FIELD OF THE DISCLOSURE

The present disclosure relates to photocatalytic coating compositions wherein photocatalytic titanium dioxide particles are combined with binders, extenders, and further ingredients, the compositions being effective to form coatings exhibiting photocatalytic activity and improved durability.

BACKGROUND

Titanium dioxide has long been used in coating compositions as a pigment and, more recently, has been used in a photocatalytic form to provide coatings capable of catalyzing reactions wherein various pollutants may be removed from air. More specifically, when coatings containing photocatalytic titanium dioxide are subjected to ultraviolet (UV) and near-UV radiation, electrons from the valence band are promoted to the conduction band. This begins a cascade effect wherein hydroxyl radicals and superoxide radicals are formed, such radicals being effective to degrade oxides of nitrogen (or NOx) and volatile organic compounds (VOCs). Coatings including photocatalytic titanium dioxide are thus useful for removing pollutants from the air. Further, because various organic materials (grease, mildew, mold, algae, etc.) may also be oxidized at the surface of such coatings, the coatings may also have the advantage of being self-cleaning.

One effect of the oxidation of NOx compounds utilizing coatings with photocatalytic titanium dioxide is the formation of nitric and nitrous acids. In previous coating compositions, various alkaline fillers or extenders have been included for the purpose of neutralizing the acidic materials to form nitrites and nitrates. The most commonly used extender is calcium carbonate, and it has typically been recognized that calcium carbonate is a necessary ingredient for coating compositions that include photocatalytic titanium dioxide.

In addition to such extenders, coating compositions that comprise photocatalytic titanium dioxide typically include different types of organic binders. Because of the photocatalytic reactions due to the presence of the titanium dioxide, many types of binders are subject to degradation. To address this problem, photocatalytic coating compositions are typically formulated with binder systems based on siloxane polymers and/or styrene polymers because of increased stability of these materials in the presence of active species produced from photocatalytic reactions.

Coating compositions with photocatalytic titanium dioxide are known in the art, e.g. those described in U.S. Patent 9,358,502. However, while these coating compositions have the desired activity against pollutants such as NO*, the total percentage by volume of all pigments in the composition (PVC value) is fairly high.

Because of the increasing desire for environmentally friendly coating compositions that may improve air quality and/or exhibit self-cleaning attributes, there remains a need in the field for further photocatalytic coating compositions. In particular, there remains a need for photocatalytic coating compositions which can exhibit improved durability while maintaining acceptable photocatalytic properties and using less raw materials to achieve the same catalytic effect (i.e. contribute to environmental sustainability). Ideally, any new photocatalytic coating composition would also contribute to sustainability by extending the life of the coating composition and reducing the need for multiple applications.

SUMMARY OF THE DISCLOSURE

The present disclosure relates to coating compositions that are photocatalytic and thus can provide beneficial uses, such as odor reduction, NOx reduction, de-pollution, indoor air quality improvement, and self-cleaning. The coating compositions can be formulated using various combinations of binders, extenders, and pigments that can reduce οτ eliminate reliance upon higher cost materials, such as styrene and/or siioxane materials, and that improve durability by reducing or eliminating the need for alkaline extenders, such as calcium carbonate. (For the purposes of this application, an extender does not include titanium dioxide).

Such ends may be achieved without substantial reduction in photoactivity of coatings formed from the coating compositions, even when the coatings have a pigment volume concentration that is significantly lower than previously believed to be possible.

In one or more embodiments, the present disclosure can provide a coating composition comprising: photocatalytic titanium dioxide; a binder including an acrylic binder; and an extender. The coating composition particularly may be defined in relation to one or more of the following conditions: the coating composition is substantially free of styrene containing materials; siioxane containing materials, calcium carbonate and/or clay.

In further embodiments, the presently disclosed coating compositions may be further defined in relation to one or more of the following statements, which may be combined in any number or order.

The coating composition can be completely free of styrene containing materials, calcium carbonate, siioxane containing materials and/or clay.

There can be no non-acrylic binder present in the coating composition. The extender can be selected from the group consisting of silicon dioxide, diatomaceous earth, silicates, and combinations thereof.

The coating composition can further comprise a pigment.

The pigment can comprise titanium dioxide.

The coating composition can be configured such that a coating formed from the coating composition can have a pigment volume concentration of 60% or less or can have a pigment volume concentration of 30% to 55%.

The coating composition further can comprise a dispersant that includes one or both of a hydrophilic copolymer and a polyacrylate.

The photocatalytic titanium dioxide can be in the form of agglomerates of nano-sized particles, the agglomerates having a mean size in the range of 0.1 pm to 8 pm (100 nm - 8000 nm).

The photocatalytic titanium dioxide particles can have a surface of 30 m ² /g or greater.

The coating composition can be adapted to catalyze oxidation or reduction reactions. The coating composition further can comprise a cellulosic thickener.

A coating formed from the coating composition can be substantially free of calcium carbonate and clay and can have a pigment volume concentration of 60% or less.

The coating composition can comprise at least one extender and at least one pigment in a combined total concentration of 15% by weight to 60% by weight and can be substantially free of calcium carbonate.

The coating composition can comprise: 1% to 10% by weight of the photocatalytic titanium dioxide; 10% to 50% by weight of the binder including an acrylic binder; and 1 % to 50% by weight of the extender; wherein all percentages are based on the total weight of the coating composition.

