Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF MAKING GLITTERING CUBE-CORNER
RETROREFLECTIVE SHEETING
This is a divisional application of Canadian
Patent Application No. 2,252,978, filed April 4, 1997.
TECHNICAL FIELD
This invention pertains to a method of making
cube-corner retroreflective sheeting that glitters when
exposed to light.
The subject matter of the present divisional
application is directed to a method of making a glittering
retroreflective cube-corner sheeting involving forming the
sheeting from a mold that directly creates tilted cube-
corner elements when forming the sheeting, and is further
directed to a method of making a retroreflective product
therefrom. The subject matter of the parent was restricted
to a method of making a glittering retroreflective sheeting
involving applying heat or pressure to a pre-made cube-
corner retroreflective sheeting to cause the cube-corner
elements to randomly tilt. However, it should be understood
that the expression "the invention" and the like, when used
herein, encompass the subject matter of both the parent and
this divisional application.
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
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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
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a variety of previously produced cube-corner arrays (including those disclosed
in
the patents cited in the next paragraph).
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,
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 disclos~i 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 retroreffective sheeting's
daytime
conspicuity, they possess the drawback of requiring the addition of another
ingredient namely dye or pigment, to achieve the enhanced conspicuity.
SUMMARY OFTHEINIlENT70N
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
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invention enhances conspicuity by providing a cube-corner
retroreflective sheeting that glitters when exposed to
light. In a first aspect, the method of the invention
includes: (a) providing a first retroreflective sheeting
that includes an array of cube-corner elements arranged in a
repeating pattern; and (b) exposing the first
retroreflective sheeting to heat, pressure, or a combination
thereof to produce a second retroreflective sheeting that
comprises an array of cube-corner elements that are randomly
tilted. The exposure to heat, pressure, or the combination
thereof which causes the cube-corner elements to become
randomly tilted occurs other than through securing a seal
film to the array of cube-corner elements arranged in the
repeating pattern.
In a second aspect, a method of the invention
includes providing a mold that has a structured surface that
includes an array of cube-corner elements that are arranged
such that a cube-corner sheeting that is formed thereon
glitters when exposed to light; and forming the cube-corner
sheeting from the mold. 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.
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According to one aspect of the present divisional
application, there is provided a method of making a
glittering retroreflective cube-corner sheeting, which
method comprises: forming a glittering retroreflective cube-
s corner sheeting from a mold that has a structured surface
that includes an array of cube-corner elements that are
arranged such that a dihedral angle a between faces of
adjacent cube-corner elements varies to such an extent that
a cube-corner sheeting that is formed thereon glitters when
exposed to light.
In some embodiments, the glittering effect may be
seen from both the front and back sides of the sheeting
produced in accordance with the method of the invention when
light strikes either the front or the back of the sheeting.
The glittering effect is particularly noticeable when the
resultant sheeting is 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
produced by a method of the invention also can glitter when
viewed from the backside -90 degrees to +90 degrees from a
normal or zero degree incidence angle. Even if the
incidence angle is offset from a
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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" oa and off of light
from
different cube-corners occurs, resulting in the phenomenon of glitter.
Sheetings
produced by a method of the invention may be capable of glittering under
essentially
all possible illumination and viewing angles, in all combinations.
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
product identifiers. These advantages and others are more fully descn'bed
below in
the detailed description of the imrention.
According to another aspect of the present invention, there
is provided a method of making a retroreflective product that
comprises making a retroreflective sheeting according to a method
described herein and securing a sealing film on a back surface of
the retroreflective sheeting.
BRIEFDES1CRIP?70N OF T~IEDRAH'INGS
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-corn, er element 30 that may be used in
a retroreflective sheeting produced in accordance with the present imrention.
FIG. 4 is a bottom view of a retroreflective sheeting 60 produced in
accordance with the present invention.
FIG. S is a sectional view of retroreflective sheeting 60 taken along lines 5-
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 having a seal film
63 secured to the backside of the retroreflective sheeting 60.
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FIG. 9 is a front view of retroreflective product 61 illustrating a seal
pattern
that may be used to produce hermetically-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 placed on its outer surface ?0.
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 ?l.
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.
FIG. 13 is a top view of a mold ?9 that may be used in producing a
glittering retmreflective 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
sheeting from a mold ?9.
FIG. 15 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 I04a that may be used to produce an
image in a glittering article.
FIG. 16b is a side view off' an insert 104b that may be used to produce an
image in a glittering article.
DETAILED DESCIUPTIOly OFPREFERRED EMBODINIENTs
In the practice of the present invention, a retroreflective sheeting is
provided
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 (LFY). Clear, colorless sheetings of
the
invention may demonstrate a LFY value of 38 or greater, and even 55 or
greater.
