U.S. patent number 3,900,370 [Application Number 05/335,065] was granted by the patent office on 1975-08-19 for process for treating aluminum surfaces.
This patent grant is currently assigned to Henkel & Cie G.m.b.H.. Invention is credited to Wolfgang Friedemann, Roland Geisler, Hans Gunther Germscheid.
United States Patent |
3,900,370 |
Germscheid , et al. |
August 19, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Process for treating aluminum surfaces
Abstract
In the process for treating the surface of aluminum or an
aluminum alloy which comprises subjecting said surface to an anodic
oxidation and subsequently sealing with hot water or steam, the
improvement which consists essentially of sealing said surface by
applying an aqueous solution containing calcium ions and from 0.001
to 0.05 gm per liter of at least one acid selected from the group
consisting of (A) a water-soluble phosphonic acid which forms a
complex with a divalent metal, (B) a water soluble salt of said
acid of (A), and (C) the mixtures thereof at a temperature ranging
from 90.degree.C to the solution boiling point temperature and at a
pH of from 5 to 6.5, to the anodic oxidized surface, the molar
ratio of calcium ions to phosphonic acid being at least 2:1.
Inventors: |
Germscheid; Hans Gunther
(Hosel, DT), Friedemann; Wolfgang (Neuss,
DT), Geisler; Roland (Dusseldorf-Holthausen,
DT) |
Assignee: |
Henkel & Cie G.m.b.H.
(Dusseldorf-Holthausen, DT)
|
Family
ID: |
5838488 |
Appl.
No.: |
05/335,065 |
Filed: |
February 23, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Mar 10, 1972 [DT] |
|
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2211553 |
|
Current U.S.
Class: |
205/204; 148/253;
205/324; 205/229; 205/328 |
Current CPC
Class: |
C25D
11/246 (20130101) |
Current International
Class: |
C25D
11/18 (20060101); C25D 11/24 (20060101); C23c
001/08 (); B41m 001/18 (); B44c 003/02 () |
Field of
Search: |
;117/69 ;148/6.27,6.15R
;204/35N,38A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Welsh; John D.
Attorney, Agent or Firm: Hammond & Littell
Claims
We claim:
1. In the process for treating the surface of aluminum or an
aluminum alloy which comprises subjecting said surface to an anodic
oxidation and subsequently sealing with hot water or steam, the
improvement which consists essentially of sealing said surface by
applying an aqueous solution consisting essentially of water,
calcium ions and from 0.001 to 0.05 gm per liter of at least one
acid selected from the group consisting of (A) a water-soluble
phosphonic acid which forms a complex with a divalent metal, said
acid having the formula ##EQU7## in which R is selected from the
group consisting of phenyl and alkyl of 1 to 5 carbon atoms, (B) a
water-soluble salt of said acid of (A), and (C) the mixtures
thereof at a temperature ranging from 90.degree.C to the solution
boiling point temperature and at a pH of from 5 to 6.5, to the
anodic oxidized surface, the molar ratio of calcium ions to
phosphonic acid being at least 2:1.
2. The process as claimed in claim 1 in which the ratio of calcium
ions to phosphonic acid is from 5:1 to 500:1.
3. The process as claimed in claim 1 in which said salt of (B) is
selected from the group consisting of alkali metal salts, ammonium
salts, and lower alkanolamine salts.
4. The process as claimed in claim 1 in which said solution
additionally contains from 0.1 to 5 gm per liter of dextrin.
5. The process as claimed in claim 4 in which said solution
contains from 0.01 to 2 gm per liter of dextrin.
Description
PRIOR ART
To protect aluminum or aluminum alloys against corrosion,
anodically produced oxide layers are frequently applied to aluminum
surfaces. These oxide layers protect the aluminum surfaces from the
effects of the weather and other corroding media. Further, the
anodic oxide layers are also applied in order to obtain a harder
surface and therewith to give the aluminum an increased resistance
to wear. In particular, decorative effects can be attained by the
self coloring of the oxide layers or can be attained in part by
their easy colorability.
A number of processes are known for the application of anodic oxide
layers to aluminum. For example, the production of the oxide layers
takes place using direct current in solutions of sulfuric acid (the
direct current-sulfuric acid process). However, solutions of
organic acids, such as in particular sulfophthalic acid or
sulfanilic acid or mixtures of these organic acids with sulfuric
acid, are also frequently used. The last named processes are
particularly known as the autocolor processes.
These anodically applied oxide layers, however, do not fulfill all
requirements with respect to protection against corrosion, since
they have a porous structure. For this reason it is subsequently
necesary to seal the oxide layers by after-sealing which is often
effected with hot or boiling water or steam and is known as
"sealing." This closes the pores and therefore considerably
increases the corrosion protection.
