PD052698IN-SC
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
1. Title of the invention: A DISPERSION AND PROCESSES THEREOF
2. Applicant(s)
NAME
NATIONALITY
ADDRESS
ASIAN PAINTS LTD.
Indian
Research & Technology Center, Asian Paints Limited, C3-B1, TTC MIDC, Pawane Village, Turbhe, Navi Mumbai – 400703, India
3. Preamble to the description
COMPLETE SPECIFICATION
The following specification particularly describes the invention and the manner in which it is to be performed.
1
FIELD OF INVENTION
[0001]
The present disclosure broadly relates to preparation of a stable dispersion. In particular, the present disclosure provides a stable dispersion, a composition, and processes thereof.
5
BACKGROUND OF INVENTION
[0002]
Solid materials dispersed in a liquid medium are essential for various applications, such as paints/surface coatings, inks, pesticide and agrochemical dispersions, biocide dispersions, and pharmacologically active compound dispersions. These days surface coatings are specifically engineered for certain 10 objects and/or conditions. Moreover, surface coatings are applied for decorative purposes to add colour, lustre, and finishing to an object. Thus, coatings serve two purposes, to protect and/or decorate an object. Nowadays the application of surface coating has extended its arms into various realms such as self-cleaning, antimicrobial, dust-free and odour-free properties by incorporation of specific 15 additives in the coating compositions. One such additive is antimicrobial actives in the form of dispersion which may be added to the paints/surface coatings. These significantly reduce the growth of a wide range of microbes in the surface coatings.
[0003]
However, the dispersions with high concentration of actives may have particle agglomeration which leads to instability of the dispersion. This can have a 20 negative effect on their applicability.
[0004]
To mitigate the problem of instability requires additional anti-agglomerating agents increasing the cost of preparation of such dispersions/ surface coatings as a whole. Therefore, the existing processes are limited to use in small scale applications and face difficulties in scaling up. In view of the above, there 25 exists a dire need in the art to develop a convenient yet economical process which can be scaled up for preparing stable dispersions comprising the high concentration of metal salts to be used in coating compositions.
SUMMARY OF THE INVENTION 30 2
[0005] In an aspect of the present disclosure, there is provided a process of preparing a stable dispersion, said process comprising contacting a reducing solution to an intermediate metal salt dispersion to obtain the stable dispersion wherein the reducing solution is prepared by contacting a first part of a stabilizer with a reducing agent, and a solvent and wherein the solvent is a combination of 5 water and at least one polyol in a weight ratio of 30:70 to 70:30.
[0006] In another aspect of the present disclosure, there is provided a stable dispersion obtained by the process as disclosed herein.
[0007] In yet another aspect of the present disclosure, there is provided a stable dispersion comprising metal nanoparticles capped with at least one stabilizer; and 10 at least one solvent, wherein the metal nanoparticles are in a weight range of 0.5 to 2% with respect to the total weight of the dispersion.
[0008] In still another aspect of the present disclosure, there is provided a composition comprising the stable dispersion as disclosed herein and at least one additive selected from binder, adhesive, polymer, thickener, pigment, solvent, 15 solubilizer, promoter, surfactants, or combinations thereof.
[0009] In a further aspect of the present disclosure, there is provided a coating composition comprising the stable dispersion as disclosed herein; and at least one coating additive.
[00010] In an additional aspect of the present disclosure, there is provided a 20 use of the stable dispersion as disclosed herein, the composition as disclosed herein or the coating composition as disclosed herein, in preparation of a composition for coating applications.
[00011]
These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and 25 appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
BRIEF DESCRIPTION OF THE FIGURES 30 3
[00012]
The following drawings form a part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.
[00013]
Figure 1 depicts the ultraviolet (UV)-Visible spectroscopic plot of the 5 stable dispersion comprising silver nanoparticles, in accordance with an embodiment of the present disclosure.
[00014]
Figure 2 (a), (b) and (c) depict the scanning electron microscopic (SEM) images of the silver nanoparticles in the stable dispersion A, in accordance with an embodiment of the present disclosure. 10
[00015]
Figure 3 depicts the electron diffraction x-ray spectroscopy (EDS) plot of the elemental composition of the dispersion, in accordance with an embodiment of the present disclosure.
[00016]
Figure 4 depicts the SEM image of dispersion B, in accordance with an embodiment of the present disclosure. 15
DETAILED DESCRIPTION OF THE INVENTION
[00017] Those skilled in the art will be aware that the present disclosure is subject to variations and modifications other than those specifically described. It is to be understood that the present disclosure includes all such variations and 20 modifications. The disclosure also includes all such steps, features, compositions, and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any or more of such steps or features.
Definitions
[00018]
For convenience, before further description of the present disclosure, 25 certain terms employed in the specification, and examples are delineated here. These definitions should be read in the light of the remainder of the disclosure and understood as by a person of skill in the art. The terms used herein have the meanings recognized and known to those of skill in the art, however, for convenience and completeness, particular terms and their meanings are set forth 30 below.
4
[00019]
The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.
[00020] The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”. 5
[00021] Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of element or steps but not the exclusion of any other element or step or group of element or steps.
[00022] The term “including” is used to mean “including but not limited to”. 10 “Including” and “including but not limited to” are used interchangeably.
