Peroxide compatible silica

Abstract

The invention relates to peroxide compatible heat treated precipitated silicas and preparation process thereof. The invention also relates to the use of peroxide compatible silicas in oral care formulations, in particular to improve whitening performance of toothpaste by controlling the timing of decomposition of peroxides in the toothpaste formulation.

Description

[0001] PEROXIDE COMPATIBLE SILICA

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The invention relates to precipitated silicas suitable for the use in whitening oral care formulations having improved peroxide compatibility over time and preparation process thereof.

[0004] BACKGROUND OF THE INVENTION

[0005] It is always a desire to use toothpastes providing an improved performance on whitening.

[0006] White, bright teeth and a big smile are important to many people around the world. For this purpose, cleaning silicas in combination with chemical cleaning agents have been used to provide whitening, however, they are not effective in situations where the base color of the teeth is not bright white. As a result, peroxide based whitening agents are currently utilized in formulations to not only clean teeth, but to also increase the whiteness of the base tooth as well.

[0007] Peroxides typically work by forming radical species as they decompose, and these radical species are very effective removing organic based stains and whitening teeth as they continue to decompose to form oxygen and water. The timing of the decomposition of the peroxide is important, as it is needed to happen during tooth brushing and not in the tube before use. In case decomposition starts early, inside the tube, this may cause tubes to burst due to excessive pressure from the formation of oxygen gas. Although fumed silica thickening agents are used in these oral care formulations to achieve the desired rheology, traditional precipitated silica abrasive and thickening agents are not compatible with peroxide. When precipitated silicas are used, they promote the decomposition of peroxide shortly after the formulations are produced which typically results in a burst tube, or in a loss of the active peroxide species. As such, calcium pyrophosphate abrasives and stabilized forms of peroxide are typically used in order to avoid such decomposition. Calcium pyrophosphate can be expensive and requires the use of sodium monofluorophosphate as the fluoride source, which is not as effective at cavity protection as sodium fluoride. It is desirable to have a precipitated silica that is compatible with peroxide so that sodium fluoride can be used for increased cavity protection, increased formulation flexibility related to cleaning and abrasion and a mouthfeel that is more similar to traditional toothpastes.

[0008] US 2015 / 0209252 A1 patent publication discloses, dentifrice compositions comprising a type of heat treated precipitated silica, for compatibility with peroxide and improved stability, comprising cristobolite in order to be used to replace calcium pyrophosphate.

[0009] WO 2022 / 101015 A1 patent publication also discloses a heat treated silica for improved compatibility with peroxide. The compatibility has been reached out by lowering the OH groups per surface area.

[0010] WO 1993 / 023007 A1 discloses dehydroxylated silica gels for enhanced oral care compatibility.

[0011] US 2003 / 0124069 A1 patent publication discloses a silica / metal phosphate composite for improved chemical cleaning.

[0012] US 2014 / 271900 A1 patent publication discloses, dentifrice compositions comprising a type of heat treated precipitated silica having a BET SA of less than 90 m2 / g which has lowered abrasion properties.

[0013] US 2014 / 127145 A1 patent publication discloses, a process for stability improvement for precipitated silica materials by subjecting silica particles to a temperature of above 800 °C. Although many prior arts mention about compatibility or in specific peroxide compatibility, they do not mention about use of phosphate containing additive to achieve the desired peroxide compatibility in oral care formulations.

[0014] It is therefore an object of the present invention to provide a novel precipitated silica having specific BET surface area, phosphate content and loss on ignition (LOI) that provides higher levels of compatibility with peroxide under accelerated aging tests comparing to the current products in the market.

[0015] BRIEF SUMMARY OF THE INVENTION

[0016] There is a need of improvement for another abrasive material which is compatible with peroxide since calcium pyrophosphate abrasive is an expensive ingredient and requires mainly the use of sodium monofluorophosphate as the fluoride source. After thorough investigation, the inventors of the present invention have surprisingly found that the abrasive silica as defined in claim 1 solves the above technical problem as it provides higher levels of compatibility with peroxide under accelerated aging tests comparing to calcium pyrophosphate.

[0017] Typically precipitated silicas, that are commonly used in dental compositions, comprise trace levels of metal impurities likely in the form of metal hydroxides / oxides (oxidation promoters) which can undergo a reaction with the peroxide in the dental formulation over time resulting in a tube rupture.

[0018] Advantageously, the present invention provides a novel heat treated precipitated silica abrasive having reduced BET surface area and LOI and with a level of phosphate that is believed to form an insoluble metal phosphate under heat treatment that delivers higher levels of compatibility with peroxide. Use of heat treated precipitated silicas having lower BET surface area with additional phosphate material reduces oxidation with peroxide overtime. It is believed that the addition of phosphate forms a metal pyrophosphate complex with the trace metal impurities on the silica surface after the heating step. This resulting impurities will be insoluble and do not react with peroxide which dramatically increases the stability when aging at elevated temperature.

[0019] Therefore, in a first aspect, the present invention relates to precipitates silica abrasives having specified BET surface area, loss on ignition (LOI) and phosphate level as defined in claim 1.

[0020] A second aspect of the invention is a method for preparing said heat treated precipitated silicas.

[0021] A third aspect of the invention is the use of silica in oral care formulations for improved peroxide compatibility.

[0022] Yet another aspect of the invention is an oral care formulation comprising said heat treated precipitated silicas.

[0023] DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention relates to the field of peroxide compatible precipitated silica abrasives, preparation process and usages thereof.

[0025] There are several key differences between fumed silica and precipitated silica. First, the purity of the fumed silica is much higher. Precipitated silicas can have iron levels in the 50-400 ppm range, which acting in a Fenton type mechanism, can quickly catalyze the decomposition of peroxide. The second difference is the lower silanol (-OH) density on the fumed silica, which is a result of being synthesized in a flame rather than in an aqueous precipitation process. Moreover, the fumed silicas are mainly used as thickening agents and do not provide any abrasion or cleaning effect. Therefore, in the oral care formulations it is preferred to use precipitated silicas as abrasive silicas.

[0026] Preparation of Peroxide Compatible Silicas:

[0027] In order to reduce the total -OH group number on a precipitated silica, reducing the surface area can be effective. However, simply reducing the surface area is found not to be effective in achieving peroxide compatibility. In order to further reduce -OH density per unit area, heat treatment, or calcination is required. Heating the silica to temperatures up to 1000 °C results in a further polymerization of the silica framework and a reduction of Q2 and Q3 type silanol groups. Even when low surface area silicas are calcined, the compatibility with peroxide increased from a matter of hours to a matter of days and sometimes weeks , as long as the BET surface area of the silica is sufficiently low.

