WO2024009168A1

WO2024009168A1 - Preparation of silica particles exhibiting globulous morphology

Info

Publication number: WO2024009168A1
Application number: PCT/IB2023/056502
Authority: WO
Inventors: Darshak Ramesh SHAH; Ramesh Vinaychand SHAH; Bijan Kumar Roy; Maheshkumar Ramniklal Gandhi; Nand Sammukhdas BIJLANI
Original assignee: Madhu Silica Pvt. Ltd.
Priority date: 2022-07-02
Filing date: 2023-06-23
Publication date: 2024-01-11

Abstract

The present invention relates to a process for preparation of silica particles having globulous morphology, high bulk density low porosity, low oil absorption value, and narrow particle size distribution. The globular silica obtained is suitable for use in various applications such as dentifrice formulation. The present invention also provides dentifrice formulations which demonstrate a high cleaning efficiency with lower abrasivity and better stability with the actives even at lower loading of the globular silica.

Description

PREPARATION OF SILICA PARTICLES EXHIBITING GLOBULOUS MORPHOLOGY

FIELD OF THE INVENTION

The present invention relates to a process for preparation of silica particles having globulous morphology, high bulk density low porosity, low oil absorption value, and narrow particle size distribution. The silica obtained is suitable for use in various applications such as dentifrice formulation.

BACKGROUND OF THE INVENTION

Precipitated silica is in high demand in a variety of applications. It is also useful in preparation of dentifrice compositions. For this application, non-porous silica with low oil absorption value and good sphericity is preferred for attaining low Relative Dentin Abrasion and high Pellicle Cleaning Ratio in the dentifrice.

Reference may be made to a publication in Materials Chemistry & Physics 113 (2009) 839-849 wherein silica has been precipitated in spherical morphology using oil emulsion phase. Even though, this publication teaches as to how to produce spherical silica in water - oil emulsion it did not evaluate the properties required for dentifrice formulations.

Reference may be made to a patent US4089932, 1978 wherein a process for the production of spherical silica comprising of emulsifying water glass in a dispersion medium composed of polar and non-polar solvent and precipitating spherical silica was described. The silica so obtained was porous and hence is not suitable for preparing high cleaning dentifrice formulation.

Reference may be made to US Patent US2003/0190276, wherein the process has been developed for producing non-porous spherical silica suitable for use as starting material of the filler of IC sealing resins compositions, a substrate in an electronic field.

Reference may be made to South Korean patent KR100651243, wherein silica was prepared from sodium silicate in an alkaline halide organic solvent and a dispersant (emulsion). The process involves addition of carbon dioxide gas, mineral acid followed by addition of ammonia water and ammonia gas into the reactant mixture. Even though the silica so obtained was in spherical morphology it has not been characterized for any particular applications. The process involves many inputs and hence it is complex and expensive.

Silica grades are used in oral care compositions, particularly in dentifrice compositions such as toothpaste, toothpowder, gels and dental-creams.

The medium abrasive silica grades generally used for cleaning the teeth can be precipitated silica or silica gels such as the silica xerogels described in Pader et al., U.S. Pat. No. 3,538,230, and DiGiulio, U.S. Pat. No. US 8,211,408 B2 15 3,862.307. Examples are the silica Xero-gels marketed under the trade name “Syloid¹ by the W.R. Grace & Company, Davison Chemical Division. Also there are the precipitated silica materials such as those marketed by the J. M. Huber Corporation under the trade name, “Zeodent”, particularly the silicas carrying the designation Zeodent 113, Zeodent 124, and Zeodent 119. Other precipitated silicas commercially available are Absil 100(C), and Absil 100 marketed by Madhu silica Pvt. Ltd., Similar grades of precipitated abrasive silica are also available as TIXOSIL 73, and TIXOSIL 63, all made by Rhodia. PQ corp also makes silica grades such as AC77, AC-35, AC-39 as medium abrasive silica for use in toothpastes.

Precipitated silicas may be made by the process disclosed in U.S. Pat. No. 6,740,311, White, 2004. Precipitated and other silicas are described in more detail in the Handbook of Porous Solids, edited by Ferdi Schuth, Kenneth S. W. Sing and Jens Weitkamp, chapter 4.7.1.1.1, called Formation of Silica Sols, Gels, and Powders, and in Cosmetic Properties and Structure of Fine-Particle Synthetic Precipitated Silicas, S. K. Wason, Journal of Soc. Cosmetic Chem., vol. 29, (1978), pp. 497-521.

