Note: Descriptions are shown in the official language in which they were submitted.
ZIRCONIUM/TITANIUM COATING SOLUTION FOR ALUMINUM SURFACES
,
Field of -the Invention
This invention relates to the application to
aluminum surfaces of coatings which are corrosion resis-
tant and to which overlying coatings such as those formed -
from paints, inks and lacquers adhere excellently. More
particularly, this invention relates to aqueous coating
solutions which form on aluminum surfaces the aforemen-
tioned types of coatings and coating solutions which do
not require the presence of toxic materials, such as ~ -
chromates and ferricyanide, for their effectiveness.
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It is known to coat aluminum surfaces with aqueous
coating solutions that are effective in forming thereon coat-
ings which are corrosion resistant and thereby protect the
surface from degradation due to attack by corrosive materials.
In general, the coatings formed from such coating solutions
should also have properties such that overlying coatings which
are applied thereto adhere tightly and strongly. Such over-
lying coatings are decorative or functional in nature and are
formed from materials such as paints, lacquers, inks, etc.
(hereinafter referred to as "siccative coatings").
An example of an aluminum coating operation, and
one in which the present invention has particularly good appli-
cability, is the coating of aluminum cans. In general, the
corrosion resistant and adherent coatings which are applied
to aluminum cans should also be uniformly clear and colorless
so that the coated cans have the bright shiny natural appear-
ance of the underlying aluminum. This bright shiny natural
appearance is desired in the final product even though portions
of the can may be covered with colored paints or inks. (It is
noted that there are other aluminum coating operations in which
it is desired that the corrosion resistant and adherent coating
imparts to the aluminum surface a colored appearance r for
example, a yellowish to green tint. However, this is not
generally desired when coating aluminum cans.
Another specific property that coated aluminum cans
should have is the ability to resist discoloration when the
coated can is subjected to moderately hot waker, for example,
water having a temperature within the range of about 140F to
about 170Fo By way of background, it is noted that in certain
applications, aluminum cans are so treated. (The can industry
generally refers to this process as "pasteurization" of the
cans.) This treatment has a tendency to cause an uncoated or
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even a coated aluminum surface to blacken or otherwise dis-
color thereby leaving the can with an unattractive appearance.
In general, when the term "corrosion resistance" is used in
the industry in connection with coatings for aluminum cans,
it includes within its meaning that the coated surface resists
blackening or other discoloration when subjected to pasteuri-
zation. The term "corrosion resistance" is so used herein
unless otherwise specifically stated.
There are available presently coating solutions which
form on aluminum surfaces uniformly clear colorless coatings.
One of the most widely used coating solutions, which forms
such coatings, contains chrom~c acid, phosphoric acid and
hydrofluoric acid. While such a coating solution is capable
of forming coatings of the type desired, their use creates
waste disposal problems because of the presence therein of
hexavalent chromium, a very toxic material. It would be of
great advantage to users of such coating solutions to have
available coating solutions which do not contain hexavalent
chromium.
This invention relates to the provision of an aqueous
coating solution which does not requira the use of hexavalent
chromium and which is capable of forming on an aluminum surface
a coating, including particularly a coating which is uniformly
clear and colorless in appearance, and which is corrosion
resistant and to which overlying coa-tings adhere excellently.
~,
eported Developments
There has been developed a number of types of aluminum
coating solutions for various purposes.
U.S. Patent No. 3,682,713 discloses an aqueous coat-
ing solution containing a complex fluoride such as fluorides
of boron, titanium, zirconium or iron, free fluoride ions,
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and an oxidizing agent such as sodium nitrcbenzene sulfonate
or nitrate. The patent discloses that the coating solution
forms on aluminum coatings which are dull, light grey to
yellowish iridescent. It is noted that the patent specifi-
cally excludes the use in the coating solution of e~en small
quantities of phosphoric acid or phosphates because such
materials are said to interfere with the formation of the
coating.
U~ S. Patent No. 3,066,055 discloses coating solu-
tions which are said to form on aluminum surfaces coatings
which ar~ colorless. The coating solutions contain fluoride
compounds, including simple fluorides, complex fluorides or
double metal fluorides, along with hexavalent chromium,
ferricyanide, molybdate or tungs~ate, and also a cation
selected from elements 23 to 29 of the Periodic Table. It is
noted that this patent also discloses that phosphoric acid
or salts thereof, are not suitable for use in the solution.
In U. S. Patent No. 3,160,506, there is disclosed
an aqueous coating solution containing a transition metal
fluoride which is said to be effective in forming on aluminum
printing plates coatings which are stable under relatively
high humidity and temperature conditions. There is no
disclosure in this patent concerning the color of the coat-
ings formed or the degree of corrosion resistance imparted by
the coatings to the aluminum surface. It is noted that this
patent discloses that the treated surface is sealed by con-
tacting it with a chromic acid solution. See also U. S.
Patent No. 2,825,697 which discloses an aqueous coating solu-
tion which forms on an aluminum surface coatings which are
said to be substantially colorless. The coating composition
described in this patent is an aqueous solution containing
hexavalent chromium and a complex fluorine-bearing compound
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such as fluosilicic acid, fluoboric acid, fluozirconic acid,
fluostannic acid, fluotitanic acid or soluble salts thereof
The Eollowing pa-tents disclose coating solutions
which are said to form colored coatings on aluminum sur~aces.
U. S. Patent No. 1,638,273 discloses an aqueous coating solu-
tion containing a soluble fluosilicate, a salt of a non-
ferrous, iron-group metal and an alkali salt. The patent
reports that the coatings formed ~rom such coating solutions
are mottled, speckeled or spotted in appearance. U. S. Patent
No. 1,710,743 discloses aqueous coating solutions containing
double metal fluoride compounds such as sodium zirconium
~luoride, sodium titanium fluoride and potassium titanium
fluoride. The coatings formed from such solutions are said
to be of varying color (for example, grey, yellowish, golden,
reddish and black), depending on the particular aluminum alloy
being coated and the particular ingredlents and amounts thereof
comprising the solution. U. S. Patent No. 2,276,353 discloses
aqueous coating solutions containing hydrofluosilic acid
or salts thereof, an oxidizing agen~ and optionally an
accelerating agent such as nitrate. The patent discloses the
~ormation on aluminum surfaces of coatings which are grey,
brown, white or reddish purple, depending on the specific
ingredients and amounts thereof comprising the so~ution
In the overall picture, the aforementioned patents
disclose aqueous coating solutions which contain hexavalent
chromium or other troublesome materials or which form coatings
which require the use of a hexavalent chromium post treatment,
or they disclose coating solutions which are said to form
colored coatings on aluminum surfaces.
