Note: Descriptions are shown in the official language in which they were submitted.
Polymeric or resinous coating compositions have
been developed for applying coatings to metallic surfaces,
without the aid of electricity. Such compositions are
effective in forming resinous coatings, the weights or
thicknesses of which are related to the time the metal
surface is contacted with the composition. Generally,
these coating materials comprise an acidic aqueous coating
composition having dispersed therein an organic, polymeric,
or resinous film-forming material such as styrene buta-
diene copolymer. These polymeric coatings, which are
formed by contacting the metal surface with the acidic
aqueous coating composition, are referred to as auto-
deposited coatings.
U.S. Patent Nos. 3,585,084 and 3,592,699 assigned
to the same assignee as the present invention, disclose
compositions for coating metal surfaces comprising an
organic coating-forming material, an oxidizing agent and
an acid. Among the preferred compositions disclosed therein
is one comprising a resin dispersion, hydrofluoric acid,
-1- ~
: - . : . .
, . . ~ , :
.. ,, - : . . -.
.: .
. .
. 106~2~7 11767
and an oxidizing agent selected from the group consisting
of hydrogen peroxide and dichromate.
U.S. Patent No. 3,709,743 discloses aqueous acidic
coating compositions having dispersed resin solids and nitric
acid. South African Patent No. 72/1146 discloses an aqueous
acidic coating composition prepared from an acid, a soluble
iron compound, dispersed resin solids, and optionally, an
oxidizing agent. The preferred coating composition de-
scribed therein is prepared from hydrofluoric acid, ferric
fluoride, and dispersed resin solids. Belgian Patent of
Addition No. 811,841 discloses the use of other metal
compounds such as, for example, a compound of copper,
cobalt, or silver in aqueous acidic coating compositions
which form resin coatings which grow with time.
Coatings formed from such compositions are dis-
tinctly different from coatings formed by immersing a metal
surface in a conventional latex composition comprising a
resin dispersed in water. The weight or thickness of a ~-
coating formed by immersing a metal surface in a conven- -
tional latex is not affected by the time the surface is
immersed in the coating composition. In order to obtain
a thicker coating it has been necessary to subject the
surface to a multiple stage coating operation or to employ
coating compositions having a higher solids content, that
is a higher amount of resi~ solids dispersed therein.
Autodeposited coatings offer a number of impor-
tant advantages. Thicker resinous coatings can be formed
on a metal surface in a shorter period of time and in a one
step operation. Coatings produced also have been found to
have improved corrosion resistant properties and improved
uniformity and appearance.
--2--
~06~Z87 11767
In general, autodeposited coatings are formed
from the aqueous acidic coating composition as a result
of attack and dissolution from the metal surface of metal
ions in amounts which cause the dispersed resin particles
to deposit on the surface in a manner such that there is
a con~inuous buildup of resin coating on the surface.
Prob~ems which may be encountered with auto-
deposited coatings is that the coating may be imperfect
in that it contains blisters or cracks and/or bridges.
For some applications this may not be critical, but for
other applications it is not tolerable. By way of example,
blistering may be evidenced in the cured or fused coating
by a pocket of air, water, and/or other foreign material,
for example, oils or lubricant trapped between the metal
surface and the cured coating. Such foreign materials
may be present when insufficient cleaning has been accom-
plished. With respect to cracking this can be evidenced
by hairline cracks in the cured coating. With regard to ;~
bridging of the coating, this is evidenced by the coating
separating from the underlying metal surface, on the under-
side of the surface, where the surface is non-planar, such
as when bent, curved or cornered.
It is a purpose of the present invention to pro-
vide autodeposited coatings on metal surfaces, which can
be cured or fused while reducing blistering, bridging, -
and/or cracking. -~
This invention relates to a method for treating
a coated metal surface having thereon an uncured auto-
deposited coating formed by contacting said surface with
an aqueous acidic coating composition containing a water
dispersible resinous material which comprises contacting
said uncured autodeposited coating with a coalescing agent
--3--
.
~6~Z87 11767
with the result that blistering, bridging and cracking of
said coating, after curing, is reduced.
The present invention relates to treating an
autodeposited coating prior to its being cured or fused,
with an organic material of the type generally known as
a coalescing agent. Coalescing agent, as used herein,
refers to the generally accepted function of a material
which is added to a latex paint for the purpose of causing
the resinous particles of the paint to coalesce more
readily into a continuous film.
In general, the coalescing agent to be used in
the present invention is a polyfunctional material.
Polyfunctional, when used herein, refers to coalescing
agents having two or more oxygen containing functional
groups, such as ester groups, ether linkages, hydroxy
groups and carbonyl groups. Such coalescing agents are
described in detail hereinafter.
