Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02318442 2000-07-13
WO 99/36192 PCT/US99/00377
.U~~LIQ~LQtI
PROCESS FOR IMPROVING THE CORROSION RESISTANCE OF A METAL SURFACE
FIELD OF THE INVENTION
This invention relates to a method for coating metal surfaces in order to
impart
corrosion resistance thereto. More particularly, the invention relates to a
method for the
anticorrosion coating of metal surfaces in which a resin coating is formed on
a metal
surface using an autodepositing resin composition and the resulting resin
coating is post-
treated white still in 'tts uncured condition in order to improve the
corrosion resistance and
adherence of the resin coating.
BACKGROUND OF THE INVENTION AND RELATED ART
1o Resin compositions that have the ability to form a resin coating on a metal
surface by contact between the metal surface and an acidic aqueous
autodeposition
composition containing an organic coating-forming resin are already known in
the art.
Various examples thereof are taught in Japanese Published Patent Application
(Kokoku
or Examined) Number Sho 47-17630 (17,63011972), Japanese Published Patent
Application (Kokoku or Examined) Number Sho 52-21006 (21,00611977), Japanese
Published Patent Application (Kokoku or Examined) Number Sho 54-13435
(13,43511979), and Japanese Patent Application Laid Open (Kokai or Unexamined)
Number Sho 61-168673 (168,673/1986). A characteristic feature of these known
resin
coating compositions is that their contact with a suitable clean metal surface
results in
2o the formation of a resin coating whose thickness or weight increases with
the time of
contact. In addition, since coating formation in this technology is achieved
by the
chemical activity of the resin composition at the metal surface (metal ions
eluted from the
metal surface by etching are believed to act on the resin particles to induce
deposition
thereof on the metal surface), this technology can be distinguished from
electrodeposition by its ability to efficiently form a resin coating on metal
surfaces without
the external application of electricity to the metal on which the coating is
formed.
However, the coatings afforded by the prior-art autodepositing resin
compositions
have not always evidenced a satisfactory corrosion resistance or adherence.
This has
resulted in 'the development of a variety'of tactics for engendering
additional iiriprove
3o ments in the corrosion resistance and adherence of the autodeposited resin
coating re
siding on the metal surface. For example, a number of different methods are
known in
which the stilt uncured autodeposited resin coating is subjected to a chemical
treatment
(post-treatment).
1
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WO 99/36192 PCTIUS99/00377
United States Patent Number 3,795,546 teaches that the post-drying corrosion
resistance of the resin coating can be improved by exposing the uncured
autodeposited
resin coating prior to its thermal drying to an aqueous solution that contains
approximate-
ly 2.5 to 50 g/L polyacrylic acid and hexavalent chromium. However,
environmental pol-
y lution considerations make it desirable to avoid the use of chromium-
containing
treatment baths.
Japanese Patent Application Laid Open (Kokai or Unexamined) Number Sho 52-
68240 (68,240/1977) teaches that the post-drying corrosion resistance of the
resin coat-
ing can.be.improved. by exposing the uncured.autodeposited..resin
coating..prior.to.its - .. .
f o thermal drying to an aqueous dispersion or aqueous solution whose base
component is
to 100 gIL nitrogenous organic compound, for example, at least 1 selection
from the
group consisting of amines, the amine salts of carboxylic acids, amino acids,
melamine,
and amides.
The post-treatment of autodeposited resin coatings with a nitrogenous organic
compound is an effective means for improving the con-osion resistance and
adherence
of the ultimately obtained resin coating. However, since autodeposition
coating is
typically implemented by dipping or immersion, the acid component andlor metal
ions
component (for example, the iron ions) present in the uncured autodeposited
resin
coating will elute into the treatment solution used as the post treatment
agent (the post-
treatment solution}. Since this will frequently cause a loss of stability of
the post-
treatment solution, this approach may not always be acceptable when viewed
from the
perspective of producing a resin coating that evidences a continuously stable
product
quality.
