U.S. patent application number 10/945833 was filed with the patent office on 2006-03-23 for retroflective device and method of manufacture thereof.
Invention is credited to Ian I. Durant, Richard H. Hughes.
Application Number | 20060062965 10/945833 |
Document ID | / |
Family ID | 36074381 |
Filed Date | 2006-03-23 |
United States Patent
Application |
20060062965 |
Kind Code |
A1 |
Durant; Ian I. ; et
al. |
March 23, 2006 |
Retroflective device and method of manufacture thereof
Abstract
A retroreflective device 1, for use in creating a
retroreflective surface, comprises an agglomeration of glass beads
2, formed by binding together glass beads 2 of a specific size with
an adhesive material 3. Selected properties, for example refractive
index, of each glass bead 2 are chosen in accordance with the
desired retroreflectivity of the device 1. The adhesive material 3
may be pigmented, thereby to colour light retroreflected from the
device 1. Preferably, the agglomeration of glass beads 2 is
approximately spherical or ovoid and the glass beads 2 are
approximately spherical. A retroreflective road marking coating may
comprise a road marking material applied to the surface of a road
and a plurality of the retroreflective devices 1 embedded in the
road marking material so as to protrude partially therefrom. The
retroreflective devices 1 may also be used with a coating from
which they protrude so as to provide a road surfacing material.
Inventors: |
Durant; Ian I.; (Lancashire,
GB) ; Hughes; Richard H.; (Northwich, GB) |
Correspondence
Address: |
WELSH & KATZ, LTD
120 S RIVERSIDE PLAZA
22ND FLOOR
CHICAGO
IL
60606
US
|
Family ID: |
36074381 |
Appl. No.: |
10/945833 |
Filed: |
September 21, 2004 |
Current U.S.
Class: |
428/143 |
Current CPC
Class: |
G02B 5/128 20130101;
Y10T 428/24372 20150115; E01F 9/524 20160201 |
Class at
Publication: |
428/143 |
International
Class: |
E01F 9/04 20060101
E01F009/04 |
Claims
1. A reflective device for use in creating a retroreflective
surface, including first refractive index beads, second, different,
refractive index beads and binder, the binder holding the first and
second beads together with the first and second beads being
distributed throughout the device.
2. A device as claimed in claim 1 in which the beads are in close
proximity to each other.
3. A device as claimed in claim 1 in which the spacing between
adjacent beads is less than two times the mean cross-sectional
dimension of the beads.
4. A device as claimed in claim 1 in which the ratio of the
combined volume of the beads to the volume of the binder is more
than 1:10.
5. A device as claimed in claim 4 in which the ratio is more than
6:10.
6. A device as claimed in claim 1 in which the combined number of
first and second beads in the device is more than 20.
7. A device as claimed in claim 6 in which the combined number of
first and second beads in the device is more than 40.
8. A device as claimed in claim 1 in which the first beads have a
refractive index of more than 2.0.
9. A device as claimed in claim 1 in which the second beads have a
refractive index of less than 2.0.
10. A device as claimed in claim 1 which is ovoid.
11. A device as claimed in claim 1 in which the first and second
beads are from 100 to 700 microns in their mean cross-sectional
extent.
12. A device as claimed in claim 1 in which the first and second
beads are spherical.
13. Use of a plurality of retroreflective devices as claimed in
claim 1 in combination with road marking material as a
retroreflective road marking coating or road surfacing
material.
14. Use of a plurality of retroreflective devices as claimed in
claim 1 in combination with a binder material as a retroreflective
surface dressing.
15. A retroreflective road marking coating comprising a road
marking material applied to the surface of a road and a plurality
of retroreflective devices as claimed in claim 1 embedded in the
road marking material so as to protrude partially therefrom.
16. A reflective device for use in forming a retroreflective device
including first beads having a refractive index of more than 2.0
and second reflection beads having a refractive index of less than
2.0 and binder, the binder holding the first and second beads
together with the first and second beads being distributed
throughout the device, the number of first and the number of second
beads being selected to give the required refractive properties of
the device.
17. A method of forming a reflective device having a
retroreflective surface comprising determining the number of beads
having a first refractive index and determining the number of beads
having a second, different, refractive index in order to give a
device having the required reflective properties and holding the
beads together with binder with the beads being caused to be
distributed throughout the device.
18. A method as claimed in claim 17 comprising stocking only first
and second beads.
19. A method as claimed in claim 17 comprising choosing first beads
having a refractive value of more than 2.0 and the second beads
having an index of less than 2.0.
20. A method as claimed in claim 17 comprising binding more than 40
beads into the device.