The coating composition further can comprise: 1% to 50% by weight of a pigment;

0.1 % to 2% by weight of a dispersant; and 0.1% to 2% by weight of a thickener,

DETAILED DESCRIPTION

The present disclosure will now be described more fully hereinafter with reference to exemplary embodiments thereof. These exemplary embodiments are described so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Indeed, the disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. As used in the specification, and in the appended claims, the singular forms "a", "an", "the", include plural referents unless the context clearly dictates otherwise.

All percentages disclosed herein are percent by weight based on the total weight of the composition unless otherwise indicated.

In one or more aspects, the present disclosure provides coating compositions that include photocatalytic titanium dioxide in combination with one or more binders, extenders, and further formulation ingredients. The coating compositions are formed with specific combinations of materials that provide desirable properties such that coatings made from the compositions provide photoactivity and high durability while also maintaining a matte finish. The compositions beneficially may be prepared at reduced cost compared to known coating compositions because the specific combinations of ingredients can substantially exclude the use of higher cost materials that have previously been believed to be necessary in forming effective, photocatalytic coating compositions. In particular, when applied to a substrate, the coating compositions can produce coatings that are effective to remove NOx from the environment and neutralize acidic by-products from the photocatalytic oxidation of NOx substances. The so-formed coatings can further be effective for odor reduction, de-pollution, indoor air quality improvement, and/or exhibiting self-cleaning attributes. As used herein, "NOx" is intended to refer to all species of oxides of nitrogen, including NO (nitrogen oxide) and N0 ₂ (nitrogen dioxide), either collectively or individually.

As the compositions of the present disclosure are particularly useful in the formation of coatings on substrates, the nature of the compositions as manufactured (in a liquid form) may differ from the nature of the coatings in a substantially cured state (where certain volatile elements of the composition have evaporated from the composition). Thus, unless otherwise indicated, reference to a "coating composition" or to "coating compositions" as used herein is intended to refer to the compositions as manufactured - i.e., in the liquid form. Likewise, unless otherwise indicated, reference to a "coating" or to "coatings" as used herein is intended to refer to films (typically in one or more layers on a substrate) of varying thickness that arise from the coating composition but are substantially cured - i.e., dry to the touch.

In one or more embodiments, a coating composition according to the present disclosure can comprise at least photocatalytic titanium dioxide (TiO ₂ ), a binder including an acrylic binder, and an extender. As will be further described below, the coating compositions can include one or more further materials. Likewise, one or more materials that are known to be useful in photocatalytic coating compositions (or have even been thought to be a necessity in such compositions) may be substantially or completely excluded from the present compositions.

Any form of titanium dioxide may be used in the coating compositions of the present disclosure. As such, the titanium dioxide may not necessarily be limited by specific properties, such as being specifically in the rutile form or anatase form. At least a portion of any titanium dioxide present in the coating compositions should be in the form of titanium dioxide particles that are photocatalytic and thus are capable of forming electron-hole pairs at least in the presence of electromagnetic radiation in the ultraviolet (UV), near-UV, and/or visible range.

Although the titanium dioxide may have a rutile or anatase crystalline structure, it can be preferable for the photocatalytic titanium dioxide to be predominately in the anatase form. In this context, "predominately" is intended to mean that greater than 50% by weight of the photocatalytic titanium dioxide particles in the coating composition are in the anatase form. In one or more embodiments, 75% or greater, 90% or greater, 95% or greater, or 99% or greater (by weight) of the photocatalytic titanium dioxide is in the anatase form. In some embodiments, the photocatalytic titanium dioxide particles can be characterized as being in substantially pure anatase form, meaning that the content of the rutile crystalline form is no greater than 3%, no greater than 2%, or no greater than 1% by weight. The photocatalytic titanium dioxide may be completely free of any titanium dioxide in the rutile form, meaning that the rutile crystal form is not detectable by crystallography. Particle characterization can be carried out using known techniques, such as transmission electron microscopy (TEM), X- ray diffraction spectroscopy (XRD), or light scattering techniques (such as dynamic light scattering, by Malvern Instruments Ltd., U.K.).

The photocatalytic titanium dioxide used in the present coating compositions can be characterized, in some embodiments, by mean size. In one or more embodiments, the photocatalytic titanium dioxide used in the present coating compositions can be substantially in the form of agglomerates of nano-sized particles. Such agglomerates can have a mean size in the range of 0.1 μιτι to 8 μτη, 0.2 μπι to 6 μτα, 0.5 μπι to 5 μιη, 0.6 μιη to 4 μπι, about 0.7 μm to 3 μιη, or 0.8 μιη to 2 μπι. The agglomerate size range can be achieved, for example, by grinding larger agglomerates of the particles in a disperser, such as the DISPERMAT© line available from BYK-Gardner. For example, one photocatalytic titanium dioxide material, PC105 (available from Cristal), was ground to a mean size of 1.1 μιτι after 15 minutes of grinding with a cowls blade on a DISPERMAT© disperser running at 5,000 rpm. Another photocatalytic titanium dioxide material, PC500 (available from Cristal and also known as CristalACTiV™), was ground to a mean size of 1.3 μm under the same conditions. Mean size can be determined by, for example, sonication followed by sample testing via laser diffraction particle analyzer, such as a Malvern Mastersizer 2000. PC 105 and PC500 are both examples of photocatalytic titanium dioxide that may be suitable for use in the presently disclosed coating compositions. Individual particles in the agglomerates can have a mean particle size that is less than 100 nm, less than 50 nm, less than 20 nm, or less than 10 nm, such as 2 nm to 50 nm, 3 nm to 40 nm, or 5 nm to 30 nm.