The aqueous acidic coating compositions of the
aforementioned type when contacted with the metal surface
function to attack and dissolve from the surface metal
ions, in an amount sufficient to directly or indirectly -
cause resin particles in the region of the surface to
deposit thereon in a continuous fashion, that is in a
manner such that there is a buildup in the amount of resin ~-
deposited on the surface the longer the time the surface
is in contact with the composition. This deposition of
the resin on the metallic surface is achieved through
chemical action of the coating composition on the metallic
surface. The use of electricity which is necessary for
the operation of some coating methods, such as the electro-
coating method, is not required.
-4-
lQ6~Z87 11767
The amount of the resin in the coating composi-
tion can vary over a wide range. The lower concentration
limit of the resin particles in the composition is dictated
by the amount of resin needed to provide sufficient material
to form a resinous coating. The upper limit is dictated by
the amount of resin particles which can be dispersed in the
composition. In general, the higher the amount of resin
particles in the composition, the heavier the coating
formed, other factors being the same. Although coating ~
compositions can be formulated with about 5 to about 550 -
grams/liter of resin solids, the amount of resin solids
will tend to vary depending on the other ingredients
comprising the composition and also on the specific latex
or resin used.
Latices, dispersions of insoluble resin particles
in water, for use in the composition of the present inven-
tion are readily available commercially. Examples of such ~
commercially available latices are: ~;
Hycar LX 407* (manufactured by Nihon Geon Co.,
Ltd.~... styrene butadiene copolyme~
Goodrite 1800 x 72* (manufactured by Goodrich ChemicalCorp.)...styrene butadiene
copolymer
Pliolite 491* (manufactured by Goodyear Rubber
and Chemical Corp.)
...styrene butadiene copolymer
Hycar LX 814* (manufactured by Nihon Geon Co.,
Ltd.)...acrylic copolymer
Synthemal 9404* (manufactured by Nihon Reichold
Co. Ltd.)...acrylic copolymer
-5-
. : . ' .. :
117G7
. .
106~2t~7
Polyol AP 300* (manufactured by Kobunshi Kagaku
Kogyo Co., Ltd.)
...ethylene-vinyl acetate copolymer
Poly-em 40* (manufactured by Gulf Oil Corp.)
...polyethylene
Hycar 1870 x 4* (manufactured by Nihon Geon Co.,
Ltd.)...acrylonitrile
Hycar 2600 x 112* (manufactured by Nihon Geon Co.,
Ltd.)...polyacrylaté
*(trade marks)
As to other ingredients contained in the coating
composition, U.S. Patent Nos. 3,585,084 and 3,592,699 dis-
close the use of a variety of acids, for example, hydro-
fluoric, nitric, phosphoric, and acetic, and the use of a
variety of oxidizing agents, for example, hydrogen peroxide,
dichromate, nitrite, and chlorate. The ingredients are
present in amounts which are effective in dissol~ing metal
from the metallic surface immersed therein to form in the
composition ions in a sufficient amount to cause the resin
particles to deposit on the metallic surface in a manner
such that the resinous coating grows with time. Exemplary
compositions disclosed in said patents are effective in
dissolving at least about 25 mg/sq.ft. of an iron surface ~
within the first minute of time the surface is immersed -
in the composition. For this purpose, the composition
contains sufficient acid to impart a pH of less than 7
to the composition, and preferably a pH within the range
of about 1.6 to about 3.8. The oxidizing agent is present
in an amount sufficient to provide an oxidizing equivalent
of at least about 0.01 per liter of the composition. The
preferred composition described in the aforementioned
-6-
:1060287
patents comprises about 5 to about 550 grams/liter of resin
solids, hydrofluoric acid in an amount sufficient to impart
to the composition a pll within the range of 1.6 to about 3.8
and equivalent to about 0.4 to about 5 grams/liter of fluoride,
and an oxidizing agent preferably dichromate or hydrogen
peroxide, in an amount to provide about 0.01 to about 0.2
of oxidizing equivalent per liter of composition.
United States Patent No. 3,709,743 discloses
an aqueous acidic coating composition having a resin solids
content of about 2 to about 65 wt. percent, preferably
about 5 to about 20 wt. percent and nitric acid in an amount
of about .1 to about 5 wt. percent, preferably about 0.5
to about 2 wt. percent with the preferred pH of the composi-
tion being below about 2.
South African Patent No. 72/1146 discloses an
aqueous acidic coating composition containing about 5 to
about 550 grams/liter of resin solids, a soluble ferric-
containing compound in an amount equivalent to about 0.025
to about 3.5 grams/liter ferric ion, preferably about 0.3
to about 1.6 grams/liter of ferric ion, and acid in an amount
sufficient to impart to the composition a pH within the
range of about 1.6 to about 5Ø Optionally an oxidizing
agent may be used in an amount to provide from about 0.01
to about 0.2 oxidizing equivalent per liter of composition.
Examples of the aforementioned ferric-containing compounds
are ferric fluoride, ferric nitrate, ferric chloride, ferric
phosphate and ferric oxide. Examples of acids are sulfuric,
hydrochloric, hydrofluoric, nitric, phosphoric, and organic -
acids, including, for example, acetic, chloracetic and tri-
chloracetic. Examples of oxidizing agents are hydrogen
peroxide, dichromate, permanganate, nitrate, persulfate and
- 7 -
.