21. A method as claimed in claim 17 comprising varying the
reflective properties of at least two batches of devices by
altering the ratio of first and second beads that are bound by the
binder.
22. A method as claimed in claim 17 comprising dropping liquid
binder onto the first and second beads and causing the binder to
set.
Description
[0001] The present invention relates to a retroreflective device
for use in creating retroreflective surfaces, for example for use
as reflective markings and delineators, and high visibility
coatings for improving visibility of surfaces by increasing
reflective characteristics, particularly but not exclusively on
roads and road signs, and a method of manufacturing such a
retroreflective device.
[0002] Markings for highway (road) marking are usually required to
be reflective at night. Light emitted from vehicle headlights is
reflected back in the direction of the source, i.e. retroreflected,
from the surface of the marking or other reflective surface. The
retroreflective characteristic of the marking material is typically
improved by use of added retroreflective elements or devices. In
road markings, spherical glass beads are often added to the surface
of the marking during application, or sometimes premixed in the
body of the marking material, and by this means the retroreflective
characteristics are significantly improved over the natural
reflective property of the marking surface. However, road markings
are usually applied in locations likely to be exposed to traffic,
i.e. contacted by vehicle wheels, and such contact leads to
deterioration, through abrasion and other effects, of the
reflective material, thereby reducing its retroreflective
properties.
[0003] GB 2164762 (Potters) discloses a tetrahedron retroreflective
device formed by passing a sheet between two rollers to press the
tetrahedrons out of the sheet. Lines 43 to 53 of page 4 state that
the spheres may be fabricated from some of the titanium glasses
having a higher index of refraction or they may comprise spheres
having varying indices with spheres located in the interior of the
granules having an index of 1.5 and with the exposed spheres having
an index of 1.9. Lines 81 to 89 on page 4 state that additional
spheres may be applied to the surface having an index of 1.9 for
high retroreflectivity with the interior having an index of 1.5 for
rigidity and good wear resistance. However, when the exterior of
the tetrahedron becomes worn, the high retroreflecting spheres
disappear exposing the low index spheres thus reducing
significantly the performance of the device.
[0004] U.S. Pat. No. 3,254,563 (Prismo) discloses reflecting
devices with glass spheres on the exterior of binder material. No
spheres are totally embedded. Thus when the glass spheres are worn
off the device it has no retroreflectivity qualities. Lines 7 and 8
in column 2 refer to an installation in which the devices are
covered with binder. In such installations it is said that high
index spheres of 2.4 are required. Low index spheres though may be
mixed with the high index spheres such that when the transparent
covering binder is worn away to expose the spheres, these low index
spheres may only then reflect light.
[0005] DE 19521847 (Cammann), U.S. Pat. No. 3,043,196 (Palmquist),
U.S. Pat. No. 6,398,369 (Cleanosol), U.S. Pat. No. 5,942,280 (3M),
EP 0322671 (Eigenmann) and U.S. Pat. No. 4,609,587 (Potters), all
relate to retroreflective devices.
[0006] Accordingly, it is desirable to provide a retroreflective
device which, when used in combination with a road marking paint or
coating, will impart very good and consistent reflectivity
characteristics and be durable under the action of traffic.
[0007] According to an embodiment of a first aspect of the present
invention there is provided a retroreflective device for use in
creating a retroreflective surface, which device comprises an
agglomeration of glass beads.
[0008] Preferably, the agglomeration is formed by binding together
glass beads of a selected size.
[0009] Advantageously, selected properties of each glass bead may
be chosen in accordance with the desired retroreflectivity of the
device, for example its refractive index.
[0010] Desirably, the glass beads are bound together by an adhesive
material, for example epoxy resin, acrylic, polyurethane or a hot
melt adhesive, or any other suitable adhesive.
[0011] The adhesive material may be pigmented, thereby to colour
retroreflected light from the device.
[0012] The agglomeration of glass beads is desirably approximately
spherical or ovoid and the glass beads are preferably approximately
spherical. The diameter of the glass beads is preferably selected
to be within one of the following ranges: from 100 microns to 700
microns or from 100 microns to 300 microns, from 200 microns to 400
microns, or from 400 microns to 700 microns. Larger beads may be
used to form agglomerations, but the ranges specified are preferred
sizes for the application.
[0013] The glass beads are preferably spherical and formed of good
quality clear glass substantially free from faults and inclusions.
They preferably exhibit a refractive index of 1.5, 1.9 or 2.1 or
2.3.
[0014] The spacing between adjacent glass beads may be less
than
[0015] 2 times the diameter of the beads or less than 1 or less
than 0.5.
