Silicate coatings

Abstract

The invention concerns a silicate coating, comprising at least one basic silicate, at least one filler and/or pigment, at least one water-soluble carbohydrate, water in order to produce a liquid or pasty consistency, optionally at least one organic binder, and optional conventional additives.

Claims

1. A silicate coating, comprising at least one basic silicate, at least one filler and/or pigment, at least one water-soluble carbohydrate, water in order to produce a liquid or pasty consistency, optionally at least one organic binder, and optional conventional additives.

2. The composition as claimed in claim 1, characterized in that the basic silicate comprises an alkaline-earth silicate, preferably calcium silicate.

3. The composition as claimed in claim 1, characterized in that the alkaline-earth silicate is in the form of a cement in which preferably, the proportion of SiO.sub.2 is more than 10%, preferably >15%, more preferably >20%, and preferably less than 50%, more preferably less than 40%, yet more preferably less than 30%.

4. The composition as claimed in claim 1, characterized in that the basic silicate comprises an alkali silicate, preferably water glass.

5. The composition as claimed in claim 1, characterized in that the basic silicate content is a maximum of 6% by weight, preferably at least 0.01% by weight, more preferably between 0.01 and 4% by weight, yet more preferably between 0.01% by weight and 2% by weight, more preferably between 0.01 and 1% by weight, especially between 0.05% by weight and 0.5% by weight, with respect to the total weight of the composition.

6. The composition as claimed in claim 1, characterized in that the water-soluble carbohydrate is selected from saccharides such as, in particular, mono-, di- and oligo-saccharides, especially from sugars, amino sugars and deoxy sugars, particularly preferably from mono- and di-saccharides as well as household sugar (saccharose) and/or glucosamine; and from hydroxycarboxylic acids such as, in particular, saccharic acids and their salts and derivatives.

7. The composition as claimed in claim 6, characterized in that the carbohydrate comprises household sugar and/or glucosamine.

8. The composition as claimed in claim 1, characterized by a content of a maximum of 1.0% by weight, preferably at east 0.001% by weight, more preferably between 0.005% by weight and 0.5% by weight, yet more preferably between 0.005% by weight and 0.1% by weight and most preferably between 0.01% by weight and 0.08% by weight of water-soluble carbohydrate, with respect to the total weight of the composition.

9. The composition as claimed in claim 1, characterized by a content of at least one organic binder of between 1% by weight and 40% by weight, preferably between 2% by weight and 30% by weight, particularly preferably between 2.5% by weight and 25% by weight, respectively calculated as a solid.

10. The composition as claimed in claim 1, characterized by a content of at least one filler and/or pigment of between 10% by weight and 90% by weight, preferably between 20% by weight and 85% by weight, particularly preferably between 25% by weight and 80% by weight.

11. The composition as claimed in claim 1, characterized by a water content of between 5% by weight and 50% by weight.

12. The composition as claimed in claim 1, characterized by a content of at least one organic binder selected from the group which comprises homopolymers, copolymers or terpolymers of acrylic acid and/or methacrylic acid, itaconic acid as well as acid esters such as ethyl acrylate, butyl acrylate; styrene, substituted or unsubstituted vinyl chloride, vinyl acetate, vinyl propionate, ethylene, butadiene, versatate, acrylamide and acrylonitrile; water-soluble alkyd polymers, combinations of (meth)acrylic/alkyd polymers, polyvinyl alcohol and mixtures thereof, wherein homopolymers or copolymers of acrylic acid and/or methacrylic acid are preferred.

13. The composition as claimed in claim 1, characterized by a content of at least one filler or pigment selected from the group which comprises pyrogenic precipitated silica, precipitated silica, silicon-aluminium mixed oxides, alkaline-earth carbonates such as calcium carbonate, silicon dioxide, silicates, for example aluminosilicates, sulphates, such as barium sulphate, titanium dioxide, color pigments, for example iron oxide, bismuth vanadate or mixtures thereof, wherein titanium dioxide, silicates and carbonates are preferred.

14. The composition as claimed in claim 1, characterized by a content at least one additive such as, for example, a rheological additive, a defoaming agent, a hydrophobicity agent, fibres, a film-forming agent and a dispersant.