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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
S 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 50, points of light per square centimeter (cmz)
when
the sheeting is viewed under direct sunlight. Typically, there are less than
about
250 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 5,470,058,
5,362,374,
5,276,075, 5,202,180, 3,988,494, 3,987,229, 3,697070, 3,692,731, and 3,010,845
--
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 laid 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-comer 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
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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 produced by methods 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, 316, 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 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-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 (see U.S. Patent No. 4,938,563 to Nelson
et
al.), or it may be of essentially any other shape that possesses cube-comers
(see, for
example, U.S. Patent No. 4,895,428 to Nelson et al.).
FIG. 4 shows the structured 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 306, but cube 30b's apex
may
then be farther away from another adjacent apex such as the apex of cube 30c.
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Cube-corner sheetings that may be produced in accordance with methods of the
present invention are disclosed in U . S . P a t ent No . 5 , 8 4 0 , 4 0 5 .
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. Hase edges 35 define the lowest
point
of grooves 45-47 - and because edges 35 do not all lie 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
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 s>rrface
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 (U.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-comer elements in
the
array. For purposes of 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
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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, a, 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-corner elements throughout essentially the whole array
that
is intended to glitter. Angle a 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 groove
intersections 35 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
350
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
difl'erence 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 SO 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.
The body layer 58 (FIG. 5) 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.
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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-comer elements to produce triangles 62 of different cross-
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 filin is bonded to the
body
layer 58 of the sheeting 60 through the layer of cube-corner elements 30 by a
plurality of seal lines 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 retrorefleetivity.
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,
CA 02521906 1997-04-04
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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 groups, the tendency of the polar groups to
switch orientation with the radio frequency determines the degree to which RF
energy is absorbed and converted. to kinetic motion. The kinetic energy is
conducted as heat to the entire polymer molecule, and if enough RF energy is
applied, the polymer will heat sufficiently to soften. Deta~7ed discussions of
RF
welding may be found in U. S . Patent No . 5, 691, 8Q6 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 retroreflective sheeting 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
ultrasonic welding. Ultrasonic welding is a technique where two materials are
bonded together between a horn and an anvil. The horn m'brates 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 are
positioned to
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localize 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 more effectively. Examples of materials that form good-to-
excellent
ultrasonically welded bonds include nylon, polycarbonate, plasticized
polyvinyl
chloride) (PVC), polystyrene, thermoplastic polyester, polypropylene, and
acrylics.
Polyethylene and fluoropolymers are examples of materials that form fair to
poor
ultrasonic 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 retardants, pigments, and plasticizers.
Reference is
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 sealing individual items. When the
glittering
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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 ivn parallel to bond lines
64a and
64b. Extending between bond lines 64c and 64d are bond lines 64e that are not
parallel to the sheeting's lengthwise edges. Bond 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
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 bl 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 seal 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
13
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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 S 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 specularly reflective metallic coating can be placed on the backside of
the cube-
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 18.
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 appfied include shirts, sweaters, jackets,
coats,
pants, shoes, socks, gloves, belts, hats, suits, one-piece body garments,
bags,
14
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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 arid is
capable of
displaying a retroreflective article on its outer surface.
In accordance with the. present invention, the inventive glittering cube-
s corner sheetings can be made by two techniques. In a first technique, a
glittering
cube-corner retroreflective sheeting is made by providing a fvst cube-corner
sheeting that has the cubes arranged in a conventional configuration, namely,
a
repeating 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.
When using the first technique, a retroreflective sheeting is first pmdueed or
otherwise obtained which has the cube-corner elements arranged in an ordered
configuration. There are many patents that disclose retroreflective sheetings
that
have ordered arrays of cube-corner elements: see, for example, U.S. Paterns
5,236,751, 5,189,553, 5,1?5,030, 5,138,488, 5,117,304, 4,938,563; 4,7?5,219,
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, 3,924,929, 3,811,983, 3,810,804, 3,689,346, 3,684,348,
and
3,450,459. Ordered cube-corner arrays may be produced according to a number of
known methods, including those disclosed in the patents cited in the previous
sentence. Other examples are disclosed in U.S. patents: 5,450,235, 4,6D1,861,
4,486,363, 4,322,847, 4,243,618, 3,811,983, 3,689,346, and 5, 691, 846.
Preferably, the cube-corner elements that are used in the non-randomly
oriented starting sheeting are made from materials that are harder than the
materials
used in the body portion, particularly the body layer. A selection of such
materials
allows the cube-corner elements to tdt, without significantly distorting each
cube's
shape, when the sheeting is exposed to certain amounts of heat and/or
pressure.
