U.S. patent number RE30,892 [Application Number 06/029,702] was granted by the patent office on 1982-03-30 for area-retroreflectorization of fabrics.
This patent grant is currently assigned to Minnesota Mining and Manufacturing Company. Invention is credited to Terry R. Bailey, Wallace K. Bingham.
United States Patent |
RE30,892 |
Bingham , et al. |
March 30, 1982 |
Area-retroreflectorization of fabrics
Abstract
Retroreflective-treated fabrics, and products and methods for
forming the treatments are taught. As an example, a free-flowing
mass of minute retroreflectorization particles that each comprise
hemispherically reflectorized transparent microspheres supported in
a softenable binder material are cascaded onto a fabric. The binder
material is softened during application to provide adhesion of the
particles to the fabric. A very sparse retroreflective treatment
can be provided, which leaves the fabric with nearly its full
original appearance as well as hand, feel, and breathability. Yet
the treatment will greatly increase the safety of a pedestrian by
making him visible at night.
Inventors: |
Bingham; Wallace K. (North
Saint Paul, MN), Bailey; Terry R. (Woodbury, MN) |
Assignee: |
Minnesota Mining and Manufacturing
Company (St. Paul, MN)
|
Family
ID: |
27363518 |
Appl.
No.: |
06/029,702 |
Filed: |
April 11, 1979 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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540286 |
Jan 10, 1975 |
|
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Reissue of: |
766332 |
Feb 7, 1977 |
04103060 |
Jul 25, 1978 |
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Current U.S.
Class: |
442/132; 359/518;
359/538; 427/162; 427/163.3; 427/163.4; 427/199; 427/204; 427/205;
427/412; 428/426; 428/433; 428/446; 428/450; 428/457 |
Current CPC
Class: |
D06Q
1/10 (20130101); G02B 5/128 (20130101); Y10T
442/2598 (20150401); Y10T 428/31678 (20150401) |
Current International
Class: |
D06Q
1/10 (20060101); D06Q 1/00 (20060101); G02B
5/128 (20060101); G02B 5/12 (20060101); B32B
005/16 (); B32B 017/06 () |
Field of
Search: |
;428/241,433,426,446,450,457 ;427/163,162,412,205,204,199
;350/105,109,97 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Smith; Ronald H.
Assistant Examiner: Bell; Janyce A.
Attorney, Agent or Firm: Alexander; Cruzan Sell; Donald M.
Tamte; Roger R.
Parent Case Text
REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of pending application
Ser. No. 540,286, filed Jan. 10, 1975, now abandoned.
Claims
What is claimed is:
1. Fabric treated on at least one surface with a discontinuous
sparse retroreflective treatment that has low visibility in
daylight but provides a bright retroreflection at night, said
treatment comprising discrete separated retroreflective areas that
each include a thin layer of binder material adhered to the fabric
and separated from the binder material of other retroreflective
areas, and one or more glass microspheres that average no more than
about 200 micrometers in diameter supported as a monolayer in said
layer of binder material; at least about one-third of microspheres
adhered to the fabric in said retroreflective areas having specular
reflective means in optical connection between them and the fabric
and having their outwardly facing surface optically exposed for
receiving and returning light rays, whereby they retroreflect
incident light that is normal to the fabric; there being no more
than about 2000 microspheres in any square centimeter of said
treatment; and the maximum surface dimension of said
retroreflective areas being no greater than about 1 millimeter.
2. Fabric of claim 1 in which said separated retroreflective areas
each include on the average no more than about 50 microspheres.
3. Fabric of claim 1 in which said specular reflective means
comprises a specularly reflective coating on the surface of the
microspheres.
4. Fabric of claim 1 in which the binder material is a
heat-activated adhesive.
5. Fabric of claim 1 in which there are on the average less than
about 500 microspheres per square centimeter of said treatment.
6. Fabric of claim 1 in which the maximum surface dimension of said
retroreflective areas is no more than about one-half
millimeter.
7. A garment comprising at least one piece of fabric of claim
1.
8. Fabric treated on at least one surface with a discontinuous
sparse retroreflective treatment that provides in aggregate at
least about one candella per square meter of the fabric per lux of
light incident on the fabric but leaves the fabric with nearly its
full original hand, breathability, and appearance whereby the
fabric may be made into comfortable garments having an
inconspicuous daytime appearance, said treatment comprising
discrete separated retroreflective areas that each include a thin
layer of binder material adhered to the surface of the fabric and
separated from the binder material of other retroreflective areas,
and one or more transparent microspheres that average less than
about 100 micrometers in diameter supported as a monolayer in said
layer of binder material; at least about one-third of the
microspheres adhered to the fabric in said retroreflective areas
having specular reflective means in optical connection between them
and the fabric and having their outwardly facing surface optically
exposed for receiving and returning light rays, whereby they
retroreflect incident light that is normal to the fabric; the
maximum surface dimension of said retroreflective areas being no
more than about one millimeter and there being no more than about
500 microspheres per square centimeter of said treatment.
