Photocatalytic coating

The present invention relates to compositions for providing a photocatalytic coating on the surface. More specifically, the present invention relates to a purifying self-cleaning paint containing titanium dioxide particles that does not require prior activation to achieve initial high photocatalytic activity.

The photocatalytic properties of titanium dioxide in semiconductor materials are due to electron promotion from the valence band to the conduction band under the influence of ultraviolet (UV) and near UV irradiation. The created reactive electron-hole pair migrates to the surface of the titanium dioxide particles, where the holes oxidize the adsorbed water to generate reactive hydroxyl radicals and reduce the oxygen adsorbed by the electrons. Generates superoxide radicals, both of which are NO in the atmosphere_xAnd can decompose volatile organic compounds (VOCs). Due to these properties, photocatalytic titanium dioxide is used in coatings and the like to remove pollutants from the atmosphere. The coating may also have the advantage of self-cleaning as the soil (grease, mildew, mold, algae, etc.) is also oxidized on its surface.

Despite the advantages of existing photocatalytic titanium dioxide coatings, there is room for improvement in the art. In particular, it has been observed that the initial activity of conventional photocatalytic titanium dioxide coatings is poor unless the coating is pre-activated, such as by washing with water. Without wishing to be linked by either theory, this activation step removes organic components present in the coating composition from the catalyst surface, or water on titanium dioxide particles on which reactive radical species are formed. It is likely that it is necessary to provide a summed surface. However, this additional step is time consuming and makes the application of the photocatalytic titanium dioxide coating somewhat inconvenient due to the additional cost added to the application process. It is desirable to provide a photocatalytic titanium dioxide coating that does not require prior activation (eg, cleaning steps or exposure to elements) to achieve the initial high activity levels, especially in the form of a paint.

Also, it has been difficult to provide a coating with high levels of photocatalyst because the catalyst has a tendency to oxidize and decompose the polymer binder of the coating. This problem is exacerbated when the coating is exposed to extreme UV irradiation from direct sunlight, as in the case of outdoor paints. Such coatings are often formulated with inorganic binders or organic polymers that are resistant to photocatalytic oxidation at relatively low catalytic concentrations. However, under low illumination conditions, the decontamination properties of the coating are not optimal. It incorporates a high level of photocatalyst for optimal decontamination and provides a coating for use in low lighting environments (eg indoors) that is resistant to decomposition and has high catalytic activity under indoor lighting conditions. Further provision would be desirable.

The above description is provided solely to provide a better understanding of the nature of the challenges faced in the art and should not be construed as an approval for the prior art and any of the references herein. The citation of is also not to be construed as an approval to constitute "prior art" for the present application.

<p> Therefore, it is an object of the present invention to provide a coating composition, particularly a coating composition, comprising a titanium dioxide photocatalyst capable of removing contaminants from the atmosphere and having an initial high activity without prior activation of the photocatalyst. Furthermore, it is another object of the present invention that the coating provides a durable coating with high levels of photocatalytic titanium dioxide having decontamination activity, especially in the presence of visible light.</p>

<p> For the above purposes and the like, coatings containing crystal size titanium dioxide in the range of about 1 nm (nanometers) to about 150 nm, particularly about 5 nm to about 30 nm, preferably about 5 nm to about 10 nm, are initially coated in the presence of light. It has been surprisingly found that no prior activation (eg, by washing with water) is required to achieve high levels of photocatalytic activity. The coating of the present invention exhibits substantial photocatalytic activity in the presence of visible light, which makes the coating of the present invention ideal for use as a purifying coating in low lighting environments including indoors.</p><p> In one embodiment of the invention, the self-cleaning purifying coating composition is (i) preferably about 5% by volume to about 40% by volume photocatalytic titanium dioxide of substantially pure anatase form, wherein the photocatalytic titanium dioxide is here. Titanium is characterized by an average crystal size of about 5 nm to about 30 nm and photocatalytic activity in the presence of visible light; (ii) the total pigment volume concentration (PVC) including the photocatalytic titanium dioxide is at least about about. One or more additional pigments such as 65%; and (iii) in the form of water-based paints containing styrene-acrylic copolymer binders, which are NO in the absence of prior activation in water._xThe compound can be substantially reduced.</p><p> Another aspect of the invention comprises depositing a layer of the self-cleaning purifying coating composition according to the invention on a substrate and optionally comprising a second photocatalytic titanium dioxide having a crystal size in the range of 5 nm to 30 nm. A substrate further comprising a topcoat placed on the paint layer is provided, the topcoat being formed by applying a sol to the paint layer.</p><p> In another aspect of the invention, NO from the atmosphere_XAlternatively, a method for removing other contaminants is provided, such as walls, floors, ceilings, etc., with or without prior activation by washing with an aqueous solvent, preferably without a washing step. Including applying a layer of a purifying coating according to the invention to the surface, the coating substantially removes contaminants from the atmosphere in the presence of UV and / or visible light, preferably in the presence of visible light, if desired. , A sol topcoat containing a photocatalytic titanium dioxide can be applied on the coating layer.</p><p> These and other aspects of the invention will be better understood by reference to the following detailed description and accompanying drawings.</p>

