AU675086B2 - Aqueous binders and coating agents - Google Patents

Description

0151 DATE 09/05/94 AOJP DATE 21/07/94 APPLN. I D 51777/93 PCT NUMBER PCT/EP93/02841 AU935 1777 (51) Internationale Patentklassifikation 5 (11) Internationale Vcriiffcntlichungsnummer: 'WO 94/09075] C001) 5/10, C08L 83/04 Al (43) Internationales C09D 183/04 Ver~rfentlichungsdatum: 28. April 1994 (28.04.94) (21) Internationales Aktcnzeichen: PCT/EP'93/0284 I (74) Gemeinsamer Vertreter: WACKER-CHEM IE GM BH; Hanns-Seidel-Platz 4, D-8 1737 Monchen (DE).

(22) Internationales Anmeldedatumn: 14. Oktober 1993 (14.10.93) Bestimmungsstaaten: AU, Fl, JP, KR, NO, PL, RU, UA, Prioritfitsdaten: US, europiiisches Patent (AT, BE, CH, DE, DK, ES, FR, P 42 35 323.8 20, Oktober 1992 (20.10.92) DE GB, GR, LE, IT, LU, MC, NL, PT, SE).

P 42 35 372.6 20. Oktober 1992 (20.10.92) DE Verbffentlicht (71) Anmnelder Yfir alle Bestimmungsszaaten ausser US): WAK- klit internationalein Recherchenbericla.

KER-CHEMIE GMBH [DE/DE]; Hanns-Seidel-Platz 4, D-8 1737 Mijnchen (DE).

(72) Erfinder; und Erfinder/Anmelder (nurflir US) PAUL, Klaus-Peter [DE/ DEJ; Carl- Bosch-Strasse 15, D-84489 Burghausen (DE), GELTINGER, Magdalena [DE/DE]; Fahnbacherstrasse 23, D-84533 Haiming HAUSLEITNER, Petra [DE/DE]; Josef- Lindner-Strasse 10, D-84367 Zeilarn

(DE),

(54) Title: AQUEOUS BINDERS AND COATING AGENTS (54) Bezeichnung: WXSSRIGE BINDEMITTEL UND BESCHICHTUNGSMITFEL (57) Abstract Descibed are new aqueous binders containing organopolysiloxane resins, and/or mono-organosilanolates and/or their condensation products derived from splitting off water, and water. The aqueous binders are produc'ed by mixing aqueous emulsions of organosiloxane resins with aqueous solutions of mono-organosilanolates The aqueous binders are used in aqueous coating compositions for coating metal surfaces, said compositions comprising aqueous binders, metal powder, in particular zinc dust, as needed, silicon dioxides with a BET surface of at least 50 m 2 which are made water-repellent as needed, and as needed, water.

(57) Zusammenfassung Beschrieben werden neue Waglrige Bindemnittel enthaltend Organopolysiloxanharze, und/oder Monoorganosilanolate und/oder dessen durch Wasserabspaltung entstehende Konder.,,ationsprodukte und Wasser. Die wiigrigen Bindemnittel werden hergestellt durch Vermischen von w~grigen Emulsionen von Organopolysiloxanharzen mit wiglrigen L6sungen von Monoorganosilanolaten Die wfilgrigen Bidemittel werden verwendet in wii1rigen Beschichtungszusammensetzungen zum Beschichten von Metalloberfliichen umnfassend wagLrige Bindemittel, Metalipulver, insbesondere Zinkstaub, gegebenenfalls Siliciumdioxide mit einer BET-Oberfliiche von mindestens 50 m 2 die gegebenenfalls hydrophobiert sind und gegebenenfalls Wasser.

WO 94/09075 1 PCT/EP93/02841 Aqueous binders and coating compositions The invention relates to aqueous binders and aqueous coating compositions and to processes for the preparation of the aqueous binders and aqueous coating compositions.

Inorganic binders for zinc dust or aluminium flakes have been disclosed which comprise silicates such as silicoxI dioxide and potassium dioxide and/or sodium dioxide and water and which are generally referred to as waterglasses. In this context reference may be made, for example, to US-A 4,162,169.

DE-A 40 22 186 discloses a nonaqueous, zinccontaining anticorrosion composition for phosphatized metal surfaces, which contains zinc dust and/or zinc flakes, an organic solution of a polysilicic ester and, if desired, a stabilizer.