9. Fabric of claim 8 in which said specular reflective means
comprises a specularly reflective coating on the surface of the
microspheres.
10. Fabric of claim 8 which provides a reflection in aggregate of
less than about 10 candellas per square meter of the fabric per lux
of light incident on the fabric.
11. Fabric of claim 8 in which the optically exposed surface of the
microspheres is also physically exposed to the air above the binder
material.
12. Fabric of claim 8 in which said discrete retroreflective areas
include on the average no more than about 10 microspheres.
13. Fabric of claim 8 in which there are on the average less than
about 300 microspheres per square centimeter of said treatment.
14. A garment comprising at least one piece of fabric of claim
8.
15. A method for providing a retroreflective treatment on a fabric
comprising
A. depositing onto the fabric a free-flowing mass of
retroreflectorization particles that comprise (1) on the average no
more than about fifty transparent microspheres arranged in a
closely packed monolayer; (2) a solid binder layer in which the
microspheres are supported and which may at least in part be
softened to adhere the particles to the fabric; and (3) specular
reflective means underlying the monolayer of microspheres and
supported by the binder layer in optical connection with the
microspheres whereby the microspheres are made retroreflective; the
surface of the microspheres opposite from the reflective means
being optically exposed to receive and return light rays; and
B. providing conditions to soften said binder layer, whereby at
least a portion of said retroreflectorization particles become
adhered to the fabric with the optically exposed surfaces of the
microspheres facing away from the fabric.
16. A method of claim 15 in which said binder material can be
softened with heat, and said conditions comprise the application of
heat.
17. A method of claim 15 in which said monolayer of microspheres is
partially embedded in the binder material and partially exposed,
and the embedded surfaces of the microspheres are covered with a
specular reflective coating.
18. A free-flowing mass of minute discrete retroreflectorization
particles useful for forming a retroreflective coating on a
substrate, said particles individually comprising on the average
one up to about 50 transparent microspheres supported as a closely
packed monolayer by a solid binder layer which may at least in part
be softened to adhere the particles to a substrate; and specular
reflective means underlying the microspheres and supported by the
binder layer in optical connection with the microspheres to make
the microspheres retroreflecting; the surface of the microspheres
opposite from the reflective means being optically exposed whereby,
when the particles are adhered to a substrate with said optically
exposed surface facing away from the substrate, the microspheres
will retroreflect light incident on the substrate.
19. Retroreflectorization particles of claim 18 in which the binder
layer is softenable by heat.
20. Retroreflectorization particles of claim 18 in which said
monolayer of microspheres is partially embedded in the binder layer
and partially exposed; and the embedded surfaces of the
microspheres are covered with a specular reflective coating.
21. Retroreflectorization particles of claim 18 which include on
the average no more than about 10 microspheres.
22. Retroreflectorization particles of claim 18 in which said
microspheres have an average diameter of no more than about 100
micrometers.
23. A free-flowing mass of minute retroreflectorization particles
useful for forming a retroreflective coating on a substrate, said
particles individually comprising on the average one up to about 50
transparent microspheres that have an average diameter of no more
than about 100 micrometers and are arranged as a closely packed
monolayer; a solid binder layer in which the microspheres are
partially embedded and which may be softened with heat to adhere
the particles to a substrate; and a specular reflective coating
covering the embedded surfaces of the microspheres to make them
retroreflecting; the surface of the microspheres opposite from the
reflective means being optically exposed whereby, when the
particles are adhered to a substrate with said optically exposed
surface facing away from the substrate, the microspheres will
retroreflect light incident on the substrate.
24. Retroreflectorization particles of claim 23 which include on
the average no more than about 10 microspheres.
25. Retroreflectorization particles of claim 23 in which the
specular reflective coating is metallic.
26. Retroreflectorization particles of claim 23 in which the
specular reflective coating comprises a transparent dielectric
material.
27. Retroreflectorization particles of claim 23 in which said
binder layer comprises at least two sublayers, and the microspheres
are partially embedded in one of the sublayers.
28. Fabric having retroreflectorization particles of claim 23
adhered to one surface at a density of less than 500 spheres per
square centimeter of the surface.
29. A garment comprising at least one piece of fabric of claim
2.
30. Retroreflectorization particles of claim 18 in which the
specular reflective means comprises nacreous pigment particles
underlying the microspheres.
31. Retroreflectorization particles of claim 23 in which the
specular reflective coating comprises nacreous pigment
particles.