[00023] The term “reducing agent” refers to the chemical reagent used to reduce an element from its salt form to its reduced form. In an aspect of the present disclosure, the reducing agent reduces the metal ions to its reduced nanoparticle form. In other aspects of the present disclosure, the reducing agent is selected from L-ascorbic 15 acid, sodium citrate, or combinations thereof.
[00024] The term “metal salt” is a metal compound which is obtained by the reaction of an acid with a metal. In an aspect of the present disclosure, the metal salt is used as a precursor for preparing a metal nanoparticle selected from silver nitrate, silver sulphate, silver chloride, silver bromide, silver iodide, copper 20 sulphate, copper nitrate, copper chloride, copper bromide, copper iodide, gold nitrate, gold sulphate, gold chloride, gold bromide, or gold iodide.
[00025] The term “stabilizer” refers to the chemical reagent used in a reaction to stabilize the obtained product. A “stabilizer” within the meaning of this invention is a compound that can stabilize silver-containing nanoparticles. In an aspect of the 25 present disclosure, the stabilizer gets attached to the surface of the metal nanoparticle so as to modify the surface morphology of the nanoparticle. In further aspect of the present disclosure, the stabilizer inhibits the over-growth of nanoparticles and prevents their aggregation/coagulation in colloidal suspension or dispersion. In other aspects of the present disclosure, the stabilizer is selected from 30 dioctyl sulfosuccinate, sodium bis tridecyl sulfosuccinate or combinations thereof.
5
[00026] The term “solvent” refers to the liquid component of a solution or a reaction mixture to enable the complete dispersal of a solute or reactant and thereby facilitate the reaction. In an aspect of the present disclosure, the solvent is a combination of water and at least one polyol in a weight ratio range of 30:70 to 70:30.
[00027] The term “stable dispersion” refers to a dispersion that is stable for a time 5 period of at least 30 days at room temperature. In an aspect of the present disclosure, the stable dispersion refers to the dilute mixture of a metal nanoparticle capped with a stabilizer in high concentration dispersed in a solvent mixture of water and at least one polyol along with a reducing agent.
[00028] The term “reducing solution” refers to a solution capable of reducing a 10 metal from its ionic form to its reduced form. In an aspect of the present disclosure, the reducing solution comprises a reducing agent, a stabilizer, and a solvent. In another aspect of the present disclosure, the reducing solution is prepared by contacting a first part of a stabilizer with a reducing agent, and a solvent.
[00029]
The term “intermediate metal salt dispersion” refers to the dispersion 15 comprising a metal salt. In an aspect of the present disclosure, the intermediate metal salt dispersion comprises a metal salt, a stabilizer, and a solvent. In another aspect of the present disclosure, the metal salt dispersion is prepared by contacting a second part of the stabilizer with a metal salt, and a solvent.
[00030] The terms “metal nanoparticle” and “plurality of metal nanoparticle” are 20 used interchangeably to refer to the metal atoms having size in a range of 1 to 100 nm. In an aspect of the present disclosure, the metal nanoparticle is a silver nanoparticle having size in a range of 1 to 100 nm. In another aspect of the present disclosure, the metal nanoparticles have size in a range of 1 to 50 nm.
[00031]
The term “capped” or “capping” refers to the phenomenon by which a 25 stabilizer, or a capping agent gets attached to the surface of a nanoparticle. In an aspect of the present disclosure, the stabilizer gets attached to the surface to inhibit the over-growth of nanoparticles and prevent their aggregation/coagulation in colloidal suspension or dispersion to achieve better stability of the suspension or dispersion. 30 6
[00032] The term “additive” refers to an add-on component in a specific composition. In an aspect of the present disclosure, the additive is selected from “a binder” which refers to substance used in a composition to bind the components of said composition together; an “adhesive” or “adhesion-cohesion agent” which refers to the substance used to ensure the composition in which the adhesive is 5 added to remain adhered to a surface upon which the composition has been coated for long especially under aggressive conditions; a “thickener” or “filler” which refers to the additive(s) incorporated into a composition to enhance the bulk of the composition without affecting the physical and chemical properties of the composition; a “pigment” or “colorant” which refers to the colouring agent which 10 imparts a particular color into the composition in which it is added to; a “solubilizer” which refers to the substance which is added to a composition in order to solubilize or disperse the specific components in a particular solvent; a “promoter” refers to the additive which enhances the adhesion of a composition to a substrate on to which the composition is coated upon; a “defoamer” which is an 15 additive component added to a composition to prevent or inhibit the formation of foam while processing or manufacturing said composition; an “anti-flocculating agent” which is a chemical additive that prevents the agglomeration or flocculation of constituents of the composition to which it is added; a “flow modifier” which refers to an additive substance which enhances or modifies the flowability of the 20 composition to which it is added; a “biocide” which refers to chemical substance which incorporates an antibiotic property to the composition; a “dissolvent” which refers to the liquid component added to provide a medium to solubilize, homogenize or disperse an assortment of additives or components in itself; and a “surfactant” which refers to the additive which reduces the surface tension of the individual 25 components of a solution and thereby increasing the dispersibility and wettability of the components.
