Note: Descriptions are shown in the official language in which they were submitted.
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D E W ~tESISTA N T R ET R OEUEF~E CI~E
T~L~FFIC SIG N 13L~IN G A T ~X 1U~D G L ASS S UEUFA CE
~NTRODUC~ON
In order to be effective, roadway traffic signs must be visible to motor
vehicle drivers at night as well as during the day. Because it is impractical toe all traffic signs with external li~hti~ a co~ Qn approach to
F .~h~ the visibility of roadway trafflc signs is to use ~ u-t;flective graphics on the traffic sign.
Retroreflective signs have the unique ability to return a ~ Js~ ;Al
portion of incident light back toward the light source. At ni~httime, light frommotor vehicle hf~ htc strikes the l ~;ll orenective graphics and is
r~llulenected to the motor vehicle driver. The bright image displayed by the
rc~.ult;flective sign makes the sign easier to read and gives motorists more time
to react.
A cignific~nt problem that has been encountered with rc~L~u-~ective
trafflc signs is the ac~m~ fior- of water droplets on the surface of the signs.
Dew is an e~l~e~ y commûn source of water d,uple~s and can be particularly
problematic because it occurs predf~ ly at ni~httime when the
~l,u.~nective signs are ope,aLive. When present on a traffic sign in the form
of small beaded water ~l.o~lel~, dew can seriously disrupt the path of in~.identand reL.o,t;nected light. This can make h~ru",.aLion on traffic signs much more
difficult for passing motorists to read. This problem is very well known, and
there have been a variety of attçmrtc aimed at removing dew or p~ ling
dew from rO-,. h-~, on the surface of trafflc signs.
One method of e~ ;ng dew from reL,orc;nective signs is to heat the
u~enective elempnt Gerrnan Patent NO. 4226266 to Gubela discloses an
electrical heating element placed behind the retroreflector.
European Patent Application NO. 0155572, ~cci~ned to Biersdorf
AhiPn~PsPllc~h~ ~iccloses a ~Llu~nective traffic sign having a heat radiator
--1--
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of Anotli7ed All~minllm that is mounted directly on the upper edge of the traffic
sign. The advantages attributed to this device include the lack of a need for a
hydrophilic surface coating, a heat retaining layer on the back of the sign, or an
artificial energy supply.
J~p~nese Ko~ai Patent Pl-hlicAtion No. 7-3731 ~.ei~n~d to
Ter.hnonijuichi K.K. di~rloses an anti-dew reflective road traffic sign that has a
heat storage co,llaine. tightly bonded to its back side. The heat storage
cf~ CQ..~ a heat storage agent, typically a gel co~ ;..;..g a liquid
glycol that collects heat and radiates that heat towards the sign's front surface.
U.S. Patent No. 5,087,508 to Beck di~ClQsçs a reLlulGnective trafflc
sign having a thermal reservoir layer located behind the ~el-ulenective surface.The thermal reservoir cc,nLains a material that undergoes a phase change
b~ ,n - 20~C and 40~C. The energy barrier of the phase trAn~ision pie~ s
the sign from cooling rapidly.
JApa~u~e Patent ApplicAtir~n 0614961A ae~igne(l to Kawai Musical
In~ll Ulll~ll ~g. Co., dierlQsee an anti-fog mirror in which a vibration
~ellel~Lor is ~ hed to the rear surface of a mirror. J~p~n~se Patent
Appli~tion 07259024A ~ ned to ~tellchh~ Denki Sangyo KK, ~ie~loses an
anti-fog mirror for road safety in which solar energy is stored in a heater unitlocated behind the mirror's surface.
Another method that has been used to impart anti-dew characLe,isLics to
,ellulGnective traffic signs is to apply a water-spreading, Lydlùphilic coating to
the surface of the sign. The hydrophilic coating spreads the moisture over the
sign's surface and thus makes the sign easier to read because the resulting thinwater layer does not alter the path of incidçnt and lel~ulelle~ e light to as
great an extent. U.S. Patent Nos. 5,073,404, 4,844,976 and 4,7S5,425 to T.
