Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02356190 2001-06-18
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IMPROVED SEALING METHOD FOR ANODIZED METAL SURFACES
This invention relates to the production of corrosion-inhibiting and/or
decorative
coatings on metals by anodic oxidation. It concerns an improved process for
post-
s sealing porous, electrochemically-produced anodised coatings in order
further to
improve the properties thereof, in particular to reduce dirt adherence.
Electrochemical anodic oxidation of metals in suitable electrolytes is a
widely used
process for the formation of corrosion-inhibiting and/or decorative finishes
on metals
io suitable for this purpose. These processes are briefly described in
lJllmann's
Encyclopedia of Industrial Chemistry, 5th edition, vol. 9 (1987), pp. 174-176.
According
to this article, titanium, magnesium and aluminum and alloys thereof are
anodisable,
anodisation of aluminum and alloys thereof being of the greatest industrial
significance.
The electrolytically-produced anodised coatings protect the aluminum surfaces
from
i5 the action of weathering and other corrosive media. Anodised coatings are
also applied
in order to create a harder surface, thus increasing the wear resistance of
aluminum.
Particular decorative effects may be achieved by means of the intrinsic color
of the
anodised coatings or by absorptive or electrolytic coloring. Aluminum is
anodised in an
acidic electrolyte, sulfuric acid being most commonly used. Further suitable
electrolytes
a o are phosphoric acid, oxalic acid and chromic acid. The properties of the
anodised
coatings may be greatly varied by selection of the electrolyte, the
temperature thereof
and by the current density and duration of anodisation. Anodisation is
conventionally
performed using direct current or using direct current having a superimposed
alternating current.
Freshly anodised coatings may subsequently be colored by immersion in
solutions of a
suitable dye or by an alternating current treatment in an electrolyte
containing a metal
salt, preferably containing tin. As an alternative to subsequent coloring,
colored
anodised coatings may be obtained by so-called color anodisation processes, in
which
3 o anodisation is performed in solutions of organic acids, such as in
particular
sulfophthalic acid or sulfanilic acid, each optionally blended with sulfuric
acid.
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These anodically-produced protective coatings, the structure of which has been
scientifically investigated (R. Kniep, P. Lamparter and S. Steeb: "Structure
of Anodic
Oxide Coatings on Aluminum", Angew. Chem. Adv. Mater. 101 (7), pp. 975-977
s (1989)), are frequently described as "oxide coatings". The above
investigation has,
however, demonstrated that these coatings are vitreous and contain
tetrahedrally-
coordinated aluminum. Octahedrally-coordinated aluminum, as in aluminum
oxides,
was not found. This patent application thus uses the more general term
"anodised
coatings" instead of the misleading term "oxide coatings".
io
However, such coatings do not yet fulfil all requirements with regard to
corrosion
protection, as they still have a porous structure. It is consequently
necessary to post-
seal the anodised coatings. This post-sealing is frequently performed using
hot or
boiling water, alternatively using steam, and is described as "sealing". This
treatment
15 seals the pores, so considerably increasing corrosion protection. There are
numerous
literature references relating to this post-sealing process. The following may
be
mentioned by way of example: S. Wernick, R. Pinner and P.G. Sheasby: "The
Surface
Treatment and Finishing of Aluminum and its Alloys" (vol. 2, 5th edition,
Chapter 11:
"Sealing Anodic Oxide Coatings"), ASM International (Metals Park, Ohio, USA)
and
a o Finishing Publications Ltd. (Teddington, Middlesex, England) 1987.
However, not only are the pores sealed during post-sealing of the anodised
coatings,
but a velvety deposit of a greater or lesser thickness, the so-called sealing
deposit, is
formed over the entire surface. This deposit, which consists of hydrated
aluminum
z5 oxide, is visually unattractive, reduces adhesion when bonding such
aluminum
components and promotes subsequent soiling and corrosion. Since the subsequent
manual removal of this sealing deposit by mechanical or chemical methods is
costly,
attempts have been made to prevent the formation of this sealing deposit by
means of
chemical additives in the sealing bath. According to DE C-26 50 989, additions
of cyclic
3 o polycarboxylic acids having 4 to 6 carboxyl groups per molecule, in
particular
cyclohexane hexacarboxylic acid, are suitable for this purpose. According to
DE-A-38
20 650, certain phosphonic acids, for example 1-phosphonopropane-1,2,3-
tricarboxylic
acid, may also be used. The use of other phosphonic acids is known from EP-A-
122
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129.