32. Retroreflectorization particles of claim 18 in which the
specular reflective means comprises a transparent dielectric
layer.
33. Fabric having retroreflectorization particles of claim 18
adhered to one surface.
34. A garment comprising at least one piece of fabric of claim
33.
35. A method of claim 15 in which said retroreflectorization
particles comprise on the average no more than about ten
microspheres. .Iadd. 36. Fabric treated on at least one surface
with a retroreflective treatment that comprises transparent
microspheres distributed over the surface of the fabric in a
discontinuous sparse arrangement and adhered there by a thin layer
of binder material; the microspheres averaging no more than about
200 micrometers in diameter, and at least about one-third of the
microspheres having specular reflective means in optical connection
between them and the fabric to make them retroreflective, and
having their outwardly facing surface optically exposed for
receiving and returning light rays; there being no more than about
2000 microspheres in any area occupying one square centimeter of
said treatment and the maximum surface dimension of discrete
retroreflective areas of said treatment being no greater than about
1 millimeter, whereby the treatment provides low visibility in
daylight but bright retroreflection at night. .Iaddend..Iadd. 37.
Fabric of claim 36 in which discrete retroreflective areas of said
treatment include on the average no more than about 10
microspheres. .Iaddend..Iadd. 38. Fabric of claims 36 or 37 in
which there are on the average less than about 500 microspheres per
square centimeter of said treatment. .Iaddend..Iadd. 39. A garment
comprising at least one piece of fabric of claim 36.
.Iaddend..Iadd. 40. Fabric of claim 36 in which the microspheres
are hemispherically coated with specularly reflective material.
.Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention is directed toward a need, as we conceive it,
for a retroreflective treatment for fabrics that is so
inconspicuous in daylight and of so little effect on hand, feel,
and breathability, that garments made from the fabric will be
widely worn by pedestrians; and that yet is so brightly
retroreflective that the pedestrians will be readily visible at
night for several hundred feet and more under illumination from
oncoming motorists.
The need to increase the visibility of pedestrians walking along
streets or highways at nighttime has long been recognized. A
three-year study of 12 United States cities having populations of
more than 500,000 found that 50 percent of the total nighttime
traffic fatalities were pedestrian deaths.sup.1 (footnote
references are at the end of the specification). And the accident
rate per million vehicle-miles for all fatal and serious traffic
accidents is 21/2 to 3 times higher at night than it is during the
day.sup.2. The low visibility of pedestrians during hours of
darkness is a major factor in these statistics.
Reflectorized clothing would greatly increase the visibility of
pedestrians at nighttime. Tests have demonstrated that motorists
detect pedestrians clothed in reflectorized garments much earlier
than they detect pedestrians clothed in nonreflectorized clothing.
In one test,.sup.3 pedestrians were simulated by placing boxes 12
inches by 12 inches by 48 inches (30 by 30 by 120 centimeters)
covered with different test fabrics along a course traveled by test
observers in cars. The fabrics tested were black, grey, white, and
grey with a strip of silver reflectorized tape 1 inch by 11 inches
attached horizontally 15 inches from the ground. The results of the
tests in terms of the percentages of pedestrians who were safely
visible to test observers at distances greater than "critical
visibility distances" (reaction distance plus braking distance) are
summarized in the following table:
______________________________________ Simulated Miles per Hour
Pedestrians 20 40 60 80 ______________________________________
Black 86.4 45.4 0 0 Grey 100 47.2 5.5 0 White 100 100 97.2 52.7
Reflectorized 100 100 100 100
______________________________________
The problem is that very few persons wear reflectorized garments.
Such garments were available at least by the late 1940's, and many
efforts have been made over the years to promote their use. Only
limited success has resulted from these efforts, undoubtedly
because existing commercial reflective treatments for garments are
conspicuous in daytime and do not permit a desired variety in
fashion.
Retroreflective tapes have provided the most accepted way to
reflectorize garments. These tapes typically comprise a monolayer
containing many thousands of glass microspheres per square
centimeter supported over specular reflective means in a flexible
binder material (see Palmquist et al, U.S. Pat. No. 2,567,233,
later patents teaching improved varieties include Bingham et al,
U.S. Pat. No. 3,551,025, which teaches a wet-or-dry reflecting
material having a flexible transparent flat-surfaced top layer over
the layer of microspheres; Bingham, U.S. Pat. No. 3,700,305, which
teaches the use of visibly transparent but reflective dielectric
layers as the specular reflective means, and thus makes possible
more variety in the underlying color of retroreflective materials;
and Bingham, U.S. Pat. No. 3,758,192 which teaches retroreflective
materials that use nacreous pigments underneath the microspheres to
provide retroreflectivity while permitting variety in the color of
the material). These tapes ordinarily have little resemblance to
fabric to which they are applied, and their use on fabrics has
generally been limited to situations where they serve as trim that
is part of an ornamental design for the garment. By far the
majority of outerwear garments do not use such tapes.