Huang disclose a lellulenective ~ e~ g that has a ll~"~are.,l coating
CClll~ illg colloidAl silica and a pûlymer selected from ~liph~ttc pol~/ult;lt~Alles7
polyvinylchloride co-polymers and acrylic polymers. The colloid~l si~ica is
disposed in the polymer at about 10-80 weight % (10-70 weight % in the case
of polyacrylates). The l,~nsl ale"~ coatings provide superior dew repellency,
--2--
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allowing the r~forcnective ~h~eting to retain a higher percentage of its original
bri,~htne,cs aflLer being exposed to moisture.
There are numerous ~ pl~ of anti-dew, water-spreading layers that
are made with inorganic colloidal particles disposed in a polymeric binder.
S U.S. Patent No. 4,576,864 to Krautter et al. rliC~loses a water-spreading layer
that is composed of colloidal particles of a metal or silicon oxide in which thewater-spreading layer is adhered to a plastic substrate by an adhesive
c~u~ g a non-water-soluble, organic-solvent-soluble, and e~eentiAlly non-
~ ,llable, polar-group-c~ .g-polymer. U.S. Patent No. 4,478,909 to
TAni~-r.hi et al. discloses an anti-fogging coating having finely divided silicaparticles disposed in a matrix of polyvinyl alcohol and an or~Anf silicon alkoxycompound or hydrolysates thereo~ A similar coating is also described in U.S.
Patent No. 5,134,021 to Hosono et al.
In the area of pavement marker technology, it has been known to bond
a flat glass plate to a .Gllorènective chçeting's surface to improve abrasion
reCict~n~e U.S. Patent Nos. 4,232,979, 4,340,319 and 4,596,622 to Heenan et
al., ~ close road pavement IlI&~kG.:i that have a glass sheet fixed to a
l~,t~u,~nective cheeting~s front face. The glass is plefelled to be an l~nt~mp~red
and ~ FAled sheet about 2-15 mils thick. There is a particular need for
improving the abrasion . ~ ce of pavement markers since they must be able
to resist tire impacts in the p- e~ence of abrasive materials such as grit and sand
as well as roadway çh~.mi~Alc and telllpèl~ re and weather eAllènles.
Unlike pavement markers, however, trafflc signs are not disposed on
road sllrfAcFc and, as a conse.luence, do not require the extreme abrasion
reci~Ance that is required of pavement III~.Iktl~. For trafflc signs, loss of
intensity caused by P.t;~ ;Qn, ~spe~i~lly dew, is of great concern.
SU~LURY OFTHE~NVE~ON
The present invention provides an anti-dew reL.uleflective sign
comprising a glass plate having a textured outer surface disposed over a
r~,L.ulenective graphic. The textured glass surface is exposed to air, and, in
--3 -
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dew con~lition~ spreads ple~ lion in a thin film over the glass plate's
surface.
The present invention also provides a method for making an anti-dew
u~cnective sign in which a glass plate having a textured outer surface is
placed over the le~lolt;nective graphic.
The present invention provides an economical and elegantly simple
method of making an anti-dew .~ ilective traffic sign. The anti-dew
characteristics of the inventive ~ ,nec~ e traffic sign are achieved without
the need for cle~l.ical inputs, heating flF~ , heat storage layers, infrared
bearn radiators, phase transition materials or vibration gc~ . Other
advantages provided by the textured glass surface include~ e to
organic solvents, thus f~r.ilit~ting removal of graffiti from the sign; ~ allltl;llg
rPcict~nce and protection from ultraviolet (UV) light, thus ~yt~n~li~ the
lifetime of underlying polymers and inks.
These and other features of the present invention are more fully shown
and desclll,ed in the dli~wh~gs and detailed description of this invention, where
like It;rtl~,nce numerals are used to repleselll similar parts. It is to be
understood, however, that the description and d~wi~ s are for the purposes of
illu~ ion and should not be read in a manner that would unduly limit the
scope of this invention.
