CA2145041A1 - Process for preparing bubble-free adhesive compositions - Google Patents

Abstract

Light transparent, visible bubble-free, curable adhesive compositions, their method of manufacture and their use in producing optically brilliant three-dimensional signs for both interior and exterior use are disclosed. The compositions include acrylate based UV light curable monomers and oligomers and moisture curable room temperature vulvanizing silicones, optionally comprising UV stabilizers. The compositions may contain dispersed pigments and are made by low shear mixing, such as static mixing or rolling, optionally, followed by spinning to remove visible air bubbles.

Description

- ~ 2115041 s PROCESS FOR PREPARING BUBBLE-FREE
ADHESIVE COMPOSITIONS

FIELD OF l~ ; INVENTION

This invention relates to curable, bubble-free adhesive compositions, particularly curable acrylic and silicone compositions; to the prep~dlion of said bubble free compositions; to the use of said compositions in the m~mlf~cture of illl~.nina~ed signs; and to such signs compri~ing cured said bubble-free compc!siti~n~.

BACKGROUND TO l~l~; INVENTION

As is well-known, illll..lin~ signs have long been made by sealing neon, or other suitable inert gas, in a low-pr~ss.ll~ tube through which electricity is passed. This causes the neon to "glow" and if the tube is shaped apprupliately, a "neon sign" displaying desired information is achieved. Three-dim~-nsional lighted signage is believed to be more noticeable and appealing than two--limPn.cional signage.
It is, therefore, a better meAium for advertising and why neon signage is so prevalent.
Traditionally, there have been two ways to make three-dimen~iQnal lighted signs. In the case of "Neonn, glass tubing is bent into the desired shape of the characters to be ill~ in~ed, the tubes filled with a fluo~scellt gas and a high voltage arc passed through it. The second method is to back-light a clear or opaque molded sheet of plastics m~t~ri~l, wherein most of the background except the figures through which light is to emerge is bl~el~ out. In this latter method a mold is made over which a heated thermoplastic sheet is drawn. The sheet holds its shape upon cooling and can then be painted or printed with both light blocking and transparent inks and paints.
However, both of the aforesaid products suffer from being very time con~uming to manufacture and are not easy or flexible to produce.

