Metal cleaning and de-icing compositions

A metal cleaning composition comprising EDDS is described. Preferably, the compositions comprise optical isomers of EDDS, such as (s,s)EDDS. The compositions are particularly well suited for cleaning iron, zinc, aluminum, and copper. De-icer compositions comprising EDDS are also described. Also disclosed are processes for using the compositions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the use of a compound. In particular, the 
present invention relates to the use of ethylene diaminedisuccinic acid 
"EDDS". 
2. Description of Related Art 
In some applications it is desirable to clean metal surfaces, such as in 
the automotive and aeronautical industries, and in applications such as 
metal machining and forming, as well as in the preparation of circuit 
boards and integrated circuits. 
Many of the metal cleaning compositions used contain, as their active 
agents, acids. However, whilst the acids may remove the external layers of 
dirt, grease, unwanted paint and the like, they can remove some or all of 
the protective metal oxide layers and, in doing so, make the cleaned metal 
more prone to corrosion. This is very undesirable. 
There is therefore a need to have a metal cleaner that is non-corrosive, 
i.e. will not remove the metal's protective oxide layer (see for example 
Business Communications Company Inc. Report C.173 page 20, June 1993). 
Generally, the corrosiveness of a solution can be measured in terms of 
anodic breakdown potential (mV) of the metal oxide layer. The higher the 
anodic breakdown potential (ABDP), the less the metal will corrode during 
and after treatment with the metal cleaner. 
Ideally, metal cleaners should have ABDP values of at least 200 mV. 
Preferably, for the cleaning of aluminum it is desirable that the metal 
cleaners should have ABDP values of at least 400 mV. 
Two of the commonly used metal cleaners are ethylene diamine tetra-acetic 
acid (EDTA) and gluconic acid (GA). However, there are problems associated 
with these metal cleaners. In this regard, under certain conditions EDTA 
has an ABDP value of 0 mV for aluminum and copper, two metals which are 
often in need of cleaning; whereas gluconic acid has an ABDP value of 0 mV 
for zinc, copper and aluminum. 
Further ABDP values for these two metal cleaners are presented later in 
Tables 1-3. 
There is therefore a need for metal cleaners that are not corrosive, i.e. 
have a low-corrosive effect on the metals. 
The present invention seeks to overcome the problems associated with the 
prior art metal cleaners. 
SUMMARY OF THE INVENTION 
According to a first aspect of the present invention there is provided a 
metal cleaning composition comprising as its active agent at least EDDS. 
According to a second aspect of the present invention there is provided a 
process of cleaning metal wherein the metal is cleaned with the 
composition as defined above. 
According to a third aspect of the present invention there is provided the 
use of EDDS as a low-corrosive cleaning agent in a metal cleaning 
composition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The term "EDDS" includes racemic EDDS as well as optical isomers thereof, 
such as (s,s)EDDS, and active salts and active derivatives thereof. 
Preferably the term means (s,s)EDDS or salts thereof. Preferably the EDDS 
is (s,s)EDDS. More preferably the EDDS is (s,s)EDDS as prepared by the 
process of PCT/GB94/02397 filed 2 Nov. 1994. 
Most preferably the metal to be cleaned is iron, zinc, aluminum or copper, 
preferably aluminum. 
The term "active" means the ability to have an ABDP value of at least 200 
mV at a pH of about 3-14, preferably 5-12, for aluminum, iron, copper and 
zinc. 
The term "at least EDDS" means that other cleaning agents or acids may be 
present. 
However, for some applications, preferably the acid is EDDS alone. 
The term "metal" includes any suitable metal for cleaning. For example, the 
metal can be iron, zinc, copper or aluminum. The metal can even be pre or 
post formed into a substrate, such as a circuit board. Preferably the term 
"metal" means aluminum. 
In more detail, the present invention is based on the surprising discovery 
that EDDS can be used as a low-corrosion metal cleaner. More in 
particular, the present invention is based on the surprising discovery 
that EDDS has an ABDP value of at least 200 mV for iron, aluminum, copper 
and zinc. This is an important advantage. 
