EP1397319A1

EP1397319A1 - Coating which is easy to clean

Info

Publication number: EP1397319A1
Application number: EP02747157A
Authority: EP
Inventors: Bernd Metz; Gerhard Weber; Mevluda Blecker
Original assignee: Carl Zeiss AG; Schott Glaswerke AG
Current assignee: Schott AG
Priority date: 2001-05-18
Filing date: 2002-05-17
Publication date: 2004-03-17
Also published as: WO2002094729A1; JP2004529057A; CA2447414A1; DE10292191D2; CN1509258A

Abstract

The invention relates to a method for producing a product having a long-life surface which is easy to clean. A mixture is applied to the surface, said mixture comprising a hydrolysable, network-forming gel, and the hydrophobic substance. Said gel preferably consists of SiO2, Al2O3, Fe2O3, In2O3, SnO2, ZrO2, B2O3 and/or TiO2 and the hydrophobic substance is preferably chemically linked to the gel network.

Description

Easily cleanable coating

Description:

The invention relates to a method for producing a product with an easily cleanable surface by coating the surface with a hydrophobic material, and to the products obtainable by the method.

The equipping of objects with dirt-repellent substances is generally known. For example, it is also known to treat the surface of glasses, glass ceramics, glazes or stones with silicones in order to make them dirt and water repellent. The usual procedure is to hydrophobize the surface of the objects to be treated by applying a liquid composition. A large number of chemicals are usually used for this, but in particular silicone oils and / or fluorinated silanes. The surfaces treated in this way prove to be difficult to wet, causing the water to roll off. Dirt adheres only weakly to the treated surface and is therefore easy to remove. This has a particularly advantageous effect when used outdoors, since, for example in the case of skylights and / or roof glazing such as conservatories, etc., soiled deposits are taken away by the rainwater and are removed in the process. In this way it is possible to make such windows appear permanently clean without additional cleaning.

However, this procedure has the disadvantage that the chemicals applied only with those directly on the substrate material groups that are available can react and form strong bonds. Since there are not sufficient reactive OH groups on the surface of objects, especially glasses, without appropriate pretreatments, such as hydrogen / oxygen plasma, only a very thin, usually monomolecular, hydrophobic layer can be produced by this procedure, which in use, in particular also with mechanical stress, such as cleaning and / or abrasion by wind and dust, is quickly rubbed off, as a result of which the desired self-cleaning property is lost.

Attempts have therefore already been made to increase the durability of such coatings. For example, EP-A-0, 658, 525 describes the production of a water-repellent multilayer film. Three different target solutions are prepared, mixed, applied to a glass substrate and a gel coating is created on the glass surface. A metal oxide surface layer is then produced by heating. A fluoroalkylsilane layer is then applied to this metal oxide layer, as described above.

JP-A-11 092 175 describes a process according to which methoxysilane or an ethoxysilane compound containing a fluorocarbon chain is fixed on the surface of small particles with a diameter of 100 nm. The particles modified in this way are then dissolved in an aqueous medium and applied to a surface to be coated, the solvent is removed and the residue is then baked. In this way a surface coated with small hydrophobized particles is obtained. WO 99/64363 describes the production of a water-repellent surface, the surface of the glass first being roughened and all metal ions present on the surface being removed. A water-repellent film is then applied to the previously treated surface in a manner known per se. By roughening the surface, the roughness valleys thus obtained are filled with the hydrophobicizing agent.

WO 99/02463 describes the production of a scratch-resistant coating in which an organic substance with silicone-like networks is applied to the surface. Subsequently, a heat treatment is carried out at which the temperature and duration are selected such that the applied, purely organic layer is largely decomposed and / or removed, but a connection of inorganic molecules of the carrier material and organic molecules of the applied substance can form in the uppermost molecular layers. In this way, an organic substance, such as a methyl group, is bonded directly to the silicon atom of the glass surface, forming an Si-C bond.