<figref num="1">In FIG. 1, "Composition 1" is a coating containing a photocatalyst titanium dioxide powder having an average crystal size of about 5 to 10 nm, and "Composition 2" is a photocatalyst having an average crystal size of about 15 to 25 nm. NO of two photocatalytic titanium dioxide coatings that were not pre-activated under various lighting conditions when the coating contained titanium dioxide powder_XCompare activity.</figref>

<figref num="2">FIG. 2 shows NOs of various coating systems including a styrene acrylic resin photocatalytic coating according to the present invention having various photocatalytic titanium dioxide sol topcoats (B to G) provided on the top._XCompare activity.</figref>

All terms used herein are intended to have their usual meaning unless otherwise noted. All references to "% by weight" relate to% by weight of the total paint formulation, including solvent, rather than dry paint, unless otherwise noted. References to "% by volume" or "volume concentration of pigments" refer to% by volume of dry paint or coating unless otherwise noted. "NO_XThe term "species NO (nitrogen oxides) and NO collectively or individually"₂(Nitrogen dioxide).

In the broadest sense of the invention, the self-cleaning purifying coating composition comprises photocatalytic titanium dioxide particles, an organic binder and, optionally, one or more additional pigments such as calcium carbonate. The coating can be in the form of paints (indoor or outdoor), especially water-based paints, ideally having a high (eg, greater than 60%) total pigment volume concentration ("PVC"). Let's do it.

The coating or paint is NO in the absence of prior activation in water_XThe compound can be substantially reduced. The coatings of the present invention can substantially reduce contaminants in the absence of prior activation with water, however, treatment with water after application activates the coating to further enhance photocatalytic activity. Will be understood to be within the scope of the present invention.

When it is mentioned that the paint has substantial "early" photocatalytic activity in the absence of prior activation in water, the coating of the paint formed on the substrate provides such paint to service. Immediately after drying sufficiently and / or curing to the extent customarily permitted before being applied (eg, it is non-adhesive and does not easily transfer on contact, etc.), the paint is NO._XIt means that it has substantially measurable activity on the compound.

If the reference is made to "remove" pollutants from the atmosphere, it will be understood to include complete or partial removal of pollutants from the atmosphere. Whether the removal is "substantial" can be determined by the method provided in the Examples, where the "substantial" removal is at least about 2.5%, preferably at least about 5%, more preferably at least about 7.5%. Refers to a decrease in the total concentration of a given pollutant in a fixed amount.

The self-cleaning purification coatings of the present invention are photocatalytic titanium dioxide (TiO) capable of forming electron-hole pairs in the presence of electromagnetic radiation, especially ultraviolet (UV), near UV and / or visible light.₂) Includes particles. Preferably, the photocatalytic titanium dioxide can be substantially photoactive in the presence of visible light. To this end, careful control over the crystal morphology and particle size of titanium dioxide removes contaminants in low UV light environments, especially indoor environments, even in the absence of activation by washing with solvents (eg water). It has been surprisingly discovered that it provides a photocatalyst that can be removed and has substantial initial activity.

