CA2249608A1 - Pillowed flexible cube-corner sheeting and methods of manufacture - Google Patents

Abstract

A flexible, durable, cube-cornered retroreflective article capable of accommodating the expansion and contraction of the underlying polymeric substrate where such article has a pillowed or curved microstructured member bonded in a regular pattern to a sealing member. The retroreflective article has normal and stressed states. In the normal state, the microstructured member is substantially parallel with the sealing member. In the stressed state, the microstructured member is either compressed or elongated and the sealing member is substantially flat. The retroreflective article may be attached to traffic control devices, such as polymeric barrels, cones, or tubes to direct and guide motorists through road construction areas.

Description

Pillowed Ele~ible Cube-corner Sheeting and Methods of Manufacture ~~

Technical Field This invention relates to a lello,le[le~ /e !~l.e~ 8 and more particularly 5 a pillowed flexible cube-corner c~ ;~ that ~c-mnlodates the P ~JnnL:on and contraction of traffic control devices such as polyrneric barrels, cones, or tubes.

Background A re~,.)r~le~ e Qh~eting has the ability to r~i~e~ nc;d~nt light towards 10 its or;ein~'; .f~. source. This ability has led to the widespl~Ptl use of rellolenective sheetingQ on a variety of articles. Very often r~l~ole[lective cl.ee~ g.~ are used on flat inflr-- b!e articles, such as road signs and barric. des. However, ~ otionc frequently arise which require the sl~F~ I ;..es to be used on irregular or flexible surf~ o s For example, a retlolellective rh~;Qg may be adhered to irregular surfnces oftr~fic control devices, such as polymeric barrels, cones, or tubes. These devices are used typically near roadway construction areas to direct and guide motorists. Also, a r.,llu~ective sheeting may be adhered to a fleYible substrate such as a road wu-~-'s safety vest. In s;tll~ti~mQ- where the ulldelly;n~, s~ le is irregular or flexible, the rellur~llective sh~etin~ desirably posse~C~s good collroll..ability and flexibility without sacrificing r~tlor~lective pclr~llllance.
There may also be Citu~ti~nc where the underlying i~st~ale ~Ypsn(~s and contracts at a difrele.ll rate than the let.or~ective ~leeting For ~ ~le, for a te~ .al~re decrease of 40 ~C (92 ~F), a traffic control device such as a low density polyethylene barrel would contract by about 0.80%, based on a coeffic;ent of linear thermal eYr~nQion of 200 x 10~ (mlmK) at 20 ~C. For the same te~pe~alllre change, a ,t;lrorellective sheetin~ with a polyca~l,onale layer would contract by only about 0.23%, based on a coefficient of linear thermal eYp~nQ;r~n of S7 x lO~(rn/rnK) at 20 ~C. Thus, the barrel contracts almost 3.5 times more than the rellur~nective ~heeting Rec~llse the rel~orenective ~I.e- 1;~ is wrapped outside of the barrel, col~ ion~l sheet;.~ may wrinlcle and lift offthe barrel in response to the tc~.pe,alule change. In these situations, it is desirable for the rel~or~llective s-heeting to accommod~te the di~e~ ces in thermal . . .

W O 97/38335 PCT~US97/04041 eYll-sn~ion and co~ lion without co,..~)rc.,~s;,* r~l~urellectivity and without lifting off the substrate.
There are basically two types of lellu.t;nective .~heetin~ beaded and cube- comer .sl-eetil~e Beaded sheel;-¢ uses a multih~de of glass or ceramic S micros~,heres to ret-u-~Ilect incidçnt light. Because the microspheres are separate from each other, they do not restrict the sh~eting's flexibility. However, a cube-corner .che~ling typically uses a n -lltihlde of rigid, interco~ cle~l cube-comer f len~f nl ~ to r~tro,~nect in~ident light, as shown in U.S. Patent No. 5,450,235 (Smith et al.).
~hhoUeh dinc ellt types of flexible ch~eting are ~iSc1ose~ none addresses the need to account for the di~ercnces in the coç~ of linear themlal ~ Q on bet.~.~en the s~i~lla~e and the r~l~or~ective sheeting One way to produce a stretchsble, flexible lel,ol~necli~e .~h~et;.~g is disclosed in U.S. Patent No. 3,992,080 (Rowland). That particular che~t;.~g ~...p,ises two flexible, stretch-s.~le strips of polymeric material. The first strip is a tl~ spa~hlt synthetic resin having a mllltiplicity of minute cube-cûrner formstion~ on one surface.
The second b a-~in~ strip is of a lesser length than the first strip when both are in a relaxed con~ition The ba-~inP. strip is stretched a predete~ .ned amount, typically 3%
to 15%, before being bonded to the first strip of cube-corners. After the bonding process, the b~cl~ing material is allowed to relax thereby fo--...ng a puckered cube-20 corner .~I.Pe~ In the relaxed state, the bac~ing strip is in tension, while the cube-corner strip is in co"~pre~s;on, to maintain the puckered appe~lce of the cube-corner strip. In applying this sheeting to a non-planar surface, such as a bicycle handlebar, the ~t-urenective ~t.eel;~ must be slle~ ed to a degree sllffi~itont to el~ e the puckering. However, e.~cessive sl-elcl~ing results in distortion ofthe cube-corner 25 formstionc and cause a co--~sl,onding loss in rel-orene.;ti~ity. This loss of~or~Ilectivity translates into a loss in brightness, causing the sl.e~t;-~g to be less effective as a safety device.
In view ofthe disadvantages of convçntionsl ~~l-orenective sl-~el;ngs, it would be desirable to provide a ~heet;i~ that accommodates the dirrere..l rates of ~ y~ on and contraction b~ n the polymeric substrate and the ~I.ee~ It is also desirable to provide a sheeting that is not susceptible to brightness loss because of overstretching or because of other deru....-~;ol c in the cube-corner r~l~orenective layer.

