WO2012095835A1

WO2012095835A1 - A paint composition comprising zinc nitrate

Info

Publication number: WO2012095835A1
Application number: PCT/IE2012/000001
Authority: WO
Inventors: Igor Shvets; Fionnuala CROWLEY; Ciaran MCEVOY; Joanna BAGINSKA
Original assignee: The Provost, Fellows, Foundation Scholars, And The Other Members Of Board, Of The College Of The Holy And Undivided Trinity Of Queen Elizabeth, Near Dublin
Priority date: 2011-01-12
Filing date: 2012-01-12
Publication date: 2012-07-19

Abstract

A water based paint composition comprises anhydrous zinc nitrate or a hydrated form of zinc nitrate such as zinc hexahydrate in an amount to provide antimicrobial, particularly antifungal properties to the paint. The additive is non-carcinogenic, low in cost, not damaging to the environment, and does not have an adverse effect on the pigmentation of coatings.

Description

A PAINT COMPOSITION COMPRISING ZINC NITRATE

Introduction

The invention relates to a paint composition and a method of preparing said paint composition. It also relates to the preparation of antimicrobial/antifungal surfaces as well as fabrication of materials with antibacterial/antifungal action.

The proliferation of microbes on surfaces such as walls, door handles, worktop surfaces, and surfaces of furniture, floors and the like can be problematic and can lead to the transmission of infections such as methicillin resistant bacterial infections. Methicillin resistant S. aureus and Clostridium difficile infections are particularly problematic in hospitals and care homes and the like where patients have an underlying medical condition. It is not always possible to disinfect or clean all of the surfaces on which microbes can grow to prevent the growth of microbes and/or the spread of infection. There is therefore a need for antimicrobial surfaces.

Problems can also occur with the proliferation of fungi in interior environments susceptible to high humidity conditions or confined environments susceptible to high humidity. Such fungi can thrive in environments such as bathrooms and en-suite bathrooms or areas in rooms with reduced air circulation and compromised ventilation. This is particularly the case with so many bathrooms are only ventilated via extraction fans. Fungi can lead to respiratory problems among a wide section of society, most notable the young, old and infirmed. As with cleaning and disinfection to remove microbes, it is not always possible to completely clean surfaces to ensure they remain fungus free. This may be as a result of physical obstructions such as pipe-work or such like. There is a need for antifungal surfaces. The problems can also arise in areas with rising damp, such as lower parts of walls on ground floor or areas on the walls prone to transmitting moisture from exterior of the building to its interior through the wall. The problems can also arise on the exterior surface of buildings with increased dampness and reduced air circulation.

The invention is also related to in-can preservation of paints and related polymers. It is known that some of these liquids tend to be readily infested by fungi and microorganisms. The problem can be particularly significant once the can is open and the content is partly used. To ensure that the paint remains usable for the full duration of its shelf life time, it is sometimes necessary to add preservative chemical. The invention can be used for addressing this problem.

Statement of Invention

According to the invention there is provided a water-based paint composition comprising Ζη(Νθ₃)₂ or Zn(N0₃)₂-xH₂0 in an amount to provide antimicrobial, antibacterial, and/or antifungal, properties to the paint composition. x may be from 1 to 20. In one case x is 6. Zinc nitrate hexahydrate is a particularly stable form of zinc nitrate and is low in cost.

Zinc nitrate has the advantages that it is non-carcinogenic and does not have an adverse effect on the pigmentation of coatings.

We have found that when zinc nitrate is added to a coating, the coating has potent anti-fungal properties. In contrast to the anti-fungal additives chlorothaniol (which is potentially carcinogenic) and octlisothiazolone (which has high aquatic toxicity), zinc nitrate is non- carcinogenic and is not damaging to the environment.

The zinc nitrate is added to the paint compositions in an amount to achieve desired antimicrobial and/or antibacterial and/or antifungal properties. The zinc nitrate may be present in an amount of from 1 % to 20% by weight of the composition. In some cases the zinc nitrate is present in an amount of from 1% to 15%, 5% to 15%, 5% to 10%, 10% to 15% by weight of the composition. The % is based on the use of zinc nitrate hexahydrate as it is a common stable form of zinc nitrate. Anhydrous zinc nitrate may also be used as the active ingredient. Anhydrous Zinc nitrate is a deliquescent material and readily absorbs water from the atmosphere. This process is similar to dissolving anhydrous zinc nitrate in water. The salt breaks down into exactly the same ions, namely Zn ²⁺ and [N⁺0^3"]. Therefore, both the hydrated version (zinc nitrate hexahydrate) and the non-hydrated version (anhydrous zinc nitrate) provide the same ions to the paint and therefore impart the exact same properties. The only difference is that the percentage concentration of anhydrous zinc nitrate required should be less than the zinc nitrate hexahydrate, as zinc nitrate accounts for around 60% of zinc nitrate hexahydrate. There are also other known compositions of hydrated zinc nitrate, different from the common hexahydrate version. It will be appreciated that all such versions can also be used and the required concentrations indicated here for the hexahydrate version may need to be adjusted accordingly.

The zinc nitrate may be present in an amount of from 0.1 % to 25% by weight of the composition. The zinc nitrate may be present in an amount of from 1 % to 20% by weight of the composition. In one case the zinc nitrate is present in an amount of about 15% by weight of the composition in the hydrated form Ζη(Νθ₃)·6Η₂0. In one embodiment the zinc nitrate is uniformly dispersed in the paint.

The invention also provides a substrate coated with a paint of the invention.

The invention further provides a product coated with a paint of the invention.