Normally, precipitated silica described in above references is used as abrasive in toothpaste formulations that have low structure as defined by their oil absorption. The above grades of precipitated silica are used at typical loading of 10% in the toothpaste formulation. In general, silicas with oil absorptions less than 110 ml/100 g are considered to have low structure having RDA (Radio-active Dentine Abrasion) in the range of 100-150 and PCR (pellicle cleaning ratio) of 70-100. However such high RDA values can give rise to problem of enamel/dentine abrasion, which can lead to very serious and disruptive oral health problems, including exposure and damage to nerves and soft tissue. Dental abrasions can also lead to formation of tooth sensitivity to hot and cold food and beverages due to exposure of dental tubules in dentine. The ratio of PCR/RDA for conventional medium abrasive silica is in the range of 0.60-0.80 which is rather low. The innovative silica abrasive that can offer the PCR/RDA ratio of near to 1 or greater than 1 can give huge benefits, offering high cleaning at low abrasivity, particularly for the patients suffering from sensitive teeth problems.

There is therefore a long felt need to develop precipitated silica having desirable properties useful in variety of applications for example in dentifrice formulations and a process for preparation thereof. The present inventors have surprisingly developed precipitated silica having desirable properties and an efficient process for preparing precipitated silica which ameliorates the aforesaid shortcomings of the prior art.

OBJECTS OF THE INVENTION

It is an object of the present invention to overcome the drawbacks of the prior art.

It is an object of the present invention to provide silica useful in preparation of high cleaning efficacy dentifrice formulation.

It is another object of the present invention to provide precipitated silica of globulous morphology.

It is yet another object of the present invention to provide precipitated silica having low porosity.

It is yet another object of the present invention to produce precipitated silica having low oil absorption value.

It is yet another object of the present invention to provide precipitated silica having low BET surface area, less than 100 m²/g. It is yet another object of the present invention to provide precipitated silica having narrow particle size distribution.

It is yet another object of the present invention to provide precipitated silica having high bulk density.

It is an object of the present invention to provide a process for preparing precipitated silica having desirable properties.

It is another object of the present invention to provide a less energy intensive process for preparing precipitated silica.

It is yet another object of the present invention to recover and recycle the organic solvent used in the process.

It is yet another object of the present invention to provide dentifrice formulations which demonstrate a high cleaning efficiency with lower abrasivity and better stability with the actives even at low loading of the precipitated silica.

SUMMARY OF THE INVENTION

According to another aspect of the present invention, there is provided globular silica.

According to an aspect of the present invention, there is provided a method for preparation of low porosity globulous silica particles.

According to yet another aspect of the present invention, there is provided dentifrice formulations comprising the globular silica of present invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The above and other aspects, features and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings wherein: Figure 1: SEM (Scanning electron microscopy) images of the precipitated silica powder according to present invention at different magnification. The shape of the particle is found to be Globulous. DETAILED DESCRIPTION OF THE INVENTION

The following description is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the scope of the invention as defined by the appended claims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, steps or components but does not preclude the presence or addition of one or more other features, steps, components or groups thereof.

The term “orally acceptable carrier” as used herein means a suitable vehicle or ingredient, which can be used to form and/or apply the present compositions to the oral cavity in a safe and effective manner. Such vehicle may include materials such as thickening silica, surfactants, binders, humectants, stabilizers, actives thickening materials, flavor system, sweetening agents, cooling agents, coloring agents, other suitable materials, and mixtures thereof.

The term “effective amount” as used herein means an amount of a compound or composition sufficient to induce a positive benefit, an oral health benefit.

The term “oral composition” as used herein means a product that in the ordinary course of usage is retained in the oral cavity for a time sufficient to contact some or all of the dental surfaces and/or oral tissues for purposes of oral activity. The oral composition of the present invention may be in various forms including toothpaste, dentifrice, tooth gel, tooth powders, tablets, rinse, subgingival gel, foam, chewing gum, floss, or denture product.

The term “dentifrice” as used herein means paste, gel, powder, tablets, or liquid formulations, unless otherwise specified, that are used to clean the surfaces of the oral cavity. The dentifrice composition may be in any desired form, such as deep striped, surface striped, multilayered, having a gel surrounding a paste, or any combination thereof. The terms "toothpaste" and "dentifrice" can be used interchangeably.

The Pellicle Cleaning Ratio (PCR) is a measure of the cleaning characteristics of a dentifrice. The Radioactive Dentine Abrasion (RDA) is a measure of the abrasiveness of the treated precipitated silica when incorporated into a dentifrice.

The present invention relates to a process for preparing precipitated silica having globulous morphology, high bulk density, non-porous in nature, low oil absorption value, narrow particle size distribution and useful in myriad of applications.

