SI22911A - Preparation of tio2/sio2 sols and their use for application of self-cleaning and antifogging coatings - Google Patents

Abstract

The subject of the invention refers to a procedure of low-temperature preparation of TiO2/SiO2 sols and their use for application of thin optically permeable coatings with self-cleaning and antifogging properties. The preparation according to the invention is characterised in that the procedure consists of preparation of an acid water sol which contains photochemically active TiO2 nanoparticles and of addition of an SiO2 precursor followed by hydrolysis/condensation of SiO2 and organically modified SiO2, addition of amorphous TiO2 hydrolysate, addition of colloid SiO2, dilution of the prepared sol with water and/or organic solvents, application of the prepared sol on a substrate, evaporation of solvents and condensation reactions at a room temperature, to create a thin uniform layer of TiO2/SiO2 with self-cleaning properties.

Description

Preparation of TiO ₂ / SiO ₂ salts and their use for the application of self-cleaning and anti-corrosion coatings

The subject of the invention relates to the process of low-temperature preparation of TiO ₂ / SiO ₂ salts and their use for the application of thin, optically permeable coatings with self-cleaning and anti-corrosion properties. The invention therefore provides the preparation of optically permeable and persistent thin coatings with photocatalytic and hydrophilic properties from TiO ₂ / SiO2 colloidal solutions, i.e. salts.

On surfaces exposed to atmospheric influences and atmospheric pollution due to human activity, over time, various macroscopic particles and individual molecules of organic and inorganic origin are adsorbed. Dirt that accumulates on surfaces is both aesthetically pleasing and, in some cases, a safety issue. Dirt is most disturbing on substrates that are permeable to visible light, that is, on various glass and transparent organic polymers. Cleaning such surfaces is often a time-consuming and dangerous task, and chemicals are used for cleaning, which represents both a financial and environmental burden.

One way to keep surfaces clean for a long time is to use thin protective coatings applied to the substrate. There are two options: hydrophobic and hydrophilic coatings. Hydrophobic surfaces are characterized by the fact that the contact angle between the applied water droplet and the substrate is very large (> 150 °) and the circular water droplet with dirt consequently does not adhere to the substrate. Several methods are known for the preparation of hydrophobic surfaces using special polymers or waxes, which coat the surface by physical methods, i.e., by compression of polymer droplets, or by ion etching or chemical methods, e.g. chemical vapor deposition - KPO. Although the resulting surfaces have good self-cleaning properties, disadvantages in the preparation and stability of the resulting surfaces, this is a costly coating of the substrates, the coatings are often misty, the durability of the coatings is limited in time, preventing their wider applicability.

Another possible solution is hydrophilic coatings, which are often various semiconductor oxides of transition metals, e.g. ZnO, ZrO ₂ , TiO ₂ , WO ₂ , etc. In the presence of UV radiation and water molecules, chemical changes occur on their surface, which in turn become very hydrophilic; contact angle between the surface and the water droplet below 5 °. High hydrophilicity increases adhesion

-2 water, so that water easily flushes out poorly adsorbed inorganic particles, such as e.g. sand.

However, hydrophilicity is not the only reason for the self-cleaning properties of semiconductor oxides. Another important self-cleaning property is photocatalytic efficiency. When a particle of a semiconductor absorbs a photon of electromagnetic wave of suitable energy, most often photons of the UV part of the spectrum, a transition of the valence electron into the conduction band occurs. The resulting positive gap is a strong oxidant, and the electron plays the role of a reducing agent. Both can react with molecules adsorbed on the surface of a particle, resulting in oxidation of the molecules by the positive gap and the reduction of the molecules by the electrons. Thus, the complete mineralization of organic molecules gradually leads to CO2, H2O and inorganic acids. Of all the oxides studied so far, anatase T1O2 has proven to be the most suitable photocatalyst because it is non-toxic, chemically and physically stable, inexpensive, etc. Only nanocrystalline T1O2 is useful for window cladding because only nanocrystalline coatings can be made sufficiently optically permeable for commercial use. The classic preparation of anatase T1O2 requires firing from salts of prepared powders or thin films above 350 ° C. At lower temperatures, the anatase crystalline phase is not formed, which is crucial for photocatalytic efficiency. This required high temperature limits the applicability of that method. Such methods can only be used in specialized factories, e.g. in glass manufacturing companies. A commercial product that uses heat treatment at high temperatures is Pilkington Activ (TM). It is a glass coated with a 20-30 nm thick layer of nanocrystalline anatase TiO2. The layer is mechanically stable, photocatalytically active with extremely high transmittance in the visible part of the spectrum. Floating glass KPO techniques are used in the coating.