Accordingly, it is an objeck of the present invention ~`
to provide a coating solution which does not require the use
of hexavalent chromium or similarl~v toxic materials, and
~h .
which will form on an aluminum surface a clear and colorless
coating to provide a coated surface which resists blackening
or other discoloration even after being subjected to boiling
water.
Brief _escription of the Invention
In accordance with this invention, there is provided
an aqueous treatment or coating solution which contains as
essential ingredients zirconium and/or titanium, fluoride and
phosphate in dissolved form. Such solutions can be used to
treat a bright shiny aluminum surface in a manner such that the
bright shiny appearance of the surface is not changed, while
forming on the surface a uniformly colorless coating which is ~--
corrosion resistant and to which overlying coatings adhere
excellently. -
The corrosion resistant properties of coatings ormed
from coating solutions within the scope of the present inven~
tion include the ability of the coatin~ to withstand blackening
or other discoloration when subjected to boiling water for a
period of time of at least about 2 minutes, and as will be seen
from examples reported below, solutions can be formulated which
resist blackening or other discoloration satisfactorily when
exposed to boiling tap water for as long as 15 minutes, and ~-
even up to about 30 minutes~
The coating solution of the present invention is capa- ~ -
ble of effectively forming the aforementioned types of coatings ;~
on an aluminum surface in the absence of toxic materials and ~ -
materials of the type which create waste disposal problems,
including, for example, hexavalent chromium and elements such
as manganese, iron, cobalt, nickel, molybdenum and tungsten,
and also materials such as ferricyanide and ferrocyanide.
Accordingly~ it is not necessary to add to the coating solution
of the present invention materials, which if added, would
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mandate that effluents comprising the solution be treated
specially before the effluent is discharged to the environment
or to a sewage disposal plant.
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The overall excellent results achieved from the use of the comp-
osition are surprising in view of previous teachings that the use of phos-
phoric acid or phosphates in aqueous æirconium or titanium coating composit-
ions adversely affects the coating properties thereof. It is noted that
zirconium or titanium phosphate is highly insoluble in aqueous medium.
(A known analytical test for determining the amount of ~irconium or titanium
in aqueous solution includes the introduction into the solution of phosphate
to precipitate zirconium or titanium phosphate). Previous work which has in-
volved the formulation and use of an aqueous composition containing zircon-
ium, fluoride, and phosphate to form coatings on aluminum of the type to
which this invention relates have been carried out under conditions which
resulted in the formation of zirconium phosphate precipitate, which, as
explained in detail below, is highly undesirable in an industrial coating
operation. As will be described in detail below, the composition of the
present invention is formulated under conditions such that the aqueous coat-
ing solution of the invention contains substantially no solids of zirconium
or titanium phosphate which tend to precipitate.
As will be explained in detail below, another aspect of the present
invention relates to the use of a replenishing composition for maintaining ;
the effective operation of a coating bath as it is used continuously to
coat aluminum articles.
In accordance with the invention, there is provided an aqueous sol-
ution suitable for use in the coat~ing of aluminum and selected from an acidic
aqueous coating solution having a pH within the range of about 1.5 to about
4.0, and concentrates for making up or replenishing such a coating solution,
said aqueous solution consis~ing essentially of (a) zirconium or titanium
or a mixture thereof, (b) phosphate and (c) available fluoride, said coat-
ing solution containing such ingredients in the amounts of at least about
lO ppm of (a), at least about 10 ppm of (b), and (c) in an amount such that
together with (a~ and (b) the coating solution is capable of forming on an
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aluminum surface a uniforDIly clear and colorless non-chromate coating and
of providing a coated surface which resists blackening after the coated
surface is subjected to boiling water for a 2 ~ninute period, said concentrate
for making up said coating solution being such that it yields said coating
solution on dilution with from about 9 to about 200 times its weight of
water, and said concentrate for replenishing said coating solution consist-
ing essentially of about 5 to about 10 grams per liter of zirconium or about
2.5 to about 5 grams per liter of titanium, about 5 to about 10 grams per
liter of phosphate and a material which is a source of about 5 to about
20 grams per liter of available fluoride.
The invention also provides an acidic aqueous coating solution hav-
ing a pH within the range of about 1.5 to about 4.0 and consisting essent-
ially of at least about 10 ppm zirconium or titanium or a mixture thereof,
at least about 10 ppm of phosphate and available fluoride, the amounts and
proportions thereof being such that said solution is capable of forming on
an aluminum surface a uniformly clear and colorless coating and providing
a coated surface which resists blackening after the coated surface is sub-
jected to boiling water :Eor a 2 minute period, and wherein said solution is
substantially free of solids which tend to precipita~e.
According to another aspect of the invention, there is provided
an aqueous concentrate solution such that an aqueous coating solution
containing about 0.5 to about 10 weight percent of the concentrate has a pH
within the range of about 1.5 to about 4.0 and consists essentially of:
(A) at least about 10 ppm of zirconium or titanium or a
mixture thereof;
(B) at least about 10 ppm of phosphate; and `
(C~ fluoride in an amount at least sufficient to form a
complex with substantially all of said zirconium and/or
titanium.
Furthermore, the invention also provides an acidic aqueous coating
solution having a pH within the range of about 1.5 to about 4.0 and con-
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sisting essentially of:
(A) about 20 to about 65 ppm of titanium;
(B) about 50 to about 200 ppm of phosphate; and
(C) about 10 to about 200 ppm of available fluoride.
Finally, the invention provides an acidic aqueous coating solution
for coating aluminum and having a pH within the range of about 1.5 to about
4.0 consisting essentially of:
(A) about 10 to about 125 ppm of zirconium;
~B) about 10 to about 1000 ppm of phosphate; and -
~C) about 10 to about 500 ppm of available fluoride;
wherein said coating solution is substantially free o:F precipitate.