DE 695 02671 T2 (WO95 / 24053) describes a display device with a screen which has a non-absorbent cover layer made of a hybrid inorganic-organic material and an inorganic network made of silicon and metal oxide. The polymer chains are interwoven with the inorganic network and form a hybrid inorganic-organic network. However, it has been shown that in such a layer organic components, in particular hydrophobic organic components such as fluoroalkyls, are not homogeneously incorporated into such a layer, but rather that they essentially adhere to the surface facing away from the carrier layer. Out for this reason, this outer hydrophobic layer is relatively easy to rub off.

All of the hydrophobic and dirt-repellent properties produced with these processes do not prove to be sufficiently durable when used and are quickly lost, particularly when subjected to mechanical stress.

The aim of the invention is therefore to provide an easy-care object whose easy-care and dirt-repellent finish remains permanently and which is also abrasion-resistant under stress, as a result of which the aforementioned easy-care properties on the object or product are retained for a long time.

Another object of the invention is to provide such equipment for optical elements which does not change the optical properties of the element or does not noticeably change it.

This aim is achieved according to the invention by the method defined in the claims and the product obtained therewith.

According to the invention, it was found that a uniform, resistant coating or a coating on a product with homogeneous properties in cross section can be achieved by providing its surface with a layer which comprises a thin metal oxide network or a metal oxide matrix, in the network a hydrophobic substance is evenly distributed. The layer is usually a uniform layer made of a coherent sheet-like metal oxide network. The metal oxide networks according to the invention can have open or closed pores. The metal oxide layers according to the invention are formed by thermal treatment of an applied gel layer and remain on the product as a solid coating or coating. The hydrophobic substance is present in the coating according to the invention in an evenly distributed manner, that is to say from the layer side adhering to the carrier material to the outer layer surface over the cross section in a homogeneous concentration and does not accumulate, exclusively or mainly on the outer coating surface. In this way, the surface layer retains the properties desired according to the invention even in the case of surface abrasion.

The gels used according to the invention are in particular metal oxide gels which can be produced by means of a sol-gel process. The gels are formed in situ during application to the object or product to be coated, as a result of which a uniform, continuous gel network is generated on the surface of the object to be coated. Preferred metal oxides are Si0 _{2 /} A1 ₂ 0 ₃ , Fe ₂ 0 ₃ , In ₂ 0 ₃ , Sn0 ₂ , Zr0 ₂ , B ₂ 0 ₄ and / or Ti0 ₂ . Preferred gels are hydrogels, alkogels, xerogels and / or aerogels. The inventive addition of the hydrophobic, possibly also oleophobic, substance to the sol mixture before or during the formation of the gel has the effect that the hydrophobic substance is contained in an evenly distributed manner in the entire volume of the gel network being formed and is chemically bound, for example, by its silanol groups by polycondensation , In this way it is possible to impart particularly abrasion-resistant and permanent dirt-repellent properties to the surface treated in this way.

The general production of gel layers by means of a sol-gel process is known per se and has been described in many different ways. The usual procedure is that in a solution, preferably a water-containing and / or alcoholic solution, with inorganic metal salts or organometallic compounds such as metal alkoxides, a polymer reaction is produced by hydrolysis, a colloidal suspension, ie a sol, being formed. A continuous gel network is formed from the sol by further hydrolysis. The formation of the gel is preferably generated directly during the coating. The final formation of the entire gel network is preferably accelerated by heating. Typical temperatures for this are between 0 ° C. and 200 ° C., preferably between 20 ° C. and 200 ° C., in particular between room temperature and 170 ° C., a temperature of 150 ° C. being particularly preferred. By selecting the hydrolysis conditions, gel networks that are as dense as possible, that is to say more or less pore-free or only have tiny pores, can be generated. Metal alkoxides are preferably C3-C ₄ metal alkoxides, with metal methylates and metal ethylates being particularly preferred. Metal nitrates are preferred among the metal salts. The hydrolysis with formation of the sol is usually started with an excess of distilled water and by standing for a longer period, for example two to four days, is carried out at ambient temperature and if necessary. the sol is formed even at elevated temperature.