For the wider applicability of self-cleaning T1O2, it is necessary to prepare a T1O2 salt, which can be applied to surfaces under normal atmospheric conditions, which does not require additional thermal treatment and which results in optically transparent and solid coatings. In an article by Ichinose, H.; Terasaki, M.; Katsuki, H. J Sol-Gel Sci Technol 2001, 22, 33-40 describes the preparation of a peroxo-modified anatase salt that is useful for low-temperature photocatalytic coating preparation. The prepared glass coated glasses are photocatalytically active and the adhesion of the coatings to the substrate is satisfactory. However, the optical quality of the prepared coatings is not reported. The downside is also the rather demanding preparation of salt, using a considerable number of chemicals.

-3In an article by Matsuda, A.; Matoda, T.; Kotanim Y .; Kogure, T.; Tatsumisago, M.; Minami, T. J Sol-Gel Sci Technol 2003, 26, 517-521 describes the preparation of nanocrystalline coatings on glass and on organic optically permeable polymers, achieving crystallization of TiO ₂ into anatases by treating hot water coatings. Due to the higher strength of the coating, its salts also contain SiO ₂ precursors. The coatings are photocatalytically active, the adhesion to the surface of the substrate and the hardness of the coating are satisfactory. The downside of film making is the impractical treatment of boiling water coatings for commercial use.

U.S. Patent 5,149,519 discloses the preparation of a low-temperature salt containing crystalline anatase TiO ₂ and does not use the prepared salt to prepare thin TiO ₂ layers.

In article Yun, YJ; Chung, JS; Kirn, S.; Hahn, SH; Kirn, EJ Mater Lett 2004, 58, 37033706 describes the preparation of a nanocrystalline TiO ₂ coating on ordinary sodium glass at low temperatures, with Yun et al. prepared a titanium tetraisopropoxide salt in acidic aqueous solutions, which was refluxed for several hours to obtain crystallization of amorphous TiO ₂ . The method of salt preparation using conventional chemicals and technologically simple process as well as the ease of applying the prepared salt to different substrates are advantages of the system under study. By design, it is also closest to the present invention, which in our case further comprises an additional SiO ₂ component to achieve better mechanical and hydrophilic properties of the coatings.

EP 0 913 447 discloses the preparation of self-cleaning liquids for various substrates using commercially available TiO ₂ and SiO ₂ salts. In the preparation of self-cleaning liquids, they also use various additives, such as surfactants, organic solvents, silicones. The coatings are photocatalytically active and the adhesion to the surface of the substrate and the hardness of the coatings are good in certain cases. A disadvantage of the invention is the use of commercially available TiO ₂ and SiO ₂ salts. In the patent EP 1 544 269, the invention is made of commercial TiO ₂ nanocrystalline particles and SiO ₂ colloidal solutions, thereby adding a binder made of hydrolyzed titanium alkoxide. The coatings thus obtained have good mechanical and hydrophilic properties even in the dark.

EP 0 826 633 discloses the preparation of aqueous dispersion and a thin transparent TiO ₂ coating in the low temperature route of T1CI4, which is a much cheaper raw material than any titanium alkoxide, but the removal of chloride ions by electrodialysis is required in this process. In the patent document WO 2004/060555, the invention is based on titanium peroxide salts and nanoanatase particles with the addition of urethane acrylic polymers to improve the wettability of the coating surface and to reduce the contribution of the yellow coloration in thin layers by the peroxide process. The non-volatile organic additives introduced have the disadvantages of having good sides

-4view of the additional chemical in the synthesis and the associated additional cost and in view of the questionability of the long-term integrity of such thin layers due to the degradation of organic matter in the photocatalysis process. There are more patent documents, e.g. WO 2004/108846 and WO 2004/005577 dealing with the preparation of photocatalytically active hybrid organic-inorganic thin films based on siloxanes and TiO ₂ dispersions or salts.

A technical problem that has not been satisfactorily solved so far is thin optically permeable coatings with self-cleaning and anti-scouring properties, which will be based on a simple process of preparing salts from accessible and not expensive chemicals, where it will be an easy way to apply salt to the substrate without further hardening the layers with thermal treatment where there will be a good relationship between the mechanical strength and the photocatalytic effect of the thin coating, where there will be high optical transmittance of the coating over the entire visible spectrum and high hydrophilicity of the coating in the presence of UV radiation.

The object of the invention is such a process of low-temperature preparation of TiO ₂ / SiO ₂ salts and their use for the application of thin, optically permeable coatings with self-cleaning and antifouling properties, which will be based on the simple process of preparing salts from accessible and not expensive chemicals, which will be an easy way of applying salt to the substrate without further hardening of the layers by thermal treatment, where there will be a good ratio of mechanical strength to the photocatalytic effect of the thin coating, where there will be high optical transmittance of the coating over the entire visible spectrum and high hydrophilicity of the coating in the presence of UV radiation.

According to the invention, the problem is solved by the process of preparing TiO ₂ / SiO ₂ salts and their use for applying thin coatings according to an independent claim.

The invention will be described by way of embodiments and illustrations showing:

Figure 1: X-ray diffractograms of a sample prepared from thin TiO ₂ / SiO ₂ layers according to the procedure in Example 7.

Figure 2: Demonstration of photocatalytic activity of prepared self-cleaning layers.

