DE2947823A1 - AQUEOUS SILICONE RESIN DISPERSION - Google Patents

Description

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description

The invention relates to a composition for protective coatings and more particularly, it relates to a coating composition made of a silicone resin, which after application on a substrate (in a protective abrasion-resistant Forms coating.

Recently learned of the replacement of glass glazing by glazing made of transparent materials that do not shatter or are more resistant to shattering than glass, a wide one Spread. For example, one is currently being made from synthetic organic Polymers made transparent glazing in public Transportation uses such as trains, buses, taxis, and planes. Lenses too, such as those for glasses and others optical instruments as well as glazing for large buildings, use shatterproof, transparent plastics. The lesser Weight of these plastics compared to glass is another benefit, especially in the transportation industry where the weight of a vehicle is a major factor in fuel consumption is.

While transparent plastics have the main advantage of greater resistance to shattering and lower weight than glass, a serious disadvantage of these plastics is that they are easily scratchable due to the fact that they are easily scratched daily contact with abrasives such as dust, cleaning equipment and / or ordinary weather. The continued scratching leads to impaired See-through and also degrades the appearance, causing frequent replacement of glazing or lens or the like is required.

One of the most promising and widely used trnns-

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Parent plastic for glazing is polycarbonate, like it sold by the General Electric Company under the Lexan trademark. This polycarbonate is a tough material high impact resistance, high thermal deformation temperature, a rod dimensional stability and a good self-extinguishing and which is also easily manufactured.

Attempts have been made to improve the abrasion resistance of transparent plastics. For example, they are scratch-resistant Coatings made from mixtures of silica, such as colloidal silica or silica gel, and hydrolyzable Known as silanes in a hydrolysis medium composed of alcohol and water. Such compositions are described, for example, in U.S. Patents 3,708,225, 3,986,997 and 3,976 Ί97.

Although the known top coat formulations have been found to be acceptable, there is still room for improvement. The top coating compositions according to the invention produce, for example, coatings with improved resistance to moisture and UV light _/ compared to the coatings according to US Pat. No. 3,986,997. Furthermore, in direct contrast to the teaching of the aforementioned US Pat Invention with a pH of 7.1 to 7.8 do not gel immediately, but give excellent coatings with good properties on solid substrates.

Protective coatings on metals, be they shiny or dull, are also required. For example, they are shiny metallized Plastics, for which small amounts of metal are deadened by vacuum decomposition, or vacuum vapor deposition can be applied to the plastic, currently due to its light weight in the automotive industry poDu-IcIr, however, they require protective layers in order to be impaired to prevent the brilliant surface from being scratched and the like. Hubcaps also require protective covers on theirs Conservation.

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The coating composition according to the invention comprises a dispersion of colloidal silicon dioxide in a solution of the partial condensate of a silanol of the formula RSi (OH) ₅ in a solution of aliphatic! Alcohol and water, where R is selected from alkyl radicals having 1 to 3 carbon atoms and aryl and at least 70% by weight? of the silanol are CH, -Si (OH) - and the composition is 10 to 50% by weight? Contains solids consisting essentially of 10 to 70? colloidal silicon dioxide and 30 to 90 weight? of the partial condensate and the composition has a pH in the range from 7.1 to about 7.8.

The coating compositions of the invention are made by hydrolyzing a trialkoxysilane or a mixture of trialkoxysilanes of the formula RSi (OR) ,, wherein R is the has the above meaning in an aqueous dispersion of the colloidal silicon dioxide. An example of an aryl group is the phenyl group.

