COMPOSITE PIGMENTS

Abstract

There is provided a paint formulation comprising a composite pigment, said composite pigment being selected from the group consisting of metal oxide/silica, metal oxide/silicate, metal oxide/alumina, metal oxide/metal oxide and metal oxide/zirconia, wherein the size and amount of said composite pigment are selected to increase the opacity of said paint formulation.

Claims

1.-10. (canceled)

11. A composite pigment configured to increase opacity of a paint formulation, the paint formulation comprising a metal oxide as a first component and a second component selected from the group consisting of silica, silicate, and a metal oxide; the metal oxide of the first component being selected from the group consisting of zinc oxide, aluminum oxide, antimony oxide, barium oxide, magnesium oxide, and zirconium oxide; the metal oxide of the second component, when present, being selected from the group consisting of zinc oxide, aluminum oxide, antimony oxide, barium oxide, magnesium oxide, and zirconium oxide; the metal oxide of the first component being at least partially covered by the second component; a particle size of the metal oxide in the first component being in a range of 5 nm to 100 nm; the composite pigment having a particle size effective to provide opacity to the pigment and a specific surface area in a range of from 20 m.sup.2/g to 100 m.sup.2/g; and at least one of: the composite pigment comprising a mixture of nanorods and multifaceted morphology; and the composite pigment comprising a hollow core-shell structure.

12. The composite pigment of claim 11, wherein the composite pigment comprises a mixture of nanorods and multifaceted morphology.

13. The composite of claim 11, wherein the composite pigment comprises a hollow core-shell structure.

14. The composite pigment of claim 13, wherein a shell of the hollow core-shell structure is formed of alternating layers of the first and second components.

15. A method of preparing the composite pigment of claim 11, comprising: providing a metal salt as a first component precursor, the metal salt being selected from a zinc salt, an antimony salt, a barium salt, a magnesium salt, and a zirconium salt; providing a second component precursor selected from a silica precursor and an alumina precursor; providing a base solution selected from sodium hydroxide, potassium hydroxide, and calcium hydroxide; reacting the first component precursor, the second component precursor, and the base solution to form a reaction mixture; and adjusting a pH of the reaction mixture to be in a range of 7-10 to form the composite pigment of claim 11.

16. The method of claim 15, further comprising: adding a surfactant or dispersant to a solution comprising the first component precursor to reduce particle size of the first component to a nano-range size.

17. The method of claim 15, further comprising: filtering or centrifuging the reaction mixture to separate the composite pigment; washing the separated composite pigment; and drying the separated composite pigment.

18. A method of preparing the composite pigment of claim 11, comprising: (a) mixing a metal salt and a base solution to form a first component, which is a metal oxide; (b) adding a second component to the metal oxide of step (a) to form a reaction mixture; and adjusting a pH of the reaction mixture to be in a range of 7-10 to form the composite pigment of claim 11; the base solution being selected from sodium hydroxide, potassium hydroxide, and calcium hydroxide; the second component being selected from the group consisting of a silica, a silica precursor, an alumina, an alumina precursor, a metal oxide, and a metal oxide precursor; the metal oxide in the first component being selected from the group consisting of zinc oxide, aluminum oxide, antimony oxide, barium oxide, magnesium oxide, and zirconium oxide; the metal oxide precursor in the second component, when present, being selected from the group consisting of a zinc salt, an antimony salt, a barium salt, a magnesium salt, and a zirconium salt; and the metal oxide in the second component, when present, being selected from the group consisting of zinc oxide, antimony oxide, barium oxide, magnesium oxide, and zirconium oxide.

19. The method of claim 18, further comprising: adding an amine surfactant to the metal oxide obtained in step (a) to create a charge on the first component before step (b).

20. The method of claim 18, further comprising: adding a surfactant or dispersant to a solution comprising the first component precursor to reduce particle size of the first component to a nano-range size.

21. The method of claim 18, further comprising: filtering or centrifuging the reaction mixture to separate the composite pigment; washing the separated composite pigment; and drying the separated composite pigment.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0050] 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.

[0051] FIG. 1 shows the X-Ray Diffraction (XRD) pattern of silica coated on nano zinc oxide composite formed in accordance with Example 2.

[0052] FIG. 2 shows a transmission electron micrograph (TEM) of silica coated on nano zinc oxide composite formed in accordance with Example 2. FIG. 2(a) is at low magnification, FIG. 2(b) is at a higher magnification, and FIG. 2(c) is at high resolution. The magnifications of these figures are indicated indirectly by the “line scale” corresponding to the size in nano-meter.

