Note: Descriptions are shown in the official language in which they were submitted.
CA 02248~68 l998-09-09
Wo 98/30652 PCT/US97/00006
ACID DEOXIDIZING/ETCHING COMPOSITION AND PROCESS SUITABLE
FOR VERTICAL ALUMINUM SURFACES
Field of the Invention
This invention relates to an improved composition and process for etching and/ordeoxidizing aluminum and aluminum alloy surfaces that may be at any angle to the local
gravitational force of the earth and are not immersed in the composition. (Hereinafter,
unless the context requires otherwise, the simple term "aluminum" is to be understood
as including alloys cont~ining at least 50 % by weight of aluminum.) As a result, the
compositions must have sufficient viscosity at low shear rates to resist flowing off the
surfaces to which they are applied under the influence of the gravitational force of the
earth.
10 Discussion of Related Art
Common chemical and mechanicaJ treatments of aluminum often leave the
surface with an oxide coating that must be removed before subsequent surface finishing
steps can be satisfactorily completed. This process is generally known in the art as
"deoxidizing" or, if the oxide coating is dark colored, alternatively as "desmutting". In
order to assure full removal of the undesired oxide coating, the surface is often etched,
i.e., some fraction, preferably a small one, of the metal of the surface itself is removed,
along with the oxide layer on it.
For aluminum objects of sufficiently small size, a deoxidizing/etching process is
normally accomplished by immersing the objects in a relatively low viscosity aqueous
liquid, traditionally an aqueous acid solution including hexavalent chromium. This
method is generally effective, but it can not be practically applied to large aircraft, rail
cars, and the like which are too large to immerse in any available container. For such
substrates a composition that will cling for a sufficient time to the entire surface to be
deoxidized/etched, even if all or part of the surface is vertical to the local gravitational
force of the earth, is needed.
DESCRIPTION OF THE INVENTION
Objects of the Invention
A major object of the invention is to provide a new type of flow resistant deoxi-
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dizing/etching eomposition that is improved with respeet to available prior art eounter-
parts in at least one of the following desiderata: (1 ) an etching rate of 2.5 + 0.5 micromet-
res per hour of exposure (hereinafter usually abbreviated as "~lm/hr") on all parts of an
aluminum surfaee to whieh it is applied; (2) minim:~l etch of titanium or ferriferous sur-
faces, whieh are often adjacent to alurninum surfaees desired to be deoxidized and diffi-
cult to protect completely against some exposure to the eomposition applied to deoxidize
neighboring aluminum parts of a eomposite structure; (3) easy visual detection of the
presenee of the composition on a large aluminum strueture being treated with it; (4) fac-
ile removal of the composition when its desired aetion is complete by an at least predom-
10 inantly aqueous rinsing liquid; (5) effective removal of any moderate amounts of organiecont;~min~nts that may be on the aluminum surface to be deoxidized; (6) facile wetting
of and/or spreading over ahlminum surfaees to be treated with the eomposition; (7) uni-
formity of visual appearance of the substrate surfaee after treatment with the
composition; and (8) minim~l pollution from the compositions. Other objeets will be ap-
parent from the deseription below.General Principles of Deseription
Exeept in the elaims and the speeific examples, or where otherwise expressly in-dieated~ all numerieal quantities in this deseription indieating amounts of material or eon-
ditions of reaetion and/or use are to be understood as modified by the word "about" in
describing the broadest seope of the invention. Praetiee within the numerieal limits stat-
ed is generally preferred, however. Also, unless expressly stated or necessarily implied
h! the context to the contrary: percent, "parts of", and ratio values are by weight; the
term "polymer" includes "oligomer", "copolymer", "terpolymer", and the like; the first
definition or description of the meaning of a word, phrase, aeronym, abbreviation or the
like applies to all subsequent uses of the same word, phrase, acronym, abbreviation or
the like and applies, mutatis mutandis, to normal grammatical variations thereof; the
deseription of a group or class of materials as suitable or preferred for a given purpose
in eonnection with the invention implies that mixtures of any two or more of the mem-
bers of the group or class are equally suitable or preferred; specifications in chemical
terms of materials in compositions refer to the materials at the time of addition to any
composition so specified, and do not necessarily exelude the possibility of reaction
between sueh materials and other materials already present in the eomposition at the time
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of addition of the specified materials; specification of materials in ionic form implies the
presence of sufficient counterions to produce electrical neutrality for the composition as
a whole; and any counterions thus implicitly specified preferably are selected from
among other constituents explicitly specified in ionic form, to the extent possible; oth-
erwise such counterions may be freely selected, except for avoiding counterions that act
adversely to the objects of the invention.
