Method of making encapsulated-lens retroreflective sheeting

In encapsulated-lens reflective sheeting of the prior art, a monolayer of glass microspheres is embedded in a binder layer, a specularly reflective layer underlies the microspheres, and a cover film encapsulates the microspheres, within a plurality of hermetically sealed cells. In the invention, a HMW thermoplastic binder film, affords improved structural integrity, greater toughness, and better conformability to irregular surfaces without cracking. The cover film preferably is of the same polymer family as said binder film.

FIELD OF THE INVENTION 
The invention concerns encapsulated-lens retroreflective sheeting of the 
type disclosed in U.S. Pat. No. 3,190,178 (McKenzie) having a binder layer 
in which a monolayer of lenses such as glass microspheres is partially 
embedded. A cover film is sealed to the binder layer such that the lenses 
are encapsulated within hermetically sealed cells. The invention 
particularly concerns an improved binder layer for such encapsulated-lens 
sheeting. 
BACKGROUND ART 
The earliest retroreflective sheeting had an exposed-lens construction, but 
its reflex-reflective light was blanked out when the lenticular surface of 
the exposed lenses was covered with water. This problem was answered by 
enclosed-lens retroreflective sheeting in which, as first taught in U.S. 
Pat. No. 2,407,680 (Palmquist et al.), the lenses were embedded within the 
sheeting which had a flat, transparent cover film. This allowed incident 
light rays to be focused onto the specularly reflective layer irrespective 
of whether the front of the sheeting was wet or dry. The above-cited 
McKenzie patent solved the same problem in a different way, namely, by 
modifying retroreflective sheeting of the exposed-lens type wherein lenses 
are partially embedded in a binder layer. In the McKenzie patent, the 
exposed lenses are protected by a cover film to which the binder layer is 
sealed along a network of interconnecting lines, thus forming a plurality 
of hermetically sealed cells within which the lenses are encapsulated and 
have an air interface. Such exposed-lens sheeting is called 
"encapsulated-lens retroreflective sheeting". 
In the method taught in the McKenzie patent for making encapsulated-lens 
retroreflective sheeting: (1) substantially a monolayer of lenses such as 
glass microspheres is embedded into a carrier web to a depth not exceeding 
50% of the diameter of each microsphere, (2) specularly reflecting 
material is deposited over the lens-bearing surface of the carrier web, 
(3) a solution of binder material is applied over the specularly 
reflecting deposit, (4) after drying the binder, the carrier web is 
stripped off, (5) a cover film is laid over the exposed microspheres, and 
(6) heat and pressure are applied along a network of interconnecting lines 
to soften the binder material to allow it to flow around the microspheres 
and into contact with the cover film, thus forming the aforementioned 
hermetically sealed cells. It is believed that in the manufacture of all 
such encapsulated sheeting, the binder material includes a white pigment 
such as TiO.sub.2 to give the sheeting a whiter color as well as a cleaner 
color in any area to which another color has been applied by silk 
screening. The whiteness of the sheeting is enhanced if the specularly 
reflective material, usually aluminum, between the microspheres is carried 
away by the carrier web. To this end, the binder material may include a 
release agent such as stearic acid, but a release agent tends to interfere 
with the bonds between the binder layer and both the glass microspheres 
and the cover film. Better structural integrity is needed for uses in 
which the retroreflective sheeting is to be subjected to flexing or 
abrasion, as in roadlane markers, or impact, as in traffic cones. 
Another method for making encapsulated-lens retroreflective sheeting is 
taught in U.S. Pat. No. 4,075,049 (Wood). The first two steps of the Wood 
method are substantially the same as the first two steps of the McKenzie 
method, but in the third step of the Wood patent, some of the lenses 11a 
are forced into the carrier web 13 along a network of grid lines 18 as 
illustrated in FIGS. 3 and 4. Then a cast binder layer 23 is applied over 
the undisplaced lenses 11 such that some of the binder layer flows into 
the grid pattern between the undisplaced lenses (FIG. 5A). After the 
carrier web and the displaced spheres have been stripped off (FIG. 6) 
comparably to step (4) of the McKenzie patent, a flat, transparent cover 
film 27 is adhered to the binder layer at the grid pattern, between which 
the lenses are encapsulated and have an air interface 28 as shown in FIG. 