[0028] When looking at ways to remove elemental impurities from the silica, washing with different acids and chelating agents were tried. It was found that while washing a silica with an acid can be an effective way at removing metal ion impurities, however, if they are not thoroughly washed away from the silica surface, peroxide compatibility is actually decreased as the metal ions are more available to participate in peroxide decomposition mechanisms. Some benefit was observed when washing with phosphoric acid, however, it was difficult to tell if all the metal ion impurities were washed away from the silica surface and improvements in peroxide compatibility were not always observed.

[0029] During further trials to improve the process, it is found that the addition of phosphate containing material, which is selected from the group of a polyphosphates; such as sodium tripolyphosphate (STPP) at a concentration above 200 ppm before the calcination (heating) step, is sufficient to dramatically increase the compatibility of a low surface area silica (having BET Surface area of equal or lower than 20 m2 / g, preferably lowerthan 6 m2 / g, more preferably lowerthan 4 m2 / g). Polyphosphates at concentrations of 5000 ppm or more can dramatically increase the compatibility of a higher surface area silica (having BET Surface area higher than 20 m2 / g, preferably in a range from 20 to 100 m2 / g. Even if there is no restriction to use high surface area silicas with high concentration of phosphate containing material, it is desired to use low surface area silicas which requires less amount of phosphate addition for peroxide compatibility.

[0030] Not to be bound by any particular theory, it is believed that the residual phosphate remaining on the surface of the silica after calcination seems to passivate the metal ion impurities on the silica surface (possibly forming a metal pyrophosphate species), resulting in the inability to participate in peroxide decomposition reactions. The addition of a phosphate salt to the silica before calcination results a dramatic increase in compatibility with peroxide, with precipitated silica prototypes outlasting the calcium pyrophosphate controls by up to 10 times.

[0031] Oral Care Compositions

[0032] The precipitated silica and / or silicate particles can be used in any suitable composition and for any suitable end-use application. Often, the silica and / or silicate particles can be used in oral care applications, such as in a dentifrice composition. The dentifrice composition can contain any suitable amount of the silica and / or silicate particles, such as from about 0.5 to about 50 wt. %, from about 1 to about 50 wt. %, from about 5 to about 35 wt. %, from about 10 to about 40 wt. %, or from about 10 to about 30 wt. %, of the precipitated silica and / or silicate particles. These weight percentages are based on the total weight of the dentifrice composition.

[0033] The dentifrice composition can be in any suitable form, such as a liquid, powder, or paste. In addition to the silica and / or silicate particles, the dentifrice composition can contain other ingredients or additives, nonlimiting examples of which can include a humectant, a solvent, a binder, a therapeutic agent, a chelating agent, a thickener other than the silica and / or silicate particles, a surfactant, an abrasive other than the silica and / or silicate particles, a sweetening agent, a colorant, a flavoring agent, a preservative, and the like, as well as any combination thereof.

[0034] Humectants serve to add body or "mouth texture" to a dentifrice as well as preventing the dentifrice from drying out. Suitable humectants include polyethylene glycol (at a variety of different molecular weights), propylene glycol, glycerin (glycerol), erythritol, xylitol, sorbitol, mannitol, lactitol, and hydrogenated starch hydrolyzates, and mixtures thereof. In some formulations, humectants are present in an amount from about 20 to about 50 wt. %, based on the weight of dentifrice composition.

[0035] A solvent can be present in the dentifrice composition, at any suitable loading, and usually the solvent comprises water. When used, water is preferably deionized and free of impurities, can be present in the dentifrice at loadings from 5 to about 70 wt. %, or from about 5 to about 35 wt. %, based on the weight of dentifrice composition.

[0036] Therapeutic agents also can be used in the compositions of this invention to provide for the prevention and treatment of dental caries, periodontal disease, and temperature sensitivity, for example. Suitable therapeutic agents can include, but are not limited to, fluoride sources, such as sodium fluoride, sodium monofluorophosphate, potassium monofluorophosphate, stannous fluoride, potassium fluoride, sodium fluorosilicate, ammonium fluorosilicate and the like; condensed phosphates such as tetrasodium pyrophosphate, tetrapotassium pyrophosphate, disodium dihydrogen pyrophosphate, trisodium monohydrogen pyrophosphate; tripolyphosphates, hexametaphosphates, trimetaphosphates and pyrophosphates; antimicrobial agents such as triclosan, bisguanides, such as alexidine, chlorhexidine and chlorhexidine gluconate; enzymes such as papain, bromelain, glucoamylase, amylase, dextranase, mutanase, lipases, pectinase, tannase, and proteases; quaternary ammonium compounds, such as benzalkonium chloride (BZK), benzethonium chloride (BZT), cetylpyridinium chloride (CPC), and domiphen bromide; metal salts, such as zinc citrate, zinc chloride, and stannous fluoride; sanguinaria extract and sanguinarine; volatile oils, such as eucalyptol, menthol, thymol, and methyl salicylate; amine fluorides; peroxides and the like. Therapeutic agents can be used in dentifrice formulations singly or in combination, and at any therapeutically safe and effective level or dosage.

[0037] Thickening agents are useful in the dentifrice compositions to provide a gelatinous structure that stabilizes the toothpaste against phase separation. Suitable thickening agents include silica thickener; starch; glycerite of starch; gums such as gum karaya (sterculia gum), gum tragacanth, gum arabic, gum ghatti, gum acacia, xanthan gum, guar gum and cellulose gum; magnesium aluminum silicate (Veegum); carrageenan; sodium alginate; agar-agar; pectin; gelatin; cellulose compounds such as cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxymethyl cellulose, hydroxymethyl carboxypropyl cellulose, methyl cellulose, ethyl cellulose, and sulfated cellulose; natural and synthetic clays such as hectorite clays; and mixtures thereof. Typical levels of thickening agents or binders are up to about 15 wt. % of a toothpaste or dentifrice composition.

[0038] Useful silica thickeners for utilization within a toothpaste composition, for example, include, as a non-limiting example, an amorphous precipitated silica such as ZEODENT® 153, 163, 165, 167, 168 and AEROSIL® 200 pharma, all available from Evonik Corporation.

[0039] Abrasive silicas; for utilization within a toothpaste composition, for example, include, as a non-limiting example, ZEODENT 103, 113, 120, 124, 115, 116, SPHERILEX 145, 148 all available from Evonik Corporation.

