AU759525B2 - Method of reducing yellowing of water-borne road marking paints and composition used therein - Google Patents

Description

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AUSTRALIA

PATENTS ACT 1990 DIVISIONAL APPLICATION NAME OF APPLICANT: ROHM AND HAAS COMPANY ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street Melbourne, 3000.

INVENTION TITLE: "METHOD OF REDUCING YELLOWING OF WATER-BORNE ROAD MARKING PAINTS AND COMPOSITION USED THEREIN" The following statement is a full description of this invention, including the best method of performing it known to us: This invention is concerned with a method for reducing or preventing yellowing of water-borne road marking paints (hereinafter sometimes referred to as "traffic paints").

Much research has been devoted to ensuring that white water-borne traffic paints remain white and stain free for as long as possible after application. However, it has been observed that portions of clean white surfaces of newly applied traffic paint can turn to a dirty yellow or brown color, sometimes along long stretches of traffic markings on the road. Such a staining phenomenon is known as "yellowing". Although the visibility of the paint is normally not seriously affected, the yellowing is undesirable for aesthetic reasons, and particularly because users of the traffic paint may believe that a paint which turns yellow within days of application is of poor quality.

Until now there has been no explanation for this phenomenop, o.oo which is noted for the apparent randomness of its appearance, and the fact that it occurs soon after applicatiih or not at all. An identical paint applied on the same stretch of road on two occasions may turn yellow at one time, and not the next. As a result of this lack of understanding of the problem, a solution has so far not been found.

We- have now established a possible cause for this phenomenon, rB. and as a result have been able to unexpectedly develop a solution. We believe that the yellowing is caused by iron reacting with materials in the paint formulation to produce what is essentially rust inside the paint, thereby o: causing yellowing. There is no obvious source of iron in the vicinity of an S applied traffic paint. It is believed that it may come from vehicles or even from some components of the road surfaces, such as, asphalt, on which the paint has been applied. The iron may be able to penetrate the paint if there is high humidity or rain in the first 24 to 48 hours after application, when the paint is not fully dry and hence is still susceptible to water penetration.

Having been introduced into the paint layer in this way, water then is believed to react with certain components of the paint to form a yellow or brown "rust", which stains the paint and causes yellowing. However, if the rain is particularly heavy, the iron and "rust" may be washed out, thereby -2removing the yellow color. This would, without reliance thereon, explain the apparent randomness of the phenomenon.

EP-A-34383 I discloses a top coat paint for protecting a surface from external rust staining, rust from an external source that drips or falls onto the surface. The paint contains a chelating agent capable of reacting with iron ions in rust to form a colorless complex. GB 2172599A discloses a similar paint, which contains as chelating agent, which is a polyphosphonate salt pigment. Neither of these references, nor any of the other prior disclosures of such anti-rust staining paints, mention such a problem with traffic paints.

Indeed, there is nothing in the prior art to explain the aforedescribed yellowing problem, or to suggest that it is in any way connected with rust stainine.

According to the present invention there is provided a method for reducing or preventing yellowing of a road marking paint, said method comprising the steps of: (i) T applying to a road surface a water-borne road marking paint comprising a binder having a total weight; (ii) applying a chelating agent capable of chelating iron ions to form a substantially colorless complex, said chelating agent comprising a material selected from the group consisting of aminocarboxylic acid, ammonium or alkali metal salts thereof; phosphonocarboxylic acid, ammonium or alkali metal salts thereof; phosphonic acid, ammonium or alkali metal salts thereof; aminophosphonic acid, ammonium or alkali metal salts thereof; tripolyphosphoric acid, ammonium or alkali metal salts thereof, pyrophosphoric acid, ammonium or alkali metal salts thereof; hexametaphosphoric acid, S ammonium or alkali metal salts thereof; organic acid, ammonium and alkali metal salts thereof; diketone derivative of 2,4-pentandione; hydroxamic acid; and combinations 25: thereof, wherein said chelating agent is applied simultaneously with said road marking S* paint, or subsequently to the application of said road marking paint, while said road marking paint is still in a wet state; (iii) drying or allowing to dry said road marking paint.

