Note: Descriptions are shown in the official language in which they were submitted.
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GLITTERING CUBE-CORNER RETROREFLECTIVE SHEETING
TECHMCAL FIELD
This invention pertains to a cube-corner retroreflective sheeting that
glitters
when exposed to light.
BACKGROUND
Retroreflective sheeting is characterized by its ability to reflect
substantial
Quantities of incident light back towards the light source. This unique
ability has
promoted wide-spread use of retroreflective sheetings on signs, barricades,
traffic
cones, clothing, and other items that need to be visible at nighttime.
Retroreflective
sheeting improves the conspicuity of the articles onto which the sheeting is
placed,
particularly at nighttime.
A very common retroreflective sheeting uses an array of cube-corner
elements to retroreflect light. FIGS. 1 and 2 illustrate an example of such a
retroreflective sheeting, noted generally by numeral 10. The array of cube-
corner
elements 12 project from a first or rear side of a body portion 14 that
includes a
body layer 18 (also referred to in the art as an overlay) and may also include
a land
layer 16. Light enters the cube-corner sheeting 10 through the front surface
21; it
then passes through the body portion 14 and strikes the planar faces 22 of the
cube-
corner elements 12 to return in the direction from which it came as shown by
arrow
23.
FIG. 2 shows the back side of the cube-corner elements 12, where each
cube-corner element 12 is in the shape of a trihedral prism that has three
exposed
planar faces 22. The cube-corner elements 12 in known arrays are typically
defined
by three sets of parallel v-shaped grooves 25, 26, and 27. Adjacent planar
faces 22
on adjacent cube-corner elements 12 in each groove form an external dihedral
angle
(a dihedral angle is the angle formed by two intersecting planes). This
external
dihedral angle is constant along each groove in the array. This has been the
case for
a variety of previously produced cube-corner arrays (including those disclosed
in
the patents cited in the next paragraph).
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The planar faces 22 that define each individual cube-corner element 12
generally are substantially perpendicular to one another , as in the corner of
a room.
The internal dihedral angle -- that is, the angle between the faces 22 on each
individual cube-corner element in the array -- typically is 90°. This
internal angle,
S however, can deviate slightly from 90° as is known in the art; see U.
S. Patent No.
4,775,219 to Appeldorn et al. Although the apex 24 of each cube-corner element
12 may be vertically aligned with the center of its base (see, for example,
U.S.
Patent No. 3,684,348), the apex also may be offset or canted from the center
as
disclosed in U.S. Patent No. 4,588,258 to Hoopman. Other cube-corner
configurations are disclosed in U.S. Patents 5,138,488. 4,066,331, 3,923,378,
3,541,606, and Re 29, 396.
While known cube-corner retroreflective sheetings come in a variety of
configurations that provide very effective nighttime retroreflectivity, and
hence very
effective nighttime conspicuity, known retroreflective sheetings generally
have had
somewhat limited conspicuity under daytime lighting conditions. This is
because
under daytime conditions the retroreflected light is not easily
distinguishable from
the surrounding ambient light. Thus, other measures have been taken to enhance
daytime conspicuity, including adding fluorescent dyes to the retroreflective
sheeting, -- see U.S. Patent Nos. 5,387,458 and 3,830,682. Or, as disclosed in
U.S.
Patent No. 5,272,562 to Coderre, white opaque pigment particles have been
dispersed in the front of the cube-corner elements. Although the presently
known
techniques are very effective for improving a retroreflective sheeting's
daytime
conspicuity, they possess the drawback of requiring the addition of another
ingredient namely dye or pigment, to achieve the enhanced conspicuity.
SU~M~fARY OF THE IM~ENTTON
The present invention provides a new and very different approach to
improving a retroreflective sheeting's daytime conspicuity. Rather than use a
fluorescent dye or bright pigments, as has been done in the prior art, the
present
invention enhances conspicuity by furnishing the cube-corner sheeting with a
glittering effect that can attract an onlooker's attention. In brief, the
invention is a
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retroreflective sheeting that includes an array of cube-
corner elements that are arranged in the array to make the
sheeting glitter when light is incident thereon. As
described in more detail below, the glittering effect is
noticeable in the sheeting regardless of whether a seal film
is bonded to the array of cube-corner elements.
According to one aspect of the present invention,
there is provided a glittering retroreflective sheeting that
comprises an array of cube-corner elements that have faces
of adjacent cube-corner elements arranged such that a
dihedral angle a located between adjacent faces varies to
such an extent that the sheeting glitters when light is
incident thereon, the glitter being noticeable from a front
side of the sheeting.
According to another aspect of the present
invention, there is provided a retroreflective product that
includes the retroreflective sheeting as described herein
and further comprises a seal film secured to a back side of
the array of cube-corner elements.
According to still another aspect of the present
invention, there is provided an article of clothing that
comprises the retroreflective product as described herein
secured to an outer surface thereof.
According to yet another aspect of the present
invention, there is provided a retroreflective article that
includes the retroreflective sheeting as described herein,
placed in a tubular configuration.
According to a further aspect of the present
invention, there is provided a glittering article that is
capable of retroreflecting light, which article comprises:
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(a) a base surface; and (b) a structured surface opposite
the base surface, the structured surface comprising an array
of cube-corner elements, which array is defined by three
sets of intersecting grooves, wherein each groove set
includes two or more generally parallel grooves, and at
least one groove in at least one of the sets has faces of
adjacent cube-corner elements arranged such that a dihedral
angle located between the adjacent faces varies along the at
least one groove in the set, the variance of the dihedral
angle being unassociated with the securement of a seal film
to the structured surface.
According to yet a further aspect of the present
invention, there is provided a glittering retroreflective
sheeting that comprises: a structured surface that includes
a multiplicity of discreet cube-corner elements, the cube-
corner elements each including a base surface and three
faces, the cube-corner elements being arranged such that the
base surfaces do not reside in the same plane when the
sheeting is laid flat and such that the retroreflective
sheeting glitters when light is incident thereon.
According to still a further aspect of the present
invention, there is provided a glittering article that is
capable of retroreflecting light, which article comprises:
(a) a base surface; and (b) a structured surface opposite
the base surface, wherein the structured surface comprises
an array of cube-corner elements that are randomly tilted to
such an extent that the retroreflective article glitters
when light is incident thereon, the random tilting of the
cube-corner elements being unassociated with the securement
of a seal film to the structured surface.
3a
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The terms "glitter", "glitters", or "glittering"
are used herein to mean a multiplicity of discreet regions
of light that appear as distinct points of light, each of
which may be noticed by the unaided eye of an ordinary
observer when light is incident on the sheeting, but which
points of light disappear or become unnoticeable to the eye
of the same observer when either the angle of the incident
light source to the sheeting, the angle of observation, the
sheeting's orientation, or a combination thereof are
changed. Some points of light may appear, for example,
violet in color, while others may display orange, green,
yellow or any of the other colors of the visible spectrum.
In some embodiments, the glittering effect may be
seen from both the front and back sides of the sheeting when
light strikes either the front or the back. The glittering
effect is particularly noticeable when viewed under
sunlight. The glittering effect may be seen from the front
side at observation angles of -90 degrees to +90 degrees
from an incidence angle extending normal (zero degrees) to a
flat sample. Sheetings of the invention also can glitter
when viewed from the back side -90 degrees to +90 degrees
from a normal or zero degree incidence angle. Even if the
incidence angle is offset from a line normal to the
sheeting, the glittering effect may also be noticeable at
all viewing angles. As a sample is rotated 360 degrees, the
glitter may be seen continuously. During the rotation, some
points of light disappear but others appear. This provides
a broad range of angles over which continual "blinking" on
and off of light from different cube-corners occurs,
resulting in the phenomenon of glitter. Sheetings of the
invention may be capable of glittering under essentially all
possible illumination and viewing angles, in all
combinations.
3b
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The glitter enhances the sheeting's daytime
conspicuity, and to some extent may also improve its
nighttime conspicuity. The glitter also adds aesthetic
appeal to the retroreflective sheeting and may be useful for
producing graphic images such as
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product identifiers. These advantages and others are more fully described
below in
the detailed description of the invention.
BRIEFDE.S1CRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of a prior art retroreflective sheeting 10.
FIG. 2 is a bottom view of the prior art retroreflective sheeting 10
illustrated
in FIG. 1.
FIG. 3 is an isometric view of a cube-corner element 30 that may be used in
a retroreflective sheeting of the invention.
FIG. 4 is a bottom view of a retroreflective sheeting 60 in accordance with
the present invention.
FIG. 5 is a sectional view of retroreflective sheeting 60 taken along lines S-
5
of FIG. 4
FIG. 6 is a bottom view of retroreflective sheeting 60, illustrating apex and
groove intersection heights from a reference plane.
FIG. 7 is a sectional view of retroreflective sheeting 60 taken along lines 7-
7
of FIG. 5.
FIG. 8 is a sectional view of a retroreflective product 61 in accordance with
the present invention having a seal film 63 secured to the backside of the
retroreflective sheeting 60.
FIG. 9 is a front view of retroreflective product 61 illustrating a seal
pattern
that may be used to produce henmetically-sealed chambers 65 (FIG. 8) behind
the
cube-corner elements 30 (FIG. 8).
FIG. 10 illustrates a safety vest 69 that has glittering retroreflective
products
61 of the present invention placed on its outer surface 70.
FIG. 11 is a schematic view of how a glittering retroreflective sheeting can
be made in accordance with the present invention by exposing a retroreflective
sheeting 10 to heat and/or pressure in a laminating apparatus 71.
FIG. 12 is a schematic view of an alternative method of exposing a
retroreflective sheeting 10 to heat and/or pressure to produce a glittering
retroreflective sheeting 60 in accordance with the present invention.
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FIG. 13 is a top view of a mold 79 that may be used to produce a glittering
retroreflective sheeting in accordance with the present invention.
FIG. 14 is a schematic view of a second technique for making a
retroreflective sheeting 60 in accordance with the present invention by
casting the
S sheeting from a mold 79.
FIG. 1 S is a front view of an imaged retroreflective sheeting 101 that has
glittering and non-glittering regions 102 and 103, respectively.
FIG. 16a is a side view of an insert 104a that may be used to produce an
image in a glittering sheeting.
FIG. 16b is a side view of an insert 104b that may be used to produce an
image in a glittering sheeting.
DETAILED DESCRIPTION OF T~IEPREFERRED EMBODIMENTS
In the practice of the present invention, a retroreflective sheeting is
provided
1 S that can exhibit a glittering effect under daytime lighting conditions as
well as under
nighttime or retroreflective lighting conditions (although not to as
noticeable an
extent). The glittering effect can provide the sheeting with good daytime
brightness
or lightness as measured by a standardized test, ASTM E 1349-90, where
lightness
is expressed by the Luminance Factor Y (I,FY). Clear, colorless sheetings of
the
invention may demonstrate a LFY value of 38 or greater, and even SS or
greater.
Of course, LFY values may differ depending on the color of the glittering
sheeting.
Further, the LFY value may be higher depending on the degree of texture or
pattern
present in the glittering sheeting. The measurement geometry imposed by
ASTM E 1349-90 (0/45° or 45/0°) excludes detection of
substantial portions of the
lightness due to glittering because the glittering sheetings reflect large
amounts of
light at angles that are not detected. The sheeting may display at least about
10,
and preferably at least about S0, points of light per square centimeter (cmZ)
when
the sheeting is viewed under direct sunlight. Typically, there are less than
about
2S0 points of light per cm2 when viewed under direct sunlight. . The glitter
is
achieved not through incorporating metal particles or flakes in a sheeting or
a coating as
is commonly done in the glittering art -- see, e.g., U.S. Patents 5,470,0S8,
5,362,374,
5,276,075, 5,202,180, 3,988,494, 3,987,229, 3,697070, 3,692,731, and 3,010,845
--
S
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but instead is achieved through an entirely different and new approach,
namely, by
orienting cube-corner elements in a new geometric arrangement.
In a preferred embodiment of this new geometric arrangement, at least one
set of parallel grooves in an array of cube-corner elements has faces of
adjacent
cube-corner elements arranged such that the external dihedral angle formed
between
the faces varies along at least one groove in the set.
In another preferred embodiment, the external dihedral angle between faces
of adjacent cubes varies in all grooves to such an extent that the cubes are
randomly
tilted across the array. What is meant by "randomly tilted" is that the cubes
in the
sheeting are tilted in a nonrepeating pattern relative to a reference plane
that can be
the front surface of the retroreflective sheeting when said flat. A cube is
considered
"tilted" when its optical axis is not perpendicular to the reference plane.
The
"optical axis" is customarily understood as being the internal line that
extends from
the cube apex and forms equal angles with each cube edge that extends from the
apex. In other words, the optical axis is the line defined by the intersection
of three
planes that each bisect one of the three internal dihedral angles formed by
the cube-
corner element's three planar faces. All previously known retroreflective
sheetings
have had the cube-corner elements arranged in a predetermined repeating
pattern
throughout the array. If a known cube-corner sheeting is thought of as an army
that
marches in cadence in strict formation, a randomly-oriented sheeting would be
a
drunken army where each cube-corner element represents individual soldiers
that
stagger and possibly bump into each other as they march.
FIG. 3 illustrates a cube-corner element 30 that is useful in retroreflective
sheetings of the invention (60, FIG. 4) as well as in sheetings of the prior
art {10,
FIG. 1). As shown, a cube-corner element 30 is a body that has three mutually
perpendicular faces 31a, 31b, and 31c that meet at the element's apex 34. The
cube-corner element's base edges 35 are generally linear and generally lie in
a single
plane that defines the base plane 36 of the element 30. Cube-corner element 30
also
has a central or optical axis 37, which is the tri-sector of the internal
angles defined
by lateral faces 31a, 31b, and 31c. The optical axis may be disposed
perpendicular
to the base plane 36, or it may be canted as described in U.S. Patent No.