15. The composition as claimed in claim 1, characterized in that the composition is a render, a paint, in particular an emulsion paint, a decorative final coating or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0033] The invention solves the problem of spot or streak formation when applying silicate coatings onto absorbent and/or strongly alkaline substrates, primarily by retarding the silicification reaction. This retardation is carried out by adding a water-soluble carbohydrate to the silicate coating before it has been applied.

[0034] Thus, the invention concerns silicate coatings, especially silicate paints, comprising at least one basic silicate, at least one filler and/or pigment, at least one water-soluble carbohydrate, water in order to produce a pasty consistency, optionally at least one organic binder, and optional conventional additives.

[0035] When using silicate coatings or dispersion silicate coatings on old purely polymer-bonded coatings, problems also arise with adhesion, unless the substrate has been appropriately pre-treated. Silicification with the substrate cannot take place. Because of the high organic polymer binder fraction and with a relatively low basic silicates fraction, appropriate embodiments of the coating compositions in accordance with the invention can also be applied to such substrates without problems.

[0036] Thus, if the occasion arises, there would be no need for complicated substrate treatment, either on absorbent alkaline substrates or on substrates which cannot undergo silicification.

[0037] In the context of the invention, in preferred embodiments of the invention, the basic silicate is an alkaline-earth silicate, in particular calcium silicate, for example cement, cement clinker, granulated slag and/or hydraulic lime, and/or an alkali silicate, for example lithium, sodium or potassium water glass. Particularly preferred embodiments of the invention contain both alkaline-earth silicate as well as alkali silicate.

[0038] When manufacturing the compositions in accordance with the invention, in the case of the alkaline-earth silicates, the basic silicate is used as the hydrate-free silicate, i.e. free or at least substantially free from alkaline-earth or calcium silicate hydrate (CSH) phases. This is understood not just by the person skilled in the art to mean that the alkaline-earth silicates or the materials containing alkaline-earth silicates, such as cement, are used in the non-set condition. CSH phases may be detected in a known manner, for example using X-ray diffraction.

[0039] Hydrate-free calcium silicates are components of cement clinker or of cement. In the context of the invention, the terms cement clinker (abbreviated to clinker) and cement are frequently used synonymously, but more correctly, it should be noted that cement clinker is the fired component of cement which is responsible for setting with the addition of water and which carries the basic silicates.

[0040] Cement is manufactured by grinding cement clinker with Ca sulphates. Cement clinkers are manufactured by sintering limestone, clay (marl) and quartz sand at high temperatures.

[0041] Clinker primarily consists of the following phases:

[0042] tricalcium silicate (alite), abbreviated in construction chemistry to C3S (3 CaO*SiO.sub.2)

[0043] dicalcium silicate (belite), abbreviated to C2S (2 CaO*SiO.sub.2)

[0044] tricalcium aluminate, abbreviated to C3A (3 CaO*Al.sub.2O.sub.3)

[0045] tetracalcium aluminate ferrite, abbreviated to C4AF or C4(A,F) (4 CaO*Al.sub.2O.sub.3*Fe.sub.2O.sub.3) and C2(A,F).

[0046] The simplified chemical reactions of the main clinker phase with mixing water to form calcium silicate hydrate can be written as follows:

2C3S+6H.fwdarw.CSH+3CH

[0047] written in full:

2(3 CaO*SiO.sub.2)+6 H.sub.2O.fwdarw.3 CaO*2 SiO.sub.2*3 H.sub.2O+3 Ca.sup.2++6 OH.sup.

[0048] In the invention, the calcium silicate phases are of particular interest, because they cause the substantial rise in pH when mixed with water. The aluminate phases as well as the CaO are of less interest, because their reaction is not as basic as the hydrate-free silicates. This means that cements and clinkers which have a particularly high basic silicate content (more C2S phases than C3S phases) are of great significance, because this basic silicate contributes substantially more to raising the pH than CaO. It is the stronger base.

[0049] Silicate-rich cements and clinkers with a SiO.sub.2 fraction of more than 10%, preferably >15% and more preferably >20%, are preferred.