BRUEF DESCR~r~ON OFTHE DRA~NGS
FIG. 1 is a front view of a It;llolenective sign of the present invention
in which the r~,l-urenective graphic is "St. Paul 10 km".
FIG. 2 is a cross-sectiorl~l view taken along line 2-2 of FIG. 1.
FIG. 3 is a plot of light inlells;ly versus time of day from rellu~ ective
~heeti~ having a flat glass surface.
FIG. 4 is a plot of light ;llh.l~.ly measured versus time of day from
u- ellective ~h.oeting having a textured glass surface.
FIG. S is an SEM photomicrograph of the surface of a flat glass plate.
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FIG. 6 is an SEM photo,l"crograph of the surface of a textured glass
plate.
FIG. 7 is an SEM photomicrograph of the surface of a highly textured
glass plate.
DETAILED DESCRnY~ON OFTHE ~NVE~ON
In FIG. 1, a I t;ll ùrt;nective sign 2 of the present invention is shown that
co~ .C il~ulll.alion in the form of a lc;~lolcnective graphic 3. In this case, the
l~t.o.~le~ilive graphic is in the form of lettering that spells "St. Paul 10 krn".
In FIG. 2, the ~ ùlenective graphic 3 is disposed on substrate 4. An
h,l~laye~ 5 overlies the ~~ I.or~ nective graphic 3. At the sign's top, outer layer
lies a glass sheet 6 having one major glass surface 7 that faces the substrate and
a second major textured glass surface 8 that is exposed to the ~tmosphto~re.
Retroreflective graphics of the present invention are defined as
~ c;llective ~hFel;~ g or .~tlu-enective ei~ a-,~lu~ed in the form of
Ch&~nl;~el'~ .llllbtl'~ or symbols. Retroreflective graphics do not include a
ullirOllll lt;~lurenective cheeting or layer over the entire surface. Thus, gl ~-
are not merely plain reflectors such as a pavement marker; however, the
lell Ul ~aective graphics can be disposed over a uniform l el- urenective
bacL~uulld. The ~ ù~lective graphics can also be an inverse design such as
a ~~l~ult;flective bacL~,.ound for non-leL-ù~flective characters, numbers or
syrnbols such as a non-reflective profile of a cow or deer. In the latter case, the
l~,l-u.t:necli~e graphic would include both the I~I-u-enective bacl~uund and
the non-reflective profile.
The l~lr~ Ile~;Li~e graphic 3 is typically bonded to the substrate 4 or to
a background materiai by an adhesive or by mechqnic,q~l means such as qno-li7ed
"h~ rivets. Adhesives are p-~;r~ id, and p-cis~.l'e sensitive adhesives are
esrer~iqlly prefellt;d. The lelru-tinective characters, numbers or symbols can be
bonded to a re~lu~nective bac~roul,d. For example, the ~el-u,ellective
A 30 characters, numbers or symbols can be cut from white l~L,ur~,nective sheetin~
and bonded to a bacl~lound of l~;Llu~ellective ~heeting that has been overlaid
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with a clear, colored polyrner film such as an acrylic film. Common
background colors are green, brown or blue. Another way of making the
r~h orGllective graphic is to cut out letters, numerals or symbols from a
L,~l..s~,alenl colored polymer film, and l~min~te the colored letters, numerals or
symbols onto white lGI.orGnective ~hf~etin~ A suitable, commercially available
clear colored acrylic film is ScotchliteTM Elc_l.u.~c Cuttable Film Series 1170,available from 3M, St. Paul, MN. In still another alternative, the rGllulGnective
graphic can be produced by printing over portions of a lGLlurGllec~ e sheet.
