POLYMER DISPERSION

Abstract

The present invention generally relates to a dispersion comprising a plurality of core-shell particles, wherein the core comprising non-fluorinated polymer and the shell comprises fluorinated polymer. It also relates to the use of the said dispersion as an additive in a coating formulation in at least 10 wt %, wherein substrates coated with said coating formulation exhibit improved solar-reflective and anti-dirt properties. In preferred embodiments, the said core comprises methyl methacrylate monomer and the said shell comprises hexafluorobutyl acrylate, hexafluorobutyl methacrylate, tridecafluorooctyl arylate or perfluorooctyl acrylate.

Claims

1. A dispersion comprising a. a plurality of core-shell particles, wherein the core comprises at least one non-fluorinated polymer and the shell comprises at least one shell layer having at least one fluorinated polymer or fluorinated copolymer therein; and b. a solvent; wherein said dispersion has a solid content of the core-shell particles of at least 10 wt %.

2. The dispersion of claim 1, wherein said shell comprises a fluorinated copolymer of at least two fluorinated monomers in the same shell layer.

3. The dispersion of claim 1, wherein said fluorinated polymer or fluorinated copolymer comprises a fluoroalkyl monomer with at least one of an acrylate monomer or a methacrylate monomer, or mixtures thereof.

4. The dispersion of claim 3, wherein said fluorinated polymer is selected from the group consisting of poly(2,2,2-Trifluoroethyl Acrylate), poly(2,2,2-Trifluoroethyl Methacrylate), poly(2,2,3,3-Tetrafluoropropyl Acrylate), poly(2,2,3,3-Tetrafluoropropyl Methacrylate), poly(2,2,2,3,3-Pentafluoropropyl Acrylate, poly(2,2,2,3,3-Pentafluoropropyl Methacrylate, poly(2,2,3,4,4,4-Hexafluorobutyl Acrylate), poly(2,2,3,4,4,4-Hexafluorobutyl Methacrylate), poly(2,2,3,3,4,4,4-Heptafluorobutyl Acrylate), poly(2,2,3,3,4,4,4-Heptafluorobutyl Methacrylate), poly(2,2,3,3,4,4,5,5-Octafluoropentyl Acrylate), poly(2,2,3,3,4,4,5,5-Octafluoropentyl Methacrylate), poly(3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooctyl Acrylate), poly(3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooctyl Methacrylate), poly(1H,1H-Perfluorooctyl Acrylate), poly(1H,1H-Perfluorooctyl Methacrylate) poly(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptadecafluorodecyl Acrylate), poly(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptadecafluorodecyl Methacrylate), poly(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-Heneicosafluorododecyl Acrylate), poly(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-Heneicosafluorododecyl Methacrylate, and mixtures thereof.

5. The dispersion of claim 3, wherein said fluorinated copolymer comprises at least two monomers selected from the group consisting of 2,2,3,4,4,4-Hexafluorobutyl Acrylate, 2,2,3,4,4,4-Hexafluorobutyl Methacrylate, 3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooctyl Acrylate, 3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooctyl Methacrylate, 1H,1H-Perfluorooctyl Acrylate, and 1H,1H-Perfluorooctyl Methacrylate.

6. The dispersion of claim 1, wherein the solvent is an aqueous solvent.

7. The dispersion of claim 1, wherein the core-shell particles have an average particle size in the range of 50 nm to 800 nm.

8. The dispersion of claim 1, wherein the core-shell particles have an average shell thickness in the range of 5 nm to 50 nm.

9. The dispersion of claim 1, wherein the solid content of the dispersion is in the range of 35% to 60%.

10.-19. (canceled)

20. A method of increasing total solar reflectance (TSR) of a substrate comprising the step of forming a coating of a mixture of a dispersion with a coating material on a surface of said substrate, wherein said dispersion comprises a solvent with a plurality of core-shell particles disposed therein, said core-shell particles having at least one non-fluorinated polymer in the core and at least one fluorinated polymer or fluorinated copolymer in at least one shell layer of the shell, and said core-shell particles forming a solid content of at least 10% of the dispersion.

