FIELD OF THE INVENTION

The present invention relates to a single component anti-algal, anti-fungal and antibacterial additive to deter or prevent microbial growth in stored coatings and on susceptible surfaces. More particularly the present invention provides a novel process for preparing micro-nano zinc oxide-based biocidal additive useful as a preservative due to its resistance to leaching from the substrate to which it is mixed.
BACKGROUND AND THE PRIOR ART
Many materials such as outdoor and indoor coatings that gather moisture become susceptible to harmful attacks by a range of microorganisms including fungi, yeast, algae and bacteria. Fungal growth on indoor and algal/fungal growth on outdoor surfaces is a major environmental concern today seriously affecting home, work and recreational environments. Not only can fungus (e.g., mold, mildew) be unpleasant on exposed surfaces, it can have damaging effect on wood, fiber and other materials if left untreated, causing severe loss to buildings and other structures and equipment. Since past few years, it has become increasingly evident that exposure to certain fungi or their spores can seriously impact the health of humans as well as other animals. In fact, the term "sick building syndrome" was recently coined to describe buildings in which various physical, chemical, and biological factors, including growing fungi and/or their spores, have severely compromised the air quality leading to discomfort or illness of the occupants. Allergies, asthma, infections, and the long-term repercussions of mold toxins are just a few of the many major concerns associated with mold contamination of indoor and outdoor environments.

As mentioned earlier, paints and paint films or coatings are known to be vulnerable to mold contamination due to the presence of common organic components that act as cellulosic thickeners, surfactants and defoamers, and which can also serve as a source of food for fungus cells. Some of these components are acrylic, polyvinyl and other carbon polymers. For example, latex is a water-dispersed binder comprising a carbon-based polymer. Inside the paint can, certain fungi (e.g., yeasts) can convert enough carbon-containing food sources to CO2 to swell or even explode the can. Fungi can also discolor and reduce the viscosity of the paint and produce foul odors. Both in-can preservation of paints and protection of the end use paint films, and the surfaces they cover, from mold, mildew and yeasts is necessary. To combat fungi, a variety of coating materials have been formulated which include biocide package to discourage or prevent the growth of mildew on the paint film. Ideally, these chemical fungicides or mildewcide slowly leach out of the paint to the surface and maintain their inhibitory properties for the life of the paint film, causing little or no harm to the environment. In practice, however, the antifungal properties of most coating compositions in use today persist for variable lengths of time, depending on the amount of exposure to the elements, abrasion, and erosion.

Commercial biocide package in general contains iodopropylbutylcarbamate (IPBC), n- Octylisothiazolinone (OIT), methylene thiocyanate (MTC), thiocyanomethylthiobenzothiazole (TCMTB), thiazolylbenzimidazole (TBZ), benzimidazolylcarbamic acid methyl ester (BCM), Triazoles such as chlorophenylethyldimethylethyltriazole ethanol (Tebuconazole, commercially available from Bayer), substituted triazolines such as t-butylaminocyclopropylaminomethylthio-s-triazole, and Chlorophenyl dimethylurea (Diuron, commercially available from Bayer), and combinations thereof.

Due to ever increasing environmental and safety concerns, there is continuous demand today on the coatings industry to eliminate some of the more effective but more toxic chemical preservatives from paints and other coating compositions. Yet at the same time, consumers wish to avoid pay for poorly performing products. Thus, there is a great need in the coating industry today for safe and effective alternatives to conventional antimicrobial agents.

That inorganic biocidal agents can be viable alternatives since they are nontoxic to human-body safety, antibacterial and their mold proof ability is strong, has wide antibacterial range, little or no smell, appearance color is shallow, good heat stability, water-fastness, and long self-life.