-- 11767
106()287
perborate. The preferred composition is described as
being prepared from about 5 to about 550 grams/liter of
resin solids, about 1 to about 5 grams/liter of ferric
fluoride trihydrate, and hydrofluoric acid in an amount
sufficient to impart to the composition a pH within the
range of about 1.6 to about 5Ø
Belgian Patent of Addition No. 811,841 discloses
a coating composition containing about 5 to about 550
grams/liter of resin solids, a metal-containing compound
which is soluble in the composition and acid to impart
to the composition a pH within the range of about 1.6 to
about 5Ø Examples of the soluble metal-containing com-
pound are silver fluoride, ferrous oxide, cupric sulfate,
cobaltous nitrate, silver acetate, ferrous phosphate,
chromium fluoride, cadmium fluoride, stannous fluoride,
lead dioxide, and silver nitrate. The metal compound is
present in the composition in an amount within the range
of about 0.025 to about 50 grams/liter. Examples of acids
that can be employed are sulfuric, hydrochloric, hydro- ~ -
fluoric, nitric and phosphoric and organic acids such as
acetic, chloracetic and trichloracetic. The use of hydro-
fluoric acid is preferred. Optionally, an oxidizing agent
may be used in an amount sufficient to provide from about
0.01 to about 0.2 oxidizing equivalent per liter of
composition. Examples of oxidizing agents are hydrogen
peroxide, dichromate, permanganate, nitrate, persulfate
and perborate.
British Patent No. 1,241,991 discloses an acidic
aqueous coating composition containing an oxidizing agent
and solid resin particles stabilized with an anionic sur-
factant. The composition is substantially free of nonionic
--8--
.
~L~6~287 ll767
surfactant. The resin particles comprise about 5 to
about 60 wt. percent, preferably about 10 to about 30 wt.
percent, of the composition. The anionic surfactant com-
prises about 0.5 to about 5 wt. percent, preferably about
2 to about 4 wt. percent based on the weight of the resin.
Examples of anionic surfactant are the alkyl, alkyl/aryl
or naphthalene sulfonates, for example sodium dioctyl
sulphosuccinate and sodium dodecylbenzene sulfonate. The
oxidizing agent is described as being of the kind commonly
known as a depolariser, and preferably is present in the
composition in an amount of about 0.02 to about 0.2 N.
Examples of oxidizing agents are hydrogen peroxide, p-
benzoquinone, p-nitrophenol, persulfate and nitrate. Acids
such as phosphoric, hydrochloric, sulfuric, acetic, tri-
chloracetic and nitric are used to impart to the composi-
tion a pH of preferably less than 5, most preferably less
than 3.5.
Various factors should be taken into account in
determining whether the metallic surace should or should
not be cleaned, and the extent of cleaning, prior to
contact with the coating composition including, for example,
the nature of foreign materials (if any) on the surface and
the desired quality of the coating. F oreign materials which
are present on the met~allic surface can lead to the forma-
tion of coatings which are not uniform. Also, the adhesion
and corrosion resistant properties of the resinous coating
can be affected adversely as a result of the presence on
the metallic surface of foreign materials during the coating
step. Generally speaking, improved quality coatings can
be consistently obtained the cleaner the surface. Excellent
results can be achieved consistently by subjecting the
_9_
~ 11767
~06028~
metallic surface to a cleaning operation which results in
a surface on which there can be formed a water break-free
film. The selection of the cleaning agent and mode of
application thereof to the metallic surface will depend
on the type of foreign materials present on the metallic
surface. Available cleaning agents can be used in accord-
ance with known technology. Thus, depending on the type of
soil or foreign materials which are present, acidic, alka-
line or other cleaning agents can be used. By way of
example, dilute phosphoric acid can be used to clean
lightly rusted parts and hot alkaline compositions can be
used for the removal of oils, greases, fingerprints and
other organic deposits.
After the metallic surface has been cleaned, it -~
may or may not be water rinsed prior to immersing the
metallic surface in the coating composition. Water rinsing
the surface removes therefrom foreign materials, for
example, residual cleaning, agent, which may tend to
adversely affect the coating operation. For example,
foreign materials carried into the coating composition may ~-
have adverse effects thereon. Whether or not a water rinse
should be used in a particular application can be best
determined by taking into account the quality of the
coatings desired and observing whether or not unrinsed
surfaces adversely affect the coating bath and coating
quality. To avoid or minimize such adverse effects, it
is recommended that the clean surface be rinsed with ~
deio~ed water for a sufficient period of time to remove ~-
fore.ign materials therefrom and that most of the rinse
water be removed from the surface (for example, by allowing
-10-- ~
11767
~60Z87
it to drain therefrom) before the surface is immersed
in the coating bath.
