Note: Descriptions are shown in the official language in which they were submitted.
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~ ~ - 1 - Case 118-5160
IMPROVEMENTS IN OR RELATING TO ORGANIC COMPOUNDS
The present invention relates to the stabilization of acidic
Sn(II) containing electrolytes used for colouring oxide layers
on anodized aluminum or aluminum alloys, or for electroplat-
ing.
Sn(II)-salts e.g. in the form of acidic sulphate, fluoroborate
or chloride solutions are employed both for electroplating
and for colouring anodic oxide layers on aluminum or aluminum
alloys.
It is known that practically only the acidic sulphate bath
contains simple Sn(II)-ions. In all other electrolytes the tin
is at least partly bonded in the form of complexes.
One difficulty encountered in electroplating or in colouring
anodic coatings on aluminum or its alloys in acidic solutions
is that the Sn(II)-ions are oxidized to Sn(IV)-ions during the
process. By adding substances to the electrolyte, so called
stabilizers, the oxidation can be more or less prevented,
i.e. the Sn(II)-ions can be more or less stabilized.
The effectiveness of the stabilizer is decisive for the
quality of the deposit or the colouring of the anodic oxide
layer. It is generally well known that the quality of the
A
1 336~ 29
~ - 2 - Case 118-5160
surface treatment diminishes in the presence of large
quantities of both types of ion, Sn(II) and Sn(IV) due to
inadequate stabilizing of the Sn(II). One should therefore
endeavour to maintain the tin in the acidic solution as
Sn( II )-ions.
Also known as stabilizers for acidic electrolytes are aromatic
compounds containing amino groups e.g. aminophenol, dimethyl-
aniline.
These compounds have a stabilizing effect on Sn(II)-ions; they
cannot, however, prevent a fraction of the Sn(II)-ions being
oxidized to Sn(IV). Consequently the quality in particular of
the colouring of the anodic coatings on aluminum and aluminum
alloys is affected. If the Sn(II)-ions are not adequatly sta-
bilized, the depth of colour in the dark colour ions and the
uniformity of the colour are often unsatisfactory. This is a
significant disadvantage of the stabilizers used up to now. An
ideal stabilizer would be one that achieves complete stabili-
zation of the Sn(II)-ions. In fact it is, however, difficult
on colouring anodic coatings on aluminum and its alloys to
produce colours such as dark bronze or black using the above
mentioned additives. Mostly the scattering behaviour of the
electrolyte is also unsatisfactory, with the result that
lighter and darker colouring of the edge regions occurs. As
the period of colouring progresses - after about 10 minutes -
excessive colouring occurs and one obtains a metallic depositon the surface. This leads to problems in cleaning the
1 33 6 1 29
- 3 - Case 118-5160
coloured surface; contamination of the sealing baths and
corrosion problems follow.
It has been found now that diphenylamine and substituted
diphenylamine derivatives substantially stabilizes Sn(II)-ions
in an acidic solution. These compounds also improve the
- scattering properties of the tin(II)-electrolyte and
consequently the distribution of the current.
Accordingly, there is provided a stabilizing composition for
Sn(II)-ions containing, as active ingredient, diphenylamine or
a substituted diphenylamine derivative or a mixture thereof,
said ingredient being soluble in an acidic medium.
Advantageously, the diphenylamines of the invention are
soluble in water at 20C in an amount of at least 5 mg/l at a
pH < 5.
Particularly suitable diphenylamines according to the inven-
tion are the compounds of formula I
_~ R 1~_ 1
in which R4 R5 10 9
each substituent R1 to R1o, independently, is selected from
the group consisting of hydrogen; halogen (at most one
for each ring); nitro (at most one for each ring); -COOM
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- ~ - 4 - Case 118-5160
(at most two for each ring); -S03M (at most two for each
ring); -NH2 (at most two for each ring); C1 4alkyl; and
phenylamino (at most one for each ring),
R11 is hydrogen; C1 4alkyl; ~-to ~-hydroxy-C1_4alkyl;
phenyl; or -~B-O ~ R12 where each B, independently, is
-C2H4-, -C3H6- or -C4Hg-, n is a number from 1 to 20
inclusive and R12 is H, -S03M or -CH2COOM, and
M is hydrogen or the equivalent of a cation,
or a mixture of such compounds.
Halogen can be fluoro, chloro or bromo, preferably chloro.
When M is the equivalent of a cation, it is preferably an
alkali metal, an equivalent of an alkali earth metal or a
substituted ammonium. Preferably M is hydrogen.
In the -t-B--tn R12 residu, each B is preferably selected
from -C2H4- and -CH-CH2-.
CH3
More preferably each B is -C2H4-.
n is preferably a number from 1 to 5 inclusive.
R12 is preferably -S03M.
Preferably each ring, independently, bears 1, 2 or 3
C1_4alkyl groups.
Preferred compounds of formula I are those substituted on the
phenyl rings (R1 to R1o) by a total of one or two amino
groups, a total of one or two -COOM, or a total of one or two
-S03M, or a combination of the indicated amino with the -COOM
or -so3M groups.
