially solidified to bond said back sealing film to said
cube corner segments.
40. The method of claim 30 comprising bonding said front major
surface of said initial sheeting to a conformable carrier layer
through a layer of a conformable resin to form an intermediate
composite, then carrying out said body portion dividing step to
form a segmented composite comprising said cube corner segments,
causing said conformable resin to flow into and substantially fill
said separations, and effecting substantial solidification of said
conformable resin.
41. The method of claim 40 wherein said conformable carrier layer
comprises a continuous, transparent film.
42. The method of claim 40 further comprising stretching said
conformable carrier layer and said conformable resin to increase
the width of said separations.
43. The method of claim 30 wherein a cutting device utilizing a
laser beam or a sharp edge is used in carrying out the body portion
dividing step.
44. The method of claim 30 wherein a tool having a plurality of
raised protrusions is used in carrying out the body portion
dividing step.
45. The method of claim 44 wherein said body portion dividing step
comprises applying pressure against said front major surface of
said initial sheeting with said protrusions of said tool.
46. The method of claim 30 further comprising chilling said initial
sheeting prior to said body portion dividing step.
47. The method of claim 30 further comprising depositing a
specularly reflective coating on said cube corner point sides of
said cube corner segments.
48. The method of claim 47 further comprising applying an adhesive
onto said specularly reflective coating.
49. A conformable cube corner retroreflective sheeting comprising a
plurality of cube corner segments bonded together through a
conformable carrier layer, each cube corner segment comprising a
plastic body portion having a substantially planar front major
surface and comprising at least one minute cube corner
retroreflective element projecting rearwardly from said body
portion and defining a cube corner point side of said cube corner
segment, wherein the peripheries of said cube corner segments are
defined by grooves extending vertically from said cube corner point
sides toward said front major surfaces and terminating at
connecting bridges which are disposed horizontally between and are
integral with adjacent cube corner segments, said connecting
bridges being at least one of fractured and frangible.
50. The sheeting of claim 49 wherein each of said connecting
bridges is substantially thinner than and made of the same material
as adjacent body portions of said cube corner segments.
51. The sheeting of claim 49 wherein said grooves have a
cross-sectional shape selected from the group consisting of: an
inverted V-shape, an inverted U-shape, and an inverted V-shape
wherein the apex of the V is truncated.
52. The sheeting of claim 49 wherein said cube corner segments are
defined by a pattern of said grooves.
53. The sheeting of claim 52 wherein said pattern comprises a
plurality of contiguous polygons selected from the group consisting
of parallelograms, triangles, and hexagons.
Description
FIELD OF INVENTION
[0001] The present invention relates to retroreflective articles,
particularly cube corner type retroreflective articles.
BACKGROUND
[0002] Retroreflective articles are made in a variety of forms,
including sheetings such as are used on traffic signs and license
plates, rigid safety reflectors mounted on motor vehicles and
bikes, and patches and appliques such as are applied to garments
and book bags, etc. One major use of retroreflective sheeting is in
the field of highway markings and signs to improve the visibility
and legibility of informational signs, traffic directions,
barriers, etc. to drivers.
[0003] One common type of retroreflector employs transparent
microspheres, typically with hemispheric reflectors thereon.
Illustrative examples of such retroreflectors are disclosed in U.S.
Pat. No. 3,190,178 (McKenzie), U.S. Pat. No. 4,025,159 (McGrath),
and U.S. Pat. No. 5,066,098 (Kult).
[0004] A second common type of retroreflector employs what are
referred to as cube corner retroreflective elements. Such cube
corner retroreflectors typically comprise a sheet having a
generally planar front surface and an array of cube corner elements
protruding from the back surface. In use, the retroreflector is
arranged with the front surface disposed toward the anticipated
location of intended observers. Light incident to the front surface
enters the sheet, passes through the body of the sheet to be
internally reflected by the faces of the elements so as to exit the
front surface in a direction substantially toward the light source,
i.e., retroreflection. Illustrative examples of cube corner type
retroreflectors are disclosed in U.S. Pat. No. 3,712,706 (Stamm),
U.S. Pat. No. 4,025,159 (McGrath), U.S. Pat. No. 4,202,600 (Burke
et al.), U.S. Pat. No. 4,243,618 (Van Arnam), U.S. Pat. No.
4,349,598 (White), U.S. Pat. No. 4,576,850 (Martens), U.S. Pat. No.
4,588,258 (Hoopman), U.S. Pat. No. 4,775,219 (Appeldorn et al.) and
U.S. Pat. No. 4,895,428 (Nelson et al.). Cube corner
retroreflectors have commonly been employed as safety devices on
bicycles, automobiles, and other vehicles as well as on traffic
signs.
[0005] Cube corner retroreflectors typically have a higher
retroreflective efficiency than microsphere-based retroreflectors
and are sometimes preferred for application to substrates for this
reason. However, retroreflective posts, cones, barrels, safety
helmets, and corrugations or rivets on truck trailer surfaces
require that the sheeting bend and conform to curved substrates.
The cubes of cube corner retroreflectors are typically made of
resins having high glass transition temperatures so that the cubes
maintain their dimensions, and thus are capable of providing bright
retroreflection, upon being exposed to high temperatures or high
levels of humidity over time. Such resins are typically rigid
(i.e., have a high flexural modulus). Unlike microsphere-based
sheetings where the microspheres are generally much higher in
modulus than the binder resin in which the microspheres are
embedded, the cube corner retroreflective elements of cube corner
retroreflectors tend to undergo significant optically degrading
deformation as the retroreflector is conformed to a non-planar
substrate because the high modulus cubes are typically similar in
modulus to the rest of the sheeting.
[0006] U.S. Pat. No. 3,684,348 (Rowland) discloses a
retroreflective composite material which is adapted to be shaped
and mounted to surfaces of various configurations. The composite
material comprises a flexible body portion to which a multiplicity
of minute cube corner elements are adhered. The cube corner
elements have a side edge dimension of up to 25 mils (625 microns),
but preferably less than 10 mils (250 microns) along the side
edge.
[0007] In U.S. Pat. No. 3,992,080 (Rowland), it is noted that the
cube corner elements of the retroreflective composite material
disclosed in U.S. Pat. No. 3,684,348 are distorted when the
material is stretched during application to a support surface, and
such distortion renders the cube corner faces non-orthogonal to a
degree, resulting in significant loss of brightness.
[0008] U.S. Pat. No. 4,555,161 (Rowland) discloses a
retroreflective laminar sheet assembly comprising flexible base and
cover sheets and an array of retroreflective film pieces seated
within discrete adjacent cells formed by bonding of the base and
cover sheets at selected areas. One retroreflective film piece is
contained within each cell and typically is made of minute cube
corner retroreflective elements. Typically, there is a gap of about
{fraction (1/8)} to {fraction (1/2)} inch (0.3 to 1.3 cm) between
the edge of each film piece and the adjacent bonding area. The
retroreflective laminar sheet assembly can be formed into a collar
and mounted upon a traffic cone as shown in FIG. 3 of the patent.
However, it is believed that the sheet assembly is not particularly
useful when mounted to non-planar substrates which have intricate
shapes or very small dimensions such as truck trailer rivets and
corrugations because of the shear size of the gaps and film pieces
in the sheet assembly. These gaps are typically much smaller than
the retroreflective film pieces, which are rigid. The gaps present
areas of the sheet assembly which are not capable of
retroreflecting light. It is believed that if more film pieces and
gaps were provided in a given unit of area of the sheet assembly to
achieve greater flexibility, retroreflective brightness would be
greatly sacrificed because of the width of the gaps relative to the
width of the film pieces. In other words, the gaps can likely be
made only so small before bonding of the base and cover sheets in
the bonding areas is not possible. In addition, the patent
discloses that the base and cover sheets are flexible to provide
for flexible constructions, but does not disclose conformable base
and cover sheets to provide for conformable constructions. Lastly,
the sheet assembly is typically difficult to manufacture because
the retroreflective film pieces must generally be cut and arranged
in stacks in the manufacturing process.
