Note: Descriptions are shown in the official language in which they were submitted.
~ETRORE~FL,ECTIVE SHEETING ~ND METHODS
FOF< MAKING SAME
. . .
P~CKGRO~ O7~ TH1~ rIoN
Re~rore~lective sheeting has particul~r use il~ making highwey ~igns, Ytre~t
signs and the l;ke, and is now employed extensively. Tne ~edernl government h~
recognized two primary types ot retrore~lec~ive 6heeting~ glass ~ead snd cube-
corner. Such approved sheeting materlals ar¢ tound in c specirlcation entitled FP-
79nl published by the U.S. Depnrtment or Tr~nsportation, Federal ~Ighwny
Adminlstrntion. Speclrication PP-7~ presently has been adopted as n purchaslng
standard by many slate highway depar~rnents~ ~nd it sets forth certRln mlnlmum
spccl~ic~tions whlch must be met by retror~rlective sheetlng o? the cube-corner
~ype. Includcd among the specified characteristics are those for r~lectivity, color,
10 flexibillty ot m~terial and resi~tnnce to cr~cking ~nd weatherlng.
Cub0-corner type reflector elements gener~lly provide a higher speeiric
intensit~ at 0.2~ observation an~le ~nd oD entrQnce angle thàn do glass bead type
re~lector elements, but, to applic~nts knowledge, no one successrully has ~urnished R
sheeting material in commerclal quant;tie~ which generally will meet the
requirements ~or the Class IIJB sheeting set forth in the sforement;oned FP-7
speci~ication. Accordingly, the present invention seeks to provide a
unique sheeting pr~duct which will SU~StElntiBIly meet such ~pecitied criter~a and
wh;ch can be produced in ~ccordance with the novel methods disclosed herein in nn
economjcal fashion and in commercilll quantitie~.
Retlore~iectivity is achieved by cube-corner type reîle~tol- elements
primarily through the principle oî total internal re~lection. It i5 well known ~hat
any sur~sce contact made by another material with the races o~ the ~ube-corner
elements generally hss a deleterious cffect on ~he renect~veness of the reflector
element.
However, when all of the element fa~es are metallized, or mirrored,
-t~en, rsther than relying upon total internal rerlection, retroreflectl~n is achieved by
specular retlection from the mirrored ~aces. Generally, metallizing w;ll provide a
gr~yish or black coloration under certain daylight conditions vis-a-vis unmetallized
cube~orner type elements.
The present inventlon relates generally to methods and appQratus ~or
pr~ducing retrorenective sheeting conslructions ~nd, more particularly, to methods
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flnd ll~)pllrntllS ~0~` producing a rlexlble lnminnto shceting constructlon ln~luding nn
upper th~rmopInst;c shcct, ~he reverse o~ which is provided with n repe~t5n~,
r~trorefl~ctine pattern of fine or precise detnil, ~ backcoatlng to protect the ~ormed
pattern~ and a selectively npplied intermediate layer allowin~ bonding ot the
b~ckcoating to overlay the formed pattern on the thermoplastic sheet wh51~
preserving and enhancing the re~rore~lective properties o~ both the forrned pnttern
~nd the l~min~ted sheet. More precisely, the present Invention 1~ applicable to the
production of cube-corner type retrore~lective ~heeting laminates.
With;n the ar~ of desi~ning reflector~ ~nd retrorerlective mut~rial, the
10 terms "cube~orner" or "trihedral," or "tetrahedr~ re recogni~ed In ~he art as
describin~ s~ructure or patterns consisting Or three rnutually perpendi~ular ~aces, not
limi~ed to any partictIlar size or shnpe of ths faces, or the orIentation o~ the
optical A%is of the cube-corner element E~ch or the cube~corner fAces can assurne
A different 3ize nnd shApe relative to the other~, depending upon the angul~r
reflective response charncteristics desired, and the cube rorming techniques
employed.
Examples of prior cube-corner type refleetor~ m~y be found in V.8.
Patent No. 1,906,655, issued to Stimson, and U~S. P~tent No. 4,073,568, issued to
~. Stimson shows ~ renex light reflector including an obverse ~ace and a
20 reverse light-renec~ing face consisting of ~ plur~lity of cube-corner type renector
elements with esch such element having three mutual]y perpendicular sur~ces
adap~ed for total internal reflection ~f light impîn~in~ thereon frorn the obverse
face ~ describes a cube~orner type reflector in the ~orm Or a rectangu~r
par~llelpiped.
It long has been desired to obtain the bene~its of cube~orner rene~tlve
properties in the form of nexible sheeting. As noted above; one ~dvantageous
aspect of such ~heeting is in the manufacture o~ highway and street signs, markers
and the like, where graphics are printed, psinted, silk-screened or otherwise applied
to a highly reflective substrate mounted to a nat, stif~, supportive surface.
30 Flexible retroreflective sheeting, when used ~s such a substrate, e~n ~e stored and
ship~>ed while wound onto rol~s, and can readily be cut or otherwlse ~ormed into the
desired shape and size required for a particular application. The reflective nature
o~ the sheeting allows such si~ns, markers, ~nd the like to retlect li~hS from a
vehicle1s headli~hts, permltting the item to be réad by the driver, without requirlng
a F~ermanent light source to illuminate the sign or merker.
7~
Production of such re~rorefloc~ive sheeting h~s been m~de pr~atlcable by
nppnrntlls ~nd methods to torm preclss cube-corner patterns ~n gre~tly reduced sl~e~s
on flexible thermoplnstic sheeRng. Desirably, such sheeting may then be assembled
in the form of sel~-adhesive laminntes.
Others h~ve recognized the desireability ot produ¢ing retrore~lecti~e
thermoplastic material in sheet rorm. Unlted States P~tents Nos. ~,31û,790,
2,380"1~7, and 2,481,757, grRnted to Junç!ersenl, descri~e ~nd te~ch thc shortcomings
ot previously known re~lectors msnutactured ~rom gless, and the advnntRges inherent
in providing a reflective mRteri~l in a less rrngile and more ~lexible sheet ~orm.
While so suggesting, it is no~ known if ~;en in tact ever commerclali~ed any
procluct disclosed ln such pRtentS-
In U.S. Pntents Nos. 4,244,683 and 4,332,847 issued to ~ the
desirnbility ot manufaaturlng cube-corner retrore~le¢tive sheeting In a continuous,
non-StOp process is presented, but the approach selected by Rowland i8 e ~emi-
continuous proces~s (Rowland 683, column 2, lines 18 - 38~, presum~bly so-calledbecause the process requires frequent repositioning o~ th~ moldJng p~tes.