DE-C-22 11 553 describes a process for post-sealing anodic oxide coatings on
aluminum and aluminum alloys in aqueous solutions containing phosphonic acids
or
s the salts thereof and calcium ions, wherein the molar ratio of calcium
ions:phosphonic
acid is adjusted to at least 2:1. A higher ratio of calcium ions:phosphonic
acids of about
5:1 to about 500:1 is preferably used. Phosphonic acids which may, for
example, be
considered are: 1-hydroxypropane-, 1-hydroxybutane-, 1-hydroxypentane-, 1-
hydroxyhexane-1,1-diphosphonic acid, together with 1-hydroxy-1-phenylmethane-
1,1-
lo diphosphonic acid and preferably 1-hydroxyethane-1,1-diphosphonic acid, 1-
aminoethane-, 1-amino-1-phenylmethane-, dimethyl-aminoethane-, dimethylamino-
butane-, diethylaminomethane-, propyl- and butylaminomethane-1,1-diphosphonic
acid, aminotrimethylene phosphonic acid, ethylene diamine-tetramethylene
phosphonic
acid, diethylene triamine-pentamethylene phosphonic acid, aminotri-(2-
propylene-2-
15 phosphonic acid), phosphonosuccinic acid, 1-phosphono-1-methylsuccinic acid
and 2
phosphonobutane-1,2,4-tricarboxylic acid. On the basis of the practical
examples of
the said patent, this process is a conventional hot post-sealing process using
post
sealing times of between 60 and 70 minutes at anodised coating thicknesses of
between about 18 and about 22 Nm. Post-sealing time is thus about 3 minutes
per Nm
a o of coating thickness.
When using water which contains no additives other than the stated sealing
deposit
inhibitors, elevated temperatures (at least 90°C) and relatively long
treatment times of
the order of about 1 hour for an anodised coating of about 20 Nm are necessary
for
a s effective post-sealing. This corresponds to a post-sealing time of about 3
minutes per
micrometer of anodised coating thickness. The post-sealing process is thus
highly
energy intensive and, due to its duration, may act as a bottleneck in the
production
process. Attempts have thus already been made to find additives for the post-
sealing
bath which promote the post-sealing process, so that it may proceed at lower
3 o temperatures (so-called cold post-sealing or cold sealing) and/or using
shorter
treatment times. The following have, for example, been proposed as additives
which
facilitate post-sealing at temperatures of below 90°C: nickel salts, in
particular
fluorides, which are sometimes used in practice (EP 171 799),
nitrosylpentacyano-
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ferrate, complex fluorides of titanium and zirconium, together with chromates
or
chromic acid, optionally in conjunction with further additives. As an
alternative to actual
post-sealing, hydrophobisation of the oxide coating by means of long-chain
carboxylic
acids or waxes has been recommended, as has treatment with acrylamides, which
should apparently be polymerised in the pore voids. Further details in this
connection
may be found in the above-stated reference by S. Wernick et al.. With the
exception of
post-sealing using nickel compounds, it has not proved possible to implement
these
proposals in practice.
io An accelerated, hot post-sealing process is known from US-A-5 411 607 in
which the
anodised metal components are immersed in an aqueous solution containing
lithium.
The lithium concentration is preferably in the range from 0.01 to 50 g/I and
in particular
in the range from 0.01 to 5 g/I. It is moreover suggested that the post-
sealing solution
should additionally contain a sealing deposit inhibitor. This is preferably
present in a
i5 concentration of between 0.1 and 10 g/I and is preferably an aromatic
disulfonate.
According to US-A-5 478 415, which has the same priority as the above-
mentioned
US-A-5 411 607, accelerated hot post-sealing may proceed using an aqueous
solution
which contains at least 0.01 g/I of lithium ions and 0.1 to 10 g/I of a
sealing deposit
inhibitor. Here too, the sealing deposit inhibitor is preferably an aromatic
disulfonate.
2 o DE-A-195 38 777 discloses an accelerated hot post-sealing process in which
the
anodised metal components are contacted with an anodising solution which
contains a
total of 0.1 to 5 g/I of one or more alkali metal and/or alkaline earth metal
ions and a
total of 0.0005 to 0.2 g/I of a sealing deposit inhibitor in the form of
phosphonic acids or
cyclic polycarboxylic acids.
The teaching of the latter three cited documents allows hot post-sealing times
to be
substantially shortened. DE-A-196 21 819 provides similar teaching. It relates
to a
process for post-sealing anodised metal surfaces, characterised in that the
anodised
metal is contacted with an aqueous solution for a period of between 0.5 and 2
minutes
3 o per micrometer of anodised coating thickness, which solution is at a
temperature of
between 75°C and its boiling point and has a pH in the range from 5.5
to 8.5 and which
contains:
(a) a total of 0.0001 to 0.01 g/I of one or more alkali metal and/or alkaline
earth
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metal ions;
and
(b) a total of 0.0005 to 0.5 g/I of one or more organic acids selected from
cyclic
polycarboxylic acids having 3 to 6 carboxyl groups and/or phosphonic acids;
s the solution containing a larger quantity of the metal ions (a) than is
required for
complete neutralisation of the acids (b).