SUMMARY OF INVENTION
[0009] The present invention provides cube corner type
retroreflective sheetings which are conformable to non-planar
substrates and methods for making such sheetings. Such sheetings
are particularly adapted to be applied to the corrugated surfaces
of truck trailers and protruding rivets thereof. Other possible
applications are in construction work zones, personal safety,
safety at sea, and any other area where conformability of highly
efficient retroreflective sheetings is needed.
[0010] In brief summary, the invention provides in one of its
aspects a conformable cube corner retroreflective sheeting
comprising a plurality of discrete cube corner segments which are
conformably bonded together, each cube corner segment comprising a
plastic body portion or land having a substantially planar front
major surface and side walls and at least one minute cube corner
retroreflective element projecting rearwardly from the body portion
and defining a cube corner point side of the cube corner segment.
The word "conformable" is used herein to describe a material which
is capable of being shaped or formed. In particular, the term
"conformable" is used herein to describe materials such as carrier
layers and sheetings which are omni-directionally extensible at
some ambient application temperature or elevated temperature and
can take essentially the same shape as non-planar substrates to
which the materials are conformed. The word "discrete" is used
herein to indicate that the cube corner segments are not rigidly
connected together. The phrase "conformably bonded together" and
close variants of this phrase are used herein to indicate that
adjacent cube corner segments are at least one of the following:
(1) separated by a gap of less than about 1 millimeter and bonded
together through a conformable carrier layer; or (2) separated by a
gap which is substantially filled with a conformable resin that
bonds the side walls of adjacent cube corner segments together.
Each cube corner retroreflective element typically has a plurality
of facets or faces and a base adjacent the body portion. Typically,
substantially all of the cube corner retroreflective elements
located closest to the side walls of the body portions are intact
and capable of retroreflecting light.
[0011] The peripheries of the cube corner segments can be defined
by a plurality of separations extending from the cube corner point
sides to the front major surfaces of the cube corner segments, the
separations being disposed between adjacent cube corner segments.
The term "separations" is used interchangeably herein with the term
"gaps," and is intended to denote any separations in the continuity
of a sheeting, whether the separations are caused by:
[0012] a) cutting the sheeting with a cutting device utilizing a
laser beam or a sharp edge;
[0013] b) stretching or flexing the sheeting with the sheeting
optionally being scored in the areas where separations are
desired;
[0014] c) molding the sheeting to form such separations;
[0015] d) propagating a discontinuity in the sheeting, the
discontinuity typically being initiated by thermally shocking the
sheeting, mechanically or ultrasonically vibrating the sheeting,
impacting the sheeting for a short duration, or mechanically
stressing the sheeting; or
[0016] e) any other suitable process.
[0017] Typically, the cube corner segments are defined by a pattern
of the separations. Such a pattern can comprise a plurality of
contiguous polygons selected from the group consisting of
parallelograms, triangles, and hexagons.
[0018] As noted above, adjacent cube corner segments can be
separated by a gap of less than about 1 millimeter and bonded
together through a conformable carrier layer. The conformable
carrier layer can comprise a continuous, transparent film which is
bonded to the front major surfaces of the cube corner segments,
typically through a transparent adhesive.
[0019] Also, as noted above, the cube corner segments can be bonded
together through a conformable resin disposed in the gaps between
adjacent cube corner segments. The conformable resin bonds the side
walls of adjacent cube corner segments together. The gap between
adjacent cube corner segments can range between about 0.5 and about
3 millimeters. Further, a back sealing film can be disposed
adjacent the cube corner retroreflective elements and bonded to the
cube corner segments through the conformable resin. Also, a
continuous, transparent film can be bonded to the front major
surfaces through the conformable resin, the conformable resin
typically being transparent.
[0020] In another of its aspects, the invention relates to a method
for making a conformable cube corner retroreflective sheeting,
comprising:
[0021] a) providing a tool having a molding surface which comprises
a plurality of raised protrusions and retroreflective
element-forming cavities adapted for molding a cube corner
retroreflective sheeting comprising a plurality of the
above-described cube corner segments;
[0022] b) depositing a hardenable molding material on the molding
surface of the tool, the molding material being sufficient in
amount and fluidity to essentially completely fill the
cavities;
[0023] c) applying a conformable carrier layer to the molding
material on the molding surface under sufficient pressure to effect
intimate surface contact between the carrier layer, the raised
protrusions of the tool, and the molding material;
[0024] d) effecting substantial solidification of the molding
material and bonding of the molding material to the carrier layer
to form the conformable sheeting; and
[0025] e) removing the conformable sheeting from the molding
surface.
[0026] In another of its aspects, the invention relates to a method
for making a conformable cube corner retroreflective sheeting,
comprising:
[0027] a) providing the tool described in the above method;
[0028] b) placing a thermoplastic sheet on the tool;
[0029] c) heating the resin of the sheet to a temperature at least
as high as its softening temperature;
[0030] d) pressing the sheet onto the molding surface of the tool
to thereby form a plurality of cube corner segments;
[0031] e) conformably bonding the cube corner segments together
with a conformable carrier layer to form the conformable sheeting;
and
[0032] f) removing the conformable sheeting from the tool.
[0033] The term "softening temperature" is a well known term of
art. It is used herein to denote the temperature at which a
material first softens and is capable of being pressed into a
desired shape upon heating the material. U.S. Pat. No. 5,117,304
(Huang et al.) discloses a suitable method for measuring the
softening temperature of a polymer sample and is incorporated
herein by reference.
[0034] The invention also relates to a method for making a
conformable cube corner retroreflective sheeting, comprising the
steps of:
[0035] a) providing an initial cube corner retroreflective sheeting
comprising a plastic body portion having a substantially planar
front major surface and a multiplicity of minute cube corner
retroreflective elements projecting rearwardly from the body
portion and defining a cube corner point side of the initial
sheeting;
[0036] b) dividing the body portion into a plurality of the
above-described cube corner segments so that they are discrete and
so that the peripheries of the cube corner segments are defined by
a plurality of separations extending from the cube corner point
sides of the cube corner segments to the front major surfaces of
the cube corner segments; and
[0037] c) conformably bonding the cube corner segments together to
form the conformable sheeting.
[0038] A tool having a plurality of raised protrusions or a cutting
device utilizing a laser beam or a sharp edge can be used in
carrying out the body portion dividing step. Typically, if the tool
is used, pressure is applied against the front major surface of the
initial sheeting with the raised protrusions of the tool.
[0039] Further, the method can comprise the steps of substantially
filling the separations with a conformable resin so that the
conformable resin contacts the side walls of adjacent cube corner
segments, and effecting substantial solidification of the
conformable resin so that it conformably bonds the cube corner
segments together. If desired, the conformable carrier layer and
conformable resin can be stretched to increase the width of the
separations (i.e., to increase the gap between adjacent cube corner
segments).