Limited or strip reflectorization can also be provided, as taught
in Longlet et al, U.S. Pat. No. 3,535,019, with liquid coating
compositions that comprise hemispherically-aluminum-covered glass
microspheres dispersed in a water-emulsion of a flexible
thermoplastic resin. Such liquid coating compositions have not been
commercially successful probably because, as the patent states,
"some relative stiffening of the fabric occurs in the area of the
applied marking" (column 1, lines 61 and 62), and because the
markings contemplated cause daytime conspicuity.
In a different approach, it has been suggested that pellets of a
synthetic resin- or elastomer-based paste dissolved in a solvent be
pressed onto a foil such as may be used for raincoats, after which
glass microspheres are sprayed onto the pellets; see Swiss Pat. No.
514,731. Like other approaches, this suggestion contemplates
visibly apparent treatments, but suggests use of forms that will
contribute to decoration of the foil.
In another approach tried without success, retroreflective sheeting
carrying a heat-activatable adhesive on its back surface was
chopped into approximately 1/16-inch or 1/8-inch segments; the
segments sprinkled onto a first piece of fabric; a second piece of
the fabric laid over the sprinkled area; and the assembly heated
and pressed, as with an iron. The retroreflective segments thus
became adhered to one of the pieces of fabric, depending by chance
on which fabric their adhesive side faced. Success was lacking,
among other reasons, because the treatment was rather unattractive,
with a scattering of irregularly shaped conspicuous segments; and
the method was not adapted to rapid processes; e.g., the segments
tended to clump together and did not cascade freely, apparently
because the binder material of the segments was soft and
flexible.
Others have suggested reflectorizing the whole fabric of a garment,
but insofar as known, none of these has proved commercially or
otherwise feasible. Carey et al, U.S. Pat. No. 2,937,668 teaches
glass-microsphere-enveloped yarns for inclusion in small proportion
with conventional yarns to form a composite fabric that could be
made into garments. For a variety of reasons, such a technique has
never been commercially successful. McGaugh, U.S. Pat. No.
2,581,549 suggests adhering conventional retroreflective sheeting
over the back portion of a glove to provide brilliantly
retroreflective signaling gloves, where daytime conspicuity is not
an obstacle. Tung, U.S. Pat. No. 3,790,431 describes a
reflectorized open-mesh fabric that is useful for many purposes,
but as wearing apparel is generally used only as brilliantly
retroreflective vests or jackets for police or highway construction
or maintenance workers.
Certain decorative fabrics from the prior art have exhibited a
limited reflectivity but not the retroreflectivity (a return of
light along essentially the same path that the light traveled to
the reflector, which, for example, provides a brilliant reflection
to the driver of an automobile whose headlamps illuminate the
reflector) that is needed to provide pedestrian safety. For
example, Kaphan, U.S. Pat. No. 2,582,132 teaches ornamental
"studded" fabrics that have enlarged round glossy plastic elements
adhered over the surface of the fabric for decorative effects.
Glass beads have also been adhered to fabrics for decorative
effects, as indicated by Kukoff, U.S. Pat. No. 3,377,184, which
suggests the use of plastic particles instead; but these beads have
not been used in combination with underlying reflective means
needed to turn the glass beads into a brilliantly retroreflective
element. None of these decorative fabrics would appear to have any
useful retroreflective effects.
In summary, no one has previously suceeded in providing a
retroreflective treatment for wearing apparel that would both
provide desired levels of safety and be fashionably acceptable over
a wide range of outerwear garments. Until there is such a
treatment, there can apparently only be limited improvements in
pedestrian visibility at nighttime.
SUMMARY OF THE INVENTION
Briefly, a retroreflective treatment of the invention for fabrics
that are to be worn comprises discrete retroreflective areas
applied in a spaced, sparse manner over the surface of a base
fabric. These retroreflective areas include a thin layer of binder
material adhered to the base fabric and transparent microspheres
supported or held in the binder material. At least about one-third
of the microspheres have reflective means between them and the
fabric whereby the microspheres are made retroreflective, and their
surface that faces away from the fabric is optically exposed for
receiving and returning the light rays. On the average there are
less than about 2000 microspheres, and preferably less than about
500 microspheres, in any square centimeter of said surface of the
fabric, and the smallest surface dimension (that is, a dimension
along the surface of the fabric) of the continuous portions of said
coating is no greater than about 0.5 centimeter.
A retroreflective treatment as described may be provided in
different ways, but one method is at present very much preferred.