In another aspect the invention provides the use of Zn (N0₃)₂ or Zn (Νθ₃)₂·χΗ₂0 as an additive to provide antimicrobial, and/or antibacterial and/or antifungal properties to a coating, x may be from 1 to 20. In one case x is 6. The zinc nitrate may be present in an amount of from 0.1 % to 25% by weight of the coating. The zinc nitrate may be present in an amount of from 1 % to 20% by weight of the coating. In one case the zinc nitrate is present at a concentration of from 1% to 15% by weight of the coating.

The zinc nitrate is preferably uniformly dispersed in the coating. The coating may be a paint such as a water based paint.

In a further aspect the invention provides a method of preparing a paint composition comprising the steps of:

• adding Zn (N0₃)₂ or Zn ( 0₃)₂·χΗ₂0 to a paint; and • allowing the zinc nitrate to become uniformly dispersed in the paint. In one case the method comprises the step of:

• dissolving the zinc nitrate in water prior to the step of adding the zinc nitrate to the paint. In another aspect, the invention provides a method of preparing a paint composition comprising the steps of:

• adding anhydrous zinc nitrate [Zn ( 0₃)₂] or a hydrated form of zinc nitrate [Zn (N0₃)2-xH₂0] to ingredients of a paint composition; and

• allowing the zinc nitrate to become uniformly dispersed in the ingredients of the paint composition.

Such that zinc nitrate can be incorporated into the paint composition at any stage of manufacture for example zinc nitrate may be added to a polymer forming a paint or to a dye or other ingredient. The zinc nitrate may be dissolved in water prior to the step of adding zinc nitrate to the ingredients of a paint composition. x may be from 1 to 20. In one case x is 6.

In one embodiment the zinc nitrate is present in an amount of from 0.1% to 25% by weight of the paint. The zinc nitrate may be present in an amount of from 0.1 % to 20% by weight of the paint. In one case the zinc nitrate is present in an amount of about 15% by weight of the paint. In another aspect the invention provides use of Zn (N0₃)₂ or Zn ( 0₃)₂ H₂0 as an additive to provide antimicrobial, antibacterial and/or antifungal properties to a paint as in-can preservative. x may be from 1 to 20. In one case x is 6. The zinc nitrate may be present in an amount of from 0.1% to 25% by weight of the paint. The zinc nitrate may be present in an amount of from 1 % to 20% by weight of the paint. The zinc nitrate may be present in an amount of from 1 % to 15% by weight of the paint. In one case the zinc nitrate is uniformly dispersed in the paint. The paint may be a water-based paint.

The coating material could be a water based polymer. The coating material could be a water based varnish.

The invention further provides for a substrate or product coated with a paint as described herein. The substrate and/or product may be a conventional building or architectural material such as plywood, plasterboard, brick, concrete and the like. The substrate and/or product may also be a conventional marine hull building material such as steel, iron, aluminium and the like.

The coating material may be a paint. The coating material may be a polymer.

The polymer could be a water based polymer.

The zinc nitrate may be uniformly dispersed at or adjacent to the surface of a substrate and/or product.

The zinc nitrate may be incorporated to leach through the surface of the substrate and/or product.

The substrate and/or product may be a plastic, ceramic, wood, leather, fabric, technical textile or such like.

The coating material may be applied to surfaces of substrates and/or products such as plastic, ceramic, wood, leather, fabric, technical textile or such like. The substrates and/or products impregnated with the zinc salt may be plastic, ceramic, wood, leather, fabric, technical textile or such like.

The invention also provides for the use of a zinc nitrate as an additive to provide antimicrobial properties to a surface. The invention further provides for the use of a zinc nitrate as an additive to provide antibacterial properties to a surface.

The invention also provides for the use of a zinc nitrate as an additive to provide antifungal properties to a surface.

In the context of the invention, the term "antimicrobial paint" will be understood to mean a paint that has some antimicrobial properties. This is a paint that reduces or prevents the growth of a microbe when the paint is in a liquid form or dry (coalesced) form, for example when the paint has dried to form a coating on a surface or substrate or product to which the paint is applied. The term "microbe" includes gram positive and gram negative bacteria and fungi. In the context of the invention, the term "antifungal paint" will be understood to mean a paint that has some antifungal properties. This is a paint that reduces or prevents the growth of a fungus when the paint is in a liquid form or dry (coalesced) form, for example when the paint has dried to form a coating on a surface or substrate or product to which the paint is applied.

In the context of the invention, the term "in-can preservative" will be understood to mean a paint that has some in-can preservative properties. These properties will reduce or prevent the formation of microbes in the paint that could adversely affect the quality of the paint or the storage lifetime of the paint in the can. It will also be understood to mean an in-can preservative that works even after the paint can has been opened and continues to provide in- can preservative properties on multiple openings of the paint can. In the context of the invention, the term "antimicrobial surface" will be understood to mean a surface that has some antimicrobial properties. This is a surface that suppresses the growth and life of microbes compared to the surfaces that do not have antimicrobial properties. It will be appreciated by a person skilled in the art that the term "microbe" encompasses gram positive and gram negative bacteria, fungi, and viruses.

In the context of the invention, the term "antifungal surface" will be understood to mean a surface that has some antifungal properties. This is a surface that suppresses the growth and life of fungi compared to the surfaces that do not have antifungal properties.

In the context of the invention, the term "antibacterial surface" will be understood to mean a surface that has some antibacterial properties. This is a surface that suppresses the growth and life of bacteria compared to the surfaces that do not have antibacterial properties.

Brief Description of the Drawings

The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:

Figs. 1 A and IB are photographs of the positive antimicrobial effects of a water-based paint comprising zinc nitrate hexahydrate on MRSA (NCTC 252), and Klebsiella pneumonia (ATCC 13833), respectively.