Summary of the Invention
It has been discovered that the above stated object of the invention can be
achieved with a viscous liquid composition that comprises, preferably consists essentially
of, or more preferably consists of, water and:
(A) an amount of a source of dissolved fluoride ions;
(B) an amount of a source of an acid with a larger ionization constant than hydro-
fluoric acid;
(C) an amount of a viscosity increasing agent that is not part of any of the previously
recited components;
(D) an amount of anionic surfactant that is not part of any of the previously recited
components;
(E) an amount of nonionic surfactant that is not part of any of the previously recited
components; and, optionally, one or more of the following:
20 (F) a hydrotroping agent that is not part of any of the previously recited components;
(G) a coloring agent that is not part of any of the previously recited components;
(H) a biocidal agent that is not part of any of the previously recited components; and
(J) an oxidizing agent that is not part of any of the previously recited components.
Another embodiment of the invention is a process comprising, preferably consist
ing essentially of, or more preferably consisting of, at least steps of:
(I) forming on an aluminum substrate surface to be deoxidized/etched a coating of
a viscous liquid composition according to the invention as described above;
(II) m~int~ining in place the coating formed in step (I) for a time sufficient to deoxi-
dize/etch the aluminum substrate surface; and
30 (III) subsequently removing the coating of viscous liquid composition formed in step
(I) from further contact with the aluminum substrate surface.
Other steps, including those conventional per se, may be included in a process according
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WO 981306~2 PCT/USg7/00006
to the invention along with these necessary steps.
Other embodiments of the invention include substrates prepared by a process ac-
cording to the invention as described above, the use of such substrates in any application
to which aluminum articles are adapted? and the like.
Detailed Description of the Invention~ Including Preferred Embodiments
For various reasons, it is often preferred that compositions according to the inven-
tion be substantially free from various constituents that can cause practical difficulties
when present. More particularly, with increasing preference in the order given and with
independent pl~relellce for each noted component, compositions according to the inven-
10 tion preferably contain no more than 4.0, 2.2, 0.90, 0.50, 0.20, 0.12, 0.070, 0.030, 0.010,0.0050, 0.0020, 0.0010, 0.00050, 0.00020, or 0.00010 grams of constituent per kilogram
of total composition (hereinafter usually abbreviated as "g/kg") of any of the following:
metal cations with a valence of 2 or higher; chloride, bromide, or iodide ions (which can
cause pitting corrosive attack on aluminum); any anions containing a metallic element
in a valence state of +3 or more; organic peroxides; halate or perhalate anions; and any
organic molecules containing at least two but not more than twelve moieties selected
from the group consisting of hydroxyl, amino, phosphino, carboxyl, and carboxylate
moieties, wherein any two of said at least two but not more than twelve moieties are
separated from each other by exactly 2 or 3 other atoms within the organic molecule, so
that a chelate complex can readily be forrned between the organic molecules and metal
ions.