The presence of EDDS in a metal cleaning composition is advantageous 
because its use does not lead to the corrosion of the metal, such as 
stripping away substantial amounts of the protective metal oxide outer 
coatings. This is particularly advantageous with aluminum. 
The use of EDDS in or as a metal cleaning composition is advantageous 
because it has a greater cleaning effect than, for example, EDTA and 
gluconic acid. 
Our studies with EDDS, some of which are reported in the following 
experimental section, showed that EDDS is an effective metal cleaner. The 
results also indicate that EDDS is also effective if mixed metal ions are 
present. Another important advantage is that EDDS does not destroy 
aluminum surfaces. In this regard, EDDS selectively removes deposits of 
unwanted metal ions such as for example copper ions and iron ions, which 
are generally deposited on the aluminum surface, in the forms of their 
oxides without removing the aluminum. This is particularly advantageous. 
This effect of EDDS is in complete contrast to the effects of chelates 
such as EDTA. 
Accordingly the present invention also provides the use of EDDS to clean 
aluminum surfaces by removing unwanted other metal deposits thereon 
without substantially destroying the aluminum surface. 
One important application of this aspect is in the metal forming 
industries, such as the use of aluminum or other metals to make supports, 
fittings and other parts for aeronautical and automotive applications. The 
use of EDDS in these applications is advantageous as it enables one to 
effectively clean the surfaces of the met al before, during or after the 
forming process. Thus the EDDS will prevent or reduce or remove the build 
up of unwanted metal deposits. 
In addition, the use of EDDS is also useful as a metal cleaner when 
incorporated in solutions that are used for other applications in the 
aeronautical and auto motive industries, such as their use in de-icer 
compositions. 
Typically, the EDDS will be present in an de-icer composition in an amount 
of from about 0.1% to about 10%, preferably from about 1% to about 10%, 
more preferably from about 2% to about 7%, typically about 5% (wherein % 
is the w/w % of the final composition). 
Typical de-icer composition comprise organic chelating agents, such 
polyphosphates, aminocarboxylic acids, 1,3-diketones, hydroxycarboxylic 
acids, polyamines, amino alcohols, aromatic heterocyclic bases, phenols, 
aminophenols, oximes, Schiff bases, tetrapyrroles, sulphur compounds, 
synthetic macrocycles, polymeric chelates and phosphonic acids. For 
example, the de-icer composition of EP-A-0386886 comprises an organic 
chelating agent and an alkaline earth and/or an alkali metal carboxylate. 
The preferred alkaline earth carboxylate is calcium magnesium acetate 
(CMA). The preferred alkali metal carboxylate is sodium formate. The 
preferred chelating agents of EP-A-0386886 are said to be aminocarboxylic 
acids containing 2 to 4 carboxylic acid groups. The chelating agents 
listed in EP-A-0386886 are ethylenediaminetetraacetic acid, 
hydroxyethylethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid 
(NTA), N-dihydroxyethylglycine (2-HXG), and 
ethylenebis(hydroxyphenylglycine) (EHPG). The most preferred chelating 
agent of EP-A-0386886 is EDTA in its partially neutralized form as a 
calcium salt. 
With the present invention a de-icer composition comprises as the organic 
chelating agent at least EDDS. In this regard, the de-icer composition can 
comprise chelating agents other than EDDS. However, it is preferred that 
the chelate is just EDDS. When the de-icer compositions of the present 
invention are used they do not destroy metal surfaces that come into 
contact with the de-icer composition. This is very advantageous. 
The present invention will now be described only by way of example, in 
which reference shall be made to FIG. 1 which shows the formula of EDDS. 
Reference is also made to FIGS. 2-8 which are plots of soluble metal ion 
concentrations after addition of chelates to substrates. 
EDDS 
The structure of EDDS is shown in FIG. 1. 
PREATION OF EDDS 
A preferred method for making EDDS is disclosed in co-pending PCT Patent 
Application No. PCT/GB94/02397 filed 2 Nov. 1994, herein incorporated by 
reference. 
