WO2004058419A1

WO2004058419A1 - Method for producing super hydrophobic surfaces on substrates

Info

Publication number: WO2004058419A1
Application number: PCT/EP2003/013618
Authority: WO
Inventors: Oliver Bedford; Manfred Jaumann; Michael Kraus; Werner GÖDEL; Martin Möller
Original assignee: Sustech Gmbh & Co. Kg
Priority date: 2002-12-27
Filing date: 2003-12-03
Publication date: 2004-07-15
Also published as: EP1587638A1; DE10261285A1; AU2003293753A1

Abstract

The invention relates to a method for producing super hydrophobic surfaces on substrates, involving: i) the application of a first liquid, non-aqueous composition containing at least one poly(alkoxy(semi)metal oxane) H, which is liquid at room temperature, and containing at least one fine-particle material M in a quantity of at least 5 % by weight with regard to the weight of H to at least one surface of the substrate, and; ii) the application of a second liquid composition, which contains at least one fluoroorganic substance with (per)fluoroalkyl groups, to the coating obtained in step i).

Description

Process for the production of ultrahydrophobic surfaces on substrates

The present invention relates to a method for producing ultrahydrophobic surfaces on substrates and to articles which have an ultrahydrophobic surface.

Conventional surfaces are usually wetted by liquids, especially water. The degree of wetting is an interplay between the cohesive forces in the liquid and the adhesive forces between the liquid and the surface. The contact angle of a drop of liquid on this surface is often used as a measure of the wettability of a surface (see Barthlott et al., Biologie in heute, 28, No. 5, pp. 314-322; K. Henning, SÖFW- Journal, Chemical specialties 127 (2001), pp. 96-107).

A very high contact angle, which is generally at least 130 ° and in particular at least 150 °, is characteristic of ultrahydrophobic surfaces. Another characteristic feature is the easy rolling off of liquid drops, which is due to a very low contact angle hysteresis. The contact angle hysteresis is the difference between the advancing contact angle θ _a and the receding contact angle 0 _{r of} a dropping liquid on a surface (for the definition of the contact angle and the contact angle hysteresis see Dörfler "interfaces and colloidal disperse systems", Springer Verlag, Berlin, Heidelberg, New York 2002, Pp. 85-88).

In addition to their water-repellent effect, ultrahydrophobic surfaces are usually characterized by a self-cleaning effect. Soiling of surfaces is closely linked to the wettability of the surface by liquid (see Barthlott et al. Log. Cit. And K. Henning et al. Log. Cit.) And the sticking of liquid drops on a surface. For example, the wetting of surfaces with water leads to water drops remaining on the surface and evaporating, the solids dissolved or suspended in water being ugly residues on the surface Remain on the surface. In addition, heavy wetting by water can cause corrosion of the surface or an infestation with microorganisms as well as fouling with algae, areas, mosses, mussels and the like. The production of ultrahydrophobic surfaces is therefore the subject of intensive investigations.

Ultrahydrophobic surfaces are usually characterized by the fact that they consist of a material with a low surface energy and also have a structure.

A wide variety of strategies are used to produce ultrahydrophobic surfaces, for example plasma polymerization of

Heptafluorobutyl acrylate on structured poly (ethylene terephthalate) surfaces (Langmuir 15 (1999) 3395-3399), photolithography (Langmuir 16, (2000) 7777- 7782), laser application (WO 00/39051), sandblasting (WO 00/38845), anodized - Process (WO 00/39368), self-organization of wax melts (Langmuir 12, 1996, 2125-2126) and the use of coating agents made from finely divided, inorganic particles and fluoroorganic polymers as binders.

Even if these methods are basically all suitable for the production of ultrahydrophobic surfaces, they are very complex and / or very expensive because of the use of large amounts of fluoroorganic polymers.

Variously hydrophobic surfaces have been described in the prior art which contain hydrolysis products of hydrolyzable silicon compounds. For example, EP 545201 describes a water-repellent, transparent coating for glass, which is produced by first applying a primer solution, which contains a low molecular weight, hydrolyzable silicon compound, to the glass surface, curing the coating thus obtained by moisture and then a fluoroorganic substance on this surface. However, the surfaces obtained in this way show no ultrahydrophobic property (contact angle <130 °). From EP 867490, in turn, a method for producing water and oil-repellent glass surfaces is known, in which a silicate layer is first applied as a primer to a glass surface and then the primer layer thus obtained is brought into contact with a composition which a perfluoroalkylsilane which has hydrolyzable groups and optionally contains a finely divided inorganic oxide. Similar coatings are also known from EP 1142845. In both methods, however, ultrahydrophobic surfaces are only obtained if additional measures for pretreating the substrate surface, such as sandblasting or electrolytic etching, are taken. Alone by coating in the manner described there, no ultrahydrophobic surfaces are obtained (contact angle for water <120 °).