The photocatalytic titanium dioxide particles used in the coating composition are preferably mainly anatase type crystals because of their higher photoactivity than the rutile type. "Mainly" means that the level of anatase in the titanium dioxide particles of the paint exceeds 50% by weight, but the anatase level can exceed about 80%, more preferably more than about 90%. preferable. In some embodiments, the photocatalytic titanium dioxide particles of the paint are in the substantially pure anatase form, which has a rutile crystal content of less than about 5% by weight, more specifically less than about 2.5% by weight. , Still more preferably, means less than about 1% by weight. In some embodiments, the photocatalytic titanium dioxide particles are not rutile-type, which means that rutile-type crystals cannot be detected by crystallography. In another method, the photocatalytic titanium dioxide particles may contain 100% anatase form. Crystallinity and crystal phase properties are measured by X-ray diffraction.

The photocatalytic titanium dioxide particles used in the coating composition will typically have an average particle size that allows the particles to predominantly absorb light rather than scatter it. When the particle size becomes very small, the band gap between the valence band and the conduction band decreases. Thus, it has been observed that titanium dioxide particles can absorb light in the visible spectrum at sufficiently small particle sizes. The titanium dioxide particles included in the coatings of the present invention will typically have a particle size of about 1 nm to about 150 nm. More typically, the particle size will be from about 5 nm to about 20 nm, from about 5 nm to about 25 nm, or from about 5 nm to about 30 nm. In a preferred embodiment, the particle size of titanium dioxide in the paint will be from about 5 nm to about 15 nm, in particular from about 5 to about 10 nm. References herein to the size of titanium dioxide particles (or crystallite) will be understood to mean the average particle size of titanium dioxide particles. Different methods for measuring particle size, as will be apparent to those skilled in the art, including particle sizes slightly larger or smaller than the values shown when the particle size is modified by the term "about". It will be understood to explain the inherent experimental error in measurement and variability between. The diameter can also be measured, for example, by a transmission electron microscope (TEM) and XRD.

Alternatively, the particles can be characterized by surface area. Typically, powdered titanium dioxide photocatalyst is about 70 m²Exceeding / g, more typically about 100m²Over / g, preferably about 150m²It will have a surface area that exceeds / g and is measured by any suitable method, including 5 point BET. In some embodiments, the titanium dioxide photocatalyst is about 200 m.²Over / g, about 250m²Over / g, or about 300m more²Will have a surface area greater than / g.

The photocatalytic titanium dioxide available from Millennium Inorganic Chemicals under Label PCS300 and PC500 has been found to be particularly useful for inclusion in the paints according to the invention. PCS300 is a 100% anatase-type titanium dioxide powder having an average crystal size of about 5 nm to about 10 nm. Also, PC500 is 100% anatase-type titanium dioxide powder, which is about 82% by weight to about 86% by weight of TiO.₂Approximately 250-approximately 300m with content and measured by 5 point BET²It has a surface area of / g, which is converted to an average particle size of about 5 nm to about 10 nm. The product labeled PC105 by Millennium Inorganic Chemicals will also find usefulness in some embodiments of the present invention. This photocatalytic powder contains more than 95% weight of titanium dioxide and its TiO₂Is 100% anatase type, the powder has an average crystal size of about 15 nm to about 25 nm and about 80 to about 100 m.²It has a surface area of / g.

The photocatalytic titanium dioxide will typically make up about 2 to about 40% by volume of the paint formulation. More typically, the photocatalytic titanium dioxide will make up about 5% to about 20% by volume, preferably about 7.5% to about 15% by volume of the paint. In a typical embodiment, the photocatalytic titanium dioxide constitutes about 10% by volume of the paint formulation. The said amount represents the volume of the photocatalyst in the final paint formulation (eg, including solvent) rather than the volume percentage in the dry paint coating. Typically, the weight percent of titanium dioxide in the paint formulation is from about 1% to about 20% by weight, more typically from about 5% to about 10% by weight, preferably about 7.5% by weight. Let's go.