[0050] However, the SiO.sub.2 fraction must also not be too high and should be below 50%, preferably below 40%, more preferably below 30%. Otherwise, the cement condenses too quickly and is then difficult to retard.

[0051] Thus, not only can cement and clinker act as a source of the calcium silicate phases, but granulated slag (slad sand) can as well; as a rule, this consists of approximately 30-45% CaO, 30-45% SiO.sub.2, 5-15% Al.sub.2O.sub.3, 4-17% MgO, 0.5-1% S and traces of other elements.

[0052] Granulated slag is highly suitable, not only because of the high SiO.sub.2 content, but especially also because of the fact that granulated slag is a latent hydraulic binder. Latent means that granulated slag is relatively inert and does not set quickly. Because setting of the hydraulic additive is not desired, granulated slag is highly suitable. However, it is substantially more expensive than cement/cement clinker. For reasons of cost, when using cement, the use of Portland cement, white cement or corresponding composite cements is preferred.

[0053] In the broadest embodiment, alkali silicates (Li, Na, K water glass, silica sols) and/or the hydrate-free alkali silicates (solid water glass) may be used as the basic silicates.

[0054] The basic silicate preferably comprises a hydrate-free alkaline-earth silicate, preferably calcium silicate (tricalcium silicate (alite, 3 CaO*SiO.sub.2), dicalcium silicate (belite, 2 CaO*SiO.sub.2). Particularly preferably, the alkaline-earth silicate entirely consists of calcium silicate.

[0055] The basic silicate also preferably comprises an alkali silicate, in particular water glass.

[0056] In preferred embodiments, the basic silicate comprises both alkaline-earth and alkali silicate.

[0057] In preferred embodiments, the basic silicate content is a maximum of 6% by weight, preferably at least 0.01% by weight, more preferably between 0.01 and 4% by weight, yet more preferably between 0.01 and 2% by weight, still more preferably between 0.01 and 1% by weight, especially between 0.05 and 0.5% by weight, with respect to the total weight of the composition.

[0058] In preferred embodiments, the substance which retards the setting or silicification of the basic silicate is a water-soluble carbohydrate which is preferably selected from saccharides such as, in particular, mono-, di- and oligo-saccharides, especially from sugars, amino sugars and deoxy sugars. Mono- and di-saccharides as well as household sugar (saccharose) and/or glucosamine are particularly preferred. Furthermore, hydroxycarboxylic acids such as, in particular, saccharic acids and their salts and derivatives may be used. Polysaccharides such as starch as well as other carbohydrates which are used in the prior art as thickeners are less suitable or even unsuitable as setting retardants due to their poor solubility.

[0059] Preferred embodiments of the invention have a content of a maximum of 1,0% by weight, preferably at least 0.001% by weight, more preferably between 0.005% by weight and 0.5% by weight, yet more preferably between 0.005% by weight and 0.1% by weight and most preferably between 0.01% by weight and 0.08% by weight of at least one water-soluble carbohydrate, with respect to the total weight of the composition.

[0060] Preferred embodiments of the invention have a content of at least one organic binder of between 1% by weight and 40% by weight, preferably between 2% by weight and 30% by weight, particularly preferably between 2.5% by weight and 25% by weight, respectively calculated as a solid.

[0061] Preferably, compositions in accordance with the invention comprise a content of at least one filler and/or pigment of between 10% by weight and 90% by weight, preferably between 20% by weight and 85% by weight, particularly preferably between 25% by weight and 80% by weight.

[0062] The water content of the composition is preferably between 5% by weight and 50% by weight.

[0063] The at least one organic binder is preferably selected from the group which comprises homopolymers, copolymers or terpolymers of acrylic acid and/or methacrylic acid, itaconic acid as well as acid esters such as ethyl acrylate, butyl acrylate; styrene, substituted or unsubstituted vinyl chloride, vinyl acetate, vinyl propionate, ethylene, butadiene, versatate, acrylamide and acrylonitrile; water-soluble alkyd polymers, combinations of (meth)acrylic/alkyd polymers, polyvinyl alcohol and mixtures thereof, wherein homopolymers or copolymers of acrylic acid and/or methacrylic acid are preferred, Aqueous polymer dispersions which are sufficiently stable to saponification are generally preferred.