No. 6,210,750 describes a process for the production of water-repellent glass surfaces, in which a dispersion of crosslinked, spherical silicon dioxide particles and linear polysiloxanes is first prepared, in which an alkoxysilane is first treated with water in an organic solvent and the colloidal product obtained in the process Silicon dioxide suspension treated under acidic conditions. The dispersion of silicon dioxide particles thus obtained is mixed with a mixture of alcohol and acid and applied to a glass surface. After heat treatment of the silicon dioxide layer, a water-repellent surface is then applied to the coating thus obtained, for example an organofluorine polymer. A disadvantage of this process is the aqueous hydrolysis of alkoxysilanes, which gives poorly reproducible results. In addition, this manufacturing process is very complex.

The present invention is therefore based on the object of providing a method for producing ultrahydrophobic surfaces which is simple to use and leads to coatings which, in addition to their ultrahydrophobic property, also have good adhesion to the substrate. The procedure should also be easy to perform. This object is achieved by a process in which firstly a liquid, non-aqueous composition, the at least one poly (alkoxy (semi) metaloxane) H liquid at room temperature and at least one finely divided material M in an amount of at least 5% by weight. -%, based on the weight of H, applied to at least one surface of a substrate and applied to the coating thus obtained a second liquid composition containing at least one fluoroorganic substance with (per) fluoroalkyl groups.

Accordingly, the present invention relates to a method for producing ultrahydrophobic surfaces on substrates, comprising:

i) applying a first liquid, non-aqueous composition comprising at least one poly (alkoxy (semi) metal oxane) H which is liquid at room temperature and at least one finely divided material M in an amount of at least 5% by weight, based on the weight of H contains, on at least one surface of the substrate,

ii) applying a second liquid composition, which contains at least one fluoroorganic substance with (per) fluoroalkyl groups, to the coating obtained in step i).

The coatings obtained in this way are distinguished on the one hand by their ultra-hydrophobic properties, i. H. the contact angle for water is generally at least 130 °, preferably at least 140 ° and in particular at least 150 °. In addition, the coatings are stable against mechanical influences, in particular against abrasion.

According to the invention, the first composition contains a poly (alkoxy (semi) metal oxane) which is liquid at room temperature. Are preferred

Poly (alkoxy (semi) metal oxanes) of silicon, titanium, zirconium or hafnium. In a particularly preferred embodiment, the first composition contains a polyalkoxysiloxane. Here, alkoxy generally represents an alkyl radical which is bonded via oxygen and preferably has 1 to 4 carbon atoms. Examples of alkoxy are in particular methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy and 2-butoxy and particularly preferably ethoxy.

Preferred are oligomers whose number average molecular weight M _{n is} at least 1000 daltons, preferably at least 1500 daltons and in particular at least 2000 daltons. Products with molecular weights of at least 3000 daltons can be beneficial. The upper limit of the number average molecular weight M _{n of} the poly (alkoxy (semi) metalloxanes) is of minor importance and will often be 100,000 daltons, in particular 20,000 daltons. The only requirement is that the poly (alkoxy (semi) metalloxane) is liquid at room temperature. This is ensured if the viscosity of the poly (alkoxy (semi) metal oxane) is not more than 100,000 Pa.s and preferably in the range from 0.01 to 100,000, in particular in the range from 0.02 to 50,000 Pa.s and especially in the range from 0.1 to 50000 Pa.s.

For the application according to the invention, it has proven to be advantageous if the poly (alkoxy (semi) metal oxanes) do not have a linear structure, but branching points. Preference is given to poly (alkoxy (semi) metal oxanes) which have a degree of branching according to Frey in the range from 0.2 to 0.8 and in particular in the range from 0.3 to 0.7. The degree of branching DB according to Frey (see D.Hölter, A.Burgath, H.Frey, Acta Polym. 1997, 48, p. 30) is defined by the following formula:

DB 2Q, + Q ₃

- (3Q ₄ + 2Q ₃ + Q ₂ )

In this formula, Q ₄ stands for the percentage of those atoms M which are linked to 4 neighboring atoms M via 4 oxygen atoms (dendritic units). Accordingly, Q ₃ stands for the percentage of atoms M which are linked to 3 neighboring atoms M via oxygen atoms (semi-dendrical Units) and Q ₂ for the percentage of atoms M which are linked via oxygen atoms to 2 neighboring atoms M (linear units). (Notation according to G.Engelhardt, H.Jancke, D.Hoebbel, W.Wiecker, Z. Chem 1974, 14, p. 109). In the case of polyalkyl silicates, which are obtainable by condensation of tetraalkyl silicates, the degree of branching can be determined by means of ²⁹ Si NMR spectroscopy. The signal in the range from -94 to -97 ppm corresponds to the linear Si-O units, the signal in the range from -102 to -105 ppm with the semidendritic units and the signal in the range from -109 to -111 ppm with the dendritic units , Terminal units Q ₄ are in the range of - 88 to -90 ppm. observed. The area under the signals allows, if necessary after taking into account the different

Relaxation behavior to calculate the relative number of terminal, linear, semidendritic and dendritic units in the polyalkyl silicates.