DE-A 15 46 050 discloses copolymers of siloxanes and silicates which inhibit the corrosion of metals coming into contact with aqueous liquids to which the copolymers are added as corrosion inhibitors.

The brochure "SilokophenR P40/W" from Tego Chemie Service USA, October 1989, describes, as a binder for zinc dust, SilikophenR P40/W, an aqueous phenylmethylsilicone resin emulsion having a solids content of 50 The object for the incorporation of metal powder, especially zinc dust, was to provide suitable water-based binders which can be used to obtain aqueous coating compositions for metal surfaces, which compositions cure at room temperature and give coatings having good anticorrosion properties, especially in a salt-containing medium, good solvent and/or water resistance and good drying characteristics. This ubject is achieved by the invention.

The invention relates to aqueous binders comprising organopolysiloxane resins and/or S(b) monoorganosilanolates and/or the condensation products thereof formed by the elimination of water, and WO 94/09075 2 PCT/EP93/02841 water.

The invention also relates to a process for the preparation of aqueous binders, characterized in that aqueous emulsions of organopolysiloxane resins are mixed with aqueous solutions of monoorganosilanolates The invention further relates to aqueous coating compositions comprising aqueous binders, metal powder, if desired, silicon dioxides having a BET surface area of at least 50 m2/g, which are hydrophobicized if desired, and if desired, water.

The invention finally relates to a process for the preparation of aqueous coating compositions, characterized in that aqueous binders are mixed with metal powder, if desired, silicon dioxides having a BET surface area of at least 50 m 2 which are hydrophobicized if desired, and if desired, water and, if desired, further substances.

The organopolysiloxane resins used in the binders according to the invention are preferably those comprising units of the formula RaSi04-a 2 which contain from 0 to 10 by weight of Si-bonded hydroxyl groups and/or alkoxy groups, in which R is in each case identical or different and is a monovalent hydrocarbon radical having 1 to 18 carbon atoms per radical, and a is 0, 1, 2 or 3, on average from 1 to The organopolysiloxane resins employed may be liquid or solid at room temperature.

SExamples of radicals R are alkyl radicals such as WO 94/09075 3 PCT/EP93/02841 the methyl, ethyl, n-propyl, isopropyl, 1-n-butyl, 2-nbutyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl or tert-pentyl radical; hexyl radicals such as the n-hexyl radical; heptyl radicals such as the n-heptyl radical; octyl radicals such as the n-octyl radical and isooctyl radicals such as the 2,2,4-trimethylpentyl radical; nonyl radicals such as the n-nonyl radical; decyl radicals such as the n-decyl radical; dodecyl radicals such as the n-dodecyl radical; octadecyl radioals such as the n-octadecyl radical; cycloalkyl radicals such as cyclopentyl, cyclohexyl, cycloheptyl radicals and methylcyclohexyl radicals; aryl radicals such as the phenyl, naphthyl, anthryl and phenanthryl radical; alkaryl radicals such as m- and p-tolyl radicals; xylyl radicals and ethylphenyl radicals; and aralkyl radicals, such as the benzyl radical and the aand A-phenylethyl radical. The methyl and phenyl radical is preferred.

The organopolysiloxane resins which are employed in accordance with the invention may comprise one kind of organopolysiloxane resin or a mixture of at least two different kinds of organopolysiloxane resins.

The monoorganosilanolates employed in the binders according to the invention are preferably those of the formula RIsi(OM)m(OH) 3 m (II), in which R 1 is in each case identical or different and is a monovalent hydrocarbon radical having 1 to 8 carbon atoms per radical, M is an alkali metal cation or an ammonium group, and m is an integral or fractional number whose value is from 0.1 to 3.

Examples of radicals R 1 are alkyl radicals such as the methyl, ethyl, n-propyl, isopropyl, 1-n-butyl, 2n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl or tert-pentyl radical; hexyl radicals such as the n-hexyl radical; heptyl radicals such as the n-heptyl WO 94/09075 4 PCT/EP93/02841 radical; and octyl radicals such as the n-octyl radical and isooctyl radicals.

A preferred example of the radical R 1 is the methyl radical.

Examples of radicals M are the cations of alkali metals such as those of lithium, sodium and potassium, and radicals of the formula +NR24 in which R 2 is in each case identical or different and is a monovalent hydrocarbon radical having 1 to 6 hydrocarbons [sic] per radical.