DE-A-196 21 818 teaches a process for post-sealing anodised metal surfaces,
characterised in that the anodised metal is contacted with an aqueous solution
for a
to period of between 0.5 and 2 minutes per micrometer of anodised coating
thickness,
which solution is at a temperature of between 75°C and its boiling
point and has a pH
in the range from 5.5 to 8.5 and which contains:
(a) a total of 0.0004 to 0.05 g/I, preferably 0.005 to 0.02 g/I, of one or
more
cationic, anionic or non-ionic surfactants;
15 and
(b) a total of 0.0005 to 0.5 g/I of one or more organic acids selected from
cyclic
polycarboxylic acids having 3 to 6 carboxyl groups and/or phosphonic acids.
Despite the prior art, there is a need for post-sealing processes which either
reduce the
a o cost of post-sealing or improve the properties of the post-sealed anodised
coatings.
Properties of the post-sealed anodised coatings which are in particular need
of
improvement are soiling behavior and dirt adherence. Superficially soiled
anodised
metal surfaces are, on the one hand, aesthetically displeasing, which is
regarded as
problematic, particularly in architectural applications. On the other hand,
layers of dirt
as accelerate corrosion. There is therefore a particular need for anodised
metal surfaces
to which dirt does not readily adhere. In this way, dirt, on the one hand,
becomes fixed
less rapidly and on the other hand is extensively washed off again by
precipitation.
The present invention relates in the first instance to a process for post-
treatment of
3 o anodised metal surfaces, wherein the metal surfaces are contacted, for the
purpose of
post-sealing or after post-sealing, with an aqueous solution which exhibits a
pH in the
range from 1 to 14 and contains from 0.01 to 10 g/I of one or more acids with
fluoroalkyl groups having 2 to 22 carbon atoms and/or fluorinated polymers or
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copolymers of acrylic acid and/or methacrylic acid or respectively the salts
of these
acids.
The above-mentioned monomeric and/or polymeric acids having fluoroalkyl groups
s may constitute the only active substances dissolved in the aqueous solution,
except for
additives for adjusting the pH. Substances which may be used, if necessary, to
adjust
the pH are in particular ammonia or acetic acid. In principle, it is
irrelevant whether the
monomeric and/or polymeric acids are used as such or in the form of salts. As
a result
of the adjustment of the pH to within the stated range, the equilibrium
between free
to acid and acid anions is thus established in accordance with the acidity
constant of the
respective acid.
In one embodiment of the process according to the present invention, the above-
mentioned fluorine-containing acids are introduced during post-sealing of the
anodised
i5 coatings. This embodiment of the present invention is accordingly
characterised in that
the anodised metal surfaces are post-sealed by contacting the metal surfaces
with an
aqueous solution for a period of between 0.5 and 4 minutes per micrometer of
anodised coating thickness, which solution has a pH in the range from 5.5 to
8.5 and
which contains 0.01 to 10 g/I of one or more acids with fluoroalkyl groups
having 2 to
a o 22 carbon atoms and/or fluorinated polymers or copolymers of acrylic acid
and/or
methacrylic acid or respectively the salts of these acids.
The above-mentioned acids having fluoroalkyl groups may also be used in
conjunction
with other components, which are known to have a favourable effect on the post-
z5 sealing of anodised coatings and which may, for example, contribute to
reducing the
sealing deposits, lowering the sealing temperature and shortening the post-
sealing
time. Examples of such groups of substances and individual substances were
given in
the description of the prior art. Accordingly, preferred embodiments of the
present
invention may involve the aqueous solution used for post-sealing additionally
3 o containing one or more of the following components:
(a) a total of 0.0005 to 0.5 g/I of one or more organic acids without
fluoroalkyl
groups, selected from cyclic polycarboxylic acids having 3 to 6 carboxyl
groups and/or
phosphonic acids;
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(b) a total of 0.0004 to 0.05 g/I of one or more cationic, anionic or nonionic
surfactants;
(c) a total of 0.0001 to 0.01 g/I of lithium and/or magnesium ions;
(d) 1.2 to 2.0 g/I of nickel ions and 0.5 to 0.8 g/I of fluoride ions.
In a further embodiment of the process according to the present invention, the
anodised coatings are post-sealed by one of the processes known from the prior
art,
which were described by way of example in the introduction. Following this
post-
sealing, optionally after intermediate rinsing with water, the anodised and
post-sealed
io metal surfaces are contacted with the above-mentioned fluorine-containing
acids.
