Compositions: coating or plastic – Coating or plastic compositions – Silicon containing other than solely as silicon dioxide or...
Reexamination Certificate
2002-08-26
2004-02-24
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Silicon containing other than solely as silicon dioxide or...
Reexamination Certificate
active
06695904
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composition comprising silicon compounds which is used essentially for producing a coating on surfaces and also as a base material for paints. The present invention further relates to a process for preparing such a composition. The invention additionally relates to coatings and articles obtainable by applying such a composition or a corresponding formulation.
2. Description of the Background
Organofunctional silanes and siloxanes are widely used for modifying surface properties: for example, as adhesion promoters, as binders, or for imparting water, oil or dirt repellancy properties to a surface.
Accordingly, organofunctional silanes and silica sols are part of numerous solventborne or aqueous formulations, such as in compositions for coating surfaces, such as topcoats, paints or anticorrosion compositions, to give but a few examples.
A coating may have the effects, inter alia, of improving the resistance of a substrate to external influences and of preserving the visual appearance or altering it in some desirable way. For instance, substrates sensitive to scratching, in particular, are provided with a more or less scratchproof coating through the application, for example, of paint to iron, steel, aluminum, copper, silver, magnesium, zinc, tin, nickel or alloys based, for example, on magnesium/aluminum. Additionally, metals or other substrates, such as ceramic, brick, glass, artificial stone, and plastics are coated to improve their corrosion resistance, weathering stability, or properties of repelling bioorganisms.
The requirements imposed on such a coating are generally stringent, especially as regards elasticity, impact strength, scratch resistance, UV and chemical resistance, gloss retention, surface quality—particularly visual appearance—and, not least, in respect of economics—particularly as regards ease of processing, duration of processing, consumption of material, emissions, and/or flash point. Examples of desirable features are low coat thicknesses, effective and durable attachment, easy and effective processing of the coating composition, and stability of the composition on storage. It is frequently observed, however, that the coating—especially on a highly elastic or ductile material, such as aluminum or copper—is unable to conform to the material properties of the substrate, and the coating ruptures or even flakes off. In many cases it is necessary, before a coating is applied, to subject the substrates to a complex pretreatment, by passivating, phosphating, chromating, sputtering, etc., for example. Additionally, and particularly with aqueous coating compositions, the resulting surface qualities are not always satisfactory. On the other hand, coating compositions containing ethanol, in particular, possess a very low flash point, so that their transportation, storage, and processing entail compliance with special conditions, which are usually complicated and costly. The aim generally is for a coating which is thin, smooth, adheres well, is elastic, incombustible where appropriate, stable toward UV, and also, where appropriate, is extremely easy to produce.
DE 197 15 940 A1 discloses a process for preparing a ceramic composition which is intended for application as a layer on a support material and which comprises as its components from 25 to 28% ceramic particles, especially silica, alumina, zirconium oxide, silicon carbide, silicon nitride, and from 5 to 12% pigment, in each case with a particle size of from 0.5 to 1&mgr; as filler, from 30 to 40% binders, such as metal oxides, hydrolysates and/or condensation/polymerization products of metal alkoxides, such as methoxy, ethoxy or butoxy, of aluminum, silicon, tin, titanium or zirconium, and also silicates, zirconium salts, phosphates, organic metal oxides, and the like, and from 30 to 40% alcohol, especially isopropanol, as solvent. In the preparation, the particulate solids are dispersed with the solvent in a 1:1 ratio in a boremill, after which the dispersion is admixed with the binder in the sol state in a 6:4 ratio and stirred under well-defined conditions. This preparation process is very complex.
Similar compositions comprising silicon compounds for sol-gel coatings, as foundry binders, for producing glass layers for anodic bonding, for producing structured inorganic layers, for producing composite materials or for protecting a metallic substrate from corrosion are disclosed, for example, in DE 44 17 405 A1, EP 0 830 324 B1, EP 0 842 967 A2, DE 196 47 369 A1, DE 198 13 709 A1 or WO 98/22241.
In addition, DE 198 14 605 A1 discloses a water-based anticorrosion composition for sealing metallic substrates which is composed of an aqueous dispersion (a) of at least one silane derivative, particularly a glycidyloxy-functional or terminally diol-functional alkoxysilane derivative, and (b) of a colloidal silica and/or a colloidal silicate. Preferred compositions are those which are substantially free from organic solvents, although hydrolysis alcohol or other alcohol, such as propanol, is not ruled out as an additional component.
A drawback of all of these coating compositions is their flash point, which is <21° C., which comes about through the formation of alcohols as a byproduct in the partial hydrolysis of the monomeric alkoxysilanes, remaining in the formulation as a solvent. The low flash point necessitates additional, and usually costly, measures for observing the statutory provisions, particularly for transportation, storage, and in connection with the industrial processing of the coating compositions, in the coil coating process, for example. Since effective filming and adhesion of the coating require the addition of further solvents, the solids content of the coating compositions is often relatively low as well, usually less than 35% by weight.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a composition for coating substrates which features a flash point of more than 21° C., a high solids content combined with sufficient stability on storage, and, on application, coatings having a good surface quality.
This object is achieved in accordance with the invention with a composition comprising a reaction mixture of
(i) at least one alkyltrialkoxysilane,
(ii) at least one alkoxysiloxane or at least one tetraalkoxysilane, or a mixture thereof,
(iii) at least one water-containing silica sol,
(iv) at least one acid, and
(v) at least one alcohol or at least one glycol, or a mixture thereof, wherein component (v) has a flash point >21° C.
It has surprisingly now been found that a composition possessing substantial stability on storage, preferably 6 months, while retaining a flash point of more than 21° C. is obtainable by mixing and reacting
(i) at least one alkyltrialkoxysilane, preferably from 50 to 70% by weight,
(ii) at least one alkoxysiloxane and/or at least one tetraalkoxysilane, preferably from 10 to 25% by weight,
(iii) at least one aqueous silica sol, preferably having an SiO
2
content of from 20 to 50% by weight,
(iv) at least one acid, preferably from 0.1 to 5% by weight, and
(v) at least one alcohol or at least one glycol or a corresponding mixture, especially 1-methoxypropanol, n-propanol, n-butanol, ethylene glycol, butyl glycol or tert-amyl alcohol or a mixture of n-butanol and n-butyl glycol (for example, a mixture containing from 1 to 20% by weight n-butyl glycol), component (v) appropriately having a flash point >21° C., preferably ≧25° C., with particular preference >25° C., with very particular preference ≧30 to 50° C.; preference is further given to from 0.1 to 60% by weight of component (v),
the sum of the above components being 100% by weight and the fraction for the aqueous silica sol resulting preferably from the necessary amount of hydrolysis water, in a simple arid economic way by introducing components (i) and (ii) and also, if desired, a fraction of component (v) as an initial charge, adding component (iii), adjusting the mixture to a temperature in t
Borup Bjoern
Burger Rosemarie
Edelmann Roland
Monkiewicz Jaroslaw
Brunsman David
Degussa - AG
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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