The coating solution of the present invention can be used to coat ~ :~
surfaces of pure aluminllm or alloys of aluminum, for example, aluminum - ~ -
~ .
alloys containing minor amounts of metals ~ ~;
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such as, for example, magnesium, manganese, copper and sili-
con. Presently, the most popular alloy used in the aluminum
can industry is aluminum alloy 3004. It is believed that
one of the widest uses of the coating solution of the present
invention will be the coating of aluminum surfaces which have
a bright shiny appearance. Aluminum cans and aluminum strip
are e~amples of articles that can be treated effectively with
the composition of this invention.
The acidic aqueous coating solution can be prepared
from a variety of compounds which contain the aforementioned
essential ingredients (zirconium and/or titanium, fluoride and `
phosphate) and which are soluble in the solution. As to the
source of the zirconium and/cr titanium, there can be used
soluble fluozirconate and/or fluotitanate compounds such as,
for example, acids (fluozirconic and fluotitanic) thereof and
ammonium and alkali metal fluozirconate6 and fluotitanates.
The coating solution can also be pre~ared from zirconium fluo- -
ride (ZrF4) and/or titanium fluorides (TiF3, TiF4). In addi- ~ -
tion, the coating solutions can be prepared from a mixture of
soluble compounds, one of which contains zirconium or titanium
and the other of which contains fluoride. Examples of such
compounds are zirconium nitrate, zirconium sulfate, and titanium
(iv) sulfate and hydrofluoric acid and water soluble salts
thereof~ for example, ammonium and alkali metal salts. Zirco-
nium carbonates such as ammonium and alkali metal zirconium
carbonates can also be used.
Any compound soluble in the solution and a source of
phosphate can be usedO For example, phosphoric acid and ammo-
nium and alkali metal phosphates can be used. Although the
use of ortho-phosphoric acid is preferred, there can also be
used phosphoric acid in its meta-, pyro-, tri-poly- and hypo-
forms and salts thereof.
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De~relopmental work has shown that zirconium and/or
tltanium must be present in the coating, that is, they must
be directly or indirectly bonded to the aluminum surface in
order to achieve coatings having satisfactory properties.
Satisfactory coatings can be formed from coating solutions
containing as little as about 10 ppm of either of these ingre~
dients. ~When utilizing a mixture of zirconium and titanium,
the ~otal of the amounts of zirconium and titanium should
be at least about 10 ppm.) However, as will be explained
below, greater amounts of these ingredients may be required
to produce satisfactory coatings depending on other parameters
of the coating process.
Zirconium and/or titanium can be used in amounts up
to their solubility limits in the acidic aqueous coating solu-
tion. The solubility limits of the ingredients will depend
on other parameters of the coating solution, including parti- ;
cularly, the acidity of the coating r,olution, the amount of
fluoride in the coating solution, and the amount of phosphate
present in the coating solution. These parameters should be
controlled so that the formation of zirconium and titanium
phosphate precipitate is avoided. The formation of such
precipitate is undesirable for several reasons. Precipitation
depletes the amounts of the ingredients. Also, the deposition
on the coated aluminum surface of precipitate can adversely
affect the coating properties. In addition, the formation and
accumulation of any type of precipitate can tend to interfere
with the application of the coating solution. For example, it
can clog spray nozzles. If precipitation is encountered in a
specific applicatlon, the amount of phosphate should be reduced
and/or the pH of the coating solution should be lowered, and/or
the amount of fluoride can be increasedO
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As to the phosphate ingredient, it has been found
that the use of phosphate in the coating solution allows the
user to conduct a simple test to confirm the formation on the
aluminum surface of the coating. In an industrial operation
which can involve the treatment of vast ~uantities of alumi-
num in a relatively short time, it is helpful to have a simple
test to confirm that the coating solution is forming a coat-
ing since the coating is not visible to the eye. ~An
unnoticed change in the operating parameters of a bath of the
coating solution which renders it ineffective may take place
as a result of mechanical or human failure. For example,
improper replenishment of the coating solution may go unnoticed.)
It has been found that an aluminum surface coated with the -~
composition of the present invention changes in color varying
from light yolden brown to darker shad~s of brown or purple
when subjected ko a relatively high temperature for a relative-
ly short period of time, for example, 1000F for 5 minutes.
Work has shown that this discoloration is indicative of the
presence of zirconium and phosphorous in the coating. This
test, referred to herein as the "muffle test", can be used to
randomly sample treated aluminum surfaces to determine whether
or not the coating solution is depositing zirconium and phos~
phorous on the aluminum surfaca. If zirconium and phosphorous
is not being depositedt the aluminum surface has a dull greyish
appearance after the muffle test. It is noted also that
electron probe analysis of coated surfaces treated with the
composition of the present invention shows the presence of
both ~irconium and phosphorous.
It has been found also that the use of phosphate con-
t~ibutes to the corrosion resistance and adherent properties
of the coatings, particularly coatings formed from a coating
solution having a pH below abou-t 3.5.
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Coatings having satisfactory properties and capable
of dlscoloring when sub~ected to the aforementioned muffle
test have been produced from coating compositions containing
as little as about 10 ppm of phosphate. However, as will be
explained below, greater amounts of phosphate may be required
to produce satisfactory coatings depending on other parameters
of the coating process.
Excess amounts of phosphate in the coating solution
can lead to the formation of coatings having reduced corrosion
resistant properties. In general, the phosphate concentration
should be no greater than about 1000 ppm. In selecting a phos-
phate concentration~ there should be taken into account also
the guidelines set forth above in connection with the tendency
of phosphate to precipitate with zirconium or titanium.
As to the fluoride concentxation, the minimum concen-
tration should be that which is sufficient to combine with all
of the zirconium or titanium to form a soluble complex there-
with, for example, a fluo~irconake or fluotitanate. Complexing
the æirconium or titanium with fluoride deters or prevents the
formation of zirconium and/or titanium phosphate precipitate.
Accordingly, the minimum amount of ~uoride is dependent on the
amount of zirconium or titanium in the solution. In general,
when the amount of zirconium present in -the solution is about
10 ppm, the minimum amount cefluoride is about 13 ppm. When
the amount of titanium present in the solution is ahout 10 ppm,
the minimum amount o~ fluoride is about 25 ppm.
Other considerations respecking the minimum fluoride
concentration should be taken into account in an~ application
in which a coating solution which has been contacted with alu-
minum is reused for contact with additional aluminum. By wayof explanation, it is noted that the coating solution of the
present invention dissolves aluminum. Thus, in an application
in which the aluminum is contacted with the coating solution
by immersing it in a bath of the coating solution, there is a
build-up in concentration of dissolved aluminum in the bath.