Figure 3: UV-Vis spectrum of the TiCh / SiCh thin layer on the glass compared to the glass itself.

According to the invention, the preparation of the anatase TiO ₂ salt is first carried out, followed by the preparation of the photocatalytically active liquid and its application to different surfaces.

The first part of the invention is a modification of the process for preparing an anatase TiO ₂ salt made in acidic aqueous media at temperatures up to 100 ° C. As a basis, we used the process of preparation of low-temperature TiO ₂ sol, published in 2004 by Yun et al. By modifying their process, we were able to prepare a stable salt with weakly aggregated TiO ₂ particles, in which anatase crystalline phase was demonstrated by X-ray diffraction. The prepared TiO _{2 is} very easily dispersed in water and a mixture of water and certain organic solvents to give stable salts.

(i) Titanium tetrachloride (T1CI4), titanium oxysulphate (TiOSCL) or various titanium alkoxides may be used as the source of TiO ₂ . Preferably titanium tetraisopropoxide TTIP is used. TTIP (5 to 45 mL) was added while stirring at room temperature to absolute ethanol (between 1 and 10 mL). Immediately thereafter, the resulting liquid mixture was added dropwise with an aqueous acid solution while stirring at room temperature. In the presence of acid, the hydrolysis reaction of the titanium compounds takes place, leaving a weakly soluble, amorphous titanium oxide from the reaction mixture. The inorganic acids used are conc. HNO3, conc. HCIO4, conc. HCl and conc. H ₂ SO4, the organic acids used are formic, ethanoic, propanoic. Aqueous acid solution was prepared by mixing water (between 30 and 100 mL) and concentrated acid (between 0.1 and 10 mL). The preferred acid concentration is between 1 and 3 mL of acid in 90 mL of water. Too low and high acid concentrations lead to the aggregation of TiO ₂ particles, which is an undesirable process if we want to produce as transparent a coating as possible. HCIO4 has been shown to be the preferred acid.

(ii) TiO ₂ is photocatalytically active in crystalline form, be it anatase or rutile. The anatase crystalline form is more photocatalytically active than rutile. Crystallization of amorphous TiO ₂ into crystalline form is achieved by heating the salt. The advantages of the present invention are: a) crystallization is already achieved by heating to a temperature below 100 ° C; b) crystallization and dispersion of TiO ₂ particles is achieved directly in the aqueous salt, ie without additional stages of separation and resuspension of TiO ₂ . The resulting suspension from (i) is refluxed for 2 to 100 hours. The optimum reflux time is between 30 and 60 hours. The shorter reflux time is reflected in the unfinished crystallization of TiO ₂ , but the longer time does not lead to a significant increase in the activity of sol or. the resulting coatings. After refluxing, a basic colloidal solution of crystalline TiO ₂ (basic TiO ₂ salt) is obtained. The basic TiO ₂ salt is stable at room temperature for at least 1 year. The weight fraction of TiO ₂ in the salt is between 2 and 10%. The size of TiO ₂ particles in the sol obtained from dynamic light scattering measurements (3D DLS SLS apparatus) is between 15 and 80 nm.

The second part of the invention relates to the preparation of a photocatalytically active liquid consisting of (i) anatase TiO ₂ particles; (ii) a binder made by mixing colloidal SiO ₂ and hydrolyzed and condensed molecules of silicon alkoxides and organosilanes; (iii) a binder made by hydrolysis and condensation of titanium alkoxide; (iv) an organic solvent and (v) water. The process for preparing a photocatalytically active liquid is as follows.

In particular, a solution or salt containing SiO ₂ , i.e. a binder, is prepared. The appropriate silicon alkoxide or mixture of silicon alkoxides or silicon alkoxide and the corresponding organosilane are mixed together with a commercially available colloidal solution of SiO ₂ . A constant volume of inorganic acid is added during constant stirring. After ten minutes, add a certain volume of any of the lower primary alcohols to the salt. The salt thus prepared can be used after 24 hours of mixing and should then be used for further work within 3 weeks. All phases are carried out between 15 and 30 ° C.

A pre-prepared binder is added to the metered volume of TiO ₂ aqueous salt, the preparation of which is described in the first part of the invention. Then water is added to the prepared salt and the organic solvent is stirred. All phases are carried out between 15 and 30 ° C.

(i) The aqueous TiO ₂ salt described in the first object of the invention is used as the source of the anatase TiO ₂ particles. TiO ₂ is a mandatory component of the photocatalytically active liquid. Without this, no self-cleaning coating or coating can be prepared because TiO ₂ is the component that has self-cleaning properties (both superhydrophilicity and photocatalytic activity). The water content of the aqueous TiO ₂ salt in the final liquid is between 0.5 and 50%. Too low TiO ₂ concentration leads to the formation of optically high quality and completely permeable coatings, which, due to the low TiO ₂ concentration, have a low photocatalytic activity. Too high concentration of TiO ₂ in the final fluid leads to photocatalytically very active coatings, which do not meet optical standards.