Fluoride ions component (A) is preferably supplied by one or more substances
selected from hydrofluoric acid and all of its water soluble salts, including fully and
partially neutralized salts, and the stoichiometric equivalent as fluoride of all of these
dissolved materials present in the composition is to be considered as part of component
(A), irrespective of the actual extent of ionization existing in the composition. Inasmuch
as "free fluoride" is needed to achieve the levels of etching speed desired, complex
fluoride anions such as fluoborate, fluotitanate, fluosilicate, and fluozirconate are not
considered part of component (A) if present in a composition according to the invention
and preferably, at least for reasons of economy, are not present at all. Ammonium and
alkali metal fluorides and/or bifluorides are preferred and arnmonium fluoride and/or
bifluoride is most preferred.
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Irrespective of the source, the amount of fluoride ions present in a working com-
position according to the invention preferably is at least, with increasing preference in
the order given, 2.0, 4.0, 6.0, 8.0, 10.0, 12.0, 14.0, 16.0, 17.0, or 18.0 grams per kilogram
of total composition (hereinafter usually abbreviated as "g/kg") and independently pref-
erably is not more than, with increasing prer~lence in the order given, 60, 50, 40, 35, 30,28, 26, 24, 22, 20.07 or 19.0 g/kg.
Component (B) of strong acid is, primarily for reasons of economy, preferably
selected from inexpensive strong mineral acids such as sulfuric7 hydrochloric, and nitric
acids, with sulfuric most preferred. Irrespective of the source, the amount of acid from
10 component (B) in a working composition according to the invention preferably is such
as to provide at least, with increasing preference in the order given, 0.080, 0.15, 0.30,
0.40, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, or 0.78 moles of ionized hydrogen atoms per
kilogram of total composition (hereinafter usually abbreviated as "mH/kg") and
independently preferably to provide not more than, with increasing preference in the
order given, 6.0, 5.0, 4.0, 3.0, 2.5, 2.0, 1.5, 1.2, 1.0, or 0.80 mH/kg. In calculating these
amounts of hydrogen ions for known chemical compositions, all of the hydrogen atoms
of any acid present that ionize with a larger ionization constant than hydrofluoric acid are
assumed to be completely ionized. Thus, for example, both hydrogen atoms of eachdissolved H2SO4 molecule are assumed to be ionized, because the second ionization
constant of sulfuric acid is 0.012 while that for HF is only 0.00072. For H3PO4, however,
only its first ionization constant is greater than that for HF, so that only one hydrogen
would be assumed to ionize from this molecule.
Independently of their separate amounts, the amount of ionized hydrogen ions in
mH/kg preferably has a ratio to the amount of fluoride in g/kg that is at least, with in-
creasing preference in the order given, 0.0040:1.0, 0.0060:1.0, 0.0080:1.0, 0.0100:1.0,0.015:1.0, 0.020:1.0, 0.025:1.0, 0.030:1.0, 0.035:1.0, 0.038:1.0, 0.040:1.0, or 0.042:1.0
and independently preferably is not more than 0.40:1.0, 0.30:1.0, 0.20:1.0, 0.15:1.0,
0.10:1.0, 0.090:1.0, 0.080:1.0, 0.070:1.0, 0.060:1.0, 0.055:1.0, 0.050:1.0, or 0.045:1Ø
A working liquid substrate coating composition according to this invention pref-
erably is highly thixotropic, i.e., it preferably has a relatively high viscosity when begin-
ning to be disturbed from a motionless state, but becomes relatively low in viscosity
when subjected to stronger forces, so that it may readily be applied by convenient meth-
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ods such as spraying, dipping, brushing, and the like to a substrate to be protected, to
form a coating that will remain in place against the influence of natural gravity without
becoming thinned to an undesirable degree. The thixotropy may convenient}y be mea-
sured by means of a well known type of instrument, a Brookfield viscometer, using
spindle # 4. The viscosity at 25 ~C of a viscous liquid working composition according
to the invention measured in this way, when measured at 0.5 revolution per minute
(hereinafter usually abbreviated as "rpm") preferably is at least, with increasing
preference in the order given, l O0, 200,300, 400, 500, 600, 650, 700, 750, 800, 850, 870,
890, or 910 poises (hereinafter usually abbreviated as "ps"); independently preferably is,
10 when measured at 2.5 rpm~ at least, with increasing preference in the order given, 25, 50,
75, 100, 150, 200, 250, 300, 350~ 370, 390~ or 400 ps; and also independently preferably
is, when measured at 20 rpm~ not more than, with increasing preference in the order
given~ 400, 350, 300, 250, 210, 170, 130, 105, lO0, 95, 90, or 86 ps.
