New photo-catalytic coatings based on titanium di:oxide in a mineral or organic dispersion

SUBSTRATE WITH PHOTOCATALYTIC PROPERTIES BASED ON TITANIUM DIOXIDE

AND ORGANIC DISPERSIONS BASED ON TITANIUM DIOXIDE

The present invention relates to substrates provided with a coating with photocatalytic property based on titanium dioxide incorporated in the form of particles as well as novel dispersions based on monodisperse titanium dioxide particles and an organic solvent.

Currently, attempts are made to protect architectural materials (glasses, metals, ceramics, etc.) by giving them properties such as, in particular, anti-UV, anti-fouling, bactericidal, anti-reflection, anti-static properties, etc. ..

In the case of soiling (grease, soot, organic residues, etc.), it is known, for example, to deposit on the substrates a coating ensuring degradation of this soiling by photocatalysis.

This degradation can be induced by any compound which generates radicals under the action of light (photocatalytic effect). It may in particular be titanium dioxide which is already used for the treatment of architectural substrates and especially glass substrates.

Thus, it is known to use solutions of titanium compounds or colloidal dispersions of titanium dioxide to create photocatalytic properties on the substrates. However, it has been found that the specific characteristics of said solutions of titanium compounds or colloidal dispersions of titanium dioxide used to treat the substrate influence the quality of the photocatalytic coating. According to these specific characteristics, the quality of the adhesion of the coating on the substrate can also be very variable. Finally, it happens, in the case where the substrate is glass, that the coating induces a lack of transparency and a blurring on the glass.

An aim of the present invention is therefore to provide new substrates having a titanium dioxide-based coating exhibiting good photocatalytic properties, said coatings being durable, transparent and capable of being prepared industrially.

To this end, the invention relates to a substrate provided on at least part of one of its faces with a coating with photocatalytic property based on titanium dioxide at least partially crystallized and incorporated into said coating in the form of particles obtained by deposition. a dispersion of fine monodisperse particles of partially crystallized titanium dioxide.

The invention also relates to a dispersion comprising monodisperse titanium dioxide particles and at least one organic solvent, preferably having a latent heat of vaporization lower than that of water.

Finally, the invention relates to the use for the formation of a surface layer with photocatalytic property of the preceding dispersion by depositing the latter on a substrate.

The invention relates firstly to a substrate provided on at least part of one of its faces with a coating with photocatalytic property based on titanium dioxide at least partially crystallized and incorporated into said coating in the form of particles obtained by deposition a dispersion of fine monodisperse particles of partially crystallized titanium dioxide.

The partially crystallized titanium dioxide forming the coating of the substrate is in the crystalline form of anatase, rutile or in the form of a mixture of anatase and rutile with a degree of crystallization of preferably at least 25%, in particular about 30%. at 80%. The degree of crystallization represents the amount by weight of TiO₂ crystallized relative to the total amount by weight of TiO₂ in the coating

Preferably, the crystallized titanium dioxide forming the coating is in the form of crystallites, that is to say of single crystals, having an average size of between 2 and 60 nm, preferably between 2 and 50 nm, in particular between 10 and 40 nm.

The coating of the substrate according to the invention is obtained by depositing a dispersion of titanium dioxide exhibiting specific characteristics. This dispersion must in fact comprise at least partially crystallized and monodisperse titanium dioxide particles.

The term "monodisperse" means particles having a dispersion index of at most 0.5, preferably at most 0.3, the dispersion index being given by the following formula:

084 - 0^

2050 in which :

- 084 is the diameter of the particles for which 84% of the particles have a diameter less than 084,

- 0-| ₆ is the particle diameter for which 16% of the particles have a diameter less than 0₁₆,

- 050 is the average particle diameter.

The diameters are measured by transmission electron microscopy (TEM).

Such monodisperse particles can be obtained from a so-called wet preparation process, that is to say in solution (thermolysis, thermohydrolysis or precipitation of a titanium salt) as opposed to oxidation or pyrolysis processes. high temperature of a titanium salt. They may for example be particles of titanium dioxide obtained by the process described in application EP-A-0 335 773 of the Applicant.