7. 
DISCLOSURE OF INVENTION 
The invention provides encapsulated-lens retroreflective sheeting which can 
have better structural integrity than has been achievable in the prior 
art. Both the method by which the sheeting can be made and the sheeting 
itself are believed to be novel. The novel encapsulated-lens 
retroreflective sheeting of the invention can be made by the method of the 
McKenzie patent except that instead of applying the binder material from 
solution, the novel method uses a preformed binder film which is a tough, 
flexible, weather-resistant thermoplastic polymer of high molecular weight 
(here called a "HMW thermoplastic binder film", or more simply a "binder 
film") as evidenced by a melt index no greater than 750 (ASTM Test Method 
D1238-79). Typically the HMW thermoplastic resin has a weight average 
molecular weight from 60,000 to substantially more than 1,000,000. Such a 
polymer is extrudable, although with some difficulty when the melt index 
is about 750. Preferably the melt index of the binder film is less than 
300, more preferably less than 150, because polymers of lower indices are 
easier to extrude and have better resistance to softening at elevated 
temperatures. 
Best results in the practice of this invention are obtained when the HMW 
thermoplastic binder resin has a gradual change in viscosity over a wide 
range of temperatures as taught in U.S. Pat. No. 4,505,967 (Bailey) at 
col. 8, lines 16-59 and FIG. 6. As taught there, representative resins 
having such a gradual change in viscosity exhibit a 
less-than-order-of-magnitude reduction in loss modulus, measured in dynes 
per square centimeter, when the resins are heated over a 
50-degree-centigrade temperature interval within the softening range of 
the material. 
Briefly, the encapsulated-lens retroreflective sheeting of the invention, 
like those of the McKenzie and Wood patents, comprises a binder layer in 
which substantially a monolayer of lenses such as glass microspheres is 
partially embedded, a specularly reflective layer underlying the 
microspheres, and a cover film sealed to the binder layer along a network 
of interconnecting lines forming hermetically sealed cells within which 
the lenses are encapsulated and have an air interface. The novel 
retroreflective sheeting differs from those of the McKenzie and Wood 
patents in that the binder layer is a HMW thermoplastic binder film which 
affords to the retroreflective sheeting improved structural integrity, 
greater toughness, and better conformability to irregular surfaces without 
cracking. 
The melt viscosity of the HMW thermoplastic binder film is quite high 
compared to the solvent-cast binders which have been used in 
encapsulated-lens sheeting such as in examples of the McKenzie patent. 
While this should make ho difference in the resulting encapsulated-lens 
sheeting when using a hard transparent cover film, as do the examples of 
the McKenzie patent, there may be a difference when using a cover film 
which is relatively soft at its inner-facing surface, especially when 
heated. If so, microspheres may partially penetrate the inner surface of 
the cover film before the HMW thermoplastic binder film can fully envelope 
them. In such event, it is well to select the cover film so that good 
adhesion develops between the microspheres and the cover film. 
