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| United States Patent |
5,714,527
|
|
Jilek
, et al.
|
February 3, 1998
|
Method of reducing yellowing of water-borne road marking paints and
composition used therein
Abstract
A water-borne road marking paint composition which includes a chelating
agent capable of chelating iron ions to form a substantially colorless
complex is provided. A road marking produced from the traffic paint of the
present invention substantially reduces or prevents yellowing of white
road marking from iron and iron compound debris strewn on the road
surfaces. A method of reducing or preventing yellowing of a newly-applied
road marking on a road surface of a water-borne road marking paint is also
disclosed. The method comprises incorporating in the water-borne road
marking paint a chelating agent capable of chelating iron ions to form a
substantially colorless complex. Further reduction of yellowing of the
road marking is observed when a pigment dispersant is incorporated in the
water-borne road marking paint.
| Inventors:
|
Jilek; Josef Hans (Vienna, AT);
Sanfilippo; Angelo (Valbonne, FR);
Schall; Donald Craig (Lansdale, PA);
Trapani; Andrew Paul (Valbonne, FR)
|
| Assignee:
|
Rohm and Haas Company (Philadelphia, PA)
|
| Appl. No.:
|
651836 |
| Filed:
|
June 4, 1996 |
Foreign Application Priority Data
| Intern'l Class: |
F21S 007/22 |
| Field of Search: |
523/172
524/127,128
|
References Cited
U.S. Patent Documents
| 4325856 | Apr., 1982 | Ishikawa et al. | 523/201.
|
| 4654397 | Mar., 1987 | Mueller-Mall et al. | 524/460.
|
| 4814209 | Mar., 1989 | Arnold | 427/409.
|
| 4814373 | Mar., 1989 | Frankel et al. | 524/460.
|
| 4916171 | Apr., 1990 | Brown et al. | 523/161.
|
| 5527853 | Jun., 1996 | Landy et al. | 524/521.
|
| Foreign Patent Documents |
| 343831 | May., 1989 | EP.
| |
Primary Examiner: Cain; Edward J.
Attorney, Agent or Firm: Deshmukh; Sudhir
Claims
We claim:
1. A road marking of a water-borne road marking paint applied on a road
surface, said paint comprising a chelating agent capable of chelating iron
ions to form a substantially colorless complex.
2. A method of reducing or preventing yellowing of a newly-applied road
marking on a road surface of a water-borne road marking paint, said method
comprising incorporating in said water-borne road marking paint a
chelating agent capable of chelating iron ions to form a substantially
colorless complex.
3. The method of claim 2 further comprising incorporating in said
water-borne road marking paint, a pigment dispersant for further reducing
or preventing yellowing of said newly-applied road marking.
4. A road marking paint applied as a road marking on a road surface in
accordance with the method of claim 2.
5. A road marking of claim 1 wherein the chelating agent capable of
chelating iron ions comprises a compound bearing one or more PO(OH).sub.2
groups or EDTA.
6. A road marking of claim 1 wherein the chelating agent capable of
chelating iron ions is amino-tris-methylene phosphonic acid.
7. A road marking of claim 1 wherein said paint comprises 0.1 to 5 percent
by weight based on the total weight of polymer solids of said chelating
agent.
8. A road marking of claim 1 wherein said paint further comprises a pigment
dispersant.
9. A road marking of claim 1 wherein said paint further comprises a white
pigment.
10. The method of claim 2 wherein the chelating agent capable of chelating
iron ions comprises a compound bearing one or more PO(OH).sub.2 groups or
EDTA.
11. The method of claim 2 wherein the chelating agent capable of chelating
iron ions is amino-tris-methylene phosphonic acid.
12. The method of claim 2 wherein said paint comprises 0.1 to 5 percent by
weight based on the total weight of polymer solids of said chelating
agent.
13. The method of claim 2 further comprising incorporating in said
water-borne road marking paint, a white pigment.