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- - - 5 - Case 118-5160
Of the described group of compounds according to the invention
the following substances have been found to be particularly
advantageous additives:
2-amino-diphenylamine
4-amino-diphenylamine
4-amino-diphenylamine-2-carboxylic acid
diphenylamine-4-sulfonic acid
2-amino-diphenylamine-4-sulfonic acid
4-amino-diphenylamine-2-sulfonic acid
4,4'-diamino-diphenylamine-2-sulfonic acid
4'-amino-4-nitrodiphenylamine-2-sulfonic acid
1-amino-2,4-di(phenylamino)benzene-5-sulfonic acid, and
diphenylamine -4,4'-disulfonic acid, and their mixtures.
Preferred mixtures are those based on diphenylamine-
monosulfonic acid with diphenylamine-disulfonic acids.
The compounds of formula I can be prepared according to known
methods.
The stabilizing composition is preferably an aqueous solution
which may contain, as further assistants, an organic or in-
organic acid for the adjustment of the pH-value, preferably
sulphuric or chlorhydric acid, a further solubilising agent
and/or a sequestering agent. The stabilizing composition has
preferably a pH ~5. The concentration of
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~ - - 6 - Case 118-5160
the stabilizing agent may vary up to 95% by weight.
According to a preferred embodiment, the composition of the
invention may contain, in addition to the stabilizing agent
and the optional assistants as mentioned, a tin(II)-
electrolyte.
Suitable tin(II)-electrolytes are tin(II)-salts as used for
the surface treatment, particularly the colouring of oxide
layers on aluminum or aluminum alloys produced by anodizing or
for electroplating purposes. Preferred tin(II)-electrolytes
can be for example acidic tin(II) sulphate, fluoroborate or
chloride; tin(II)sulphate is particularly preferred.
The concentration of the tin(II)-electrolyte and the
stabilizing agent may vary within a large range; concentrated
compositions may be diluted. The stabilizing agent is
advantageously present in a concentration as required for the
effective stabilization of the tin(II)ions present in the
composition. The stabilizing agent may also be present in an
excess.
The composition of the invention comprising a stabilizing
agent and a Sn(II)-electrolyte has advantageously an acidic
pH. Preferably the pH is from 1 to 5; more preferably as low
as 1. When the Sn(II)-electrolyte is tin sulphate, the pH of
the composition is preferably adjusted with sulphuric acid.
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- 7 - Case 118-5160
The present invention also provides a process for stabilizing
an acidic tin(II)-electrolyte comprising contacting the
electrolyte with an effective amount of diphenylamine or a
substituted diphenylamine derivative or a mixture thereof to
prevent the oxidation of the Sn(II)ions.
5 Acidic tin(II)-electrolyte baths stabilized with a diphenyl-
amine as disclosed above, particularly a bath as used for
electroplating or colouring oxide layers on anodized aluminum
or aluminum alloys, form also part of the invention.
Furthermore, the invention also provides a process for colour-
10 ing oxide layers on anodized aluminum or aluminum alloys or
for electroplating with a Sn(II) containing electrolyte, in
which the Sn(II) electrolyte is stabilized by diphenylamine or
a substituted diphenylamine derivative or a mixture thereof.
The colouring of oxide layers on anodized aluminum or aluminum
15 alloys or the electroplating, particularly of a metal surface,
with a tin(II)-electrolyte stabilized according to the inven-
tion, can be effected in accordance with known methods, e.g.
as disclosed in USP 3,849,263. After the electrolytic colour-
ing, the resulting aluminum or metal surface may be sealed or
at first be dyed with an organic dyestuff and then sealed ac-
20 cording to known methods.Preferably the stabilizing agent of the invention is used in
the tin(II)-electrolyte treatment bath in an amount of from
20 mg/l to 1 g/l, more preferably 20 mg/l to 500 mg/l, par-
ticularly 100 mg/l to 200 mg/l.
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~ ~ - 8 - Case 118-5160
The stabilizing agent may be added separately or as a combina-
tion with the Sn(II)-electrolyte to the treatment bath.
Preferably, in the composition of the invention as well as in
the treatment bath, the weight ratio of Sn( II )-electrolyte to
the stabilizing agent is 2-30:0.02-1.
It has surprisingly been found that by adding to the electro-
lyte baths, compounds of the group according to the invention
the problems of overcolouring in the advanced stages of the
colouring process no longer occur in the colouring of aluminum
oxide layers obtained by anodizing. The problem of the often
disadvantageous occurrence of the dark colour tones and the
non-uniformity of the colour, which always recurred on colour-
ing oxide coatings in the presence of the conventional
stabilizers mentioned at the start, is substantially alleviat-
ed or completely eliminated by using the stabilizing agent
according to the invention. The excellent colouring properties
apply not only to the light colour tones, but in particular
also to the dark colour tones which up to now were very
difficult to achieve both with respect to the depth of colour
tone and the uniformity of colour.