The heat, pressure, or both that are applied to the sheeting should be su~ciem
to
alter the array significantly from its ordered configuration. With a very soR
body
layer, pressure alone, that is, pressure above atmospheric, or heat alone,
namely,
CA 02521906 1997-04-04
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heat greater than the softening temperature may be sufficient to change the
array
from an ordered configuration.
A cube-corner retroreflective sheeting that has hard cubes and a softer body
layer is disclosed in U.S. Patent No. 5,450,235 to Snvth et al. As descn'bed
in this
patent, the body portion includes a body layer that contains a polymeric
material
that has an elastic modulus less than 7 x l Os Pascals. The cube-corner
elements, on
the other hand, contain a polymeric material that has an elastic modulus
greater than
16 x 10' 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
U.S. Patent Nos. 5,614,286 and 5,691,846.
U.S. Patent No. 5,691,846 also discloses a
number of materials that may be used to 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 10g
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 10g Pascals.
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.
16
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' 60557-5979D
Under some'circumstances, the polymer may be so hard and brittle that it is
diff cult
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 "Nanoindentation Technique" may
be
employed. This test may be carried out using a microindentation device such as
a
UIvaS 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 function 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
gradient 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. Int. J. Eng. Sci. 3, pp. 47-~7 (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-v2) _ (dF/dlk)F,~1/(3.3h~tan(6)) ,
where:
v is Poisson's ratio of the sample being tested;
(dF/dh~) is the gradient 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 Berkovich 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 ?1 that includes
first and
17
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second pressure-applying surfaces 7Z and 74. that can be moved towards each
other
The laminator may be, for example, a ITtx model N-800 heat transfet machine
available from l3ix Corporation ofPittsburg, Kansas.
A llix N-800 laminator has a first pressure-applying surface ?2 that is made
S of metal and that may be heated to temperatures as high as 500 °~.
The second
pressure-apph~ng 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 carries 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 (set, for example,
U.S. Patent No. 5 691,846 at the discussioan describing ite FIG. 4,
where the carrier is represented by numeral 28) and may optioa~a~ly
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
psper 76 are arranged in the heat lamination machine as shown in F1G. I1, 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
FJG. 11
may be omitted, and the pattern or image of the lower, unheated surface ?4 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
s
Scotchlite'"'r Neat Lamp Applicator available from Dayco Industries, lne.,
Miles,
l~~Lchigan; P.M. Hlack Co., Stillv~~ater, T~nnesota; and Convening
Technologies,
lnc., Goodard, Kansas-- may be used. .
23 The amount of heat andlor pressure applied to a cube-corner sheeting 10
may vary depending on the materials from v~hich 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 10' to 25 x 10' are used in the cube-corner
elements .
12 (and an optional land layer 1 ~, . and a polymeric material having an
elas~ttc
modulus of about 0.05 x 10' to 13 X 1,0~ pascals is used in the body layer 18,
the
cube-corner sheeting, preferably, is heated to a temperature of about 300 to
400 °F
18
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60557-5979D
(150 to 205 °C) and that about 7 x 10" to 4.5 x lOs 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
Darocur'~ 4265 photoinitiator (Ciba Geagy) and having an elastic modulus of
about
16 x 10g to 20 x 10g to 1 x 108 pascals, and the body layer is made from a
plasticized polyvinyl chloride) film having an elastic modulus of around 0.2 x
10g
pascals, the cube-corner sheeting preferably is exposed to temperatures of
about
320 to 348 °F (160 to 175 °C) and pressures of about 1.4 x 105
to 2.8 x 103 pascals
(20 to 40 psi). Using polymers that have a relatively high elastic modulus,
for
example, greater than 16 x 10g 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 77'. 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 formed between adjacent cube-corner elements
vary
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 rolls
is
capable of producing a glittering effect, whereas the cube-corner sheeting 10
that
has not been exposed to sufficient 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
19
CA 02521906 1997-04-04
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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
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
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.
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.
CA 02521906 1997-04-04
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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
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
forth the cube-corner elements. The mold may be used to form retroreflective
sheeting or to generatc 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 dihedral 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 parallel v-shaped
grooves
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 groove 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 described above for
producing
21
CA 02521906 1997-04-04
60557-5979D
glittering of cube-corner sheeting with the exception of being a negative
thereon
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 glittering retroreflective sheetings is descnbed 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 through a
cast
and cure process 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 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 roller 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 raith 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 vis'ble light,
depending
22
CA 02521906 1997-04-04
60557-5979D
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 degee 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 79, exposing the sheeting's cube-
corner elements 30. One or more secondary curing treatments 100, selected
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 penmit 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
23
CA 02521906 1997-04-04
60557-5979D
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 selectcd.