The present invention provides a process for preparation of globular precipitated silica comprising the steps of: i. Preparing an aqueous solution of alkali silicate, adding organic solvent and non-ionic surfactant and mixing to form a water-in-oil emulsion; ii. Adding emulsion to an aqueous solution of mineral acid of step (i) and stirring the reaction mixture; iii. Heating the reaction mixture of step (ii) followed by aging; iv. Separating organic phase of the mixture in step (iii), filtering the aqueous phase containing silica and washing the filtered cake; v. Drying the washed cake of step (iv) and sieving the dried powder; vi. Calcining the dried powder of step (v) and sieving to form globular precipitated silica.

In an embodiment, the alkali metal silicate to be used includes any metal alkali silicate such as sodium, potassium lithium silicates but is not limited to sodium silicate. In an embodiment, the silica concentration in the aqueous solution of alkali silicate ranges from 10 to 25% (w/w).

In an embodiment, the organic solvent to be used includes hexane, cyclohexane, dichloromethane, and mineral oils but is not limited to iso paraffinic oils. In an embodiment, the ratio of silica to solvent ranges from 1:1.5 to 3 (w/w).

In an embodiment, the non-ionic surfactant to be used includes nonionic surfactant but is not limited to sorbitan monooleate. In an embodiment, the ratio of silica to surfactant ranges from 1:0.04 to 0.08 (w/w).

In an embodiment, the mixing at step (i) is carried by conventional methods in the art. Preferably, homogenization is carried out at 2000 to 3000 rpm for 5 to 10 minutes.

In an embodiment, the mineral acid to be used includes hydrochloric acid, nitric acid, sulfuric acid but is not limited to sulfuric acid. In an embodiment, the aqueous solution of mineral acid has an acid concentration ranging from 15-25% (w/w).

In an embodiment, stirring the reaction mixture at step (ii) is carried out for 30 to 60 minutes.

Step (iii) involves heating of the reaction mixture (de-emulsifying treatment) to 80 - 110 °C followed by aging for 20 to 40 minutes.

The subsequent steps involve separating organic phase by allowing to stand the mixture obtained in step (iii) preferably for 1 to 2 hours, filtering the aqueous phase containing silica and washing the filtered cake. In an embodiment, the washing is done using ultra filtered water till the washed water exhibits pH of 5 and above and conductivity less than 500 pS/cm.

Subsequently, the washed cake is dried and thereafter sieved using a sieve of appropriate mesh size. In an embodiment, the sieving is through a 45-micron sieve.

Next, the sieved powder is subjected to calcination. In an embodiment, the calcination is done at a temperature ranging from 800 to 1000 °C for 1 - 2 hours. Thereafter, the calcined powder is sieved to obtain the final product.

In an embodiment, there is provides a process for preparation of globular precipitated silica comprising the steps of:

(i) Diluting sodium silicate solution with water to obtain a solution having 10 to 25% (w/w) silica concentration;

(ii) Adding organic solvent in the ratio of silica to solvent 1:1.5 to 3 (w/w);

(iii)Adding non-ionic surfactant in the ratio of silica to surfactant 1:0.04 to

0.08 (w/w);

(iv) Mixing the content obtained in (iii) above by stirring in a homogenizer at

2000 to 3000 rpm for 5 to 10 minutes;

(v) Diluting sulfuric acid with water to obtain acid concentration 15-25%

(w/w);

(vi) Adding the emulsion prepared in (iv) above into the diluted acid (v) in 15-

30 minutes;

(vii) Stirring the reaction mixture so obtained for 30 to 60 minutes;

(viii) Heating the reaction mixture to 80 - 110 °C followed by aging for 20 to 40 minutes;

(ix) Separating organic phase by allowing to stand the mixture obtained in step

(viii) for 1 to 2 hours;

(x) Filtering the aqueous phase containing silica;

(xi) Washing the filtered cake using ultra filtered water till the washed water exhibits pH of 5 and above and conductivity less than 500 pS/cm;

(xii) Drying the washed cake;

(xiii) Sieving the dried powder using 45-micron sieve; (xiv) Calcining the powder at 800 to 1000 °C for 1 - 2 hours;

(xv) Sieving the calcined powder to pass through 45-micron sieve to obtain the final product. The obtained silica product has the following specification as described in below Table A:

Table A In an embodiment, the precipitated silica is utilized in the preparation of dentifrice formulations. A dentifrice formulation is defined as a powder, paste, cream or other preparation for cleansing the teeth and other parts of oral cavity (gums) using a finger or a toothbrush.

