Photocatalytic coating

FIELD OF THE INVENTION [0001] [0001] The present invention relates to compositions for applying a photocatalytic coating on a surface. In particular, the invention relates to contaminating, self-cleaning paints containing titanium dioxide particles that do not require prior activation to achieve high initial photocatalytic activity.

BACKGROUND OF THE INVENTION [0002] [0002] Photocatalytic properties of a semiconductor material - titanium dioxide - result from the excitation of electrons from the valence band to the conduction band under the influence of ultraviolet (UV) and near UV radiation. The reactive electron-hole pairs formed migrate to the surface of the titanium dioxide particles, where the holes oxidize the adsorbed water to produce reactive hydroxyl radicals, and the electrons reduce the adsorbed oxygen to form peroxide radicals, both of which can degrade NOx and volatile organic compounds compounds, VOC) in the air. Because of these properties, photocatalytic titanium dioxide has been used in coatings and the like to remove air impurities. The advantage of such coatings can be self-cleaning, because dirt (fat, fungi, mold, algae, etc.) also oxidizes on the surface.

[0003] Despite the advantages of existing photocatalytic titanium dioxide coatings, there is room for improvement in this field. In particular, it has been observed that the initial activity of conventional photocatalytic titanium dioxide coatings is poor, unless the coating has been pre-activated, for example by washing with water. Without wishing to be bound by theory, it is believed that the activation step is required to remove the organic components present in the coating composition from the catalyst surface or possibly provide a hydrated surface on the titanium dioxide particles from which the chemical forms of reactive radicals are formed. However, this additional step makes applying the photocatalytic coating of titanium dioxide a bit inconvenient, because it is time consuming and causes additional costs for the application process. It would be desirable to provide a photocatalytic coating of titanium dioxide, especially in the form of paint that does not require pre-activation (e.g., washing or exposure to nature) to achieve high initial levels of activity.

[0004] [0004] Coatings with high levels of photocatalyst have also been difficult to obtain because the catalyst tends to oxidize and break down the polymeric binder of the coating. This problem is exacerbated when the coating is exposed to intense radiation

UV from direct sunlight, as is the case with external paint. Such coatings are often formulated with inorganic binders or with organic polymers that are resistant to photocatalytic oxidation at relatively low catalyst concentrations. However, under low light conditions, the coating's removal properties are less than optimal. It would be desirable to provide a coating for use in low light conditions (e.g. inside), which contains high levels of photocatalyst for optimal removal of impurities, and which is resistant to degradation, while providing high catalytic activity in indoor lighting conditions.

[0005] [0005] The object of the present invention is therefore to provide a coating composition, in particular paint compositions, which contain titanium dioxide photocatalysts capable of removing impurities from the air, which photocatalysts have high initial activity without prior activation. Another object of the invention is to provide durable coatings with high levels of photocatalytic titanium dioxide, which coatings have the activity of removing impurities in low light conditions, in particular in the presence of visible light.

[0006] US 2007/0167551 A1 discloses a coating composition for forming an inorganic layer on the surface of a substrate, comprising at least an effective amount of photocatalytic titanium dioxide particles, an opacifying agent, inorganic binder particles, an organic binder and a solvent, wherein the organic binder and photocatalytic dioxide particles titanium are present in a weight ratio, photocatalytic titanium dioxide / organic binder in the range of 0.1 to 6.

[0007] WO 2005/118726 A1 discloses a composition for coating walls, facades or the like. The composition comprises at least one binder that has an absorbance (F (R8) function of Kubelki-Munk) less than 0.8, in particular less than 0.5, at least at one absorption wavelength in the range from 380 to 500 nm, especially from 400 to 450 nm, and at least one photocatalytically active substance that has an absorbance (Kubelle-Munk F function (R8)) above 0.005, primarily above 0.01, and most preferably 0.2 or more at said absorption wavelength.

[0008] [0006] The above discussion has been presented solely to better understand the nature of the problems facing the field and should not be interpreted in any way as an admission to the prior art, nor should any citation of any reference herein be construed as acknowledging that such reference is "prior art" for the present application.

SUMMARY OF THE INVENTION [0009] [0007] The invention is defined in the claims. In accordance with the above objectives and others, it has surprisingly been found that coatings containing titanium dioxide having a crystallite size in the range from about 1 nm (nanometer) to about 150 nm, in particular about 5 nm to about 30 nm, and preferably about 5 to about 10 nm , do not require initial activation (e.g. by washing with water) to achieve a high initial level of photocatalytic activity in the presence of light. The coatings according to the invention exhibit significant photocatalytic activity in the presence of visible light, making them ideal for use as coatings to remove contaminants in low light conditions, including indoors.

[0008] In one aspect of the invention, there is provided a self-cleaning, dirt-removing paint as defined in claim 1. Also disclosed are self-cleaning, dirt-removing coating compositions in the form of water-based paints that comprise (i) from about 5% to about 40% by volume photocatalytic titanium dioxide, preferably in substantially pure anatase form, photocatalytic titanium dioxide has an average crystallite size of from about 5 nm to about 30 nm and exhibits photocatalytic activity in the presence of visible light; (ii) one or more additional pigments, such that the total pigment volume ("PVC") of the paint, including said photocatalytic titanium dioxide, is at least about 65%; and (iii) a styrene acrylic copolymer binder; the paint being able to significantly reduce NOx in the absence of prior activation with water.