In general, all hydrophobic substances that can be stored in the forming gel are suitable as hydrophobic substances. For the process according to the invention, it is preferred to use hydrophobic substances which are distributed as evenly as possible in the gel-forming sol solution. The hydrophobic substances used in the process according to the invention are therefore preferably themselves to a small extent water-soluble or can be made water-soluble by means of solubilizers or by hydrolysis. In a In another preferred embodiment, the oleophobic substances used according to the invention have a chemical modification which imparts water solubility. Such modifications are water-soluble groups such as amino groups or acid groups. Examples include natural and synthetic oils and / or longer-chain fatty acids, in particular fatty acids with a chain with at least 6 carbon atoms, preferably at least 10 carbon atoms. However, hydrophobic oleophobic substances, in particular silicones and silanes, siloxanes, silicone oils, silicone greases, are particularly preferred. The silicone compounds used according to the invention can be straight-chain or branched or, if appropriate, also contain cyclic silane groups. In a preferred embodiment, they contain a water-solubilizing function, such as an amino group, the hydrogen atoms of which may also be substituted.

The hydrophobic substances used according to the invention are preferably fluorine-containing and in particular have at least 5%, preferably at least 10%, fluorine atoms (based on the total number of atoms of the hydrophobic substance that has been incorporated after sintering). However, they preferably have at least 20% fluorine atoms, with at least 30% being particularly preferred. Although it has been shown that the storage of the hydrophobic substances according to the invention in the in situ process makes the dirt-repellent finish permanent, it is preferred to chemically bond the hydrophobic substances to the gel network by means of reactive groups, in particular by means of reactive silanol groups. Hydrophobic materials with methoxy, ethoxy, propoxy, butoxy or isocyanate groups and chlorosilanes are particularly suitable. Preferred silanes in the process according to the invention have the general formula

(CF _x H _y ) - (CF _a H _b ) _n - (CF _a , H _b .) _M -Si- (OR) ₃

where x and y are independently 0, 1, 2 or 3 and x + y = 3, a, a 'and b, b' are independently 0, 1 or 2 and a + b and a 'and b '= 2 results and n and m independently of one another are an integer from 0 to 20 and together result in a maximum of 30 and R is a straight-chain, branched, saturated or unsaturated (optionally containing heteroatoms) C 1 -C ₈ -alkyl radical. Preferred alkyl radicals are methyl, ethyl and propyl radicals, and their amino derivatives. According to the invention, preference is given to silanes which have functional groups which comprise heteroatoms or heteroatoms and which increase or mediate the water solubility of the silane. The heteroatoms and / or functional groups are built into the backbone of the alkyl carbon chain and / or the fluoroalkyl carbon chain and / or are present as a substituent thereon. Aminoalkyl groups and / or amino-fluoroalkyl groups are particularly preferred according to the invention.

In a preferred embodiment, x = 3 and y = 0, so that the above general formula has a terminal CF ₃ group. In a further preferred embodiment according to the invention, a = 2 and a '= 0, so that CF ₂ and CH ₂ blocks are formed. Of course, there may also be more than 2 blocks in the chain and the CF ₂ blocks and CH ₂ blocks may be interchanged. However, it is preferred to arrange the fluorinated blocks as terminally as possible to the Si atom. Preferred values for n are 1-10, in particular 1-8, and for m 0-10, in particular 0-8. In the gel solution to be applied, the weight ratio of hydrophobic substance to gel network is preferably se 0.01: 1 to 1: 1, with ratios between 0.05: 1 and 0.2: 1 being preferred.

The mixture of gel and hydrophobic substance according to the invention is applied by means of customary coating methods, spraying and dip coating being preferred. The thickness of the coating can be controlled by controlling the viscosity and the rate at which the object to be coated is pulled out of the dipping solution. In a special embodiment, the coating mixture therefore also contains viscosity modifiers such as PVP, PVA and PEO. Layer thicknesses which can preferably be produced according to the invention are between 0.5 nm and 1 μm, layer thicknesses of <200 nm being preferred. After application, the layer is preferably dried at room temperature for at least 1 minute, preferably at least 3 minutes, and then cured at elevated temperature, any substances added, such as the viscosity modifiers, being pyrolyzed or burned. The drying time depends on the layer thickness generated, the actual temperature and the vapor pressure of the solvent and is preferably at least 1 minute and in particular at least 3 minutes. Usual drying times are 4 - 6 minutes. The applied layer is preferably sintered or hardened at temperatures of 150 ° C. to 400 ° C., preferably at 250 ° C. to 380 ° C. The duration of the curing is usually a maximum of 1 hour, with a maximum of 45 minutes and in particular a maximum of 30 minutes being preferred.

