WO1994007964A2 - Silicon as a pigment in coatings - Google Patents

Abstract

The invention pertains to a method of coating metals by applying a substance that contains (A) at least one polymer and/or at least one constituent that cures into a polymer and (B) elementary silicon. Component (A) preferably contains a polyorganosiloxane and/or a constituent that cures into a polyorganosiloxane.

Description

 Silicon as pigment in coatings

The present invention relates to a method for coating metals with polymers and / or with materials which react to form polymers and contain elemental silicon.

State of the art

From US-A 5,093,289 it is known to apply a suspension of silicone resin and silicon powder in xylene to a polyurethane display with an open-cell pore structure. The foam coated in this way is then pyrolyzed. What remains is a ceramic material based on silicon that is reaction-bonded in the presence of carbon.

Coating compositions containing zinc powder are described, inter alia, in US Pat. No. 3,817,905, which contain a partial hydrolyzate of a tricarbonoxyorganosilane as a binder.

task

The object of the present invention was to provide a suitable pigment for metal coatings. Another object of the present invention was to develop coatings which are stable even at high temperatures. It was also an object of the present invention to develop a method for coating metals with metal-pigmented agents, the metal pigment not giving rise to the formation of hydrogen.

solution

The above objects are achieved by the present invention, by a method for coating metals by applying a mass which

(A) contains at least one polymer and / or at least one constituent which cures to polymer, characterized in that the composition also

(B) contains elemental silicon.

In this sense, metals are also to be understood as metal alloys, such as bronzes, brass types, steels, nickel silver and other copper-nickel alloys, duralumin, magnesium alloys, aluminum bronze, tombac, letter metal and the like. Metals in this sense are also to be understood as semimetals, such as silicon, and alloys of such semimetals. Component (B) used in the abovementioned composition is preferably silicon powder, in particular those having an average grain size of 0.3 μm to 30 μm, especially those having an average grain size of 1 μm to 10 μm, very particularly 2 μm to 7 μm.

Such silicon powder can be produced from silicon with coarser grains by conventional comminution processes. Such procedures can include include the following steps: crushing in the jaw crusher, roll crusher, cone crusher, in the hammer mill, rod mill, drum mill, tube mill, ball mill; Classification by air classifiers, hydrocyclones, sieves; Atomizing silicon melt and the like.

The silicon used in the process according to the invention does not have to meet high purity requirements. The contaminated silicon obtained as waste from the Rochow synthesis is extremely suitable for this purpose. This generally has a silicon content of about 60 percent by weight. The Rochow synthesis is the direct synthesis of methylchlorosilanes by reacting methyl chloride with silicon in the presence of copper as a catalyst.

The elemental silicon used as component (B) in the process according to the invention is preferably contained in the coating material mentioned in an amount of from 10 to 75 parts by weight, in particular from 25 to 60 parts by weight, in each case based on 100 parts by weight of component (A).

Component (A) which can be used in the process according to the invention preferably contains a polyorganosiloxane, a constituent which is curable to polyorganosiloxane and / or a copolymer resin composed of organosiloxane units and units of other organic resins. The polyorganosiloxanes or constituents curable to polyorganosiloxane can be used as mixtures with organic resins, such as alkyd, acrylic, epoxy and phenolic resins. The reaction products of organosilane and / or organosiloxanes with other organic resins, such as polyester, alkyd and acrylic resins, and their prepolymers can be used as copolymer resins, also called combination resins.

Preferred polyorganosiloxanes in this context are those of the formula (1):

R _x (RO) _y SiO ₍ 4_ _x _ _{y) 2} (1)

where in the above formula R is the same or different, optionally substituted

C * _j _ to C ^ g hydrocarbon radicals ° of the hydrogen atoms, R 'identical or different radicals bonded to silicon via oxygen, namely optionally substituted

C _] _ to Cig hydrocarbon radicals or hydrogen atoms, x an integer from 0 to 3 with an * average value from 1.1 to 1.9, y an integer from 0 to 3 with an average value from 0.1 to 1.8, with the proviso that the sum x + y has a maximum value of 2.5.