The silicas are characterised in terms of many parameters like Oil Absorption Value (OAV), RDA, PCR, PAV (Perspex Abrasion Value), Surface area (BET) and pore volume (PV). The globular silica grades of present invention can be used in oral care compositions, particularly in dentifrice compositions such as toothpaste, toothpowder, gels and dental-creams.

Toothpaste consists of many ingredients like abrasive silica (for cleaning), Thickening silica (for providing viscosity), surfactants, binders, humectants such as Sorbitol and Glycerine, stabilisers, sodium phosphate, sodium pyro phosphates, actives such as sodium or stannous fluoride (anti-caries agent), zinc salts (antiplaque agent), Cetyl pyridinium Chloride (anti-bacterial agent), potassium nitrate (anti-sensitivity agent) etc.

The globular inventive silica described herein, is characterised by its low structure, low surface area, low porosity and rounded shape has very different properties as compared to current precipitated abrasive silica commonly used in dentifrice formulation having RDA (Radio active Dentine abrasion) in range of 100-150 and PCR (Pellicle cleaning ratio) of 70-100 at high loading. While high PCR > 80 are desired to effectively remove the bacterial film formed on enamel called dental plaque, which is the root cause of most common oral care problems such as cavities and gingivitis. This is currently achieved at a high value of RDA (>100) which is rather detrimental to achieve this objective. High RDA can give rise to problem of enamel/dentine abrasion, which can lead to very serious and disruptive oral health problems, including exposure and damage to nerves and soft tissue. Dental abrasions can also lead to formation of tooth sensitivity to hot and cold food and beverages due to exposure of dental tubules in dentine. Hence patients having sensitive tooth would expect their toothpaste to have good PCR but lower RDA. The Ratio of PCR/RDA for current medium abrasive silica is in the range of 0.60-0.80 which is rather low.

In an embodiment, the PCR value of the globular silica of the present invention ranges from 85 to 125.

In an embodiment, Relative Dentine Abrasion (RDA) value of the globular silica of the present invention ranges from 67 to 134. In an embodiment, the ratio of PCR/RDA of the globular silica of the present invention ranges from 0.9 to 1.3.

The globular silica of present invention achieves higher PCR (meaning a higher cleaning efficiency) and lower RDA value (meaning lesser damage to dentine) at very low loading in the toothpaste. The ratio PCR/RDA for this inventive globular silica is also near to or greater than 1; thus giving the enormous advantage over the conventional abrasive silica used in such dentifrices. Due to its very low loading used in the formulation, it would be economically attractive to use globular in regular-use toothpastes, without compromising cleaning efficacy and offering lower abrasivity at the same time.

Without wishing to be bound by any theory, it is believed that due to unique properties of globular silica in terms of its lower porosity and surface and coupled by its rounded shape (absence of sharp edges), the abrasivity of particles on enamel is expected to be lower due to its rolling effect during tooth-brushing and therefore has potential to give lower RDA and high PCR even at very lower loadings in the toothpaste formulation.

Advantages of present invention:

• The present process for preparing globular silica is energy efficient, economically attractive, less polluting and produces product having high cleaning efficacy.

• In the present process, energy input is reduced by carrying out calcination of silica at lower temperature.

• Recovering and recycling the solvent used in the process to reduce pollution and making the product cost effective.

• The product silica has globulous morphology, high bulk density, low porosity, low oil absorption value, narrow particle size distribution.

• Globular silica is useful for dentifrice formulations. Gives a high cleaning efficiency with lower abrasivity due to higher PCR (meaning a higher cleaning efficiency) and lower RDA value (meaning lesser damage to dentine) at very low loading in the toothpaste. The ratio PCR/RDA for this inventive globular silica is also near to or greater than 1; thus giving the enormous advantage over the conventional abrasive silica used in such dentifrices.

• Better stability with actives used in toothpastes: Another advantage of globular silica is about its very good compatibility with actives like sodium fluoride, stannous fluoride, Zinc citrate and CPC (Cetylpryridinium Chloride) that are commonly used in toothpaste for anti-cavity and anti-bacterial benefits.

US patent no.6, 946, 119 B2 (2005) describes the process of preparation of precipitated silica product comprising silica particulate having lower BET specific surface area from 1 to 50 square meters per gram for the silica particulate and present in an amount effective to reduce attachment of cetylpyridinium chloride (CPC) to the silica particulate as compared to the silica particulate without the surface deposits. Globular silica of present invention not only has very low surface area but has low porosity that is likely to reduce any interaction of active molecules like CPC etc.