Using the degree of hydrolysis, it is possible to set the viscosity of the coating solution, in particular the immersion solution, exactly to a drawable value. In this way, with a known viscosity and a known drawing speed, the layer thickness produced in each case can be accurately be produced producible. A change in the viscosity when using the coating or immersion solution can be adjusted to the desired value in a simple manner by dilution with solvents, for example ethanol or by metering in further sol-gel solution capable of hydrolysis.

In the method according to the invention it is also possible to adapt the refractive index of the coating to the carrier material. This is possible, for example, by mixing different metal oxides. Si0 ₂ has a refractive index of n = 1.45, Ti0 ₂ of n - 2.3. In a Si0 ₂ / Ti0 _{2 system} , depending on the composition, any refractive indices can be set within these extreme values. By adjusting the refractive index and the layer thickness, the method according to the invention is also particularly suitable for producing interference coatings, such as, for example, for anti-reflective treatment.

In a special embodiment according to the invention, the permanently hydrophobic layer is provided with a surface microstructure by means of suitable measures before, during or after the thermal curing, as a result of which the hydrophobic properties of the coating are strengthened and its cleaning is facilitated or the layer is given an anti-reflective effect or is enhanced , Such measures can be created by embedding particles or embossing. In this way, surface microstructures can be achieved which, for example, have knobs which restrict contact of contaminating parts with the surface coated according to the invention to a few points of contact, as is the case, for example, with the so-called lotus effect. In this way, the desired cleaning effect is further increased. In principle, it is possible to coat any materials that survive the previously described sintering temperature using the method according to the invention. These include in particular metals, plastics, inorganic minerals and stones such as marble, granite, fired clays. However, it is particularly preferred to coat glass and glass ceramics by means of the method according to the invention. Preferred glasses are borosilicate glasses, soda-lime glasses and optical glasses. The method according to the invention is particularly suitable for the production of easily cleanable flat and, in particular, float glasses, of curved glasses, optical lenses, glass tubes, TV and PC screens and cover panes therefor, of glass ceramic products, vehicle glazing, enamelled and / or ceramic products. Preferred flat glasses are, for example, window glass, mirror glasses, shower cubicle glasses, glass shelves, cover glasses for solar collectors, sight glasses, instrument glasses, glass keyboards, touch screen panels, display cover glasses, for example for mobile telephones and laptops, glasses for cookers, such as oven panes, glass baking dishes or / and glass baking molds, lamp cover glasses, as well as glasses for refrigerators and furniture. Domed glasses are, for example, headlight glasses, lamp cover glasses, watch glasses and / or sanitary glasses. Glass lenses are, for example, glasses, eyepieces and objective glasses in optical devices. Glass tubes are, for example, solar collector tubes and sewage pipes. Vehicle glazings are, for example, windows and instrument cover glasses for motor vehicles, rail vehicles such as trains etc., ships and planes. Enamelled products include baking trays, saucepans and sanitary objects such as wash basins, urinals, bathtubs and toilet bowls. Ceramic products are, for example, tiles, roof tiles and the sanitary objects already mentioned. The method according to the invention is also suitable for coating objects in the household, such as drinking glasses, glass cookware and cooktops made of glass ceramic, as are available, for example, under the trade name CERAN. The method according to the invention has also proven to be suitable for coating enamelled cookware, such as pans and pots.

However, the method according to the invention can also be used to generate interference-optical layer packets, such as reflections. Such anti-reflective coatings according to the invention are preferably produced as the outermost layer adjacent to the environment or air.

The invention is illustrated by the following examples.