Organosilanes which contain condensable groups are preferred as constituents which can be hardened to form polyorganosiloxanes. In particular, there are silanes or silane mixtures of the formula (2):

R _z SiX (4_ _z - ₎ (2), where R has the meaning given above under formula (1),

X identical or different condensable groups, preferably halogen atoms, hydroxyl groups, C * - * _- to C ₄ - alkoxy groups, Si-ON-bonded di-CC ^ to C ₄ ~ alkyl -) - ketoxime groups, Si-OC-bonded C * j_ to C ₄ acyloxy groups, Si-N-bonded groups of the formula -NH ₂ -NHR and -NR ₂ , and z is an integer of 0, 1, 2 or 3

and their partial hydrolysates and partial condensates.

Examples of the abovementioned radicals R and R 'are alkyl radicals, such as the methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert.-butyl, n Pentyl, iso-pentyl, neo-pentyl, tert-pentyl; Hexyl radicals, such as the n-hexyl radical; Heptyl residues, such as the n-heptyl residue; Octyl radicals, such as the n-octyl radical and iso-octyl 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; Octa-decyl residues, such as the n-octadecyl residue; Alkenyl groups such as the vinyl and allyl groups; Cycloalkyl residues such as cyclopentyl, cyclohexyl, cycloheptyl residues and methylcyclohexyl residues; Aryl radicals, such as the phenyl, naphthyl, anthryl and phenanthryl radical; Alkaryl residues, such as o-, m-, p-tolyl residues, xylyl residues and ethylphenyl residues; Aralkyl radicals, such as the benzyl radical, the α- and the β-phenylethyl radical;

Examples of substituted radicals R and R 'are cyanoalkyl radicals, such as the β-cyanoethyl radical, and halogenated hydrocarbon radicals, for example haloalkyl radicals, such as the 3,3,3-trifluoro-n-propyl radical, the 2,2,2,2 ', 2', 2'-hexafluoroisopropyl radical, the heptafluoroisopropyl radical, and haloaryl radicals, such as the o-, m- and p-chlorophenyl radical. Preferred examples of compounds of the formula (2) are tetramethyl silicate, tetraethyl silicate lan, Methyltrimethoxysi-, methyltriethoxysilane, phenyltrimethoxysilane, vinyltriethoxysilane, vinyl triethoxysilane, i-octyltriethoxysilane, dimethyldimethoxysilane, methylphenyldimethoxysilane, nyldimethoxysilan diphenyl, chloropropyltrimethoxysilane, vinyltris (ethoxyethoxy) silane, vinyltriacetoxysilane , N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyldi ethoxysilane, N- (cyclohexyl) aminopropyltrimethoxysilane, methacryloxypropyltriethoxysilane, glycidoxypropyltriethoxysilane de mercaptil ren partial hydrolysates.

The components (A) used in the coating process according to the invention are preferably in the form of a solution in organic solvent or in the form of an aqueous dispersion.

In the first case, the composition used in the process according to the invention contains at least one organic solvent as component (C).

If solvents are used, solvents or solvent mixtures with a boiling point or boiling range of up to 120 ° C. at 0.1 MPa are preferred. Examples of such solvents are alcohols, such as methanol, ethanol, n-propanol, iso-propanol; Ethers, such as dioxane, tetrahydrofuran, diethyl ether, diethylene glycol dimethyl ether; chlorinated hydrocarbons, such as dichloromethane, trichloromethane, carbon tetrachloride, 1,2-dichloroethane, trichlorethylene; Hydrocarbons, such as pentane, n-hexane, hexane-isomer mixtures, heptane, octane, white spirit, petroleum ether, benzene, toluene, xylenes; Ketones, such as acetone, methyl ethyl ketone, methyl isobutyl ketone; Carbon disulfide and nitrobenzene, or mixtures of these solvents.

The term solvent does not mean that all components have to dissolve in it. The reaction can also be carried out in a suspension or emulsion of one or more reaction partners. The reaction can also be carried out in a solvent mixture with a mixture gap, at least one reactant being soluble in each of the mixed phases.

If component (A) to be used in the process according to the invention is in the form of an aqueous dispersion, at least one emulsifier is preferably added to stabilize this dispersion.

The following are particularly suitable as anionic emulsifiers:

1. Alkyl sulfates, especially those with a chain length of 8 to 18 carbon atoms, alkyl and alkaryl ether sulfates with 8 to 18 carbon atoms in the hydrophobic radical and 1 to 40 ethylene oxide (EO) or propylene oxide (PO) units.