During the subsequent consolidation of anodically applied oxide
layers, however, not only are the pores closed, but a substantially
thick and velvety film may also be formed over the whole surface.
This velvety film is the so-called sealing coating and consists of
amorphous aluminum hydroxide which is not resistant to handling, so
that the decorative effect of the layer is thereby impaired.
Furthermore, it reduces the adhesive strength during the bonding of
such aluminum parts and, due to the increased effective surface,
this sealing film promotes later soiling and corrosion. For these
reasons it has previously been necessary to remove the coating by
hand, mechanically or chemically.
It is already known to detach the film from sealed surfaces covered
with a sealing film by a further mineral acid treatment. With this
process, therefore, a further treatment step is needed, and
moreover it necessitates a very careful treatment with the mineral
acid in order to avoid damage to the oxide layer. Further, it is
also known to prevent formation of sealing films by carrying out a
sealing with solutions which contain nickel acetate and lignin
sulfate. This method has the disadvantage that the oxide layers may
become yellowed under the influence of light. Finally it is known
from U.S. Pat. Nos. 3,672,966 and 3,657,077 to prevent the
formation of sealing films without impairing the anodic oxide
coating or the quality of the after-sealing by applying a solution
of polyacrylates or specified dextrins to the surface. These
processes have proved satisfactory. In some cases, however,
especially if not carefully carried out, it is possible that
residues may remain upon drying. These are undesirable, but they
can be removed by a further rinsing.
OBJECTS OF THE INVENTION
It is an object of the present invention to provide a development
in the process for treating the surface of aluminum or an aluminum
alloy which comprises subjecting said surface to an anodic
oxidation and subsequently sealing with hot water or steam, the
improvement which consists essentially of sealing said surface by
applying an aqueous solution containing calcium ions and from 0.001
to 0.05 gm per liter of at least one acid selected from the group
consisting of (A) a water-soluble phosphonic acid which forms a
complex with a divalent metal, (B) a water soluble salt of said
acid of (A), and (C) the mixtures thereof at a temperature ranging
from 90.degree.C to the solution boiling point temperature and at a
pH of from 5 to 6.5, to the anodic oxidized surface, the molar
ratio of calcium ions to phosphonic acid being at least 2:1.
Other and further objects of the invention will become apparent as
the description thereof proceeds.
DESCRIPTION OF THE INVENTION
The invention relates to a process for the treatment of surfaces of
aluminum or aluminum alloys by anodic oxidation with a subsequent
sealing step in aqueous solutions at elevated temperatures. In this
manner, the formation of troublesome aluminum hydroxide coatings
(sealing films) on the surfaces are prevented and difficulties
caused by the salts producing hardness in the water are avoided by
the addition of certain phosphonic acids.
The present invention is further directed to a development in the
process for treating the surface of aluminum or an aluminum alloy
which comprises subjecting said surface to an anodic oxidation and
subsequently sealing with hot water or steam, the improvement which
consists essentially of sealing said surface by applying an aqueous
solution containing calcium ions and from 0.001 to 0.05 gm per
liter of at least one acid selected from the group consisting of
(A) a water-soluble phosphonic acid which forms a complex with a
divalent metal, (B) a water soluble salt of said acid of (A), and
(C) the mixtures thereof at a temperature ranging from 90.degree.C
to the solution boiling point temperature and at a pH of from 5 to
6.5, to the anodic oxidized surface, the molar ratio of calcium
ions to phosphonic acid being at least 2:1.
A relatively large number of phosphonic acids is known which form
complexes with divalent metals; and suitable examples of compounds
to be utilized according to the present invention include those
having the following formulae: ##EQU1## in which R represents
phenyl or alkyl of 1 to 5 carbon atoms; ##EQU2## in which R.sub.1
and R.sub.2 each represent hydrogen or alkyl of 1 to 4 carbon
atoms, R.sub.3 represents hydrogen, alkyl of 1 to 4 carbon atoms,
or phenyl; ##EQU3## in which X and Y each represent hydrogen or an
alkyl or 1 to 4 carbon atoms, R.sub.4 represents --PO.sub.3 H.sub.2
or a group of the formula: ##EQU4## or ##EQU5## in which X and Y
each have the above-defined meaning; and ##EQU6## in which R.sub.5
represents hydrogen, methyl or --CH.sub.2 --CH.sub.2 --COOH.
Examples of 1-hydroxyalkane-1,1-diphosphonic acids of formula I
which may be used are 1-hydroxypropane-1,1-diphosphonic acid,
1-hydroxybutane-1,1-diphosphonic acid,
1-hydroxypentane-1,1-diphosphonic acid,
1-hydroxyhexane-1,1-diphosphonic acid, as well as
1-hydroxy-1-phenylmethane-1,1-diphosphonic acid and preferably
1-hydroxyethane-1,1-diphosphonic acid.
