CA2188413A1 - Polymeric article having improved hydrophilicity and a method of making the same - Google Patents

Abstract

A hydrophilic polymeric article (10) has metal oxide particles dispersed throughout a polymeric binder material (12). A major surface (18) of the polymeric material (12) is treated so as to remove polymeric binder to provide a higher ratio of metal to carbon atoms on the major surface (18) of the polymeric article (10) relative to its interior. The polymeric article (10) provides extraordinary water-spreading effects on the major surface (18), making the article (10) particularly suitable for use as a surface covering on a retroreflective sheeting (16).

Description

w095/32237 ~ ~ 8 g 4 li~ r~
POLYMERIC ARr~CLE EAVING IMPROVED
EYDROPHILICITY AND A METHOD OF M~KING THE SAME
TF.(~r1~cA~ FrF.~.n This invention pertains to (i) a hydrophilic polymeric article that contains metal oxide partides, ~li) a method of making such a polymeric article,and ~lii) a .et~ull n -~_ sheding that employs the hydrophilic polymeric artide as a surface covering.
~c~R~7r~rn OF Tr~r~ INVF.7YTrON
Hydrophilic polymeric articles have been used as water-spreading materials. The hydrophilic nature of the pûlyrner causes water droplets to spread out over the surface of the polymer as a thin lsyer. This water-spreading property can be very important in certain instances, particularly on atraffic sign that employs a cllul.,nvvt;._ sheeting.
RvLlulcnv`vLive sheetings have the ability to return a substantial portion of incident light in the direction frûm which the light originated. This unique ability has made le~lul~n .v sheetings ,' on traffic signs. At nighttime, light from motor vehicle headGghts is IcLlule~cvti,~ by the sheeting to display r - on the sign to motor vehicle drivers.
Frequently, light i to and from a lc11ulcnvvL;ve sheeting is impaired by l~.cv;~J;LaL;u... A prominent form of IJIcv;~,;LaL;u.. that affects light - is dew formation, which can be particularly ~ ' ' because it occurs ~ at nighttime when the .e~.ul,n ~v sheetings are 25 operative. When dew is present on a traffic sign in the form of small beaded water droplets, the path of incident and ~cL~ul~n ' light can become rj~ / altered. This can make; r - on the sign much more difficult for passing motorists to read. In contrast, when the small water droplets spread out over the surface of the ~cLI~/lcnvvtl~v traffic sign, the 30 r on the sign is easier to read because the resulting thin layer of I

w0 95/32237 ~ i 8 ~ ~ ~ 3 water does not disturb the path of the incident and It;LIu~ light to as great an extent.
To improve the I " of Idlu.~ .t;.~, traffic signs under dew conditions, ~ , have developed hydrophilic surface coatings for s Idlu cil~l;vc sheetings which allow water to spread out over the surface ofthe trsfhc sign. In United States Patents 5,073,404, 4,844,976, and 4,755,425, for instance, T. Huang discloses a letlul~u~,Livc sheeting that has a transparent coating comprising colloidal silica and a polymer selected from aliphatic pUI). ~ ul~ J ~ , and acrylic polymers. The colloidal silica is disposed in the polymer at about 10 to 80 weight percent (10to 70 weight percent in the case of ~ ' ). The transparent coatings provide superior dew repellency, allowing the IcLlulcn~livc sheeting to retain a higher percentage of its original brightness Rer being exposed to such moisture.
A nunlber of other documents have disclosed hydrophilic materials; see, for example, U.S. Patents 4,906,379, 4,S76,864, 4,536,420, 4,478,909, and 4,409,285; U.K. Patent Application GB 2,249,041 A; arld Japanese Patent Kokai H341402. The disclosures of each of these documents are brie'dy described below.
U.S. Patent 4,906,379 to Hodgins et al. discloses a hydrophilic article that comprises a matrix containing molecules of a nitrile-containing polymer.
Solely on the surface of the matrix, the polymer provides sufficient, uncharged,substituted alnide groups to render the surface hydrophilic.
U.S. Patent 4,576,864 to Krautter et al. &scloses a water-spreading layer that is composed of colloid particles of metal or silicon oxide. The water-spreading layer is adhered to a plastic base by an adhesive comprising a non-water-soluble, organic solvent soluble and essentially non-swellable polar group containing poly ner.
U.S. Patent 4,536,420 to Rickert discloses a coating ~ ~I"J'';""
comprising a clear water-bome carboxylic acid functional polymer blended with an aqueous colloidal dispersion of a surface b, J. u~l~ic~ silica. The carboxylic - ~88~1~
R. ~ She~t acid functional polymer may be an acrylic resin. The ~ produces a film when applied to a surface, and when hardened or curcd, provides discrete canals in the film which tend to break up the water droplets and facilitate drainage of water from the surface.
U.S. Patent 4,478,909 to Taniguchi et al. (cu~l~ r 1 to EP-A
0051405Al) discloses an anti-fog8ing fLim compri5ing pul~Yh~r' ' ' l, f~nely divided silica, an organic silicon compound and a ;~ ul~ thereo The anti-fogging film is in the form of a cured film coated on a substrate, where the uallJu~ weight ratio of the surface layer of the fiim is larger than that of the entire coating film and is not less than 1.7/1Ø
U.S. Patent 4,409,285 to Swerdlow discloses a surfac~ g coating ~ for reducing surface misting. The coating cul..pu~;~iù.l comprises an inorganic particulate component having an average particle size in the range of 7 to 50 ,.~ , another inorganic particulate component having an average particle size in the range of 75 to 150 ~ , polymer binder, and a volatile liquid medium. The inorganic particulate may be colloidal silica and/or alumina particles.
U.K. Patent Application GB 2,249,041 A to the Imperial College of Science, Technology and Medicine discloses a mûdified ~ydlu~ ù~;c plastic surface which has been subjected to an oxidation treatment and carries on the treated surface a layer of colloidal particles of hydrous metal oxide. The hydrous metal oxide causes the treated surfacc when wetted with water to d~ ull~la~ ai;~ra~,~uly non-fogging ~)~,.~JIIIIOII~C without loss of optical ....
Japanese Patent Kokai H3-41402 to Mitsubishi Rayon KK discloses a L~ lJalci.L, anti-dew material which is ~llal~ tcl~ in that a porous layer of silicon oxide with a thickness of 3,000 angstroms to 10 ll~lu~ is formed on the surface of a Ll~l~a~ lL synthetic resin substrate. The silicon oxide layer has a preferred average grain diameter of below 2,000 angstroms. The porous silicon oxide layer can be formed by sputtering or ion ;