Providing paints with two or more different titanium dioxide photocatalysts is within the scope of the present invention, and at least one of the titanium dioxide photocatalyst materials, preferably each, meets the above specifications. Thus, for example, the present invention includes the use of bimodal photocatalytic titanium dioxide material formed by combining two different titanium dioxide powders or sol, wherein at least one, preferably both. , With the particle size and / or surface area defined above. In another embodiment, the photocatalyst will be "substantially from" the particular titanium dioxide material described herein. This means that any additional photocatalyst with materially different activity is excluded, or the amount of additional photocatalyst that materially affects the durability, purification or self-cleaning properties of the paint is excluded. To do.

The paint of the present invention contains an organic binder. It is believed that any polymer binder may be used in the broadest aspect of the invention. In one embodiment, the polymer binders include, but are not limited to, latex binders such as natural latex, neoprene latex, nitrile latex, acrylic latex, vinyl acrylic latex, styrene acrylic latex, styrene butadiene latex and the like. Latex polymer. Typical polymers for these compositions are, but are not limited to, methyl methacrylate, styrene, 2-hydroxyethyl acrylate polymers (CAS No. 70677-00-8), to name a few. , Acrylic acid, methyl methacrylate, styrene, hydroxyethyl acrylate, butyl acrylate polymer (CAS number 7732-38-6), butyl acrylate, methyl methacrylate, hydroxyethyl acrylate polymer (CAS number 25951-38-6) , Butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, polymer acrylate (CAS number 42398-14-1), styrene, butyl acrylate polymer (CAS number 25767-47-9), butyl acrylate, acrylate Includes 2-ethylhexyl, methacrylic acid polymer C (CAS No. 31071-53-1), acrylic polymers and carboxylated styrene-butadiene polymers. Moreover, it is considered that a combination of more than 1 organic binder is useful for practicing the present invention.

In particular, the organic binder may be selected among styrene / butadiene copolymers and polymers and copolymers of acrylic acid esters, in particular copolymers of polyvinyl acrylic and styrene acrylic acid esters. In the present invention, the styrene-acrylic copolymer includes a copolymer of the styrene-acrylic acid ester. Trademark name ACRONAL^TMStyrene acrylic emulsions sold under 290D (BASF) have proved to be particularly useful as organic binders in the paints of the present invention.

In some embodiments, the organic binder in the coatings of the present invention will be the preferred styrene acrylic binder "more substantial". This excludes the presence of additional organic binders in amounts that materially reduce the durability of the paint coating on the substrate compared to other identical paint coatings containing only the styrene acrylic binder as the organic binder. Means to be done.

In some embodiments, the coatings of the present invention will be substantially free of inorganic binders. This means that in the absence of the organic binder, the level of the inorganic binder is not sufficient to form a continuous adhesive film on the substrate. In a representative embodiment, the coating material comprises 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 an inorganic binder. In some embodiments, the coatings of the present invention do not contain inorganic binders. Inorganic binders include, without limitation, alkali metals silicate, such as potassium silicate, sodium silicate and / or lithium silicate.

The paint according to the invention may further contain one or more pigments. The term "pigment" includes, without limitation, pigments used as colorants, including white pigments, as well as components commonly known in the art, such as opaque agents and "fillers". Intended. Includes any particulate organic or inorganic compound capable of providing hiding power to the coating, in particular at least one inorganic compound such as non-photocatalytic titanium dioxide. Such non-photoactive titanium dioxide pigments are disclosed in US Pat. No. 6,342,099 (Millennium Inorganic Chemicals Inc.), whose disclosure is hereby incorporated herein by reference. In particular, the titanium dioxide pigment can be particles of Tiona 595 sold by Millennium Inorganic Chemicals Ltd. The pigment also contains calcium carbonate, which is typically added to the paint as a filler. One suitable calcium carbonate material is sold under the trade name Setacarb 850 OC (Omya).

The paints according to the invention typically, but not always, have a pigment volume of about 60% to about 90%, more typically about 65% to about 80%, preferably about 70% to about 75%. Has a concentration (PVC). The term "PVC" refers to the sum of the volume percent of all pigments in the composition, where the term "pigment" refers to all types of titanium dioxide, photocatalytic (eg, PC500) or non-photocatalytic. Includes any (eg, Tiona 595), and without limitation, any other component commonly considered in the art as a pigment, including calcium carbonate and other particle fillers.