PROBLEMS) TO BE SOLVED BY THE INVENTION
The present invention provides a method for the anticorrosion coating of metal
surtaces that produces an excellent adherence and resistance to corrosion and
that
maintains its ability to generate these properties even after its post-
treatment solution
has been used to treat a substantial amount of metal surface.
BRIEF SUMMARY OF THE INVENTION
3o It has been discovered that a high-quality autodeposited resin coating can
be
obtained by forming an uncured resin coating on a metal surtace by bringing
the metal
surface into contact with an autodepositing coating composition; by then
executing a
post-treatment on the uncured resin coating prior to its thermal drying using
a post-
treatment solution that contains as its essential components a water soluble
amino resin
bearing specific reactive functional groups and an amine compound; and by
thereafter
drying and curing the post-treated resin coating.
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DETAILED DESCRIPTION OF THE INVENTION
A process according to the present invention for the anticorrosion coating of
metal surfaces characteristically comprises operations of:
(I) forming an adherent wet uncured resin coating on a metal surface by
bringing the
s metal surface into contact with an aqueous autodepositing resin composition
that
contains oxidizing agent, acid, and water-dispersible or water-soluble organic
resin, said resin containing a product of the polymerization of at least one
selection from carboxyl-functional condensation potymerizable monomers and
hydroxyl-functional condensation polymerizable monomers;
(11) subjecting the resulting uncured resin coating to a post-treatment by
bringing the
aforesaid resin coating, while it is stilt in its uncured cond~ion, into
contact with
an aqueous solution that contains:
- from 10 to 100, or more preferably from 20 to 50, grams per liter,
hereinafter usually abbreviated as "gIL", of water-soluble amino resin that
bears in each molecule at least two reactive functional groups selected
from the alkoxymethylamino, methylotamino, and imino groups; and
- from 0.5 to 5.0 g/L, or more preferably from 1.0 to 2.0 gIL, of at least one
organic amine compound that does not contain more than 20, or, with
increasing preference in the order given, not more than 18, 16, 14, 12,
10; or 8 carbon atoms per molecule; and
(III) subjecting the resin coating afforded by operation (It) as described
immediately
above to drying and curing.
The solution for the post-treatment of aqueous autodepositing resin
compositions
according to the present invention preferably contains its water soluble amino
resin and
its other amine compound as described above in a weight ratio from 2.0 : 1.0
to 200
1.0, or more preferably from 5.0 : 1.0 to 50 : 1Ø
When the post-treatment agent and post-treatment solution contain less than
the
specifies! amount of viiater-soluble amino resin, the ukimately obtaihed resin
coating will
usually exhibit an inadequate corrosion resistance and adherence. The effects
provided
3o by the water soluble amino resin do not increase at amounts in excess of
the specified
upper limit, and such amounts are also problematic because they cause the
content of
the amine compound to be too low on a relative basis. More specfically, a too
low
content of amine compound causes the resulting post-treatment solution to have
an
unsatisfactory stability during continuous use; this results in variations in
the quality of
the resin coating product. A too high content of the amine compound causes the
content
of the water-soluble amino resin to be too low on a relative basis, resulting
in an unsatis-
3
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WO 99/36192 PCT/US99/00377
factory corrosion resistance and adherence.
Each molecule of the water-soluble amino resin used by the present invention
preferably contains at least two reactive functional groups represented by at
least one
OF the following chemical moiety formulas (1 ), (2), and (3):
s (1) ~
-N-CH20R, where R is -CH3, --C2H5, C3H,, or -C,Ho (alkoxymethylamino);
(2) -N-CHzOH (methyiolamino);
(3) -N-H (imino)
The water-soluble amino resin used in the present invention can be selected
from methylated melamine resins ,(the degree of methylation is not critical
and highly
is methyiated melamine resins and. partially methylated melamine resins can be
used),
imino-type methylmelamine resins, imino-type methylated melamine resins,
methylolated
melamine resins, benzoguanamine resins, and glycoluryl resins.