Photocatalytic titanium dioxide useful according to the present disclosure, preferably exhibits a substantially high surface area. In one or more embodiments, the titanium dioxide particles used in the present coating compositions will exhibit a crystalline structure with a mean pore sizes in the nanometer range - e.g., 1 nm to 150 nm, 2 nm to 100 nm, 3 nm to 75 nm, 4 nm to 50 nm, or 5 nm to 40 nm. Particle characteristics on the nanometer scale may be measured, for example, using transmission electron microscopy (TEM) or X-ray diffraction (XRD) techniques.

Because of the crystalline structure of the photocatalytic titanium dioxide particles with its pore sizes in the nanometer range, the particles may still exhibit significantly high surface areas - e.g., 30 m ² /g or greater. In one or more embodiments, the surface area of the photocatalytic titanium dioxide can be 50 m ² /g or greater, 100 m ² /g or greater, 200 m ² /g or greater, or 250 m ² /g or greater. More particularly, surface area of the particles can be 50 m ² /g to 500 m ² /g, 100 m ² /g to 450 m ² /g, or 150 m ² /g to 400 mVg.

The amount of photocatalytic titanium dioxide present in the coating compositions can vary. In one or more embodiments, photocatalytic coating compositions can include 0.5% or greater, 1% or greater, or 2% or greater of photocatalytic titanium dioxide, said weight being based on the total weight of the coating composition. More particularly, the photocatalytic titanium dioxide can comprise 0.5% to 12% by weight, 1 % to 10% by weight, 1.5% to 9% by weight, or 2% to 8% by weight of the coating composition.

In addition to the photocatalytic titanium dioxide, the coating compositions of the present disclosure may further comprise one or more pigments. As used herein, a ""pigment" is intended to encompass particulate materials that impart color (including white) to the coating composition and which thus may be referred to as colorants. A pigment can also encompass materials that may be commonly referred to as "opacifying agents." A pigment thus may be organic or inorganic compound in particulate form that is adapted to cause a coating formed from the coating composition to be non-transparent or less transparent, which ability may be referred to as hiding power. In one or more embodiments, the present coating compositions particularly may include pigmentary titanium dioxide (TiO ₂ ). Pigmentary TiO _z may be distinguished from photocatalytic titanium dioxide in relation to the hiding power of the material. Thus, although photocatalytic titanium dioxide may provide some level of hiding power, it is to be expected that pigmentary TiO ₂ will provide significantly greater hiding power. Such difference may relate, at least in part, to the particle size of the titanium dioxide and/or the crystalline structure of the material. Pigmentary TiO ₂ is substantially non-photocatalytic in nature.

In one embodiment of the invention, pigmentary TiO ₂ may be predominately, substantially, or completely in the rutile form. Pigmentary TiO ₂ may have individual particles that are greater in size that the individual particles of the photocatalytic titanium dioxide. The individual particles of the pigmentary TiO ₂ may have a size in the same range as the agglomerates of the photocatalytic titanium dioxide.

In another embodiment of the invention, the amount pigmentary TiO ₂ is selected from the group consisting of 1-50% by weight, 2-40% by weight, 3-35% by weight and 5-30% by weight.

In another embodiment of the invention, the ratio by weight of pigmentary TiO ₂ to photocatalytic TiO ₂ is selected from the group consisting of 1 : 1 - 15: 1 , 1.1 : 1 - 10: 1 and 1.2: 1 - 6: 1 .

Examples of pigmentary grade TiO ₂ that may be suitable for use in the present coating compositions are provided in U.S. Patent 6,342,099 to Millennium Inorganic Chemicals Inc., the disclosure of which is hereby incorporated by reference. Specific, non-limiting examples of TiO ₂ pigment that may be used include TIONA™ 595 and TIONA™ 596, both of which are available from Cristal.

Another means of distinguishing between photocatalytic titanium dioxide and pigmentary TiO ₂ is that the former is not surface treated while the latter is surface treated. The surface of pigmentary TiO ₂ may comprise a surface treatment of alumina, silica, or the like as a passivating layer.

In one or more embodiments, the coating compositions of the present disclosure can be defined in relation to the pigment volume concentration (PVC) of the compositions. PVC defines the percent by volume of pigment in a coating and thus quantifies the volume of pigment in a coating relative to the total volume of all solids in the coating. In calculating PVC, the pigment volume includes the volumes of all pigments, photocatalytic titanium dioxide, and extenders present in the coating, and the total solids volume will include binder solids as well. Critical pigment volume concentration (CPVC) is understood to mean the pigment volume concentration at which there is just enough binder to wet the pigment particles. Thus, below the CPVC, there is excess binder and, above the CPVC, there is just sufficient binder to wet all pigment particles.