(ii) The main components of the SiO ₂ binder are the corresponding silicon alkoxide and the colloidal SiO ₂ . Alkoxy groups in silicon alkoxide contain from 1 to 4 carbon atoms. Examples of tetraalkoxysilanes are tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane ... The most preferred tetraalkoxysilane is tetraethoxysilane (TEOS). SiO ₂ hydrolyzate increases 1) the strength and abrasion resistance of the final coating, 2) increases and prolongs the superhydrophilic effect of the final coating. It can also be used in addition to tetraalkoxysilanes

-7different organosilanes having an attached organic group instead of one alkoxide group. Such a group may be saturated, e.g. methyl, ethyl, octyl, phenyl, and the corresponding organosilanes are methyl triethoxysilane, ethyl triethoxysilane, octyl triethoxysilane and phenyl triethoxysilane. Bis (triethoxysilyl) octane also belongs to this group of organic silanes, and its special feature is the possibility of cross-linking via Si-0 bonds at both ends of the organic chain. The use of such organosilanes is intended to reduce the brittleness of the TiO ₂ thin layer, and in particular bis (triethoxysilyl) octane also acts as a crosslinker, which increases the strength of the final layer.

Alternatively, organosilanes have an unsaturated carbon-carbon bond instead of one alkoxy group, most often using epoxies or acrylates. The most preferred organic silane is 3-glycidoxypropyl trimethoxysilane (GPMS). The function of organically modified silanes is to increase the strength of the prepared thin film as a result of polymerization reactions between organic groups. The initiation of such polymerization does not require radical conditions, but can be carried out at slightly elevated room temperature with the aid of catalysts or the reaction can be initiated by UV radiation. These organosilanes thus further solidify the thin layer of the photocatalyst at low temperatures. Too high a hydrolyzate concentration in the final photocatalytically active liquid reduces the photocatalytic activity of the prepared self-cleaning coating because it reduces the density of the photocatalytically active TiO ₂ particles in the final self-cleaning coating. Too low a concentration of SiO ₂ hydrolyzate reduces the strength of self-cleaning coatings. The molar ratio of Ti from the anatase TiO ₂ sol to Si from the SiO ₂ hydrolyzate is between 3: 1 to 0.5: 1, the preferred ratio being between 2: 1 to 1: 1.

Colloidal SiO ₂ is a colloid prepared by dispersion of very pure SiO ₂ in aqueous medium. The average size of SiO ₂ particles must be between 1 and 200 nm in order to avoid visible light scattering on the particles. The advantage of colloidal SiO ₂ SiO ₂ hydrolysates from their greater stability in water. Namely, the SiO ₂ hydrolyzate can be slowly dissolved in water because the hydrolysis and condensation reactions are not yet complete. Otherwise, the colloidal silica nanoparticles are completely condensed and therefore have a higher water resistance. The main functions of colloidal silica in the final photocatalytic fluid are 1) to increase the abrasive resistance of the self-cleaning coating; 2) increase in the superhydrophilicity of the self-cleaning coating. The patent described uses commercially available colloidal silica, namely Levasil 200/30% or 300/30% or 200/30% A (manufactured by HC Starck GmbH) and Snowtex IPA-ST (manufactured by Nissan Chemical Industries, Ltd.). The molar ratio of Ti of the anatase TiO ₂ sol (i) to Si of colloidal silica (iv) is between 3: 1 to 0.1: 1.

-8The classic preparation of a binder is carried out by mixing the appropriate silicon alkoxide or mixture of silicon alkoxides or silicon alkoxide and the corresponding organosilane together with a commercially available colloidal solution of SiO ₂ , e.g. with Levasil 200/30%. The molar ratio between Si from the corresponding silicon alkoxide (and / or organosilane) and between Si from colloidal SiO ₂ is between 2: 1 to 1: 2. Levasil 200/30% also contains sufficient water, which is necessary for the further phase in the hydrolysis of silicon compounds. During constant stirring of the prepared mixture, an appropriate volume of strong inorganic acid is added, which may be nitric (V) acid, hydrochloric acid, sulfuric (VI) acid, chlorine (VII) acid. The molar ratio between the protons of acid and Si of the corresponding alkoxide (or organosilane) is between 1:10 and 1:20. After ten minutes, a certain volume of any of the lower primary alcohols, e.g. 1-propanol, ethanol, 1 butanol. The binder to alcohol ratio is between 1: 1 and 1: 3. The salt thus prepared can be used after 24 hours of mixing and should then be used for further work within 3 weeks. All phases are carried out between 15 and 30 ° C.

In certain cases, the corresponding silicon alkoxide was mixed directly into the nanocrystalline TiO ₂ salt. In such a case, the procedure was as follows. Appropriate silica alkoxide was added to the metered volume of TiO ₂ aqueous salt. It is stirred at room temperature for 1 to 24 hours, thereby achieving hydrolysis and condensation of the SiO ₂ precursor. Then add other components to the prepared salt.

