Compositions – Preservative agents – Anti-corrosion
Patent
1991-07-23
1992-06-30
Kyle, Deborah L.
Compositions
Preservative agents
Anti-corrosion
106 1434, 25238923, 2523893, 2523894, 25238961, 25238962, C23F 1118
Patent
active
051260743
DESCRIPTION:
BRIEF SUMMARY
Strontium chromate-containing primers are of great significance in practice in the aircraft industry in conjunction with the production of coatings serving for the protection of metals, in particular of pre-treated aluminum alloys. The best coating systems for passenger aircraft have for quite some time been made to consist of a chemical conversion layer, viz. a chromate-, phosphate-protective layer, which is produced on Al-surfaces by the dipping, wipe-on, spraying or roller application processes as anticorrosive, and which is known e.g. under the designation Alodine 1200, or of an acid wash primer, and thereafter an epoxyamine or polyamide-corrosion protection coating or a polyurethane (PUR) corrosion protection layer with a high-gloss aliphatic PUR-topcoat. By using strontium chromate in the corrosion protection coating filiform corrosion is prevented. Filiform corrosion is observed only on pre-treated substrates, such as Fe, Zn, Mg, steel, Ni, Cr and, in particular, Al. A (star-shaped) loss in adhesion going out from a damaged location in the lacquer film occurs--referably at values of humidity of air of from 65-95% and temperatures of approximately 30.degree. C.--between the chemically pre-treated substrate and the coating, which results in the coating chipping off.
There is, for instance, also known from DE-PS 74 77 80 a group of anticorrosive pigments, in the case of which a compound mixture, which contains as the cation at least two of the metals calcium, strontium, barium, magnesium, zinc and as the anion chromate ion and yet at least one anion selected from the carbonic, phosphoric, silicic, hydrofluoric or boric acids, is deposited onto inactive fillers. In that way, a chromate always is present, with best results likewise being obtained with strontium chromate.
However, strontium chromate belongs to the anticorrosive pigments which, as zinc chromate, are hazardous from the physiologic standpoint on account of their cancerogenic activity and should, if possible, no longer be utilized.
It has been attempted to use, by way of substitutes, zinc phosphate and modified zinc phosphates, such as shown in EU-A no. 0054266 and 0054267, which are for environmental protection reasons being employed increasingly in lieu of zinc chromate. These zinc phosphates do not, however, lead to any change in regard to filiform corrosion. Strontium hydrogen phosphates have also been tested, but they did not provide the protective effect which may be determined in the case of strontium chromate.
EU-PS 0011223 shows a corrosion inhibiting pigment and a paint on the basis of phosphate, consisting of a mixture of from 3 to 97% by wt. of MgHPO.sub.4 .multidot.3H.sub.2 O, the balance being CaHPO.sub.4 .multidot.2H.sub.2 O. The pigment is especially suited for the protection of iron and iron alloys and may be applied as a paint or a paste. The pigment may be exchanged up to 95% by wt. by pigment extenders, for instance barytas, talc, alkaline earth carbonates or wollastonite, and the pigment is to be present in the dried protective layer in a pigment volume concentration of from 10 to 60% by volume.
These combination-type pigments of magnesium and calcium hydrogen phosphate are, however, not very well suited for aluminum or mixed substrates, which do not consist exclusively of iron and iron alloys.
There still exists, therefore, a need for an anticorrosive coating for metals, in particular aluminum, which is non-toxic and yet comparable with the known strontium chromate as concerns its resistance to filiform corrosion.
It has now been found that carbonate-containing alkaline earth hydrogen phosphates, in particular magnesium and strontium hydrogen phosphates, exhibit better stability values to filiform corrosion than other metal phosphates, also than, in particular, magnesium hydrogen phosphate and strontium hydrogen phosphate without any carbonate component of the same alkaline earth metal. The complex effect of these carbonate-containing alkaline earth phosphates is yet further improved by additions of fluorosilicates and/o
REFERENCES:
patent: 4294621 (1981-10-01), Maurer et al.
patent: 4347285 (1982-08-01), Batdorf
Chemical Abstracts, vol. 90, 1979, p. 25591, Abstract No. 25594t, Matsushima, Hisao, "Calcium Hydrogen Phosphates-Calcium Carbonate Composite".
Dr. Hans Heubach GmbH & Co. KG
Fee Valerie D.
Kyle Deborah L.
LandOfFree
Anti corrosive pigments based on alkaline earth hydrogen phospha does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Anti corrosive pigments based on alkaline earth hydrogen phospha, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Anti corrosive pigments based on alkaline earth hydrogen phospha will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1862037