Particularly surprising is that these compounds are highly
effective even in very small concentrations. Already at a
concentration of 20 ppm a substantial stabilizing effect is
achieved.
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- 9 - Case 118-5160
In all it was found that the disadvantages mentioned at the
start concerning the known stabilisizers for acidic Sn(II)
containing electrolytes for colouring aluminum oxide layers
obtained by anodizing or for electroplating purposes did not
occur with the electrolytes according to the invention, or
else only to a degree that did not disturb and was therefore
negligable.
In order that the advantages of the electrolyte stabilized
according to the invention over the electrolytes used up to
now are fully recognized, all factors viz., stabilizing of the
Sn(II)-ions, scattering characteristic/current distribution,
colouring effect, must of course be judged together.
The following two test series and colouring trials were carri-
ed out to demonstrate the excellent effect of the stabiliza-
tion and the resultant better colouring properties obtainedwith anodized aluminum and aluminum alloys in acidic solu-
tions. The purpose of the test series is to show, by means of
a quick test involving treatment with pure oxygen, the stabil-
izing effect of the additives according to the invention.
Test Series 1
An aqueous electrolyte was prepared containing 10 g/l of H2S04
and 20 g/l of SnS04. Under these conditions the tin is
initially present as Sn(II). The electrolyte was divided into
7 containers all having the same geometric form. Each contai-
ner contained 1 litre of electrolyte.
1 3~6 1 29
- 10 - Case 118-5160
Bath No. 1: no stabilizer
The other baths contained the following stabilizer additions:
Bath No. 2: Paraphenolic sulfonic acid, 20 g/l (the addition
normally used up to now).
Bath No. 3: N,N-dimethylaniline, 100 mg/l (known additive)
Bath No. 4: diphenylamine, 100 mg/l
Bath No. 5: diphenylamine-4-sulfonic acid, 100 mg/l
Bath No. 6: 2-amino-diphenylamine-4-sulfonic acid, 100 mg/l
Bath No. 7: 4-amino-diphenylamine-2-carboxylic acid, 100 mg/l
In all baths the pH had a value of 1; the baths were all at
room temperature and were stirred continuously by a magnetic
stirrer. Each bath had pure oxygen, 200 cm3 per minute, bubb-
led through it via glass chips, and was analyzed every half
hour for Sn(II)-ion content. The results are presented in
figure 1, Where the ordinate represents loss of Sn(II) and the abscessa
represents time in hours.
Test Series 2
The same basic solution as in test series 1 was prepared and
likewise 1 litre of electrolyte filled into each of the same
container as used in that test series. In all of the baths the
pH had a value of 1; the baths were at room temperature and
were stirred continuously by a magnetic stirrer.
1 3~6 1 29
~ Case 118-5160
Bath 8 corresponded to bath No. 1 in the first test series and
contained no additives. The following three baths all con-
tained diphenylamine-4-sulfonic acid viz.,
Bath No. 9: 20 mg/l
S Bath No. 10: 100 mg/l
Bath No. 11: 200 mg/l
Bath No. 10 therefore corresponded to bath No. 5 in the first
test series.
As in the first test series each bath had pure oxygen bubbled
through it via glass chips at a rate of 200 cm3/minute; again
the Sn(II) content WdS determined every half hour. The results
are presented in figure 2, where the ordlnate represents loss of Sn(II)
and the abscessa represents tLme in hours.
What can be seen from both figures 1 and 2 is that, when no
addition had been made, a large fraction of the Sn(II)-ions
had been converted to Sn(IV)-ions within a relatively short
time. Furthermore, it can be seen that the stabilizing effect
is dependent both on the substance added and on the amount
added. rn spite of the much larger amount added the known
ddditives, pardphenolic-sulfonic acid and N,N-dimethylaniline,
were much less effective stabilizers for Sn(lI)-ions than the
additives according to the invention.
1 336 1 29
~ ~ - 12 - Case 118-5160
The following Example illustrates the invention without limit-
ing the scope.
Example
Half-hard PERALUMAN-100 panels having each a dimension of 200
x 300 x 1.5 mm were anodized using the normal direct current/
H2S04process. The thickness of the oxide layer was 20 ~m.
These panels were introduced in 60 litres of a bath containing
10 g/l H2S04, 20 g/l SnS04 and 200 mg/l diphenylamine-4-
sulfonic acid and were treated for 8 minutes with a voltage of
15V.
The procedure was repeated using a treatment bath based on the
compositions 1 to 11 as disclosed above in test series 1 and
2, and at a treatment time varying from 1 to 12 minutes.
In all cases where a stabilizing agent of the invention was
used a completely uniform bronze colour was obtained, free of
edge discolouration. With the additions normally used up to
now one frequently encounters edge effects in the bronze
colour tones; this is due to the poor scattering characterist-
ic of the electrolyte. This means that the Sn(II)-containing
electrolytes with the new stabilizers have better scattering
behaviour than the electrolytes used up to now for that pur-
pose. The result is a better current distribution and thus a
related more uniform colouring of the anodic oxide layer.