The titanium dioxide particles entering into the dispersion used have a size of between 5 and 70 nm in general, preferably between 15 and 50 nm. The size is measured by MET.

The nature of the crystalline phase of these titanium dioxide particles is preferably predominantly in the anatase crystalline form. Mainly * means that the level of anatase in the titanium dioxide particles of the dispersion according to the invention is greater than 50% by mass. Preferably, the particles of the dispersions used exhibit a level of anatase greater than 80%.

The dispersion of titanium dioxide particles used to prepare the substrates according to the invention can be an aqueous or organic dispersion. Preferably, an organic dispersion is used.

When the dispersion of titanium dioxide particles is a dispersion in an organic solvent, an organic solvent having a latent heat of vaporization lower than that of water is preferably used. By latent heat of vaporization is meant the number of calories required to vaporize 1 g of liquid at the boiling point of said liquid. The latent heat of vaporization of water at its boiling point is 540 cal / g (Handbook of Chemistry and Physics, 75th ed.). Such an organic solvent can be chosen from alcohols and in particular glycols, esters such as ethyl acetate, etc.

When such organic dispersions are used, the latter may comprise, depending on the type of process used to prepare it, a water content of at most 10% by weight, preferably at most 5% and even more preferably at most. 1%.

Whatever the type of dispersion used, aqueous or organic, the level of titanium dioxide in the form of particles of the dispersion can be between 1 g / l and 300 g / l.

Advantageously, it is also possible to use a dispersion comprising at least one organometallic compound based on a metal M chosen from titanium, silicon, tin, zirconium or aluminum.

They can be organometallic compounds of general formula M (OR)₄ in which M represents the metal chosen from titanium, silicon, tin, zirconium or aluminum, and R an alkyl, cydoalkyl, aryl, alkylaryl or aryiakyte, alkenyl or aicynyl radical, an acetyiacetonate radical or one of its derivatives (methylacetoacetonate, ethylacetoacetate, ...), an amine or one of its derivatives (tri-ethanolamine, diethanolamine, ...), a glycolate, ...

It is preferred to use compounds of the titanate or stanate type. The organometallic compound Ti (OC4Hg)₄ particularly suitable as an organometallic compound.

These organometallic compounds are generally in solution in the dispersion used to coat the substrate. They can be advantageously stabilized by products such as diethanolamine (DEA), acetylacetone derivatives such as ethylacetoacetate, glycols, etc.

The proportion of the organometallic compound in the dispersion used is generally such that the ratio of the mass of metal M provided by the organometallic compound to the mass of Ti provided by the titanium dioxide particles and optionally the organometallic compound is between 5 and 95%.

In order to exacerbate the photocatalytic effect of the titanium dioxide-based coating, it is possible to add catalysts and additives to the titanium dioxide, making it possible to better absorb UV rays, or to shift the absorption band towards the surface. visible, or metals allowing titanium dioxide to be doped in order, among other things, to increase the number of electronic carriers.

According to a first variant, it is possible to use a dispersion further comprising additives in the form of particles based on metal compounds chosen from cadmium, tin, tungsten, zinc or zirconium. These particles are of colloidal size, generally between 5 and 100 nm. Their content in the dispersion is between 0.1 and 20% by weight.

Metal compounds can be metal oxides or sulphides, such as CeO₂, SnO₂, WO₃, ZnO, ZrO₂ or CdSe_xSy with x and y ranging between 0 and 1, and x + y = 1.

According to a second variant, it is possible to use a dispersion of which at least part of the titanium dioxide particles can comprise in their crystal lattice metal ions chosen from iron, copper, ruthenium, cerium, molybdenum, bismuth, tantalum, niobium, cobalt, nickel, vanadium. The ratio of the mass of these metal ions relative to the mass of titanium dioxide is between 0.01 and 10%.

According to a third variant, it is possible to use a dispersion in which at least part of the titanium dioxide particles can be covered at least in part with a layer of salts or metal oxides, the metal being chosen from iron, copper. , ruthenium, cerium, molybdenum, bismuth, tantalum, niobium, cobalt, nickel, vanadium. The ratio of the mass of these metals relative to the mass of titanium dioxide is between 0.01 and 20%.