A wide variety of natural and synthetic materials, such as natural gums and other
15 polysaccharides, various synthetic polymers, and finely divided inorganic solids such as
certain clays and silica sols, are known in the art for achieving thixotropy and may be
used in a composition according to the invention. The most preferred material for com-
ponent (C) is xanthan gum, preferably a type of this gum which has been modified from
its natural state to result in smoother flow properties at low shear rates, as described in
20 more detail in connection with the working examples according to the invention below.
For any viscosity modifying component, the amount preferably should be selected to
achieve preferable values of viscosities at various measuring speeds as already specified
above. For the preferred modified xanthan gum as noted above, along with other pre-
ferred types and amounts of components (A) and (B), the concentration of the modified
25 xanthan gum in a viscous liquid working composition according to the invention prefer-
ably is at least, with increasing preference in the order given? 2.0, 4.0, 6.0, 8.0, 10.0,12.0,
14.0, 15.0, 16.0, 17.0, 18.0, l9.0, 20.0, 21.0, or 22.0 g/kg and independently preferably
is not more than, with increasing preference in the order given, 150, 125, 100, 80, 60, 50,
40, 30, 25.0, or 22.5 g/kg.
A wide variety of commercially available and other known materials are suitable
for component (D) of anionic surfactants. Examples include sulfonic acids, partial esters
of sulfuric and phosphoric acids, and the like, and salts of all of these acids, in each
CA 02248~68 l998-09-09
WO 98130652 PCT/US97/00006
instance selected from molecules that contain a hydrophobic moiety cont~ining from 8
to 22, more preferably from 10 to 20, or still more preferabiy from 12 to 18, carbon
atoms and not more than, with increasing preference in the order given, 5, 3, 2, 1, or 0
atoms other than carbon, hydrogen, and halogen atoms. Largely for reasons of economy,
sulfonic acids, partial esters of sulfuric acid, and salts of both these types of are preferred.
Linear alkylbenzene sulfonic acids and their corresponding sulfonates are most preferred
for component (D). The amount of component (D) in a working composition according
to the invention preferably is at least, with increasing preference in the order given, 2, 4,
6, 8, 10? 1 1.0, 12.0, 13.0, 14.0, 15.0, or 15.8 g/kg and independently preferably is not
10 more than, with increasing preference in the order given, 75, 60, 50, 40, 35, 30, 25, 23,
21, 19, 18.0, 17.0, 16.5 or 16.2 g/kg.
As with component (D), a wide variety of commercially available and other
known surfactants are suitable for component (E) of non-ionic surfactant. Preferred
molecules for component (E) conform to the general chemical formula (I):
RlO(CH7CH2O)y(CH2CHCH3O)zH (I)
where R' is a moiety selected from the group consisting of saturated-and-unsaturated
straight-and-branched-chain-aliphatic-monovalent-hydrocarbon-moiety-substituent -
bearing phenyl moieties in which the aromatic ring of the phenyl moiety is directly bond-
ed to the oxygen atom appearing immediately after the R' symbol in formula (II); y is a
positive integer; and z is zero, one, or two. More preferably, independently for each
preference stated, z is 1 or 0, most preferably zero; the aliphatic monovalent hydrocarbon
moiety substituent in R' has at least, with increasing preference in the order given, 5, 6,
7, 8, or 9 carbon atoms and independently preferably has not more than, with increasing
preference in the order given, 12, 11, 10, or 9 carbon atoms; the aliphatic monovalent
hydrocarbon moiety substituent in R' is straight chain rather than branched; and the
average value of y is at least, with increasing preference in the order given, 3, 4, 5, 6, 7,
or 8 and independently preferably is not more than, with increasing preference in the
order given, 16,15,14,13, 12,1 1,10, or 9.