4,588,258
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to Hoopman and U.S. Patent No. 5,138,488 to Szczech. Retroreflection can occur
when light incident on base plane 36 is internally reflected from a first
lateral face
31a to a second face 31b, and then to a third face 31c, and then back through
base
36 toward the light source. In addition to defining a single cube-corner by a
three-
s sided pyramid having a triangular base plane such as disclosed in the
Hoopman
patent, the cube-corner elements may be defined by a rectangular base, two
rectangular sides, and two triangular sides such that each structure has two
cube
corners each such as disclosed in U.S. Patent No. 4,938,563 to Nelson et aL,
or
may be of essentially any other cube-corner shape (see also U.S. Patent No.
4,895,428 to Nelson et a1.).
FIG. 4 shows the stnlctured surface or backside of a cube-corner sheeting
60, that includes a unitary or single layer of an array of cube-corner
elements 30,
like the element depicted in FIG. 3. Each cube-corner element 30 meets, but is
not
necessarily connected to, an adjacent cube-corner element at a base edge 35.
The
array includes three sets of generally parallel grooves 45, 46, and 47. The
external
dihedral angles (a, FIG. 5) between faces 31 of adjacent cube-corner elements
30
vary along the grooves 45-47 in the array. The cube-corner elements in the
array
are randomly tilted, and because of this, the apex 34 of one cube, such as
cube 30a
may be relatively close to another apex such as cube 30b, but cube 30b's apex
may
then be farther away from another adjacent apex such as the apex of cube 30c.
FIG. 5 also illustrates the position of one cube apex relative to another and
additionally shows how the cube's base edges 35 do not lie in the same common
plane. The base edge 35 of one cube may be disposed closer to or farther away
from the front surface 51 of retroreflective sheeting 60 than the base edges
of other
adjacent cube-corner elements. And in a single cube, points on one of its base
edges 35 may be located closer to or farther away from front surface 51 than
points
on another base edge 35 in the same cube. Base edges 35 define the lowest
point
of grooves 45-47 -- and because edges 35 do not all Iie in the same plane, the
grooves have a varying pitch along their length. If the cube-corner sheeting
possesses a land layer 56, it too is also not uniformly spaced from the front
surface
51. When the cube-corner elements are tilted, the base planes 36 (FIG. 3) of
each
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cube-corner element are not parallel, and they do not reside in the same
plane.
Many of the base planes also do not reside in the same plane as the front
surface 51
-- that is, the base planes are not parallel to the sheeting's front surface
51 when the
sheeting is laid flat on a surface.
Cube-corner element sheetings have been produced where some of the
element's base planes do not reside parallel to the sheeting's front surface
when the
sheeting is laid flat. Such sheetings, however, have had the array of cube-
corner
elements disturbed or rearranged in certain areas by sealing a film to the
backside of
the array (such as discussed below with reference to FIGS. 8 and 9) or by
creating
bubbles (11.S. Patent 5,485,311 to McAllister). The seal line and the bubbles
upset
the sheeting's front surface and the orientation of the cube-corner elements
in the
array. ror purposes ot-this invention, therefore, a sheeting is not considered
to be
"laid flat" in those areas where the sheeting is disturbed by seal lines (item
64 FIGS.
8 and 9) or bubbles (24 of the '311 patent). The base planes 36 (FIG. 3) in
sheetings of the invention may be offset at angles of zero to 90 degrees from
the
reference plane or front surface when the sheeting is laid flat. The base
planes that
are tilted relative to the front surface of the sheeting when laid flat
typically form an
angle of about 1 to 10 degrees from the front surface.
FIG. 5 also shows the external dihedral angle, oc, that defines the angle
between faces 31 (FIG. 4) of adjacent cube-corner elements 30. Angle a, may
vary
along some or all grooves in a single generally parallel groove set, it may
vary along
some or all grooves in two generally parallel groove sets, or it may vary
along some
or all grooves in all three generally parallel groove sets in the array. In an
array of
randomly tilted cube-corner elements, angle a varies randomly amongst adjacent
faces of adjacent cube-comer elements throughout essentially the whole array
that
is intended to glitter. Angle ac may vary from zero degrees to 180 degrees,
but on
average ranges from about 35 to 115 degrees for dihedral angles between faces
of
adjacent cubes.
FIG. 6 illustrates some typical distances of apexes 34 and goove
intersections from the sheeting's front surface 51 (FIG. 5). The cube-corner
element in the upper left hand corner of the array has an apex that is spaced
3 50
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micrometers from the front surface 51. The fourth cube over from the upper
left-
hand corner, however, has an apex height of 335 micrometers. There is thus a
difference in apex height of 15 micrometers between cubes that are fairly
close to
one another. The cube-corner elements typically have an average height of
about
20 to 500 micrometers, more typically of about 60 to 200 micrometers. For cube-
corner elements that are about 60 to 200 micrometers high, the variation in
height
between adjacent apexes typically is about 0 to 60 micrometers and typically
is
about 1 to 40 micrometers on average, more typically 5 to 25 micrometers on
average, but preferably does not exceed more than 50 micrometers on average.
The
variation in height between adjacent groove intersections for such cubes
typically is
about 0 to 100 micrometers and typically is about 3 to 50 micrometers on
average,
but preferably does not exceed more than 60 micrometers on average. For
purposes of this description, the "base valleys" are defined as the
intersecting points
of the v-shaped grooves in the cube-corner array.
The body layer 58 (FIG. S) in body portion 54 (FIG. 5) typically has an
average thickness of approximately 20 to 1200 micrometers, and preferably is
about
50 to 400 micrometers. The optional land layer 56 (FIG. 5) preferably is kept
to a
minimal thickness of 0 to less than about 100 micrometers.
In the cube-corner element array shown in FIGs. 4-6, the groove sets 45,
46, and 47 are illustrated as being parallel. It is within the scope of this
invention,
however, for grooves of the same set to be other than parallel. Some grooves
may ,
be parallel and others may not. Some grooves may run parallel to adjacent
grooves
of the same groove set in some regions of the sheeting but may also cross
paths or
overlap those same grooves. In such instances, the cube-corner elements may
pile
up on each other. As long as there are two or more grooves that extend in the
same
general direction roughly parallel to each other, those grooves are viewed as
being
"generally parallel" regardless of whether the grooves at some other point
cross
paths, overlap, converge, or diverge.
FIG. 7 shows cube-corner elements intersected by a plane that is parallel to
the retroreflective sheeting's front surface 51 (FIG. 5). As illustrated, the
plane
intersects the cube-corner elements to produce triangles 62 of different cross
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sectional areas. Some cubes may be tilted to such an extent that the
intersecting
plane only passes through a tip of the cube, resulting in a small triangular
cross-
section -- whereas, a cube that stands upright may be intersected such that
the
triangle resulting from the cross-section is relatively large. Thus, even
though the
cube-corner elements in the array may be of similar size, they can produce
triangles
of random sizes when intersected as described because of the manner in which
the
cubes are tilted with respect to a reference plane.
FIG. 8 shows a retroreflective product 61 that has a seal film 63 disposed
over the backside of cube-corner elements 30. The seal film is bonded to the
body
layer 58 of the sheeting 60 through the layer of cube-corner elements 30 by a
plurality of seal Iines 64. The bonding pattern produces a plurality of
hermetically-
sealed chambers 65 that maintain a cube/air interface and prevent moisture and
dirt
from contacting the backside of the cube-corner elements. Maintenance of the
cube/air interface is necessary to prevent loss of retroreflectivity.
The seal film may be bonded to the retroreflective sheeting using known
techniques; see for example, U.S. Patent 4,025,159. Sealing technique examples
include radio frequency welding, thermal fusion, ultrasonic welding, and
adhesive
bonding. When applying a seal film to the backside of a retroreflective
sheeting,
considerable attention must be paid to the composition and physical properties
of
the seal film. The seal film must be able to bond securely to the sheeting,
and it
should not contain components that could adversely affect retroreflectivity or
the
appearance of the retroreflected product. For example, the seal film should
not
contain components that could leach out (e.g., dyes) to contact the backside
of the
cube-corner elements. The seal film typically comprises a thermoplastic
material
because such materials lend themselves to fusing through relatively simple and
commonly available thermotechniques.
Radio frequency ("RF") welding accomplishes sealing using radio
frequency energy that heats the polymer. When a radio frequency field is
applied to
a thermoplastic polymer with polar goups, the tendency of the polar groups to
switch orientation with the radio frequency determines the degee to which RF
energy is absorbed and converted to kinetic motion. The kinetic energy is
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conducted as heat to the entire polymer molecule, and if enough RF energy is
applied, the polymer will heat sufficiently to soften. Detailed discussions of
RF
welding may be found in U.S. Patent No. 5,691,846 and in the article, "RF
Welding
and PVC and Other Thermoplastic Compounds" by J. Leighton, T. Brantley, and
E. Szabo in ANTEC 1992, pp. 724-728.
A seal film also may be secured to the reuorefleaive sheewtg through
thermal fusion which involves pressing thermoplastic materials together
between
heated dies or platen surfaces. The contact forms the desired sealing pattern.
While the heated die or platen surfaces press the thermoplastic materials
together,
the polymer areas that are in contact melt and the polymer molecules flow
together
while hot and form a fusion bond on cooling.
An alternative to radio frequency welding and thermal fusion methods is
uluasonic welding. Ultrasonic welding is a technique where two materials are
bonded together between a horn and an anvil. The horn vibrates at ultrasonic
frequencies, commonly in the range of about 20,000 - 40,000 Hz. Pressure is
applied to the cube-corner sheeting and the seal film, and the vibrational
energy is
dissipated as heat. The frictional heating softens the polymer molecules to
create a
fusion bond between the sheeting and the film. The horn and anvil art
positioned to
localise heat in the area where the bond is intended. Heat localization
assures
softening and melting of the bonding materials in very small regions which in
turn,
helps minimize damage to the surrounding material from heat exposure.
Amorphous materials. that have broad softening ranges may be ultrasonically
bonded better than crystalline materials because the former tend to dissipate
frictional heat mote effectively. Examples of materials that form good-to-
exceUent
ultrasonically welded bonds include nylon, polycarbonate, plasticized
polyvinyl
chloride) (PVC), polystyrene, thermoplastic polyester, polypropylene, and
acrylics.
Polyethylene and fluoropolymers art examples of materials that form fair to
poor
uhrasonic welds.
Ultrasonic welding is sensitive to other factors including plastic variation
from batch to batch, molding parameter changes, moisture absorption, mold
release,
lubricants, fillers, regrind, flame retardarrts; pigments, and plasticsztrs.
Reference is
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made to the following articles: "Heating and Bonding Mechanisms in Ultrasonic
Welding of Thermoplastics" by M.N. Tolunay, P.R. Dawson, and K.K. Wang in
Polymer Engineering and Science, September 1983, Vol. 23, No. 13, p. 726;
"Update on Welding: More Science, Less Art" by M. Rogers in Plastics
Technology, June 1981, pp. 56-62; "Ultrasonic Welding" in Engineering
Materials
and Design, April 1981, pp. 31-34.
Adhesive bonding can be achieved by coating an adhesive onto a cube-
corner sheeting's backside and then bringing the seal film into contact with
the
adhesive coated sheeting. Alternatively, the seal film may be coated with an
adhesive before bonding to the cube-corner sheeting. Adhesive coating may be
done in essentially any desired pattern such that the areas not coated with
adhesive
form retroreflective cells 65 as shown in FIG. 8. The adhesive also may be
coated
over a reflective coating that is disposed on the back side of the cube-corner
sheeting. See U.S. Patent 5,376,431 to Rowland for a description of adhesive
bonding.
When the glittering sheeting is sealed piecewise, the radio frequency
technique is preferred because the process is generally practiced as a "step
and
repeat process" that is compatible with seating individual items. When the
glittering
sheeting is sealed continuously from roll goods, ultrasonic welding is
preferred
because this process can be easily practiced as a continuous method.
FIG. 9 illustrates an example of a seal pattern that may be used to produce a
retroreflective product 61. As shown, retroreflective product 61 is in the
form of a
strip that has a length dimension that substantially exceeds the width
dimension.
Bond Lines 64a and 64b are disposed along the lengthwise edges of sheeting 61
to
prevent delamination of seal film 63 (FIG. 8). Disposed laterally inward from
bond
lines 64a and 64b are bond lines 64c and 64d that run parallel to bond lines
64a and
64b. Extending between bond lines 64c and ~~d are bond lines 64e that are not
parallel to the sheeting's Lengthwise edges. B~ .d lines 64c-64e define a
number of
completely enclosed geometric patterns 67 that define the hermetically sealed
chambers 65 shown in FIG. 8. The surface area of the geometric patterns 67 may
12
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vary depending, for example, on the width of product 61 but typically are
about 0.5
to 30 cm2, more typically about 1 to 20 cm2.
Retroreflective product 61 typically comes in sizes ranging from one-half
inch (1.27 cm) to three inches (7.6 cm) wide. Typical widths are one-half inch
(1.27 cm) wide, three-quarters of an inch {1.9 cm) wide, one inch (2.54 cm)
wide,
one and three eighths inches (3.5 cm) wide, one and one-half inches (3.81 cm)
wide,
two inches (5.08 cm) wide, or two and three fourths inches (7.0 cm) wide.
Lengths
of product 61 may typically be as large as about 100 meters, with the product
being
supplied in roll form.
Panels of retroreflective products that have seat films disposed thereon also
may be produced. Panel sizes may be, for example, 200 cm2 to 1000 cm2. The
whole area within the panel, or certain selected areas, within it, may
glitter.