In practicing the invention, suitable aqueous colloidal silica dispersions generally have a particle size of 5 to 150 millimicrons in diameter. These silicon dioxide dispersions are known and are commercially available, for example under the names Ludox from DuPont and Nalcoag from NALCO Chemical Company. The colloidal silicon dioxides are available as both acidic and basic hydrosols. For the purposes of the present invention where the pH of the coating composition is on the basic side, basic colloidal silica sols are preferred. However, acidic colloidal silicon dioxides, the pH of which has been adjusted to the basic level, can also be useful. In addition, it was found that colloidal silicon dioxides with a low alkali content (eg Na "0) lead to a more stable coating composition. Colloidal silicon dioxides with an alkali content of less than 0.35 % (calculated as Na ₀ O) have proven to be preferred. Except-

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dem are colloidal silicas with a particle size from 10 to 30 millimicrons preferred. A particularly preferred one aqueous colloidal silica dispersion for the present Invention is the under the trade name Ludox LS from dispersion available from DuPont Company.

According to the present invention, the aqueous colloidal silica dispersion is added to a solution of a small amount of alkyltriacetoxysilane in alkyltrialkoxysilane or aryltrialkoxysilane. For the purposes of this invention, from about 0.07 parts by weight to about 0.1 part by weight of the alkyltriacetoxysilane is used based on 100 parts by weight of the total composition. The temperature of the Feaktionsmischung is maintained in the range of about? 0 to about UO ° C, with a range of 20, preferably to about 0 ^ ⁰ C and a temperature is preferably below 25 ° C in this Bernich most. It has been found that sufficient trialkoxysilane has been hydrolyzed in about 6 to 8 hours to convert the initially two phase liquid mixture to a liquid phase in which the treated silica is now dispersed. Pan silica is treated, for example, by mixing it with the alkyltrialkoxysilane or aryltrialkoxysilane. In general, the hydrolysis is allowed to take place for a total time of about 2½ to 48 hours, depending on the desired viscosity of the product. The longer the hydrolysis is allowed to proceed, the higher the viscosity of the product obtained. After the hydrolysis has ended, the solids content is adjusted by adding alcohol to the reaction mixture, for which purpose i-butanol is preferably used. Other suitable alcohols for the purposes of the present invention include lower aliphatic alcohols such as methanol, ethanol, pronanol, i-propanol, n-butyl alcohol and t-butyl alcohol. Mixtures of these alcohols can also be used. The solvent system should contain around 20 to 75% alcohol by weight to ensure the solubility of the partial condensate (a siloxanol). Optionally, other water-miscible polar solvents can be added in small amounts, such as

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Acetone, butyl cellosic acid and the like in amounts not exceeding 20% by weight ¹ ? based on the total solvent.

The solids content of the coating compositions of the present invention is preferably in the range of about 18 to 25 percent, and most preferably about 20 percent by weight. of the overall composition. The pH of the composition ranges from about 7.1 to about 7.8, and is preferably greater than 7.2. If necessary, a dilute base such as ammonium hydroxide or a weak acid such as acetic acid can be added to the composition to adjust the final pH to the desired range. At the stated basic pH values, the compositions are translucent liquids which are stable for at least several weeks at room temperature. When stored at temperatures below about 5 ° C, this stability period is extended even further.

Additives and other modifying agents can be added to the composition Agents are added, such as thickeners, pigments, dyes and the like. A particularly desirable addition to the compositions according to the invention is a small amount of one Polysiloxane polyether copolymers, such as in U.S. Patent 3,629,165 described. Such a copolymer prevents the occurrence of undesirable flow marks and wear marks, such as those without one such polymer is sometimes formed when the coating composition is applied to the substrate. A particularly useful one Polysiloxane polyether copolymer for this purpose is available from General Electric Company under the trade designation SF-IO66 available.

The alkyltriacetoxysilane is used to buffer the basicity of the reaction mixture, which initially consists of two liquid phases, and thereby also the rate of hydrolysis to moderate. While the use of the alkyltriacetoxysilane is preferred, glacial acetic acid can also be used in its place.

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are used as well as any other acid, for example propionic, butyric, citric, penzoic, formic, oxalic acid and the like. Fn alkyltriacetoxysilanes in which the alkyl group contains 1 to f> carbon atoms and preferably has 1 to 3 carbon atoms can be used. Most preferred is methyltriacetoxysilane.