The poly (alkoxy (semi) metal oxanes) used in accordance with the invention are known in some cases from the prior art and are commercially available. For example, polyethylene silicates (= polyethoxysiloxanes) with molecular weights <1000 Dalton are available from Wacker (Wackersilikat TES 40 WN), Degussa (Dynasil® 40) and from Silbond Corp. (Silbond® 50).

Among the poly (alkoxy (semi) metalloxanes), preference is given to those which are obtained by condensation of tetraalkyl metallates, in particular tetraalkyl metallates of the general formula I.

M (OR) ₄ (I)

are available in the absence of water, wherein in formula I the variable M stands for Ti, Hf or Zr, and in particular for Si, and R is C 1 -C ₄ -alkyl. R here means in particular methyl or ethyl.

Such a method is used, for example, for the condensation of tetraalkyl silicates by VV Kazakowa et al. (Doklady Chemistry, Vol. 349, 1996, Pp. 190-193). This gives branched polyalkyl silicates with number average molecular weights in the range from 1000 to 1500 daltons.

Furthermore, the poly (alkoxy (semi) metalloxanes used according to the invention can be prepared by adding a tetraalkyl (semi) metallate I, as defined above, with the anhydride II of an aliphatic C ₂ -C monocarboxylic acid in an amount of 0.8 to 1.2 mol, in particular 0.9 to 1.1 mol and especially approximately stoichiometric amounts (0.95 to 1.05 mol) per mol of tetraalkyl (semi) metallate I in the absence of water and removal of at least 80%, based on the theoretical amount , The resulting C-ι-C alkyl ester III of the aliphatic C ₂ -C - monocarboxylic acid removed from the reaction mixture.

The absence of water here and below means a water content in the reaction mixture of less than 1000 ppm, in particular less than 500 ppm and especially less than 200 ppm.

The amount of alkyl ester III which theoretically forms during the reaction corresponds to twice the molar amount of anhydride II. In order to achieve the desired low content of monomeric starting material I, it is important that at least 80%, preferably at least 85%, in particular at least 90% and specifically at least 95% of the CrC ₄ alkyl ester III formed in the reaction is removed from the reaction mixture. The alkyl ester II will usually be removed by distillation.

In order to achieve a sufficiently high conversion rate, the reaction will usually be carried out at an elevated temperature. The pressure and temperature will preferably be chosen so that the alkyl ester III distills off, but the starting materials II do not. The reaction is therefore preferably carried out at temperatures above 60 ° C., in particular at least 100 ° C. and especially in the range from 100 to 150 ° C.

The reaction is usually carried out in the normal pressure range, ie in the range from 0.7 × 10 ⁵ Pa to 1.2 × 10 ⁵ Pa. Examples of suitable anhydrides II are acetic anhydride, propionic anhydride and n-butyran anhydride, and mixed anhydrides such as the anhydride of acetic acid with formic acid or propionic acid. Preferred anhydride II is acetic anhydride.

The process according to the invention can be carried out in one step or in two steps. In the two-stage procedure, the tetraalkyl (semi-) metalate I with the anhydride II is firstly added to a compound of the formula IV

M (OR) ₃ (OC (O) R ¹ ) (IV),

in which M and R have the abovementioned meanings and R ^{1 is} C ¹ -C ₃ -alkyl, in which case the CrC ₄ -alkyl ester III of the monocarboxylic acid formed is removed and the reaction mixture is then worked up by distillation to the extent that a product is obtained, which contains at least 80% by weight and preferably at least 90% by weight and in particular at least 95% by weight of compound IV. The product thus obtained is then reacted at elevated temperature with removal of the C ₄ -C ₄ -alkyl ester III formed, until a total of at least 80%, preferably 90% and in particular at least 95% of the theoretically possible amount of C 1 -C ₄ alkyl ester is removed is.

Typically, the first step is in the absence of an organic solvent or diluent. The reaction in step 1 usually takes place at temperatures above 60 ° C., in particular above 100 ° C. and especially above 120 ° C. and especially in the range from 120 to 150 ° C. The reaction is continued until at least 0.6 mole of compound IV per mole of compound I formed. In particular, the reaction is carried out in the first stage until at least 0.6 mol, in particular 0.6 to 1.2 mol, of ester III per mol of anhydride II used have been removed from the reaction mixture. The reaction time required for this is usually at least 12 hours and is often in the range from 24 hours to 100 hours. The reaction mixture is then worked up by distillation. The distillative workup is carried out in such a way that the product IV obtained has a purity of at least 80%, preferably at least 90% and in particular at least 95%.

The compound IV thus obtained is then reacted at elevated temperature with removal of the ester III formed until the total amount of ester formed in both stages is at least 80%, preferably at least 90% and in particular at least 95% of the theoretically possible amount of ester III corresponds. The temperatures required for this are generally above 100 ° C. and in particular in the range from 120 to 150 ° C. As the reaction progresses, the molecular weight increases, which can be followed by gel permeation chromatography. The reaction is then stopped when the desired molecular weight has been reached.