[0011] A further aspect of the invention provides a substrate after applying a coating system as defined in claim 12. Also disclosed are substrates on which a layer of self-cleaning, dirt removal coating compositions of the invention have deposited, and optionally further comprising a top coat applied to said paint layer comprising a second photocatalytic titanium dioxide with a crystallite size in the range from 5 nm to 30 nm, the top coat being created by applying a sol to a paint layer. [0012] In another aspect of the invention, there is provided a method of forming a self-cleaning, dirt removal coating on a substrate as defined in claim

4. Also disclosed is a method of removing NOx or other impurities from air, including applying to a surface such as a wall, floor, ceiling, etc., an impurity removal coating layer according to the invention, with or without prior activation, by washing with an aqueous solvent; and preferably without a washing step, said coating being capable of substantially removing impurities from the air in the presence of UV and / or visible light, preferably in the presence of visible light, and optionally applying an outer layer of the sol containing photocatalytic titanium dioxide on said paint layer.

[0013] These and other aspects of the present invention will be better understood with reference to the following detailed description and accompanying figures.

BRIEF DESCRIPTION OF THE FIGURES [0014] [0012] Fig. 1 compares NOx activities of two photocatalytic titanium dioxide coatings that have not been pre-activated, under different lighting conditions, where "Comp. 1 "is a coating containing a photocatalytic titanium dioxide powder with an average crystallite size of about 5-10 nm and" Comp. 2 "is a coating containing a photocatalytic titanium dioxide powder with an average crystallite size of about 1525 nm.

[0013] Fig. 2 compares the NOx activities of various coating systems containing the photocatalytic styrene acrylic paint according to the invention with different external layers (BG) of the sol with photocatalytic titanium dioxide placed on it.

DETAILED DESCRIPTION [0015] [0014] All terms used herein have their usual meanings, unless otherwise specified. All references to "wt%" here refer to wt% of the total paint formulation, including solvent, and not dry paint, unless otherwise specified. Reference to "volume%" or "pigment volume concentration" refers to volume% dry paint or coating, unless otherwise specified. The term "NOx" refers to the chemical forms NO (nitric oxide) and NO2 (nitrogen dioxide), either together or individually.

[0016] In the broadest sense of the disclosure, the self-cleaning, dirt-removing coating compositions comprise photocatalytic titanium dioxide particles, an organic binder, and optionally one or more additional pigments, such as calcium carbonate. The coatings may be in the form of paints (internal or external), in particular water-based paints, and ideally will have a high (e.g. over 60%) total pigment volume concentration ("PVC").

[0017] Coatings or paints are able to significantly reduce NOx compounds in the absence of prior activation with water. It should be understood that although the coatings of the invention are capable of significantly reducing impurities in the absence of prior activation with water, it is within the scope of the invention to activate the coatings by treatment with water after application to further enhance photocatalytic activity.

[0018] Where it has been found that the paint has significant "initial" photocatalytic activity in the absence of prior activation with water, this means that the paint has significant measurable activity against NOx compounds immediately after the paint coating has been completely formed on the substrate dried and / or cured to the usual extent before allowing such paint to be used (e.g. it is not sticky and does not transfer easily when touched, etc.).

[0019] When referring to "removing" impurities from air, it should be understood that it includes complete or partial removal of impurities from the air. Whether removal is "significant" can be determined by the methods given in the examples, wherein "significant" removal refers to a reduction in the total concentration of a given amount of a given impurity by at least about 2.5%, preferably at least about 5%, and more preferably at least about 7.5%.

[0019] The self-cleaning, dirt-removing paint according to the invention contain particles of photocatalytic titanium dioxide (TiO2) which are capable of forming electron-hole pairs in the presence of electromagnetic radiation, in particular ultraviolet (UV) radiation, close to UV and / or light visible. Preferably, photocatalytic titanium dioxide is capable of significant photoactivity in the presence of visible light. To this end, it has been surprisingly discovered that careful control of the crystalline form and size of titanium dioxide particles provides photocatalities that are capable of removing impurities in low UV light environments, especially indoors, and which have significant initial activity, even when not activated by washing solvent (e.g. water).

[0021] Photocatalytic titanium dioxide particles for use in the paint compositions of the disclosure are preferably mainly in the crystalline form of anatase due to its higher photoactivity than the rutile form. "Mainly" means that the level of anatase in the titanium dioxide particles in the paint is greater than 50% by mass, although it is preferred that the level of anatase is greater than about 80%, and more preferably greater than about 90%. In the invention, the photocatalytic titanium dioxide particles in the paint are in the form of substantially pure anatase, which means that the content of rutile crystal form is less than 5%, in particular less than about 2.5%, and even more preferably less than about 1% by mass . In some embodiments, the photocatalytic titanium dioxide particles will be rutile free, which means that the crystalline form of rutile cannot be detected by crystallography. In other words, photocatalytic titanium dioxide particles can contain 100% anatase forms. The degree of crystallization and the nature of the crystalline phase are measured using X-ray diffraction.