The silntriols are RSi (nil) as a result of mixing the corresponding trialkoxysilanes with the aqueous medium, 'i.h. the aqueous dispersion of colloidal silica formed in situ. Exemplary trialkoxysilanes are those the methoxy, ethoxy, isopropoxy and n-butoxy substituents which lead to the silanetriol during hydrolysis and further to the formation of alcohol. That way, at least a portion of that present in the final draft composition Alcohol delivered. Will be a mixture of trialkoxysilanes used, you get a mixture of different Silanetriols and various alcohols. After the formation of the rilanetriols or mixtures of silanetriols in the basic one aqueous medium occurs under condensation of the hydroxyl groups I'.ildunp; of -Si-O-Si bonds. This condensation takes place takes place during a certain time and is not exhaustive, but the siloxane retains a considerable amount of silicon-bonded material Hydroxyl groups that make the polymer soluble in the mixed solvent of alcohol and water. This soluble partial condensate can be characterized as a hiloxanol polymer which has at least one silicon-bonded hydroxyl group for every three -SiO units.

The non-volatile pesticide content of the coating composition; is a mixture of colloidal silicon dioxide and the partial condensate (or siloxanol) of a silanol. The main part or all of the partial condensate or siloxanol is obtained by condensation of CH Si (OH), and depending on the addition of the Ingredients to the hydrolysis mixture can be minor

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Quantities of a Partialkondensat.ps can be obtained, e.g. by condensation of CH Si (OH) ₁₅ with C ₀ H ₁₅ Pi (OH) ₅ or C ₃ U ₇ Si (OH)

or with Cy-H _n Si (OH), or mixtures of the aforementioned compounds. For best results in the cured paint coating, it is preferred to use only methyl trimethoxysilane in the preparation of the coating compositions, which results in exclusively monomethylsilanetriol. In the preferred over-ZURSzusamnensetzünden the partial condensate is in a flenne of about 55 to 75 weight :? of the total solids content is present in a cosolvent of alcohol and water, the alcohol making up about 50 to 95% by weight of the cosolvent.

The coating compositions of the present invention Harden on a substrate at temperatures of e.g. 120 ° C without the aid of a hardening catalyst. For milder conditions To be able to use, however, buffered latent condensation catalysts can be added. These include Alkali metal salts of carboxylic acids such as sodium acetate, potassium formate and similar, amine carboxylates, v / ie dimethylamine acetate, ^. ethanolamine acetate, dimethyl anilin formate and similar, quaternary Ammonium carboxylates, such as tetramethylammonium acetate, "enzyltrimethylammonium acetate, Metal carboxylates such as tin octoate and amines such as triethylamine, triethanolamine, pyridine and the like Links. Rs can also use alkali hydroxides, such as sodium hydroxide and ammonium hydroxide, as curing catalysts to be used. Typical commercially available colloidal silicas, especially those with a basic pH, contain free alkali metal base and therefore alkali metal carboxylate catalysts are used in situ during hydrolysis generated.

The amount of curing catalyst can be varied within a wide range, depending on the curing conditions desired. In general, however, the catalyst in amounts of about 0.05 to about 0.5 weight can ^1, preferably? About

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0.1 weight *, based on the composition, can be used. Compositions containing catalysts in these amounts can be deposited on a solid substrate in a relatively short time are cured at temperatures in the range of about 75 to 150 ° C and result in a transparent, abrasion-resistant surface coating.

The coating compositions of the present invention can applied to a variety of solid substrates by conventional methods such as flowing, spraying, or dipping, to form a continuous surface film. In particular, transparent substrates are provided for coating, albeit non-transparent substrates as well as plastics and Metals can also be coated. More specifically, these plastics are synthetic organic polymeric substrates, such as acrylic polymers, e.g., polymethyl methacrylate, polyesters, e.g. Polyethylene terephthalate, polybutylene terephthalate, polyamides, polyimides, acrylonitrile / styrene copolymers, styrene / acrylonitrile / Butadiene copolymers, polyvinyl chloride, butyrates, polyethylene and others.