Suitable examples of 1-aminoalkane-1,1-diphosphonic acids of
formula II are 1-aminoethane-1,1-diphosphonic acid,
1-amino-1-phenylmethane-1,1-diphosphonic acid,
1-dimethylaminoethane-1,1-diphosphonic acid,
1-dimethylaminobutane-1,1-diphosphonic acid,
1-diethylaminomethane-1,1-diphosphonic acid,
1-propyl-aminomethane-1,1-diphosphonic acid, and
1-butyl-aminomethane-1,1-diphosphonic acid.
Suitable examples of aminopolymethylene phosphonic acids of the
formula III include aminotrimethylenephosphonic acid,
ethylenediaminotetramethylenephosphonic acid,
diethylenetriaminopentamethylenephosphonic acid,
aminotri(2-propylene-2-phosphonic acid).
Suitable examples of phosphono succinic acids of formula IV include
phosphonosuccinic acid, 1-phosphono-1-methylsuccinic acid and
2-phosphonobutane-1,2,4-tricarboxylic acid.
Instead of the phosphonic acids mentioned above, their
water-soluble salts may also be used, such as alkali metal salts
especially the sodium salt or potassium salt, as well as the
ammonium salts, or the lower alkanolamine salts for example
triethanolamine salt. The phosphonic acids or their water-soluble
salts are preferably employed in a concentration of 0.001 to 0.05
gm/liter of solution. They may be used singly or in mixtures
thereof.
A mixture of 1-hydroxyethane-1,1-diphosphonic acid and
aminotrimethylenephosphonic acid in the proportion by weight of 4:1
to 1:4 has been found to be preferred.
The solutions containing phosphonic acids or their salts are
adjusted, where necessary, to a pH in the range of from 5 to 6.5.
This adjustment may be effected with ammonia or acetic acid.
Ordinary water which is neither completely deionized or softened
may be used for the solutions. If completely deionized water,
distilled water, or very soft water is used for making the
solutions, it is necessary to add calcium ions, and, preferably,
water-soluble calcium salts such as CaCl.sub.2 or
Ca(NO.sub.3).sub.2 are used. The molar ratio of calcium ions to
phosphonic acids should be at least 2:1. Generally it is
advantageous to use a higher molar ratio of calcium ions to
phosphonic acids of 5:1 to about 500:1.
A preferred form of the process comprises adding from 0.1 to 5
gm/liter, preferably from 0.1 to 2 gm/liter, of a dextrin
additionally to the sealing solutions. For this purpose, those
dextrins are specially used which have a viscosity of 50 to 400 cP
in 50% solution at 20.degree.C, the viscosity being measured with a
Brookfield rotary viscosimeter.
The advantages of the present invention include preventing the
formation of a sealing coating without causing damage to the anodic
oxide layer. Difficulties do not occur because of the water
hardness components in the aqueous sealing solutions, so that
deionized or softened water need not be used. Precipitates of water
hardness causing components are usually avoided. However in the
case of water with a high degree of hardness, only flocculent heavy
precipitates are formed; but these precipitates are not deposited
on the sealed portions, instead however, they fall to the bottom of
the bath and may be easily rinsed thereout. The appearance of the
surface is not affected by the process of the invention; the effect
obtained by the pre-treatment and anodization remain unchanged.
Only very small amounts of additives are necessary for the process
according to the invention.
The following examples are merely illustrative of the present
invention without being deemed limitative in any manner
thereof.
In the examples, the notation of the aluminum alloys is based upon
nomenclature according to DIN 1,725. The quality of the oxide
layers was determined by the so-called Testal value according to
DIN 50,949 and by the loss factor d (Anotest apparatus) according
to DIN 50,920 (design). Further, the products of the after-sealing
were tested by means of the Green test according to DIN 50,146. DIN
is the abbreviation for "Deutsche Industrie-Norm" representing a
series of standard German published test procedures.
EXAMPLE 1
Aluminum sections (AlMg.sub.3) degreased with an aqueous alkali
metal hydroxide solution and pickled in the usual manner, were
anodically oxidized in direct current-sulfuric acid process (layer
thickness 22.mu. ) and were sealed at 100.degree.C for 70 minutes
with a solution of 0.003 gm/liter of
1-hydroxyethane-1,1-diphosphonic acid and 0.5 gm/liter of dextrin
(viscosity 100 cP, measured in 50% solution at 20.degree.C) in
water of 15.degree.dH (German hardness) which had been adjusted to
pH 5.8 with ammonia prior to the sealing. The sections showed no
sealing film. The layer thickness was unchanged after the sealing;
and the Testal value of 8.5 and the loss factor d of 0.41 both
indicated a satisfactory sealing. After a relatively prolonged use
of the sealing solution, no solid precipitates of the water
hardness causing components appeared in the sealing solution. A
flocculent heavy coating was formed on the bottom of the bath
container, which was not deposited on the sections and could easily
be removed from the bath by flushing it out.