Similarly, if sprayiny or flow coating techniques are used
for contacting the aluminum, and excess or unreacted solutlon
is recycled to the bath of solution, there is a build-up of
dissolved aluminum in the bath. In order to deter or prevent ~
adverse effects on the coating process as a result of a build- ;
up of aluminum in the coating solutionr the coating solution
should contain sufficient amount of fluoride to complex the
dissolved aluminum. This is important for the satisfactory
operation of a continuous coating process. The amount of
fluoride needed will depend on the extent to which aluminum
builds up in the coating solution~ And this in turn depends
on various factors such as the shape of the aluminum surface
being treated and the manner in which the surface is contacted
with the solution.
Any material which is soluble in the coating solution
and which is a source of fluoride capable of complexing alumi-
num and which does not contain a constituent which adverselyaffects the coating process can be used. However, i fluoride
is added as a complex fluoridè of titanium or zirconium, there
should also be added to the solution another material which is
a source of fluoride for complexing aluminum which builds up
as the process is continued. The amount of fluoride available
from hydrolysis of such complex fluoride may not be sufficient
to complex the aluminum, and the extent of hydrolysis may be ~ ~ -
such thak uncomplexed zirconium or titanium combines with phos~
phate to form an undesired precipitate. By utilizing another
material which will readily provide sufficient fluoride for
complexing the aluminum, the aforementioned is avoided. Exam-
ples of such materials are hydrofluoric acid, salts thereof,
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NH4F.HF and alkali metal bifluorides. Hydrofluoric acid is a
particularly good source of fluoride because it provides suf-
ficient fluoride to complex the aluminum and is not a source . ~.
of extraneous cations which may interfere with the coating
process.
From a practical standpoint, the coating solution .
should contain, when operating on an industrial scale, an
excess of fluoride, that is, an amount above that complexed
with aluminum and any other metal constituents in the solution
that form complexes with the fluoride. Such excess fluorideis referred to herein as "available fluoride" and includes
fluoride present as HF and fluoride ion, that is, F not asso-
ciated with other materials in the solution. The available
fluoride concentration is that found when a sample of the coat-
ing solution, diluted with a constant ionic strength buffer
which contains 40.8 g/l of sodium acetate, 28.5 ml/l of glacial
acetic acid and 58.0 g/l of sodium chloride in deionized water .`
and adjusted t~ a pH within the range of 5.0 to 5.3 with
NaOH, is tested with an Orion psI meter (model No. 9409~ having
an Orion fluoride ion specific electrode (model No. 90-01).
A coating solution which contains available fluoride is one :`
in which fluoride is available to complex with aluminum.
The upper concentration of available fluoxide is
that which does not result in undue etching of the aluminum
surface. Undue etching tends to produce a dull and frosty
surface. It has been observed that the presence of an excess
of available fluoride can adversely affect the corrosion resis-
tant and adherent properties of the coating. The availablefluoride concentration which leads to such problems can vary
depending on other parameters of the coating process, includ-
ing, for example, the pH of the solution and time and tempera-
ture of contact. It is recommended that the available fluoride
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concentration be no greater than about 500 ppm.
The pII of the coating solu~ion should be within the
range of about 1.5 to about 4Ø At higher pHs phosphate pre
cipitation can be a problem. Preferably, a pH within the
range of about 2.6 to about 3.1 is used. The pH of the solu-
tion may be adjusted by using appropriate amounts of nitric
acid or ammonium hydroxide. Although nitric acid and ammonium
hydroxide are recommended as pH adjusters, any acid or base
which will not interfere with the coating process can be used.
For example, perchloric acid or sulfuric acid can be used.
When using sulfuric acid, it is recommended that the pH of the
coating solution be no less than 2. Below this value, sulfuric
acid can tend to adversely affect the coating operation.
With respect to optional ingredients, it has been -~
observed that the use of fluoboric acid in the coating 501u~
tion can improve the gloss or hardn~ss of paint films which
are applied to surfaces treated with the coating solution of
the present invention. ~lso~ the addition of fluoboric acid
helps maintain the stability of a coating so]ution formulated
from hard water. Calcium and magnesium ions in hard water
have an affinity for fluorideO If fluoride is extracted from
the zirconium and/or titanium fluoride complex by such ions,
the uncomplexed zirconium and/or titanium may tend to combine
.
with the phosphate to form insoluble ~irconium and/or titanium
phosphate precipitate. It is believed that fluoboric acid
acts as a buffered source of fluoride for calcium and magnesium
ions in hard water. An excess amount of fluoboric acid can
tend to reduce the corrosion resistant properties of the coat-
ing. In general, fluoboric acid can be used in an amount
within the range of about 8 to about 200 ppm.
A polyhydroxy compound may be added to the coating
solution to provide coatings which have improved adhesion to
.~..,.
. .~?~. --14--
53
paint or ink coatings. Any compound soluble in the coatiny
solution which when dissolved yields polyhydroxy compounds
having six or fewer carbon atoms and which does not interfere
with the ability of the coating solution to coat or provide
coatings having the desired corrosion resistance and paint
adherence may be used. Examples of such compounds include
gluconic acid, salts of gluconic acid, sorbitol, mannitol,
dextrose, ethylene glycol, and glycerine.
Particularly preferred polyhydroxy compounds are
gluconic acid and alkali metal and ammonium salts thereof.
Any compound soluble in the coat,ing solution which yields
gluconate and/or gluconic acid may be used. Examples oE such
compounds are stable gluconolactones such as glucono-delta~
lactone and glucono gamma-lactone.
It is recommended that at least about 40 ppm of the
polyhydroxy compound be used. Although higher amounts can be
used, it is recommanded that the polyhydroxy compound be pre-
sent in an amount no grea~er than about 1000 ppm. Preferably
about 40 to about 400 ppm of the polyhydroxy compound are used.
The coating solution should be free of chromium and
other toxic materials such as iron cyanides and any materials
which form in the solution solids which tend to precipitate.
A particularly preferred coating solution for use in
the practice of this invention has a pH within the range of
about 2.6 to about 3O1 and contains:
ApprQximate Concentration
Ingredient in ppm
.