The poly (alkoxy (semi) metal oxanes) can also be produced in a one-step procedure. The statements made above apply to the reaction temperatures, reaction pressure and stoichiometry.

In the one-stage procedure, the reaction of the tetraalkyl (semi) metallate I is generally carried out until at least 80% and preferably at least 90% and in particular at least 95% of the theoretical amount of ester III have been removed from the reaction mixture.

In a preferred variant of the one-stage embodiment, a compound I is reacted in the presence of a catalyst which is selected from tetra (Cr C -alkyl) titanates or zinc bis (CrC ₄ -alkanolate). The amount of catalyst is generally 0.01 to 1 mol% and in particular 0.05 to 0.5 mol%, based on the compound I. This variant is particularly preferred for the condensation of compounds I with M = Si.

A further increase in molecular weight can be increased by a thermal aftertreatment of the reaction product obtained primarily Temperature and reduced pressure can be reached. The temperature required for the aftertreatment is generally above 100 ° C., preferably above 120 ° C., in particular in the range from 150 to 350 ° C. and especially in the range from 200 to 300 ° C. The pressure will generally be less than 0.1 x 10 ⁵ Pa, preferably less than 0.05 x 10 ⁵ Pa, in particular less than 0.01 x 10 ⁵ Pa and especially less than 0.005 x 10 ⁵ Pa. These conditions lead on the one hand to distilling off oligomers with a lower molecular weight and on the other hand to a progress of the condensation reaction.

The process described here gives poly (alkoxy (semi) metalloxane) H with a branched structure. The poly (alkoxy (semi) metaloxanes) obtained in this way generally has a number average molecular weight Mn> 1600 daltons, frequently> 2000 daltons and in particular> 2200 daltons.

In the case of the particularly preferred condensation products, they have a silicon content of at least 23 and in particular at least 24% by weight. This corresponds to a weight fraction of at least 50% by weight of SiO ₂ . Despite their high metal oxide content, the poly (alkoxy (semi) metal oxanes) H thus produced are liquid and soluble in organic solvents.

The degree of branching of the poly (alkoxy (semi) metaloxanes) obtained in this way, in particular the polyalkyl silicates, is generally in the range from 0.2 to 0.8 and in particular in the range from 0.3 to 0.7. The content of unreacted compounds I in the products obtainable in this way is generally less than 5% by weight and in particular less than 2% by weight.

The molecular weight of poly (alkoxy (hal) metaloxanes) can be varied over a wide range by the method described above. The molecular weight depends on the reaction time or on the amount of ester III removed. The products obtained by the process described here generally have number average molecular weights M _n of at least 1600 daltons, for example 1600 to 20,000 daltons, preferably 2000 to 12000 and in particular in the range from 3000 to 10000 daltons, determined by means of gel permeation chromatography. (To record the absolute Molecular weights are calibrated using standards obtained by fractionation with a narrow molecular weight distribution.) By means of a thermal aftertreatment as described above, products with number average molecular weights above 3000 daltons, in particular above 4000 daltons, particularly preferably above 5000 daltons up to values above 6000 Dalton can be obtained.

In addition to the poly (alkoxy (semi) metal oxane), the first composition used according to the invention contains a finely divided material M in an amount of at least 5% by weight, preferably at least 10% by weight and in particular in an amount of 10 to 50 % By weight, based on the weight of the poly (alkoxy (hal) metaloxane).

The chemical nature of the finely divided material M is of minor importance. Examples of suitable finely divided materials are inorganic oxides such as aluminum oxide, titanium dioxide, zirconium dioxide, hafnium dioxide and silicon dioxide, inorganic carbonates such as calcium carbonate, and furthermore organic materials such as polymer powder, for example polytetrafluoroethylene powder or C ₂ -C ₄ polyolefin powder. Among the aforementioned fine-particle materials, oxidic powders and, in particular, silicon dioxide powders are preferred.

For the application according to the invention, it has proven to be advantageous if at least 90% of the particles of the finely divided material have a particle size below 100 μm, in particular below 50 μm and particularly preferably below 10 μm. The smallest diameter, which at least 90% by weight of the particles of the finely divided material have, is generally about 50 nm, preferably at least 100 nm and in particular at least 200 nm. The particles of the finely divided material preferably have a broad or polymodal eg a bimodal size distribution.

Among the aforementioned fine-particle materials, those are preferred which have a porous structure. Such materials M are generally characterized by a specific BET surface area of at least 1 m ² , preferably at least 10 m ² and in particular characterized by a specific surface area in the range from 10 m ² to 1000 m ² / g. Examples of such materials are so-called pyrogenic (semi-) metal oxides produced by flame hydrolysis, for example pyrogenic silicon dioxide, pyrogenic titanium dioxide, pyrogenic zirconium dioxide and precipitated silica. The particles in such materials are secondary particles (agglomerates) of very finely divided primary particles with particle sizes in the range from 1 to 100 nm, preferably in the range from 2 to 50 nm.