[0040] The disclosed abrasive silica and / or silicate particles can be utilized alone as the abrasive in the toothpaste composition, or as an additive or co-abrasive with other abrasive materials known in the art. Thus, any number of other conventional types of abrasive additives can be present within the dentifrice compositions of the invention. Other such abrasive particles include, for example, precipitated calcium carbonate (PCC), ground calcium carbonate (GCC), chalk, bentonite, dicalcium phosphate or its dihydrate forms, silica gel (by itself, and of any structure), precipitated silica, amorphous precipitated silica (by itself, and of any structure as well), perlite, titanium dioxide, dicalcium phosphate, calcium pyrophosphate, alumina, hydrated alumina, calcined alumina, aluminum silicate, insoluble sodium metaphosphate, insoluble potassium metaphosphate, insoluble magnesium carbonate, zirconium silicate, particulate thermosetting resins and other suitable abrasive materials. Such materials can be introduced into the dentifrice compositions to tailor the polishing characteristics of the target formulation.

[0041] Surfactants can be used in the dentifrice compositions of the invention to make the compositions more cosmetically acceptable. The surfactant is preferably a detersive material which imparts to the composition detersive and foaming properties. Suitable surfactants are safe and effective amounts of anionic, cationic, nonionic, zwitterionic, amphoteric and betaine surfactants such as sodium lauryl sulfate, sodium dodecyl benzene sulfonate, alkali metal or ammonium salts of lauroyl sarcosinate, myristoyl sarcosinate, palmitoyl sarcosinate, stearoyl sarcosinate and oleoyl sarcosinate, polyoxyethylene sorbitan monostearate, isostearate and laurate, sodium lauryl sulfoacetate, N-lauroyl sarcosine, the sodium, potassium, and ethanolamine salts of N- lauroyl, N-myristoyl, or N-palmitoyl sarcosine, polyethylene oxide condensates of alkyl phenols, cocoamidopropyl betaine, lauramidopropyl betaine, palmityl betaine and the like. Sodium lauryl sulfate is a preferred surfactant. The surfactant is typically present in the compositions of the present invention in an amount from about 0.1 to about 15 wt. %, from about 0.3 to about 5 wt. %, or from about 0.3 to about 2.5 wt. %.

[0042] Sweeteners can be added to the dentifrice composition (e.g., toothpaste) to impart a pleasing taste to the product. Suitable sweeteners include saccharin (as sodium, potassium or calcium saccharin), cyclamate (as a sodium, potassium or calcium salt), acesulfame-K, thaumatin, neohesperidin dihydrochalcone, ammoniated glycyrrhizin, dextrose, levulose, sucrose, mannose, and glucose.

[0043] Colorants can be added to improve the aesthetic appearance of the product. Suitable colorants include without limitation those colorants approved by appropriate regulatory bodies such as the FDA and those listed in the European Food and Pharmaceutical Directives and include pigments, such as T1 O2, and colors such as FD&C and D&C dyes.

[0044] Flavoring agents also can be added to dentifrice compositions. Suitable flavoring agents include, but are not limited to, oil of Wintergreen, oil of peppermint, oil of spearmint, oil of sassafras, and oil of clove, cinnamon, anethole, menthol, thymol, eugenol, eucalyptol, lemon, orange and other such flavor compounds to add fruit notes, spice notes, etc. These flavoring agents generally comprise mixtures of aldehydes, ketones, esters, phenols, acids, and aliphatic, aromatic and other alcohols.

[0045] Preservatives also can be added to the compositions of the present invention to prevent bacterial growth. Suitable preservatives approved for use in oral compositions such as methylparaben, propylparaben and sodium benzoate can be added in safe and effective amounts.

[0046] Other ingredients can be used in the dentifrice composition, such as desensitizing agents, healing agents, other caries preventative agents, chelating / sequestering agents, vitamins, amino acids, proteins, other anti- plaque / anti-calculus agents, opacifiers, antibiotics, anti-enzymes, enzymes, pH control agents, oxidizing agents, antioxidants, and the like.

[0047] EMBODIMENTS

[0048] Thus, the present invention relates to a heat treated precipitated silica material characterized by; a phosphate content of 1 to 1500 ppm a loss on ignition of less than 1 .4 wt. %, preferably less than 1 .25 wt. % and a BET surface area of equal or less than 20 m2 / g.

[0049] In one embodiment, the heat treated precipitated silica material is characterized by; a phosphate content of 25 ppm to 1500 ppm, preferably 50 to 1300 ppm a loss on ignition is less than 1 .25 wt. % and preferably less than 1 wt. % a BET surface area of less than 6 m2 / g, preferably less than 4 m2 / g, more preferably between 2 to 4 m2 / g.

[0050] In another embodiment of the present invention, a precipitated silica material is characterized by; a phosphate content of 1 to 200 ppm, a loss on ignition of less than 1 .25 wt. % and a BET surface area of less than 2 m2 / g, preferably less than 1 m2 / g

[0051] In one embodiment of the invention according to any preceding embodiments wherein the Median Particle Size (D50) of the silica is between 7 to 15, preferably is 8-11 pm.

[0052] In one embodiment of the invention according to any preceding aspects / embodiments wherein oil absorption of the silica is in a range from 20 to 80 cc / 100 g; preferably from 30 to 60 cc / 100 g.

[0053] In yet another aspect of the present invention, a precipitated silica material is characterized by; a phosphate content of at least 1500 ppm, preferably 1500 to 2500 ppm, a loss on ignition of less than 1 .4 wt. %, preferably less than 1 .25 wt. % and a BET surface area of more than 20 m2 / g, preferably more than 20 to 100 m2 / g In one embodiment of the invention, above precipitated silica material in another aspect has a Median Particle Size (D50) between 10 to 25 pm and oil absorption in a range from 100 to 250 cc / 100 g.

[0054] In one aspect of the present invention, the heat treated precipitated silica, according to above defined embodiments, is obtained by phosphate addition to the precipitated silica in an aqueous medium followed by calcination of the silica.

[0055] Another aspect of the present invention is a process for preparing a heat treated precipitated silica material comprises the following steps; a) Providing a precipitated silica material in an aqueous medium b) Adding a phosphate material into the precipitated silica slurry and mixing it c) Spray drying the silica to a moisture level of lower than 10% and optionally milling and d) Calcining the silica at a temperature of greater than 700 °C to reduce the LOI to a level of less than 1 .4 wt. %.

[0056] In one embodiment of the present invention, the process for preparing a treated precipitated silica material according to the invention, comprises the following steps; a) Synthesis of a silica according to the known methods in the art followed by a washing step to remove sodium sulfate, b) Addition of an appropriate amount of a phosphate salt to the silica slurry before drying c) Spray drying the silica to a moisture level of lower than 10% and optionally milling to a particle size of 3-25 pm and d) Calcining the silica at a temperature of greater than 700 °C to reduce the LOI to less than 1 .4 wt. %.

