DE10325768A1 - Coating system for glass surfaces, process for its production and its application - Google Patents

Abstract

A coating system containing TiO ₂ and a coating based on silanes and / or siloxanes is described. The coating system is produced by applying a TiO ₂ coating to a substrate and then a silane coating. The coating system is used in the production of "self-cleaning" or easy-care surfaces (e.g. glass surfaces) and the production of surfaces with switchable hydrophobic and hydrophilic properties, e.g. B. in the production of printing plates or drums, which are described with UV radiation.

Description

The The invention relates to a coating system for glass surfaces Process for its production and use.

Solutions based on silanes and / or siloxanes with which the glass surface is coated are used to refine glass surfaces (eg float glass, tempered, partially tempered, hardened or curved glass). In the patent EP 0783464 B1 describes such a mixture for treating silicon-containing substrates. This mixture is also sold under the name Crystal Guard ^® . Applying Crystal Guard ^® to a glass surface changes its surface properties: The glass surface becomes water-repellent (hydrophobic). This manifests itself in the fact that water on the glass surface contracts into drops so that it can roll off more easily. When it rolls off, the water picks up and removes dirt particles. Soiling of the glass surface is reduced. Due to the changed surface properties, the glass is also easier to clean ("easy-to-clean" effect). Furthermore, the glass surface by the in the EP 0783464 B1 described mixture advantageously permanently protected from glass corrosion.

Of The disadvantage of this type of coating is that smaller drops of water stick to the glass surface stick and leave stains after drying.

task of the present invention is to overcome the disadvantages of the prior art Technology to overcome to improve the known coating system and in particular to develop a coating system which has "self-cleaning" properties and which is simple Way on a glass surface can be applied.

The object is achieved by a coating system which contains TiO ₂ (preferably in the anatase form) and a coating based on silanes and / or siloxanes.

Surprisingly, it was found that the application of a based silanes and / or siloxanes coating such as Crystal Guard ^®, unexpected to a photocatalytically activable titanium dioxide coating properties of the coating combination causes.

Photocatalytically active titanium dioxide coatings are known to develop photocatalytic activity after activation by UV light and to have hydrophilic properties. Due to the photocatalytic activity, organic compounds such as dirt are broken down. Accordingly, photocatalytically active TiO ₂ coatings have "self-cleaning" properties. If there is no further activation of the TiO ₂ coating by UV light, the photocatalytic activity and thus both the dirt-degrading properties and the hydrophilic properties are lost. The coating then has no effect.

In the combination of TiO ₂ and a coating based on silanes and / or siloxanes, as represented by the coating system according to the invention, activation of the photocatalytic properties of the TiO ₂ coating by UV light, contrary to expectations, does not lead to photocatalytic degradation of the silane. or siloxane layer. Rather, the properties of the originally hydrophobic "easy-to-clean" coating system change when irradiated with UV light: the hydrophobic character that is present in the non-activated state is lost and the hydrophilic properties of the TiO ₂ coating dominate. Furthermore, the coating system as a whole is photocatalytically active after activation by UV light, so that the dirt-degrading properties of this system emerge.

Surprised it was further found that the coating system is reversible behave if there is no further activation by UV light: the coating system loses the hydrophilic properties, becomes hydrophobic and is also no longer photocatalytically degrades dirt. The "easy-to-clean" properties appear again. Repeated exposure to UV light again leads to a hydrophilic one and photocatalytically active coating, and so on.

The advantage of the coating system according to the invention is that both the properties of the TiO ₂ coating and the properties of the coating based on silanes and / or siloxanes can be set in a targeted manner, or in other words can be “switched” in a targeted manner by UV light.

The coating system according to the invention preferably contains TiO ₂ with an average grain size (particle size) d ₅₀ of 1 to 100 nm, particularly preferably of 5 to 20 nm, the layer thickness of the TiO ₂ layer preferably 1 to 1000 nm, preferably 5 to 100 nm and is very particularly preferably 10 to 50 nm.

The coating based on silanes and / or siloxanes contains silanes or siloxanes linked via Si-O-Si bonds, which form a two- or three-dimensional network. The silane layer preferably contains one or more fluorosilanes. Examples of fluorosilanes are tridecafluorotetrahydrooctyltrihydroxysilane CF ₃ - (CF ₂ ) ₅ - (CH ₂ ) ₂ -Si (OH) ₃ and perfluorodecyltrihydroxysilane CF ₃ - (CF ₂ ) ₇ - (CH ₂ ) ₂ -Si (OH) ₃ .