The amine compound in the post-treatment agent and post-treatment sotutiori
used in the present invention can be selected from the group consisting of
monoalkyla-
2o mines, dialkylamines, trialkyfamines, monoalkenylamines, dialkenylamines,
trialkenyl-
amines, monoalkanolamines, dialkanolamines, and trialkanolamines, as
preferably ex-
emplfied- by ethyl~imine, propylamine, isopropylamine, butylainine,
dimethyl~mine,
diethylamine, dipropylamine, dibutylamine, triethylamine, tripropylamine,
allylamine,
diallylamine, triallylamine, dimethylethanolamine, diethylethanoiamine,
ethanolamine,
25 diethanofamine, and triethanolamine. Each of the alkyl, alkenyi, and
alkanol groups in
the subject alkylamines, alkenylamines, and alkanolamines independently
preferably
contains from 1 to 15 carbon atoms, or more preferably, with increasing
preference in
the order given, not more than 10, 8, 6; or 4 carbon atoms.
The amine compound used in the post-treatment solution in a method accord-
3o ing to the present invention for the anticorrosion coating of metal
surfaces is most
preferably selected from the group consisting of ethylamine, propylamine,
isopropylamine, butyiamine, dimethylamine, diethylamine, dipropylamine,
dibutylamine,
triethylamine, tripropylamine, allylamine, diallyfamine, triallylamine,
dimethylethanolamine, diethylethanolamine, ethanolamine, diethanolamine, and
35 triethanolamine.
The post-treatment solution used in the present invention may also optionally
contain one or more ammonium salts. Preferred ammonium salts can be selected
from
those taught in Japanese Patent Application Laid Open (Kokai or Unexamined)
Number
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WO 99/36192 PCT/US99/00377
Hei 3-505841 (505,84111991) and Japanese Patent Application Laid Open (Kokai
or
Unexamined) Number Hei 5-186889 (186,889/1993), for example, ammonium bicarbon-
ate and ammonium hydroxide.
The aqueous autodepositing resin composition used in the method of the
s present invention contains metal ions, oxidizing agent, acid, and water-
dispersible or
water-soluble coating-forming organic resin that contains the product of the
polymerization of at least one selection from carboxyl-functional monomers and
hydroxyl-
functional monomers.
Carboxyl-functional monomers employed in the production of the coating-
to forming organic resin used in a method according to the present invention
are
ethylenically unsaturated carboxylic acid monomers, for example, acrylic acid,
methacryl-
ic acid, malefic acid, itaconic acid, and fumaric acid. Hydroxyl-functional
monomers em-
ployed in the production of the coating-forming organic resin used by the
method accord-
ing to the present invention are ethylenically unsaturated hydroxylated
monamers, for
~ 5 example, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl
methacrylate,
2-hydroxypropyl methacrylate, hydroxybutyl acrylate, and hydroxybutyl
methacrylate. In
addition to the carboxyl-functional monomers and hydroxyl-functional monomers,
the po-
lymerization that produces the coating-forming organic resin used in the
method ac-
cording to the present invention may also employ one or more other
ethylenically
2o unsaturated monomers. These other ethylenically unsaturated monomers can be
selected from, for example, methyl acrylate, ethyl acrylate, n-butyl acrylate,
2-ethylhexyl
acrylate, methyl methacrylate, ethyl methacrylate, and n-butyl methacrylate.
The film-forming organic resin used in the method according to the present
invention can also be selected from polyester polyol compounds as afforded by
the
25 polyesterification of pofyhydric alcohol molecules bearing at least two
hydroxyl groups
each with organic acid molecules bearing at least two carboxyl groups each.
The former
are exemplified by ethylene glycol, propylene glycol, and 1,6-hexanediol,
while the latter
can be exempl~ed by phthalic acid, isophthalic acid, and terephthalic acid.
The coating-
forming organic resin used by the method according to the present invention
will
3o comprise at least one selection from the above-described polymers,
copolymers, and
polyester polyofs.
While the molecular weight of the coating-forming organic resin used in the in-
vention method is not crittical, molecular weights of, for example, 20,000 to
1,000,000 are
preferred and molecular weights of 100,000 to 1,000,000 are particularly
prefer-ed. This
35 molecularweight can be measured by gel permeation chromatography in
tetrahydrofuran
using polyethylene or polyacrylate ester as the reference material.