EXAMPLES

Following examples are given by way of illustration and therefore should not be construed to limit the scope of present invention:

Methods of measurement:

Oil Absorption

The oil absorption is determined by the ASTM spatula rub-out method (American Society of Test Material Standards D 281). The test is based on the principle of mixing linseed oil with the silica by rubbing with a spatula on a smooth surface until a stiff puttylike paste is formed which will not break or separate when it is cut with a spatula. The oil absorption is then calculated from the volume of oil (V cm) used to achieve this condition and the weight, W. in grams, of silica by means of the equation:

Oil absorption=(VxlOO), W, i.e. expressed in terms of cm oil/lOOg silica.

BET Surface Area and pore volume (porosity)

Surface area and pore volume of the silica is measured using standard nitrogen adsorption methods using micrometrics tristar 3020.

Weight Mean Particle Size and Particle Size Distribution

The weight mean particle size of the silica is determined using a Malvern Particle sizer (Mastersizer - 2000)

Radioactive Dentine Abrasion Test (RD A)

The procedure follows the method for assessment of dentifrice abrasivity recommended by the American Dental Association (Journal of Dental Research 55(4) 563, 1976). In this procedure, extracted human teeth are irradiated with a neutron flux and subjected to a standard brushing regime. The radioactive phosphorous 32 removed from the dentin in the roots is used as the index of the abrasion of the dentifrice tested. The test is carried out by Indiana University, USA.

Pellicle Cleaning Ratio (PCR)

The PCR is measured using the test described by G. T. Stookey et al. in Journal of Dental Research, November 1982, pages 1236 to 1239. Full details are available in this paper.

Scores represent the ability of the test dentifrice to remove the stain. A standard lot of calcium pyrophosphate is assessed as a slurry and allotted the arbitrary cleaning value of 100.

The cleaning scores of the test materials (PCR) are expressed as a PCR = Mean decrement for test material/Mean decrement of reference material x 100 Tapped Bulk Density

Tapped bulk density is determined by weighing approximately 10 gm of silica in silica into a dry 100 cm measuring cylinder. The column reading is taken after 50 tappings and the density is evaluated.

Fluoride Compatibility Test

The test material is immersed in a fluoride solution of known concentration. The loss of fluoride from the solution over a standard period of time gives a measure of the fluoride compatibility of the material.

Example -1

1310 g of 23% Sodium Silicate solution taken in a beaker which contain Na2O = 7.14 % & SiCh = 23.12 %. 709 g of water was added into it. 757 g of Isoparaffinic Hydrocarbon oil (Garasol 1924, KL-80) & 18.2 g of Sorbitan monooleate (Span® 80, Sigma- Aldrich) were added into sodium silicate solution. The resultant mixture was agitated at high rpm (3050) to form a water in oil emulsion. 5678 g of 19.09% sulfuric acid taken in another glass beaker. The oil in water emulsion as prepared above was added in 15 minutes at room temperature into sulfuric acid under stirring at 500 rpm. The stirring was continued for 40 min at 500 rpm. The resultant mixture was heated up to 100 °C and maintained the temperature for 30 minutes while continuing the stirring. The resultant reaction mixture was allowed to stand for 1 hours for organic layer to separate. The organic & aqueous phase were separated. The aqueous phase was filtered & the cake was washed with DM water till the filtrate exhibits pH >5 and conductivity <500 pS/cm. The cake was dried in an oven at 110 °C and the dried powder was sieved to past through 45 micron sieve. The dried silica powder was subjected to calcination at 850 °C for 2 hrs. in a furnace. The calcined silica powder was sieved to pass through 45 micron sieve. The product was characterised as detailed in the following table- 1. Table- 1

The silica powder was examined in SEM (Scanning electron microscopy) at different magnification as shown in Figure-1 (a, b, c, d) the shape of the particle is found to be Globulous.

Example -2

1379 g of 22% Sodium Silicate solution taken in a beaker which contain Na20 = 6.86 % & SiCh = 21.96 %. 640 g of water was added into it. 757 g of Isoparaffinic Hydrocarbon oil (Garasol 1924, KL-80) & 12 g of Sorbitan monooleate (Span® 80, Sigma- Aldrich) were added into sodium silicate solution. The resultant mixture was agitated at high rpm (3050) to form a water in oil emulsion. 5678 g of 19.09% sulfuric acid taken in another glass beaker. The oil in water emulsion as prepared above was added in 15 minutes at room temperature into sulfuric acid under stirring at 500 rpm. The stirring was continued for 40 min at 500 rpm. The resultant mixture was heated up to 100 °C and maintained the temperature for 30 minutes while continuing the stirring. The resultant reaction mixture was allowed to stand for 1 hours for organic layer to separate. The organic & aqueous phase were separated. The aqueous phase was filtered & the cake was washed with DM water till the filtrate exhibits pH >5 and conductivity <500 pS/cm. The cake was dried in an oven at 110 °C and the dried powder was sieved to past through 45 micron sieve. The dried silica powder was subjected to calcination at 850 °C for 2 hrs. in a furnace. The calcined silica powder was sieved to pass through 45 micron sieve. The product was characterised as detailed in the following table-2.