[0022] Photocatalytic titanium dioxide particles for use in paint compositions will usually have an average particle size that allows mainly light absorption rather than light scattering. When the particle sizes become very small, the energy gap between valence and conductivity bands decreases. Thus, with sufficiently small particle sizes, it has been observed that the titanium dioxide particles are able to absorb light in the visible spectrum. Titanium dioxide particles for inclusion in the disclosed paints will usually have a particle size between about 1 nm and about 150 nm. More typically, the particle size will be between about 5 nm and about 20 nm, 25 nm or about 30 nm. In a preferred aspect, the size of the titanium dioxide particles in the paint will be between about 5 nm and about 15 nm, and in particular between about 5 and about 10 nm. Reference to the particle size (or crystallite) of titanium dioxide will be understood as the mean particle size of the titanium dioxide particles. If the particle size is modified by the term "about", it should be understood that it includes slightly larger or smaller particle sizes than the indicated value to take into account experimental errors related to measurement and variability between different methods of measuring particle size, as will be apparent to one of ordinary skill in the art. . Diameters can be measured, for example, by transmission electron microscopy (TEM) as well as XRD.

[0023] Alternatively, the particles can be characterized by surface area. Typically, a titanium dioxide photocatalyst powder will have a surface area, measured by any suitable method, including a 5-point BET, greater than about 70 m²/ g, more often than about 100 m²/ g, and preferably greater than about 150 m²/ G. In the invention, the titanium dioxide photocatalyst will have an area larger than 250 m²/ g or even more than about 300 m²/ G.

[0023] Photocatalytic titanium dioxide available from Millennium Inorganic Chemicals under the designations PCS300 and PC500 has been found to be particularly useful for inclusion in the paints of the invention. PCS300 is a titanium dioxide powder with 100% anatase, with an average crystallite size from about 5 nm to about 10 nm. PC500 is also a titanium dioxide powder with 100% anatase, which has a TiO2 content of from about 82% to about 86% by weight and which has an area of ​​about 250 to about 300 m²/ g, measured with 5-point BET, which translates into an average particle size of from about 5 nm to about 10 nm. The product labeled PC105, also from Millennium Inorganic Chemicals, will also find use in some embodiments of the invention. This photocatalyst powder contains more than 95% by weight of titanium dioxide, TiO2 which is 100% anatase and has an average crystallite size of about 15 nm to about 25 nm and a surface area between about 80 and about 100 m²/ G.

[0025] In the disclosure, photocatalytic titanium dioxide will typically make up from about 2 to about 40% by volume of the paint formulation. In the invention, photocatalytic titanium dioxide will constitute from 5 to 40% by volume of the paint formulation. More typically, photocatalytic titanium dioxide will constitute from about 5% to about 20% by volume of paint, and preferably from about 7.5% to about 15% by volume. In a representative embodiment, photocatalytic titanium dioxide accounts for about 10% by volume of the paint formulation. The above amounts represent the volume of photocatalyst in the final paint formulation (e.g. including solvent), not the volume percentage of the dried paint coating. Typically, the weight percentage of titanium dioxide in the paint formulation will be between about 1% by weight and about 20% by weight, more typically between about 5 and about 10% by weight, and preferably about 7.5% by weight.

[0026] It is within the scope of the invention to provide paints having two or more different titanium dioxide photocatalysts, wherein at least one, and preferably each, of the titanium dioxide photocatalyst materials meets the above specifications. Thus, for example, the invention includes the use of a bimodal photocatalytic titanium dioxide material formed by combining two different titanium dioxide powders or sols, wherein at least one, and preferably both, have the particle size and / or surface area as defined above. In other embodiments, the photocatalyst will "consist essentially of" a specific titanium dioxide material as defined herein, which means that any additional photocatalyst with significantly different activities are excluded, or those amounts of additional photocatalyst that have a significant effect on durability, removal are excluded impurities, or the self-cleaning properties of the paint.

[0027] The paints according to the invention contain an organic binder. In the broadest aspect of the disclosure, it is contemplated that any polymer binder may be used. In one aspect of the disclosure, the polymeric binder is a water dispersible polymer, including, but not limited to, latex binders such as natural latex, neoprene latex, nitrile latex, acrylic latex, vinyl acrylic latex, styrene acrylic latex, styrene latex butadiene and the like.

Exemplary polymers for these compositions include, but are not limited to, methyl methacrylate, styrene, methacrylic acid 2-hydroxyethyl acrylate polymer (CAS # 70677-00-8), acrylic acid, methyl methacrylate, styrene, hydroxyethyl acrylate, butyl acrylate polymer (CAS # 7732-38-6), butyl acrylate, methyl methacrylate, hydroxyethyl acrylate polymer (CAS # 2595138-6), butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, acrylic acid polymer (CAS # 42398-14-1), styrene . butyl acrylate polymer (CAS # 25767-47-9), butyl acrylate, 2-ethylhexyl acrylate, methacrylic acid polymer C (CAS # 31071-53-1), acrylic polymers and polymers of carboxylated styrene-butadiene, to name a few. In the invention, the paint comprises a styrene acrylic copolymer binder. Combinations of more than one organic binder are also considered useful in the practice of the invention.