21. The method of claim 20, wherein said coating has a thickness in the range of 50 nm to 500 m.

22. The method of claim 20, further comprising the step of heat treating the coating.

23. The method of claim 20, wherein the coating formed on the substrate is capable of repelling dirt.

24. A coated article comprising a layer of a dispersion coated thereon, said dispersion comprises a solvent with a plurality of core-shell particles disposed therein, said core-shell particles having at least one non-fluorinated polymer in the core and at least one fluorinated polymer or fluorinated copolymer in at least one shell layer of the shell, and said core-shell particles forming a solid content of at least 10% of the dispersion.

25. The coated article of claim 24, wherein said coated article is capable of reflecting solar light and repelling dirt.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0132] The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0133] FIG. 1 is a number of scanning electron microscopy (SEM) images. FIG. 1a is the SEM image of the core particles prepared according to Example 1; FIG. 1b is the SEM image of the core-shell particles prepared according to Example 1. The scale bar on both images is 1 m.

[0134] FIG. 2 is a number of transmission electron microscopy (TEM) images. FIG. 2a is the TEM image of the core particles prepared according to Example 1; FIG. 2b is the TEM image of the core-shell particles prepared according to Example 1. The scale bar on both images is 100 nm.

[0135] FIG. 3 is a number of images shown to measure the water contact angle. FIG. 3a is the image of the water contact angle of the core particles prepared according to Example 1; FIG. 3b is the image of the water contact angle of the core-shell particles prepared according to Example 1.

[0136] FIG. 4 is a schematic diagram of the coating procedure of CSMP modified commercial coatings (CCs) for characterization purposes.

[0137] FIG. 5 is a number of SEM images. FIG. 5a is the SEM image of the pure commercial coating, CC (no dispersion of Example 1 added) with a magnification of 5,000; FIG. 5b is the SEM image of the mixture prepared according to Example 2 (with 10% of CS4 in the dispersion) with a magnification of 10,000; FIG. 5c is the SEM image of the mixture prepared according to Example 2 (with 20% of CS4 in the dispersion) with a magnification of 10,000; FIG. 5d is the SEM image of the mixture prepared according to Example 2 (with 40% of CS4 in the dispersion) with a magnification of 10,000.

[0138] FIG. 6 is a number of graphs comparing the contact angle of the CC and CSMP modified CC single layer film (CSMP content is 40% w/w in dry film) based on the measurement of the contact angle described in Example 3. FIG. 6a is the water contact angle of CC and CSMP modified CCs before and after annealing; FIG. 6b is the hexadecane contact angle of CC and CSMP modified CCs before and after annealing.

[0139] FIG. 7 is a number of images related to the experiment according to Example 4. FIG. 7A is the image of UV/Vis/NIR Spectrometer (360 degree contour measurement) used for TSR measurements; FIG. 7B is a schematic diagram of an experimental set-up used for heat build-up measurement of the coatings.

[0140] FIG. 8 is a number of graphs showing the overlay percent reflectivity plot of commercial coating (CC) and CSMP modified CCs using single layer of coating described in Example 4a. FIG. 8a is the overlay percent reflectivity plot of CC and CC+CS1; FIG. 8b is the overlay percent reflectivity plot of CC and CC+CS4.

[0141] FIG. 9 is bar diagrams showing total solar reflectivity (TSR) commercial coating (CC) and CSMP modified CCs as well as the surface temperature of commercial coating (CC) and CSMP modified CCs using single layer of coating described in Example 4a. FIG. 9a is the histogram comparing TSR of CC and CSMP modified CCs; FIG. 9b is the histogram comparing the bottom surface temperature of commercial coating (CC) and CSMP modified CCs.

[0142] FIG. 10 is a number of graphs showing the overlay percent reflectivity plot of commercial coating (CC) and CSMP modified CCs as well as the surface temperature of commercial coating (CC) and CSMP modified CCs using top layer approach of coating as described in Example 4b. FIG. 10a is the overlay percent reflectivity plot of CC and CC+CS3; FIG. 10b is the histogram comparing TSR of CC and CSMP modified CCs with CSMP modified CCs as the top layer; FIG. 10c is the histogram comparing the bottom surface temperature of commercial coating (CC) and CSMP modified CCs with CSMP modified CCs as the top layer; FIG. 10d is a schematic diagram describing the refraction and diffraction due to the mismatch of the refractive index (RI) between matrix and CSMPs as described in Example 4b.