(iii) TiO ₂ hydrolyzate has the function of a binder of colloidal SiO ₂ and colloidal TiO ₂ particles and has the function of a catalyst for the polymerization of epoxy organic silanes. It is not a condition that both the SiO ₂ hydrolyzate and the TiO ₂ hydrolyzate are present simultaneously in the self-cleaning fluid. Titanium alkoxides whose alkoxy groups contain from 1 to 4 carbon atoms are used as the precursor of TiO ₂ . Examples of titanium tetraalkoxides used are titanium tetramethoxide, titanium tetraethoxide, titanium tetrapropoxide, titanium tetraisopropoxide, titanium tetrabutoxide. For the sake of affordability and sufficiently high stability, the most suitable candidate is titanium tetraisopropoxide (TTIP). TiO ₂ hydrolyzate is prepared separately. It is prepared so that in a mixture of water (between 0.5 and 2 mL), the conc. HNO3 (between 0.5 and 2 mL) and an organic solvent (between 4 and 10 mL) were added dropwise a mixture of titanium alkoxide (between 10 and 30 mL) and an organic solvent (between 5 and 15 mL). The optimum molar ratio of water to titanium alkoxide must be between 1: 1 and 3: 1, and in any case less than 4: 1. A higher molar ratio of water to titanium alkoxide leads to complete hydrolysis and condensation of titanium alkoxide. Fully condensed titanium alkoxide loses the function of the binder. The resulting mixture was stirred at room temperature between 2 and 10

-9hours to achieve hydrolysis and condensation of titanium alkoxide. The prepared hydrolyzate does not contain crystalline TiO ₂ , in that it differs from TiO ₂ sol (i). Finally, dilute the prepared hydrolyzate with an organic solvent so that the final weight fraction of TiO _{2 is} between 1 and 5%. Monoalkyl ethers of various glycols having good wettability of partially hydrophobic surfaces such as e.g. glass. The organic solvent exemplified was 2methoxyethanol, propylene glycol butyl ether, 2-propoxyethanol. The prepared TiO ₂ hydrolyzate was added to TiO ₂ salt (s), giving a molar ratio of Ti in the anatase TiO ₂ grains (i) to Ti in the TiO ₂ (iii) hydrolyzate between 5: 1 and 1: 1.

(iv) Unless an organic solvent is added to a self-cleaning liquid (otherwise based on water), the prepared salt cannot be uniformly applied to the substrate, since after the solvent has evaporated, a thin, thin TiO ₂ layer remains. The main function of the organic solvent is thus to increase the wettability of the self-cleaning liquid on various substrates, especially hydrophobic ones (glass and polymeric substrates such as polyacrylates, polycarbonates, polyethylene, polypropylene, polystyrene ...). As the wettability of the substrate is increased with the use of organic solvents, the proper selection of more viscous solvents makes it very easy to apply a thicker layer of self-cleaning fluid to the substrate, which is reflected in the higher photocatalytic activity. The organic solvents used must not be too volatile to allow them to evaporate at room temperature for a short period of time at the same time as they must not have a boiling point below 100 ° C to prevent them from evaporating from the surface before water. The organic solvents used must be at least partially soluble in water because the self-cleaning liquid contains a high proportion of water. Furthermore, the solvents used must not cause the aggregation of TiO ₂ anatase grains. A further condition is the non-toxicity of the compounds used and the low flammability. Monoalkoxy ethers of various glycols and mixtures of monoalkoxy ethers of glycols and primary alcohols with less than 4 carbon atoms have proved to be an appropriate choice. The best combination was 2-propoxyethanol in combination with 1-propanol, 2-methoxyethanol in combination with 1-butanol. The percentage by volume of organic solvent sum must be less than 0.8 in the final photocatalytic fluid. If higher, TiO ₂ aggregation occurs. If the content of organic solvents is too low, it becomes difficult to evenly coat a sufficiently thick TiO ₂ / SiO ₂ layer on the surface. The optimum percentage by volume of organic solvent sum is between 0.5 and 0.8.

(v) Water is added to the final photocatalytic fluid to cheapen the product and to maintain the stability of the prepared photocatalytically active liquid. Too much organic solvents lead to salt destabilization, resulting in the aggregation and deposition of TiO ₂ . Such a product is gone

-10usable. The water content of the final photocatalytically active liquid must be between 0.7 and 0.2.

A third part of the invention is the deposition of photocatalytically active fluids on various surfaces. Surfaces can be transparent to visible light, such as. glass, polypropylene, polyethylene, polystyrene, various polyacrylates, polycarbonate ... The self-cleaning fluid can also be applied to light-tight surfaces: concrete, tiles, ceramic tiles, wood, brick ... The surface to which the self-cleaning fluid should be applied must be clean and dry. Different application methods are used: (i) spraying the liquid with the help of sprays; (ii) application of the fluid by means of a roller; (iii) application of a liquid by brush; (iv) application of a liquid by means of a cloth; (v) immersion of the object in self-cleaning fluid.