[0016] There may be a ratio of glass beads to volume of binder of
more than 1:10 or 2:10 or 4:10 or 6:10 or 1:1 or 1.5:1.
[0017] Each device may include more than 20 or 30 or 40 or 50 or 60
or 80 or 90 or 100 beads.
[0018] Retroreflective devices embodying the present invention can
advantageously be used to enhance the reflectivity of road
surfacing materials and road markings, including coloured road
surfacing, traffic calming, etc.
[0019] The use of a pigmented adhesive or binder allows for
coloured reflection of light depending on the type and properties
of the pigment and binder/adhesive used. Retroreflective devices
embodying the present invention, and which comprise pigmented
adhesive or binder, have been found to exhibit far superior
reflectance of colour when compared to known products. This
beneficial property is due to a number of factors including: the
use of glass beads of a specific quality/refractive index and of a
predetermined uniform size, and the closely packed construction of
the device, i.e. the glass beads are bound together in very close
proximity. In addition to close packing of glass beads throughout
the body of the retroreflective device, the glass beads on the
surface of the bead cluster are also close packed thereby achieving
optimum reflective performance and resistance to traffic and/or
weathering. A retroref lective device embodying the present
invention will therefore have a high density of glass spheres on
the surface which are in contact with a large surface area of
colour thereby maximising the extent to which the colour of
incident light will be modified by the device. This achieves far
superior colour density and intensity of reflected light and is
demonstrably better than known products comprising ordinary glass
beads of various sizes simply embedded or partially embedded in a
coloured binder.
[0020] According to an embodiment of a second aspect of the present
invention there is provided use of a plurality of retroreflective
devices embodying the first aspect of the present invention in
combination with road marking material as a retroreflective road
marking coating or road surfacing material.
[0021] According to an embodiment of a third aspect of the present
invention there is provided use of a plurality of retroreflective
devices embodying the first aspect of the present invention in
combination with a binder material as a retroreflective surface
dressing.
[0022] According to an embodiment of a fourth aspect of the present
invention there is provided a retroreflective road marking coating
comprising a road marking material applied to the surface of a road
and a plurality of retroreflective devices embodying the first
aspect of the present invention embedded in the road marking
material so as to protrude partially therefrom. The retroreflective
devices may be premixed or otherwise immersed in the road marking
material.
[0023] According to an embodiment of a fifth aspect of the present
invention there is provided a retroreflective surface dressing
comprising a binder material coating the surface to be dressed and
a plurality of retroreflective devices embodying the first aspect
of the present invention adhering to the binder material so as to
protrude partially therefrom.
[0024] According to an embodiment of a sixth aspect of the present
invention there is provided a method of manufacturing a
retroreflective device, which method comprises the steps of (a)
forming a bed of glass beads of a selected size, and (b)
introducing droplets of a binder material into the bed of glass
beads so as to cause groups of the glass beads to bind together as
the binder material hardens, or is cured, to form respective
retroreflective devices, the size of the droplets being controlled
in dependence upon the size of the glass beads so as to obtain a
plurality of retroreflective devices in a preselected size
range.
[0025] The binder material may be sprayed, with suitable droplet
size, onto the bed of glass beads.
[0026] Preferably, the bed of glass beads is moved from a first
position at which the binder material is introduced to a second
position at which, after the binder material has set/cured, the
retroreflective devices are removed from the bed and any loose
beads are returned to the first position.
[0027] Reference will now be made, by way of example, to the
accompanying drawings, in which:
[0028] FIG. 1 shows a retroreflective device embodying the first
aspect of the present invention; and
[0029] FIGS. 2A, 2B and 2C show respective alternative embodiments
of the first aspect of the present invention.
[0030] As shown in FIG. 1, a retroreflective device 1 embodying the
present invention is manufactured by binding a quantity of
spherical glass beads 2 of a desired size with an adhesive 3 so as
to form a spherical or ovoid agglomeration or cluster 1, preferably
2 to 4 mm in diameter (although other sizes may be useful according
to the application). The size of the glass beads 2 is preferably
selected to be within one of the following ranges, from 100 to 700
microns or from 100 to 300 microns, from 200 microns to 400
microns, or from 400 microns to 700 microns diameter, although
larger beads may also be used to form agglomerations where
appropriate. The adhesive 3 may, for example, be epoxy resin,
acrylic, polyurethane or hot melt adhesive. The cluster 1 of beads
2 so formed has retroreflective properties as its surface is made
up of a number of glass spheres in close packed formation
presenting a large number of reflecting elements. Light entering a
bead 2 is reflected internally and re-emitted in the direction of
the source. The light returning to the source (e.g. the vehicle)
can be modified in colour by using a pigmented adhesive 3a, 3b or
3c to bind the beads 2, as shown in FIGS. 2A to 2C. The pigmented
adhesive 3a, 3b, 3c forms a coloured backing to the glass beads 2.
