Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The invention relates to a coating
composition containing a dispersion of electrically
conductive particles in a dispersant, which consists of
at least an electrically conductive polymer
precipitated or adsorbed onto a first binder,
containing a non-doping polymer.
Such a coating composition is known from
EP-A-589,529. The composition described herein consists
of a dispersion of electrically conductive polymer
precipitated or adsorbed onto a binder, consisting of a
non-doping polymer.
In 1981 already Mengoli et al. suggested in
J. Appl. Polym. Sci. 1981, 26, 4247-4257, that
conductive polymers could be used in the protecting of
metals against corrosion. The first good results were
however obtained only 10 years later, by Thompson,
using a coating based on polyaniline, reported in Los
Alamos National Report LA-UR-92-360. It was found that
soft steel was in saline and acid environments
protected against corrosion, even in places where
scratches were made in the coating.
The coating composition known from EP-A-
589,529 can also well be used to provide metals with a
coating preventing corrosion. In particular because of
the coating composition s high stability, a high
concentration of conductive polymer can be obtained, as
a result of which such a coating composition can be
simply applied to an object, in a single layer
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homogeneously.
A drawback of this known coating
composition, however, is that the anticorrosive effect
of a coating based on it is much poorer in a damp or
wet environment than in a dry environment. In view of
the fact that corrosion of metal generally occurs in a
damp environment, this can be seen as a major drawback
for the application as anticorrosive paint.
The aim of the invention is to provide a
coating composition that does not present said
drawback.
This aim is achieved according to the
invention because the coating composition contains 50
to 99 wt.% of a second binder, relative to the total
solid substance present, which consists of electrically
non-conductive particles and the dispersant contains a
non-aqueous solvent.
The coating composition according to the
invention ensures that the coating based on it shows a
good anticorrosive effect in damp and wet environments.
It has surprisingly been found that, in spite of the
fact that the coating composition according to the
invention shows no or only very little electric
conductance, an excellent anticorrosive coating can
nevertheless be obtained with it.
A coating composition containing more than
99 wt.% of a second binder proved to afford little or
no protection against corrosion, as did a coating
composition that contained less than 50 wt.% of the
second binder.
Preferably the coating composition
according to the invention contains 70-90 wt.% of the
second binder. In this area a coating obtained with the
coating composition proved to show good dry and wet
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adhesion, in addition to good protection against
corrosion.
A non-doping polymer is used as the first
binder in the composition according to the invention.
The non-doping polymer preferably has good coating
properties. Such a polymer is for example chosen from
the group comprising alkyd resins, polyester resins,
amino resins, phenolic resins, polyurethane resins,
epoxy resins, acrylate resins, cyclic rubbers, for
to example polyisoprene, natural rubber, silicone resins,
polyvinyl chlorides, (poly)vinyl esters, for example
polyvinyl acetate, polyolefines, which for example
contain units chosen from the group comprising
ethylene, propylene, butadiene and styrene, and
hydrocarbon resins, for example (co)polymers of
cyclopentadiene.
The alkyd resins that can be used as the
first binder in the dispersion of electrically
conductive particles are for example composed of poly-
ols, chosen from the group comprising glycerol,
pentaerythritol, ethylene glycol, sorbitol,
trimethylolethane, trimethylolpropane, dipentaery-
thritol, tripentaerythritol, neopentyl glycol and
diethylene glycol, and polycarboxylic acids or
derivatives thereof, for example chosen from the group
comprising phthalic anhydride, phthalic acid,
isophthalic acid, malefic acid, malefic anhydride,
fumaric acid, fumaric anhydride and fatty acids, for
example linoleic acid and oleic acid. Possible
" 30 preparation methods of the alkyd resins are known to a
person skilled in the art and are for example described
by H.F. Mark et al. in the Encyclopedia of Chemical
Technology, 1978, Vol.2, pages 18-50.