As mentioned above, the longer the metallic
surface is immersed in the coating composition, the
greater the buildup in coating thickness. It is believed
that for most applications, desired coating thicknesses
can be obtained by immersing the metallic surface in the
composition for a period of time within the range of about
30 seconds to about 3 minutes. However, it should be
understood that longer or shorter periods of time can be
used.
Agitating the composition aids in maintaining
it uniform. Also, agitation of the composition is effec-
tive in improving the uniformity of the coatings formed.
Other factors held constant, heating of the
coating composition will result in heavier coatings. For
example, a composition having a temperature of about 35F
formed a coating having a thickness of about 0.8 mil,
whereas at a temperature of about 100F, the coating
formed had a thickness of about 1.1 mils. Satisfactory
results can be obtained by operating the coating process
at ambient temperatures.
Once the metal surface has been contacted with
the coating composition, it may or may not be rinsed with
water before significant drying takes place. Water
rinsing is effective in removing residuals such as acid --
and other ingredients that adhere to the coated surface.
If such residuals are allowed to remain on the coated ';
surface, they may change or adversely affect the quality
of the coating. For a specific application, a determi-
nation can be made as to whether the residuals cause
- : :
: ' ' . ,
,
11767
1060Z87
adverse affects which are not tolerable. If they do,
they should be removed, for example by water rinsing
with tap or deionized water. If they do not, this step
of removing them can be avoided.
Following contact with the aqueous coating
composition, and in certain instances the optional water
rinse with tap or deionized water, the coated metal
surface can then be treated according to the present
invention.
The aqueous rinse composition for use in the
practice of this invention comprises a coalescing agent.
The coalescing agent to be used can be selected from a
wide variety of compounds. Examples of such compounds
include:
a) alcohols having two or more hydroxy groups
such as ethyleneglycol and triethylene
glycol;
b) ketones having two or more carbonyl groups,
such as acetonylacetone (methyl butoxyketone~; -
c) alcohol esters having a hydroxy group and
an ester group such as butyl lactate,
isopropyl lactate, ethyl lactate;
d) ketone esters having a carbonyl group and
an ester group such as ethyl aceto acetate;
e) alcohol ethers having a hydroxy group and
an ether linkage such as diethylene glycol
diethyl ether, 2-ethoxyethanol, 2-butoxy-
ethanol, diethylene glycol monoethyl ether,
diethylene glycol monomethyl ether, diethyl-
ene glycol monobutyl ether, dipropylene glycol
methyl ether, dipropylene glycol ethyl ether,
tripropylene glycol methyl ether;
-12-
'~~ 11767
~0b;~)2~7
f) ketone ethers having a carbonyl group and
an ether linkage such as acetonyl methanol
ethyl ether; and
g) ester ethers having an ester group and an
ether linkage such as 2-ethoxy ethyl acetate,
diethylene glycol monoethyl ether acetate,
and diethylene glycol monobutyl ether acetate.
It is noted that the compounds mentioned above
contain two or more oxygen atoms in groups, or oxygen
containing functional groups, such as hydroxyl, carbonyl,
ester, and ether.
Compounds mentioned above are water miscible
and have a lower evaporation rate than water. In addition,
compounds among those mentioned above are generally
effective in causing the resin particle to swell or soften,
and in effect, tend to lower the minimum film formation ~;
temperature of the resin particles.
The preferred coalescing agents for use in the
practice of the present invention are alcohol ethers and
ester ethers and most preferably 2-butoxyethanol and diethyl-
ene glycol monobutyl ether acetate. Although other means
can be utilized to apply the coa~escing agent to the
uncured coating, it is recommended and preferred that it
be applied from an aqueous carrier. The selection of the
particular coalescing agent to be employed will depend on
its commercial availability and on its solubility properties.
It is noted that the above listed compounds are soluble
in water, having a solubility of more than 3 percent by `;
weight in water. It is further noted that each of the
above listed compounds have a boiling point of at least
134C. It is preferred that the coalescing agent have a
-13-
- ~ .
,
~060~87 11767
solubility of more than 3 percent by weight in water
and a boiling point above 140C., Thus, during the
baking step, which is generally used to cure or fuse
the coating, the water of the wet coating will tend to
evaporate at a faster rate than the coalescing agent, ,
thereby tending to concentrate the coalescing agent in
the resinous coating.
Generally, the mere presence of the coalescing
agent in the aqueous rinse composition will be effective
in reducing the tendency of the coating to crack, blister,
and/or bridge. However, to realize a significant improve-
ment, the amount of coalescing agent in the aqueous carrier
should be at least about 10 gramstliter. Preferably,
the aqueous rinse composition will contain from about 20
grams/liter to about 100 grams/liter of coalescing agent.
Optimum results have been obtained wherein there is from
about 20 grams/liter to about 30 grams/liter of diethyl-
ene glycol monobutyl ether acetate in the rinse composition.
Treatment of the uncured coating can be accom-
plished by employing any of the contacting techniques knownto the art, for example immersion, mist spray, and shower-
ing. Preferably, the uncured coating is rinsed with an
aqueous solution comprising the coalescing agent by mist
spray or immersion methods.