~ ` 21~5041 Recently, there has been a move to manufacture ill~ lin~P~I signs that do not require the use of neon or other gases through which e1~tricity is passed. One development is the m~nuf~ctllre of such signs using an ultra-violet curable, adhesive composition in the form of a gel applied to a base or S~Sll~d~, such as a sheet of a clear acrylate, polycarbonate, glass, most common metals, thermoplastics and thermoset m~t.ori~l~ The base may be overlaid with a vinyl m~teri~l or screen printed, with clear areas known as "light channels" left uncovered until the curable, adhesive gel is applied thereafter and ~ul)selluently cured. When these signs are lit by normal light e.g. a fluole3cellt light, from the rear, the light is tr~n~mitte~ through the cured, adhesive gel and seen. The gel is preferably coloured and accordingly, the light tr~n~mitt~ from the gel is also of that colour. The adhesive gel on the sign is generally cured in a semi-cylin-lri~l form on the substrate, which gives the tr~n~mitted light an a~pal~nt three-~im~n~ional char~ct~ri~tic and the sign a look like a typical "neon signn.Different effects and char~ctP-ri~tics may be achieved using different pigmPnt~ in the adhesive gel and with different subslldtes.
The curable, adhesive gel generally is made having the con~i~tency of toothpaste so that when applied to the s~slldle and allowed to cure, it retains the aforementioned generally semi-cylin~lri~l shape thereon. In order to achieve this toothpaste con~istpncy~ the viscosity and thixotropy of the curable adhesive generally must be increased by the addition of inert fillers. Unfortunately, this ~ ition of inert fillers normally entrains undesirable visible air bubbles into the adhesive. Since the cured, adhesive gel is to have light ll~nclllil~ed through it, it is most desirable that the cured adhesive composition be essenti~lly free of visible air bubbles since the light tr~nsmitt~l through the cured gel will be refracted by the air bubbles and make the sign less attractive. It will be understood that "visible" bubbles, other than air bubbles, such as water vapour or mixed fluid bubbles also produce an inferior product.
The curable, adhesive gel compositions of the prior art made for the purpose of illll..,in~ed signs comprise photc-initi~tors to cause ~e gel to cure upon exposure to ultra-violet light. Ultra-violet curable, acrylic adhesive gels are es~nti~lly polymeri7Prable reactive monomers and oligomers that are inhibited from premature curing, typically, by the presence of suitable inhibitors. Once the photo inhibitors are activated, preferably by exposure to ultra-violet light, the curable, gels polymerize into - ` 2145041 a cured, solid plastics m~ter1~l form. Other known conditions instead of e~-~osu-c; to ultra-violet light can also bring about polymtori7~tion. For example, high ~he~ring during the mixing process in the manufacture of the compositions may cause polym~ri7~tiQn. It has also been found that ~ignifi-~nt de-airing of the curable, adhesive gel composition may cause polymeri7~tion. Thus, the prior art teaches that the latter two conditions of high sh~ring or de-airing are to be avoided if ple ~-alule, u-~w~lled polymeri7~tion of the adhesive gel is to be prevented.
Air bubbles enll~ined into the curable adhesive gel during the addition of inert fillers would norm~lly be removed by the use of vacuum means. However, vacuum ~eg~ing not only removes the large, visible air bubbles from the adhesive, but also, detrimentally, removes subst;~nli~lly all air, i.e., inclu~ing desirable oxygen, to cause a reduction in the efficacy of the air-stabilized inhibitors in the curable, adhesive I~ lul`e. This either causes the adhesive to comm~nce significant polymeri7~tion, immeAi~te1y, or a slower, but effective polym~ri7~tion to cause a ~ub~ ial reduction in the shelf life of the curable adhesive co~--posilion.
Organopolysiloxane co...posilions, es~i~lly RTV (Room Te...p~l~lw~
Vulc~ni7ing) silicones are known in the art, see for example, USP 3474064 P. ~ittm~ir et.al. issued October 21, 1969; USP 3491165 - K. Seyfried et. al. issued January 20, 1970; USP 3532664 - A.H. Smith, issued October 6, 1970; USP 5107008 - A. Ravis et. al. issued April 21, 1992; and USP 5247046 - Takayo et al. issued September 21, 1993. However, the methods of prep~tion according to the present invention of prior art RTV silicones provide improved curable silicone compositions having bPnefici~l pru~ ies for the light sign utility hereinabove ~1iscl~sse~1 Thus, the invention is not limited to only those compositions exemplified, he.~ ar~er, for the utility described but to all bubble-free adhesive compositions capable of being prep~ed by methods according to the invention suitable upon being cured for lighted sign use, as would be readily determined by the skilled artisan.
It is known that in order to cure an ultra-violet (UV) curable monomer or oligomer, the ultra-violet light must be able to penetrate through all levels of the composition with sufficient energy to initiate the polymeri7~tion reaction. This means that (1) the pigm~nt~ used to colour the cured co.l,position must allow sufficiPnt UV
light to pass through the curable composition, which sets an upper limit on the amount of pigment that can be used, and (2) UV light blockers and absorbers cannot be present in the required amounts s~lfflcient to protect the pigmPntc or polymers in the cured co~posi~ion from the degenerating effects of W exposure since too much pigment or UV light blocking colllpound(s) will inhibit the subsequent, desired complete curing o the polymer.
It is also known that pigmPnt colour lightf~ctnP.ss when the composition is exposed to the elemPnts of heat and UV radiation, depends upon the stability of the pigmPnt and composition. The more exposure a pigment has to heat and UV radiation the faster it will degrade. Fluor~scent pigmPnts are espe~i~lly s~lsceptihle to photolysis and autodegradation, and when used indoors tend to fade under constant bombardment from fluolescellt lighting. UV blockers are, thus, typically, used to cover the light source and applied to the sign panel after the composition has cured, in order to extend the life expectancy. T ightf~t pi~mPntc have been used for the outdoor versions of prior art compositions but they fade under the intense radiation and heat from the sun.
There thus remains a need for improved, non-neon light signs having visible buWle-free, cured polymer m~teri~lc.
There also remains a need for improved non-neon light signs conL~ g cured polymer m~tPri~l~, having improved light, particularly slmlight stability, which offers improved outdoor usage.
SUMMARY OF THE INVE~ ON
It is an object of one aspect of the present invention to provide a method of prepating an ultra-violet curable, adhesive gel composition that is light transparent and ~s~ L;~lly free of visible air-bubbles, but that nevertheless con~ c sufficient air to prevent undesirable deactivation of UV inhibitors.
It is an object of a further aspect of the present invention to provide a method of prepa,illg a light transparent curable, bubble-free adhesive gel composition for use in providing an improved cured product for exterior sign usage.
The present invention, thus, in one aspect relates to methods for prepalillg curable, adhesive gels intended to be used in sign-making. The adhesive gel is free of visible air, moisture or other bubbles which if present after curing of the gel would enhance the amount of the incidence of refraction of the light tr~mmitt~P~ there ` ` 2145041 through. The adhesive gel in the case of UV curable compositions should, however, have sufficiently trapped air to provide enough oxygen to interact with any inhibitors that may be present to inhibit polym~ori7~tion until the adhesive gel is intentionally exposed to ultra-violet light.
S Accordingly, in its broadest aspect, the invention provides a method for the prepa~lion and storage of a light transparent, visible bubble-free homogenous, curable, adhesive composition for use in the manufacture of ill~l."in~t~ signs, said col~.posilion comprising a curable, adhesive compound and an inert filler, said method comrrieing the steps of:
(a) mixing under low shear conditions an effective amount of powdered said inert filler into said curable adhesive coll~pound to provide a mixe curable, adhesive composition of desired viscosity and thixotropy;
(b) treating said curable, adhesive composition to effect removal of subst~nti~lly all visible bubbles thelcfi~l-- to provide said bubble-free, curable, adhesive comrosition; and (c) storing said bubble-free, curable, adhesive comrosition in subst~nti~lly, fluid-tight cont~in~rs.
It is within the scope of this invention that a mixing step alone may constitute suitable mixing and treating of the ad---ibclulc of filler and curable, adhesive composition as hereinafter defined should no undesirable visible bubbles be present after the mixing step.
Thus, the invention provides in a further aspect a process as hereinabove defined comprising mixing under low shear cor~ditions an effective amount of powdered said inert filler into said curable adhesive compound to provide a mixed, curable, adhesive composition of desired viscosity and thixotropy such that no visible bubbles are produced.
By the term "low shear" in this speçific~tiQn and claims is meant those rates of shear which bring about s~ti~f~t~ry mixing of the conlponents but which does not initiate plclllalule polym-qri7~ti-1n of the curable monomers or oligomers of use in the present invention.
In one plcfe.led aspect, the invention provides a method for the prcpal~lion of a light transparent, visible homogenous, curable, adhesive composition `- ` 2145041 for use in the manufacture of i11~1min~tecl signs, said composition comprising an inert filler and a curable, adhesive co-l,pound se1~tçd from a monomer and an oligomer, said method comprising the steps of:
(a) mixing under low shear conditions an errecli~e amount of powdered said inert filler into said curable, adhesive compound to provide a mixed, curable, adhesive composition of desired viscosity and thixotropy;
(b) spinning said mixed curable adhesive co~"position in a cenl,iruge at a spin rate and for a time period s~1fficient to subst~nti~lly remove all visible air bubbles ther~fn)m; and (c) storing said spun curable, adhesive composition in a subst~nti~1ly air-tight and ultra-violet opaque co~t~iner, wherein said spin rate and said time period allow sllffiriçnt invisible air bubbles and absorbed air to remain in said spun adhesive composition to thereby provide suitable shelf life to said curable, adhesive composition prior to curing.
lS The invention provides in the method as hereinabove defined that said monomer and said oligomer are UV light curable; said composition further comprises an effective amount of an inhibitor for inhibiting pre",alule curing of said monomer and oligomers; and an effective amount of a phot~inil;~lor for effecting desired curing of said monomer and oligomer when exposured to ultra-violet light.
In a further aspect, the invention provides a light sign comprising a substrate having a portion dçfining a light ch~nnP1~ said light ch~nnç1 having adhered thereto a visible bubble-free and homogenous curable, adhesive composition prepared by a method as hereinabove dçfined. In yet a further aspect, the invention provides a light sign as herinabove defined wl-er~in said curable, adhesive composiiton has been cured.
I have found that the most plere r~d inert filler to enhance viscosity and thixotropy is amorphous fumed silica in an amount of 5-20% w/w. While not being bound by theory it is believed that air is bçnpfi~ y entrained and enll~pped in the silica filler of the curable composition.