According to a fourth variant, it is possible to use a dispersion in which at least part of the titanium dioxide particles can be covered at least in part with a layer of metal chosen from platinum, silver or rhodium. The ratio of the mass of these metals relative to the mass of titanium dioxide is between 0.01 and 5%.

The substrates according to the invention can be of all types of architectural substrates such as ceramics, metals, tiles, roofs, floors, materials for internal and external walls and in particular glass.

The deposition of the dispersion of titanium dioxide on the substrate can be carried out by any known technique for coating the substrate. This generally involves coating the substrate with the dispersion and possibly its additives, then heat treating the coated substrate. It may be the following deposition techniques: spraying, liquid pyrolysis, sol-gel type dipcoating (dipping), spin-coating or laminar coating.

Preferably, the deposition is carried out by the sol-gei method or the liquid pyrolysis method.

These methods are advantageously followed by heat treatment.

The substrates according to the invention are covered with a transparent coating exhibiting good photocatalytic and adhesion properties.

It is also observed that the coating gives the substrate anti-fog properties, which are more particularly advantageous in the case of glass. In fact, the use of the dispersions according to the invention makes it possible to give the substrates a hydrophilic character preventing the formation of mist on its surface.

The thickness of the coating of the substrate according to the invention is variable, it is generally less than 1 μm, preferably between 5 and 500 nm.

Between the substrate and the coating based on titanium dioxide, it is possible to deposit one or more other thin layers with a function different or complementary to that based on titanium dioxide. In particular in the case of a glass substrate, it is possible to deposit a layer having an alkali barrier function based, for example, on silicon oxide, nitride, oxynitride or oxycarbide. This layer has the advantage of preventing the migration of sodium ions into the titanium dioxide-based coating, which could lead to an alteration of the photocatalytic properties.

The invention also relates to a dispersion comprising monodisperse titanium dioxide particles and at least one organic solvent, preferably having a latent heat of vaporization lower than that of water.

The definitions of monodispersity and latent heat are the same as above.

The particles of such dispersion can be obtained by a so-called wet process leading to aqueous dispersions of such particles and which are then transferred into an organic medium by any process known to those skilled in the art, for example by transfer processes such than those described below.

These so-called wet particle preparation processes have the advantage of leading to monodisperse titanium dioxide particles as we have mentioned previously.

The titanium dioxide particles entering into the dispersion according to the invention have a size of between 5 and 70 nm in general, preferably between 15 and 50 nm. The size is measured by MET.

The nature of the crystalline phase of titanium dioxide must predominantly be in the anatase crystalline form. Mostly * has the same meaning as above

The level of titanium dioxide in the form of particles of the dispersion according to the invention can be between 1 g / l and 300 g / l.

The organic solvent can be chosen from alcohols and in particular gtycols, esters such as ethyl acetate, etc.

The dispersion according to the invention can advantageously comprise at least one organometallic compound based on a metal M chosen from titanium, silicon, tin, zirconium or aluminum.

They may be organometallic compounds of general formula M (OR) <in which M represents the metal chosen from titanium, silicon, tin, zirconium or aluminum, and R an alkyl, cycloalkyl or aryl radical. , alkylaryl or arylakyl, alkenyl or alkynyl, an acetytacetonate radical or one of its derivatives (methylacetoacetonate, ethyiacetoacetate, ...), an amine or one of its derivatives (tri-ethanoiamine, diethanolamine, ...), a glycolate ,. ..

These are advantageously compounds of the titanate or stanate type. The organometallic compound TiKX 3 Hg 4 is particularly suitable as the organometallic compound.

These organometallic compounds are generally in solution in the dispersion according to the invention. They can be advantageously stabilized by products such as diethanolamine (DEA), acetylacetone derivatives such as ethylacetoacetate, glycols, etc.

The proportion of the organometallic compound in the dispersion according to the invention is such that the ratio of the mass of metal M provided by the organometallic compound to the mass of Ti provided by the particles of titanium dioxide and optionally the organometallic compound is between 5 and 95%.

The dispersion according to the invention may comprise, depending on the type of process used to prepare it, a water content of at most 10% by weight, preferably at most 5% and even more preferably at most 1%.