P:OPER\Axd\2320934 res.doc-2I/0OM3 -2A- As used herein: "GPC weight average molecular weight" means the weight average molecular weight determined by gel permeation chromatography (GPC) which is described on page 4, Chapter I of The Characterization of Polymers published by Rohm and Haas Company, Philadelphia, Pennsylvania in 1976, utilizing polymethyl methacrylate as the standard. The GPC weight average molecular weight can be estimated by calculating a theory weight average molecular weight. In systems containing chain transfer agents, the theory weight average molecular weight is simply the total weight of polymerizable monomer in grams divided by the total molar amount of chain transfer agent used during the polymerization. Estimating the molecular weight of an emulsion polymer system that does not contain a chain transfer agent is more complex. A cruder estimate can be obtained by taking the total weight of polymerizable monomer in grams and dividing that quantity by the product of the molar amount of an initiator multiplied by an efficiency factor (in our persulfate initiated systems, we have used a factor of approximately 1 Further information on theoretical molecular weight calculations can be found in Principles of Polymerization 2nd edition, by George Odian published r r c by John Wiley and Sons, N.Y. in 1981 and in Emulsion Polymerization edited by Irja Pirma published by Academic Press, N.Y. in 1982.

"Dispersed polymer" means particles of polymer colloidally dispersed and stabilized in an aqueous medium.

"Solubilized polymer" means a water soluble polymer dissolved in an aqueous medium. Solubilized polymer results in a polymer solution characterized by having the self-crowding constant of the Mooney equation Il/lnIrrel 1/BC K/2.5] equal to zero. By contrast, dispersed polymer has equal to 1.9. The details of Mooney equation are disclosed in an article entitled'"Physical Characterization of Water Dispersed and Soluble Acrylic Polymers" by Brendley et al., in "Nonpolluting Coatings and Coating Processes" published by Plenum Press, 1973 and edited by Gordon and Prane.

"Polymer solids" means polymer in its dry state.

The term "(meth)acrylate" includes acrylate and methacrylate.

15 "Chelating agent" means a compound which interacts with a metal, such as, iron, through more than one coordinating atom.

"Pigment dispersant" means a material used for improving the dispersion of pigment particles in a paint composition. The pigment dispersant is believed to adsorb on the surface of pigment particles in a paint composition to increase the negative charge thereon. As a result, it is believed that the columbic repulsion between pigment particles is increased and the dispersion of pigment particles in the paint composition is thereby improved.

:Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or .ij group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The water-borne road marking paint useful in the method of the present invention includes one or more a dispersed or a solubilized polymers in an aqueous medium. Such polymers are well known in the art.

polymerized in an aqueous medium by copolymerizing at least one of the following monomers, some of which are alkyl (meth)acrylate monomers, such as, (C1-C20)alkyl (meth)acrylate monomers. As used herein, the terminology "(C1-C20)alkyl" denotes an alkyl substituent group having from 1 u o 20 carbon atoms per group. Suitable (C1-C20)alkyl (meth)acrylate lomers include, for example, acrylic and methacrylic ester monomers 0

PFI

P\.OPER\Axdl559I 1.96 spdoc-03)A94A) -3Aincluding methyl (me th)acryla te, ethyl (methi)acryla te, bu tyl (meth)acrylate, 2ethyliexyl (me th)acrylate, decyl (meth)a cryla te, lauryl (me th)acrylate, cetyl (meth)acryla te, eicosyl (me th)acrylate, isobornyl (me th)acryla te, isodecyl (meth)acrylate, oleyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate, vinyl ester monomers including, for example, vinyl acetate, vinyl propionate, vinyl neononanoate, vinyl neodecanoate, vinyl-2- P:\OPER\Axd\5591 1-96 spec.doc 5/4/00 ethylhexanoate, vinyl pivalate, vinyl versatate or a mixture thereof. Suitable vinyl monomers include, for example, vinyl halide, preferably vinyl chloride, vinylidene halide, preferably vinylidene chloride, or various mixtures thereof. Suitable vinyl aromatic monomers include, for example, one or more polymerizable vinyl aromatic compounds and mixtures thereof and also include styrene, alkyl-substituted styrenes, such as, a-methylstyrene, aethylstyrene, p-methylstyrene and vinyl xylene, halogenated styrenes, such as, chlorostyrene, bromostyrene and dichlorostyrene, other styrenes having one or more nonreactive substituents on the benzene nucleus, vinyl naphthalene or various mixtures thereof. Suitable neutral monomers include, for example, one or more monomers, such as, acrylonitrile, acrylamide, alkyl substituted acrylamide monomers, hydroxy alkyl (meth)acrylate monomers, such as, aceto acetoxyethyl (meth)acrylate, hydroxyethyl (meth)acrylate, and hydroxypropyl (meth)acrylate and isomers of hydroxy butyl (meth)acrylate or 15 various mixtures thereof.

