[0001] Annual losses due to destruction by rust and other corrosion are enormous, and this
destruction is rising rapidly due to the increasing content of corrosive substances
such as road salt, sulphur compounds etc. in the modern environment.
[0002] Particular attention has been given to the problem of rust in automobiles, and the
present invention will be described with reference to automobiles even if it can,
to be sure, also be used with advantage for similar problems in other constructions
of iron and steel such as bridges, ships etc.
[0003] For rust protection of automobiles, undercarriage treatments of various types have
been used, usually based on petroleum products, and the so-called ML method has been
used for rust protection inside beams and other cavities.
[0004] Much has been done directly at the factory to give the automobile an initial basic
protection; the sheet metal has been galvanized, various plastic coatings have been
tried and various types of sealants have been tested.
[0005] In retreating the car, it must first be carefully cleaned and washed and then carefully
dried in order for the protective petroleum products to adhere correctly. Cars are
usually washed prior to undercarriage treatment with steam and hot water and are then
dried carefully before the rust protection is applied. According to the present invention,
however, a water-based anti-rust agent is used thus eliminating the need for drying
but still having the anti-rust agent diffuse into and passivate the metal surface.
[0006] It is previously known to use water-based anti-rust agents, but the results have
up to now not been satisfactory and the present invention is the first to achieve
practically acceptable results.
[0007] The invention will be described in more detail below with reference to examples relating
to rust protection in automobiles, but similar advantages can of course also be achieved
in other iron and steel constructions.
[0008] An automobile is washed in the usual manner in an automatic carwash and immediately
after washing, while the automobile is still wet, it is sprayed with an aqueous solution
of a first anti-rust agent and, after a period of time, with an aqueous solution of
a second anti-rust agent. The solutions are sprayed on in mist form, suitably with
spray pistols or in automatic carwashes with fixed nozzles which spray the anti-rust
agents in mist form. The solutions are applied on the one hand from below in a moving
ramp, and on the other hand from above and from the side via the movements of the
carwash portals. Under the present conditions, a spraying time of about 15 seconds
for each solution was found to be suitable. The first anti-rust agent consists of
an aqueous solution of an anionic corrosion inhibitor, which disperses very easily
and rapidly over the moist, clean metal and forms a protective film. A number of different
anionic,corrosion inhibitors have been used and tested, but particularly good results
have been obtained with polyphosphates. Polyphosphate is a linear polymer with the
general formula

in which n is 2 or more. Optimal values of n for corrosion protection lie between
3 and about 20.
[0009] Especially good results have been obtained with sodium hexametaphosphate, "Graham's
salt", which contains tri- and tetrametaphosphate and high polymer polyphosphate ions.
[0010] The negative hexametaphosphate ion can also form under special conditions,positive
ions of the type

thus having a cathodic inhibiting effect.
[0011] The polyphosphate film formed increases the cathodic polarisation markedly. The second
cationic rust inhibitor sprayed on thereafter is fixed with its hydrophilic portion
in the polyphosphate film thus imparting water-repellant characteristics to the resulting
film. The second spraying also covers "greasy" portions of the metal, remaining paint,
spots etc. A number of cationic compounds were investigated and the best result was
achieved with amines, especially long-chained,quaternary ammonium compounds, preferably
tallow amine ethoxylate.
[0012] Highly hydrophobic amines have proved to produce the best results. Shorter fatty
acid chains increase the water solubility and the effect is poorer. Water solubility
also increases with the ethylene oxide content. Diamines have proved to be more effective
than monoamines.
[0013] The best results have been obtained with Ethoduom:,ne T 13; a reaction product between
N-alkyl-trimethylene diamines and ethylene oxide.
[0014] The molecular structure for this compound is

in which R is derived from a fatty acid and x+y+z varies between 3 and 10 or higher.
The presence of two amino groups in the molecule increases the cationic properties.
[0015] Non-ionic surfactants have also been tested, since they have certain advantages in
handling, e.g. less tendency to foam, but the results have not been as favourable.
[0016] By virtue of the fact that the anti-rust agent according to the invention is water-based
and has a very low surface tension, it has a very good spreading ability and penetrates
easily into all places where it is at all possible for moisture to reach such as joints,
cracks in the undercarriage surface, beneath layers of dirt, etc.
[0017] The simplicity of the treatment makes it possible to repeat it often, thus protecting
the areas most subjected to mechanical stresses, stones hitting the automobile and
wheel spray.
[0018] The composition of the-solutions can be varied within very wide limits, and below
will be given only an example of two solutions and the test results with them.
Testing of the corrosion properties The composition of the solutions:
[0019]