[0057] In the first step, it can be started with a pre-existing silica where it is wet out (as described in the previous aspect), and continued with the same steps of addition of an appropriate amount of a phosphate salt to the silica slurry, re-drying and then calcining to reach out the same particle size and LOI ranges.

[0058] In one embodiment of the present invention, the precipitated silica can be obtained by any known method in the art by following the steps of; a) Providing an alkaline silicate solution comprising an alkali metal silicate such as sodium silicate and water b) Adding sulfuric acid and alkaline silicate solutions together with agitation c) After precipitation, precipitated silica is recovered by filtration, washed of salts.

[0059] Another aspect of the invention is a heat treated precipitated silica material obtained by a further phosphate addition followed by calcination according to the above defined process.

[0060] In one embodiment of the present invention, the precipitated silica can be obtained by the known method in the art and later can be treated with phosphate followed by calcination step to obtain heat treated precipitated silica by following the steps of; a) Providing an alkaline silicate solution comprising an alkali metal silicate such as sodium silicate and water b) Adding sulfuric acid and alkaline silicate solutions together with agitation c) Precipitation of the silica and filtering the precipitated silica followed by washing of salts d) Addition of an appropriate amount of a phosphate salt (such as STTP) to the silica slurry before drying e) Spray drying the silica to a moisture level of lower than 10% and optionally milling to a particle size of 3-25 pm and f) Calcining the silica at a temperature of greater than 700 °C to reduce the LOI to less than 1 .4 wt. %.

[0061] In one embodiment of the invention, according to preceding embodiments, the phosphate material is added to the mixture at a level of above 200 ppm; preferably above 200 ppm for a silica having a BET surface area of equal or less than 20 m2 / g; and above 5000 ppm for a silica having a BET surface area of more than 20 m2 / g, and no phosphate is added for a silica having a BET surface area of less than 1 m2 / g.

[0062] In one embodiment of the invention, according to preceding embodiments, calcination is applied at a temperature between 700 to 1000 °C for 1 to 120 minutes, preferably at 825 °C for 60 minutes.

[0063] According to the present invention, any type of phosphate material can be used as long as it is soluble in water, preferably the phosphate material is selected from the group polyphosphates, orthophosphates or pyrophosphates such as; sodium tripolyphosphate (STTP), tetrasodium pyrophosphate (TSPP) and any mixtures thereof. The phosphate material may be selected from metal or organophosphates, hydrogen phosphates, dihydrogen phosphates or phosphoric acid and any mixtures thereof. The phosphate material may also be selected from poly phosphates such as sodium polyphosphate, potassium polyphosphate, sodium hexametaphosphate.

[0064] Addition of the phosphate amount depends on the surface area of the silica wherein low surface area silicas having BET surface area equal or less than 20 m2 / g, preferably less than 6 m2 / g, more preferably less than 4 m2 / g require low levels of phosphate addition but high surface area silicas having BET surface area more than 20 m2 / g require higher levels of phosphate addition. Accordingly the level of phosphate at the final silica products would be at least 25, preferably 50 ppm for low BET surface area silicas, and at least 1500 ppm for silicas with higher BET surface areas. No phosphate addition can be followed for silicas having very low surface area namely lower than 1 m2 / g.

[0065] In a preferred embodiment of the present invention, according to preceding embodiments, it is preferred to use STPP in an amount sufficient to deliver at least 25 ppm preferably at least 50 ppm of elemental P in final silica product wherein the BET surface area is equal or less than 20 m2 / g, preferably less than 6 m2 / g; and 0 to 200 ppm of elemental P in final silica product wherein the BET surface area is less than 2 m2 / g, preferably less than 1 m2 / g.

[0066] In a preferred embodiment the final amount of elemental phosphate in the silica product, according to preceding embodiments, is in the range from 0 to 1500 ppm, more preferably from 25 to 1500 ppm, more preferably from 50 to 1300 ppm wherein the BET surface area is equal or less than 20 m2 / g, preferably less than 6 m2 / g.

[0067] In a preferred embodiment of the present invention, according to preceding embodiments, it is preferred to use STPP in an amount sufficient to deliver at least 1500 ppm, preferably 1500 to 2500 ppm of elemental P in final silica product wherein the BET surface area is more than 20 m2 / g.

[0068] A further aspect of the invention is the use of precipitated silica material according to the invention, in oral care compositions.

[0069] In one embodiment of the present invention the precipitated silica material, given in above embodiments or either treated according to the given above methods (phosphate treatment followed by calcination), is being used in oral care compositions wherein the oral care composition is a toothpaste formulation comprising a peroxide-releasing compound.

[0070] In one embodiment of the present invention, the oral care composition comprises the treated precipitated silica according to above embodiments, in a range from 3 to 35% by total weight of the composition.

[0071] In one embodiment of the present invention, the oral care composition may comprise additional abrasive precipitated silica, solvent, thickening agents such as fumed silica thickener, therapeutic agents, surfactants sweeteners, colorants, fluoride source and / or other ingredients such as desensitizing agents, healing agents, other caries preventative agents, chelating / sequestering agents, vitamins, amino acids, proteins, other anti-plaque / anti-calculus agents, opacifiers, antibiotics, anti-enzymes, enzymes, pH control agents, oxidizing agents, antioxidants, and the like.

[0072] In another embodiment, the oral care composition is a toothpaste formulation having a tube stability at 60° C of at least about 5 days, preferably at least 14 days or more.

[0073] While the invention has been described in terms of its preferred embodiments, it is known that the invention can be practiced with modification within the scope of the claims.

[0074] EXPERIMENTAL PART

[0075] The invention is further illustrated in detail hereinafter with reference to examples and comparative examples, without any intention to limit the scope of the present invention.

[0076] Abbreviations

[0077] LOI : Loss of ignition

[0078] STPP: sodium tripolyphosphate

[0079] MR: Molar Ratio

[0080] Methods of Silica Characteristics Determination

[0081] The BET surface areas disclosed herein were determined on a Micromeritics TriStar II 3020 V1.03 using the BET nitrogen adsorption method of Brunaur et al., J. Am. Chem. Soc., 60, 309 (1938), and such technique is well known to those skilled in the art. The D50 median particle size refers to the particle size for which 50% of the sample has a smaller size and 50% of the sample has a larger size. Median particle size (d50), mean particle size (average), and d95 were determined via the laser diffraction method using a Horiba LA 300 instrument. Dry particles were submitted to the instrument for analysis.