Suitable polyester resins are for example
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composed of dicarboxylic acid units or derivatives
thereof, chosen from the group comprising malefic
anhydride, fumaric acid, adipic acid, phthalic acid,
isophthalic acid, terephthalic acid, tetrahydrophthalic
acid and tetrachlorophthalic acid, and diol units, for
example chosen from the group comprising 1,2-propanol,
1,3-butanol, ethylene glycol, neopentyl glycol,
diethylene glycol, bisphenol-A and tricyclodecane
dimethanol. Monofunctional and/or trifunctional monomer
units may optionally also be used. Possible preparation
methods of the polyester resins are known to a person
skilled in the art and are for example described by the
Oil and Colour Chemists' Association, Australia, in
"Surface coatings, Vol.1 - Raw materials and their
usage", Chapman and Hall Ltd, 1983, pages 78-87.
Suitable epoxy resins are for example
derived from bisphenol-A and epichlorohydrin. Use may
also be made of epoxidized aliphatic and cycloaliphatic
dienes, for example 3,4-epoxycyclohexylmethyl-3,4-
epoxycyclohexane carboxylate and 4-epoxyethyl-
1,2-epoxycyclohexane. Possible preparation methods of
epoxy resins are known to a person skilled in the art
and are for example described in Ullman's Encyclopedia
of Industrial Chemistry, 1985, Vol.A9, pp. 547-563.
Suitable polyurethane resins are for
example reaction products of isocyanates and polyols.
The isocyanates are for example chosen from the group
comprising 1,6-hexamethylene diisocyanate,
polymethylene polyphenylisocyanate, 4,4'-methylenebis-
(phenylisocyanate), 1,5-naphthalene diisocyanate,
bitolylene diisocyanate, methylene-
bis(cyclohexylisocyanate), isophorone diisocyanate,
trimethylhexamethylene diisocyanate, m-xylylene
diisocyanate, 1,3-bis(isocyanatomethyl)cyclohexane and
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1,4-bis(isocyanatomethyl)cyclohexane. The polyols are
usually chosen from the group comprising polyether
polyols and polyester polyols. Possible preparation
methods of polyurethane resins are for example
described in Kirk Othmer~s Encyclopedia of Chemical
Technology, 1982, Vo1.23, pages 576-608.
A dispersion of a polyurethane resin can
for example be stabilised by adding polyoxyethylene
segments to the polyurethane chain as for example
described by J.W. Rosthauser et al. in Advances in
Urethane Science and Technology, 1987, Stanford,
Vo1.10, pages 121-162, and by D. Dieterich in Progress
in Organic Coatings, 1981, Vol.9, pages 291-332. The
segments may be composed of modified diol or isocyanate
units, but it is also possible to add monohydroxyl-
functional polyoxyethylene polyethers directly onto the
polyurethane chain.
Suitable amino resins are for example
reaction products of formaldehyde with compounds
containing amino groups, for example melamine,
benzoguanamine, glycoluril and urea. Amino resins and
their preparation methods are for example described by
the Oil and Colour Chemist s Association, Australia, in
"Surface coatings, Vol.i - Raw materials and their
usage", Chapman and Hall Ltd, 1983, pages 87-98.
Suitable phenolic resins are for example
reaction products of a phenol compound and an aldehyde
compound or derivatives thereof. The phenol compound is
for example chosen from the group comprising phenol,
o-cresol, 2,4-xylenol, bisphenol-A, p-phenylphenol and
p-tertiary-butylphenol. The aldehyde compound is for
example formaldehyde. Phenolic resins and their
preparation methods are for example described by the
Oil and Colour Chemists Association, Australia, in
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"Surface coatings, Vol.l - Raw materials and their
usage", Chapman and Hall Ltd, 1983, pages 99-104.
Suitable silicone resins are for example
hydrolysis products of di- or trifunctional
chlorosilanes. The chlorosilanes are to this end for
example dissolved in an organic solvent such as toluene
or xylene and subsequently hydrolysed with water.
Silicone resins can also be prepared by treating
alkoxysilanes, for example methoxy, ethoxy and/or
propoxysilanes, with a strong acid in an aqueous medium
and subsequently causing polymerisation to take place.
Silicone resins and their preparation methods are for
example described by the Oil and Colour Chemists'
Association, Australia, in "Surface coatings, Vol.l -
Raw materials and their usage", Chapman and Hall Ltd,
1983, pages 134-143.