The coated surface is brought into contact with
the aqueous rinse composition under suitable conditions
of temperature and contact time. The time of treatment
of the coated surface with the rinse composition need
only be long enough to insure complete wetting of the
coating. Preferably, the rinse composition can be
applied to the coated surface for from about 30 seconds
~ 11767
10602~37
to about 5 minutes. In certain commercial operations,
such as formed parts lines, it is beneficial to have
longer contact time periods so that the entire metal
workpiece is sufficiently contacted with the rinse
composition. The uncured coating should not be con-
tacted with the coalescing agent for lengthy periods
of time such that adhesion of the coating to the under-
lying metal surface is impaired. Rinsing can be accom-
plished over a broad temperature range, for example,
from about 10C to about 80C. Satisfactory results
are obtained by utilizin-g a rinse composition at room
temperature.
After treatment with the coalescing agent,
the uncured coating can then be fused, for example by
baking as will be discussed hereinbelow.
However, if desired, the corrosion resistant
properties of the coated surface can be improved by
contacting the uncured coated surface with an acidic rinse
solution containing hexavalent chromium.~ Such chromium
rinse solutions are prepared from chromium trioxide or water
soluble dichromate or chromate salts, for example,
ammonium, sodium, and potassium salts. There can also
be used a chromium composition obtained by treating a
concentrated aqueous solution of chromic acid with
formaldehyde to reduce a portion of the hexavalent
chromium. This type of rinse, which is described in
U.S. Patent No. 3,063,877 to Shiffman, contains chromium
in its hexavalent state and reduced chromium in aqueous
soLution. By way of example, such an aqueous rinse
solution can comprise a total chromium concentration
within the range of about .15 grams/liter (expressed as
-15-
.
,,
11767
1060Z1~7
CrO3) to about 2 grams/liter, wherein from about 40-95
percent of the chromium is in its hexavalent state and
the remainder of the chromium is in its reduced state.
A small amount of phosphoric acid can also be added to
the rinse solution to prevent gel formation and as little
as .05 ml of 75 percent H3P04 solution per gram of total
chromium has been found effective.
The amount of hexavalent chromium or hexavalent
chromium and reducedchromium will, in general, be governed
by the corrosion resistant properties required for the
specific application. It is preferred that at least
about .01 grams/liter of hexavalent chromium be used and
that the amount be adjusted upwardly as required, if neces-
sary.
While the aqueous rinse composition of the
present invention can be applied to the coated metal
surface prior to or after contacting the coated surface
with a rinse solution containing hexavalent chromium, it
has been found that the aqueous rinse composition of the
present invention can be prepared containing the hexa-
valent chromium therein. Therefore, both the chromiumand the coalescing agent can be contacted with the coated
metal surface simultaneously, thereby eliminating the
necessity for multiple treating steps. Of course, the
particular coalescing agent to be employed when the
chromium is also incorporated in the aqueous rinse compo-
sition must be selected so that it is stable in the
composition at the operating parameters of the rinse
composition. The preferred coalescing agent to be -
employed along with chromium in the aqueous rinse
composition is diethylene glycol monobutyl ether acetate.
-16-
r
11767
~(~60287
Following contact with the aqueous rinse
composition, the coating should be cured or fused.
Fusion of the resinous coating renders it continuous,
thereby improving its resistance to corrosion and
adherence to the underlying metallic surface. The
drying of the coated surface can be accomplished under
varying conditions dependent upon the type of resin or '
polymeric material employed in the coating process.
Generally, heating or baking will be required to fuse
the resin coating. When a heated invironment or baking
is employed, the drying or fusion step can be accomplished
at temperatures from about 110C to about 250C. Most
of the resin coatings require heated drying stages or ~
baking steps in order to fuse the resin and to insure ~ ;
that optimum corrosion resistant properties of the
coating are obtained.
It is not fully understood why the use of the
coalescing agent reduces the tendency of the cured coating
to crack, blister and/or bridge. However, it is believed
that during drying or curing, surface stresses arise in the
coating as it contracts in volume. This volume contraction
results in stresses which may be resolved in directions
parallel to the surface. It is these stresses on a
planar surface which, it is believed, causes visible
cracks to open. On the underside of a surface, where
the surface is non planar, such as where it is bent,
curved or cornered, these stresses resulting from
contraction, it is believed causes the coating to separ-
ate from-the underlying metal surface to form bridges.
The cracks or bridges which form relieve the surface
stresses, and it has been observed that cracks form
perpendicularly to any surface stresses. The use of the ~ -
-17-
.. ~ ., . ., ~ . .
` ~060287 11767
coalescing agent in the rinse composition appears to
alleviate the effects of volume contraction, thereby
reducing cracking and/or bridging. It is also believed
that the use of the coalescing agent reduces formation
of blisters by enhancing adhesion of the coating to the
underlying metal surface.