In short, PCT/GB94/02397 discloses a process for the preparation of amino 
acid derivatives in free acid or salt form, herein referred to as an amino 
acid linking reaction in which the nitrogen atoms of two or more amino 
acid molecules are linked by a hydrocarbonyl or substituted hydrocarbonyl 
group, which comprises reacting, in an aqueous medium at a pH in the range 
7-14, a compound of the formula X-A-Y where X and Y are halo atoms which 
may be the same or different and A is a hydrocarbonyl or substituted 
hydrocarbonyl group, in which X and Y are attached to aliphatic or 
cycloaliphatic carbon atoms, with an amino acid (or salt thereof), wherein 
the reaction is carried out in the presence of dissolved cations of an 
alkaline earth metal or of a transition metal. 
For example, (s,s)EDDS may be prepared according to the following 
teachings, in which DBE means 1,2-dibromoethane. 
A reaction mixture containing 150.1 g L-aspartic acid, 140.0 g of 50% aq. 
NaOH, and 210.9 g water at a pH of 10.2 at 25.degree. C. together with 
57.8 g of DBE was heated at 85.degree. C. for 4 hours. During this time an 
additional 50.1 g of 50% aq. NaOH was added to maintain the pH. At the end 
of the reaction period the solution was heated to boiling point for 1 hour 
then cooled to room temperature and 1633 g of water added. The solution 
was acidified with 36% HCl to pH 3 maintaining the temperature below 
50.degree. C. The solid product was collected by filtration. The solid 
product was (s,s)EDDS (51.5 g on 100% basis), representing a yield on 
L-aspartic acid charged of 31.3%, no other isomers being detected in the 
product. In the mother liquors was 85.7 g unreacted L-aspartic acid. The 
conversion of L-aspartic acid was 42.9% and selectivity to (s,s)EDDS was 
72.8%. 
ELECTROCHEMICAL CORROSION TESTS 
The electrochemical corrosive properties of (s,s)EDDS, EDTA and gluconic 
acid were tested by dissolving an appropriate amount of chelate in a 
standard 3.5 ww % NaCl solution. The solutions were analyzed by use of AC 
impedance techniques. 
The results are shown in the following Tables 1-3. 
TABLE 1 
______________________________________ 
PURE ALUMINUM 
CARBON STEEL 
C.R. ABDP C.R. ABDP 
(mm/v) (mV) (mm/v) (mV) 
______________________________________ 
(s,s)EDDS 
3.5% NaCl + 4.02E-03 none 6.25E-02 
none 
500 ppm EDDS pH 5.1 
3.5% NaCl + 3.12E-02 615 9.15E-02 
73 
500 ppm EDDS pH 7.0 
3.5% NaCl + 4.69E-02 660 8.93E-02 
none 
500 ppm EDDS pH 9.1 
3.5% NaCl + 4.69E-02 623 8.70E-02 
none 
500 ppm EDDS pH 10.5 
EDTA 
3.5% NaCl + 5.80E-02 none 7.36E-02 
none 
500 ppm EDTA pH 3.97 
3.5% NaCl + 3.35E-02 none 4.47E-02 
none 
500 ppm EDTA pH 4.86 
3.5% NaCL + 7.14E-02 550 1.21E-01 
none 
500 ppm EDTA pH 6.88 
3.5% NaCl + 8.48E-02 370 4.24E-02 
none 
500 ppm EDTA pH 9.42 
3.5% NaCl + 1.42E-01 600 8.93E-02 
none 
500 ppm EDTA pH 10.6 
GLUCONIC ACID 
3.5% NaCl + 2.45E-02 none 1.14E-01 
none 
500 ppm GA pH 6.40 
3.5% NaCl + 3.35E-02 none 4.46E-02 
none 
500 ppm GA pH 8.45 
3.5% NaCl + 1.02E-02 none 1.19E-01 