If desired, various other compounds may be added to the compositions of the invention, but preferably such additions do not diminish the shelf life, photoactivity, durability or non-staining properties of the resulting coating. Examples of such additional compounds are fillers such as quartz, calcite, clay, talc, barite and / or Na-Al silicate; TiO₂, Pigments such as lithopons and other inorganic pigments; dispersants such as polyphosphates, polyacrylates, phosphonates, naphthenes and lignin sulfonates; anionic, cationic, amphoteric and / or nonionic surfactants. Wetting agents, including, for example, silicone emulsions, defoamers such as hydrocarbons and long-chain alcohols; for example, stabilizers, including most cationic compounds; without limitation, alkali-stabilizing esters, glycols and hydrocarbons. Combines included; Leologic additives such as cellulose derivatives (eg, carboxymethyl cellulose and / or hydroxyethyl cellulose), xanthan gum, polyurethanes, polyacrylates, chemical starches, Benton and other layered silicates; alkyl silicates, siloxanes, Includes wax emulsions, water repellents such as Li fatty acids; and conventional fungicides or biobacterial agents.

Example 1 NO_XThe ability of the coatings of the present invention to remove contaminants, their self-cleaning properties and their durability were investigated by preparing three water-based styrene acrylic paints. Each of the comparative samples "Composition 1" and "Composition 2" contained 10% by volume photocatalyst titanium dioxide, but no photocatalyst was present in the control sample. The photocatalytic titanium dioxide used in Composition 1 was PCS300 from Millennium Inorganic Chemicals. PCS300 is a photocatalytic titanium dioxide powder having an average crystal size of about 5 to about 10 nm (nanometers). The photocatalytic titanium dioxide used in Composition 2 is PC105 from Millennium Inorganic Chemicals, which has an average crystal size of about 15-25 nm. Both PCS300 and PC105 have an anatase content of approximately 100%. The complete paint formulation is provided in Table 1.

<tables num="1"><img file="JP5450418B2_D0001.tif" /></tables>

The remaining ingredients in Table 1 are: The thickener is a 3% solution of hydroxyethyl cellulose sold under Label Natrosol 250 MR (Hercules). The defoamer Foammaster NXA is proprietary and 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 a pigment titanium dioxide from Millennium Inorganic Chemicals. Acronal 290D is a styrene-acrylic copolymer latex used as an organic binder available from BASF. Acronal 290D contains 50% by weight solid in water. Texanol is an ester alcohol coalescing solvent sold by Eastman Kodak. Acticide SPX is a fungicide from Acti Chem Specialties Inc.

The components of Part A and Part B were mixed separately under high shear mixing. Part A is then added to Part B under high shear mixing to form a complete paint. 770 g / m of each paint sample on the substrate²Applied with coverage (based on the dry weight of the coating), the substrate underwent the following tests.

NO by I-coating_XRemoval decision NO_XA complete method for measuring removal is described in US Patent Publication No. 2007/0167551, the disclosure of which is hereby sourced and is considered part of this specification. In short, the sample was placed in an airtight sample chamber and sealed. The sample chamber communicates with a three-channel gas mixer (Brooks Instruments, Holland) through which NO (nitric oxide), NO.₂Compressed air containing (nitrogen dioxide) and water vapor is introduced into the sample chamber at a predetermined level. Samples from UV Lamp Model VL-6LM 365 &amp; 312 nanometer wavelength (BDH) in the range of 300-400 nm 8 W / m²Illuminate with UV irradiation. NO_XThe initial and final values (after 5 minutes of irradiation) were measured by the Nitrogen Oxides Analyzer Model ML9841B (Monitor Europe) connected to the sample chamber. NO_X% Decrease in (ΔNO_X/ Initial NO_X) × 100. Each sample was investigated without prior activation and with prior activation. The results are summarized in Table 2.