The examples presented below are illustrative
of this invention and are not considered as limiting for
other materials and operating conditions falling within
the scope of the invention that might be substituted.
In the examples cold-rolled steel panels were
cleaned with an alkaline cleaner, rinsed with water, and
immersed, as indicated in each example, in an aqueous
coating composition to form an autodeposited coating.
Upon being withdrawn from the coating composition, the -~
autodeposited coating was formed on the surface and the
panels thereafter underwent the particular treating steps
indicated in each example- In some instances the coated
panels were rinsed first with tap water then rinsed with
the aqueous rinse composition, in some instances said
aqueous rinse composition containing both coalescing
agent and chromium. Thereafter, the coated panels were -
placed in an oven at the specified temperatures and
specified baking time. After being withdrawn from the
oven the appearance of the coatings was observed visually
for the purpose of evaluating the presence of cracking, ~;
blistering, and/or bridging.
-18-
11767
1060287
EXAMPLE I ~;
An aqueous coating composition was prepared
containing the following:
Parts by wei~ht
styrene butadiene copolymer 200
(Nippol LX 407*- sold by
Nippon Zeon)
Chromate pigment (KiKu Jerushi 50
OEN 5G-3KB~sold by Kikuchi
Kogyo)
iron oxide pigment (Tenyo50
Bengara*sold by Tone Sangyo)
anionic surfactant (Demol-P ^ 5
sold by Kao Atlas Co.)
ferric fluoride (trihydrate) 10
hydrofluoric acid 3
tap water 692
The aqueous coating composition is prepared by
adding lead chromate pigment, anionic surfactant, ferric
fluoride trihydrate, iron oxide pigment and a portion of
the tap water to a porcelain ball mill and mixed for 16 hours
until dispersed to form a pigment paste. Thereafter the
styrene butadiene copolymer is added to the pigment paste
with mixing and thereafter, the remainder of tap water is
added. Hydrofluoric acid is then added with stirring.
Cold Rolled Steel panels (Nos. 1-6) were
immersed in the above aqueous ccating composi~ion at
room temperature for 3 minutes. After being withdrawn
from the aqueous coating composition each panel was per- -
mitted to stand for 10 minutes and each was thereafter
immersed in a particular composition comprising diethyl-
ene glycol monoethyl ether acetate and water for specified
time periods. The particular compositions comprising
diethylene glycol monoethyl ether acetate in specified
*(trade mark)
-19-
1~6~287 117G7
concentrations are listed in Table 1 below. The panels
were withdrawn from the composition comprising diethylene
glycol monoethyl ether acetate and thereafter were placed
in an oven having a temperature of 180C and were baked
for 5 minutes. The appearance of the coated panels was
thereafter observed and the observations are noted in
Table 1 below.
One set of control panels was immersed in the
aqueous coating composition under the identical conditions
as above and was permitted to stand after being withdrawn
from the aqueous coating composition for a period of 10
minutes, thereafter placed in an oven having a temperature
of 180C and baked for 5 minutes. The appearance of the
control panels was observed and is noted in Table l below.
Table 1
_ . :-~
Concentratlon o~,
diethylene glycol Immersior
monoethyl ether Time Appearance of
No. acetate (g/l) (min.) coated film
1 100 .5 Good - No cracking or
blistering ;
2 100 2 Good - No cracking or
blistering
3 100 60 - Blistering and peeling
4 5 2 Cracking
2 Good - No cracking or
blistering
6 500 2 Good - No cracking or
blistering
_ Control cracking
EXAMPLE II
An aqueous coating composition was prepared
containing the following:
-20-
~06()28~
styrene butadiene copolymerParts by Weight
(Darex 673* sold by W. R. Grace) 200
hydrogen peroxide 3
hydrofluoric acid 4
tap water 800
The styrene butadiene copolymer is diluted with
tap water to which the hydrogen peroxide and hydrofluoric
acid is added with stirring.
Steel panels (Nos. 7-13) were immersed in the
coating composition at room temperature for 3 minutes.
Thereafter the panels were withdrawn from the coating
composition and permitted to stand for a period of 10
minutes. The panels were then immersed in particular
aqueous rinse compositions, having constituent concentrations
and for periods of time as indicated in Table 2 below. ~;
The panels were thereafter removed from the rinse compo-
sitions and were placed in an oven having a temperature
of 180C for a period of 5 minutes. The baked coatings
were thereafter visually observed and their appearance ~ -
is noted in Table 2.
*(trade mark) Table 2
Rinsing Condition Appearance- . .
Rinsin~ Solution Time ~ of coated .
No. Aqueous solvent Concentration (Min.) film
7 Ethylene glycol 500 1 Good - No ::
cracking or
blistering
8 Diethylene glycol 200 2 ,
monoethyl ether
9 Diethylene glycol
monobutyl ether acetate 100 3
Dipropylene glycol 50 4
methyl ether
11 Dipropylene glycol 100 5
methyl ether
12 Tr-propylene glycol 200 2
methyl ether
13 2-ethoxy ethyl acetate 500 3
.