Accordingly, an alternative embodiment of the present invention involves the
anodised
metal surfaces being post-sealed by contacting the metal surfaces with an
aqueous
solution for a period of between 0.5 and 4 minutes per micrometer of anodised
coating
thickness, which solution has a pH in the range from 5.5 to 8.5 and which
contains one
i5 or more of the following components:
(a) a total of 0.0005 to 0.5 g/I of one or more organic acids without
fluoroalkyl
groups, selected from cyclic polycarboxylic acids having 3 to 6 carboxyl
groups and/or
phosphonic acids;
(b) a total of 0.0004 to 0.05 g/I of one or more cationic, anionic or nonionic
a o surfactants;
(c) a total of 0.0001 to 0.01 g/I of lithium and/or magnesium ions;
(d) 1.2 to 2.0 g/I of nickel ions and 0.5 to 0.8 g/I of fluoride ions;
and thereafter by contacting them with an aqueous solution for a period
ranging from 5
seconds to 15 minutes, which solution has a pH in the range from 1 to 14 and
which
a5 contains 0.01 to 10 g/I of one or more acids with fluoroalkyl groups having
2 to 22
carbon atoms and/or fluorinated polymers or copolymers of acrylic acid and/or
methacrylic acid or respectively the salts of these acids.
In these two embodiments, the organic acids (a) are preferably selected from
3 o saturated, unsaturated or aromatic carbocyclic six-membered ring
carboxylic acids
having 3 to 6 carboxyl groups. Preferred examples of such acids are trimesic
acid,
trimellitic acid, pyromellitic acid, mellitic acid and the particularly
preferred cyclohexane-
hexacarboxylic acid. The total quantity of carboxylic acids is preferably in
the range
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. $ .
from 0.001 to 0.05 g/I.
The preferably used cyclohexane hexacarboxylic acid exists in the form of
various
stereoisomers. As is known from DE-A-26 50 989, preferred cyclohexane
s hexacarboxylic acids are those which bear 5 carboxyl groups in cis position
and 1 in
trans position or 4 carboxyl groups in cis position and 2 in trans position.
In a second specific embodiment, the organic acids (a) are selected from the
phosphonic acids: 1-phosphonopropane-1,2,3-tricarboxylic acid, 1,1-
io diphosphonopropane-2,3-dicarboxylic acid, 1-hydroxypropane-1,1-diphosphonic
acid,
1-hydroxybutane-1,1-diphosphonic acid, 1-hydroxy-1-phenylmethane-1,1-
diphosphonic
acid, 1-hydroxyethane-1,1-diphosphonic acid, 1-aminoethane-1,1-diphosphonic
acid,
1-amino-1-phenylmethane-1,1-diphosphonic acid, dimethyl-aminoethane-1,1-
diphosphonic acid, propylaminoethane-1,1-diphosphonic acid, butylaminoethane-
1,1-
15 diphosphonic acid, aminotri(methylene phosphonic acid), ethylene
diaminotetra-
(methylene phosphonic acid), diethylene triaminopenta-(methylene phosphonic
acid),
hexamethylene diaminotetra-(methylene phosphonic acid), n-propyliminobis-
(methylene-phosphonic acid), aminotri-(2-propylene-2-phosphonic acid),
phosphono-
succinic acid, 1-phosphono-1-methyl-succinic acid and 1-phosphonobutane-1,2,4-
zo tricarboxylic acid. Of this selection, 1-phosphonopropane-1,2,3-
tricarboxylic acid, 1,1-
diphosphonopropane-2,3-dicarboxylic acid, aminotri(methylenephosphonic acid)
are
particularly preferred. The phosphonic acids (b) are preferably used in a
quantity of
0.003 to 0.05 g/I. Polyphosphino-carboxylic acids which may be considered as
copolymers of acrylic acid and hypophosphites are also suitable. One example
of such
z s a compound is Belclene7 500 from FMC Corporation, Great Britain.
Various groups of surfactants may be used as a further optional component in
the
process according to the present invention. Cationic surfactants (b) may, for
example,
be selected from quaternary ammonium salts, in which at least one alkyl or
arylalkyl
3 o residue comprises at least 8 carbon atoms. An example of such a surfactant
is C,2-,a-
alkyl-dimethylbenzylammonium chloride. Pyridinium salts, such as
dodecylpyridinium
chloride, may also be used as additional cationic surfactants. Examples of
anionic
surfactants (b) which may be used are alkyl or alkylaryl sulfates and
sulfonates. Linear
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alkyl sulfates, such as lauryl sulfate, are preferred for environmental
reasons. The
anionic surfactants may be used as alkali metal or ammonium salts, lithium
salts being
particularly preferred.