none 
500 ppm GA pH 9.42 
______________________________________ 
TABLE 2 
______________________________________ 
MONEL 400 STAINLESS STEEL 316 
C.R. ABDP C.R. ABDP 
(mm/v) (mV) (mm/v) (mV) 
______________________________________ 
(s,s)EDDS 
3.5% NaCl + 6.26E-02 none 2.25E-03 
270 
500 ppm EDDS pH 5.1 
3.5% NaCl + 5.41E-03 155 4.51E-04 
275 
500 ppm EDDS pH 7.0 
3.5% NaCl + 3.98E-04 100 7.99E-05 
400 
500 ppm EDDS pH 9.1 
3.5% NaCl + 6.26E-04 140 7.58E-05 
530 
500 ppm EDDS pH 10.5 
EDTA 
3.5% NaCl + 1.25E-01 none 1.43E-03 
170 
500 ppm EDTA pH 3.97 
3.5% NaCl + 7.40E-02 none 1.82E-03 
200 
500 ppm EDTA pH 4.86 
3.5% NaCL + 3.13E-02 115 2.66E-03 
350 
500 ppm EDTA pH 6.88 
3.5% NaCl + 1.31E-03 110 1.52E-04 
260 
500 ppm EDTA pH 9.42 
3.5% NaCl + 3.41E-02 150 9.22E-05 
450 
500 ppm EDTA pH 10.6 
GLUCONIC ACID 
3.5% NaCl + 5.12E-03 180 6.35E-04 
165 
500 ppm GA pH 6.40 
3.5% NaCl + 3.70E-03 110 1.25E-03 
380 
500 ppm GA pH 8.45 
3.5% NaCl + 2.05E-03 none 2.05E-04 
260 
500 ppm GA pH 9.42 
______________________________________ 
TABLE 3 
______________________________________ 
COPPER ZINC ALLOY 5 
C.R. ABDP C.R. ABDP 
(mm/v) (mV) (mm/v) (mV) 
______________________________________ 
(s,s)EDDS 
3.5% NaCl + 7.19E-02 none 2.69E-01 
none 
500 ppm EDDS pH 5.1 
3.5% NaCl + 3.82E-02 90 3.47E-01 
none 
500 ppm EDDS pH 7.0 
3.5% NaCl + 9.66E-02 none 2.02E-01 
none 
500 ppm EDDS pH 9.1 
3.5% NaCl + 1.53E-01 160 3.18E-01 
180 
500 ppm EDDS pH 10.5 
EDTA 
3.5% NaCl + 6.96E-02 none 1.04E-01 
none 
500 ppm EDTA pH 3.97 
3.5% NaCl + 1.68E-01 none 1.85E-01 
none 
500 ppm EDTA pH 4.86 
3.5% NaCL + 1.19E-01 none 1.47E-01 
100 
500 ppm EDTA pH 6.88 
3.5% NaCl + 2.47E-01 100 2.28E-01 
none 
500 ppm EDTA pH 9.42 
3.5% NaCl + 2.04E-01 90 8.09E-02 
none 
500 ppm EDTA pH 10.6 
GLUCONIC ACID 
3.5% NaCl + 1.26E-01 none 5.49E-02 
none 
500 ppm GA pH 6.40 
3.5% NaCl + 9.21E-02 none 4.04E-02 
none 
500 ppm GA pH 8.45 
3.5% NaCl + 1.20E-01 none 6.07E-02 
none 
500 ppm GA pH 9.42 
______________________________________ 
The results show that (s,s)EDDS is a good metal cleaner. The results also 
show that (s,s)EDDS has a low corrosive effect on metals such as aluminum. 
Further Metal Cleaning Studies 
Molar equivalent amounts of metal or metal oxides were added to 5% w/w 
ligand solution (50 g). The mixture was stirred in a sealed container for 
24 hours. The mixture was then filtered and the filtrate was analyzed for 
metal ions by ICP (Inductively Coupled Plasma Atomic Absorption 
Spectrometry). 
______________________________________ 
Test Conditions 
______________________________________ 
Ligand: (s,s)EDDS 50 g of 5% w/w solution 
EDTA 50 g of 5% w/w solution 
Solid: Copper as foil (0.5441 g) 
Aluminum as foil (0.2312 g) 
Iron (III) Oxide as powder 
(1.3672 g) 
Copper (II) Oxide as powder 
(0.6849 g) 
Temperature: 
25.degree. C., 75.degree. C. 
pH: 7,10 
______________________________________ 
The results of these further tests are reported in the Tables below and in 
FIGS. 2-5. 