[0040] In yet another of its aspects, the invention relates to
another type of conformable cube corner retroreflective sheeting
comprising a plurality of cube corner segments bonded together
through a conformable carrier layer, wherein the peripheries of the
cube corner segments are defined by grooves extending vertically
from the cube corner point sides toward the front major surfaces
and terminating at connecting bridges which are disposed
horizontally between and are integral with adjacent cube corner
segments, the connecting bridges being at least one of fractured
and frangible. The connecting bridges are typically substantially
thinner than and made of the same material as the body portions of
adjacent cube corner segments.
BRIEF DESCRIPTION OF DRAWING
[0041] The invention will be further explained with reference to
the drawing, wherein:
[0042] FIG. 1 is a diagrammatical cross section through a
conformable cube corner retroreflective sheeting of the invention,
showing a plurality of discrete cube corner segments of the
sheeting, the sheeting being cut away at each end;
[0043] FIG. 2 is a bottom view of the sheeting of FIG. 1, showing
the microreplicated grooves which define the facets of the cube
corner retroreflective elements of the sheeting, showing the apices
of the cube corner elements, and showing a hexagonal pattern of
separations separating the discrete cube corner segments;
[0044] FIG. 3 is similar to FIG. 2 but shows a parallelogram
pattern of separations;
[0045] FIG. 4 is similar to FIG. 2 but shows a triangular pattern
of separations;
[0046] FIG. 5 is a diagrammatical cross section through a composite
of an initial cube corner retroreflective sheeting, conformable
carrier layer, and optional adhesive layer used in making the
conformable sheeting of FIG. 1, the composite being cut away at
each end;
[0047] FIG. 6 illustrates the composite of FIG. 5 being fractured
by a tool having a raised pattern of protrusions to thereby form a
conformable sheeting like the conformable sheeting of FIG. 1;
[0048] FIG. 7 is similar to FIG. 1 but shows a specularly
reflective coating, adhesive layer, and release liner applied to
the sheeting thereof;
[0049] FIG. 8 is a diagrammatical cross section through a composite
of an initial cube corner retroreflective sheeting, specularly
reflective layer, adhesive layer, and release liner used in making
a conformable sheeting, the composite being cut away at each
end;
[0050] FIG. 9 illustrates the composite of FIG. 8 with the initial
sheeting being divided into a plurality of discrete cube corner
segments by a tool having a raised pattern of protrusions to
thereby form a conformable sheeting;
[0051] FIG. 10 is a cross section of a conformable sheeting
comprising a conformable resin which substantially fills the
separations of the sheeting, contacts cube corner segments
separated by the separations to bond them together, and bonds a
conformable back sealing film to the cube corner segments through
rearwardly extending wall members or septa formed by beads of the
conformable resin, the septa defining therebetween hermetically
sealed cells or pockets for maintaining a substantially complete
facet-air interface on the facets of the cube corner
retroreflective elements;
[0052] FIG. 11 illustrates a sheeting which is similar to the
sheeting of FIG. 10 but the gaps separating the cube corner
segments have been made wider;
[0053] FIG. 12 is a cross section of a conformable cube corner
retroreflective sheeting and a tool used to make the sheeting, the
sheeting comprising a plurality of discrete cube corner segments
having peripheries defined by inclined walls, the cube corner
segments being conformably bonded together through a conformable
carrier layer and optional adhesive layer;
[0054] FIG. 13 is a cross section of a conformable sheeting which
is similar to the sheeting of FIG. 12 but shows a specularly
reflective coating, adhesive layer, and release liner applied to
the sheeting;
[0055] FIG. 14 is a cross section of a conformable sheeting
comprising cube corner segments having peripheries defined by
rearwardly extending septa which contact a back sealing film and
define therebetween hermetically sealed cells or pockets for
maintaining a substantially complete facet-air interface on the
facets of the cube corner retroreflective elements;
[0056] FIG. 15 is a cross section of a conformable cube corner
retroreflective sheeting which comprises a plurality of cube corner
segments having peripheries defined by grooves having inverted
V-shape cross sections, and comprising connecting bridges which are
above the grooves and disposed horizontally between and integral
with adjacent cube corner segments, the connecting bridges being at
least one of fractured and frangible; and
[0057] FIG. 16 is similar to FIG. 15 but shows a specularly
reflective coating, adhesive layer, and release liner applied to
the sheeting thereof.
[0058] These figures, which are idealized, are not to scale and are
intended to be merely illustrative and non-limiting.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0059] Turning now to the figures of the drawing, like reference
numerals refer to like parts of the illustrated embodiments.
Referring to FIG. 1, conformable cube corner retroreflective
sheeting 10 of the invention comprises a plurality of discrete cube
corner segments 12 which are conformably bonded together. Each cube
corner segment 12 comprises plastic body portion or land 14 having
substantially planar front major surface 16, side walls at the
locations of reference numeral 50, and at least one and typically a
plurality of minute cube corner retroreflective elements 20
projecting rearwardly therefrom and defining cube corner point side
22 of cube corner segment 12.
[0060] Several types of cube corner retroreflective elements are
known in the art and may be used in the present invention.
Illustrative examples are disclosed in the aforementioned U.S. Pat.
Nos. 3,712,706, 4,202,600, 4,243,618, 4,349,598, 4,588,258,
4,775,219 and 4,895,428. Each of these patents is incorporated by
reference herein in its entirety.
[0061] Each cube corner retroreflective element 20 comprises a
plurality of (e.g., three) facets, faces, or sides which project
rearwardly from body portion 14 and are defined in part by a
plurality of microreplicated grooves 32 (see also FIG. 2) formed in
conformable sheeting 10. For example, the bases of the cube corner
retroreflective elements can be equilateral triangles, each
triangle having a height of between about 5 mils (125 microns) and
about 15 mils (375 microns). Referring to FIG. 2, cube corner
retroreflective elements 20 are typically provided in the form of
an array (i.e., an orderly arrangement such as a regularly
repeating pattern) by providing an orderly arrangement of
microreplicated grooves 32. In each of FIGS. 2, 3, and 4, there are
shown three sets of parallel microreplicated grooves 32 although it
is certainly contemplated that other types of microreplicated
groove patterns could be used such as, for example, the pattern
disclosed in the aforementioned U.S. Pat. No. 4,895,428. In this
patent, the cube corner retroreflective elements thereof comprise
rectangular bases formed by two sets of parallel microreplicated
grooves. Referring again to FIG. 1, cube corner retroreflective
elements 20 are preferably integral with body portion 14, i.e.,
body portion 14 may be structured in the form of or integral with
cube corner retroreflective elements 20.
[0062] The periphery of each cube corner segment 12 is defined by a
plurality of separations or gaps 50 extending from cube corner
point side 22 to front major surface 16 of the cube corner segment.
In other words, cube corner segments 12 are discrete (not attached
to each other in a rigid manner) and separated by separations 50.
Conformable sheeting 10 typically comprises between about 1,000 and
about 10,000 cube corner segments per square foot (between about
10,000 and 110,000 cube corner segments per square meter). Greater
conformability of the sheeting can be achieved with high numbers of
cube corner segments per unit of area of the sheeting. Typically,
substantially all of the cube corner retroreflective elements
located closest to the side walls of body portions 14 of cube
corner segments 12 are intact and capable of retroreflecting light.
Further, cube corner segments 12 are typically defined by a pattern
of separations 50. For example, illustrative patterns of
separations 50, 50a, and 50b are depicted in FIGS. 2, 3 and 4,
respectively. In FIG. 2, the pattern comprises a plurality of
contiguous hexagons. In FIG. 3, the pattern comprises a plurality
of contiguous parallelograms. In FIG. 4, the pattern comprises a
plurality of contiguous triangles. Thus, in the embodiment of FIG.