According to a first variant, the dispersion according to the invention may further comprise additives in the form of particles based on metal compounds chosen from cadmium, tin, tungsten, zinc or zirconium. These particles are of colloidal size, generally between 5 and 100 nm. Their content in the dispersion is between 0.1 and 20% by weight.

Metal compounds can be metal oxides or sulphides, such as CeO₂, SnO₂, WO₃, ZnO, ZrO₂ or CdSexSy with x and y between 0 and 1, and x + y »1.

According to a second variant, at least part of the titanium dioxide particles of the dispersions according to the invention can comprise in their crystal lattice metal ions chosen from iron, copper, ruthenium, cerium, molybdenum, bismuth, tantalum, niobium, cobalt, nickel, vanadium. The ratio of the mass of these metal ions relative to the mass of titanium dioxide is between 0.01 and 10%.

According to a third variant, at least part of the titanium dioxide particles of the dispersions according to the invention can be covered at least in part with a layer of salts or metal oxides, the metal being chosen from iron, copper. , ruthenium, cerium, molybdenum, bismuth, tantalum, niobium, cobalt, nickel, vanadium. The ratio of the mass of these metals relative to the mass of titanium dioxide is between 0.01 and 20%.

According to a fourth variant, at least part of the titanium dioxide particles of the dispersions according to the invention can be covered at least in part with a layer of metal chosen from platinum, silver or rhodium. The ratio of the mass of these metals relative to the mass of titanium dioxide is between 0.01 and 5%.

The dispersion according to the invention can be obtained by any process making it possible to carry out the suspension of titanium dioxide particles in an organic phase from an aqueous dispersion of titanium dioxide obtained by a wet process.

The dispersion can thus be obtained by bringing an aqueous dispersion of titanium dioxide particles obtained from a wet route into contact with the desired organic solvent and then heating so as to remove the water by distillation. Such a process can only be implemented in the case where the organic solvent chosen has a boiling point higher than that of water and is soluble in water. This is the case, for example, with ethylene glycol.

The dispersion can also be obtained by grafting a hydrophobic chain to the surface of titanium dioxide particles suspended in water and then mixing with an organic solvent immiscible with water so as to cause the particles of carbon dioxide to migrate. titanium in the organic phase.

The aqueous dispersions of titanium dioxide used as starting material in these processes can be prepared according to the teaching of patent application EP-A-0 335 773.

When the dispersions according to the invention also comprise an organometallic compound, said compound is added by mixing a solution of the organometallic compound and a dispersion based on particles of titanium dioxide and on an organic solvent. It is possible, depending on the nature of the organometallic compound used, to also add, during this mixing, additives such as cosolvents, surfactants or stabilizing agents. The mixing can also be improved by stirring the dispersion with ultrasound.

The solution of organometallic compound added to the dispersions based on particles of titanium dioxide and of organic solvent is generally an organic phase solution, said organic phase possibly being chosen from: ethanol, isopropanol, acetate. ethyl,...

It is also possible to add the organometallic compounds to the titanium dioxide dispersions in pure form.

When the first variant of the invention is implemented, the dispersions further comprise additives in the form of particles based on metal compounds chosen from cerium, cadmium, retin, tungsten, zinc or zirconium. These latter particles can be introduced into the dispersions by simple mixing with an aqueous dispersion of titanium dioxide particles obtained by a wet route and then transfer of all the particles from the aqueous phase to the organic phase.

When the second variant of the invention is implemented, at least part of the titanium dioxide particles of the dispersions comprise, in their crystal lattice, metal ions chosen from among iron, copper, ruthenium, cerium, molybdenum, bismuth, tantalum, niobium, cobalt, nickel, vanadium. These dispersions can be obtained by introducing salts of the metal ions during the preparation of the titanium dioxide particles. Thus, if the titanium dioxide particles are obtained by thermohydrolysis of a titanium compound as described in application EP-A-0 335 773, it is possible to add the metal ions to the thermohydrolysis medium in such a manner. introducing the ions into the crystal lattice of titanium dioxide.