Afler 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
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 also 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
fiuther 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-corner elements, and to drive ofrunreacted
moieties
and byproducts. Typically, the sheeting is heated to an elevated temperature,
for
24
CA 02521906 1997-04-04
60557-5979D
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
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. 11. Thin material in the shape of the desired image, such as an insert
104 (104
refers generically to any suitable insert including 104a and 104b of FIGS. 16a
and
166) in FIG. 11 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 exampie, 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
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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
material 105. 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 104a 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
26
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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 andlor
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
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 constcvction 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 --
e.g.
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
27
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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 that 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
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 andlor
cured. Removal of the patterned sheeting reveals a newly formed mold that
bears
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
28
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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
S 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
resins. The elastic modulus of such polymers preferably is greater than about
10 x 108 pascals, and more preferably is greater than about 13 x 108 pascals.
Examples of thermoplastic polymers that may be used in the cube-corner
elements include acrylic polymers such as poly(methyl methacrylate);
polycarbonates; cellulosics such as cellulose acetate, cellulose (acetate-co-
butyrate),
cellulose nitrate; epoxies; polyurethanes; polyesters such as poly(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
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
silicone 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.
29
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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 acrylate group.
Preferably
the resin blend contains a difunctional 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,
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 retror effective 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:
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ethylacrylate, n-butylacrylate, isobutylacrylate, 2-ethylhexylacrylate,
n-hexylacrylate, n-octylacrylate, isooctylacrylate, isobornyl acrylate,
tetrahydrofurfuryl acrylate, 2-phenoxyethyl acrylate, N,N-dimethylacrylamide;
(2) Difunctionai compounds;
1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, neopentylglycol
diacrylate,
ethylene glycol diacrylate, triethyleneglycol diacrylate, and tetraethylene
glycol
diacrylate, and diethylene glycol 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
vinyl caprolactam, monoallyl, polyallyl, and polymethallyl esters such as
diallyl
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
isobutyl
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-hydroacy-2-
methylpropan-1-one, 2-benzyl-2-N,N-dimethylamino-1-(4-morpholinophenyl)-
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.
Cationically polymerizable materials include but are not limited to materials
containing epoxy and vinyl ether functional groups. These systems are
photoinitiated by opium salt initiators such as triarylsulfonium, and
diaryliodonium
salts.
31
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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 polymers are preferred for one or more 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.
A good interface prevents spreading of retroreflective Iight 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 10g pastels, and may also
be
less than 3 x 10g pastels. 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 10$ Pascals. Generally,
the
polymers of the body layer have a glass transition temperature that is less
than
32
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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 Vicar softening temperature that is greater than
SO°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 UV 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
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 available from Pennwalt Corporation, Philadelphia,
Pennsylvania;
ionomeric ethylene copolymers such as: polyethylene-co-methacrylic acid)
with sodium or zinc ions such as Suriyn-8920 and Surlyn-9910 available from
E.I. duPont Nemours, Wilmington, Delaware;
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);
33
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non- or unplasticized rigid vinyl polymers such as Pentaprint'''"d 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-maieic acid), and polyethylene-co-fumaric acid); acrylic
functional polymers such as poly(ethylene-co-alkylacrylates) where the alkyl
group
is methyl, ethyl, propyl, butyl, et cetera, or CH3(CHz)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-1,2-butylene oxide glycol,
and
combinations of these polydiols, and (3) chain extenders such as butanediol or
hexanediol. Commercially available urethane polymers include: PN-04, or 3429
from Morton International 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 groups or esters of
carboxylic
acids such as polyethylene-co-acrylic acid), polyethylene-co-methacrylic
acid),
polyethylene-co-vinylacetate); the ionomeric ethylene copolymers; plasticized
polyvinyl chloride); and the aliphatic urethanes. These polymers are preferred
for
one or more of the following reasons: suitable mechanical properties, good
adhesion to the land layer or cube-corner elements, clarity, and environmental
stability.
Selection of certain resins for the cube-corner elements and the body layer
may result 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.
34
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Priola, A., Gozzelino, G., and Ferrero, F., Proceedings of the Xlll
International
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 elements.
The tie-
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 available
from K.J. Quinn and Co., Inc., Seabrook, New Hari~pshire; 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,
NeoCryl~"'~
A-601, A-612, A-614, A-621, and A-6092, available from ICI Resins US,
Wilmington, Massachusetts; or an alkyl acrylate and aliphatic urethane
copolymer
water borne dispersion, for example NeoPac~ R-9000, available from ICI Resins
US, Wilmington, Massachusetts. In addition, an electrical discharge method,
such
as a corona or plasma treatment, 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 ate 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
CA 02521906 1997-04-04
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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 article of the invention is prepared in accordance with the second
technique, soft polymers - that is, polymers having an elastic modulus less
than
x 10g pascals - may be used to produce the cube-corner elements in glittering
10 retroreflective sheeting. In the second technique, the cube-corner elements
are not
subjected to the heat andlor 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
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; alkyla&oxysilanes; 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
36
CA 02521906 1997-04-04
60557-5979D
technique can also yield soft materials. The properties of the nonreactive
polymers
can be adjusted by changing the concentration of additives such as
plasticizer, 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-50, available
from BASF Corporation, Clifton, New Jersey, or CyasorbTM UV531 from Cytech
Industries, West Patterson, New Jersey; Syntase~ 230, 800, 1200 available from
Nevilie-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.
