Coating composition having surface depolluting properties

ES 2 344 066 T3

DESCRIPTION

Coating composition exhibiting surface decontaminating properties.

The present invention relates to a coating composition useful for the formation of an inorganic layer of paint and / or antifouling and / or decontaminating dirt cleaning coating on the surface of a substrate.

Conventional procedures for performing the cleaning of dirt from the surface of materials comprise treating the surface to provide the ability to remove stains or dirt deposited on the surface. In other processes, the excellent oxidative degradation activity of a photocatalyst fixed on the surface is used to degrade organic matter or stains or dirt deposited on the surface and also any gaseous contamination that comes into contact with said surface.

In particular, heterogeneous photocatalysis has been efficiently used to oxidize and thus remove unwanted compounds from fluids, including water, and air. Thus, UV illuminated catalyst such as titanium dioxide absorbs ultraviolet light which produces electrons and holes that migrate to the surface of the catalyst. At the surface, electrons reduce adsorbed oxygen while holes oxidize adsorbed organic compounds or water molecules.

However, satisfactory anti-pollution properties cannot be provided with just one such simple photocatalytic coating compositions over a long shelf life, that is, more than 5 years.

An object of the present invention therefore is to provide a coating composition, which regardless of the environment, such as an outdoor or indoor environment, can semi-permanently in a single coating show excellent surface anti-pollution properties, particularly Excellent dirt cleaning against greasy stains, including mildew, mold, algae or dirt and is also resistant to abrasion.

According to a first aspect of the present invention, there is provided a coating composition for the formation of an inorganic layer on the surface of a substrate, the coating composition comprising at least

- an efficient amount of photocatalytic titanium dioxide particles,

- an opacifying agent, selected from among pigments, colorants and / or fillers,

- inorganic binder particles

- an organic binder and

- a solvent, in which said photocatalytic titanium dioxide particles and the organic binder are present in a weight ratio of organic binder / photocatalytic titanium dioxide in the range of 0.1 to 6, and in which the organic binder comprises a or more amorphous substances selected from the group consisting of alkali silicates, alkali aluminates, alkali zirconates, alkali borates, alkali phosphates, alkali phosphonates, and mixtures thereof.

According to a specific embodiment, said composition is a silicate emulsion paint.

According to a second aspect of the present invention, a method is provided for providing a dirt cleaning and / or anti-pollution coating on a substrate comprising at least the steps consisting of:

- applying a coating composition according to the invention on a surface of a substrate to form a coating and

- fix the coating to obtain an organic layer on the surface of the substrate.

According to a third aspect of the present invention, there is provided a method for preventing and / or treating fungi, mildew, mold, algae and / or bacteria on a substrate that comprises at least the steps consisting of:

- applying a coating composition according to the invention on a surface of the substrate to form a coating, and

- fix the coating to obtain an inorganic layer on the surface of the substrate.

ES 2 344 066 T3

Inorganic binder

It includes at least one amorphous substance selected from the group consisting of alkali silicates, alkali aluminates, alkali zirconates, alkali borates, alkali phosphates, alkali phosphonates, and mixtures thereof.

Specific examples of the preferred inorganic binder include alkali silicates represented by the formula

M₂O.nSiO₂ where M represents an alkali metal, and n is 2.0-3.0.

In accordance with the present invention, the inorganic binder includes at least one metal selected from the group consisting of rubidium, potassium, sodium, and lithium. Preferred alkali metal silicates include, for example, potassium silicate, sodium silicate, and / or lithium silicate.

The combined use of a plurality of alkali metal silicates can improve the water resistance, alkali resistance and acid resistance of the inorganic layer. Commercially available alkali metal silicates in the form of an aqueous solution are also soluble.

The use of an alkali metal silicate can form an inorganic layer that exhibits good adhesion even at a low temperature of about 5 ° C to the surface of the substrate.

According to a preferred embodiment of the present invention, the concentration of the inorganic binder and in particular the alkali metal silicate in the coating composition is preferably 0.5 to 35% by weight, in particular 1 to 30% by weight, more particularly 2 to 25% by weight on a solid basis. Such a concentration is advantageous to obtain a surface that exhibits good dirt cleaning and good resistance.

The alkali silicate in the inorganic binder system can be cured in different ways. The desired cure can be generated by atmospheric carbon dioxide.

Also, the coating can be hardened by removal of water. Advantageously, the coating thus obtained forms an inorganic structure exhibiting sufficient pores to provide a sufficiently high permeation to water vapor.

Organic binder

It was unexpectedly found that said compound was particularly advantageous in obtaining a photocatalytically active coating exhibiting a long pot life.