The present coating compositions, in light of the specific combinations of materials utilized, can beneficially provide photocatalytic coatings with a lower PVC than typically recognized as being necessary in the art. In particular, it is generally held in the art that a higher PVC is necessary to provide a coating with a porous surface and thus increase photoactivity. According to the present disclosure, however, photoactivity can be maintained in coatings having a PVC that is 60 or less, 55 or less, or 50 or less. In one or more embodiments, coatings formed according to the present disclosure can have a PVC of 20 to 60, 25 to 55, or 30 to 50. If desired, higher PVC values can be utilized; however, the ability to achieve photocatalytic coatings with a lower PVC can be beneficial to reduce overall cost by reducing the amount of TiO ₂ used.

As discussed in relation to Example 4 below, it has been shown that lower PVC coatings as may be formed according to the present disclosure can still provide desired levels of photoactivity and maintain desired attributes of durability. TABLE 5 specifically shows that photoactivity and durability of a 45PVC coating was not significantly lower than the photoactivity and durability of a 65PVC coating.

Coating compositions according to the present disclosure also include one or more binders. In one embodiment of the invention, the binder includes organic polymers. In another embodiment of the invention, the binder is an acrylic/acrylate polymer binder which may optionally be acrylic/acrylate copolymers (except for copolymers with styrene),

Exemplary acrylic/acrylate polymer binders for these compositions include, but are not limited to: (CAS # 70677-00-8 - butyl acrylate, 2-hydroxyethyl acrylate, styrene, methyl methacrylate, methacrylic acid polymer); (CAS # 25951-38-6 - butyl acrylate - hydroxyethyl acrylate - methyl methacrylate copolymer); (CAS # 42398-14-1 - butyl acrylate, 2- ethylhexyl acrylate, methyl methacrylate, acrylic acid polymer); (CAS # 31071-53-1 - 2- propenoic acid, 2-ethylhexy ester, polymer with butyl 2-propenoate and 2-methyl-2- propenoic acid); (CAS #901 1-14-7 - PMMA - Poly(methyl methacrylate); acrylic polymer, vinyl acrylic polymer, vinyl acetate-ethylene polymer and combinations thereof. The organic binder may also be in nanoparticle size (e.g. nanoparticle acrylate polymer). Unlike the previously known photocatalytic coating compositions, presently disclosed coating compositions can provide desired levels of photoactivity without the limitation of including styrene-containing materials or siloxane-containing materials.

Accordingly, in some embodiments, the present coating compositions may be defined in relation to being substantially free of any styrene-containing material, such as styrene acrylic polymers. Likewise, the present coating compositions may be defined in relation to being substantially free of any siloxane-containing materials, such as polysiloxanes.

In this regard, being substantially free of styrene-containing materials or siloxane- containing materials binders can mean that the coating composition comprises less than 2% by weight, less than I % by weight, less than 0,5% by weight, or less than 0.1 % by weight of such binders.

In some embodiments, the present coating compositions may be completely free of any styrene-based material (including vinyl styrene polymers) and/or may be completely free of any siloxane-based material (including polysiloxanes). The coating compositions may further be characterized in that no non-acrylic binder is present. As such, the binder of the coating compositions may comprise 100% of an aery late polymer binder.

Completely free refers to not separately adding a styrene-based or siloxane-based material to the coating composition of the invention. Completely free also recognizes that it is possible that insignificant trace amounts of styrene-based or siloxane-based material could inadvertently find their way into the coating composition as an impurity of another compound used in the process to make the coating compositions of the invention.

This is a departure from the known art wherein it has previously been believed that binders such as styrene-containing binder and/or siloxane-containing binders were necessary to achieve coatings that exhibit desired levels of photoactivity.

In relation to the presently disclosed coating compositions, testing was carried out to evaluate the effect of binder choice on photoactivity for coatings. The testing showed that coating compositions using acrylic binders yielded coatings with photoactivity that was equal to or better than previous technologies using only styrene and siloxane systems. The test is described in Example 1, and the test results are shown in TABLE 1A which shows that the desired levels of photoactivity can be maintained even when using 100% acrylic binder systems when completely free of styrene and/or siloxane materials.

In some embodiments, the total concentration of binders used in the present coating compositions can be in the range of 5% to 60% by weight. In particular, the coating compositions can comprise 10% to 50% by weight, 12% to 40% by weight, or 15% to 35% by weight.

Coating compositions according to the present disclosure also include one or more extenders. As used herein, an "extender" or "filler" can be an inorganic material or a mixture of inorganic materials that have refractive indices similar to the medium of the coating so that they are usually transparent in the coating medium below the critical pigment volume concentration but have significant opacity (although lower than titanium dioxide) above the critical pigment volume concentration. The extender materials are typically lower in cost than the pigments, including titanium dioxide, and allow for the replacement of some of the pigment in certain situations.

Extenders or fillers can be effective to thicken coating films and/or support the structure of the coating composition. Some extenders may also provide hiding power and function as pigments, particularly above the critical pigment volume concentration. Extenders typically are color neutral. Extenders that have commonly been used in coating compositions and may be used according to one or more embodiments of the present disclosure include clays (e.g., kaolin clays and China clays), talcs, quartz, barites (e.g., barium sulfate), and carbonate salts (e.g., calcium carbonate, zinc carbonate, magnesium carbonate), or mixtures thereof.

