Compositions: coating or plastic – Coating or plastic compositions – Corrosion inhibiting coating composition
Patent
1997-07-22
1999-03-09
Green, Anthony
Compositions: coating or plastic
Coating or plastic compositions
Corrosion inhibiting coating composition
106 1414, 106 1441, 1062871, 1062876, 427387, 4273884, 428469, 428472, 428594, C09D18302, B32B 1501
Patent
active
058794379
DESCRIPTION:
BRIEF SUMMARY
This invention relates to aqueous compositions for surface treatment. One purpose of the treatment is to increase the adhesion of subsequently applied coatings, such as paint, lacquer, varnish or adhesive. Although the invention is of application to solid surfaces generally, it is of major importance in relation to metals generally, and in particular to aluminium.
Polydiethoxysiloxanes are used as refractory binders for metal casting moulds, and as binders for zinc-rich primers. They are made by the controlled hydrolysis of tetraethyl silicate to a 40% hydrolysed product known as "Ethyl Silicate 40" or "Silicate 40". This is a mixture of tetraethyl silicate and various polydiethoxysiloxane oligomers. These are generally used in solution in organic solvent; but such solvent necessarily carries a fire hazard.
WO 92/15650 (Alcan) describes an aqueous composition for the treatment of surfaces such as metal particularly aluminium, comprising a tetraalkyl silicate or a monomeric or oligomeric hydrolysis product thereof, and an inorganic passenger powder below 100 nm diameter such as fumed silica, both in dispersion in a fluid aqueous medium. The composition can be applied as a pretreatment coating to improve the adhesion of subsequently applied paint, lacquer or adhesive. Non-aqueous intermediate products comprising the silicate component and passenger powder can be diluted with water to make the coating composition.
This invention arises from our discovery that the nature of the inorganic component may be critical, and that advantages may result from replacing it. In particular, storage stability may be improved.
In one aspect this invention provides a coating composition comprising a tetraalkyl silicate or a monomeric or oligomeric hydrolysis product thereof, present in a proportion of 40-90% by weight on the non-volatile content of the composition, and a hydrous oxide sol, present in a concentration such that the oxide constitutes 10-60% by weight of the non-volatile content of the coating composition, optionally together with a surface wetting agent, marker material, defoamer, stabiliser, corrosion inhibitor and/or a catalyst which assists in chain-extension and cross-linking of the hydrolysis products in the presence of moisture, in dispersion in a fluid aqueous medium.
This coating composition is suitable for the pretreatment of solid surfaces such as metals generally, including steel, titanium, copper, zinc and, particularly aluminium, which term is used herein to include the pure metal and its alloys. The composition improves the adhesion properties of the pretreated surface, by improving the adhesion thereto of a subsequently applied coating such as paint, varnish, lacquer; or of adhesive either in the presence or absence of a lubricant. The pretreatment may improve either the initial adhesion of the subsequently applied coating to the surface or the maintenance of such adhesive properties in service, or both the initial adhesion and maintenance of adhesive properties. For example, so far as subsequently applied adhesive is concerned, the benefits of the invention may be shown mainly not in the initial adhesive strength obtained, but in the maintenance of adhesive strength in hostile or corrosive environments.
Tetraalkyl silicates (or tetraalkoxy silanes) can be progressively hydrolysed to silica according to the following equation: open-st.Si(OR).sub.2 O.brket close-st..fwdarw..brket open-st.Si(OH).sub.2 O.brket close-st..fwdarw.SiO.sub.2
Preferably R in these formulae is ethyl. The unhydrolysed tetraalkylester can be used for this invention, and is preferred, but a partially hydrolysed product is a possible alternative. This component should generally be present in a proportion of 40-90%, preferably 50-80% by weight of the non-volatile content of the composition.
As hydrolysis proceeds, a starting solution of tetraalkyl silicate thickens and finally sets-up so as to be unusable. The oligomeric partial hydrolysis products that may be present in the compositions of this invention are of such size or suc
REFERENCES:
patent: 5139888 (1992-08-01), Selwood et al.
English Language Abstract of Japanese Patent Application No. 6-240207 (Aug. 30, 1994).
English Language Abstract of Japanese Patent No. 3-079675 (Apr. 4, 1991).
English Language Abstract of Japanese Publication No. 62-79274, Apr. 11, 1987.
Alcan International Limited
Green Anthony
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