2, cube corner segments 12 have the shapes of hexagons when viewed
from the bottom of the sheeting. In the embodiment of FIG. 3, cube
corner segments 12a have the shapes of parallelograms when viewed
from the bottom of the sheeting. In the embodiment of FIG. 4, cube
corner segments 12b have the shapes of triangles when viewed from
the bottom of the sheeting.
[0063] Although cube corner segments 12 are discrete, they are
conformably bonded together. For example, as shown in FIG. 1,
adjacent cube corner segments 12 can be separated by a gap of less
than about 1 millimeter and bonded together through conformable
carrier layer 52. Conformable carrier layer 52 is typically bonded
to front major surfaces 16 of body portions 14 of cube corner
segments 12.
[0064] If desired, conformable carrier layer 52 can comprise a
continuous, transparent film which is bonded to front major
surfaces 16 through optional, typically transparent, adhesive layer
54. For example, conformable carrier layer 52 can comprise a 2 mil
(50 micron) thick, plasticized poly(vinyl chloride) film or
polyurethane film (made from polyurethane pellets having the trade
designation 58277 from B.F. Goodrich Company, Specialty Polymers
& Chemical Division of Cleveland, Ohio or polyurethane pellets
having the trade designation PN-3429 or PN-03 from Morton
International, Specialty Chemicals Group, of Seabrook, N.H.).
Alternatively, conformable carrier layer 52 can comprise ionomers
of polyethylene copolymers such as Surlyn.TM. 9910 from Du Pont
Company, Polymer Products Department, of Wilmington, Del.;
poly(ethylene-methacryl- ic acid) copolymers; poly(ethylene-acrylic
acid) copolymers; or fluorocarbon polymers.
[0065] In any event, the conformable carrier layer comprises a
conformable material such as, for example, a material which is
omni-directionally extensible at some ambient application
temperature or elevated temperature. In particular, the conformable
carrier layer can comprise a conformable material which is
characterized as being omni-directionally extensible upon being
heated to a temperature above room or ambient temperature. However,
the cube corner segments must be made of a material which will
remain dimensionally stable at the elevated temperature needed for
making the carrier layer extensible. For example, a suitable
conformable sheeting can be made if conformable carrier layer 52
comprises rigid (non-plasticized) poly(vinyl chloride) resin and
cube corner segments 12 comprise poly(methyl methacrylate) resin.
When such a conformable carrier layer is heated to a temperature of
about 90.degree. C., it can be conformed as needed to non-planar
substrates while conformably bonding cube corner segments 12
together. Because poly(methyl methacrylate) does not soften at this
elevated temperature, cube corner segments 12 remain dimensionally
stable so that the optical clarity of cube corner retroreflective
elements 20 is not affected.
[0066] Conformable carrier layer 52 typically has a softening
temperature greater than about 50.degree. C. If conformable carrier
layer 52 is intended to be extensible at room temperature, it will
typically have a tensile modulus of less than about
100.times.10.sup.3 lbs/in.sup.2 (about 6.9.times.10.sup.8
N/.sup.2). When it is intended that conformable carrier layer 52
form a permanent part of the conformable sheeting even after
application of the sheeting to a substrate, it may be desirable
that conformable carrier layer 52 be resistant to degradation from
ultraviolet radiation and have good light transmission properties.
However, it is further contemplated that conformable carrier layer
52 could comprise a release liner, e.g., a polyethylene or
polyester film. The release liner could be bonded to front major
surfaces 16 and easily removed therefrom after application of
conformable sheeting 10 to a substrate.
[0067] Body portions 14 and cube corner retroreflective elements 20
are typically made of a material having a relatively high modulus
in comparison to the materials of conformable carrier layer 52 and
optional adhesive layer 54. Body portions 14 and cube corner
retroreflective elements 20 typically have good light transmission
properties and tensile moduli of greater than about
150.times.10.sup.3 lbs/in.sup.2 (about 10.3.times.10.sup.8
N/m.sup.2) and preferably above about 200.times.10.sup.3
lbs/in.sup.2 (13.8.times.10.sup.8 N/m.sup.2). Thus, both
conformable carrier layer 52 and optional adhesive layer 54
typically comprise a relatively low modulus material in comparison
to the material of body portions 14 and cube corner retroreflective
elements 20. Illustrative examples of polymers that can be used in
making body portions 14 and cube corner retroreflective elements 20
include acrylic polymers, such as poly(alkyl methacrylate),
especially poly(methyl methacrylate); polyacrylonitrile;
celluloses, such as cellulose (acetate-co-butyrate); epoxies;
fluoropolymers, such as poly(vinylidene fluoride); polyamides, such
as nylons; poly(amide-coimide); polycarbonate, such as Lexan.TM.
from General Electric Company of Pittsfield, Mass.; polyesters,
such as poly(butylene terephthalate) and poly(ethylene
terephthalate); acrylic modified vinyl chloride polymers; styrene
copolymers, such as poly(styrene-co-acrylonitrile) and
poly(styrene-coacrylonitrile-co-butadiene); polysulfone; poly(vinyl
chloride); certain thermosetting and alkyd materials, such as
poly(melamine-formaldehyde); and mixtures of such polymers, such as
polyester and polycarbonate blends and fluoropolymer and acrylic
polymer blends.
[0068] Referring to FIG. 5, a conformable cube corner
retroreflective sheeting like conformable sheeting 10 (shown in
FIG. 1) can be made by first providing an initial, generally rigid
cube corner retroreflective sheeting 110 comprising plastic body
portion 114 having substantially planar front major surface 116 and
a multiplicity of minute cube corner retroreflective elements 120
projecting rearwardly from body portion 114 of sheeting 110 and
defining cube corner point side 122 of initial sheeting 110. Each
cube corner retroreflective element 120 has a plurality of (e.g.,
three) facets which project rearwardly from body portion 114 and
are defined in part by a plurality of microreplicated grooves 132
formed in sheeting 110.
[0069] Many types of cube corner retroreflective sheetings are
known in the art and would be suitable for use herein as initial
sheeting 110. Illustrative examples are disclosed in the
aforementioned U.S. Pat. Nos. 3,712,706, 4,202,600, 4,243,618,
4,349,598, 4,588,258, 4,775,219, and 4,895,428.
[0070] After providing initial sheeting 110, conformable carrier
layer 52 is typically bonded to front major surface 116 of initial
sheeting 110 although it could alternatively be bonded (either
directly or through an intermediate layer) to the facets of the
cube corner retroreflective elements. Conformable carrier layer 52
can be bonded to the initial sheeting through optional adhesive
layer 54. Then, as shown in FIG. 6, tool 162 having a plurality of
raised protrusions 164 can be used to form separations in the
initial sheeting and thereby form conformable sheeting 10. The
protrusions of the tool apply pressure against conformable carrier
layer 52, which transmits the pressure to adhesive layer 54, which
transmits the pressure to the front major surface of the initial
sheeting to thereby divide the body portion into a plurality of
discrete cube corner segments 12. For example, tool 162 can be
pressed against conformable carrier layer 52 at a pressure of about
200 lb/in.sup.2 (1.38.times.10.sup.6 N/m.sup.2) for less than a
second. Typically, rubber cushion 166 is provided on the side of
the sheeting opposite tool 162 to assist in fracturing the body
portion of the initial sheeting cleanly along the apices of the
microreplicated grooves which are closest to protrusions 164.