A key element of certain extenders in previously known photocatalytic coating compositions is alkalinity in that they can be used to neutralize acidic species (e.g., nitric and nitrous acid) that are formed from the photocatalytic oxidation of NOx. The nitrites and nitrate salts formed from the neutralization of nitric and nitrous acids are dissolved and removed from the coating upon contact with water. Carbonate salts, and particularly calcium carbonate, have previously been believed to be required for effective photocatalytic coating compositions for this reason. It has been found according to the present disclosure, however, that alternate extenders and/or pigments may be used to arrive at coating compositions that are substantially free of calcium carbonate and/or carbonate salts in general. In this context, substantially free indicates that the coating composition comprises less than 2% by weight, less than 1 % by weight, less than 0.5% by weight, or less than 0.1% by weight of the carbonate salt. In some embodiments, the coating compositions (and thus the formed coatings) can be completely free of calcium carbonate and may be completely free of any carbonate salt.

As with the styrene-based or siloxane-based material, completely free with respect to the calcium carbonate and the coating composition of the invention means that there is no separate addition of calcium carbonate to the coating composition of the invention and that it is possible that insignificant trace amounts of calcium carbonate could inadvertently find their way into the coating composition as an impurity of another compound used in the process to make the coating compositions of the invention.

Beneficially, such compositions can exhibit increased durability, such as shown in

Example 9 below. Moreover, as discussed in Example 7 below, the complete absence of calcium carbonate from coating compositions does not prevent coatings formed therewith from still exhibiting desired photoactivity.

In one embodiment of the invention, the extenders for the present coating compositions can include silicon dioxide, diatomaceous earth, silicates, and combinations thereof. In another embodiment of the invention, the extender is diatomaceous earth or silicon dioxide,

In some embodiments, the total concentration of extenders used in the present coating compositions can be in the range of 1% to 50% by weight. In particular, the coating compositions can comprise 2% to 40% by weight, 3% to 35% by weight, or 4% to 30% by weight.

In addition to the foregoing, the coating compositions of the present disclosure can include one or more further ingredients. For example, in some embodiments, the coating compositions can include one or more of thickeners, rheology modifiers, dispersants, antifoam agents, coalescents, stabilizing agents, biocides, and/or other components recognized as being useful in coating compositions.

In some embodiments, choice of dispersant can relate to the type of photocatalytic material that is used. Non-limiting examples of dispersants that can be particularly useful in coating compositions include photocatalytic titanium dioxide include hydrophilic copolymers, such as those sold under the name TAMOL™ 1 124 by Dow Chemical and sodium polyacrylates dispersants such as those sold under the name DISPEX® N40 by BASF, Dispersants can be beneficial to decrease the overall viscosity of the coating composition. The total amount of dispersant that may be included in coating compositions according to embodiments of the present disclosure can be 0.05% to 3% by weight, 0.1% to 2% by weight, or 0.2% by weight to 1.5% by weight based on the total weight of the coating composition.

In some embodiments, the addition of a thickener to the coating composition can provide notable improvements. For example, clay extenders have previously been included in photocatalytic coating compositions because of the ability to impart stability to the composition during storage.

The use of clay, however, has the undesired effect of reducing photoactivity of the coating composition. By including certain thickeners, however, the use of clay can be reduced. In some embodiments, coating compositions according to the present disclosure can be substantially free of clay or can be completely free of clay.

In this regard, being substantially free of clay can mean that the coating composition comprises less than 2% by weight, less than 1 % by weight, less than 0.5% by weight, or less than 0.1 % by weight of such binders. Completely free of clay refers to not separately adding clay to the coating composition of the invention. Completely free also recognizes that it is possible that insignificant trace amounts of clay could inadvertently find their way into the coating composition as an impurity of another compound used in the process to make the coating compositions of the invention,

It has particularly been found that the inclusion of cellulosic materials (e.g., hydroxyethylcellulose) in the coating compositions can reduce or eliminate the need for any clay for storage stability.

In some embodiments, the present coating compositions may further comprise a rheology modifier in an amount of 0.1 % to 1 % by weight. In some embodiments, the present coating compositions may further comprise a defoamer in an amount of 0.05% by weight to 0.5% by weight.

In some embodiments, the present coating compositions may further comprise a biocide in an amount of 0.05% to 0.5% by weight. In some embodiments, the present coating compositions may comprise one or more further additives in a total amount of 0.05% to 2% by weight.

EXPERIMENTAL

The present invention is more fully illustrated by the following examples, which are set forth to illustrate the present invention and is not to be construed as limiting thereof. Unless otherwise noted, all parts and percentages are by weight, and all weight percentages are expressed on a dry basis, meaning excluding water content, unless otherwise indicated.

EXAMPLE 1 - Effect of Binder Choice on Photoactivity

Five coating compositions were formed using, separately, a 100% acrylic binder, a styrene acrylic binder, a vinyl acetate ethylene binder, a nanoparticle acrylic binder, or a vinyl acrylic binder. The composition components are provided in TABLE 1 with relative quantities being provided in weight (grams). The coating compositions were prepared in two parts (Part A and Part B in TABLE 1). The ingredients in Part A were combined and mixed together in a high shear mixer for 15 minutes at 4000 rpm. The ingredients in Part B were then added to the Part A mixture sequentially as listed in TABLE 1 while mixing at 500 rpm. The combined mixture with all ingredients was then mixed at 500 rpm for an additional 5 minutes.

TABLE 1

NATROSOL™ is a non-ionic, water soluble hydroxyethylcellulose available from Ashland Inc.