CA 02318442 2000-07-13
WO 99/36192 PCT/US99/00377
The coating-forming organic resin employed by the invention is preferably
used in the form of an aqueous emulsion, which in many cases can be prepared
by a
conventional emulsion polymerization technique. However, this aqueous emulsion
can
also be prepared by taking a coating-forming organic resin prepared by another
polymerization technique and emulsifying the resin in water.
On the subject of the resin emulsion as afforded by emulsion polymerization,
the polymerization conditions used therefor are not criticat and the usual
methodologies
can be employed for this emulsion polymerization. For example, an emulsion of
the
coating-forming resin can be prepared by running a polymerization reaction in
a mixture
comprising at leastwater, anionic andlor nonionic surfactant, monomerforthe
resin com-
ponent as described above, and polymerization initiator.
The autodepositing resin composition used by the present invention can be
prepared by mixing coating-fom~ing organic resin obtained as described above,
acid, oxi-
dizing agent, and optionally a compound capable of furnishing metal ions and
by then
~ 5 also adding water as necessary or desired.
The aad used in the subject autodepositing resin composition preferably is at
least one selection from fluorozirconic acid, fluorotitanic acid,
fluorosilicic acid,
fluoroboric acid, hydrofluoric acid, phosphoric acid, and nitric acid. The use
of
hydrofluoric acid is most preferred.
20 The oxidizing agent preferably is hydrogen peroxide, potassium
permanganate, or sodium nitrite; the use of hydrogen peroxide is most
preferrerd.
The compound capable of furnishing metal ions is not critical as long as this
compound is stable in the resin composition. This compound preferably is
ferric fluoride,
ferric nitrate, ferrous phosphate, or cobaltous nitrate, with ferric fluoride
being most pre
25 ferred.
The aqueous autodepositing resin composition used by the method of the
present invention preferably contains from 5 to 550. gIL and more preferably
from 50 to
100 gIL of the above-described coating-forming organic resin, in each case
measured
as the concentration of resin solids. The acid concentration is preferably
from 0.1 to 5.0
3o g/L and more preferably from 0.5 to 3.0 gIL, and the oxidizing agent
concentration is
preferably from 0.01 to 3.0 gIL and more preferably from 0.03 to 1.0 gIL. A
metal ions
source compound need not be present, but the use of this compound is
preferred, in
which event its concentration is preferably no greater than 50 g!L and more
preferably
is from 1.0 to 5.0 g/L.
3s The aqueous autodepositing resin composition used in a method of the
present invention may contain optional components in addition to the
components
6
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described above. Thus, this composition may contain a coalescing agent such
as, for
example, trialkylpentanediol isobutyrate or alkyl carbitol, and pigment such
as, for
example, carbon black, phthalocyanine blue, phthalocyanine green, quinacridone
red,
Hansa yellow, and benzidine yellow. The coalescing agent functions to lower
the
minimum temperature for coating formation during formation of the deposited
resin
coating and thereby further facilitates melt-bonding of the deposited resin.
The technique for effecting contact between the metal surface and the aque-
ous autodepositing resin composition is not critical to the method according
to the pres-
ent invention. Dipping, applicator methods, and spraying can be used, with
dipping
to being preferred. Nor are the treatment temperature and treatment time
critical to the
instant method. In the case of dipping, the metal stock is generally
preferably dipped in
the composition at room temperature, for example, 18 to 25 °C, for from
30 to 300
seconds and preferably from 90 to 180 seconds.
The extent of resin coating formation on the metal surface is also not
critical,
but dried film thicknesses of 10 to 40 micrometers are preferred and dried
film thickness
es of 20 to 30 micrometers are particularly preferred. As a general matter the
metal
surface is preferably degreased and then rinsed with water prior to its
contact with the
resin composition.