[00033] The term “coating additive” refers to the additives which are added to the coating composition in order to enhance the properties of the composition for use as a coating composition. 30 7
[00034]
The term “composition”, in aspects of the present disclosure refers to a blend comprising at least one additive and an active. In an aspect of the present disclosure, the composition is used to facilitate the incorporation of the active into a coating composition. In another aspect of the present disclosure, the composition comprises the stable dispersion obtained by the process as disclosed in the present 5 disclosure along with other additives.
[00035] The term “antimicrobial activity” refers to the property of a substance by virtue of which the substance exhibits inhibition or elimination of microorganisms at a particular concentration to a specific amount. In an aspect of the present disclosure, the stable dispersion of the present disclosure which comprises a metal 10 nanoparticle exhibits antimicrobial activity against bacteria and fungi.
[00036]
Ratios, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, 15 but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, 55 to 75℃ should be interpreted to include not only the explicitly recited limits of 55 to 75℃ but also to include sub-ranges, such as 59 to 70℃, 55 to 65℃, 70 to 75℃, and so forth, as well as individual amounts, including fractional 20 amounts, within the specified ranges, such as 60℃, 65℃ and so on.
[00037] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the 25 disclosure, the preferred methods, and materials are now described. All publications mentioned herein are incorporated herein by reference.
[00038]
As discussed in the background, large scale synthesis of stable dispersions comprising metal salts in high concentration is quite challenging. Even though a dispersion of metal nanoparticles in high concentration was achieved, the stability 30 of such a dispersion was observed to be difficult to attain due to the increasing
8
agglomeration
of the particles of active with increasing concentration. Moreover, to attain a stable yet high concentration metal nanoparticle dispersion, costly reducing agents and stabilizers are to be used. In addition, the currently available process to prepare such stable dispersions comprising metal nanoparticles in high concentrations employs highly intricate processes which limit them from being 5 scaled up to a larger scale. Further, it was observed that metal salt particle dispersion was strenuous to be employed in a coating composition while processing without any processing aids due to the presence of various reducing agents and stabilizers. In view of the above-mentioned challenges, there is a dire need in the art to develop a convenient yet economical process to obtain a stable dispersion 10 comprising metal nanoparticle in high concentration which could be easily employed in the surface coating compositions and scaled up to exploit the commercial aspects of the process. Accordingly, the present disclosure provides a process of preparing a stable dispersion comprising the metal nanoparticles.
[00039]
In an embodiment of the present disclosure, there is provided a process of 15 preparing a stable dispersion, said process comprising contacting a reducing solution to an intermediate metal salt dispersion to obtain the stable dispersion.
[00040]
In an embodiment of the present disclosure, there is provided a process of preparing a stable dispersion, said process comprising contacting a reducing solution to an intermediate metal salt dispersion to obtain the stable dispersion, 20 wherein the reducing solution is prepared by contacting a first part of a stabilizer with a reducing agent, and a solvent, wherein the solvent is a combination of water and at least one polyol in a weight ratio of 30:70 to 70:30.
[00041]
In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the intermediate metal salt dispersion is prepared by 25 contacting a second part of the stabilizer with a metal salt, and a solvent.
[00042]
In an embodiment of the present disclosure, there is provided a process of preparing a stable dispersion, said process comprising: contacting a reducing solution to an intermediate metal salt dispersion to obtain the stable dispersion, wherein the solvent is a combination of water and at least one polyol in a weight 30 9
ratio of 30:70 to 70:30, and the
intermediate metal salt dispersion is prepared by contacting a second part of the stabilizer with a metal salt, and a solvent.
[00043]
In an embodiment of the present disclosure, there is provided a process of preparing a stable dispersion, said process comprising contacting a reducing solution comprising a reducing agent, a stabilizer, and a solvent, to an intermediate 5 metal salt dispersion comprising a metal salt, a stabilizer, and a solvent, to obtain the stable dispersion.
[00044]
In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the reducing agent is selected from L-ascorbic acid, sodium citrate, ammonium formate, or combinations thereof. In another 10 embodiment of the present disclosure, the reducing agent is L-ascorbic acid. In yet another embodiment of the present disclosure, the reducing agent is sodium citrate. In still another embodiment of the present disclosure, the reducing agent is ammonium formate.
[00045]
In an embodiment of the present disclosure, there is provided a process of 15 preparing a stable dispersion, said process comprising: contacting a reducing solution comprising a reducing agent, a stabilizer, and a solvent to an intermediate metal salt dispersion comprising a metal salt, a stabilizer, and a solvent to obtain the stable dispersion, wherein the stabilizer is selected from dioctyl sulfosuccinate, sodium bis tridecyl sulfosuccinate or combinations thereof; and the solvent is a 20 combination of water and at least one polyol in a weight ratio of 30:70 to 70:30. In another embodiment of the present disclosure, the reducing agent is L-ascorbic acid and the stabilizer is dioctyl sulfosuccinate. In yet another embodiment of the present disclosure, the reducing agent is sodium citrate and the stabilizer is dioctyl sulfosuccinate. In still another embodiment of the present disclosure, the reducing 25 agent is ammonium formate and the stabilizer is dioctyl sulfosuccinate.