For reasons mentioned above in discussing the McKenzie patent, the binder 
film may include a white opacifying agent such as a white pigment. The 
whiteness can be enhanced by a dual-layer (e.g., coextruded) binder film 
wherein the layer which contacts the lenses is relatively thin and has a 
greater proportion of white pigment and a higher melt index to enhance 
flow around the lenses. For such a dual-layer binder film, the polymer 
selected for the lens-contacting layer should afford especially good 
adhesion to the lenses, and the polymer selected for the other relatively 
thick layer should afford especially good toughness and flexibility 
Briefly, the novel retroreflective sheeting can be made as follows: 
(1) partially embed substantially a monolayer of lenses into a carrier web, 
(2) deposit specularly reflecting material over the lens-bearing surface of 
the carrier web, 
(3) under heat and pressure, contact with a HMW thermoplastic binder film 
portions of the specularly reflecting deposit which are on microspheres 
without contacting any portion of the specularly reflecting deposit which 
is on the surface of the carrier web between lenses, 
(4) strip off the carrier web, 
(5) lay a cover film over the exposed lenses, and 
(6) apply heat and pressure along a network of interconnecting lines to 
soften and deform the binder material into contact with the cover film, 
thus forming hermetically sealed cells within which the lenses are 
encapsulated and have an air interface. 
The lenses preferably are glass microspheres, and the diameter of each of 
the glass microspheres preferably is from 50 to 200 micrometers. At a 
preferred average microsphere diameter of about 65 micrometers, the 
thickness of the binder film should be at least 25 micrometers, preferably 
at least 50 micrometers so that the bases of the microspheres remain fully 
covered by the binder layer in the foregoing 6-step method. This also 
provides sufficient binder film to flow around the microspheres in the 
sealed areas. More than 150 micrometers may be uneconomical. 
Because the binder film does not contact portions of the specularly 
reflecting deposit between the lenses, the carrier web, when stripped off 
in step (4) of the above 6-step method, removes those portions of the 
deposit, thus leaving areas of the binder film between the lenses 
completely free from the specularly reflective material and its unwanted 
color. 
Preferably the binder film is extruded rather than cast from solution, thus 
avoiding the solvent cost and possible pollution from driving off the 
solvent. Furthermore, extrusion permits faster production rates as 
compared to the time delay in drying a solvent-cast film. An extruded 
binder film can either be extruded directly onto the specularly reflecting 
deposit on the microsphere-bearing surface of the carrier web, or it can 
be preformed and then reheated in step (3). The binder film should be 
supported by a dimensionally stable sheet such as biaxially oriented 
poly(ethylene terephthalate) film, preferably at least 12 micrometers in 
thickness to permit it to be stripped readily from the finished 
encapsulated-lens retroreflective sheeting. At thicknesses above about 50 
micrometers, it may interfere with the formation of well-defined cells in 
step (6). 
Between steps (4) and (5) may be an added step of pressing the exposed 
lenses into the binder film. When the lenses are glass microspheres, they 
may be pressed to a depth as great as about 95% of the microsphere 
diameter, preferably while applying heat. This mechanically locks the 
microspheres into the binder film, which is especially important for uses 
requiring stretching during application (e.g., to a cone) or involving 
repeated flexing (e.g., reflective highway lane markers). Depths exceeding 
50% of the microsphere diameter result in some sacrifice in brilliance and 
limited angularity, but the mechanical locking obtained, especially with 
embedding of 60 or 75% or more, outbalances such a sacrifice. 
The novel retroreflective sheeting could also be made by the method of the 
Wood patent except using a HMW thermoplastic binder film. However, it 
would be difficult to form a strong bond between the HMW thermoplastic 
binder film and a cover film except by selectively applying pressure to 
the grid network. It is questioned whether such pressure could be 
accurately applied at commercially useful rates. 
To enhance adhesion of the binder film to the inner surface of the cover 
film, the cover film at that surface preferably is highly compatible with 
and thus has great affinity to the binder film at useful sealing 
temperatures, and more preferably is of the same polymer family. Such 
materials tend to have greater toughness, flexibility, and extensibility 
than do materials which have been used in the prior art for transparent 
cover films. On the other hand, those materials may have less resistance 
to weathering and dirt accumulation, in which event the transparent cover 
film may be multi-layer, the outer layer of which provides good resistance 
to weathering and dirt accumulation. 