One of the most significant features of the invention is the excellent
stability
of the post-treatment solution. If the amino resin component were used by
itself, the
hydrofluoric acid (acid component) and iron ions (metal ions) eluting and
admixing into
the post-treatment solution during post-treatment of the resin coating with
the post
treatment solution would cause the coagulation of the water-soluble amino
resin
component present in the post-treatment solution and hence would cause a
substantial
dedine~in the stability of the post-treatment solutiori: This ~in tum would
lead to variations
in the quality of the post-treated coating. However, the amino compound
present in the
treatment solution, which can neutralize the eluting acid component and
complex the iron
ions, inhibits adverse effects on the water-soluble amino resin and stabilizes
the post-
treatment solution.
3o With regard to the process conditions in the post-treatment process of the
method of the invention, the temperature of the post-treatment solution is
preferably from
10 to 40 °C as a general rule and is particularly preferably from 20 to
25 °C, and the
treatment time is preferably in the range from 20 to 180 seconds. Solution
temperatures
below 10 °C result in a pronounced tendency for the resin coating to
crack during the
thermal drying step, while temperatures in excess of 40 °C tend to
produce an undesir-
able appearance of the coating due to a pronounced tendency for the coating to
whiten
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after thermal drying. The effects from the post-treatment normally will be
inadequate at
treatment times of less than 20 seconds, while treatment times greater than
180 seconds
have a tendency to impair the adherence of the coating and the uniformity of
appearance
of the coating.
After the post-treatment process as described hereinabove the resin coating
is submitted to drying and curing. The conditions used in the drying and
curing process
will vary as a function of the type of coating-forming organic resin used in
the autode-
positing resin composition, but thermal drying will generally be carried out
at from 110
to 200 °C for a time that is from 5 to 30 seconds.
This invention will be illustrated in greater detail below by working and
comparative examples.
Examples of synthesis of coating-forming organic resins
"Resin (A)"
A monomer component of 5 parts of methacrylic acid, 5 parts of 2-hydroxyethyl
methacrylate, 12 parts of styrene, 40 parts of acrylonitrile, and 38 parts of
ethyl acrylate
was mixed with 1 part of acrylate ester-type reactive surfactant, 0.3 part of
ammonium
persulfate, and 398.7 parts of water. The resulting mixture was emulsion-
polymerized
at 75 °C to give a coating-forming organic Resin (A) with a resin
solids content of 20 %.
"Resin (B)"
2o A monomer component of 8 parts of methacrylic acid, 12 parts of methyl
methacrylate, 40 parts of acrylonitrile, 20 parts of ethyl acrylate, and 20
parts of butyl
acrylate was mixed with 1 part of acrylate ester-type reactive surfactant, 0.3
part of
ammonium persulfate, and 398.7 parts of water. The resulting mixture was
emulsion
poiymerized at 75 °C to give a coating-forming organic Resin (B) with a
resin solids con
tent of 20 %.
Examples of preparation of post-treatment solutions
"Post-treatment Solution (A)"
A methyiol-functional water-soluble resin (solids = 88%, a partially
methylated
melamine-formaldehyde resin from Mitsui Cytec Ltd.) was dissolved in deionized
water
3o so as to provide a resin concentration of 10 gIL. Triethanolamine was added
to the re
sulting solution so as to give a triethanolamine concentration of 0.2 gIL. The
solution
was then brought to a total of 1 liter with deionized water to give Post-
treatment Solution
(A).
"Post-treatment Solutions (B) to (G)"
Post-treatment Solutions (B) to (G) were each prepared as described for Post-
treatment Solution (A), but using the components and component additions
reported in
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Table 1 below.