AMP 95© is 2-amino-2-rriethyl- l-propanol containing 5% water and is available from Angus Chemical Company.

TAMOL™ 1 124 and TAMOL™ 731 are hydrophilic copolymer dispersants available from Dow Chemical. TERGITOL™ 1 124 is nonylphenol ethoxylate nonionic surfactant available from Dow Chemical.

TIONA™ 596 is pigmentary Ti0 ₂ available from Cristal.

CELITE® 281 is flux calcined diatomaceous earth that is available from Imerys Performance Materials.

ATTAGEL© 50 is powdered attapulgite and is available from BASF.

RHOPLEX™ VSR-2015 is a 100% acrylic low solvent binder available from Dow Chemical Company.

TEXANOL' ^M is an ester alcohol available from Eastman Chemical Company.

Irradiating titanium dioxide with UV light/radiation results in the production of holes and electrons which are capable of forming reactive species (e.g. peroxide, hyperperoxide, hydroxyl ions). Photoactivity was measured based on the ability of the coating to oxidize methylene blue present in the coating via these reactive species when exposed to UV radiation. The level of photoactivity is monitored by measuring the L* (brightness) and b* value (blue/yellow) - referring to the CIELAB system. The difference in L* and b* between the unexposed and exposed test results is a measure of photoactivity. For this test, the prepared coatings were exposed to 340 nm UV light in a QUV* (by Q-Lab) accelerated weathering chamber for 24 hours. (Additional test details given in Example 3) Test results are shown in TABLE 1 A below.

TABLE 1A - % photoactivity after 24 hours of exposure to UV radiation

As can be seen from the above data, the selecting an alternative acrylic polymer besides the traditionally used styrene acrylic polymer resulted in little difference in photoactivity.

EXAMPLE 2 - Photocatalytic Coating Compositions

It has previously been believed that a styrene polymer system was a necessary component for an effective photocatalytic coating composition. However, it was found that complete replacement of a styrene polymer system with an all acrylic polymer or a vinyl acrylic polymer system showed no significant impact on photoactivity of the composition.

Three compositions as shown in TABLE 2 were prepared using the method described in Example 1. Each of compositions in TABLE 2 differed only in relation to the polymer binder system that was utilized. The compositions were all 65PVC paints, and all of the compositions included calcium carbonate as an extender. The composition components in TABLE 2 are given in weight (grams). TABLE 2

EXAMPLE 3 - Determination of Percent Photoactivitv In Coatings

Coatings were formed utilizing each of the compositions prepared according to Example 2 and evaluated for percent photoactivity with the methylene blue test. The test is based on the recognition in the art that photocatalytic oxidation of methylene blue (MB) under UV light irradiation can be used to demonstrate the photoactivity of a composition containing a photocatalytic TiO ₂ .

To perform the testing for each of the compositions in TABLE 2, 3.5 grams of MB solution (1 % Methylene Blue Solution available from Fisher Scientific) was weighed into a lined half pint paint can. To the MB solution was added 100 grams of the respective composition to be tested. The can containing the composition containing MB was mixed for 5 minutes on a paint shaker, and composition was then allowed to rest for 15 minutes. On the coated side of white Byko-charts (available from BYK-Gardner USA), the rested composition containing the MB solution was drawn down directly next to a standard composition (the respective composition being tested but containing no MB solution) with a 2 mil bird bar. The chart was placed in a constant humidity cabinet overnight for drying. The color data (L*, a*, b*) of the composition was then measured. Equipment used for this testing was a Datacolor 600 Spectrophotometer- illuminant D65 observer 10° - 20mm aperture, specular excluded, 0% UV filter. The charts with the respective coatings were then irradiated in a QUV Accelerated Weathering Tester for 8 hour increments at 1.3 W/m ² /nm using a UVA-340 bulb. The color data was measured after 8 hours and again at 16 hours of exposure and recorded to determine the % photoactivity using the following three equations (iwhite = initial white).

In the above equations, initial white is the color data of the respective composition containing no MB. Initial blue is the color data of the respective composition containing the MB solution, and +8hrs is the color data of the respective composition containing the MB solution at each 8 hour increment of exposure. The percent photoactivity after 16 hours or exposure for each composition from TABLE 2 is provided below in TABLE 3.

TABLE 3 - % photoactivity after 16 hours of exposure to UV radiation

As can be seen therein, percent photoactivity was not significantly impacted by utilizing all acrylic or vinyl acrylic polymer systems (Compositions 6 and 7, respectively) instead of a styrene containing polymer system, as in Composition 8.

EXAMPLE 4 - Effect of PVC on Photoactivity and Durability

To examine the effect of PVC on photoactivity and durability in a composition with calcium carbonate present, two compositions were made in similar fashion to those discussed in Example 2 and described in Table 2. Both compositions were prepared with an all acrylic polymer system. The formulations are provided below in TABLE 4. TABLE 4

The two compositions were tested for % photoactivity using method as described in Example 3. The durability was tested in accordance with ASTM method D4214-07 where the TNO chalking scale was applied. Briefly, coatings were formed on test panels and, after completing 152 hours of exposure, clear adhesive tape was applied to the test panels. The tape was then rubbed 10 times with moderate pressure to remove all air bubbles. The tape was then removed and adhered to black paper to determine the amount of chalking. The most severe chalking would be given a TNO rating of 10, whereas a coating that had no visible chalking present would be scored a 0. The results from both tests are provided in TABLE 5. TABLE 5

As demonstrated in TABLE 5, lowering the PVC did not significantly impact the photoactivity or the durability of the coating with exposure. It is generally accepted that the polymer system used in a coating composition significantly impacts coating durability. The results seen in TABLE 5 confirm the expectations of conventional durability attributes being applicable in photocatalytic coatings as well.