For ~ .~ n ~'e, a stop sign graphic can be made by screen printing a red clear ink
with a negative legend on a white lGl~ulGflective .~;h.~?eting
The reL-ol~nective graphics typically contain ,el.~-Gnective .~l-c~
FY~mrles of col"--le~.iially available l~l- ur~lective ~heetin~ that may be used to
make the graphic include ScotchliteTM Reflective Sh~etin~ High Intensity Grade
Series 3870, ScotchliteTM Reflective Sheeting Diarnond Grade VIP Series
3990, and ScotrhliteTM Reflective SheetinE~ Diamond Grade LDP Series 3970,
available from 3M, St. Paul, ~i~-l-f.~ Retroreflective ~l~e~ typically
Cûl~ )li3eS a reflective surface and optical fJe~ ; The reflective surface
serves to reflect inr;~nt light, and the optical f~lPm~nt~ serve to redirect theinr,idçnt light toward the light source. The reflective m~t.~?ri~l may _om~lise a
~ e~;~.lAr metal reflector such as ~hlmim~m or silver (see, for e.Y~mrle, U.S.
Patent No. 5,283,101) or a diffilse .Gne~ lor such as a heavy metal pigment or apolymeric material wherein reflect~n~e is caused by a di~G-t;--ce in refractive
indices at an interfiace (frequently a plastic-air interface~. Optical ,el~ s
typically come in one of twû forms: beaded lens ~.?lçmlo.nt~ and cube corner
f~ E~ -ples of ~I.urGnective ~h~etin~ that employ beaded lens
~ " ,l~ have been ~ ;losed in U.S. Patent Nos. 2,407,680, 3,190,178,
4,025,159,4,265,938,4,664,966,4,682,852,4,767,659,4,895,428,4,896,943,
4,897,136, 4,983,436, 5,064,272 and 5,066,099. Fy~ es of rGtlu.~nective
~llee~ g that employ cube corner el~...e .I.s have been ~licc~1osed in U.S. Patent
- 30 Nos. 3,684,348, 4,618,518, 4,801,193, 4,895,428, 4,938,563, 5,264,063 and
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S,272,562. Disclosures of the patents cited in this paragraph are incorporated
in their entirety here by ~GrelG.,ce.
The substrate 4 is typically a mP.t~llic, wooden or polymeric material.
~ Preferably, the sulJ~ Le is a rigid material, with ~Illmimlm being the most
co,.. noll The substrate may also be a flexible polymeric material or a
co~ on in which a flexible polymeric material is mounted onto a rigid
material such as ~I.,.,.;.,~.i~, or plywood. The substrate is usually prGrGllGd to be
opaque. Typical ~ -ples of com~nercially available subsL.,lles include: a 2
mm (~ çrs) thick acid etched and deglcased ~ panel, a high
density 2 cm (cf~ntim~otf~rs) thick plywood, or a 4 mm thick rll)e~gl~s.,-
l~,hlru~ied plastic panel; all these substrates are cûll~nonly used in trafflc sign
industries and are available from the Lyle Sign Co~ , Eden Prairie, MN.
In some embodim~nt~ ,I,ol ~nective signs of the present invention can
be produced without a substrate. In this case, the . G~S Ol Gnective sign would be
com~,ised of a textured glass sheet ~tt~h~d to the rGllu-Gnective graphic. In
one embodiment, the glass sheet is att~h~d to the .GLrolenective graphic by a
clear adhesive. In another embodiment, a clear pressure sensitive adhesive with
releasable liner is att?~(~hed to the back of the ~ellult;nective graphic. Release
liners are typically sheets of a non-stick polymer such as a fluoropolymer or a
silicone-treated polyethylene, polypropylene, poly(ethylene tele~ te), etc.
For ~ ition~ lel~h and rigidity, the leLlorenective sign can subsequ~ntly be
mt l-nted onto a rigid substrate. Alternatively, the .GIlorGnective graphic and
LulGd glass plate (with or without an adhesive layer) can be molmted in a
frame.
The lcLlùlcnec~ e sign of the present invention further c~llLa;ns an
interlayer ~ over the leL~ulcnective graphics. In general, the interlayer may beany light-Lla..c...i~-:ble layer. In one prerG--cd embodiment described above,
the interlayer comprises an adhesive that bonds the lcllûrcnective graphic and
the glass plate. In another prc~c-.ed embodiment, the interlayer comprises an
30 air gap.