Figs. 2A to 2K are photographs of the negative antibacterial effects of a water-based paint comprising different transition metal salts and oxides on E. coli (C600);

Fig. 3 (A-D) are photographs of the antibacterial action of water based paint containing varying concentrations of zinc nitrate hexahydrate. Fig. 4 is a photograph of the positive antifungal effect of zinc nitrate hexahydrate dissolved in water on Aspergillus fumigatus;

Figs. 5A - 5B are photographs of the negative antifungal effect of an untreated water- based paint on Aspergillus fumigatus;

Figs. 45C - 5D are photographs of the positive antifungal effect of a water-based paint comprising zinc nitrate hexahydrate on Aspergillus fumigatus; and Fig. 6 (A-F) are photographs of the antifungal action of zinc nitrate hexahydrate against three different types of fungi i.e. S. chatarum, P. voilecea, R. rubra.

Detailed Description

We describe a paint composition that suppresses the proliferation of microbes such as bacteria and fungi and compromises their physiological functions. The paint composition retains its antimicrobial and/or antifungal properties when it has dried to form a coating on a substrate onto which the paint has been applied. Advantageously, because of the formation of the paint, the antimicrobial, and/or antifungal agent present in the paint composition is dissolved in the paint and dispersed so that when the paint is applied to a surface, the antimicrobial, agent is dispersed throughout the paint layer.

We describe a surface preparation that suppresses the proliferation of microbes such as bacteria and fungi and compromises their physiological functions. The surface composition described herein retains is antimicrobial, and antifungal properties post-fabrication, when the surface is in its usual functional state. Advantageously, because of the formation of the zinc nitrate solution pre incorporation into the surface the zinc salt is uniformly dispersed within and/or on the surface and retains its antimicrobial and antifungal properties.

Coatings formulated in accordance with the invention may be water based paints, varnishes and polymers with similar method of application such as the ones available from Dulux, 3M, Ace Hardware, Akzo Nobel, Altana Group, Ameron International, Arch Chemicals, Asian Paints, BASF, Becker Group, Benjamin Moore, Behr Paint, Bona Kemi, Chugoku Marine Paints, Cloverdale Paint, COMEX Group, Corimon, Diamond-Vogel Paints, Dunn-Edwards, DuPont, Duron Paint & Wallcoverings, Ferro, Hempel, H B Fuller, ICI Paints, Jotun, Kelly- Moore Paints, Lord, MAB Paints, PPG Industries, Professional Paint, Red Spot Paint and Varnish, Renner-Herrmann, Rinol, Rodda Paint, Rohm and Haas, RPM International, Sherwin-Williams, Sico, SigmaKalon, Sika Group, Smiland Paint, Stahl International, Sto Group, Tigerwerk, Total, Tnemec, Truserv, Valspar, Wattyl. Adler, Boero Bartolomeo, Brillux , Caparol, CD Color, CIN, Degussa, Dyrup, Emil Frei, Feidal, Flugger, Grebe, Imper, Industrias Titan, Inver, J W Ostendorf, Karl Worwag, Mader, Materis, Meffert, Milesi, Nippon Paint, Remmers, Robbialac, Swiss Lack, Teknos, and Tikkurila. It will be understood by a person skilled in the art that the term "paint" includes any liquid, liquefiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film. Water-based paints, sometimes referred to as latex paints, are alternatives to solvent-based paints. The volatile organic compound (VOC) content of water-based paints is significantly lower than conventional solvent-based paints, thereby reducing VOC emissions. Latex paints may include resins such as acrylics, vinyls, and epoxies, among others. In addition to the resins, latex paint may comprise solvents, pigments, and additives. Water-based paints may contain small amounts of coalescing solvents that allow the resin particles to fuse together (coalesce) as the water evaporates, forming a continuous surface coating. Latex paints are often less detrimental to the environment than oil-based paints because they contain fewer hazardous materials, reducing hazardous waste (HW) generation (depending on the type of paint used). There are families of other related polymers such as water based varnishes. These are also included in the specification and the term "paint" comprises these polymers as well.

Examples of some water-based paints and their possible applications that are suitable for use in accordance with the present invention include but are not limited to:

• Latex paints for internal applications on materials such as but not limited to concrete, bricks, stone, concrete blocks, plasterboard, layer of plaster, plastic, gypsum, wood, wood boards, plywood, hardboard, cardboard, chip boards, wall paper, ceilings, doors, aluminium surfaces, walls, tiles, floors, furniture surfaces, other internal and external architectural surfaces.

• Latex paints for interior applications in the areas of aggregation of public citizens such as canteens, restaurants, hotels, swimming pools, schools, child care facilities, cinemas, shopping malls, theatres.

• Latex paints for interior applications in places where health concern of the public is enhanced such as hospitals, homes for the elderly, hospices, medical facilities, healthcare facilities, academic laboratories, hospital laboratories.

• Exterior Acrylic Paint: suitable for use on concrete, masonry, stucco, and wood, aluminium siding. Can also be used for interior applications. • Concrete Floor Sealer/Finisher: resin-based, water emulsion sealing and finishing compound for use on cured and uncured concrete floors. It may also be used on other masonry, linoleum, rubber tile, magnesite, and troweled asphalt.

• Wood Varnish: resin-based wood varnish for used on, but not limited to, untreated or newly restored wood floors, cabinets, presses, cupboards, skirting boards, wood panelling, stairs banisters, wooden door handles, tables, chairs, household furniture and wooden toys.

• Traffic and Airfield Marking Paint: water-based, 100% acrylic, suitable for application on traffic bearing surfaces such as Portland cement concrete, bituminous cement concrete, asphalt, tar, and previously painted areas of those surfaces.