Example 1 - Preparation of hydrophobically modified SiQ dipping solutions

a) A mixture of 13.6 g of tetramethyl orthosilicate (CAS: 681-84-5 available under the name Dynasil ™ M from Degussa Frankfurt / Germany) and 13.6 g of 96% ethanol is prepared (mixture A) , and a mixture of 3.75 g of distilled water and 0.15 g of 36% HC1 (mixture B). Mixtures A and B are combined and stirred at room temperature for 10 minutes. A mixture of 1.4 g of a water-soluble modified fluoroalkylsiloxane (available on CAS 64-17-5 under the name Dynasylan ™ F8800 from Degussa Frankfurt / Germany) and 175 g of 96% ethanol is then added with stirring. This mixture is added used as a diving solution. b) Analogous to a), a mixture A consisting of 13.6 g of ethyl polysilicate (from tetraethyl silicate available under the name Dynasyl ™ 40 from Degussa AG Frankfurt / Germany) and 13.6 g of 96% ethanol and a mixture B of 3 , 8 g of water and 0.15 g of 36% hydrochloric acid, then combined both mixtures and stirred for 10 minutes. Thereafter, a mixture of 1.4 g of a water-soluble modified fluoroalkylsiloxane which contains aminoalkyl-functional substituents (CAS No. 64-17-5, available from Degussa AG Frankfurt am Main / Germany under the name Dynasylan ™ F8800) and 175 g of 99 , 5% ethanol, added with stirring. c) A mixture of 254.2 g of 99.5% ethanol, 77.6 g of water, 7.2 g of glacial acetic acid and 90.8 g of tetramethyl orthosilicate (Dynaysil ™ M so) is stirred together and left to stand for 24 hours. Thereafter, 25 g of the concentrate obtained in this way are mixed with 75 g of 99.5% ethanol with stirring and then a mixture of 100 g of 99.5% ethanol and 1.4 g of a fluoroalkyl-functional water-soluble polysiloxane, which by means of a Aminoalkyl functional substitution is made water-soluble (CAS No. 64-17-5, Dynasylan ™ F8800), stirred together, whereby the finished immersion solution is formed. d) 88.6 ml of methyl silicate, 80 ml of distilled water and 10 ml of glacial acetic acid are stirred into 240 ml of ethanol. The solution thus obtained is left to stand for 72 hours. The mixture is then diluted with 1,580 ml of ethanol and the hydrolysis is stopped with 2 ml of 37% hydrochloric acid. After that

8.6 ml of tridecafluorooctyltriethoxysilane (available under the name Dynasylan F8261 from DEGUSSA-HÜLS, Frankfurt, Germany) was added with stirring.

According to the invention, the coating was applied by means of a single immersion process. It was then dried for five minutes at room temperature and at 250 ° C for burned in for a maximum of 30 minutes, causing the silica gel to harden.

Example 2 - Production and testing of a coating according to the invention

A cleaned, 10 x 20 cm large and 2 mm thick plate made of borosilicate glass was immersed at room temperature in the SiO ₂ immersion solution previously described in Example 1 and pulled out of the solution at a rate of 20 cm / min. The coated layer was then dried for 5 minutes at room temperature and then baked in an oven at 250 ° C. (Table 1, layer 1) or at 300 ° C. (Table 1, layer 2) for 20 minutes. After baking, the layer according to the invention had a thickness of approximately 120 nm. The hydrophobization was assessed by determining the contact angle with water. It was carried out with a contact angle measuring device "G10" from KRÜSS, Hamburg. For example, freshly cleaned glass surfaces show a contact angle of ≤20 degrees, stored glass surfaces about 60 degrees and freshly hydrophobicized surfaces ≥ 100 degrees.

Directly after the preparation according to the invention, a value of 110 degrees was measured in this way at room temperature. A scrubbing test was then carried out as follows: a felt flap moistened with water and having a contact area of approximately 3 cm ² was loaded with a total contact mass of m = 1 kg and moved back and forth on the sample. A load cycle corresponds to a back and forth movement.

After 500 load cycles using this scrub test, the contact angle was still 102 degrees, after 1000 load cycles cycles 103 degrees and after 2000 load cycles still 100 degrees with a measuring accuracy of ± 3 degrees.