Preferred examples of radicals M are Na and K Examples of radicals R 2 are alkyl radicals such as methyl, ethyl, n-propyl, isopropyl, 1-n-butyl, 2-nbutyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl radicals and hexyl radicals such as the n-hexyl radical.

The monoorganosilanolates which are employed in accordance with the invention may comprise one kind or else a mixture of at least two different kinds of such monoorganosilanolates.

In order to prepare the aqueous emulsions of organopolysiloxane resins which are employed in accordance with t-he invention, organopolysiloxane resins (a) are emulsified with water by the methods which are customary in silicon chemistry, with the addition of emulsifiers. In this context the emulE.ifier, in accordance with its chemical nature, may be initially charged both to the aqueous phase and to the oil phase. The emulsification step can be carried out in conventional mixing devices which are suitable for the preparation of emulsions, such as high-speed stator-rotor stirrers according to Prof. P. Willems, as are known under the registered trademark "Ultra-Turrax".

The aqueous emulsions employed in accordance with the invention contain organopolysiloxane resins (a) preferably in quantities of from 25 to 75 by weight, WTO 94/09075 5 PCT/EP93/02841 most preferably from 40 to 60 by weight, based in each case on the overall weight of the aqueous emulsions.

In the preparation of the aqueous emulsions, the emulsific:s employed may be all previously known, ionic and nonionic emulsifiers, both individually and in mixtures of different emulsifiers, with which the preparation of stable aqueous emulsions of organopolysiloxane resins has also been possible to date. Emulsifiers such as those described in US-A 4,757,106 can also be employed. It is preferred to employ nonionic emulsifiers.

Examples of nonionic emulsifiers are fatty alcohol polyglycol ethers and partially hydrolyzed polyvinyl alcohols. Fatty alcohol polyglycol ethers are available, for example, under the trade name "Arlypon SA4" or "Arlypon IT16" from Grinau, and partially hydrolysed polyvinyl alcohols are available, for example, under the trade name "Polyviol W25/140" from Wacker.

The aqueous emulsions which are employed in accordance with the invention contain emulsifiers in quantities of preferably from 0.1 to 10 by weight, most preferably from 2 to 4 by weight, based in each case on the overall weight of the aqueous emulsions.

The aqueous solutions which are employed in accordance with the invention contain monoorganosilanolates in quantities of preferably from 10 to by weight, most preferably from 40 to 50 by weight, based in each case on the overall weight of the aqueous solutions.

The aqueous solutions of monoorganosilanolates which are employed in accordance with the invention, are prepared, for example, by hydrolysis of organotrichlorosilanes such as methyltrichlorosilanes, followed by dissolution of the hydrolysate in an aqueous solution of an alkali metal hydroxide such as potassium hydroxide.

In the process according to the invention for the preparation of the aqueous binders, the aqueous solutions of monoorganosilanolates are employed in quantities of preferably from 0.1 to 50 by weight, most preferably from 2 to 20 by weight, based in each case on the h WO 94/09075 6 PCT/EP93/02841 overall weight of the aqueous emulsions of organopolysiloxane resins The metal powder used in the aqueous anticorrosion compositions according to the invention is preferably zinc dust, aluminium powder or copper powder.

Preference is given to the use of zinc dust having an average dust particle size of from 2 to 9 pm.

Under alkaline conditions, zinc reacts with water and hydrogen is evolved. At a pH of less than 8.5 the evolution of hydrogen is low. A suppression of hydrogen evolution is achieved by the addition of silicon dioxide The coating compositions according to the invention preferably include the use of silicon dioxides (C) having a BET surface area of at least 50 m 2 /g.

The silicon dioxides used, having a BET surface area of at least 50 m 2 are preferably pyrogenically prepared silicas. Precipitated silicas having a BET surface area of at least 50 m2/g can also be used.

The silicon dioxides are preferably hydrophobicized, for example by treatment with organosilicon compounds such as hexamethyldisilazane, organosilanes or organosiloxanes.

The aqueous coating compositions according to the invention preferably contain 100 parts by weight of aqueous binders, from 10 to 1500 parts by weight, most preferably from 50 to 1000 parts by weight, of metal powder, from 0 ti r:ts by weight, most preferably from 1 to 2 parts .by weight, of silicon dioxides having a BET surface area of at least 50 m 2 which are hydrophobicized if desired, and from 0 to 300 parts by weight, most preferably from to 200 parts by weight, of water.