In the coating system according to the invention, the TiO ₂ coating and the silane coating are cross-linked via Si-O-Ti bonds. If the substrate contains Si (eg glass, ceramic or enamel), the coating system is also linked to the substrate via Si-O-Si or Si-O-Ti bonds. If the substrate does not contain Si, the coating system can be bound to the substrate, for example by physical interaction.

A method for producing the coating system according to the invention can be carried out as follows: titanium dioxide in sol form is added to the surface to be coated. TiO ₂ sol consists of TiO ₂ crystals that are smaller than 1 μm and are either charge or sterically stabilized. The brine can be produced in organic or inorganic media. For example, an aqueous TiO ₂ sol with an average particle size of d ₅₀ from 5 to 100 nm, preferably d ₅₀ from 10 to 50 nm and particularly preferably d ₅₀ from 15 to 30 nm (measured with photon correlation spectroscopy, PCS) is included in HNO ₃ a pH of 0.5 to 2, preferably from 0.8 to 1.7 and particularly preferably from 1 to 1.2 and a solids concentration of 1 to 30% by weight, preferably from 2 to 20% by weight and particularly preferably from 4 to 15 wt .-% added to the glass surface. The aqueous TiO ₂ sol is prepared in a known manner and is described, for example, in Gmelin's manual of inorganic chemistry, Verlag Chemie, Weinheim, 8th edition, volume Titan (41, 1951, p. 100).

Alternatively, the acidic TiO ₂ sol can be mixed with an organic acid (for example citric acid) (for example 1 part by weight of acid to 3 parts by weight of TiO ₂ ). The mixture is then adjusted to a preferred pH of 5 to 8, particularly preferably 6 to 8, with stirring with aqueous ammonia solution (for example about 25%).

The TiO ₂ sol can be applied to the surface to be coated, for example by spraying, dipping or rolling. The TiO ₂ coating hardens at room temperature. The TiO ₂ layer is preferably annealed after application at 100 to 800 ° C., particularly preferably at 250 to 500 ° C. and very particularly preferably at 275 to 325 ° C., the temperatures preferably being between one minute and two hours, particularly preferably between 15 and 60 minutes and most preferably between 30 and 45 minutes. This increases the abrasion resistance of the TiO ₂ layer.

Alternatively, the TiO ₂ layer can be produced by magnetron sputtering. A low-temperature plasma in an inert gas (usually argon) is used to remove a target material (here titanium) and to deposit it on an opposite substrate in the presence of oxygen (this is mixed with the sputtering gas argon), forming a layer of TiO ₂ . The TiO ₂ layer can also be deposited from organic sols or from precursor compounds (for example Ti alcoholates).

A further layer, which is based on silanes and / or siloxanes, is applied in a known manner to the transparent layer of TiO ₂ thus produced.

For this purpose, for example, a mixture which contains three components A, B and C and a solvent which is inert to these components can be applied to the surface coated with TiO ₂ .

widergegeben wird, wobei R ein Alkylrest mit 1 bis 12 C-Atomen und/oder ein nicht substituierter oder substituierter Phenylrest ist, wobei die Reste R teilweise durch Wasserstoff ersetzt sind und wobei n in der Formel I eine Zahl von 2 bis 50 und in der Formel II eine Zahl von 4 bis 50 ist. Bevorzugt wird ein lineares Polysiloxan mit einer Molmasse von 350 bis 15000 eingesetzt.Component A contains at least one polysiloxane which contains Si-H bonds and the general formulas

is reproduced, where R is an alkyl radical having 1 to 12 carbon atoms and / or an unsubstituted or substituted phenyl radical, where the radicals R are partially replaced by hydrogen and where n in the formula I is a number from 2 to 50 and in the Formula II is a number from 4 to 50. A linear polysiloxane with a molecular weight of 350 to 15000 is preferably used.

Component B contains at least one bi-, tri- or tetrafunctional silane with the general formula R ' _z SiR'' ₄ _ _z III where R 'is an unsubstituted or substituted alkyl radical having 1 to 12 carbon atoms, a cycloalkyl radical having 5 to 6 carbon atoms, an unsubstituted or substituted phenyl radical and / or a vinyl radical, where R''is an alkoxy or a CH _{3 is} COO or an isocyanide radical or a halide and acts as a functional radical, the alkyl part of the alkoxy radical having 1 to 12 carbon atoms and z being a number from 0 to 2. A dialkyldialkoxysilane, a dicycloalkyldialkoxysilane, a diphyenyldialkoxysilane, a dialkyldiacetoxysilane, a diphenyldiacetoxysilane, a vinylmethyldialkoxysilane, a vinylmethyldiacetoxanialysiloxysiloxysilane, or a fluoromethyldialkoxysilane or fluoroxysilane. The trifunctional silane that can be used is, for example, a monoalkyltrialkoxysilane, a monocycloalkyltrialkoxysilane, a monophenyltrialkoxysolane, a monoalkyltriacetoxysilane, a monocycloalkyltriacetoxylilane, a monophenylacetoxysilane, a vinyltrialkoxysilane, vinylanilylanilane, a vinyl. Component B can additionally contain a disiloxane and / or a monofunctional silane (for example fluoroalkylmonoalkoxysilane).