In United States Patent No. 3,187,068, lssued to ~,
continuous production ot retlective sheeting is disclose~, utiliz(ng encapsulated glass
rnicrospheres RS the reflecting medlum. ~i~,~ descrlbes th0 application of
2 0 a pressure-sc~ivR~ed adhesive layer to such sheeting to enable attschment o~
sheeting segrnents to selected sur~aces.
In United Ststes Patent No. 3,649,352, issued to ~ ~ beaded
sheeting construction is described, portlons of which becorne reflective when he~ted,
snd which includes a pressure-activated adhesive layer allowlng ~ttechment Or the
sheeting construction to other articles.
~L~ 2,407,680 teach the utlliz~tion of glass microspheres or
besds included as the reflective elements in flexible sheet torms; Tung~ et Al., in
United States Patent ~o. 4,367,920, also describes a lamir!ated sheet construction
using glass microspheres as the reflective e1ernents.
A common prob]en~ in the construction ot re~lective 1sminate sheetlng Ig
to rind means to bond the ~amins firmly together in a way which preserves the
reguired retrorenective qualities ot the retlective elements selected ~or use. An
exsmple of prior e~forts to solve this problem with respect to gl~ mlcrospheres
may be seen in United States Patent No. ~,190,~78, issued lo Mcl~enzle, whereln ~
cover sheet or tilm ls s~ecured over exposed gl~ss micr~spheres by use ot die ~ ~ .
elements which torce a por~ion ot the materlal In which the gl~ss microspheres nre
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embe(lded into contnct wi~h the eover shcct. The dia elernents thus areate ~ grid
pnt~ern on the resultin~ shceting construction, wi~h eflch grid forming ~ 6eparRte
cell. Withln ench cell, nn nir space is m~int~ined between the mlcrosphere% and ~he
cover sheet, nnd incident light tr~verses the cover sheet and the alr sp~ce to b~
retrorenected by the embedded m;crospheres.
Holmen et ~1 U.S. Pa~ent No. 3,924,9~g, t~ach a cube~orner type upper
rigid sheet hnving upstflndin~ wnlls, or septn, inlegr~lly ~ormed ~s p~rt ot the cube
pattern. Ille septa extend to form e regular geometric pattern o~ Indiv1du~1 cell~,
with the sept~ extending ~t least as rar rrom t'he upper sheet as the cube-corner
10 ele~ents. A particulnte packing mny be used to ~ill each o~ the cells, ~nd a
backing 6hect is then ~ttached to the rear of the upper sheetg wlth the ~epts
sorving as the nttachment sites. ~L~_ use rel~tively lnr~e cube~orner
elements fnshioned as rigid sections bound to Q tlsxible baek, and h~s limited
flexibility In use.
In ~, U.S. Patent No. 4,025,l59, the cellular concept i~ desoribed
with respect to cube-corner type retrore~lective sheetin~, through use oi~ dies to
force a carrier film into contact with the reverse side of the cube-corner sheeting.
The carrier filrn must then be cured with rndiation to bind it to the cube-corner
sheeting snd, as in ~~, the resulting cells include sn Qirspace extending
20 between the c~rrier ~ilm snd the reverse side o~ the cube-corner she~t. The ~ir
cell structure apparently wns intended to provide a hermetically sealsd cell, avoldin~
the need for metalizing the cube-corner elements, ~nd providing ~n air/thel-moplastic
interr~ce to enhance retroreîlection.
None Or the roregoin~ teach the assembly o~ molded or embossed ~ube
corner type retroreflective sheeting into sel~-adhesive laminates whlch protect and
enhance the renective properties of the sheeting without requir;ng the use of die~
or o~ integrally-molded septa or walls ineluded 85 part of the eube p~ttern.
Purther, none o~ the roregoing permits the material to bene~it from enc~psulated
seclions or cube~orner e]ements while enhancing and substantially meeting the
30 requjrements speciried in the ~forementioned DOT FP~7~ Speciric~tion.
~RIEP DESCRIPTION O~ THE INVENTION
,, ~
A thermoplastio sheet or web ;s provided on ~ts reverse s1de with Q
retrorerlective cube~orner type p~ttern. A thin leyer o~ n 11quld vehicle or solvent
containing hydrophobic gr~nul~r rn~terial ~such ns gilic~ tre~ted w1th sllnnes~ it~- -
deposited on the reverse side ot the web, n~ by screen printing, in n pnttorn leavln~
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selQctad s~Ltes devo-Ld oE grilnul~r materLal.. The weh Is then drled to drLve
oEE the solvent and, thereafterJ a water-based backcoating i9 app].ied over
the grflllular material pattern, with portions of the backcoating being in
direct contact with the thermoplastic web at those sites on the web devoid
of granular material. Thereafter, the backcoating is dried or cured, and a
layer of adhesive such as pressure-sensitive or heat-activated adhesive is
applied thereto. This procedure thus enables the assembly of patterned web
material into laminates which include an activated adhesive layer while
protecting the retroref].ective properties of the precise:Ly formed cube-
corner pattern.
~ ore particularly, one aspect of the invention pertains to a flexlbleretroreflective cube corner type laminate sheet construction including a
thermoplastic web w:Lth a l:Lght-receiving and transmitting first side and a
second side coextensive with the first side, and a cube corner type retro-
reflective pattern formed on at least a portion of the second side. The
construction comprises a layer of hydrophoblc granular material deposited
on the second side to cover selected portions of the formed cube corner
retroreflective pattern with remaining portions of the second side devoid of
said hydrophobic granular material. A layer of backcoating material is
deposited on the second side to substantially completely overlay the hydro-
phobic granular material without disturbing the pattern formed by the granular
material. The backcoating material substantially fully contacts the portlons
of the second side devoid of the granular material and is fixedly secured
thereto, thereby ~ncapsulating the hydrophobic granular material between
the second side and the backcoating layer. The particle si~e of the
hydrophobic granular material is such that the area in which it is deposited
will be effectively impervious to the backcoating material whereby the
backcoating material is unable to penetrate the granular material and
interact with the second side except in the area devoid of the granular
material.
Another aspect of the invention comprehends a method for producing
a cube corner type retroreflective laminate sheet construction comprising
the steps of applying to a web of thermoplastic material having a retro-
reflective cube corner formed pattern on at least a portion of one side a
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laya~ of hydl~ol-llol-l.c grfln~ll.nr ma~arl.nl. do~)091.t:ecl ~so a'J to Eorm a reg~.l.l..lr
nnd ~al)en~l.nu nrrny Oll ~he rc~rorcE:I.ec~:Lve pattern and ~ormLng, as pnrt oE
thc nrray, n pl~lrnl:Lty o~ paths on the one .s:Lde clevold oE the hydrophobic
grannlar mflter:Lal. A layer o~ backcoati.ng materi.al is applled to overlay the
hydrophobic granular mater:Lal and to flll the paths, and i5 adhered to
encapsulate the hydrophobic granular material between the formed side and
the backcoating materlal. The particle 9ize of ths hydrophobic granular
material is selected so that the area in whi.ch it i9 deposited will be
effectlvely lmpervlous to the backcoating material whereby the backcoating
material ls unable to penetrate the granular material and lnteract wlth the
second slde except l.n the area devold of the granular materlal.