[00046]
In an embodiment of the present disclosure, there is provided a process of preparing a stable dispersion, said process comprising: a. contacting a first part of a stabilizer with a reducing agent and a solvent to obtain a reducing solution; b. contacting a second part of the stabilizer with a metal salt and the solvent to obtain 30 an intermediate metal salt dispersion; c. contacting a reducing solution to an 10
intermediate metal salt dispersion
to obtain the stable dispersion, wherein the solvent is a combination of water and at least one polyol in a weight ratio of 30:70 to 70:30.
[00047]
In an embodiment of the present disclosure, there is provided a process of preparing a stable dispersion, said process comprising: contacting a reducing 5 solution to an intermediate metal salt dispersion to obtain the stable dispersion, wherein the reducing solution is prepared by contacting a first part of a stabilizer with a reducing agent and a solvent; the intermediate metal salt dispersion is prepared by contacting a second part of the stabilizer with a metal salt and the solvent; the stabilizer is selected from dioctyl sulfosuccinate, sodium bis tridecyl 10 sulfosuccinate or combinations thereof; and the solvent is a combination of water and at least one polyol in a weight ratio range of 30:70 to 70:30. In another embodiment of the present disclosure, the solvent is a combination of water and at least one polyol in a weight ratio range of 40:60 to 60:40. In yet another embodiment of the present disclosure, the solvent is a combination of water and at 15 least one polyol in a weight ratio of 50:50.
[00048]
In an embodiment of the present disclosure, there is provided a process as disclosed herein, stabilizer is selected from dioctyl sulfosuccinate, sodium bis tridecyl sulfosuccinate or combinations thereof; and the solvent is a combination of water and at least one polyol selected from propylene glycol, ethylene glycol, 20 diethylene glycol, or combinations thereof, in a weight ratio of 30:70 to 70:30.
[00049]
In an embodiment of the present disclosure, there is provided a process of preparing a stable dispersion, said process comprising: contacting a reducing solution to an intermediate metal salt dispersion to obtain the stable dispersion, wherein the reducing solution is prepared by contacting a first part of a stabilizer 25 with a reducing agent and a solvent; the intermediate metal salt dispersion is prepared by contacting a second part of the stabilizer with a metal salt and the solvent; the stabilizer is selected from dioctyl sulfosuccinate, sodium bis tridecyl sulfosuccinate or combinations thereof; and the solvent is a combination of water and propylene glycol in a weight ratio range of 30:70 to 70:30. 30 11
[00050]
In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the metal salt is selected from silver nitrate, silver sulphate, silver chloride, silver bromide, silver iodide, copper sulphate, copper nitrate, copper chloride, copper bromide, copper iodide, gold nitrate, gold sulphate, gold chloride, gold bromide, and gold iodide. In another embodiment of the present 5 disclosure, the metal salt is selected from silver nitrate, silver sulphate, silver chloride, silver bromide, and silver iodide. In yet another embodiment of the present disclosure, the metal salt is silver nitrate.
[00051]
In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the metal salt, reducing agent and stabilizer are in a mole 10 ratio range of 0.8 : 2.2 : 2 to 1.2 : 3: 0.8. In another embodiment of the present disclosure, the metal salt, reducing agent and stabilizer are in a mole ratio range of 0.9 : 2.6 : 1.5 to 1.1 : 2.9: 1. In yet another embodiment of the present disclosure, the metal salt, reducing agent and stabilizer are in a mole ratio of 1 : 2.8 : 1.2. In a further embodiment of the present disclosure, the metal salt, reducing agent and 15 stabilizer are in a mole ratio of 1 : 2.9 : 1.3.
[00052]
In an embodiment of the present disclosure, there is provided a process of preparing a stable dispersion, said process comprising: contacting a reducing solution comprising a reducing agent, a stabilizer selected from dioctyl sulfosuccinate, sodium bis tridecyl sulfosuccinate or combinations thereof, and a 20 solvent combination of water and propylene glycol in a weight ratio range of 30:70 to 70:30, to an intermediate metal salt dispersion comprising a metal salt, a stabilizer, and a solvent to obtain the stable dispersion, wherein the metal salt, reducing agent and stabilizer are in a mole ratio range of 0.8 : 2.2 : 2 to 1.2 : 3: 0.8. in another embodiment of the present disclosure, the metal salt, reducing agent and 25 stabilizer are in a mole ratio range of 0.9 : 2.4 : 1.7 to 1.1 : 2.9: 1. In still another embodiment of the present disclosure, the metal salt, reducing agent and stabilizer are in a mole ratio of 1 : 2.8 : 1.2. In a further embodiment of the present disclosure, the metal salt, reducing agent and stabilizer are in a mole ratio of 1 : 2.9 : 1.3. 30 12
[00053]
In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the contacting is carried out at a continuous rate in a range of 8 to 12 mL/min. In another embodiment of the present disclosure, the contacting is carried out at a continuous rate in a range of 9 to 11 mL/min. In yet another embodiment of the present disclosure, the contacting is carried out at a continuous 5 rate of 10 mL/min.