2. sulfonates, especially alkyl sulfonates with 8 to 18 carbon atoms, alkylarylsulfonates with 8 to 18 carbon atoms, taurides, esters and half esters of sulfosuccinic acid with monohydric alcohols or alkylphenols with 4 to 15 carbon atoms; if appropriate, these alcohols or alkylphenols can also be ethoxylated with 1 to 40 EO units.

3. Alkali and ammonium salts of carboxylic acids with 8 to 20 carbon atoms in the alkyl, aryl, alkaryl or aralkyl radical. 4. partial phosphoric acid esters and their alkali and ammonium salts, especially alkyl and alkaryl phosphates with 8 to 20 carbon atoms in the organic radical, alkyl ether or alkylene ether phosphates with 8 to 20 carbon atoms in the alkyl or alkaryl radical and 1 up to 40 EO units.

The following are particularly suitable as nonionic emulsifiers:

5. Alkyl polyglycol ethers, preferably those with 8 to

40 EO units and alkyl residues from 8 to 20 carbon atoms.

6. Alkylaryl polyglycol ethers, preferably those with 8 to 40 EO units and 8 to 20 C atoms in the alkyl and aryl radicals.

7. ethylene oxide / propylene oxide (EO / PO) block copolymers, preferably those having 8 to 40 EO or PO units.

8. Fatty acids with 6 to 24 carbon atoms.

9. Natural products and their derivatives, such as lecithin, lanolin, saponins, cellulose; Cellulose alkyl ethers and carboxy-alkyl celluloses, the alkyl groups of which each have up to 4 carbon atoms.

10. Linear organo (poly) siloxanes containing polar groups, in particular those with alkoxy groups with up to 24 C atoms and / or up to 40 EO and / or PO groups.

The following are particularly suitable as cationic emulsifiers:

11. Salts of primary, secondary and tertiary fatty amines with 8 to 24 carbon atoms with acetic acid, sulfuric acid, hydrochloric acid and phosphoric acids. 12. Quaternary alkyl and alkylbenzene ammonium salts, in particular those whose alkyl group has 6 to 24 carbon atoms, in particular the halides, sulfates, phosphates and acetates.

13. Alkylpyridinium, alkylimidazolinium and alkyloxazolinium salts, especially those whose alkyl chain has up to 18 carbon atoms, especially the halides, sulfates, phosphates and acetates.

Depending on the type and nature of component (A), the coatings produced in the process according to the invention can be cured at room temperature or at elevated temperature. The coatings can contain catalysts and other additives which accelerate this hardening.

Such additives can be acids, bases and the metal compounds known as condensation catalysts, such as tin compounds, organotin compounds, titanium compounds, organotitanium compounds and the like.

Examples of acids are Lewis acids such as BF ₃ , AICI ₃ , TiCl ₃ , SnCl4 SO ₃ PCI5, POCI ₃ , FeCl ₃ and its hydrates and ZnCl2, "Brönstedt acids such as hydrochloric acid, hydrobromic acid, sulfuric acid, chlorosulfonic acid, Phosphoric acids, such as ortho-, eta- and polyphosphoric acids, boric acid, selenic acid, nitric acid, acetic acid, propionic acid, haloacetic acids, such as trichloro- and trifluoroacetic acid, oxalic acid, p-toluenesulfonic acid, acidic ion exchangers, acidic zeolites, acid-activated bleacher , acid activated carbon black, hydrogen fluoride, hydrogen chloride and the like. Examples of bases are Lewis bases, such as the hydroxyl ion, the methanolate ion and the ethanolate ion and the isopropanolate ion;

Br0nstedt bases, such as alkali and alkaline earth metal hydroxides, such as LiOH, NaOH, KOH, RbOH, CsOH, Mg (OH) ₂ , Ca (OH) ₂ , Sr (OH) ₂ , Ba (OH) 2, and amides, such as sodium - and potassium amide, hydrides such as sodium, potassium and calcium hydride; Tetrakohlenwasser¬ ammonium hydroxides, such as tetramethylammonium hydroxide and benzyltrimethylammonium hydroxide; Tetrahydrocarbon phosphonium hydroxides, such as tetramethylphosphonium hydroxide.

If component (A) is curable by condensation of organosilicon compounds, that is to say in particular by condensation of compounds of the formulas (1) and / or (2), if the use of catalysts is desired or advantageous at all, the catalysts used are tetrahydrocarbons. ammonium hydroxides and tetrahydrocarbon phosphonium hydroxides preferred.