<tables num="2"><img file="JP5450418B2_D0002.tif" /></tables>

The results show that a paint containing a photocatalytic titanium dioxide powder with an average crystal size of about 5 to about 10 nm (Composition 1) has a surprisingly high NO, even without a conventional cleaning step to pre-activate the photocatalyst._XShows activity. In comparison, composition 2 containing titanium dioxide powder with an average crystal size of about 15 nm to about 25 nm has a much smaller degree of NO in the absence of a prior activation step._XShows a decline. Both Composition 1 and Composition 2 are excellent NO after cleaning to pre-activate the catalyst._XShows removal characteristics. However, even when the composition 2 sample was pre-activated, the non-pre-activated composition 1 was unexpectedly superior to the composition 2.

II-Determining coating photoactivity for methylene blue The method used to determine the photoactivity to methylene blue is similar to that described in US Patent Publication No. 2007/0167551, the disclosure of which is hereby sourced and is considered part of this specification. The method has been modified as described herein. The self-cleaning properties of each paint sample were investigated based on their ability to decompose the organic pigment methylene blue. Color loss is observed as the pigment decomposes into water, carbon dioxide and nitrogen-containing species. Photoactivity is L^*Monitored by (brightness) measurement. The protocol is as follows:

Prepare the coating on a suitable substrate such as Melinex film, aluminum panel or glass plate. The thickness of the coating is similar to that used for the final application and will generally be 25 microns or more when dried. The coating is allowed to dry at least overnight.

A solution of methylene blue in water is prepared by dissolving 0.3739 g in 1 liter of water to obtain a concentration of 1 mmol / L. Pour the methylene blue solution into a suitable dish for dipping the coating. Immerse the coating film in a methylene blue solution for 30 to 60 minutes, and methylene blue becomes TiO.₂Ensures that it is chemically absorbed on the surface of the.

Remove the coating from the solution and remove the excess with absorbent tissue. The coating is completely dried and then using a colorimeter or spectrophotometer, the brightness (L)^*) Measure the value.

30-60W / m as in the Atlas Suntest cabinet²The coating is exposed to UV light for a period of 18-48 hours at an intensity of (wavelength 300-400 nm).

L^*Remeasure the value. Early and final L^*The difference between measurements is a measure of the self-cleaning power of the coating. L^*The larger the difference in the values, the greater the self-cleaning effect. Table 3 shows the results of each paint after irradiation for 18 hours and 36 hours.

<tables num="3"><img file="JP5450418B2_D0003.tif" /></tables>

The results show that the paint (Composition 1) containing the photocatalytic titanium dioxide powder with an average crystal size of about 5 to about 10 nm exhibits substantially greater self-cleaning activity than Composition 2 after irradiation for 18 and 36 hours.

III-Determining coating durability A complete method for determining the durability of a paint is described in US Patent Publication No. 2007/0167551, the disclosure of which is hereby sourced and is considered part of this specification. The method is 550 W / m at 340 nm.²Includes accelerated weathering of 20-50 micron thick coatings on stainless steel substrates in Ci65A Weatherometer (Atlas Electric Devices, Chicago) under 6.5 kW xenon source with UV irradiation. The sample was heated to about 63 ° C and the water spray was applied every 120 minutes for 18 minutes without the dark cycle. Durability is measured as a function of sample weight loss after exposure.

Table 4 summarizes the results of durability tests for Composition 1 and Composition 2 at various time intervals up to 1,551 hours.

<tables num="4"><img file="JP5450418B2_D0004.tif" /></tables>

As shown in Table 4, the durability of the composition 2 paint is substantially the same as the durability of the low photoreactive composition 1 after exposure for about 1,000 hours. This result is not expected, as it was expected that the more highly photoreactive coatings of Composition 2 would substantially deteriorate more rapidly than the less photoreactive Composition 1 under these conditions. It was a thing. At the end of 765 hours, the% weight loss was slightly greater for the more active composition 1 paint, the largest difference being observed after about 451 hours. This seems to be due to the fact that composition 1 has a very large initial activity compared to composition 2 without prior activation (see Table 2). However, in weathering, it can be seen that both paints become fully activated in the presence of water and their% weight loss converges at longer intervals. Over the entire period of accelerated weather resistance, Composition 1 showed very good durability comparable to Composition 2.