WO g7/38335 PCT/US97/04041 Sum nary of the Invention The present invention provides a flexible relrorellective ~heeting that cornpe~l~n~- s for dimpncion~l çhq~ s in the substrate without sacrificing let~orcnectivity. The present invention also c~ tçs any need to rely on stretching the .~l.çe~ing to a predetermined length to provide optimal rel.orenective pelro--llance.
In one embo~im~nt the present invention in~ des a microstructured .nenlber having a body portion and a ml~ltitude of cube-corner elF,~c.~ ttach- d to a first side of the body portion, a sealing ...~ bçr, a n~,lwul~ of intersecting lines bond;l~
the first side of the body portion and the sealing .. ~,-.. b~ ~ together in a regular pattern of cells, and optionally an adhesive. This relrol~llective sheetine ~"~}~ils a normal state where the microstructured ...ç -~cr is curved and is subs~ 1ly parallel to the sealing ~l. .llh.,., and a colllpleised state where the microstructured membpr is arched and the sealing ...~..l.c~ is s~ y flat.
In sumrnary, the process of making the ~:l.o-ellective .~heetin~ incl~ldçs providing a microstructured 111~ .r having a body portion and a m~lhitude of cube-corner elem-,nt~ projeclh~g from the first side of the body portion, providing a sealing IllC.ll~ ., corl~1;ng these two ~--f n~bf~ ~ at appro~ PIy the same speed with the cube-corner ~lem~ntc facing the sealing .. I.u, and bonding the first side ofthe bodyportion and the sealing ~ e to each other in a regular pattern to form sealed cells each having a curved microstructured ..~f ..b~l.
In accordal~ce with this invention, the sheel;ng is useful for accommodating e~ ;onC and contractions oftraffic control devices without co~ rol~ ng r~tlol~nectivity and ~.itLoul causing wrinlcles in the ~heetin~ Because of its flexible nature, the sl~eet;ng is also useful for apphc~tionc to polyrneric s~r ç~, irregularly shaped sll~ ,çs such as a bicycle helmet, and flexible s~ces such as a safety vest.

BriefDesc~ ion ofthe Dl~wings Figure 1 is a cross-section~l view of a cube-corner r~tl Ol ~nective ~heetine in a normal state in accordance with the present invention;
Figure 2 is a cross-sectional view of a microstructured ...~ ..b.,"

....

Figure 3 is a cross se~,l ;on~l view of a cube-comer r~t.orenective vl.ec~ g in a co."pressi.~e state; and Figure 4 is a sCl~ ;c l ep~ cs~ l ;on of a bonding process for making the ~heeting of the present invention.
These figures, which are ide~~li7ed, are not to scale and are intf~n~lf d merely to be illustrative and non-limiti.~g Detailed De~cl i~Jtion of the Invention The inventive lelrorelleclive cheeting allows for e~ ~ on and contraction ofthe traffic control devices without c~",prc~ t,o.t;llectivity, will,o~l wrinkling, and without de~ t;i~g The ~l~C~ 8 has a pillowed microstructured mçmhen The term "pillowed" as used herein means the .. ~ hf~r has curvature. This pillowing allows the ,I,icl or~l ~lctured ~--~ hf l to arch to acco. ~....o~~~e the contraction of a traffic control ele~llellt that occurs when the ~ m~:~nt te",pt;lalule decr~ses.
Conversely, the pillowing allows the r"iti.us~luctured .--f ~.. ber to flatten to acccs.. --.. o~r~te the ~,~Lr p ---:on of a traffic control device when the ambient t~ clalure in~ ases.
F~l,ll,.,.ll,ol~, the pillowed microstructured ~ I.er allows for some elr~ng~ n in the ~heeti~ which aids in its applic~tion onto traffic control devices. The overall effect of the invention is to provide a versatile ~el~olenective ~he~ 8 that can acccmmodate for the di~e.el-ces in e r~ n and contraction be~ n the device and a shfeling and that is easy to apply onto traffic control devices.
The lel,o,~nc~ e ~hee~ e ofthe present invention exhibits normal and stressed states. A"normal" state ~epl~ve.~lv a conditiQn where neither the microstructured ,..~ er nor the sealing membçr is in tension or in co",pl.,sv;on. In such 25 a normal state, the microstructured l"~."~cr has curvature and is v.ll~v~ 1y parallel with the sealing ll.e."ber except where the ~ o are bonded together. The term "parallel"
means lines, inrh~i~ curved lines, that a ~aced an equal ~ n( e apart. The cheeti~ would typically be in a normal sta~. ~er fabrication.
A "stressed" state l ~resc lLs a conflitiQn where the microstructured ".~.. h,~l has deviated from its normal state, and is in, for ~y~mple~ a co"lyle3sed state or an elong~ted state. A "c~"~ ssed" state occurs when the microstructured ~,le.,~l~c. has arched. An ~Y~mple of a cor,lpl~,;,sed state is where the ~ e~ contracts in le~yonse W 097/38335 PCT~US97/04041 to a contraction of the underlying substrate. The shP,etine co...pc..Qstes for the contraction by comi)res~,hl~, and thereby arching the microstructured mP.mher. An "elollg~led" state occurs when the rnicrostructured member has fl~s~ttçn~ , Çl .~ A~ g almost all curvature. An ~ - ~ ..ple of an Plon~,sted state is where the $h~e~ g responds 5 to an eypsn~ion of the underlying substrate. The cheeting co...ren~les for theeYpsnQion by flattening the rnicrostructured mPmher thereby eYpsndine with the s~ ate In both ~lltss~d states, the sealing memher is SUbSlA ~ Y flat.