-21-
: :
- 11767
~06~)Z87
EXAMPLE III
An aqueous coating composition was prepared
containing the following:
Ingredients Amounts
styrene butadiene copolymer
sold under the trademark
Goodright 1800X73 (pH 3.5 '
surface tension 70 dynes/cm
48% solids) 180 grams
black pigment dispersion 5 grams
ferric fluoride 3 grams
hydrofluoric acid 2.3 grams
water to make 1
liter
A steel panel was immersed in the above aqueous
coating composition for 90 seconds at ambient temperature.
After withdrawal from the coating composition, the coated
panel was allowed to stand in air for a period of 60
seconds and thereafter was rinsed with running tap water.
Thereafter the coated panel was immersed for a period of
30 seconds in a solution comprising about 9 g/l of
Na2Cr207.2H20. The coated panel was then baked for 10
minutes in an oven at 170C. The cured coating was
visually observed and blistering was evident.
A second steel panel was immersed in the above
coating composition, thereafter removed and allowed to
stand in air for a period of 60 seconds, and then immersed
in an aqueous rinse composition comprising 9 g/l of
Na2Cr207.2H20 and 18.06 g/l of 2-butoxyethanol for a period
of 30 seconds. Thereafter the coated panel was baked
for 10 minutes in an oven at 170C. The cured coating
was visually observed and was virtually free of blisters.
The rinse composition comprising butyl 2-butoxyethanol and
Na2Cr207.2H20 appeared to substantially eliminate blistering.
~602~7 11767
EXAMPLE IV
An aqueous coating composition was prepared
containing the following:
Ingredients Amounts
styrene butadiene copolymer
(sold under the trademark
Darex 637) 180 grams
black pigment dispersion 5 grams -
ferric fluoride 3 grams
hydrofluoric acid 2.3 grams
water to make 1
liter
Steel panels were prepared for coating to measure
any blistering, bridging, or cracking by forming conex
deformations on each panel by impactlng the panel surfaces
with a one inch ball with a measured force. The impacted
test panels were immersed in the above coating composition -
for two minutes at ambient temperature. After withdrawal
from the coating composition, the coated panels were
allowed to stand in air for a period of sixty seconds and
thereafter rinsed by immersion in tap water.
Thereafter, the coated panels were immersed in
compositions indicated in Table IV. Control panels were
immersed for a period of thirty seconds in an aqueous
composition comprising about 2 gramstliter hexavalent ~`-
chromium, about .9 grams/liter trivalent chromium and .6
grams/liter phosphoric acid. The composition is prepared by
combining an aqueous solution of partially reduced (with
formaldehyde) hexavalent chromium having phosphoric acid
therein with an aqueous solution of soluble dichromate
salt, such as Na2Cr207.2H20, Na2CrO4, NH4Cr207, or
LiCr207.2H20, thereafter adding sufficient water to give
the desired concentration of constituents. Test panels `
1060287 11767
were immersed in particular compositions comprising the
above chromium containing composition and having added
thereto the particular materials indicated in Table IV,
present in the amounts as indicated in Table IV. There-
after, the coated panels were baked for five minutes in :
an oven at 215.5C. The cured coatings were visually -
observed and the results are listed in Table IV below.
TAsLE IV
Concentration
(~/1) Appearance
Control Blisters over planar
surface and bridging
around impacted area
Propylene glycol S0 Blisters over planar
monomethyl ether (100% surface and bridging
soluble in water and around impacted area
boiling point 121C)
Triethylene glycol (100~/D 50 No blisters
soluble in water and
boiling point 290C.)
____________________________________________________________________ .
Control Two large blisters on
planar surface
Propylene glycol 50 Bridging around impacted
nomethyl ether area
Triethylene glycol 50 No blisters or bridging
____________________________________________________________________
Control Bridging around entire
impacted area
Propylene glycol 100 Bridging around 2/3
monomethyl ether of impacted area
_____________________________________________________________________ .
Control Three separate bridges
4 cm around impacted area .
Triethylene glycol 10 1.5 X 1.5 cm blister
inside impacted area
Triethylene glycol 30 No blisters or bridging
Triethylene glycol 50 No blisters or bridging - :
Control Four separate 1 cm bridges
Triethylene glycol 10 Four separate small
bridges ~:
Triethylene glycol 30 One small bridge
Triethylene glycol 50 No blisters or bridging
______________________________________________________________________
24.
`- 1060287 11767
EXAMPLE V
An aqueous coating composition was prepared
containing the following:
Ingredients Amounts
styrene butadiene copolymer180 grams
(sold under the trademark
Darex 637)
black pigment dispersion 5 grams
ferric fluoride 3 grams
hydrofluoric acid 2.3 grams
water to make 1 liter
Steel panels were prepared for coating to measure
cracking. Control panels were immersed in the above coating
composition for one minute at ambient temperature. After
withdrawal from the coating composition, the coated panels
were allowed to stand in air for a period of 60 seconds and
thereafter were rinsed by immersion in tap water for 30
seconds.