Best results have been achieved when the HMW thermoplastic binder film has 
been selected from (a) aliphatic urethane polymer or (b) a copolymer of 
monomers comprising by weight a major proportion of at least one of 
ethylene and propylene and a minor proportion of another monomer. Those 
HMW thermoplastic binder films can be expected to afford the elongation 
required to permit the retroreflective sheeting to stretch sufficiently to 
be applied to a traffic cone or to irregular surfaces such as sidewalls of 
various automotive vehicles. Good stretchability also is required when the 
novel retroreflective sheeting is to be embossed, e.g., when mounted on a 
license plate blank. To permit the blank to be embossed in a male/female 
die to a depth of 2.5 mm with no danger of cracking, the elongation of the 
HMW thermoplastic binder film should be at least 100%, preferably at least 
200%. Good stretchability is also required for use of the novel 
retroreflective sheeting in flexible traffic markers which must withstand 
repeated flexing under the tires of automotive vehicles. 
A preferred aliphatic urethane polymer is prepared from an aliphatic 
polyfunctional isocyanate and a polyfunctional hydroxyl-containing 
polymer, e.g., "Q-thane" P3429 of K. J. Quinn & Co., Inc. Among other 
preferred HMW thermoplastic binder films are ethylene copolymers, a number 
of which are commercially available at reasonable cost, including 
______________________________________ 
Melt 
Weight 
Supplier Designation 
Comonomer % Index 
______________________________________ 
Dow Chemical 
"Primacor" 
acrylic acid 
9 20 
3460 
E. I. duPont 
"Elvax II" 
methacrylic 
11 100 
5720 acid 
E. I. duPont 
"Elvax" 230 
vinyl acetate 
28 110 
______________________________________ 
Each of these polymers has excellent flexibility at temperatures as low as 
-4020 C. and also has good adhesion to glass microspheres, both with and 
without a specularly reflective metal coating. Other thermoplastic binder 
films which may be useful include polyesters, especially copolyesters of a 
glycol and two or more acids. 
A preferred encapsulated-lens retroreflective sheeting of the invention 
employs an ethylene copolymer as the HMW thermoplastic binder film and 
employs a cover film which also is an ethylene copolymer. Such a cover 
film is tough and has good resistance to impact, abrasion, solvents, 
moisture, and weathering. It also is relatively inexpensive. An espcially 
preferred cover film is multi-layer, the outer layer being an ionomeric 
ethylene copolymer and the inner layer being a nonionomeric ethylene 
copolymer. The ionomeric outer layer provides improved resistances to 
softening at elevated temperatures that may be encountered in use and also 
improved resistance to dirt accumulation. While it hasn't been 
established, an ionomeric ethylene copolymer may provide better resistance 
to weathering. 
When the HMW thermoplastic binder film is an aliphatic urethane polymer, at 
least the inner layer of the cover film preferably also is an aliphatic 
urethane polymer. It is exceedingly tough and resistant to impact and 
abrasion, but preferably is covered with a very thin film comprising an 
acrylic copolymer of monomers including methyl methacrylate and another 
acrylate or methacrylate wherein methyl methacrylate comprises at least 
20%, but not more than 90%, by weight of those monomers. 
It may be desirable to form the HMW thermoplastic binder film from two or 
more polymers, because a blend of polymers often provides greater 
toughness and flexibility than would either polymer by itself. One of the 
polymers may be selected to enhance adhesion to the cover film and 
possibly also to the lenses.

The sheet 10 shown in FIG. 1 comprises a carrier web 12 which is a 
composite of paper carrier 14 and polyethylene film 16. A plurality of 
glass microspheres 18 have been embedded to about 25% of their diameter 
into the polyethylene film while applying heat sufficient to enable each 
microsphere to fit snugly into the polyethylene. A thin-film layer 20 of 
aluminum has been vapor-deposited onto the microspheres 18 and onto the 
surface of the polyethylene film between the microspheres. While being 
vapor deposited, the aluminum vapors strike the microsphere-bearing 
surface of the carrie web 12 substantially orthogonally, thus leaving 
substantially free from aluminum the areas of the polyethylene surface 
lying immediately beneath a microsphere. 