In the case of the present invention, the organic binder must not decompose during the formation of the expected coating. However, after prolonged exposure to UV light, the initial content in the organic binder will slowly decrease until it is fully degraded.

More specifically, the organic binder can be selected from styrene / butadiene copolymers and acrylic acid ester polymers and copolymers and in particular polyvinyl acrylic and styrene / acrylic ester copolymers.

In the present invention, the styrene acrylic copolymer includes styrene / acrylic ester copolymers thereof.

Said effect is particularly appreciated when this compound is a styrene / acrylic copolymer and more particularly used in a weight ratio of photocatalytic TiO2 / organic binder particles and in particular styrene / acrylic copolymer in the range of 0.3 to 4 , 5, in particular from 0.5 to 3.6, more particularly from 1 to 2.5.

In particular, an acrylic styrene emulsion such as ACRONAL 290D from BASF GmbH can be used.

Photocatalytic particles

In the present invention, the term "photocatalytic particles" as used in the present invention refers to particles based on a material that, when exposed to light (excitation light), exhibits a higher energy (that is, length of shorter wave) than the energy interval between the conduction band and the valence band

ES 2 344 066 T3 of the crystal, can cause excitation (photoexcitation) of electrons in the valence band to produce a conduction band electron and leave a hole in the valence band.

More particularly, the photocatalytic titanium dioxide particles are selected from the group consisting of titanium oxide which can be of any type, for example anatase or rutile, although anatase-containing titanium oxide is especially preferred for its superior photoactivity.

For the titanium dioxide particles in the coating, the nature of the particle is preferably predominantly the crystalline form of anatase. "Predominantly" means that the level of anatase in the titanium dioxide particles in the coating is greater than 50% by mass. The coating particles preferably show an anatase level greater than 80%.

The degree of crystallization and the nature of the crystalline phase are measured by X-ray diffraction.

The crystalline titanium dioxide particles incorporated into the coating show a mean size of between 5 and 80 nm, preferably between 5 and 50 nm, still more preferably between 10 and 40 nm. Diameters can be measured by transmission electron microscopy (TEM) and also XRD.

Preferred photocatalyst particles have a high surface area per gram, for example greater than 30 µm²/ g, preferably greater than 50 m²/ g and even more preferably greater than about 100 μm²/ g when measured by the BET procedure.

Particularly suitable for the invention are the photocatalytic titanium dioxide particles sold under the name PC 105 by Millennium Inorganic Chemicals Ltd.

The present invention may also involve a titanium dioxide coated pigment. This may include titanium dioxide particles, a first deposit of a phosphate compound contiguous with the base TiO2 particles, optionally a deposit of a dense silica compound contiguous with the phosphate deposit, optionally a second deposit of a phosphate compound. contiguous with the dense silica compound and optionally a deposit of an alumina compound contiguous with the second phosphate deposit.

In an alternative embodiment, the titanium dioxide particles can be coated with a zirconia compound in place of the silica compound.

Preferably, the phosphate compound is formed from a water soluble phosphate compound, such as for example tetrapotassium pyrophosphate, sodium polyphosphate, tetrasodium pyrophosphate (Tetron^TM), sodium tripolyphosphate, potassium tripolyphosphate, sodium hexametaphosphate (Calgon^TM), phosphoric acid, and the like. Most preferably, the water soluble phosphate compound is sodium hexametaphosphate. The percentage by weight of the phosphate compound can vary depending on the layer deposited on the titanium dioxide base. It is not necessary for the phosphate compound to coat each titanium dioxide particle, but only some of the phosphate to be deposited on the particle. Preferably, the phosphate compound in the first layer is deposited in an amount of from about 0.05% to about 1.0%, more preferably from about 0.05% to 0.75%, and still more preferably from about 0, 05% to about 0.5% based on the weight of the titanium dioxide base.

The silica content in weight percent can vary depending on the layer deposited on the first phosphate layer. Silica compounds suitable for use in the present invention include water soluble alkali metal silicates. Preferred alkali metal silicates include sodium silicate, potassium silicate, and the like. Most preferably, the silica compound is sodium silicate. Preferably, the silica compound is deposited in an amount of from about 0.5% to about 5.0% by weight of silica based on the total weight of the titanium dioxide base.

Suitable zirconia compounds for use in the present invention include the acidic salts of zirconia such as zirconium oxychloride, zirconyl sulfate, and the like. More preferably, the zirconia compound is zirconium oxychloride or zirconyl sulfate. Preferably, the zirconia compound is deposited in an amount of from about 0.1% to about 5.0% by weight of zirconia based on the total weight of the titanium dioxide base.