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The interlayer may also comprise a polymeric material. One preferred
polymeric material is poly(methyl methacrylate). Other suitable polymers
inc1ude: ~iiph~tic polyurethane, {meth)acrylic acid and ethylene copolymers, or
a flexible poly(vinyl chloride). The polymeric material may also be a
S copolymer, polymer blend, or a multilayer film. The polymeric material is
preferably ~ J~Glll and will ~ 1slllil more than 80% of the inci~çnt visible
light; more pleîGl~bly more than 90%. For ~dt1ition~l stability, the polymeric
material may contain W absolbGl~ and free radical scavengers. Common
of such addit;ves include hindered amines, b~,l~ophf..ol-Pc
bel~o~ c,les, o~nilides and alyll)~n~o~tec
mples of COIIIIIIGI C;a1IY available hindered amines include
Chim~ccorb(TM) 944, Tinuvin(TM) 144, 622, and 770 available from Ciba-
Geigy Corp., Hawlllollle, New York. Common e~lnples of W absc,-l,tl~ are
b.,~ li~oles, such as Tinuvin(TM) 327, 328, 1130, or P, available from Ciba-
Geigy Corp., Hawthorne, New York; n~nilicle~, such as Sanduvor(TM) EPU
or VSU, available from Sandoz Ch~m;c~l~ Corp., Charlotte, North Carolina;
and arylbe~l~oal~c such as W-Chek AM-340, available from Ferro Corp.,
Cleveland, Ohio. The polymeric layer may also contain coloring agents or
fluorescent compoul-ds for m~mlf~ctllring various colored such as yellow,
orange, brown, green, blue, fluorescent orange or yellow-green ~ ul~ective
~heetings The polymeric layer is preferably about 0.05 to 2.5 mm thick.
The glass plate 6 is a silica-based glass, preferably soda-lime glass. The
glass plate can not be an organic polymeric material. It has been discovered
that organic polymeric materials (with or without textured .s~ es), such as
poly(methyl methacrylate), do not provide the full range of de~ }le
characteristics inr,~ ing anti-dew p-u~G~lies~ durability, ~w~alll~ bility (e.g.,
re.~i~t~nee to mlcrobes), le~ ce to organic solvents, etc. that are provided by
the textured glass plates of the present invention. The glass plate is light
tr~ncmi~eible, and plG~el~bly capable of ~ .g at least 80%, more
plt;r~,.ably 90%, of the intensity of visible light pel~G .~liy~l~rly incident to the
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W0 97/31357 PCT~IJS97~00628
glass plate. The thicL-nPc~ of the glass plate is preferably 0.1 to 10 mrn; morepreferably 0.5 to 6 mm; and still more pl~re,ably I to 4 mm.
The glass plate has two major surfaces. In the le~lo.enective sign of
~ the present invention, the outer major surface of the glass plate is exposed to
the air. The outer surface is â textured glass surface having rnicroscopic
surface v~ on~ of at least about 3 nm (n~nolnete~)~ The textured surfaces
are pre~.~bly defined as co..~ g ~"~ upOl ~ having rli~m~ters in the size
range of between about 0.003 to 10 ~m (ll,icl~ll.el~.~), more pltir~ bly
b~,h.~n about 0.005 to 1 ~m, still more p ,~r~l~bly b~v~ n about 0.01 to 0.5
llm, and even more p-t r~,~ly between about 0.01 and 0.05 ,um.
The surface rnicropores can be better understood with l~r~l~,nce to
Figs. 5-7 which show sc~nning el~ rui- mi~"oscopc (SEM) photomicrographs
of three di~lellL glass s~ ces Fig. 5 shows an ~ ed, flat glass surface
which appears re~ ss under SEM analysis. Fig. 6 shows a textured glass
surface with ~ic(opG~es having ~1i~...... ;le. ~ in the size range of about 10 to 60
nm (the size scale is shown in the lower right hand corner of each
photomicrograph~. Fig. 7 shows a more highly textured glass surface; the
surface of this glass appears frosted when viewed by the unaided eye. The
texturing can be either patterned or random, but is plerel~bly random (i.e., is
without a regular pattem).