The Component C contains at least one (preferably anhydrous) organic (also chlorinated) or inorganic acid (such as chlorosulfonic acid, benzenesulfonic, p-toluenesulfonic acid, Acetic acid, Chloroacetic acid, dichloroacetic trichloroacetic formic acid, Chloroformate, glutaric, maleic acid) or instead of the acid a catalyst, e.g. Amines, metal salts of organic acids (such as Dibutyltin dilaurate (DBTL) or dibutyltin diacetate (DBTA)), organotin compounds, Titansäureester and quaternaries Ammonium salts,

As inert solvents hydrocarbons with 5 to 12 carbon atoms are preferably used, Ketones or, under normal conditions, liquid carboxylic acid esters. Examples are: methyl, ethyl or butyl acetate, n-hexane, n-heptane, Isooctane, cyclohexane, pentane, toluene, xylene, acetone or methyl ethyl ketone, or mixtures of these substances.

With some silanes, alcohols can also be used as inert solvents. If necessary, this should be determined in preliminary tests. Preferred alcoholic solvents are methanol, etha nol or propanol (all isomers) used.

Some of the silane / siloxane-containing mixtures described here are also in the EP 0783464 B1 and this publication is expressly referred to here.

The layer, which is based on silanes and / or siloxanes, can also be produced as follows: A mixture which contains components B and C described above and a solvent which is inert to these components is applied to the surface coated with TiO ₂ .

The silane and / or siloxane-containing mixture is preferably applied to the surface in an amount of at least 15 g / m ² , particularly preferably in an amount of 25 to 35 g / m ² . The preferred concentration of the sum of components A, B and C described above is 0.01 to 15% by weight, particularly preferably 0.5 to 10% by weight, and very particularly preferably 1 to 8% by weight; the rest is usually solvent.

After application to the substrate, a layer is formed by progressive polymerization and / or crosslinking of components A and B or component B, with Si-O-Si bonds being formed. Si-O-Ti bonds are formed to the TiO ₂ layer. In addition, the layer which is formed is anchored to the substrate on a glass surface via Si-O-Si bonds or via Si-O-Ti bonds. After a reaction time of 15 to 60 minutes (at room temperature), the unreacted silane / siloxane mixture can be removed from the surface again using a solvent and, if necessary, a cloth, if a clear, transparent surface is desired. If the crosslinking is carried out at higher temperatures (for example 50 to 80 ° C.), the unreacted silane / siloxane mixture can be removed after only 1 to 10 minutes. The silane / siloxane mixture can also be polished after application to the substrate coated with TiO ₂ . Removing unreacted mixture is then not necessary to achieve a clear, transparent surface. The finished coated surface is preferably aftertreated at 50 to 150 ° C. for 1 to 5 hours. This accelerates post-networking.

The coating system can also be produced by mixing a TiO ₂ sol with a mixture of components A, B and C or with a mixture of components B and C and then applying this mixture to the substrate. The entire mixture is preferably applied to the substrate within 24 hours, particularly preferably within 12 hours after the mixing.

The coating system may include discrete TiO ₂ and silane layers, or the coating system may include a layer in which TiO ₂ and silane are mixed in one layer.

1 shows an exemplary and schematic of a coating system on a glass surface with a discrete TiO ₂ layer on which a cross-linked silane layer is applied. The silane layer here contains water-repellent groups, for example perfluorinated alkanes, straight-chain and branched substituted and unsubstituted alkanes. The rest R in 1 is preferably the methyl or the ethyl radical. 2 shows an example and schematic of a coating system on a substrate (which does not necessarily have to be a Si-containing substrate) with a discrete TiO ₂ layer, on which a silane layer is also applied.

use finds the coating system according to the invention in the production of "self-cleaning" or easier to care for Surfaces, e.g. "self-cleaning" glass, enamel and Ceramic surfaces, especially float glass surfaces and heat treated glass surfaces. The coating system can be used both indoors and outdoors. preferred Applications are in the facade area, sanitary area, kitchen area, on tiles Greenhouses and in vehicle glazing. As further materials, whose surfaces with the coating system according to the invention can be provided to be mentioned: architectural materials (e.g. stone, concrete, glass, Building ceramics: tiles) shower cubicles, kitchen sinks, plastics (e.g. polycarbonate, Polymethyl methacrylate, polypropylene, refrigerator cladding), so-called white Goods (outside), Wood and fabric (e.g. shower curtains), garden furniture and awnings. The antibacterial should also be emphasized Properties of the coating according to the invention. The coating is therefore also used on surfaces who are concerned about sterility or poverty.