Zinc oxide (ZnO) based materials find several industrial applications technological fields. For example, ZnO materials show excellent optoelectronic properties (M. Bitenc et al., Cryst. Growth Des. 2010, 10, 830-837, Z. Hou et al., Nanoscale Res. Lett., 2012, 7, 507 -513) due to its high band gap of 3.37 eV and high exciton binding energy (K. Foe et al., Thin Solid Films, 2013, 534, 76-82, K. He et al. Cryst Eng Comm, 2014, 16, 3853-3856). Not only have they been widely studied as catalyst supports, such as in the synthesis of methanol or in the decomposition of industrial and experimental processes (Phuruangrat, A. et al., Journal of Nanomaterials, 2014 (2014), but they also have excellent use in other applications such as in semiconductors in solar cells (P. Li et al., Mater. Chem. Phys. 2007, 106, 63-69; M. Klaumünzer et al., Cryst Eng Comm, 2014, 16, 1502-1513). For antimicrobial applications, of which antifungal applications have been reported (Patra P. et al., Langmuir, 2012, 28, 16966-16978 ; L. He et al., Microbiol. Res. 2011, 166, 207-215) along with antibacterial properties (Talebian N. et al., J. Photochem. Photobiol. B: Biology, 2013, 120, 66-73; N. Padmavathy and R. Vijayaraghavan, Sci. Tech. Adv. Mater. 2008, 9).

Moreover, ZnO is a particularly interesting oxide in materials engineering because its self-assembly can be fine-tuned, allowing the formation of micro and nanostructures with precise control at the molecular level that in turn dictates its structure, properties, and function. Examples of ZnO particles in 1D configuration are nanorods (Schlur L. et al., Chemical Communications, 2015, 51, 3367-3370), nano-needles (Park WI et al., Adv Mater, 2002, 14, 1841-1843), nanowires (Yang P. et al., Advanced Functional Materials, 2002, 12, 323-331) and nanoribbons (Pan ZW et al., Science, 2001, 291, 1947 1949). The most common 2D structures are nanoblades (Pan A. et al., J. Cryst. Growth, 2005, 282, 165-172) and nanogranules (Chiu WS et al., Chem. Eng. J., 2010, 158, 345 - 352). Regarding 3D structures, these include cauliflower (Lin L. et al., RSC Advances, 2015, 5, 25215-25221), snowflakes (Li C. et al., Nanoscale, 2010, 2, 2557- 2560) and nano boxes (Gao PX and Wang ZL, JACS., 2003, 125, 11299-11305). Self-assembly of inorganic basic nanocomponents into ordered one-dimensional, two-dimensional, and three-dimensional nanostructures is attractive because fine-tuning the way the basic components are organized provides a method for adjusting the final properties of the resulting material. K. Shingange et al., Materials Research Bulletin, 2016, vol. 85, 52-63, discloses ZnO nanostructures consisting of flower-like structures of a group of nanorods composed of small particles that nucleate from a center.

In WO 2010/018075 A1, biocidal properties of ZnO nanoparticles are disclosed. Other documents disclose nanoscale ZnO particles such as Liu et al., Journal of Materials Processing Technology, 2007, vol. 189 (1-3), 379-383; Srinkanth CK et al., Journal of Alloys and Compounds, 2009, vol. 486 (1-2), 677-684 or CN 1192991 A. CN 102 079 540 A discloses porous 3D ZnO particles composed of aggregated nanoparticles.

In case of antimicrobial applications of ZnO based materials, the vast majority of the state of the art refers to antibacterial applications (Li, M. et al., Environ. Sci. Technol., 2011, 45, 1977- 1983, Jones, N. et al., FEMS Microbiol. Lett., 2008, 279, 71-76) with little mention of their antifungal properties (Sharma, D., Thin Solid Films, 2010, 519, 1224-1229). Factors such as particle concentration, size, and specific surface area are deciding factors in ZnO's antimicrobial efficacy. A clear common trend in the state of the art is that the smallest ZnO nanoparticles show increased antibacterial efficacy. Although little is known about the antifungal activity of ZnO materials, published research reveals a similar trend for ZnO antifungal activity: ZnO nanomaterials possess increased antifungal activity relative to micro- or mesoparticles. This effect is usually associated with an increase in the specific surface area of smaller materials compared to larger ones. In summary, when it comes to the antimicrobial activity of ZnO, the consensus so far published is that the smaller the better.