• Latex Stain: intended for new or previously painted areas of those surfaces.

• Recycled Latex Paint: contains a minimum of 50 percent post-consumer waste and is intended for use on interior or exterior wallboard, concrete, stucco, masonry, and wood.

• Stencil Paint: water-emulsion paint, intended for markings and for obliterating markings on wood and fibreboard containers.

• Water-Based Metal Primer: acrylic primer can be used on exterior or interior metal surfaces in all non-marine environments.

• Water-Based Epoxy Coating Kits: formulated for use on wood and concrete floors, these coatings are water-based, non-flammable, and non-toxic.

• Water-Based varnishes for floor applications.

• Semi-gloss Paint, Water-Based for Metal Surfaces: acrylic or modified acrylic topcoat paint is suitable for use on exterior or interior metal surfaces in all non-marine environments.

• Paint and material for coatings for the surfaces placed in regular contact with water.

• Preserving the paint in a can so that during its shelf life the paint is not infested by bacteria and fungi making it usable. Such infestation can be particularly significant once the can is open, the contents of container are partially used and remainder is stored.

The invention will be more clearly understood from the following examples.

Examples Bacteria

A non-pathogenic strain of Klebsiella pneumonia bacteria (ATCC 13883) and a strain of Methicillin Resistant Staphylococcus aureus (MRSA NCTC 252) were used in the experiments. A non-pathogenic strain of E. coli C600 K12 bacteria (ATCC 12435) was used in the specific experiments.

Fungi :

Strains of Aspergillus fumigatus (IMI 16152), Rhodotorula rubra (IMI 358541), Stachybotrys chatarum (IMI 1 15289) and Phoma voilacea (IMI 4948ii) were used. Stock cultures of these fungi were maintained separately on an appropriate medium such as Sabouraud Dextrose agar plates. The stock cultures were kept for not more than 4 months at approximately 3 to 10°C (37 to 50°F). Individual fungi were subcultured onto plates for 7 to 20 days at 28 to 30°C prior to each experiment, and these subcultures were used in preparing the spore suspension. Zinc Salts

Water soluble zinc salts were incorporated into paints and their antimicrobial, antibacterial and antifungal properties tested. Paints with the zinc salt additive are referred to as "active paints", while paints without the zinc salt additives are referred to as "control paints".

Example 1 - preparation of an antimicrobial and in-can preservative active paint composition

Transition metal compounds were added to samples of paint at a concentration of between about 1% to about 20.5% by weight and thoroughly mixed. We found that for water-based paints, if the transition metal compound is initially dissolved in a small amount of water prior to adding to the paint, the process of mixing the transition metal compound with the paint was simplified.

Typically, the following procedure was used for the preparation of an "active paint" comprising 15% by weight transition metal compound: A 15 ml sterile glass container was placed on a calibrated weighing scale and its weight recorded. The scale was subsequently "tared" to re-set the weight to zero. Commercially available Dulux paint was poured from its container into the 15 ml sterile glass container and the final weight noted. The weight of the paint was calculated by subtracting the weight of the glass container full of paint from the weight of the empty glass container. A calculation of 15% of the weight of the paint was performed. Subsequently a weight of transition metal compound equivalent to 15% by weight of the paint was dissolved in a small amount of water and added to the paint. The paint was vigorously stirred to uniformly disperse the transition metal compound in the paint and the paint was left to stand for 1 hour. It will be appreciated that paints comprising a different percentage by weight of a transition metal compound were prepared by a similar methodology with the weight of the transition metal compound being adjusted accordingly.

Example 2 -preparing painted glass slides for antibacterial and antifungal testing

The following procedure was used to assess the antimicrobial actions of the active paint. Sterile glass slides which had been previously autoclaved were wiped with a cloth containing acetone to remove any grease or grime on the surface of the slides. The slides were then left to dry in Petri dishes in a laminar flow cabinet for approximately one hour. Active paint prepared in accordance with Example 1 was shaken to ensure complete mixing and applied to half of the surface of a glass slide. Control paint, (paint without the addition of transition metal compounds), was applied to another slide in the same way. The control paint acts as a control. The slides were then placed in Petri dishes and covered to avoid atmospheric contamination. The slides were left to dry overnight at room temperature.

Example 3 - MRSA and Klebsiella pneumonia bacterial sample preparation, corresponding to Fig. 1

The pathogens chosen were MRSA (NCTC 252) and Klebsiella pneumonia (ATTC 13883), with MRSA representing the gram positive bacteria and Klebsiella pneumonia representing the gram negative bacteria. The MRSA was grown on TSA plates containing 17g Tryptone, 3g Soytone, 3g Dextrose, 5g Sodium Chloride, 2.5g K₂HP0₄ and 15g Agar and refrigerated at 4 °C. The Klebsiella pneumonia was grown on L agar plates containing lOg Tryptone, 5g yeast extract, lOg Sodium Chloride and 15g agar and refrigerated at 4 °C. A single colony of MRSA was taken with a sterile loop and placed in 100 ml of Tryptic Soy Broth (TSB). A single colony of Klebsiella pneumonia was taken from the plate using a sterile loop and inoculated into 100 ml of L. Broth. Both were incubated overnight at 37 °C. The next day 10 ml of the Tryptic Soy Broth (TSB) containing the MRSA was pipetted in 100 ml of warm Tryptic Soy Broth. Similarly, 10 ml of the L. Broth containing the Klebsiella pneumonia was pipetted into 100 ml of warm L. Broth. The TSB was incubated at 37 °C in an agitated incubator for 150 minutes (2 ½ hours). Similarly, the L. Broth was incubated at 37 °C in an agitated incubator for 150 minutes (2 ½ hours). Subsequently, the O. D. [optical density] of each sample was taken to ensure all assumptions of bacterial counts were correct.