I. General Structure ofthe Sheeting ~IG 1 shows an example of a microstructured lelluldle~'Li~e .che,.~ g 10 of the present invention in a normal state. Retroreflective shf~ g 10 c~ ..;~s a ctured l~ el 11 bonded to the first side 26 of sealing Illc~ el 24 through multiple bond lines 30. As seen in F~G. 1, the microstructured and se~Jing ",~ have similar curvatures and are said to be s~b~t~ ~l;q~ly parallel to each other. The bonding ofthe two llld~ creates sealed cells 17 ~ ~ air. The cells form an array of poly~ns.
Optional adhesive layer 32 with liner 33 may be l~ AIed to the second side 28 ofthe sealing nle.ll'o~ 24 to permit the sl.~;,~g to be adhered to a surface when the liner has been removed.
FIG. 2 shows an example of microstructured ulc~ èl 11, tsaken at 2 in ~IG.
1, co.~ a multitude of cube-corner e~ s 12 and a body portion 14. The body portion 14 can include a land layer 16 and a body layer 18. The cube-corner ~ 12project from a first or re r side 20 of body portion 14. The cube-corner Ple~ di 12 and tne body layer 18 CQ..~l..;.~ Iight tral~s.ll.ssible polymeric ~A1~;s~ls Light enters the microstructured ,Il~.llbel 11 through the front surface 21. The light tnen passes through the body portion 14 and strikes the mutuaUy perpPn~ qr planar faces 22 ofthe cube-comer pl~ 12, and returns in the dir~Lion from which it came as shown by arrow 23, as is known in the art.
In a preféllèd construction, the cube-comer pl~-" ~l~, 12 and land layer 16 are made from similar or the same kind of polymers, and the land layer 16 is kept to a minimal thickness. The land layer 16, typically, has a thickness in the range of about 0 to 150 microlll~Lel." and preferably in the range of applo-;,..A~Ply about 1 to 100 miclulll~e Body layer 18 typicaUy h s a thickness ûfapplu~ ql-ly 20 to 1,000 micrullleL~ and W O 97/38335 PCTrUS97/04041 preferably in the range of about 50 to 250 mic,u.,.. tc~. The cube-corner elc ..~ 12 ~~
typically have a height in the range of about 20 to 500 mic,u,,,~tc,~, and more typically in the range of about 60 to 180 micl~lllGlGI~. ~Ithf~ Igh the embodiment ofthe invention shown in ~IG. 2 has a single body layer 18, it is within the scope ofthe present invention to provide more than one body layer 18 in the body portion 14.
~IG. 3 shows an example of a microstructured ~cllulcnective ~l.~1;.~g 10' in a stressed state while attached to a traffic control device 50. In ~ u.~, the sh~t;-~g is in a CGl~lpl~ s3~ state wherein the microstructured ".eml)er has arched in les~,ollse to a COIII~ force placed upon it by co.~clion ofthe device 50. A tC~ Gl~ulc declease is one example of such a stress. When the ambient temperature dec,~s, the traffic control devioe contracts. A desirable ch~ L; must respond to this col,l,~1ion without wrinkling, delaminating, or li~ing offthe ~ale. It is believed that as a polymeric traffic control devioe contracts, the sealing lll. .ll~Gl 24 relaxes slightly and the mic,o~huc1uled mcl,ll~el 11 arches upward to a~c4 ....o(l-le this contraction.
The elimination of wrinldes in the sh~; ~g creates several advantages. For example, the ~ ulGIl~;li~ity pc~rw~lance ofthe ~h~ g is not ~"")r~)ll..sed becal~se there is no ~ ifir~nt distortion ofthe cube-corna F~ Also, the adhesive on the sh~ g and the polymeric j~ute remain in contact with each other. Rer~ e ofthis contact, dirt and water cannot come bGt~ the adhesive and the substrate, which may cause delamination ofthe ~h~ , The microst uctured and sealing r.f~n-l,~-~ are f~ ~d in more detail below.