The coating compositions of the present invention are particularly useful as coatings for polycarbonates such as those sold under the trademark Lexan by General Electric Company are available. The metal substrates on which the protective coatings of the invention are used close shiny and matte metals such as aluminum and shiny metallized surfaces such as sputter deposited Chrome alloy. Other solid substrates to be coated include wood, painted surfaces, leather, glass, ceramics and ' Textiles a.

By choosing the right formulation, application conditions and pre-treatment including the use of Primers, as well as the choice of substrate, allow the coatings to be applied to essentially any solid substrate will. A hard coating with all of the aforementioned properties

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th and benefits is obtained by removing solvent and volatile materials. The topping composition will air dry to a tack free coating, but heating to a temperature in the range of 75-200 ° C required to achieve the condensation of the remaining silanols in the partial condensate. This final hardening leads to the formation of silsesquioxane (RSiO ._). In the finished hardened coating is the ratio of RSiO, .. units to SiOp in the range from about 0.1 M to about 9.0, preferably from 1 to "^. A hardened coating with a ratio from RSiO ,,,, to SiO_ of 2 where R is methyl is most preferred. The coating thickness can be varied by means of the particular application technique, but coatings are generally used from about 0.5 to 20 µm, preferably from 2 to 10 µm, in thickness used.

The invention is explained in more detail below with the aid of examples.

example 1

22.1 parts by weight of Ludox LS, a silica sol which is an aqueous dispersion of colloidal silica, having an average particle size of 12 millimicrons and a pH of 8.2 and sold by DuPont, became a 0.1 part by weight solution Methyltriacetoxysilane added in 26.8 parts by weight of methyltrimethoxysilane. The temperature of the reaction mixture was kept at 20 to 50 ° C., preferably below 25 ° C. The hydrolysis was allowed to proceed for 21 hours. The solids content of the resulting reaction mixture was 10.5 % and the mixture was made by adding i-butanol diluted to about 20 % solids The pH of the product was about 7.2.

This composition was applied to a transparent Lexan sheet (consisting of polybisphenol-A-car-

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bonat), which had been primed with a thermosetting acrylic resin emulsion. After air drying for 30 minutes, the plate was air dried for one hour at 120 ° C. After 500 cycles with the Taber grinder (500 g load, CS-10F disks) (according to ANSI-Z26.1-1977) the percentage change with regard to the haze was 1.8. The sample passed the adhesion test (cross-hatched, according to DIN-53-151) after 7 days in water at 65 ⁰ C. The sample was also the same test after 1000 hours under RS-lamp lighting on a

rotating platform 25 cm away from the faces of a row of 6 lamps arranged 120 ° from each other. the Platform rotated at about 3 revolutions per minute.

Example 2

300 g of a 30% aqueous colloidal silica dispersion with an average particle size of 20 millimicrons and a pH of 9.2 (prepared by diluting Nalcoag 1050, a product of the NALCO Chemical Company) were added to a solution of 0.9 g of glacial acetic acid and 3 ^ 6 g methyltrimethoxysilane added. The temperature of the reaction mixture was kept below 30 ^° C. The hydrolysis was allowed to proceed for 3 days. The solids content of the resulting reaction mixture was 10.5 % and the mixture was diluted with 119 grams of isopropanol to a final 25 % solids dilution, the pH of which was about 7.5.

This composition, which contained 3 % of a 3% solution of tetramethylammonium acetate, was applied by flow to a transparent Lexan plate which had been primed with a solution of 1.5% by weight of γ-aminopropyltriethoxysilane and 1.5% by weight. of a preformed reaction product of gamma-aminopropyltriethoxysilane and maleic anhydride in ethanol / i-butanol. After air drying for 30 minutes, the plate was cured at 120 ° C for one hour. After 500

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Cycles with the Taber grinder, the percentage change in haze &% U was 1.15.

Example 3

17.9 g of Ludox LS were added to a solution of 0.06 g of glacial acetic acid in 27.2 g of methyltrimethoxysilane. The temperature of the reaction mixture was kept below 30 ° C. The hydrolysis was allowed to proceed for 6 hours. The solids content was LJL _t 6% and the mixture was diluted with 30 g of i-butanol to a Peststoffgehalt of 25%. The pH was 7.2.