However, nonionic surfactants are preferably used as surfactants (b). These
may be
selected, for example, from alkoxylates, such as ethoxylates and/or
propoxylates of
fatty alcohols or fatty amines. By fatty alcohols and fatty amines are meant
compounds
having an alkyl residue of at least 8 carbon atoms. Such substances may exist
as pure
substances having a defined alkyl residue or consist of mixed products, as may
be
io obtained from natural fats and oils. It is also possible for the end groups
of the
alkoxylate to be blocked, i.e. etherification may be repeated at the terminal
OH group.
Examples of such nonionic surfactants are octanol x 4 EO (EO = ethylene oxide)
and
octanol x 4.5 EO-butyl ether. If fatty amine oxylates are used as nonionic
surfactants
instead of fatty alcohol ethoxylates, improved post-sealing results tend to be
obtained.
Therefore, the nonionic surfactants (b) are preferably selected from fatty
amine
ethyoxylates having 10 to 18 carbon atoms in the alkyl residue and 3 to 15
ethylene
oxide units per molecule. Specific examples are coconut oil amine x 5 EO and
coconut
oil amine x 12 EO.
2o A further preferred embodiment involves the aqueous solution additionally
containing a
total of 0.0001 to 0.01 g/I of lithium and/or magnesium ions. The use of
components
(a), (b) and/or (c) makes it possible to select post-sealing times which lie
in the lower
half of the stated range and may amount to between about 0.5 and about 2
minutes
per Nm of anodised coating thickness.
Irrespective of the embodiment of the present invention selected, the post-
sealing bath
may contain 1.2 to 2.0 g/I of nickel ions and 0.5 to 0.8 g/I of fluoride ions.
This
component allows post-sealing to be carried out as so-called cold post-
sealing, i.e. at
temperatures ranging between about 15 and about 70°C. Without the
addition of nickel
3 o fluoride or other additives, which allow the post-sealing temperature to
be lowered so
that it falls within this so-called "cold post-sealing range", post-sealing
may be
performed in the so-called intermediate temperature range, i.e. from about 70
to about
90°C, or in the so-called hot temperature range, i.e. between
90°C and the boiling
CA 02356190 2001-06-18
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point of the post-sealing bath. These temperature ranges apply to the post-
sealing
process, irrespective of which of the two above-described embodiments of the
process
according to the present invention is used.
s If the process is performed in accordance with the latter embodiment, in
which the
treatment with fluorine-containing acids is performed after post-sealing
itself, the
aqueous solution of fluorine-containing acids may be at a temperature ranging
between about 15°C and the boiling point of the solution. The period of
time over which
the post-sealed metal surfaces are contacted with the aqueous solution of the
fluorine-
io containing carboxylic acids may be shorter, the higher the temperature of
this aqueous
solution.
The acids, to be used according to the present invention, with fluoroalkyl
groups having
2 to 22 carbon atoms is preferably selected from fluorocarboxylic acids,
15 fluoroalkylphosphinic acids, fluoroalkylphosphonic acids,
fluoroalkylphosphonic acid
esters, which still have free acid functions, and fluoroalkylsulfonic acids.
Acids of this
type having fluoroalkyl groups are particularly preferred, these fluoroalkyl
groups being
perfluoroalkyl groups. However, this does not mean that the entire acid
molecule has
to be perfluorinated. Rather, it may additionally bear unfluorinated methylene
or methyl
ao groups. Indeed, this statement is intended to mean that, whenever a
fluorine atom is
bonded to a carbon atom, the other valencies of this carbon atom, which are
not
saturated by bonding to adjacent carbon atoms or heteroatoms of the acids, are
saturated by bonding to fluorine atoms. In other words, acids are preferred
whose
carbon atoms do not bear both hydrogen atoms and fluorine atoms. It is
particularly
25 preferred to use acids in which the carbon atoms adjoining the acid
function constitute
normal methylene groups, while more remote carbon atoms constitute either
perfluoro-
methylene or perfluoromethyl groups. If fluorinated polymers or copolymers of
acrylic
acid and/or methacrylic acid are used, the distribution of the fluorine atoms
and
hydrogen atoms bonded to the individual carbon atoms is irrelevant.
In each of the above-described embodiments, the process according to the
present
invention may be used for the post-treatment of anodised metal surfaces, the
thickness
of the anodised coating lying within the range of normal anodised coating
thicknesses
CA 02356190 2001-06-18
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(about 15 to about 25 Nm, in particular about 18 to about 22 m) or within the
thin-
layer anodisation range (about 1 to about 15 Nm).