This method uses a unique retroreflectorizing material, namely a
free-flowing mass of minute retroreflectorization particles. These
minute retroreflectorization particles each comprise one or more
transparent microspheres arranged in a closely packed monolayer; a
solid binder layer in which the microspheres are supported and
which may at least in part be softened to adhere the particles to a
substrate; and specular reflective means underlying the
microspheres and supported by the binder material in optical
connection with the microspheres to make the microspheres
retroreflective. The surface of the microspheres opposite from the
reflective means is optically exposed to receive and return light
rays.
These retroreflectorization particles are generally applied by
cascading, metering, or otherwise depositing them onto a base
fabric under conditions that soften the binder layer. At least a
portion of the cascaded particles become adhered to the base fabric
with the optically exposed surface of the microspheres facing away
from the fabric.
The particles may be applied in amounts that provide the density of
microspheres per unit area of the fabric described above. Such
treatments are unique in their combination of sparsity and
area-wide character. For example, popular conventional
retroreflective sheetings used in traffic control signs have a
density over their surface of 25,000 microspheres per square
centimeter, instead of the less than 2000 and preferably less than
500 microspheres per square centimeter on fabric of the
invention.
Further, the particles are very small. For example, some typical
retroreflectorization particles of the invention use
50-micrometer-diameter microspheres and mostly include only one to
three microspheres. Such particles occupy about 1/50,000 of a
square-centimeter-sized area, and in themselves are almost
undetectable to the unaided eye.
On textured materials the particles preferably rest in recesses of
the surface, which further reduces their visibility. Such a
positioning in recesses can be encouraged by agitating a fabric or
"ironing" it, that is, passing a heated plate over the fabric which
tends to move the particles into the recesses.
We have found that when microspheres are used at the described low
densities and in the described scattered or spaced arrangements,
they are substantially invisible in daylight. That is, depending on
the color and texture of the base fabric, a preferred treatment of
the invention can often be detected only under unusual lighting
conditions or by bringing the treated fabric to within several
centimeters of the eye and manipulating the fabric to cause the
microspheres to provide a sparkle of retroreflection. Treatments of
the invention can accordingly be applied to a garment and leave the
appearance of the garment only slightly changed, and preferably
essentially unchanged, to an unstudied viewing.
Yet, because the sparse treatment extends over the whole area of a
fabric, a surprising aggregate effect on reflectivity is achieved.
Although the treatment is unnoticed on a garment under ordinary
daylight viewing, the garment "lights up" when it is viewed at
night under illumination from the headlamps of an approaching
automobile and becomes strikingly visible. Typically, a pedestrian
wearing a jacket made from a fabric of the invention is easily
visible at 500 feet and more from an oncoming automobile under
high-beam illumination at night, and in preferred embodiments is
visible at such distances under low-beam illumination.
In presently less preferred versions the properties achieved with
retroreflectorization particles are approached by using other
reflectorizing materials and procedures. For example, a sparse
discontinuous retroreflective treatment may be applied by printing
a liquid coating composition to provide discrete small
retroreflective areas having microsphere-densities per unit area of
fabric as described above. Such printed fabrics are also of low
daytime visibility and have little effect on hand, feel, or
breathability. But upon illumination at nighttime they provide a
surprising brightly visible reflection to an oncoming motorist.
All in all, retroreflective treatments of the invention constitute
a "breakthrough" in retroreflectorization of garments. For the
first time, pedestrians can be provided with retroreflective
garments that are hardly different for most purposes from a
conventional garment and yet will provide nighttime visibility
sufficient to greatly improve their safety.
DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are enlarged sectional views of illustrative sheet
materials prepared in the course of manufacturing
retroreflectorization particles of the invention;
FIG. 3 is an enlarged sectional view of illustrative
retroreflectorization particles of the invention; and
FIG. 4 is an enlarged schematic sectional view of a
retroreflectorized fabric of the invention.
DETAILED DESCRIPTION
The invention will first be illustrated by two examples.
EXAMPLE 1
The steps in this example are discussed with reference to the
illustrative showings in FIGS. 1 to 4. Visibly transparent glass
microspheres 10, which averaged 60 micrometers in diameter and had
a refractive index of 1.92, were coated in a monolayer onto a
composite web 11 which comprised a Kraft paper 12 and a
polyethylene layer 13. The web was heated so that the microspheres
sank into the polyethylene layer 13 to approximately 30 percent of
their diameters. The exposed microspheres were then vapor-coated
with a layer 14 of aluminum in a thickness of approximately 250
angstroms to produce a web 15 as shown in FIG. 1.