In a pl~rt;.led embodim~nt the textured glass has the characteristics of
scallops, islands and micropores described in U.S. Patent No. 4,944,986,
illccl~ol~led herein by reference. The scallops are generally in the range of
100 to 2,000 ~m. The islands are in the range of 10 to 120 ~m. These scallops
and islands tend to diffluse the ;.. co,.. ;.-~ visible light. For higher clarity, the
etched glass should have fewer scallops and islands, but more of the
microporous surface texture. In a p,ert;"cd embodiment, the textured glass
plate is AR glass purchased from Zuel Company, St. Paul, Minnesota.
The textured glass surface may alternatively be defined by its water
spreading p,upe,lies. Thus, in a p,erellt;d embodiment, the static contact angleof deionized stationary water droplets on the textured glass surface at 25~C
g
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remains below 40~, more I~lG~lably less than 30~, and still more plcrGlably lessthan 20~. Static contact angles can be measured on a deionized water droplet
of O.O1 ml with a contact angle goniometer.
At least the outer major surface 8 of the glass plate must be textured.
S The glass plate can be textured either before or after it is affixed to the sign.
The surface of the glass can be ~C~IUl ed by physical means such as grinding or
sand blasting or by chemicai means. P~,rel~bly, the glass is etched with an
acid, typically hydrofluoric acid. In a particularly pl~,f~ ed embodim~nt, the
glass is etched with an aqueou~ solution of hydrofluoric acid, ~.. lo~.;.. l1~ bifluoride and a water-soluble organic compound such as sorbitol. The inner
major surface of the glass 7 may be either smooth or ttAIu~cd. In a prere,~d
embodiment, the inner surface is also textured in order to reduce cost or
,~"I~ r.e l~al~ JalGl~y.
The .t:L....e~lective signs of the invention may also include adhesive
layers. The adhesive can serve to bond any of the layers in the sign. For
GA rlc, an adhesive layer may be disposed on the second major glass surface;
thus, bonding the glass plate to the leL-ulGne~iLi~e graphic. The adhesive layeror layers can be corltin~o~l~ or I~ol~Gl~ Qus The ~-ol-co.~ oll~ layer or
layers provide an air gap bt~ween layers. In some emborlim~nt~ the major
glass surface 7 is coated with a silane prior to col t~cting the adhesive (see U.S.
Patent No. 4,596,622, i.,co.~or~Led herein by reference). An adhesive layer
can also be disposed on the outer surface of the substrate (i.e., the major
substrate surface facing away from the graphic). In in~t~nces where adhesive is
disposed on the outer surface of the substrate, the substrate is p.Gre.~bly a
flexible polymeric sheet. In some preferred embo~imtonts~ adhesive can be
disposed on the rear of the retroreflective graphic or on the outer surface of the
sulJ~LIale and covered with a release liner made of a polymeric material such assilicone treated polyethylene. Types of adhesives usable in the leL.u.enective
signs include, but are not limited to, hot melt and pressure sensitive adhesives.
Foam adhesives are especially advantageous in those embodiments in which an
adhesive is used to bond the ~G~-o,GnecLi~/e graphic to the substrate, since foam
--10-
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adhesives are likely to 'oe more durable. Adhesives ~ c1osed in U.S. Patent
Nos. 4,906,S23 and 5,264,063 may be used, and are incorporated herein by
reference.
lrlhion to, or in place of adhesives, the signs can use me~h~ni~
means to attach the glass plate to the signs. Examples of suitable ~l-e.h~
means include: clamps on the edges of the sign; a frame, preferably a heavy
duty ~1.. ,;.. frarne; or screws through the glass plate. Additionally, gaskets
or silicone sealer may be used around the edges of the sign to prevent l~ L~
or Cb~l;1l.l;l.~lll~ from e~ be~ween any ofthe sign's layers.