[0071] Because the sheeting typically tends to fracture along the
apices of its microreplicated grooves rather than in a random
fashion, few or no cube corner retroreflective elements are
destroyed or optically distorted during the fracturing step. Thus,
the resulting conformable sheeting suffers minimal brightness loss
as a result of the fracturing process. If desired, the initial
sheeting can be chilled, e.g., by contacting it with dry ice (a
temperature of about -78.degree. C.) for about three minutes, prior
to fracturing the sheeting to make the sheeting more brittle, to
facilitate extremely rapid fracturing at the apices of the
microreplicated groove sites, and to minimize the amount of optical
distortion on either side of the groove sites.
[0072] After the fracturing step (i.e., the division of the body
portion into a plurality of discrete cube corner segments), cube
corner segments 12 are conformably bonded together by conformable
carrier layer 52 and optional adhesive layer 54. Although as
described above, conformable carrier layer 52 and optional adhesive
layer 54 were secured to the initial sheeting prior to the
fracturing step, cube corner segments 12 could be bonded together
at some point after the fracturing step if the initial sheeting
were held in a fully supported position such that cube corner
segments 12 would not be disoriented upon fracturing the initial
sheeting. In particular, cube corner segments 12 can be bonded
together after the fracturing step by securing conformable carrier
layer 52 to front major surfaces 16 of cube corner segments 12.
[0073] Typically, protrusions 164 of tool 162 are arranged in the
form of a pattern which is adapted to form a pattern of separations
on the cube corner point side of the initial sheeting. Since cube
corner segments 12 of conformable sheeting 10 are maintained in
fixed relative positions by conformable carrier layer 52, the
pattern of separations can generally be preserved after fracturing
the sheeting. The pattern typically comprises a plurality of
contiguous polygons selected from the group consisting of hexagons,
parallelograms, and triangles (see FIGS. 2, 3, and 4
respectively).
[0074] Further, although a tool having a raised pattern of
protrusions is typically used to form the separations in the
sheeting, it is contemplated that a cutting device utilizing a
laser beam or a sharp edge, e.g., a razor blade, could be used to
form the separations by cutting completely or partially through the
initial sheeting. If the cutting device were used to cut only
partially through the initial sheeting, the initial sheeting could
then be chilled and flexed to form separations completely through
the initial sheeting at the positions of the partial cuts.
[0075] In an embodiment illustrated in FIG. 7, conformable sheeting
10a differs from conformable sheeting 10 because specularly
reflective coating 56 has been deposited onto the facets of
elements 20 to modify the retroreflective performance of the
sheeting, and also eliminate the need for a back sealing film.
Specularly reflective coating 56 can comprise metallic specularly
reflective material such as aluminum or silver, or can comprise a
dielectric mirror. U.S. Pat. No. 3,700,305 (Bingham) discloses
retroreflective sheetings containing dielectric mirrors, and is
incorporated herein by reference. If desired, adhesive layer 58 may
be applied to the back side of specularly reflective coating 56.
Adhesive layer 58 typically comprises a pressure-sensitive adhesive
although other types of adhesive may be used if desired. Release
liner 60 can be removably secured to adhesive layer 58. Release
liner 60 is adapted to be easily removed from adhesive layer 58,
typically immediately prior to adhering sheeting 10a to a substrate
(not shown).
[0076] Referring to FIG. 8, a conformable cube corner sheeting can
alternatively be made by providing initial sheeting 110, depositing
specularly reflective coating 56 on the cube corner point side 122
(onto the facets of cube corner elements 120) of initial sheeting
110, applying adhesive layer 58 onto the back side of specularly
reflective coating 56, and removably securing release liner 60 to
adhesive layer 58. In this embodiment of the invention, adhesive
layer 58 and release liner 60 serve as the conformable carrier
layer. Thus, adhesive layer 58 functions analogously to the
above-described adhesive layer 54, and release liner 60 functions
analogously to the above-described conformable carrier layer
52.
[0077] Next, referring to FIG. 9, raised protrusions 164 of tool
162 are pressed against the front major surface of the initial
sheeting in the same manner described above in connection with FIG.
6 to form separations 50 in the initial sheeting and thereby form
conformable sheeting 10b. Rubber cushion 166 is typically provided
on the side of the sheeting opposite tool 162 to assist in
fracturing the sheeting. As the sheeting is fractured to form
conformable sheeting 10b, specularly reflective coating 56 may also
fracture at locations adjacent to separations 50, although these
possible separations are not illustrated. In conformable sheeting
10b, adhesive layer 58 and release liner 60 conformably bond cube
corner segments 12b together. Release liner 60 is adapted to be
easily removed, typically immediately prior to adhering sheeting
10b to a substrate (not shown).
[0078] In embodiments which are to be used in environments where
the conformable cube corner retroreflective sheeting is likely to
be exposed to moisture, e.g., outdoors or in high humidity, it may
be preferred that cube corner retroreflective elements 20 be
encapsulated with a conformable back sealing film. The
aforementioned U.S. Pat. No. 4,025,159, which is incorporated in
its entirety herein by reference, discloses encapsulation of cube
corner retroreflective elements using a back sealing film. Such
encapsulation provides an air interface adjacent the facets of cube
corner elements 20 rather than a specularly reflective coating
adjacent the facets and also provides a flat rear surface for
bonding the sheeting to a substrate. An adhesive layer may be
applied to the back side of the sealing film to provide a means for
securing the sheeting to a substrate.
[0079] Referring to FIG. 10, conformable sheeting 10c comprises a
conformable back sealing film and is thus particularly useful in
environments where the sheeting is likely to be exposed to
moisture. Sheeting 10c also differs from conformable sheeting 10
because it comprises cube corner segments 12 conformably bonded
together through conformable resin 62 which substantially fills
separations 50 (i.e., the gaps between adjacent cube corner
segments) and bonds the side walls of adjacent cube corner segments
12 together. Conformable resin 62 can comprise a material which has
a low modulus relative to the materials of cube corner segments 12.
Alternatively, conformable resin 62 can comprise a material which
is extensible only at an elevated temperature (see the above
analogous discussion of this concept relative to the conformable
carrier layer). In particular, conformable resin 62 can comprise a
conformable, natural or synthetic resin such as a thermally cured,
urethane-modified polyester resin which is crosslinked with a
melamine resin; a one-part urethane which can be cast and dried and
is available under the trade designation Permuthane.TM. U 6729 from
Permuthane Company, a division of Beatrice of Peabody, Mass.; a
water-borne urethane which is available under the trade designation
NeoRez R-963 from Zeneca Inc., a member of the ICI Group, of
Elmhurst, Ill.; an ultraviolet radiation-curable aliphatic urethane
acrylate; a water-based acrylic emulsion available under the trade
designation Neocryl.TM. m A 655 from ICI Polyvinyl Chemicals;
polyurethanes; and plasticized poly(vinyl chloride).
[0080] Conformable sheeting 10c typically does not include an
adhesive layer because conformable resin 62 acts as an adhesive in
conformably bonding cube corner segments 12 together and in
conformably bonding conformable carrier layer 52 to cube corner
segments 12. Also, in sheeting 10c, conformable carrier layer 52
typically comprises a transparent, continuous top film which is
adhered to front major surfaces 16 of cube corner segments 12
through conformable resin 62 which is also typically transparent.
However, conformable carrier layer 52 could comprise a release
liner which would typically be adhered to front major surfaces 16
of cube corner segments 12 through conformable resin 62. Further,
sheeting 10c typically includes conformable back sealing film 64
disposed rearwardly of cube corner retroreflective elements 20.