II. Rcl~u~cnc~ive Microstructured Me.-ll c, The two main el~ ofthe ~l~ol~nective rnicrostructured lllcml~r are the cub~corner rO.. ~;0,.~ and the body layer. Both P~ include polymers which are light ;./e, ~ ;np that they are able to ll~lJ.~ at least 70 percent ofthe light incident upon them. P~cr~bly, these polym~ ~,ul greater than 80 percent and more preferably greater than 90 percent ofthe incidem light. F~~ .lllorc, the microstructured m~ cr maintains good ~limPn~ion~l stability and high degrees of lctlulclle~ ~nce under highly flexed condition~
The cube-corner formations fim~tion as the rclrulcne~ e ...~1.~ ... There are many cube-corner c~nfi~-rations known in the art, see, for ~..~le, U.S. Patents 4,938,563 ~elson et al.), 4,775,219 (~p~l~orn),4,243,618 ~an AiT~Jn), 4,202,600 ~13urke et al.), 3,712,706 (Stamm), and 4,588,258 (Hoopman). However in the practice of this invention, the cube-comer confi~ration de~ ~ in Hoopman may be p,~f~ .-t;d because it provides wide angle l~O,~nf~;Q,. along multiple viewing planes.
5The polymeric ~~ .;&ls that are used in the cube-comer el~ -.... f .ll~ tend to be hard and rigid and may be Ihe,...l pl~t;c Examples ofthe"..opla~t;c polymers that may be used in the cube-comer ele. IfJ.-~ include acrylic polymers such as poly(methyl ~"elllac,~late);
polycarbonates; cellulosics; polyesters; pol~ e~k~lQl~f~ 5, poly(etherimide); polyolefins;
poly(styrene) _nd poly(styrene) copolymers; polysulfone; u~c ll~s including aliphatic and 10 aromatic polyurethanes; and n~lu.~s ofthe above polymers such as a poly(ester) and poly(f~l.onale) blend, and a fluoropolymer and acrylic polymer blend.
~ f1~1;t;nnAI I~ r~ 1C suitable for forming the cube-comer e,~ are reactive resin systems capable of being crosslinked by a free radical poly---~,- ;,Aflnn ,..f ~ . . by exposure to actinic radiation. Such systems are further deY~ in, for example, U.S.
Patent No. 5,450,235 (Col. 6 lines 3~68; Col. 7, lines 148).
The polymeric materials used to make the land layer may be the same as the polymers that are used to make in the cube-comer el~ provided that the land layer is kept to a minirnal thickness. ~ most instances, the land layer is integral with the cube-comer clc ..c~ The polymers that are used in the cube-comer el~ and land layer can have refractive indices which are din'ercnl from the body layer. ~lth.~h the land layer desirably is made of a polymer similar to that ofthe cubes, the land also may be made from a softer polymer such as those used in the body layer.
The body layer pr~t~ the .~h~;.~g from the en~l~"~ , and can provide mechanicaLl~hy to the ~h~t;.~ It also gives the ~h~; ¢ the abili~y to bend, to curl, or to flex. ~cf.,.,~d polymeric materials used in the body layer are flexible and re~; ,~l1 to degradation by ultraviolet (IJV) light radiation so that the r~ "~e iLh~e sh~~ g can be used for long-term outdoor ap~ ;on~ Examples of polymers that rnay be used to make the body layer include fl.lorinAt~ polymers; i~ . ~---, ;c ethylene copolymers; low density polyethylenes; pl ~l;c;~d vinyl halide polymers; polyethylene copoly ners; and aliphatic and ~u"~c poly~lhal1~s. Co"""e~c;ally available polyu,~ es include: PNO3-214 (from Mortonkl1r~..A~;on~l Inc., Seabrook NewT~ e) orX-4107 (fromB.F. Goodrich Company, Cleveland, Ohio).

W O 97/38335 PCTrUS97104041 Co. ..h~ ;on~ of the above polymers also rnay be used to make the body layer~of the body portion. Pleréllcd polymers for the body layer include: ethylene copolymers that contain units that contain cLbuAyl groups or esters of ~buA~Lc acids such as poly(ethylene-co-acrylic acid), poly(ethylene-co-ll..,lha~lylic acid), poly(ethylene-co-vinylacetate);
jOllo~ jr, ethylene copolymers; p~ cd poly(vinylchloride); and ofirhAotir, ~I~ es.
These polymers are plerelled for one or more ofthe following ~ 7 suitable mechanical properties, good adhesion to the land layer, clarity, and en~.lull,,,wlt~l stability.
Colorants, W absoll~cl~, light ~ 7~ free radical scavengers or ~.~1;n.i~- ~1s, pl~ ~~ ;~ aids such as antiblocking agents, ~ ,y7 agents, 1..1,.;~.~1~, and other additives may be added to the body portion or cube-comer P~ These componc,lt~ are known in the art7 and are further des~;,il ed in, for example, U.S. Patent No.
5,450,235 (Col. 9, lines 46 68 and Col. 10, lines 1-14).

m. Sealing Member In FIG. 1, the microstructured rellûlènective sheetin~ 10 ofthe present invention also inrl~ldes a sealing .- - -..be~ 24. The sealing ,.,e...be~ filnr.tiQnC to provide a ...ec.h~ c... to fomm sealed cells 17 and to protect the cube-corner elc...~ 12.F.~ of polyrners that may be used in the sealing ~-~-.n~l)e- include POIY~ AOneC polyethylene terephtho~-otej polyethylene copolymer, alkylene/alkyl acrylate copolymers such as ethylene/methyl acrylate copolyrner, ethylene/N-butyl acrylate copolymer, ethylene/ethyl acrylate copolymer, ethylene/vinyl acetate copolymers, polymerically ploctir.i7ed polyvinyl chloride (PVC), and polyurethane primed ethylene/acrylic acid (EAA) copolymer. The term "polyu~ell,ane77 typically inrl~des polymers having welllane and/or urea linkages and such is the intt~nt~ed ".~ni~g herein. Also, polyulethane incl~des polyether polyu,~l.An~c polyester polyurethAnes, and polycal7llonate polyulel~ -ec. -Blends of such materials may be used if desired.
An example of a suitable EAA material for use in the invention is PRIMACORTM 3440 (from Dow Chemical Co., MiAl~n~l, Mirhig~n), It is a copolymer of ethylene and acrylic acid, the latter present at about 9 weight percent of the total weight of ethylene and acrylic acid monomer; the copolyrner has a melt index of about 10.