~ 7 ~ SL475 Pr~ft;l.ed inhibitors are selected from the group con~i~ting of hydroquinone monomethylether and hydroquinone.
In a more plef~lf~d aspect the invention provides a method as hereinabove defined further comprising dispersing a pigment in said curable compoulld or composition; yet more preferably, prior to the spinning step if carried out.
In a non-UV curable colllposilion of use in the present invention, the curable compound is a silicone.
Although not pler~l-ed, the invention includes compositions compri~ing free radical peroxide and pers~llph~te curable monomer and oligomer adhesives.
In the case of pfefelled UV curable comro~itic)n~ of the invention monomer and oligomer acrylic adhesive colnpuu-lds are present in ~ ..;x~ with polymerizerable isocyanales, polyesters and ole4inPs such that the cured compound is comprised of a base m~tPri~l such as an acrylated urethane, acrylated epoxy or acrylated polyester. Acrylated urethane is the prere fed base m~tPri~l obtained from the curable, acrylic adhesive.
Thus, the invention provides in one aspect a method as defined hereinabove, wherein said adhesive compound comprises a monomer or oligomer selecteA from a polymP-ri7~hle acrylic acid, acrylate, meth~crylate~isocyanate~ polyester, polyol and epoxy resin, to provide on curing a curable polymer s~l~ted from the group con~i~ting of an acrylated urethane, acrylated epoxy and acrylated polyester resin.
Photoinitiators are present in ad~..ixl~ with the adhesive composition to cause polym~-ri7~tic~n of the oligomers and monomers upon exposure to W light.
Inhibitors are also present in the adhesive to inhibit pfelllalule polym~-ri7~tion of the oligomers and monomers. The inhibitors are, lh~l~ç~ ~, intended to inhibit the polymeri7~tiQn reaction until the adhesive gel is actually exposed to UV light. The inhibitors, preferably hydlo4uinone monemethylether or hydr~uillone, are thought to interact with any oxygen present in the adhesive gel to inhibit polymPri7~tion. It has been found that substantial ~e~ ing of the adhesive gel, particularly by vacuum ~lep;~ing, results in the immeAi~te onset of polym~ri7~til~n, or results in a relatively short shelf life of the adhesive gel. By shelf life it is meant the time during which the adhesive gel can be stored prior to unw~led polymeri7~tiQn occ~ inE.

As referred to hereinabove, the use of adhesive gels in sign-making requires that the gels have a con~i~tency similar to that of toothpaste. Thus, inert fillers must be added to the adhesive ~ ule to increase the ~ lU~'S viscosity and thixotropy.
The method of the present invention provides that the adhesive compounds, particularly the UV curable compositions are prepared by mixing the oligomers, monomers, photoiniti~tors and inhibitors under low shear conditions. The inert filler, is added to the ~ lur~ during the low shear mixing step until the filler, most preferably, fumed silica has been completely wetted by the other components of the IllL~ure. It has been found that mixing under low shear conditions, as opposed to high shear conditions, reduces the likelihood of polymPri7~ti-)n occllrring.
The addition and mixing of inert filler, particularly amorphous fumed silica, to the ~ luie results in air bubbles being entrained and ent~dppPd in the lu~e. Re~l-~e of the relatively high viscosity and thixotropy of the adhesive colllpow~d, it is believed the entrained invisible air bubbles remain trapped within the adhesive compound. According to the method of the present invention, the larger,visible air bubbles are removed from the curable, adhesive composition by spinning of the composition in a cenlli~uge. The adhesive compound is spun at a spin rate and for a time period s-lffici~Pnt to cause subst~nt~lly all the visible air bubbles to be removed from the colllpound, while allowing suffici~Pnt air to remain in the compound. The r~ inillg air provides oxygen that interacts with the inhibitors, thereby ~ ting in inhibiting polymerization of the reaction. This, in turn, provides increased shelf life to the adhesive colllpoul-d as conlpaled to an adhesive colll~und that has been ~eg~sed by vacuum means.
Thus, the present invention provides in one aspect a method for prepa,illg an ultra-violet curable adhesive composition that is s~st~n~;~lly free of visible air bubbles. The compositi~n is spun in a centrifuge until all visible bubbles are removed, yet leaving suffl~iP-nt air in the adhesive composition to assist in inhibiting polymPri7~tion.
In a more pr~e~,ed aspect, the invention provides non-UV curable adhesive com~s;lions comprising as base SUlJSlldle a light transparent, curable, silicone polymer, preferably a room lelll~l~lule vulc~ni7in~ (RTV) slightly opaque, fully 21~50~1 transparent or translucent silicone polymer, optionally mixed with UV light blocking and absorbing agents, dyes, pigmPnt~ and other fillers. The curable silicones are cured by hydrolysis with water in the form of moisture, steam and the like. The RTV
silicones may be either neutral or acid catalysed curable silicone polymers. The cured S compositions are used as optically brilliant three--limen~ional signs and 1Pttering for both interior and exterior use. To P~ in~1e or prevent the presence of visible bubbles, either water or air, the curable silicone and filler compositions are plef~.~blymanufactured through the use of static mixers.
Pref~.ed silicones of use in the present invention, for eY~mple, in~ e., methy1trimethoYysilane, dimethylpolysilane and methyl dimethyl polydimethylsilane RTV resins.
The fillers comprise amorphous or hydrophobic fumed silica for viscosity and thixotropy control, W blocking/absorbing agents, such as, for eY~mple TINUVIN~ (Ciba-Geigy) and fluorescent and non-fluorescent inorganic and organic coloured pigmPnt~
The curable silicone composition is compounded with the desired fillers in effective amounts to form the gel or paste by use of precision effective mPtering and static mixing under an inert, ultra-dry atmosphere and, ~imil~r1y, stored in a fluid (air and moisture) tight CQ,lt;~in~r.
Preferred, curable compositions comprise RTV silicone adhesives. Most prefelr~d RTV silicone compositions comprise ll~lules of methyltrimPtlloxy silane (CAS# 1185-55-3), ME-Dimethoxy/STP Polydimethyl siloxane (CAS# 68037-58-1) and dimethylpolysiloxane (CAS# 63148-62-9), for example, provided under the RTV5810 series of silicone rubber se~1~nt~ (General F.lP~tric Co.) which absorb water from the atmosphere to effect cure.
The pigment fillers are added, generally, as a dispersion of the organic or inorganic pigment in a silicone fluid col.~ g, for example, 80-90% w/w dimethylpolysiloxane (CAS# 63148-62-9). Pigments of p~felled use are known as "transparent" pigmPnt~ because of their very small primary particle size and high degree of dispersion. The pi~mPnt~ may be of the fluolescellt type dyes in a resin matrix ground into extremely fine particles. The pigmPnt in the cured colllposilion absorbs all of the wavelengths of light other than those wavelengths it reflects or tr~n~mit~. Fluo.escent pigment~ appear to amplify the light passing through the cured bead, possibly by conversion of UV light to a wavelength in the visible spectrum.
T.llmin-q.scence is often seen with such transparent pigmPnt.~ which causes the cured coloured bead to glow.
Although not ne~s~.~, even for outdoor use, the silicone colllposilion of the invention may comprise UV blocking agents, such as of the hindered amine type known as HALS.
In further ~ltern~tive ~spect~, the invention provides compositions prepared by methods as hereinabove dçfin~, and three-~iim~n~ional beads comprising cured said compositions when cured on a s~sll~te.
A curable colllposilion as hereinabove defined may be ~i~pen~l manually or most preferably using a colllpuler controlled lispen~ing appa,~lus for highly repeatable reproclucti~ns according to the prior art.