Process Examples and Comparison Examples
Example 1
Preliminarily cleaned cold-rolled steel sheets (70 x 150 x 1 millimeters,
herein-
after usually abbreviated as "mm") were coated by dipping for 180 seconds into
a treat-
ment bath comprising Autodepositing Resin Composition (1) described below
while the
bath temperature was maintained at 20 to 22 °C. After a water rinse,
the resulting
uncured autodeposited resin coating was then dipped in Post-treatment Solution
(A) at
Table 1
Identify-g/L g/L Performance
ing in in Test
Post-treat- Post-treat- Results
meat meat for:
Solution Solution
of of
LetterAmino Amine Coating% Remaining Creep
for Resin Type: Thiclc-in in
Post- Type: Adheaioa mm
treatmen Test after
t SolutionPMMR HMMR Dietha-Trietha-n~s' Pre-Im-Post s on
nolaminenolamiae~m mersioaIm- Test
mersion
A 0 10.0 0 0.2 25 100 100 7.0
B 80.0 0 0.2 1.0 30 100 100 5.0
C 40.0 0 0 2.0 28 100 100 6.0
D 20.0 0 0 4.0 32 100 100 6.0
E 40.0 0 0 0 27 100 100 6.0
F 80.0 0 0 6.0 33 100 50 15.0
G 10.0 0 0 0.05 24 100 100 7.0
H No post-treatment 25 100 100 Overall
rust
Abbreviations for Table 1
"PMMR" means "partially methylated melamine resin" (88 % solids, from Mitsui
Cytec Ltd.).
"HMMR" means "highly methylated melamine resin" (100 % solids, from Mitsui
Cytec Ltd.).
"pm" means "micrometres".
24 °C followed by dfying ire a convection oven for 1-80 °C fflr
20~ rnmutes. The coated
sheet afforded thereby was subsequently tested for coating performance.
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WO 99/36192 PCT/US99/00377
Aut'odepositing Coating Composition (1)
Comment Amount Blended (glt,)
Resin (A) 250.D0
Coalescing Agert (A) 4.00
s Hydrofluoric acid t.00
Ferric fluoride 3.00
HYd~n pgro~e 0.10
Deionaed water amount sufficient to make a total of 1 liter
Coal agent (A) was trialkylpernansdrol isobutylste. Its ac~ition cs4sed the
i o minimum eostingiomng temperaane of the resulting canposit~on (1 ) to
b~come about
20 °C.
Example 2
A res~-coated shoat was pfeparod generally ats descxibad in Example 1. but in
this example me uncurod aertodeposvtecl rosin croattng afforded by
Autodepositing
>.s Costing Composition (1) was dipped st 24 °C in Post treatment
Solution (B) with the
composition reported in Table 1. This was fo0owed by drying in a convection
oven at
180 °C for 20 minutes and suamisaion to the various coating performanca
tests.
Example 3
A rosins stwet was pnepar~ad genetaNy as described in Example 1, but m
2o this example coating was run using AutabeposrtJng Coating Composition (2)
with the
composition desuibed deiow. The resulting uncured autodepoesed resin coating
was
dipped at 24 °C in Post treatment Sdution (C) wrth the composition
reported in Taale 1
This was foJlowad by drying in a convscximt oven at 180 °C for 20
minutes and
submission to the vari~rs coating perfomnance tests.
zs Autodapositing Coating Composition (2)
Component Amount Alended (g/l.)
R~esm (8) 250.00
Coalesang Agent (A) 3.00
Hydrofluoric aad 1.00
3o Femc ffuonde 3.00
Hydrogen peroxide 0.10
Deionized water amount suf5cient to make a total of 1 ~ter
Example 4
A n~in-nested chee~t was pt~arad gener~y as m Example 7, but in this example
3s usir~ the Autodep~iting Coating Composition (3) with the composition
described below
prepared using a water based autodepos~tmg polyester resin (txand name_
Aronmelt.
to
CA 02318442 2000-07-13
WO 99/36192 PCT/US99/00377
30 °~ solids, from Toa Gosei Co., Ltd.). The resulting uncured
autodeposited resin
coating was dipped at 24 °C in Post-treatment Solution (D) with the
composition reported
in Table 1. This was followed by drying in a convection oven at 180 °C
for 20 minutes
and submission to the various coating performance tests.
Autodepositing Coating Composition (3)
Component Amount Blended (gIL}
Water-based polyester resin 165.00
Hydrofluoric acid 1.00
Ferric fluoride 3.00
Hydrogen peroxide 0.10
Deionized water amount sufficient to make a total of 1 liter
Comparative Examples 1 to 3
Resin-coated sheets were prepared generally as described in Example 3, but
using the above-described Autodepositing Coating Composition (2). The
resulting
t5 uncured autodeposited resin coatings were dipped at 24 °C in one of
the Post-treatment
Solutions (E) to (G) with the compositions reported in Table 1. This was
followed by
drying in a convection oven at 180 °C for 20 minutes and submission to
the various coat-
ing pertormance tests.