The control panels were then immersed, for a
period of 30 seconds, in an aqueous composition comprising
about 2 grams/liter hexavalent chromium, .9 grams per liter `
trivalent chromium and .6 grams/liter phosphoric acid. ~,
The composition was prepared as set forth in Example 4 ;-;~
combining an aqueous solution of partially reduced hexa-
valent chromium with an aqueous solution of soluble
dichromate salt. After immersion in the aqueous chromium
containing composition, the control panels were air dried.
Test panels were immersed in the above coating
composition for a period of 60 seconds at ambient tempera-
ture. Ater withdrawal from the coating composition, the
coated test panels were allowed to stand in air for a
period of 60 seconds. Thereafter each test panel under-
went a separate processing sequence as follows:
25.
106~287 11767
Test Panel No. 1 - immersed in an aqueous rinse
composition comprising 20 grams/liter of diethylene glycol
monobutyl ether acetate for a period of 30 seconds. After
withdrawal from said composition, the panel was immersed
in the above chromium containing composition for a period
of 30 seconds. Thereafter, the panel was air dried.
Test Panel No. 2 - immersed in an aqueous
composition comprising 30 grams/liter diethylene glycol
monobutyl ether acetate for a period of 30 seconds. After
withdrawal from said composition, the panel was immersed
in the above chromium containing composition for a period
of 30 seconds. Thereafter, the panel was air dried.
Test Panel No. 3 - immersed in tap water for a
period of 30 seconds. After withdrawal from the tap
water, the panel was immersed in an aqueous composition -
comprising the above chromium containing composition
having added thereto 20 grams/liter of diethylene glycol
monobutyl ether acetate for a period of 30 seconds.
Thereafter, the panel was air dried.
The control panel and the test panels were
visually observed for cracking and the results are listed
in Table V below.
TABLE V ~-
Panels A~earance
Control Severe cracking of entire
surface
Test Panel #l No Cracks
Test Panel #2 No Cracks
Test Panel #3 No Cracks
, , , :
-
106~87 11767
EXAMPLE VI
An aqueous coating composition was prepared
containing the following:
Ingredients Amounts
styrene butadiene copolymer
(sold under the trademark
Darex 637) 180 grams
black pigment dispersion 5 grams
ferric fluoride 3 grams
hydrofluoric acid 2.3 grams
water to make 1 liter
Steel panels were prepared for coating to
measure blistering. Control panels were immersed in
the above coating composition for 5 minutes at ambient
temperature. After withdrawal from the coating composi- ;
tion the coated panels were allowed to stand in air for
a period of 60 seconds and thereafter were rinsed by
immersion in tap water for a period of 30 seconds.
The control panels were then immersed for a
period of 30 seconds in an aqueous composition comprising
9 grams/liter of Na2Cr207.2H20. After withdrawal from the
chromium containing composition, the control panel was :
placed in an oven for 10 minutes at 210C. After with-
drawal from the oven, the coating was visually observed
and a heat blister was present over the entire surface
of the panel. Upon attempting to peel the coating from
the surface, mechanically by scraping, 100% of the coating
was removed.
Test Panel No. 1 was immersed in the above
coating composition for a period of 5 minutes at ambient
temperature. After withdrawal from the coating composition,
27.
.
,
106028'~ 11767
the coated test panel was allowed to stand in air for
a period of 60 seconds and thereafter was rinsed by
immersion in tap water for a period of 30 seconds. The
test panel was then immersed for a period of 30 seconds
in an aqueous composition comprising 9 grams/liter of
Na2Cr207.2H20 and 20 grams/liter of diethylene glycol
monobutyl ether acetate for a period of 30 seconds.
After withdrawal from said chromium containing composition,
the test panel was placed in an oven for 10 minutes at
~10C. After withdrawal from the oven, the coating was
visually observed and a heat blister was present over
about 50% of the surface. Upon attempting to remove the
coating, mechanically by scraping, the coating was peeled
from about 50% of the surface, corresponding to the area
where the blister had been evident. ~ -
Test Panel No. 2 was immersed in the coating
composition for 5 minutes at ambient temperature. After
withdrawal from the coating composition, the coated panel
was allowed to stand in air for a period of 60 seconds and
thereafter was rinsed by immersion in tap water for 30
seconds. The panel was then immersed for a period of 30
seconds in an aqueous composition comprising 9 gramstliter
of Na2Cr207/2H20 and 30 grams/liter of diethylene glycol
monobutyl ether acetate for a period of 30 seconds. After
withdrawal from the chromium containing composition, the
panel was placed in an oven for 10 minutes at 210~. After
removal from the oven, the coating was visually observed
and was found to be uniform in appearance with no blister-
ing evident. An attempt was made to remove the coating
mechanically by scraping, and none of the coating could be
removed and no loss of adhesion was evident.
28.