BRIEF DESCRIPIION OF THE DRAVVINGS

In order that the invention may be better understood prere~d emb~imPnt~ will now be described by way of eY~mple only with reference to the accoll,l)anying drawings; wherei 20Fig. 1 is a diagli.... ,.",~l;c cross-sectional view, in part, of a light sign showing a raised bead printed on a ~sll~te, wherein a light c~nn~l is formed by the application of a light blocking substance upon the underside of the substrate, in accordallce with the present invention;
Fig. 2 is a diag~ ;c cross-section~l view, in part, of a light sign showing a raised bead printed on a ~ te wherein a light cll~nnel is formed by the application of a light blocking substance upon the topside of the subsll~dle, inaccor~ce with the present invention;
Fig. 3 is a diagr~mm~tic cross-section of a bead of cured m~t according to the invention;
Fig. 4 is a diagr~mm~tic cross-section of a bead of cured m~tPri~l according to the prior art; and whe~ the same numerals denote like parts.

- ` 21450~1 DETAILED DESCRIPIION OF PREFERRED EMBODIMENTS

With reference to Figs. 1 and 2, these show, in part, an illumin~ted sign case shown generally as 10, having plastics frame side walls 12, a W light source 14 and a sign front s~ le 16 formed of a transparent polycarbonate.
In Fig 1, substrate 16 at its b~c1f~i~e 18 has a light blocking film 20 adhered thereto or printed thereon. Film 20 may be a thermoplastic, a thermoset, a metal foil or a paint or ink. Film 20 has portions de-fining a light ch~nnel ap~,lule 22 through which light passes to cured composition bead 24, adhered over light ch~nne1 22 to front side 26 of substrate 16.
The embodiment shown in Fig. 2 has no light blocking film 20 on b~ e 18 of substrate 16 but has such a film 28 on front side 26 of substrate 16.Film 28 has por~ons ~efining light ch~nnel 30 through which light from source 14passes to bead 24.
Fig. 3 rep.c;senls cured bead 24 having no visible bubbles, air or water, according to the invention. Light tr~nsmi~ion through bead 24 is denoted by arrows 32.
Fig. 4 rep~cs~llts a cured bead 34 of the prior art having air bubbles 36 which diffract and absorb light as f~p,c~sented by arrows 38.
In a pr~ d embo~imPnt of the method of the present invention, the mixed adhesive compound is spun in a centrifuge at a spin rate in the range of about 2500 rpm to about 6000 rpm. Preferably, the spin rate is between about 3000 rpm and about 4500 rpm, and most preferably 4000 rpm. The time period during which the mixed adhesive composition is spun in order to provide the desired adhesive composilion is inversely related to the spin rate. That is, the faster the spin rate, the smaller the time period. The spin rate and time period are s~1e~ted to remove subst~nti~lly all visible air bubbles from the adhesive composition, while leaving enough invisible air to assist the inhibitors. As well, the spin rate and time should not cause the other individual components of the adhesive composition to se~te. Thatis, spinning of the composition at too fast a spin rate or for too long causes the individual compol ents to separate, based on their respective specific gravities. The result is a non-homogeneous Illi~lule of the co..-ponents.