[0028] In particular, the organic binder can be selected from styrene / butadiene copolymers and polymers and copolymers of acrylic acid esters, in particular polyvinylacrylate and styrene / acrylic copolymers. In the present invention, the styrene acrylic copolymer includes styrene / acrylic esters thereof. It was found that the styrene acrylic emulsion sold under the trade name ACRONAL ™ 290D (BASF) is particularly useful as an organic binder in the paints of the invention.

[0029] In some embodiments, the organic binder in the paints of the invention will "consist essentially of" a preferred styrene acrylic binder, which means that the presence of additional organic binders in quantities that significantly reduce the durability of the paint coating on Substrate, compared to an paint coating that is identical in other respects and only contains a styrene acrylic binder as an organic binder.

[0030] In some embodiments, the paints of the invention will be substantially free of inorganic binders, which means that levels of inorganic binder are not sufficient to form a continuous adherent film on the substrate in the absence of an organic binder. In the invention, the paints contain less than 0.5% by weight, preferably less than about 0.2% by weight, and even more preferably less than about 0.1% by weight of inorganic binders. In some embodiments, the paints of the invention are free of inorganic binders. Inorganic binders include, without limitation, alkali metal silicates such as, for example, potassium silicate, sodium silicate and / or lithium silicate. [0031] The paints of the invention may further comprise one or more pigments. The term "pigments" is intended to include, without limitation, pigment compounds used as dyes, including white pigments, as well as ingredients commonly known in the art as "opacifying agent" and "fillers". This includes any organic or inorganic compound in the form of particles capable of providing opacity to the coating, in particular at least one inorganic compound, such as non-photocatalytic titanium dioxide. Titanium dioxide pigments that are not photoactive are disclosed in US Patent No. 6,342,099 (Millennium Inorganic Chemicals Inc.). In particular, the titanium dioxide pigment may be Tiona ™ 595 particles sold by Millennium Inorganic Chemicals Ltd. Pigments also include calcium carbonate, which is usually added to the paint as a filler. One suitable calcium carbonate material is that sold under the trade name Setacarb ™ 850 OC (Omya).

[0032] The paints of the invention typically, but not necessarily, have a pigment volume (PVC) concentration between 65% and about 90%, more typically between 65% and about 80%, and preferably between about 70% and about 75%. The term "pigment volume concentration" refers to the total volume percent of all pigments in the composition, the term "pigment" includes all forms of titanium dioxide, both photocatalytic (e.g. PC500) and non-photocatalytic (e.g. Tiona ™ 595), as well as any other ingredients generally considered in the art as pigments, including without limitation calcium carbonate and other molecular fillers.

[0033] If necessary, various other compounds may be added to the composition of the invention, but preferably such addition does not affect shelf life, photoactivity, durability or non-darkening properties of the resulting coating. Examples of such additional compounds include filler (s) such as quartz, calcite, clay, talc, barite and / or Na-Al silicate, and the like; pigments such as TiO2, lithopone and other inorganic pigments; dispersing agents such as polyphosphates, polyacrylates, phosphonates, naphthenic and lignin sulfonates, to name a few; wetting agents, including anionic, cationic, amphoteric and / or nonionic surfactants; anti-foaming agents such as, for example, silicone emulsions, hydrocarbons and long chain alcohols; stabilizers, including, for example, mainly cationic compounds; linking agents, including, without limitation, alkali-stable esters, glycols and hydrocarbons; rheological additives such as cellulose derivatives (e.g. carboxymethyl cellulose and / or hydroxyethyl cellulose), xanthan gum, polyurethane, polyacrylate, modified starch, bentone and other lamellar silicates; hydrophobic agents such as alkyl silicates, siloxanes, wax emulsions, Li salts of fatty acids; and conventional fungicides or biocides.

Example 1 [0034] The ability of the coatings according to the invention to remove NOx impurities, their self-cleaning properties and durability were tested by producing three aqueous styrene acrylic paints. Each comparative sample "Comp. 1 "and" Comp. 2 ”contained 10% photocatalytic titanium dioxide by volume, while no photocatalyst was present in the control sample. The photocatalytic titanium dioxide used in Comp. 1 is PCS300 from Millennium Inorganic Chemicals. PCS300 is a photocatalytic titanium dioxide powder with an average crystallite size of about 5 to about 10 nm (nanometers). The photocatalytic titanium dioxide used in Comp. 2 is PC105, also from Millennium Inorganic Chemicals, which has an average crystallite size of about 15-25 nm. Comp. 2 is a reference example. PCS300 and PC105, both, have anatase content of about 100%. The complete paint formulations are given in Table 1.