For the application according to the invention, it has also proven to be advantageous if the finely divided material has a hydrophobic surface. A hydrophobic surface is generally guaranteed if the surface has a large number of alkyl groups or (per) fluoroalkyl groups. In the case of the preferred finely divided oxidic materials, these groups are often in the form of (perfluoro) alkylsilane groups or (perfluoro) alkylsiloxane groups which are linked to an oxidic support material, for example by physical interaction or by covalent interaction. Fine-particle materials with a hydrophobic surface based on the aforementioned oxidic fine-particle materials are obtained, for example, by treating a non-hydrophobic fine-particle oxidic material with a suitable compound which enters into a chemical reaction with the free OH groups of the oxidic carrier material. Examples of such compounds are hexamethyldisilazane, alkyltrialkoxysilanes, for example octyltrimethoxysilane, silicone oils and mono-, di- and trichloroalkylsilanes, such as chlorotrimethylsilane or dichlorodimethylsilane. Hydrophobicized pyrogenic metal oxides are commercially available, for example, under the names Aerosil®, Acematt®, Sipernat®, Ultrasil® (all Degussa).

In addition to the aforementioned two components, the first composition can also contain an organic solvent in order to set a favorable processing viscosity. The viscosity of the first composition depends in a manner known per se on the desired application. In principle, all organic solvents which dissolve the poly (alkoxy (semi) metaloxane) in the desired concentration are suitable as solvents. It is only essential to the invention that this Preparation is essentially free of water to avoid premature hydrolysis of the poly (alkoxy (semi) metal oxane). This is usually guaranteed if the water content in the first composition is below 1000 ppm and in particular below 500 ppm.

Examples of suitable organic solvents are alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butanol, aliphatic and cyclic ethers such as diethyl ether, diisopropyl ether, methyl tert-butyl ether, tetrahydrofuran, dioxane, ether alcohols such as ethylene glycol , Methyl ether and diethylene glycol methyl ether, chlorinated hydrocarbons such as dichloromethane, trichloromethane, dichloroethane, aromatic hydrocarbons such as benzene, toluene, xylenes, tert-butylbenzene and the like and mixtures of the aforementioned organic solvents.

In the first compositions, the concentration of poly (alkoxy (semi) metalloxane) will generally be in the range from 10 to 60% by weight and preferably in the range from 20 to 50% by weight. Accordingly, the concentration of finely divided material M is generally in the range from 1 to 30% by weight, preferably in the range from 4 to 20% by weight, based on the total weight of the composition.

The first liquid composition is applied in a manner known per se, for example by knife coating, brushing, spraying or by spin coating.

The amount in which the first composition is applied to the substrate to be coated is generally of minor importance. The amount, based on the non-volatile constituents poly (alkoxy (semi) metaloxane) and finely divided material M 1, is preferably 1 to 500 g / m ² , in particular 10 to 300 g / m ² and especially 40 to 200 g / m ² .

Subsequently, the still moist (or liquid) coating obtained in this way is solidified in a conventional manner. For this purpose, volatile constituents will generally be removed and, if necessary, crosslinking of the Effect poly (alkoxy (semi) metalloxanes) H in a manner known per se. Before the second composition is applied, the coating obtained in step i) is preferably cured in an atmosphere containing water vapor. The curing can be carried out both at room temperature and at elevated temperature, preferably above 40 ° C. and in particular at at least 50 ° C. The upper limit of the curing temperature is of minor importance and, depending on the stability of the coated substrate, can be up to 1000 ° C, preferably up to 700 ° C. During the curing process, the alkoxy groups and the poly (alkoxy (semi) metal oxane) are first split off with crosslinking of the poly (alkoxy (semi) metal oxanes). As the temperature increases, the poly (alkoxy (semi) metal oxane) crosslinked in this way converts to the corresponding metal oxide.

Furthermore, it has proven to be advantageous if the curing is carried out in an atmosphere which, in addition to water vapor, also contains ammonia and / or volatile amines.

In a preferred embodiment of the invention, the curing is carried out at 50 to 200 ° C. and in particular in the range from 50 to 150 ° C. In a further preferred embodiment, this hardening is followed by hardening at elevated temperature, i. H. Temperatures above 200 ° C and in particular in the range of 400 to 700 ° C. This leads to an extensive to complete conversion of the poly (alkoxy (halI) metal oxanes) into the corresponding metal oxides.

There are basically no restrictions with regard to the substrates to be coated. However, preference is given to substrates whose surface has a large number of free OH and / or NH ₂ groups. Examples of such substrates are glass, wood, paper and ceramics. In the case of substrates whose surface does not have any OH or NH ₂ groups, it is advantageous to generate such groups in a manner known per se by activation, for example by plasma treatment in an oxygen atmosphere or by etching with acid. In step ii), a liquid composition is then applied to the coating thus obtained which contains at least one organofluorine substance with (per) fluoroalkyl groups. Here and below, (per) fluoroalkyl groups are understood to mean linear or branched alkyl groups which are optionally interrupted by one or more non-adjacent oxygen atoms, in which some or all of the hydrogen atoms are substituted by fluorine atoms. As a rule, these alkyl groups have 1 to 20 carbon atoms. Preferred (per) fluoroalkyl groups can be described by the general formulas a to d:

(CH ₂ ) _n - (CF ₂ ) _m F (a)

C ₆ H ₄ - (CF ₂ ) _k F (b)

(CF ₂ ) _k F (c)

[OCF ₂ CF (CF ₂ )] _q F (d)

Herein n stands for 1, 2, 3 or 4, m for 1 to 16, in particular 4 to 10, k for 1 to 14, in particular 6 to 10, and q for 1 to 10 and in particular 2 to 6.