A~ cN~D S'. l~t~

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5~)MMA~YOF THEINVE~I10~
The present inYention~ provides a nev hydrophilic article that !' ' ' 1~ " y ~.. ~l~vl 1~ effects. In brief s=ary, the article of the mvention comprises a polymeric sheet having metal oxide S particles dispersed m a polymeric material. The polymeric sheet has a first major surface and an interior, and on the first major surface of the polymeric sheet there is a higher ratio of metal to carbon atoms relative to the interior thereo The present invention also provides a new method of making an article 10 having improved water-spreading effects. The method comprises: providing a polymeric sheet that has a first major surface and comprises 5 to 90 weight percent metal oxide particles in a polymeric binder; and treating the first rnajor surface of the sheet so as to remove polymeric binder therefrom to increase exposure of the metal oxide particles. The method of the invention may be 15 utihzed in providing improved water-spreading 1~, r to the known hydrophilic ~ mentioned above which contain metal oxide particles dispersed in a polymer. Accordingly, the disclosures of the d,u._ di~vu, documents disclosing such are I~UI~ herein by reference.
The present invention also provides a new cL ul~vvL;~ article, which 20 comprises: (a) a IcLlul~ sheeting having first and second major surfaces;
arld (b) a transparent water-spreading layer disposed on the first major surfaceof the Iclluleil_..~ive sheeting. The transparent water-spreading layer has first and second major surfaces and an mterior and comprises a polymeric material that has metal oxide particles dispersed therein. The first major surface of the25 water-spreading layer represents the exposed surface of the ~cl~u--,n~Lin;
article and possesses a higher ratio of metal to carbon atoms relative to the mterior of the water-spreadmg layer. The second major surface of the water-spreading layer is juxtaposed against the first major surface of the .eL.u.,,L_,Livc sheeting.
30 The present invention is an . u._.. _.li over known hydrophilic materials. In the articles amd method of the invention, a polymeric sheet is W095132237 ~ 4 ~
provided thst has 8 higher rstio of metal to carbon atoms on a first major surface of the sheet relative to its interior It has been discovered in this invention that improved water-spreading capabilities are schieved when the metal to carbon atom ratio is increased on the exposed surfsce of the polymeric sheet. In view of the msny dangers that are present on the highway, it is very important from a safety standpoint that trs~ic signs are easy to read by motor vehicle drivers under sii conditions, especiaUy at nighttime when dew conditions are prevalent. The . ~ " e advantage provided by applicants' discovery enables .eL. " ._ ~highway signs to perform better under dew conditions, making the roads safer for motor vehicle drivers and others.
The sbove and other advantages of the invention are more fuiiy shown and described in the drawings and detailed description of this invention, where like reference numerals are used to represent similar parts. It is to be , ' - d, however, that the description snd drawings are for the purposes of iiiustration only and should not be read in a manner that would unduly limit thescope of this invention.
ARlFF~;Jh.~ (.)~ OF ~h--PRA W7NG~
FIG 1 is a cross-section of a lcl.o.~,Li_~,i;vc article 10 m accordance with the present invention.
F~G. 2 is a cross-section of a hydrophiiic polytneric articie 20 in accordance with the present invention.
E~G. 3 is a I ' " . ' of a . ~ hydrophiiic polymeric sheet 30 magnified 100,000 times to iiiustrate metai oxide particles 34 in a polymeric binder 36.
F~G. 4 is a photograph of a hydrophilic polymeric sheet 32 in accordance with the present invention magnified 100,000 times to iiiustrate metai oxide particles 34 in a polymeric bmder 36.

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In describing the preferre; ' ' of the invention, specific ' ~,, is used for the sako of clarity. The invention, however, is not intended to be limited to the specific terms so selected, and it is to be understood that each term so selected includes all the technical equivalents that operate similarly.
In the practice of the present invention, a hydrophilic polymeric article is provided that ~ good water-spreading capabilities making the article particularly useful as a surface covering for a ~ lu~ ive highway sig,n. In reference to this invention, the term "hJd~ means the polymeric article has an affnity for water which tends to cause the water droplets to spread out over the surface of the article. The hydrophilic polymeric article contains metal oxide particles dispersed in a polymeric binder material. The metal element of the metal oxide may be a Group 2-14 metal (using the new T ' " ' Union of Pure and Applied Chemistry (IUPAC) notation issued by the C~ of ~ ' c; of Inorganic Chemistry in 198~). The metal oxide particles can be, for example, an oxide of one or more of the following metals: aluminurn, silicon, tin, 2inc, titanium, vanadium, zirconium, and chromium. As iUustrated by the previous sentence, the term "metal" is used herein to include metalloids such as silicon. It also is to be understood that the term metal oxide includes surface modified metal oxides such as silica particles treated with a silane coupGng agent. Oxides of aluminum and silicon are the more preferred metal oxides, particularly siGcon dioxide, SiO2, and aluminum oxide, Al203. The metal oxide particles typicaUy have si2es of about 0.001 to 100 1 , , preferably 0.002 to 10 l.G.,l~ , and more preferably 0.005 to 0.08 U~ (5 to 80 nanometers (nm)). GeneraDy, smaller particles are preferred for purposes of obtaining better i . ~..~ in resulting article; however, large colloidal silica particles may be blended with6mall siGca particles in the water-spreading polymeric layer to produce a 30 transparent polymeric film. The metal oxide particles preferably are uniformly dispersed throughout the polymeric sheet at about 5 to 90 weight percent, W095/32237 ~ r~
more preferably at about 30 to 85 weight percent, and even more preferably at about 40 to 80 weight percent, based on the weight of the dried polymeric sheet.
The metal oxide particles can be obtained in the form of a colloidal 5 dispersion, such as: a colloidal silica dispersion marketed as NyacollM 1440 colloidal silica, having a size of about 14 nm and a, of 40 weight percent silica, available from Nyacol Products, Inc., Ashland, Maryland;
` NalcolM 1140 silica, having a silica patticle size of about 15 mm and a ;... of 40 weight percent silica in water, available from Nalco Chemical Company, Oakbrook, Illinois; NalcolM TX2146 colloidal tin oxide dispersion; and Nalco~ 88SN-126 colloidal titanium oxide dispersion. The NyacolTU and Nalco~M colloidal metal oxide dispersions mentioned above are suspended in an alkaline aqueous media. Other . . "~v available metal oxide dispersions use other solvents such as a glycol ether solvent. For example, Nalco Chemical Company sells Nalco~ 84SS-258 which has a silica particle size of about 20 nm and which can be used with polylner resins dissolved in organic solvents. Colloidal silica stabilized in an ammonium oxide aqueous media also may be used to prepare a water-spreading polymeric layer.
Examples of such colloidal silica include: NalcoTM 2327 having average silica particle size of 20 nm; Nalco~M 2326 having average silica particle size of 5 nm;
and Ludox ~ AS having particle size of 22 mn, available from E.I. Dupont de Nemours, ~ , Delaware. Colloidal silica may be surface modified with other metal oxides such as aluminum oxide to improve the dispersion stability. An example of surface modified colloidal silica includes Ludox~U AM
from ~.I. Dupont de Nemours. Organic compound modified colloidal silica also may be useful for preparing a hydrophilic polymeric sheet. Acrylate, amino, hydroxy, and mercapto, and glycidoxy functional organic compound modified colloidal silica can be prepared according to the procedure described by Larry N. Lewis and Dimitris K ' in Journal of Applied Polymer Science, v. 42, pp. 1551-1556 (1991) and in U.S. Patents 4,885,332 and 5,104,929 issued to 2:. Bilkadi. Examples of ~ "~v organic compound wo 95m237 ~ 41~ r ~ 7C
modi~ied coiioiW dispersions include HighlinlclM OG-4, OG-8, OG-100, and OG512, ava;iable from Hoechst Cdanese Co., Somerviiie, New Jersey.
Examples of coiioidai siiica dispersions contair~ing large coiioidai siiica particles (which may be used in ~ with srnalier siiica particles) include:
Nyacol~M 5050 having particle size of 50 nm~ avaiiable from Nyacol Products Inc.; and Naico~M 1060 and 2329 having particle sizes of 60 nm arld 80 nm, ..,.."~,.,l; . _1~ .
The metai oxide particles rnay be dispersed in, for example, the polymeric materiais described in U.S. Patents 5,073,404; 4,844,976; and 4,755,425. Thus, the areicle may contain a transparent polymer selected from the group consisting of: aiiphatic pcl~ ' pGI~ ' ' ' ' ' copolymers having a minor portion (iess than 15 weight percent) of a containing at ieast one carboxyiic acid or hydroxyl moiety; and acrylic polymershaving a giass transition . ~ (T~) of about -20 C eo 60 C, preferably less than 45 C, wherein the siiica comprises about 10 to 80 weight percent (10-70 weight percent in the case of acryiic polymers) of the transparent polymeric article. As used herein, the term "i , ~ t" means " at least 80 percent of incident iight in the visible spectrum (about 400 to 700 nanometers (nm) ~ h); more preferably the sheet transmits 90% of the 20 visible iight. T , ~,~ can be determirled using an IBM model 9420 W-visible *~ ' ' . The polymeric materiai generaily comprises 5 to 85 weight percent of the polymeric sheet preferably 15 to 50 weight percent, and even more preferably 20 to 40 weight percent, based on the weight of the dried polymeric sheet. The mixtures used to form hydrophiiic polymeric articles can be formulated by mixing various ' ' of metai oxide sol (aquasoi, hydrosol or colloidai dispersion) with the polymer (for example, an aiiphatic pu~u.~'' , an acryiic polymer, or a polyvinyl chioride copolymer) in an organic solvent or in an aqueous solution The term aiiphatic POIJU~ ' means a PC~ derived from at least one aliphatic pc.~ o_, ~, preferably without any aromatic pul~;~ Aiiphatic pu!~;.. u, that may be useful in forming the w0 95/32237 2 ~ 8 8 ~
aliphatic ~ ' include: 1,4 ."~ bis( !'' J~ ,,. ', 1,6 :' , -2,2,4,1; ~ ,"
1,6-hexane !'-' , ', 1,6 :' , -2,4,4-i ~" and 5 isophorone ' , _ The polyols used to form aliphatic ~ul~. ~ ' may be polyester or polyether polyols.
When the hydrophilic polymeric article is used on a cLlulcn~,t~._ shwtin6 the raw materials selected for making the polymeric articles of the invention should not adversely affect the .ehul~wLiv~ F f( of the 10 underlying IC~IUI~ " '-.~, sheeting. For example, the raw materials should not require drying conditions ~vhich would distort the sheeting and affect the optical .~' ', necessary to achieving good ~cL~u.ell~ . The raw materials desirably do not contain solvents or other ingredients which would dissolve or corrode underlying .cl.u..n~ , sheeting ~ . Coating 15 mixtures contairling toluene, iau~ and butyl cellosolve have bcen found to be suitable for use in applying the hydrophilic poly~neric article to a ctlu.~.iive sheeting.
The polymer mixed with the metal oxide sol preferably is somewhat elastic, especially in cases where the Icllulcllwlive sheeting is to be applied to 20 a ~exible substrate. Several of the polymers which have been found to be useful are set forth below (all monomer percents being expressed jn weight percent):
Aliphatic rul~
NeoRez~M R-960 and R-963 ru~ ' , f~exible p~ ' sold 25 in an ~ '.y 30-35 percent by weight in water by Zenwa Resins, U"' ~ ~' -' This pGI~ c'' is believed to be derived from d;VJI' ~ d '' d;;.~u~ ', and its molecular weight is believed to be at least 200,000 grarns per mole. Other aliphatic l,ul~ ~ ' dispersions include Sancure~M 774, 847, 899, and A-1364, available from 30 Sancor Chemical Co., Leominster, r ~ ~
g wo 95/32237 2 ~ 8 ~ 7<;
r~U-6729 urethane re!lin sold in a 1:1 mixture of i~,u~
and toluene at a of 25% resin by r. Coatings, Peabody, ?~ ' Tilis resin is beGeved to be derived from the foiiowing monomers: d ~ ' , , adipic acid; neopentyl giycol;
5 and 1,6 1 ' ' It is beGeved to have a weight average molecular weigbt ~w) of about 33,000 grams per mole and a number average molecular weight (Mn) of about 11,000 grams per mole. r, U-23-327 urethane resin sold in a 1:1 mixture of , . ' and toluene or methyl ceGosolve at a of about 35% resin.
Polyvinyl chioride C~".. JI~.. _.~.
VROH copolymer, believed to have the foiiowing monomer content:
vinyl ci~ioride (79-83%), vinyl acetate (5%), and vinyl aicohol (15%). It is beGeved to have 1.8 to 2.2 weight percent hydroxyl content.
VMCH copolymer beGeved to have the following monomer content:
vinyl chioride (85-88%), maieic acid (0.8-1.2%) and vinyl acetate (about 13%).
In Geu of maieic acid, acryGc and methacrylic acids may be r ' ~ into the useful polyvinyl chioride ~u~vl) VAGH partiaily hydrolyzed copolymer beGeved to have the following monomer content: vinyl chioride (89.5-91.5%), vinyl acetate (3%) and vinyl 20 aicohol (5.2-6.5%). VROEI, VMCH and VAGH copolymers are avaiiable from Union Carbide Corporation. When using the poiyvinyl ci1ioride transparent polymers, they are normaily furnished dissolved in an organic solvent (for example, 10 weight percent in methyl ethyl ketone). In this case, siGca may be furrlished in an organic medium, for example, a NaicorM 84SS-258 coiioidai 25 SiO2 dispersion in glycol ether.
Acrylic Polymers:
NeoCryi~ A601 polymer, NeoCryl'M A612 polymer, and NeoCryi~M
A614 polymer, ali available from Zeneca Resins in water emuision form. These polymers are beGeved to be copolymers of methyl ' ~' and butyl ' ~' having a weight ratio of methyl ' yl.. i~; units to butyl W0951~2237 ~8~
' ~' urlits in the polymer in the range of 0.25-0.6. The ratio for the tbree named polymers are believed to be as shown below:
NeoCryl~U A601 0.33 NeoCrylTM A612 0.43 NeoCryllM A614 0.47 The molecular weights of the polymers typically is: Mw in the range of 300,000-350,000 grams per mole and Mn in the range of 50,000-70,000 grams per mole. The following molecular weights have been determined through analyses of two of the NeoCryl~f polymers.