In a preferred embod.lment, an outer protectlve layer of thermoplastlc
mater:Lal, used to provide additional weather resistant properties, is secured
to the thermoplastic web on the side opposlte from that upon which the retro-
reflective pattern is formed during or before the cube formlng process.
The completed lamlnate is then CutJ trimmed, or otherwise shaped for
application to supporting surfaces, such as street or highway signs, and
graphics or other indicia may thereafter be painted, printed, silk-screened,
or otherwise affixed to the uppermost surface of the laminate, thus producing
a readily and easily constructed highly retroreflective finished product.
These and further aspects of the present invention will become more
apparent upon consideration of the accompanying drawings, wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an enlarged perspective and somewhat schematic view
of one preferred aspect of the retroreflective sheeting of the present
invention as a completed construction;
FIG. 2 is a view along line 2-2 of Eig. 1;
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B
Pla. 3 is n grcntly onl~lrged pl~ln vlew Illustr~ting a secllon ot the
~ormcd surfnce o~ reflectlve sheeting comprislng on~ aspect of ~he present inventlon;
~ la. 4 is a somewhnt schemntic Rnd symbolic vlew of the proaesses and
rnnchinery utilized in n pre?erred Aspect ot the present inven~ion;
~ IG. 5 is fl plnn vlew o~ one form of screen p~ttern used to apply th~
hydrophobic gr~nul~r leyer of the present invention;
PIG. 6 is an enlnrged view, In partial detail, of an indivlduQI cell o~ ~he
sheeling ot the present invention; and
PIG. 7 is an enlarged perspectiv~ v~ew illustr~tln~ a ~econd preferred
10 embodiment of the retroreflective sheetin~ ot the present Invention.
D~rAll,ED_DESCRlPTlO~INGS
Reterring now to Pig. 3, the numeral 10 indicates generally B segment o~
cube-corner type retrorerlective thermopl~ic web used in forming the lamina~e or
the present inventlon. As seen In Pig. 3, there is ~epicted the rear su~f~c~ ot a
portion or (lexible retrorerleclive sheeting 12 ~ashioned rrom transp~rent
thermopla5~jc ma~erial in web form which hQs formed thereon, preferRbly by
embossing, a retrorenective ~nd repeating pRtterl of cube~orner re~lector element~
characterjzed by cu~e faces 14, 16 ~nd 18. In ~ preferred aspect of suc~ sh0~ting,
sheet 1~ is formed from an impact-modified acrylic material having t~Y inhibitors or
20 absorbers ndded thereto, Qnd which, prior to embossing, had par~llel ~ront ~nd bnck
surf~ces ~nd W1~5 initially on the order Or ~bout O.OOB inches thick. One such
materi~l is known ns Plexiglas DR, sold by the ~ohm and HnAs Comp~ny.
The cube-corner pattern formed on sheeting 12 is formed in ~n optically
precise, Iinely~etailed pattern. Por examplet as seen in Pig. ~, the depth to whlch
the cube~orner pattern is embossed onto sheet 12 may be o~ the order or ~.OD338
inch, (dimension X~. As shown at dimension Y in Pig. 3, the cubes formed on sheet
12 may be spaced ap~rt by a distance on the order of about 0.0072 inch, ~r the
depth as shown at X as set ~orth above~ While the cube pattern shown in ~lg. 1
i]lustrates cubes formed with their optical ~xes normal to the race Or sheet 12, it is
80 to be understood that other versions and p~tterns m~y also ~e utilized ~15 ~ormlng
the retrore~ective web of the Inminnte of the presen~ invention.
~ e~errin~ now to Pig. 1, the numeral 20 indicstes gener~lly a roll ot
retrorenectlve l~minate 22 manufactured In ~ccordance with prererred ~spec~s o~
the present InventlorI to be described hereinbelow. As hereln shown, Inmlnata 22 i~
rGlled onto Q core 24. A thermoplastic web 2~ h~ving a front or obvcrse ~urlrfl~o 28
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nnd ~ rcnr or roversc surtncc 30 upon which i~ embossed th0 cu~e-corner type
retroretlective pnttern LLlustrated ln FLg. 3. Th~ thermop1astic web 26 may be on
~he ordcr or about 6 mils in thicknes~ (0.006 inch).
Bonded to the reverse surrsce 30 Or the thermoplasticw~b 26 i~
bsckcosting or ~ilm 32. In Q prererred sspect of the present inventlon, a
hydrophobic granular silica materiRl 34 is Intetposed between th~ b~ckco~t tilm 32
and the reverse side 30 in ~ manner to be! Jescribed hereinbelow.
In sccorda.nce with a preterred embodiment of the pres~nt lnventlon, n
layer ot adhesive 36 is bonded to a release sheet 38 in n prasently well-known
10 fnshic>n~ and is ~here~rter bonded to cured baokcost film 32 In order to proYld~ a
tinished laminate 22 which includes a prcssure-6en~itive or heat-activated ~dhe~lve
laycr 3~ upplied to sheeting 12 in a mBnn~r which preserves the retroretleetlv~
cluali~ics nnd properties ot the cube-corner pattern embossed thereon. The release
sheet 38 is used to protect adhesive l~yer 36 until It is desired to npply l~minBte 2a
to El given ~urf~ce.
Pig. 4 shows~ in schematic form, a preferred arrRngment ot equipment
and sequence of operatlons to produce e retrorenectSve sheeting l~minnte ot the
type shown ln ~ig. 3.
The applicat~on of adhesive directly to the reverse sid~ o~ Q CU~e-Corner
20 embossed thermopl~s~ic web 26 will cause ~n undesira~lo and unac~ceptable lo~s of
retrorenectjye cap~bility. This ~rises from the contact ot the sdheQlve materi~l
with the reverse side o~ embossed thermoplastic~ web 26, ~ ~ ~ the ~ ng o~ the
"valleys rormed by the embossed pnttern Qnd the subseguent inter~ace formed
between substances that ~re too similar in refractive indices to produce adequ~te
retroreflection, so the transparent film can no longer utillze the phenomenon o~
total internQI renection to efticiently effect retroretlection or lJght. Tb solve thls
problem, A sub~tantial portion of the cube~orner pattern either must be
hermetjcQLly sealed with an air space ~etween the bsck wall ~nd the oube-corner
elements, or the cube~orner elements must be backed in e way whirh would
30 preserve the rstrorenectlve properties o~ the ~ormed web while providing slte~ ror
rirm ~lt~chment of an adhesive Isyer (or other adhesive m~terisl). Without such
protection, and without such atteching sites, the use of, ~nd e~fectiveness o~ a
retrore~lective embossed web is seriously compromlsed and curtslled.