Independently of its specific chemical composition, the amount of component (E)
in a composition according to the invention preferably is such that it has a ratio to the
amount of component (D), measured in the same units, in the same composition that is
at least, with increasing preference in the order given, 0.015:1.0, 0.030:1.0, 0.045:1.0,
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0.060:1.0, 0.075:1.0, 0.090:1.0, 0.100:1.0, 0.110:1.0, 0.115:1.0, 0.120:1.0, or 0.123:1.0
and independently preferably is not more than, with increasing preference in the order
given, 2.0:1.0, 1.5:1.0, 1.0:1.0, 0.50:1.0, 0.40:1.0, 0.30:1.0, 0.25:1.0, 0.20:1.0, 0.1~:1.0,
0.16:1.0, 0.150:1.0, 0.140:1.0, or 0.130:1Ø
The presence of optional hydrotroping agent component (F) is generally preferredin concentrates according to the invention. Conventional hydrotroping agents such as
the salts of alkyl benzene sulfonic acids, particularly of cumene sulfonic acid, are suitable
for compositions according to this invention and are generally preferred for reasons of
economy. However, if very low tolerances for residual sulfur on the deoxidized surface
are prescribed, at least one of two other types of hydrotropes are then preferred: (i)
organic phosphate esters and (ii) alkyl and alkenyl substituted cyclic acid anhydrides,
particularly the anhydrides of C4 6 terminal dicarboxylic acids substituted with alkyl or
alkenyl groups having 6 to 20 carbon atoms. Particularly preferred examples of this type
of hydrotrope are octenyl and nonenyl succinic anhydrides.
The amount of hyd~ vping agent, when it is used at all, is preferably such as tohave a ratio to the amount of component (E), measured in the sarne units, that is at least,
with increasing preference in the order given, 2:1.0, 4:1.0, 6:1.0, or 8:1.0 and independ-
ently, primarily for reasons of economy, preferably is not more than, with increasing
preference in the order given, 25:1.0, 20:1.0, 15:1.0, 13:1.0, 1 1:1.0, or 9:1.0, with the
higher ratios within this range generally preferred for very highly concentratedcompositions according to this invention and lower ratios, including omission of any hy-
drotroping agent at all, often satisfactory for working compositions.
Optional colorant component (G) is often preferred in a composition according
to this invention, to serve as a visual indicator of the thickness of the coating applied to
a substrate surface with a complicated shape and thereby make it easier to achieve the
usual goal of an approximately equally thick coating over the entire surface to be deoxi-
dized/etched. Numerous conventional dyes and/or pigments, as known to those skilled
in the art, may be used for component (G).
Optional biocidal component (H) is not normally needed, but may be preferably
present in a liquid composition according to the invention in an amount effective to re-
press the biodegradation of any of the components of the composition, when the compo-
sition is used in an environment in which acid-tolerant microorg~ni~m~ are prevalent.
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WO 98/306~2 - PCT/US97/00006
Optional oxidizing agent component (J) is not normally needed, but may be
useful to accelerate the etching process on some substrates. Hydrogen peroxide is
preferred when this component is used; it also has some biocidal activity and may be
used for that purpose as part of component (H).
sIn preparing the compositions according to this invention, it is preferable to add
the viscosity increasing agent to water before adding any of the other ingredients. If this
is not done, long term viscosity instability may be experienced.
Preferably a substrate to be deoxidized and/or etched in a process according to
this invention should be cleaned to remove most gross soils before being exposed to a
10composition according to this invention as described above.