It has been found that ~ti~f~ctory results are achieved if the mixed adhesive composition is spun for about 5 ~ llulPs at a spin rate of 3000 rpm and for about 1.5 .~ PS at a spin rate of 4500 rpm. Preferably, the mixed adhesive composition is spun for 2 Il~inules at a spin rate of 4000 rpm. It should be noted that the term "time-period" as used herein refers to the total time that the co-"posilion is spun, in~lu-ling the initial accelerating phase of the cenlliruge and the final deceleration phase. Thus, for eY~mple, at the prefelled spin rate of 4000 rpm, the composition is spun for a total time period of about 2 minutes in which about 100 seconds are at the actual spin rate of 4000 rpm.
I have also found that the mixed, curable, adhesive composition most preferably should be spun at an angle subst~nti~lly horizontal, i.e. perpendicular to the axis of rotation. Deviation from this horizontal rot~tio~l plane does not provide visible air bubble removal, due to adhesion thereof to the sides of the centrifuge tubes holding the composition.
It has been found that using the method of the present invention, the shelf life of cured acrylic adhesive composition is about 6 months, and can in some cases be a lot longer. This is co",palable to a shelf life of about 1 1/2 months in the case of the acrylic adhesive co".l~s;~;on~ deg~seA by vacuum, although the adhesive composition may polymeriæ during, or shortly after, such vacuum de.p;~ing.
In a p~ef~led emho limPnt of the method of the present invention, a pigm~nt to provide colour to the adhesive compound is dispersed within the co~llpoun prior to the mixing step. Any suitable pigmPnt may be used to provide the desired colour to the compound.
The method of the present invention may be carried out as follows, although it is understood that the present invention is not limited to the particular con~itions described.
Typically, a 300 pound batch of UV light curable, acrylic adhesive composition is made at one time. The monomer, oligomer, pholoinitiator and inhibitor con-pollell~ are placed in a bottom-ported plastic barrel and mixed using a low shear helical mixer until the colllponellts are thoroughly blended. A pigment, if used, is added to the liquid coll,ponents prior to mixing. The inert filler, plef~,~bly amorphous fumed silica, is added while the liquid colllponents are continuously ~it~t~ The inert - ` 2145041 filler makes up between about 5% and about 15% by weight of the total adhesive composition, and preferably 10% by weight if amorphous fumed silica is used.
The ~ ure is further mixed under low shear conditions until homogenous. The barrel is then capped and placed on a roller, on which the barrel is rolled at a rate of about 6 inches per second, as measured on the outside di~mPt~r of the barrel. After 12 hours of rolling, the barrel is taken off the roller and the adhesive composition m~h~ni~lly mixed with a helical mixer until all the composition has been repositioned in the barrel. The barrel is then l~apped and rolled for another 12 hour period, during which time the co-l-posilion becomes uni~o,.-- in the barrel, and builds in viscosity and thixotropy.
After the second twelve hour rolling period, the rheological char~ct~ristics of the mixed adhesive composition are tested. P~ef~ldbly, the viscosity of the adhesive composition will be in the range of about 100,000 cenlipoises to about 800,000 cenli~ises, as measured using a spindle number 7 at 2.5 rpm on a Brookfield DV-l viscometer. The thixotropy of the adhesive composition is measured on a flow test jig. In a three minute test, the ~ t~nce the sample travels should, preferably, be between 2.5 and 5.75 centimetreS.
If the rheological char~cteristics of the mixed adhesive co~pos;~ion~ are acceptable, the composition is then loaded into cartridges through a mandrel f~tPned to a positive disp1 cPm~nt pump affixed to the bottom of the barrel. The cartridges are, preferably, opaque to ultra-violet light to prevent ~ d~n~l polymeri7~ti~n of the composition. Any large, visible air bubbles that were entrained and enll~ped into the adhesive compound during the mixing and pumping stages are s~ rd by spinning the cartridges in a cel lliruge.
The cartridges are placed into ~up~ollive retainer sleeves. The sleeves are placed into trunnion rings which are ~ ch~ to the rotor of the centrifuge. When the rotor spins, the retainers swing oulw~d to a horizontal position with the plugged ends of the cartridges furthest away from the rotor and the open ends closest to the rotor, i.e. perpendicular to the axis of rotation. The adhesive composition in the cartridges becomes stratified by specific gravity. The heaviest parts (fluids) are forced furthest from the rotor while the lighter air bubbles move closer to the rotor until they are sepal~led from the fluid altogether. If the composition is spun too long or too fast, - ` 21450~1 the fluid cclllpollents will start to s~p~le. It has been determined that the optimal time is about 100 second at a speed of 4000 rpm. Thèse conditions sepal~te the visible air bubbles from the fluid without se~andling the fluid itself.
After spinning, plungers are inserted into the cartridges. These plungers are transparent and do not have wiper seals so as to minimi7P the oppollunily to further trap air bubbles during plunging and to be able to see any inad~l~lllly ent,~ped air.
A custom designPcl plllnging m~hinP "walks" the plunger into the cartridge and fii~pl~f~es any air trapped under the plunger up the side of the plunger, and out of the back of the cartridge. The p1unging m~chinP, also ensures an occlusive seal around the plunger so the plunger will not move during shipping and h~n~ling. The excess composition behind the plunger is removed and the cartridge is labelled and shipped.
In the process according to the invention wherein the inert filler and visible, bubble-free, curable co,l,pos;liQn~ are mixed, such as not to form visible bubbles under low shear, a static mixing process is most prer~ d. The resllltingcurable co,-l~silion from the motionlps~ static mixer is ~i~pen~d through a mandrel direc~ly into an ultra-dry nitrogen purged cartridge sealed at the outlet end. The cartridge is removed from the mandrel and the back of the cartridge is purged with ultra-dry nitrogen. The cartridge plunger is pushed into the cartridge while thecartridge is deformed until all of the gas belween the plunger and the curable adhesive composition has been eYh~-lsted. This ensures an air and moisture tight seal.
~ltprn~tively, the cartridge may be filled from the outlet end, whereby, prior to filling, the plunger is inserted and bottomed out in the cartridge. The outlet of the cartridge is purged with ultra-dr.,v nitrogen and is coupled to the outlet of the meter-mix m~hine. As the composition is ~ ren~e~ from the meter-mix m~chine it is injected into the cartridge and pushes the plunger back. When full, the cartridge is removed from the meter-mix mae~ine and a tip cap is inserted to seal it.
~ltern~tively, the printing composition of the invention can be rli~pPn~
directly from the same meter-mix into a larger container such as a one gallon pail, or a five gallon pail, or a twenty litre pail, or a forty-five gallon drum, or a 200 litre drum or similar, the main con~iderations being that it is first purged with ultra-dry nitrogen, that it is impervious to moisture penetration and there are f~-.iliti~s available to remove the printing composition from said container without introducing air or - '` 21450gl cont~minating it with water or any foreign debris. It must also seal completely and be r-h~-mic~lly col,-palible with the printing composition.
.Altern~tively, the printing composition may be packaged directly from the meter-mix m~chinP into a collapsible p~c1~e such as a toothpaste type tube or bag or any other format that can keep it from being con~ ed by water from which it can be ~ pen~ In the case of moisture-curable silicone monomers and polymers, the package must be ultra-dry nitrogen purged before filling and prior to sealing in any case.
A pr~f~lled method of applying the curable bubble-free compositions of the invention to a substitute for curing thereon to provide the cured three--iimPn~ional sign or lettering, is by use of compuler controlled dispensing m~hine of the type produced by T.~min~rt Inc, Mi~ ~ng~, Ontario, Canada or Camelot Systems Inc., Haverhill, Mass., U.S.A.
In operation, the curable printing cGI-Iposilion is loaded into cartridges, each cartridge having a hole at one end to accommo~te a ~i~pçn~ing needle. the ~ pen~ing needles can be of dirre~ t shapes and sizes. At the opposite end of the cartridge is a plunger which fits snugly within the intçrn~ mPtP~r of the cartridge.
The plunger can move the entire length of the cartridge. When the cartridge is filled with the printing composition the plunger is in~t~lled and makes intim~tP contact with the printing composition trapping it between the plunger and the outlet.
The cartridges are loaded into a form fitted retainer which is ~tt~h~A to the moveable arm of the iispensing m~hine. The retainer is orient~t~ in a holder which holds it straight up and down with the outlet of the cartridge at the bottom. The retainer is fitted to a switched co"~pressed air outlet by means of a length of tubing. When the switch is turned on, regulated colllplessed air enters the retainer and plc~.. ;7.es it. The col"p~ssed air advances the plunger in the cartridge displacing the printed composition through the outlet.
To make a sign, the opc;l~tor programs the path along which the printing composition is applied, t~ehing the m~chine the coor~inat~s of each point along the path and giving it instructions as to how high the retainer should be held at each point and whether or not a ~Illplessed air switch should be opened or closed. In the "Run"
mode, the ~i~pen~ing m~chine retraces the pn)gla",med path with the retainer at the -21450~1 proper height, opening the co---pl~ssed air switch, ples, ~;7inE the retainer and displacing the printing composition at the be~hlllillE and during the length of each line, and closing the ail~.~vilch and de-ple..~.; ,;ng the retainer, stopping the displ~r~mPnt at the end of each line. At the end of each line the retainer lifts relative to it ~ pen~inE
S height.
~lt-~rn~tively, rather than ~ n~in~ from a cartridge, the printing composition may be fed to a valved 1ispen~in~ a~a dlus from a larger l~ oir such as a one gallon pail, or a five gallon pail, or a twenty litre pail, or a forty-five gallon drum, or a 200 litre drum or similar. The outlet of this app~dlus will be affixed to the moveable arm of the ~ispen~in~ m~hine which will tell it when to open and close.When open, this app~dlus will allow a constant stream of printing composition to flow upon the substrate in the form of a bead. When closed, the ~ peM~in~ will cease and the bead of the printinE composilion will end.
A sign is created with one or many of these beads applied over light lS ch~nn~
Before, during and after m~mlf~ct~rinE~ the co---ponents and fini~h~
printinE composition are ."~inl;.in~ in an inert moisture-free environment, prior to curing. After the printinE composition 11 has been applied to substrate 12, it is placed in a dust-free, ambient environment where it polym~ri7Ps through the absorbtion of water primarily from the ~tmosphere.
~lt~rn~tively, it can be placed in a chamber which incol~.dles higher levels of heat and humidity to speed up the polym~ri7~tion process.
The cur~ble, adhesive composition after application to the lighted sign substrate may be cured by the applir~tion of UV light, if UV light curable; or by water if curably sensitive thereto.