Description
This invention is concerned with water-borne road marking paint
(hereinafter sometimes referred to as "traffic paints"), and in particular
the problem of yellowing which sometimes occurs after application of the
paint on the road.
Much research has been devoted to ensuring that white water-borne traffic
paints remain white and strain 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 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 phenomenon, which is noted
for the apparent randomness of its appearance, and the fact that it occurs
soon after application 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, 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
causing yellowing. There is no obvious source of iron in the vicinity of
an 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 removing 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, i.e., 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 staining.
The present invention provides for a water-borne road marking paint
comprising a chelating agent capable of chelating iron ions to form a
substantially colorless complex. A further aspect of the invention is a
method of reducing or preventing yellowing of a newly-applied road marking
on a road surface of a water-borne road marking paint, said method
comprising incorporating in said water-borne road marking paint a
chelating agent capable of chelating iron ions to form a substantially
colorless complex.
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, Pa. 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 0.5). Further information on theoretical molecular weight
calculations can be found in Principles of Polymerization 2nd edition, by
George Odian published by John Wiley and Sons, N.Y., N.Y. in 1981 and in
Emulsion Polymerization edited by Irja Pirma published by Academic Press,
N.Y., 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 (K) of the Mooney equation
›1/ln.sub..eta.rel =1/BC-K/2.5! equal to zero. By contrast, dispersed
polymer has (K) 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.
"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.
The water-borne road marking paint 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.
Preferably, the dispersed or solubilized polymer is emulsion polymerized in
an aqueous medium by copolymerizing at least one of the following
monomers, some of which are alkyl (meth)acrylate monomers, such as,
(C.sub.1 -C.sub.20)alkyl (meth)acrylate monomers. As used herein, the
terminology "(C.sub.1 -C.sub.20)alkyl" denotes an alkyl substituent group
having from 1 to 20 carbon atoms per group. Suitable (C.sub.1
-C.sub.20)alkyl (meth)acrylate monomers include, for example, acrylic and
methacrylic ester monomers including methyl (meth)acrylate, ethyl
(meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl
(meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate, eicosyl
(meth)acrylate, isobornyl (meth)acrylate, 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-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,
.alpha.-methylstyrene, .alpha.-ethylstyrene, 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 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
5 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, 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-2-methylpropanesulfonic 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 a
commonly assigned U.S. patent application filed on Nov. 14, 1994, entitled
"SHELF STABLE FAST-CURE AQUEOUS COATING" having a Ser. No. 08/340,461,
which has been allowed. 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 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 chain
transfer agents include well known halo-organic compounds, such as, carbon
tetrabromide and dibromodichloromethane; sulfur-containing compounds, such
as, alkylthiols including ethanethiol, butanethiol, tert-butyl and ethyl
mercaptoacetate, as well as aromatic thioIs; 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 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 particles 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 U.S. Pat. No.
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. 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 U.S. Pat. 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 5 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.
Some of 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-1,1-diphosphonic
acid, aminotri(methylenephosphonic acid), diethylenetriamine
penta(methylene 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 ammonium and alkali metal
salts thereof; diketone derivatives, such as, Zn.sup.2+ salt of
2,4-pentandione; hydroxamic acid; glass capable of releasing phosphate
ions and polyphosphonate salt of a pigment, such as, those disclosed in EP
0 343 831 A1; 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).sub.2 groups) and ethylenediamine tetraacetic acid. Particularly
preferred is amino-tris-methylene phosphonic acid, sold under the trade
name DEQUEST.RTM. 2000 by Monsanto Chemical Company, Saint Louis, Mo.
The traffic paint of the present invention further includes a conventional
white pigment, preferably, titanium dioxide, at concentrations in the
range of 5 to 20 percent, 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, Del.
under the trade name as TiPure.RTM. titanium dioxide white pigment.