In order to achieve a sufficient effect, the fluorine content in the organofluorine substance is generally at least 10% by weight and preferably at least 20% by weight, for example 20 to 80% by weight. The molar content of (per) fluoroalkyl groups in the organofluorine substance is generally at least 0.5 mol / kg, preferably at least 1 mol / kg and in particular at least 1.5 mol / kg, for example 1.5 mol to 10 mol / kg.

Examples of suitable fluoroorganic substances are partially fluorinated carboxylic acids and their alkyl esters, homo- and copolymers of ethylenically unsaturated monomers in which at least one monomer component has a (per) fluoroalkyl group and (per) fluoroalkylsilanes, which may also contain 1, 2 or 3 hydrolyzable groups such as alkoxy or have halogen.

In a preferred embodiment, the fluoroorganic substance is an organic homo- or copolymer with a CC backbone. Such polymers can be obtained by at least one ethylenically unsaturated monomer M1, which has at least one (per) fluoroalkyl group, and optionally one or more monomer M2, which are different from the monomers M1, homo- or copolymerized. Examples of suitable monomers M1 are the esters and the amides of monoethylenically unsaturated carboxylic acids such as acrylic acid and methacrylic acid with (per) fluoroalkanols of the formula IIIa, IIb or with (per) fluoroalkylamines purple - d:

HO (CH ₂ ) _a - (CF ₂ ) _b F (lla)

H [OCF ₂ CF (CF ₂ )] _q F (llb)

H ₂ N (CH ₂ ) _a - (CF ₂ ) _b F (purple)

HN [(CH ₂ ) _a - (CF ₂ ) _b F] ₂ (IIIb)

H ₂ NC ₆ H ₄ - (CF ₂ ) _k F (never)

H ₂ N (CH ₂ ) _r [OCF ₂ CF (CF ₂ )] _q F (llld)

wherein a is 0, 1, 2, 3 or 4, b is a value from 1 to 16 and in particular 4 to 10, k and q are as defined above and r is 2, 3 or 4. Examples of monomers M1 are furthermore derivatives of styrene which carry a (per) fluoroalkyl group or a group of the formula d on the benzene ring of styrene. Other suitable monomers are perfluorinated olefins. The proportion of monomers M1, based on the total amount of the monomers forming the organofluorine polymer, is generally at least 50 mol%, preferably at least 60 mol% and in particular at least 70 mol%, e.g. 50 to 99 mol%.

Suitable comonomers are in principle all monoethylenically unsaturated monomers copolymerizable with the monomers M1. Among these, preference is given to those comonomers which are nonpolar, in particular monoethylenically unsaturated olefins, esters of acrylic acid or methacrylic acid with C ₁ -C ₂ -alkanols, vinylaromatic compounds and the like (comonomers M2a). Suitable comonomers are also monoethylenically unsaturated carboxylic acids and dicarboxylic acids such as acrylic acid, methacrylic acid and maleic acid (comonomers M2b). However, the proportion of such comonomers is generally not more than 30 mol%, based on the total amount of the monomers constituting the fluoroorganic polymer be.

Such fluorine-organic polymers with a C-C backbone are sufficiently known from the prior art, for example from JP 09296134, JP 04120148, JP 03287615 and DE 10150954.

Suitable organofluorine polymers are also polymer-analogous reaction products of copolymers of maleic acid with alcohols of the general formula IIa, bwz. llb and / or amines of the general formula purple to llld. Suitable comonomers are the aforementioned monomers M1 and the aforementioned non-polar comonomers M2a. Such copolymers are known, for example, from DE 10150954.5 and from WO97 / 11218.

In another embodiment of the present invention, the second liquid composition contains a (per) fluoroalkylorganosilane which has at least two functional groups suitable for condensation with OH groups, such as C 1 -C ₄ -alkoxy or halogen. In addition to the fluoroorganic substance, the second liquid composition usually contains a solvent or dispersant. The second liquid composition is preferably a solution of the organofluorine substance in a suitable organic solvent. Suitable organic solvents are ketones, esters of aliphatic carboxylic acid, aliphatic and cycloaliphatic hydrocarbons, hydrocarbon mixtures such as mineral oils, aromatic hydrocarbons and in particular fluorinated organic solvents, for example fluoroalkanes, chlorofluoroalkanes and fluoroalkylbenzenes, e.g. B. Bistrifluoromethylbenzene.