[0143] FIG. 11 is a number of drawings related to the experiment described in Example 5. FIG. 11a describes the general schematic diagram of the experimental procedure to measure anti-dirt properties described in Examples 5a and 5b; FIG. 11b depicts the experimental set-up for dirt wash-off in Example 5b.

[0144] FIG. 12 is a number of graphs describing the results of dirt-recovery of the commercial coating (CC) and CSMP modified CCs as described in Examples 5a and 5b. FIG. 12a is the overlay TSR vs. various reflectance plot of CC, CC+CS2, and CC+CS4 before dirt loading, after dirt loading by wet method and after dirt wash-off experiment; FIG. 12b is the histogram comparing reflectivity recovery after wash-off experiment for CC, CC+CS2, and CC+CS4.

[0145] FIG. 13 is a histogram comparing the heat build-up of the commercial coating (CC) and CSMP modified CCs as described in Example 5b, before and after wash off experiments.

[0146] FIG. 14 is a schematic diagram of the experimental set-up of dry dirt deposition described in Example 6a.

[0147] FIG. 15 is a number of graphs describing the results of wash-off of the dry soiled coupons as described in Example 6b. FIG. 15a is the overlay TSR vs. various reflectance plot of CC, CC+CS2, and CC+CS4 before dirt loading, after dirt loading by wet method and after dirt wash-off experiment; FIG. 15b is the histogram comparing reflectivity recovery of washing for CC, CC+CS2, and CC+CS4.

DETAILED DESCRIPTION OF DRAWINGS

[0148] Referring to FIG. 4, there is provided a schematic diagram showing a process 100 of coating a substrate with CSMP modified commercial coating or commercial coating. In step 2, there is provided a substrate 10. In step 4, a commercial coating 12 or CSMP modified commercial coating 12 is applied to substrate 10 to afford wet coating film 14. In step 6, a drying temperature is applied to dry the coating from the wet coating film 14 to the dry coating film 16 for a period of time sufficient to dry the coating. The drying temperature may be at ambient temperature and the period of drying may be in the range of one day to 10 days. The dry coating film 16 may optionally undergo annealing process at an annealing temperature for a suitable period of time to afford annealed coating film 18. The annealing temperature may be in the range from 40 C. to 60 C. The suitable annealing duration may be from one day to 10 days.

[0149] For a single layer coating method, substrate 10 is coated by CSMP modified commercial coating 12 following the process 100 and the configuration is denoted as 20 in FIG. 4. As for top layer approach, commercial coating 12 is applied to substrate 10 following the process 100 above, followed by a second process 100, in which CSMP modified commercial coating 12 is coated on the previously coated substrate and such configuration is denoted as 22 in FIG. 4.

[0150] Referring to FIG. 11A, there is provided a schematic diagram showing a process 200 for analysing the anti-dirt properties of the substrate coated with CSMP modified commercial coating or commercial coating. In step 2, there is provided a coated substrate 22. In step 4, the deposition of dirt or soiling is undertaken to afford soiled substrate 24. In step 6, a wash-off or dirt-removal step is performed to afford washed substrate 26. Coated substrate 22, soiled substrate 24 and washed substrate 26 are then subjected to total solar reflectance (TSR) measurement experiment of step 8.

EXAMPLES

[0151] Non-limiting examples of the invention and a comparative example will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1: Preparation of Core-Shell Microparticle (CSMP) Dispersions

[0152] The polymerization of methyl methacrylate was undertaken in a 1 L-reactor under nitrogen equipped with mechanical stirrer. The reactor was deoxygenated prior to use by charging the reactor with a continuous flow of nitrogen. 80 mL of methyl methacrylate was introduced into the deoxygenated reactor containing 800 mL of deionized water (degassed by nitrogen) with a stirring rate of 200 rpm to form an oil-in-water suspension. The suspension was then heated to about 70 C. for a 30 minute equilibration time. 10 mL of aqueous solution of ammonium persulfate (APS, 0.682 grams, purchased from Sigma-Aldrich of St. Louis, Mo. of the United States of America) was added into the heated suspension. The resulting mixture changed its colour from semi-transparent to opaque-white colour after about two hours. After about 6-8 hours, the reactor was cooled to ambient temperature while stirring.