The execution of the test:
[0020] Corrosion test. The test was carried out with weighed test panels, protectively painted
on the reverse side, of cold- rolled steel with dimensions and surface treatment according
to the following.

[0021] The test panels under (c) and (d) were provided with a cross-scratch down to the
sublayer.
Exposure
[0022] The test panels were exposed lying on a rack in a chamber with the bottom surface
covered with water. In the chamber, which was provided with a misting nozzle, a water
mist was sprayed for 10 minutes per day without spraying the test surface directly,
but allowing water mist to fall down freely on all test surfaces. The test temperature
was 23 ± 2°C, and the relative humidity was 85-90% except during the spray periods
when it was 100%. The total exposure tine was 28 days.
The testing procedure
[0023] A. Two test panels each from groups (a), (b) and (d) , and one test panel from group
(c) were moistened with tap water, were sprayed with inhibitor solution 2 and thereafter
with inhibitor solution 1 in a total amount of about 35 g/m
2. The test panels were then coated with a 2-3 mm thick layer of synthetic road dirt.
The synthetic road dirt was prepared as follows: Washed quarts sand 112 g of No. 65,
26 g of No. 30 and 50 g of No. 18 as well as 12 g of kaolin powder was added to 20
ml of a 15% aqueous solution of sodium chloride and was mixed thoroughly. After an
exposure time of one.week the test panels were cleaned by high-pressure spraying with
water and new inhibitor solutions were applied as well as well as new road dirt. The
process was repeated at one week intervals throughout the entire exposure period.
A pair of plates from each of the groups (a), (b) and (d) were treated in the same
manner but at two week intervals and a pair of plates from each group were treated
only once prior to the beginning of the exposure.
[0024] B. Test panels from group A were first coated with road dirt, were moistened with
tap water and sprayed with the inhibitor solutions. Without removing the road dirt,
the test panels were then sprayed with the inhibitor solutions according to the same
schedule as under A.
[0025] C. The testing was carried out as according to A without coating the test panels
with road dirt.
[0026] D. The panels from groups (a), (b), (c) and (d), with and without road dirt, were
used as control panels. They were exposed without treatment during the entire exposure.
[0027] E. Two test panels from groups (c) and (d) were moistened and treated with the inhibitor
solutions. After exposure for one day, the test panels were rinsed off with tap water
and returned to the test chamber. After six days of further exposure, one test panel,
E 1 of each type, was removed and treated again according to the above. This was repeated
once per week during the entire test period. The two other test panels, E 2, were
exposed without further treatment.
[0028] After completed exposure, the road dirt was removed and the test surfaces were examined
with regard to the extent of rust, any defects in the anti-rust treatment, and under-film
corrosion at the scratches.
[0029] The protective coating was then removed from the reverse side of the test panels
from groups (a) and (b), and the metal loss was calculated by derusting in Clarke's
solution and subsequent weighing.
[0030] The effect on metals was determined according to SS 18 60 13. Two plates each of
aluminium, copper, cold- rolled steel and galvanized steel with known weight were
immersed in a mixture of equal parts of corrosion protectors 1 and 2 for 7 days at
50°C.
[0031] Two other plates of each type with known weight were first sprayed with corrosion
protector 2 and then with corrosion protector 1. After drying at room temperature
for 1 day, the plates were stored for 7 days in air at 50°C. After completion of the
testing, all of the plates were cleaned and examined with regard to pitting. The plates
were then weighed and the weight reduction in g/m
2 was calculated.
[0032] Penetration into cracks was determined according to SS 18 60 17. Eight blasted plates
were screwed together two by two somewhat staggered in relation to each other. The
blasted surfaces faced each other and had point contact over the common surface. The
plates were placed vertically and were sprayed perpendicular to the downwardly facing
blasted side. After 7 days at 23 ± 2°C the plates were separated and-the penetration
was determined.
[0033] Spraying with the inhibitor solutions and water proceeded as according to the following:
A pair of plates was sprayed once with corrosion protector 2 and corrosion protector
1.
[0034] A pair of plates was first sprayed with water; then with corrosion protector 2 and
corrosion protector 1.
[0035] A pair of plates was sprayed with corrosion protector 2 and corrosion protector 1,
the treatment being repeated after 2 and 5 days.
[0036] A pair of plates was first sprayed with water and then with corrosion protector 2
and corrosion protector 1, the treatment being repeated after 2 and 5 days.
[0037] The rust protection on a moist surface was determined according to SS 18 60 18. 0.1
ml of corrosion protector 2 and of corrosion protector 1 was dropped on a blasted
plate surface which was moistened with 3% sodium chloride solution. After storage
at 23 i 2°C and 50 ± 5% relative humidity for 48 hours, the test plates were examined
with regard to corrosion of the surfaces coated with inhibitor solutions. The spread
of the inhibitor solutions on the plate surface was measured and the mean diameter
was calculated.
Test results
[0038] Corrosion testing, weight loss after exposure for 28 days.
[0039] Test panels from group (a), clean, degreased surfaces.