Zr 45 to 125
PO4 50 to 200
30Available Fluoride 10 to 200
-r~ ~
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The preferred source of Zr in the above composition is
ammonium fluozireonate and the preferred source of phosphate
is H3PO4. Preferably hydrofluoric acid is used as the
source of available fluoride, and nitric acid is used to
adjust the p~. The use of about 8 to about 200 ppm of fluo-
boric acid and about 40 to about 400 ppm of the polyhydroxy
compound, preferably gluconic acidr is advantageous for
reasons mentioned above.
When utilizing titanium, it is preferably used in
an amount within the range of about 20 to about 55 ppm. The
preferred source of titanium is fluotitanic acid. other of
the preferred ingredients and amounts thereof are described
immediately above for the preferred Zr-containing solution.
Amount ranges for ingredisnts comprising the compo-
sition have been described above. Considerations should
be taken into account in formulating specific compositions
for specific applications while working within the afore~
. ~
mentioned ranges. When operati~g ak a relatively high pH,
relatively small amounts of zirconium or titanium and/or
phosphate should be used to deter precipitation. ~hen con-
tacting the coating solution and the aluminum surface for a
relatively short time, relatively high amounts oF zirconium
or titaniUIn and phosphate should be used. Similarly, when
the temperature of contact between the coating solution and
the aluminum surface is relatively low, relatively high amounts
of ingredients should be used. In general, the ]ower the
amount of phosphate used in the composition, the higher the
amount of zirconium and/or titanium that can be used.
The coating solu-tion of the present invention can
be prepared conveniently by diluting an aqueous concentrate
of the ingredients with an appropriate amount of water. The
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concentrate should be such that when a coating solution com-
prises about 0.5 to about 10 weight percent of the concen-
trate, the amounts of ingredients present in the coatiny
solution are: (A) at least about 10 ppm of zirconium or
titanium; (B) at least about 10 ppm of phosphate; and (C3
fluoride in an amount at least sufficiènt to combine with
substantially all of the Zr or Ti to form a comple~ there-
with; and the pH of the coating solution is within the range
of about 1.5 to about 4Ø
10A concentrate ~or preparing a preferred coating
solution or use in the invention is such that when the
coating solution comprises about 0.5 to about 10 weight per-
cent of the concentrate, the coating solution comprises:
(A) about 45 to about 125 ppm of zirconium, added as a fluo-
zirconate such as sodium or potassium fluozirconate, most
preferably ammonium fluozirconate; (B) about 50 to about ~;
200 ppm of phosphate added as H3PO4; (C) about 8 to about
200 ppm of HBF4; a~d (D) about 10 to about 50 ppm of HF; : :~
and (E) nitric acid in an amount such that the pH of the
coating solution is within the range of about 2.6 to about
3.1. A polyhydroxy compound, preferably gluconic acid, can
also be included in the concentrate in an amount such that
the coating solution comprises about 40 to about 400 ppm
thereof.
In a continuous coating operation, it is important
to properly replenish the solution in order to maintain the
effectiveness of the coating process. Work done in connec-
tion with the development of the present invention has shown
that various of the ingredients comprising the solution are
depleted as a result of reactions which occur during the
formation of the coating. (As mentioned above, analytical
work has shown that zirconium and phosphorus are present in
-17-
the coating.) Available fluoride is consumed as a result of
complexing with aluminum, and hydrogen is consumed as the
aluminum surface is oxidi~ed. In addition, ingredients are
depleted as a result of drag~out of the solution on the
aluminum surface. Work has also shown that the rate of
depletion of ingredients is related to the shape of the sur-
face being coated and the manner in which the coating solution
is contacted with the aluminum surfare. For example, when
spraying cans, there is a greater drag-out loss than when
spraying strip.
The coating solution can be replenished as the -
ingredients are depleted. This may be accomplished by either
monitoring the amount of each ingredient in the coating solu-
tion ànd adding this ingredient as it is depleted or it can
be accomplished by adding thereto an aqueous concentrate of
the ingredients.
The replenishing ingredients should be added to the
solution to maintain the ingredients thereof in effective
operating amounts. In an applicat:ion in which there is a
build-up of aluminum in the coating solution, it is recom-
mended that the replenishing composition contain a relatively
high proportion of fluoride for complexing the aluminum.
Preferred sources of available fluoride are ~F or ammonium
bifluoride or a mixture thereof. The following is a recom-
mended aqueous concentrate for replenishing the coating
solution.
(A) about 5 to about 10 g/l of Zr or about
2.5 to about 5 g/l of Ti;
~B) about 5 to about 10 g/l of PO~; and
(C) a material which is a source of about 5 to
about 20 g/l of available fluoride, prefera-
bly HF or ammonium bifluoride or a mixture thereof.
18-
When utilizing a polyhydroxy compound, i-t should be
included in the replenishing concentrate in an amount of
about 5 to about 20 g/l. When utilizing fluoboric acid, it
should be included in the replenishing concentrate in an
amount of about 1 to about 5 g/l.
A dascription of other steps that can be utilized
in the overall coating process follows.
The coating solution should be applied to a clean
aluminum surface. ~vailable cleaning compositions such as
al~aline or acid cleaning solutions can be used to clean the
aluminum surface according to conventional -techniques.
The coating solution can be applied to the aluminum
surface by any switable method. For example, the solution
can be applied by spraying the aluminum surface, or the alu-
minum surface can be immersed in the solution, or it can be
applied by roll or flow coating techniques or misting tech-
niques. It is believed that the solution can be applied very
economicall~ by spraying. The solution can be used to coat
individual articles such as, for example, cans, or it can be
used to coat forms of aluminum, such as aluminum strip~ which
are subsequently fabricated into articles.
The temperature of the coating solution should be
such that the reactive ingredients of the solution bond to the
aluminum surface. While the coating solution can be applied
at room temperature, in general, the temperature of the coat-
ing solution should be at least about 80F. If the tempera-
ture of the coating solution is too high, a dull and frosty
appearing surface can be obtained. I'he temperature at which
this occurs depends on various of the parameters of the coat-
ing operation, including, for example, the time of contact ofthe solution with the aluminum surface and the reactivity of
the solution which depends on pH and concentration of
-19-
253
ingredients in the solutlon. An upper temperature limit of
150F is recommended. The temperature of the coating solu-
tion is preferably within the range of about 80 to about
110F.