[0153] Without further purification, 11.12 g of fluoro monomer (2,2,3,4,4,4-hexafluorobutyl methacrylate or 6FBMA, purchased from Apollo Scientific of Cheshire of the United Kingdom) was added to the as-prepared PMMA dispersion with a solid content of about 10% at room temperature. The mixture was further stirred for 18 hours. The mixture was then heated to 70 C. and an aqueous solution of ammonium persulfate (0.107 g) was injected into the heated mixture to trigger the polymerization. The polymerization was continued for 8 hours. The reaction mixture was cooled down and transferred to a 2 L glass petri dish to increase the solid content by heating the content at 40 C. under a blow of air with continuous stirring. The final solid content of the dispersion in the reaction mixture after evaporation was about 45%.

[0154] The fluoropolymer content of the resulting particles was determined by proton NMR in CDCl.sub.3. It had been found that the fluoropolymer content with respect to PMMA core was 12.8 wt %. The particle size of the PMMA is in the range from 280 to 360 nm in diameter with the shell thickness (made of fluoropolymer) of about 10 to 15 nm. Further, the experiments revealed that the concentrated of CSMPs are shown to be stable for months without any aggregation or coagulation.

[0155] In addition, the core-shell microparticles dispersions were characterized by dynamic light scattering (DLS), scanning electron microscopy (SEM, as shown in FIG. 1), transmission electron microscopy (TEM as shown in FIG. 2), contact angle measurements (FIG. 3). The SEM, TEM and contact angle analysis for the core particles are shown in FIGS. 1a, 2a, and 3a, respectively. The SEM, TEM and contact angle analysis for the core-shell particles above are shown in FIGS. 1b, 2b, and 3b, respectively.

[0156] The characteristics of the various CSMP with different shell compositions were prepared and they are termed as CS1, CS2, CS3, and CS4, respectively (refer to Table 1).

TABLE-US-00001 TABLE 1 The dispersion comprises the polymer of methyl methacrylate in the core and the fluorinated polymer in the shell layer. Z-Ave DLS Z-Ave DLS Average Average Solid core core-shell particle size - shell CSMP Core- Shell- Content particle size particle size TEM thickness Dispersion monomer monomer (%) (nm) (nm) (nm) (nm) Core MMA 46 305 203 CS1 MMA 6FBA 47 290 314 230 10 CS2 MMA 6FBMA 45 293 302 230 15 CS3 MMA 6FBA:13FOA 46 266 293 237 10 (9:1) CS4 MMA 6FBA:15FOA 45 306 356 255 15 (8:2) MMA = Methyl methacrylate (purchased from Sigma-Aldrich of St. Louis, Missouri of the United States of America) 6FBA = 2,2,3,4,4,4-Hexafluorobutyl Acrylate (purchased from Sigma-Aldrich of St. Louis, Missouri of the United States of America) 6FBMA = 2,2,3,4,4,4-Hexafluorobutyl Methacrylate (purchased from Apollo Scientific of Cheshire of the United Kingdom) 13FOA = 3,3,4,4,5,5,6,6,7,7,8,8,8-Tridecafluorooctyl Acrylate (purchased from Sigma-Aldrich of St. Louis, Missouri of the United States of America) 15FOA = 1H,1H-Perfluorooctyl Acrylate (purchased from Apollo Scientific of Cheshire of the United Kingdom)

[0157] Further information on the analytical instruments used throughout the Examples is as follow:

[0158] SEM images were obtained using JEOL JSM-6700F Field Emission SEM with Oxford INCA Energy Dispersive X-ray Spectrometer, JEOL USA, Inc. of Peabody, Mass. of the United States of America.

[0159] TEM images were obtained using Tecnai TF 20 S-twin with Lorentz Lens, FEI Company of Oregon of the United States of America.

[0160] DLS measurement was undertaken using Malvern Zetasizer Nano ZS, Malvern Instruments Ltd of Malvern of the United Kingdom.