The aqueous coating compositions according to the invention may contain further substances which can conventionally be included for use in the preparation of coating compositions. Examples of further substances are fillers such as quartz, diatcmaceous earth, calcium LL _L WO 94/09075 7 PCT/EP93/02841 silicat-, zirconium silicate, zeolites, montmorrillonites [sic] such as bentonites, mica, metal oxide powders such as aluminium, titanium, iron or zinc oxides and/or their mixed oxides, barium sulphate, calcium carbonate, gypsum, silicon nitride, silicon carbide, boron nitride, ceramic powders, glass powders and plastics powders, thickeners such as silicas, for example silicas having a BET surface area of at least 50 m 2 and corrosion inhibitors such as sodium phosphate, zinc aluminium phosphates and chromates.

The aqueous coating compositions according to the invention may be employed as 1-component systems or as 2component systems. In the 2-component systems metal powder preferably zinc dust, is in the first component and the aqueous binders and silicon dioxides (C) are in the second component. Mixing the components together is then carried out shortly before processing.

The aqueous coating compositions according to the invention can be applied to any type of metal to which coating compositions containing metal powder, especially zinc dust, ha-e also been applied to date. The term metals in this context also refers to metal alloys.

Examples of metals are iron and steels.

The aqueous coating compositions according to the invention are preferably cured at room temperature.

The aqueous coating compositions according to the invention are used as anticorrosion compositions and primer compositions. They give coatings of good temperature resistance and are therefore suitable for many applications in which heat resistance up to 420 0 C is required, for example for the preparation of coatings for tankers, bridges, drilling platforms, cranes, furnaces, refineries, combustion engines, electric -motors and exhaust systems. By applying a temperature-resistant top coat, for example an emulsion of the phenylmethylsil.icone resin pigmented with aluminium, which is described in Example 2, with baking of the top coat to the anticorrosion coat or primer coat, the temperature resistance cRAt can be increased to from 500 to 600 0 C. Furthermore, the

I_

WO 94/09075 8 PCT/EP93/02841 coatings obtained with the coating compositions according to the invention exhibit good solvent and water resistance, nonflammability and good welding characteristics.

In the following examples, all parts and percentages are by weight unless stated otherwise.

Example 1: a) 255 parts of a methylpolysiloxane which is liquid at room temperature, comprises CH 3 SiO 3 2 and (CH 3 2 SiO units with a molar ratio of 75 :25, and contains from 0.5 to 1.5 by weight of hydroxyl groups and from 2 to 5 by weight of ethoxy groups, 15 parts of fatty alcohol polyglycol ether (commercially available under the trade name "Arlypon IT16" from Griinau) and 230 parts of water were emulsified by means of a rapid stirrer.

b) A 42 strength aqueous potassium methylsilanolate solution was prepared by reacting equivalent quantities of methyltrichlorosilane with potassium hydroxide in the aqueous phase with elimination of hydrochloric acid.

c) 47.5 parts of the 50 strength aqueous silicone emulsion whose preparation is described above under a) were mixed with 2.5 parts of the 42 strength aqueous potassium methylsilanolate solution whose preparation is described above under 50 parts of the resulting aqueous binder were mixed with 400 parts of zinc dust having an average dust particle diameter of from 4 to 6 pm, 4.8 parts of hydrophobic, pyrogenically prepared silica having a BET surface area of 120 20 m 2 /g (commercially available under the trade name "HDK H15" from Wacker-Chemie), 100 parts of water, 32.5 parts of mica in leaflet form, 20 parts of an antisedimentation paste comprising from 10 to 20 of organically modified smectite (commercially WO 94/09075 9 PCT/EP93/02841 available under the trade name "Bentone" from Kronos International Inc.) and 2 parts of a 10 strength aqueous sodium phosphate solution (commercially available under the trade name "Calgon N" from Merck).

The resulting coating composition was applied, using a doctor blade, in a wet film thickness of 100 gm to cold-rolled matt steel which was 0.8 mm thick. The coating was dry to handle after drying for 23 minutes at room temperature. After drying for 24 hours or, respectively, from 1 to 6 weeks at room temperature the resistance of the coating to solvent or, respectively, water tested by rubbing under slight pressure with a cotton-wool bud stick whose end was impregnated with methyl ethyl ketone or, respectively, water. The MEK abrasions (resistance to methyl ethyl ketone) and the water abrasions (resistance to water) of the coating were measured. The results are compiled in Table 1. From Table 1 it can be seen that the water resistance markedly improves.