The same result was obtained when, instead of
1-hydroxyethane-1,1-diphosphonic acid, an equivalent amount of its
di-, tri- and tetrasodium, or potassium or ammonium salt or a
triethanolamine salt was used. In the case of the alkaline salts
the pH adjustment was carried out with acetic acid.
EXAMPLE 2
Aluminum sheets (AlSi.sub.5), degreased in the usual manner, which
had been anodically oxidized in the direct current-sulfuric
acid-oxalic acid process (layer thickness 21.mu.), were sealed at
100.degree.C for 60 minutes with a solution of 0.007 gm/liter of
1-hydroxyethane-1,1-diphosphonic acid in deionized water with the
addition of 10 mgm/liter of calcium ions, which was adjusted with
ammonia to pH 5.6 prior to the sealing. The sheets showed no
sealing film. The Testal value of 12 and the loss factor d of 0.49
both indicated a satisfactory sealing. The same results were
obtained with di-, tri- and tetra-alkali metal salts or ammonium
salts.
EXAMPLE 3
Aluminum sections (AlMgSi 0.5) degreased and pickled in the usual
manner, which had been anodically oxidized by an autocolor process
(layer thickness 18.mu.), were sealed at 100.degree.C for 60
minutes in a solution of 0.005 gm/liter of
1-hydroxyethane-1,1-diphosphonic acid, 0.005 gm/liter of
aminotrimethylenephosphonic acid and 1 gm/liter of dextrin
(viscosity 200 cP, measured in 50% solution at 20.degree.C) in
water of 35.degree. dH (German hardness), adjusted with ammonia to
pH 5.9 prior to sealing. The sections showed no sealing film. A
satisfactory sealing was indicated by the Testal value of 10.5 and
by the loss factor d of 0.47. The degree of water hardness was not
noticeably objectionable, since the water hardness causing
components were precipitated in a flocculent, easily removable,
settling form.
The same results were obtained when, instead of the above-mentioned
phosphonic acids, their alkali metal salts or ammonium salts were
used, while the alkaline salts were adjusted with acetic acid to a
pH value between 5.8 and 6.0.
EXAMPLE 4
Aluminum sections (AlMgSi 0.5) which had been degreased with an
aqueous alkali metal solution and pickled in the usual manner, were
anodically oxidized in the direct current sulfuric acid process
(layer thickness 20.mu. to 22.mu.). The sections were then sealed
at 98.degree.C to 100.degree.C for 60 minutes in a solution which
contained 0.01 gm/liter of 1-hydroxyethane-1,1-diphosphonic acid
and 2 gm/liter of dextrin (viscosity 150 cP, measured in 50%
solution at 20.degree.C), in water of 20.degree. dH (German
hardness) which was adjusted with ammonia to a pH of 5.8 prior to
the sealing. The sections showed no sealing film; and the Testal
value of 9.0 and the loss factor d of 0.40 indicated a very
satisfactory sealing. No difficulty resulted from the water
hardness causing components of the sealing solution.
EXAMPLE 5
In a manner analogous to that described in Example 4, aluminum
sections were sealed with solutions which contained,
a. of the 1-hydroxyethane-1,1-diphosphonic acid, the equivalent
amount of one of the following phosphonic acids:
2. 1-hydroxypropane-1,1-diphosphonic acid,
b. 1-hydroxyhexane-1,1-diphosphonic acid,
c. 1-aminoethane-1,1-diphosphonic acid,
d. 1,1-diphosphonic acid,
e. ethylenediaminotetramethylenephosphonic acid,
f. 2-phosphonobutane-1,2,4-tricarboxylic acid, or
g. 1-phosphono1-methylsuccinic acid.
In all cases no sealing film was formed. No difficulty resulted
from the hardness of the water. The Testal value ranged from 10 to
12 and the loss factor d ranged from 0.43 to 0.52 both of which
indicated a satisfactory consolidation.
The same results were obtained when, instead of the above-mentioned
phosphonic acids, their alkali metal salts or ammonium salts were
used in equivalent amounts.
Although the present invention has been disclosed in connection
with a few preferred embodiments thereof, variations and
modifications may be resorted to by those skilled in the art
without departing from the principles of the new invention. All of
these variations and modifications are considered to be within the
true spirit and scope of the present invention as disclosed in the
foregoing description and defined by the appended claims.
* * * * *