The post-sealing bath using fluorine-containing organic acids suitable for the
post-
s sealing process according to the present invention may, in principle, be
produced in
situ by dissolving the constituents in (preferably completely deionised) water
in the
appropriate concentration range. Preferably, however, an aqueous concentrate
already
containing all the necessary constituents of the post-sealing bath in the
correct quantity
ratio is used to prepare the post-sealing baths, from which concentrate the
ready-to-
io use solution is obtained by dilution with water, for example by a factor of
between
about 100 and about 1000. It may be necessary in so doing to adjust the pH to
the
range according to the present invention using ammonia or using acetic acid.
The
present invention accordingly also relates to an aqueous concentrate for the
preparation of the aqueous solution for use in the post-sealing process
according to
i5 the present invention, wherein the concentrate yields the ready-to-use
aqueous
solution by dilution with water by a factor of between about 10 and about
1000.
The process according to the present invention yields post-sealed anodised
coatings,
the quality features of which correspond to those laid down by industrial
regulations
a o (for example those laid down by Qualanod). However, these post-sealed
anodised
coatings additionally exhibit a further characteristic, which is less marked
in the
anodised coatings produced according to the prior art. Dirt particles adhere
less well to
the surface, such that the latter is less rapidly soiled under similar
conditions and the
dirt is relatively easy to remove. When used for external architectural
purposes, this
as means that soiling of the anodised metal surfaces post-treated according to
the
present invention is easily washed off by precipitation.
Accordingly, the present invention relates, in a further instance, to the use
of acids with
fluoroalkyl groups having 2 to 22 carbon atoms and/or fluorinated polymers or
3 o copolymers of acrylic acid and/or methacrylic acid or respectively the
salts of these
acids to reduce dirt adherence to anodised metal surfaces. This use involves
the
above-mentioned acids having fluoroalkyl groups, to which the above more
detailed
explanations relate, being used in the context of one of the post-treatment
processes
CA 02356190 2001-06-18
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described in more detail above. To reduce dirt adherence to anodised metal
surfaces,
the fluoroalkyl group-containing acids specified in more detail above are
accordingly
used in the above-described post-treatment processes. The features of this use
are
summarised again in claims 9 to 12.
It is irrelevant to the post-sealing process according to the present
invention or the use
according to the present invention whether or not the metal surfaces were
colored
during anodisation or after anodisation and prior to post-sealing. The post-
sealing
process according to the present invention and the use according to the
present
to invention may accordingly be applied both to colored and uncolored anodised
coatings.
Any coloring may be carried out electrochemically (for example conventional
coloring
using tin salts), by self-coloring or using organic dip dyes.
Examples
~A) Fluorinated acids in post-sealing bath
AIMg1 grade aluminum sheets were prepared using a treatment sequence
conventional in the prior art:
zo
degreasing: P3-almeco7 18, 5 %, 5 mins, 70°C
rinsing: process water
pickling: P3-almeco7 57, 3 %, 1 min, 50°C
rinsing: process water
z5 deoxidising: Novox7 4902, 2 %, 1 min, room temperature
rinsing: completely deionised water
anodising: sulfuric acid, 18%, 40 mins, 18°C, 1.5 A/dm2, 16 V
rinsing: completely deionised water
3 o The anodised aluminum sheets having an anodised coating thickness in the
range
from about 18 to about 20 Nm were then post-sealed using post-sealing
solutions
according to the following Tables for 60 minutes at a temperature between 95
and
100°C. In all cases, the appearance of the surface was assessed as
good. The
CA 02356190 2001-06-18
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following quality parameters were measured:
(1 ) Acid corrosion loss in mg/dm2, determined to ISO 3210. To this end, the
test
sheet is weighed to an accuracy of 0.1 mg and then immersed for 15 minutes at
38°C
s in an acid solution containing 35 ml of 85% phosphoric acid and 20 g of
chromium(VI)
oxide per liter. On completion of the test period, the specimen is rinsed with
deionised
water and dried for 15 minutes at 60°C in a drying cabinet. The
specimen is then re-
weighed. The difference in weight between the first and second weighings is
calculated
and divided by the size of the surface in dm2. Weight loss is expressed as G
in
io mg/dm2 (1 dm2 = 100 cm2) and should not exceed 30 mg/dm2.
(2) Admittance Y2° was determined to German standard DIN 50949 using an
Anotest Y D 8.1 meter supplied by Fischer. The measuring system consists of
two
electrodes, one of which is conductively connected to the base material of the
specimen. The second electrode is immersed in an electrolyte cell, which may
be
i5 placed upon the coating to be tested. This cell takes the form of a rubber
ring having
an internal diameter of 13 mm and a thickness of about 5 mm, the annular
surface of
which is self-adhesive. The measurement area is 1.33 cm2. A potassium sulfate
solution (35 g/I) in completely deionised water is used as the electrolyte.
The
admittance value read from the meter is converted in accordance with the
instructions
z o of DIN 50949 to a measurement temperature of 25°C and a coating
thickness of 20
Nm. The resultant values, which should preferably be within the range between
about
and about 20 NS, are shown in the Table.