Vnexpectedly, use of hydrophobio granular materials has been ~ound to
artord such protection or optical properties. Among such materl~l~ aro xylen~ted~
glass particles, powdcred silicone rubber, end silane-tre~ted 8111c~.
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As part Or the present inven~ion, It hns b en found thnt Q hydrophobicsilic~ mixture consisting principAlly of nmorphous silic~ treated w5th sllanes, when
used to rill the v~lleys formed by the emboss¢d pnttern, preserve6 the
retroreflective properties of the ~ormed pattern for mo t practical purposes~ Agaln,
it is not known precisely why this etfect obtsins: it has been theorl~ed thet the
point contact of gr~nules with the reverse ~ace of the ernbossed thermoplasti~ web
ncts to preserve the retrore~lective properties ot the psttern, perhnps by preservlng
A su~ticient ~ir interfnce with the reverse side ot the cube-corner pattern.
However, the present invention obtains excellent resu~ts even where the primary
10 silicn psrticlea used sre 6ignificQntly smaller thaIl~ for example, the pnrticle~
discussed in prior ~rt patents such flS ~ V~. Patent No. 3,924,929.
Use of such sllica ofrers advAntages such ns low prlce, avaIlAbJllty, ~nd
ease nnd precision of forrnulation. It further provides unlque color a~d ref~ectlve
chnrRcteristics to the tilm which improves the appenrance of the rilm even relative
to the glass bead types heretofore commonl~ used.
As discussed hereinRbove with respect to the ~ et al reference,
others h~ve nttempted to solve the problem-of loss of renectivlty by provIding
Ups~andirlg walls or septn as pnrt of the rigid molded tront fscs pstîern, with the
septa rorming indi~idual pockets for the npplication o~ granul~r ~ompound3 h~ving
20 pnrticle size~ far in excess of the silica particles used in the present inventlon.
The disadv~ntages to such nn approach, pnrticularly with respect to the cube~orner
type embossed pattern utilized in the present invention are manirest. U~e o~ ri~id
septa limit~ the size and shnpe o~ the cell. A separate mold must be formed for
each type of retroreflective sheeting reguiring ~ ~ell size other th~n thQt formed in
the origin~l mold. What is mennt by tne terrn "cell si~e" i~ the area bounded by or
closed off by the walls to torm e single pocket ~or the grsnular backing material.
Formation o~ such septa in ~ relatively r;gid mold p~ttern m~nutactured
to ~s fine ~nd precise a degree ot detMil as that shown in the present SnventSon al~o
mny cause problems with respect to stripping the formed thermoplnstic web ~rom
30 the forming tool. This rnay particulsrly be a problem where the sept~ or wsll~
extend inwardly into the mold to n distAnce grenter than the depth oî the cube-
corner pattern.
A preterred embodiment ot the present Invention includes the mixing of
hydrophobic silic~ mixtur~e using hydrophobic sill~n, orgnn5c solvents, and thickener~,
~nd the app]lcat5On or this mixture~ whlle In n Ik1~id torm, to the re~/erYe YIde Or~
~he tormed therrnoplns~ic web 5n a desired pnttern One ndvantnge ot the pre~ont
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proccss nnd pr~uct is thQt thc p-lttern CAn ¢onvcnicntly be ch~nged to eftect
chnng~s in rcrtcctive c~pabili~y oi~ ~hQ ~ilm, without changln~ the tov~5 u5ed In
torming the embossed wcb. Thereatter, the partlQlIy coated or imprinted
thermoplastic web is pnssed through a drylng oven which drives off the solvents used
to torm thc mixture, thereby drying the p~ttern on the thermopl~s~5c ~heet. l'hepattern in which the silica is applied to th~ thermoplasiic web leave~ selccted
por~ions or sites on the formed ~ace o~ the thermoplastic web devoid ot s~lica.
Re~errln~ now to Fig. 5, the numer~l 40 indicates ~enerally suoh fl
selected p~ttern. Each runner or p~th 42 represents ~n ~rea on the reYerse surrace
10 ol therrnoplastic web 26 where no silica h~s been d~j~osited. E~ch ~quar~ or
di~mond~h~ped nrea 44 represents ~n nren on the sur~Aoe Or thermopl~stic w~b 26
onto which tho slllos mixturc has been deposited.
As seen In Pig. 6, the nctual percentage of are~ covered by the ~ilic~
mixture is determined by the thicl<nes~ or width o~ each runner or path 4a, and the
pa~tern selected lor deposition ol the silica, with the cell ~14 h~vln~ an are~
~ounded by the runners 42, and rully avail~ble ~or the reception and retrorenectlon
o~ incident light by the embossed retroreflective pattern~ shown partl~lly ~t 4~.
Re~errlng now to Pig. 4"t may be seen that thermop1asti¢ web ~6 may
be drawn directly ~rom ~n associS~ted rorming machine (not herein speciJ~ie~lly ~hown~
20 in a continuous process, or m~y be drawn ~rom a separ~te suwly reel onto which
the embossed web 2~ has been wound (not herein specirical1y shown~ deslred,
web 26 may be supported by a backing sheet (not hereln specilically shown3
coextensive with obverse face 28, leaving reverse sur-ace 30 exposed.
lt ~hould be noted ~hat re~erence to web 26 E1150 ~ncludes re~erence to a
lsmin~te rormed by web 26 and a backing sheet such as described hereinabovc.