The composition, which contained 3 % of a 35% solution of tetramethylammonium acetate, was applied by flow to a transparent Lexan sheet which had been primed as described in Example 2. According to the Shepherd, the plate was 1.6.

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ORIGINAL INSPECTED

Claims (22)

Claims 1. Aqueous coating composition; Characterized by a dispersion of a colloidal silicon dioxide in a solution of a partial condensate of a silanol of the formula RSi (OH) ,, where R is selected from alkyl with 1 to 3 carbon atoms and aryl and at least 70 weight percentages !? des Silanols 011, Si (OH) -, are, in a mixture of an aliphatic alcohol and water, the composition containing 10 to 50 % by weight of solids consisting essentially of 10 to 70% by weight of colloidal silicon dioxide and J> 0 to 90 weight? of the partial condensate exist and the composition a pll- 030024/0756 ORIGINAL INSPECTED 294782a Has a value in the range of 7.1 to about 7.8. 2. Composition according to claim 1, characterized in that the aliphatic alcohol is a mixture of methanol and i-butanol. 3. Composition according to claim 1, characterized in that the partial condensate of Is CH Si (OH). Ί. Composition according to Claim 1, characterized that they are an additional 0.05 to about 0.5 weight /? a buffered latent silanol condensation catalyst contains. 5. Composition according to claim 4, characterized that the catalyst is sodium acetate. 6. Composition according to claim 4, characterized that the catalyst is tetramethylammonium acetate. 7. Composition according to claim I _1, characterized in that the pH is in the range from about 7.2 to 7.8. 8. Composition according to claim 1, characterized that the composition is about 18 to 25 weight-? Contains solids consisting essentially of 25 to ^ 5% by weight * colloidal silicon dioxide and 55 to 75% by weight of the partial condensate exist. 9. Composition according to claim B, characterized that the partial condensate that of 030024/0756 Is CH Si (OH) _3. 10. Composition according to claim 1, characterized in that the composition contains: about 20 % solids, the partial condensate is that of CH, Si (OH), and the aliphatic alcohol is a mixture of methanol and isobutanol. 11. W9ssriße coating composition prepared by mixing an aqueous colloidal silica dispersion with a solution of an alkyltriacetoxysilane in an alkyltrialkoxysilane while maintaining the temperature of the mixture in the range of about 20 to about 30 ⁰ C, for a time sufficient to turn the reaction mixture into a liquid phase while maintaining the pH of the composition in the range from about 7.1 to about 7.8 and adjusting the solids content of the reaction mixture by adding an aliphatic alcohol. 12. Composition according to claim 11, characterized that the alkyltrialkoxysilane is methyltrimethoxysilane, that the alkyltriacetoxysilane Methyltriacetoxysilane is and the aliphatic alcohol is i-butanol is. 13. Composition according to claim 12, characterized in that the aqueous colloidal silicon dioxide dispersion has a basic pH, an average particle size of about 12 .mu.m and an alkali content of about 0.1 %. 14. Solid substrate, of which at least one surface is coated with the aqueous coating composition according to claim 1 is. 15. The object of claim 1Ί, characterized that the solid substrate consists of a synthetic 030024/0756 table is composed of organic polymer. 16. The article of claim I ¹ I, characterized in that the solid substrate is a metal. 17. The object of claim 14, characterized that the solid substrate is a synthetic organic polymer that has a metallized surface having. 18. Article according to claim 15, characterized in that the polymer is transparent. 19. The article of claim 18, characterized in that the polymer is a polycarbonate. 20. The article according to claim 19, characterized that the polycarbonate is transparent. 21. The article according to claim 19, characterized in that the polycarbonate is a poly (bisphenol A carbonate) is. 22. The object of claim 14, characterized that the aqueous coating composition has been cured on the surface of the solid substrate. 030024/0756 ORIGINAL