(3) Dye droplet test to ISO 2143. This is used to test to what extent a dye
solution
is absorbed on the anodised surface. For the test, first of all a droplet of
an acid
a s solution (hexafluorosilicic acid or a solution of potassium fluoride in
sulfuric acid) at
about 23°C is placed onto the clean, dry, horizontal test surface and
left to work for
exactly one minute. Then, the acid droplet is washed off and the test area is
allowed to
dry. Then, a droplet of a dye solution (Aluminum blue 2 LW or Sanodal red B3
LW)
having a pH ranging between about 5 and about 6 and a temperature of about
23°C is
3 o placed on the same point on the test sheet and left to work for one
minute. The droplet
of dye solution is then rinsed off and the test surface is wiped with a moist
cloth and
then dried. The intensity of the colored spot remaining on the test surface is
assessed
visually by comparison with a reference scale indicated in the test
instructions. The
CA 02356190 2001-06-18
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intensity of coloring is expressed by a scale of 0 to 5, 0 representing no
coloring
(corresponding to a non-absorptive surface) and 5 representing strong coloring
(corresponding to a fully absorptive anodised coating). The lower the number,
the
better post-sealed the anodised coating.
s (4) Soiling behavior. A 5% dispersion of ground coal fly ash (grain size
about 10
Nm) in completely deionised water was used for testing soiling. A color meter
(Croma-
Meter CR-300, Minolta) and a gloss meter (mikro-TRI-gloss, Gardner) were used
for
the purpose of evaluation. Implementation and evaluation were as follows:
Implementation
to (a) Measurement of L'a'b' value of coated, as yet unsoiled test sheet using
color meter, together with 60° gloss,
(b) steeping of test sheet in completely deionised water for 15 mins,
(c) thorough stirring of test dirt, distribution of 2 ml thereof with
disposable
pipette on almost vertically disposed test sheet,
i5 (d) complete drying of test sheet in drying cabinet at 40°C (about
20 mins),
(e) rinsing in a vessel using completely deionised water (by movement to and
from 10 x respectively),
(f) re-drying of test sheet at 40°C,
(g) measurement of L*a'b' value of soiled test sheet with colour meter,
together
a o with 60° gloss.
Evaluation
Measurement of L'a'b' using Minolta colour meter:
calculation of 4 value in %:
of 0 L' _ (L'soi~ed~L'unsoiled) X 100%
z5 60? gloss measurement with Gardner micro-TRI-gloss device
calculation of of ~ value in %:
GE = (GEsoi~ed~GEunsoi~ed) X 100%
Repetition of 3(b) to (g) until of 0 L' and of 0 GE are constant or markedly
greater than those of an uncoated test sheet (blank sheet).
Post-sealing and quality parameters are listed in Table 1.
CA 02356190 2001-06-18
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Table 1: Post-sealing and quality parameters
(a) Component ("Comp 1 ") according to the present invention: perfluorinated
monoalkyl phosphate (RrCH2CH20)P(O)(ONH4)2 Rr = F(CF2 - CF2)3$ (ZonyI7FSP,
s DuPont);
optional additive: cyclohexane hexacarboxylic acid according to DE-A-26 50
989 ("CHHS")
pH 5.5 - 6.0
Ex. No. Comp 1 CHHS of o G Y2o Dye droplet
mg/I mg/I mg/dm2 of Ns test
1 1750 0 4 12 0
2 700 0 5 12 1
3 175 0 3 12 0
4 70 0 4 12 2
5 35 0 3 11 2
6 7 6.6 18 16 2
io
(b) Component ("Comp 1 ") according to the present invention: perfluorinated
dialkyl phosphate (RfCH2CH20)2P(O)(ONH4), Rf = F(CF2 - CF2)~ (ZonyI7FSE,
DuPont);
optional additive: cyclohexane hexacarboxylic acid according to DE-A-26 50
15 989 ("CHHS")
pH 5.5 - 6.0
CA 02356190 2001-06-18
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Ex. No. Comp 1 CHHS OG Y2o Dye droplet
mg/I mg/I mg/dm2 ps test
7 1260 0 4 16 0
8 700 0 5 12 2
9 12.6 6.6 17 13 1
(c) Component ("Comp 1 ") according to the present invention: perfluorinated
mono/dialkyl phosphate (RfCH2CH20)P(O)(OH)2 + (RfCH2CH20)2P(O)(OH) Rf =
F(CF2 - CF2)3$ (Zonyl7UR, DuPont);
s optional additive: cyclohexane hexacarboxylic acid according to DE-A-26 50
989 ("CHHS")
pH 5.5 - 6.0
Ex. No. Comp 1 CHHS OG Y20 Dye droplet
mg/I mg/I mg/dm2 us test
2400 0 3 17 0
11 960 0 3 15 1
12 480 0 10 18 2
13 240 0 2 11 1
to As described above, to test soiling behavior, test sheets were soiled once
per test
cycle, allowed to dry and the dirt was rinsed off. After each test cycle, the
change in
color and gloss value was measured in relation to the unsoiled sheet. Table 2
contains
data relating to relative color value and relative gloss per soiling cycle,
wherein the use
according to the present invention of perfluorinated monoalkyl phosphate is
compared
with the use of the standard post-sealing bath additive cyclohexane-
hexacarboxylic
acid serving as a comparison. Table 2 shows that colour and gloss values vary
only
slightly from cycle to cycle when subjected to the treatment according to the
present
invention, while the comparison sheets display a marked deterioration, which
indicates
CA 02356190 2001-06-18
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adherent dirt.