EXAMPLE 5 - Photocatalytic Coating Compositions

To further investigate the impact of extenders on coating photoactivity and durability, further coating compositions were made with varying types and concentrations of extenders. The compositions were 45PVC and were made with a vinyl acrylic polymer system. The compositions were 5% photocatalytic material by pigment weight. Composition 1 1 contained no calcium carbonate, composition 12 contained 10% calcium carbonate by pigment weight, and composition 13 contained 20% mica by pigment weight. The mica used was a phyllosilicate mineral available from Imerys Performance materials. The compositions were made following the method previously discussed in Example 1, and composition component quantities are provided in Table 6, wherein values are shown as weight in grams.

TABLE 6

EXAMPLE 6 - Effect of Extenders on Photoactivity and Durability

Compositions 1 1 , 12, and 13 from Example 5 were tested for percent photoactivity and durability using the methods described in Examples 3 and 4. TABLE 7 show the results. TABLE 7

Surprisingly, the addition of 10% calcium carbonate by pigment weight in composition 12 decreased the photoactivity in the vinyl acrylic polymer system. The addition of mica in composition 13 also reduced photoactivity. This demonstrated that polymer system and extender combinations can impact performance of the coating.

EXAMPLE 7 - Photocatalytic Coating Compositions

Three coating compositions were prepared for use in evaluating effect of the choice of materials as well as PVC in performance as photocatalytic paint films. The composition components are provided in Table 8 with the relative quantities being provided in weight (grams)

TABLE 8

The coating compositions were prepared in two parts (Part A and Part B in TABLE 8). The ingredients in Part A were combined and mixed together in a high shear mixer for 15 minutes at 4000 rpm. The ingredients in Part B were then added to the Part A mixture sequentially as listed in TABLE 8 while mixing at 500 rpm. The combined mixture with all ingredients was then mixed at 500 rpm for an additional 5 minutes.

Composition 14 was a 45PVC coating that was 16% by weight extenders, 6% by weight pigmentary TiO ₂ , and 5% by weight photocatalytic TiO ₂ . Composition 15 was also a 45PVC coating that was 5% by weight extender, 21 % by weight pigmentary TiO ₂ , and 3% by weight photocatalytic TiO ₂ . Composition 16 was a 72.5PVC paint that was 24% by weight extender, 12% by weight pigmentary TiO ₂ , and 8% by weight photocatalytic TiO ₂ .

It has previously been understood in the art that film surface photoactivity is increased when the surface porosity is increased. Accordingly, coating compositions for forming photocatalytic films have typically required a high PVC (e.g., above the CPVC) to provide high porosity in the paint film. Conversely, it has been believed that lowering the PVC below the CPVC increases the gloss of the paint film and decreases the porosity, which should adversely affect photoactivity of the paint film.

With the formulations of the present invention, it was found that the addition of extender agents (e.g., diatomaceous earth, silicon dioxide) allowed for the PVC to be lowered (such as to the 45PVC range of the formulations in TABLE 8) while still maintaining the flat appearance and higher porosity of the paint film.

In order to maintain the opacity of the paint film, the calcium carbonate used in U.S. Patent 9,358,502, was replaced with alternate extenders or pigmentary TiO ₂ . Thus, the present formulations with lower PVC values reduced the raw material cost (by using less TiO ₂ ) of the composition while still providing excellent photoactivity.

EXAMPLE 8 - Determination of NOx Removal by Coatings

The ability of coatings produced from the compositions prepared in Example 2 to remove NO _x was tested to evaluate the effect on the photocatalytic oxidation when replacing the calcium carbonate with alternate extenders. It was previously believed that replacing some of the calcium carbonate with a non-alkaline extender would reduce the capacity of the coatings to remove nitric and nitrous acids, possibly rendering coatings to be completely ineffective.

To evaluate the NOx removal capacity of the three compositions, testing was carried out according to the NO„ removal testing methods described in U.S. Pat. Pub. No.

2007/0167551 , the disclosure of which is hereby incorporated by reference.

Coatings were prepared from each of the photocatalytic coatings compositions 14-16 from Example 7. The formed coating samples were aged for eight weeks prior to testing, For testing, the coating samples were placed in an air-tight sample chamber and sealed. The sample chamber was in communication with a three channel gas mixer (Brooks Instruments, Holland) through which NO (nitric oxide) was introduced into the chamber along with compressed air containing water vapor, the NO, air, and water vapor being provided at predetermined levels. The samples were irradiated with 8 W/m ² UV radiation in the range of 300 to 400 nm from a UV Lamp Model VL-6LM 365 & 312 nanometer wavelengths (BDH).

For each test sample, NOx concentration readings were taken without applied light to obtain an initial value and then again after five minutes of applied light to evaluate the reduction of NOx under the photocatalytic conditions. NOx concentrations were measured with a Nitrogen Oxides Analyzer Model ML9841B (Monitor Europe) connected to the sample chamber. The percent reduction in NOx was measured as (Δ NO _x /Initial NO _x ) x100, wherein Δ NO _x is difference between the sum of NO and N0 ₂ values measured under dark conditions (i.e., the Initial NO _x value) and the sum of the NO and N0 ₂ values measured while exposed to the light conditions. The results are summarized in TABLE 9.