In FIG. 2, the sheet 10 is shown being passed between a hot can 22 and a 
soft pressure roll 24 together with a laminate 26 (FIG. 3) of a HMW 
thermoplastic binder film 28 and a support 30 which is biaxially oriented 
poly(ethylene terephthalate) film (PET). The heat and pressure between the 
roller 22 and pressure roll 24 partially embed the microspheres 18 into 
the binder film 28 as shown in FIG. 3 but not to the extent that there is 
any contact between the binder film 28 and the portion of the aluminum 
layer 20 between the microspheres. After contact with a cooling roll 31, 
the carrier web 12 is stripped off, leaving the sheet 32 shown in FIG. 4 
which is wound upon itself to provide a roll 33. 
After unwinding the roll, a transparent cover film 34 (FIG. 5) which is 
resistant to weather and dirt is then laid over the exposed microspheres 
of the sheet 32, and heat and pressure are applied along a network of 
lines as taught in the McKenzie patent, thus softening and deforming the 
binder film 28 into contact with the cover film. This forms a plurality of 
hermetically sealed cells 36 within which the microspheres 18 are 
encapsulated and have an air interface. The PET support 30 may then be 
stripped away, and an adhesive layer 38 applied in its place. Preferably 
the adhesive is a pressure-sensitive adhesive and is protected by a 
low-adhesion liner 40 that may be peeled off to expose the adhesive layer 
by which the resulting encapsulated-lens retroreflective sheeting may be 
adhered to a substrate such as a signboard. 
As illustrated in FIGS. 4 and 5, each of the glass microspheres 18 is 
normally embedded into the binder film 28 only to about 10-30% of its 
diameter. However, by applying heat and pressure to the exposed 
microspheres of the sheeting 32 shown in FIG. 4, each microsphere may be 
embedded into the binder film 28 to a depth as great as about 95% of its 
diameter, thus securely locking each microsphere into the binder film to 
keep it from being dislodged when the product encapsulated-lens 
retroreflective sheeting is stretched and/or repeatedly flexed. 
Testing 
The following tests may be used to evaluate encapsulated-lens 
retroreflective sheeting. 
Seal Strength 
A 2.54-cm strip of encapsulated-lens sheeting is adhered by its adhesive 
layer to a rigid aluminum panel. A 2.54-cm tape is adhered to the 
transparent cover film. A sharp razor blade is then used to separate one 
end of the cover film from the binder film. Using an Instron Tensile 
testing device, the separated cover film is placed in the upper jaw while 
the aluminum panel is held in place by a jig attached to the lower jaw. 
The jig allows the cover film to be pulled away at 90.degree. from the 
binder layer. This measures the force required to delaminate the cover 
film from the microsphere-bearing binder film. 
Tensile and Elongation 
ASTM Test Method D882-80a in the down web direction. 
Retroreflective Measurements 
Retroreflective Intensity is measured using a retroluminometer as described 
in U.S. defensive publication No. T987,003 at a 0.2.degree. divergence 
angle and entrance angles of -4.degree. and +40.degree.. The Half 
Brightness Angle (HBA) is the entrance angle at which the retroreflective 
sample attains 1/2 of its original -4.degree. Retroreflective Intensity. 
Stretch-Flex 
This test measures the retention of Reflective Intensity at 0.2.degree. 
divergence angle and -4.degree. entrance angle when the encapsulated 
reflective sheeting undergoes a combination of stretching and bending or 
flexing. At ordinary room temperature, a sample of the sheeting 
(101.6.times.76.2 mm with or without any adhesive) is stretched lengthwise 
either 25% or 50%, is held in this stretched state, and then sharply 
passed over a 90.degree. bend at 90 mm/min with the bead binder layer 
against the 90.degree. bend. 