Comparative Example 4
2o A resin-coated sheet was prepared generally as in Example 1 using the above-
described autodepositing coating composition (1 ). The resulting uncured
autodeposited
resin coating was then dried, without post-treatment, in a convection oven at
180 °C for
20 minutes and submitted to the various coating performance tests.
The coating pertormance tests were as follows.
25 (1 ) Coating thickness
The thickness was measured at three locations (upper, middle, and lower
regions) on the sample sheet, and the average of these values is reported in
Table 1.
(2) Adherence (crosshatchltape peel test)
The test coupon was immersed in warm water (40 °C} for 240 hours. Both
before
30 and after this immersion, a 100-square grid (1-mm intervals} was scribed in
the test
coupon, pressure-sensitive adhesive tape was applied to the grid, the tape was
peeled
off, and the number of remaining squares of the coating was counted. The
results
before and after immersion are reported in Table 1.
(3) Corrosion resistance
35 A cross was scribed in the resin coating of the test coupon to the basis
metal,
and the scribed coupon was subjected to salt-spray exposure for 240 hours
(according
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WO 99/36192 PCT/US99/00377
to Japanese Industrial Standard Z-2371 }. The width of the rust or blistering
produced
at the scribed cross was measured post-exposure (maximum for both sides, in
mm).
Evaluation of the stability of the post-treatment solution after use
In each of Examples 1 to 4 and Comparative Examples 1 to 3, the resin coating
composition (uncured) was subjected to post-treatment at the rates of 0.05,
0.5, 1.0, and
2.0 square meters (hereinafter usually abbreviated as "m2") of surface area
per 1 liter
(hereinafter usually abbreviated as "L") of post-treatment solution. After use
each post
treatment solution was held for 1 week at room temperature and the character
of the so
lution was then visually evaluated. The results are reported in Table 2, using
the follow
ing scale:
+ + : no abnormalities
+ : turbidity has appeared
solids have appeared
Post-treatment was run in Examples 2 and 3 at the rate of 2.0 m2 of surface
~5 area per 1 L of post-treatment solution, and the resulting resin coatings
were submitted
to the coating performance tests described above.
Table 2
Post-treatmentStability
Solution of Post-tree-
Identi- tment Solution
after Use
for
fying Letter0.05 m=/L 0.5 m=IL 1.0 m=/L 2.0 m=/L
A ++ ++ ++ +
B ++ ++ ++ ++
C ++ ++ ++ ++
D ++ ++ ++ ++
x not measurednot measurednot measured
F ++ ++ ++ ++
G + + + x not measured
12
CA 02318442 2000-07-13
WO 99/36192 PCT/US99/00377
The results are reported in Tabte 3.
Table 3
IdentifyingPerformance
Test Results
for:
Letter ~.
for ~
Poat- Coating Thick-% Remaining Creep in mm after
in Corro-
treatment ness, Erm Adhesion sion Test
0 Test
1 Solution
pre-Im-Post Im-
mersionmersion
B 28 100 100 5.0
C 26 100 100 6.0
As the results reported in Tables 1 to 3 make clear, the post-treatment
solutions
15 used in Examples 1 to 4, which employed the method according to the present
invention,
were very stable and afforded highly corrosion-resistant and strongly adherent
resin
coatings. In contrast, the resin coatings afforded by Comparative Examples 1
to 3 gave
unsatisfactory results for at least one property from among con-osion
resistance, adher-
ence, and stability of the post-treatment solution.
20 BENEFITS OF THE INVENTION
The method according to the present invention for the anticorrosion coating of
metal surfaces, through its use of the specific post-treatment solution
according to the
present invention, provides a highly corrosion-resistant and strongly adherent
autodepos-
ited resin coating and does so at a continuously stable quality level. The
post-treatment
2s solution used in the method of the invention is very stable and can
therefore be used for
the continuous post-treatment of resin coatings.
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