A linear saturated hot-melt polyester adhesive material (Bostik
7979 manufactured by the Bostik Chemical Group of the USM
Corporation, Middleton, Massachusetts; a typical useful polyester
is the reaction product of terephthalic acid, isophthalic acid,
ethylene glycol and neopentyl glycol) was dissolved in a solvent
that was a mixture of equal parts of toluene and methyl ethyl
ketone to give a 60-percent-solids solution. This solution was
knife-coated over the aluminum layer 14 of the microspheres 10 of
the web 15 at a wet thickness of 0.004 inch (100 micrometers) and
then dried 10 minutes at 150.degree. F. (66.degree. C.) and 20
minutes at 200.degree. F. (93.degree. C.). The polyethylene-coated
paper 1 was then stripped away leaving sheet material 16 as shown
in FIG. 2, which comprised a monolayer of glass microspheres 10
each approximately hemispherically reflectorized by the aluminum 14
and partially embedded in a binder layer 17 of the polyester. The
sheet material 16 was then placed in a Waring Blender and chopped
to a fine particle size with the aid of a small amount of dry ice.
The resulting retroreflectorization particles 18, as illustrated in
FIG. 3, were retained on a 200-mesh (U.S. Standard) screen but
passed an 80-mesh screen, meaning that their size was between 74
and 180 micrometers. In such particles the number of microspheres
in the particles ranges from 1 to about 11.
Particles 18 prepared in the above manner were uniformly dispersed
over the surface of a dark blue denim fabric made from a blend of
cotton and polyester fibers by pulling the fabric through a curtain
of the particles as they were dropped from a vibrating inclined
plane. The coated cloth was then placed in an oven heated to
350.degree. F. (177.degree. C.) for two minutes, whereupon the
particles were bonded to the yarns and filaments of the cloth. A
fabric 19 as illustrated in FIG. 4 resulted. To further improve
nestling of the particles into crevices of the fabric, the fabric
can be briefly ironed with a conventional laundry iron heated to
about 300.degree. F. (150.degree. C.).
This fabric was tailored into jackets and pants and viewed under
automobile headlamps. A person wearing the jacket and pants was
quite visible at 300 feet with low beams and over 500 feet with
high beams. The retroreflective efficiency varied over the surface
of the fabric between 1.75 and 2.75 candella per square meter of
fabric per lux of incident light. The concentration of microspheres
was counted and measured as approximately 550 microspheres per
square centimeter over the treated surface of the fabric. The
microspheres were randomly oriented, meaning that their optically
exposed surfaces faced in a variety of directions. At least about
one-third of them were oriented so as to retroreflect light that is
perpendicular to the surface of the fabric.
The garments prepared were laundered 50 times and found to show a
retention of about 50 percent of their original retroreflective
brightness. There were no other apparent changes to the garments
after laundering in comparison with a control fabric that had not
been treated. The garments had essentially the same hand, feel, and
breathability as control garments that had not been treated, and
the glass microspheres could be discovered only by a careful
scrutiny of the garments. The overall appearance of the treated
garments under ordinary daylight viewing was almost identical to
that of the control garments.
EXAMPLE 2
A slurry was prepared from the following ingredients.
______________________________________ Parts by Weight
______________________________________ Emulsion of
self-crosslinking acrylic copolymer latex particles in water
(Rhoplex HA-8 made by Rohm and Haas) 69 2-percent solution in water
of methyl cellulose (Methocel 8000 made by Dow Chemical Co.) 15
50-percent dispersion in water of a long- chain fatty acid
antifoaming agent (Nopco DL 160 made by Nopco Chemical Co.) 1
Ammonium chloride (Catalyst A for the described acrylic emulsion
made by Rohm and Haas) 0.5 Gamma-glycidoxypropyltrimethoxysilane
(Dow Corning's Z6040) 2.5 Hemispherically-aluminum-coated
transparent glass microspheres averaging 60 micrometers in
diameter, having an index of refraction of 1.92, and treated with a
sodium dichromate water solution according to the procedure
outlined in U.S. Pat. No. 3,535,019, column 4, paragraph 2, to
resist corrosion 60 ______________________________________
The first five ingredients of the formula were blended together
using an ordinary propellor blade attached to an air mixer. After
mixing to homegeneity (about 20 minutes) the hemispherically coated
retroreflective microspheres were added and mixed for an additional
5 minutes. The volume concentration of microspheres in the
resulting liquid coating composition was lower than used in typical
commercial retroreflective coating compositions.