CAP Y 
CAP Y is a colormetric measurement of overall sheeting whiteness. This 
value is measured using a Hunter spectrophotometer. 
Optical Transmittance 
ASTM D1746-70. 
In the following examples, all parts are by weight. 
EXAMPLE 1 
Glass beads or microspheres having an average diameter of about 65 
micrometers and a refractive index of 1.91 were flooded onto a 
polyethylene-paper carrier web which had been heated to about 105.degree. 
C. Substantially a monolayer of the beads adhered to the polyethylene, and 
the excess fell off the web. The glass-bead coated polyethylene paper was 
then heated in an oven at about 140.degree. C. to soften the polyethylene 
so that the glass beads were drawn into the polyethylene to about 30% of 
their diameter by gravity and capillary forces. 
In a vacuum chamber, aluminum was deposited over the monolayer of glass 
beads to a thickness of about 100 nm. 
Onto a 20-micrometer PET support film was extruded a HMW thermoplastic 
binder film formed from a mixture of pellets of which 69.0 parts were a 
polyethylene/methacrylic acid (EMAA) copolymer and 31.0 parts were a 
concentrate consisting of 11.9 parts of a polyethylene/vinyl acetate (EVA) 
copolymer, 18.0 parts of rutile titanium dioxide white pigment, and 1.1 
parts of a weathering stabilizer system which in turn consisted of 1 part 
hindered amine light stabilizer and 0.1 part of antioxidant. The EMMA 
copolymer had a melt flow index of 100 and was understood to be a 
copolymer of 89 parts polyethylene and 11 parts methacrylic acid ("Elvax 
II" 5720 of E. I. duPont de Nemours & Co.). The EVA copolymer had a melt 
flow index of 110 and was understood to be a copolymer of 72 parts 
polyethylene and 28 parts vinyl acetate ("Elvax" 230). The extruder had a 
diameter of 4.4 cm and a length/diameter ratio of 30:1. The extruder 
temperature profile (from hopper end to die) was set at 77.degree., 
204.degree., 149.degree., 121.degree. C. The polymer transfer tube was set 
at 132.degree. C., while the film die was set at 143.degree. C. Extruder 
screw speed was adjusted to 26 rpm while the film takeaway was adjusted to 
12.2 m/min. to provide a binder film thickness of about 50 micrometers. 
Using apparatus as shown in FIG. 2, the bead-monolayer of the 
polyethylene-paper carrier web was contacted by the binder film carried by 
the PET support film while the hot can was at 104.degree. C. and the 
applied pressure was 31.6 kg/cm width at a line speed of 6 m/min. This 
pressed the glass beads into the binder film to a depth approximately 20% 
of their diameter. After peeling off the carrier web, the remaining 
laminate was wound upon itself as shown in FIG. 2. 
Examination under a microscope of the stripped carrier web and the 
bead-transferred binder film showed that 99% of the beads had transferred 
to the binder film while nearly 100% of the aluminum vapor coat between 
the beads remained behind on the carrier web. 
A transparent cover film comprising 98.85 parts ionomeric ethylene 
copolymer, 0.75 part U.V. absorber, 0.3 part hindered amine light 
stabilizer, and 0.1 part antioxidant was extruded onto another PET support 
film using the same 4.5-cm extruder. The ionomeric ethylene copolymer had 
a melt flow index of 0.7 and was understood to be a thermoplastic polymer 
which contains interchain ionic bonds based on a zinc salt of ethylene 
methacrylic acid copolymer ("Surlyn" 1706 of E. I. duPont de Nemours & Co 
). A temperature profile for the extruder from hopper end to die was set 
at 243.degree. C., 254.degree. C., 227.degree. C. and 210.degree. C. while 
the die was set at 241.degree. C. The extruder screw speed and film 
takeaway speed were adjusted to provide a transparent cover film having a 
thickness of about 100 micrometers and an Optical Transmittance of about 
89%. 