Example 4 - assessing the antibacterial properties of the active paint

20 μΐ of the MRSA bacteria suspension was inoculated on the surface of the glass slides as prepared in Example 2. Five samples of the bacteria and five samples of the control were prepared. Samples were incubated overnight at 37°C. Similarly, 20 μΐ of the Klebsiella pneumonia bacteria suspension was inoculated on the surface of the glass slides as prepared in Example 2. Five samples of the bacteria and five samples of the control were prepared. Samples were incubated overnight at 37 °C. The next day bacteria were recovered from all samples as follows: Using alginate swabs the surface of the active paint samples were swabbed for viable bacteria. Each swab taken from the MRSA inoculated active paint sample was placed in 5 ml of sterile Tryptic Soy Broth (TSB) and vortexed for 90 seconds. Immediately post vortexing 100 μΐ of each sample was pipetted onto the surface of fresh dry TSB plates. These were left to dry for approx 2 hours in the laminar flow cabinet before being incubated overnight at 37 °C. The following day colony forming units were counted, recorded and photographed.

Each swab taken from the Klebsiella pneumonia inoculated active paint sample was placed in 5 ml of sterile L. Broth and vortexed for 90 seconds. Immediately post vortexing 100 μΐ of each sample was pipetted onto the surface of fresh dry L. agar plates. These were left to dry for approx 2 hours in the laminar flow cabinet before being incubated overnight at 37 °C. The following day colony forming units were counted, recorded and photographed.

As stated,, there were five samples for each bacteria examined in the course of this experiment. Example 5 - assessing the antibacterial properties of paint using E. coli, corresponding to Fig. 2

The following procedure was used to assess the antimicrobial actions of the active paint in terms of the obtained E. coli. Active paint prepared in accordance with Example 1 was applied by brush to half of a microscope slide. The other half of the glass slide was left uncoated to serve as a control and reference point for the experiment. The active paint was allowed to dry for approx 20 minutes at ambient temperature. Both halves of the glass side were cleaned by spraying with 70% ethanol and wiping with tissue paper. The glass slide was then transferred to a Petri dish in an aseptic manner (close to the flame of Bunsen burner). Pre-prepared autoclave sterilised Luria Bertani agar containing l Og/1 Tryptone, 5g/l yeast extract, 5g/l sodium chloride and l Og/l agar was heated in a microwave for about 5 minutes to melt the agar and the agar was allowed to cool down to 50°C. 1 ml of agar was applied on each side of the glass slide (both active paint and control) under aseptic conditions (either close to a Bunsen burner flame or in laminar flow cabinet) to avoid bacterial contamination. After approximately 3 minutes, the agar on the plate had solidified. A loopful of bacteria from a previously inoculated agar dish was diluted in 5ml of sterile distilled water and vortexed. 20 μΐ of bacterial suspension was pipetted onto each side of the glass slide (both active paint and control) and the bacterial suspension was allowed to soak into agar for about 30 minutes following which the plate was incubated in 37°C for 17 hours. The antibacterial properties of the active paint composition were assessed visually. If bacterial colonies grew on both sides of the glass slide to the same extent, this meant that the active paint did not show any antibacterial properties whereas if no growth of bacterial colonies was observed on the active paint side of the glass slide but bacterial clusters grew on control side of the glass slide, the active paint had antibacterial action. Experiments for each of the active paint samples against each of the microorganisms listed below were repeated at least three times.

Example 6 - antibacterial testing of prepared active paints at varying concentrations using Escherichia coli.

The active paint was prepared by the method outlined in Example 1. The desired concentrations were 2%, 5 %, 8% and 10%. These were prepared accurately using zinc nitrate hexahydrate and the concentrations reported are with the hexahydrate form of the zinc nitrate. The key active ingredient is zinc nitrate and the hexahydrate is merely the common form of this compound. It will be appreciated by those skilled in the art that if zinc nitrate were used instead of zinc nitrate hexahydrate, then the concentrations of 2%, 5%, 8% and 10% would need to be recalculated and multiplied by the ratio equal to the molecular ratios of zinc nitrate to the zinc nitrate hexahydrate. Likewise, other hydrated forms of zinc nitrate could be used and therefore the concentrations would have to be recalculated accordingly.

The E. coli was grown on L agar plates containing lOg Tryptone, 5g yeast extract, l Og Sodium Chloride and 15g agar and refrigerated at 4 °C. A single colony of E. coli was taken from the plate using a sterile loop and inoculated into 100 ml of L. Broth. Broth was incubated overnight at 37 °C.

The next day 10 ml of the L. Broth containing the E. coli was pipetted into 100 ml of warm L. Broth. The TSB was incubated at 37 °C in an agitated incubator for 150 minutes (2 ½ hours). Similarly, the L. Broth was incubated at 37 °C in an agitated incubator for 150 minutes (2 ½ hours). Subsequently, the O. D. [optical density] of each sample was taken to ensure all assumptions of bacterial counts were correct.

20 μΐ of the E. coli bacteria suspension was inoculated on the surface of the glass slides as prepared in Example 2. There were five samples of the bacteria and five samples of the control prepared. Samples were incubated overnight at 37 °C. The next day bacteria were recovered from all samples as follows: Using alginate swabs the surface of the active paint samples were swabbed for viable bacteria. Each swab taken from the E. coli inoculated active paint sample was placed in 5 ml of sterile L. Broth and vortexed for 90 seconds. Immediately post vortexing, 100 μΐ of each sample was pipetted onto the surface of fresh dry L. agar plates. These were left to dry for approx 2 hours in the laminar flow cabinet before being incubated overnight at 37 °C. The following day colony forming units were counted, recorded and photographed.