Table 1

<td>Ingredient</td><td>Function</td><td>Komp.1</td><td>Comp. 2 (reference)</td><td>Control</td>

<td colspan="2">Part A</td><td colspan="3">Weight (g)</td>

<td>Water</td><td>solvent</td><td> 159,94</td><td> 159,94</td><td> 152,41</td>

<td>Natrosol 250MR</td><td>thickener</td><td> 99,30</td><td> 99,30</td><td> 104,64</td>

<td>Foammaster NXA</td><td>anti-foaming agent</td><td> 0,60</td><td> 0,60</td><td> 0,63</td>

<td>Antiprex A.</td><td>dispersant</td><td> 3,30</td><td> 3,30</td><td> 3,48</td>

<td>Tiona T595</td><td>TiO2 pigment</td><td> 70,58</td><td> 70,58</td><td> 74,37</td>

<td>PC105</td><td>TiO2 photocatalyst</td><td> --</td><td> 47,06</td><td> --</td>

<td>PCS300</td><td>TiO2 photocatalyst</td><td> 47,06</td><td> --</td><td> --</td>

<td>Setacarb 850 OG</td><td>filler (CaCO3)</td><td> 145,28</td><td> 145,28</td><td> 186,55</td>

<td colspan="2">Hello B</td><td colspan="3"></td>

<td>Acronal 290D</td><td>styrene acrylic</td><td> 69,86</td><td> 69,86</td><td> 73,62</td>

<td>Texanol</td><td>connecting agent</td><td> 3,46</td><td> 3,46</td><td> 3,67</td>

<td>Acticide SPX</td><td>bactericide</td><td> 0,60</td><td> 0,60</td><td> 0,63</td>

<td>Total weight)</td><td></td><td> 600,00</td><td> 600,00</td><td> 600,00</td>

[0035] The other ingredients in Table 1 are as follows: The thickener is a 3% hydroxyethyl cellulose solution, sold under the name Natrosol ™ 250 MR (Hercules). Foammaster ™ NXA defoamer is proprietary sold by Henkel Corp. Setacarb ™ 850 OG is a calcium carbonate filler obtained from Omya. Antiprex ™ A is a water-soluble polymer dispersant from Ciba Specialty Chemicals. Tiona ™ T595 is pigment titanium dioxide from Millennium Inorganic Chemicals. Acronal ™ 290D is a styrene acrylic latex copolymer used as an organic binder available from BASF. Acronal ™ 290D contains 50% by weight solids in water. Texanol ™ is an alcohol bonding solvent sold by Eastman Kodak. Acticide SPX is a bacteriocide from Acti Chem Specialties Inc.

[0035] The components of Part A and Part B were separately mixed under high shear mixing conditions. Part A was then added to Part B under high shear mixing to produce finished paints. Each paint sample is applied with a covering of 770 g / m2² (based on the dried weight of the coating) on ​​the substrate and substrates were subjected to the following tests.

[0036] I-Determination of NOx Removal by Coatings [0037] The full methodology for determining NOx removal is described in US Patent Publication 2007/0167551. In brief, the samples were placed in a sealed sample chamber and sealed. The sample chamber is connected to a three-channel gas mixer (Brooks Instruments, The Netherlands), through which NO (nitric oxide), NO2 (nitrogen dioxide) and compressed air containing steam are introduced into the chamber at predefined levels. The samples are irradiated at 8 W / m² UV radiation in the range of 300 to 400 nm from a UV lamp model VL-6LM with a wavelength of 365 and 312 nanometers (BDH). Initial and final values ​​(after five minutes of irradiation) of NOx were measured using a model ML9841B nitric oxide analyzer (Monitor Europe) connected to the sample chamber. The% NOx reduction was measured as (Δ NOx / NOx initial) x 100. Each sample was tested without pre-activation and with pre-activation (after washing with water). The results are collected in Table 2.

Table 2

<td colspan="2">no initial activation</td><td colspan="2">pre-activated</td>

<td>A sample</td><td>% NOx reduction</td><td>A sample</td><td>% NOx reduction</td>

<td>Comp. 1</td><td> 58,6</td><td>Komp.1</td><td> 68,3</td>

<td>Comp. 2 (reference)</td><td> 8,3</td><td>Comp. 2 (reference)</td><td> 55,2</td>

<td>Control</td><td> 0</td><td>Control</td><td> 0</td>

[0038] The results indicate that the paint containing the photocatalytic titanium dioxide powder with an average crystallite size from about 5 to about 10 nm (Comp. 1) exhibits surprisingly high NOx activity even without the conventional washing step for the initial activation of photocatalytes. For comparison, comp. 2, which contains titanium dioxide powder with an average crystallite size from about 15 nm to about 25 nm, shows a significantly lower degree of NOx reduction in the absence of a pre-activation step. Comp. 1 and Comp. 2, both, have excellent NOx removal properties after washing to preactivate the catalyst. However, Comp. 1 without pre-activation was unexpectedly better than Comp. 2 even if the Comp. 2 sample was pre-activated.