TABLE 9 - % NO _x removal after 8 weeks of exposure

The results in Table 9, however, demonstrate that even with complete removal of the calcium carbonate and significantly lower PVCs, compositions 14 and 15 still removed 15- 20% of the NO _x compounds under the test conditions. The testing thus showed that, in the complete absence of calcium carbonate, NO _x removal was still achieved. It is believed that such retained capability arises at least in part from the replacement of the calcium carbonate with other extenders and/or pigmentary TiO ₂ .

Surprisingly, the NO _x removal was still acceptable even in the compositions having less photocatalytic TiO ₂ by weight. Acceptable NO _x removal was also possible despite the complete absence of calcium carbonate and despite the fact that the compositions were formulated with lower pigment volume concentrations.

This is further illustrated by comparing the % NO* reduction in combination with PVC value. An A value is established via the formula:

A = (adjusted % NO _x removal/adjusted PVC value) where A is a function of desiring to increase % NO _x while decreasing the PVC value (the amount of TiO ₂ used). The highest values in the Example 8 data set are normalized to 1 and all other data are adjust accordingly which results of the adjusted data depicted in Table 9A below:

TABLE 9 A - % NO _x removal after 8 weeks of exposure (normalized to Composition 16)

The data shows that a comparable level of performance to use of a styrene acrylic polymer can be achieved with an all acrylic polymer despite using a lesser amount of TiO ₂ (PVC value).

EXAMPLE 9 - Coating Durability

In addition to the surprising finding that complete removal of the calcium carbonate did not hinder ability to remove NO _x compounds with exposure, testing further surprisingly showed that removing the calcium carbonate from the compositions and lowering the PVC resulted in a significant improvement in coating durability. The durability testing methodology utilized is described in U.S. Pat. Pub. No. 2007/0167551, and is again incorporated herein by reference.

The testing method used accelerated weathering of 20 to 50 micron thick paint films formed from each of the compositions from Example 8 on a stainless steel substrate in a Ci65A Weatherometer (Atlas Electric Devices, Chicago) under a 6.5kW Xenon source emitting 550 W/m ² UV at 340 nm. The black panel temperature in the Weatherometer was 63°C, and water spray was applied to the coatings during the accelerated weathering for a duration of 18 minutes out of every 120 minutes. No dark cycle was provided during the testing. The durability was measured as a function of the weight loss of the film sample (i.e., film weight before exposure versus film weight after exposure). Coatings produced from each of compositions 14-16 from Example 8 above were exposed under the conditions described above for 2800 hours, and the weight loss of each sample after testing was determined. The durability testing results are summarized in TABLE 10.

TABLE 10

As shown in TABLE 10, Composition 14 exhibited a 230% (3.3x) increase in durability relative to Composition 16, which contained 25% calcium carbonate by weight. Composition 15 exhibited a 430% increase (5.3x) in durability relative to Composition 16. The testing illustrated that the combination of lowering the coating composition PVC while also using alternate extenders and/or pigmentary Ti(¼ instead of any calcium carbonate not only did not hinder the removal of NO _x compounds by films formed with the compositions but also significantly increased durability of the formed films.

When considering the data from Example 8 and Example 9 in combination, it can be seen that the compositions of the invention offer a surprisingly superior coating selectivity factor (CSF) over the use of styrene acrylic polymer, where the CSF is defined as:

CSF = A x B, where;

A is as defined in Example 8 above; and B = durability relative to control.

A is multiplied by B (durability) to give a CSF representative of the coatings overall desirability to remove NO _x , reduce the amount of TiO ₂ required for the coating and having suitable durability. The highest values from Tables 9 and 10 are normalized to 1

(Composition 16) with the other data adjusted accordingly and results in the following CSF values as depicted below in TABLE 10A:

TABLE 10A

When collectively considering NO _x removal, PVC values (lower values = less TiO ₂ used) and durability, the compositions of the invention surprisingly show much greater CSF values than previously used styrene acrylic polymers. The coating compositions with all acrylic polymers showed acceptable ability to remove NO* and did so while use far less TiO ₂ while greatly enhancing durability. An embodiment of the invention also includes providing coating compositions which have a CSF value at least 1.5x greater than styrene acrylic polymer containing coating compositions. Another embodiment of the invention is providing coating compositions which have a CSF value between 2x - lOx greater than styrene acrylic polymer containing coating compositions. In yet another embodiment of the invention, is providing coating compositions which have a CSF value between 3x - 5x greater than styrene acrylic polymer containing coating compositions.

Therefore, the coating compositions of the invention not only provide environmental benefits by reducing the amount of NO _x from the atmosphere, but also contribute to environmental sustainability by reducing the amount of titanium dioxide necessary to produce a suitable coating composition for the purpose of reducing the amount of NO _x .

Many modifications and other embodiments of the disclosure will come to mind to one skilled in the art to which this disclosure pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings, Therefore, it is to be understood that the disclosure is not to be limited to the specific embodiments disclosed herein and that modifications and other embodiments are intended to be included within the scope of the appended claims.