Example 7 - antifungal testing on prepared active paint using Aspergillus fumigatus

A laboratory strain of Aspergillus fumigatus was streaked onto a SDA plate, containing 40g/l dextrose, l Og/1 peptone, 20g/l agar at a pH of 5.6, using a sterile loop and left to grow for approximately 4 days at 30 °C. 1 ml of molten SDA was pipetted on the surface of samples of active paint slides as prepared, in Example 2 so that it covered the entire slide and evenly coated the paint. Testing was also performed on slides prepared in a manner similar to Example 2, but which did not contain the active transition metal salt, (control paint). Using a sterile loop a loopful of fungal hyphae was removed from the SDA plate and streaked down the centre of the SDA on the paint, both active and control. These were then incubated at 30 °C for approximately 4 days and checked regularly to monitor progress. Results were recorded and photographed.

The experiment was repeated 5 times. Example 8 - to assess the antifungal activity of zinc nitrate hexahydrate or another form of zinc nitrate.

Preparation of Test Specimens

A set of coatings to be tested should preferably contain a positive and a negative growth control. That is, one that is known to support fungal growth, (sterile water) and one to test the efficacy against fungal growth (zinc nitrate hexahydrate). The disks or drawdown sections were handled with sterile tongs or tweezers. Coatings to be tested were applied to 4.2-cm glass fiber filter paper disks. The samples were prepared for evaluation by brushing coating strips of drawdown paperboard, or glass filter disks with each sample. Care was taken to apply a thin, even coating, with the same thickness for all coating. After application, the sample disks were suspended from drying racks and allowed to air dry for 24 to 72 h at room temperature.

Filter paper was applied to agar plate and left to settle for 24 hours.

Preparation of the Fungal Spore Inocula: (Stachybotrys chatarum)

A spore suspension of each of the test fungi was prepared by pouring a sterile 10-mL portion of water into one subculture of each fungus. The plate was agitated to loosen the spores. The water and spore suspension was aspirated carefully with a sterile pasteur pipette (trying to avoid obtaining mycelia). Inoculation of test Specimens. Using a pipette 1.5 ml of the spore suspension was inoculated onto the filter paper on the agar plate. These were left to dry for 3 hours in a Laminar flow cabinet and incubated for 3-5 days at 28-30°. They were then checked for zone of inhibition. This experiment was repeated exactly in the same way for other fungal species such as Phoma voilacea and Rhodotolura rubra.

Results:

Table 1 summarises the results of zinc nitrate hexahydrate in which 0 means complete antibacterial action and 1 means no antibacterial action was observed. Photographs of the results of the experiments with MRSA (NCTC 252) and Klebsiella pneumonia (ATTC 13883) are shown in Figs. 1A and IB.

Fig. 1A - Zn(N0₃)₂ · 6H₂0 at 15% against MRSA. The right hand side, denoted R is a representation of a swab taken from a paint treated with the antimicrobial active ingredient, the antimicrobial paint. The left hand side, denoted C, is the control and is representative of a swab taken from a paint not treated with the antimicrobial active ingredient. The absence of any MRSA growth on the right hand side of the Petri dish is indicative of total antimicrobial action against MRSA. MRSA can be seen to populate the control side of the Petri dish (side C).

Fig. I B - Zn(N0₃)₂ · 6H₂0 at 15% against Klebsiella pneumonia. The right hand side, denoted R is a representation of a swab taken from a paint treated with the antimicrobial active ingredient, the antimicrobial paint and inoculated with Klebsiella pneumonia. The left hand side, denoted C, is the control and is representative of a swab taken from a paint not treated with the antimicrobial active ingredient and inoculated with Klebsiella pneumonia. The absence of any Klebsiella pneumonia growth on the right hand side of the Petri dish is indicative of total antimicrobial action against Klebsiella pneumonia. Klebsiella pneumonia can be seen to populate the control side of the Petri dish.

Table 2 summaries the negative results of the experiments for various transition metal compounds in which 1 means no antibacterial action was observed. Photographs of the negative results with E. coli C600 are shown in Figs. 2A to 2K.

Table 2 - antibacterial properties of transition metal salts in water based paint against E. coli

Table 3 below summarises the results of zinc nitrate hexahydrate in water based paint at varying concentrations on the growth of E. coli in which 0 means complete antibacterial action; 0.5 means partial inhibitory effect on the growth of the bacteria; and 1 means no antibacterial action was observed.

Table 3: antibacterial testing of prepared active paints at varying concentrations of zinc nitrate hexahydrate using Escherichia coli.

Referring to Fig. 3 (A-D): Photographic evidence of the ability of zinc nitrate to kill E. coli at varying concentrations. Partial reduction is seen at 2 %, however complete antibacterial action is not visible until 5% of zinc nitrate hexahydrate is added to the paint. This continues through the higher concentrations. A control sample is visible in 3C beside the 8% sample.

Table 4 below summarises the results of zinc nitrate hexahydrate in water based paint on the growth of Aspergillus fumigatus in which 0 means complete antifungal action; 0.5 means partial inhibitory effect on the growth of fungi; and 1 means no antifungal action was observed.

Referring to Fig. 4 a small amount of zinc nitrate hexahydrate is dissolved in a small amount of water. The Aspergillus fumigatus is swiped down the centre of the Petri dish. Small drops of the zinc nitrate solution are placed on either side of the Petri dish, right and left in the photograph. Figure 3 shows that no fungus (Aspergillus fumigatus) grows in the zone of inhibition created by the zinc nitrate solution, thus denoting antifungal property of the solution. Photographic results for the antifungal action of control paint and active paint are shown in Figs. 5A - 5D.