Desired coatings can be form~d by con-tacting the
coating solution and the aluminum surface for at least about
5 seconds, preferably a-t least about lS seconds. The lower
the temperature of the coating solution, the longer should be
the contact time and the higher the temperature of the solu-
tion the shorter the contact time required. In general, itwill be unnecessary to contact the surface with the coating
solution for more than one minute.
The acidic aqueous coating solution is capable of
forming a very thin and very light weight coating. The coat-
ing weight will vary depending upon the concentration of the
various ingredients in the coating solution, the temperature
of application, and the time of application. For uses o the
type referred to herein, it is preferred that the coating
have a weight of about 2 to about 20 mg/sq. ft., preferably
about 5 to about lO mg/sq. ft~ Coatings having such weights
can be formed by operating within the conditions described
above. Higher coating weights can create problems in the
aluminum can coating industrv. The machinery which applies
paint or ink to coated aluminum cans has precise tolerances
to accommodate cans having very thin coatings. Cans with
relatively thick coatings can foul the machinery.
Utilizing the coating solution of the present
invention, it is possible to form coatings which are very uni-
form. This permits paint or ink to be applied evenly and
with desired coverage to the coated aluminum surface. In
the aluminum can industry, paint and ink coatings are applied
to coated aluminum cans by an automatic roller coating
-,~
-20-
machine ln which paints and inks are applied to a roller and
then to the surface of the coated can as the roller i5
rotated across the surface of the coated can. If the can has
a non-uniform coating, the subsequently applied ink or paint
composition may not cover the desired areas of the can.
After the coating solution has been applied to the
aluminum surface, it should be water rinsed, including a
final deionized water rinse. Rinsing with water that con-
tains a small amount of dissolved solids may lead to a coat
ing which has poor paint adhesive properties. In utilizing
the present invention, it is not necessary to rinse the
coated surface with an aqueous solution of chromium such as, ~ -
for example, a hexavalent chromium solution.
After the coated surfac~ has been water rinsed, or
otherwise treated as described above, the coating should be
dried. This can be done by any practical means, such as, for
example, oven drying or forced circulation of hot air. Other
available drying methods can be used.
After ~he coating has been applied, it can be sub~
jected to sanitary or decorative coating operations which
include~ for example, applying to the coated surface siccative
coatings. These coatings are usually applied after the
aluminum surface has been coated, water-rinsed and dried. In
some applications, the sanitary coating is applied after the
water rinse and both the coating of the present invention and
the sanitary coating are dried simultaneously.
By way of example, ik is noted that in an applica-
tion where aluminum cans are filled wi-th beer, the cans are
treated with the coating solution of the present invention
and then sanitary and/or decorative coatings are applied.
Thereafter, the cans are illed with beer and sealed, after
which the beer-filled cans are subjected to pasteurizationO
21-
;3
It is believed that in coating solutions of the :~
present invention and containing zirconium and/or titanium, :
fluoride and phosphate, zirconium and/or titani.um is presenk
in the solution in a complexed form which is soluble in the
solution and in a form which .is reactive with -the aluminum
surface to form thereon a coating containing zirconium
and/or titani~n without affecting the bright shiny appearance
of the aluminum surface. Accordingly~ the solution should
be free of constituents which combine with zirconium and/or
titanium to form zirconium and/or titanium-containing com-
pounds and/or complexes which precipitate from the solution
and/or zirconium and/or titanium-containiny compounds or
complexes which are not reactiv~ with the aluminum surface
or which are reactive, but in a manner such that the briyht
shiny appearance of the aluminum surface is altered. ::
'~k7' :
-22-
EXAMPLFS
Examples below are illustrative of the practice of
the present invention. Comparative examples are set forth
also.
Unless stated otherwise, the aluminum surfaces
txeated with the solutions identified in the examples were
drawn and ironed aluminum cans which were first degreased,
as necessary, in an acidic aqueous clean~r containing sul-
phuric acid and detergents. Unless stated otherwise, the
coating solutions were applied by spraying for about 25
seconds at a temperature of about 110F. After treatment with
the solutions identified in the examples, the aluminum sur- -
faces were rinsed in deionized water and dried in an oven
for 2 minutes at about 400F.
Thereafter, the aluminum surfaces were tested for
corrosion resistance by subjecting them to a pasteurization
test. This test consisted of immersing the aluminum surface
in water having a temperature, as indicated, and for a period
of tlme, as indicated. A cleaned-only aluminum sur~ace, when
subjected to the pasteurization test, turns bllack after a few
minutes. It will be seen from examples set forth below that
prior treatment of the aluminum surfaces with coating solu-
tions of the present invention resulted in the provision of
coated surfaces which were not blackened or otherwise dis-
colored or which resisted blackening or other discoloration.
The results of the tests were rated as follows: 5, perfect,
no blackening; 3+, acceptable; and 0, total failure, severe
blackening.
Aluminum surfaces treated with th~ solution described
in the examples were tested also for paint adhesion. After the
treated surface was dried, as described ahove, a Portion oF ~e
surface was painted with a white base coat (No. 12WlOOA
-23-
~ 2~
whlte polyester sold by H C.I.) and ~he other portion of
~he surface was painted with an interior modified vinyl
epoxy lacquer. Af~er the pain~ was cured, the pain~ed
surace was im~lersed either in boiling water-detergent
or wa~er-NaCl solutionO After removing the p~inted
surface from the solution, it was rinsed in water, and
the excess water was removed fr~m the surface by wiping.
The painted surface was then cross hatched, using a
sharp metal object to expose lines of aluminum which
showed through the paint or lacquer, and tested for
paint adhesion. This test included applying cellophane
tape firmly over the cross hatched area and then drawing
the tape back against itself with a rapid pulling motion
such that the tape was pulled away from the cross hatched
area. The results of the test were rated as follows:
10 $ perfect, when the tape did not peel any paint from
the surface; 8, acceptable; and 0, total failure.
The various compositions of tke first 6 examples
and the first 7 comparative examples are listed in Table 1
below and include CompOSitiQnS within the scope of the in-
vention and comparative compositions. TabIe 2 below lists
the results of the pasteurization and paint adhesion tests.
Solutions in Table 1 were adjusted to pH of 2.7 by adding
concentrated nitric a~id or ammonium hydroxide. The surfaces
were subjected to either boiling tap water for 15 minutes
or hot tap water ~160F) for 45 minutes, as indicated in
Table 2.