Suitable acrylate resins are for example
prepared through homopolymerisation of (meth)acrylate
monomers, for example methyl methacrylate, ethyl
methacrylate or ethyl acrylate, or copolymerisation of
these monomers with monomers that can react with them,
for example acrylonitrile, methacrylamide, malefic
anhydride, aliphatic chains with a terminal acrylate
group, methacrylic acid, vinyl acetate or styrene.
Acrylate resins and their preparation methods are for
example described by the Oil and Colour Chemists'
Association, Australia, in "Surface coatings, Vol.l -
Raw materials and their usage", Chapman and Hall Ltd,
1983, pages 144-157.
The conductive polymer in the coating
composition according to the invention consists of
monomers. These monomers are for example chosen from
the group comprising pyrrole, thiophene, indole,
carbazole, furan, benzene, aniline, acetylene and
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derivatives of these monomers. In view of the level and
the stability of the conductive properties, an
electrically conductive polymer consisting of pyrrole,
thiophene or aniline units or derivatives of these
( 5 monomers is preferable.
Examples of derivatives of these monomers
are N-methylpyrrole, N-ethylpyrrole, N-n-propylpyrrole,
N-n-butylpyrrole, N-phenylpyrrole, N-tolylpyrrole,
N-naphthylpyrrole, 3-methylpyrrole,
3,4-dimethylpyrrole, 3-ethylpyrrole, 3-n-propylpyrrole,
3-n-butylpyrrole, 3-phenylpyrrole, 3-tolylpyrrole,
3-naphthylpyrrole, 3-methoxypyrrole,
3,4-dimethoxypyrrole, 3-ethoxypyrrole,
3-n-propoxypyrrole, 3-phenoxypyrrole,
3-methyl-N-methylpyrrole, 3-methoxy-N-methylpyrrole,
3-chloropyrrole, 3-bromopyrrole, 3-methylthiopyrrole,
3-methylthio-n-methylpyrrole, 2,2'-bithiophene,
3-methyl-2,2'-bithiophene,
3,3'-dimethyl-2,2'-bithiophene, 3,4-dimethyl-2,2'-
bithiophene, 3,4-dimethyl-3',4'-dimethyl-2,2'-
bithiophene, 3-methoxy-2,2~-bithiophene,
3,3'-dimethoxy-2,2'-bithiophene,
2,2',5,2"-terthiophene, 3-methyl-2,2',5',-
2"-terthiophene, 3,3'-dimethyl-2,2',5',2°-terthiophene,
2-cyclohexylaniline, aniline, 4-propanoyl-aniline,
2-(methylamino)aniline, 2-(dimethylamino)-aniline,
o-toluidine, 4-carboxyaniline, n-methyl-aniline,
m-hexylaniline, 2-methyl-4-methoxy-carbonylaniline,
n-propylaniline, n-hexylaniline, m-toluidine,
' 30 o-ethylaniline, m-ethylaniline, o-ethoxyaniline,
m-butylaniline, 5-chloro-2-ethoxyaniline,
m-octylaniline, 4-bromoaniline, 2-bromoaniline,
3-bromoaniline, 3-acetamidoaniline, 4-acetamidoaniline,
5-chloro-2-methoxyaniline, 2-acetylaniline,
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2,5-dimethylaniline, 2,3-dimethylaniline,
N,N-dimethylaniline, 4-benzylaniline, 4-aminoaniline,
2-methyl- thiomethylaniline, 4-(2,4-dimethyl-
phenyl)aniline, 2-ethylthioaniline,
n-methyl-2,4-dimethylaniiine, n-propyl-m-toluidine,
n-methyl-o-cyanoaniline, 2,5-dibutylaniline,
2,5-dimethoxyaniline, o-cyanoaniline,
tetrahydronaphthylamine, 3-(n-butane sulphonic
acid)aniline, 2-thiomethylaniline, 2,5-dichloroaniline,
l0 2,4-dimethoxyaniline, 3-propoxymethylaniline,
4-mercaptoaniline, 4-methylthioaniline,
3-phenoxyaniline, 4-phenoxyaniline,
n-hexyl-m-toluidine, 4-phenylthioaniline, n-octyl-m-
toluidine, tetrahydrobenzo[c]thiophene,
4-trimethylsilylaniline and
3,4-(alkylene-vic-dioxy)thiophene.