A process according to the invention is normally performed at ambient tempera-
ture, if for no other reason than that m~int~ining a different temperature would be a con-
siderable practical difficulty in view of the large size of the substrates usually treated.
A contact time from 1 to 20 minutes, or more preferably from 8 to 12 minutes, is5normally preferred in a process according to this invention.
The invention may be further appreciated by consideration of the following ex-
amples and comparison examples.
Materials Used
BRIJTM 35 surfactant was obtained commercially from ICI Americas, Inc. and is
20reported by its supplier to consist of ethoxylates of lauryl alcohol with an average of 23
moles of ethylene oxide per mole of lauryl alcohol.
CAB-O-SILTM M5 dispersion of finely divided silica in water was obtained com-
mercially from Cabot Corp. and is recommended as a viscosity increasing agent
CALSOFTTM LAS 99 surfactant was supplied by Van Waters and Rogers,
25Icirklzlnfl~ Washington and is reported by its supplier to be linear alkyl benzene sulfonate.
KELZANTM AR xanthan gum powder was commercially obtained from the Kelco
division of Merck & Co., Inc. and is reported by its supplier to contain 86 - 92 % solids
of xanthan gum (which is constituted of polymers of ~-l ,4-linked D-glucose units) that
has been modified to give lower viscosity at low shear rates than unmodified natural xan-
30than gum. For example, a solution of 0.3 % of each of potassium chloride and KEL-
ZANTM AR in water has a viscosity of about 800 centipoises (hereinafter usually
abbreviated as "cps") at a shear rate of 0. l reciprocal seconds (hereinafter usually abbre-
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WO 98/306s2 PCT/US97/00006
viated as "sec~"'), whereas an otherwise identical solution of natural xanthan gum has a
viscosity of almost l 0,000 cps. At a shear rate of l 0 sec-', the viscosities of these solu-
tions are about l 00 and 500 cps respectively.
NAXONATETM SC hydrotroping agent was obtained commercially from Ruet-
gers-Nease Chemical Co., Inc., Ross, Ohio and was reported by its supplier to be 93 %
sodium cumene sulfonate.
TRITONTM N-l01 surfactant was commercially supplied by Van Waters and
Rogers, Kirkland, Washington and was reported by its supplier to be a nonionic
surfactant consisting of ethoxylated nonylphenol molecules with residues from an10 average of 9.5 molecules of ethylene oxide per molecule of surfactant;
UNISPERSETM Blue colorant was obtained commercially from Ciba-Geigy as
a paste. It is reported by its supplier to contain about 50 % of copper phthalocyanine
blue pigment in dispersion.
VEEGUMTM T was obtained commercially from R. T. Vanderbilt Co., Norwalk,
Connecticut and is reported by its supplier to be hydrated magnesium aluminosilicate
smectite clay. It is recommended as a viscosity increasing agent.
Working Coating Compositions and Processes Therewith
Example and comparison example working compositions are set forth in Table
l below. Blank cells in the table indicate that none of the material was added to the com-
position, or that the property value that would properly appear in the cell was notmeasured. The viscosities reported in Table l were measured with a Brookfieldviscosimeter using spindle # 4. The balance of each composition not shown in Table l
was water.
In the lower part of Table l, etch rates and times of exposure that achieved
satisfactory deoxidizing/etching with some of the working compositions are also shown.