[0039] Il-Determination of the photoactivity of the coating against methylene blue [0039] [0040] The methodology used to determine the photoactivity against methylene blue is similar to that described in US Patent Publication 2007/0167551 and is modified as described herein. The self-cleaning properties of each paint sample were tested based on their ability to degrade the organic methylene blue dye. When the dye degrades to water, carbon dioxide, and nitrogen-containing chemical forms, loss of color is observed. Photoactivity is monitored by measuring L * (brightness). The protocol is as follows:

[0040] [0041] Prepare a paint film on a suitable substrate, such as Melinex foil, aluminum panel or glass plate. The film thickness should be similar to that used in the final application and generally not less than 25 microns after drying. The paint film is allowed to dry at least overnight.

[0041] Prepare a solution of methylene blue in water by dissolving 0.3739 g in one liter of water to obtain a concentration of 1 mmol / L. Pour the methylene blue solution into a suitable container in which you will immerse the paint layer. Immerse the paint layers in the methylene blue solution for 30 to 60 minutes to ensure that the methylene blue is chemically absorbed on the TiO2 surface.

[0042] [0043] Remove the paint layer from the solution and remove the excess with an absorbent wipe. Dry the paint layers thoroughly, and then measure the brightness (L *) value with a colorimeter or spectrophotometer.

[0044] [0044] Exposing the paint layers to UV rays for 18 to 48 hours at an intensity of 30 to 60 W / m² (300-400 nm long), just like in the Atlas Suntest cabinet. [0044] [0045] Measure the L * value again. The difference between the initial and final L * measurement is a measure of the self-cleaning strength of the coating. The greater the difference in L *, the greater the self-cleaning effect. The results for each paint after 18 hours and 36 hours of irradiation are shown in Table 3 below.

Table 3

<td></td><td colspan="2">AL *</td>

<td>A sample</td><td>18 hours</td><td>36 hours</td>

<td>Comp. 1</td><td> 15,3</td><td> 18,2</td>

<td>Comp. 2 (reference)</td><td> 10,6</td><td> 12,5</td>

<td>Control</td><td> 0</td><td> 0</td>

[0045] The results indicate that the paint containing the photocatalytic titanium dioxide powder with an average size of about 5 to about 10 nm (Comp. 1) shows significantly more self-cleaning activity than Comp. 2 sample after 18 hours and 36 hours of irradiation.

[0047] Ill-Determination of Coating Durability [0046] [0048] Full methodology for determining paint durability is described in US Patent Publication 2007/0167551. The methodology is based on the accelerated action of atmospheric factors on 20 to 50 micron paint layers on a stainless steel substrate in a Ci65A (Atlas Electric Devices, Chicago) at a 6.5 kW xenon source emitting 550 W / m² UV at 340 nm. Samples were heated to approximately 63 ° C and water sprayed for 18 minutes out of every 120 minutes, without a dark cycle. Stability is measured as a function of weight loss of the sample after exposure.

[0047] Table 4 summarizes the results of stability tests for Comp. 1 and Comp. 2 at various intervals of up to 1551 hours.

Table 4

<td></td><td>Comp. 1</td><td>Komp.2 (reference)</td>

<td>hours</td><td colspan="2">Weight loss (%)</td>

<td> 0</td><td> 0,0</td><td> 0,0</td>

<td> 286</td><td> 24,6</td><td> 21,1</td>

<td> 451</td><td> 38,7</td><td> 33,5</td>

<td> 586</td><td> 48,6</td><td> 43,3</td>

<td> 765</td><td> 59,6</td><td> 55,5</td>

<td> 997</td><td> 70,0</td><td> 69,6</td>

<td> 1181</td><td> 76,7</td><td> 80,1</td>

<td> 1365</td><td> 83,4</td><td> 84,6</td>

<td> 1551</td><td> 88,9</td><td> 90,7</td>

[0050] As shown in Table 4, the durability of Paint 2 is essentially identical to that of less photoactive Paint 1 after about 1000 hours of exposure. This result was unexpected because it could be expected that a more photoactive paint Comp. 2 would deteriorate much faster than a less active Komp 1 under these conditions. It should be noted that for 765 hours, the% weight loss was slightly higher for the more active paint Comp. 1 with a maximum difference observed after about 451 hours. This is probably due to the fact that Comp. 1 has a much higher initial activity without initial activation compared to Comp. 2 (see Table 2). However, when aging under atmospheric conditions, both paints become fully activated due to the presence of water, and the percentage of weight loss coincides over longer intervals. For the entire period of accelerated aging in atmospheric conditions, Comp. 1 showed excellent durability comparable to Comp. 2.

[0051] Ill-Determination of NOx Removal at Different Light Sources [0049] [0052] The procedure for determining NOx removal, described above in Part I of this Example, was used to determine the appropriate abilities of paint samples Comp. 1 and Comp. 2 for removing NOx at different light sources. In addition to UV, low-intensity fluorescent light, daylight (filtered through glass) and incandescent light sources were used

Osram. In each case, the paints were tested without prior activation. The results are summarized in the table below (Table 5) and illustrated in Fig 1.