Examples of hindered anune light stabilizers include Tinuvin~-144, 292, 622,
770,
and Chimassorbz'~''-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, KronitexT"i TCP,
from
37
CA 02521906 1997-04-04
60557-5979D
FMC Corporation, Philadelphia, Pennsylvania - also may be added to the
polymeric
materials of the inventive sheeting to optimize its overall properties, as weU
as-the
properties of the article to which it may be attached.
Flexible gliriering 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
warning flags,
road signs, traffic cones, Iight 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. Retroreflective sheetings produced in accordance with the
method
of the invention also may be embossed or otherwise adapted into three
dimensional
IS structures as taught in U.S. Patent No. 5,763, 049.
The invention is further illustrated in detail by the following Examples.
While the Examples serve this purpose, it should be understood that the
particular
ingredients used as weU as other cbnditions and details are not to be
construed in a
manner that would unduly limit the invention.
EXAMPLF~
RetroreJlective Brightness Test
The coefliciern of retroreflection, R,~ was measured in accordance with
standardized test ASTM E 810-93b. R,~ values are expressed in candelas per lux
per square meter (cd~bt'1~m ~. The entrance angle used in ASTM E 810-93b was -
4
degrees, 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 sentence.
38
CA 02521906 1997-04-04
60557-5979D
Zighrness Test
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 .- r~rfect diffusing reflector.
Zero degree
illumination and 45 degree circumferential viewing were employed in
detainining
the LFY. LFY values range from 0 to 100, where a LFY value of 0 represents
black and a LFY value of 100 represents wl'~ite.
Examples 1 a-l ee - Batchwise Production 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,
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 DarocurT"~ 4265 as photoinitiator, a 0.01 inch (230 pm) thick cleat,
colorless, flexible vinyl body layer, and a polyethylene terephthalate carrier
film
0.002 inches (50 pm) thick. The resin was cured through the film with a FUSION
H lamp (available from Fusion UV Curing Systems, Gaithersburg, Maryland)
operating at 235 Watt/cm at 25 ft/min (7.6 mlmin), 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 ftlmin (7.6 m/min). The sheeting was placed onto Kraft release
paper (ScotchcaP~ SCW 98 Marking 1 ilm, 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 (H'nc 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.?5 X
10s
39
CA 02521906 1997-04-04
60557-5979D
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 is was tested for lightness, and this sample exhibited an LFY value
of 37.73.
CA 02521906 1997-04-04
60557-5979D
TABLE 1
Effect of Batchwise Process
Conditions on Formation of Glittering Sheeting
Mean
Brightness
R,, at
(cdllux~~)
Entry Temp Tune Pressure0 90 Courrents
sec si
la 195 45 40 528 440 No
lb 225 45 40 599 514 No f
lc 249 45 40 721 608 No litterin
ld 2?5 45 40 1270 739 No
le 300 45 40 919 834 No litterin
if 324 45 40 543 582 SIi t litterin
1 340 45 40 303 302 Full I'
lh 349 45 40 253 268 Full litterin
li 374 45 40 197 238 Full 'tterin
1' 401 45 40 105 I37 FuU
lk 350 60 40 254 222 Full litterin
11 350 40 40 23.4 222 Full lute
lm 350 30 40 342 356 Full f
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 li
lr 350 12 40 655 743 Full litterin
is 350 10 40 1086 874 Medium lifts
It 350 8 40 1357 860 Medium line
lu 350 6 40 1136 847 Sli t litterin
lv 350 4 40 1245 789 No litte '
lw 350 2 40 845 727 No li
lx 350 10 5 --- --- Sli t litterin
1 350 10 10 - Medium itterin
lz 350 10 20 - - Full line '
laa. 350 10 30 --- - Full litterin
lbb 350 10 40 - -- Full line '
lcc 350 10 50 - - Full U
ldd 350 10 60 --- --- Full litterin
lee 350 10 70 - --- Full litre '
41
CA 02521906 1997-04-04
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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
Hix 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.