If desired, the dispersed or solubilized polymer further includes in ;the range of from 0.5 percent to 20.0 percent, preferably in the range of from percent to 15 percent, of a monomer containing an acid functionality, all percentages being in weight percent based on the total weight of polymer solids.

The acid functionality results from including in the monomer mixture one or more of the monoethylenically unsaturated carboxylic acid monomers, such as, for example, acrylic acid, methacrylic acid, itaconic acid, crotonoic acid, aconitic acid, atropic acid, maleic acid, maleic anhydride, 25 fumaric acid, vinyl benzoic acid, half-esters of ethylenically unsaturated dicarboxylic acids, half-amides of ethylenically unsaturated dicarboxylic acids and various mixtures thereof. Other suitable monomer include one or more monomethyl itaconate, monomethyl fumarate, monobutyl fumarate, acrylamido propane sulfonate, sodium vinyl sulfonate, 2 acrylamido-2methylpropanesulfonic acid, 2-methacryloxyethyl phosphate (MOP) and phosphoethyl(meth)acrylate. The monomer containing the monoethylenically unsaturated carboxylic acid are preferred and acrylic acid, methacrylic acid and mixtures thereof are more preferred.

Preferably, the traffic paint further includes a polyfunctional amine, polymerized from one or more monomers, such as, dimethylaminopropylmethacrylamide, oxazolidinoethylmethacrylate and dimethylaminoethylmethacrylate. Such a composition is disclosed in United States Patent No. 5527853 entitled "SHELF STABLE FAST-CURE AQUEOUS COATING". If desired, an amine modified dispersed or solubilized polymer, or a blend of the amine modified dispersed or solubilized polymer with a polyfunctional amine or a combination thereof, preferably in equal proportions, of the blend and the amine modified latex binder. The blend includes from 0 to 20 percent, preferably 0.5 to 10, and more preferably 2 to 5 percent, of the polyfunctional amine, all in weight percentages based on the total weight of blend solids.

The polymerization process is typically initiated by conventional free radical initiators, such as, for example, hydrogen peroxide, t-butyl hydroperoxide, ammonium and alkali persulfates, typically at a level of 0.05 percent to 3.0 percent by weight, all weight percentages based on the weight of total monomer. Redox systems using the same initiators coupled with a suitable reductant such as, for example, sodium bisulfite, sodium hydrosulfite 15 and isoscorbic acid, may be used at similar levels.

Chain transfer agents may be used in an amount effective to provide the desired GPC weight average molecular weight. For the purposes of regulating molecular weight of the polymer being formed, suitable chaij transfer agents include well known halo-organic compounds, such as, carbon tetrabromide and dibromodichloiomethane; sulfur-containing compounds, such as, alkylthiols including ethanethiol, butanethiol, tert-butyl and ethyl mercaptoacetate, as well as aromatic thiols; or various other organic compounds having hydrogen atoms which are readily abstracted by free radicals during polymerization. Additional suitable chain transfer agents or ingredients include but are not limited to butyl mercaptopropionate; isooctylmercapto propionate; bromoform; bromotrichloromethane; carbon tetrachloride; alkyl mercaptans, such as, 1-dodecanthiol, tertiary-dodecyl mercaptan, octyl mercaptan, tetradecyl mercaptan, and hexadecyl mercaptan; alkyl thioglycolates, such as, butyl thioglycolate, isooctyl thioglycoate, and dodecyl thioglycolate; thioesters; or combinations thereof. Mercaptans are preferred.