The particles exhibiting photocatalytic activity are present in an amount of 0.5 to 20%, preferably 1 to 15% and more preferably 3 to 12% by weight of the total weight of the composition.

In one embodiment of the invention, the combination of small photocatalytic particles (1-8 nm) with larger non-photocatalytic particles (about 250-350 nm), and more particularly non-photocatalytic TiO2 particles produces a paint composition useful for Self-cleaning.

The photocatalytic titanium oxide particles can be introduced into the composition as a sol prepared by dispersion in a dispersant, as a paste containing solvent or water, or as a powder. Preferred examples of the dispersant used to prepare a sol include water, alcohols such as methanol, ethanol, isopropanol, n-butanol, and isobutanol, and ketones such as methyl ethyl ketone and methyl isobutyl ketone.

ES 2 344 066 T3

The composition according to the present invention includes at least one solvent.

Examples of solvents usable herein include water, an organic solvent, and a mixed solvent composed of water and an organic solvent. Water, an alcohol, or a mixed solvent composed of water and an alcohol, is particularly preferred.

The addition of water as the solvent is often preferred.

Opacifying Agents

According to the invention, the opacifying agent includes any organic or inorganic compound that can provide hiding power to the coating. These include pigments, colorants and / or fillers as mentioned below. More preferably, it includes at least one inorganic compound such as titanium dioxide.

Such non-photoactive titanium dioxide pigments are disclosed in US Patent No. 6,342,099 (Millennium Inorganic Chemicals Inc.).

In particular, the titanium dioxide pigment may be the Tiona 595 particles sold by Millennium Inorganic Chemicals Ltd.

If necessary, various other compounds can be added to the composition of the invention, provided that such addition does not compromise the shelf life, UV durability or non-staining properties of the resulting coating.

Examples of such additional compounds include fillers such as quartz, calcite, clay, talc, barite, and / or Na-Al silicate; pigments such as TiO₂, lithopone and other inorganic pigments; dispersants such as polyphosphates, polyacrylates, phosphonates, naphthene, and lignin sulfonates; wetting agents such as anionic, cationic, amphoteric and nonionic surfactants; defoamers such as silicon emulsions, hydrocarbons, long chain alcohols, ...; stabilizers such as primarily cationic compounds; coalescing agents such as alkali-stable esters, glycols, hydrocarbons; Rheological additives such as cellulose derivatives (carboxymethyl cellulose CMC, hydroxymethyl cellulose HEC), xanthan gum, polyurethane, polyacrylate, modified starch, benthone and other lamellar silicates; water repellants such as alkyl siliconates, siloxanes, wax emulsions, Li salts of fatty acids and conventional fungicides or biocides.

Of course, none of the additives should be saponifiable or otherwise unstable to the alkalinity of the finished coating (pH values ​​of about 11.5).

The present invention also provides a process for the production of a photocatalytically active coated substrate which comprises depositing the coating composition on a material by contacting the surface of the material with said composition.

The composition of the present invention can be applied to the surface of the material by any appropriate procedure, and examples of appropriate procedures include spray coating, drip coating, flow coating, spin coating, roll coating, brush coating, and lining with sponge.

The composition after application to the surface of the substrate is then fixed, generally by drying or curing to form an inorganic layer, generally in the form of a thin film. The term "drying or curing" used herein refers to the binders contained in the composition, according to the present invention, being made into a film. Therefore, drying can be done by air drying.

Advantageously, the formation of the coating does not require heat treatment at high temperatures such as 50-450 ° C for several hours.

The composition according to the present invention can be applied on the surface of a wide variety of materials.

The material is not particularly limited, and its examples include metals, ceramics, glasses, woods, stones, cements, concretes, and combinations of the above materials and the laminates of the above materials. Specific examples to which the composition can be applied include, houses, building materials; exterior of buildings; interior of buildings; windowframes; glasses; structural materials; exterior of machines and articles; dustproof covers and coatings; and films, foils and seals.

In preparing the preferred embodiments of the present invention, various alternatives may be used to facilitate the objectives of the invention.

ES 2 344 066 T3

The following examples are provided to better understand the present invention and are not intended to, and will not be construed to, limit the invention in any way. All the alternatives, modifications and equivalents that are apparent to the person skilled in the art from the present description are within the spirit and scope of the invention.

The present invention is described in more detail with reference to the following non-limiting examples.