In a typical retroreflective product 61, essentially the whole area within the
enclosed geometric pattern displays the glittering effect, where each point of
light is
referenced by number 68. If desired, some geometric patterns may display the
glittering effect while others do not. For example, it may be possible to have
the
triangular patterns 67 alternate between glittering and non-glittering. It may
also be
possible to provide glittering portions or images within each geometric
pattern as
described below in detail. Although the glittering effect typically would not
be
noticeable, or significantly noticeable, within each seal line because the
cube-corner
elements typically become engulfed in the seal line, the glittering effect is
very
noticeable "substantially beyond" the seal line(s). That is, the glittering
effect may
be noticed at a distance beyond where heat and/or pressure from the sealing
operation would affect the cube-corner elements in the array. Typically, a
sealing
operation that used heat and/or pressure would not affect the cube-corner
elements
at a distance greater than two millimeters (mm), and more typically at 5 mm or
more from a seal line. Sheetings of the invention are capable of glittering
across an
array of cube-corner elements regardless of whether a seal film is bonded to
the
backside of the cube-corner element array.
In lieu of (or possibly in addition to) a seal film 63, a reflective coating
such
as a specularIy reflective metallic coating can be placed on the backside of
the cube-
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WO 97/41465 PCT/US97/05594
corner elements to promote retroreflection; see, for example, U. S. Patents
5,272,562 to Coderre and 5,376,431 to Rowland and in WO 93/14422. The
metallic coating may be applied by known techniques such as vapor depositing
or
chemically depositing a metal such as aluminum, copper, silver, or nickel.
Instead
of a metallic coating, a layer of dielectric material may be applied to the
back side of
the cube-corner elements, see, for example, U.S. Patents 4,763,985 and
3,700,305
to Bingham.
Although placing a metal coating on the backside of the cube-corner
elements can reduce the sheeting's daytime lightness, the glittering effect
can
counter this reduction. Metal coated glittering samples may demonstrate LFY
lightness values of at least 10, and even greater than 25.
FIG. 10 illustrates an example of an article of clothing onto which a
retroreflective product 61 of the invention may be disposed. The article of
clothing
may be a safety vest 69 that has glittering retroreflective products 61
secured to its
outer surface 70. Other vests that may display retroreflective products of the
invention are shown, for example, in U.S. Patents 5,478,628, Des. 281,028, and
Des. 277,808. Examples of other articles of clothing onto which the
retroreflective
products of the invention may be applied include shirts, sweaters, jackets,
coats,
pants, shoes, socks, gloves, belts, hats, suits, one-piece body garments,
bags,
backpacks, helmets, etc. The term "article of clothing" thus, as used here,
means
any article sized and configured to be worn or carried by a person and is
capable of
displaying a retroreflective article on its outer surface.
The inventive glittering cube-corner sheetings can be made in accordance
with two techniques. in the first technique, a glittering cube-corner
retroreflective
sheeting is made by providing a first cube-corner sheeting that has the cubes
arranged in a conventional configuration, namely, a non-random orientation,
and
exposing this sheeting to heat, pressure, or a combination of both. In the
second
technique, a mold is produced that is a negative of a cube-corner sheeting of
the
invention. This mold may then be used to provide glittering retroreflective
sheetings. A method of making glittering retroreflective sheetings is
described in
14
. CA 02252433 2005-04-15
60557-5972
U.S. Patent No. 5,770,124.
When using the first technique, 8 retroreflective sheeting is first produced
or
otherwise obtained which. has the cube-corner elaneMs arranged in an ordered
S configuration. There are many patents that disclose retroreflective
sheeting= that
have ordered array: of cube-corns elements: see, for example, U S. Patents
5,236,751, 5,189,553, 5,175,030, 5,138,488, 5,117,304, 4,938,563, 4,775,219,
4,668,558, 4,601,861, 4,588,258, 4,576,850, 4,555,161, 4,332,847, 4,202,600,
3,992,080, 3,935,359, 3,934,929, 3,811,983, 3,810,804, 3,68946, 3,684,348, and
3,450,459. Ordered cube-corner arrays may be produced according to a numbs of
known methods, including those disclosed in the patents cited in the prtvio~
sentence. Other examples are disclosed is U.S. patents: 5,450,233, 4,601,861,
4,486,363, 4,322,847, 4,243,618, 3,811,983, 3,689,346, and 5, 691, 896.
IS Preferably, the cube-corner elements that are used in the non-randomly
oriemed staring sheeting are made from materials that are harder than the
materials
used in the body portion, particularly the body lays. A selection of such
materials
allows the cube-corner elements to tOt, without significantly distorting each
cube's
shape, when the sheeting is exposed to certain amounts of heat andlor
pressers.
The heat, pressure, or both that are applied to the sheeting should be
sufficient to
alter the array significantly from its ordered configuration. With a very soft
body
layer, pressure alone, that is, pressure above atmospheric, or heat alone,
namely,
heat pester than the softening temperature may be sufficient to change the
array
from an ordered con5guration.
A cube-corner retroretlective sheeting that has hard cubes and a soflet body
layer is disclosed in U.S. Patent No. 5,450,?35 to Smith et al. As descnbed in
this
patent, the body portion includes a body layer that contains a light
transmissible
polymeric material that has, an elastic modules less than 7 x 10~ pascals. The
wb~.
corner elements, on the other hand, contain s light transnusstble polymeric
material
that has an elastic modules greater than 16 x 10' pascalt. U.S. Pate~rt
No. 5,691,846 also discloses a number of materials that may be used to
CA 02252433 1998-10-20
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produce cube-corner sheetings in accordance with this invention. This patent
application specifies that the elastic modulus of the cube-corner elements is
at least
1 x 10' Pascals greater than the elastic modulus of the body layer and that
its cube-
corner elements may be made from materials that have an elastic modulus
greater
than about 2.0 x 10$ pascals (preferably greater than about 25 x 10g pascals)
and
that the body layer or overlay may be made from materials that preferably have
an
elastic modulus less than about 13 x 108 pascals. When a cube-corner sheeting
made from materials of those designated elastic modulus values is exposed to
certain amounts of heat and pressure, the body layer softens, allowing the
cubes to
move in response to the pressure and thus become tilted relative to the
sheeting's
front surface. When using such a construction, the land layer (56, FIG. 7)
ideally is
kept to a minimal thickness (for example, less than ten percent of the cube-
corner
element height), and preferably zero thickness, so that the cubes can easily
tilt along
their base edges. For this same reason, it is also preferred in this invention
that the
cube-corner elements are fractured along their base edges as disclosed in U.S.
Patent Application Serial No. 08/139,914 filed October 20, 1993 and in U.S.
Patent
Application Serial No. 08/472,444 filed June 7, 1995.
Elastic modulus may be determined according to standardized test
ASTM D 882-75b using Static Weighing Method A with a five inch initial grip
separation, a one inch sample width, and an inch per minute rate of grip
separator.
Under some circumstances, the polymer may be so hard and brittle that it is
difficult
to use this test to ascertain the modulus value precisely (although it would
be
readily known that it is greater than a certain value). If the ASTM method is
not
entirely suitable, another test, known as the "Nanoindentatlon Technique" may
be
employed. This test may be carried out using a microindentation device such as
a
UMIS 2000 available from CSIRO Division of Applied Physics Institute of
Industrial Technologies of Lindfield, New South Wales, Australia. Using this
kind
of device, penetration depth of a Berkovich pyramidal diamond indenter having
a 65
degree included cone angle is measured as a fi~nction of the applied force up
to the
maximum load. After the maximum load has been applied, the material is allowed
to relax in an elastic manner against the indenter. It is usually assumed that
the
16
~ CA 02252433 2005-04-15
60557-5972
gadient of the upper portion of the unloading data is found to be linearly
proportional to force. Sneddon's analysis provides a relationship between the
indenting force and plastic and elastic components of the penetration depth
(Sneddon LN. Ins J. Eng. Sci. 3, pp. 47-57 (1965)). From an examination of
Sneddon's equation, the elastic modulus may be recovered in the form FJ(1-~.
The calculation uses the equation:
FJ(1-~ _ (dF/dh~)F~1/(3.3h~tan(6))
where:
v is Poisson's ratio of the sample being tested;
(dF/dh~) is the gadient of the upper part of the unloading curve;
F~ is the maximum applied force;
h~ is the maximum plastic penetration depth;
8 is the half included cone angle of the Herkovich pyramidal indenter, and
E is the elastic modulus.
It may be necessary to correlate the results of the nanoindentation technique
back to
the ASTM method.
FIG. 11 illustrates how to prepare a glittering cube-corner sheeting using
heat and/or pressure in a batchwise process. Using this technique, a cube-
corner
retroreflective sheeting that contains an ordered array of cube-corner
elements such
as sheeting 10 may be placed in a platen press or laminator 71 that includes
5rst and
second pressure-appl~~ng surfaces 72 and 74. The laminator may be, for
example, a
I-Ftx model I'T-800 heat transfer machine available from Ntx Corporation of
Pittsburg, Kansas.
A Hix N-800 laminator has a first pressure-applying surface ?2 that is made
of metal and that may be heated to temperatures as high as 500 °F. The
second
pressure-applying surface 74 is an unheated rubber mat. In operation, two
layers of
release paper 76 may optionally be disposed between the surfaces 72 and 74 and
the
cube-corner sheeting 10. A carrier 78 (such as made from polyester) may be
disposed on the cube-corner sheeting's front surface 51. Carrier 78 is a
byproduct
of the process used to produce sheeting 10 (see, _ for example, U.S. Patent
No. 5,691,846 at the discussion describing its FIG. 4, where the carrier is
17
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WO 97141465 PCT/US97/05594
represented by numeral 28) and may optionally remain thereon until after the
cube-
corner elements have been rearranged from exposure to heat and/or pressure.
When the ordered, non-glittering cube-corner sheeting and optional release
paper 76 are arranged in the heat lamination machine as shown in FIG. 11, the
machine is activated so that the pressure-applying surfaces 72 and 74 move
toward
each other and hold the ordered cube-corner sheeting at a desired temperature
and
pressure for a predetermined time. If desired, the lower release paper 76 in
FIG. 11
may be omitted, and the pattern or image of the lower, unheated surface 74 of
the
heat laminating machine may be transferred to the retroreflective sheeting in
a
glittering pattern. In Lieu of a laminating machine, a vacuum former -- such
as a
ScotchIiteTM Heat Lamp Applicator available from Dayco Industries, Inc.,
Miles,
llnchigan; P.M. Black Co., Stillwater, Minnesota; and Converting Technologies,
Inc., Goodard, Kansas -- may be used.
The amount of heat and/or pressure applied to a cube-corner sheeting 10
may vary depending on the materials from which the cube-corner sheeting is
made.
It has been discovered in this invention that when polymeric materials having
an
elastic modulus of about 10 x 108 to 25 x 108 are used in the cube-corner
elements
12 (and an optional land layer 16), and a polymeric material having an elastic
modulus of about 0.05 x 108 to 13 x 108 pascals is used in the body layer 18,
the
cube-corner sheeting, preferably, is heated to a temperature of about 300 to
400 °F
(150 to 205 °C) and that about 7 x 104 to 4.5 x 145 pascals (10 to 60
psi) of
pressure are applied to the article. More particularly, when cube-corner
elements
are employed that are made from 1,6-hexanediol diacrylate, trimethylolpropane
triacrylate, bisphenol A epoxy diacrylate in a ratio of 25 parts to 50 parts
to 25
parts, respectively, and containing one weight percent (based on resin weight)
of
DarocurTM 4265 photoinitiator (Ciba Geigy) and having an elastic modulus of
about
16 x 108 to 20 x 108 pascals, and the body layer is made from a plasticized
polyvinyl chloride) film having an elastic modulus of around 0.2 x 108 to 1 x
108
pascals, the cube-corner sheeting preferably is exposed to temperatures of
about
320 to 348 °F (i60 to 175 °C) and pressures of about 1.4 x 103
to 2.8 x lOs pascals
(20 to 40 psi). Using polymers that have a relatively high elastic modulus,
for
18
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WO 97/41465 PCT/(TS97/05594
example, greater than 16 x 108 pascals, the geometry of each cube, namely, its
internal dihedral angles, are generally maintained to within a couple of
degrees.
In FIG. 12, a continuous method is shown for applying heat and/or pressure
to a retroreflective sheeting 10 to produce a glittering sheeting 60. In this
method,
the retroreflective sheeting 10, having the optional carrier film 78 disposed
thereon,
is fed through the nip formed by rolls 77 and 7T. As shown, cube-corner
elements
12 are in a non-random, ordered configuration before being exposed to the heat
and/or pressure from rolls 77 and 7T, but after exiting the rolls they are
randomly
tilted, and the dihedral angles fonmed between adjacent cube-corner elements
vary
i0 along each groove in the array. The base planes of each cube-corner element
also
do not reside in the same general plane. The sheeting 60 that exits the roils
is
capable of producing a glittering effect, whereas the cube-corner sheeting 10
that
has not been exposed to suff cient amounts of heat and/or pressure is
incapable of
producing such an effect. The amounts of heat and/or pressure that may be used
in
this continuous method are similar to those used in the batchwise method for
similar
starting materials. When using heat, either or both rolls 77 and 7T may be
heated
to the temperature sufficient to alter the cube configuration.
In the second technique for producing a glittering cube-corner
retroreflective sheeting, a mold may be used that is a negative of a
glittering cube
corner sheeting. Such a mold may be made from a glittering cube-corner
retroreflective sheeting that is produced by the first technique described
above.
That is, the structured surface or backside of an array of, for example,
randomly-
tilted cube-corner elements can be used as a pattern to produce the mold. This
can
be accomplished, for example, by depositing suitable mold materials) onto the
back
ZS side of an array of randomly tilted cube-corner elements and allowing the
mold
materials) to harden in place. The randomly tilted cube-corner sheeting that
is used
as the pattern may then be separated from the newly formed mold. The mold is
then capable of producing cube-corner sheetings that glitter.
As an alternate method of producing a mold, a diamond tool may be used to
fashion the array of cube-corner elements. This may be accomplished by, for
example, using a number of diamond cutting tools, each tool being able to cut
the
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groove which forms one of the desired dihedral angles between adjacent cube-
corner elements. Groove depth and angle between adjacent cube-corner element
faces in any single groove is determined by the profile of the diamond cutting
tool
that is used to cut the mold material.