[0082] Oil absorption values were determined in accordance with the rub-out method described in ASTM D281 using linseed oil (cc oil absorbed per 100 g of the particles). Generally, a higher oil absorption level indicates a particle with a higher level of large pore porosity, also described as higher structure.

[0083] The concentration of the phosphate on silica was determined by ICP analysis, which directly determined the phosphorus content from polyphosphorus content calculation. The %P (phosphorous concentrations) were determined by the following method. 2.0000 g of silica was wet with a few drops of deionized water in a platinum crucible. 10 ml of perchloric acid (72 %) and 10 ml of hydrofluoric acid (48-50 %) were added and the platinum dish was slowly heated on a stir plate in a fume hood. As the platinum dish was heated, dense white fumes were evolved. The sides of the crucible were then carefully rinsed with boric acid (4 %) and it was also heated to fumes. After cooling, the contents of the crucible were transferred to a 250 ml volumetric flask and the crucible was washed with deionized water to make sure all remaining contents were quantitatively transferred. The dish was then rinsed with 5 ml of hydrochloric acid (36 %) and the washings were also added to the volumetric flask. Approximately 200 ml of deionized water were added to the volumetric flask, and if the resulting solution was cloudy, it was heated on a low temperature hot plate until it became clear. After cooling, 2.50 ml of a scandium internal standard solution was added and the volumetric flask was filled to the mark with deionized water. The concentrations of the metals in the solution were then determined by ICP / OES.

[0084] The % silica, %LOI and % moisture were determined by recording the weight of a clean, dry platinum dish (weight 1). To this, approximately 1 g of silica was added and the weight of the silica and platinum dish were recorded to 4-decimal places (weight 2). The platinum dish was heated to 105 °C for 2 hours. It was cooled and weighed to 4-decimal places (weight 3). The platinum dish was heated to 1000 °C in a muffle furnace for 2 hours. It was cooled in a desiccator and the “ignited weight” was recorded to 4-decimal places (weight 4). The sample was then wet with a few drops of deionized water, 6 drops of sulfuric acid and approximately 10 mL of hydrofluoric acid. It was heated to dryness on a hotplate in the fume hood. The platinum dish was then placed in a muffle furnace and was heated for 1 hour at 1000 °C. It was cooled in a desiccator and its weight recorded to 4-decimal places (weight 5). The % moisture and % LOI can be calculated by the following:

[0085] % moisture = (weight 3)(100) I (weight 2-weight 1)

[0086] % LOI = (weight 4)(100) / weight 3 - weight 1)

[0087] % silica can be determine by determining the apparent silica loss by: % apparent silica loss = weight 4 - weight 5. The apparent silica loss must be corrected for the gain in sample weight due to the conversion of sodium ions interacting with the silica surface to sodium sulfate from the addition of sulfuric acid pH and conductivity were determined by measuring a 5% aqueous slurry of silica. Set 1 : Comparison of Inventive Low Surface Area Silicas (wherein silicas treated with phosphate addition and calcination) with Non-treated Control Examples in Toothpaste Formulations

[0088] Low surface area silicas can be produced by many methods in art however, the ability to produce low surface area spherical materials with a controlled particle size distribution are desired. Therefore hereby a specific method of low surface area precipitated silica production method has been described below in Example Set 1 and 4. Commercially available silicas are also phosphate treated with a calcination step applied after phosphate treatment as given in Example 4.

[0089] The present invention is not bound to any specific precipitated silica. The below precipitated silica preparation method is given as an example for preparation of low surface area silica, without having any boundaries for the invention. Many other commercially available low surface area silicas can be used for treatment with phosphate and calcination. ZEODENT® 103, 120 or 124 would be too abrasive due to their density and particle shape after a calcination step. Therefore, low surface area silicas are obtained according to the preparation method described below.

[0090] Preparation of Precipitated Silica Example 1

[0091] Initial Set-Up / Pre- Treatment Step (To be applied for silicas, such as ZEODENT 103 (as explained below), wherein control of abrasiveness is needed and to obtain a reduced BET SA before phosphate treatment and / or calcination steps)

[0092] Prior to the introduction of acid and silicate into the system, precipitated silica, sodium sulfate, sodium silicate and water can be added and recirculated at 80 L / min. This step is performed to fill the recycle loop with the approximate contents and concentrations of a typical batch to minimize the purging time before the desired product could be collected. This step is used to avoid the possibility of forming gel in the reactor. Without any restriction, the acid and silicate can be added directly to the loop filled with water without gelling or plugging the system.

[0093] 1 .5 kg of Zeodent® 103 (from Evonik Corporation), 1 .34 kg of sodium sulfate, 11 .1 L of sodium silicate (3.3 MR, 19.5%) and 20 L of water are added to the recirculation loop and heated to 90 °C with recirculation at 60 L / min with the Silverson operating at 30 Hz (1742 RPM) with the stator screen removed. Sodium silicate (3.3 MR, 19.5%) and sulfuric acid (17.1 %) were added simultaneously to the loop at a silicate rate of 1 .7 L / min and an acid rate sufficient to maintain a pH of 7.5. If necessary, the acid rate was adjusted accordingly to maintain the pH. Acid and silicate were added under these conditions for 40 minutes to purge unwanted silica out of the system before the desired material was collected. After 40 minutes had passed, the collection vessel was emptied and its contents discarded. The silica product was then collected in a vessel with stirring at 40 RPM while maintaining the temperature at approximately 80 °C. After the desired quantity of product was collected (700 L), addition of acid and silicate were stopped and the contents of the loop were allowed to circulate.

[0094] The silica product in the collection vessel was transferred to a batch reactor and was heated to 95 °C with stirring at 80 RPM. Sodium silicate (3.3 MR, 19.5%) was added to the reactor until a pH of 9.5 (+ / - 0.2) was reached. Once pH 9.5 (+ / - 0.2) was reached, sodium silicate (3.32 MR, 20.0%) and sulfuric acid (17.1 %) were added at rates of 1.66 L / min and 0.80 L / min, respectively. If needed, the acid rate was adjusted to maintain pH 9.5 (+ / - 0.2). After a total time of 60 minutes, the flow of sodium silicate was stopped and the pH was adjusted to 7.0 with continued addition of sulfuric acid (17.1 %) at 0.81 L / min. The batch was digested for 15 minutes at pH 7.0, and was then filtered and washed to a conductivity of < 1500 pS. Prior to drying, the pH of the silica slurry was adjusted to 5.0 with sulfuric acid and was spray dried to a target moisture of 5.0%.

[0095] The sample(s) are then treated with phosphate, followed with calcination step as explained below and according to the conditions given in Table 2 below.