III-NO under different light sources_XRemoval decision NO described above in Part I of this example_XNO under different light sources using the procedure for removal decisions_XThe respective capacities of the composition 1 and the composition 2 of the paint sample for removing the coating were determined. In addition to UV, low intensity fluorescent linear illumination, sunlight (filtered through glass) and Osram incandescent light source were used. In each case the paint was tested without prior activation. The results are shown in Figure 1 in the table below (Table 5).

<tables num="5"><img file="JP5450418B2_D0005.tif" /></tables>

The UV light was from the UV Lamp Model VL-6LM 365 &amp; 312 nanometer wavelength (BDH) used in Part I of this example. The fluorescence was the light generated from the illumination by a conventional indoor linear fluorescent lamp. Sunlight is filtered through glass, 2.4 micro W / cm²Provided the strength of. Incandescent light was provided by an Osram incandescent lamp.

The results shown in Table 5 show that the composition 1 paint is substantially NO without prior activation under each light source._XThe composition 2 paint, which exhibits scavenging activity but in the absence of prior activation, has no activity under linear fluorescence or incandescent light and is exposed to sunlight (2.4 microW / cm).²) Demonstrate that it has virtually no activity. The excellent efficiency of the Composition 1 paints under these ultra-low UV light conditions is believed to be due to the ability of the PCS300 photocatalyst to absorb in the visible spectrum. Although not bound by any particular theory, very small crystal sizes (eg, about 5-10 nm) result in a reduction in the bandgap between the valence band and the conduction band, thereby the particles. Is thought to be able to create electron-hole pairs in the presence of visible light.

Example 2 A paint having a photocatalytic crystal size of about 5 to about 15 nm is, for example, a photocatalyst TiO of about 5 to 10 nm.₂Although preferred embodiments of the present invention are represented including the composition 1 of Example 1 having a particle size and the designated paint, the benefits of high PVC (Pigment Volume Concentration) achievable through the use of styrene acrylic binders are also Titanium dioxide crystal size (ie, about 15 to about 50 nm), which is less preferred, was found to be milder. Also, for example, paints that use a high level PC105 photocatalyst (crystal size of about 15 nm to about 25 nm) are also NO._XWould be useful in coatings to remove.

This example demonstrates the potency of the paint designated as Composition 2 of Example 1 in the removal of contaminants under "real world" conditions. The corners of the parking garage are sealed by building two walls, 917m with a ceiling height of 2.85m³Provided a closed area of. 322m while covering the walls (existing and artificial) with nylon²The ceiling surface was coated with composition 2 of Example 1. The photocatalytic paint was not pre-activated by washing with water. NO_XDuring the removal experiment, illuminate with 20 UV lamps symmetrically fixed 20 cm from the ceiling, 1 W / m²The total UV irradiance of.

Exhaust from vehicles located outside the enclosure was piped to the enclosed area so that the exhaust was released 4.74 m inside the enclosure. Ventilators (entrance and exit) maximize the concentration of pollutants near the ceiling, 566m³It was installed in the room through its artificial wall to provide airflow and velocity of / h and 14.3 m / h, respectively. The airflow and velocity of the exhaust gas from the car is 50.6 m each so that the positive pressure is maintained in the enclosed space to avoid the inflow of air from outside the enclosure.³Estimated to be / h and 2 m / s.

NO from the car_XExhaust gas was continuously measured using a portable gas analyzer. Also, NO_XMeasurements were taken continuously at the inlet and outlet vents and at a third sampling point near the ceiling about 15 m from the outlet vents.

After allowing the exhaust gas to reach steady state in its enclosure (about 3 hours), the UV lamp was turned on for 4 or 5 hours. NO and NO₂The decrease in was measured as the difference between the steady-state concentration and the final concentration after irradiation. Its value is the reduction of NO concentration and NO in vehicle exhaust over the test period to isolate the contribution of the photocatalytic paint to the reduction of the total of these pollutants.₂Corrected for increased concentration. The experiment was repeated for 3 consecutive days. On day 4, control measurements were taken in the absence of UV irradiation. The results are shown in Table 6 (% NO photocatalytic decomposition) and Table 7 (% NO).₂Photocatalytic decomposition).