Light entering the glass beads 2 is subject to internal reflection
and allows some diffusion into the pigmented adhesive 3a, 3b, and
3c. By this means the light colour is modified by the effect of the
pigmented adhesive 3a, 3b, 3c and is thus modified before it
returns in the direction of the source. The adhesive material 3 may
be pigmented with white, red, yellow, green, or indeed any strong
colour, to produce a reflected colour as required. Alternatively,
the glass may itself be coloured to modify the light, either by the
chemical composition of the glass or by a suitable coating
treatment. By this means the bead clusters 1 may be used in road
markings and other road surfacing to produce a coloured appearance
as an aid to driver safety and to provide information about road
layout and possible hazardous situations.
[0031] The properties of the glass used to make the beads 2, such
as its chemical formulation, may be varied to achieve a greater
degree of reflectivity. In particular, glass of different
refractive index, for example values of 1.5, 1.9 and 2.1 or 2.3,
may be used, since glass beads 2 manufactured from higher
refractive index glasses return more light and therefore improve
the retroreflective performance. Additionally, a mixture of glass
beads of different refractive indices may be used.
[0032] Glass beads having a higher refractive index are relatively
expensive compared to lower index beads. In one example a stock of
high index beads of 2.3 and a stock of low index beads of 1.5 were
kept. Different quantities from these two stocks were mixed in
varying quantities to obtain devices having different illumination
values. This obviates the need to keep a stock of beads having the
specific index required to achieve the illumination values. For
example, a mix of 20% by number of beads of a reflective index of
2.3 with a mix of 80% 1.5 beads may give a device having reflection
of 200 milli candela, a mix of 40% of 2.3 and 60% of 1.5 a
reflection of 400 milli candela and 80% of 2.3 and 20% of 1.5 a
reflection of 800 milli candela. Furthermore, the required candela
will remain even after wear of the product as the beads are closely
packed throughout the device.
[0033] In order to obtain a retroreflective surface, a plurality of
retroreflective devices 1 embodying the present invention are
applied to the still liquid or semi-liquid surface of a road
marking material painted onto a road and become embedded in the
surface so that they are anchored in the surface with a portion of
each retroreflective device 1 protruding above the surface of the
marking, such that the exposed part of the bead clusters 1 can
become illuminated with light from head lamps of vehicles and
reflect light back to the driver. The bead clusters 1 embedded into
the surface are firmly held by the road marking material, the
surface structure of each cluster 1 being textured by the presence
of glass beads 2 so that the road marking material is absorbed into
the textured surface of the cluster 1, this keying effect
increasing retention and strength of adhesion of the bead cluster
1.
[0034] As mentioned above, the size of the cluster 1 is usefully in
the range from 2 mm to 4 mm diameter; however, larger or smaller
clusters 1 may be used in accordance with the thickness of the
coating for which they are intended and the degree of embedment.
Thus a road marking paint line nominally 500 microns in thickness
could use clusters 1 in the size range 1 mm to 2 mm diameter,
whereas a thicker line such as a thermoplastic road marking
nominally 3 mm in depth would require clusters 1 of 4 mm to 6 mm
diameter to be effective.
[0035] An alternative use of the retroreflective devices 1 would be
in a road surface dressing, coloured road surfaces for hazard
warning, or on vertical surfaces, for example safety barriers, road
signs (vertical), etc. These applications would require a
relatively low thickness of binder material to allow a large
exposed area of reflective material. Such usage requires a
particularly strong and durable binder to hold the clusters 1 to
the substrate, for example (but not exclusively) two component
materials epoxy resin, acrylic and polyurethane.
[0036] Unlike prior art road markings whose reflectivity is
provided by individual glass beads and which therefore lose or
change reflectivity as the beads become damaged or are dislodged
from the surface due to the action of traffic, retroreflective
devices 1 embodying the present invention comprise an agglomeration
of mixed glass beads 2 having a multilayer structure which enables
continuity of reflectivity by exposing a new, inner layer of glass
beads 2 after the original outer layer of mixed beads 2 has been
removed, for example by the action of road traffic.