[0096] Inventive Example 7: SPHERILEX® 145 from the Evonik Corporation is treated according to the conditions in the Table 2 below, without a pre-treatment step.

[0097] Phosphate Treatment Step:

[0098] The precipitated silica produced above in Example 1 is treated with a phosphate additive material (acid or salt). 250 g of precipitated silica is added into 1 L of deionized water. The phosphate (STTP) is added in an amount above 200 ppm to reach elemental phosphate amount in the final silica products in the range from 0 to 1500 ppm and the solution is mixed for 30 minutes. After 30 minutes of mixing, the silica is dried overnight at 105 °C.

[0099] Calcination Step:

[0100] 250 g of the phosphate treated silica is placed in a crucible (vessel) and heated at 825 °C for 60 minutes. After the 60 minute heating time, the silica is allowed to slowly cool to room temperature.

[0101] The calcined and phosphate treated silica samples are formulated into a toothpaste formulation, tubed and aged at 60 °C. The tubes are checked daily for failure observance.

[0102] Calcination can be applied by heating in a furnace and there is no restriction to apply other means of calcinations such as spray calcination.

[0103] Toothpaste Formulation:

[0104] The toothpaste formulation is used as described in detail in US 10,363,210 B2 patent. Inventive heat treated silica examples are added into the toothpaste formulation instead of calcium pyrophosphate as abrasive and tested for peroxide compatibility.

[0105] Table 1 : Toothpaste formulations of control example and inventive example

[0106] Peroxide Compatibility Testing:

[0107] In order to test whether the silica material is compatible with peroxide, a toothpaste formulation (as shown in Table 1) is prepared and placed into toothpaste tubes and sealed to be aged at 60 °C. The tubes are observed daily and failure time is determined when the tubes rupture and began to expel toothpaste from their seams. Failure is reported at the first sign of tube failure. The calcium pyrophosphate control formulation (Formulation A) typically fails between 14 and 21 days. It is desirable for an experimental silica used in formulation B or C to match the stability of the calcium pyrophosphate abrasive in Formulation A, and even more desirable to outlast the calcium pyrophosphate Formulation A control. Below precipitated silica examples (1A to 1 E) are prepared according to invention (phosphate addition and calcination) and being used in toothpaste formulation B shown in Table 1 . Examples 1A to 1 E are prepared by adding phosphate before calcination step (as explained in the phosphate treatment and calcination steps above), 1 F (comparative) is prepared with phosphate treatment but no calcination step, 1 H (comparative) is prepared by phosphate addition after calcination step and no phosphate addition or calcination step applied to Example 1 G (comparative).

[0108] Example 7A (inventive) refers to Spherilex 145 sample which is directly treated with phosphate and followed with calcination as explained above. Last two examples refer to comparative example formulations comprising calcium pyrophosphate and prepared according to comparative formulation A and inventive formulation B given above in Table 1.

[0109] Table 2: Peroxide compatibility test results

[0110] Table 3: Physical and chemical characterization of inventive and / or comparative silicas used in toothpaste formulation

[0111] It is obvious from Table 2 that the addition of the phosphate (such as; STPP) before the calcination step resulted in an increase in peroxide compatibility (1 C-E) comparing to the formulations comprising calcium pyrophosphate as the abrasive ingredient in toothpaste formulation or comparing to the formulations where phosphate is added into the precipitated silica after calcination (1 H). Addition of STPP after the calcination step, if the STPP is added to the calcined silica or directly to the toothpaste formulation with no calcination, the resulting toothpaste is not compatible with peroxide as the tubes ruptured before the end of day 1 (1 F- G).

[0112] Moreover, it is also obvious from Table 3 that the phosphate amount in the resultant silica also has an effect on increasing the compatibility when we see Examples 1 A to 1 E. Silica materials compatible with peroxide for 14 days or above at 60 °C can be considered as working silica example. The increased amount of phosphate helps to dramatically increase the compatibility (as seen from examples 1 C to 1 E) as the failure of the toothpaste tubes was increased to 91 days, compared to 21 -25 days for the formulations containing the calcium pyrophosphate abrasive as comparative examples.

[0113] Example 7 illustrates that peroxide compatibility can be improved up to 42 days when commercially available SPHERILEX® 145 is treated with phosphate and calcined at 825 °C, when BET surface area is 19.

[0114] Example Set 2: Comparison of Inventive High Surface Area Silicas (Treated ZEODENT® 113 and ZEODENT® 165 examples) with Non-treated Control Examples in Toothpaste Formulations Examples 2A-C: ZEODENT® 113 from Evonik Corporation is treated in the following experiments.

[0115] Examples 3A-B: ZEODENT® 165 from Evonik Corporation is treated in the following experiments.

[0116] Examples 2B, C and 3B samples are mixed with STPP in accordance with the procedure as described in Example 1 and 7 via phosphate treatment and followed by calcination and formulated into toothpaste formulation B or C according to the Table 1. Table 4: Peroxide compatibility test results of Inventive Examples 2B,C and 3B compared to Control

[0117] Examples 2A and 3A

[0118] Table 5: Physical and chemical characterization of Inventive Example 2 and 3

[0119] It is obvious from Table 4 that the addition of the phosphate (such as; STPP) before the calcination step resulted in an increase in peroxide compatibility (Examples 2B, C and 3B) comparing to examples wherein no phosphate has been added before calcination (Example 2A, 3A). It is obvious from Table 5 that higher amount of phosphate is needed when the BET surface area of silica is increased. Therefore, 1500 ppm or more phosphate is required for high BET SA silicas to reach out the desired compatibility, namely at least 14 days of compatibility. Moreover, the best result is observed from Example 3B wherein ZEODENT® 165 is used and phosphate is added before calcination when compared to Calcium pyrophosphate control example and also comparing to the other examples wherein ZEODENT® 113 is used. On the contrary, above Table 4 and 5 shows that higher surface area silicas requires more phosphate addition and does not provide the same compatibility improvement as observed for low surface are silicas (See example Set 1 and 4). It is, however, an improvement into the 14-21 day compatibility range that is exhibited by the calcium pyrophosphate control. Since calcium pyrophosphate is currently used as the abrasive material in peroxide containing formulations, matching the performance with a higher surface area silica is still desirable. To achieve the highest levels of compatibility, lower surface area silicas are needed.