Table-2

Example -3

1310 g of 23% Sodium Silicate solution taken in a beaker which contain Na2O = 7.14 % & SiO₂ = 23.12 %. 709 g of water was added into it. 757 g of Isoparaffinic Hydrocarbon oil (Garasol 2633, Mineral Oil, KL-130) & 18 g of Sorbitan monooleate (Span® 80, Sigma-Aldrich) were added into sodium silicate solution. The resultant mixture was agitated at high rpm (3050) to form a water in oil emulsion. 5744 g of 18.87 % sulfuric acid taken in another glass beaker. The oil in water emulsion as prepared above was added in 15 minutes at room temperature into sulfuric acid under stirring at 500 rpm. The stirring was continued for 40 min at 500 rpm. The resultant mixture was heated up to 100 °C and maintained the temperature for 30 minutes while continuing the stirring. The resultant reaction mixture was allowed to stand for 1 hours for organic layer to separate. The organic & aqueous phase were separated. The aqueous phase was filtered & the cake was washed with DM water till the filtrate exhibits pH >5 and conductivity <500 pS/cm. The cake was dried in an oven at 110 °C and the dried powder was sieved to past through 45 micron sieve. The dried silica powder was subjected to calcination at 850 °C for 2 hrs. in a furnace. The calcined silica powder was sieved to pass through 45 micron sieve. The product was characterised as detailed in the following table-3.

Table-3

Example -4

706 g of 22% Sodium Silicate solution taken in a beaker which contain Na2O = 6.86 % & SiCh = 22.05 %. 332 g of water was added into it. 234 g of Isoparaffinic Hydrocarbon oil (Garasol 1924, KL-80) & 9.3 g of Sorbitan monooleate (Span® 80, Sigma- Aldrich) were added into sodium silicate solution. The resultant mixture was agitated at high rpm (3050) to form a water in oil emulsion. 2627 g of 21.22 % sulfuric acid taken in another glass beaker. The oil in water emulsion as prepared above was added in 15 minutes at room temperature into sulfuric acid under stirring at 500 rpm. The stirring was continued for 40 min at 500 rpm. The resultant mixture was heated up to 100 °C and maintained the temperature for 30 minutes while continuing the stirring. The resultant reaction mixture was allowed to stand for 1 hours for organic layer to separate. The organic & aqueous phase were separated. The aqueous phase was filtered & the cake was washed with DM water till the filtrate exhibits pH >5 and conductivity <500 pS/cm. The cake was dried in an oven at 110 °C and the dried powder was sieved to past through 45 micron sieve. The dried silica powder was subjected to calcination at 850 °C for 2 hrs. in a furnace. The calcined silica powder was sieved to pass through 45 micron sieve. The product was characterised_as detailed in the following table-4. Table-4

Example -5

541 g of 20% Sodium Silicate solution taken in a beaker which contain Na2O = 6.18 % & SiO₂ = 20.00 %. 270 g of Isoparaffinic Hydrocarbon oil (Garasol 1924, KL-80) & 6.5 g of Sorbitan monooleate (Span® 80, Sigma- Aldrich)_were added into sodium silicate solution. The resultant mixture was agitated at high rpm (3050) to form a water in oil emulsion. 1795 g of 21.57 % sulfuric acid taken in another glass beaker. The oil in water emulsion as prepared above was added in 15 minutes at room temperature into sulfuric acid under stirring at 500 rpm. The stirring was continued for 40 min at 500 rpm. The resultant mixture was heated up to 100 °C and maintained the temperature for 30 minutes while continuing the stirring. The resultant reaction mixture was allowed to stand for 1 hours for organic layer to separate. The organic & aqueous phase were separated. The aqueous phase was filtered & the cake was washed with DM water till the filtrate exhibits pH >5 and conductivity <500 pS/cm. The cake was dried in an oven at 110 °C and the dried powder was sieved to past through 45 micron sieve. The dried silica powder was subjected to calcination at 850 °C for 2 hrs. in a furnace. The calcined silica powder was sieved to pass through 45 micron sieve. The product was characterised as detailed in the following table-5.