Another supplier of titanium dioxide white pigment, under the trade name
as TITAN.TM. 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 waterborne traffic paints of the present invention typically include
fillers, such as, calcium carbonates, talcs, silicas, and sometimes solid
glass beads; coalescing and anti-freeze solvents. If desired, the
waterborne traffic paints of the present invention includes additives,
such as, surfactants, biocides and thickeners.
The present invention is also directed to a method of reducing or
preventing yellowing of a newly-applied road marking on a road surface of
a water-borne road marking paint. The method includes incorporating in the
water-borne road marking paint the chelating agent capable of chelating
iron ions to form a substantially colorless complex. The method further
comprises incorporating in said water-borne road marking paint, a pigment
dispersant for further reducing or preventing yellowing of said
newly-applied 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 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
______________________________________
Example 1 & 4
Example 3 Examples 2 & 5
Component Weight (g/liter)
Weight (g/liter)
Weight (g/liter)
______________________________________
Binder.sup.1
487.0 487.0 487.0
Pigment 8.4 0.0 8.4
dispersant.sup.2
Chelating agent.sup.3
0.0 24.3 24.3
Non-silicone
4.0 4.0 4.0
defoamer.sup.4
Water 69.0 53.1 44.7
Titanium dioxide
265.0 265.0 265.0
pigment.sup.5
Ca carbonate 5
394.0 394.0 394.0
microns.sup.6
Ca carbonate 10
394.0 394.0 394.0
microns.sup.7
______________________________________
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 5:
TABLE 2
______________________________________
Examples 1-5
Component Weight (g/liter)
______________________________________
Freeze-thaw 26.0
stabilizer.sup.8
Coalescent.sup.9
23.0
Water 10.0
Base.sup.10 0.2
Non-silicone 1.0
defoamer.sup.4
Water 25.0
Total 1718.0
______________________________________
The components described in Tables 1 and 2 above are listed below:
1 is a PRIMAL.RTM. E-2706 (50%) polymer emulsion supplied by Rohm and Haas
Company, Philadelphia, Pa.
2 is a OROTAN.RTM. 901 (30%) is a pigment dispersant supplied by Rohm and
Haas Company, Philadelphia, Pa.
3 is a chelating agent formulated by mixing 45 grams of water with 15 grams
of a 28% ammonia solution, and then adding 40 grams DEQUEST.RTM. 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 DREW.TM. TG 4250 non-silicone defoamer supplied by Drew Ameroid
Nederland B.V., Triathlonstrasse 33, 3078 HX Rotterdam, The Netherlands.
5 is a TITAN.TM. TR 92 Titanium dioxide white pigment supplied by Tioxide,
West Site, Haverton Hill Road, Billingham, Cleveland TS23 1PS, United
Kingdom.
6 is a DURCAL.TM. 5 filler supplied by Omya, Pluess-Stauffer AG, CH-4665
Offringen, Switzerland.
7 is a DURCAL.TM. 10 filler supplied by Omya, Pluess-Stauffer AG, CH-4665
Offringen, Switzerland.
8 is Ethanol.
9 is a TEXANOL.RTM. Coalescent supplied by Eastman Chemical Co., Kingsport,
Tenn.
10 is ammonia used to adjust the pH of the formulation to 9 5.
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.sub.4 solution (3 g FeSO.sub.4.7H.sub.2 O, 1997 g
water, 6 drops 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
______________________________________
Yellowing
Yellowing
Chelating Pigment after after
Example
Agent Dispersant 2 hrs l6 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), which did
not contain the chelating agent. However, when the composition contained,
not only the chelating agent but also a pigment dispersant (Example 2),
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, i.e., 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 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 Tristimulus (Filter) Colorimetry". The b*
value is described in ASTM E-284 "Standard Terminology of Appearance"
under 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 "b* 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 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 5.
TABLE 4
______________________________________
Example
b* value
______________________________________
4 9.4
5 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 conditions when it is compared to a road marking from a traffic
paint composition (Example 4) which did not contain the chelating agent.
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