When a dispersion of polymer particles is utilized, the polymer particle size is controlled by the amount of conventional surfactants added during the emulsion polymerization process. Conventional surfactants include anionic, nonionic emulsifiers or their combination. Typical anionic emulsifiers include the salts of fatty rosin and naphthenic acids, condensation products of naphthalene sulfonic acid and formaldehyde of low molecular weight, carboxylic polymers and copolymers of the appropriate hydrophile-lipophile balance, alkali or ammonium alkyl sulfates, alkyl sulfonic acids, alkyl phosphonic acids, fatty acids, and oxyethylated alkyl phenol sulfates and phosphates. Typical nonionic emulsifiers include alkylphenol ethoxylates, polyvinyl alcohols, polyoxyethylenated alkyl alcohols, amine polyglycol condensates, modified polyethoxy adducts, long chain carboxylic acid esters, modified terminated alkylaryl ether, and alkylpolyether alcohols. Typical ranges for surfactants are between 0.1 to 6 percent by weight based on total weight of total monomer.

If desired the dispersed polymer may include multi-stage polymer particles having two or more phases of various geometric structures, such as, for example, core/shell or core/sheath particles, core/shell particles with shell phases incompletely encapsulating the core, core/shell particles with a multiplicity of cores and interpenetrating network particles. In all of these cases, the majority of the surface area of the particle will be occupied by at least S 15 one outer phase and the interior of the polymer particle will be occupied by at least one inner phase. The outer phase of the multi-stage polymer particles weighs 5 weight percent to 95 weight percent based on the total weight of the particle. It is often desirable for each stage of the multi-stage polymer pirticles to have a different Tg. If desired, each stage of these multi-stage polymer particles may be provided with different GPC number average molecular weight, such as, the multi-stage polymer particle composition disclosed in US Patent 4,916,171.

The multi-stage polymer particles of the dispersed polymer are prepared by -conventional emulsion polymerization process in which at least two stages differing in composition are formed in a sequential fashion. Such a process usually results in the formation of at least two polymer compositions.

*I Each of the stages of the multi-stage polymer particles may contain the same chain transfer agents, surfactants, as those disclosed earlier. The emulsion polymerization techniques used for preparing such multi-stage polymer particles are well known in the art and are disclosed, for example, in the US Patents No. 4,325,856, 4,654,397, 4,814,373 and 4,916,171.

The applicants have unexpectedly discovered that the incorporation of a chelating agent in a waterborne traffic paint substantially reduces or prevents the iron, scattered on road surfaces, from reacting with paint surface to form the "rust" compounds that cause the yellowing effect. As a result, the applied traffic paint surface remains substantially white under varied traffic conditions. Tests which the applicants have conducted using a solution of ferrous sulfate to mimic the effect of the iron confirm the efficacy of this approach. The traffic paint includes in the range of from 0.1 percent to percent, preferably in the range of from 1 percent to 3 percent of the chelating agent, all percentages being in weight percentages based on the total weight of polymer solids.

The chelating agents suitable for use in the present invention include aminocarboxylic acids, such as, ethylenediamine tetraacetic acid, nitrilotriacetic acid, diethylenetriamine pentaacetic acid, hydroxyethylethylenediaminetriacetic acid, diethanolglycine, ethanoldiglycine, ethylenediamine disuccinic acid, iminodiacetic acid and ammonium and alkali metal salts thereof; phosphonocarboxylic acids, such as, 2-phosphonobutane-1,2,4-tricarboxylic acid and ammonium and alkali metal salts thereof; phosphonic and aminophosphonic acid and ammonium and alkali metal salts thereof, such as, 1-hydroxyethylidene-l,l-diphosphonic acid, aminotri(methylenephosphonic acid), diethylenetriamine penta(methylene 15 phosponic acid), hexamethylene diamine tetra(methylene phosphonic acid); tripolyphosphoric acid and ammonium and alkali metal salts thereof; pyrophosphoric acid and ammonium and alkali metal salts thereof; hexametaphosphoric acid and ammonium and alkali metal salts thereof; organic acids, such as, fumaric acid, citric acid, oxalic acid, itaconic acid, crotonic acid, maleic acid, and arimonium and alkali metal salts thereof; diketone derivatives, such as, Zn 2 salt of 2,4-pentandione; hydroxamic acid; and various combinations of the foregoing chelating agents.

