Silicate compound

Details Silicate compound Silicate compound

1997-02-20

1998-10-20

Marcantoni, Paul

Compositions: coating or plastic

Coating or plastic compositions

Alkali metal silicate containing

106624, 106626, 106632, 106635, 106737, C04B 1404

Patent

active

058241477

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

The invention relates to a silicate compound having at least one amorphous binder matrix containing alkali oxide and silicon dioxide, and also containing oxides from the group aluminium oxide, calcium oxide, titanium dioxide, magnesium oxide, zirconium dioxide and/or boric oxide.
Such a silicon compound can be used to coat building elements, in particular roof tiles. The surface of concrete roof tiles, i.e. rooftiles made of concrete, is coated to avoid efflorescence and to achieve an aesthetic appearance. With the passage of time the coating of a roof tile is exposed to severe corrosion from the elements. While in summer under strong solar radiation the surface temperature can rise to up to about 80.degree., in winter under frost conditions it can fall to -30.degree.. Of critical importance is corrosion by freeze-thaw cycles and by acid rain. Concrete roof tiles are usually protected with a coating of plastic dispersion paint.
The drawback of such plastic coatings is that the coating does not have long-term resistance to ultraviolet radiation in particular, and therefore disintegrates after a few years.
From DE-25 39 718 B2 a process is known for coating preformed building components based on inorganic binders containing customary aggregates with glaze-like silicate and/or phosphate-containing coverings, whereby a plastic mix is produced from the inorganic binder and water and customary aggregates, which mix is shaped into building components onto which is applied a thin layer of an aqueous paste containing water glass and/or phosphates and metal oxides and possibly pigments and fillers, which layer is then cured, whereby soluble inorganic salts in a minimum quantity of 0.5% by weight related to the inorganic binder, or in the case of sand-lime bricks related to the binder plus aggregates, are blended into the mix, which salts transform the aqueous paste, which is applied to the preformed building component at the rate of 190 to 400 g per m.sup.2, into a gel-like, non-flowing state, whereupon the preformed building component as well as the coating are cured. For the purposes of coating, aqueous, alkaline pastes are applied with 42 to 63 % mol SiO.sub.2, 11 to 27 % mol alkali oxide and between 19 and 42% mol metal oxide, related to the total weight of these constituents. As metal oxides ZnO, MgO, PbO, CaO, B.sub.2 O.sub.3 and/or Al.sub.2 O.sub.3 for example are added to the paste.
Alternately combining the top and bottom limits results purely arithmetically in a mol ratio of silicon dioxide to alkali oxide of between 1.56 and 3.82. However, the description and the examples of embodiment only mention the use of water glass of 37.degree. to 40.degree. Be in which the silicon dioxide/alkali oxide mol ratio is a maximum of 3.52. In order to transform such a paste into a gel-like, non-flowing state it is necessary to add soluble inorganic salts, which addition is the mandatory characteristic included in the main claim of DE-25 39 718 B2. In accordance with the process described here the paste is applied to the preformed building component and, together with the latter, is cured either in the autoclave under pressure at high temperatures or in a purely thermal treatment at normal pressure.
An inorganic silicate coating is known from EP 0 247 910, in which the binder matrix contains in relation to solids approx. 100 parts by weight potassium silicate, approx. 10 to 40 parts by weight fine particles of silicon dioxide and approx. 15 to 100 parts by weight nacreous lustre pigment. When using water glass with a silicon dioxide/alkali oxide mol ratio of 3.95, the mol ratio of silicon dioxide to alkali oxide in the coating may be up to 6.15. As a method for the production of a coated object, EP 0 247 910 B1 states that the coating compound is applied to the substrate and must then for purposes of curing be heated with this substrate to a temperature of approx. 200.degree. C. to approx. 400.degree. C. The nacreous lustre pigment is contained in the coating in the form of particles which are surrounded by t

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