However, most of the nano-ZnO synthesis are not easy to scale up and they use either complex synthesis process such as high temperature, hydrothermal as well organic solvents, microwave heating. This makes the process less environment friendly as well as not commercially viable. So, there is a need to develop commercially viable ZnO based biocidal agents that acts as a single component anti-algal, anti-fungal and antibacterial additive in paint formulation for both indoor and outdoor applications which can be easily produced in industrial scale.

OBJECT OF THE INVENTION
It is an object of the present invention to provide a water based single step synthesis method for producing flower type ZnO with micro-nano roughness, particularly but not exclusively as an additive for a surface coating, such as a paint composition, that may be added to the surface coating during manufacturing to impart anti-algal, anti-fungal and anti-bacterial properties.

It is a further object of the present invention to provide a highly efficient and environment friendly process of production that when added to a coating composition, such as a paint composition, having bactericidal and/or antimicrobial properties that aims to overcome or at least alleviate drawback posed by traditional organic biocides.

SUMMARY OF THE INEVNTION
Accordingly, the present invention provides a process for producing flower type ZnO with micro-nano roughness at room temperature, said process comprising the steps of:

(a) preparing a solution of a capping agent in water and stirring;
(b) adding Zinc Nitrate Hexahydrate (Zn(NO3)2 · 6H2O) to the solution of step a) and stirring to obtain a clear solution;
(c) adding sodium hydroxide (NaOH) to said clear solution of step b) to obtain a white milky solution; and
(d) filtering the solution of step c) followed by vacuum drying;

wherein said capping agent in step a) is selected from TriSodium Citrate Dihydrate (HOC(COONa)(CH2COONa)2 · 2H2O), Sodium Citrate Dibasic, Sodium Citrate Monobasic;
and
said flower type ZnO with micro-nano roughness has bactericidal, antimicrobial and antifungal properties.

According to another embodiment of the present invention, there is provided a flower type ZnO with micro-nano roughness prepared by the process of the present invention.

According to yet another embodiment of the present invention there is provided a paint formulation comprising a flower type ZnO with micro-nano roughness, wherein said flower type ZnO is prepared by the process of the present invention.

BRIEF DESCRIPTION OF ACOOMPANYING FIGURES
Figure 1 illustrates the FE-SEM images of the ZnO having micro-nano roughness.
Figure 2 illustrates the antibacterial efficacy test on a High PVC water-based emulsion paint following JIS Z 2801:2010.

Figure 3 illustrates the anti-algal efficacy test on a High PVC water-based emulsion paint following ASTM D5589.

Figure 4 illustrates the anti-fungal efficacy test on a High PVC water-based emulsion paint following ASTM D5590.

Figure 5 illustrates the anti-algal efficacy test on a Low PVC water-based emulsion paint following ASTM D5589.

Figure 6 illustrates the anti-fungal efficacy test on a Low PVC water-based emulsion paint following ASTM D5590.

Figure 7 illustrates the anti-algal efficacy test on water-based Lime paint following ASTM D5589.

Figure 8 illustrates the anti-fungal efficacy test on water-based Lime paint following ASTM D5590.

Figure 9 illustrates the SEM images of spindle-type ZnO structures produced without structure-directing agents.

Figure 10 illustrates the anti-algal efficacy test on water-based paint having spindle-type ZnO additive following ASTM D5589.

Figure 11 illustrates the anti-fungal efficacy test on water-based paint having spindle-type ZnO additive following ASTM D5590.

DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a water-based single step synthesis method for producing flower type ZnO with micro-nano roughness. Unlike the processes of the prior art, the process of the present invention can be performed in room temperature. The nano-flower type ZnO obtained by the process of the present invention have FE-SEM images as depicted in Figure 1 and possesses anti-algal, anti-fungal and anti-bacterial properties. The flowerlike ZnO of the present invention has average size ranging from 2 to 4 µm. It comprises a petal-like primary structure with each petal having an average thickness of 40 to 50 nm.