Example 2: Preparation of the CSMP Modified Coating and the Coated Surface

[0161] Compatibility of the additive comprising the dispersion prepared according to Example 1 to the parent coating material was tested to determine whether the additive of Example 1 can be successfully used in real application. The water-based CSMP dispersions obtained in Example 1 were slowly added to commercial water-based acrylic coating (termed as commercial coating or CC, supplied by SkyCool Pte Ltd of Singapore) with stirring (200-300 rpm) and upon visual inspection, it appeared to be well compatible with CC during or after mixing. The resulting mixture, which is referred as CSMP modified CC, remained homogeneous without any phase separation or coagulation for an extended period of time.

[0162] Various CSMP modified CC, with different shell compositions as termed as CS1, CS2, CS3, and CS4, respectively, were produced via mixing the CSMP with CC. The resulting CSMP modified CCs are then termed as CC+CS1, CC+CS2, CC+CS3, and CC+CS4, respectively.

[0163] The CSMP modified CCs were sprayed over 6.56.5 cm2 steel plates by a spray gun (purchased from BADGER Air Brush Model 100, Badger Air-Brush Co. of Illinois of the United States of America.) The coating process of FIG. 4 was used whereby the substrate 10 was the steel plate, the coating was either 12 (CSMP modified CC) or 12 (commercial coating) as the first coating layer and 12 as the second coating layer, the temperature used in step 6 to dry the wet coating film 14 was about 23 C. for 3 days. The dried coating film 16 was then annealed in step 8 at 40 C. for 7 days to give annealed coating film 18. The thickness of the coating was 100 to 400 m. The range of thickness here refers to the thickness of the dried films. The configuration of the coated substrate for single layer approach is denoted as 20 in FIG. 4. The configuration of the coated substrate for the top layer approach is denoted as 22 in FIG. 4.

[0164] The thickness of the coating layer or coating film was measured by Elcometer 456 dual FNF thickness gauze, Model B (purchased from Elcometer Inc. of Michigan of the United States of America). The coated films (having dispersion with the amount of CS4 varied from 0 to 40%) were then analysed by SEM (refer to FIGS. 5a to 5d). Upon visual inspection and based on the surface roughness measurement, in general, the CSMP modified CC films were smoother in appearance. Further, the microparticles appear to be well dispersed in the coated film without any aggregation (refer to FIGS. 5b to 5d).

[0165] The smoothness of the CSMP modified CCs is likely the result of the filling up of peaks and troughs due to the presence of other irregular shaped additives of the coating by regular shaped CSMPs. Further, it is to be noted that the surface roughness caused by the addition of CSMPs are in nanometre range and therefore does not interfere the actual roughness of the material as observed by virtual inspection or the roughness measurement by any instrumental techniques (in micrometre range).

Example 3: Water and Hexadecane Contact Angles Measurement

[0166] The annealed coated plates obtained in Example 2 were subjected to the contact angle analysis. The measurement of the water and hexadecane contact angles was undertaken separately. The result for water contact angle measurement will indicate the level of hydrophobicity of the coating, while the hexadecane contact angle will provide information on the degree of oleophobicity of the coating. The results shown in FIG. 6 suggest the omniphobic nature of the CSMP modified CCs. In general, the introduction of the CSMP additives significantly enhanced water contact angle and drastically improved hexadecane contact angle (refer to FIGS. 6a and 6b, respectively). More surprisingly, annealing of CSMP modified CCs resulted in the increase of both water and hexadecane contact angles which is most likely due to the stratification to afford more fluorinated CSMPs present at the surface of the film. The increase in contact angles is dependent on the duration of annealing. However, the experimental result suggest that no further increase was observed after three days (refer to both FIGS. 6a and 6b).

Example 4: Solar Reflectivity and Heat Build-Up Measurement of CSMP Modified CCs

[0167] The CSMP modified coated steel coupons with the controlled thickness obtained in Example 2 were used for the solar reactivity and heat build-up measurements. TSR analysis was carried out using a UV/vis/NIR spectrometer (Perkin-Elmer Lambda 950 Spectrometer of San Diego of the United States of America) as shown in FIG. 7A. The in house set-up of the experiment is shown in FIG. 7b. In this example, there are two approaches adopted, the first one is via application of single layer of CSMP modified CC coating and the second one is via top layer approach by applying a thin layer of CSMP modified CC coating over CC coating.

[0168] The surface (bottom) temperature of the coated steel coupons was measured using the infrared (IR) lamp set-up as shown in FIG. 7b The equilibrium was attained in the range of about 4 to 8 minutes.