Example 3 (comparative example) - Hydrophobization by using a fluoroalkylsilane

By applying tridecafluorooctyltriethoxysilane ("F8262" from DEGUSSA-HÜLS), a hydrophobic glass surface was produced according to the state of the art: application of the fluoroalkylsilane over the entire surface with a textile cloth and fixing for 20 minutes at 200 ° C or 250 ° C. The measurement of the contact angle of water gave a value of 108 degrees immediately after the preparation. After 500 cycles of the scrubbing test (see above) the contact angle was 81 degrees, after 1000 cycles 68 degrees and after 2000 cycles 67 degrees. Similar values were also measured on identically tested hydrophobic glass surfaces from different manufacturers.

Example 4 (comparative example) - Hydrophobization by using a silicone oil

By applying hydromethylpolysiloxane ("Fluid 1107" from DOW CORNING), a hydrophobic glass surface was produced according to the state of the art: application of the silicone oil over the entire surface with a textile cloth and fixing for 20 minutes at 180 ° C. The measurement of the contact angle of water showed a value of 102 degrees directly after the production. After 500 stress cycles of the scrub test (see above), the contact angle was 87 degrees, after 1000 stress cycles 71 degrees and after 2000 stress cycles still 51 degrees. Similar values were also measured on identically tested hydrophobic glass surfaces from different manufacturers. Example 5 (Comparative Example) - Behavior of Commercially Available Hydrophobic Glass Surfaces

4 different commercially available hydrophobized glasses from different manufacturers were subjected to a stress or scrub test as described in Example 2. The results are summarized in Table 1.

Table 1: Contact angle of water in degrees after n load cycles for various hydrophobic glass surfaces

Claims

Easily cleanable coating

1. A process for producing a product with a durable, easily cleanable surface by coating the surface with a hydrophobic material, characterized in that a mixture is applied to the surface, which comprises a hydrolyzable, a network-forming gel and the hydrophobic substance.

2. The method according to claim 1, characterized in that the gel is hardened after application.

3. The method according to any one of the preceding claims, characterized in that the gel is a hydrogel, alkogel, xerogel and / or airgel.

4. The method according to any one of the preceding claims, characterized in that the gel of Si0 ₂ , Al ₂ 0 ₃ , Fe ₂ 0 ₃ , ln ₂ 0 ₃ , Sn0 ₂ , Zr0 ₂ , B ₂ 0 ₃ and / or Ti0 _{2 is} formed becomes.

5. The method according to any one of the preceding claims, characterized in that the hydrophobic substance is chemically linked to the gel network.

6. The method according to any one of the preceding claims, characterized in that a silane is used as the hydrophobic substance.

7. The method according to any one of the preceding claims, characterized in that the silane has the general formula

(CF _x H _y ) - (CF _a H _b ) _n - (CF _a .H _b ,) _m -Si- (OR) ₃

, where x and y are independently 0, 1, 2 or 3 and x + y = 3, a, a 'and b, b ^{1 are} independently 0, 1 or 2 and a + b and a' + b '= 2 and n and m independently of one another are an integer from 0 to 20 and together give a maximum of 30 and R is a straight-chain, branched, saturated or unsaturated, optionally heteroatom-containing C 1 -C ₈ -alkyl radical.

8. The method according to any one of the preceding claims, characterized in that a metal organic sol solution which can be hydrolyzed with gel formation is produced, a hydrophobic substance is dissolved therein and this solution is applied to a surface to be treated.

9. The method according to claim 8, characterized in that the application is carried out by dipping, spraying, spin coating, rolling, curtain casting or screen printing in the solution.

10. Product with an easily cleanable surface, obtainable according to one of claims 1 to 9.

11. Product according to claim 10, characterized in that it is a window glass, a mirror glass, a shower cabin glass, a glass shelf, a cover glass for solar collectors, a sight glass, an instrument glass, a glass keyboard, a touch screen panel, a display cover glass, a glass for cookers , a glass for refrigerators or furniture, a headlight glass, a lamp cover glass, a watch glass, a sanitary glass, an eyeglass lens, an eyepiece and objective glass in optical devices, a solar collector tube, a sewage pipe, a TV and PC screen, a TV and PC cover glass, a window, a dashboard cover glass for motor vehicles, trains, ships or planes, a baking sheet, a saucepan, a sanitary object , a tile or a roof tile.

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