[0120] Example Set 3: Comparison of Treated and Non-treated examples of Tixosil 63&73 (from WO 2022 / 101015 A1 prior art) with the Control Example in Toothpaste Formulations

[0121] Comparative Examples showing the effect of Loss of Ignition on Compatibility

[0122] The examples disclosed in prior art WO 2022 / 101015 A1 (heat treated silicas having reduced number of OH groups per surface area), are used in the below Example Set 3 to show that exemplified high BET SA examples in the prior art do not provide desired compatibility even treated with phosphate and / or calcined.

[0123] Non Treated Examples of Tixosil 63 (Example 1 of WO 2022 / 101015 A1) and Tixosil 73 (Example 2 of WO 2022 / 101015 A1)

[0124] Example 1A, B - Tixosil 63 is prepared according to Rhodia patent application (WO 2022 / 101015A1) Example 2A, B - Tixosil 73 is also prepared according to Rhodia patent application (WO 2022 / 101015A1)

[0125] Treated Examples of Tixosil 63 and 73

[0126] Example 4A- Tixosil 63 is treated with STPP and calcined at 600 °C according to the methods described in Inventive Example 1 .

[0127] Example 5A- Tixosil 73 is treated with STPP and calcined at 600 °C according to the methods described in Inventive Example 1 .

[0128] Table 6: Peroxide compatibility test results of Tixosil 63 and Tixosil 73 Examples Table 7: Physical and chemical characterization of Tixosil 63 and Tixosil 73 Examples having high surface area

[0129] It can be seen from Table 6 that the heat treated examples of Tixosil 63 and Tixosil 73 (having higher surface area) from WO 2022 / 101015 A1 prior art, do not provide an improved peroxide compatibility even if they are treated with phosphate and / or calcined at higher temperatures than described in the application. For BET surface area values in the 25-35 m2 / g range, additional phosphate and calcination at temperatures higher than 600 °C are needed to reduce LOI values and improve the compatibility into the range of the calcium pyrophosphate control.

[0130] When the physical and chemical characterizations of Tixosil 63 and Tixosil 73 examples compared to the inventive examples, it can be understood that the lower the surface area, the less P from a phosphate containing additive needs to be present on the silica surface before the heat treatment step (calcination) in order to improve peroxide compatibility.

[0131] Example Set 4: Comparison of Inventive Silicas having very low Surface Area (wherein silicas treated with phosphate addition and calcination) with Non-treated Control Examples in Toothpaste Formulations

[0132] Preparation of Inventive Silica Example 6

[0133] Initial Set-Up (same as Inventive Silica Example 1 )

[0134] Prior to the introduction of acid and silicate into the system, precipitated silica, sodium sulfate, sodium silicate and water can be added and recirculated at 80 L / min. This step is performed to fill the recycle loop with the approximate contents and concentrations of a typical batch to minimize the purging time before the desired product could be collected. This step is used to avoid the possibility of forming gel in the reactor. Without any restriction, the acid and silicate can be added directly to the loop filled with water without gelling or plugging the system.

[0135] 1 .5 kg of Zeodent® 103 (from Evonik Corporation), 1 .34 kg of sodium sulfate, 11 .1 L of sodium silicate (3.3 MR, 19.5%) and 20 L of water are added to the recirculation loop and it is heated to 90 °C with recirculation at 180 L / min with the Silverson operating at 60 Hz (3480 RPM) with the stator screen removed . Sodium silicate (3.3 MR, 26.0%) and sulfuric acid (22.8 %) are added simultaneously to the loop at a silicate rate of 2.0 L / min and an acid rate sufficient to maintain a pH of 7.5. If necessary, the acid rate is adjusted accordingly to maintain the pH. Acid and silicate are added under these conditions for 40 minutes to purge unwanted silica out of the system before the desired material was collected. After 40 minutes passes, the collection vessel is emptied and its contents discarded. The silica product is then collected in a vessel with stirring at 40 RPM while maintaining the temperature at approximately 80 °C. After the desired quantity of product is collected (500 L), addition of acid and silicate are stopped and the contents of the loop are allowed to circulate.

[0136] The silica product in the collection vessel is transferred to a batch reactor and was heated to 95 °C with stirring at 80 RPM. Sodium silicate (3.3 MR, 19.5%) was added to the reactor until a pH of 9.5 (+ / - 0.2) was reached. Once pH 9.5 (+ / - 0.2) was reached, sodium silicate (3.32 MR, 26.0%) and sulfuric acid (22.8%) were added at rates of 1.66 L / min and 0.80 L / min, respectively. If needed, the acid rate was adjusted to maintain pH 9.5 (+ / - 0.2). After a total time of 60 minutes, the flow of sodium silicate was stopped and the pH was adjusted to 7.0 with continued addition of sulfuric acid (22.8%) at 0.80 L / min. The batch was digested for 10 minutes at pH 6.0, and was then filtered and washed to a conductivity of < 1500 pS. Prior to drying, the pH of the silica slurry was adjusted to 5.0 with sulfuric acid and was spray dried to a target moisture of 5.0%.

[0137] This sample is then treated with phosphate addition and followed with calcination same as Example 1 as explained above. The treatment conditions and test results have been provided in Table 8 below.

[0138] Comparative Example 8

[0139] The silica from Inventive Example 6 is treated at different conditions as shown in the table below.

[0140] Table 8: Peroxide compatibility test results of Examples 6, 7 and 8

[0141] Table 9: Physical and chemical characterization of Examples 6, 7 and 8

[0142] Examples 6A-D show that even with a silica that has a BET SA <1 m2 / g that calcination is still needed. Calcining the silica helps to more tightly bind the metal ion impurities to the silica surface, even when no phosphate is present. This is evident with the compatibility improvement between Example 6D (uncalcined lasting 1 day) to Example 6A (calcined lasting 29 days). When phosphate is added to the silica before calcination, dramatic improvement in peroxide compatibility were observed, as illustrated in Examples 6B and 6C. Example 8 shows that heat treatment at temperatures of 600 °C and lower are not sufficient for improvements in peroxide compatibility, even silicas with BET surface area values that are less than 5 m2 / g, regardless if phosphate is present or not. This means that very low surface area (less than 1 m2 / g), phosphate is not needed to achieve compatibility greater than the calcium pyrophosphate. But, when phosphate is added to these very low SA materials, compatibilities of up to 120 days can be achieved. Example Set 5. Cleaning and Abrasion Performance in Toothpaste Formulation

[0143] In order to verify the Inventive silicas have acceptable cleaning and abrasion performance in toothpaste, Example 6C silica was used in toothpaste formulations and tested for PCR (Pellicle Cleaning Ratio) and RDA (Relative Dentin Abrasion) at the Indiana University School of Dentistry.