The electrically conductive polymer may
optionally consist of a mixture of several of the
aforementioned monomer units.
The stabiliser of the first binder may be
chosen within a wide range and may be physically
adsorbed onto the binder particles (physically bound)
or be incorporated in the binder (chemically bound).
The stabiliser may be an ionic stabiliser or a non-
ionic stabiliser.
The weight ratio of the electrically
conductive polymer and the first binder may vary within
a wide range. Usually this ratio will lie between
0.1:99.9 and 80:20, preferably between 0.1:99.9 and
40:60, more preferably between 10:90 and 25:75. It has
however been found that a degree of variation in said
weight ratio in the composition of the electrically
charged particles or the use of several binders, onto
which the electrically conductive polymer has been
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precipitated or adsorbed, does not offer a solution for
the desired protection against corrosion under damp or
wet conditions.
Essential for the effect of the invention
is that the coating composition contains 50 to 99 wt.%
of a second binder, relative to the total amount of
solid substance present, which second binder consists
of electrically non-conductive particles.
The aforementioned weight percentages are
calculated on the basis of a coating composition from
which the dispersant has been removed, resulting in a
dry substance. The weight percentages mentioned in this
application are understood to be the weight percentages
based on the dry substance.
The second binder may be chosen from the
aforementioned group of suitable first binders. In this
case the second binder may also consist of the same
material as the first binder.
In addition to the option of choosing a
binder from the first group as the second binder it is
also possible to opt for a two-component binder system.
Examples of such a two-component binder system are
epoxide-thiol, epoxide-amine, epoxide-polyamide,
epoxide-acid, for example epoxide-carboxylic acid or
epoxide-phosphoric acid, epox'ide-anhydride, isocyanate-
thiol, isocyanate-alcohol, isocyanate-amine,
isocyanate-acid, anhydride-alcohol, anhydride-amine,
anhydride-thiol or melamine-formaldehyde systems.
The dispersant in the coating composition
according to the invention contains a non-aqueous
solvent. The dispersant is usually a mixture of the
dispersant used for the dispersion of electrically
conductive particles and the dispersant for the second
binder. Aqueous dispersants for the second binder at
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least proved to be disadvantageous for obtaining a good
adhesion of cured coating. The dispersant preferably
contains no or virtually no water. This is achieved if
the dispersion of electrically conductive particles is
also dispersed in a non-aqueous solvent. It has been
found that the wet adhesion in particular improves
considerably as the dispersant contains less water.
The invention also relates to a process for
preparing a coating composition according to the
invention. According to this process monomers are
polymerised in a solution to form an electrically
conductive polymer in the presence of a dispersion of a
first binder that has been stabilised with a non-ionic
stabiliser. This part of the process, in which the
electrically conductive particles are prepared, is
known and is described in detail in EP-A-589.529. The
coating composition according to the invention is
obtained because after the polymerisation of the
monomers:
- a second binder is added, the second binder being
dispersed in a dispersant containing a non-
aqueous solvent and the first binder containing a
non-ionic stabiliser,
or the dispersion precipitates, whether or not as
a result of the addition of a strong base, after
which the dispersion is again dispersed in a non-
aqueous solvent containing an organic acid and a
second binder,
the second binder consisting of electrically non-
conductive particles and the coating composition
containing 50 to 99 wt.% of the second binder, relative
to the total amount of solid substance present.
If a second binder dispersed in a
dispersant containing a non-aqueous solvent is added
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after the polymerisation of the monomers, the first
binder contains a non-ionic stabiliser. As in EP-A-
589,529, this ensures the stability of the dispersion
of electrically conductive particles.
