Coating processes – Optical element produced – Polarizer – windshield – optical fiber – projection screen – or...
Reexamination Certificate
1999-12-10
2002-03-12
Mills, Gregory (Department: 1763)
Coating processes
Optical element produced
Polarizer, windshield, optical fiber, projection screen, or...
C216S007000, C156S345420
Reexamination Certificate
active
06355302
ABSTRACT:
BACKGROUND
The present invention relates generally to continuous methods of making beaded retroreflective products. The invention has particular application to methods of making bulk quantities of retroreflective end-use materials such as fabrics for use or application in shoes, vests, backpacks, handbags, appliques, or similar personal belongings.
The reader is directed to the glossary at the end of the specification for guidance on the meaning of certain terms used herein.
The use of beaded retroreflective fabrics (sometimes referred to in the literature as reflective fabrics) to increase the visibility of pedestrians has long been known. Such fabrics have the property of reflecting incident light, such as light from a vehicle headlamp, back in the general direction from which the light originated, regardless of the angle at which the incident light impinges on the surface of the fabric. Thus, a person wearing such a fabric can be highly visible to drivers of such vehicles at night, depending on (i) the amount of retroreflective fabric used, and (ii) the reflectivity of the particular fabric.
The retroreflectivity is provided by a layer of tiny glass beads or microspheres that cooperate with a reflective agent such as a layer of aluminum. The beads are partially embedded in a binder layer that holds the beads to the fabric, and partially exposed to the atmosphere. Incident light enters the exposed portion of a bead and is focused by the bead onto the reflective agent, which is disposed at the back of the bead embedded in the binder layer, whereupon the light is reflected back through the bead, exiting through the exposed portion in a direction opposite to the incident direction. This type of construction is referred to as an “exposed lens” retroreflector, because it uses microspheres with portions that are exposed to the atmosphere.
There is a wide variety of such beaded retroreflective fabrics available today from a number of manufacturers. However, the methods currently used to make such fabrics on a commercial basis fall into three basic types.
The first type of known process is referred to herein as the “randomized bead” process. In it, a solution that consists of a water-based ink, specially prepared beads, and a coupling agent is applied to the fabric by screen printing, or alternatively by flexographic or continuous roll printing. Each specially prepared bead has been provided with a hemispherical coating of aluminum. When the solution dries, at least some of the beads protrude from the bead bond that secures them to the fabric. No attempt is made to orient each bead so that the uncoated portion is exposed to the air and the aluminum-coated portion is embedded in the bead bond, but in practice enough beads are so oriented (because of their random alignment) so that the treated fabric achieves a reflectivity of up to about 60-70 cd/(lux·m
2
), and more typically about 25-30 cd/(lux·m
2
). An advantage of this process is its simplicity, but a major drawback is the relatively low reflectivity achieved.
The second type of process is referred to as the “bead drop” process. In it, a resin that contains tiny flakes of aluminum is roll coated onto the fabric. The coated fabric is then passed through a bead application station, where uncoated glass beads are dropped onto the resin from a bead reservoir above the web. The beads sink partially into the resin. Finally, the web is passed through an oven that cures the resin. Because of the optically inefficient distribution of the aluminum reflector, fabrics prepared using this process achieve reflectivities of only about 30-90 cd/(lux ·m
2
) at best. Like the randomized bead process, the bead drop process is relatively simple to implement in production, but it also achieves only low reflectivity values.
The third type of known process, referred to as the “release liner” process, is more complex and generally more expensive than the other two, but can produce high performance retroreflective fabrics having reflectivities of 500 cd/(lux·m
2
) or more.
FIGS. 1-3
depict some aspects of a representative process, variations of which can be found in published literature, e.g. U.S. Pat. No. 3,172,942 (Berg), U.S. Pat. No. 5,344,705 (Olsen), U.S. Pat. No. 5,474,827 (Crandall et al.), and U.S. Pat. No. 5,510,178 (Olsen et al.).
FIG. 4
depicts a portion of a reflectorized fabric made by such representative process. In
FIG. 1
, a carrier layer
10
comprising a paper sheet
12
and a heat-softened polymer lining
14
(see detail in
FIG. 1
a
) passes underneath a bead application station
16
. Glass microspheres or beads
18
cascade from a reservoir
20
down onto the carrier layer. The beads
18
sink partially into the lining
14
, forming a monolayer of beads, portions of which are exposed (see detail in
FIG. 1
b
). After the lining
14
has cooled, the carrier layer
10
with the monolayer of beads
18
is wound up into a roll so that it can be transported to a vacuum chamber
21
, shown in FIG.
2
. The carrier layer roll is unwound in the vacuum chamber
21
so that, at a metal coating station
22
, a specularly reflective metal
24
such as aluminum can be applied to exposed portions of beads
18
and to any exposed portions of lining
14
, forming a reflective aluminum film
26
(see detail in
FIG. 2
a
). The carrier layer is wound up, removed from the vacuum chamber, and unwound again for the next operation, shown in FIG.
3
. In that figure, a layer of prebinder composition
28
is applied by roll-coating to the aluminum-coated monolayer of beads. This yields a carrier layer web the details of which are substantially as shown in
FIG. 3
a
. The fabric
30
to be reflectorized is then introduced and brought into contact with the prebinder composition
28
. In
FIG. 3
, this is shown by passing the fabric
30
and the carrier layer with its various coatings through a nip formed between rollers
32
.
FIG. 3
b
shows the details of the resulting web. The web so constructed then passes through an oven
31
, where prebinder composition
28
solidifies. In a final step (not shown), the carrier layer
10
is stripped away and discarded to make fabric
30
retroreflective as shown in
FIG. 4
, by virtue of the partially exposed monolayer of beads
18
cooperating with the underlying reflective film
26
, both held to the fabric by binder layer
28
. Such a fabric can achieve reflectivities of 500 cd/(lux·m
2
) or more because of the consistent placement of the reflective aluminum film on the embedded portion of each bead.
Each of the three above-described processes has been used commercially since at least about the mid-1970s. However, until now there has been no continuous process that is both: (i) considerably simpler than the release liner method, and (ii) capable of producing highly retroreflective fabrics. This is so despite a general awareness of other methods of making certain exposed lens retroreflective articles, including the method of U.S. Pat. No. 3,790,431 (Tung), where a binder material is coated on an open web type fabric, microspheres completely covered with a reflective material are applied to the coated fabric, the binder material is dried or cured, and reflective material covering exposed surfaces of the microspheres is removed, as by etching. See also U.S. Pat. No. 3,934,065 (Tung); U.S. Pat. No. 3,989,775 (Jack et al.); U.S. Pat. No. 4,005,538 (Tung); and 4,678,695 (Tung et al.). Thus, there has been a long-felt need for a relatively simple continuous process capable of making large quantities of high performance reflectorized fabric.
BRIEF SUMMARY
Disclosed herein are continuous processes capable of manufacturing commercial quantities of high performance reflective fabric, i.e., fabric having a reflectivity of at least about 100 cd/(lux ·m
2
), but which are greatly simplified compared to the release liner method because they do not require the use of any release liner.
Instead, in the disclosed processes, an extended length of fabric is provided such as by unwinding an input roll of the fabric to be reflecto
Billingsley Britton G.
Fox Frederick J.
Reule Joey L.
Vandenberg John L.
Hassanzadeh P.
Jensen Stephen C.
Mills Gregory
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