Mn NeoCryllMA612 323,000 60,000 NeoCrylTM A614 304,000 54,000 These emulsions are believed to have a pH similar to that of the silica sols with which they are used. These emulsions are believed to be ~ by: 32 weight percent sobds, pH of 7.7-8.0, viscosity at 25 C of 100-200 centipoise, and specific gravity of 1Ø They are also believed to contain aniorlic surfactants and some organic solvents (11-14 weight percent) said by the ~ e. to be coalescing solvents, as follows:

~ ~88 4~ 3 ~", f601 ~ A61~ ~: A614 aromatic napthta 4.8% 4.3% 3.7%

2 ! ~ 1.3% 1.1%
2{2-~ ua~_~h.Ja~ ' ' - 2.2% 1.9%
2~ r ~ 5 0% 4.3%
ethylene glycol - 1.0% 0.8%
diacetone alcohol 7.9%
Coalescing solvents have an afiinity for the polymer and water and a higher 5 boiling point than water, at . ' pressure.
The NeoCrylnd acrylic polymers can be blended with the NeoRez~M
pu~ ' to form a clear coating with colloidal silica. Such blends (for example, a 2:1 weight ratio of acrylate to pGI~ '' ) have been found to have excellent i . ._..~, fiexibility, and adhesion.
Copolymers of acrylic and aliphatic pol~ ' also may be used to form a hydrophilic polymeric article. Examples of the copolymers may be NeoPacT~ R-9000, R-7061, and R-9030 available from Zeneca Resins.
, copolymers also can be used; examples include: poly(ethylene-co-(meth)acrylic acid), such as AdcotelM 7R4, 50C12, and 50C35, available from 15 Morton T ' Inc., Chicago, Illinois; poly(ethylene-co-acrylic acid);
poly(ethylene-co. .,' ); ionomeric ethylene copolymers such as Surlynn'f 1705, 8940, and 9970 available from E.I. Dupont de NeMours.
When the waterborne resins are used such as NeoRezTM resins or Sancure~U resins of aliphatic pul~. ' , NeoCrylTM resins Of pcl~
20 NeoPac~ resins of copolymer of acrylate and aliphatic urethane, AdcotelM
resins of poly(ethylene-co-( b~ acid), it has been found useful to include a l--r " 7 aziridine ~,, " ' ~ compoun~ such as CX-100 cross-bnker (from Zeneca Resins), a ' ~ ' ' compound such as cross-linker X~29SE (from Union Carbide Co., Danbury, wo95~3223~ 2~8~1~ Y
C~ t), a melamine curing ag,ent, or epoxy curing agent, to improve the physicai properties of the finai coating.
A reactive resin system aiso can be used with . ~ S ~-group-modified coiioidai siiica to form a hydrophiiic polymeric layer. The polymeric 5 precursors can be uvl~ ' by exposure to actinic radiation, for examplc, dectron beam, ultraviolet iight, or visible iight. ~ , these materiais may be ~ ' by thermai means with the addition of a thermai initiator such as benzoyl peroxide. Radiation initiated cationicaliy p~ ' ' resins aiso may be used. Reactive resins suitable for forming the water-spreading 10 polyrneric layer may be blends of at least one compound bearing an acrylate group, a metai oxide, and a I ' . Preferably, the resin biend contains !'-" '- ' or pu~ ...L;u.~dl compound to ensure the formation of a crossiinked polymeric network upon irradiation.
Examples of resins that are capable of being i,~,l) ' by a free radicai meci~lanism include acrylic based resins derived from epoxies, polyesters, polyethers and urethanes, ~:Lh.~' "~, ' ~ , '.
aminoplast derivatives having at least one pendant acrylate group, isocyanate derivatives having at ieast one pendant acrylate group, epoxy resins other than acrylated epoxies, and mixtures and ' thereo The term acrylate is 2û used in here to encompass both acrylates and ' ~' ELi~,' "~ I ' resins include both monomeric and polymerjc compounds that contain atoms of carbon, hydrogen and oxygen, and optionaiiy rlitrogen, suifur and the haiogens. Oxygen or nitrogen atoms or both are generaily present in ether, ester, urethane, amide and urea groups.
EL~ , ' compounds preferably ilave a molecuiar weight of less than about 4,000 and preferably are esters made from the reaction of ' containing aiiphatic . ', ' u~ groups or aiiphatic l.ul~.,.' u~
groups and I ' carboxyiic acids, such as acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maieic acid, and the iike.
Examples of compounds having an acryiic or methacryiic groups are iisted below.