The method for producing flower type ZnO of the present invention with micro-nano roughness comprises the steps of:
a) preparing a solution of structure-directing reagent in water and stirring.
b) adding Zinc Nitrate Hexahydrate (Zn(NO3)2 · 6H2O) to the solution of step a) and stirring to obtain a clear solution;
c) adding sodium hydroxide (NaOH) to obtain a white milky solution; and
d) filtering the solution of step c) followed by vacuum drying.

The structure-directing reagent in step (a) can be a capping agent selected from TriSodium Citrate Dihydrate (HOC(COONa)(CH2COONa)2 · 2H2O), (Sodium Citrate Dibasic and Sodium Citrate Monobasic. The stirring is carried out for about 10 minutes.

In step (b), Zinc Nitrate Hexahydrate (Zn(NO3)2 · 6H2O) is added to the solution of step (a) under stirring until a clear solution is obtained. Typically, the solution is stirred for about 30 minutes at a speed of about 500 RPM. It has been found that the stirring speed contributes to the formation of the target nanostructure since the rate of stirring can dictate the shape, size, and uniformity of the nanostructure formed.

In step (c) sodium hydroxide (NaOH) is added to the clear solution of step (b) to obtain a white milky solution. Sodium hydroxide (NaOH) pellets are added in solid form. Typically, it takes about 2 hours for the solution to turn from a clear solution to white milky solution at a speed of 500 RPM. The milky white colour indicates the formation of the ZnO particles.

In the final step d), the solution of step (c) is filtered using a filter paper followed by vacuum drying at about 60°C. White free-flowing powder was recovered as the finished product.

The process according to the present invention is a water based single step synthesis for producing flower type ZnO with micro-nano roughness, particularly as an additive for a surface coating, such as a paint composition, that may be added to the surface coating during manufacturing to impart anti-algal, anti-fungal and anti-bacterial properties. It has been found that this unique flower type structure of ZnO with micro-nano roughness is obtained only when the process of the present invention is followed. Not bound by any theory it has been found that such structured ZnO impart anti-algal, anti-fungal and anti-bacterial properties to the composition. The present inventors have found that slight modification in the present synthesis process result in distinctive structures with inferior properties. For example, spindle-type ZnO structures (having SEM images shown in Figure 9) were produced without using trisodium citrate, which showed antibacterial properties. However, its antialgal and antifungal properties are much inferior compared to the ZnO nano-flower of the present invention.

The process is a highly efficient, energy saving and environment-friendly process which can be easily scaled up for industrial purpose. The zinc oxide thus formed when added to a coating composition, such as a paint composition, imparts bactericidal, antifungal and antimicrobial properties and overcomes or at least alleviates the drawback posed by traditional organic biocides.

According to another aspect of the present invention there is provided a paint composition comprising the ZnO nano-flower of the present invention and other excipients. The excipients that can be included in the composition of the present invention are the ones known in the art such as water, thickener, neutralizing agent, dispersing agent, defoamer, pigment and extenders, emulsion binder and preservatives.

The present invention is now being illustrated by way of non-limiting examples.

Example 1
Example of gm scale synthesis: In a Glass vessel equipped with a magnetic stirrer, 9 litres of distilled water was taken followed by the addition of 240 gm of Trisodium Citrate. It was stirred for 10 mins followed by the addition of 160 gm of Zinc Nitrate. The mixture was stirred for 30 minutes to generate clear solution. Stirrer speed was set at 500 RPM and 80 gm of solid Sodium Hydroxide was added at once. Within a few seconds, white colloidal solution appeared. It was stirred for 2 hours at 500 RPM at ambient conditions. After completion, the solution was vacuum filtered using a Buchner Funnel and Whatman 42 filter paper. The recovered white wet powder was dried at 60°C overnight in a hot air oven resulting in a free-flowing white powder of 45 grams.