Table 5

<td></td><td>Comp. 1</td><td>Comp. 2 (reference)</td>

<td>Source of light</td><td colspan="2">% NOx reduction</td>

<td>UV</td><td> 61,6</td><td> 14,1</td>

<td>Fluorescent strip</td><td> 9,1</td><td> 0,0</td>

<td>Daylight</td><td> 22,4</td><td> 1,0</td>

<td>incandescent</td><td> 7,8</td><td> 0,0</td>

[0050] The UV light came from a UV lamp model VL-6LM with a wavelength (BDH) 365 and 312 nanometers as used in Part I of this Example. Fluorescent light was light produced from conventional internal fluorescent lighting. Daylight was filtered through the glass to provide an intensity of 2.4 microW / cm². The incandescent light was provided by the Osram incandescent lamp.

[0051] The results shown in Table 5 show that the paint Comp. 1 has significant NOx removal activity, without pre-activation, with each of the lighting sources, while the paint Comp. 2, without pre-activation, does not show activity on the strip fluorescent or incandescent lighting and negligible daylight activity (2.4 microW / cm²). It is believed that the excellent performance of a Komp. 1 paint under these ultra-low UV lighting conditions is due to the ability of the PCS300 photocatalyst to absorb in the visible spectrum. Without wishing to be bound by any particular theory, it is believed that a very small crystallite size (e.g., about 5-10 nm) reduces the energy gap between valence and conductive bands, thus allowing molecules to form an electron-hole pair in the presence of visible light .

Example 2 (reference) [0052] Although paints with a photocatalyst crystallite size from 5 to 10 nm are in accordance with the invention, including, for example, the paint designated Comp. 1 in Example 1 with a TiO2 photocatalytic particle size of about 5-10 nm , the advantages of high PVC (pigment volume concentration) obtainable by using styrene acrylic binder are also visible, though modestly, with other titanium dioxide crystallite sizes (i.e. about 15 to about 50 nm). For example, paints using high levels of the PC105 photocatalyst (crystallite size from about 15 to about 25 nm) will also find use in NOx removal coatings, [0053] This example illustrates the effectiveness of the paint designated Comp. 2 in Example 1 in removing pollution in "real" conditions. The corner of the parking garage was separated by building two walls providing 917 m³ closed area with a ceiling height of 2.85 m. Ceiling area 322 m² was covered with paint Comp. 2 from Example 1, while the walls (existing and artificial) were covered with nylon. Photocatalytic paint was not pre-activated by washing with water. During NOx removal experiments, the housing was illuminated with twenty UV lamps symmetrically mounted 20 cm from the ceiling to ensure a total UV intensity of 1 W / m².

[0054] The exhaust gas from a vehicle located outside the housing was connected by a pipe to the enclosed area, so that the exhaust gas was released 4.74 m inside the housing. Ventilation (inlet and outlet) was provided in the room by artificial walls to maximize the concentration of pollutants near the ceiling and ensure air flow and speed of 566 m³/ h and 14.3 m / h, respectively. The air flow and exhaust gas velocity were estimated at 50.6 m³/ h and 2 m / s, respectively, so that overpressure was maintained in the enclosed space to avoid air inflow from outside the housing.

[0055] The NOx exhaust from the car was measured continuously using a portable gas analyzer. NOx measurements were also made continuously at the inlet and outlet fan and at the third sampling point near the ceiling, about 15 m from the outlet fan.

[0056] After allowing the exhaust gas to reach a steady state in the housing (about 3 hours, the UV lamps were turned on for four or five hours. Reduction of NO and NO2 was measured as the difference between steady-state concentration and final concentration after irradiation. The values ​​were corrected for a decrease in NO concentration and an increase in NO2 concentration in car exhaust gases during the test period in order to separate the contribution of photocatalytic paint in the total reduction of these impurities. The experiments were repeated for three consecutive days. On the fourth day, control measurements were taken in the absence of UV radiation. The results are shown in Table 6 (% NO photocatalytic degradation) and Table 7 (% NO2 photocatalytic degradation).

Table 6

<td>Experimental Day</td><td>Initial steady-state NO concentration (ppb)</td><td>Irradiation time UV (h)</td><td>Final NO concentration (ppb)</td><td>Total% of NO removed</td><td>% NO removal in car emissions</td><td>% NO degradation due to TiO2</td>

<td> 1</td><td> 1092</td><td> 5</td><td> 581</td><td> 46,8</td><td> 28</td><td> 18,8</td>

<td> 2</td><td> 623</td><td> 5</td><td> 351</td><td> 43,6</td><td> 28</td><td> 15,6</td>

<td> 3</td><td> 1286</td><td> 4</td><td> 898</td><td> 30,2</td><td> 23,5</td><td> 6,7</td>

<td rowspan="2"> 4</td><td rowspan="2"> 1151</td><td rowspan="2"> 0</td><td> 829</td><td>28 (5h)</td><td>28 (5h)</td><td rowspan="2"> 0</td>

<td> 880</td><td>23.5 (4h)</td><td>23.5 (4h)</td>

Table 7

<td>Experimental Day</td><td>Initial steady-state NO2 concentration (ppb)</td><td>Irradiation time UV (h)</td><td>Final concentration NO2 (ppb)</td><td>Total% of NO2 removed</td><td>% NO removal in car emissions</td><td>% NO degradation due to TiO2</td>

<td> 1</td><td> 892</td><td> 5</td><td> 767</td><td> 14</td><td> 8,5</td><td> 22,5</td>