Table-5

Example -6

704 g of 22% Sodium Silicate solution taken in a beaker which contain Na2O = 6.88 % & SiO₂ = 22.15 %. 336 g of water was added into it. 390 g of recycle Isoparaffinic Hydrocarbon oil (Garasol 1924, KL-80) (recycle of Example- 1) & 6.1 g of Sorbitan monooleate (Span® 80, Sigma- Aldrich) were added into sodium silicate solution. The resultant mixture was agitated at high rpm (3050) to form a water in oil emulsion. 2631 g of 21.22% sulfuric acid taken in another glass beaker. The oil in water emulsion as prepared above was added in 15 minutes at room temperature into sulfuric acid under stirring at 500 rpm. The stirring was continued for 40 min at 500 rpm. The resultant mixture was heated up to 100 °C and maintained the temperature for 30 minutes while continuing the stirring. The resultant reaction mixture was allowed to stand for 1 hours for organic layer to separate. The organic & aqueous phase were separated. The aqueous phase was filtered & the cake was washed with DM water till the filtrate exhibits pH >5 and conductivity <500 pS/cm. The cake was dried in an oven at 110 °C and the dried powder was sieved to past through 45micron sieve. The dried silica powder was subjected to calcination at 850 °C for 2 hrs. in a furnace. The calcined silica powder was sieved to pass through 45 micron sieve. The product was characterised as detailed in the following table-6.

Example 7

Toothpaste formulations comprising the globular silica prepared according to present invention (a) High cleaning efficacy with lower abrasivity

The globular inventive silica described herein, is characterised by its low structure, low surface area, low porosity and rounded shape has very different properties as compared to current precipitated abrasive silica commonly used in dentifrice formulation. The typical value of conventional medium abrasive silica viz. Absil

100(C) and Absil- 100, and high cleaning silica Absil-HC, as described in published catalogue on “High Performance oral care silica”, manufactured by Madhu Silica, used in toothpaste formulations by various toothpaste manufacturers, are given below in Table 7.

It is observed from the aforesaid Table, that the ratio of PCR/RDA for conventional medium abrasive silica is in the range of 0.60-0.80 which is rather low.

Toothpaste formulations with standard precipitated silica using Absil 100 (C) and globular silica were prepared as shown in below Table 8.

Table 8: Toothpaste formulations comprising standard/conventional precipitated silica and Globular Silica according to present invention The dentifrice formulations prepared above were evaluated for PCR and

RDA properties. The properties of globular silica along with its PCR and RDA values when used in toothpaste formulation are shown the Table 9 below. The PCR data for all the 3 formulations were obtained from Oral Health Research Institute of Indianapolis, Indiana University.

Table-9

It is seen from above table that globular silica of present invention gives excellent value of PCR (85.5 vs. standard 70) at very low loading in the toothpaste (0.5% vs. standard 10%), thus giving excellent efficacy for cleaning at l/20th of the loading of standard precipitated silica. The formulation of toothpaste with globular silica also gives lower RDA of 67.87 as compared to 90 (meaning lesser damage to dentine), which is good not only for regular type of toothpastes but particularly the one that are marketed with sensitive teeth benefits. The ratio PCR/RDA for this inventive globular silica is also near to or greater than 1 thus giving the enormous advantage over the conventional abrasive silica used in such dentifrices. Due to its very low loading used in the formulation, it would be economically attractive to use globular in regular-use toothpastes, without compromising cleaning efficacy and offering lower abrasivity at the same time. Toothpaste are also marketed with “Whitening” benefits and values RDA,

PCR values of such conventional products were evaluated and reported by P. WulKniz (cleaning power and abrasivity of European toothpastes; Adv. Dental Research 1997, 11-4, p- 576-9), some of which are reported below in Table 10

Table -10

The results in Table 10 show that globular silica when used at higher loading of 5% in the toothpaste formulation, it gives excellent PCR value of 124.95 with low RDA value of 133.74, comparable to toothpaste that are positioned on “whitening” benefits. Those skilled in the art know that such toothpastes are formulated with combination of regular and high abrasivity silicas at the loading of 10-15% in the toothpaste formulation. The main advantage of the formulation with globular silica is that it gives the similar performance in terms of PCR at much lower loading of silica (5%) in the formulation but at significantly lower ratio of PCR/RDA, thus giving the advantage of lower abrasivity of dentine. (b)Better stability with actives used in toothpastes:

The stability of sodium fluoride was measured for globular silica and following results were obtained given in Table 11

Table- 11

Table 11 clearly indicates the benefit of giving better stability of fluoride compounds commonly used in toothpaste formulations with the globular silica of present invention as compared to standard precipitated silicas. It is to be understood that the present invention is susceptible to modifications, changes and adaptations by those skilled in the art. Such modifications, changes, adaptations are intended to be within the scope of the present invention.