Furthermore, the coating system according to the invention is used in the production of surfaces with switchable hydrophobic and hydrophilic properties. These surfaces can be used, for example, in the printing industry for the production of printing plates or drums with UV radiation be described and change their polar state at the exposed areas in order to then only take up the printing ink there. The information on the plates or drums is deleted by storing them in the dark. The plates or drums can then be used again.

The Advantage of those provided with the coating system according to the invention surfaces lies in easier cleaning and care of these surfaces. soiling the surface are reduced, pushed back and partly completely prevented. The usage amount of conventional This reduces cleaning agents. The coating system protects also generally permanent against corrosion and especially against glass corrosion.

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

Example 1: Production of a coating system on a glass surface (without heat treatment the finished coating)

A window glass pane made of float glass was wetted with an aqueous titanium dioxide sol (nitric acid, pH = 1.2) with a concentration of 6% by weight of TiO ₂ and wiped off with a doctor blade. The wet layer thickness was 15 μm. The disc was annealed at 300 ° C for 30 minutes.

The Mixture containing silane-siloxane was prepared as follows: 200 g of hydrogen-methylpolysiloxane with a molecular weight of approx. 2000, 100 g phenyltrimethoxysilane, 5 g of dimethyl diethoxysilane, 45 g of isobutyltrimethoxysilane and 280 g Octyltriethoxysilane was mixed with 62 g trichloroacetic acid. The mixture was kept under constant stir to 60 to 65 ° C heated and held at this temperature for about 15 minutes. To cooling down the mixture to approx. 30 ° C 50 ml of isopropanol and 500 ml of heptane were added in succession. The solution was then diluted with heptane, until it had a dry matter concentration of 4 to 8% by weight.

This mixture was then sprayed evenly onto the window glass pane coated with TiO ₂ and evenly distributed with a cloth. After evaporation of the solvent (approx. 30 minutes) there was a firmly adhering, thin, hardened resin film with hydrophobic properties on the TiO ₂ layer. The excess silane / siloxane mixture was then removed with isopropanol and a cloth.

Example 2: Production of a coating system on a glass surface (with heat treatment the finished coating)

A glass pane was coated as in Example 1. The glass pane coated with TiO ₂ and silane / siloxane in this way was then aftertreated for 2 hours in a drying cabinet at 90 ° C. in order to complete the crosslinking.

Claims (14)

Coating system containing TiO ₂ and a coating based on silanes and / or siloxanes. Coating system according to claim 1, characterized in that the TiO ₂ particles in the coating have an average grain size d ₅₀ of 1 to 100 nm. Coating system according to claim 2, characterized in that the TiO ₂ particles in the coating have an average grain size d ₅₀ of 5 to 20 nm. Coating system according to one of claims 1 to 3, characterized in that the layer thickness of the TiO ₂ layer is 1 to 1000 nm. Coating system according to claim 4, characterized in that the layer thickness of the TiO ₂ layer is 5 to 100 nm. Coating system according to one of claims 1 to 5, characterized in that the TiO ₂ coating and the silane coating are cross-linked via Si-O-Ti bonds. Method for producing a coating system, characterized in that a TiO ₂ coating and then a silane coating are applied to a substrate. A method according to claim 7, characterized in that the TiO ₂ coating is carried out by applying a TiO ₂ sol and subsequent drying. A method according to claim 8, characterized in that the applied TiO ₂ sol is dried (tempered) at elevated temperatures. A method for producing a coating system, characterized in that a TiO ₂ sol is mixed with a mixture of a silane and a catalyst and optionally a siloxane, and this mixture is applied to the substrate and dried. Use of the coating system according to one of the Expectations 1 to 6 for the production of "self-cleaning" or easier to care for Surfaces. Use of the coating system according to one of the Expectations 1 to 6 for the manufacture of corrosion protection Surfaces. Use of the coating system according to one of the Expectations 1 to 6 for the creation of surfaces with switchable hydrophobic and hydrophilic properties. Use of the coating system according to one of the Expectations 1 to 6 for the production of printing plates or drums, which are described with UV radiation and change their polar state in the exposed areas.