The preferred chelating agents include ammonium and alkali metal phosphonates or phosphonic acid (a compound bearing one or more PO(OH) 2 groups) and ethylenediamine tetraacetic acid. Particularly preferred is aminotris-methylene phosphonic acid, sold under the trade name DEQUEST® 2000 by Monsanto Chemical Company, Saint Louis, Missouri.

The traffic paint of the present invention preferably further includes a conventional white pigment, preferably, titanium dioxide, at concentrations in.the range of 5 to 20 percent, more preferably 6 to 16 percent, all by weight percent based on the total weight of the composition. Some of the white pigments suitable for use in the present traffic paint include those supplied by E. I. du Pont and Company, Incorporated, Wilmington, Delaware under the trade name as TiPure titanium dioxide white pigment. Another supplier of titanium dioxide white pigment, under the trade name as TITANTM TR 92 Titanium dioxide, is Tioxide, Cleveland, United Kingdom.

If desired the traffic paint may include 0.25 percent to 2 percent of a pigment dispersant in combination with 0.25 percent to 3 percent of the chelating agent to further prevent or reduce the yellowing of the traffic paint marking, all percentages being in weight percentages based on the total weight of polymer solids. Some of the suitable pigment dispersants include polymeric carboxylic acids, and ammonium and alkali metal salts thereof.

Some of the suitable polymeric carboxylic acids include polyacrylic acid, polymethacrylic acid, copolymers of (meth)acrylic acid and maleic acid, all typically having a weight average molecular weight in the range of from 4000 to 10,000. Some of the other suitable pigment surfactants include copolymers of meth(acrylic) acid and polar compounds, such as, hydroxyethyl methacrylate, and non-polar compounds, such as, butyl methacrylate; and reaction products of maleic anhydride and diisobutylene. Polymethacrylic acid and ammonium and alkali metal salts thereof are preferred.

The water-borne traffic paints typically include fillers, such as, calcium carbonates, talcs, silicas, and sometimes solid glass beads; coalescing and anti-freeze solvents. If desired, the water-borne traffic paints of the present invention includes additives, such as, surfactants, biocides and thickeners.

The method may further comprise incorporating in said water-borne road marking paint, a pigment dispersant for further reducing or preventing yellowing of said newlyapplied road marking. The method of present invention contemplates incorporating the chelating agent in the traffic paint or after a road marking of the traffic paint has been applied on the road surface by conventional applying means, such as, mobile spraying devices. Thereafter, the chelating agent may be conventionally applied, such as, by *i spraying, on top of the road marking, while the road marking is still in a wet state. If desired, glass beads may be applied on top of the road marking, while the traffic paint is still wet, to produce reflective road markings having enhanced visibility. It is further contemplated that the reflective glass beads may be mixed with the chelating agent before the mixture of thereof, is applied on top of the wet road marking.

EXAMPLES

The Examples 1 through 5 of the present invention were based on the following formulations: Table 1 Component Binder 1 Pigment dispersant 2 Chelating agent 3 Non-silicone defoamer 4 Water Titanium dioxide pigment Ca carbonate 5 microns 6 Ca carbonate 10 microns 7 Example 1 4 Weight (g/liter) 487.0 8.4 0.0 4.0 69.0 265.0 394.0 394.0 Example 3 Weight (g/liter) 487.0 0.0 24.3 4.0 53.1 265.0 394.0 394.0 Examples 2 Weight (g/liter) 487.0 8.4 24.3 44.7 265.0 394.0 394.0 The above components were mixed for 20 minutes until smooth, and then the following components were added to complete the preparation of Examples 1 through Table 2 p Component Examples Weight (g/liter) Freeze-thaw 26.0 stabilizer 8 Coalescent 9 23.0 Water 10.0 Base 10 0.2 Non-silicone defoamer 4 Water 25.0 Total 1718.0 The components described in Tables 1 and 2 above are listed below: 1 is a PRIMAL® E-2706 polymer emulsion supplied by Rohm and Haas Company, Philadelphia, Pennsylvania.