When the third variant of the invention is implemented, at least part of the titanium dioxide particles of the dispersions are covered at least in part with a layer of salts or metal oxides, the metal being chosen from iron. , copper, ruthenium, cerium, molybdenum, bismuth, tantalum, niobium, cobalt, nickel, vanadium. These dispersions can be obtained by precipitation of metal salts on the titanium dioxide particles before placing in an organic medium. Thus, when the titanium dioxide particles are still in an aqueous medium following a wet preparation process, metal salts are introduced into the aqueous phase and they are precipitated so as to cover at least part of them. titanium dioxide particles.

When the fourth variant of the invention is implemented, at least part of the titanium dioxide particles of the dispersions are covered at least in part with a layer of metal chosen from platinum, silver or rhodium. These dispersions can be obtained by reduction of metal salts on the titanium dioxide particles before placing in an organic medium. For example, when the titanium dioxide particles are still in an aqueous medium following a wet preparation process, metal salts are introduced into the aqueous phase and reduced so as to at least partially cover them. titanium dioxide particles.

The invention finally relates to the use for the formation of a surface layer with photocatalytic property of a dispersion according to the invention by depositing the latter on a substrate.

The following examples illustrate the invention without, however, limiting its scope.

EXAMPLES

Example 1: preparation of a dispersion based on titanium dioxide and ethylene glycol and application to a glass surface

Preperation :

An aqueous dispersion of titanium dioxide particles is prepared according to the teaching of patent application EP-A-0 335 773. An aqueous dispersion is obtained comprising anatase titanium dioxide particles with a diameter of 35 nm measured by TEM and of which the dry extract is 20% by weight.

100 parts by mass of this dispersion are mixed with 100 parts of ethylene glycol. The mixture is then heated to 80 ° C. so as to remove the water by controlled distillation under reduced pressure (100 mbar), then to 120 ° C. in order to remove the bound water.

A dispersion is obtained comprising particles of titanium dioxide and ethylene glycol. The dry extract is 20% by weight. The size of the particles measured in ethylene glycol by TEM is 35 nm. The residual water content is 0.7% by weight relative to the titanium dioxide.

ApplicatiQn:

The dispersion obtained is deposited on a glass substrate as follows. The substrate is immersed in the dispersion defined above, then it is extracted therefrom so as to deposit a film thereon. The substrate is then heat treated for 1 h at 100 ° C. then for approximately 3 h at 550 ° C. with a gradual rise in temperature.

A transparent treated substrate having the following properties is obtained.

- Photocatalytic test: a fingerprint is placed on the treated glass and the latter is left under a UVA lamp with a power of 30 mW / cm² for 3 h. We observe that the fingerprint disappears

Example 2: preparation of a dispersion based on titanium dioxide, ethylene glycol and an organometrium and application to a glass surface.

Preperation

The dispersion based on titanium dioxide and ethylene glycol obtained in Example 1 is diluted so that the titanium dioxide content is 10% by weight.

Then added to 10 ml of this dispersion 200 ml of 0.2 M TiiCX ^ Hg ^ in ethanol stabilized with diethanolamine (DEA) with one mole of DEA per mole of Ti (OC₄Hg)₄. Then stirred with ultrasound.

Application :

The dispersion obtained is deposited on a glass substrate as follows. The substrate is immersed in the dispersion defined above, then it is extracted therefrom so as to deposit a film thereon. The substrate is then heat treated for 1 h at 100 ° C. then for approximately 3 h at 550 ° C. with a gradual rise in temperature.

A transparent treated substrate having the following properties is obtained.

- Photocatalytic test: a fingerprint is placed on the treated glass and the latter is left under a UVA lamp with a power of 30 mW / cm² for 3 h. We observe that the fingerprint disappears

- Anti-fog test 1: a qualitative evaluation of the anti-fog effect is made by suddenly heating the coated substrate initially stored in the cold or simply by blowing on the substrate, then looking for any fog appearing.

It is observed that the treated glass is never covered with mist unlike an untreated control glass substrate.

- Anti-fog test 2: the contact angle of a drop of water on the surface of the treated glass is measured, after having left the substrate for one week in the dark then 20 min under UVA radiation.

It is observed that, on the treated glass, the contact angle is less than 5 °, while on an untreated glass, it is 40 °.