A steel cylinder approximately 10 centimeters in diameter was
etched to provide a pattern of recessed bars 1.3 millimeter wide,
12.5 millimeters long, and 100 micrometers deep, located on centers
separated from one another by 3.7 millimeters. The top surface of
the cylinder was pressed against a rubber squeeze roll at a
pressure of about 20 pounds per square inch (1.4 kilogram per
square centimeter), and the bottom of the cylinder was dipped into
a fountain of the slurry described above, with the excess being
doctored off the cylinder with a steel blade. A cotton denim cloth
was passed between the etched cylinder and rubber roll with its
face side against the cylinder and the slurry was transferred to
the cloth from the cylinder partly by contact and partly as a
result of capillary absorption. The printed cloth was cured at
300.degree. F. (150.degree. C.) for 10 minutes and subsequently
tailored into a jacket and pants for a child. The retroreflective
efficiency was on the order of 8 candella per square meter per lux
and when the garments were viewed at night using automobile
headlights, visibility was excellent and the visual effect
astonishing.
In a somewhat different type of printing process, binder material
only is printed in a scattered pattern onto cloth. Then, while the
binder material is tacky, hemispherically reflectorized
microspheres are cascaded onto the cloth. Where they strike a dot
of tacky binder material, the microspheres become adhered to the
fabric. Such a process is of advantage, since very small areas of
binder material may be applied which are especially hard to see
even after microspheres have been adhered to the areas.
The practice of the invention illustrated by Example 1, that is,
using retroreflectorization particles, is presently preferred. Such
an approach has a minimal effect on appearance. In addition, it is
an inexpensive practical method that makes efficient use of
microspheres and binder material; the very small particles require
little binder material to adhere them to the fabric, and there is
no need for continuous binder material between particles.
The smaller the individual retroreflective areas and the lower the
density of microspheres over the area of the fabric, the more
inconspicuous is a treatment of the invention. Quite useful
retroreflectivity and extreme inconspicuity are obtained with
densities of 300-500 microspheres per square centimeter or less,
especially with retroreflective areas that contain just a few
microspheres (e.g. that average less than 10 microspheres per
area). Conspicuity increases slightly as density or size of
retroreflective area increases, but even densities of 1,000
microspheres per square centimeter can be substantially invisible
to ordinary inspection; and densities as high as 2,000 microspheres
per square centimeter provide useful inconspicuity. To achieve
uniformity of effect, these density values preferably also apply to
any area of the treatment occupying one square centimeter.
Small retroreflectorization particles provide the smallest
retroreflective areas, and retroreflectorization particles of the
invention can be prepared that average no more than about 3-5
microspheres per particle. Such particles generally have surface
dimensions, and provide retroreflective areas on fabric having
surface dimensions, of about 250 micrometers or less; while
particles averaging 10 microspheres generally have surface
dimensions, and provide retroreflective areas having surface
dimensions, of about 500 micrometers or less.
In retroreflective treatments of the invention prepared by other
means than retroreflectorization particles, as well as with
retroreflectorization particles, the continuous areas of a
treatment may include more than an average of 10 microspheres.
Further, when the color of the retroreflectorization particles
matches or blends with the underlying fabric, or is transparent (as
in the case of treatments in which the microspheres are coated with
transparent dielectric mirrors as subsequently described), the size
of the continuous areas can be increased while still providing
acceptable daytime inconspicuity. Larger retroreflectorization
particles also have the advantage that they are in general
optically more intact, since they have been subjected to fewer
chopping operations. However, the retroreflectorization particles
to be used on garment fabrics will generally always average no more
than about 50 microspheres per particle. Even such particles are
still quite minute, typically averaging less than one millimeter in
surface dimension.
The small amount and discontinuous nature of the binder material
applied by using retroreflectorization particles also minimizes the
effect on hand, feel and breathability of a treated fabric. In
general, to minimize effects on hand, breathability, and appearance
for fabrics that are to be worn, the smallest surface dimension of
the continuous areas of the treatment on the fabric should be less
than 0.5 centimeter, preferably less than 0.25 centimeter, and more
preferably less than 1 millimeter. The maximum surface dimension of
the continuous areas also is preferably less than these values. It
is also desirable for there to be over the treated surface of a
fabric on the average less than a milligram of binder material and
more preferably less than 0.5 milligram of binder material per
square centimeter.
Generally, sufficient microspheres are included to provide at least
one candella, and preferably at least 1.5 or 2 candellas, of
reflected light per square meter of a treated surface per lux of
light that is incident on the surface. On the other hand, to
minimize daytime visibility, the treatment usually provides less
than 20, more often less than 10, and most often less than 5,
candellas per square meter of treated surface per lux of incident
light.
A variety of binder materials can be used in the
retroreflectorization particles. Often the binder material is a
heat-activatable adhesive, softening upon exposure to elevated
temperatures so as to wet and develop adhesion to the fabric.
Examples of useful binder materials of this kind are polyesters,
acrylics, polyurethanes, and polyamides. Use of a binder material
that is of the same chemical class as the synthetic fibers of a
fabric to which a treatment is being applied is often advantageous;
for example, polyester binder materials are often preferred for
fabrics that include polyester fibers. The binder material of a
retroreflectorization particle may also be activated or softened in
other ways, as by application of solvent.