To prepare a mold having cube-corner elements with varying dihedral angles
between faces of adjacent cube-corner elements along the groove, it is
necessary to
position a diamond cutting tool capable of cutting the first desired dihedral
angle,
insert it into the mold material and cut the groove portion that extends from
one
groove intersection to the adjacent groove intersection. The tool is then
removed
from the mold material, and the diamond cutting tool is replaced by a tool
that is
capable of cutting the next desired dihedral angle along the groove. The newly
selected tool is then positioned in the growing groove as close as possible to
the
location where the first cutting tool finished cutting. Cutting the groove is
then
continued with the second cutting tool until the next groove intersection is
reached.
1 S The second cutting tool is then removed from the mold material and
replaced with a
cutting tool capable of cutting the third desired dihedral angle in
preparation for
cutting the next groove portion. This process is continued for the length of
the
groove. After completion of the first groove, the next or adjacent groove may
be
cut in the same manner using various cutting tools and incremental cuts until
the
desired number of parallel, or generally parallel, grooves have been
completed.
After the first set of grooves is complete, the diamond cutting tool is
adjusted so that the second set of parallel grooves may be cut such that they
intersect with the first set and contain varying dihedral angles between
adjacent
cube-corner faces. This process is continued until the desired number of sets
of
generally parallel grooves are cut into the mold material.
A mold also may be produced using pin bundling techniques. Molds
manufactured using pin bundling are made by assembling together individual
pins
that each have an end portion shaped with features of a cube-corner
retroreflective
element. U.S. Patent No. 3,632,695 to Howell and U.S. Patent No. 3,926,402 to
Heenan et al. disclose illustrative examples of pin bundling. A plurality of
pins are
typically fashioned to have an optically active surface on one end disposed at
an
CA 02252433 2005-04-15
60557-5972
oblique angle to the longitudinal axis of the pin. The pins are bundled
together to
form a mold having a structured surface in which the optical surfaces combine
to
form the cube-corner elements. The mold may be used to form retroreflective
sheeting or to generate other molds useful in manufacturing cube-corner
sheeting.
Pins may be arranged such that the dihedral angle between optical faces of
adjacent
cube-corner elements vary. One advantage associated with pin bundling
techniques
is that the d~edral angle may be varied in a single groove set, or in two or
more
groove sets. The pins also can be configured such that there are no generally
parallel grooves and/or such that the cube-corner elements do not possess base
planes that are parallel to one another when the resulting sheeting is laid
flat. Pin
bundling thus can provide additional flexibility in producing glittering
retroreflective
sheeting.
FIG. 13 illustrates a mold 79 that is a negative of an array of cube-corner
elements that comprise a glittering retroreflective sheeting. The mold (also
referred
to in the art as a tool) therefore may possess three sets of generally
parallel
v-shaped gooves 85, 86, and 87, and the planar faces 81 of adjacent cube-
corner
elements 80 can form dihedral angles that vary in dimension along each groove
in
the mold's array. For example, in goove 86a, faces 81a and 81b of adjacent
cubes
80a and 80b form a tighter dihedral angle a (FIG. 5) than faces 81c and 81d of
cubes 80c and 80d. The mold may be essentially the same as the array of cube-
corner elements of the invention with the exception of being a negative
thereof and
since it may not need to transmit light or be conformable, it may be made from
an
opaque material that is relatively inflexible, for example, metal. A mold
useful for
producing gliriering retrore~lective sheetings of the invention is described
in
U.S. Patent No. 5,814,355.
FIG. 14 schematically shows how a structured article that is capable of
glittering and retroreflecting light may be formed from a mold 79 that is
adapted to
continuously produce glittering sheeting 60. The method includes an apparatus,
shown generally as 90, for casting and curing composite sheeting 60. As shown,
body layer 58 is drawn from a roll 92 to a nip roller 93 such as a rubber
coated
21
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60557-5972
roller. At roller 93, the body layer 58 contacts a suitable resin formulation
94
previously applied to an endless patterned mold 79 on a roll 95 (or other
suitable
endless carrier that forms a loop, e.g. a belt) through a coating die 96. The
excess
resin 94 extending above the cube-corner elements 80 may be minimized by
setting
nip roller 93 to a width setting that is effectively less than the height of
the cube-
corner forming elements of mold 79. In this fashion, mechanical forces at the
interface between nip mDer 93 and mold 79 ensure that a minimum amount of
resin
94 extends above the mold elements 80. Depending on its flexibility, the body
layer
58 may be optionally supported with a suitable carrier film 78 that provides
structural and mechanical integrity to the body layer 58 during casting and
curing,
and which is stripped from the body layer 58 after the sheeting is removed
from the
mold 79 at roll 98. Use of a carrier film 78 is preferred for low modulus body
layers 58.
The method shown in FIG. 14 may be altered such that the resin 94 is
applied to the body layer 58 first rather than being first deposited on the
mold 79.
This embodiment for a continuous process is discussed in U.S. Patent No.
5,691,846
with reference to its figure 5.
As shown in FIG. 14, the resin composition that forms the array of cube-
corner elements can be cured in one or more steps. Radiation sources 99 expose
the resin to actinic radiation, such as ultraviolet light or visible light,
depending
upon the nature of the resin, in a primary curing step. The actinic radiation
from
source 99 irradiates the resin through the layer 58 -- thus imposing a
requirement
that the body layer 58 transmit radiation to allow curing to occur.
Alternatively,
curing can be performed by irradiation through the mold 79 -- if the mold used
is
sufficiently transparent to transmit the selected radiation. Curing through
both the
tool and the body layer also may be carried out.
The primary curing may completely cure the cube-corner elements, or may
partially cure the resin composition to a degree sufficient to produce
dimensionally
stable cube-corner elements that no longer require the support of the mold 79.
The
sheeting 60 can then be removed from the mold ?9, exposing the sheeting's cube-
corner elements 30. One or more secondary curing treatmems 100, selected
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WO 97/41465 PCT/US97/05594
depending upon the nature of the resin, can then be applied to fully cure the
array of
cube-corner elements and strengthen the bond between the array of cube-corner
elements and the body layer. This bifurcated curing approach can permit
optimized
processing and materials selection. For instance, a sheeting made from a body
layer
that contains an ultraviolet absorber (to impart greater durability and
weathering
ability) can be made by applying a primary curing treatment of visible light
through
the light-transmissible body layer, and then removing the sheeting from the
mold 79
at roll 98 and applying a second curing treatment 100 of ultraviolet radiation
to the
exposed cube-corner elements. Such a bifurcated approach may permit faster
overall production.
The extent of the second curing step depends on a number of variables,
among them the rate of feed-through of the materials, the composition of the
resin,
the nature of any crosslinking initiators used in the resin formulation, and
the
geometry of the mold. In general, faster feed rates increase the likelihood
that more
than one curing step is needed. Selection of curing treatments depends in
large part
on the specific resin chosen for producing the cube-corner elements. Electron
beam
curing could be used, for example, in lieu actinic radiation.
Thermal curing materials also may be used when making glittering
retroreflective sheeting from a mold of the invention. In this case, the mold
is
heated to a temperature sufficient to cause development of enough cohesion in
the
newly formed glittering cube-corner material to allow it to be removed from
the
mold without damaging the physical or optical properties of the newly formed
sheeting. The selected temperature is a function of the thermal curing resin.
Thermal curing may be achieved, for example, by heating the resin, by heating
the
mold, or by heating the glittering sheeting by indirect means. Combinations of
these
methods also may be used. Indirect heating includes methods such as heating
with
lamps, infrared or other heat source filaments, or any other convenient
method.
The mold may also be housed in an oven or other environment that is maintained
at
the temperature required by the thermal curing resin selected.
After the glittering retroreflective sheeting has been removed from the mold,
it may be further treated by exposure to heat from an oven or other heated
23
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WO 97/41465 PCT/t7S97/05594
environment. Such subsequent heat treatment may adjust the sheeting's physical
or
other properties to some desired state, complete reactive processes in the
sheeting,
or remove volatile substances such as solvents, unreacted materials, or by-
products
of the thermal curing system.
Thermal curing resins may be applied to the mold as solutions or as neat
resin formulations. Resins aiso may be either reactively extruded or extruded
in the
molten state onto the mold. Methods of thermal curing after applying the
resins to
the mold, and any subsequent exposure of the sheeting to heat, may be done
independent of applying the thermal curing resin to the mold.
An advantage of glittering retroreflective sheeting made from thermal curing
materials in a mold is that both the cube-corner elements 30 (FIG. 3) and body
portion 54 (FIG. 5) may be made from the same substance, which may be applied
to
the mold in a single operation. A consequence of this construction is that the
sheeting may exhibit uniform materials and properties throughout the sheeting.
A
1 S further advantage is that constructions of this type do not require a
separate body
layer to be applied as illustrated in FIG. 14
In addition to curing treatments, sheeting may also be heat treated after it
is
removed from the mold. Heating serves to relax stresses that may have
developed
in the body layer or in the cube-comer elements, and to drive off unreacted
moieties
and byproducts. Typically, the sheeting is heated to an elevated temperature,
for
example, above the polymer's glass transition temperature(s). The sheeting may
exhibit an increase in retroreflective brightness after a heat treatment.
In lieu of the above methods, glittering retroreflective sheetings also may be
produced by embossing a polymeric sheet over a mold that possesses cube-corner
elements arranged in accordance with the present invention. Examples of
embossing methods are disclosed in United States Patents: 5,272,562,
5,213,872,
and 4,601,861.
Glittering retroreflective sheetings that display images also may be produced
in accordance with the present invention.
FIG. 15 illustrates a retroreflective article 101 that displays the image
"ABC". The image 102 in this case is characterized by a retroreflective
glittering
24
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WO 97141465 PCT/US97/05594
area, while the background 103 is characterized by a retroreflective non-
glittering
area. As used herein, an "image" may be any combination of alphanumeric
characters or other indicia that stands out in contrast to the background.
Glittering
imaged retroreflective articles, like article 101, may be produced as
described
below.
Imaged glittering sheeting may be produced in a first embodiment by
inserting a material in the shape of the desired image into the assembly shown
in
FIG. 1 I. Thin material in the shape of the desired image, such as an insert
104 (104
refers generically to any suitable insert including 104a and 1046 of FIGS. 16a
and
16b) in FIG. I 1 can be placed between the cube-corner reflective elements 30
and
the optional lower release liner 76. The image materials may be a polymeric
film
made from, for example, polyester. The insert 104 may comprise a large, smooth
sheet from which the desired image has been cut, forming a negative image in
the
insert. Subjecting this arrangement to processing conditions of elevated
temperature and/or pressure results in a retroreflective sheeting that bears
the
desired image as a glittering portion on a background that is substantially
not
glittering or that has a low level of glittering. When the insert 104 is in
the size and
shape of the desired image, subjecting the sheeting 10 to elevated temperature
and/or pressure results in retroreflective sheet material that bears a non-
glittering
image corresponding to the insert 104 on the glittering background. A
preferred
embodiment is without the release liner 76.
An insert 104 can be placed with the image forming elements in contact with
exposed cube-corner elements 30 as shown in FIG. 11, or on the top face of the
ordered retroreflective sheeting 10 with image forming elements 106 contacting
the
optional polyester film liner 78 or directly contacting the front surface 51.
Alternatively, an ordered cube-corner sheeting 10 may be inserted in laminator
71
with the cube-corner elements 30 facing the heated laminator surface 72, and
the
front surface 51 (and optional carrier 78) facing an unheated laminator
surface 74.
Thus, an image forming insert may be disposed either above or below the
sheeting.
In FIG. 16a an image insert 104a is shown that may comprise a durable
material 105 that bears projections 106 rising away from the surface of the
sheet
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material I05. In this embodiment, the projections 106 form the desired image.
An
example of such a device is a flexographic printing plate. When this type of
image
bearing device is placed in the arrangement of FIG. 11 such that the image
forming
projections 106 of insert I04a contact the exposed cube-corners and the
assembly is
subjected to elevated temperature and/or pressure, a retroreflective sheeting
is
produced that bears a glittering image on a substantially non-glittering
background.
The degree and extent of glittering may be controlled by the process
conditions. For example, processing with a flexographic printing plate for
short
time periods results in an image that is capable of glittering only at the
points where
projections 106 directly contact the backside of the cube-corner elements 30.
Non-
contact areas remain retroreflective and substantially not glittering. As
processing
time increases, and as processing temperature increases, the extent of
glittering
extends away from the contact points of projections 106, and the resulting
image
gradually changes from {a) glittering only at contact points to (b) a
glittering image
on a glittering background, to (c) a non-glittering image (where cube-corners
have
been substantially pushed out of the contact areas) on glittering background.
In FIG. 16b, an image forming element 104b is shown that may comprise a
carrier material 108 on which a heat-transferrable material 110 has been
deposited
in the shape and size of the desired image. For example, heat-transferrable
ink 110
may be deposited on a carrier film 108 in the form of the image to be
transferred.
The carrier film 108 bearing the desired image is placed as an insert 104 in a
laminator 71 of FIG. 11 such that the exposed back side of the cube-corner
elements 30 contacts the image surface 110 on carrier film 108. The
arrangement is
subjected to the processing conditions of elevated temperature and/or
pressure, and
the resulting retroreflective sheeting bears a non-retroreflective image on a
glittering
retroreflective background.
The image bearing insert 104 in FIG. 11 also may be a large piece of fabric
(not shown) or other material bearing an overall pattern or texture. In the
case of a
fabric insert, the image carried by the insert is derived from the fabric's
configuration. Additionally, the image on the sheeting may correspond to an
image
cut from the fabric. When a fabric type insert is placed in contact with the
exposed
26
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WO 97/41465 PCT/LTS97I05594
back side of the cube-corner elements 30 and the arrangement is subjected to
elevated temperature and/or pressure, the resulting retroreflective cube-
corner
sheeting bears an overall image that is capable of glittering and that
exhibits the
configuration or texture of the fabric. Further, the fabric's texture or weave
can
enhance the glittering effect in the imaged area. Coarse fabrics tend to
encourage
more glittering. If desired, the lower release paper 76 in FIG. 11 may be
removed
completely, and the pattern or image of the lower, unheated surface 74 of the
heat
laminating machine may be transferred to the retroreflective sheeting in a
glittering
pattern.