The effect on metals
[0040] Total immersion test in equal parts of corrosion protectors 1 and 2 at 50°C for 7
days.

[0041] Sprayed and air-dried test plates after storage at 50°C for 7 days.
[0042] Weight loss g/m
2 0.05 0.5 0.7 0.7
1) Pits in phase boundary between precipitate and liquid lying on top. %
2) Zinc completely dissolved in the precipitate phase.
Penetration in cracks
Maximum penetration 3-5 mm upon spraying 1 or 3 times.
Anti-rust protection on moist surface
No rusting.
Extent, diameter 35 mm.
[0043] The test performed has demonstrated that the inhibitor system, under the conditions
prevailing in the test chamber, on an average was able to bring down the rate of corrosion
of unprotected pure steel coated with synthetic road dirt by about 45%, for unprotected
pure steel without coating with road dirt by about 90%, for rusty steel coated with
road dirt by 40-75% and for rusty steel without coating with road dirt by about 90%.
[0044] As regards the protected panels in groups (c) and (d), the testing time was too short
to reveal any reliable differences between test and control panels.
[0045] As can be seen from the results, the inventive corrosion protector is also very effective
on other metals than iron, as the results with aluminium, copper and zinc demonstrate.
It is mentioned above that the spreading capacity of the inventive water-based corrosion
protector makes it possible to protect all places where moisture can penetrate. The
entire rust film also provides improved adhesion for the underseal which can be applied
e.g. in the wheel housing to protect against stones.
[0046] Thus the anti-rust agents according to the invention provide a synergetic anti-rust
effect from the two inhibitors when applied in the manner described above. The effect
is however totally eliminated if the anti-rust agents are mixed prior to spraying,
or if the spraying is done in another order.
[0047] This method makes it possible to rust-protect an automobile simply and inexpensively
without the customer having to relinquish his automobile. The treatment can be easily
done as a standard step in washing.

1. Method of protecting metals against corrosion, characterized in that there is applied
to the metal surface, with an intervening period of time, a solution of an anionic
corrosion inhibitor and a solution of a cationic corrosion inhibitor.
2. Method according to claim 1, characterized in that the anionic corrosion inhibitor
solution is sprayed on first and then, after a period of time, the cationic corrosion
inhibitor solution.
3. Method according to claim 1, characterized in that the inhibitors are present in
aqueous solutions.
4. Method according to claims 1-2, characterized in that the solutions are sprayed
in mist form on water-washed, still wet surfaces one after the other.
5. Method according to claim lr characterized in that the corrosion protection is used for automobiles in conjunction
with washing.
6. Corrosion protection for spraying on metals, characterized in that a first solution
consists of polyphosphate 23%, alcohol 2% and water 73%, and that a second solution
for subsequent spraying consists of tallow diamine .ethoxylate 5%, alcohol 2% and
water 93%.