Back sealing film 64 typically comprises a continuous film. For
example, back sealing film 64 can comprise a 2 mil (50 micron)
thick polyurethane film (made from polyurethane pellets having the
trade designation 58277 from B.F. Goodrich Company or polyurethane
pellets having the trade designation PN-3429 or PN-03 from Morton
International), or plasticized poly(vinyl chloride) film. Back
sealing film 64 is conformably bonded to cube corner segments 12
through beads 66 of conformable resin 62. Beads 66 are disposed
between adjacent cube corner segments 12 and function as wall
members or septa which typically intersect with each other to
separate the space between them into hermetically sealed cells or
pockets 94 which are each free from contamination by dust particles
or moisture to maintain a substantially complete facet-air
interface on the facets of the cube corner retroreflective
elements. When back sealing film 64 comprises a plasticized
poly(vinyl chloride) film, conformable resin 62 preferably
comprises a thermally cured, urethane-modified polyester resin
which is crosslinked with a melamine resin.
[0081] Sheeting 10c can be made by providing a continuous,
transparent film for use as conformable layer 52 and applying a
layer of conformable resin 62 onto the film, the conformable resin
62 typically comprising a pressure-sensitive or a hot-melt
adhesive. The film can then be laminated to the front major surface
of an initial cube corner retroreflective sheeting with the
conformable resin being adjacent the initial sheeting to form an
intermediate composite. After an optional step of chilling this
intermediate composite, the intermediate composite is pressed
between a raised pattern die and a rubber cushion as described in
connection with FIG. 6 to thereby divide the body portion of the
initial cube corner retroreflective sheeting into discrete cube
corner segments. This segmented composite can then be heated to
about 200.degree. F. (93.degree. C.) and then pressed to soften the
conformable resin. The cube corner segments should remain
dimensionally stable under these conditions. The pressure forces
the softened conformable resin to flow toward the rear of the
sheeting through separations 50 to substantially fill separations
50. Typically, back sealing film 64 is placed adjacent the cube
corner retroreflective elements of the segmented composite prior to
heating and pressing the segmented composite. As back sealing film
64 and the segmented composite are heated and pressed, the softened
conformable resin flows into separations 50 and then contacts back
sealing film 64 at a location adjacent each separation 50 to form
beads 66. Each bead 66 is typically in contact with a plurality of
cube corner segments 12. Then, substantial solidification of the
conformable resin is effected, typically by cooling it to a
temperature at which it is no longer soft or by crosslinking the
conformable resin to thereby bond back sealing film 64 to the cube
corner segments of sheeting 10c.
[0082] In yet another embodiment of a conformable sheeting, as
shown in FIG. 11, conformable sheeting 10d comprises separations
50d which are relatively wide in comparison to the separations of
the previously discussed sheetings of the invention. The width of
each separation 50d, i.e., the gap between cube corner segments 12,
is typically between about 0.5 and about 3 millimeters. Like
sheeting 10c, sheeting 10d is particularly useful in environments
where the sheeting is likely to be exposed to moisture because it
comprises conformable back sealing film 64.
[0083] Conformable sheeting 10d differs from conformable sheeting
10c in the following respects. First, separations 50d are wider
than separations 50 of sheeting 10c as noted above. Second, beads
66d of conformable resin 62 are typically larger in volume than
beads 66 of sheeting 10c because beads 66d are used to conformably
bond separations which are much wider than the separations of
sheeting 10c. Thirdly, the thickness of the layer of conformable
resin 62 disposed between front major surfaces 16 of cube corner
elements 12 and conformable carrier layer 52 is typically less in
sheeting 10d than in sheeting 10c because more conformable resin 62
is urged into the separations during the process of making sheeting
10d. In fact, if desired, sheeting 10d can be made such that there
is very little conformable resin 62 disposed between front major
surfaces 16 and conformable carrier layer 52 by urging nearly all
of the conformable resin into separations 50d during the process of
making sheeting 10d.
[0084] Sheeting 10d is made in the same manner as sheeting 10c
except that after the discrete cube corner segments are formed and
before the segmented composite and back sealing film are pressed
together, the segmented composite is typically heated to about
200.degree. F. (93.degree. C.) to soften conformable resin 62 and
conformable carrier layer 52. Conformable carrier layer 52 and
conformable resin 62 are then stretched or tentered in at least one
direction, preferably at least two directions, in their respective
planes to widen the separations of the segmented composite
(increase the gaps between adjacent cube corner segments) and
increase the area of conformable carrier layer 52 and conformable
resin 62. Next, the segmented composite and back sealing film are
pressed together in the same manner as described above in
connection with sheeting 10c. The pressing operation forces the
softened conformable resin to flow into separations 50d and toward
the rear of the sheeting. As back sealing film 64 and the composite
are pressed together, the softened conformable resin flows into
separations 50d to form beads 66d. The conformable resin is then
cured to complete the product.
[0085] In another of its aspects, the invention relates to a method
for making a conformable cube corner retroreflective sheeting
comprising a conformable carrier layer. Referring to FIG. 12, in
the first step of the method, tool 262 is provided, tool 262 having
a plurality of raised protrusions 264 and retroreflective
element-forming cavities or recesses 266 adapted for molding a
conformable cube corner retroreflective sheeting like sheeting 10e.
Next, a conformable sheeting like sheeting 10e can be made by
placing a thermoplastic sheet onto the tool, heating the resin of
the thermoplastic sheet to a temperature at least as high as its
softening temperature, and pressing the sheet onto the tool to make
a plurality of cube corner segments 12e. Raised protrusions 264 of
tool 262 are typically used to form cube corner segments 12e having
inclined walls 80 defining their peripheries. Preferably, the
raised protrusions comprise a cross sectional shape in the form of
an inverted and truncated V-shape so that the raised protrusions
are adapted to form inverted and truncated V-shape separations in
the completed sheeting between the cube corner segments so that
cube corner segments 12e are discrete. The protrusions of the tool
would typically form a pattern of separations in the sheeting. The
pattern could comprise a plurality of contiguous polygons selected
from the group consisting of hexagons, parallelograms, and
triangles. Next, while the resin of the thusly formed cube corner
segments is still at a temperature at least as high as its
softening temperature, the resin is contacted with and laminated to
conformable carrier layer 52 and optional adhesive layer 54, and
the resin is then cooled to below its softening temperature,
preferably to about room temperature, to conformably bond the cube
corner segments together and form sheeting 10e. The completed
sheeting is thereafter removed from the tool and is typically
easily removed therefrom because cube corner segments 12e comprise
inclined walls 80. Cube corner segments 12e of the sheeting are
conformably bonded together through conformable carrier layer 52
and adhesive layer 54, with the gaps or separations between
adjacent cube corner segments of a sheeting not yet removed from
the tool being defined as equal to the widths 268 of protrusions
264.
[0086] If desired, this method can be practiced in continuous
fashion by following the teachings of U.S. Pat. No. 4,601,861
(Pricone et al.) and U.S. Pat. No. 4,486,363 (Pricone et al.), each
of which is incorporated herein by reference. Also, referring to
FIG. 13, the method could further comprise coating the cube corner
point side (the facets of the cube corner retroreflective elements
and grooves of the conformable sheeting) with a specularly
reflective coating 56f. An adhesive layer 58 could be applied onto
specularly reflective coating 56f, and a release liner 60 could be
removably secured to the adhesive layer to form completed sheeting
10f.
[0087] In yet another of its aspects, the invention relates to a
method for making a conformable cube corner retroreflective
sheeting. This method is an alternative to the embossing method
described immediately above. Referring again to FIG. 12, in the
present method, tool 262 is again provided. However, in the next
step of the method, a hardenable molding material is deposited on
the molding surface of tool 262, the molding material preferably
being essentially transparent and sufficient in amount and fluidity
to essentially completely fill recesses 266 and typically
sufficient in amount to cover raised protrusions 268. Then,
conformable carrier layer 52 and optional adhesive layer 54 are
applied to the molding material on the molding surface under
sufficient pressure to effect intimate surface contact between
carrier layer 52, raised protrusions 264, and the molding material.