[00054]
In an embodiment of the present disclosure, there is provided a process as disclosed herein, wherein the contacting is carried out while stirring at a temperature in a range of 55 to 75°C and for a time period in a range of 20 to 40 minutes. 10
[00055]
In an embodiment of the present disclosure, there is provided a process of preparing a stable dispersion, said process comprising: contacting a reducing solution to an intermediate metal salt dispersion at a continuous rate in a range of 8 to 12 mL/min while stirring at a temperature in a range of 55 to 75°C and for a time period in a range of 20 to 40 minutes, to obtain the stable dispersion, wherein the 15 metal salt, reducing agent and stabilizer are in a mole ratio range of 0.8 : 2.2 : 2 to 1.2 : 3: 0.8. In another embodiment of the present disclosure, the contacting is carried out at a continuous rate in a range of 9 to 11 mL/min, while stirring at a temperature in a range of 58 to 70°C and for a time period in a range of 25 to 35 minutes. In yet another embodiment of the present disclosure, the contacting is 20 carried out at a continuous rate of 10 mL/min, while stirring at a temperature of 60°C and for a time period of 30 minutes.
[00056]
In an embodiment of the present disclosure, there is provided stable dispersion obtained by the process as disclosed herein.
[00057]
In an embodiment of the present disclosure, there is provided stable 25 dispersion comprising: (a) metal nanoparticles capped with at least one stabilizer; and (b) at least one solvent, wherein the metal nanoparticles are in a weight range of 0.5 %-2% with respect to the total weight of the dispersion. In another embodiment of the present disclosure, the metal nanoparticles are in a weight range of 0.5 %-1.5% with respect to the total weight of the dispersion. In yet another 30 13
embodiment
of the present disclosure, the metal nanoparticles are in a weight of 1 % with respect to the total weight of the dispersion.
[00058]
In an embodiment of the present disclosure, there is provided a stable dispersion as disclosed herein, wherein the plurality of metal nanoparticles is in a size range of 1 to 100nm. In yet another embodiment of the present disclosure, the 5 plurality of metal nanoparticles is in a size range of 1 to 50nm.
[00059]
In an embodiment of the present disclosure, there is provided a stable dispersion as disclosed herein, wherein the dispersion is stable for a time period of at least 30 days at room temperature.
[00060]
In an embodiment of the present disclosure, there is provided a 10 composition comprising the stable dispersion as disclosed herein and at least one additive selected from binder, adhesive, polymer, thickener, pigment, solvent, solubilizer, promoter, defoamer, anti-flocculating agent, surfactants, or combinations thereof.
[00061]
In an embodiment of the present disclosure, there is provided a 15 composition as disclosed herein, wherein the composition exhibits antimicrobial activity.
[00062]
In an embodiment of the present disclosure, there is provided a coating composition comprising: (a) the stable dispersion as disclosed herein; and (b) at least one coating additive. 20
[00063]
In an embodiment of the present disclosure, there is provided a coating composition comprising: (a) the stable dispersion as disclosed herein; and (b) at least one coating additive selected from adhesive-cohesive agent, filler, colorant, dissolvent, dispersant, developer, anti-caking agent, filler, anti-foaming agent, biocide or combinations thereof. 25
[00064]
In an embodiment of the present disclosure, there is provided a coating composition as disclosed herein, wherein the stable dispersion is in a weight range of 0.05 to 1.5% with respect to the total weight of the coating composition. In another embodiment of the present disclosure, the stable dispersion is in a weight range of 0.1 to 1% with respect to the total weight of the coating composition. In 30 14
yet
another embodiment of the present disclosure, the stable dispersion is in a weight of 0.5% with respect to the total weight of the coating composition.
[00065]
In an embodiment of the present disclosure, there is provided a coating composition as disclosed herein, wherein the stable dispersion comprises metal nanoparticles in a weight range of 0.001 to 0.01% with respect to the total weight 5 of the coating composition. In another embodiment of the present disclosure, the stable dispersion comprises metal nanoparticles in a weight range of 0.003 to 0.009% with respect to the total weight of the coating composition. In yet another embodiment of the present disclosure, the stable dispersion comprises metal nanoparticles in a weight of 0.005 % with respect to the total weight of the coating 10 composition.
[00066]
In an embodiment of the present disclosure, there is provided a use of the stable dispersion as disclosed herein, the composition as disclosed herein or the coating composition as disclosed herein, for preparation of a composition for coating applications. 15
[00067] Although the subject matter has been described in considerable detail with reference to certain examples and implementations thereof, other implementations are possible.
EXAMPLES
[00068]
The disclosure will now be illustrated with working examples, which is 20 intended to illustrate the working of disclosure and not intended to take restrictively to imply any limitations on the scope of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described 25 herein can be used in the practice of the disclosed methods and compositions, the exemplary methods, devices, and materials are described herein. It is to be understood that this disclosure is not limited to particular methods, and experimental conditions described, as such methods and conditions may apply.
Example 1 30
Preparation of a stable dispersion
15
[00069]
About 8.91 g of dioctyl sulfosuccinate (DOSS, i.e., stabilizer) was added to a solvent containing 76 mL of water and 76 mL of propylene glycol (polyol) while stirring followed by heating to 60°C for complete dissolution of DOSS to obtain a stabilizer solution. The whole of the stabilizer solution was divided into two equal parts, say first part and second part. To the first part of the stabilizer 5 solution, 8.3 g of L-ascorbic acid (reducing agent) was added while continuous stirring and maintaining the temperature at 60°C to obtain a reducing solution.