This transparent cover film was sealed to the bead-bearing surface of the 
binder film along a network of interconnecting lines as taught in the 
above-cited McKenzie patent under the following conditions: 
Surface temperature of embossing can: 174.degree. C., 
Embossing speed: 3 m/min, 
Nip roll pressure: 21.2 kg/cm width, thus encapsulating the glass beads in 
hexagonal cells about 3 mm across and a seal width of about 0.5 mm. After 
stripping off both PET support films, a pressure-sensitive adhesive layer 
carried by a protective liner was laminated to the exposed surface of the 
binder film, thus providing encapsulated-lens retroreflective sheeting as 
illustrated in FIG. 5. 
EXAMPLE 2 
Encapsulated-lens retroreflective sheeting was made as in Example 1 except 
that instead of the single-layer cover film of Example 1, a dual-layer 
cover film was prepared as described below. 
Layer A contained 96.45 parts of a copolymer of 91% polyethylene and 9% 
acrylic acid (EAA) having a melt index of 3.0 ("Primacor" 1420 of Dow 
Chemical Co.), 2.0 parts U.V. absorber, 1.5 parts of hindered amine light 
stabilizer, and 0.05 parts of antioxidant. Layer B contained 96.45 parts 
of ionomeric ethylene copolymer ("Surlyn" 1706) and the same amounts of 
the same three additives used in Layer A. A 6.4-cm extruder (L:D=30:1) was 
used for Layer A, and a 3.2-cm extruder (L:D=30:1) was used for Layer B. 
The temperature profile for the 6.4 cm extruder was 210.degree. C., 
290.degree. C., 297.degree. C. 283.degree. C. and 284.degree. C. while the 
temperature profile for 3.2-cm extruder was 229.degree. C., 253.degree. 
C., 239.degree. C. and 219.degree. C. The two layers were co-extruded 
through a 86-cm multi-manifold die at a face temperature of 280.degree. C. 
with end plates at 305.degree. C. Extruder screw speeds and film takeaway 
speed were adjusted to produce a dual-layer transparent cover film having 
a thickness of 100 micrometers with a thickness ratio of A:B=3:1. Optical 
transmission of the dual-layer cover film was about 88%. 
Layer A of the dual-layer cover film was sealed to the bead-bearing binder 
film under the following conditions: 
Surface temperature of embossing can: 174.degree. C. 
Embossing speed: 5 m/min. 
Nip roll pressure: 21.1 kg/cm width 
EXAMPLE 3 
Encapsulated-lens retroreflective sheeting was made as in Example 1 except 
as indicated below: 
The HMW thermoplastic binder film consisted of a mixture of 70 parts of a 
copolymer of 91% ethylene and 9% acrylic acid (EAA) having a melt index 
10.0 ("Primacor" 3440), 12 parts of the EVA copolymer used in Example 1, 
and 18 parts rutile titanium dioxide white pigment. Temperature profile 
for the extruder was set at 171.degree., 182.degree., 160.degree. and 
160.degree. C. while the die was set at 99.degree. C. Extruder screw speed 
and film takeaway speed were adjusted to provide a binder film thickness 
of approximately 75 micrometers. 
Conditions for developing the bead-transferred binder film were: 
hot can: 102.degree. C. 
nip roll pressure: 31.6 kg/cm width 
line speed: 6 m/min. 
A transparent cover film identical to that used in Example 1 was sealed to 
the bead-bearing surface of the binder film in the same manner as in 
Example 1 except under the following conditions: 
Surface temperature of embossing can: 216.degree. C. 
Embossing speed: 4.5 m/min 
Nip roll pressure: 23.8 kg/cm width 
EXAMPLES 4, 5 AND 6 
Encapsulated-lens retroreflective sheetings were made as in Example 1 
except as indicated below. 