Example 1

Three coating compositions according to the invention are prepared with the following components:

- photocatalytic titanium dioxide: PC 105 (TiO₂ 30% by weight in water containing 1% sodium hexametaphosphate) from Millennium Inorganic Chemicals,

- titanium dioxide pigments: Tiona595 from Millennium Inorganic Chemicals,

- calcium carbonate (filler): Omyacarb 5 GU and Setacarb 850 OG from Omya UK,

- styrene acrylic copolymer latex (organic binder): Acronal 290D (50% by weight in dry water) from BASF,

- potassium silicate solution (inorganic binder)> 3.2 molar ratio: Betolin P35 from Woellner Silikat GmbH,

- tetrapotassium ethylenediamine tetraacetic acid: Betolin A11 from Woellner Silikat GmbH,

- unsaturated fatty acid esters (antifoam agent): Foamex K3 from Tego,

- hydroxyethylcellulose (thickening agent): Natrosol 250 MR from Hercules,

- heteropolysaccharide (thickening agent): Betolin V30 from Woellner Silikat GmbH,

- alkaline salt of special phosphonic acid: Sapetin D20 from Woellner Silikat GmbH, and

- quaternary alkyl ammonium compound: Quart 25 from Woellner Silikat GmbH.

The compounds are used in the following amounts.

Part A

<td></td><td>% in weigh</td>

<td>Water</td><td></td>

<td></td><td> 18,4</td>

<td>Dispersant</td><td> 0,2</td>

<td>Heteropolysaccharide</td><td> 0,1</td>

<td>Hydroxyethyl cellulose</td><td> 0,4</td>

<td>Viscosity stabilizer</td><td> 0,4</td>

<td>Antifoam agent</td><td> 0,2</td>

<td>Titanium dioxide pigments</td><td> 7,9</td>

<td>Calcium carbonate</td><td> 28,1</td>

ES 2 344 066 T3

Part b

Photocatalytic Titatium Dioxide

Water

Ethylene acrylic (50%)

Antifoam agent

Texanol

Inorganic binder

Tetrapotassium ethylenediamine tetraacetic acid as required

6,4

0,1

0,3

15,9

0,9

The paintings are prepared in two parts.

For part A, the following is added successively to the water, the alkaline salt of the special phosphonic acid, thickening agents, the viscosity stabilizer and the antifoam agent, the resulting mixture is mixed for 2 minutes then added with T595 (TiO₂), followed by calcium carbonate.

The components are mixed under high shear stress for 20 minutes.

Water is added to the photocatalytic titanium dioxide followed by the addition of the styrene acrylic copolymer latex, the antifoam agent, the Texanol, the inorganic binder, and tetrapotassium ethylenediamine tetraacetic acid. The components are mixed for 5 minutes to form part B.

Part A is then mixed with Part B under high shear mixing.

The paints thus obtained are tested for effectiveness. The tested paint is applied to a cover of 770 g / m²on the substrate surface and the coated substrate is exposed to the following tests.

I - Determination of NO / NO extraction₂ by coatings

He does not_x used is NO at 450 ppm. After the initial measurement, the paint films are irradiated with 55 W / m² UV in the 300 to 400 nm range for 18 hours using a filtered Xenon light source. For measurements NO_x, the samples are irradiated with a UV fluorescent tube emitting 10 W / m² UV in the range of 300 to 400 nm.

1. Team

Nitrogen Oxide Analyzer Model ML9841B

- former Monitor Europe

UV Lamp Model VL-6LM 365 and wavelength of 312 nanometers

- ex BDH

Air-sealed sample chamber

3 channel gas mixer

- ex Brooks Instruments, The Netherlands

2. Gases

NO Nitric Oxide

NO2 Nitrogen Dioxide

NOx Mixture of NO and NO2

Compressed air containing water vapor.

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3. Process

The results of NO_x They were obtained by first washing the paint films for two hours to extract the soluble potassium carbonate that forms between the excess potassium hydroxide in the potassium silicate and the carbon dioxide in the atmosphere.

The measurement procedure is as follows:

1. The Analyzer is turned on and the pump empties. Make sure the outlet pipe goes to atmosphere.

2. Heating is allowed. Several internal components are required to reach operating temperature before the analyzer begins operation. The process typically takes 60 minutes from cold start and the STAR-UP SEQUENCE ACTIVE message is displayed until operating conditions are met.

3. After heating, the air and test gas supply to the gas mixer is turned on.

Four. Calibrate the analyzer on the test gas supply only (turn the air channel to zero on the gas mixer), according to the manufacturer's instructions.

5. After calibration turn off the test gas supply to the gas mixer.

6. The test sample is placed in the test chamber and the chamber is sealed.

7. Turn on both the air and the test gas and adjust each until the required level of test gas is reached, shown by the analyzer's output register level.