<td> 2</td><td> 879</td><td> 5</td><td> 708</td><td> 19,4</td><td> 8,5</td><td> 27,9</td>

<td> 3</td><td> 1110</td><td> 4</td><td> 1059</td><td> 4,6</td><td> 8,5</td><td> 13,1</td>

<td> 4</td><td> 1031</td><td> 0</td><td> 1119</td><td> 8,5</td><td> 8,5</td><td> 0</td>

[0057] From the data in Tables 6 and 7 it appears that styrene acrylic paint containing photocatalytic titanium dioxide crystallites with an average size of about 15-25 nm at 10% by volume (about 8% by weight) effectively reduces NOx pollution from air , even without prior activation. In addition, this example underlines the usefulness of the paint coating in applications such as the interior of a parking garage where it is desirable to remove concentrated contaminants from the air.

Example 3 [0058] Styrene acrylic paint was prepared essentially as described in Example 1, except that PCS300 was replaced with a comparable photocatalytic titanium dioxide powder with 100% anatase, available from Millennium Inorganic Chemicals under the trade name PC500. The PC500 has an area of ​​about 300 m²/ g, which translates into an average crystallite size of about 5 to about 10 nm. The PC500 was contained in the paint at a level of 8% by volume, and the styrene acrylic binder constituted about 50% by volume. The ability of this paint to remove NOx without prior activation was tested as a function of UV intensity in the intensity range from 0.5 W / m² up to 8 W / m² according to the procedure described above in Example 1. The results are given in Table 8.

Table 8

<td>Intensity UV (W / m²)</td><td>% NOx reduction</td>

<td> 0.5</td><td> 31,3</td>

<td> 1</td><td> 37,1</td>

<td> 2</td><td> 40,6</td>

<td> 3</td><td> 44,2</td>

<td> 4</td><td> 45,5</td>

<td> 5</td><td> 46,4</td>

<td> 6</td><td> 46,9</td>

<td>Intensity UV (W / m²)</td><td>% NOx reduction</td>

<td> 7</td><td> 46,9</td>

<td> 8</td><td> 47,3</td>

[0059] These results show that even at very low UV intensities, the paints according to the invention ensure high removal of impurities, even without initial activation. In fact, the difference in NOx reduction was only 16% (47.3% - 31.3%) relative to the increase in UV intensity by more than one order of magnitude.

[0063] Paint PC500 was coated with various sols of photocatalytic TiO2 listed in Table 9 to examine whether further improvements in de-NOx properties could be obtained.

Table 9

<td>A sample</td><td>Outer layer of the sol</td>

<td>AND</td><td>lack</td>

<td>B</td><td>S5300</td>

<td>C</td><td>SP300N</td>

<td>D</td><td>S5300B (23.6% w / w TiO2)</td>

<td>E</td><td>S5300B (10.0% w / w TiO2)</td>

<td>F</td><td>S5300B (5.0% w / w TiO2)</td>

<td>G</td><td>AW1610 (0.24% w / w TiO2)</td>

[0061] Sample A shows a styrene acrylic paint containing a PC500 photocatalyst without any outer layer of sol. BG samples show the paint of sample A, on which the indicated outer layer of the sol was applied. S5300A is a photocatalytic titanium dioxide sol available from Millennium Inorganic Chemicals. It is an aqueous colloidal dispersion of very fine TiO2 (anatase) acid peptized with a pH of about 1.1 (± 0.4), with a titanium dioxide content of about 20 (± 2)% by weight, a density of about 1.2 g / ml and a surface area more than 250 m²/ g according to 5-point BET (on dried product). S5300B, also available from Millennium Inorganic Chemicals, is also an aqueous colloidal dispersion of very fine TiO2 (anatases) peptized with a base with a pH of about 11.4 (± 1), with a titanium dioxide content of about 17.5 (± 2.5)% by weight, a density of about 1.1 g / ml and an area greater than 250 m²/ g according to 5-point BET (on dried product). The various sols S5300B in Table 9 have been modified to obtain the indicated titanium dioxide content based on weight. AW1610 is a sol containing photocatalytic TiO2 with an average crystallite size of about 3.6 nm, pH 9.2, a density of about 1.00 g / ml and a TiO2 content of about 0.25%. SP300N is a suspension of photocatalytic TiO2 (about 17% by weight) with an average crystallite size of about 5-10 nm, pH 7.0 and a density of about 1.15 g / ml.

[0062] [0065] The ability of each coating system (paint + sol) to remove NOx was tested as a function of UV light intensity from 0.5 W / m² up to 8 W / m². The results are shown in Fig. 2. As can be seen, the D coating system containing the PC500 paint with the S5300B top coating (23.6% w / w TiO2) showed unexpectedly better de-NOx over the entire UV intensity range 5 with minimal variation in% NOx reduction in the whole range.

[0063] Many modifications and variations of this invention can be made without departing from its scope, as will be apparent to those skilled in the art. The specific embodiments described in the present invention are offered by way of example only, and the invention is to be limited only by the appended claims.

Tronox LLC, United States of America Representative:

Z-19144/19