Example of synthesis in Kg scale: 450 litres of distilled water was taken in a Stainless-steel stirring vessel equipped with a variable speed stirred. 18 Kg of Trisodium Citrate was added under stirring and stirred for 10 min followed by the addition of 12 Kg of Zinc Nitrate salt. After stirring for approximately 30 min a clear solution was produced. 6 kg of solid NaOH beads were added at once keeping stirring speed at 500 RPM. The stirring was continued for 2 hrs at ambient conditions. After 2 hrs, the solution was vacuum filtered in custom-designed system having 2-micron PP filter cloth. The resulting wet cake was dried in a hot -air oven for 6 hrs at 80°C which resulted in a free-flowing white powder of nano-ZnO. In this process, approximately 3.5-3.6 Kg of nano-ZnO can be produced per batch.

All resulted products showed ano-flower type ZnO having FE-SEM images as depicted in Figure 1.

Example 2
Process of making emulsion-based paint having commercial biocide package and nano-ZnO biocide additive and a comparative study of their antibacterial, antialgal and antifungal properties.
Table 1
Standard formulation for a high PVC Water based paint:
Standard Paint with commercial biocide Paint with nano-ZnO biocide
Compound Content % Content %
Water 27.1 27.6
Thickener 0.3 0.3
Neutralizing agent 1.0 1.0
Dispersing agent 0.4 0.4
Defoamer 0.6 0.6
Pigment + Extenders 49.6 49.6
Emulsion Binder 20.2 20.2
Preservative 0.8% EP Paste (20% Diruon , 10% Carbendazim, 2.5% Octyl isothiazoline) 0.3% nano-ZnO

Table 2
Standard formulation for a low PVC Water-based paint:
Standard Paint with a commercial biocide Paint with nano-ZnO biocide
Compound Content % Content %
Water 23.15 24.6
Thickener 0.3 0.3
Neutralizing agent 2.4 2.4
Dispersing agent 0.2 0.2
Defoamer 0.2 0.2
Pigment + Extenders 17.5 17.5
Emulsion Binder 54.5 54.5
Preservative 1.25% EP Paste (20% Diruon, 10% Carbendazim, 2.5% Octyl isothiazoline)
+ 0.5% Diuron 100 0.3% nano-ZnO

Table 3
Standard formulation for a Lime-based paint with high Lime content:
Lime paint without any biocide Lime paint with commercial biocide Lime paint with ZnO biocide
Compound Content % Content % Content %
Water 41.7 40.2 41.3
Thickener 0.4 0.4 0.4
Dispersing agent 2 2 2
Defoamer 0.4 0.4 0.4
Pigment + Extenders 21 21 21
Lime 22.5 22.5 22.5
Emulsion Binder 4 4 4
Preservative NIL (Due to high pH >12, Lime based paint is considered to have natural anti-microbial properties)
1.5% Diuron 100 0.4% nano-ZnO
Additives 8.0 8.0 8.0

o Typical Procedure:
1. All the ingredients were added by weight with the help of a calibrated measuring scale.
2. Ingredients such as soft water, defoamer / anti-foaming agent and thickener were added one by one and mix well at the stirrer speed of 60-70 RPM for 10-15 minutes. Then dispersing agents, wetting agents were added and mixed well for 10-15 minutes for homogeneous mixture.
3. Pigments and extenders were added one by one and dispersed at 1150 to 1250 RPM for 35-45 minutes. In case of nano-ZnO biocide, it was added along with pigment and extenders for uniform dispersion.
4. For standard formulation, biocides package, others additive and part defoamer were added one by one and mix well for 10-15 minutes.
5. Emulsion binder, part defoamer, neutralizing agents were added into mixer tank one by one and mix well for 10 - 15 min at the stirrer speed of 30-50 RPM.
6. Rest of the ingredients were mixed well for another 15-20 min.