In its finished state, the ~cLlulGnective sign should ~ urenect light
Pffici~ntly. Thus, using the ASTM E810-94 procedure described in the
FY~ CS section, the ,~lrùrenective signs of the present invention ltL~ulenect
p.e~e.al)ly at least 50%, more ~l~Çel~bly at least 70%, and most plt~,~ly at
least 90% of in~ident light as col~l,ualed with leLlo~t;flective ~h~eti~ without a
glass cover plate.
EXA~LES
The following non-limiting eY~mple~ have been selected to illustrate the
invention.
In a colllp~a~ e test of dew l~ nl properties, various glass or
plastic cover plates were mounted over identic~l sheets of l~;;llol~nective
.l.ee~ , (ScotchlitelM Reflective Sheeting Diamond Grade - Visual Impact
Pelrull~lallce, Yellow 3991, available from 3M, St. Paul, Mimleso~a) that was
l~---;--~led onto an ~ .. panel via a plc~ule sensitive adhesive. The glass
plates were held in place by upper and lower plywood mounts (61(L) x 3.8(H3
x 1.6(W) cm) having two parallel grooves (61 cm length x 1.3 cm depth x 0.4
cm width) sepa,~led by 0.62 cm. The surrounding edges were sealed with
col~lll.able plastic tape to prevent moisture from c~mrlPn~ing on the interior
surfaces. The glass-covered sheeting~ were tested for dew ,~c;~ ce loy
pl~ ent side by side on an open deck on an autumn night in St. Paul,
Minnesota. IllLe~ y of ,eLIc,rt;nected light having an el~Ll~u~ce angle of about
-11-
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W O97/31357 PCT~US97/00628
5~ from the main axis perpçn~icul~r to the test panel was measured using a
retro-lu."il~o.lleLer (model 1980A, Spectra Pritchard) at an angle about 0.2~ off
from the light source (i.e., a 0.2~ observation angle). The light source was a
500 watt floodlamp. Each test sign rc:~lulenection was measured in a 10
minute interval from 6 p.m. to 6 a.m. the following day. The ~ ul~nective
data were then rec~lc~ ted to the standard unit of c~n-lPI~/lux/m2 by a
calibration factor, which was obt~ine~i according to the method leco.. -~nrled
in ASTM E810-94, from the fraction of ~~l~u~c:nected light measured by the
photolnminomet~r without any con~lPnC~tion on test panel.
Fig. 3 shows the measurement of the intensity of light ~~l-u-~nected
from ~heeting with a flat glass cover plate. The flat glass plate was 2.4 mm (95mil) thiclc, obtained from AFG Industries, Kingsport, Tennlsssee (average
visible light ~.i.n~ ce of 91%). The initial intensity of letlulènected light
was about 430 c~ndel~ per lux square meter (cd/lux/m2). At about 8:30 p.m.,
the formation of dew began to ~l;" ,;l~ cl. the intensity of light . èllvl ~nected from
the ~h~etin~ and by 10:00 p.m., il.l~.nsily of r~l~o,enected light d;...;~ l.ed to
about 50 cd/lux/m2. As shown in Fig. 3, intensity of retlorenected light
gradually inc~.ased until it reached an i~lc;nsily of about 350 cd/lux/m2 at 3:00
a.m.
Fig. 4 shows the measurement of intensity of light lt;L-olcnected from
~h~etin~ with a textured glass cover plate. The textured glass was 2.4 mm (95
mil) thick, textured glass obt~ined from Zuel Company, St Paul, Minnesota
(id~ ;r.ed as AR glass). At about 8:30 PM, the formation of dew began to
,I;..,:.~i~l, the intensity of light lel-u,t;nected from the ~heetin~ and by lû:00
p.m. the hllell"ly of rel,urenected light rliminiched to about 200 cdllux/m2. Asshown in Fig. 4, intensity of Icllu~;nected light then h~cl~,ascd, and by about
12:30 a.m."el~olt;nected light had recovered to its initial intensity.