8. The UV lamp turns on when the test gas levels are at the desired point.

9. The irradiated sample value is allowed to reach equilibrium, typically up to 5 minutes.

10. The value displayed on the analyzer is recorded.

eleven. Report the "Initial Value" this is without UV, "Final Value", after exposure to UV during the established period, ValueA this is the Initial - Final and% reduction this is Λ value / initial value x 100.

The results are presented in the table below.

II - Procedure for determining the photoactivity of the coating towards methylene blue

Irradiation of titanium dioxide with ultraviolet light results in the production of holes and electrons that can then form reactive species such as peroxide, hydroperoxide, and hydroxyl ions. These can then oxidize organic molecules such as methylene blue to water, carbon dioxide, and nitrogen-containing species with the associated loss of color. The level of photoactivity is observed by measuring the L * (brightness) and b * (blue / yellowness) value.

The procedure is best suited for water-wet coatings such as latex or emulsion paints. The porosity of the coatings will affect the amount of staining the films receive, but this is minimized by the addition of a thickener to the methylene blue solution. Changes in the color of blue may also occur due to pH effects.

Preparation of methylene blue solution

Methylene blue is first dissolved in demineralized water to a concentration of 0.05% by weight. Using low speed stirring, the equivalent of 1% Natrasol MR® (Hydroxy Ethyl Cellulose) is then added. In order for the Natrosol to hydrate, the pH is raised to about 8.0 with dilute ammonia. This requires only a few drops. The solution is stirred for an additional hour to fully hydrate the Natrosol.

Paint film staining

The paint film to be tested is overcoated with a film of the methylene blue solution by lowering a film using a spiral wound rod. The test film had been previously prepared by applying a wet paint film to a 30 micron thick Melinex or Mylar sheet. The

ES 2 344 066 T3 spirally wound rods are specified to provide various film thicknesses, but those providing 25 to 50 microns of wet film are generally used. The coatings are allowed to dry at 23 degrees C. 50% RH overnight.

Measurement

A suitably sized area of ​​the coatings is cut from the film and L * and b * measurements are made using a spectrophotometer. The paint films are then exposed to light from an Atlas Suntest machine to provide a light output of 550 W / M² from 250 to 765 nm. Paint films are re-measured at 18 hours. The difference in L * and b * between the exposed and unexposed results is a measure of the photoactivity of the coating towards self-cleaning.

The data is provided in the table below.

III - Procedure for the determination of durability

The durability of the coatings was evaluated by preparing the coatings on stainless steel panels and exposing them to simulated weathering conditions in a machine designed for that application. The amount of weight the coating loses during exposure was a measure of its durability.

The stainless steel panels measure 75 by 150 mm and were 0.75 mm thick. The panels were weighed to 0.0001 g before and after application of the paint film so that the weight of the coating can be calculated.

The panels can be coated by any convenient means comprising brushing, spraying, twisting or by means of a spiral wand applicator. Only the surface to be exposed was coated. The dry film thickness was typically in the range of 20 to 50 microns.

The coatings were allowed to dry for 7 days prior to exposure to the Weather Gauge.

The Weather Meter used for the exposures was a Ci65A made by Atlas Electric Devices, Chicago. The light source was a 6.5 kW xenon source emitting 0.5 W / m² UV at 340 nm. The black panel temperature was 63 degrees Celsius. A water spray was applied for 18 minutes every 120 minutes and there was no dark cycle.

The values ​​thus obtained are presented in the following table. They show that only about 60% by weight of the initial total weight of the paint according to the invention has been efficiently lost after 760 hours of exposure.

TABLE

<td rowspan="2">Formulation</td><td rowspan="2">% NO extraction</td><td colspan="2">Washed film stain test</td><td>% durability loss in weight after 760 hours of exposure</td>

<td>TO THE*</td><td>Ab *</td><td></td>

<td>Comparative (0% photocatalyst)</td><td> 0</td><td> 1,2</td><td> 0,8</td><td></td>

<td>F, (5% w / w of photocatalyst)</td><td> 6,3</td><td> 1,4</td><td> 1,2</td><td> 65</td>

<td>F₂ (10% w / w photocatalyst)</td><td> 8,9</td><td> 2,0</td><td> 1,8</td><td> 68</td>

* The quantity is expressed in quantity of commercial product, that is, solvent and dry matter.

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IV - Resistance to mildew fungi

The tested paint was applied at a coverage of 300 g / m2 on the surface of an aluminum-based substrate and exposed for three months according to the international procedure ASTM D3274-95.

The resistance was compared to a raw paint, that is, free of photocatalyst. The results thus obtained show that the substrate treated according to the invention shows a resistance at least twice as great as the substrate treated by the comparative paint.