If, after the mass has been applied, the coating is exposed to elevated temperatures, temperatures from 140 ° C. to 400 ° C., in particular from 180 ° C. to 250 ° C., are preferred.

The coatings produced according to the invention have the advantage over the conventional ones filled with zinc powder that the pigment does not react with the other components to form hydrogen. The coatings produced according to the invention are, at least when components (A) of the formulas (1) and / or (2) are used, resistant to temperatures of up to at least 650 ° C. use

The coatings produced by the process according to the invention can be applied to any type of metal to which polymer-based coatings have also previously been applied. Because of their high temperature resistance, those of the coatings produced according to the invention which contain compounds of formulas (1) and / or (2) as component (A) are particularly suitable as high temperature coatings for all purposes for which zinc and aluminum have hitherto been used Pigment used.

In the following examples, unless otherwise stated,

a) all quantities based on weight;

b) all pressures 0.10 MPa (abs.);

c) all temperatures 20 ° C.

Examples

example 1

In a mixture of

14.0 g combination resin of a methylphenyl silicone resin and an epoxy resin (EPIK0TE ^R 1001 from Shell Chem. Comp.) In xylene with a solids content of about 50 wt .-% and a silicone content of 50 wt .-%, based on the solids content (VP 4404 from Wacker-Chemie GmbH, Munich)

20.0 g of a mixture of aliphatic hydrocarbons (crystal oil K 30), 2.0 g of butanol and 5.0 g of tetra- (n-butyl) titanate

were

35.0 g technical silicon powder with a grain size of 7 μm and a silicon content of 98% by weight and 3.0 g hydrophobic fumed silica with a BET surface area of about 120 m ² / g (Wacker ^R HDK H 15)

stirred in rapidly at a speed of about 20 m / sec.

Example 2

In a mixture of

44.0 g of ethyl silicate with a viscosity of 37-38 mm ² / s at 25 ° C (TES 55 from Wacker-Che ie GmbH, Munich),

22.0 g crystal oil K 30,

22.0 g of ethyl glycol and 1.2 g of acrylic plasticizer (Plexisol ^R PM 709 from Röh GmbH, Darmstadt)

were

35.0 g technical silicon powder with a medium

Grain size of 7 μm and a silicon content of 98% by weight and • I _/ O g fumed silica with a BET surface area of 200 m ² / g (Wacker ^R HDK N 20)

stirred in rapidly at a speed of about 20 m / sec.

The coating compositions prepared in Examples 1 and 2 were applied to VA steel sheets using a 100 μm doctor blade. After drying at room temperature, the mixture was heated to 1000 ° C. in the course of 3 hours and cooled overnight. The coatings adhered well to the steel sheets, although they warped strongly at the high temperatures.

Example 3

In 75 parts by weight of an emulsion of 50% by weight of water and 50% by weight of an emulsion of a medium-hard methylphenyl silicone resin with a content of 7% by weight of xylene, with a solids content of 42%, a viscosity from 40 mm ² / s, a nonionic emulsifier and an average particle size of about 1900 nm (Silres MP 42E from Wacker-Chemie GmbH, Munich) 25 parts by weight of technical silicon powder with an average grain size of 2 microns and a silicon content of 98 wt .-% slowly stirred in with a 30 mm diameter dissolver disc. The mixture was then stirred at 4000 rpm for 10 minutes.

The coating agent was applied to VA steel sheets using a 60 μm doctor blade. Then it was dried for 1 hour at room temperature. It was then baked in the drying cabinet at 200 ° C. for 1 hour and heated in air in steps of 100 ° C. to 1000 ° C. in a muffle furnace.

The coating adhered very well up to 800 ° C. At 900 ° C and 1000 ° C the sheet warped and scaling occurred.