W0 95/32237 21 g X ~1~ r~
clh~' ~', n-l-ul~ ', 2-~ " yla~
n ~ ' , n-G~ ' , isobornyl acrylate,; ,,-, r r yl acrylate, 2~ ,Ih,: acrylate, N,~ ." ~' J' ' ~, (2) n r 1,4-butanediol diaclylate, 1,6 ' " ' diacrylate, . , ~ ul diacrylate, cthylene glycol diacrylate, IlU,lh,' ~ .1 diacrylate, t~ ~l}.,k,..~, glycol diacrylate;

(3) Pul~ .
' ~!ùl~ . triacrylate, ~ L~c~ t~.,.ylluilul triacrylate, ,yi ' ~ t~,llnA,.I~ , and tris(2 ~_lyluJIuA~Llyl)i~
Some lqJl~ examples of other e~
compounds and resms include styrene, ~i~ yl' .,~ ., vinyl toluene, N-vinyl ~., ..~ ' ' , N-vinyl ~ ' , monoallyl, polyallyl, and ~,ol~ 1 esters 15 such as diallyl phthalate, diallyl adipate, and atnides of carboxylic acids N,N :" "~' lil ' Examples of I ' r ~ i~L~ initiators which can be blended with the acrylic compounds include the following illustrative initiators: benzil, methyl o-benzoate, benzoin, benzoin ethyl ether, benzom isopropyl ether, 20 benzoin isobutyl ether, et cetera, L . ' 't~ y amine" .' such as 2,2 d;~lllu~_ .' , benzil methyl ketal, 1 ~J.II~ U~ .Ayl phenyl ketone, 2-hydroxy-2-methyl-1-1' ,!pl,r l-one, 1-(4-iau~ yl)-2-hydroxy-2 ' ,!~ r l-one, et cetera. These compounds may be used individuaUy or in Cationically p~l~ '' materials include but are not limited to materials containing epoxy and vinyl ethers functional groups. These systems can be i ' I by onium salt initiators such as ~ ' r , and Ji~" ' salts.
Other compounds that may be ~.u.~lc~ into the polymeric . . of this invention include surfactants, ultraviolet ~[lV) light stabilrzers, W absorbers, curing agents, coupling agents, et cetera. The W0 95/3~237 2 ~ 3 ~ ?C
surfactant may be a pul~ " ,!~,..~, oxide modified pclj ' ' ,' ' sold under the trademark S~WET by Union Carbide Cl . W light stabiiizers or absorbers may be employed to improve the stability and ~. ' ' "~ of the protective coating. One suitable W Gght absorber is Uvinui~M N-539 from GAF, New York, New York. Uvinul~ N-539 (2-ethylhexyl-2-cyano-3,3-diphenyl acrylate) has been used as a W absorber in aGphatic pG4_ ~'' polymers. Tinuvin~ 292, 328, and 1130, (from Ciba-Geigy Corporation of Ardsley, New York) also may be used as general purpose W absorbers. CoupGng agents such as siianes, acrylato chromic 0 ----T ', and orOanic titanates may be ~., ' into the polymeric .- to produce a strong chemical bond between the metal oxide particles and the polymeric binder. Examples of silane compounds include '` ' silanes such as O , u~ u~ ' snd N-bet~: hyl O - . u~ . ' , mercapto-functional silanes such as ~ w~u~u~ ' , glycidoxy "
silanes such as ~ 61~ _;JU~I Ul~J~ , and beta-3,1 ~u~y~.' ' yl-elh.~ , and Ucarsil~M AF-1 (from Union Carbide Corp., Danbury, C~ ). An example of an acrylato chromic compound is Volan~ (from Zaclon-Dupont, Cleveland, Ohio).
Examples of organic titanates are TyzorT~ AA, LA, and TE, (avail~ble from E.I. Dupont de Nemours). The ranges for the minor ingredients in the ~ ... that forms the polymeric sheet may be: 0 to 3 weight percent for the surfactant; I to 6 weight percent for the W stabiiizer; 1 to 6 weight percent for the W absorber; 1 to 4 weight percent for the curing agent;
and 2 to 6 weight percent for the coupling agent.
The polymeric article of the invention may be used in sheet form as a surface coating dGsposed on the first or front surface of a ~L-u.~
sheeting to provide a hydrophilic .~.u.~ article that .l good water spreading capabiGties. The polymeric sheet or layer in generai is a fiim having a thickness of about 0.1 to 100 , , preferably 0.2 to 15 , and more preferably 0 3 to 5 1111~ A v:~iety of wo95/32237 ~g ~ 3 r ~ c ,.~ ~
UlCA ._ shedings have bcen disclosed in the art, and this invention may be uscful as a surface covering on essentially any .c~..,.~ '- ._ sheeting.
A IcLIul~[i__L;._ sheding typicaiiy comprises a reflective materiai and opticai elements. The reflective '.,~ D to reflect mcident iight, and the 5 opticai eiements serve to redirect thè mciderlt Gght towards the iight source.T_e reflective materiai often comprises a specuiar mdai reflector such as an aiuminum or silver-containing iayer (see, for example, U.S. Patent 5,283,101) or a didectric reflector (see, for example, U.S. Paterlts 3,700,305 and 4,763,985) but aiso may comprise a diffuse refiector such as a heavy mdai 10 pigment(s). The opticai elements typicaily come in one of two forms: beaded lens elements and cube corner elements. Examples of lCL.u~ _ sheetmg that employ beaded lens eiements have been disclosed in U.S. Patents 2,407,680, 3,190,178, 4,025,159, 4,896,943, 5,064,272, and 5,066,099.
Examples of d~ i__L;vc sheeting that employ cube corner elements have been disclosed in U.S. Patents 3,684,348, 4,801,193, 4,895,428, 4,938,563, and 5,272,562. The disclosures of the patents cited in this paragraph are ~u-~LcJ here by reference.
As shown in FIG. 1, a water-spreading polymeric layer 12 of the irlverltion may be juxtaposed on the first or front major surface 14 of a 20 lcL-u.cnc_L;ve sheeting 16. The first or front surface is the surface of the eilule~i~L;ve sheding through which incident Gght passes so as to be .LIulc~i~L~,~i by the sheding. When juxtaposed in such a position, incident iight must pass through the polymeric layer 12 in order to pass through the opticai elements (nût shown) and be reflected by the reflective materiai (not 25 shown) in the ICLlu~ '` ._ shed 16. Typicai front surfaces fûr .cL u,~i__L;._ sheetmgs are comprised of pol~ - (for example, pGI~ ..._L~., ' ~ ), copolymers of dhylene and acryiic acid units (see, for example, U.S. Patent 5,064,272), pul~ (typicaily aiiphatic p~ - ), pGI~. ,- - ', or pcl~ The polymeric iayer 12 may be secured to the front surface 30 14 by use of an adhesive (not shown). In a distinctly different ~ l ' t, however, the front surface can be primed to make it receptive to the polymeric w095/32237 ~1~8~1~ r~ !4"~
layer. The prirAing step may include corona treating the front surface 14 of the.e~lU..n ._ article, and this can permit the polymeric layer 12 to be secured thereto without an adhesive.
A leLIu ~ll~L;ve sheeting of this invention may be prepared by the 5 foDowing steps:
A) Preparing a dispersion by miA~ing coDoidal metal oxide with a selected polymer, such as a ~ol). ~ ' ~" and any other desired ingredients, such as light stabili~er or .,.u..~ agent;
B) Providing a ,eL.u.GA '.~ sheeting and prir.Aing the front surface of 10 the sheeting by a corona treatment or other suitable means;
C) CoatiAg the dispersion onto the front sur~ace of the .~:~ ul~nu_Liv~
sheeting as a layer by any suitable means, such as a wire wound bar coating, kAife coatirlg, roll coatin6 or dip coating;
D) Drying the wet coating from step C and curing it by p]acing the 15 It:LI Ul ~ ;._ film in an oven or otber suitable curing apparatus; and E) Treating the cured polymeric layer to remove polymeric binder from the exposed surface of the coating to increase the exposure of the metal oxide particles.
In some ' ' the water-spreading polymeric layer may be 20bonded directly to a IGL-u~ ,Liv~ sheetin6 for eAample, when the front surface possesses a pGI~ , " , however, for a .~i~.ul.ll__li._ sheeting with a ~ul~ ' front surface, it has been found desirable to pretreat the front sur~ace of the sheeting with a corona treatment to achieve a good bond between the sheeting and the water-spreading polymeric layer. A
25 general discussion of corona treatment of webs may be found in RH. CrarAm and D.V. Bibee, The Theo~y and Practice of Corona Treaf~nentfor Improvtng ~dhesion, TArPI, pp. 75-78 (Aug., 1982). The apparatus used in such corona treatment has been a Softal-Electric Company machine from West Germany, Model 3û25DW, having 1.2 kilowatt (Kw) maximum power and electrode 0.56 30 meters (m) long. The front surface of the ~ ult;l]~_Liv~ sheeting has been treated using a current of 180 to 300 milliamps and drawing the sheeting ~8~
through the apparatus at a rate of 10 to 100 meters per minute for a sheet about 0.3 meters wide. A typical treatment levd is about 0.3 to 1.5 joules per square centimeter a/cm2).