To achieve a uniform coating of the surface with the organofluorine substance, it has proven to be advantageous if the second liquid composition contains the organofluorine substance in a low concentration and preferably at most 10% by weight, in particular in a concentration of 0.1 to 10% by weight. and contains in particular in a concentration of 0.5 to 5 wt .-%. The second liquid composition can be applied to the surface obtained in step i) in a manner known per se, for example by brushing, spraying, knife coating or rotary spinning. The application amount is preferably selected such that an coating with organofluorine substance in the range from 10 mg / m ² to 10 g / m ² , in particular 50 mg / m ² 5 g / m ^2, results. After removal of the volatile constituents of the second liquid composition, for example by evaporation, an ultrahydrophobic surface according to the invention is obtained.

The ultrahydrophobic surfaces obtained by this process are characterized by contact angles for water of> 130 °, in particular> 140 ° and particularly preferably> 150 °. Surprisingly, the surface is also characterized by low wettability for organic solvents, especially for hydrocarbons. In addition, the surfaces obtainable according to the invention have a self-cleaning effect in the sense of the lotus effect. In addition, the surfaces according to the invention are advantageously distinguished by good mechanical strength, in particular by high abrasion resistance.

The following examples are intended to illustrate the invention without, however, restricting it.

Examples

I. Production of poly (alkoxy (semi) metalloxanes)

Production Example 1: Branched poly (diethoxysiloxane) via the acetoxytriethoxysilane route

2.1 acetoxytriethoxysilane

In a reaction vessel equipped with a microdistillation bridge and gas inlet, 104 g (0.5 mol) of tetraethoxysilane and 51 g (0.5 mol) of acetic anhydride were heated to 137 ° C. for 36 hours in an argon atmosphere, with the result being that formed during the reaction Ethyl acetate distilled off (29.8 g; 0.34 mol). Subsequently, a fractional distillation (3 mbar, 30 cm Vigreux column) of the reaction mixture was carried out, 43 g (0.19 mol, 39% of theory) of acetoxytriethoxysilane having a boiling point of 61 ° C./3 mbar in 95% strength Purity ( ¹ H-NMR) was obtained.

¹ H-NMR (CDCI ₃ , 400 MHz): <5 (ppm) = 1, 25 (t, J = 7.1 Hz, 9H), 2.12 (s, 3H), 3.93 (q, J = 7.1 Hz, 6H).

2.2 Branched polyethoxysiloxane

In a reaction vessel, with the exclusion of water, an argon atmosphere of a 3 g of the acetoxytriethoxysilane obtained in 2.1 was stirred at 137 ° C. for 33 hours, the ethyl acetate formed during the polymerization being evaporated. After 33 hours, the reaction mixture was allowed to cool to room temperature and 1.0 g of the polymer (55% of theory) was obtained.

The branched poly (diethoxysiloxane) contained 22.5% by weight of silicon. The degree of branching according to Frey was 0.44. The number average molecular weight was 12,000 Daltons, the weight average molecular weight was 2220000 Daltons. Production Example 2: Branched poly (diethoxysiloxane) via the one-step route

In a reaction vessel equipped with a dephlegmator, distillation bridge with thermometer and gas inlet, 416 g (2 mol) of tetraethoxysilane (for synthesis, Merck), 204 g (2 mol) of acetic anhydride (pure, Merck) and 0.7 g (in a nitrogen atmosphere) were heated in a nitrogen atmosphere. 0.154 mol%) titanium ethylate (pure, Aldrich) with stirring to 130 ° C. 330.5 g (3.76 mol) of the ethyl acetate released during the reaction distilled off within 14.5 hours. Another 24 g of distillate could be removed in vacuo (1 mbar) at 40 ° C. 264.5 g (1.97 mol) of branched poly (diethoxysiloxane) were obtained as a yellowish, oily liquid.

263 g of the product thus obtained were heated at 130 ° C./1 mbar for 2 hours, and 70 g of tetraethoxysilane were removed at the same time. 193 g of polymer with a viscosity of 0.658 Pa.s. The number average molecular weight was 3600 daltons, the weight average molecular weight 18000 daltons.

Elemental analysis calculated: C 31, 39 H 6.57Si 24.05 found: C 31, 47 H 6.60Si 24.05

This corresponds to the empirical formula [SiO (OC ₂ H5) ₂ ] ₀ . 6_SiO ₂ ] o.24 ■

Production Example 3: Branched polyethylene titanate

3.32 g (14.55 mmol) of titanium (IV) ethylate (technical grade, Aldrich) were placed in a reaction vessel with a dropping funnel, drying tube, gas inlet for nitrogen and thermometer. While stirring with a magnetic stirrer, 1.31 g (12.83 mmol) of acetic anhydride (ultrapure, pa> 99%, Fluka) was added dropwise so that the internal temperature did not exceed 45.degree. The dropping funnel was then exchanged for a distillation bridge with a drying tube filled with silica gel and the flask was flushed with nitrogen. The mixture was heated to 130 ° C. for 24 hours, and the by-product was distilled into quantitative yield formed from ethyl acetate. 2.16 g (92% of theory) of the title compound were obtained as a yellowish, highly viscous substance.