~ A non-ionic stabiliser is for example
chosen from the group comprising alkylamines, alkyl-
amides, (ethoxylated) alkylalcohols, alkylpyrrolidones,
(ethoxylated) alkylphenols, polyoxyalkylesters,
polyoxyalkylethers, glycolalkylethers,
glycerolalkyiethers, esters of fatty acids and
(ethoxylated) sorbitanalkylates, (hydroxy(m)et-
hyl)cellulose, polyvinyl alcohols, polyvinyl
pyrrolidones, polyacrylamides. It is preferable to use
polyo~cyalkylethers on account of their high
effectiveness. Extremely suitable polyoxyalkyl ethers
are for example polyoxyethylene ethers, for example
polyethylene glycol, alkoxypolyethylene glycol, for
example methoxypolyethylene glycol, and ethylene
oxide/propylene oxide copolymers. In other cases it is
preferable to use polyoxyalkylesters on account of the
fact that they are not very toxic. A survey of
non-ionic stabilisers is given by Helmut Stache and
Kurt Kosswig in the Tensid-Taschenbuch, Carl Hanser
Verlag Wien, 1990.
If, after the polymerisation of the
monomers, the dispersion precipitates, whether or not
as a result of the addition of a strong base, it is
possible to work without the presence of a non-ionic
stabiliser in the first binder.
If the first binder~contains no stabiliser,
or an ionic stabiliser, the dispersion will usually
precipitate spontaneously after polymerisation. If the
first binder contains a non-ionic stabiliser, the
dispersion can be caused to precipitate by adding a
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strong base. A strong base may be for example alkali
hydroxide.
An ionic stabiliser may be an anionic or a
cationic stabiliser. Suitable anionic stabilisers are
for example alkyl sulphates and alkyl sulphonates,
ethoxylated alkyl sulphates, alkyl sulphonates and
alkyl phosphates, ethoxylated alkylcarboxylic acids and
alkyl phenol carboxylic acids, ethoxylated alkyl phenol
sulphates and alkyl phenol sulphonates,
sulphosuccinates and salts of carboxylic acid.
Suitable cationic stabilisers are for
example primary, secondary, tertiary and quaternary
ammonium salts, alkyl pyridinium salts and acetylated
polyainines .
Suitable stabilisers usually have a weight
average molecular weight of between 100 and 1000000,
preferably between 500 and 5000. A polymeric stabiliser
that is suitable for the invention usually consists of
monomer units containing 1-50 carbon atoms. This is
preferably 1-20 carbon atoms. The polymeric stabiliser
optionally contains several units containing different
numbers of carbon atoms. An example of such a
stabiliser is an ethylene oxide/propylene oxide
copolymer. The stabiliser that is not chemically bound
to the binder may have been added to the dispersion of
binder particles in the usual manner.
The stabiliser is preferably chemically
bound to the binder employed. This can be realized by
incorporating units of the stabiliser in the binder by
adding the stabiliser during the polymerisation of the
binder. It is also well possible to graft the
stabiliser onto an already polymerised binder.
The dispersion of binder particles usually
contains between 1 and 35 wt.% stabiliser, based on the
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total weight of the binder plus the stabiliser. This is
preferably 5-25 wt.%.
The invention also relates to the use of
the coating composition according to the invention in
an anticorrosive paint. For the preparation of such a
paint up to 60 and even up to 90 wt.% fillers and/or
antioxidants may optionally also be added to the
mixture of a first binder with an electrically
conductive polymer and a second binder without a
conductive polymer. Examples of fillers that may be
added are talc, barium sulphate, calcium carbonate,
fibres, (light-absorbing) pigments, for example
titanium white, and coloured pigments like iron oxide
and Si02, kaolin, wollastonite and glass. Adhesion-
promoting agents, plasticisers, fillers, thickeners,
surface-improving agents, antifoaming agents,
anticorrosive agents, hardeners, drying agents,
conductive materials, for example carbon black,
conductive fibres and conductive flakes and stabilisers
may also be added.
The invention also relates to an
anticorrosive paint containing the coating composition
according to the invention. Such an anticorrosive paint
is preferably used to protect metals like aluminium,
copper or iron or alloys with'these metals. For these
metals in particular the electrically conductive
polymer acts as a protective layer of a precious metal.
The aforementioned anticorrosive paint can be cured at
room temperature or at elevated temperature. Depending
on the binder composition and the curing temperature,
the curing can be accelerated by the presence of a
curing catalyst. Examples of this are siccatives,
bases, for example tertiary amines, acids, for example
paratoluene sulphonic acid.