In some cases, more than one sample of the aluminum
surface was treated in the same way. In such cases a plu-
rality of ratings are set forth in the tables which follow.
-24-
V3
Table 1
In~redients of Solutions and ~m~unts Thereo~ in g/l
No. (4)2ZrP6 BF4 H25iF6 E12TiF6 HF ~3PO4
1 0.240 - - 0.16~ 0.050 0.294
2 - - - 0.164 0.050 0.294
3 - 0~264 - 0.164 0.050 0.294
4 0.240 0.264 - 0.16A 0.050 0.294
0.240 0.264 - - - 0.294
6 0.240 0.264 - 0.164 - 0.294
C-l* 0 0 0 0 0 0
C 2 0.240 - - - 0.050
C-3 0.240 0.26~ - - 0.050
C-4 - 0.264 - - 0.050 0.294
C-5 0.240 - 0.442 - 0.050
C-6 - - 0.442 - 0.050 0.294
C-7 0.240 - - 0.164 0.050
Tabl~ 2
EX. Pasteurization Test Paint Adhesion Test**
20 No. 212F, 15 mln i60F/ 45 n~n ~nite Base Coat_ _ ~erior Vinyl Lac~er
1 3~ 4- lor9-~vg+/9 10,10,10,10
2 3 3 lO,g+,9+,9 10,10,10,10
3 2 3- 9,g,9,8 10,10,10,10
4 3 3+ 9+,8+,8,8 10,10,10,10
4+ 4~ 10,10,9+,9 10,10,10,10
6 4+ 4+ 10,10,10,10 10,10,10,10
C-l* 0 0 ,r1 10,10,9+,8
C-2 0 0 g,8+,8,6 10,10,10,10
C-3 0 0 6,~ 5,0 1O~1OI1OJ1O
30 C-4 0 0 0,0,0,0 10,10,10,9+
C-5 0 0 0,0,0,0 10,9+,9+,9+
C-6 0 0 0,0,0,0 10,10,10
C-7 0 0 7,6,~5,C5 10,10,10,9+
* Cleaned only, no treatment.
** 0.7~ detergent, 212F, 15 minutes
-25~
` The examples li.sted in Table 3 b~low illustrate
the effect of varying the phosphate concentrati.on in fl~ozirsonate
solutions. The solutiors of these examples had a pEI of 2.5,
exc~pt that of Example C-9 which had a pH of 3.25. ThQ. pasteuriza~
tioll tes~ invol~ed immerslon oE an unpain~ed alumi.fium can dome .in
ta~ water (160F) for 45 rninutes. Paint adhesi.on of both white
base coat and interior vinyl lacquer was tested by imrnersion of
painted cans in a hoil.ing 1~ detergen~ Joy soluticn) for 1.5
m:i.nutes foliowed by the stanc.ard cross hatching and taping.
--26~
~, ~
.,,
a~
o o o o
~r .~ r-~ r~r~
. ~ , .. .
h t~ O O O OO
v~ O ~1
a) ~rt
E-- ' I ,-1 o o oc~ o
F,~r1 O O ~ OO O
~r~~ .~ r~
U~
a
¢ " .
+
.~_) ~ G~
~ U~ c~ U) G-
r~ ~d .~ ,~ ^ +
) oG'~ ;G'`
r_ Ip.~t~) A ~ 7~
(D O O ~ * + +
td~ ~ ) ~G .OCCi~
. ^ ^ '`^ O
^ + t '+ .
r~ ~ COG~ C~G~ G~ O
~O
S
U)
E~ 0
:~ ~ ::
.~ .0 I I +
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'E~ td ::
~ G)
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U~
'O Lr~ ~ LQ U~Lr) L~'~
. . O O O O O O
IJ~
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1 ~ ~C
^r~
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~ ¦ In oG'~ cr~ CO
P.,I . .. ~ ~
l`rJI O OO O C~ O
'1~I
.
. I 0~ ~ ~ 0~ ~ o ~n
:~ o l ,-, ,
Example 11
,
This example illustrates the use of a make-up
so]ution and a replenishing solution in a continuous can
coating process in which 400 cans were coated. The make-up
concentrate contained 4.8 g/l of ammonium fluozirconate,
3 g/l of phosphoric acid, 0.44 g/l of hydrofluoria acid,
2.64 g/l of fluoboric acid~ 11.4 g/l of nitric acid, and
1.92 g/l of sodium gluconate. This make-up concentrate was
then diluted to 2.5~ in an aquaous solution. The pH of the
solution was 2.70. The replenishing solution was made up of
24 g/l of ammonium fluo~irconate, 9.4 g/l of phosphoric acid,
11.7 g/l of hydrofluoric acid, 0.68 g/l of fluoboric acid,
21.4 g/l of nitric acid, and 0.4 g/l of sodium gluconate.
As the aluminum cans were processed, replenishing
solution was added, as needed, to maintain the bath at a pH
of 2.70 ~ 0.02. (The pH was checked af-ter every 10 cans were
coated. Subsequent calculations showed that an average of
abou~ 0.3 ml of replenishing solu-tion per can was used.) The
pasteurization test involved immersion in boiling tap water
for 15 minutes. Paint adhesion was tested by immersion in
boiling water with 0.7~ de;tergent (Orvus K) for 15 minutes,
followed by cross hatching and taping. Test results are
shown in Table A below. ~ i
-28- -
,
;3
Table 4
Paint Adhesion Test
Number of Cans PasteuriZatlon White Base Interior Vinyl
Processed Test Coat Lac~uer
1 3 10,10 10,10
4-~ 10,10 10,10
51 4+ 10,10 10llO
100 4+ 10,8-~ 10,10
101 3 8~,7 10,10
]50 4-~ 9~,8 10,10
151 4-~ 9+,9 10,10
200 4-~ 10,8~ 10,10
201 4+ 10,8~ 10,10
250 4+ 10,9 10,10
251 4+ 9+,9~ 10,10
300 4+ 9,g 10,10
301 4 10,10 10,10
350 4~ 10,9~ 10,10
351 4+ 10,10 10,10
400 4 10,10 10,10
Table 4 shows the results of ~he pasteurization and the
paint adhesion tests. During the coatiny operation, cans
3, 80, 1~0, 240, 320 and 399 were subjected to a temperature
of about 1, OOO~F ~or about 5 minutes. The entire surface of
such cans turned a uniform brown color.