There is broad latitude in producing images by contacting the ordered cube-
corner retroreflective sheeting with an image forming element. The appearance
of
the image depends on process conditions, the construction from which the
imaged
glittering sheeting is made, and on the size, shape, and materials of the
image
forming elements. The degree of glittering in imaged and in nonimaged areas
may
be successfully altered when one or more of these variables is changed. When
the
image forming element 104 is, for example, a textured surface such as fabric --
such as a woven polyester mesh -- the glittering effect may be considerably
enhanced when compared with the glittering sheeting prepared in the absence of
such a textured surface. Photomicrographs of sheeting with enhanced glittering
showed a substantially greater degree of cube-corner element reorientation,
including groups of cube-corner elements piled upon each other, than sheeting
formed in the absence of a textured image forming element. It is believed that
the
enhanced glittering effect is related to the additional reflective paths
available to
light incident on the piled cube-corner elements. Accordingly, there is a
general
range of glittering image forming abilities of the article of the invention
which can
be achieved by changing these or other variables.
A retroreflective sheeting capable of displaying the glittering effect,
prepared from either the first or second technique described above, may also
be
made to bear an image by printing directly onto the outer surface 51 of the
body
layer 58. When transparent inks are used, the glittering effect and
retroreflection
are visible through the transparent image and are dominated by that color.
When
27
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WO 97/41465 PCT/US97/05594
opaque inks are used, the retroreflection and the glittering effects are
blocked only
at the image area when viewed from the front side of the sheeting. Transparent
and
opaque inks also may be placed on the backside of the cube-corner elements to
produce images.
Retroreflective sheetings capable of glittering and bearing images also may
be prepared by the second technique, directly from a mold. Essentially any
method
used to prepare retroreflective sheetings that display glittering images on a
non-
glittering background or non-glittering images on a glittering background
according
to the first technique (FIG. 11) is also applicable to the second technique
(FIG. 14}.
When a glittering image is located on a glittering background, the imaged area
and
the background exhibit varying degrees of glitter so that the imaged area is
discernible from the background. A glittering retroreflective sheeting that
displays
an image may be used as a pattern on which mold materials are deposited and/or
cured. Removal of the patterned sheeting reveals a newly formed mold that
bears
I S the image formed on the pattern material. Use of such molds produces
sheeting
that is capable of retroreflecting light and that displays the glittering
effect and still
contains the image applied to the original sheeting from which the mold was
prepared. Images printed, deposited, or formed directly on the exposed back
side
of the cube-corner elements by various techniques may be faithfully replicated
in the
mold making process. Images placed on the body layer 58 may also end up being
replicated in the mold making process.
Light transmissible polymeric materials may be used to produce a
retroreflective sheetings of the invention. Preferably the selected polymers
can
transmit at least 70 percent of the intensity of the light incident upon it at
a given
wavelength. More preferably, the polymers transmit greater than 80 percent,
and
still more preferably greater than 90 percent, of the incident light.
For some applications, particularly when producing a glittering article
according to the first technique (that is, using heat and/or pressure), the
polymeric
materials that are employed in the cube-corner elements preferably are hard
and
rigid. The polymeric materials may be, for example, thermoplastic or
crosslinkable
28
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WO 97/41465 PCT/US97/05594
resins. The elastic modulus of such polymers preferably is greater than about
x 108 pascals, and more preferably is greater than about 13 x 108 pascais.
Examples of thermoplastic polymers that may be used in the cube-corner
elements include acrylic polymers such as poly(methyl methacrylate);
5 polycarbonates; cellulosics such as cellulose acetate, cellulose (acetate-co-
butyrate),
cellulose nitrate; epoxies; polyurethanes; polyesters such as poiy(butylene
terephthalate), polyethylene terephthalate); fluoropolymers such as
poly(chlorofluoroethylene), poly(vinylidene fluororide); polyvinyl halides
such as
polyvinyl chloride) or poly(vinylidene chloride); polyamides such as
10 poly(caprolactam), poly(amino caproic acid), poly(hexamethylene diamine-co-
adipic
acid), poly(amide-co-imide), and polyester-co-imide); polyetherketones;
poly(etherimide); polyolefins such as poly(methylpentene); poly(phenylene
ether);
poly(phenylene sulfide); polystyrene) and polystyrene) copolymers such as
polystyrene-co-acrylonitrile), poly(styrene-co-acrylonitrile-co-butadiene);
polysulfone; silicone modified polymers (i.e., polymers that contain a small
weight
percent (less than 10 weight percent) of silicone) such as silicone polyamide
and
si&cone polycarbonate; fluorine modified polymers such as
perfluoropoly(ethyleneterephthalate); and mixtures of the above polymers such
as a
polyester) and poly(carbonate) blend, and a fluoropolymer and acrylic polymer
blend.
The cube-corner elements also may be made from reactive resin systems that
are capable of being crosslinked by a free radical polymerization mechanism by
exposure to actinic radiation. Additionally, these materials may be
polymerized by
thermal means using a thermal initiator such as benzoyl peroxide. Radiation
initiated cationically polymerizable resins also may be used.
Reactive resins suitable for forming the cube-corner elements may be blends
of a photoiniator and at least one compound bearing an acryiate group.
Preferably
the resin blend contains a difirnctional or polyfunctional compound to ensure
formation of a crosslinked polymeric network when irradiated.
Examples of resins that are capable of being polymerized by a free radical
mechanism include: acrylic-based resins derived from epoxies, polyesters,
29
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WO 97/41465 PCTIL1S97/05594
polyethers, and urethanes; ethylenically unsaturated compounds; aminoplast
derivatives having at least one pendant acrylate group; isocyanate derivatives
having
at least one pendant acrylate group; epoxy resins other than acrylated
epoxies; and
mixtures and combinations thereof. The term acrylate is used here to encompass
both acrylates and methacrylates. U.S. Patent 4,576,850 to Martens discloses
examples of crosslinked resins that may be used in the cube-corner elements of
glittering retroreflective sheeting.
Ethylenically unsaturated resins include both monomeric and polymeric
compounds that contain atoms of carbon, hydrogen and oxygen, and optionally
nitrogen, sulfur and the halogens. Oxygen or nitrogen atoms or both are
generally
present in ether, ester, urethane, amide and urea groups. Ethylenically
unsaturated
compounds preferably have a molecular weight of less than about 4,000 and
preferably are esters made from the reaction of compounds containing aliphatic
monohydroxy groups or aliphatic polyhydroxy groups and unsaturated carboxylic
acids, such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid,
isocrotonic
acid, malefic acid, and the like.
Some examples of compounds having an acrylic or methacrylic group are
listed below. The listed compounds are illustrative and not limiting.
(1) Monofunctional compounds:
ethylacrylate, n-butylacrylate, isobutylacrylate, 2-ethylhexylacrylate,
n-hexylacrylate, n-octylacrylate, isooctylacrylate, isobornyl acrylate,
tetrahydrofurfuryl acrylate, 2-phenoxyethyl acrylate, N,N-dimethylacrylamide;
(2) Difunctional compounds:
1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, neopentylglycol
diacrylate,
ethylene glycol diacrylate, triethyleneglycol diacrylate, and tetraethylene
glycol
diacryiate, and diethylene giycol diacrylate;
(3) Polyfunctional compounds:
trimethylolpropane triacrylate, glyceroltriacrylate, pentaerythritol
triacrylate,
pentaerythritol tetraacrylate, and tris(2-acryloyloxyethyl)isocyanurate.
Some representative examples of other ethylenically unsaturated compounds
and resins include styrene, divinylbenzene, vinyl toluene, N-vinyl
pyrrolidone, N-
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vinyl caprolactam, monoallyl, polyallyl, and polymethallyl esters such as
dialIyl
phthalate and diallyl adipate, and amides of carboxylic acids such as and N,N-
diallyladipamide.
Examples of photopolymerization initiators that may be blended with the
acrylic compounds include the following illustrative initiators: benzyl,
methyl o-
benzoate, benzoin, benzoin ethyl ether, benzoin isopropyl ether, benzoin
isobutyi
ether, etc., benzophenone/tertiary amine, acetophenones such as 2,2-
diethoxyacetophenone, benzyl methyl ketal, 1-hydroxycyclohexyl phenyl ketone,
2-
hydroxy-2-methyl-1-phenylpropan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-
methylpropan-1-one, 2-benryl-2-N,N-dimethylamino-1-(4-morpholinophenyI)-
1-butanone, (2,4,6-trimethylbenzoyl)diphenylphosphine oxide, 2-methyl-1-4-
(methylthio)phenyl-2-morpholino-1-propanone, bis(2,6-dimethoxybenzoyl)-2,4,4-
trimethylpentylphosphine oxide, et cetera. These compounds may be used
individually or in combination.
I S Cationically polymerizable materials include but are not limited to
materials
containing epoxy and vinyl ether functional groups. These systems are
photoinitiated by onium salt initiators such as triarylsulfonium, and
diaryliodonium
salts.
Preferred polymers for use in the cube-corner elements include
poly(carbonate), poly(methylmethacrylate), polyethylene terephthalate),
aliphatic
polyurethanes and crosslinked acrylates such as mufti-functional acrylates or
acrylated epoxies, acrylated polyesters, and acrylated urethanes blended with
mono-
and mufti-functional monomers. These nOlvmers are »refPrrer~ fnr nnP nr mnrP
of
the following reasons: thermal stability, environmental stability, clarity,
release from
the tooling or mold, or high receptivity for receiving a reflective coating.
The polymeric materials employed in a land layer, if one is present, may be
the same as the polymers that are employed in the cube-corner elements. The
optional land layer preferably has a smooth interface with the cubes and the
body
layer. Cavities and/or interfacial roughness preferably are avoided between
the
cubes and the optional land layer or the body layer so that optimum brightness
can
be displayed by the retroreflective sheeting when light is retroreflected
therefrom.
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WO 9?/41465 PCT/US97/05594
A good interface prevents spreading of retroreflective light from refraction.
When
present, the land layer, in most instances, is integral with the cube-corner
elements.
By "integral" is meant the land and cubes are formed from a single polymeric
material -- not two different polymeric layers subsequently united together.
The
polymers that are employed in the cube-corner elements and land layer can have
refractive indices that are different from the body layer. Although the land
layer
desirably is made of a polymer similar to that of the cubes, the land layer
also may
be made from a softer polymer such as those described above for use in the
body
layer.
The body layer may comprise a low elastic modulus polymer for easy
bending, curling, flexing, conforming, or stretching, and for allowing the
cube-
corner elements to become reoriented when an ordered array is exposed to heat
and
pressure. The elastic modulus may be less than 5 x 10$ pascals, and may also
be
less than 3 x 108 pascals. A low elastic modulus body layer, however, is not
always
required. If it is desired to make glittering retroreflective sheetings which
are less
flexible, sheetings with body layer having higher elastic modulus may be used,
such
as rigid vinyl with elastic modulus about 21 to 34 x 108 Pa. Generally, the
polymers
of the body layer have a glass transition temperature that is less than 50
°C. The
polymer preferably is such that the polymeric material retains its physical
integrity
under the conditions to which it is exposed during processing. The polymer
desirably has a Vicat softening temperature that is greater than 50°C.
The linear
mold shrinkage of the polymer desirably is less than 1 percent, although
certain
combinations of polymeric materials for the cube-corner elements and the body
layer may tolerate a greater degree of shrinking of the body layer polymer.
Preferred polymeric materials that are used in the body layer are resistant to
degradation by W light radiation so that the retroreflective sheeting can be
used
for long-term outdoor applications. As indicated above, the materials or
polymer
body layer is light transmissible and preferably is substantially transparent.
Body
layer films with a matte finish -- that became transparent when the resin
composition is applied thereto, or that become transparent during the
fabrication
process, for example, in response to the curing conditions used to form the
array of
32
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WO 97/41465 PCT/US97/05594
cube-corner elements -- are useful. The body layer may be either a single
layer or a
mufti-layer component as desired. Examples of polymers that may be employed in
the body layer include:
fluorinated polymers such as: poly{chlorotrifluoroethylene), for example
Kel-F800~ available from 3M, St. Paul, Minnesota; poly(tetrafluoroethylene-co
hexafluoropropylene), for example Exac FEP~ available from Norton
Performance, Brampton, Massachusetts; poly(tetrafluoroethylene-co
perfluoro(alkyl)vinylether), for example, Exac PEAS also available from Norton
Performance; and poly(vinylidene fluoride-co-hexafluoropropylene), for
example,
Kynar Flex-2800'M available from Pennwalt Corporation, Philadelphia,
Pennsylvania;
ionomeric ethylene copolymers such as: polyethylene-co-methacrylic acid)
with sodium or zinc ions such as Surlyn-8920"''i and Surlyn-9910 available
from
E.I. duPont Nemours, Wilmington, Delaware;
1 S low density polyethylenes such as: low density polyethylene; linear low
density polyethylene; and very low density polyethylene;
plasticized vinyl halide polymers such as plasticized polyvinyl chloride);
non- or unplasticized rigid vinyl polymers such as Pentaprinfi'M PR 180 from
Klockner Pentaplast of America, Inc., Gordonsville, Virginia;
polyethylene copolymers including: acid functional polymers such as
polyethylene-co-acrylic acid) and polyethylene-co-methacrylic acid)
polyethylene-co-malefic acid), and polyethylene-co-fumaric acid); acrylic
functional polymers such as polyethylene-co-alkylacrylates) where the alkyl
group
is methyl, ethyl, propyl, butyl, et cetera, or CH3(CH2)n- where n is 0-12, and
polyethylene-co-vinylacetate); and
aliphatic and aromatic polyurethanes derived from the following monomers
(1~(3): (1) diisocyanates such as dicyclohexylmethane-4,4'-diisocyanate,
isophorone diisocyanate, 1,6-hexamethylene diisocyanate, cyclohexyl
diisocyanate,
diphenylmethane diisocyanate, and combinations of these diisocyanates, (2)
polydiols such as polypentyleneadipate glycol, polytetramethylene ether
glycol,
polyethylene glycol, polycaprolactone diol, poly-i,2-butylene oxide glycol,
and
33
CA 02252433 2005-04-15
60557-5972
combinations of these polydiola,. and (3) chain extenders such as butanediol
or
hexanediol. CommerciaDy available urethane polymers include: PN-04, or 3429
from Morton lnternational Inc., Seabrook, New Hampshire, or X-4107 from B.F.