[0053] FIG. 3 shows a XRD pattern of alumina coated on nano zinc oxide composite formed in accordance with Example 4.

[0054] FIG. 4 shows a TEM of alumina coated on nano zinc oxide composite formed in accordance with Example 4. FIG. 4(a) is at low magnification, FIG. 4(b) is at higher magnification, and FIG. 4(c) is at high resolution. The magnifications of these figures are indicated indirectly by the “line scale” corresponding to the size in nano-meter.

[0055] FIG. 5 is a X-ray diffraction pattern of the nano zinc oxide obtained in Comparative Example 1.

[0056] FIGS. 6 and 7 are scanning electron microscopy images showing the hollow silica-based composite particles.

EXAMPLES

[0057] Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples and a comparative example, which should not be construed as in any way limiting the scope of the invention.

Example 1

Direct In-Situ Preparation of Nano-ZnO-Silica Composite

[0058] 204 grams of anhydrous zinc chloride (obtained from Mega chemicals, Singapore) was dissolved in 150 grams of water and 0.5 grams of Indoemul CO-02 was added to this solution and stirred at 1500 RPM for 5 minutes. 300 grams of 40% sodium hydroxide was added to this stirred solution for a period of 2.5 hours. The reaction mixture was then stirred for 2 additional hours. The pH of the reaction mixture was then adjusted to 7 to 7.5 using glacial acetic acid and 15.6 grams of sodium silicate solution (10% sodium oxide and 28% silicon dioxide, obtained from SD Fine chemicals Ltd, Mumbai of India) was added. The pH was adjusted from 10 to 8.5 and reaction mixture was stirred for one hour until pH gradually reaches 9.5. The pH was again adjusted to 7.5 and the reaction mixture was stirred for an additional one hour. The reaction mixture was then filtered and washed with water. The filtered solid was dried in an oven at 80° C. for 24 hours.

[0059] The dried solid was powdered and characterised using BET surface area analysis (21.97 m.sup.2/g), XRD (see FIG. 1) and TEM (FIG. 2).

[0060] From the XRD pattern of FIG. 1, the major peaks are at about 31.76, 34.39, 36.24, 47.52, 56.59, 62.81, 66.37 and 67.92 (° 2θ), which confirmed the presence of ZnO with hexagonal structure (space group-P63mc). Using Scherrer's equation, the crystalline size of 23.5 nm was calculated. The remaining peaks correspond to SiO.sub.2 and Zn(OH).sub.2. From the pattern, it is evident that the formation of SiO.sub.2 was amorphous. After silica coating on ZnO, this shifted the ZnO peaks 0.02 Å towards the left side which confirmed the presence of SiO.sub.2.

[0061] From the TEM image of FIG. 3(a), it can be seen that the synthesized powder had an inhomogeneous morphology, which is a mixture of nanorods and multifaceted morphology. Higher magnification (see FIG. 3(b)) showed that the nanorods consisted of ˜10 nm ZnO embedded in a continuous amorphous SiO.sub.2 phase. The inter-planar spacing (see FIG. 3(c)) was 3.3 Å and was close to the inter-planar spacing of (100) plane of ZnO (3.25 Å).

Example 2

Synthesis of Nano Zinc Oxide-Silica Composite

[0062] About 90 grams of nano ZnO (obtained from Example 1) was suspended and stirred in 105 ml of water with 0.1 grams of tertiary amine surfactant-Coco bis (hydroxyl ethyl) amine (Indoemul CO-02, obtained from Indoamine Ltd, Baroda of India). 15 grams of a 30% solution of commercial Colloidal Silica (Bindzil, obtained from Akzo Nobel, Netherlands) was added to this suspension and stirred at 1500 rpm for 15 minutes. Then 0.7 grams of 10% aluminium chloride (obtained from Access Chemicals, Singapore) solution was added to the reaction moisture and stirred for 1 hour. The thick paste obtained was dried in an oven and used for characterization. The surface area of the powder was 23.43 m.sup.2/g.

Example 3

Paint Formulation Using Nano-ZnO-Silica Composite

[0063] The nano-ZnO-silica composite obtained from Example 1 together with titanium dioxide (TiO.sub.2) as the main pigment was used to formulate an acrylic water-based paint. The formulation was named “N—ZnO-silica composite Formulation”. The weight of the TiO.sub.2 present in this formulation was reduced as compared to that present in the Standard Formulation described below. A comparative acrylic water-based paint formulation based on TiO.sub.2 pigments alone was made. This formulation was named “Standard Formulation”.