Details of the Antimicrobial process used for efficacy evaluation:
(A) Anti-bacterial products test for antibacterial activity and efficacy according to JIS Z 2801:2010
• Test Organism:
i. Escherichia coli
ii. Staphylococcus aureus
iii. Pseudomonas aeruginosa
• Procedure:
1) 18-24 hrs. Culture of the organisms was grown at 37°C for 24hrs.
2) 5.0 x 5.0 cm2 samples of treated and untreated test materials were prepared. The whole surface of the test piece is lightly wiped with pharmacopeia gauze or absorbent cotton immersed in ethanol two or three times and dried completely.
3) Each sample was placed on sterile glass slides into a sterile 15 x 100mm petri dish.
4) Bacterial broth culture was adjusted to 2.5x105 – 1x106 cells/with a cell counting chamber or spectrophotometer.
5) 0.4 ml of test bacterial suspension was pipetted onto the test and control samples. The suspension was covered with a sterile polyethylene plastic film in such a way that the contact of the suspension with the material was optimal.
6) The samples were placed in a moist chamber having humidity above 75% at 37°C for 24hrs.
7) Serial dilutions of the test bacterial suspension recovered immediately (which form “0” hr control samples) were made and spread to pour each dilution to determine CFU/ml recoverable at time “0” hr.
8) After specified contact time surviving microorganisms were recovered via elution of the bacterial suspension from the test substrate into neutralizing broth and extracted via methods that provide complete removal of the inoculum from the test materials (such as sonication, vortexing/or manual extraction i.e., stomacher).
9) Serial dilutions of the initial neutralizing broth were performed.
10) Each dilution was spread (0.1 ml) or pour plate (1 ml) on agar medium and the plates were incubated at an optimal temperature for the organism for 48±2 hours.
11) Bacterial colonies from each dilution were counted and recorded.
12) Calculation of percent reduction of bacteria from treated v/s untreated samples was made.
• Calculation:
R = (Ut-U0) - (U0-At) = Ut-At
Where, R = anti-bacterial activity
Ut = average of logarithm numbers of viable bacteria after inoculation on untreated test pieces after 24 hrs.
At = average of logarithm numbers of viable bacteria after inoculation on test pieces after 24 hrs.
U0 = average of logarithm numbers of viable bacteria immediately after inoculation on untreated test pieces.

• Rating system:
*R = Reduction (log) value
R value = 2 Acceptable Anti-bacterial activity
R value > 3 Good
R value > 5 Best

• Determination of Test Validation
1. The flowing equation is established for the log value of the no. of viable bacteria immediately after inoculation on the untreated test piece.
(Lmax-Lmin)/Lmean = 0.2 , Lmax = max. Log.no. of the viable bacteria
Lmin = min. Log.no. of the viable bacteria
Lmean = average. Log.no. of the viable bacteria of the three test
pieces.
2. The average of the no. of viable bacteria immediately after inoculation on the untreated test piece shall be within range of 6.2x103 – 2.5x104 cells/cm2.
3. The no. of viable bacteria on untreated test pieces after 24 hrs shall not be less the 62 cells/cm2 for all three test pieces.
• Calculation of no. of viable bacteria:
N = CDV/A N = no. of viable bacteria (per 1 cm2 of the test piece)
C = count of colonies (average of the two petri dishes)
D = dilution factor
V = volume of broth used for wash-out
A = surface area covering film (cm2)

(B) Determining the resistance of Paint Films and related Coatings to algal Defacement following ASTM D5589
• Test organism:
Unicelluar green: Chlorella sp
Filamentous Green: Ulohtix sp
Filamentous Blue Green: Scytonema sp.
Colony-forming Green: Scenedesmus sp.

• Procedure:
1. Coatings to be tested were applied on art paper of filter papers
2. The sample disks or panels were allowed to dry for 24-72 hrs.
3. A leaching test may be conducted with distilled water with the help of leaching apparatus. The paint panels were then allowed to dry for 48 hrs.
4. Allen’s agar or BG-11 or Bold’s Basal agar (1.5%) were prepared and autoclave at 121C for 15 minutes.
5. The sterile media was poured into petri plates.
6. After solidification of the agar, a thin coat of algal suspension was applied to each specimen using a sterile atomizer or pipet, making sure that the surface is covered but not to oversaturate the samples.
7. Alternatively, a separate sterile cotton swab may be used to apply and evenly spread the inoculum over the surface of each test sample. The amount of inoculum used is the same between each of the various samples under test.
8. All the plates were incubated at 25-28 C under 85-90% humidity for 4 weeks.