W 0 97/38335 PCT~US97/04041 _9_ Polymerically pl~c$içi7ed PVC is conQ;~ered a ~1ictinctly difrerenl material from monomericly pl~ti~ i7~d PVC because pl~tici7ers from the former will not migrate from PVC. Polymerically plsctiçi7ed PVC will remain flexible and will not cause deterioration in the optical pe~rollllance of the r~ ll orenective memh~r P~efel~ed polymers for the sealing .. I~.Ib. . include polyether polyureth~nP~ polyester poly~ n~s~ polycarbonate polyureth~ne~ all of which may be aliphatic or aromatic Also, blends ofthese may be used. A sl~it~b'e blend col.lp-ises betw~;t;l~ applv~ ely 50 and 99 weight percent ~liph~tic polyester polyu.elh~e with between appro~ cl ~ly 1 and 50 weight percent of a pi~ led aromatic polyether polyul~ One e-~ ple of suitable blend CGIIIl liSes 60 weight percent ofthe ~firh~tiC polyester polyur~L-al e known as MORTHANE TM PNO3-2 14 (from Morton Il.l~,.~.-1;on~l, Seabrook New ~ ,l.sh: e) with 40 weight percent of a pi mentedaromatic polyether polyu,~lhal~e. The pi~ ed aromatic polyether polyul~ e further col-.p-;ses 50 weight percent aromatic polyuletl.~e known as ESTANE
58810 (from B F. Goodrich Co., Cleveland, Ohio) and 50 weight percent titanium ~;~Yi~e, previously co.~ ounded by suitable means, such as in a twin screw extruder and s~lbse~lu~ntly pr,~ d Another eY~mplc of a suitable polyur~tL~c may be pr~d by twin screw con~l vu ~ g b~ n applu~ ely 1 and 50 weight percent oftitanium dioxide directly into an alirh~tiC polyurethane such as MORTHANElM PNO3-214.
These polymers are pr~;ll~d for one or more ofthe following reasons: suitable menh~l-;c~l prope.Les, en~i-on~c 11~1 stability, ease of proces~i~ and good n~h~Q;~n to the microstructured ~.. ber S~l;t~hle thiC'L~.e5sF~ for the sealing l~ c~ iS be~ ,n appro~ ely 25 and 200 micrometers and pl~Ç~-ably in the range bet~cen applvx; ~ ~lely 50 and 130 IlliClO~ ,t~
m Methods of M~n~lf~chlring Retroreflective sheetingc of the present invention can be made by - providing a microstructured rel-orenective mçmber having a body poniOn and a plurality of cube-corner elPmçntc projecting from a first side of the body portion;
providing a sealing member; conveying the microstructured mPmher and the sealing~nemher at appro~ a~p~ly the speed; and bondi-~g the first side ofthe body ponion and the sealing ...e..lber to each other in a regular pattern to form sealed cells each having a curved microstructure l"~",ber. The microstructured and sealing members may be bonded by thermal or ultrasonic means.
In a thermal bonding process, thennal energy and pressure are used to bond the microstructured and sealing ~k.~.,. j togethP~r. Typically, one ....~....bçr is placed against a steel roll while the other n~P.mhPr is placed against a rubber roll. The steel roll, referred to as the "embossing roll," has a raised ridge embossing pattern on its surface. The embossing roll is usually heated to enh~nce the bond between the two members. The temperature at which the embossing roll is heated to depends on which ",..."~r it contacts, and can range from b~weell appro,.;~ tely 193 ~C and 260 ~C
(380 ~F to 500 ~F). P~rel~.bly, the te"~pe~a~ range is from between app,o~ ely 204 ~C and 243 ~C (400 ~F to 470 ~F). The Pmbosci~ roll and the rubber roll are allowed to come togP,thPr with the rubber roll c ,.e, ling pres~ule against the embossing roll. The pressures cG.. ol~ly used range from b~ ,., appro,~ Ply 34 and 136 N/cm (20 to 80 lb~m). The raised ridges bond the two ...~P....hç. s along a plurality of ;,ll~,~e~ Ih~g bond lines.
~ IG. 4 shows a sC~ ';c r~resr..-~l;on of a thermal bonding process used to produce a plefe~,ed embodinnent Microstructured .. ~ ..b~;~ 11 with its cube-corner e~ 12 ~AIJosedis u~voulld from roll 34. Sealing ...~ ber 24 is unwound from roll 36. Typically, microstructured lllell,ber 11 is covered with a protective film 13 20 which is allowed to contact the embossing roll 38 turning at a surface velocity of V~.
Likewise, sealing member 24 is covered with a protective film 25 which is allowed to contact the rubber roll 42 turning at a surface velocity of V2. Velocities V, and V2 are appro~ q~ely the same. Bonding b~l~.,en the two members occur at raised ridges 40 to form sealed cells. In these cells, there is typically air bel~ ,en the microstructured and sealing ~ . . .hP.. j.
The prefelled thermal bonding process des~libed in EIG. 4 is rere,led to as "front face" bonding, because the embossing roll cont~ctc the front, or microstructured side of the article. As a result of front face bonding, the microstructured ~"e",~er of each cell has curvature and is said to be pillowed. In 30 contrast, if the pl~cennent ofthe m~mhers are reversed so that the sealing ...~ er cont~ctC the heated embossing roll, the process is referred to as "back face" bonding.