2 is a OROTAN® 901 is a pigment dispersant supplied by Rohm and Haas Company, Philadelphia, Pennsylvania.

3 is a chelating agent formulated by mixing 45 grams of water with grams of a 28% ammonia solution, and then adding 40 grams DEQUEST® 2000 (at 50% strength), to give a pH of 9.5. The ammonia was not added last as this fails to give adequate neutralization.

4 is a DREWTM TG 4250 non-silicone defoamer supplied by Drew Ameroid Nederland Triathlonstrasse 33, 3078 HX Rotterdam, The Netherlands.

5 is a TITANTM TR 92 Titanium dioxide white pigment supplied by Tioxide, West Site, Haverton Hill Road, Billingham, Cleveland TS23 1PS, United Kingdom.

6 is a DURCALTM 5 filler supplied by Omya, Pluess-Stauffer AG, CH- 4665 Offringen, Switzerland.

15 7 is a DURCALTM 10 filler supplied by Omya, Pluess-Stauffer AG, CH- 4665 Offringen, Switzerland.

8 is Ethanol.

9 is a TEXANOL® Coalescent supplied by Eastman Chemical qo., Kingsport, Tennessee.

10 is ammonia used to adjust the pH of the formulation to 9 Examples 1 through 5 were equilibrated for 1 day.

A coating from Examples 1 through 3 having a thickness of 380 micrometers were applied to a glass surface, and left to dry for one hour, at which point, -10 drops of FeSO 4 solution (3g FeSO 4 .7H 2 0, 1997g water, 6 drops 25 25% sulfuric acid) were applied to the coating surface to mimic the effect of yellowing by iron on traffic markings. The coatings were then visually examined after drying for yellowing. The results are described in Table 3 below: Table 3 Example Chelating Pigment Yellowing Yellowing Agent Dispersant after after 2 hrs 16 hrs 1 Not present Present Yellow Yellow 2 Present Present White White 3 Present Not present Off-white Off-white It can seen from Table 3 that when a composition (Example 3) containing a chelating agent is utilized in a traffic paint, no significant yellowing was observed when it to compared to a composition (Example 1), -11which did not contain the chelating agent. However, when the composition contained, not only the chelating agent but also a pigment dispersant (Example even further improvement in reducing yellowing of the coating was observed when compared to Example 3.

The road markings, also known as, test tracks, were prepared and applied in accordance with ASTM D 713-90. The road markings from Examples 4 and 5 having a thickness in the wet state of 450 micrometers were spray applied transversely to the direction of traffic flow, perpendicular to the flow of traffic, over a bituminous asphalt road by means of a walk behind, self-propelled striping machine Model No. LT 20, supplied by CMC, Como, Italy. The reason for applying the test tracks in a direction transverse to the traffic flow was to accelerate the degradation of test tracks by increasing the number of vehicle passes over the test tracks, particularly where the vehicle tires pass most frequently, which is defined as "wheel track area". The S 15 yellowing of the test tracks was observed 106 days after their application to the road surface with a portable tristimulus colorimeter supplied by Minolta Camera Company Limited, Japan. Color difference measurement is described in ASTM E-1347 "Color and Color-Difference Measurement by Tristimilus (Filter) Colorimetry". The b* value is described in ASTM E-284 "Standard Terminology of Appearance" und'r CIELAB color difference. The color difference was calculated by using the CIE 1976 L*a*b* opponent color scales where the b* scale is positive in the yellow direction and negative in the blue direction, b* opponent color scales are also described in "Principles of Color Technology, 2nd Edition", Fred W Billmeyer, Jr., John Wiley Sons, 1981.