The conditions for step D are generally about 50 to 100 ~C for 1 to 10 S minutes in an air atmosphere. Generally, a .~CtlU.~ iV~ sheeting having a p~ ' front surface can withstand somewhat higher: , ~,.., and a curing condition of 93 C for 2 to 3 minutes is ay~ ' In the case of p~ ' front surfaces, however, conditions are preferably about 65 to 75 C for 3 to 10 minutes.
Sometime before or after securing the water-spreading polymeric layer to the front surface of the ICL~u~ ivc sheeting, the former is treated to remove polymeric binder from the first or exposed major surface 18 of polymeric layer 12. The "exposed major surface" is the major surface of the polymeric layer 12 which is not juxtaposed against the first or front surface 1415 of the Ic:LIul~ sheeting 16. The language "juxtaposed against" is not to be interpreted in a manner that means the second or lw.. eA~u.._d surface 19 of the polymeric layer 12 must be in contact with the ,c~,u,c, _~;._ sheeting 16.
There may be other layers, for example, prime layers, adhesive layers, clear topfilms, et cetera, between the two surfaces. Thus, the language merely means 2û the front surface 14 of the lc~lulcnu_~ive sheeting 16 faces the cA~Ju~cJ
major surface 19 of the water-spreading polymeric film 12 in some kind of secured ~ ~ The water-spreading polymeric layer may be first applied to a top fihn, treated to remove polymeric binder, amd then secured to the .c;~,u,~ ivc sheeting on the top film. In this situation, it is considered that 25 the water-spreading layer is disposed on and juxtaposed against the ulcn__~ivc sheeting.
There are a variety of ways of treating the exposed major surface of the water-spreading polymeric layer in accordance with the present invention. The eAposed major surface may be corona treated, oxygen plasma treated, 30 chemically treated such as with a solution or chemical etchant, ozone treated, or an excimer laser treated. Regardless of the particular method chosen, what wo95/32237 ~1~g 4~3 Y
is important is that the polymeric binder be removed from the exposed majorsurface to increase exposure of the rnehl oxide particles so that there is a higher ratio of metal to carbon atoms on the exposed major surface relative to the interior thereof. As the temm is used herein, "interior" means tbat portion of 5 the polymeric layer that is moj re than 50 nanometers below the top of the first or exposed rnajor surface of the water-spreading polymeric layer. Preferably, the exposed major surface has a metal to carbon atom ratio of at least 0.01, more preferably 0.3 to 3, and even more preferably of 0.4 to 1.5. The exposed major surface of the polymeric article generally has at least about a 20 percent10 higher ratio of metal to carbon atoms relative to the interior, preferably at least about a 30 percent higher ratio. More preferably, the exposed major surface has a metal to carbon ratio that is at least 45 percent higher than that of the interior. In some ~ ' - ' the metal to carbon atom ratio may be 100 percent higher than the interior and may be as much as 400 percent higher.
When air corona treatment is used to remove polymeric binder from the exposed surface, the energy level generally is at least I j/cm2, and typicaUy isabout 2 to 20 j/cm2. If the exposed major surface is subject to a single air corona treatment, the energy level preferably is about 7 to 12 j/cmZ; whereas ifthe exposed major surface is multiply treated, the energy level is about 3 to 5 20 j/cm2 for each pass. OveraD, it is preferred that the exposed major surface be subject to a total ~ 5 to 15 j/cmZ of energy, preferably by two .,u..~__uL;~, air corona treatments.
Although the hydrophilic polymeric article of the invention has been iDustrated as a surface covering for a ~ u~,[l~l;~e sheeting, there are a 25 variety of other surfaces onto which the article of the invention may be used.
For example, the hydrophilic polymeric attide may be disposed on a glass or plastic window (for example, in a ~ ), a mirror, eyeglass lenses, goggles, et cetera.
In ~IG. 2 there is shown an article 20 that can be applied to any of the 30 substrates mentioned above. Article 20 includes a polymeric water-spreading layer 22, a transparent plastic layer 24, an adhesive 26, a release liner 27, and a W095,3223~ 13 protective sheet 28. The water-spreading layer 22 may be the hydrophiiic polymeric uticle of the invention described above. The transparent plastic layer 24 can be, for example, a iayer of an acryiic poiymer ilaving a thicicness of about 10 to 250 ~ The acryiic layer may be biaxiaily oriented and may contain W iight absorbGrs and stabiiizers. The adhesive 26 is disposed on the backside of the transparent plastic lay 24. The adhesive 26 preferably is apressure-sensitive adhesive and may comprise acryiic ,u~,ul~ The adhesive layer 26 preferably is transparent to visible Gght and has a thicicness of about 10 to 150 , A release iiner 27 may be disposed on the back sur~ace of the adhesive layer to protect the sarne until article 20 is intended to be adhered to a substrate (not shown). Sheet 28 can be disposed over the front surface of the polymeric water-spreading layer 22 to protect that layer untii article 20 is placed in use.
The invention is further iiiustrated by the followirlg Examples, which are intended to be purely exemplary. It is to be l ' -~i, however, that whiie the Examples serve this purpose, the particular ingredients and amounts used as weii as other conditions and detaiis are not to be construed in a mannerthat would unduly iimit the scope of this invention. In the Examples, of the protective coating . in the water-spreading iayer are expressed as weight percent, taicing the totai of the metai oxide particles and polymer and additives as 100 weight percent.
~Mpr.F,.
_arni~le I
This Example describes preparing an aqueous coating dispersion containing metai oxide puticles, coating the dGspersion on a plastic substrate, arld treating the dried coating to remove polymeric binder from the exposed surface.
To a stirring solution containing 102.78 gruns of NeoRez~ R-960 und 384 grams of water was added 17.66 grams of a W light stabiGzer, Tinuvin~M
292. After further stirring, 1170.82 grams of an acryGc waterborne polymer R~ h~e~,8t 8 ~ ~ 3 ~ -resin NeoCryl~M A-614 was added to the mixture Tinuvinn~ 1130 (27.32 grams), another W light stabilizer, was added to the stirring mixture. To the NeoRezlM/NeoCryl~ mixture was added 1056 gr4ms of Nalco~M 1140 colloidal silica dispersion. When the addition of the colloidal silica was completed, 835.58 grams of water was added to the stirring mixture. CX-100 (25.60 grams), a pOI1r ' aziridine crosslinker, was then added to the milky mixture. The mixture was stirred for about 5 minutes. The content of the dispersion is ~ below in Table 1.
The dispersion waS coated on a surface of a S~ '" ~ Electronic Cuttable Film Series 1170 (EC-Film) available from 3M, St. Paul, Minnesota.
The EC-Film was a poly...~ ' ' yl4~-based film which had a clear pressure sensitive adhesive and paper liner backing on one side. Prior to the coating of the dispersion, the EC-F~m was pre-treated with an air corona at a poweF of abo~t 1.25 joulelcm2. The dispersion was coated on the EC-Film by means of a Gravure coater with a 100 line stylus having ce31 volume of 14.2 billion cubic ~ .IUII~.CI:~ per square inch. The coated EC-Film W45 dried and cured by passing the filrn through a series of forced air ovens wilh ~tlllr~A 4~UI~:
control in oven 1 at 43 C and in ovens 2 to 5 at 88 C. Total length of the series of ovens was 41.15 meters (135 feet), and the web speed was controlled at 15.24 meters (50 feet) per minute.
Dried samples of the coating on EC-Flm were then treated on their exposed major surface with a high energy air corona discharge at power levels ~f 0, 2.8, 8.3, 11.1 joules/cm2 using a Sherman corona treating unit (Sherman Tr_aters, Ltd., United Kingdom) in the bare ground role ~OIILi~.U14LiUII. The identi~ying sample numbers for each air corona treated sample in this Example are listed in Table 3 as Samples 1~ through lD.
A sample of the coating on EC-Film also was treated with an oxygen plasma The plasma instrument was configured with parallel plate electrodes at a gap of 3 centimeters wiith a plate dimension of 22.9 by 33 r.~rltim~r~rs The oxygen pressure was set to 200 millitorr at a net power of 300 watts. The time AME~iD'~ S~ET