______________________________________ 
pH 7 pH 10 
______________________________________ 
CONCENTRATION ( ppm) OF Cu(II) IONS IN 5% (s,s)EDDS 
SOLUTIONS EXPOSED TO Cu (II) OXIDE 
25.degree. C. 2595 2195 
75.degree. C. 4960 2820 
CONCENTRATION ( ppm) OF Fe(III) IONS IN 5% (s,s)EDDS 
SOLUTIONS EXPOSED TO Fe (III) OXIDE 
25.degree. C. 4.6 0.2 
75.degree. C. 84 6 
CONCENTRATION ( ppm) OF Fe(III) IONS REMOVED FROM 
Fe(III) OXIDE USING 5% LIGAND SOLUTIONS AT 25.degree. C. 
(s,s)EDDS 4.6 0.2 
Racemic EDDS &lt;0.1 &lt;0.1 
______________________________________ 
The results show that the cleaning effect of the cleaning composition 
according to the present invention is better than cleaning compositions 
containing EDTA or gluconic acid. 
The results also show that (s,s)EDDS is a much better metal cleaner than 
racemic EDDS. This result is very surprising. 
In particular, the results show that EDDS, unlike EDTA, does not 
substantially destroy aluminum substrates. Instead, EDDS selectively 
removes non-aluminum metal ions from the surface of the aluminum 
substrate. These results may be found in FIGS. 2 and 3. 
FIGS. 4 and 5 show that EDDS is a better cleaner for removing copper ions 
than EDTA at low pH--such as pH 7 --and even at high pH--such as pH 10. 
FIG. 6 shows that EDDS is a better cleaner for removing iron ions than EDTA 
at a low pH--such as pH 7. 
FIGS. 7 and 8 concern mixed metal systems, such as systems comprising Fe 
ions and Cu ions. 
These results show that EDDS, in particular (s,s)EDDS is a very good 
cleaner for removing each respective metal ion. 
Moreover, the results show that there is a surprising synergistic effect 
when Fe(III) oxide and Cu(II) oxide are cleaned together. 
ASTM TEST METHOD 
In these studies a series of specialist corrosion tests were performed in 
accordance with a standard test method for sandwich corrosion testing, 
namely ASTM test method F1110-90. 
SOLUTIONS/MATERIALS TESTED 
Five different Calcium Magnesium Acetate (CMA) solutions were provided and 
were evaluated by Test Method ASTM F1110-90. 
The solutions were: 
CMA+1% w/w ssEDDS:CMA 
CMA+3% w/w ssEDDS:CMA 
CMA+1% w/w ssEDTA:CMA 
CMA+3% w/w ssEDTA:CMA 
CMA solution 
The CMA concentration was 5% w/w CMA: water at pH 10. 
The 100.times.50.times.1.5 mm coupons were of the three metals: 
Aluminum AL 1200--99% pure Aluminum. 
Aluminum 2024--T3 
Aluminum 7075--T6 
The Aluminum coupons were bead blast finished and sequentially numbered. 
TEST METHOD 
The coupons pairs were arranged in sets of the three different metals in 
numerical order, three sets for the testing of each solution. 
______________________________________ 
Metal Metal Metal 
Al 1200 2024-T3 7075-T6 
______________________________________ 
Solution 1 
15% CMA plus 3% (s,s)EDDS 
Set 1 1 & 2 1 & 2 1 & 2 
Set 2 3 & 4 3 & 4 3 & 4 
Set 3 5 & 6 5 & 6 5 & 6 
Solution 2 
15% CMA plus 3% EDTA 
Set 1 7 & 8 7 & 8 7 & 8 
Set 2 9 & 10 9 & 10 9 & 10 
Set 3 11 & 12 11 & 12 11 & 12 
Solution 3 
15% CMA plus 1% (s,s)EDDS 
Set 1 13 & 14 13 & 14 13 & 14 
Set 2 15 & 16 15 & 16 15 & 16 
Set 3 17 & 18 17 & 18 17 & 18 
Solution 4 
15% CMA plus 1% EDTA 
Set 1 19 & 20 19 & 20 19 & 20 
Set 2 21 & 22 21 & 22 21 & 22 
Set 3 23 & 24 23 & 24 23 & 24 
Solution 5 
15% CMA 
Set 1 25 & 26 25 & 26 25 & 26 
Set 2 27 & 28 27 & 28 27 & 28 
Set 3 29 & 30 29 & 30 29 & 30 
______________________________________ 
The 25.times.75 mm pieces of fibre glass filter paper were saturated with 
the test solutions and placed between the pairs of coupons which were then 
positioned flat on trays to enable the transfer of test specimens between 
the condensation cabinet and oven during the exposure testing period. 