Example 1 Table 1 Table 1 gives ~Y~mples of UV-curable formulations compri~inE acrylic based compositions and, optionally, a pigment in the amounts stated, hereinbelow.

21450~1 Component A B C D E
(% wlw) (% wlw) (% wlw) (% wlw) (% wlw) Acrylated 32.5 40 45 48.2 40 oligomerl 1,6 ~eY~n~Aiol 20 24 20.2 30 15 diacrylate N-vinyl 17.5 4.3 4.3 - 18.3 Pyrrolidinone2 2-Ethoxy- 17.5 17 17.5 8.7 18.3 ethoxy-ethylacrylate3 2-hydroxy- 3 2.6 3.5 3.5 3.6 2methyl 1-phenyl -propane -l-one4 Hydrophobic 9.5 9.5 9.5 - 4.8 fumed silica5 Amorphous - - - 9.2 fumed silica6 Key 1. 15-1512 Acrylated oligomer (McWhorter):
~lk~neAioic acid, polymer with a-hydroxy-w-hydro~yl~oly (oxy-1,4, but~nn~Aiyl), 5-isocyanato-1-(isocyanomethy)-1,3,3-tlimethylcuclyhexane and mixed ~lk~nol~, 2-hydroxy ethyl acrylate blocked (urethane-acrylate polymer) 2. V-PYROL, RC asP TECHNOLOGIES) 3. SR256 (SARTOMER) 4. DARDOCUR 1173 photoiniti~t~r (CIBY-GEIGY) 5. R972 aDEGUSSA) 6. AEROSIL 300 aDEGUSSA) The above compositions were used as base curable formulations in ,ix~,-.e with suitable pi~m~nt~ as follows in either (a) back lit, or (b) front lit systems.
FIRE RED - (STERLING 920-21) 5 parts: 95 parts co--lposilion A(b) OLYMPIC BLUE - (STERLING B10-70) 4 parts: 96 parts composition B(b) WARM ORANGE - aLANTER TS13) 2.5 parts: 97.5 parts composition E(a) 21450~1 GLOSS WHITE - (HOECHST 01-DUE-27) 0.5 parts: 99.5 parts composition C(a) CANARY YELLOW - (DAYGLO Z-16-3) 0.03 99.97 parts composition D(a) The component parts were combined in a "Ross Ve~ " low shear mixer. The silica coll~ponent was added last because it was most difficult to entrain.
Once the full amount of silica was wetted out, the mixer was activated in the mixer for about 2 hours. The high speed dispersion blade was run at about 100 RPM and the Anchor blade assembly was run at about 200 RPM. At the end of the cycle, a sample was taken and tested for thixotropy and flow char~rteri~tics. When it passed in~ tion, the batch was mixed under 30" hg vacuum for 3-5 Illinules. The mixed composition was then pressed out of the mixing vessel through its bottom port through a st~inless steel strainer into a cartridge mandrel filler. A cartridge was filled to a weight of 189 grams of curable colll~silion and spun in a centrifuge such that the tip of the cartridge was subjected to 4,000 gravities for four minutes After spinning, the cartridge was removed from the centrifuge and visually in~pe~t~ to be air bubble-free.
A sealess plunger was placed in the cartridge to provide an air-tight seal.

FY~mple 2 Table 2 gives examples of moisture curable RTV silicone adhesive compositions based on RTV5810 series (General Fl~tric Silicones), comprising Il~i~lures of methyltrimethoxysilane, methyl ~im~thoxy/STP polydimethyl siloxane and dimethyl poly~iloY~nP resins.