[0064] When the TiO.sub.2 was replaced in the “N—ZnO-silica composite Formulation” with the composite, there was a decrease in the total pigment volume. This decrease in pigment volume was compensated by increasing the amount of silica and/or talc to keep the pigment volume concentration the same in the formulations shown in Table 1 below.

[0065] Contrast Ratio was measured using the ZEHNTNER Reflectometer (Zehntner Testing Instruments, Switzerland). Accelerated storage studies were made by storing the paint at 60° C. for fourteen days and assessing the paint appearance visually for any cake formation, hard settlement and paint flow.

TABLE-US-00001 TABLE 1 Paint formulation using Nano-ZnO-silica composite Standard n-ZnO-Silica Formulation Formulation No. Materials (in grams) (in grams) 1. Thickener: Bermocoll 0.50 0.50 E411 (Akzo Nobel, Netherlands 2. Anti-Microbial Agent: 1.00 1.00 Zinc Omadine (Arch Chemicals, USA) 3. Dispersing agent: Orotan 1.00 1.00 1850E-Dow Chemicals, USA) 4. Defoamer: Dapro 7010 0.25 0.25 (Elementis Korea) 5. Water 18.94 20.34 6. n-ZnO-Silica composite -NA- 2.00 7. Titanium dioxide R900 23.00 16.67 (Dupont, USA) 8. Calcium Carbonate 3.64 5.62 9. Talc 1.87 2.82 10. Fumed Silica 0.30 0.30 11. Acrylic Resin emulsion 35.00 35.00 (UCAR ™ 352, obtained from The Dow Chemical Company, California, USA) 12. ROPAQUE ™ emulsion 12.00 12.00 (obtained from The Dow Chemical Company, California, USA) 13. Texanol (obtained from 0.70 0.70 Eastman Chemical Company, Tennessee, USA) 14. 2-Amino-2-methyl-1- 0.30 0.30 propanol + 5% water (AMP ™-95 obtained from The Dow Chemical Company, California, USA) 15 Mono Ethylene Glycol 1.00 1.00 (Dow Chemicals, USA) 16 Tergitol NP 9 (Dow 0.50 0.50 Chemicals, USA) Contrast Ratio (Opacity) 95.15 95.84 (%) Accelerated storage test Pass- Paint Pass-- with slightly homogeneous reduced flow Paint with slightly more viscosity and reduced flow

[0066] As shown in Table 1 above, the stability and opacity of the paint formulation with the composite are comparable to that of the paint formulation without the composite. In addition, the composite can reduce the amount of titanium dioxide required by about 27%, leading to cost savings.

Example 4

Direct In-Situ Preparation of Nano-ZnO-Alumina Composite

[0067] 68 grams of anhydrous zinc chloride was dissolved in 90 ml of water and 2.5 grams of anionic dispersing agent Coatex P90 (obtained from Arkema, USA) was added to this solution and stirred at 1500 RPM for 5 minutes. 100 grams of 40% sodium hydroxide was added to this stirred solution for a period of 2.5 hours. The reaction mixture was then stirred for 2 additional hours. The pH of the reaction mixture was then adjusted 8.5 using glacial acetic acid. About 12.2 grams of aluminium chloride hexa hydrate was added and pH of the reaction turns to 7. About 14 grams of 40% sodium hydroxide was added for fifteen minutes with very good agitation. The pH of the reaction was maintained at 8.0 to 8.5 for a period of 1.5 hours. The precipitated solid was then filtered, washed with water and dried 80 degree C. oven for 24 hours.

[0068] The surface area of the powder from the dried solid was 78.9 m.sup.2/g. The XRD pattern and TEM of nano-ZnO-alumina composited are shown in FIG. 3 and FIG. 4 respectively.

[0069] From the XRD pattern of the alumina coated on nano ZnO composite as shown in FIG. 3, the major peaks are at about 31.76, 34.39, 36.24, 47.52, 56.59, 62.81, 66.37 and 67.92 (° 2θ), which confirmed the presence of ZnO with hexagonal structure (space group-P63mc). Using Scherrer's equation, the crystalline size of 25.1 nm was calculated. Along with nano ZnO, the other phases of Al.sub.2O.sub.3 and AlZn.sub.7O.sub.10 were formed. Form the pattern, it is obvious that the crystalline phase of Al.sub.2O.sub.3 was coated on nano ZnO and which confirmed the presence of composite coating.

[0070] The TEM images (FIG. 4(a), FIG. 4(b)) showed that the synthesized powder was multifaceted phase. The inter-planar spacing (see FIG. 4(c)) was 2.5 Å and was close to the inter-planar spacing of (002) plane of ZnO (2.6 Å).