Table 1: Water abrasions MEK abrasions 24 hours 3 1 1 week 5 2 2 weeks 12 4 3 w!teks 26 4 4 weeks 30 4 weeks 70 4 6 weeks 90 9 The steel panel treated with the coating composition was subjected to a salt spray test in accordance with DIN 50 021 using 5 strength aqueous sodium chloride solution. In Fig. 1, the plot 1 shows the WO 94/0-9075 10 PCT/EP93/02841 results of the salt spray test. The evaluation number x in accordance with DIN 53 210 is based on the proportion of the surface which is affected by rust. In this context the evaluation number x 0 denotes freedom from rust and x 5 denotes rusting over the entire area. The time axis t is dimensioned in hours [h The salt spray test was carried out as being representative, as a time-saving measure, of a prolonged outdoor weathering test.

Fig. 2 shows the quantity (ml, based on in each case ml of coating composition) of hydrogen formed, measured within 48 hours after mixing the components ?f the coating composition, as a function of the quantity employed by weight, based on the overall weight of the coating composition) of the abovedescribed hydrophobic, pyrogenically prepared silica. From Fig. 2 it can be seen that the addition of hydrophobic, pyrogenically prepared silica in a quantity of 1.2 by weight, based on the overall weight of the coating composition, suppresses the formation of hydrogen.

Example 2: a) 100 parts of an 82 strength solution of an organopolysiloxan resin which is solid at room temperature and comprises PhSiO3/ 2 (Ph phenyl radical) and (CH 3 2 SiO units with a molar ratio of 63 37 in xylene, 6 parts of fatty alcohol polyglycol ether (commercially available under the trade name "Arlypon IT16" from Grinau) and 100 parts of water were emulsified by means of a rapid stirrer.

b) The procedure of Example 1 c) was repeated, with the modification that 47.5 parts of the aqueous silicone emulsion whose preparation is described above under WO 94/09075 11 PCT/EP93/02841 a) were employed instead of the aqueous silicone emulsion of Example 1 and 80 parts of water were employed instead of the 100 parts of water.

The coating composition was applied, using a doctor blade, in a wet film thickness of 100 pm to coldrolled matt steel whose thickness was 0.8 mm. The coating was dry to handle after drying for 55 minutes at rc-m temperature. After drying for 24 hours at room temperature, the MEK abrasions and the water abrasions of the coating were determined as described in Example 1. MEK abrasions (resistance to methyl ethyl ketone) of 5 and water abrasions (resistance to water) of more than 150 were measured.

The steel panel treated with the coating composition was subjected to a salt spray test as described in Example 1. The results of the salt spray test are shown by plot 2 in Fig. 1.

Corparative Experiment 1: The procedure of Example 1 was repeated, with the modification that 50 parts of an aqueous sodium silicate solution having a solids content of 35 and a molar ratio of SiO 2 to Na20O of 25.5 7.5 (corresponding to a weight ratio of 28.5 8.5) were employed instead of the aqueous binder of Example 1 and 110 parts of water were employed instead of 100 parts of water.

The coating composition was applied, using a doctor blade, in a wet film thickness of 100 pm to coldrolled matt steel whose thickness was 0.8 mm. The coating was dry to handle after drying for 20 minutes at room temperature. After drying for 24 hours at room temperature MEK abrasions and water abrasions of the coating were determined as described in Example 1. MEK abrasions (resistance to methyl ethyl ketone) of more than 150 and water abrasions (resistance to water) of 10 were c' ,5 measured.

I

k 3J WO 94/09075 12 PCT/EP93/02841 The steel panel treated with the coating composition was subjected to a salt spray test as described in Example 1. The results of the salt spray test are shown by plot 3 in Fig. 1.

Comparative Experiment 2: The procedure of Example 1 was repeated, with the modification that 50 parts of an ethyl silicate binder having an SiO 2 content of 37.5 (commercially available under the trade name "Wacker TES 55" from Wacker-Chemie) which is obtained from ethyl silicate having an SiO 2 content of 40 were emp7 'd instead of the aqueous binder of Example 1, 2 pa- were employed instead of 4.8 parts of the silica described in Example 1, 30 parts of xylene and 7.5 parts of butanol were employed instead of 100 parts of water, and, in addition, 10 parts of an acrylate resin (commercially available under the trade name "Plexisol PM 709" from R'dhm ~mt- GmbH) were employed as thickener.

