Compositions – Preservative agents – Anti-corrosion
Reexamination Certificate
2000-11-16
2004-09-07
Thexton, Matthew A. (Department: 1714)
Compositions
Preservative agents
Anti-corrosion
C252S389620, C524S096000, C524S106000, C524S251000, C524S252000, C524S257000, C524S429000
Reexamination Certificate
active
06787065
ABSTRACT:
The invention concerns the use of a composition or premix based on volatile corrosion inhibitors for limiting to a maximum the degradation or release of volatile corrosion inhibitors during the preparation of the said composition.
It also concerns a composition or premix based on volatile corrosion inhibitors.
It furthermore concerns articles based on polymers and of which one of the components consists of this composition or premix, as well as the method for preparing these articles which comprise in particular packaging films, packages constructed from sheets and other parts based on polymers.
It also concerns articles in the form of pasty solids based on structuring agents and of which one of the components consists of the said composition or premix.
It finally concerns the use of the abovementioned composition and articles for the protection of metal parts against corrosion.
The use of volatile corrosion inhibitors is known when metal parts which are sensitive to corrosion are to be protected, in particular those which are made of mild steel with a low carbon content and which, once machined, are despatched as they are to their destination by maritime container with a view to their being finished on site, in particular by painting. The risks of corrosion are then considerable, especially when the parts in question are dispatched to hot and humid areas.
Volatile corrosion inhibitors offer very good protection against corrosion under these conditions and have the advantage of making it possible to avoid having to use conventional techniques for protecting metal parts; these conventional techniques consist of applying paints, varnishes, plastics, waxes, greases and oils which have to be removed before finishing on site, which leads to additional costs and pollution.
Volatile corrosion inhibitors, generally denoted by VCI, employ additives of which the vapour pressure may be considered appreciable at the temperature of use (for example of the order of 10
−5
to 10
−1
mm Hg at 20° C.) and which are capable of inhibiting the corrosion of metals.
These VCIs act by virtue of the fact that they are conveyed in vapour form to the metal surface to be protected, to be absorbed thereon or even dissolved in any condensation water.
Products are also known which are classified in a wider sense as VCIs by the fact that one of their reaction products has an adequate vapour pressure. Accordingly, for example, sodium nitrite, in the presence of ammonium ions, can form ammonium nitrite which is relatively volatile. The original sodium nitrite is then considered as a VCI.
The use of a mixture of different products classified in a wider sense as VCIs in an inert liquid vehicle is recommended in order to obtain an optimum anticorrosive effect whatever the composition of the material to be protected (BE 702592).
When the metal parts to be protected are packaged inside films, the VCIs are incorporated in the material constituting these films, and given that these films may be situated in direct contact with the surface of the products to be protected, corrosion inhibitors acting by contact are also incorporated in the mass constituting these films.
The advantages of this protective technique by means of packaging in a film containing VCIs, lie in its great ease of application and the overall protection provided, given that the vapours penetrate into the most inaccessible places of parts with complex forms without it being necessary to resort to cleaning or previous preparation, any de-protection operation and any pollution being moreover eliminated.
It is sometimes necessary to protect against corrosion only portions of large metal parts having a complex geometry. Pasty solids formed by the normal techniques of the polymer industry (moulding, modelling, extrusion) provide metal parts with the necessary localized protection, considerably minimizing costs.
In order to incorporate VCIs in the mass constituting films or other packaging articles which are often based on thermoplastic polymers, it is known to produce direct mixtures of VCI powders with polymers and to form packaging films or solid parts such as sheets directly by extrusion or blowing.
At the extrusion temperature, which is approximately 160° C. for low density polyethylene and 240° C. for polypropylene, VCIs have an extremely high volatility which leads, in the case of the manufacture of a film, to the appearance of a high porosity and a high risk of degradation and/or decomposition with elimination of at least part of the VCIs. The efficiency of such films from the anticorrosion point of view is thus greatly reduced following the loss of active materials.
In order to overcome this disadvantage, i.e. in order to limit the loss of VCI during the actual preparation of the finished articles, it has been proposed to use premixes containing VCIs, i.e. concentrates of active material dispersed in supports such as polymers, solvents and plasticizers. Premixes based on polymers (Patent BR-A-9001035) have the general advantage of being homogeneous and easy to handle; these premixes are then incorporated in the polymers with a view to preparing packaging articles.
Given however, that the temperatures employed when premixes are prepared are often above 150° C., at least partial degradation of the said premixes is observed and thus, as an example, it is noted that dicyclohexylamine nitrite, mixed and extruded with polyethylene at 160° C., results in granules of premix which have a dark yellow coloration, characteristic of a high degree of degradation i.e. a loss of activity.
In order to prevent this excessive degradation by heat, it has been proposed to use liquid premixes, based on oil, which do not need high temperatures during their manufacture (U.S. Pat. No. 4,913,874).
However, given that VCIs are not frequently soluble in these oily media, a heterogeneity of the premix results, as well as the appearance of difficulties due to local excess or reduced concentrations when they are subsequently incorporated in polymers from which the final articles are made.
It has also been proposed to overcome this disadvantage by using liquid premixes in the form of solvent-containing or oily solutions containing VCIs, premixes which are not incorporated during extrusion but are applied onto these films by spraying, forming in this way, after the evaporation of the solvent, either a powdered VCI layer (patent DE 3 417 149 A1), or an oily layer containing the VCIs (patent GB 2 188 274 A).
The disadvantage of these premixes lies in the fact that the VCIs are not imprisoned in a matrix to give a slow release, so that the protection obtained is of short duration. In addition, the adhesion of the layers deposited on the articles is low and leads to losses during handling and the need to clean the parts which have to be protected, which is precisely what one wishes to avoid.
The object of the invention is especially to overcome the disadvantages of the previous techniques and to provide compositions based on VCI, responding better to the various practical requirements than those which already exist. Its objective is also to provide finished articles employing at least one composition based on VCI according to the invention.
The object of the invention is finally to provide novel uses for these compositions based on VCI, such as the partial and localized protection of certain large metal parts having complex forms.
In addition, it is to the credit of the Applicant Company that it has found, following in-depth research, that these objectives were achieved as soon as structuring agents were incorporated in a composition based on volatile corrosion inhibitors, said structuring agents being capable of enabling a premix to be prepared at sufficiently low temperatures so as to limit to a maximum the release and/or degradation of VCIs during this preparation.
Consequently, the object of the invention is the use of a composition or premix based on volatile corrosion inhibitors which includes, in order to limit to a maximum the release and/or degradation of VCIs
Delalande Patrick
Droniou Patrick
Guillou Loic
Schapira Joseph
Stoianovici Gabriela
Henkel KGaA
Kilpatrick & Stockton LLP
Thexton Matthew A.
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