Example 4

a) In a mixture of

44.0 g of ethyl silicate with a viscosity of 37-38 mm ² / s at 25 ° C (TES 55 from Wacker-Chemie GmbH, Munich), 22.0 g of crystal oil K 30, 22.0 g of ethyl glycol and 1.2 g Plexisol ^R PM 709 were

150.0 g of technical grade silicon powder having an average grain size of 7 microns and a silicon content of 98 wt .-%, and • _1/0 9 fumed silica having a BET surface area of 200 m ² / g (Wacker HDK N ^R 20)

dispersed at a speed of about 20 m / sec.

b) In a mixture of

40.0 g of the methyl ester of a mixture of oligomeric methyl silicas of the average formula CH3Si (0) _{1 1} (OCH3) Q 8 ^and a viscosity of 25-35 mm ² / sec at 25 ° C (Silres MSE 100 from Wacker-Chemie GmbH, Munich ),

3.0 g tetra (n-butyl) titanate and 15.0 g xylene

were

10.0 g of silicon powder from Example 4 a),

• _1/0 <? fumed silica from Example 4 a) and 30.0 g talc

dispersed at a speed of about 20 m / sec.

c) In 75 g of an emulsion of a medium-hard methylphenyl silicone resin with a content of 7 wt .-% xylene, with a solids content of 42 wt .-%, a viscosity of 40 mm ² / s, a nonionic emulsifier and a particle size of about 1900 nm (VP 4302 from Wacker-Chemie GmbH, Munich) were

24.0 g of silicon powder from Example 4 a), 0.5 g of silicone antifoam (S 1176 from Wacker-Chemie GmbH, Munich) and 0.5 g of highly disperse silica with a BET surface area of 200 m ² / g using a dissolver disc stirred with a diameter of 30 mm. The mixture was then stirred at 4000 rpm for 10 minutes.

All coating agents were applied to VA steel sheets using a 100 μm doctor blade. The mixture was then dried at room temperature for 1 hour. The mixture was then baked at 200 ° C. for 1 hour, then at 300 ° C. and then at 400 ° C. All coatings adhered very well.

These sheets treated with the coating agent according to Example 4 c) were subjected to a salt spray test according to DIN 53210. Table I below shows the results after 200, 500 and 1000 hours of salt spray test with VA steel sheets which were treated at 200 ° C., 300 ° C. or 400 ° C. The rating number according to DIN 53210 is based on the proportion of the surface affected by rust. The rating number means 0 = rustproof and 5 = more than 50% rust attack. The coating agent of Example 4 c is suitable as an anti-rust paint.

Table I

Comparative Example 1

Examples 4 a) and 4 b) were repeated, the silicon powder in Example 4 a) being replaced by 400.0 g of zinc dust and in Example 4 b by 10.0 g of zinc dust.

Zinkoli 615 from Stoiberger Zincoli GmbH, GE, was used as zinc dust.

The coating compositions were applied to VA steel sheets and baked as in Example 4.

A water-containing coating agent with zinc dust analogous to Example 4 c) is not suitable for baking, since hydrogen is formed due to a zinc-water reaction.

The sheets from Examples 4 a), 4 b) and the corresponding comparative examples with zinc as the metal pigment were subjected to a salt spray test analogous to Example 4. In addition, the sheets were tested after drying at room temperature (20 ° C). Table II shows the results. With a long test duration, here at 500 and 1000 hours, and High baking temperatures, silicon is superior to zinc as a pigment also in rust protection.

Table II

Claims

Claims Process for coating metals by applying a mass, which (A) contains at least one polymer and / or at least one polymer-hardening component, characterized in that the composition also (B) contains elemental silicon. A method according to claim 1, wherein the mass contains as component (B) silicon powder, preferably that of an average grain size of 0.3 μm to 30 μm. The method of claim 1 or 2, wherein the elemental silicon is contained in the mass of from 10 to 75 parts by weight, based in each case on 100 parts by weight of component (A). A method according to claim 1, 2 or 3, wherein the component (A) contains a polyorganosiloxane, a component curable to polyorganosiloxane and / or a copoly resin composed of organosiloxane units and units of other organic resins. 5. The method according to claim 4, wherein component (A) is a polyorganosiloxane of the formula (1) R _χ (R'0) _y SiO ₍₄ _ _χ _ _{y) 2} (1) contains, wherein in the above formula R is the same or different, optionally substituted C ~ ~ to Cig hydrocarbon radicals or hydrogen atoms, R 'identical or different radicals bonded to silicon via oxygen, namely optionally substituted C * _j _ to C ^ g hydrocarbon radicals or hydrogen atoms, x an integer from 0 to 3 with an average value from 1.1 to 1.9, y an integer from 0 to 3 with an average value from 0, 1 to 1.8, with the proviso that the sum x + y has a maximum value of 2.5. Method according to one of claims 1 to 5, wherein the mass contains as component (C) at least one organic solvent. Method according to one of claims 1 to 6, wherein after the application of the mass, the coating is exposed to increased temperature.