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The invention also relates to a coating
based on the coating composition according to the
invention and to metal objects at least parts of which
are coated with this coating.
The invention will be further elucidated
with reference to some examples.
The surface resistance, in Ohm/C3, of the
coated products was determined with the aid of the
method described by H.H. Wieder in Laboratory Notes on
Electrical and Galvanomagnetic Measurements, Elsevier,
New York, 1979.
The adhesion was measured according to ISO
2409 (cross-cut tape test), in which G=0 stands for
excellent adhesion and G=5 for no adhesion. The values
measured under dry conditions were obtained in a cross-
cut tape test before the (wet) corrosion test and the
wet values were measured after the corrosion test.
For the tests, unless otherwise indicated,
the homogenised mixtures were applied to a standard
steel plate (Q-panel R-46) with the aid of a coating
knife, cured at room temperature and conditioned for I
week. Next, the dry adhesion was determined with the
aid of the cross-cut tape method.
Two scratches were cut through the coating
into the conditioned plates with the aid of a Stanley
knife. The steel plates were subsequently for 3 days
suspended in a 3.5% NaCl solution, through which a
continuous stream of air bubbled, after which the
plates were visually inspected to see whether any
corrosion had taken place. "+" corrosion observable;
"-" no corrosion observable.
Next, the same plates were subjected to the
"wet" cross-cut tape test.
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A solution was prepared of 4.86 grams of
FeCl3 (from Merck, free of water) in 21.25 grams of
demineralised water (solution A). Next, a solution was
prepared of 0.89 grams of pyrrole (from Aldrich,
vacuum-distilled) in 19.34 grams of demineralised water
(solution B).
At a temperature of 20°C solution A was
added, drop by drop, to 20 grams of a dispersion of
polyurethane (first binder) in water (Uraflex XP 401
UZ, DSM Resins, solids content 40%, average particle
size 60nm, which had been stabilised by means of
incorporated methoxypolyethylene glycol chains (Mw=750
g/mol). The addition of the drops took place while the
dispersion was being stirred with the aid of a stirring
bar. During the addition of the drops the temperature
was kept at 20°C. The dispersion was yellow/green.
After half an hour s stirring solution B
was subsequently added, drop by drop, with stirring.
After solution B had been added, the dispersion s
colour changed to dark green and then black.
After 20 hours stirring at a temperature
of 20°C, a portion of the dispersion was centrifuged for
half an hour at a rate of 20000 rpm. Next, the
supernatant water layer was poured away and the
sediment (2.63 grams) was redispersed in 13.1 grams of
demineralised water with the aid of an Ultra-Torrax T
25 (Janke & Kunkel JK Labortechnik). A stable
dispersion of electrically conductive particles
containing 20 wt.% solids was obtained (solution C).
A 20 wt.% solution of UracronRZW3410 (from
DSM Resins) in 2-methoxypropanol was prepared as the
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second binder (solution D). 1 wt.% paratoluenesulphonic
acid-was added to a mixture of solutions C and D (see
Table 1 for the different mixing ratios). The
dispersion thus obtained was homogenised for 5 minutes
using an Ultra-Torax. The results are given in Table 1.
Sol. C' Sol. D corro- resista adhesion adhesio
sion nce (dry) n
(wt.%) (wt.%) (Ohm/0) (wet)
0 100 + ~1p12 0 0
90 - X1012 0 0
80 - X1012 0 0
70 - 1010 0 2
60 + 108 0 5
As the second binder, a solution was
prepared of 6.44 g of Uracron XP780CB (92% solids) and
11.58 g of Uracron XP770CB (50% solids) in 2-methoxy-
propanol (total solids content 20%) (solution E).
Solutions C and E were mixed in different ratios (see
Table 2), after which the mixture was homogenised for 5
minutes using the Ultra-Torrax. The results of the
corrosion test and the cross-cut tape test are given in
Table 2.