42
CA 02521906 1997-04-04
60557-5979D
.5 ~ 00 0 o ai .5 00 ~ .~~.: c °' °'~ c
a oo ~ ~ ~ 'C o N as
au o ~ .5 ~; '-~-o ~ o
~ 04. >, ~., ~ ° o
a a ~~ E '~ ~ ao ~~ o ~ o
.c oo ~ ~., ~ ~ . ~ 8 p o b a~ ~ ~ ° on
° ~ 3 a~ c .~ a .- c ~ o °4 .x
o -r .~ ~ ~ w ~ °Q ~ c z ~ pp y,~ ~ ~ a~a
'.° o .E 3 ~ .~ 'b ~ v o4 ~ ~ .c
~~ a.°' .~ ~ ~,~ w.c c~ ~ ~.x ~~5
04 ~ ~ ~ ~ 'o op '~' a.' c~.
A ~ .a = ~ > as '~, o ~ ~ .~ °~' ~ o. ~ a, a .~
ap.~ .a tp.. p '~f.". '~ ~ j '~"~' 4: ~5 ai ~ ~. W
dpp ~d ~ O ai a~
Z! ~ ~ (> 47 O C ~ ~ ~ ~=,O,'
'''~ ~ a~ ~s c~ ~ aEa .° .~ ~ E .~ as '~' ~ .~ ~
o c ~ ~~ .a k o ='' np ~ ~ °' c
v ,E ~~ p .,.r .b di W b 3 ~bp~E ' ed
U a~ ~ ~ ~ o .~ ~ , C .5 ~ a a~ o 0
gS ~
~~ .°~' c ~ .x _, a. ~ °~' ~ 3 0 .~ 3
a~ :.: ~ o -° a~ e~ = a~ = .~ p ~w 3 .~ '° °' = :a-' ~ ~
a
w w z C7 .o z .5 > a, - > ~ w 8 .c w ~ .~ > 'au ~ .c v~ C7 ~
0
00
o '~
.i. ~ v
o ~, ~n ~", 0 0 0 ~n o ,p
et N N N ~ N
N ,'i,
W .Q
d d
v~1 N N M Vo1
C ~d
q~ 't7
C
C p E ~ >> >, i> >, ~ E
0 ~ O p ~ ~ ~ .~ ~ O O
r"'' ~ xp,~ ~ ~ 'b b b b
p ~.O ~ ~ ~ :D ~ .po
c ~ ~ ~ ~~ .~ .~ ,c
.~ .r ..~
c ~ 0 0 0 0
U U U U U U U U
c c c a a ~ c c
od
'o ~.'~ ~ .~c" .a ~ ~ ~ .a a
~44V Q ~ d Q a Q w w
NNNNN~''1N N
43
CA 02521906 1997-04-04
60557-5979D
_ayv g o o o
~ o~ g w
~ .~
~
.
~
w ~ ~-cw ~'
~ w
p p ~ _~ ~
p
N
...
~.x~b; ~'o~~ o"~~ ~
.
o
~ ~ .
'ao
i ~ ~ ~ ~ w'~
n o ''
~ ~ W
a ~."' .
~ '~ ~ N
E
~
c, a~ .., a 5
~ ~" .-. ~
~
. , . b
._ ~ o
~ ~ s ~
A ~; ac ~ c
~ c
v ~ ~ .~ .~ 3 .~ r
o ~ .~ ~
3 ~
i~i
E ''
"
a.E ~ '~ b "~_ ~
b 'ab c
E
04 ~ .
~ ~ E ~
E ~ -o
o ...,
~
"' " ~ a
o o ~
o ~
C7 ~ st~e ~ c no ~
a ~ -o -a .
~ ~ x '
a~
~ o o . . ~ =
: ~ 3 . ~
' ~ ~ 0
~ ~ ~
~
. c7. V~ .
N m V~ 0. V~
V .a t3.
.C N
fV
Er N M M vp
~.
i
O 0 N N
E E E E
c, o o o
~ .
~
~" .
.
o ~ ~ ~ >,
e~oa" ~ F~ ~ ~ o
a.
V _C L' C L
C~ C7 C~ V
~
_~ _
Car ~w'
U ~ U U o
U
o a ~ v
oh
v ~ w
~~C~ a. w a, w a~
N N ~V
N
CA 02521906 1997-04-04
60557-5979D
Examples 3a - 3f - Creation of Images Using a Polyester Film
Ordered retroreflective cube-corner sheeting and the apparatus described in
Examples 1 a-1 ee 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
Pa). Descriptions of the imaged sheetings are listed in Table 3.