Web 26 is drRwn by, for example, powered rollers ~not herein 6peclfically
shown), to ~ilicQ mixture ~pplication st~tion 48. ~ herein diagrAmmaticalty shown,
a pre~erred me~ns and method Or applying the sill~a mJxture to web 26 may be
accompllshed through use ot a screen-printing cylinder 50 which hQs moun~ed about
30 ~he outer periphery thereor, a metal screen lormed to provlde the shape or pattern
to which it is desired to apply the ~llica mlxture~ Th~ mixtura Ts ~orced under
pre~we from the interior of screen-printing drum 50 onto the reverse side 30 of
the thermopla.stic web 26,~ As herein shown, the web 26 is directed by idler rol-
ler 52 ~o pass bel:ween the screen-printing drum 50 and a backin~ roller 54,
A prererred ~orm of the ~pp~ratus utllized to Apply th~ silica mlxturs et
application station 48 consists of ~ drum prlnter manufacturod by Stork BrabAnt BY
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o ~ lloxoc~r, llollnn(i, ot the lype hnvlnE n drum wlth clcclro-~ormed mcsh scrcer~s
ovcr which n ~ oto-resist p~tSern ~such ~s used ~OI oonventionnt silk screen) mQy be
moun~ecI, with n screcn pattern providing a dinmond cell ~Ize in the range of trom
nbout 0.096 inch to 0.300 inch, nnd ~ runner or cell wall thIckness of trom flbout
0.010 inch to ~bout 0.050 inch. Vnriations Ih the shnpe or the cell~ ttern repeQt
ot She cellc, nnd thickness of the runnerY msy be accolnplished by changing the
printing screen used on screen-printing drum 50. Also, the con~t~nt wldth o~ theweb mny be of various sizes, and the printing 6creens used will be o~ ~ compntlble
width.
ln its preferred rorm~ the silica mixture Is mede ~rom a. hydrophobi¢
silicn such ~s that manutactured by the Pigments Division ot De~uss~, ot Prnnk~urt,
West Germnny, under the tr~de desi~nnti~n ~ipernat DIO~ A prererred composltlon
ot ~he mixtur¢ includes hydrophobic silic~ in Q mixture contàining npproxlm~lely g8
perccn~ sllnne-trested silicon dioxide (SiO2~; 0.8 percen~ sodium oxide (N~20), ànd
0.8 percent o~ sulfur trioxide (SO~ non-polar nliphatic hydrocarbon soIvent
c~rrjer; R polar solventj And, where desired or required, ~ thickening agent. One
aliph~tic non-polnr hydrocarbon solYent successfully used is low odor mlner~l ~pirlts~
and Q workable mixture hss been creQted through use o~ an orgsnic nlcohol,
pre~erQbly butsnol, as the polar solvent mQterisI. ~ smect;te clay-b~sed thixotropic
20 thickener also m~y be used in vQrying amounts to produce a well^derined screen-
prinled p~ttern or the silic~ slurry on the embossed thermopl~stic web.
In ~ts preferred embodiment, the primary pQrticle size of the slllcs is
~bout 18 nanometers, and the Qgglomerated particle sizc of the hydrophoblc ~51ics in
its final form is about S microns. However, it will be understood th~t the only
critic~l limitation on the p~rticle size Is such that the ares in which It ;s deposited
will be 6ubst~ntiE~IIy impervious to the backcoQting ma~eri~l 32, whereby the
bsckcosting rn~teri~l ;s unable to penetrate the hydrophobic sillc~ and intersct with
the cu~e-corner psttern except In those ~reas devoid ot the silic~
l~e p~rticular combinstion ot solvents and thickeners is import~nt to
30 sstistactory deposition and definition ot the silica in Q precise 6nd accurst~ pAttern.
Screen printing of p~rticulste material commonly requlr~s use ot resins or otherbinder5 to hold the deposited ~ar~icles in place. A resln or blnder c~nnot however
be used in this instance because o~ the adverse eî~ect on renectlvlty ot the webbecsuse ot retrsctive Index Ylmil~rIties.
Another importnnt consider~tion 15 the rheology, or nOw chQrQct~rlstlcs o~
the silicn slurry ns It iB ~orced ~hrough thc printlng 6creen. The 61urry must
1 -
~,. ..
'74~'~
"rolnx," or thin ns lt is ~orce~l throllgh the screen npertures, ~nd therentter regain
ulfricicnt viscoslty to rctaln a wel)-detined pattern with good leve!lng qll~lities and
appenrance cha-acteristics. Yet another consider~tion 1~ use Or n ~olvent vehlcle
which obtAins the a~orcmentioned qualities without ~ttacking or degrsding the
thermoplastic web upon which the retroreflective pattern it ~ormed.
Use or pol~r solvents, such as butanol, enables the slurry to malntaln an
increflsed concentrfltion of solids (silics~. Such solvents, however, resct with the
thermoplastic matelial used to form the web. Non-polar solvent~, su¢h n5 mlnerB
spirits, preserve the embossed web, yet do not sct to provide n shtls~ctory slllca
10 p~ttern l`herefore Q blend of polnr snd non-polnr solvents has been round to be
use~ul in carrying enough solids without degrading rerlectivity or degrading the web.
Preferably, the hydrophobic silicA is present in proportions rHnging rrom
about t5 percent to about 35 percent by weight, the non-po2ar solvent carrler ls
present in amounts ranging ~rom about 40 percent to about 70 percènt, the poIar
solvent i5 present in amounts ranging from about 10 percent to about 30 percent,
and the thickening ~gent may be present in arnounts from about 2 percent to About
8 percent. One preferred formulation of the silica mi~ture includes 20 percent ~y
weight Sipernat D10 hydrophobic silica, 56 percent mineral SpilitS, 20 percent
butanol, and 4 percent thickener. It has been found th~t such proportions preserve
20 the web while providing a useful silica p~ttern.
A~te~ application of the s51ica mixture, web 2~ is passed through ~
he~ting oven 56 where the resulting silic~ pattern is heated to drive off the orgnnic
solvents without heQting web 26 to the ~oint where heat distortion o~ the cube-
corner elements o~ the l~minate will occur.
Arter drying, the silicn is mechanically held to the cube~orner element~
on the reverse face 30 o~ web 26 by, it is believed, electroststic force~ and
physical inter-engsgement Or the silica j~rticle~ themselves.
Thu~, RS web 26 exlts rnixture application stRtiOn 48~ It has t~ken on the
rorm o~ n ~irst modified laminate 58, ~ ~, a web 26 h~ving cube~orner element3
30 with s precisly îormed pattern of silic~ mixture screened thereon over n pc~rtion Or
the elements, wlth an uncovered portion Or the cube~orner elements stll~ exposed.
As modi~ied laminate 58 exits drying oven 5B, it t~kes on a second modi~led
laminate construction 60 wherein the solvents present in the sillca mixture hnva
been drlven o~ ~nd the silica itselr has remained dried into it~ ~raened-on p~ttern.