It is not~d that the solution was clear during the
coating of the first 100 cans. I'hereafter, the coating
solution became faintly hazy and was still faintly hazy when
the 400th can was treated. No sludge or precipitate was
isolated when the bath was cenkrifuged at the conclusion of
the test run.
The concentrations of zirconium, available fluoride,
and phosphate were determined throughout the run. The con-
centration of zirconium increased from an initial value of
46 ppm to 111 ppm during the run. The concentration of
phosphate increased from 70 ppm to 110 ppm during the run.
29-
~ i3 ~ ~
The concentration of available fluoride increased from 85 ppm ~ -
io about 95 ppm and e~entually decreased to 87 ppm. ~
. ,'-.
?
;' ~;',.'`' ~
-: :,:-.
::.`~ ''; ~' '
(, ~ . .
.~
''';';' ~'';
~: ,` :
29a
, ' ' ' ''
'
Examples 12 through 26, as set forth in Tables 5
and 6 below, illustrate the improved ink adhesion obtained
by the use of polyhydroxy compounds in the coating solution
of ~he present invention. More specifically, Table 5 il-
lustrates the use of various concentrations of sodium
gluconate ln a coating solution containing ammonium
fluozirconate and/or fluotitanic acid, phosphoric acid~
and hydrofluoric acid. Table 6 illustrates the results
obtained by the use of polyhydroxy compounds other than
sodium gluconate. In these examples, the coating solutions
were applied by spraying for 15 s,econds at a temperature
of 90F and the thus coated aluminum cans were then coated
wi~h a white base polyester inkO Prior to curing the ink,
an alkyd-amine overvarnish was applied to the wet ink coat-
ing. Curing was effected for 6 minutes at 375F.
-30~
32~
L
O ~ ~r~ .
'~, O + + ~ +
a~ ~ Ln oc~0~ G`l G G'`
.~ ~ ~ +
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1 ~L~ r~ ~'~ ~J
r, ~- +
-- L~ ! n
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,rl ~ ~ 1 cn O ~ C~)
r-l O r-l O O ~ e!~ r~ r~ ~ .
t~ ~ t~ ~ O ^ ~ O C~
C~ O ~ `t O O C~ O O O
r~ ~J ~ ~.
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r~ O OO O O OO O O
r-lr-l r I1-~r~ r--l ~ r-l
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--32--
;j3
The ne~t t~o groups ~f e,~amples illustrate the
use of prior art coatiny solutions containing a phosphate,
flouricle, and ei~ner ~ir~onium or titanium. The examples
show the undeslrable resul-ts that are o~tained ~hen utilizing
the coating solutions to coat alurrlinum. Ex~mples C-10, C-ll,
C~12 and C-13 s'now the application of coat.ing solutions
disclosed respectively in examples 7, 9, 14 and 15 o~
U. S. Patent ~o. 3,109,757 to aluminum cans.
For Ex~mples C-10, C-ll, C 12 and C-13, the f~]low-
ing ooncentrate was prepaxed:
Percent by wei~ht
ZnO 8.0
EI3POLI (7~39.5
Ni(MO3),V-6lI20 6.75
HNO3 (3~ ~e-~ 2.87
100. ~0
'
The above concent~ate was dil~lted with water to ~
strength of 4% by volume and had added thereJo 0.2$~ weight/ ;:
vo~LIrne) of caustic soda. The~e were ac1~ed to the dilute
so:lu..ion a glycerophosphate compound and a complex metal
ïoride in the amoLInt~ set forth in ~able 7 below. Tlle
~vlutlo~s were he~ted tG about 145F and sprayed on alu~itll~n
canc, ~or 30 ~econds. In Example C~l~, Cu~MO3)2~61I2G was :~ :
adde~ in an amount to pro-vide 0.00S% cop~er ion.
,;
Table 7 sho~s thc~ properties o~ the coatin~ solutlon
all~ 'c]le ~ ~ p--ovi.~ `r~ er~
~ r 8~i3
+ +
~ ~ r~
r~ 1
a I ~) r--I
u~ ~
~J 1~
o 3 3 31 3
t~ r rJ
3 ~ 3 5
'~
~r
~ ~ ~ ~ J~ ; ~
r--I r--l r~
r o r~
'(Y' E~ o o O O
~ 5
o`? ~
~ ~ n Ln ,.,
~ o o O O
~g
o~o ~
~f,~ ~, t.,~
O fi r~ r,~
r '
~ .'
Q) O
r~C~ C,) V~J
~æ,~3
Example C-14
This example shows the use oE a coating solution
of the type described in Example 8 of U. S. Patent No.
2,813~814. A concentrate was prepared containing the follow-
ing ingredients:
Çrams
MnCO3 183.
~3PO4 (75%) 555.3 -~
HNO3 (70%) 2Z.5
NH4CQ3 77-3
NaHF2 6~0
K2TiF6 15.8
H2O 573.5
Total1433.8
In the above formulation, the manganese carbonate and
phosphoric acid were reacted to form manganese dihydrogen
phosphate. Eight hundred forty grarns of the above concen-
trate were added to 4 liters of water. Then 44.8 g of MnCO3
and 9.2 g of NaHF2 were added. The solution was heated to
200F and sprayed for 30 seconds on an aluminum can. The
coating solution contained substantia~ amounts of precipitate
,~ . .
and formed a gray coating on the can. Corrosion resistance
. ~.
was tested by immersing the can in water at a temperature of
212F for 15 minutes. The can turned very dark and was
rated 0. White base coat adhesion was tested by immersing ;~
the can in 1% Joy at 212~F for lS minutes. The can passed
the adhesion test and was rated 9+.
.,
-35-
From cxamples set ~orth abo~e, it can he seen that the
present invention provides a coating solution fre2 of hexavalent
cnxomium and one which i5 capabl.e of orm~ng on an aluminum sur--
lace a,colorless an~ clear coating without modi.f~Ying ..he. appear--
ance of the a].uminum sur:Eace. The coa-ted surface resi.sts dj.s-
coloration e~en after be.ing subjected to boiling water and has
excellent adhesion to overl~Yi.nc3 siccative coatings~ The coating '~.
solution can be ~Ised in a conti.nuous lndustri.al coating operat.ion
to ei~cellent advanta~e.
.
- ,
~:
.
: ~:
. ~ .
-36~-
