Spray calcined silica in flame reactor

Abstract

The invention relates to a method for preparing a thermal treated precipitated silica by application of spray calcination, precipitated silica obtained thereof and the use of thermal treated precipitated silica in oral care applications.

Description

[0001] SPRAY CALCINED SILICA IN FLAME REACTOR

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention is in the field of thermal treated precipitated silica(s) obtained by spray calcination by spraying silica into a flame reactor and the use of thermal treated precipitated silicas mainly in oral care applications.

[0004] BACKGROUND OF THE INVENTION

[0005] The invention relates to a thermal treated precipitated silica obtained by application of spray calcination conducted by means of a flame spray by subjecting flame on silica in a flame reactor and the method of production thereof. The invention also relates to the use of thermal treated precipitated silica in oral care applications that has reduced -OH density and improved thickening and / or cleaning performance.

[0006] There has been a growing interest in the use of thermal treated precipitated silicas for different applications such as; oral care compositions or cosmetic applications.

[0007] Commercial oral care compositions, such as dentifrices, lozenges, chewing gums, etc., generally contain a variety of constituents. These constituents (such as therapeutic agents, carrier fluids, humectants, abrasives, thickeners, flavorings, fragrances, etc.) are typically selected based on various criteria such as cost, efficacy and compatibility.

[0008] There is a constant desire from toothpaste manufacturers to improve the performance of their products. Since precipitated silica thickeners and / or cleaners account from 1-30% of the toothpaste formulation, improving or at least keeping the level of compatibility of silica with active ingredients if of constant interest. Progress has been made improving relationships between surface area, hydroxy (-OH) density and the ability of a silica to absorb ingredients such as cetylpyridinium chloride and stannous fluoride have been used to develop new, low surface area silica products. While these types of products function well as cleaning silicas, reducing the hydroxy (-OH) density and / or surface area dramatically reduces the ability the thickening silicas to deliver the proper rheological performance.

[0009] WO 93 / 23007, Grace filing is in the field of an oral care composition containing thermal treated silicas to improve the compatibility without a focus on stannous or fluoride compatibility impact, but with application of pre-treatment and longer calcination treatment which will have negative impact on thickening performance.

[0010] US 2016 / 2501 14 A1 , P&G filing is also in the field of a process for heat treatment of precipitated silica particles and to oral care compositions comprising such treated precipitated silica particles, wherein treatment occurs at higher temperatures in shorter time periods, but still in minutes, and does not provide the desired thickening property.

[0011] US 2021 / 0163304 A1 , Evonik filing relates to a process for preparing metal silicate / zeolites within the form of crystalline silicates by use of a flame spraying, which are not in the field of oral care applications. None of above disclosed prior arts disclose spray calcination of silica slurry conducted by means of a flame spray in seconds or less than seconds by reducing the -OH density on the surface of silica as described in the present invention in order to improve, the cleaning performance (abrasiveness) of the precipitated silica while no significant decrease have been observed on surface area and improved thickening performance when being used in an oral care composition. While reducing the -OH surface density, at least the stannous and fluoride compatibility of silica should be improved or preserved, but without subjecting to heat for a long time which negatively effects the thickening performance.

[0012] Therefore, there is a need of process improvement to obtain reduced silanol (-OH) density on the surface of precipitated silica without negatively effecting the thickening, compatibility and / or cleaning properties.

[0013] It is therefore an object of the present invention to provide spray dried precipitated silica conducted via flame spraying in seconds or less than seconds, having reduced silanol density and increased cleaning effect while keeping the desired thickening performance and compatibility in the oral care formulation.

[0014] BRIEF SUMMARY OF THE INVENTION

[0015] After thorough investigations, the inventors of the present invention have surprisingly found that applying spray calcination of precipitated silica via a flame spray in a flame reactor wherein the residence time of silica in the flame reactor is about less than one second to seconds, solves the above technical problem as it provides reduced silanol density on silica surface with a reduced Sears number which is a direct measure of -OH density on silica surface, reduced LOI as it is an indicator that the silica material has been heated sufficiently to have a dehydroxylated surface, without reducing the surface area or pore volume to the extent that negatively affects the thickening performance or introduces unwanted crystallinity into the silica material.

[0016] The present invention provides a method to reduce the -OH density of the silica surface by increasing the degree of polymerization of the silica by flame spraying in a very short time period without significantly reducing the surface area, active stannous and fluoride compatibility, absorption abilities and negatively compromising the thickening performance.