[0169] a. Single Layer Coating

[0170] Total Solar Reflectance (TSR) and heat build-up measurements were first performed using coupons coated with single layer of CSMP modified CC of about 100-400 m. A graph showing the relationship between reflectivity and wavelength in the range of solar spectrum was then obtained. TSR values of coating films of similar thickness were compared as it is well known to have the coating thickness effect on TSR (<400 m) and this is presented in Table 2.

TABLE-US-00002 TABLE 2 The variation of TSR and surface temperature with the coating thickness and various inventive dispersion of the present invention when single layer coating method was used Average Average thickness of Total Solar Surface coating film Reflectivity temperature Sample (m) (TSR) ( C.) No coating (only steel 93.3 0.1 coupon used as substrate) Steel coupon coated with 110 0.795 76.2 0.2 CC Steel coupon coated with 260 0.799 CC Steel coupon coated with 400 0.809 71.8 0.5 CC Steel coupon coated with 110 0.831 67.9 0.2 CC + CS1 Steel coupon coated with 110 0.806 69.9 0.4 CC + CS2 Steel coupon coated with 110 0.811 64.0 0.1 CC + CS3 Steel coupon coated with 120 0.82 67.7 0.5 CC + CS4

[0171] The Commercial coating (CC), which is deemed to have a high-reflective roof cool coating, was used as a control. The experimental results suggest that all CSMP modified CCs (using four different CSMPs) display higher solar reflectivity than the pure CC. The absolute amount of increase in TSR is, albeit being low, still significant by considering the fact that the concentration of the active ingredient such as TiO.sub.2 and silica microsphere present in CC was reduced to about 60 wt % of its original amount in the CSMP modified CC and yet still shows increase in reflectivity. This is surprising as in general, a person skilled in the art would expect that a reduction in the reflectivity would be observed as the concentration of the TiO.sub.2 is decreased.

[0172] In addition, by comparing the thickness of the coating used, only one-quarter thickness of the CSMP modified CC films (versus that of the pure CC) were required to produce similar, if not slightly better, results in reflectivity. This has major implications, particularly when one considers reducing the amount of the coating material and thus the cost of the coating materials.

[0173] The above was further confirmed by the overlay reflectivity plots of CC vs. CSMP modified CCs (refer to FIGS. 8a and 8b) showing that the reflectivity of CSMP modified CCs is generally higher in mostly visible and near infrared regions than CC. The histogram shown in FIG. 9a. confirms similar observations. The comparison of the surface (bottom) temperature is depicted in FIG. 9b indicating that the bottom surface temperature of the CSMP modified CCs has a lower heat build-up property in comparison with the commercial coating.

[0174] b. Top Layer Approach

[0175] Another approach adopted in the coating experiment was top layer approach by considering efficient utilization of CSMPs. In this methodology, a thin layer of CSMP modified CC of about 100 m was applied on the CC-coated steel coupon. The TSR values of coating films of similar thickness were then compared. Similar observation as previously found was obtained. For all cases of CSMP modified CCs, which were applied as top layers, the CSMP modified CCs-coated coupons exhibit significant improvement in TSR values (refer to FIGS. 10a, 10b, 10c and Table 3).

TABLE-US-00003 TABLE 3 The variation of TSR and surface temperature with the coating thickness and various inventive dispersion of the present invention when top layer method was used Average Average thickness of Total Solar Surface coating film Reflectivity temperature Sample (m) (TSR) ( C.) No coating (only steel 93.3 0.1 coupon used as substrate) Steel coupon coated with 400 0.797 71.8 0.5 CC Steel coupon coated with CC 300 0.851 67.1 1.4 (CC + CS1) over CC (CC + CS1) 110 Steel coupon coated with CC 300 0.815 63.0 0.2 (CC + CS2) over CC (CC + CS2) 120 Steel coupon coated with CC 300 0.871 61.1 0.1 (CC + CS3) over CC (CC + CS3) 120 Steel coupon coated with CC 300 0.83 65.3 0.8 (CC + CS4) over CC (CC + CS4) 120