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TABLE 1
INGREDIENT PERCENT BY WEIGHT OF INGREDIENT IN COMPOSITION NUMBE~:
2 3 4 5 6 7 8
Ammonium 1.4 1.4 2.8 2.8 2.8 2.8 4.2 4.2
Bifluoride
H2SO4,96.5 % 2.0 2.0 4.0 4.0 4.0 4.0 6.0 6.0
CAB-O-SILTM M5 4.0 4.0
KELZANTM AR 2.0 2.5 3.0 2.5 3.0
VEEGUMTM T
CALSOFTTM LAS 99 0.80 0.80 1.60 1.60 1.60 1.60 2.40 2.40
BRIJTM 35 1.0 1.0
TRITONTM N-101 0.10 0.10 0.20 0.20 0.20 0.20 0.30 0.30
NAXONATETM SC 0.40 0.40 0.80 0.80 0.80 0.80 1.20 1.20
30 % H202 in water
UNISPERSET''' BIUC 0.0050.005 0.005 0.005 0 005
VISCOSITY IN POISES
OF COMPOSITION 1 2 3 4 5 6 7 8
NIIMBER:
At 20 RPM 14 6.7 22.6 85.2
At 10 RPM 145 131 166
At 5.0 RPM 246
At 2.5 RPM 410 480
At 1.0 RPM 652
At 0.5 RPM 920
PROCESS CIIARACTER_
ISTICS
Minutes of Contact 20 20 20 20
Etch Rate, ~lm/hr 0.38 2.67 2.84 3.5
Abbreviation in Table 1: "RPM" means "Revolutions per Minute"
... Ihis table is continued on the next page....
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WO 98/30652 PCT/US97/00006
TABLE I continued
INGREDIENT PERCENT BY WEIGHT OF INGREDIENT IN COMPOSITION NUMBER:
9 10 11 12 13 14 15 16
Ammonium 5.6 5.6 5.6 6.7 6.9 2.8 5.6 6.7
Bifluoride
H2SO4,96.5 % 8.0 8.0 8.0 9.6 9.8 4.0 8.0 9.6
CAB-O-SILTM M5 4.0
KELZANTM AR 2.0 2.5 3.0 2.0 2.0
VEEGUMTM T 4.0 4 0
CALSOFl'rM LAS 3.2 3.2 3.2 3.8 3.92 ].6 3.2 3.8
99
BRIJTM 35 1 0
TRITONTM N-101 0.40 0.40 0.40 0.48 0.49 0.20 0.40 0.48
NAXONATETM SC 1.60 1.60 1.60 1.92 1.96 0.80 1.60 1.92
30 % H2O2 in water 2.0 4.0 4.8
UNISPERSETM 0.005 0.005 0 005 0.0050.005 0 005 0 005
Blue
VISCOSITY IN 9 10 11 12 13 14 15 16
POISES OF
COMPOSITION
NIJMBER:
At20RPM 11.5 < 1 91 14 11.5 < 1
At 10 RPM 13] 194
At 5.0 RPM
At 2.5 RPM
At 1.0 RPM
At 0.5 RPM
PROCESS
CHARACTERISTICS
Minutesof 20 20 20 20 20
Contact
Etch Rate, ~m/hr 4.7 4.3 4.9 1.1 18.5
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The coatings were formed for these examples simply by immersing the test panels in the
composition and then withdrawing them after a few seconds, with no deliberate aid or
hindrance to drainage of the composition from the panel surface. The coated panel was
then held with its highest area surfaces vertical for the contact time indicated in the
Table. The viscous liquid coating over the panel surfaces was then rinsed away with
water. Panels had been weighed before applying the working composition and were
weighed again after this rinsing and subsequent drying to determine the mass loss which
was converted to an etch rate by the usual mathematical calculations (i.e., dividing the
total mass loss for the panel by the area of the panel to determine loss per unit area, then
1C dividing the loss per unit area by the density of the panel to determine the thickness of
metal corresponding to the mass loss.)
Some of the panels treated, instead of being dried to determine etch rates, weretreated after rinsing with a commercially available composition (ALOD~NE~) 1000
Chromate Conversion Coating Liguid, available from the Parker Amchem Division ofHenkel Corp., Madison Heights, Michigan) to produce a conventional chromate conver-
sion coating on the panel surfaces. The coatings produced are fully as good in properties
as those produced by using the same treatment on otherwise identical panels that had
been deoxidized/etched by a conventional high quality, low viscosity liquid composition
for use by immersion of the substrates being treated.