Table 2: Soiling behavior. Invention: post-sealing with the addition of 35
mg/I of
perfluorinated monoalkyl phosphate (ZonyI7FSP); comparison: post-sealing with
the
s addition of 13.2 mg/I cyclohexane hexacarboxylic acid ("CHHS")
Test cycle %4L ~ %OGE
Zonyl FSP CHHS Zonyl FSP CHHS
0 100 100 100 100
1 99.5 84.5 96.4 37.4
2 98.4 63.3 96.3 9.9
3 98.4 51.2 94.7 1.8
4 97.6 46.7 95.1 1.2
97.4 43.9 92.2 1.0
6 96.5 42.3 91.0 1.0
7 96.7 41.9 88.1 1.0
8 97.8 87.4
9 98.4 86.9
(B) Post-treatment using fluorinated acids after post-sealing
to Aluminum sheets were prepared as described under (A). They were then post-
sealed
by a process according to the prior art in an aqueous solution of 13.2 mg/I
cyclohexane-hexacarboxylic acid at a temperature of 95°C and having a
pH value in
the range from 5.5 to 6 for 30 or 60 minutes. They were then immersed, when
still
moist, in a solution which contained 7 g/I ZonyI7FSP (c.f. Table 1 ), was at
room
temperature and exhibited a pH of 7. The sheets were subsequently dried using
compressed air. The surface quality thereof was tested in accordance with
Qualanod,
CA 02356190 2001-06-18
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as described above under (A). The results are given in Table 3.
Table 3: Treatment parameters and surface qualities relating to post-sealing
and
subsequent treatment with perfluorinated monoalkyl phosphate ZonyI7FSP
Ex. No. Post-sealingTreatment OG in Y20 in Dye droplet
time using time mg/dm2 NS test
CHHS in using
minutes ZonyI7FSP
in
minutes
14 60 5 14 11 1
60 1 16 10 1
16 30 5 19 16 1
17 30 1 22 16 2
Comp.1 60 none 18 15 1
Comp.2 30 none 25 25 2 - 3
In another series of tests, sheets which had been post-sealed and post-treated
using
perfluorinated monoalkyl phosphate as described under (B) were examined with
regard
io to the effect of the variables concentration of active substance,
temperature and
treatment time on the surface coverage of test sheets with perfluorinated
monoalkyl
phosphate. The sheets had been post-sealed for 60 minutes. The post-sealed
test
sheets were left in the ZonyI7FSP solution, respectively for one minute, 5
minutes and
15 minutes. Surface coverage was measured using the count rate (in kilopulses
per
15 second) determined by X-ray fluorescence measurement of phosphorus. The
results
are contained in Tables 5 to 7.
CA 02356190 2001-06-18
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Table 5: X-ray fluorescence pulse rates for different concentrations of
ZonyI7FSP; pH
= 7, room temperature
15 minutes 5 minutes 1 minute
2 % 0.448 0.4668 0.527
1 % 0.2257 0.2369 0.216
0.50 % 0.1703 0.1573 0.153
0.10 % 0.1386 0.1071 0.097
Table 6: X-ray fluorescence pulse rate exhibited by ZonyI7FSP solution at
different
temperatures; concentration 0.7 wt.%, pH = 7
15 minutes 5 minutes 1 minute
20 C 0.1712 0.1573 0.153
40 C 0.4618 0.3803 0.215
60 C 0.9507 0.3635 0.307
io Table 7: X-ray fluorescence pulse rates exhibited by ZonyI7FSP solution at
different pH
values, adjusted using acetic acid or ammonia; concentration 0.7 wt.%, room
temperature
15 minutes 5 minutes 1 minute
PH 5 1.0981 0.7926 0.56
pH 7 0.1712 0.1573 0.153
PH 9 0.1432 0.1405 0.138