[0176] The increase in TSR of the CSMP modified CCs is likely due to the combination of the following factors: [0177] i) The presence of homogenously distributed spherical CSMPs. As evidenced by the light scattering analysis, the CSMPs modified CCs are homogenously distributed and there was no aggregation detected; [0178] ii) The microparticle nature of the core-shell additives having the particle size of about 300 to 400 nm, which falls within the required size of most intense wavelengths (400 to 1350 nm) in solar spectrum. Previous studies suggest that the particle size in the range of to of the incident wavelength are well suited to achieve high reflectivity and increased diffraction; [0179] iii) Increased refraction and diffraction due to the mismatch of the refractive index (RI) between matrix and CSMPs. The acrylate binder has RI of about 1.489 and the RI of fluoropolymer used in the shell is about 1.36; [0180] iv) Significant increase in grain boundary area due to core-shell nature, which is approximated about twice as much as using a homogeneous particle (refer to FIG. 10d)

Example 5: Dirt Removal Properties of CSMP Modified CCs (Wet Deposition/Wet Removal)

[0181] Fluorinated polymers are well-known for their omniphobic properties. Owing to its low surface energy, a fluorinated surface reduces interaction with water, oil or any other contaminants including dirt, which is composed of a combination of different components with different structure and polarity.

[0182] Being a microparticle with large surface area and due to the presence of fluoropolymer in the very thin shell component, these microparticle additives maximize the improvement of these properties by utilizing small amount of otherwise expensive fluoromonomers. The fluorinated CSMP additives were prepared according to Example 1, via emulsion polymerization in water and were well compatible with water based commercial coatings as shown in Example 2.

a. Wet Soiling (Dirt-Deposition) Experiment

[0183] The wet soiling experiment mimic the natural dirt-deposition process where rain drops transport the airborne particles onto the roof surface and then evaporated out leaving behind the particles on the surface. Real dirt used was collected from air-conditioning inlet system and was used for evaluation.

[0184] The above real dirt was characterized by different analytical techniques and was shown to contain a complex mixture of organic, inorganic, hydrophilic and hydrophobic components. The experimental overview of the wet soiling (dirt-deposition) is illustrated in FIG. 11a. Firstly, the real dirt was dispersed into the deionized water, followed by loading of the soiled liquid (step 4) onto silicone sealed coupon to afford soiled substrate 24. Step 4 using dry soiling method is described in Example 6a. The coupon was then dried in the oven. This methodology allows the loading of exact designated amount of dirt onto the coupons surface. Following this step, soiled substrate 24 undergoes a wash-off or dirt removal step 6 described in part b below to afford washed substrate 26.

b. Dirt Wash-Off (Dirt-Removal) Experiment

[0185] In this experiment, rainfall of 82.8 L/m.sup.2 h was used to replicate the flash flooding rainfall intensity. In addition to considering the intensity of rainfall, another parameter used was the amount of water fall that the coupons were exposed to. The reference point was the average rainfall which was 2217 mm (2217 L/m.sup.2). Calculation showed that 26.8 L of spraying is proportional to a monthly rainfall. Therefore, the samples would be exposed to rain in the box for two hours and 14 minutes at a flow rate of 12 L/h to simulate an equivalent exposure of a month long of flash flooding rainfall. A complete cycle of the wash off experiment will be a study for spraying of 3 month equivalent of flash flooding rainfall.

[0186] Steel coupons coated CC and CSMP modified CC were used to evaluate dirt-removal performance and the experimental. The experimental design is depicted in FIG. 11b.

[0187] Solar reflectivity was used to quantify dirt loading and wash off. The linear relationship between solar reflectivity and dirt amount has been established previously. The dirt-removal results are shown in FIG. 12a. As can be seen, the CSMP modified has improved dirt-removal properties than CC, which was used as reference. The actual extent of wash-off recovery of the CSMP modified CCs was dependent on the type of CSMP additive used, particularly the type of fluoropolymer shell present in the CSMPs. The results reveal that CS2 and CS4 were the best additives among all CSMPs. From FIG. 12b, it is shown that CSMP modified CC with CS2-type of core-shell structure has best dirt-wash-off recovery (up to about 36%, refer to FIG. 12b). This is most probably due to the high glass translation temperature (T.sub.g) of shell composition.