The exposure Schedule consisted of the coupons being exposed alternatively 
to Relative humidity of 95-100% Ambient both at 37.7.degree. C. 
(100.degree.F.) for 168 hours as per the following schedule. 
______________________________________ 
Exposure time 
Step (Hrs) Temp .degree.C. 
Rel. Humidity 
______________________________________ 
1 8 37.7 Ambient 
2 16 37.7 95-100 
3 8 37.7 Ambient 
4 16 37.7 95-100 
5 8 37.7 Ambient 
6 16 37.7 95-100 
7 8 37.7 Ambient 
8 16 37.7 95-100 
9 8 37.7 Ambient 
10 64 37.7 95-100 
______________________________________ 
RESULTS 
SOLUTION 1 
15% CMA plus 3% (s,s)EDDS 
AL 1200: No corrosion on all three pairs 1/2 3/4 5/6 
2024-T3: No corrosion on all three pairs 1/2 3/4 5/6 
7975 T6: No corrosion on all three pairs 1/2 3/4 5/6. There is some very 
slight staining but does not appear to be a loss of metal but rather an 
infill 
SOLUTION 2 
15% CMA plus 3%EDTA 
AL 1200: No corrosion on all three pairs 7/8 9/10 11/12 
2024-T3: No corrosion on all three pairs 7/8 9/10 11/12. Slight staining no 
loss of metal 
7075-T6: Considerable staining on all pairs 7/8 9/10 11/12. Definite 
corrosion pattern 
SOLUTION 3 
15% CMA plus 1% (s,s)EDDS 
AL 1200: No corrosion on all three pairs 13/14 15/16 17/18 
2024-T3: Corrosion pattern some staining oxide very slight incipient 
corrosion very slight 
7075-T6: Staining and discoloration up to 75% of area 
SOLUTION 4 
15% CMA Plus 1% EDTA 
AL 1200: Slight discoloration bottom coupon number 20. No appreciable 
corrosion. 
2024-T3: Discoloration corrosion pattern oxide 
7075-T6: Discoloration slight general corrosion 
SOLUTION 5 
15% CMA 
AL 1200: No corrosion on three pair 25/26 27/28 29/30 
2024T-3: Slight corrosion pattern less that 5% 25/26 27/28 possible pit in 
small area coupon 29 (top) 
7075-T6: Discoloration, oxidized layer 
The relative, corrosion severity rating system results for both 
discoloration and corrosion are shown in Tables 4 and 5. 
TABLE 4 
______________________________________ 
Discoloration 
Solution 
AL 1200 2024-T3 7073-T6 
______________________________________ 
1 0 0 0-1 
2 0 1 2 
3 0 1 2 
4 0 2 3 
5 0 3 3 
______________________________________ 
TABLE 5 
______________________________________ 
Corrosion 
Solution 
AL 1200 2024-T3 7073-T6 
______________________________________ 
1 0 0 0 
2 0 0 1 
3 0 1 2 
4 0 2 2 
5 0 1 3 
______________________________________ 
The above mentioned studies show that EDDS is an effective metal cleaner. 
The results also indicate that EDDS is a particularly effective if mixed 
metal ions are present. Another important advantage is that EDDS does not 
destroy aluminum surfaces. In this regard, EDDS selectively removes 
deposits of unwanted metal ions such as copper ions and iron ions in the 
forms of their oxides without removing the aluminum. This is particularly 
advantageous. This effect of EDDS is in complete contrast to the effects 
of chelates such as EDTA. 
Other modifications of the present invention will be apparent to those 
skilled in the art.