The coating composition was applied, using a doctor blade, in a wet film thickness of 100 pm to coldrolled matt steel whose thickness was 0.8 mm. The coating was dry to handle after drying for 105 minutes at room temperature. After drying for 24 hours at room temperature, the MEK abrasions and water abrasions of the coating were determined as described in Example 1. MEK abrasions (resistance to methyl ethyl ketone) of 100 and water abrasions (resistance to water) of more than 150 were measured.

The steel panel treated with the coating composition was subjected to a salt spray test as described in Example 1. The results of the salt spray test are shown by plot 4 in Fig. 1.

Comparative Experiment 3: 91.5 parts of an ethyl silicate binder having an SiO 2 content of 20 the ethyl silicate binder being a 1_1 WO 94/09075 13 PCT/EP93/02841 hydrolysate of 47 parts of ethyl silicate having an SiO 2 content of 40 (commercially available under the trade name "TES 40" from Wacker-Chemie), 28 parts of anhydrous ethanol, 19.85 parts of methoxypropanol, 0.15 part of concentrated hydrochloric acid (37 and 5 parts of water, were mixed with 363.5 parts of zinc dust having an average dust particle diameter of from 4 to 6 Am, 18 parts of mica in leaflet form, 18 parts of an antisedimentation paste comprising from 10 to 20 of organically modified smectite (commercially available under the trade name "Bentone" from Kronos International Inc.) and 9 parts of a 40 by weight strength solution of polyvinylbutyral in ethanol as thickener.

The coating composition was applied, using a doctor blade, in a wet film thickness of 100 Am to coldrolled matt steel whose thickness was 0.8 mm. The coating was dry to handle after drying for 6 minutes at room temperature. After drying for 24 hours at room temperature, MEK abrasions and water abrasions of the coating were determined as described in Example 1. MEK abrasions (resistance to methyl ethyl ketone) of 3 and water abrasions (resistance to water) of more than 150 were measured.

The steel panel treated with the coating composition was subjected to a salt spray test as described in Example 1. The results of the salt spray test are shown by plot 5 in Fig. 1.

Comparative Experiment 4: The procedure of Example 1 was repeated, with the modification that 50 parts of an aqueous phenylmethylsilicone resin emulsion having a solids content of 50 and a xylene content of about 10 (commercially available under the trade name "Silikophen P40/W" from Tego Chemie Service USA) were employed instead of the 50 parts of aqueous binders of Example 1 and 80 parts of water were employed instead of the 100 parts of water.

The coating composition was applied, using a I WO 94/09075 14 PCT/EP93/02841 doctor blade, in a wet film thickness of 100 kim to coldrolled matt steel whose thickness was 0.8 mm. The coating was not dry to handle until it had been dried for 4 hours at room temperature. After drying for 24 hours at room temperature, the MEK abrasions and water abrasions of the coating were determined as described in Example 1. MEK abrasions (resistance to methyl ethyl ketone) of 2 and water abrasions (resistance to water) of 3 were measured.

The steel panel treated with the coaing composition was subjected to a salt spray test as described in Example 1. The results of the salt spray test are shown by plot 6 in Fig. 1.

Example 3: parts of a 42 strength aqueous potassium methylsilanolate solution which was prepared by reacting equivalent quantities of methyltrichlorosilane with potassium hydroxide in the aqueous phase with elimination of hydrochloric acid were mixed with 400 parts of zinc dust having an average dust particle diameter of from 4 to 6 14m, 4.8 parts of hydrophobic, pyrogenically prepared silica having a BET surface area of 120 20 m 2 /g (commercially available under the trade name "HDK H15" from Wacker-Chemie), 80 parts of water, 32.5 parts of mica in leaflet form, 20 parts of an antisedimentation paste comprising from 10 to 20 of organically modified smectite (commercially available under the trade name "Bentone" from Kronos International Inc.) and 2 parts of a 10 strength aqueous sodium phosphate solution (commercially available under the trade name "Calgon N" from Merck).

The resulting coating composition was applied, using a doctor blade, in a wet film thickness of 100 im to cold-rolled matt steel whose thickness was 0.8 mm. The coating was dry to handle after drying for about 30 minutes at room temperature. After drying for 24 hours at room temperature, the resistance, of the coating to solvent and, respectively, to water w I [h-r tested by WO 94/09075 15 PCT/EP93/02841 rubbing under slight pressure with a cotton-wool bud stick whose end was impregnated with methyl ethyl ketone or, respectively, water. MEK abrasions (resistance to methyl ethyl ketone) of more than 150 and, correspondingly, water abrasions (resistance to water) of were measured.