The HMW binder film consisted of 82 parts of a thermoplastic aliphatic 
urethane polymer believed to be the reaction product of 1,1-methylene 
bis(4-isocyanatocyclohexane), adipic acid, isophthalic acid, and 
1,4-butane diol ("Q-thane" P3429 made by K. J. Quinn and Co. Inc.), and 18 
parts rutile titanium dioxide. Binder film was extruded onto a duplex 
support film consisting of 12.5 micrometer low-density polyethylene (LDPE) 
and 12.5-micrometer PET. Prior to being extruded, the materials had been 
dried to remove excess moisture content in a dehumidification type dryer 
at 66.degree. C. for 16 hours. Extrusion conditions for the binder film 
were 171.degree. C., 193.degree. C., 210.degree. C. and 216.degree. C. 
Extrusion die end plates were set at 204.degree. C. while the body of the 
die was set at 193.degree. C. Extruder screw speed and film takeaway speed 
were adjusted to provide a binder film about 50 micrometers in thickness. 
Conditions for developing the bead-trasferred binder film were: 
hot can: 110.degree. C. 
nip roll pressure: 25.2 kg/cm width 
line speed: 32 m/min. 
Heat and pressure were applied to the bead-bearing surface of two portions 
of this bead-bearing binder film in order to enhance the bead bond to the 
binder film, thus reducing the danger that the beads might be dislodged in 
use. Those two portions were used in making enclosed-lens retroreflective 
sheeting of Examples 5 and 6, respectively, while an unmodified portion 
was used in making that of Example 4. Bead-sink conditions were: 
______________________________________ 
For binder film of: 
Example 4 Example 5 Example 6 
______________________________________ 
Applied Temperature 
-- 152.degree. C. 
152.degree. C. 
Applied pressure 
-- 25.2 25.2 
(kg/cm width) 
Line speed -- 4.6 m/min 1.0 m/min 
Approximate depth of 
20 50% 85% 
beads in binder 
______________________________________ 
A transparent cover film was extruded using the 4.4-cm extruder and the 
thermplastic aliphatic urethane polymer used in making the HMW binder 
film. Extrusion conditions were 171.degree. C., 182.degree. C., 
188.degree. C. and 193.degree. C. The die end plates were set at 
199.degree. C. while the body of the die was set at 193.degree. C. Screw 
speed and film takeaway speed were adjusted to provide a thickness of 
approximately 100 micrometers. Optical Transmittance of the resulting 
cover film averaged 86%. 
Pieces of the transparent cover film were sealed to the binder films under 
the following conditions. 
______________________________________ 
Example 4 
Example 5 Example 6 
______________________________________ 
Embossing can surface 
168.degree. C. 
168.degree. C. 
168.degree. C. 
temperature 
Line speed (m/min) 
4.6 4.6 4.1 
Nip roll pressure 
19.5 19.5 19.5 
(kg/cm width) 
______________________________________ 
Properties of the encapsulated-lens retroreflective sheetings of Examples 
1-6 were: 
______________________________________ 
Example 
1 2 3 4 5 6 
______________________________________ 
Seal width 
0.56 0.46 0.48 0.25 0.25 0.3 
(mm) 
Seal strength 
1150 1150 550 1250 1600 2150 
(g/cm width) 
Tensile 
strength at 
break (MPa) 
15.5 10.0 12.6 28.2 31.6 29.9 
Elongation (%) 
300 390 380 430 450 440 
Retroreflec- 
270 260 260 300 290 310 
tivity at -4.degree. 
(cancellas 
per lumen) 
Retroreflec- 
-- -- -- 390 395 190 
tivity at +40.degree. 
(candellas 
per lumen) 
HBA -- -- -- 56.degree. 
54.degree. 
42.degree. 
Stretch-flex 
-- -- -- 47 97 98 
(%) at 25% 
Stretch-flex 
-- -- -- 31 74 97 
(%) at 50% 
CAP Y -- -- -- 21.6 24.7 28.2 
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