The second modi~ied laminnte 60 then enters n btlckcoatln~ apptl~ntion
s~a~ion B2. The appllcatlon of n water-bnsed ~ckconting nccompllshw .qevor~l
-12-
rcslllt~q. ~irst, tho~c nrons onto whlch no sillc~ has boen screcned or deposlted witlallow direc~ conlnct between the bnckco~ting nnd the revelse ~Ide 30 or the
embosscd or otherwise ~ormed thermoplastic web a6, thus "wetting" web 2~ wlth the
liquid backcoa~ing mix~ure. Second, a layer or b~ckcoating materi~l will oYerlay the
silica pnttern formed on thermopl~stic web 26 ~nd, when applied etfecti-/ely, will
not disturb or disrupt the printed or screened-on silic~ p~ttern. Third~ th~
backcoat;ng may then be dried and/or cured to provide a rirm ~tt~hment to
thermopla5tjc web 26 to provide B flat, smooth ~nd integral surrace upon which
further layers, such flg a l~yer or pressure-~ensitive or he~t-activ~ted adhesive m~y
10 be ef~ectively and conveniently applied, and to protectively cover or encapsulate the
silica pattern. A surprising and unexpected result Is thQt the slllc~ prevent~
perrnefltlon by the liquid bnckcoating to the cube-corner i~ttern. As deYcribed
nbove, such permention would adversely artect the reflectivlty of the rinal
sssembled laminate.
Applicntion o~ the backcoating mix~ure to the second moditied laminata
60 msy be sccom~lished in a number o~ ways, such as by spraying, roller
applicat;on, squeegeelng, or the like. The m~nner in which the bRckcoQt i~ appl;Qd
will be determined by, inter ~ the precise formulation Or the backcoat and the
pressure, or ~orc~, which can be withstood by the silica psttern aft~r i~ lu5 b~en
20 drie~.
Por purposes o~ illustration, a bsckcoating app~ication stat;on ~2 may be
char~cterized fl~ having a supply header or tsnk 64 ~ommunicating with an
flpplication means B6 which may ~e a nozzle or series of nozzles, or the 13ke. An
implement such as a doctor bl~de 68 may be used to more unii~ormly spread the
bnckcoating a~ter i~ has been applied without damaging the slllca pattern. A pl~ten
70 provides support ~or the second modified laminate 60 during application ot ths
backcost .
A~ter application, the third modified Iflminate 72 enters drying oven 74i
wherein the backcoat material is heat~ured, resulting in backcoating layer 32 as
30 shown in ~ig. 1.
Succes~tul use or fl backcorlting requires that the backcontlng ~ormulstion
meet several p~srticu!Qrly important workln~ parRmeters. On~ ~s th~t the
b~ckcoating have rlow charflcteristics such that ~he relatively narrow ancl 8hal10w
runners formed by the silica pattern wlll be filled, while not dewetting or disturbing
the dried ~llica p~tterri itselr. ~is me~r~ thflt the viscosity of the backco~ltln
must be cnre~ully controlled to ~ssure thnt the bnckco~tlng chn be flppliod ~hilo
13~
'7~
cornplctely encnpsu~nt;ng wi~hout disturbing the sillc~ pnttern. Another chAr~c-
~eristic Is that lhe b~ckco~ting cnnnot penetr~tQ or interRct with the npplied s(lica
to reach the Inter~ace belween the sillc~ ~nd the cube-c~rner pnt~ern. Yet 8nother
requirement is that the backcoatin~, when dried, hsve the reguired ~lexlbil5ty and
toughness to withstand use in a laminate. Ideally, the b~ckcoflting ~hou~d also be or
a color which enhances day~ime vislbility Or artlcles rnadé w3th ~uch l~minates.
Several preferred backcoatings have beerl utilized. ~ch may be
characteri~ed generally as including a water-borne or w~ter-bssed polymerlc mixture
or system, B whitening ~gent, Q defosmer, a thickener for use In ~d~ustlng the rin~l
10 viscosity~ and a pH-adJusting componont.
A ~irst prererred ~ormulation o~ n b~ckcoating i~ presented herewlth a~
Example 1-
~ *
1. DP-101, a water-borne polymeric
system consisting o~ about 34%
acrylic/urethane copolymer,
61% water and 5% coAlescent
solvent, such a~ M-pyrol 6~.7% to 7~.7%
2. UCD-1D60Q, a pre~ispersed
whitening agent (tltanium dioxide)
containing about 72% solids 21.5% to ~3.5%
3. Balab 3017A, ~ de~oamer 0.4~6 to 0.~%
4. CP-15 (50 percent in water)
acrylic/based thickener to
ad)ust viscosity 1.596 to 2.5
5. Ammonla (28 percent aqueous
sollJtion) to adJust pH
to 8.5 to 10.0 None to 0.~%
The foregoing mixture is ~ormed by sdding the detoamer to the ~ater-
30 borne acrylic/weShane copolymer system with gentle ~tirrlng. Therea~ter, tha
whitenin~ agent and the ammonia, i~ necessary, are added as gentle stirrlng l!s
continued The ~hickener i8 thereatter added with incre~sin~ bl~dc speed and the
entire mixture is ~stirred ror about 30 rninutes at m~derate speed. A preferred
* 'l' r ~ nfl r k .~J
14~
.~
mix~r tor sllch nn operntion is mLInu~cturcd by Meyers En~lneering or E3ell,
Cnli~ under the trade or model designntion "550."
DP-101 is n tr~de designation of Polyvinyl Chem5cal Industries, Inc, o~
WiJmlng~on, !~ssachusetts. While the preclse ~ormulation i3 not known, Polyv~nyl
Chemic~l Industries has flssigned the trade deslgnst5On DP-101 ,~, to the p~rticular
urethane/acrylic copolymer resin utilized ~n lhe ~or~going backcoat ~ornnu]atlon.
DP-lOL is de~ined by Polyvi~yl Ch~mic~ll Inc. as ~ water dispersio~ of ~
gr~ft copolymrr of an aliphatic urethane ~oined to a ~tyrene-acryllc copolymer.
Its wei~ht per gallon is 8.6 pounds, its acid value is ~.5, and its index of
reEractlon is 1.3956. Its molerular weight, ~ith respect to tha~ portlon of
the re~in solub:Le in tetrahydroE~Iran, when measured by GPC, is: Mw 450,569;
M 65,660; and M~ 1,204,300, and its viscoslty, as measured by ~he Brookfield
Viscosity Method a~ 25C is 200 cps. UCD-1060 is a trade designation
of the Universal Color Dispersion Company of Lansing, Illinois, used to identify
a dispersion product for water-based systems. Balab 3017-A is also
identified by the trade designation bubble breaker and is a product of
the Organic Division of Witco Chemical Corporation of New York, N.Y.
CP-15 i~ a trade designation of the Rohm ~nd Haas Compan~r and is an acrylic-
based thickening agent. M~yrol ls Q trade designation of the G.A,P. Corporation
20 Used to identify a methy~pyrolictive coalescent solvent. The amount o~ organlc
, co~lescent in ~he water based systems pre7erably should not exceed, sbout 10% by
formula weight, otherwise the backcoating rnight permeate the hydrophob5c granular
matter into the ~ormed cube-corner p~ttern.