Table 4 - antifungal properties of zinc nitrate hexahydrate in water based paint, active paint, against Aspergillus fumigatus

Fig. 5A and 5B show results of antifungal testing on control paint (paint without the addition . of the active ingredient). The fungus used was Aspergillus fumigatus. From both Fig. 5A and Fig. 5B it can be seen that rapid growth is observed, meaning the control paint did not have any antifungal properties. Fig. 5A is tested using a microscope slide prepared in accordance with Example 2. Fig. 5B is tested on a piece of painted plasterboard, to more realistically mimic normal environment.

Fig. 5C and 5D show results for water based paint with the zinc nitrate hexahydrate added at a concentration of 15%, active paint. Fig. 5C is tested on a microscope slide prepared in accordance with Example 2. Fig. 5B is tested on a piece of painted plasterboard, to more realistically mimic normal environment. The fungus used was Aspergillus fumigatus. Fig. 5C and Fig. 5D show the absence of fungal growth on the antifungal paint surface indicating the active paint has antifungal properties.

The dark zone of inhibition around the membrane filter paper observed in the antifungal testing on R. rubra, S. chatarum and P. voilacea show the ability of zinc nitrate to prevent fungal growth in the ideal conditions of the SDA plates.

Referring to Fig. 6(A-B) one can see the ability of zinc nitrate hexahydrate to inhibit fungal growth. Fig. 6A shows SDA plate with zinc coated filter paper that has been inoculated with Stachboyrys chatarum spores. 0% of the fungal spores grew. Fig. 6B SDA plate with water coated filter paper (control). You can see that Stachbotrys chatarum grew very well and completely covered the filter paper.

Referring to Fig. 6(C-D) we can see the ability of zinc nitrate to inhibit fungal growth. Fig. 6C shows a SDA plate with zinc nitrate coated filter paper that has been inoculated with Rhodotolura rubra spores. 0% of the fungal spores grew on the membrane paper.

Fig. 6D shows a SDA plate with water coated filter paper (control). One can see that Rhodotolura rubra grew well.

Referring to Fig. 6(E-F) one can see the ability of zinc nitrate hexahydrate to inhibit fungal growth. Fig. 6E shows an SDA plate with zinc nitrate coated filter paper that has been inoculated with Phoma voilacea spores. 0% of the fungal spores grew.

Fig. 6F shows an SDA plate with water coated filter paper. One can see that Phoma voilacea grew well and an environmental contaminant was also able to grow and compete for the nutrients.

The following table (table 5) summarises the results obtained with various concentrations of zinc nitrate hexahydrate added to paint.

Table 5

Zinc nitrate hexahydrate has proven to be a very strong antifungal agent. It inhibits the growth of many common environmental fungi. Similar results were obtained with other forms of zinc nitrate (hydrated and non-hydrated) when their concentrations were recalculated accordingly to achieve the same level of zinc nitrate in the paint. One of the possible mechanisms of the antimicrobial properties of zinc nitrate incorporated into water-based paint is that it is dissolved in water and slowly release active ions (Zn ²⁺ in the case of zinc nitrate hexahydrate) that strongly interact with thiol groups of vital enzymes and inactivate them. In addition, structural changes in the cell membrane may also occur. The invention is not bound to this possible mechanism of antimicrobial action, it is possible that other mechanisms contribute or even dominate in the antimicrobial action process.

Structure of zinc nitrate, indicating the presence of the Zn ion

We have found that zinc nitrate hexahydrate exhibited antimicrobial properties at a reasonable incorporation rate (about 15%). The zinc nitrate hexahydrate [Zn(N0₃)₂-6H₂0] was also tested at concentrations below 10% by weight and above 10% by weight. The final concentration of the zinc nitrate or zinc nitrate hydrate may depend on the intended use of the paint and the extent of it is desired antibacterial properties. Our findings suggest that the range of 1% to 25% of zinc nitrate hexahydrate is a suitable range for most of the applications described in the field of use of this invention. While the examples all refer to zinc nitrate hexahydrate as it is a common stable form of zinc nitrate, it will be appreciated by those skilled in the art that anhydrous zinc nitrate would be as effective as an active ingredient (antimicrobial). Anhydrous Zinc nitrate is a deliquescent material and readily absorbs water from the atmosphere. This process is similar to dissolving anhydrous zinc nitrate in water. The salt breaks down into exactly the same ions, namely Zn ²⁺ and [N⁺0^3"]. Therefore, both the hydrated version (zinc nitrate hexahydrate) and the non- hydrated version (anhydrous zinc nitrate) provide the same ions to the paint and therefore impart the exact same properties. The only difference is that the percentage concentration of anhydrous zinc nitrate required should be less than the zinc nitrate hexahydrate, as zinc nitrate accounts for around 60% of zinc nitrate hexahydrate. There are also other known compositions of hydrated zinc nitrate, different from the common hexahydrate version. It will be appreciated that all such versions can also be used and the required concentrations indicated here for the hexahydrate version may need to be adjusted accordingly.

In order to mimic everyday conditions, paint containing zinc nitrate hexahydrate was brushed over plasterboard. Plasterboard was cut into pieces of size 2x2 cm² and each piece was treated with undercoat to simulate walls. After the undercoat had fully dried out, paint comprising zinc nitrate hexahydrate was applied to the plasterboard with a brush. Plasterboard samples prepared in this way underwent the same procedure of bacterial growth as described for the glass microscope slides described in Example 2 above. The paint comprising zinc nitrate hexahydrate retained its antibacterial effect.