wo g~ 2 ~ 8 ~
of exposure of the coating to the plasma was I minute. The identifying number for this sample is listed in Table 3 as Sample IE.
T' ~ .
2 ,: `
In this Example, the coatirlg dispersion was prepared similar to the procedure of Example 1, except a different coating apparatus was used and the amount of the , in the coating dispersion were as shown in Table I .
The dispersion was coated on an EC-Film that had been previously treated with an air corona at an energy level of about I joulelcm2. The dispersion was coated on the EC-Film by means of a wire wound coating bar (wire 0.914 mm diameter). The coated EC-Film was dried in a forced air oven at 82 C for about 10 minutes. Samples of the coating on the EC-Film were treated on their exposed major surface with high power air corona discharge post-treatment at power levels of 0, 2.8, 8.3, and 11.1 joule/cm2. The identifying sample rlumbers for this Example are listed in Table 3 as Samples 2A through 2D.
r ~ 3-5 These Examples also illustrate how to prepare products similar to but different from those of Example 1. Examples 3-5 were prepared according to the procedure of Example 1, except there were variations in the coating conditions, and the content and amount of the, . in the coating dispersion were modified as shown in Table 1. The dispersions were coated on an EC-Film that had been previously treated with an air corona. Variations of the coating conditions of Example 3-5 are listed below.

w0~2237 ~i 3~ 3 .~ c A~rCo~~ K~r~ gpe~d 3 1.5 100 40 4 1 . ~4 79 20 1.14 120 20 To dry and cure the coatings, the coated EC-Films were passed through aseries of forced air ovens that were , ~: controlled. In Example 3, 5 coated EC-Film was dried and cured with oven I at room t-,...~dtUlC and ovens 2 to 5 at 88 C. Total length of the series of ovens was 135 f~et. The coated EC-Films of Ex~unples 4 and 5 were dried and cured in another series cure ovens with oven I at room i . ~; and ovens 2 to 4 at 88 C. Total length of this series of ovens was 72 feet. Samples of the coated EC-Film 10 Ex~unples 3-5 were treated on their exposed major surface with high power aircorona discharge post-treatment at power levels of 0, 2.8, 8.3, and 11.1 joule/cm2. The identi~ing sample numbers for these Examples are listed in Table 3 as Samples 3A through 5D.

WO 95/3Z237 ~ ~ 8 ~
N æ ~ 0~ ~
5,~ 5~ o o oo S ~ ~ ,~, N N
5.~S,'~
S ~ ~ N ~ N ~`I
o N N
5:~.
,.~
5~5S~
O ~ o~ _ -- N C~ ~ ~
O_ ~ W0 95/32237 ~ 1 8 ~ . s Example 6 An aqueous coating dispersion containing colloidal tin oxide was nlade using the following mdhod: to a stirring solution of 5.9 grams of NeoRez~U
R-960 was added 1.0 grams of Timlvin~ 292 and 20 grams of water. To this mi%ure was added o4.8 grams of NeoCrylTU A-614 followed by 1.5 grams of Tinuvin~ 1130. To the stirring mixture was then added 109.3 grams of Nalco~s TX2146 colloidal tin oxide. The dispersion was diluted with 46.1 grams of water, and 1.4 grams of CX-I00 was added to the stirring mixture.
The ~ . of the .~ ' " is ' ' below in Table 2. The coating dispersion was coated to an EC-Film in a manner sin~ilar to Example 2.
The coated EC-Film was treated with an air corona discharge at 11.1 joule/cm2 using a Sherman corona discharge treating unit as described in Example 1. The sample numbers for this Example are identrfied below in Table 3 as Samples 6A and 6B.
Exam,ole 7 A coating dispersion using a titanium oxide colloidal dispersion was prepared according to Example 6, cept the content and amount of the were modified as shown below in Table 2 The coating dispersion was applied to an EC-Film in a manner similar to Example 6. The coating on the EC-Film was treated with an air corona discharge at a power of 11.1 joule/cm2 using a Sherman corona discharge treating unit as described in Example 6. The sample numbers for this Example are identified below in Table 3 as Samples 7A and 7B.

WO 95/32237 2 i ~ 8 ~ c ~
~_`'~' . ~
o, ~ ~ o ., ,x ~ D
p~
. .. p P

~P~

w0 9~32237 ~ ~ 8 8 ~ ~ ~
Table 3 Post-Treatment Conditions and Samples ':~P.. . .
` i'~t 46.8 IA lB IC ID IE
2 35.1 2A 2B 2C 2D
3 58.6 3A 3B 3C 3D
4 58.6 4A 4B 4C 4D
69.1 5A 5B 5C 5D

6 47.0 6A 6B

7 47.0 7A 7B
T.~Ct ~ thrl~c ~
The following tests and analyses were used to evaluate the metal oxide 5 containing polymeric sheets.
S~ E~
The atomic at the sutface of the colloidal metal oxide coatings was evaluated using X-ray ~ ' un a~ u~,o~Jy (XPS) before 10 and after post-treatment with air corona dischatge or oxygen plasma. A
Hewlett-Packatd 5950B X-ray j' ~ ' u.. ~c~,~.u...~,t~,. set at a take-off angle of 38 was used to analyze the test surface. This technique measutes the sutface of the atomic elements present at ~~ , the top 2 to 3 nanometers of the coating. Preferably, upon use of the approptiate post 15 tteatment as desctibed in these Examples, the sutface metal content will increase while the carbon content will decrease. This would be the result of a WO 9~/32237 ~ c 218~13 larger amount of the colloidal metal oxide particles and a smaDer amount of the polymer resin binder (NeoCryl~M and NeoRezTM binders) exposed at the surface of the coating a~er the ~ ~. Table 4A lists the carbon, oxygen, and silicon content by the atoml~c . - percent of each element 5 present and the metal atom to carbon atom ratios of Examples 1-5. Each sample .,u~ r ' to the different post-treatment cûnditions as listed in Table 3. Other minor elements may be present at the surface that are not listed in this Table.