The product had a titanium content of 29.3% by weight.

Production of the coatings according to the invention:

A glass plate was first treated with hydrogen peroxide / sulfuric acid, then cleaned with demineralized water and acetone.

To produce a first coating composition, 8 g of hydrophobic precipitated silica with an average particle size of about 2 μm (Acematt OK607, Degussa) were dispersed in 52 g of ethanol together with 40 g of the polyethoxysiloxane from preparation example 2. Subsequently, 200 .mu.l of the dispersion thus obtained were applied to the glass sheet in a "spin coater" and treated at 3000 rpm for 30 sec. The glass plate thus obtained was cured for one hour at 60 ° C. in an atmosphere saturated with ammonia and water.

200 .mu.l of a 1% by weight solution of a fluoropolymer (solution A) were then applied to the coating thus obtained and the coating thus obtained was dried.

The coating thus obtained showed a contact angle for water> 150 °.

Solution A of the fluoroorganic polymer was a 1% by weight solution of a copolymer

Heptadecafluorodecyl methacrylate with maleic anhydride in a molar ratio of 97: 3 and 1,3-bis (trifluoromethyl) benzene. Example 2:

A coating was produced analogously to Example 1, with a commercially available solution of a fluoropolymer (Rukogard, 1% by weight, Rudolph Chemie) being used instead of solution A of the fluoroorganic polymer. The surface so obtained was also ultrahydrophobic.

Example 3:

A coating was produced analogously to Example 1, with 5 parts by weight of precipitated silica being used instead of 8 parts by weight of precipitated silica. The contact angle for water was above 150 °.

Example 4:

A coating was produced analogously to Example 1, a 1% by weight solution of a terpolymer of heptadecafluorodecyl methacrylate, maleic anhydride and butyl methacrylate in a molar ratio of 48:24:28 being used instead of solution A. The contact angle for water was above 150 °.

Example 5:

A coating was produced analogously to Example 1, the polyethoxysiloxane from Preparation Example 2 being used instead of the polyethoxysiloxane from Preparation Example 2. The contact angle for water was above 150 °.

Example 6:

A coating was produced analogously to Example 1, the process being carried out in place of the polyethoxysiloxane from Preparation Example 2 Polyethylene titanate from Preparation Example 3 was used. The contact angle for water was above 150 °.

Comparative Example:

A coating was produced analogously to Example 1, monomeric tetraethyl silicate being used instead of the polyethoxysiloxane from Preparation Example 2. In contrast to the coatings of Examples 1 to 6, the coating thus obtained was not resistant to abrasion and could be wiped off with a cloth.

Claims

claims

1. A method of making ultrahydrophobic surfaces on substrates comprising:

i) Application of a first liquid, non-aqueous composition comprising at least one poly (alkoxy (semi) metalloxane H which is liquid at room temperature and at least one finely divided material M in an amount of at least 5% by weight, based on the weight of H , contains, on at least one surface of the substrate,

2. The method of claim 1, wherein the poly (alkoxy (semi) metaloxane) is a polyalkoxysiloxane.

3. The method of claim 1 or 2, wherein the poly (alkoxy (semi) metalloxane) has a number average molecular weight of at least 1000 daltons.

4. The method according to any one of the preceding claims, wherein the poly (alkoxy (semi) metal oxane) has a degree of branching according to Frey in the range of 0.2 to 0.8.

5. The method according to any one of the preceding claims, wherein the poly (alkoxy (semi) metalloxane) is obtainable by condensation of tetraalkyl metallates in the absence of water.

6. The method according to any one of the preceding claims, wherein at least 90 wt .-% of the particles of the finely divided material M have a diameter below 100 microns.

7. The method according to claim 6, wherein the finely divided material M has a porous structure.

8. The method according to claim 6 or 7, wherein the particles of the finely divided material M have a hydrophobic surface.

9. The method according to claim 8, wherein the finely divided material is selected from hydrophobicized precipitated silica and hydrophobicized pyrogenic silica.

10. The method according to any one of the preceding claims, wherein the first composition in an amount of 1 to 500 g / m ² , based on poly (alkoxy (semi) metaloxane and finely divided material) is applied to the surface to be coated.

11. The method according to any one of the preceding claims, wherein before the application of the second composition, a curing of the coating obtained in step i) is carried out in an atmosphere containing water vapor.

12. The method according to any one of the preceding claims, wherein the substrate surface has a plurality of OH groups.

13. The method according to any one of the preceding claims, wherein the substance with (per) fluoroalkyl groups is an organic polymer with a C-C backbone.

14. The method according to any one of claims 1 to 12, wherein the substance with (per) fluoroalkyl groups is a (per) fluoroalkylorganosilane which has at least two functional groups suitable for condensation with OH groups.

5. An article having at least one ultrahydrophobic surface which is obtainable by a method according to any one of the preceding claims.