[00070]
To the second part of the stabilizer solution, about 2.7 g of silver nitrate (metal salt) was added while continuously stirring and maintaining temperature at 60°C to obtain an intermediate metal salt dispersion. The process employed 10 includes silver nitrate, L-ascorbic acid and DOSS are in a mole ratio of 1 : 2.8 : 1.2.
[00071]
The reducing solution was contacted to intermediate metal salt dispersion under stirring at a transfer rate of 10 mL/min while maintaining the temperature at 60°C. The dispersion was stirred further for 30 mins to obtain a dark greenish yellow coloured dispersion A comprising silver nanoparticles. 15
Example 2
Analysis of the effect of using different polyols
[00072]
The effect of using different polyols such as propylene glycol, polyethylene glycol, diethylene glycol, and other glycols, were analysed comparatively in aspects of the stability of dispersion and particle size of the silver 20 nanoparticles. In another example, a dispersion B was prepared using a similar process as explained above with L-ascorbic acid as reducing agent, silver nitrate as metal salt, DOSS as stabilizer, but with a combination of water and polyethylene glycol as the solvent in a weight ratio of 50:50 and the same process parameters as explained above. However, the dispersion B resulted in formation of grey coloured 25 dispersion with bigger particles which was found to be not sufficiently stable.
[00073]
Further, the dispersions were prepared following the process as described in Example 1 but using different solvent combinations of water and ethylene glycol (50:50), water and diethylene glycol (50:50), water and glycerol (50:50), water and hexylene glycol (50:50), water and 2-butoxy ethanol (50:50), water and butyl 30 carbitol (50:50).
16
[00074]
The data provided in Table 1 below shows that the dispersion achieved by using the solvent combination of water and propylene glycol, water and ethylene glycol, and water and diethylene glycol, results in better stability and desired particle size.
Table 1 5
Solvent combination (weight ratio of
50 + 50)
Stability
Particle size
water + propylene glycol
at least 30 days
1 to 50 nm
water + ethylene glycol
at least 30 days
1 to 50 nm
water + diethylene glycol
at least 30 days
1 to 100 nm
water + glycerol
Less than 30 days
More than 100 nm
water + polyethylene glycol
Not stable
More than 100 nm
water + hexylene glycol
Not stable
More than 500 nm
water + 2-butoxy ethanol
Not stable
More than 500 nm
water + butyl carbitol
Not stable
More than 500 nm
Example 3
Analysis of the effect of the weight ratio of water and propylene glycol in the preparation
[00075]
In another example, a dispersion C was prepared using a similar process 10 as explained above with L-ascorbic acid as reducing agent, silver nitrate as metal salt, DOSS as stabilizer, and a combination of water and propylene glycol in a weight ratio of 80:20 and the same process parameters and sequence as explained above. It was observed that the dispersion C was a grey coloured dispersion indicating that the particle size of the silver nanoparticles was undesirably bigger 15 17
than
50nm which led to the instability of the dispersion. Below Table 2 shows the stability of the dispersion and the particle size of the silver nanoparticles achieved when various weight ratios of water and propylene glycol was used for the preparation.
5
Table 2
Weight ratio
Stability
Particle size
10:90
Less than 30 days
More than 100 nm
20:80
30:70
at least 30 days
1 to 100 nm
40:60
50:50
at least 30 days
1 to 50 nm
40:60
at least 30 days
1 to 100 nm
30:70
20:80
Less than 30 days
More than 100 nm
10:90
[00076]
The data provided in Table 2 above shows that the dispersion achieved by using the solvent having a weight ratio of propylene glycol to water in the range of from 30:70 to 70:30, in particular 50:50, resulted in better stability and desired 10 particle size of the silver nanoparticle. Hence, it was inferred that the particle of the silver nanoparticles was desirably in a range of 1 to 100nm, and preferably in a range of 1 to 50nm, for the dispersion to be stable for at least 30 days.
[00077]
In addition, in still another example, when the continuous stirring after the contacting of reducing solution to the intermediate metal salt dispersion was 15 maintained at a temperature of 50°C, the obtained dispersion was found to be not forming desired product as it took longer reaction time up to 120 min) and formed grey coloured dispersion indicating that the particle size of the silver nanoparticles was undesirably bigger than 50nm which lead to the instability of the dispersion.
18
[00078]
Theoretical calculations performed for the obtained stable dispersions A and B resulted in about 1 g/L concentration of silver nanoparticles in a whole of the dispersion.
Analysis of the effect of using a mild reducing agent in the preparation 5
[00079]
The effect of using mild reducing agents, such as, L-ascorbic acid, sodium citrate, and ammonium formate, were analysed comparatively in aspects of the stability of dispersion and particle size of the silver nanoparticles.
[00080]
In this view, dispersions were prepared by following the process as described above but using different reducing agents, such as, sodium citrate, 10 ammonium formate, sodium, hydrazine, sodium borohydride, and phenyl hydrazine. The below Table 3 shows the stability of the dispersion and particle size of the silver nanoparticles.