(i) Pour the resulting self-cleaning fluid into a sprayer, which can be manual or electric, and spray on the desired surface until a homogeneous layer of liquid is formed on the surface.

(ii) The roller is immersed in a self-cleaning fluid and then applied to the surface, leaving a homogeneous layer of liquid behind the roller which dries at room temperature.

(iii) Soak the brush in self-cleaning fluid and then coat the surface, leaving a homogeneous layer of liquid behind the brush that dries at room temperature.

(iv) Removing the cloth over the surface leaves a very thin trace of salt behind the cloth, which dries quickly and hardens. The resulting layer is very thin.

(v) Immerse the object to be coated with the self-cleaning layer in the self-cleaning liquid. The object is then uniformly withdrawn from the liquid, with the excess fluid draining off, and the remaining self-cleaning fluid on the object is dried at room temperature and cured.

In all the above cases, after application, a thin liquid layer is left on the surface of the substrate, which dries at room temperature to form a solid, semi-crystalline self-cleaning coating which is transparent to visible light. Its thickness is less than 100 nm, and in most deposition methods it is less than 20 nm, which, given its high optical quality, is also sufficient for a good self-cleaning effect. The coating does not need to be (but can be) further cured by heating. The coating is temperature resistant (X-ray diffractograms show the persistence of the anatase phase up to 1000 ° C and only then begins to transition to rutile), has proven self-cleaning properties, its hydrophilicity is expressed in the dark, and further increases under the influence of UV radiation.

-11This coating is also useful on surfaces where we have blurring problems. This prevents various mirrors (such as car rearview mirrors, bathroom mirrors, saunas) and lenses (such as prescription glasses) from blurring.

The invention is explained, but by no means limited, by the following embodiments.

Example 1

TTIP (15 mL) was dissolved in absolute ethanol (2.5 mL). Particularly, 70% perchloric acid (1 mL) and water (90 mL) were mixed. This solution was added dropwise to TTIP solution while stirring. An exothermic reaction of uncontrolled hydrolysis and condensation of TTIP takes place, resulting in a white precipitate of hydrated, amorphous T1O2. The resulting mixture was refluxed for 48 hours, crystallizing and deaggregating T1O2. After heating, a stable basic salt is obtained.

Example 2

TTIP (15 mL) was dissolved in absolute ethanol (2.5 mL). 65% nitric acid (1) and water (90 mL) were mixed separately. This solution was added dropwise to TTIP solution while stirring. An exothermic reaction of uncontrolled hydrolysis and condensation of TTIP takes place, resulting in a white precipitate of hydrated, amorphous T1O2. The resulting mixture was refluxed for 48 hours, crystallizing and deaggregating TiO ₂ . After refluxing, the salt was cooled and filtered through filter paper. Discard the insoluble residue on the filter paper.

Example 3

The basic anatase T1O2 salt was prepared by the same procedure as described in Example 1, except to change the ratio of TTIP, HCIO4 to water. In this case, 15 mL TTIP, 45 mL water, and 3 mL HCIO4 were used.

Example 4

The basic anatase T1O2 salt was prepared by the same procedure as described in Example 1, except to change the ratio of TTIP, HCIO4 to water. In this case, 15 mL TTIP, 45 mL water, and 1 mL HCIO4 were used.

Example 5

-12The basic anatase TiO ₂ salt was prepared by the same procedure as described in Example 1, except to change the reflux time. In this case, the salt was refluxed for 24 hours.

Example 6

A mixture of TEOS (1.11 mL) and colloidal SiO ₂ Levasil 200/30% (0.42 mL) was added 30 pL of 32% HCl while stirring. After stirring at room temperature for 10 minutes, 1propanol (5 mL) was added and allowed to stir for 24 hours to complete the hydrolysis of TEOS. The content of hydrolyzed and colloidal SiO ₂ in the prepared hydrolyzate is 8.1%.

Example 7

A mixture of TEOS (1.11 mL) and colloidal SiO ₂ Levasil 200/30% (1.7 mL) was added 30 pL of 32% HCl while stirring. After stirring at room temperature for 10 minutes, 1propanol (5 mL) was added and allowed to stir for 24 hours to complete the hydrolysis of TEOS. The content of hydrolyzed and colloidal SiO ₂ in the prepared hydrolyzate is 11.5%.

Example 8

The basic salt of Example 1 (6 mL) was removed and the SiO ₂ salt of Example 6 (6 mL) was added. The mixture was stirred at room temperature and 8 mL of water was added followed by 12 mL of 1-propanol, finally 39 mL of 2-propoxyethanol. In the salt thus prepared, the molar ratio of Ti to Si is 1: 2.3, and the concentration of TiO ₂ in the salt is approximately 3.3 g / L. The prepared salt is stable for at least half a year.