W09~32237 ~ ~ 88~1~ r ~
Table 4A
XPS Atomic C~ Analysis of Colloida, I
Silica Coatirlgs at Different Air Cororla Post-Treatlnent Levels lA~ 57 33 9.0 0.16 IB 45.7 40.0 12.3 0.27 IC 37,1 44.6 16.0 0.43 ID 36.8 44.1 16,1 0,44 11~ 26 43 17 0.65 2A 68 26 4,0 0.06 2B 61 32 5,0 0.08 2C 55 35 8.0 0.15 2D 53 37 9.0 0,17 3Aa 42.0 42.3 12.7 0.30 3B 31.1 47.6 18,6 0.60 3C 25.8 51.5 20.5 0.79 3D 26.0 52,7 19.7 0.75 4A" 45.3 39.3 13.5 0.30 4B 36.5 44.5 16.8 0,46 4C 31,0 48.6 18.9 0.61 4D 29.6 49.0 19.9 0.67 5A~ 34 48.1 14.5 0.43 5B 25.7 51.3 21,1 0.82 5C 25.2 50.3 21,0 0.83 5D 24.5 51.4 21.5 0.87 a. C~ , Sample -- coating had no post-treatment w0 95/32237 ~ ~ 8 g a~ 1 3 As Table 4A illustrates, there was an increase in silicon atom content at the surface when the high power air corona discharge treatment was applied to the coatmgs. It is believed that this mcrease was caused by an increase iri the colloidal silica particle exposure at the;surface of the coatmgs upon ablation of 5 the polymer binder present at the surface. Example 2, which contained the lowest irlitial amount of colloidal silica m the coating r ~ '- , had an increase in surface silicon content at each successive corona power increase.
Example 5, which contained the highest irlitial amount of colloidal silica im the coating fnnml~ n reached a maximum silicon surface at the 10 lower air corona discharge power level but had a decrease in carbon atom content after each treatment. The other Examples, which contained initial colloidal silica amounts m their r ~ '- within these two upper and lower limits, had surface silicon atom behaviors that were somewhat between these Examples 2 amd 5. Use of the oxygen plasma post-treatment 15 (sample IE) on the coating described in Example I also resulted in an increased silicon content and decreased carbon content of the surface to a level similar to that obtained usimg the air corona post-treatment.
The removal of polymeric binder from the surface of the colloidal metal coatings apparent in the Xl?S results also was observed with scanning electron 20 microscopy (SEM). FIGs. 3 and 4 are SEM ~ , , ' - images taken with a Hitachi S-900 Field Emission Scamling Electron Mi_. u ,~,ù~,e (SEM), of samples IA 30 and lD 32. As shown in FIGs. 3 amd 4, the air corona treated sample 32 removed polymeric binder 36 to provide imcreased exposure of the colloidal silica particles 34 at the surface of the sample relative to an untreated 25 sample 30.
Applicants note that other 1' " .' have beerl taken which do not illustrate this effect to as great an extent or if at all. However, the samples that did not illustrate very clearly the removal of polymeric binder, tended to contain a very high or a very low, aliuA of metal oxide particles relative 30 tû the polymeric biAder. From an overall perspective, it is believed that the w095/32237 ~18~A 13 .~11, ..~
,' when viewed in total show that polymeric binder is removed by the surface treatment operation, and thus FIGs. 3 and 4 are prese~ted here merely to illustrate this effect.
The increase in the ratio of metal atoms to carbon atoms after 5 post-treatment with a high power air corona discharge also was apparent with coatings using coDoidal metal oxide particles other than silica oxide. Table 4B
details the atomic surface of the coatings of Examples 6 and 7, which used colloidal tin oxide and titanium oxide dispersions in the coatings.
Upon post-treatment with a high power air corona discharge at 11.1 joule/cm2, 10 the atomic of the metal present in the colloidal particles of each coating increased at the surface while the carbon content decreased. It is believed that this was caused by an increase in exposure of the colloidal particle at the surface as a result of the removal of the polymer binder.
Table 4B
XPS Atomic Cl Analysis of Colloidal Tin Oxide and Titanium Oxide Coatings at Different Air Corona Post-Treatment Levels J .~ ?,~
6A 0 75 22 2.2 - 0.03 6B 11.1 63 29 6.0 - 0.10 7A 0 79 20 - 0.2 0.003 7B 11.1 72 25 - 1.1 0.02 Water C~nt~t An~les To :l the water-spreading effect of Samples of the invention, the advancing and receding contact angles of water on the surface of the 20 treated and untreated coatings were measured using a contact angle goniometer , ~r0 9s~32237 2 1 8 3 ~
~Rame-Hart, Inc., Model 100-00-(115)). The advancing contact angle was measured using the advancing contact angle test. In this test, a drop of water was placed on the sample surface and the drop volume was increased by adding water through a syringe until just before't`he water drop periphery increased on5 the'surface. At the point ' ' '.~ before the physical movement of the periphery, the advancing contact angle was measured with the ,, ' .
The receding contact angles were measured by decreasing the volume of the drop by Wilhdlh~ water from the drop through a syringe until just before the drop's periphery receded. At the point ' '' '~, before the physical 10 moYement of the periphery of the drop, the receding contact angle was measured with the goniometer. The test surface was prepared by soaking in water for periods of 0, 1, 4, 8, and 24 hours followed by air drying of the surface. The preferred results are to maintain low advancing contact angles after the initial exposure to water. The advancing contact angle is a very good ~ of the ability of a drop of water to spread out and wet a surface.
Tbe advancing contact angle preferably is less than 40 degrees, and more preferably less than 30 degrees, before and after exposure to water soaking.
The advancing contact arlgles for the samples that were post-treated with the air corona discharge at 0, 2.8, 8.3, and 11.1 joule/cm2 or oxygen plasma 20 post-treated are listed in Table S. The receding contact angles for all of the colloidal silica samples were less than 20 degrees before and after soaking.