Example 5

Hollow Silica Based Composite Pigment

[0071] 30 grams of Nano Calcium Carbonate (obtained from Nano Materials Technology Pte Ltd, Singapore) was suspended in 300 ml of rapidly stirring water. About 34.8 grams of Tetra ethyl ortho silicate (obtained from Sinopharm Chemical Reagent Company Limited, China) was added and pH was adjusted to 8.5 with ammonia. The reaction mixture was then stirred for 1 hour and pH was adjusted to 6 by slowly adding glacial acetic acid. After all the carbon dioxide evolution ceases, the sample of hollow silica was isolated by filtration and drying.

[0072] The above reaction can directly be converted into hollow silica-zinc oxide-silica composite pigment. About 408 grams of anhydrous zinc chloride was dissolved in the reaction mixture followed by Indoemul co-02 (0.25 grams). 450 grams of 54% sodium hydroxide solution was added for 2.5 hours. The reaction mixture was stirred for additional 2 hours and pH was adjusted to 8-8.5 About 33 grams of colloidal silica was added to this reaction mixture and stirred for 1 hour. At the end of the reaction, hollow composite pigment was filtered and washed with water and dried in oven at 80 degree Celsius.

TABLE-US-00002 TABLE 2 Paint formulation using Hollow silica-ZnO-silica composite Standard n-ZnO-Silica Formulation Formulation No. Materials (in grams) (in grams) 1. Thickener: Bermocoll 0.40 0.40 E411 (Akzo Nobel, Netherlands 2. Anti-Microbial Agent: 1.00 1.00 Zinc Omadine (Arch Chemicals , USA) 3. Dispersing agent: Orotan 1.00 1.00 1850E-Dow Chemicals, USA) 4. Defoamer: Dapro 7010 0.25 0.25 (Elementis Korea) 5. Water 22.54 22.14 6. Hollow Silica-ZnO-Silica -NA- 2.00 composite 7. Titanium dioxide R900 23.00 16.98 (Dupont, USA) 8. Calcium Carbonate 4.94 7.42 9. Talc 1.86 2.57 10. Fumed Silica 0.30 0.30 11. Acrylic Resin emulsion 34.00 34.00 (UCAR ™ 362, obtained from The Dow Chemical Company, California, USA) 12. ROPAQUE ™ emulsion 9.00 9.00 (obtained from The Dow Chemical Company, California, USA) 13. Texanol (obtained from 1.00 1.00 Eastman Chemical Company, Tennessee, USA) 14. 2-Amino-2-methyl-1- 0.30 0.30 propanol + 5% water (AMP ™-95 obtained from The Dow Chemical Company, California, USA) 15 Mono Ethylene Glycol 1.00 1.00 (Dow Chemicals, USA) 16 Tergitol NP 9 (Dow 0.50 0.50 Chemicals, USA) Contrast Ratio (Opacity) 95.84 95.89 (*) Accelerated storage test Pass- Paint Pass-- with slightly homogeneous reduced flow Paint with slightly more viscosity and reduced flow

Comparative Example 1

Synthesis of Nano Zinc Oxide in Methanol/Water

[0073] 32 grams of zinc nitrate hexahydrate (obtained from Accesschem Pte Ltd, Singapore) was dissolved in 67.5 grams of methanol (obtained from Accesschem Pte Ltd, Singapore) and 40 grams of water.

[0074] 8.7 grams of sodium hydroxide (obtained from Sigma Aldrich, Mo., United States of America) was dissolved in 40 grams of water separately and added to the zinc nitrate hexahydrate mixture slowly over a period of 1 hour and 15 minutes.

[0075] After the addition, the reaction was stirred for 1.5 hours. Thereafter, about 120 ml of water was added and the mixture was stirred for additional 1.5 hours.

[0076] The reaction mixture was then filtered and washed with water till the filtrate showed a pH of 7. The solid residue material obtained was dried in an oven at 80° C. and grounded to get fine white powder.

Characterization of Nano Zinc Oxide

[0077] The fine white powder was analyzed by X-ray diffraction (XRD) and the XRD pattern is shown in FIG. 5. From FIG. 5, the XRD pattern confirms that pure zinc oxide (ZnO) was obtained. Specifically, the three main 2 Theta peak values in FIG. 5 are at 31.72; 34.45; and 36.21, which correspond to standard ZnO peaks as mentioned in the Joint Committee on Powder Diffraction Standards (JCPDS) Card No. 36-1451 P6.sub.3 mc space group.