PeT/US97/0404 l ~osslus PARTNER GbR
Minnesota Mining and ~ nl~f~ct lnng Co. EUROPEAN PATENT ATTORNEYS
Our ~ef.: B 2473 PCT , . ~ . S~bert~tr. ~ - 81C75 Munch~n ... . . .. . . . .... .
- : ~ - ---- ~ - - -- 0 9~ 2 l997 Alternatively, ultrasonic energy may be used in place of thermal energy.
However, the embossing roll wou~d not be keated ~1d the rubber roll would be replaced with a suitable means for supplying ultrasonic energy, such as an ultrasonic horn and a - power supply.
In either bonding processes, the microstructured mçmhPr and sealing mPmher are bonded along bond lines that form a regular array of polygons. A suitable polygon allows the microstructured member to grow in curvature or to f~atten as a response to a dirnensional change of the traffic control devices. Prefe.led polygons include parallelograms, such as recs-q-ngles or squares. The length of the rectq-ng~Ps can range between applo~;-. qteiy 5 and 150 mrn (0.2 to 6 in); the width ofthe rectqnglPs can range from ~l~.een appro~..qtely 5 and 25 rnm (0.2 to 1 in). The width is taken to ~ be the longh1dinql direction ofthe sheeting In one prefe,led embo~liment the r~l.or~ ~ective shPeting is bonded in a repeating rectq-ngl-lq- pattem of 12.7 mm by 8.6 mrn (0.50 x 0.34 in).
An adhesive may be lq~tin~ted to one side of the sealing member. Those skilled in the art will recognize that care must be taken in selecting an adhesive that will adequately adhere to polymeric trafflc control devices because of their low surface energies. S~it~le adhesive may be distingni~hed by acceptably high shear strength, by acceptably high peel ~dhPcion a~d by re~ist~nce to ~PI~min~tion after an approp~iate water soak test. One suitable adhesive is a tackified synthetic rubber based pressure sensitive adhesive.
A~er the retrorenective sheeting is fabricated, it can be applied to polyrneric trafflc control devices, such as barrels, cones or tubes. A wide variety of p~llC.~ may be used to fabricate traffic control devices. ~-efelably, the trafflc control 2S de~ices will be selPoted from a group of polymers that have a coefT;~ n~ of linear thermal e~p~n~ior~ in the range of appro~ tely 100 x 10 6m/mK and 250 x l0 6m/mlK ~ 20~~.
Furtherrnore, the ratio of the coefflcient of linear therrnal eYp~n~ion bel~ee. the traffic control device and the r~t~ol~flective sheeting is at least 1.5;1 and no greater than 6:1.
Plef~lled polymers for traffic control elP ..~ nt~ include low density polyethylene, high 30 density polyethylene, polypropylene, pi~stici~pd polyvinyl chloride, and their copolymers.

~ .

W O 97/3833S PCT~US97/04041 The ~cheeting may be applied to traffic control devices m~ml~lly or through mech~nic.~l means as ~lic. losed in U.S. Patent No. 5,047,107 (Keller et al.). In a manual application, tension is placed on the sheel;l~g as it is being applied to the devices.
An advantage of the present invention is that because of the pillowed rnicrostructure ~,~n~.. ke:r, the sheeting can exhibit some elone~tiQn typically less than 3% with rninirnql cube-corner distortions. This elA~ngPtio~ is enough to allow the .chee~ p to be guided in a straight line on a traffic cont!ol device thereby further enhAl-c;i~g ease of manual appli~tion Because the ~long~tiA~n comes from flstt~ni~ the pillowed l.,iclos~ ctured .,r, there is minim~l cube-corner distortions and thus mi.~;rn~l reduction in br;ghtne~.