[0017] Spray calcination of the silica slurry is conducted by means of flame spray in a flame reactor in less than one second wherein the adiabatic temperature of the flame in the flame reactor is between 600 - 1500 °C wherein all gases are included in the calculation (also the secondary air as mentioned in the examples below). Accordingly, temperature in the flame reactor is definitely much more higher than the temperature outside of the reactor.

[0018] Advantageously, the precipitated silica obtained by the method as defined in claim 1 provides reduced -OH density on silica surface while preserving the stannous and fluoride compatibility with an improved cleaning performance / abrasiveness, especially when used in oral care formulations.

[0019] Therefore, in a first aspect, the present invention relates to thermally treated precipitated silica obtained by subjecting the precipitated silica particles to a flame by subjection flame on silica surface in a flame reactor, as described in claim 1 .

[0020] A second aspect of the present invention is a process for obtaining the heat treated precipitated silicas wherein the flame reaches an adiabatic combustion temperature in a range of 600-1500 °C and the residence time of the silica in the flame reactor is from 0.1 to 10 seconds.

[0021] A third aspect of the invention is use of thermally treated precipitated silica in oral care formulations for improved cleaning performance.

[0022] BRIEF DESCRIPTION OF THE FIGURES

[0023] For the purpose of better illustrating the object of the present invention, advantages and properties of the claimed precipitated silica obtained by the method defined in the claims; SEM images, pore size distribution charts and compatibility charts are provided to present the improved effect of the present invention with non-limiting examples.

[0024] In the examples, commercially available Evonik precipitated silica grades have been used for flame spray calcination.

[0025] Figure 1 : SEM images of AC EM ATT® HK 400 control (Comparative example 1 B) at 5,000x (left) and 50,000x (right).

[0026] Figure 2: SEM images of ACEMATT® HK 400 spray calcined (Inventive Example 2A) at 10,000x (left) and 50,000x (right).

[0027] Figure 3: SEM images of ACEMATT® HK 400 spray calcined (Inventive Example 2B) at 5,000x (left) and 50,000x (right).

[0028] Figure 4: SEM images of ZEODENT® 168 control (Comparative example 1 A) at 5,000x (left) and 50,000x (right).

[0029] Figure 5: SEM images of ZEODENT® 168 spray calcined (Inventive Example 3A) at 5,000x (left) and 50,000x (right).

[0030] Figure 6: SEM images of ZEODENT® 168 spray calcined (Inventive Example 3B) at 5,000x (left) and 50,000x (right).

[0031] Figure 7: Isotherm and BJH pore size distribution charts for ACEMATT® HK400 control (Comparative Example 1 B) and ACEMATT® HK400 spray calcined (Inventive Example 2B)

[0032] Figure 8: Isotherm and BJH pore size distribution charts for ZEODENT® 168 control (Comparative Example 1A), ZEODENT® 168 spray calcined and (Comparative Examples 3A and 3B)

[0033] Figure 9: Toothpaste viscosity chart showing the comparison of ZEODENT® 165, ACEMATT® HK 400 control (Example 1 B) and spray calcined ACEMATT® HK 400 (Example 2B), and ZEODENT® 168 control (Example 1A) and spray calcined ZEODENT® 168 (example 3A) and (Example 3B).

[0034] Figure 10: SEM images of ZEODENT® 113 control (Comparative Example 4A) at 5,000x (left) and 50,000x (right).

[0035] Figure 11 : SEM images of ZEODENT® 113 spray calcined (Inventive Example 5A) at 5,000x (left) and 50,000x (right). Note the lack of fusing in the primary structure of the image at 50,000x.

[0036] Figure 12: SEM images of ZEODENT® 113 spray calcined (Inventive Example 5B) at 5,000x (left) and 50,000x (right).

[0037] Figure 13: Isotherm and BJH pore size distribution for ZEODENT® 113 spray dried compared to spray calcined example (Example 5A) and (Example 5B).

[0038] Figure 14: Hgl Isotherm and pore size distribution for ZEODENT® 113 spray dried compared to spray calcined and (Examples 5A and 5B).

[0039] Figure 15, 16, 17: Fluoride compatibility, Sn compatibility and 5%pH trends of ZEODENT® 113 (Example 4B) made standard calcination compared to spray calcination method (Example 5B).

[0040] DETAILED DESCRIPTION OF THE INVENTION

[0041] The invention provides a new method for spray calcination of precipitated silicas and inventive calcined precipitated silica to be used in oral care compositions wherein the sears number and LOI is reduced which are direct measure of lowered -OH density on the surface of the silica. Calcination processes are known in the art wherein calcination is applied to a precipitated silica whereby the silica is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air).