[0188] The reflectivity restoration over loss in percent (or %) may be defined as the ratio of the restored reflectance by washing (R2-R1) with respect to lost reflectance by soiling (R0-R1), where:

[0189] R0=Reflectance of coupons before dirt loading;

[0190] R1=Reflectance of coupons after dirt loading;

[0191] R2=Reflectance of coupons after dirt wash-off;

[0192] R0, R1 and R2 were measured according to step 8 of FIG. 11A. The formula to calculate the reflectivity restoration over loss is shown below:

[00001]$\mathrm{Reflectivity}.Math..Math.\mathrm{restoration}.Math..Math.\mathrm{over}.Math..Math.\mathrm{loss}.Math..Math.\left(\%\right)=\frac{\mathrm{Restored}.Math..Math.\mathrm{reflectance}.Math..Math.\mathrm{by}.Math..Math.\mathrm{washing}.Math..Math.\left(R.Math..Math.2-R.Math..Math.1\right)}{\mathrm{Lost}.Math..Math.\mathrm{reflectance}.Math..Math.\mathrm{by}.Math..Math.\mathrm{soiling}.Math..Math.\left(R.Math..Math.0-R.Math..Math.1\right)}100$

[0193] The selected dirt-washed off coupons (CS2 and CS4 modified CCs) were tested for heat build-up measurements and the results are shown in FIG. 13. Overall, the CS2 modified CC coated coupons maintained the less heat build-up properties than the pure CC coated coupons.

Example 6: Dirt Removal Properties of CSMP Modified CCs (Dry Deposition/Wet Removal)

[0194] a. Dry Soiling (Dirt-Deposition) Method

[0195] The dry soiling was undertaken inside a customized dry deposition chamber. The chamber was made of stainless steel and had the inner dimensions of 60 cm (W)60 cm (H)60 cm (L). Four mixing fans (Paps, Series 8000N), each providing 50 cm.sup.3/h of airflow rate were installed inside the chamber to provide air mixing. The above chamber was also equipped with a circular inlet port at the centre of the chamber through which the dirt particles were introduced.

[0196] The set-up of the above experiment is depicted in FIG. 14.

[0197] The fans in the chamber were operated for five minutes prior to the onset of the experiment to ensure that a fully turbulent air flow condition was generated within the chamber. A funnel with fine cloth sieve having opening size of 100 m was placed in the inlet port of the deposition chamber. The weight ball milled particles was introduced into the dry soiling chamber via a fine cloth sift (opening size of 100 m) with shaking over the period of three minutes. The fans were switched off five minutes after the loading to allow the particles to settle. Pre-weighed coupons were retrieved after two hours and sent for TSR and weight measurement.

b. Dirt Wash-Off/Recovery (Dirt-Removal) Experiment of Dry Soiled Coupons

[0198] The dry soiled coupons were then subjected to similar wash off recovery (dirt-removal) described in Example 5b (refer to FIG. 11b).

[0199] With reference to FIG. 15a, the experimental results suggest that the CS2 and CS4 modified CC exhibit improved dirt-removal properties compared to the pure CC. CS4 modified CC was able to achieve up to 100% recovery in comparison to the original CC, which could only recover 60% of its initial reflectance (refer to FIG. 15b). Further, the performance of CS2 modified CC is comparable to the CS4 modified CC.

INDUSTRIAL APPLICABILITY

[0200] As shown above, the dispersion of the present invention is highly compatible with the parent coating material. As such, the dispersion described herein may be used as an additive. Further, since the dispersion described herein are omniphobic and have low surface energy, the coating comprising the dispersion therein may be used in various applications such as non-stick coating for cookware, bake-ware and electric appliance industry.

[0201] Further, as stated above, the coating may also be applied for roof coating (termed as cool roof), where cool roof can benefit a building and its occupants by: reducing energy consumption by decreasing air conditioning requirements, improving indoor comfort for spaces that are not air conditioned, such as garages or covered storage room as well as decreasing roof temperature, which may extend roof service life. Beyond the building itself, cool roofs may also benefit the environment, especially when many buildings in a community have them. Some of the advantages include reducing the local air temperatures, lowering the peak electricity demand, which in turn may help in preventing power outages, reducing power plant emissions, including carbon dioxide, sulfur dioxide, nitrous oxides, and mercury, by reducing cooling energy use in buildings.

[0202] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.