IV. F.Y,--.IeY
The following examples illustrate di~ere,ll embo.limentc ofthe invention.
However, the particular ingredients and amounts used as well as other con-litions and details are not to be construed in a manner that would limit the scope ofthis invention.
All pc.ce~ ges are by weight, unless o~ .;sc stated.
Example 1 (colllp~al;~e) A l e~. orenective microstructured ~-.elnber was produced as follows.
Molten polycarbonate resin (MARKLON TM 2407 from Mobay Col~olalion~ Pil~ u~h, Pennsylvania) was cast onto a heated microstructured nickel tooling CQ.. ~
microcube prism lecesses having a depth of about 86 micrometer (0.034 in). Theserecesses were formed as m~tched pairs of cube-corner elem-nt~ with the optical axis canted or tilted 8.15 degrees away from the plh~ groove, as generally de,i_,il,ed in U. S. Patent No. 4,588,258 (EIoopman). The nickel tooling th AI~ne~c was 508 micrometers (0.02 in) and it was heated to 215.6 ~C (420 ~F). The molten polycarbonate, at a telll~elalule of 287.8 ~C (550 ~F), was cast onto the nickel tool at a pressule of about 1.03 x 107 to 1.38 x 108 Pascals (1500 to 2000 psi) for about 0.7 seconds to replicate the microcube rec,ec~. Simlllt~n~o--cly with filling the cube rec~s.se~, additional polycarbonate was deposited in a contim-o..~ land layer above the tooling with a thicl~ness of about 86 micrometers (0.0034 in). A previously-extruded 64 micrometer (0.025 in) thick aliphatic polyester urethane (MORTHANE IM PNO3-214 from Morton Intern~tion~l Seabrook, New ~A~.~p~i~e) film was l~min~ted onto the top surface ofthe continUous poly.a,l,ondte land when the surface telllpclalllre ofthe land was about 190 ~C (375 ~F). This ~liphstic polyester urethane was protected by a 61 ~lli.,rolllelers (0.024 in) thick polyester terepht~ te (PET) film. The nickel tooling, along with the polyca~bonate and ~ ated polyurethane, was cooled with room tempc.dl-lre air for about 18 seCon~ to a te~l~p~aLulre bcl~eell 71 ~C and 88 ~C (160 ~F
and 190 ~F), allowing the l~minqte material to solidify to form the microstructured n,e.llber. This l,lelllber, having a subst~nti~lly flat first side and a rn~lfit~de of cube-corners on the second side, was then removed from the nickel tooling.
A sealing nl~.l,ber was produced as follows. A blend of 60% aliphatic polyester u re~ c (MORTHANE ~M PNO3-214) and 40% aromatic polyester polyu,elhane (inclll~ing 50% aromatic polyester urethane, ESTANE TM 58810 from B.F.
Goodrich Co., Cleveland, Ohio and 50% tit~nillm di~.xi~e, previously colll~)ou,lded in a twin screw extruder and pe~ ;,ed) was extruded. One side ofthe sealing n~ ber was protected by a 51 "liclolnelers (0.002 in) thick PET film.
Subsequently, the microstructured and sealing .. ~e~ nl-e- ~ were fed into a nip at apploAilllalely the same speed b~,lweell a steel embossing roll and a rubber roll having a 7S Shore A durometer. The emhoscing pattern on the steel roll was of leclangnl~- configuration with d;..~ on~ of 0.86 cm by 2.54 cm (0.34 x 1 in).
The PET film of the microstructured l,lel"ber was allowed to contact the rubber roll with the cube-co",ered side exposed. The PET film of the sealing m~rnh~r was allowed to contact the steel e nbGs3lllg roll with the sealing l..e.,-bel exposed (i.e.
back face bonding). The steel embossing roll was heated to 216 ~C (420 ~F). The rolls turned at a speed of 1.52 meters/min (5 feet/min) and the force on the nip was held at 43 25 N/cm (25 Ib/in). As the members passed through-the nip, bonds were created bet~een the exposed sealing ...~nher and the cube-corners ofthe microstructured ~ ber. Both - PET protective films were then removed. A previously coated 63 r.Lclollleter (0.0025 in) thick tackified synthetic rubber based pressure sensitive adhesive was lA~..;n~ted to the unbonded side of the sealing member.
The res.. lt~nt r~ ,r~nective sl.e~ g had a subst~nti~lly smooth microstructured top surface. This C~eeting was applied m~nu~lly onto traffic control W O 97/38335 PCTrUS97/04041 device such as a barrel as generally described in U.S. Patent No. 5,026,204(Kulp et al.).
The low density polyethylene barrels (from Traffix Devices Inc., San Clemente, California) are about 4 feet tall and had 5 tapered rings each slightly larger than the next and is molded as one piece. The base of the barrel was molded separately.
The barrels were placed onto a mandrel rotaling at 1.52 meters/min (0.5 reva' ltiorl~/min). They were heated to a surface temperature of 49~C (120 ~F). This heating ~im llqted Opc,allllg condition~ used by some monufio~ lters who apply r~t.u~nective ~heeting after flame-llcaling the barrels. ~mmPAiot~ly after the he,o,tir~e the ~I.fel;Qgs were applied mqnl~olly to the barrels.
As the barrels cooled to room te.. ,pcralule of about 21 ~C (70 ~F), the ~,h~ 3 lifted offthe barrel. It is believed that because the sheeti~ had a smooth microstructured . .~ , one way for the cl-ee~ g to respond to the barrel contracting was ~uelrling and lifting offthe subsllale thereby formi~ wrinkles.
Consequently, rain and dirt can aCcllm~ ste behind these wrinlcled areas and promote them causing a reduction in bnghtness As the wrinkles get p~ o.. oted, there may be regions where the ~he~l;Qp. de1~...;n~les from the barrels.
Example 2 The microstructured and sealing ~..en~he~ ~ were made in accoldance with F.Y~ ..ple 1 except as described below.
The PET film of the microstructured mçmher was allowed to contact the steel emboss roll with the cube-cû...ered side exposed (front face bonding). The PET
film ofthe sealing ..l~.lber was allowed to contact the rubber roll with the sealing m-omh~r exposed as shown in ~IG. 4. The steel e..lbos~;ng roll was heated to 243 ~C
(470 ~F). The rolls turned at a speed of 1.52 meters/min (5 feet/min) and the force on the nip was held at 86 N/cm (50 Ib/in) to create bonds between the cube-corners and the exposed sealing llwlllber. Both PET films were then removed. A previously coated o3 micrometer (0.0025 in) thick tac~ified synthetic rubber based pressure sensitive adhesive was lominoted to the unbonded side of the sealing member.
The resultont .eLlure[lective sl-e~t;~.g had a suhsto-ntislly pillowed or curved microstructured member. The ~heeti~ was lsmin~ted to a barrel as generally CA 02249608 l998-09-22 W O 97/38335 PCTrUS97/04041 described in FY~mrle 2. As the barrels cooled to room tenlpe.dlure of about 21 ~C (70 ~F), the sl~ee~ re~n~ fd secured to the barrel. It is believed that the pillows cl ~nged their shaped and arched to accommod~te for the contraction of the barrel.
Measurements of the ~;-0~11L ons of the pillows were made to determine the growth in curvature. The two ~;~. er.~:ons measured in~ ded the height ofthepillows and the base of the pillows. The base is taken to be the length one side of the rect~ngle The height represenled the ~lict~nce from the midpoint of the base to the top of the microstructured member.
Table 1 Sh~eting StateHeight BaseRatio (H to B) (cm) (cm) normal 0.051 1.27 0.040 co,npressed 0.11 1.26 0.081 l~eferring to Table 1, the "normal" state ler~lred to a .cheeting ofthis eY~ npl~ a~er adhesive lamination; the "col,l~ressed" state referred to the cheeting applied on a barrel that had seen a l~.,lpGlal,lre change from 49 ~C to 4 ~C (120 ~F to 40 ~F). As Table 1 shows, the height to base ratio applux;~ y doubled as the cl.r~~ g changed ~om a normal to a colllplessed state in response to the contraction ofthe barrel resl.lting from the te"lp~.al~lre decrease.
This invention may take on various mo~lific?tions and alterations without depa, ling from the spirit and scope thereo~ Accordingly, it is to be understood that this invention is not to be limited to the above-described but is to be controlled by the limit~tion~ set forth in the following claims and any equivalents thereof.