[0037] The performance of the device is enhanced as the mixture of
beads is present and evenly distributed throughout the device. As
the resin is more readily worn away than the beads, as soon as one
bead becomes detached the next bead is relatively quickly exposed
as the resin wears away and remains exposed for some considerable
time as the surface of the new bead is now exposed to the traffic
and this will not wear anywhere near the same extent as the
resin.
[0038] Rather than being applied on a surface, the retroreflective
devices 1 can also be advantageously used as premixed additives to
a road marking material, in a quantity proportional to the
thickness of the coating to be applied, the devices becoming
exposed as the road marking material wears away.
[0039] In a method of manufacturing a retroreflective device 1
embodying the present invention a small droplet of adhesive or
binder material 3 is applied to a mass or bed of glass beads 2 and
the binder material 3 is absorbed onto the surface of the beads 2
immediately surrounding the droplet. The binder material 3 is then
cured and the resultant agglomeration or cluster 1 of glass beads 2
is separated from the uncoated beads 2. The size of the binder
droplet, physical properties of the binder material 3 (particularly
is viscosity and cure rate) and the size/gradation of the glass
beads 2 are key factors which determine the quality of the
agglomeration of beads produced. Two examples of production methods
are given below:
Method 1
[0040] A flat bed of glass beads 2 of mixed refractive index
comprising 40% by number of 2.3 index beads and 60% by number of
1.5 index beads is produced and onto the surface is applied
individual droplets of the binder material 3 using a suitable
device 1 for generating controlled size of droplets. The droplet
size and gradation of glass beads 2 will determine the size of bead
clusters 1 produced, the agglomeration of beads 2 increasing in
size if there is more binder 3 available. As the binder 3 flows
from its point of application it will contact further layers of
glass beads 2 and increase the size of cluster 1 formed. An example
of a workable system is a glass bead size of nominal diameter 200
microns with a droplet size of 2 mm; this will agglomerate a
quantity of beads 2 to produce a cluster 1 of size 3 mm to 4 mm
diameter. The flat bed can be produced as a moving bed of beads 2,
for example on a moving belt, with binder 3 applied dropwise with a
collection device 1 at a suitable distance to separate clusters 1
from loose beads 2, the loose beads 2 being recycled back into the
moving belt to enable a continuous process. The time between
application of the binder 3 and the collection and separation
process needs to be controlled to enable setting/curing of the
binder 3 to a sufficient degree to allow handling of the product
without damage or disruption to the agglomeration of beads 2. The
process of binder cure can be speeded up by, for example, the
application of heat, allowing faster processing of the beads 2.
Method 2
[0041] An alternative to the drop application method is to spray
the binder 3 on to the surface of a moving bed of mixed refractive
index beads comprising 20% of 2.3 index beads and 80% of 1.5 index
beads by number of glass beads 2. This may be advantageous in terms
of droplet size, particularly if smaller diameters of droplet are
required, for example less than 100 .mu.m in diameter. It may also
be advantageous in allowing faster production rates. Various spray
devices may be used, for example air assisted atomisation, spinning
disc (prilling), etc.
[0042] Thus, retroreflective devices 1 embodying the present
invention have a retroreflectivity performance providing efficient
retroreflection of incident light. When used in road marking or
surfacing materials to increase visibility in low light or
night-time conditions the devices have higher durability under
traffic than the individual index glass beads or the varied
concentration of different index glass beads used in the prior art,
owing to the multi-layering of the mixed index glass beads 2 in the
cluster 1 and the keying effect of the surface characteristics of
the cluster 1. Larger bead clusters 1 are likely to give extra
visibility performance in so-called "wet night conditions", because
the clusters 1 stand proud of the road marking line and are more
visible when there is water on the road.
[0043] Attention is directed to all papers and documents which are
filed concurrently with or previous to this specification in
connection with this application and which are open to public
inspection with this specification, and the contents of all such
papers and documents are incorporated herein by reference.
[0044] All of the features Idisclosed in this specification
(including any accompanying claims, abstract and drawings), and/or
all of the steps of any method or process so disclosed, may be
combined in any combination, except combinations where at least
some of such features and/or steps are mutually exclusive.
[0045] Each feature disclosed in this specification (including any
accompanying claims, abstract and drawings) may be replaced by
alternative features serving the same, equivalent or similar
purpose, unless expressly stated otherwise. Thus, unless expressly
stated otherwise, each feature disclosed is one example only of a
generic series of equivalent or similar features.
[0046] The invention is not restricted to the details of the
foregoing embodiment(s). The invention extends to any novel one, or
any novel combination, of the features disclosed in this
specification (including any accompanying claims, abstract and
drawings), or to any novel one, or any novel combination, of the
steps of any method or process so disclosed.
* * * * *