Table 3 15
Reducing agent
Stability
Particle size
L-ascorbic acid
at least 30 days
1 to 50 nm
sodium citrate
at least 30 days
1 to 100 nm
ammonium formate
at least 30 days
1 to 100 nm
hydrazine
Not stable
More than 500 nm
sodium borohydride
Not stable
More than 500 nm
phenyl hydrazine
Not stable
More than 500 nm
[00081]
The data provided in Table 3 above shows that using mild reducing agents like L-ascorbic acid, sodium citrate and ammonium formate according to the present disclosure, over other strong reducing agents resulted in a more stable 19
dispersion
of at least 30 days and the silver nanoparticle had a desired size in a range of 1 to 100nm.
[00082]
The dispersion was found to be more stable when the particle size of the silver nanoparticles was in a range of 1 to 100nm, or preferably 1 to 50nm. Accordingly, the dispersion was found to undergo settling after 30 days when the 5 particle size of the silver nanoparticles was above 100nm. In addition, it was also observed that when the dispersion comprises silver nanoparticles in a weight range above or below the weight range of 0.5 to 2%, the particles settled within a day and dispersion was not stable.
10
Example 4
Preparation of coating composition
[00083]
The dispersion prepared by the process as disclosed above was directly employed for the preparation of a coating composition. About 0.005% of the stable dispersion A was directly mixed with appropriate amounts of coating additives 15 selected from adhesive-cohesive agent, filler, colorant, dissolvent, dispersant, developer, anti-caking agent, filler, anti-foaming agent, flow modifier, and biocides to obtain a coating composition which possesses antibacterial property.
Example 5
Characterization of the stable dispersion. 20
[00084]
The stable dispersion was characterised to analyse its composition, morphology of silver nanoparticles, and stability.
a.
UV-Visible (UV-Vis) spectroscopy
[00085]
The dispersions A and B obtained by the process as explained in example 1, was analysed using UV-Vis spectra for confirming the presence of silver 25 nanoparticles in the obtained stable dispersion. The Figure 1 which depicts the UV-Vis spectra of the dispersion A, confirms the presence of silver nanoparticles. The spectra depicted the maximum absorption at 410nm owing to the surface plasmon resonance (SPR) of free electrons from silver nanoparticles. 20
b. Scanning electron microscopy (SEM) analysis
[00086]
The dispersions A and B obtained by the process as explained in example 1, was analysed using SEM for examining the particle size of the obtained silver nanoparticles in the dispersion. 5
[00087]
The SEM images depicted in Figure 2 (a), (b) and (c) shows that the silver nanoparticles obtained in the stable dispersion A are in a particle size range of less than 50 nm and the stable dispersion had a plurality of silver nanoparticles capped with DOSS. Figure 4 depicts the SEM image of dispersion B showing silver particles possessing a higher particle size range of few microns. 10
c. Energy-dispersive X-ray spectroscopy (EDS) analysis
[00088]
The stable dispersion obtained by the process as explained in example 1, was analysed using EDS technique for the elemental analysis of the dispersion.
[00089]
Figure 3 depicts the EDS spectra of the silver nanoparticle dispersion 15 obtained by the process as disclosed in the Example 1. The spectra recorded on the nanoparticles clearly showed the presence of silver indicating that the particles were indeed made up of silver.
d. Stability analysis 20
[00090]
The stability of the dispersions A and B obtained by the process as explained in Example 1, was analysed. The dark greenish, yellow-coloured dispersion A and grey coloured dispersion B obtained by the process as explained in example 1 were transferred into a glass bottle, closed airtight, covered with aluminium foil, and kept in dark for observation at a later stage. The stability of the 25 dispersions was monitored periodically by observing for change in colour and/or sedimentation. The dispersion A was found to be stable for at least for 30 days. After a period of about 30 days, the dispersion A started to exhibit settling and colour change. However, the dispersion B was found to be stable for only a period of about 1 hr. 30 21
Characterization of the coating composition.
[00091]
The coating composition was characterised to analyse its antimicrobial property. The antibacterial and antifungal properties were evaluated for the coating compositions.
a. Analysis of antimicrobial property 5
[00092]
The antimicrobial property of the water-based coating composition comprising the stable dispersions A obtained by the process as explained in example 1, was analysed.
[00093]
The stable dispersion A was incorporated into the coating composition along with coating additives while grinding to obtain a coating composition. The 10 coating composition was subjected to washability test and oven stability test for 15 days to analyze the stability of the dispersion against leaching out from the coating matrix when subjected to harsh environmental conditions. The antibacterial and antifungal activities of coating composition; as such composition, composition after washability and oven stability tests were evaluated by subjecting them to a bacterial 15 culture derived from the standard method JIS Z 2801. The results are compared with a commercially available coating composition which employs costly biocides and antimicrobial additives. The antibacterial results showed that the coating composition of the present disclosure exhibited impressive antimicrobial activity in comparison to the commercially available coating composition. Hence, despite the 20 absence of costly biocides and antimicrobial actives, the coating composition of the present disclosure exhibited appreciable antimicrobial activity using a dispersion comprising higher concentration (1% w/w) of silver nanoparticles as a commercially viable antibacterial active. 25
Antifungal evaluation:
[00094]
The coating composition of the present disclosure and a commercially available coating composition were parallelly exposed to fungal culture by a method derived from the standard method ASTM D3274-09 for about 30 days and the antifungal property of the compositions were evaluated. 30 22
[00095]
Similar to the results obtained for the antibacterial property, the coating composition of the present disclosure comprising silver nanoparticle as an antimicrobial active showed excellent antifungal results. Hence, the process as disclosed in Example 1 of the present disclosure provides a stable dispersion comprising a high concentration (1 % w/w) of silver nanoparticle to be employed 5 in a coating composition for imparting antimicrobial activity on the surface of the articles upon which the composition was coated.