[0144] Relative Dentin Abrasion (RDA) The RDA values of dentifrice compositions of Examples 9A-9C were determined according to the method set forth by Hefferen, Journal of Dental Res., July-August 1976, 55 (4), pp. 563-573, and described in Wason U.S. Pat. Nos. 4,340,583, 4,420,312 and 4,421 ,527, the contents of which are incorporated herein by reference in their entirety. Pellicle Cleaning Ratio (PCR)

[0145] The cleaning properties of dentifrice compositions of Examples 9A-9C were expressed in terms of Pellicle Cleaning Ratio ("PCR") values. The PCR test measures the ability of a dentifrice composition to remove pellicle film from a tooth under fixed brushing conditions. The PCR test is described in "In Vitro Removal of Stain with Dentifrice" G. K. Stookey, et al., J. Dental Res., 61 , 12-36-9, 1982. Both PCR and RDA results vary depending upon the nature and concentration of the components of the dentifrice composition. PCR and RDA values are unit-less, and the toothpaste formulation is shown in Table 10.

[0146] Table 10. Toothpaste formulation used for PCR / RDA testing. It was observed that the PCR values for formulation 9B were approximately 20 units higher than the ZEODENT® 103 control formulation shown in Example 9A. Example 9C was shown to have a similar level of cleaning compared to the control Example 9A, at a loading level of only 10%, indicating a very good cleaning performance. The RDA values for inventive Examples 9B and 9C were the same or lower than the ZEODENT® 103 control formulation of 9A, indicating acceptable levels of abrasion.

[0147] Overall Assessment

[0148] It has been found that a reduced LOI, lower BET SA and the presence of phosphate allows for improved compatibility with peroxide. The lower the surface area requires the less P from a phosphate containing additive that needs to be present on the silica surface before the heat treatment step (calcination) to improve compatibility. With surface area values for silicas less than 1 m2 / g, it would found that no phosphate is needed before the calcination step to improve the compatibility with peroxide. But even these very low BET SA silica is being used and phosphate is added, compatibilities of up to 120 days can be achieved.

[0149] Regardless of the surface area, a calcination step was needed to improve peroxide compatibility, which results in a reduction in the LOI values of the silica. Not to be bound by any particular theory, it is believed that heat treatment causes all impurities found on the silica surface to convert to less soluble forms so that di and tri valent ions do not readily act to decompose peroxide. It also reduces the -OH density on the silica surface as a result.

[0150] It is not clear at this time if the reduction in -OH density is necessary, but it occurs as a result of heat treatment step. Also critical is the presence of P on the silica surface. The P likely forms a metal pyrophosphate species on the surface of the silica, which further prevents the metal ion impurities to participate in Fenton type reactions to decompose the peroxide and essentially passivates the surface of the silica with a peroxide protective layer, thereby increasing the peroxide compatibility.

Claims

CLAIMS1. A heat treated precipitated silica material characterized by; a phosphate content of 25 to 1500 ppm, preferably 50 to 1300 ppm, a loss on ignition of less than 1 .4 wt. %, preferably less than 1 .25 wt. % and a BET surface area of equal or less than 20 m2 / g, preferably less than 6 m2 / g, more preferably less than 4 m2 / g.

2. The heat treated precipitated silica material according to claim 1 characterized by; a phosphate content of 25 to 200 ppm, a loss on ignition of less than 1 .25 wt. % and a BET surface area of less than 2 m2 / g, preferably less than 1 m2 / g.

3. The heat treated precipitated silica material according to any preceding claims wherein; Median Particle Size (D50) is between 7 to 15 pm, preferably is 8 to11 pm.

4. The heat treated precipitated silica material according to any preceding claims wherein; oil absorption is between 20 to 80 cc / 100 g; preferably from 30 to 60 cc / 100 g.

5. A heat treated precipitated silica material characterized by; a phosphate content of at least 1500 ppm, preferably 1500 to 2500 ppm, a loss on ignition of less than 1 .4 wt. %, preferably less than 1 .25 wt. % and a BET surface area of more than 20 m2 / g, preferably more than 20 m2 / g to 100 m2 / g.

6. The heat treated precipitated silica material according claim 5 wherein; Median Particle Size (D50) is between 10 to 25 pm.

7. The heat treated precipitated silica material according to claims 5 or 6 wherein; the oil absorption is in a range from 100 to 250 cc / 100 g.

8. The heat treated precipitated silica according to claims 1 to 7, wherein the silica is obtained by phosphate addition to the precipitated silica in an aqueous medium followed by calcination of the silica.

9. A process for preparing a heat treated precipitated silica material according to claims 1 to 8 comprises the following steps; a) providing a precipitated silica material in an aqueous medium, b) adding a phosphate material into the precipitated silica slurry and mixing it, c) spray drying the silica to a moisture level of lower than 10% and optionally milling, d) calcining the silica at a temperature of greater than 700 °C to reduce the LOI to a level of less than 1 .4 wt. %.

10. The process for preparing the heat treated precipitated silica according to claim 9, may comprise below further steps as; a) providing an alkaline silicate solution comprising an alkali metal silicate such as sodium silicate and water, b) adding sulfuric acid and alkaline silicate solutions together with agitation, c) precipitation of the silica and filtering the precipitated silica followed by washing of salts, d) addition of an appropriate amount of a phosphate salt to the silica slurry before drying, e) spray drying the silica to a moisture level of lower than 10% and optionally milling and f) calcining the silica at a temperature of greater than 700 °C to reduce the LOI to less than 1 .4 wt. %.

11. The process for preparing the heat treated precipitated silica according to claims 9 or 10, wherein the phosphate material is added to the mixture at a level of above 200 ppm for a silica having a BET surface area of equal or less than 20 m2 / g; or at a level of above 5000 ppm for silica having a BET surface area of more than 20 m2 / g.

12. The process for preparing the heat treated precipitated silica according to claims 9 to 11 , wherein the calcination is applied at a temperature between 700 to 1000 °C for 1 to 120 minutes, preferably at 825 °C for 60 minutes.

13. The process for preparing the precipitated silica material according to claims 9 to 12, wherein the additional phosphate material is selected from the group polyphosphates, orthophosphates or pyrophosphates such as; sodium tripolyphosphate (STTP), tetrasodium pyrophosphate (TSPP) and any mixtures thereof.

14. Use of precipitated silica material according to claims 1 to 8, in oral care compositions wherein the oral care composition is a toothpaste formulation comprising a peroxide-releasing compound, and optionally an abrasive silica, a fumed silica thickener and / or a fluoride source.

15. An oral care composition comprising the heat treated precipitated silica according to claims 1 to 8, wherein the composition comprises the silica from 3 to 35% by total weight of the composition.

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