Parts Percenta~e Pink 100 Sil 90.9 9.5 H9502 (HCC19466 & A 21) 8.636 0 5 A 300 0.455 110 PARTS 100%
Fire Red 100 Sil 90.9 7.308 H9502 (HCC19466 & A 21) 6.644 0.385 A300 0 35 2.308 T 171 2.098 110 PARTS 100%

- 21 150~1 Olympic Blue 100 Sil 90.9 7.746 DC 200 7.042 0.399 A 300 0.363 0.176 H9502 (HCC 19466 & A21) 0.159 110 PARTS 100%
Gloss White 100 Sil 90.9 6.249 DC 200 5.681 0.322 A300 0.293 0.141 H9502 (HCC19466 & A21) 0.128 1.974 T171 1.795 1.33 T292 1.209 110 PARTS 100%
Canary Yellow 100 Sil 90.9 9.21 DC 200 8.372 0.475 A 300 0.431 0.209 STANTONE RED 0.19 110 PARTS 100%
Warm Orange 100 Sil 90.9 7.164 DC 200 6.513 0.368 A 300 o 335 0.162 STANTONE RED 0.147 2.328 T 171 2.116 110 PARTS 100%

%WIW
Wherein Sil is RTV5818:
Methyltrimethoxysilane (CAS #1185-55-3) 1 - 5 Methyl~imethoxy/STP Polydimethyl-siloxane (CAS #68037-58-1) 60 - 80 Dimethylpolysiloxane (CAS #63148-62-9) 10 - 30 and DC 200 - OCTAMETHYLTRISILOXANE, DOW CORNING 200 A 300' - AMORPHOUS FUMED SILICA

STANTONE
RED - SILICONE FLUID CONTAINING 80-90%
DIMETHLYPOLYSILOXANES CAS # 63148-62-9 - QUINACRIDONE CI PIGMENT VIOLET 19, CL #46500 T 292 - BIS (1,2,2,6,6 - PENTAMETHYL - 4 - PIPERIDINYL) SEBACAE

T 171 - (2-h-BENZOTRIAZOL-2-YL)-4-METHYL-6-DODECYLPHENOL
Sil RTV5810 A moisture RTV curable silicone composition was made as follows:
16 parts of Dayglo ~ Corona Magenta part number A-21, 12 parts of Ciba Geigy's Tinuvin 292 ~ Hindered Amine Light Stabilizer, 18 parts Tinuvin 171 0 Ultra Violet Light Absorber, and 3 parts of Degussa's Aerosil 300 ~ amorphous fumed silica in 51 parts dimethylepoysiloxane fluid (CAS# 63148-62-9), were mixed using a three-roll mill or a "Ross POWG1111iX" disperser. This dispersion was deg~ed until aU
visible air was stripped from it. It was then transferred to an ultra-dry nitrogen purged reservoir where it was bl~nkPted with ultra-dry nil~vgen gas. The reservoir was then ~tt~h~d to a two-pump volllm~-tric mPt~ring m~ine The other pump was ~tt~`hed to a reservoir which had also been ultra-dry nillogen purged and loaded with RTV 5818 single co",ponent, unpolymeri7~d silicone rubber comrosition. The dispersion andRTV silicone rubber co",l)osilion were metered in the ratio of 1 part dispersion to 10 parts RTV Rubber composition and lispen~d through a static mixer. The size and number of e1emPnts in the mixer may vary, but best mixing results were obtained using a "Combination" static mixer. The 12 beginning e1e-mPnt~ in this mixer are 1.3 cm.
in ~ mPtPr in a 1.3 cm. inside ~ mpter housing foUowed by a 2.0 cm. di~mptpr housing, in which there are 26 elPmPnt~ 2.0 cm. in ~i~metpr. The section between the two different sized P,lemP.nt.~: iS about 7.5 cm. long where there are no elempnts. The rli~m~tPr of the housing at this point is 7.5 cm.. The combined silicone rubber col.lpound and dispersion were l!lGsenled to the large ~ mPter mixing element~, simultaneously, in the aforesaid ratio. The components pass by the e1~mPnt~ to combine split and recombine effectively layering the two compositions in the housing in a m~lltitude of layers. At the end of the e1emP-nt~, the housing restricts to 7.5 cm inches in ~ mPtPr. There is a section about 7.5 cm. long having no e1emPnt~. Thecol"~nents proceed through this section to a second group of 26 e1em~nt~ which are - ` 2145041 smaller in rli~m~o,t~o,r than the first element~, where they were again divided reoriented and recombined at each e4-ment to form more layers until the compositions were completely blended. The number of layers formed at the outlet of this mixer is 2 to 38th power. The pumps are sized such that given the plcs~ule drop of the mixer and the high viscosity of the co.-~posilion, the flow rate at the outlet is about 400 grams per minute. At the end of the mixer is a mandrel whose outside rli~met~,r approxim~tes the int~.rn~ meter of the cartridge in which the mixed bubble free curable composition was packaged. A cartridge was ultra-dry nil,ogèn purged, placed over the mandrel and an aliquot of composition taken into it. The cartridge was pushed off the mandrel by the fluid being injected into it. At the completion of the metered shot, the cartridge was removed completely from the mandrel, the eYpos~ composition ultra-dry nilfJgel-purged and a plunger inserted to seal off the back end of the cartridge. ~lle..,i.~;vely, the composition was ~lisrpn~ed di~eclly from the static mixer into a pail or drum which had been dried and nitrogen purged before and after the filling operation. A sealing cap was placed on it, immyii~t~ly.

214~041 -This example describes a typical bubble-free curable epoxy adhesive composition of use in the present invention.
s Part "A" Parts Per Hundred Epoxy Resin 68 ~lip~thic Glycidyl Ether 23 Amorphous Fumed Silica 9 Part "B" Parts Per Hundred N-Aminoelhylpi~l~zine 18 Trieth~nolamine 13.5 Amido-amine Resin 13.5 Diethylen~ inP. g Nonylphenol 6 Triethylento.tri~min~. g Aliphatic Glycidyl Ether 6 Ri~ph~.nol "A" 6 Pip~ ine 5 Diamine 3 Amorphous Fumed Silica 9 Bis (12266 - pe.nt~mPthyl~-piperidinyl) seb~te Hydrophenylbenzotriazole - . 2145041 On adllli~lu,c, 4 parts of "A" were mixed with 4 parts of "B".
Pl~al~lion:
The co.llponellls of Part "A" and Part "B" were mixed together under high shear and vacuum to Pli--,;n~e e~ pped air and then loaded bubble-free into a S meter-mix--lispen~e device. They were metered in the ratio of 4 parts of Part "A" to 1 part of Part "B", with both streams being introduced, simultaneously, into a static mixer. The outlet of the static mixer was conn~ted either to the cartridge filling device or directly into an X-Y-Z tli~pen~,r. The viscosity and thixollll~)yr of the composition were suffi~i~nt to keep it from slumping on the sign substrate once it has been applied until curing took place. This co.. los;l;on was a thermoset resin and began to polymerize within 0.5-2 hours after the two components were brought together.