<tables num="6"><img file="JP5450418B2_D0006.tif" /></tables>

<tables num="7"><img file="JP5450418B2_D0007.tif" /></tables>

Styrene acrylic paint containing photocatalytic titanium dioxide crystallite of approximately 15-25 nm average size at the level of 10% by volume NO from the atmosphere, even in the absence of prior activation_XIt is clear from the data in Tables 6 and 7 that it is effective in reducing pollutants. In addition, this example emphasizes the usefulness of the paint coatings of the present invention in applications such as parking garage interiors where it is desirable to remove concentrated contaminants from the atmosphere.

Example 3 A styrene acrylic paint was substantially prepared as described in Example 1, except that the PCS300 was replaced with a photocatalytic titanium dioxide powder of 100% anatase available from Millennium Inorganic Chemicals under Commercial Label PC500. PC500 is about 300m converted to an average crystal size of about 5 to about 10nm²It has a surface area of / g. PC500 was included in the paint at a level of 8% by volume and contained about 50% by volume of styrene acrylic binder. NO without prior activation_XThe ability of this paint to remove is 0.5 W / m according to the procedure described in Example 1.²~ 8W / m²Tested as a function of UV intensity across the intensity range of. The results are shown in Table 8.

<tables num="8"><img file="JP5450418B2_D0008.tif" /></tables>

These results indicate that even at very low UV intensities, the coatings of the present invention provide high removal of contaminants even without prior activation. In fact, NO_XThe difference in decline was only 16% (47.3% -31.3%), even when UV intensity increased by more than an order of magnitude.

Various photocatalysts TiO listed in Table 9 for PC500 paints₂Topcoat with sol and remove-NO_XWe investigated whether further improvements in properties could be achieved.

<tables num="9"><img file="JP5450418B2_D0009.tif" /></tables>

Sample A represents a styrene acrylic paint containing a PC500 photocatalyst without any sol topcoat. Samples B-G represent the paint of Sample A applied to Sample A and having the indicated sol topcoat. S5300A is a photocatalytic titanium dioxide sol available from Millennium Inorganic Chemicals. It is an ultrafine TiO deflated with acid at about pH 1.1 (± 0.4).₂An aqueous colloidal dispersion of (anatase) with a titanium dioxide content of about 20 (± 2)% by weight, a density of about 1.2 g / ml, and 250 m with a 5-point BET.²Has a surface area greater than / g (relative to dry products). S5300B, also available from Millennium Inorganic Chemicals, is an ultrafine TiO glutinated with a base of approximately pH 11.4 (± 1).₂An aqueous colloidal dispersion of (anatase) with a titanium dioxide content of about 17.5 (± 2.5)% by weight, a density of about 1.1 g / ml and 250 m with a 5-point BET.²Has a surface area greater than / g (relative to dry products). Various S5300B sol in Table 9 Weight was modified to have a titanium dioxide content indicated an amount based. AW1610 has an average crystal size of about 3.6 nm, pH 9.2, a density of about 1.00 g / ml and about 0.25% TiO.₂Photocatalyst with content TiO₂Is a sol containing. SP300N is a photocatalyst TiO with an average crystal size of about 5-10 nm, a pH of 7.0 and a density of about 1.15 g / ml.₂It is a slurry (about 17% by weight).

NO_X0.5W / m capacity of each coating system (paint + sol) to remove²~ 8W / m²It was investigated as a function of UV light intensity. The result is shown in figure 2. As you can see, S5300B (23.6% w / wTiO₂Coating system D, including PC500 paint with a topcoat of), unexpectedly excels at de-NO across the entire range of UV intensity_XIndicates,% NO in that range_XThe decline had an optimal minimum variation.

All references cited herein, including patent applications and publications, are hereby sourced and considered to be part of the specification, and they are individually published or patented. Or part of this specification for all purposes to the same extent as indicated specifically and individually so that the patent application sources all of them for all purposes and considers them as part of this specification. Consider it as. Numerous modifications and alterations of the invention have been made without departing from their spirit and scope, which will be apparent to those skilled in the art. The specific examples described herein are provided by way of illustration only, and the present invention is limited only by the terms of the appended claims, along with the equivalents of the full scope of such claims. Is to be done.