[0064] The at least one filler or pigment is preferably selected from the group which comprises pyrogenic precipitated silica, precipitated silica, silicon-aluminium mixed oxides, alkaline-earth carbonates such as calcium carbonate, silicon dioxide, silicates, for example aluminosilicates, sulphates, such as barium sulphate, titanium dioxide, color pigments, for example iron oxide, bismuth vanadate or mixtures thereof, wherein titanium dioxide, silicates and carbonates are preferred.

[0065] Preferably, compositions in accordance with the invention contain at least one additive such as, for example, a rheological additive, a defoaming agent, a hydrophobicity agent, a wax or a wax preparation, a stabilizer, fibres, a film-forming agent and a dispersant and wetting agent.

[0066] The compositions in accordance with the invention may advantageously be used in order to produce a render, a paint, in particular an emulsion paint, a decorative final coating or the like.

[0067] Exemplary Embodiment 1: Emulsion Paint:

TABLE-US-00003 water 28 parts by weight aqueous polymer dispersion (approx. 50% 30 parts by weight solid content) fillers and pigments 37 parts by weight basic silicates 0.5 parts by weight sugar 0.05 parts by weight additives (in particular rheological additives, 5 parts by weight hydrophobicity agents, defoaming agents, film-forming agents, fibres, dispersants, etc)

[0068] The pH of this paint formulation was 11.6; after 16 weeks, it was in fact 11.7.

[0069] Exemplary Embodiment 2: Dispersion Silicate Paint:

TABLE-US-00004 water 31 parts by weight aqueous polymer dispersion (approx. 50% 9 parts by weight solid content) fillers and pigments 52 parts by weight basic silicates 4 parts by weight sugar 0.08 parts by weight additives (in particular rheological additives, 3.5 parts by weight hydrophobicity agents, defoaming agents, film-forming agents, fibres, dispersants, etc)

[0070] The pH of this paint formulation was 11.2; after 16 weeks, it was in fact 11.3.

[0071] Exemplary Embodiment 3: Dispersion Silicate Paint:

TABLE-US-00005 water 33 parts by weight aqueous polymer dispersion (approx. 50% 8 parts by weight solid content) fillers and pigments 54 parts by weight basic silicates 1.5 parts by weight sugar 0.05 parts by weight additives (in particular rheological additives, 4 parts by weight hydrophobicity agents, defoaming agents, film-forming agents, fibres, dispersants, etc)

[0072] The pH of this paint formulation was 11.1; after 16 weeks, it was still 11.0.

[0073] The rheological properties (viscosity) during this time period remained practically unchanged. No microbial attack could be detected sensorially. The emulsion paint had been shown to be storage-stable.

[0074] Comparative Tests:

[0075] A commercial cementitious reinforcement mass was applied to fibre-cement plates. After drying for 24 hours under normal conditions, half of the test pieces were also treated with a commercial primer. After a further 24 hours, the paint coatings from exemplary embodiments 1, 2 and 3 as well as a commercial dispersion silicate paint and an emulsion paint were applied to all of the test pieces in a reproducible manner. Prior to this, the pH of the surfaces of the reinforcement layer was determined using indicator paper. The pH was approximately 11 in all cases. 48 hours later, the paint coatings of the test pieces were subjectively assessed as regards spot formation or the homogeneity of the surface, wherein 5 represented a perfect, very homogeneous appearance without spot formation and 1 represented clearly visible spot formation and a non-homogeneous appearance.

TABLE-US-00006 Test piece without Test piece with Paint coating primer primer Exemplary embodiment 1 5 5 Exemplary embodiment 2 4 5 Exemplary embodiment 3 4 4 Dispersion silicate paint 1 2 Emulsion paint 5 5

[0076] The coating compositions in accordance with the invention combine the advantages of silicate coatings or dispersion silicate coatings with those of pure dispersion coatings without suffering from the disadvantages of the other type.

[0077] Thus, in a similar manner to silicate coatings, the coating compositions in accordance with the invention are resistant to contamination and fouling and also consolidate the substrate by slow silicification.