To prepare the thin layer, take the cleaned glass surface in a vertical position. Pour the salt into the sprayer, then spray the salt over a vertically positioned surface so that it is poured over the whole. Allow the excess liquid to drain from the glass surface and the rest to dry on the surface. Allow the resulting layer for at least one week at temperatures above 20 ° C to allow the final condensation of SiO ₂ and the hardening of the thin layer.

Example 9

Remove the base salt of Example 1 (6 mL) and add the SiO ₂ salt of Example 7 (6 mL). The mixture was stirred at room temperature and 8 mL of water was added followed by 12 mL of 1-propanol, finally 39 mL of 2-propoxyethanol. In the salt thus prepared, the molar ratio of Ti to Si is 1: 3.75, and the concentration of TiO ₂ in the salt is approximately 3.3 g / L. The prepared salt is stable for at least half a year.

To prepare the thin layer, take the cleaned glass surface in a vertical position. Pour the salt into the sprayer, then spray the salt over a vertically positioned surface so that

-13 pours over the whole. Allow the excess liquid to drain from the glass surface and the rest to dry on the surface. Leave the resulting layer for at least one week at temperatures above 20 ° C to allow the final condensation of S1O2 and the thin layer to solidify.

Example 10

Remove the base salt from Example 1 (6 mL) and add the SiO2 salt from Example 7 (6 mL). Stirred at room temperature and added 7.5 mL of 1-propanol and finally 27 mL of 2-propoxyethanol. In the salt thus prepared, the molar ratio of Ti to Si is 1: 3.75, and the concentration of T1O2 in the salt is approximately 5 g / L. The prepared salt is stable for at least half a year.

To prepare the thin layer, take the cleaned glass surface in a vertical position. Pour the salt into the sprayer, then spray the salt over a vertically positioned surface so that it is poured over the whole. Allow the excess liquid to drain from the glass surface and the rest to dry on the surface. Leave the resulting layer for at least one week at temperatures above 20 ° C to allow the final condensation of S1O2 and the thin layer to solidify.

Example 11

The basic salt of Example 1 (5 mL) was removed and TEOS (450 pL) was added. A two-phase system is formed because TEOS is poorly soluble in aqueous medium. It is stirred at room temperature, resulting in the gradual hydrolysis and condensation of TEOS. After 12 hours, TEOS as the basic precursor is no longer present, and the salt still retains its stability. To the prepared mixed salt was added 40 mL of water, 85 mL of 2-methoxyethanol and 85 mL of 1-butanol and stirred well. In the salt thus prepared, the molar ratio of Ti to Si is 1: 1, and the concentration of T1O2 in the salt is approximately 0.9 g / L. The salt is stable at room temperature for at least 6 months.

To prepare the thin layers, we take the cleaned glass surface. The prepared salt is applied to the surface of any material using one of the described procedures (cloth, spray, brush, dipping ...).

Example 12

Remove the base salt from Example 1 (5 mL) and add TEOS (400 pL). A two-phase system is formed because TEOS is poorly soluble in aqueous medium. It is stirred at room temperature, resulting in the gradual hydrolysis and condensation of TEOS. After 12 hours, TEOS as the basic precursor is no longer present, and the salt still retains its stability. To the prepared mixed salt, 40 mL of water was added and stirred well. In the salt thus prepared, the molar ratio of

-14Ti and Si 1.3: 1, and the concentration of TiO ₂ in the salt is approximately 4.2 g / L. The salt is stable at room temperature for at least 6 months.

To prepare the thin layers, we take the cleaned glass surface. Soak the cotton cloth in dilute salt, then very thinly coat the glass with this cloth. When the solvent evaporates from the applied salt, a very thin layer of photocatalytically active coating remains on the glass.

Example 13

Mixtures of water (0.30 mL), conc. HNO3 (0.84 mL) and 2-propoxyethanol (4.1 mL) were added dropwise to a mixture of TTIP (4.7 mL) and 2-propoxyethanol (9.5 mL). The resulting mixture was stirred at room temperature for 4 hours to achieve hydrolysis and condensation of titanium alkoxide. Finally, dilute the prepared hydrolyzate with 2-propoxyethanol (35 mL). The percentage by weight of TiO ₂ in the prepared hydrolyzate is 2.5%.

Example 14

Remove the base salt (5 mL) from Example 1 and add the colloidal SiO ₂ salt Levasil 200/30% (0.47 g), which was previously mixed with 415 pL GPMS and 10 ml 2-methoxyethanol. Mix for 2 hours. To this was added partially hydrolyzed TTIP (TiO ₂ hydrolyzate) (4.1 mL) prepared according to the procedure described in Example 9. The salt maintained its stability. To the prepared mixed salt was added 40 mL of water, 75 mL of 2-methoxyethanol and 85 mL of 1-butanol and stirred well. The salt thus prepared contains 1.3 g / L TiO ₂ per liter of salt, the molar ratio of anatase Ti, non-crystalline Ti from hydrolyzate, Si from GPMS and Si from colloid is 1: 0.5: 1: 1.