Goodrich Company, Cleveland, Ohio.
Combinations of the above polymers also may be employed in the body layer of
the
body portion. Preferred polymers for the body layer include: the ethylene
copolymers that contain units that contain carboxyl goupa or esters of
carboxylic
acids such as polyethylene-co-acrylic aad), polyethylene-co-methacrylic sad),
polyethylene-co-vinylacetate); the ionomeric ethylene copolymers; plasticized
polyvinyl chloride); and the aliphatic urethanes. These polymers are preferred
for
one or more of the foDowing reasons: suitable mechanical properties, good
adhesion to the land layer or cube-corner elements, clarity, and emrironmentai
stability.
Selection of certain resins for the cube-comer elements and the body layer
may resuh in an interpenetrating network after curing. Particular combinations
of
resins for cube-corner elements and body layer can be readily screened for
penetration by application of a quantity of the cube-corner resin to the body
layer.
Priola, A., Gozzelino, G., and Ferrtro, F., Proceedings o,~ the Xlll
Internutiorwl
Conference in Organic Coatings Science and Technology, Athens, Greece, July
7-11, 1987, pp. 308-18, discloses a watch glass test suitable for this
purpose. See
also U.S. Patent No. 5,691,846.
In an embodiment that contains polycarbonate cube-corner elements and/or
a polycarbonate land layer and a body layer that contains a polyethylene
copolymer
such as polyethylene-co-{meth)acrylic acid), polyethylene-co-vinylacetate) or
polyethylene-co-acrylate), the interfacial adhesion between the body layer and
the
land layer or cube-corner elements can be improved by placing a thin tie-layer
(not
shown) therebetween. The tie-layer can be applied on the body layer before
laminating the body layer to the land layer or to the cube-corner detnsnts.
The tio-
layer can be applied as a thin coating using, for example: an aliphatic
polyurethane
in organic solution, for example Permuthane~ U26-248 solution, available from
Permuthane Company, Peabody, Massachusetts; Q-thanes QC-4820 ava~able
34
CA 02252433 2005-04-15
60557-5972
from KJ. Quinn and Co., -Inc., Seabrook, New Hampshire; an aliphatic
polyurethane waterborne dispersion, for example NeoRez~ R-940, R-9409, R-960,
R-962, R-967, and R-972, available from ICI Resins US, Wilmington,
Massachusetts; an acrylic polymer water borne dispersion; for example,
NeoCtyl~
A-601, A-612, A-614, A-621, arid A-6092, avaflable from IQ Resins US,
Wilmington, Massachusetts; or an alkyl acrylate and aliphatic urethane
copolymer
water borne dispersion, for example NeoPac"; R-9000, avaflable from ICI Resins
US, Wilmington, Massachusetts. In addition, an electrical ~ discharge method,
such
as a corona or plasma ueatmem, can be used to further improve the adhesion of
tie-
layer to the body layer or the tie-layer to the land layer or to the cube-
corner
elements.
Cube-corner retroreflective sheetings that are produced in accordance with
the second technique may be made from polymers discussed above as being
applicable in the first technique. That is, the cube-corner elements may
comprise
harder, or high modulus polymers) and the body portion may comprise softer, or
lower modulus polymer(s). In addition to these materials, cube-corner
sheetings
that comprise harder body layer polymers such as polyesters or polycarbonates
may
also be made by the second technique. Further, when sheeting is made by the
second technique the chemistry applicable to the cube-corner elements is
broader
than in the first technique, that is, cube-corner elements may comprise either
hard or
soft polymers. U.S. Patent No. 5,754,338 discloses examples of polymers that
may
be used in the cube-corner elements of the present invention.
When an anicie of the invention is prepared in accordance with the second
technique, soft polymers -- that is, polymers having an elastic modulus less
than
10 x 10s pascais -- may be used to produce the cube-comer elements in
glittering
retroreflective sheeting. In the second technique, the cube-corner elements
are not
subjected to the heat and/or pressure conditions of the batchwise or
continuous
processes of the first technique because the cube-corner ,element orientations
are
determined by the configuration of the mold. That is, glittering sheetings
made by
the second technique receive cube-corner element orientations directly from
the
CA 02252433 1998-10-20
WO 97/41465 PCT/US97/05594
mold. Distortion of the cube-corner elements therefore is much less a concern,
and
it is possible to produce glittering sheetings that comprise only, or consist
essentially of, soft polymers throughout the construction.
Example of soft polymers that can be used to make glittering cube-corner
sheeting using the second technique include flexible polyvinyl halides) such
as
polyvinyl chloride), poly(vinylidene chloride); PVC-ABS; reactive and
nonreactive
vinyl resins; vinyl acrylates; mixtures of vinyl acrylates with acrylated
epoxies;
polysiloxanes; alkylalkoxysilanes; acrylated polysiloxanes; polyurethanes;
acrylated
urethanes; polyesters; acrylated polyesters; polyethers; acrylated polyethers;
acrylated oils; poly(tetrafluoroethylene); poly(fluoroethylene-co-
fluoropropylene);
poly(ethylene-co-tetrafluoroethylene); polybutylene; polybutadiene;
poly(methylpentene); polyethylenes such as low density, high density, and
linear low
density; polyethylene-co-vinyl acetate); polyethylene-co-ethyl acrylate).
These polymers can be used either alone or may be blended together.
Further, they can be blended with those described for the first technique to
give
glittering cube-corner retroreflective sheeting via the second technique. In
addition,
adjusting the crosslink density of the reactive polymers or blends listed for
the first
technique can also yield sob materials. The properties of the nonreactive
polymers
can be adjusted by changing the concentration of additives such as
plasticizes, or by
selection of different polymer grades.
Colorants, UV absorbers, light stabilizers, free radical scavengers or
antioxidants, processing aids such as antiblocking agents, releasing agents,
lubricants, and other additives may be added to the body portion or cube-
corner
elements. The particular colorant selected, of course, depends on the desired
color
of the sheeting. Colorants typically are added at about 0.01 to 0.5 weight
percent.
UV absorbers typically are added at about 0.5 to 2.0 weight percent. Examples
of
UV absorbers include derivatives of benzotriazole such as Tinuvin~ 327, 328,
900,
1130, Tinuvin-Pte, available from Ciba-Geigy Corporation, Ardsley, New York;
chemical derivatives of benzophenone such as Uvinul~-M40, 408, D-S0, available
from BASF Corporation, Clifton, New Jersey, or Cyasorb'''M UV531 from Cytech
Industries, West Patterson, New Jersey; Syntase'M 230, 800, 1200 available
from
36
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WO 97/41465 PCT/US97105594
Neville-Synthese Organics, Inc., Pittsburgh, Pennsylvania; or chemical
derivatives
of diphenylacrylate such as Uvinul~-N35, 539, also available from BASF
Corporation of Clifton, New Jersey. Light stabilizers that may be used include
hindered amines, which are typically used at about 0.5 to 2.0 weight percent.
S Examples of hindered amine light stabilizers include Tinuvin~-144, 292, 622,
770,
and Chimassorb~-944 all available from the Ciba-Geigy Corp., Ardsley, New
York. Free radical scavengers or antioxidants may be used, typically, at about
0.01
to 0.5 weight percent. Suitable antioxidants include hindered phenolic resins
such
as Irganox~-1010, 1076, 1035, or MD-1024, or Irgafos~-168, available from the
Ciba-Geigy Corp., Ardsley, New York. Small amount of other processing aids,
typically no more than one weight percent of the polymer resins, may be added
to
improve the resin's processibility. Useful processing aids include fatty acid
esters,
or fatty acid amides available from Glyco Inc., Norwalk, Connecticut, metallic
stearates available from Henkel Corp., Hoboken, New Jersey, or Wax E~
available
from Hoechst Celanese Corporation, Somerville, New Jersey. Flame retardants -
such as Tetrabromo Bisphenol A Diacrylate Monomer, SR 640, from Sauromer
Company, Inc., Exton, Pennsylvania, or Tricresyl phosphate, KronitexTM TCP,
from
FMC Corporation, Philadelphia, Pennsylvania -- also may be added to the
polymeric
materials of the inventive sheeting to optimize its overall properties, as
well as the
properties of the article to which it may be attached.
Flexible glittering retroreflective sheeting may be used on irregular surfaces
such as corrugated metal. For example, the sheeting may be placed over the
sidewall of a truck trailer or on a flexible surface such as an article of
clothing.
Other applications for such glittering retroreflective sheeting include
warming flags,
road signs, traffic cones, light wands, and vehicle conspicuity markings. When
used
on light wands, the sheeting may be placed in a tubular configuration. For
example,
the sheeting can be adapted in the form of a tube or cylinder, and a light
source may
be directed into the tubular glittering article. The tubular glittering
sheeting may be
adapted with a fitting that allows it to be secured to a light source such as
at the end
of a flashlight. Glittering retroreflective sheetings also may be embossed or
otherwise adapted into three dimensional structures as taught in U.S. Patent
37
CA 02252433 2005-04-15
60557-5972
No. 5,763,049.
The invention is further illustrated in deta~ by the following Examples.
While the Examples serve this purpose, it should be understood that the
particular
ingedients used as well as other conditions and deta~s are not to be conswed
in a
manner that would unduly limit the irrvartion.
RetroreJleetivt Brightness Test
The coe~cient of retroreflettion, R,~, was measured in accordance with
standardized test ASTM E 810-93b. The valves for Rw is expressed in candelas
per
lux per square meter (cd~1X'~rri z). The entrance angle used in ASTM E 810-93b
was -4 degees, and the observation angle was 0.2 degrees. Further reference to
"ASTM E 810-93b" means ASTM E 810-93b where the entrance and observation
angles are as specified in the previous sernence.
Lightness Ttst
Lightness of the cube-corner sheeting was measured using a
spectrocolorimeter according to standardized test ASTM E 1349-90. Lightness is
expressed by the parameter termed Luminance Factor Y (LFY), which is defined
as
the lightness of the test sample relative to a perfect diffusing reflector.
Zero degree
illumination and 45 degee circumferential viewing were employed in determining
the LFY. LFY values range from 0 to 100, where a LFY value of 0 represents
black and a LFY value of 100 represems white.
Examples 1 a-l ee - Batchwise ProdueA~on of Glittering Article
Ordered retroreflective cube-corner sheeting prepared as descn'bed in
Example 1 of U.S. Patent No. 5,691,846 was used. The sheeting included cube-
corner retroreflective elements that measured approximately 0.0035 inches
(90 micrometers (pm)) from apex to base,
38
CA 02252433 1998-10-20
WO 97/41465 PCT/US97/05594
and made from 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, and
bisphenol A epoxy diacrylate, in a ratio of 25:50:25 parts by weight with 1 %
resin
weight DarocurTM 4265 as photoinitiator, a 0.01 inch (250 p.m) thick clear,
colorless, flexible vinyl body layer, and a polyethylene terephthalate carrier
film
0.002 inches (50 p,m) thick. The resin was cured through the filin with a
FUSION
H lamp (available from Fusion UV Curing Systems, Gaithersburg, Maryland)
operating at 235 Watt/cm at 25 ft/min (7.6 m/min), and then postcured from the
back side of the cube-corner elements with an AETEK medium pressure mercury
lamp (available from AETEK International, Plainfield, Illinois) operating at
120
Watt/cm at 25 ffiJmin (7.6 m/min). The sheeting was placed onto Kraft release
paper (Scotchcal''M SCW 98 Marking Film, 3M, Saint Paul, Minnesota) with the
exposed cube-corner elements pointing downward toward the paper. Together the
Kraft paper and ordered cube-corner sheeting were placed onto the rubber
surface
of a Hix Model N-800 heat lamination machine (Hix Corporation, Pittsburg,
Kansas) that was preheated to 350° F (175° C), with the Kraft
paper resting on the
rubber surface. The lamination machine was adjusted to apply 40 psi (2.75 X
105
pascals (Pa)) air line pressure at 350° F (175° C) for 45
seconds. The lamination
machine was activated and, at the end of the heating period, the cube-corner
sheeting was removed. After cooling to room temperature, the polyester film
was
removed from the body layer to reveal cube-corner retroreflective sheeting
capable
of glittering. Other processing conditions were used to prepare glittering
retroreflective sheeting where the temperature, time, and pressure were
changed.
The effects of these changes on glittering and retroreflective brightness are
illustrated in Table 1.
Example 1 s was tested for lightness, and this sample exhibited an LFY value
of 37.73.