• Results:
Rate the growth weekly for four weeks according to the following:
0 = no growth
1 = Traces of growth (<10%)
2 = Light growth (10-30%)
3 = Moderate growth (30-60%)
4 = Heavy growth (60% - complete coverage)
Z = Zone of inhibition (measured in mm)
ZX = Growth within the zone
NB: A large zone of inhibition indicates good biocidal efficacy against test organisms; however, it also suggests that the biocide is rapidly migrating out of the coating system (high potential of leaching). Leached samples showing a significant decrease in efficacy versus the corresponding unleached sample indicate that the biocide is leaching from the coating to some extent. This may indicate the potential for diminished performance.

(C) Evaluation of Dry-film anti-fungal efficacy by ASTM D5590
• Preparation of Fungal Spore suspension:
10 ml of sterile deionized water was added to each of the well sporulating slant of the above culture. The slant surface was scratched with sterile inoculating loop (try to avoid obtaining mycelia) and the contents were mixed thoroughly on vortex mixer. The spores suspension was diluted with sterile nutrient salts solution such that the resultant spore suspension contains 0.8 to 1.2 x 104 spores/ml as determined with a counting chamber. The spore suspension may be prepared fresh each day or may be held in the refrigerator at 3-10 C for not more than 4 days.
• Procedure:
All the process are same as mentioned in case of algal test except potato dextrose agar was used.
• Results:
Rate of growth was evaluated following the same methodology as mentioned earlier in case of algal test.
? Antibacterial performance evaluation: High PVC paint with commercial biocide package against nano-ZnO biocide.
All testing were conducted by using the JIS Z 2801:2010 method.
o Results:
Table 4
Sample Antibacterial Activity % Reduction
Blank - -
High PVC paint with commercial biocide package R= 1.642
<99.0%
High PVC paint with nano-ZnO biocide R=4.489
99.99%

Piant with spindle type ZnO R= 3.37 99.9%

Figure 2 discloses the test results of the High PVC water-based emulsion paint with commercial biocide package against nano-ZnO biocide of the present invention according to JIS Z 2801:2010.

? Anti-algal and anti-fungal performance evaluation: High PVC paint with commercial biocide package against nano-ZnO biocide.
All testings are conducted by using the ASTM D5589 (Anti-algal) & ASTM D5590 (Anti-fungal) method.

o Results:
Table 5
For algae
Sample Standard scoring System ( 3rdweek ) Remarks
Leached panel
High PVC paint with a commercial biocide 3 Z1
>30% algal growth observed on leached sample.
High PVC paint with nano ZnO 0 Z2 No algal growth is observed on leached sample.
Blank 4 ZX >60% algal growth is observed on blank sample.

Figure 3 depicts the results of the anti-algal efficacy test on a High PVC water-based emulsion paint following ASTM D5589.

Table 6
For fungi
Sample Standard scoring System ( 3rdweek ) Remarks
Leached panel
High PVC paint with a commercial biocide 4 ZX
>60% fungal growth observed on leached sample.
High PVC paint with nano ZnO 0 ZX No fungal growth is observed on leached sample.
Blank 4 ZX 100% fungal growth is observed on blank sample.

Figure 4 depicts the results of the anti-fungal efficacy test on a High PVC water-based emulsion paint following ASTM D5590.

? Anti-algal and anti-fungal performance evaluation: Low PVC paint with commercial biocide package against nano-ZnO biocide.

Table 7

Observation Dry Film test
Low PVC paint with Commercial biocide package Low PVC paint with nano-ZnO biocide
Algal test Fungal test Algal test Fungal test
1st Week 0 Z3
(Nil) 0 Z4
(Nil) 0 Z1
(Nil) 0 Z2
(Nil)
2nd Week 0 Z2
(Nil) 0 Z3
(Nil) 0 Z1
(Nil) 0 Z2
(Nil)
3rd Week 0 ZX
(Nil) 0 Z1
(Nil) 0 ZX
(Nil) 0 ZX
(Nil)
4th Week 0 ZX
(Nil) 0 Z1
(Nil) 0 ZX
(Nil) 0 ZX
(Nil)

Figure 5 depicts the results of the anti-algal efficacy test on a Low PVC water-based emulsion paint following ASTM D5589. Figure 6 depicts the results of the anti-fungal efficacy test on a Low PVC water-based emulsion paint following ASTM D5590.