Following application of the particles to a fabric, the binder
material hardens as by cooling, loss of solvent or other volatiles,
or by chemical reaction including crosslinking or polymerizing. Use
of chemically reactive materials may be of special advantage, since
they often melt at low or moderate temperatures and achieve a
low-viscosity condition very rapidly after reaching the melting
point. The result is that they rapidly wet and penetrate into
fabric, and a treating operation can be performed at lower
temperatures and/or with shorter heating cycles. Chemically
reactive materials can also be obtained in forms that are quite
brittle and friable before reaction, which assists in fracturing
sheet material into retroreflectorization particles. Illustrative
useful chemically reactive materials include thermosetting resin
compositions such as epoxy-based resin compositions,
melamine-formaldehyde resin compositions, and acrylic-based resin
compositions.
The layer of binder material in a retroreflectorization particle
may comprise two or more sublayers. For example, in some
embodiments the microspheres are embedded in one sublayer of binder
material, and a second sublayer of binder material is used to bond
the particles to fabric.
The binder material in retroreflectorization particles may be
rather rigid without affecting the hand or feel of the fabric,
because the retroreflectorization partices are so small. Particles
with a rigid binder material also tend to flow more freely. For
treatments as described in Example 2, however, the binder material
is desirably a flexible, even elastomeric, material. The preferred
binder material is a water emulsion since it may be applied to a
variety of fabrics, and in low concentration will have little if
any effect upon the hand or feel of the fabric. Acrylic emulsions
are preferred because they can be crosslinked to produce soft,
flexible films resistant to alkaline solutions and with excellent
adhesion to fabrics. Other useful emulsions are polyvinyl acetate
and styrene-butadiene emulsions.
The transparent microspheres used in the invention are usually
glass microspheres (the microspheres are generally visibly
transparent though they may be transparent to other types of
radiation which it is desired to reflect). Generally, when the
optically exposed surfaces of the microspheres in a treatment of
the invention have an air interface, the microspheres have an index
of refraction of at least 1.8 and preferably about 1.9. At those
indices, the microspheres achieve good retroreflective efficiency
with specular reflective coatings applied directly to them.
Microspheres of lower refractive index can be used by spacing the
specular reflective means from the microspheres with materials of
lower refractive index. And microspheres of high index of
refraction, such as 2.5, can be used to obtain retroreflection when
the microspheres are wet or covered with a transparent polymeric
film.
The microspheres should average less than about 200 micrometers in
diameter to achieve the least conspicuous treatment and preferably
they are less than about 100 micrometers in average diameter. Most
often the specular reflective means in a reflective treatment of
the invention is provided by a coating of specular reflective
material over an approximately hemispherical portion of the surface
of the microspheres. Specular reflective coatings on the
microspheres are often of a metallic material such as silver of
aluminum, but they may also be dielectric reflective coatings such
as taught in Bingham, U.S. Pat. No. 3,700,305. Such coatings, which
can be visibly transparent while reflecting sufficient light to
provide good retroreflection, may improve the color or appearance
of a reflective treatment by letting an underlying color be visible
through the reflective treatment.
Reflective means can also be provided by use of a specular
reflective material in the binder material underlying the
microspheres. For example, aluminum flakes may be dispersed in the
binder material, or a continuous metal coating separated from the
microspheres by a transparent spacing layer can be used. In
addition, nacreous pigments such as described in Bingham, U.S. Pat.
No. 3,758,192 may be used. Whatever the form, they are in optical
connection with the microspheres; that is, rays to be reflected
will pass through the microspheres and strike the specular
reflective means.
The microspheres in a retroreflective treatment of the invention
preferably have an air interface, but they may also be covered by a
transparent layer having an index of refraction that causes the
microspheres, in combination with the underlying reflective means,
to be retroreflective. Such a structure is useful under either wet
or dry conditions. The principles on which such a structure is
based are taught in more detail in Palmquist et al, U.S. Pat. No.
2,407,680.
Retroreflective treatments of the invention may be provided on a
variety of fabrics (fibrous sheet material). The invention is
particularly beneficial with dark fabrics which have the least
visibility at night. Textured fabrics are advantageous because of
the nestling of reflectorization particles previously described.
The fabrics may be prepared by a variety of techniques; e.g., they
may be woven, knitted, or nonwoven.
While fabrics of the invention are most often made into garments,
they are useful for other purposes such as portable traffic-control
signs and flags. In such uses, a high density of microspheres may
be applied to the fabric, even higher than that described above.
Although retroreflectorization particles of the invention as
illustrated by Example 1 are of special usefulness for forming
discontinuous sparse retroreflective treatments, they may also be
applied to form dense treatments.
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