39
CA 02252433 1998-10-20
WO 97/41465 PCT/US97/05594
TABLE 1
Effect of Batchwise Process
Conditions on Formation of Glitterin Sheeting
Mean
Brightness
R,, at
lcdlluxln~)
Entry Temp Tune Pressure0 90 Comrents
r sec si
la 195 45 40 528 440 No litterin
!b 225 45 40 599 514 No litterin
1 c 249 45 40 721 608 No 'tte
!d 275 45 40 1270 739 No line
!e 300 45 40 919 834 No litterin
if 324 45 40 543 582 Sli t litterin
1 340 45 40 303 302 Full litterin
!h 349 45 40 253 268 Full litterin
l i 3 45 40 197 23 Full litterin
74 8
1' 401 45 40 105 137 Full litterin
!k 350 60 40 254 222 Full litterin
11 350 40 40 234 222 Full litterin
lm 350 30 40 342 356 Full litterin
In 350 20 40 482 502 Full litterin
l0 350 18 40 624 602 Full litterin
1 350 16 40 670 670 Full litterin
1 350 14 40 580 658 Full litterin
!r 350 12 40 655 743 Full litterin
is 350 10 40 1086 874 Medium litterin
It 350 8 40 1357 860 Medium litterin
!u 350 6 40 1136 847 Sli t litterin
!v 350 4 40 1245 789 No litterin
!w 350 2 40 845 727 No litterin
lx 350 10 5 - - Sli t litterin
1 350 10 10 - - Medium litterin
!z 350 10 20 - - FuII litterin
laa 350 10 30 - - Full litterin
!bb 350 10 40 ~ - Full
litterin
!cc 350 10 50 - - _
Full litterin
ldd 350 10 60 - - Full litterin
lee 350 10 70 - - Full litterin
CA 02252433 1998-10-20
WO 97/41465 PCT/US97I05594
Examples 2a-2m - Imaged Glittering Article Formed Using Flexographic
Printing Plate
Ordered cube-corner retroreflective sheeting, as described in Examples
la-lee, was used. A sheet of Kraft release paper was placed on the rubber mat
of a
S HTix Model N-800 heat lamination machine. On top of the paper sheet was
placed a
flexographic printing plate having a raised image (FIG. 16a) in the shape of
the
letters "JPJ" surrounded by a circle. Ordered retroreflective cube-corner
sheeting
having a polyester carrier on top of the body layer was placed onto the
flexographic
printing plate such that the backside of the cube-corner elements contacted
the
projecting image elements of the printing plate. A second piece of Kraft
release
paper was placed on top of the cube-corner sheeting. This arrangement
corresponds to FIG. 11 where the flexographic plate is represented by 104. The
assembly was heated to 350 °F (175 °C) with an air line pressure
(psi) and for the
times listed below in Table 2. When the lamination cycle ended, the lamination
machine was opened and the retroreflective cube-corner sheeting was removed.
When the sheeting cooled to room temperature, the optional polyester film (if
used)
was removed to reveal a cube-corner retroreflective sheeting capable of
glittering.
Several types of "JPJ" image were prepared depending on construction and
processing conditions and these are outlined below in Table 2.
41
CA 02252433 1998-10-20
WO 97/41465 PCT/I1S97/05594
04 0 o ai .~ a c a~ c4 a~
0
=, c ~ °' ~, N ~ _c .~ 3 .~ a~
o~°o '~ .'~ ~ ao
-° .~ E ~~ "~ ~ ~ ~' o v o
a~ a~ .,r ~ E ' o"b 2
0
c. ~.~.E o o'° ~' c o0
° E ° ' ~ o ' o, ~ z ono ~ ~c o ,x
' a' ~ w ~' °' .g .5~ ° >' ~
a ~' ° ~,", .~ a b w ~ ~ hi c
~ a v .a ~., 'C
,a ~ ' ° w ~ .~ 'ab .n
a ~ a a ~ a N C a .~
'° ~~ a°'~o~ 'c
00 ~ .~ ~ '~ ~ w
o ° G ~ o ~ o '" "
.., ~ ors o .
C Ø, C ~ ~ '~ C .C '~ c~ W G ,~ °
o 'T~ ~ ~ ~ b" w ~ ar
>,'~ ~ a_~ .x ~ c w c .~ .~
V ~ ~ ~ ~ '~ ~ ~ ~ ~ ~ ~ ~ ~~ ~ O ~~ U
ww zc~.~z.s~r~~~~w ~~w ~.~>'~~~.~
0
an ~', ~ M N N N ~ N
N ,>, C
~ w
H 0 1i. ~ ~ , jj N N M V~1
~U
c
~°- ° c~ r o ~p ~ ~a
t~ U ~, >, >, >, v
.~w'. C ~,~.,. N ~ '~ 'd 'C 'C7 O
r. o a ~ ~° ~° ~° .a
a
GJ (, pip U V d0 d4 b4 dp V
'a~.~ 'w C C,~~r'
. U ~~ ~ cUd
G C p C
U V V U U U V
c c ~ c c
O 4~ '~r
c c s~
o'~~y v a a a a a a
N N N N N N
N
42
CA 02252433 1998-10-20
WO 97/41465 PCT/US97/05594
O. ~ ~ ~5 G» ~ .C G. C 'c3 v O
a. ~ ~ ° Z
,p ~ by e~ ~ p4 ai
° W ~ °n C 'C W .~ '~ W .~ ° c~
.5 b4 ~ ~ ~~ ~' ~ .~ O ~ x O ~ O,
''~ ~ ''~ U ~ >,
' ,t'~", ~ b ~ H ~ ~ w OUD ~ "a [~ t~r
p G7 ~ V N .~ O e~s ~p
~ :d ~ V t3.... -~ ~ N ~ N ~ p O
Via, ... ..» .5~... ,5 ~ °
°' ~ a C ° ° ~ b
4 .= N ~ ° H .ao ~ a do ~ ao ~ an
Ca a ~ p°p .~ ~ ~,,3 ' ~ iV C
.a .~ ~-~~ ~ .4: W
~ H ~ .5 "" ~ "° ~ o ,° '~ ~ oo >,~
a~ a a a
ova ~ ~ ~ .n ~ ~ a~ S W ~ 'r~'
c'° o_~u EE° ~~° ~~' ~~''e
.C .~ ~ v C~7 0~ a .C c~ ~D .~ op .CEO c, ~ ~ a~ .C
E ~ ~ .D U , ~ ~ U
C%~ U' .G ' N H U f%~ V .~O N f%~ ~Cl..a N ~ L1..VD ~ r.r
y0 N M cW D N
L
O ~ N N
4,
H ~ H H H U
a a ~ a a
V ~ O O O ~ ~ V
O V V V
N ~ N ~ H
V U U V V
C ~ C C C
5 ., a4
.v .5
c ~ c c
O y
U U U U U o
U
~,d ~ ~ ~ C ~ C
O 4~ ~ H ~ ~ a~ a~
N U V ~ ~ 0~7
f~ ~. 0.~ ~, p, p
N N~ N N N
43
CA 02252433 1998-10-20
WO 97/41465 PCT/CTS97/05594
Examples 3a - 3f - Creation of Images Using a Polyester Film
Ordered retroreflective cube-corner sheeting and the apparatus described in
Examples la-lee above were used in the absence of the lower release paper 76.
Polyester film of several thicknesses was used as the image forming element
104
and was positioned so that it touched the back side of the cube-corner
elements. To
make positive images on glittering sheeting, the shape of the geometric
figures of a
square, a circle, and a triangle (each approximately 0.5 inch ( 1.25 cm) in
outside
dimension) were cut from a 4 x 6 inch sheet of polyester film of known
thickness.
The resulting polyester film image forming element was positioned as 104 as
shown
in FIG. 11. To make negative images on glittering, textured sheeting, the
geometric
figures that had been cut out to make the positive image forming element were
placed directly on the unheated laminator surface 74. The images were formed
in
the glittering textured cube-corner retroreflective sheeting by operating the
heat
lamination machine at 350 °F for 45 seconds at a line pressure of 40
psi (2.75 x 105
1 S Pa}. Descriptions of the imaged sheetings are listed in Table 3.
44
CA 02252433 1998-10-20
WO 97/41465 PCT/US97/05594
~ v ~' .~ b ouo '~ ~° a .~ dD a "~-,a
... c ~ ... c '2 .r ~ at c 'lea' ~.. ~ ~ O O 'T'~'
O O ~ O t,.,, ~ . ~ O a ~ ~ ~.O
~,x~ C~~O'S~C4.~ G. ~ ~ ~ e~ ~ G.,~~.. ~C y
> ~ ~ ~,, b0
b ~.~D > U.O ~ ~ ~ ~O-' N ~ x ~ 3 ~~'TJ
.C E~ m . C m .,d b4 w
U
''~ ~ ~ Ub~ .C~ U ~ ~ ~~ ,~~ O
4p C_~~a7~ O~_0~.. "'O~ q~~~ '~°'~_e~
.:9 O = O .."~'. 47 ~ ~'p'~ O ~ ~ ~~ ~~ ~ O w >,
N o4 ' x a~ ao ° a d0'~
Zt ~ ~' 'C , ~ 'Cy v.. ~ ~ 00 ~ U O ~"C U 'C ~ V O
e°'o ~~ .~ o o~o'~ ~ ~ °'°.° o c. oa ~ ~ ~ o ~ o ~
v ~ ~ ~ a a~ ~~ ~ 5i ~'~ Q a .~ ~ o "' ~ a
'1 -d ~ ° ~ c ° ~~ = ~oo ~ "- ~ o o ~ °°~ .~ N --
0 0
o ~ ~ x'~' .o c ~r ~ c wo ~ ~ a~ ~ ~ aio ~ ~ ~ ~
o .b ~ ~ o ?~.~ ~ ~ c °~,' ~; ~ ~ '~ ~ b a ~ pq
°c° : ~ o °~.~ ~~~ ~ o c ° ~~ H
,4, ,~ 04 0 'v ., ° o .. o
w o~ ~. ~ ~; ~ ~ ~ ~ ~o ~ ° ~ ~ a~ a~ ~s a~
A o0 0 ~, c ..~ o~.o oo~ .~ c . ~ ~''e 3''e c~ ~ EG >_ ~ ~e
c~c c ...cc.r ~'~' aW'v
°°.~ ~ >, ° ~ o ~ '~ o .~ ~ ~, o o ?~'~ ; 3 ~ ~ a o 0
N°
:... iw ~ a~ 04
O U~ b~~DO V V ~ p ~~ ~ .~.~n~ O v V
~ c~ a~ v~ c~ c~ .a ~ o~a.c ~ v~ in .o ~ v~ o°'o. ~ ~ ~ °: C7 ~
~ ~
d
E" ~°. o .r
~o.. 0 0 0 0
o fz, ~ 00 00 0 0 0 0
... ,~ .~ ,~ ~n ~n
ac ~ °°
.~ ~ w
0
0
._
w
~,'' >
0
w ~ ~, z ~, z w z
f~1 l~1 ('r1 M M M
CA 02252433 1998-10-20
WO 97!41465 PCT/US97/05594
Fxample 4 - Creation of Image Using Transfer Ink
Ordered retroreflective cube-corner sheeting and the apparatus described in
Examples la-lee were used with optional polyester carrier in place. The image
forming element was a piece of black printed label tape (FIG. 16b) made with a
Merlin Express Elite label tape machine (Varitronic Systems, Inc.,
Minneapolis,
Minnesota) and was positioned with the ink image touching the cube-corner
elements. The lamination machine was kept closed at 350° F (175°
C) for 45
seconds at 40 psi (2.75 X 105 Pa) air line pressure. At the end of the
processing
cycle, the sheeting was removed from the machine. When it returned to room
temperature, the polyester carrier was removed to reveal a glittering cube-
corner
retroreflecting sheet material with a black ink image transferred from the
label tape.
Examination of the sheeting with retroreflected illumination revealed a
retroreflectively dark image on a glittering and retroreflective background.
Example S - Glittering Image Produced from Woven Fabric
Ordered retroreflective cube-corner sheeting and apparatus described in
Examples 1 a-1 ee were used, with the optional polyester carrier in place. The
image
forming element was a piece of polyester plain weave fabric 2.2 ozlyd2 (188
g/m2)
and was located as illustrated by 104 in FIG. 1 I. The processing cycle was
allowed
to continue for 45 seconds at 350° F (175° C) with 40 psi (2.75
X 105 Pa) line
pressure. After the sheeting was cooled to room temperature, the polyester
Garner
was removed to reveal a cube-corner retroreflective sheeting that contained an
overall texture in the pattern of the fabric used and with glittering effect
in addition
to the overall texture. The glittering textured sheeting thus prepared
displayed
more intense glittering than sheeting prepared by Example 1 with no texture.
The
sample was tested for lightness and exhibited a LFY value of 54.33 {mean value
of
three measurements).
Example 6 - Glittering Sheeting Produced by a Continuous Process
Ordered retroreflective cube-corner sheeting as described in Examples
1 a-1 ee was passed through a continuous nip type lamination station as
illustrated in
46
CA 02252433 1998-10-20
WO 97141465 PCT/US97105594
FIG. 12. The apparatus was custom built and comprised a heated stainless steel
roll
77, an unheated rubber coated roll 7T, a mechanism for controlling and
adjusting,
by air pressure, the force with which the nip of heated roll 77 and unheated
roll 77'
meet, and a means of controlling the speed at which the drive roll moves. The
continuous lamination apparatus was adjusted to a speed of 1.5 ft/min (30.5
cm/min), 375 °F (175 °C) heated roll, 40 psi (2.75 X lOs Pa) nip
closure pressure.
Sheets of the ordered cube-corner retroreflective sheeting 3 inches by 17
inches (7.5
X 43 cm) were fed into the moving nip with cube-comer elements touching the
unheated rubber coated roll. The sheets were collected after passing through
the
nip, cooled to room temperature, and the polyester Garner was removed to give
a
glittering cube-corner retroreflective sheeting. Other processing conditions
were
used to prepare glittering retroreflective sheeting where the temperature,
speed, and
nip pressure were changed. Changing these conditions had similar effects on
the
glittering retroreflective sheetings as observed by changing process
conditions in the
batchwise process described in Example 1. Similar results were achieved using
a
continuous roll of sheeting.