? Anti-algal and anti-fungal performance evaluation: Lime paint with commercial biocide package against nano-ZnO biocide.

Table 8
Observation

Algal Test Fungal Test
Lime paint Lime paint with commercial biocide Lime paint with ZnO Lime paint Lime paint with commercial biocide Lime paint with ZnO
1st Week Nil Nil Nil Nil Nil Nil
2nd Week <10% Nil Nil >10% <10% Nil
3rd Week
>10% 10% <10% 60% >10% <10%
4th Week 60% >30% 10% 100% 30% 10%

Figure 7 depicts the results of the anti-algal efficacy test on water-based Lime paint following ASTM D5589. Figure 8 depicts the results of the anti-fungal efficacy test on water-based Lime paint following ASTM D5590.

? Anti-algal and anti-fungal performance evaluation: Paint with spindle type ZnO.

Table 9
Observation Dry Film test
Paint without any Biocide (Blank) Paint with non-standard ZnO biocide
Algal test Fungal test Algal test Fungal test
1st Week 1 ZX
(10%) 2 ZX
(30%) 0 Z1
(Nil) 1 ZX
(10%)
2nd Week 2 ZX
(30%) 3 ZX
(>30%) 1 ZX
(10%) 2 ZX
(30%)
3rd Week 3 ZX
(>30%) 3 ZX
(60%) 2 ZX
(30%) 3 ZX
(>30%)
4th Week 4 ZX
(>60%) 4 ZX
(>60%) 3 ZX
(60%) 3 ZX
(60%)

Figure 10 depicts the results of the anti-algal efficacy test on water-based paint having spindle-type ZnO additive following ASTM D5589. Figure 11 depicts the results of the anti-fungal efficacy test on water-based paint having spindle-type ZnO additive following ASTM D5590.

Claims:
1. A process for producing flower type ZnO with micro-nano roughness at room temperature, said process comprising the steps of:
a) preparing a solution of a capping agent in water and stirring;
b) adding Zinc Nitrate Hexahydrate (Zn(NO3)2 · 6H2O) to the solution of step a) and stirring to obtain a clear solution;
c) adding sodium hydroxide (NaOH) to said clear solution of step b) to obtain a white milky solution; and
d) filtering the solution of step c) followed by vacuum drying;
wherein said capping agent in step a) is selected from TriSodium Citrate Dihydrate (HOC(COONa)(CH2COONa)2 · 2H2O), Sodium Citrate Dibasic, Sodium Citrate Monobasic;
and said flower type ZnO with micro-nano roughness has bactericidal, antimicrobial and antifungal properties.

2. The process as claimed in claim 1, wherein in said step b) the solution is stirred for about 30 minutes at a speed of about 500 RPM.

3. The process as claimed in claim 1, wherein in said step (c) the sodium hydroxide (NaOH) are added in solid form such as pellets.

4. The process as claimed in claim 1, wherein in said step (c) the solution turns from a clear solution to white milky solution in about 2 hours while stirring at a speed of 500 RPM.

5. The process as claimed in claim 1, wherein in said step d) the solution is filtered using a filter paper followed by vacuum drying at about 60°C.

6. The process as claimed in any of the preceding claims, wherein said flower type ZnO with micro-nano roughness have FE-SEM images depicted in Figure 1.

7. The process as claimed in any of the preceding claims, wherein said flower type ZnO with micro-nano roughness having an average size of 2 to 4 µm.

8. The process as claimed in any of the preceding claims, wherein said flower type ZnO comprises a petal-like primary structure with each petal having an average thickness of 40 to 50 nm.

9. A flower type ZnO with micro-nano roughness prepared by the process as claimed in any of the preceding claims.

10. A paint formulation comprising a flower type ZnO with micro-nano roughness, wherein said flower type ZnO is prepared by the process as claimed in any of claims 1 to 8.