At the same time, tests were co~ cted with cover plates of: coarsely
textured (i.e., frosted) glass (obtained from Zuel Company, St. Paul,
Minn~sota; identified as RR glass); textured poly(methyl methacrylate); and no
cover plate. The frosted glass cover plate showed a general decrease in
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WO 97/31357 PCT~US97/00628
ily (to about 330 cd/lux/m2) due to the ~osted character, but showed
cellPnt anti-dew prope-lies that were very similar to the textured glass
described above and in Fig. 4. Retroreflective sheeting without a cover plate orwith a textured poly(methyl IllGlha~ late) cover plate both showed a loss of
inlen~ily to about 50 cd/lux/m2 and r~ h-ed at about 50 cdllux/m2 through
6:00 a.m.
Tests were also conrlucted of the r~llort;nectivity of ~l.Ç~ 8 under dry
conflition~ with various cover plates measured at various observation angles
from light having an ~..L,~ce angle of -4.0~. The measu.el..ellLs were
p~"r~lll-ed accol.lin~, to ASTM E810-94. The ,el~u,-,nective ~heetin~ was
Scotr~-liteTM Reflective Sheeting Diamond Grade LDP No. 3970. Glass cover
plates were laid over the sheeting~ and the ~hee(;.~ with plate was held by a
frarne. No adhesive was used. The results of these Illea:~UI t~ i are shown in
Table 1.
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CA 02244922 1998-07-30
W O 97/31357 PCT~US97/00628
Table 1: Intensity of Retrorçtlt~c~l Light
(cd/luxlm2) vs. Observation Angle (degree)
Observation Angle 0.20~ 0.30~ 0.50~ 1.00~ 1.50~ 2.00~
No cover 1402 967 442 29.7 7.6 3.3
Flat glass cover 1153 797 364 26.1 6.8 2.9
Textured AR glass cover 1274 886 403 28.3 7.3 3.3
Textured RR glass cover 3S3 312 228 76.8 24.4 8.5
As can be seen in Table 1, both flat glass and textured glass cover plates
are acceptable in terms of the intensity of r~Llol~nected light. Flat glass cover
plstes, however, do not perforrn as well as textured glass plates because
l-,ho,~nectivity &~,I"G.,;ably deçlines under dew conditions (see, for ~ .ple,
FIG. 3).
The frosted glass plate (i.e., textured RR glass) is acc~ al,ie for use on
,_L~olt;nective traffic signs because of its good anti-dew plopt;,Lies. It,
however, is less desirable than a less coarsely textured glass because of its
reduced r~;L,ulcnective intensity (see Table 1).
As ~iiccll~sed above, flat glass and textured glass surfaces were analyzed
by SEM. S~mples of flat glass from AFC inthlctri~, textured AR glass from
Zuel Co",pa,-y and tci~.Luled RR glass from Zuel Colll~Jally were vapor coated
with a thin layer of pl~timlm (less than 3.5 nm) by conventional techn~ es
The s~mr'e~ were then analyzed at 100,000X m~gnific~tion using a Hitachi
Model S-4500 Field Emission Sç~nning Electron Microscope. The resulting
SEM photomicrographs are shown in Figs. 5, 6 and 7 (flat glass, L~,ALu,ed AR
glass and textured RR glass, l e~,cc~ ely).
Various mo~iifiç~tiQn~ and alterations of this invention will become
appa,~." to those skilled in the art without depalL;,lg from the scope and spirit
2S of this invention. For example, lt:L.or-;nective signs of the present invention
can be made with or without a polymeric interlayer or can include additional
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WO 97/3~357 PCTllJS97J00628
layers such as adhesive layers between the graphic and substrate or graphic and
glass. It should thel~îo,~ be understood that this invention is not unduly
limited to the illustrative embo~iment~ set forth above, but is to be controlledby the limit~tions set forth in the claims and equivalents thereof.