[00096]
It was also observed that when the coating composition was prepared using silver dispersion comprising less than or more than the silver nanoparticle in the weight range of 0.5 to 2% by weight, the coating failed in both antibacterial and 10 anti-fungal results.
ADVANTAGES OF THE PRESENT DISCLOSURE
[00097]
The present disclosure provides a convenient and simple process to prepare a stable dispersion comprising a plurality of metal nanoparticles. The 15 present disclosure further provides a stable dispersion comprising the metal nanoparticles. The dispersion obtained by the process as disclosed herein is stable for at least 30 days and could be easily used for preparing the antimicrobial coating compositions. Furthermore, the present disclosure provides a composition and a coating composition comprising the metal nanoparticles with antimicrobial 20 properties. The stable dispersion obtained by the process herein can be employed in a coating composition directly or through a composition without the usage of any harsh reaction conditions or any processing aids. Moreover, the dispersion being stable for at least 30 days, it could be stored for use in the coating composition on a larger scale. 25 23

I/We Claim:

1.
A process of preparing a stable dispersion, said process comprising:
contacting a reducing solution to an intermediate metal salt dispersion to obtain the stable dispersion,
wherein the reducing solution is prepared by contacting a first part of a 5 stabilizer with a reducing agent, and a solvent; and
wherein the solvent is a combination of water and at least one polyol in a weight ratio of 30:70 to 70:30.
2.
The process as claimed in claim 1, wherein the intermediate metal salt dispersion is prepared by contacting a second part of the stabilizer with a 10 metal salt, and the solvent.
3.
The process as claimed in claim 2, wherein the reducing agent is selected from L-ascorbic acid, sodium citrate, ammonium formate, or combinations thereof.
4.
The process as claimed in any one of the claims 1 or 2, wherein the stabilizer 15 is selected from dioctyl sulfosuccinate, sodium bis tridecyl sulfosuccinate, or combinations thereof.
5.
The process as claimed in claim 4, wherein the at least one polyol is selected from propylene glycol, ethylene glycol, diethylene glycol, or combinations thereof. 20
6.
The process as claimed in claim 2, wherein the metal salt is selected from silver nitrate, silver sulphate, silver chloride, silver bromide, silver iodide, copper sulphate, copper nitrate, copper chloride, copper bromide, copper iodide, gold nitrate, gold sulphate, gold chloride, gold bromide, or gold iodide. 25
7.
The process as claimed in any one of the claims 1 to 6, wherein the metal salt, reducing agent, and stabilizer are in a mole ratio range of 0.8 : 2.2 : 2 to 1.2 : 3: 0.8.
8.
The process as claimed in claim 1, wherein the contacting is carried out at a continuous rate in a range of 8 to 12 mL/min. 30 24
9.
The process as claimed in claim 1, wherein the contacting is carried out while stirring at a temperature in a range of 55 to 75°C and for a time period in a range of 20 to 40 minutes.
10.
A stable dispersion obtained by the process as claimed in claims 1 to 9, the dispersion comprising: 5
(a)
metal nanoparticles capped with at least one stabilizer; and
(b)
at least one solvent;
wherein the metal nanoparticles are in a weight range of 0.5 to 2% with respect to the total weight of the dispersion.
11.
The stable dispersion as claimed in claim 10, wherein the plurality of metal 10 nanoparticles is in a size range of 1 to 100nm.
12.
The stable dispersion as claimed in claim 10, wherein the dispersion is stable for a time period of at least 30 days at room temperature.
13.
A composition comprising:
a.
the stable dispersion as claimed in claim 10; and 15
b.
at least one additive selected from binder, adhesive, polymer, thickener, pigment, solvent, solubilizer, promoter, defoamer, anti-flocculating agent, surfactants, or combinations thereof.
14.
The composition as claimed in claim 13, herein the composition exhibits antimicrobial activity. 20
15.
A coating composition comprising:
a.
the stable dispersion as claimed in claim 10; and
b.
at least one coating additive.
16.
The coating composition as claimed in claim 15, wherein the at least one coating additive is selected from adhesive-cohesive agent, filler, colorant, 25 dissolvent, dispersant, developer, anti-caking agent, filler, anti-foaming agent, flow modifier, biocide, or combinations thereof.
17. The coating composition as claimed in claim 15, wherein the stable dispersion is in a weight range of 0.05 to 1.5% with respect to the total weight of the coating composition. 30 25
18. Use of the stable dispersion as claimed in claim 10, the composition as claimed in claim 13 or the coating composition as claimed in claim 15 in preparation of a composition for coating applications.