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Sol. C Sol. E corro- resista adh adhesio
sion nce n n
(wt.%) (wt.%) (Ohm/) (dry) (wet)
0 100 + >1012 0 0
10 90 - >1012 0 0
20 80 - >1012 1 1
30 70 - 104 1 2
40 60 - 104 1 4
i i
Examt~le IV
Solution C was freeze-dried and redispersed
to form a 20 wt.% dispersion of electrically conductive
particles in methoxypropanol (solution F). 1 wt.%
paratoluenesulphonic acid was added to a mixture of
solutions D and F (see Table 3 for the different mixing
ratios). The dispersion thus obtained was homogenised
for 5 minutes using an Ultra-Torax. The results of the
corrosion test and the cross-cut tape test are given in
Table 3.
Sol. F Sol. D corro- resista adhesio adhesio
sion nce n n
(wt.%) (wt.%) (Ohm/) (dry) (wet)
0 ~ 100 ~ + ~ >1p12 0 ( 0
~
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90 - X1012 0 0
80 - ~1p12 0 0
70 - 109 0 0
60 + 106 0 3
In all cases the presence of the
electrically conductive particles proves to be
5 essential for the corrosion resistance, as does the
presence of at least 50 wt.% of the second binder. The
wet adhesion moreover proves to be considerably better
when use is made of a solvent free of water.
10 Example V
An NaOH solution was added to solution C to
a pH of 14, after which the solution was after 1 day
centrifuged at 1000 g. The centrifugate was decanted
and the sediment was redispersed to form a 20 wt.%
15 dispersion of electrically conductive particles in
methoxypropanol (solution G). 1 wt.%
paratoluenesulphonic acid was added to a mixture of
solutions D and G (see Table 4.for the different mixing
ratios). The dispersion thus obtained was homogenised
20 for 5 minutes using an Ultra-Torax. The results of the
corrosion test and the cross-cut tape test are given in
Table 4.
Sol. F Sol. D corro- resista adhesio adhesio
sion nce n n
(wt.%) (wt.%) (dry) (wet)
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( ohm/
D )
0 100 + ~lpl2 0 0
10 90 - X1012 0 0
20 80 - ~1p12 0 0
30 70 - 109 0 0
40 60 + 106 0 3
I
A 50 wt.% solution of EpikoteR 1001 in a
(1/1, w/w) mixture of 1-methoxy-2-propanol and
propylene glycol methyl ether acetate was prepared
(solution H). 1 wt.% paratoluenesulphonic acid was
added to solution G (solution I).
The coatings employed were prepared by
adding to solution H an equimolar amount (relative to
the number of epoxides) of isophorone diamine together
with the required amount of solution I and were
homogenised with the aid of a DispermatR at 2000-4000
rpm. Then steel plates were sprayed with the aid of a
spray gun. The coating obtained in this way was cured
at 80°C for 30 minutes. There where a top clear coat
(TCC; indicated by + in Table 5) was applied with the
aid of the spray gun as an extra layer on top of the
conductive layer, use was made of solution H and an
- 20 equimolar amount of isophorone diamine, after which the
top layer was cured for 30 min. at 80°C. All the plates
were stored at room temperature for 4 weeks to ensure
complete curing of the coating before a 1-mm-wide
cross-shaped incision was made (down to the iron) and
the plates were exposed to the outdoor atmosphere for 9
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months. The results are given in Table 5.
Sol. Sol. H + TCC Corrosion Corrosion of adhe-
I isophorone at the undamaged sion
-diamine cross material (wet)
0 100 - + + 5
+ + + 5
95 - +/- - 3
+ +/- - 3
90 - - - 0
+ - - 1
30 70 - - - 1
+ - - 1
II I I I I I !
5
Experiments analogous to solution I were
carried out for the purpose of comparing solution I
(the conductive polymer is not dispersible in water)
10 and solution C (the conductive. polymer is dispersible
in water. The results are given in Table 6.
Sol. Sol. H + TCC Corrosion Corrosion of adhe-
I isophorone at the undamaged sion
-diamine cross material (wet)
0 ~ 100 ~ ~ + ~ + ~ 5
-
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+ + + 5
5 95 - + + 4
+ + + 4
10 90 - +/- - 3
+ +/- - 3
30 70 - - - 1
+ - - 1
These experiments clearly show that the
presence of the conductive polymer is essential for the
resistance to corrosion. The experiments in Tables 5
and s also show that the resistance to corrosion is
increased if the conductive polymer is no longer
dispersible in water.