Typically, carrier layer 52 is rolled across the surface of tool
262 and pressed thereagainst to urge the molding material away from
protrusions 264 so that carrier layer 52 substantially contacts
protrusions 264 and the molding material is urged between
protrusions 264. The molding material is then subjected to
conditions sufficient to effect substantial solidification thereof
and bonding to the adjacent surface of carrier layer 52 to form
conformable sheeting 10e comprising discrete cube corner segments
12e. Conformable sheeting 10e is thereafter removed from the
molding surface.
[0088] The molding material employed may be a molten thermoplastic
resin, in which case the solidification thereof is accomplished at
least in part by cooling with the inherent nature of the
thermoplastic resin producing bonding thereof to the carrier layer.
Alternatively, the molding material may be a resin having
cross-linkable groups, in which case solidification is accomplished
at least in part by cross-linking of the resin. As an additional
possibility, the molding material may be a partially polymerized
resin formulation with solidification thereof being accomplished at
least in part by effecting further polymerization in the
formulation.
[0089] If desired, this method can be practiced in continuous
fashion by following the teachings of U.S. Pat. No. 3,689,346
(Rowland), which is incorporated herein by reference.
[0090] Referring to FIG. 14, the invention further relates to
conformable cube corner retroreflective sheeting 10g which is
similar to sheeting 10e (FIG. 12) but comprises wall members or
septa 90 which extend rearwardly into sealing contact with
conformable back sealing film 64. Septa 90 preferably comprise
inclined side walls 80g. Sheeting 10g is also somewhat similar to
sheeting 10c (FIG. 10) since both comprise rearwardly extending
septa. As shown in FIG. 14, septa 90 typically define the
peripheries of cube corner segments 12g. Because septa 90 are in
sealing contact with back sealing film 64, hermetically sealed
cells or pockets 94 are formed in sheeting 10g. The free edges of
septa 90 are spaced rearwardly a distance greater than the peaks of
the cube corner retroreflective elements such that an air space is
formed within pockets 94. A pattern of separations formed by
adjacent inclined walls 80g is typically formed in the same manner
as the pattern formed in connection with sheeting 10e (FIG.
12).
[0091] Sheeting 10g is made in the same manner as sheeting 10e
(FIG. 12) above, either by molding or embossing, except that the
tool provided should have a shape adapted to form cube corner
segments 12g, including septa 90 thereof, as shown in FIG. 14.
Also, the free edges of septa 90 are bonded to a conformable back
sealing film 64 by any of various means such as ultrasonic sealing;
heat sealing with a hot, smooth surface applied against the back
sealing film; adhesives, e.g., pressure-sensitive adhesives, hot
melt adhesives, or solvent-activatable adhesives; polymerizable
materials; or by using a solvent which attacks the septa to make
their free edges tacky and, preferably, making back sealing film 64
tacky to form a bond. Adhesives or polymerizable materials may be
applied to the face of back sealing film 64, to the free edges of
the septa, or both. It is important, however, to avoid exposure of
the facets of the retroreflective elements to solvents, adhesives,
and excessive heat or pressure.
[0092] Referring to FIG. 15, the invention also relates to
conformable cube corner retroreflective sheeting 10h comprising a
plurality of cube corner segments 12 and a plurality of connecting
bridges 70 which are disposed horizontally between and are integral
with adjacent cube corner segments 12. Each connecting bridge 70 is
typically substantially thinner than body portions 14 of cube
corner segments 12 adjacent to it and is typically made of the same
material and in the same manufacturing step. Even though connecting
bridges 70 and cube corner segments 12 are typically made from the
same or similar materials, connecting bridges 70 can be made thin
enough to be more frangible than cube corner segments 12. The
material used in making connecting bridges 70 can typically be the
same material used in making cube corner segments 12 if the
thickness of connecting bridges 70 is less than about 3 mils (75
microns), preferably less than about 1 mil (25 microns). For
example, each connecting bridge could be about 1 mil (25 microns)
thick or less, and each body portion 14 could be about 2-4 mils
(50-100 microns) thick.
[0093] Connecting bridges 70 can be made such that they are
frangible and then fractured by, for example, pressing or
stretching sheeting 10h such that connecting bridges 70 fracture.
In particular, sheeting 10h can be made in such a manner that
connecting bridges 70 are adapted to fracture upon application of
the sheeting to nonplanar substrates like rivets or corrugated
surfaces. Sheeting 10h is described as being conformable because
connecting bridges 70 are frangible and can be fractured by
applying the sheeting to nonplanar substrates. Once the connecting
bridges fracture, the cube corner segments adjacent to the
fractured connecting bridges are discrete. It is also contemplated
that connecting bridges 70 could be fractured before application of
the sheeting to a nonplanar substrate although fractured connecting
bridges are not illustrated in FIG. 15. Thus, sheeting 10h can
conform to nonplanar substrates because it comprises connecting
bridges 70 which are at least one of fractured and frangible. The
retroreflective performance of sheeting 10h is good because cube
corner segments 12 are not dimensionally distorted when the
sheeting is conformed to nonplanar substrates.
[0094] The peripheries of cube corner segments 12 are defined by
grooves 72 extending vertically from cube corner point sides 22 of
cube corner segments 12 toward front major surfaces 16 of body
portions 14 and terminating at connecting bridges 70. Although the
grooves are shown in FIG. 15 as having an inverted V-shape, the
grooves can have other cross sectional shapes such as, for example,
an inverted U-shape or an inverted V-shape wherein the apex of the
V is truncated. Thus, connecting bridges 70 are located vertically
above, and therefore span, grooves 72. Typically, the peripheries
of cube corner segments 12 are defined by a pattern of grooves 72.
The pattern can comprise a plurality of contiguous polygons
selected from the group consisting of hexagons, parallelograms, and
triangles.
[0095] Cube corner segments 12 of sheeting 10h are bonded together
through conformable carrier layer 52. Conformable carrier layer 52
can be bonded to front major surfaces 16 through thermal
lamination, and optional adhesive layer 54 can be interposed to
ensure adhesion. For example, conformable carrier layer 52 can
comprise a continuous, transparent film, and adhesive layer 54 can
comprise a transparent adhesive.
[0096] Referring to FIG. 16, sheeting 10h can be used to make
sheeting 10i. Sheeting 10i comprises specularly reflective coating
56i deposited onto the cube corner point side (the facets of the
cube corner retroreflective elements) of each cube corner segment
12. Typically, the specularly reflective coating 56i would also
coat grooves 72. Adhesive layer 58 would typically be applied on
the rear surface of specularly reflective coating 56i. Also, a
release liner 60 could be removably secured to adhesive layer
58.
[0097] It is further contemplated that a sheeting similar to
sheeting 10h illustrated in FIG. 15 could be made by providing a
tool similar to the one used in making sheeting 10g illustrated in
FIG. 14. In other words, the tool would be adapted to form
rearwardly extending septa in the sheeting on both sides of the
connecting bridges. A conformable back sealing film could be sealed
to the septa as described in connection with sheeting 10g.
[0098] Retroreflective sheetings of the present invention differ
from previously known cube corner retroreflective sheetings in that
they conform well to nonplanar substrates having intricate shapes
or very small dimensions such as rivets or corrugated surfaces and
maintain a high retroreflective brightness when thus conformed.