The value" is a measure of the degree of yellowing observed. Higher the b* value, yellower will be the appearance of the traffic markings applied over •oo oi the road surface. A b* value of 3 represents a freshly painted white surface. A b* value of 8 or less represents an acceptable degree of yellowing of the traffic marking. Table 4 represents the b* values of the road markings prepared from Examples 4 and Table 4 Example b* value 4 9.4 6.4 From Table 4 above, it is seen that a road marking from a traffic paint composition (Example 5) containing a chelating agent provides an acceptable degree of yellowing results after a prolonged exposure to traffic -12conditions when it is compared to a road marking from a traffic paint composition (Example 4) which did not contain the chelating agent.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

4 *a*

Claims (1)

13- The claims defining the invention are as follows: 1. A method for reducing or preventing yellowing of a road marking paint, said method comprising the steps of: applying to a road surface a water-borne road marking paint comprising a binder having a total weight; (ii) applying a chelating agent capable of chelating iron ions to form a substantially colorless complex, said chelating agent comprising a material selected from the group consisting of aminocarboxylic acid, ammonium or alkali metal salts thereof; phosphonocarboxylic acid, ammonium or alkali metal salts thereof; phosphonic acid, ammonium or alkali metal salts *thereof; aminophosphonic acid, ammonium or alkali metal salts thereof; etripolyphosphoric acid, ammonium or alkali metal salts thereof, pyrophosphoric acid, ammonium or alkali metal salts thereof, hexametaphosphoric acid, ammonium or alkali metal salts thereof; organic hexametaphosphoric acid, ammonium or alkali metal salts thereof; organic acid, ammonium and alkali metal salts thereof; diketone derivative of 2,4- pentandione; hydroxamic acid; and combinations thereof, wherein said chelating agent is applied simultaneously with said road marking paint, or S:i subsequently to the application of said road marking paint, while said road S. 20 marking paint is still in a wet state. (iii) drying or allowing to dry said road marking paint. 2. A method according to claim 1, wherein the aminophosphonic acid is selected from the group consisting of amino-tris-methylene phosphonic acid, diethylenetriamine penta(methylene phosphonic acid) and hexamethylene diamine tetra(methylene phosphonic acid). 3. A method according to claim 1, wherein the chelating agent capable of chelating iron ions is amino-tris-methylene phosphonic acid, ammonium or alkali metal salts thereof. 4. A method according to claim 1, wherein said paint comprises 0.1 to 5 percent by weight based on the total weight of said binder of said chelating agent. A method according to any one of claims 1 to 4, further comprising a pigment P:\OPER\Axd\2320934 rs.doc-210103 -14- 6. A method according to any one of claims 1 to 5, further comprising a white pigment. 7. A method according to claim 1, wherein the chelating agent capable of chelating iron ions comprises a compound bearing one PO(OH) 2 group or EDTA. 8. A method according to claim 1, wherein said organic acid is selected from the group consisting of fumaric acid, citric acid, oxalic acid, itaconic acid, crotonic acid and maleic acid. 9. A method according to any one of claims 1 to 8, further comprising a substance selected from the group consisting of a polyfunctional amine, an amine modified, dispersed or solubilized polymer, and a combination thereof. 10. A method according to claim 9, wherein said polyfunctional amine is polymerized from a monomer selected from the group consisting of dimethylaminopropylmethacrylamide, oxazolidinoethylmethacrylate, dimethylaminoethylmethacrylate and a combination thereof. 11. A method according to claim 1, wherein the phosphonic acid comprises 1- hydroxyethylidene-1,1-diphosphonic acid. 12. The method according to claim 1, wherein said method further comprises the step of applying to said road surface glass beads, wherein said glass beads are applied simultaneously with said road marking paint, or subsequently to the application of said road marking paint, while said road marking paint is still in a wet state. 13. A method substantially as hereinbefore described with reference to the Examples. DATED: 22 January 2003 by DAVIES COLLISON CAVE Patent Attorneys for the Applicant(s): ROHM AND HAAS COMPANY