A second ~ormulntlon for lhQ backcoetlng mlxturo l~ herewlth pr~sent~i
ag example 2 and ndd~ a cross-linking agent to irnprov~ dur~blllt~s
Exnmple 2
1. DP-101, a wa~er-borne polymerlc
system consisting or ~bo~it 3~%
~crylic/ur~thane copolymer,
B1% water, and 5% co~lescent
solvent such ag M-pyrol qO~ to ~0%
2. VCD-1060~, a pre dispersed
whitenlng ngent (tit~nlurn dioxide)
cont~inlng nbout 72% solids 10% to ~0%
3. BYK-W, a deJoamer 1~%
4. De-ionizeJ water . 5%
5. Ammoni~ ~28 percent ~queous
~olution) to adJust pH
to 3.5 to 9.û Non~ to 0.~
A~ter the foregolng ingredients ~vo been mixed, and Immedi~tely prlor
to applic~tlon, a qusntity Or the ~oregoing m5xture Is placed in a mlxing vess~l, Hnd
* Trademarks
.:0
-15a-
lX~
n frcshly prep~lred solullon ot cross-)inking ngent i.s rnlxed therewlth. A prererrod
cross-linklng AgCnt genernlly is a polyfunctionnl Qziridlnel such ~ CX-100,
m~nufnctured by Poyvlnyl Chemic~l Industrtes"nc, or Wilmington~ M~ chusetts.
preterrod prepnrntion consists o~ 35 Ibs. ot backconting rnixture comblned wlth 150
gr~lm~ or CX-100, dissolved in 150 grams or water,
BYK-W is a de~oamer manutnctur~d by MalJinckrodt ot P5elville, ~ew
York.
In thi~ embodiment, the addition o~ the cros~ linking agent enhnnces th~
weathernbility of the ~inished laminnte by increnslng the dur~bllity llnci tou~hness o~
l 0 the t~ckco~t~n~,
A third formulntion ~or the backconting mAterJal 58 herewlth presented n~
exllmple 3:
1. Emulsion ~-182~, a wQter-borne
polymeric Iscrylic emulsion 42.1% to ~2.1%
. Water 2.2% to 12.a~6
. Ethylene glycol, ~n anti-skinnlng
nOw improvement agent 1.5% to 2,59
4. UCD 10~0Q, a pre dispersed
whitening agent (titsnium
dioxide) a~02% to ~B.a%
5. Syloid 16g, silicone dioxide
fl~tting a~ent to prevent
blocking , ~.a% to 5.a%
6. Dimethylamino eth~nol p~-sdfusting
~olvent 0~6 to 0,5%
7, E~lab 3017A defoamer 0.696 to 1~0%
8, Tex~nol solvent, a co~tescent
~olvent ~or improved ~ilm
tormlstion 1.~% to t.
g. CP-15 (50 percent in water)
acrylic~sed thickener to sd~ust
viscoslty None ~o 1.~9
The toregoing bnckco~ting is prep~red.by.addlng.tho cle~o~mer to the
wnter~borne 6ystem wilh genlle mixing, then ndding the w~ter, tho nntl-~klnnlnR
* 'l' r ~ r k
, ~
,.. ~. , .
'7~
ngcnt, tho prc-disperscd whitcniIlK ngen~ nnd thc amine while contInuIng ~entlc
mixinK. Thoreart~r~ the conlescent solv~nt Is ndded. Bl~de speed 5~ thcn Increa~ed
nnd the ~hickener is Added to adjust the viscoslty to th~ deslred level ~nd the
resul~ing mix~ure is then stirred nt moderate speed rOr 30 mlnute~
Emulslon ~-18~9 is A trade desienation o~ th~ Rohm and Tla~ Compcny
of PhtladeLphla, Pennsylvania~ for an acrylic e~lul6ion vehlcle. Em~lsion E-1829
~ o sold un~er the trade designatlon 'Rhoplex AC-829r and i~ a 100% acryllc
em~ lon polymer made by typLc~l emulslon polymerl~tlon processes. with
~I mol~cular welght ln exce~ of l,OOO,OC)0. Its welght per g~llon ls 8.35
L0 pound~, Lt~ vL~coslty is 1,200 to Z,300 cP and i~9 pH range :Ls 8.6 to 9.1.
Lt~ 81~L~ trnn~sltioll temperature :Ls 3C. Syloid is a trade de~igna~ion of
the ~)avlcl~on Chemical Company, a divlsion of W. R. Grace, of Baltimore,
M~ryland for a sllicon dioxlde fl~ttlng agent. Texanol is a trade designation
of the Eastment Chem:lcal Products Company of Kingsport, Tennessee, used to
ldentlfy a coalesclng agent.
Referring now to Fig. 2, ~ partial æctIonal v~w o~ c schemat5c portion
o~ embossed thermoplestic Yreb 26 arter ~pplication o~ both ~illc~ 34 and
backco~ting 32 is shown. A~ therein seen, reverse sld~ 30 of thermopl~stlc web
includes ~ ~erie~ of v~lleys, indicated generally at 7B. Th~ valleys 7ff schematically
20 represent the cube-corner elemen~s found in web 26 when the cube-corner pattern
shown in Pig. I is embossed onto thermopiast3c web 2B. When the 5lljCQ layer 34 I~
applied, the valleys between adjacent cube-corner elements 76 are tilled (except
where the screen pattern leaves web 26 exposed) and, ~n a preterred embodiment or
the invention, enough 6jIjCA 34 is applied to extend a distance o~ about 0.0001 to
about 0.003 inch above the embossed surtace of thermoplastic web ~S, as ~hAracter-
ized by dimension A of Pig. 2. In l;ke fashion, the backcoQt layer 3~ i~ 2pplied to
a th;ckness B o~ about 0.002 to ~bout 0.004 inch above the silic~ l~yer ~4. Where
runners or paths 42 are formed, esch such runn r consist3 o~ the bacKcoQt materl~
which extends downward to wet the ~loor ot each valley 76 to ~ tot~l depth C, a3
30 shown in Pig. ~ which, prererrably, is about O.Op6 inch. In e pre~erred èmbodIment
of the present invention, each such runner is 0.001 inch deep and, as ch~r~oterized
by dimensjon D in l~ . 2 ~nd 6, m~y be on ~he order ot 0.û15 inch wlde.