The prepared salt is applied to the surface of any material using one of the described procedures (cloth, spray, brush, dipping ...). The prepared thin layer is heated at 90 ° C for half an hour.

Characterization

The formation of the anatase crystalline phase was confirmed by X-ray diffraction (Figure 1). The anatase crystalline phase, which is present in the powder sample obtained from thicker coatings by means of a sharp scraper, still prevails over rutile after drying at room temperature and even after thermal treatment of the sample at 1000 ° C. It is only at higher temperatures that the anatase phase becomes fully rutile. It should be emphasized that, according to scientific literature, this is one of the widest, if not the widest, thermal window of thermal stability of the photocatalytically active anatase phase (from room temperature to 1000 ° C). The photocatalytic function of the coating is

-15Also guaranteed at extremely high temperatures. This could be the case if a coating is applied to an object (eg a brick or a ceramic tile), which still needs to be heat treated at high temperature in the process to the finished product.

Figure 1 shows X-ray diffractograms of a sample prepared from thin TiCh / SiCh layers, which were made according to the procedure described in Example 11, namely a thermally untreated sample and a thermally treated sample at different temperatures.

The photocatalytic activity of the prepared coatings was demonstrated by attempting to discolour the resazurin dye. The procedure is described in an article by Evans, P.; Mantke, S.; Mills, A.; Robinson, A.; Sheel, DW J Photochem Photobiol A Chem 2007, 188, 387–391. In Figure 2, the left photo shows the state at 0 min and the right photo at 45 min with UVA radiation with a flux of 4 mW / cm ² . The left sample in each photo shows glass coated with a thin layer of TiCh / SiCh prepared according to the procedure described in Example 11, the right sample in each photo shows glass without TiCE- The change from blue to pink is a sign of the photocatalytic activity of the surface under the dye.

The hydrophilicity of the resulting coatings was confirmed by measuring contact angles. The measurement of the angle between the water droplet and the surface of the coating of Example 9 on a conventional window glass at a time of 0 min is between 30 and 40 °, while at 20 min irradiation with UVA flux 0.004 W / cm ² the contact angle drops from the initial value to 8 to 9 °, as evidenced by the high hydrophilicity of the coating in the presence of UV radiation.

The high transmittance of the self-cleaning coating of Example 11 in the entire field of visible light is evidenced by the UV-VIS spectrum of the coating applied to sodium glass (Figure 3). All types of coatings, prepared according to the various procedures described above, allow more than 95% of visible light. Figure 3 shows the UV-Vis spectrum of the sample compared to the glass substrate alone.

The durability of thin self-cleaning coatings was tested in a continuous condensation chamber with continuous condensation (Erichsen wet chamber), and the samples were kept under extreme conditions for 5 weeks. In the humid chamber, samples from Examples 9 and 10 deposited on the cleaned glass surface were checked. By analyzing the contact angles and photocatalytic activities using resazurin before and after treatment, it was shown that the layers had lost some activity but were still present on the glass surface.

Claims (11)

1. Preparation of TiO ₂ / SiO ₂ salts and their use for the application of thin, optically permeable coatings with self-cleaning and anti-rust properties, characterized in that the process consists of: - preparation of an acidic aqueous salt containing photochemically active TiO ₂ nanoparticles, - adding a SiO ₂ precursor with the following hydrolysis / condensation of SiO ₂ , - addition of epoxysilanes by subsequent polymerization to polyethers - the addition of an amorphous TiO ₂ hydrolyzate acting as a binder, - addition of colloidal SiO ₂ , - dilution of the prepared salt with water and / or with organic solvents, - application of prepared salt to the substrate, - solvent evaporation and condensation reactions at temperatures below 100 ° C, - the formation of a thin, uniform TiO ₂ / SiO ₂ layer having self-cleaning properties. Device according to claim 1, characterized in that HCI 4 acid is used to prepare the acidic aqueous salt. Device according to claim 1, characterized in that TEOS is used as the precursor of SiO ₂ . Device according to claim 1, characterized in that TEOS is added to the cooled, undiluted base salt. Device according to claim 1, characterized in that the SiO ₂ binder is prepared previously from TEOS and colloidal SiO ₂ , by hydrolysis of TEOS. Device according to claim 1, characterized in that GPMS is used as epoxysilane. Device according to claim 1, characterized in that the mixed TiO ₂ / SiO ₂ salt is diluted with water or with various mixtures of the listed organic solvents. 8. TiO ₂ / SiO ₂ salts, prepared according to the preceding claims. Use of TiO ₂ / SiO ₂ salts according to claim 7, characterized in that the prepared salt refers to the surface of the substrate by means of a cloth, brush, sprayer, immersion of the sample in the salt. Use of TiO ₂ / SiO ₂ salts according to claim 7, characterized in that glass, concrete, ceramics or various polymeric materials are used as a base. Use of TiO ₂ / SiO ₂ salts according to claim 7, characterized in that no additional thermal or chemical treatment of the resulting coating is required. / <L