The invention does not exclude any other common elements and ingredients added to the paint and required to achieve durable and high quality water-based paint. The invention can also be used with under coats and primers such as water-based undercoats that are used with new surfaces before application of over layer.

The invention is not limited to the embodiments hereinbefore described which may be varied in detail.

Claims

1. A water-based paint composition comprising anhydrous zinc nitrate [Ζ^η(Ν0₃)₂] or a hydrated form of zinc nitrate [Ζη(Νθ₃)₂·χΗ₂θ] in an amount to provide antimicrobial, antibacterial, and/or antifungal properties to the paint composition.

2. A paint composition as claimed in claim 1 wherein x is from 1 to 20.

3. A paint composition as claimed in claim 1 or 2 wherein x is 6.

4. A paint composition as claimed in any of claims 1 to 3 wherein the zinc nitrate is present in an amount of from 1 % to 20% by weight of the composition.

5. A paint composition as claimed in any of claims 1 to 4 wherein the zinc nitrate is present in an amount of about 15% by weight of the composition.

6. A paint composition as claimed in any of claims 1 to 4 wherein the zinc nitrate is present in an amount of from 1 % to 15% by weight of the composition.

7. A paint composition as claimed in any of claims 1 to 4 wherein the zinc nitrate is present in an amount of from 5% to 15% by weight of the composition.

8. A paint composition as claimed in any of claims 1 to 4 wherein the zinc nitrate is present in an amount of from 5% to 10% by weight of the composition.

9. A water-based paint composition comprising anhydrous zinc nitrate [Zn(N0₃)₂] or a hydrated form of zinc nitrate [Ζη(Ν0₃)₂·χΗ₂0] in an amount to provide antifungal properties to the paint composition.

10. A paint composition as claimed in claim 9 wherein x is from 1 to 20.

1 1. A paint composition as claimed in claim 9 or 10 wherein x is 6.

12. A paint composition as claimed in any of claims 9 to 1 1 wherein the zinc nitrate is present in an amount of from 1 % to 20% by weight of the composition.

13. A paint composition as claimed in any of claims 9 to 12 wherein the zinc nitrate is present in an amount of from 5% to 15% by weight of the composition.

14. A paint composition as claimed in any of claims 9 to 12 wherein the zinc nitrate is present in an amount of from 5% to 10% by weight of the composition.

15. A paint composition as claimed in any of claims 1 to 14 wherein the zinc nitrate is uniformly dispersed in the paint.

16. A substrate coated with a paint as claimed in any of claims 1 to 15.

17. A product coated with a paint as claimed in any of claims 1 to 15.

18. Use of anhydrous zinc nitrate [Zn(N0₃)₂] or a hydrated form of zinc nitrate [Zn(N0₃)₂ xH₂0] as an additive to provide antimicrobial, antibacterial, and/or antifungal properties to a coating.

19. Use of anhydrous zinc nitrate [Zn(N0₃)₂] or a hydrated form of zinc nitrate [Ζη(Ν0₃)₂·χΗ₂0] as an additive to provide antifungal properties to a coating.

20. Use as claimed in claim 18 or 19 wherein x is from 1 to 20.

21. Use as claimed in any of claims 18 to 20 wherein x is 6.

22. Use as claimed in any of claims 18 to 21 wherein the zinc nitrate is present in an amount of from 1 % to 20% by weight of the coating.

23. Use as claimed in any of claims 1 8 to 21 wherein the zinc nitrate is present at a concentration of from 1% to 15% by weight of the coating.

24. Use as claimed in any of claims 18 to 21 wherein the zinc nitrate is present in an amount of from 5% to 15% by weight of the coating.

25. Use as claimed in any of claims 18 to 21 wherein the zinc nitrate is present in an amount of from 5% to 10% by weight of the coating.

26. Use as claimed in any of claims 18 to 25 wherein the zinc salt is uniformly dispersed in the coating.

27. Use as claimed in any of claims 18 to 26 wherein the coating is a paint.

28. Use as claimed in claim 27 wherein the paint is a water based paint.

29. A method of preparing a paint composition comprising the steps of:

• adding anhydrous zinc nitrate [Zn(N0₃)₂ ] or a hydrated form of zinc nitrate [Ζη(Ν0₃)₂·χΗ₂0] to a paint; and

• allowing the zinc nitrate to become uniformly dispersed in the paint.

30. A method as claimed in claim 29 comprising the steps of:

• dissolving the zinc nitrate in water prior to the step of adding the zinc nitrate to the paint.

31. A method as claimed in claim 29 or 30 wherein x is from 1 to 20.

32. A method as claimed in any of claims 29 to 31 wherein x is 6.

33. A method as claimed in any of claims 29 to 32 wherein the zinc nitrate is present in an amount of from 1 % to 1 % by weight of the paint.

34. A method as claimed in any of claims 29 to 33 wherein the zinc nitrate is present in an amount of about 15% by weight of the paint.

35. A method as claimed in any of claims 29 to 32 wherein the zinc nitrate is present in an amount of from 1% to 20% by weight of the composition.

36. A method as claimed in any of claims 29 to 32 wherein the zinc nitrate is present in an amount of about 15% by weight of the composition.

37. A method as claimed in any of claims 29 to 32 wherein the zinc nitrate is present in an amount of from 1 % to 15% by weight of the composition.

38. A method as claimed in any of claims 29 to 32 wherein the zinc nitrate is present in an amount of from 5% to 15% by weight of the composition.

39. A method as claimed in any of claims 29 to 32 wherein the zinc nitrate is present in an amount of from 5% to 10% by weight of the composition

40. A method as claimed in any of claims 29 to 39 wherein the paint is a water based paint.