This example illustrates a pre-urethane polymer formulation of use in the present invention.
Part "A" Parts Per Hundred Polyether Polyol 87 Polysiloxane 3 Hydrophobic Amorphous Fumed Silica 10 Part "B" Parts Per Hundred Dicyclohexylm~th~ne -4,4- Diisocyanate 70 DiphenylmPth~n-~- Diisocyanate 18 Phenyl Isocyanate Hydrophobic Amorphous Fumed Silica 10 Bis (12266 - p~nt~mPthyl -4-piperidinyl) seb~ te 0.5 Hydrophenylbenzol~iazole 0.5 - . 2145041 The co...ponents of Part "A" over Part "B" were mixed together in an ultra-dry nitrogen envi~n--lent under high shear until the parts were thoroughlyblended. The compositions were then ~leg~d at 760 mm Hg vacuum for 15 milluLeS
while being ~git~tecl to e1imin~te enll~pped gas. Parts `nA" and "B" were then loaded S bubble-free into a dried meter-mix--lispen~e device. Extreme care was taken to avoid co~ ting either part, but esperi~lly Part "B", with moisture. They were metered in the ratio of 1 part of Part "AH, to 1 part of Part HB", while both streams being introduced simultaneously in a static mixer. The outlet of the static mixer was conn-P~tecl either to the cartridge filling device or directly onto an X-Y-Z lisppn~er.
The viscosity and thixotropy of the composition were slfficiPnt to keep it from ~lumring on the s~bsl,ale once it had been applied until curing occurred.
Although the ~i~closllre describes and illustrates certain p~efell~d embo limPnt~ of the invention, it is to be understood that the invention is not limited to these particular emho ~ Pntc Rather, the invention includes all embo lim~Pnt~ which are functional equivalents of the specific embo~iment~ and fealules described and illustrated.

Claims (20)

1. A method for the preparation and storage of a light transparent visible bubble-free homogeneous, curable adhesive composition for use in the manufacture of illuminated signs, said composition comprising a curable, adhesive compound and an inert filler, said method comprising the steps of:
(a) mixing under low shear conditions an effective amount of powdered inert filler into said curable, adhesive compound to provide a mixed curable, adhesive composition of desired viscosity and thixotropy;
(b) treating said curable, adhesive composition to effect removal of substantially all visible bubbles therefrom to provide said bubble free, curable adhesive composition; and (c) storing said bubble-free, curable adhesive composition in substantially, fluid-tight containers.

2. A method as defined in claim 1 for the preparation of a visible light transparent, air-bubble-free, homogeneous, curable, adhesive composition wherein said curable, adhesive compound is selected from a monomer and an oligomer, said method comprising the steps of:
(a) mixing under low shear conditions an effective amount of powdered inert filler into said curable, adhesive compound to provide a mixed curable, adhesive composition of desired viscosity and thixotropy;
(b) spinning said mixed, curable, adhesive composition in a centrifuge at a spin rate and for a time period sufficient to substantially remove all visible air bubbles therefrom to provide a visible air bubble-free and homogeneous, curable, adhesive composition; and (c) storing said spun, visible air bubble-free, curable adhesive composition in a substantilly air-tight and ultra-violet opaque container; wherein said spin rate and said time period allow sufficient invisible air bubbles and absorbcd air to remain in said spun adhesive composition to thereby provide suitable shelf life to said curable, adhesive composition prior to curing.

3. A method as defined in claim 1 wherein said mixing under low shear conditions said effective amount of powdered inert filler into said curable, adhesive compound to provide said mixed, curable, adhesive composition of desired viscosity and thixotropy is such that no visible bubbles are produced.

4. A method as defined in claim 2 wherein said monomer and said oligomer are ultra-violet light curable; said composition further comprising an effective amount of an initiator for inhibiting premature curing of said monomer and said oligomer until exposed to ultra-violet light; and an effective amount of a photoinitiator.

5. A method as defined in claim 1 wherein said inert filler is selected from amorphous silica and fumed silica and is present at a concentration of 3 to 15% w/w in said curable, adhesive composition.

6. A method as defined in claim 5 wherein said silica is at a concentration of 8 -20% w/w in said curable, adhesive composition.

7. A method as defined in claim 2 further comprising dispensing a pigment in said curable, adhesive compound in said mixing step.

8. A method as defined in claim 1 wherein said mixing under low shear conditionsstep is effected comprising static mixing conditions.

9. A method as defined in claim 1 wherein said mixing under low shear conditionsstep comprises rolling of said mixed adhesive composition.

10. A method as defined in claim 1 wherein said mixture is spun at an angle substantially horizontal.

11. A method as defined in claim 1 wherein said composition further comprises aneffective amount of an ultra-violet light stabilizer.

12. A method as defined in claim 1 wherein said compound comprises a RTV
adhesive silicone.

13. A method as defined in claim 11 wherein said RTV adhesive silicone is selected from the group consisting of methyl trimethoxysilicone, methyldimethoxy/STP
polydimethyl siloxane and dimelthypolysiloxane.

14. A method as defined in claim 12 wherein said bubble-free curable adhesive composition comprises 1-5% w/w methyltrimethoxysilane (CAS No. 1185-55-3), 60-80% w/w methyldimethoxy/STP polydimethyl-siloxene (CAS No. 68037-58-1) and 10-30% W/W (CAS No. 63148-62-9).

15. A method as defined in claim 1, wherein said adhesive compound comprises a monomer or oligomer selected from a polymerizable acrylic acid, acrylate, methacrylate isocyanate, polyester, polyol and epoxy resin to provide on curing a curable polymer selected from the group consisting of an acrylated urethane, acrylated epoxy andacrylated polyester resin.

16. A method as defined in claim 15 wherein said cured polymer is an acrylated urethane.

17. A light sign comprising a substrate having a portion defining a light channel said light channel having adhered thereto a light transparent, visible bubble-free, curable, adhesive composition prepared by a method as defined in Claim 1.

18. A light sign as defined in Claim 17 when said curable, adhesive composition has been cured to provide a flexible material.

19. A light sign as defined in Claim 18 wherein said flexible, curable, adhesivecomposition has been cured by the action of water.

20. A light sign as defined in Claim 18 wherein said flexible, curable, adhesivecomposition has been cured by the action of UV light.