Claims

CLAIMS:

1. Globular silica characterized by: a) Particle size ranging from 2 to 20 micron; b) BET surface area ranging from 1 to 100 m²/g; c) Pore volume ranging from 0.001 to 0.4 ml/g; d) Bulk density ranging from 500 to 1000 g/1; e) Oil absorption value (OAV) ranging from 20 to 80 ml/lOOg; f) Pellicle cleaning ratio (PCR) value ranging from 85 to 125; g) Relative Dentine Abrasion (RDA) value ranging from 67 to 134; and h) Ratio of PCR/RDA ranging from 0.9 to 1.3.

2. A process for preparation of globular silica comprising the steps of: i. Preparing an aqueous solution of alkali metal silicate, adding organic solvent and non-ionic surfactant and mixing to form a water-in-oil emulsion; wherein the ratio of silica to solvent ranges from 1:1.5 to 3 (w/w) and the ratio of silica to surfactant ranges from 1:0.04 to 0.08 (w/w); ii. Adding emulsion to an aqueous solution of mineral acid of step (i) and stirring the reaction mixture; iii. Heating the reaction mixture of step (ii) to 80 - 110 °C followed by aging; iv. Separating organic phase of the mixture in step (iii), filtering the aqueous phase containing silica and washing the filtered cake; v. Drying the washed cake of step (iv) and sieving the dried powder; vi. Calcining the dried powder of step (v) at 800 to 1000 °C for 1 - 2 hours and sieving to form globular silica.

3. The process as claimed in claim 2, wherein the alkali metal silicate is selected from sodium silicate or potassium lithium silicates and the silica concentration in the aqueous solution of alkali metal silicate ranges from 10 to 25% (w/w). . The process as claimed in claim 2, wherein the organic solvent is selected from hexane, cyclohexane, dichloromethane, mineral oils, turpentine oil, variants of iso paraffinic hydrocarbon oil or combinations thereof. . The process as claimed in claim 2, wherein the non-ionic surfactant is sorbitan monooleate. . The process as claimed in claim 2, wherein the mineral acid is selected from hydrochloric acid, nitric acid or sulfuric acid and the aqueous solution of mineral acid has an acid concentration ranging from 15-25% (w/w). . The process as claimed in claim 2, wherein the sieving at step (v) is through a 45-micron sieve. . A globular silica obtained by a process comprising the steps of: i. Preparing an aqueous solution of alkali metal silicate, adding organic solvent and non-ionic surfactant and mixing to form a water-in-oil emulsion; wherein the ratio of silica to solvent ranges from 1:1.5 to 3 (w/w) and the ratio of silica to surfactant ranges from 1:0.04 to 0.08 (w/w); ii. Adding emulsion to an aqueous solution of mineral acid of step (i) and stirring the reaction mixture; iii. Heating the reaction mixture of step (ii) to 80 - 110 °C followed by aging; iv. Separating organic phase of the mixture in step (iii), filtering the aqueous phase containing silica and washing the filtered cake; v. Drying the washed cake of step (iv) and sieving the dried powder; vi. Calcining the dried powder of step (v) at 800 to 1000 °C for 1 - 2 hours and sieving to form globular silica. . A dentifrice composition comprising:

(I) An abrasive comprising globular silica characterized by: a) Particle size ranging from 2 to 20 micron; b) BET surface area ranging from 1 to 100 m²/g; c) Pore volume ranging from 0.001 to 0.4 ml/g; d) Bulk density ranging from 500 to 1000 g/1; e) Oil absorption value (OAV) ranging from 20 to 80 ml/lOOg; f) Pellicle cleaning ratio (PCR) value ranging from 85 to 125; g) Relative Dentine Abrasion (RD A) value ranging from 67 to 134; h) Ratio of PCR/RDA ranging from 0.9 to 1.3; and

(II). Orally acceptable carriers. 0. The composition as claimed in claim 9, wherein the globular silica is present at 0.5 to 5 wt.% in the composition. 1. The composition as claimed in claim 9, wherein the orally acceptable carrier is selected from thickening silica, surfactants, binders, humectants, stabilizers, anti-caries agent, anti-plaque agent, anti-bacterial agent, antisensitivity agent, thickening materials, flavor system, sweetening agents, cooling agents, coloring agents, opacifier, pH adjusters and combinations thereof.