Claims (23)

I claim:

1. A method of making a pillowed retroreflective article comprising the steps of:
(a) providing a microstructured retroreflective member having a body portion and a plurality of cube-corner elements projecting from a first side of said body portion;
(b) providing a sealing member;
(c) conveying said microstructured member and said sealing member at substantially the same speed, such that the sealing member is substantially tensionsless relative to the microstructured member, and such that said cube-corner elements face said sealing member; and (d) bonding said first side of said body portion and said sealing member to each other in a regular pattern to form sealed cells each having a curved microstructured member.

2. The method of claim 1 wherein step (d) comprises thermal bonding.

3. The method of claim 2 wherein said thermal bonding process comprises a bonding temperature of between approximately 193°C and 260°C.

4. The method of claim 2 wherein said thermal bonding process comprises a bonding pressure of between approximately 34 N/cm and 136 N/cm.

5. The method of claim 2 wherein said thermal bonding process comprises a bonding temperature of between approximately 204°C and 243°C and a bonding pressure of between approximately 34 N/cm and 136 N/cm.

6. The method of claim 1 wherein step (d) comprises ultrasonic bonding.

7. The method of claim 1 wherein step (d) comprises front face bonding.

8. The method of claim 1 wherein said regular pattern comprises an array of polygons.

9. The method of claim 8 wherein said polygons comprise rectangles.

10. The method of claim 9 wherein said rectangle has a length of between approximately 5 and 150 mm.

11. The method of claim 9 wherein said rectangle has a width of between approximately 5 and 25 mm.

12. A retroreflective sheeting comprising:
(a) a microstructured retroreflective member having a body portion and a plurality of cube-corner elements projecting from a first side of said body portion;
(b) a sealing member; and (c) a network of intersecting lines bonding said first side of said body portion and said sealing member to each other in a regular pattern of cells wherein the retroreflective sheeting is adapted such that it can elongate by up to 3% with minimal distortion of the cube-corner elements and that it is changeable between:
(i) a normal state wherein said microstructured member is curved and is substantially parallel to said sealing member; and (ii) a compressed state wherein said microstructured member is arched and said sealing member is substantially flat.

13. The article of claim 12 wherein said body portion comprises a body layer.

14. The article of claim 13 wherein said body layer comprises polymers that are flexible and ultraviolet light absorbing.

15. The article of claim 12 wherein said cube-corner elements comprise polymers selected from the group consisting of acrylic, polycarbonate, polyester, polyurethane, and crosslinked acrylates.

16. The article of claim 12 wherein said sealing member comprises polymers selected from the group consisting of polyurethane, polyethylene terephthalate, polyethylene copolymers, ethylene methyl acrylate copolymer, ethylene ethyl acrylate copolymer, ethylene vinyl acetate copolymer, and polyvinyl chloride containing apolymeric plasticizer.

17. A retroreflective traffic control device comprising:
(a) a polymeric device; and (b) the retroreflective sheeting of claim 12 bonded to an outer surface of the device such that as said polymeric device contracts in response to decreasing ambient temperature said microstructured member arches, and as said polymeric device expands in response to increasing ambient temperature said microstructured member flattens.

18. The device of claim 17 wherein said polymeric device comprises polymers selected from a group consisting of low density polyethylene, high density polyethylene polypropylene, plasticized polyvinylchloride, and their copolymers.

19. The device of claim 17 wherein said polymeric device comprises polymers having a coefficient of linear thermal expansion of between approximately 100 x 10-6 m/mK and 250 x 10-6 m/mK at 20°C.

20. The device of claim 19 wherein the ratio of said coefficient of linear thermal expansion for said polymeric device to said retroreflective sheeting is about 1.5:1 to about 6:1.

21. The device of claim 17 wherein said retroreflective sheeting is bonded adhesively to said polymeric device.

22. The device of claim 21 wherein said adhesive is a tackified synthetic rubber based pressure sensitive adhesive.

23. The device of claim 17 wherein said polymeric device is a polyethylene traffic barrel.