Each sheeting of the invention comprises conformable materials
which conformably bond relatively rigid cube corner segments
together. When a sheeting of the invention is conformed to a
nonplanar substrate, the optical properties of the cube corner
retroreflective elements of the rigid cube corner segments are not
adversely affected because the cube corner segments are not
distorted in shape as a result of the conforming. This lack of
distortion is important because even slight distortion of the rigid
cube corner segments would likely significantly impair the
retroreflective brightness of the sheeting.
EXAMPLES
[0099] The invention will be further explained by the following
illustrative examples which are intended to be nonlimiting. All
parts and percentages listed below are by weight unless otherwise
indicated.
[0100] Unless otherwise indicated, retroreflectance
(retroreflective brightness) was measured using a retroluminometer
as described in U.S. defensive publication no. T987,003 at a
divergence angle of about 0.20 and at an entrance angle of about
-4.degree..
Example 1
[0101] Conformable cube corner retroreflective sheetings were used
to make a traffic cone and a police-type motorcycle helmet
retroreflective. Each sheeting was made by first obtaining a
12".times.12" (30.5 cm.times.30.5 cm) transparent poly(vinyl
chloride) sheet having a thickness of about 10 mils (250 microns)
and using this poly(vinyl chloride) sheet as a conformable carrier
layer, coating a pressure-sensitive polyalkyl acrylate adhesive
onto the carrier layer at a thickness of about 5 mils (125
microns), and drying the adhesive by forced-air drying. A
polymethyl methacrylate cube corner retroreflective sheeting was
then laminated under pressure to the adhesive with the smooth side
of the retroreflective sheeting facing the adhesive. The cube
corner point side of each composite was then scored with a razor
blade in a 0.25" (0.6 cm) square grid pattern. The entire acrylic
layer of each sheeting was cut through but the carrier layers were
not cut.
[0102] The segmented composite sheetings were then heat and vacuum
formed at about 190.degree. F. (88.degree. C.) to soften the
carrier layer but not the acrylic sheetings and firmly conform the
sheetings to the exterior surfaces of the traffic cone and
motorcycle helmet. The heat and vacuum forming caused the carrier
layer to have a larger surface area but a smaller thickness. Also,
the separations between the cube corner segments were wider after
the heat and vacuum forming. The retroreflective brightness was
measured and found to be about 350 candela/lux/meter.sup.2 for the
traffic cone and about 375 candela/lux/meter.sup.2 for the
motorcycle helmet. The initial retroreflective sheetings had
retroreflective brightnesses of about 1200
candela/lux/meter.sup.2.
Example 2
[0103] A conformable cube corner retroreflective sheeting was made
by providing a 2 mil (50 micron) thick polyurethane film (made from
polyurethane pellets having the trade designation 58277 from B.F.
Goodrich Company, Specialty Polymers & Chemical Division, of
Cleveland, Ohio) as the conformable carrier layer, coating a 2 mil
(50 micron) thick pressure-sensitive polyalkyl acrylate adhesive
onto the polyurethane carrier layer, and laminating the planar
front major surface of a 12-17 mils (300-425 microns) thick
polymethyl methacrylate cube corner retroreflective sheeting onto
the adhesive. Next, a 1,200 Angstroms (0.12 micron) thick silver
vapor coat was deposited onto the facets of the cube corner
retroreflective elements, a 5 mil (125 micron) thick polyalkyl
acrylate adhesive was coated onto the silver vapor coat, and a 4
mil (100 micron) thick polyethylene film was used as a release
liner and removably secured to the bottom adhesive layer.
[0104] This composite was then laid on dry ice having a temperature
of about -109.degree. F. (-78.degree. C.) for three minutes to
chill the acrylic cube corner sheeting. The composite was then
placed on a rubber cushion with the polyethylene release liner
adjacent the rubber cushion. A tool having a plurality of raised
protrusions in a hexagonal pattern was then pressed against the
polyurethane carrier layer at a pressure of about 200 lb/in.sup.2
(1.38.times.10.sup.6 N/m.sup.2) for less than a second. The tool
and rubber cushion cooperated to stress the portions of the cube
corner sheeting located closest to the protrusions of the tool to
cause the sheeting to generally fracture along the apices of the
microreplicated grooves located closest to the protrusions of the
tool. Thus, damage to the cube corner retroreflective elements was
minimized.
[0105] The polyethylene release liner of the conformable cube
corner retroreflective sheeting was removed to expose the bottom
adhesive layer and the conformable sheeting was firmly adhered to a
rivet on a truck trailer. After application of the sheeting to the
rivet, the sheeting was observed to have a retroreflective
brightness of about 500 candela/lux/meter.sup.2.
Example 3
[0106] A conformable cube corner retroreflective sheeting was made
by first providing an approximately 15 mil (375 micron) thick
Scotchlite.TM. Diamond Grade retroreflective sheeting made from
polymethyl methacrylate (available from 3M company of St. Paul,
Minn.). By vapor deposition under vacuum, a specularly reflective
aluminum coating was coated on the cube corner point side of the
sheeting to an opaque thickness of about 1,200 Angstroms (0.12
micron). A 5 mil (125 micron) thick 9469PC Scotch.TM. VHB Joining
System acrylic pressure-sensitive adhesive (available from 3M
Company) was laminated to the aluminum coating using a pressure of
about 40 lb/in.sup.2 (275,700 N/m.sup.2) and covered with a 4 mil
(100 micron) thick polyethylene release liner.
[0107] This composite was then laid on a tool having a plurality of
raised protrusions in a hexagonal pattern with the planar side of
the sheeting disposed adjacent the protrusions. A rubber roller was
rolled against the outside surface of the composite at a rate of
about 88 feet/minute (27 meters/minute) to press the composite
against the protrusions at a pressure of about 90 lb/in.sup.2
(620,350 N/m.sup.2). The fractured sheeting had an average
retroreflective brightness of about 1060
candela/lux/meter.sup.2.
[0108] After heating the composite to about 150.degree. F.
(65.5.degree. C.) to soften the adhesive and polyethylene release
liner, the composite was tentered or biaxially stretched to widen
the separations. The composite was stretched in two perpendicular,
planar directions to a size about 16.5% larger than its previous
size. After cooling the composite to room temperature, the
polyethylene liner was exchanged for a silicone-coated paper
release liner. The retroreflective brightness of the tentered
sheeting was measured and found to be about 760
candela/lux/meter.sup.2.
[0109] A three mil (75 micron) thick ultraviolet radiation-curable,
conformable resin layer was then bar coated on the polymethyl
methacrylate side of the composite to substantially fill the
widened separations and continuously cover each cube corner
segment. The resin comprised 75% Ebecryl.TM. 8400, an aliphatic
urethane diacrylate, available from Radcure specialties, Inc. of
Louisville, Ky., 24% Photomer.TM. 4127, an aliphatic difunctional
acrylate, available from Henkel Corp. of Morristown, N.J., and 1%
Darocur.TM. 1173, an aromatic ketone free radical photoinitiator,
available from EM Industries, Inc. of Hawthorne, N.J. A 2 mil (50
micron) thick polyester film was laminated to the resin, and the
resin was cured through the polyester with a source of ultraviolet
radiation for 2 minutes to substantially completely cure the resin.
Upon removing the polyester film, the finished product had a
retroreflective brightness of about 650
candela/lux/meter.sup.2.
[0110] Various modifications and alterations of this invention will
become apparent to those skilled in the art without departing from
the scope and spirit of this invention.
* * * * *