--L7--
In the embodlment hereln Ulu~tr~ted, each discrQte element or th~ applled
silicn p~t~ern Is square in shape wlth the length of e~ch side of the ~qu~re
ch~rQcterized by dimension :E~ In Pigs. 2 and 6. As herelnabove descrlbed, the
p~rcent~ge of surfsce sre~ svaila~le tor retrore~lection m~y be ~dJusted by ~d¦usting
the dimension~ D snd ~ as shown in ~ " 2 ~nd 6. Wher~, ~or exQmple, dimenslon
D Is 0.015 Inch und dimension E ~s 0.200 inch, the ef~ectlve ~urtace available for
retroretIec~ion 1~ 84 percent. Where dimenslon D 1~ 0.027 Inch ~nd dimenslon ~ l~
0.138 Inch, appro3timately 70 percent ot the surfnce of the resultlng ~h~t pre~erv~ -
retroretlec~ive chdracteristics. With a dimenslon D of 0.029 Inch and 0 dImenslon ~R
-17.1- . . . /lB
~,
~'~
y~
t 0 096 inch, npproximntely 55 pcrcent or ~hc totnl surtncc ot the resultin~ sheet
retnins retroreflectivc propcrties.
Thus, the degree to whlch the resulting lamin~r sheet returns Incldent
light towards it~ source may be adJusted independent o~ the actual cube~orner ~ype
pattern rormed on thermoplastic web 26, in n manner which is mùch more
convenient rlnd e~ficacious thnn chtln~ing the mold din)ensions or character~stics used
to produce the embossed cube-corner pattern.
Reterring again to Yigs. 1 tlnd 4, after fourth modiried IQminat0 ~4 exlts
drying oven 74, A pressure-sensitive or heat-nctivated adhesive l~yer 3~ m~y then ~e
10 applied by tnking the resultin~ laminate 84 and drnwing ~t past a st~tion whel~e ~
btlcking or release ~heet 38, pre-coated with adhesive 36, m~y be layered d~rectly
onto b~okcoating 3~, resulting in A completed laminate a2 as shown In Pig. 1.
~in~lly, if one is used, the carrier Stleet is stripped away, exposing obver~e ~c~ 28
as the light-receiving surface o~ the finished laminate a2.
It should ~e noted th~t the foregoing exRmples and pre~erred embodiments
have been presented with respect to a cube-corner embossed pattern hav~n~ h depth
characteriæd by dimension X in Fi~. 2 o~ 0.004 inch. It is contempltlt~d thAt
pQtterns of Yarying depth and vsrying dimensions may be utllized, and that th~
dimensions herein discussed for the depth o( silica applied, and thP wldth end depth
20 o~ the runners therby formed, mtly be varled without departing rrom the splrit and
~cope o~ the inv¢ntion as herein d;scussed.
The rinished sheet will have the physical characteristlcs enabl~ng St to
substantially meet specification ~P-79 for reflective sheeting, and it~ rene¢tive
propertses can easily be varied by utilizing t~ different screen pattern. Moreover,
the whiteness achieved by the existing laminate backcoating ~ubstantltllly enhance~
the daylight estheti¢s o~ the finished material. The he~ting oit the lnminat~ durlng
the drying and curing of the silica, backcoating or adhesive, also may have an
e~rect on the rlnal reflective performance of the lamlnate, dependent upon th~
characteristics of the initial tool and the material chosen for ths film. It has been
30 determined that for optimum per~ormanee, the laminate should not be heated above
180P during these vIlrious processing ~teps for the preterred embodiment disclosed
hereln.
It mey also ~e noted that while the silica pattern hereln presented 19
series or 6qutlres turned to present a dit~mond-like pnt~ern, other cell ~IZe5 and
sh~pe~ are tllso possible, wherever they appear ettlc~cious ~or purpo~e~ of
~r~orrnr~nce or ~ppetlrnnce, ~nd are within the splrlt ~nd 8cope of ~ha Inventlon RS
here5n discu~ed l3nd citl;med. -1~
~ s previously noted, Pig. 7 illuslrntes nnother preferred embodlment of
thc prcsent invenlion. In this embodiment, Q l~yer 25 o~ fl more weather reslstant
thermopl~stlc material ~hnn thQt forming web ~, such ~ unmodi~led or VV
modified, polymelhyl methacrylate, Is lemin~ted to the Impect modlfied ~crylic
rorming web 2~. In its preferred torrn, layer 25 wlll be ~bout ,0003 in~h, ~nc1 wlll
no~ exceed .0005 Inch ~0.5 mil) in thicknessl. lt has been round th~t the provis ion oi
~his added L~yer provldes ndditional weatherlng ch~rs.cterlstics needed for certeln
environmcnts, while, when not exceeding the noted thickness, permits th~ total
laminate to rema;n surriciently flexible. Pre~erred materlQI~ in thl~ embodirnent
may be thll~ sold under the trflde designQtion V0S2 or V044 by the Rohm ~ Hnas
CompQny, or a polyarylate sold under the trQdc design~t50n Ardel~ by ~Jnlon Carblde.
Yllrlous tcchniques m~y be employed to apply thls outer l~yer to the web beror¢ the
silicQ and b~ckco~tlng ls npplied. For example~ the additionQI layer ot thermoplastic
mnterial mey be epplied by solvent casting or m~y be co-exttuded wlth the inltlal
til m .
A preferred formulHtion for the outer Isyer 25 include~ use ot Korad-
~
the trade name or a modi~ied polymethyl methacrylat~ rn~nutactur~d by Polymeric
Extruded Productg, Inc. o~ New~rk, ?~ew Jersey. Such materi~l lncluds3 U.V. iight
absorbing substances, and is cross-linked to a nexible, rubber base substance, adding
20 flexibility. In pQrticulnr, use ot Tinuvin234, a benzotriazol compound m~nuractured
by Geigy, is used as a UV inhibitor. This substance is lcnosvn chemic~lly a~
2~2H-benzotria~ol-2-yl~4-methyl-phenol. Kor~d-D thermoplasti~ is descrlbed in
United ~tates Patent No. 3,562,235, issued on ~ebruary ~, 1971. When Korad-13
thermopla~tic i5 used, it may be applied hS a 2 mil outer l~yer durlng the cube
~orming process, or it m~y be co-extruded with,the web 26 before such formatlon,in a layer 1 mil thick, or it may be applied In solution directly to the web 28 in a
layer 1/2 rnil thick. lhe particular thickness wIll depend in part on the tot~l
thickness parame~ers of the ~inished laminate.
While the ~oregoing has presented varlous specific prererred em~odiments,
30 it is to be understo~d that these embodiments have been present~d by wQy o~
example only. It is expected that others will perceive dir~erences which, while
varying ~rom the foregoing, do not depart rrom the spririt and scope o~ the
invention as hereln cl~imed and described.
* Trademarks
, . . .