W095~12237 ~ P`~
Table 5 Contact Angle 1~ 5 .r }~ ~

22A" 62 69 68 67 67 33A' 48 52 54 55 56 44An 49 61 59 58 60 55Aa 28 45 40 44 39 a. Cl ~_ Samples -- coatLy~ had no post-treatment wo 95/32237 ~ 3 . ~
The post-treAtment, whether An oxygen plasrnA as in sample IE or An air coronA dischArge, resulted in signi'dcant decreases in the Advancing water contAct angies ofthe coatings both before and after exposure to water for times up to 24 hours. The largest decr Ase' in contact angie observed After 5 post-treatment with the high-power àir corona discharge was observed for the samples which contained a moderate amount of coiioidai SiiiCA (Examples 1,3, and 4). The coating containing the lArgest amount of coiioidai siiica ~ExAmple 5) hAd acivAncing contact angies which measured as low or lower than the other 6amples after air corona post-treAtment. The overail change in advancing 10 contact angie of Example 5 was smaiier than in Examples 1, 3, and 4 because the advancing contact angie prior to the post-treatment in Example 5 was lower than the advancing contact angles in the other three examples. The samples from these examples which were post-treated with an air corona discharge at 11.1 jouielcm2 had stable acivAncing contact angies near or below 15 30 even after exposure to water for 24 hours. Post-treatment at a lower power level (8.3 joule/cm2) resulted in surEaces with stable advancing contact Angies Afier water exposure of less than 30 for coatings from Examples 3, 4, and 5. The coating containing the lowest amount of colloidai silica (Example 2) exhibited a decrease in advancing contact angle after post-treatment with air20 corona discharge, but did not change in contact angle as drasticaily as the other coatings. The oxygen plasma post-treated sample lE exhibited a significant decrease in advancing contact angle, with an advancing contAct Angie of less than 20 after water exposure up to 24 hours in length. This test shows the abiiity of the post-treAted siiica polytneric sheets to have low advancing contact 25 arlgles thAt remain low even aEter extended exposure to water.
~llul~,n.,.,livi~y In Dew rn-~fitinnc A simuiated dew Cll. ~ ' was used to evaiuate the lc~lu~cll.,~,~ivi~y of IC~lUlCIL~ iVC sheetings having hydrophiiic sheets mAde as described above 30 disposed on the front side of the sheetings. The sheeting Ic~lul~,n~ y -Wo ss/32237 ~ ~ 8 ~ ~ ~ 3 r~
was carried out simiiar to ASTM tcst E 810-93b, except a dew simulator was used and a caiibration teci~nique was employe~i to account for the presence of a giass window. The dew simulator included an aiuminum test deck mounted on a rectangular gaivanized steel wail which was inside of an 5 insulated enclosure. The insulated enclosure had a giass window facing the test panel to measure .c~.u.~ ;vi~y. The gaivanized wail and test deck were cooled to 5C to 15 C with a heat exchanger. Humid air was introduced to the air , ' ~ the cooled test plate using a humidifier. The u. cilc_Livily (often expressed as the coefficient of C~lUIC~ iUII, RA) of the10 refiective sheeting mounted on the test deck was measured through the giass pane~ as a function of time during the water ' event (typicaily 60-80 minutes). The lc~lulcn.~ y was measured with a ICi~lUI~ ' ' '` coi by Advanced Retro Technoiogy Inc., La Mesa, Caiifornia.
Sample lc~luleli~ ivi~y was measured at an observation angie of 0.2 degrees 15 and an entrance angle of ~I degrees. The measured lc~lul~,lh,_~ y was caiibrated by a factor of the ratio of the c~-ulcn~ ;,y of the sample measured directly (without a giass window) divided by the IC~IUI~ "Vi~y of the refiective sheeting measured through the giass window prior to the ' ' U~iUC~iUII of humid air to the chamber. The lc~lulc~k,.~;vi~y was recorded 20 in candelas per lux per square meter.
The test samples were prepared by coating the coiioidal metai oxide r ' '' on an EC-Fiim as discussed above. The coated EC-Fiim was adhered to S~ ~ . TM High Intensity Sheeting (HIS 3870, 3M Co., St. Paul, 1' r ' ) The HIS 3870 was laminated to a 0.0254 inch thick aiuminum test 25 plate. The test plate with the article lanninated to the surface was soaked in a deionized water bath for 0.75 to 1.5 hours and dried at 43 C to 66 C for about 10 minutes prior to placement in the simuiator. The test plate then was placed in the simulator and was attached to the cooled aiuminum test deck.
The caiibrated ~ u~cll~ ;.y of th~ s~m,les ~- Examples 1-5 foiio ving air wo s5/32237 2 ~ 8 ~ ~ ~ 3 . ~
corona discharge post-treatments at 0, 2.8, 8.3, and 11.1 joule/cmZ are tabulated in Tables 6, 7, 8, 9, and lO, ..,~.,_~
It is preferred that the ~ei~u..i" . .y of the refiective sheeting exhibit a mirlimum decrcase during the water I event. It is also desirable 5 to have a fast recoveq a~er the initial I'oss of cl.u.~ '' .i~y. The initial loss is ty-pical at the start of the ' event.
Table 6 Example I
. .

a 281 37 25 29 30 54 52 73 97 111 n. CompDrntive Silmpl~ contillg hnd no r~' L

WO ~5~32237 1 ~
~18~41~
Table 7 }tple 2 2A" 271 102 49 35 32 31 28 29 31 31 3870b ~. Compsn~ti~ S~unple--coAting blld no post-tr~tment b. 3M Scot~liteW High Intensity Shecting without costung ul I ' L
Table 8 EXalrtple 3 3870b ~ Comp~atiYe Sumple - co~iting ~d no post-traltment b. 3M ScotchLitelM High InteDsity Sheeting y~ithout co~tulg or post-t~nent ~voss/32237 ~18~13 Table 9 Ex~tmple 4 4A^ 287 95 31 27 27 37 56 76 105 129 t~ CotnpLrntt ve St mple ~ tit g hnd no pAtit-tt eatmag Tuble 10 Exumple S
rl ~ ~
- ~ F ~l .
.
5A" 296 60 29 33 46 71 85 102 110 133 L CttinpL~tive St~nple--co~ting hnd no potit-tt~ttn~nt The air corona post-treatment of the colloidal silica coutings resulted in a significant , u._....,... in the recovery of ,cjL.~J,, A "~;~y of the rerdective sheeting to which the coatings were applied in the sunulated dew ~...;.~
In the case of the coating contuining the lowest initial ~ of colloidal silica (Example 2) used in the coating f~ n, the u.. ~ .. _.. t, ~ 8 ~
. l~p' ~ Shest . ~ --which is deflned in terms of degree and specd of the recovery of lt;Llolc{l.,~,l;v;iy during the water I ' event, was gradual and increased with increased air corona discharge power level. Samples from Examples 1, 3, 4, and 5, which contained higher ~ -. of colloida', 5 silica in their coating r~ , exhlbited faster and greater i..lyl~
of le~ c.,Livi~y recovery in dew conditions at similar air corona post-treatment power levels It should be.noted that in the absence of any . post-treatment, the recovery of ~ ul~,n~ iv;~y of the rerdective sheeting was not as ~ood.
The effect of the air corona discharge post-treatment was to remove the llydlv~llo~;L; polymer resin at the surface and increase the exposure of the hydrophilic colloidal silica particles at the surface. This process decreased the advancing contact angle and increased the llydl~ of the sample. This allowed water drops formed in the dew proc-~ss to spread and wet out the 15 surface. This in tLrn allowed the IcLIulcJ~ ;vLiy to recover quickly as compared to the non-treated flm because the formation of the small water drops disrupted the path of light entering and reflecting from the sheeting and lowered the ~c~lulcr..,~,livi~y ofthe sheeting.
_", AMC`ir' 3 ~lr ET

Claims (11)

CLAIMS:

1. A hydrophilic polymeric sheet containing metal oxide particles dispersed in a polymeric binder, the polymeric sheet being characterized by comprising:
5 to 90 weight percent of the metal oxide particles and by having a first major surface and an interior where there is a greater ratio of metal to carbon atoms on the first major surface of the polymeric sheet relative to the interiorthereof.

2. The hydrophilic polymeric article of claim 1, wherein the article is transparent.

3. The hydrophilic polymeric article of claims 1-2, wherein the metal oxide particles are silicon dioxide, aluminum oxide, or a combination thereof.

4. The hydrophilic polymeric article of claims 1-3, wherein the metal oxide particles have sizes ranging from 0.001 to 100 micrometers.

5. The hydrophilic polymeric article of claims 1-4, wherein the metal oxide particles have sizes ranging from 0.005 to 0.08 micrometers.

6. The hydrophilic polymeric article of claims 1-5, wherein the metal oxide particles are dispersed throughout the polymeric sheet at 30 to 85 weight percent.

7. The hydrophilic polymeric article of claims 1-6, wherein the polymeric sheet contains 20 to 40 weight percent of polymeric material, and 40 to 80 weight percent of metal oxide particles, and wherein the hydrophilic polymeric article has a thickness of 0.3 to 5 micrometers.

8. The hydrophilic polymeric article of claims 1-7, wherein the first major surface has a metal to carbon atom ratio of at least 0.01, and wherein there is at least a 20 percent higher ratio of metal to carbon atoms at the first major surface relative to the interior.

9. The hydrophilic polymeric article of claims 1-8, further comprising a substrate onto which the polymeric sheet is disposed.

10. A retroreflective article that comprises the hydrophilic polymeric article of claim 1 disposed on a retroreflective sheeting.

11. A method of making an article capable of providing water-spreading effects, which method comprises:
providing a polymeric sheet that has a first major surface and an interior and that comprises 5 to 90 weight percent metal oxide particles in a polymeric binder; and treating the first major surface of the polymeric sheet so as to remove polymeric binder from the first major surface but leave the metal oxide particles thereon to increase exposure of the metal oxide particles on the first major surface.