The steel panel treated with the coating composition was subjected to a salt spray test in accordance with DIN 50021 using 5 strength aqueous sodium chloride solution. In Fig. 3, plot 1 shows the results of the salt spray test. The evaluation number x in accordance with DIN 53 210 is based on the. proportion of the surface which is affected by rust. The evaluation number x 0 denotes freedom from rust and x 5 denotes rusting over the entire area. The time axis t is dimensioned in hours The salt spray test was carried out as being representative, as a time-saving measure, of a prolonged outdoor weathering test.

Example 4: The procedure of Example 3 was repeated, with the modification that 50 parts of a 46 strength aqueous solution of a mixture of equal parts of potassium methylsilanolate and potassium propylsilanolate, prepared by reacting equivalent quantities of methyltrichlorosilane and propyltrichlorosilane with potassium hydroxide in the aqueous phase with elimination of hydrochloric acid, were employed instead of the aqueous solution of potassium methylsilanolate of Example 3.

The coating composition was applied, using a doctor blade, in a wet film thickness of 100 pm to coldrolled matt steel whose thickness was 0.8 mm. The coating was dry to handle after drying for 23 minutes at room temperature. After drying for 24 hours at room temperature, the MEK abrasions and water abrasions of the coating were determined as described in Example 3. MEK abrasions (resistance to methyl ethyl ketone) of more WO 94/09075 16 PCT/EP93/02841 than 150 and, correspondingly, water abrasions (resistance to water) of more than 150 were measured.

The steel panel treated with the coating composition was subjected to a salt spray test as described in Example 3. The results of the salt spray test are shown by plot 2 in Fig. 3.

Comparative Experiment The procedure of Example 3 was repeated, with the modification that 50 parts of an aqueous sodium silicate solution having a solids content of 35 and a molar ratio of SiO 2 to Na20 of 25.5 7.5 (corresponding to a weight ratio of 28.5 8.5) were employed instead of the aqueous solution of potassium methylsilanolate of Example 3 and 110 parts of water were employed instead of 80 parts of water.

The coating composition was applied, using a doctor blade, in a wet film thickness of 100 gm to coldrolled matt steel whose thickness was 0.8 mm. The coating was dry to handle after drying for 20 minutes at room temperature. After drying for 24 hours at room temperature, MEK abrasions and water abrasions of the coating were determined as described in Example 3. MEK abrasions (resistance to methyl ethyl ketone) of more than 150 and water abrasions (resistance to water) of 10 were measured.

The steel panel treated with the coating composition was subjected to a salt spray test as described in Example 3. The results of the salt spray test are shown by plot 3 in Fig. 3.

Comparative Experiment 6: The procedure of Example 3 was repeated, with the modification that 50 parts of an ethyl silicate binder for 1-component zinc paints having an SiO 2 content of 37.5 (commercially available under the trade name "Wacker TES 55" from Wacker-Chemie) were employed instead -dl WO 94/09075 17 PCT/EP93/02841 of the aqueous solution of potassium methylsilanolate of Example 3, 2 parts instead of 4.8 parts of the silica described in Example 3 were employed, 30 parts of xylene and 7.5 parts of butanol were employed instead of 80 parts of water, and, in addition, 10 parts of an acrylate resin (commercially available under the trade name "Plexisol PM 709" from R6hm GmbH) were employed as thickener.

The coating composition was applied, using a doctor blade, in a wet film thickness of 100 pm to coldrolled matt steel whose thickness was 0.8 mm. The coating was dry to handle after drying for 105 minutes at room temperature. After drying for 24 hours at room temperature, the MEK abrasions and water abrasions of the coating were determined as described in Example 3. MEK abrasions (resistance to methyl ethyl ketone) of 100 and water abrasions (resistance to water) of more than 150 were measured.

The steel panel treated with the coating composition was subjected to a salt spray test as described in Example 3. The results of the salt spray test are shown by plot 4 in Fig. 3.