CA 02521906 1997-04-04
60557-5979D
.~ '~ ono 'C .~ >, .~ ~~ ~ °° w ~ .c o~°C ~
°° c c
4,~~ a ~o "edees Op~~" ~ .r''~' ee3.D Opas~C
o a~ ... oo .r
~ 00 ~ '~'' pp ~ ev 'd ~ y °r a~ ~ ~d0 ~ 'C
~.~ p'C O ~ 'r~' ~ i ~' ~ ~ O',.~'3 ~
.'" 'r s.. O ~ ''' O O .C O .a O
~ ~r ..~, O O U r ~ .... ~ U p >, '!"~ ~ ~~ O s.. >,
d ~ U U 04
pp ~ ~ ~ o °~ ~ a°'o ~ ~ °° ~ o o~o~ a~ -o
°° ~ o
°' ~ ~~'v c a . ~s'~ o~ ~ '~~" 04~ ~ ,,~.~c hi
d an-~ ~ ~ e~ .. dpi ~ > ~ .., O
d .~ o ~ .o ~' ~~.C o a. ~ a~ '~ o ~o 0 on'~ eu
0o a~ ~ o ~'° a ~ c 2 . .. °~s a ~ Et~ a~ ~ a = e~ ~
's~~' w 3 awC ~ a~ rn 'C ~ ~ v v~ O a~ '= e,:., ev
a ~ .x .~ ~ O a~ ~_ > .°~~ a~ ~; ~ ~ O a, ~; a~ 3
3 ~ ~" ~ _~ .. 3 ,~ co ea
~~o o ~ ~ ~'e o'bo,_.. o o... ~ .c~ 0 0
~, U OO.I~ O ~'' V ~ CD~ U GO y ~ ~ ~ .~. H d4 ~ C
y" ..~E ~ ed ~ Op U . U
E~ ~ 7.~r ai ~ ~ w ~ '~ 4. E~
C ~ 'b ~ ~ ''O' dU ~~ ~ ~ O ~ ~ ~ -s~ ~" b O 4, ~ v :r ~. a..
... ~ eu CC "O ~ O ~_ ~ O ~ ~; ~'. ~ p ~ ~ O ~ O
~v ~ 'r,~G, a ~ y° tr'e v~ °: °' °0'~ .a :c "~ ~
rn ~ ,s~ :c
U ~ ~ at U ~ ~ ee: "p ~ ~ ~ ~ ~ ~'~ ~ ai °~ ~
O 4 C" e~ai~C110 ~ O O U C~'~.y rU'' O t: r'U'' U L1.~~U.pQ~ s; ~","
Va-nJ ~.~ .~i ~ f/l ~ O ~VJ ~ 1On w >1 '~'1 ~ O ~ ~ ~ '~ ~ y V
t ~o n~~ vr~~
~ GA a~ v~ c~G4 .'~s~ > o°~~o.c a~ v~ v .'~c .'~c v~ 0~4.~ ~ ~, ''
'° '~
o
'ro~ro°o o°oo°o~ o
~ G~' ~. ~. ... ~. ~ en
r ~~
~w
a
C
O
wr
O
> > > > >
., _,
O d '~ ~ r''
~. z ~ z ~ z
M M M M M M
a6
CA 02521906 1997-04-04
60557-5979D
F_xample 4 - Creation of Image Using Transfer Ink
Ordered retroreflective cube-corner sheeting and the apparatus described in
Examples 1 a-1 ee 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 lOs 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 la-lee were used, with the optional polyester carrier in place. The
image
forming element was a piece of polyester plain weave fabric 2.2 ozJyd2 (188
g/m2)
and was located as illustrated by 104 in FIG. 11. 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
carrier
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.
F_xample 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
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,
47
CA 02521906 1997-04-04
60557-5979D
by air pressure, the force with which the nip of heated roll 77 and unheated
roll 7T
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-corner elements touching the
unheated rubber coated roll. The sheets were collected after passing through
the
nip, cooled to room temperature, and the polyester carrier 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 Electroformed Mold
Cube-corner retroreflective sheeting capable of glittering prepared as
described in Example lh 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 ounceslgallon (3.7 g/L) of nickel bromide; and 4.0 ounces/gallon
(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
maintained in the plating bath solution. A current density of 20 amps per
square
foot (215 amplsquare meter) was applied to the system for 24 hours with the
4s
CA 02521906 1997-04-04
60557-5979D
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 Darocuf~'"~ 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./min. (7.6 ri~/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-corner retroreflective sheeting that was
prepared as
described in Example lh. When the ink had dried the resulting glittering cube
corner retroreflective sheeting bearing the ink image was mounted, prepared,
and
49
CA 02521906 1997-04-04
60557-5979D
electroformed as described in Example 7. Removal of the sheeting from the
electroformed mold gave a nickel mold, approximately 0.025 inches
(approximately
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.
Examples 9a-9f - Screen Printed Images
A screen printing hand table (Model 1218 AWT World Trade, Inc.,
Chicago, Illinois) was fitted with a 110 T (meshrnch) 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 (Plant-O-Meric SP, Inc., Sussex,
Wisconsin 53089-0375), or with SX 864 B opaque purple ink (Plant-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-
corner sheetings were processed under heat and pressure as described in
Example 1.