[0078] The fine white powder was also analyzed by the Brunauer-Emmett-Teller (BET) method. The BET surface area measurement showed that the ZnO obtained has a surface area of 27.8 m.sup.2/gram.

Paint Formulation Using Nano-ZnO

[0079] The nano zinc oxide (n-ZnO) together with titanium dioxide (TiO.sub.2) as the main pigment was used to formulate an acrylic water-based paint. The formulation was named “n-ZnO Formulation”. The weight of the TiO.sub.2 present in this formulation was 70% of that present in the Standard Formulation described below. A comparative acrylic water-based paint formulation based on TiO.sub.2 pigments alone was made. This formulation was named “Standard Formulation”.

[0080] When 30% of the required TiO.sub.2 was replaced in the “n-ZnO Formulation” with nano zinc oxide, there was a decrease in the total pigment volume. This decrease in pigment volume was compensated by increasing the amount of silica and/or talc to keep the pigment volume concentration the same in the formulations shown in Table 3 below.

[0081] Contrast Ratio was measured using the ZEHNTNER Reflectometer, (Zehntner Testing Instruments, Switzerland). Accelerated storage studies were made by storing the paint at 60° C. for fourteen days and assessing the paint appearance visually for any cake formation, hard settlement and paint flow.

TABLE-US-00003 TABLE 3 Paint formulation using Nano-ZnO Standard n-ZnO Formulation Formulation No. Materials (in grams) (in grams) 1. Thickener-1 (Aquaflow ™ 0.20 0.20 NHS 300, obtained from Hercules Inc., Delaware, USA) 2. Thickener-2 (Aquaflow ™ 0.10 0.10 NHS 300, obtained from Hercules Inc., Delaware, USA) 3. Dispersing agent (Coatex 0.50 0.50 P 90, obtained from Coatex Inc, Arkema, South Carolina, USA) 4. Defoamer (Tego ® Foamex 0.45 0.45 825, obtained from Evonik Industries, Germany) 5. Water 30.58 28.00 6. n-ZnO -NA- 1.50 7. Titanium dioxide 27.00 18.90 8. Calcium Carbonate 20.50 20.50 9. Silica 0.98 5.00 10. Fumed Silica 0.98 0.98 11. Acrylic Resin emulsion 43.5 43.5 (UCAR ™ 362, obtained from The Dow Chemical Company, California, USA) 12. ROPAQUE ™ emulsion 19.5 19.5 (obtained from The Dow Chemical Company, California, USA) 13. Texanol (obtained from 2.76 2.76 Eastman Chemical Company, Tennessee, USA) 14. 2-Amino-2-methyl-1- 0.15 0.15 propanol + 5% water (AMP ™-95 obtained from The Dow Chemical Company, California, USA) Contrast Ratio (Opacity) 91.83 93.81 (%) Accelerated storage test Pass-- Fails-paint homogeneous solidified Paint with into thick slightly mass reduced flow

[0082] As can be seen from Table 3, the incorporation of nano zinc oxide, while increasing the opacity of the paint formulation, caused the paint formulation to gel and become unstable.

APPLICATIONS

[0083] The disclosed composition advantageously enhances the stability of a paint formulation without depriving the paint formulations from being economically feasible to produce or affecting the opacity of the paint formulation.

[0084] Advantageously, the disclosed composition permits a lower amount of expensive raw material required in paint formulations without depriving the paint formulations of the properties required. In embodiments, the composite of the present disclosure can be used as a partial replacement for the relatively more expensive titanium dioxide pigment in paint formulations. Furthermore, the disclosed composition possesses improved durability against the natural elements.

[0085] Advantageously, the disclosed composite confers anti-bacterial properties to the composition.

[0086] Advantageously, the disclosed composite improves the ultraviolet resistance of the composition, thereby conferring durability to the composition.

[0087] Advantageously, the disclosed composite does not leach out of the composition.

[0088] Advantageously, in embodiments, the disclosed composite of the present disclosure can be used as partial replacement for conventional ZnO in the vulcanization of rubber.

[0089] In embodiments, the disclosed composite of the present disclosure can be used as a wide band width semiconductor in certain electronic applications.

[0090] In embodiments, the disclosed composite of the present disclosure can also be used to improve abrasion and wear resistance in polymer composites whether alone or in combination with other nanomaterials such as clay.

[0091] In embodiments, the disclosed composite of the present disclosure can be dispersed in organic solvents and polymers to improve the durability of organic polymer composites to the natural elements.

[0092] 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.