Example 7- Glittering Sheeting Produced from an Electrojormed Mold
Cube-corner retroreflective sheeting capable of glittering prepared as
described in Example 1h was positioned on a backing support and fixed in place
with double sided adhesive tape. A silver metal coating was provided over the
entire surface by electroless deposition for rendering the glittering cube-
corner
retroreflecting sheeting conductive for electroplating. The resulting assembly
was
immersed in a nickel sulfamate bath containing 16 ounces/gallon (120 g/L) of
nickel; 0.5 ounces/gallon (3.7 g/L) of nickel bromide; and 4.0 ounces/gaIlon
(30
g/L) of boric acid. The remainder of the plating bath was filled with
distilled water.
A quantity of S-nickel anode pellets were contained within a titanium basket
that
was suspended in the plating bath. A woven polypropylene bag was provided that
surrounded the titanium basket within the plating bath for trapping
particulates.
The plating bath was continuously filtered through a 5 micrometer filter. The
temperature of the bath was maintained at 90 ° F (32 ° C) and a
pH of 4.0 was
47
CA 02252433 1998-10-20
WO 97/41465 PCT/LTS97/05594
maintained in the plating bath solution. A current density of 20 amps per
square
foot (215 amp/square meter) was applied to the system for 24 hours with the
mounted sheeting continuously rotated at 6 rpm to enhance a uniform deposit.
Upon removal from the electroforming bath, the cube-corner retroreflective
sheeting capable of exhibiting the glittering effect was removed from the
electrodeposited metal to give a nickel mold, approximately 0.025 inches
(approximately 0.063 cm) thick, which was the negative image of the original
glittering cube-corner retroreflective sheeting. The mold alone displayed the
properties of glittering, although it did not exhibit the rainbow hues of
which the
sheeting was capable, and the mold was retroreflective.
A mixture of 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, and
bisphenol A epoxy diacrylate in a ratio of 25:50:25 parts by weight with 1%
resin
weight of DarocurTM 4265 as photoinitiator (Radcure IRR 1010, Lot N215-0302,
UCB Radcure, Smyrna, Georgia) was carefully applied to one edge of the
electroformed mold. The bank of resin was slowly rolled across the mold
allowing
the resin to fill all features of the mold. When a smooth coating of resin was
in the
mold it was covered by rolling on a vinyl film sheet, 0.010 inches (0.025 cm)
thick
(American Renolit Corporation, Whippany, New Jersey 07981). The resulting
construction containing wet resin was cured through the vinyl film by passage
through a Fusion Model DRS-120QN system and exposure to a FUSION V lamp
operating at high power (235 Watts/cm) at a rate of 25 ft/min. (7.6 m/sec).
Removal of the cured sheeting from the mold gave a sheeting that was post
cured
on the backside of the cube-corner element array by passage under a FUSION H
lamp at 25 ft.lmin. (7.6 m/sec) at high power (235 Watts/cm}. The resulting
cube-
corner sheeting, made from the electroformed mold was retroreflective,
glittered,
and exhibited a rainbow of colors in the points of light.
Example 8 - Glittering Sheeting Produced from an Electroformed Mold with an
Ink Image
An image in the shape of "3M" was made with nonaqueous stamp pad ink
on the cube-corner side of cube-comer retroreflective sheeting that was
prepared as
48
CA 02252433 1998-10-20
WO 97/41465 PCT/US97/05594
described in Example 1 h. When the ink had dried the resulting glittering cube-
corner retroreflective sheeting bearing the ink image was mounted, prepared,
and
eiectroformed as described in Example 7. Removal of the sheeting from the
eiectroformed mold gave a nickel mold, approximately 0.025 inches
(approximately
S 0.063 cm) thick, which bore a reverse image of the rubber stamp. This mold
was
used to prepare cube-corner sheeting in accordance with Example 7. After
curing
and removing the newly formed sheeting from the mold, the sheeting was
observed
to be retroreflective, capable of exhibiting the glittering effect, capable of
exhibiting
the rainbow effect, and the sheeting bore the image of "3M" as stamped on the
original sheeting from which the mold was made. The image appeared on the
sheeting as a nonretroreflective glittering image on a retroreflective
background.
Fxamples 9a-4f - Screen Printed Images
A screen printing hand table (Model 1218 AWT World Trade, Inc.,
Chicago, Illinois) was fitted with a 110 T (mesh/inch) printing screen bearing
the
image "Atlanta 1996". Ordered cube-corner retroreflective sheeting as
described in
Examples 1 a-1 ee was placed on the printing surface and printed on with the
GV-
159 transparent permanent blue ink (Naz-Dar Corporation, Chicago Illinois
60622-
4292), or with SX 863 transparent green ink (Plast-O-Meric SP, Inc., Sussex,
Wisconsin 53089-0375}, or with SX 864 B opaque purple ink (Plast-O-Meric).
When the cube-corner elements were facing upwards during printing, the screen
printed image was formed on the back side of the cube-corner elements. When
the
cube-corner elements were facing downwards during printing, the screen printed
image was formed on the front, vinyl film surface of the cube-corner sheeting.
Sheeting with images printed with GV-159 Permanent Blue was air dried over
night
before further processing. Sheeting with images printed with SX 863 or with
SX 864 B was gelled with a Texair Model 30 screen printing belt oven (American
Screen Printing Equipment Company, Chicago, Illinois 60622) adjusted so that
the
infrared panel would operate at 1100 °F (593 °C), the
electrically heated forced air
was in the "off' position, and a belt speed to allow residence time of 42-46
seconds,
before further processing. After initial drying or gelation, the screen
printed cube-
49
CA 02252433 1998-10-20
WO 97/41465 PCT/US97/05594
corner sheetings were processed under heat and pressure as described in
Example 1.
Results of the processing are listed below in Table 4.
CA 02252433 1998-10-20
WO 97!41465 PCT/ITS97/05594
o~ °' E G .5 v
0
-° ~" o . ~ c~ c~7 .d
o ~ ~ .5 ~ o.~;b o
° ~ '~ ~ a
o ~, ,° 04 °' 04 on .a x .»
c ors ~ ~b ~ 'aW_ .~ E .°o
.~ .~e ~ .~ .a, ~ ~ ~o E w
-o ~ ~ ~ z:° ° ~ao~
(7 .° ..r ~ ,~ o ai
~ o.~ Z~~ °~
aA o o ° a
'c ~ ~ ~-° E_~ ~°' c 'c
...
4 °~ ° ~ ~w o~~ ~ 3 0 °'°c H
... ,~
o w~
.~E '~ ~ ~ ~.~ ~ ~ '~ v
° ~ .5 0 °~ j :c ° .d ~ 5 o p ,5
° .~ N E ' ... ,,.
_ ai . a a
.o
ea .° ~ ° ~ ° ~ x ~ ~' ~tw o
~ ~oa ~ o E °~' ~ W ~ ~ ~ ~ °
a o a a~ ~ E a~ ~ °'
a .~ ° ~ o ~ ~ ° o .~ y w o
° = ~ N ~w a ° °'' °:c~''~' ~.5 ~ ~.- °
o ° ~, ~ ~' ~ .r ° x ~ ~, ° ~ oo °
v as N z~"'u.~ z ~~z ~.~zz.~
0
C
W Vi ~ ~ ~, C ° V ~ C O .SC j~ ~ O .~E
a ~~ ~ 5 o v ~ ~ o v ~ ~ ° v
d >w °AO >w °c~ >w ~aA
E~ '-~ U ~ U U U
~o
v C
w rr
C C
C V n. G. C. G. ~ ~'
w ~ ~ ~ ~ ~ p O
C E-» E~ E-~ E-
L
_L
d
~ G1 G. ran ~ N ~ t~ n
~ .r ~ ,.., ~ ~ M ~ '/ M
~? a ~ °~'
z' ~ -_° ~ ° ~ 0°4 ° op
a ~ U ?~ U ~ U ~ ~ U ~
f.~ p0
M M
O ~ ~ ~ 00 N O~p ~ p~,p
C~7 w GA C~7 0: GA ~ U~ ran Ur can a1 ~ GA
o~ o'~'. o~ a o~
51
CA 02252433 1998-10-20
WO 97/41465 PCT/US97/05594
Examples l0a-lOn - Vapor Coated Sheering
Ordered nonrandom retroreflective cube-corner sheeting and the apparatus
used in Examples la-lee above were used. Retroreflective sheeting was prepared
with a vapor deposited layer of material approximately 850 ~ thick. The
ordered
cube-corner retroreflective sheeting was installed in a bell jar type vacuum
apparatus having an approximate capacity of 250 liters (Model 900-217-12,
Stokes
Vacuum Equipment, Equipment Division of Pennsalt Chemical Corporation,
Philadelphia, Pennsylvania 19120). After evacuation of the bell jar to 10-s
Ton or
less, the material intended to be vacuum deposited on the sheeting was
irradiated
with an electron beam (Airco Temescal, Electron Beam Power Supply Model CV-
10, Berkeley, California} until deposition on the cube side of the sheeting
was
complete. The resulting vapor coated, ordered nonrandom cube-corner sheeting
was processed by heat and pressure as described in Example 1 to give cube-
corner
sheeting capable of displaying very strong, extremely brilliant glittering
from both
sides. The sheeting prepared in this manner appeared to have better lightness
than
the sheeting that is vapor coated but does not have the cube-corner elements
oriented in accordance with the invention. Table 5 below lists representative
materials that have been vapor coated onto ordered, nonrandom cube-corner
sheeting. After vapor coating, all the sheetings were processed by heat and
pressure to make a sheeting capable of glittering. Table 5 also shows a brief
characterization of the vapor coated sheetings.
The two steps of this example, vapor coating, then processing by heat and
pressure, may be accomplished in reverse order with the same outcome. That is,
ordered, nonrandom cube-corner sheeting may first be processed as described in
Example 1 to provide sheeting capable of exhibiting the glittering effect. The
resulting glittering sheeting may then be subjected to vacuum deposition of
materials on the cube-corner side to give cube-corner sheeting that is capable
of
exhibiting very strong, extremely brilliant glittering from both sides. The
column
heading "Processing Sequence" in Table 5 refers to whether the cube-corner
sheeting was made glittering first and then was vapor coated or was vapor
coated
and then made glittering. The fisting "Glittering, then VC" refers to sheeting
that
52
CA 02252433 1998-10-20
WO 97/41465 PCT/US97/05594
was made glittering in a first operation then vapor coated in a second
operation.
The listing "VC then glitter and texture" refers to sheeting that was vapor
coated in
a first operation then made glittering in a second operation. In this case,
the vapor
coated sheeting was made glittering in the absence of the lower release paper
76 in
FIG. 11 and the resulting sheeting has the glittering effect superimposed on
an
overall pattern or texture from the lower, unheated rubber platen 74.
Examples 10a and lOb were tested for lightness, and these samples exhibited
LFY values of 16.7 and 18.9, respectively.
53
CA 02252433 1998-10-20
WO 97/41465 PCT/US97/05594
b .~ b ~, ~ cu
c~ ~ ~°c o ~ ~ ~ c~ ~ o ~ .c° .a ~ -c ~°
c ° ~'N ~ ~ ~'~ c a 3 3 °
._ o ~~ ~ ~ 'c ~ 3 ,.c ~
o ~N~E~~~~o~,~~~~ T'c.
0., .b ~ ~N o~ o~c°,'° ~'$ u~ ~ ~N ~, c
v ~.c a.a'~.n ~~.5 ~.0 0 3c~'~ ° 'b
in ~ ~~ ... 1r .r ~ . .. ..~ ..r
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54
CA 02252433 1998-10-20
WO 97/41465 PCT/LTS97/05594
~,~:v
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a, '~ ~ o ;~ _ o
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a~ ~ ~ ~ ~ c a o °~~' a~'~ o a 3 0 04~ ;~ o ''~ 3 ~
o ~ N o.~ o.°.~ o .~ o o.~ °' °'
~ °' °' ~~ °~,'._~ o Eye ~.c
uo~o i~ uoQ;d c.H~ a"~a~ ~; c, o.a.~._..
04 c~ b c~ pC, "" p( c~ o v~ O H " O ~ " L1 ~ as .a f~ ~ m w0
n
~i ~ a ~ ~ o
° ° N N ~ t~ °° 00
N ~ M ~ N
O) w N M N M
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c° ~ ~ o o a a H~ Hai
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a .,°~c y_ ° .~ :3 a
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CA 02252433 2005-04-15
60557-5972
Examplt 1l - Preparation ojRetro~ejlective Prodnet Having Seal ant
Glittering cube-corner retroreflective sheetings prepared according to
Example 9 were uhtasonically welded to a 0.01 inch (250 micrometers) thick
white
pigmented, embossed vinyl seal film (Nan Ya, Bachelor, Louisiana). The cubo-
corner elements of the screen printed glittering sheeting were placed in
contact with
the embossed side of the seal fpm, and a 0.002 inch (50 micrometers) thick
polyester 51m was placed on the unembossed side of the seal film. The
construction
was placed on a patterned anv0 attached to the base of a Branson Model I84V
uhrasonic welder with the polyester sheeting facing the horn of the welder and
the
vinyl body layer of the glittering cube-corner sheeting touching the patterned
snug.
The ultrasonic welder was operated at 20 lChz, 60 psi (4.2 x 10' Pa), 17 fpm
(5.2
m/min), with an amplitude equal to 60~/0 of maximum and a 2.865 inch (7.277
cm)
horn radius. The anvil comprised three 1 inch (2.5 cm) wide lance with
adjacent
triangles having sides approximately 1.5 inches (3.5 cm) in length and bases
approximately 2 inches (5 cm) in length, and one 1 inch (2.5 em) wide lane
having
diamonds with sides approximately 0.75 inches (2 cm) in length. The ultrasonic
welding process gave sealed samples whose seal lines were a clean reproduction
of
the anvil pattern.
As illustrated by the above discussion, the invention may take on various
modifications and alterations without departing from its total scope and
spirit.
Accordingly, the invention is not limited to the above-described but is to be
controlled by the limitations set forth in the claims and any equivalents
thereof.
56