Results of the processing are listed below in Table 4.
CA 02521906 1997-04-04
60557-5979D
x _ ~ x~ ~S ~.g
p ~" o ~ ~ ~° °'
b o
o ~ ~ .S ~ o ~e :0 0
w ~~ ~~v' .,°;
o, ~ ~ .~ ...
,~ ~ 'd ~ ~ do
E_ '.~ ~ ,~ o ~ °°
a~ E ,~ ~ ~ ° ~ ai ~ ~4 E ti
~b ~ ("~ '~ Z -N ~ ~ 0p cb ai
.a w w,
... .o
o ai o 0 0°'0 0
E ~' .~ " ° ~ °~ ~ .C
~r .r
a3 0 ~ ~ '~ ~ ~ w; .~ ~ a
A ~= °°~ ow ~~ 3 0 0
0 0 ~ °~ ~ ow ..
.~w ... E ~ ~ ' ~ y. ~,b
Cj ,f"",' N .~ ~ ,~ d ,~ p~ ~ ~~ ~ oTi
V > ~ G' ...0, ~ r.. vy. m y C V1 ~ O
4i .L ~ ~ ~O ~ ~ 4i ,~'~~'3 W ~ d :~~.. N ... L'
C" pp in O ~.~, ~ '~" N~ ._~, G"r G O
o p ~.~, ~ ~ O O ~ ~ v'~ ~ f~ v .~ o~
C C~ ~ .~ O ~ O i.~. ct"~, r O .b O .., p
O a. O p~ 4, t~ ,v~
c~ ~ z~~u.~ z ~~z H.~zz.~
p
v ,~ O U ~ ,~ O U ~ ~ O U
o >w ~a4 >w a~~ >w a~a4
HIV ~ U U U
V
C
,~ _ ~ ~ ~ d ~ ~ 47
Q. C4 O, O O'
..y
C H E~ H E-~
O ~ m
L
_~ ~ H a m ~ G. m
O. G. ~ ~ H ~
a e~ a e~
O ~ a" ~ LL ~D ~ M ~D 'r C~1
O m Vi CY yr O~ yr O td et O e0 '~
'o -0 0 0 ~ o r~ ~°3 a ~°3
U7~ U~ U~~U~
f~ C4
O ~ C N1 M 'Q' !f
L" rr .r ~ ~ C ~ C. ~O ~G
~ 00 00 ~ 00 ~ 00
C>7a~.~GOt>7A;~ ~U~
o~ o~. o, o~°. o~
51
CA 02521906 1997-04-04
60557-5979D
Examples l0a-10n - Vapor Coated Sheeting
Ordered nonrandom retroreflective cube-corner sheeting and the apparatus
used in Examples 1 a-1 ee 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 900-2I7-12,
Stokes
Vacuum Equipment, Equipment Division of Pennsalt Chemical Corporation,
Philadelphia, Pennsylvania 19120). After evacuation of the bell jar to 10-s
Torr 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 S 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 listing "Glittering, then VC" refers to sheeting
that
52
CA 02521906 1997-04-04
60557-5979D
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 l0a and l Ob were tested for lightness, and these samples exhibited
LFY values of 16.7 and 18.9, respectively.
53
CA 02521906 1997-04-04
60557-5979D
3 ~ >' 3 3
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54
CA 02521906 1997-04-04
60557-5979D
~ c ~ ~ ~~ ~ ~~_
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CA 02521906 1997-04-04
60557-5979D
Fxnmple 11- Preparation olRetroreJlective Product Having Seal ~Int
Glittering cube-corner retroreflective sheetings prepared according to
Example 9 were ultrasonically welded to a 0.01 inch (250 micrometers) thick
white
pigmented, embossed vinyl seal film (Nan Ya, Bachelor, Louisiana). The cube-
corner elements of the screen pointed glittering sheeting were placed in
contact with
the embossed side of the seal film, and a 0.002 inch (50 micrometers) thick
polyester film was placed on the unembossed side of the seal film. The
construction
was placed on a patterned anvil attached to the base of a Branson Model 184V
ultrasonic 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
anvil.
The ultrasonic welder was operated at 20 Khz, 60 psi (4.2 x lOs Pa), 17 fpm
(5.2
mlmin), with an amplitude equal to 60% of maximum and a 2.865 inch (7.277 cm)
horn radius. The anvil comprised three 1 inch (2.5 em) wide lanes with adjacem
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 cm) wide lane
having
diamonds with sides approximately 0.75 inches {2 cm) in length. The ultrasonic
welding process gave sealed samples whose seal.fines 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