Comparative Experiment 7: 91.5 parts of an ethyl silicate binder for 2component zinc paints having an SiO 2 content of 20 the ethyl silicate binder being a hydrolysate of 47 parts of ethyl silicate having an SiO 2 content of 40 (commercially available under the trade name "TES 40" from Wacker-Chemie), 28 parts of anhydrous ethanol, 19.85 parts of methoxypropanol, 0.15 part of concentrated hydrochloric acid (37 and 5 parts of water, were mixed with 363.5 parts of zinc dust having an average dust particle diameter of from 4 to 6 ym, 18 parts of mica in leaflet form, 18 parts of an antisedimentation paste comprising from 10 to 20 of organically modified smectite (commercially available under the trade name "Bentone" from Kronos International Inc.) and 9 parts of L- r WO 94/09075 18 PCT/EP93/02841 a 40 strength solution of polyvinylbutyral in ethanol, as thickener.

The coating composition was applied, using a doctor blade, in a wet film thickness of 100 Am to coldrolled matt steel whose thickness was 0.8 mm. The coating was dry to handle after drying for 6 minutes at room temperature. After drying for 24 hours at room temperature, the MEK abrasions and water abrasions of the coating were determined as described in Example 3. MEK abrasions (resistance to methyl ethyl ketone) of 3 and water abrasions (resistance to water) of more than 150 were measured.

The steel panel treated with the coating composition was subjected to a salt sp:ay test as described in Example 3. The results of the salt spray test are shown by plot 5 in Fig. 3.

Claims (9)

1. Aqueous coating compositions comprising aqueous binder selected from the group which consists of (Al) aqueous binders comprising organopolysiloxane resins and monoorganosilanolates and/or the condensation products thereof formed by elimination of water, and water and (A2) aqueous binders comprising monoorganosilanolates and/or the condensation products thereof formed by elimination of water, and water, metal powder, if desired, silicon dioxides having a BET surface area of at least 50 m 2 which are hydrophobicized if desired, and S(D) if desired, water.

2. Aqueous coating composition according to Claim 1, characterized in that the aqueous binder is used as organopolysiloxane resins those comprising units of the formula R SiO a 4 a -a 2 which contain from 0 to 10 by weight of Si-bonded hydroxyl groups and/or alkoxy groups, in which R is in each case identical or different and is a monovalent hydrocarbon radical having 1 to 18 carbon atoms per radical, and a is 0, 1, 2 or 3, on average from 1 to -I s

3. Aqueous coating composition according to Claim 1 or 2, characterized in that the aqueous binders used are monoorganosilanolates of the formula R 1 Si(OM)m(OH) 3 -m (II), in which R 1 is in each case identical or different and is a monovalent hydrocarbon radical having 1 to 8 carbon atoms per radical, M is an alkali metal cation or an ammonium group, and m is an integral or fractional number whose value is from 0.1 to 3.

4. Aqueous coating composition according to one or more of Claims 1-3, characterized in that the metal powder used is zinc dust having an average dust particle size of from 2 to 9 .tm.

Aqueous coating composition according to one or more of Claims 1-4, characterized in that it contains 100 parts by weight of aqueous binder from 10 to 1500 parts by weight of metal powder, if desired, from 0 to 5 parts by weight of silicon dioxides having a BET surface area of at least 50 m 2 which are hydrophobicized if desired, and from 0 to 300 parts by weight of water.

6. Process for the preparation of the aqueous coating composition according to one or more of Claims 1-5, characterized in that aqueous binders are mixed with metal powder, if desired, silicon dioxides having a BET surface area of at least m 2 which are hydrophobicized if desired, and if desired, water, and, if desired, further substances.

7. Process for the preparation of the aqueous coating composition according to Claim 6, in which the aqueous binder is prepared by mixing aqueous emulsions of organopolysiloxane resins with an aqueous solution of monoorganosilanolates

8. Process for the preparation of the aqueous coating composition according to Claim 7, in which the aqueous binder is employed by mixing aqueous solutions of monoorganosilanolates in quantities of from 0.1 to by weight, based on the overall weight of the aqueous emulsions of organopolysiloxane resins the aqueous solutions containing from 10 to by weight of monoorganosilanolates and the aqueous emulsions containing from 25 to 75 by weight of organopolysilozane resins

9. Use of an aqueous solution of organopolysiloxane resins and/or monoorganosilanolates and/or the; condensation products thereof formed by elimination of water as binders for coating compositions comprising metal powder in anticorrosion compositions. SDATED THIS 8TH DAY OF JULY, 1996 WACKER-CHEMIE GMBH WATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA IAS:SI:JC DOC 7 AU5177793.WPC