Coating processes – Removable protective coating applied – Metal base
Reexamination Certificate
2000-03-13
2001-10-30
Cameron, Erma (Department: 1762)
Coating processes
Removable protective coating applied
Metal base
C427S388400
Reexamination Certificate
active
06309697
ABSTRACT:
A subject-matter of the present invention is a composition of use in temporarily protecting metal components from corrosion, a process for the preparation of the said composition and the metal components coated with a dry film deriving from this composition.
The problem of the temporary protection of metal surfaces and more particularly of sheet metal from atmospheric corrosion is a constant preoccupation of manufacturers. Multiple possibilities therefore already exist for conferring, on the surface of the metal sheet, a form of temporary protection by fatty films, in particular based on conventional protecting oils.
However, the increase in the requirement criteria of users has led steel manufacturers to provide increasingly elaborate solutions which take into account highly varied factors (appearance, suitability for surface treatment, cleanliness of the premises, safety, toxicology and the like). These imperatives have thus been partially satisfied by the development of a non-fatty coating and of its method of application, the qualities of which confer properties of temporary protection from corrosion of the order of two months on the metal sheet thus treated (FR 92 08 037).
However, there remains a demand on the part of users for coatings which exhibit an even better corrosion stability, without, of course, prejudicing the subsequent properties of use, and in particular possess a prolonged corrosion stability with, preferably, a corrosion resistance of greater than three months.
It is a specific object of the present invention to provide a novel coating in accordance with these requirements.
A first approach consists in incorporating one or more corrosion inhibitors in coatings has base of formulations of oils for temporary protection.
Conventionally, the corrosion inhibitors present in protecting oils are chosen from:
amino compounds of alcoholamine type,
sulphonate derivatives, such as their barium or sodium salts, or alkylbenzenesulphonates, and
acids of linoleic type.
Unfortunately, the increase in corrosion resistance obtained with these conventional inhibitors is not satisfactory.
There consequently remains to this day a need for a method for the temporary protection of metal components which is significantly improved in terms of corrosion resistance (greater than three months), a dry appearance and suitability for surface treatment, with or without preparation, and which, in addition, conforms to the toxicology rules (absence of barium, of heavy metal salts, and the like).
Thus it is that the Applicant Company has demonstrated that the incorporation within an oil-in-water emulsion of a heterocyclic thioether of saturated carboxylic acids, as corrosion inhibitor, would make it possible specifically and satisfactorily to meet all these requirements.
More specifically, the present invention relates to a composition of use in conferring temporary protection from corrosion on metal surfaces comprising an oil-in-water emulsion, characterized in that the said emulsion comprises, in its aqueous phase, at least one compound of general formula I
in which formula the R, R
1
and R
2
groups are, independently of one another, a hydrogen atom, a C
1
to C
20
alkyl group, a C
1
to C
20
haloalkyl group, with the halogen being able to be fluorine, chlorine, bromine or iodine, a C
3
to C
6
cycloalkyl group, a carboxyl functional group or a C
2
to C
6
carboxyalkyl group,
n is an integer varying from 1 to 3, and
X is a sulphur or oxygen atom,
in the form of one of its water-soluble salts.
It is preferably a compound of general formula I in which R is a hydrogen atom and X a sulphur atom.
Unexpectedly, the addition of a corrosion inhibitor in accordance with the present invention to an oil-in-water emulsion confers a corrosion resistance on the corresponding coating which is very significantly prolonged over time. This improvement is in fact much greater than that expected, that is to say that equivalent to the superimposition of the respective effects of the emulsion and of the said inhibitor in terms of corrosion resistance. It is advantageously the reflection of a synergy between the two components.
The novelty of the claimed composition is additionally based on the incorporation of a compound of general formula I in the aqueous phase and not in the lipid phase of the emulsion employed in the claimed composition. This compound, which is water-insoluble in nature, is therefore present in the composition in a neutralized form for the purpose of conferring a satisfactory solubility in water on it.
This neutralization of the compound or compounds of formula I employed according to the invention can be carried out conventionally by a person skilled in the art. It can be obtained, for example, from aqueous ammonia, morpholine, ethanolamine, ethanol or potassium hydroxide. Depending on the reagent employed, it may be necessary, if appropriate, to adjust the pH of the final composition to a value compatible with the recommended application, that is to say to a value of between 8.2 and 9.5 and preferably between 8.5 and 9. This can be easily carried out by adjusting the pH of the final emulsion by a further addition of neutralizing agent, such as ethanolamine, for example.
The corrosion inhibitor of general formula I is preferably present in the claimed composition in a proportion of 1 to 10 g/l and preferably of 1 to 3.5 g/l.
Mention will very particularly be made, as preferred compounds of general formula I, of the water-soluble salts of benzothiazolylthiosuccinic, &agr;-(benzo-thiazolylthio)stearic, &agr;-(benzooxazolylthio)lauric, &agr;-(benzothiazolylthio)caproic and &agr;-(benzothiazolylthio)-caprylic acids.
It is more preferably a water-soluble form of benzothiazolylthiosuccinic acid (BTSA) and more specifically its ammonium or ethanolamine salt.
As regards the emulsion, it can be defined as comprising, in dispersion in water, 3 to 13% by volume of an oily phase comprising from 75 to 90% by volume of at least one oil and from 5 to 10% by volume of at least one surface-active agent. If appropriate, a supplementary corrosion inhibitor can be present in a proportion of 5 to 15% by volume in the oily phase.
The emulsion preferably comprises, in dispersion in the aqueous phase, between approximately 3 and 8% and preferably approximately 6% by volume of an oil.
The oil present in the oily phase of the emulsion can be composed of a mineral, vegetable or animal oil.
It is advantageously a mineral oil and preferably an oil of paraffinic or naphthenic type or a mixture of these.
Mention will very particularly be made, as mineral oil preferably employed according to the present invention, of the soluble oil Aquasafe 21® from Castrol.
It is preferable to use, as surface-active agent of the oily phase, a surfactant of polyoxyethylene type.
Use is advantageously made, as corrosion inhibitor of the oily phase, of a carboxylic acid, a barium or sodium alkylsulphonate or a fatty acid amine salt.
According to a preferred form of the invention, the claimed composition comprises, as corrosion inhibitor, a water-soluble salt of benzothiazolylthiosuccinic acid (BTSA) present, at a concentration of between 1 and 3.5 g/l and preferably of the order of 2.5 g/l, in the aqueous phase of an emulsion comprising 6% of soluble oil which is preferably the oil Aquasafe 21® from Castrol. It is preferably the ammonium salt of benzothiazolylthiosuccinic acid present at a concentration of the order of 2.5 g/l.
The present invention also relates to a process for the preparation of the said composition.
More particularly, this process is characterized in that the compound or compounds of general formula I are incorporated in the form of an aqueous solution in the aqueous phase of the emulsion prior to its emulsification with the oily phase.
This is because the Applicant Company has noticed, unexpectedly, that the method of incorporation of the compound of general formula I in the emulsion has a significant effect on the anticorrosion activity of the corresponding composition. Thus it is that it proves to be partic
Antoine Philippe
Kefferstein Ronald
Scherer Lothaire
Cameron Erma
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sollac
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