[0042] Calcination can be carried out in a furnace or reactor (sometimes referred to as kilns or calciners) of various designs including shaft furnaces, rotary kilns, multiple hearth furnaces, and fluidized bed reactors. Spray calcination of silica slurries by means of a flame spray is new to the art and within the present invention it has been detailed as below.

[0043] The invention is further illustrated by the following embodiments. However, the invention is not limited to the details of the embodiments below.

[0044] The present invention relates to a thermally treated precipitated silica obtained by spray calcination, by subjecting the precipitated silica particle to hot air by means of a flame spray wherein the adiabatic combustion temperature of the flame in the flame reactor is between 600 °C - 1500 °C, and wherein said thermally treated precipitated silica particle has;

[0045] LOI less than 3 % and

[0046] Sears number less than 11 .

[0047] The silica is subjected to a hot air in that the average residence time of the silica in the reactor is in a range from 0.1 to 10 seconds, preferably from 0.1 to 1 .5 seconds.

[0048] Second aspect of the present invention is a process for spray calcination of silica, wherein the calcination is carried out by means of flame spray at an adiabatic combustion temperature in a range of 600-1500 °C, and the average residence time of the silica in the reactor is in a range from 0.1 to 10 seconds; preferably at an adiabatic combustion temperature between 700 °C - 1400 °C and the average residence time of the silica in the reactor is in a range from 0.1 to 1 .5 seconds.

[0049] Third aspect of the present invention is the use of thermal treated precipitated silica in an oral care composition.

[0050] Yet another aspect of the invention is an oral care composition comprising the thermal treated precipitated silica and at least one therapeutic agent.

[0051] In one embodiment of the present invention, precipitated silica is subjected to a hot flame for 1 second, preferably less than 1 second, wherein the adiabatic combustion temperature of the hot flame is between 800 °C - 1300 °C .

[0052] In one embodiment of the invention, the calcination temperature can be measured 1 .5 m below the ignition site (°C), as shown in the examples and Figures 15 to 17, wherein the calcination temperature (hot air flame temperature) measured 1.5 m below the ignition site (°C) is between 100 to 850 °C, preferably 300 to 750 °C, most preferably between 500 to 700 °C.

[0053] In one embodiment of the present invention, precipitated silica has a sears number from 11 ml / 1 .5 g to 1 ml / 1 .5 g.

[0054] In one embodiment of the present invention, thermally treated precipitated silica has a LOI equal or less than 2.5 %. In one embodiment of the present invention, thermally treated precipitated silica has a quartz content of less than 0.1 %, preferably less than 0.05%.

[0055] In one embodiment of the present invention, thermally treated precipitated silica has a stannous (Sn) compatibility greater than 40% silica.

[0056] In one embodiment of the present invention, thermally treated precipitated silica has a fluoride compatibility (F) of greater than 63% , preferably in the range of 65 to 73 % . In one embodiment of the present invention, thermally treated precipitated silica has an Acorn SA in the range of from 9.5 to 4 m2 / g.

[0057] In one embodiment of the present invention, the thermally treated precipitated silica has median particle size from 1 to 100 pm.

[0058] In one embodiment of the present invention, thermally treated precipitated silica has a BET surface area from 20 to 250 m2 / g, preferably from 40 to 60 for cleaning silica or preferably from 140 to 180 m2 / g for thickening silica.

[0059] In one embodiment of the present invention, thermally treated precipitated silica has a CTAB surface area from 20 m2 / g to 250 m2 / g, preferably from 40 to 60 for cleaning silica or preferably from 140 to 180 m2 / g for thickening silica.

[0060] In one embodiment ofthe present invention, thermally treated precipitated silica has a pore volume of at between 0.5- 1 .5 cm3 / g.

[0061] In one embodiment of the present invention, an oral care composition may comprise treated precipitated silica according to invention, from 3 to 35% by total weight ofthe composition.

[0062] Method of Spray Calcination by Means of Flame Spray:

[0063] The main disadvantage of the known thermal treatment application is reduction of porosity and surface area, loss of absorption abilities which all reduces the thickening performance of the precipitated silica, mainly due to the residence time of silica in a reactor and being subjected to heat for a longer time in the reactor.

[0064] According to the present invention, the thermal treatment is not performed to such an extent as to result in a loss of porosity and reduced surface area which will negatively affect the thickening performance.

[0065] According to the present invention, spray calcination occurs in a very short time period by providing all desired technical effects without a requirement of pre-drying step which requires longer residence time under high temperatures.

[0066] According to the present invention, the spray calcination conducted via flame spray in a flame reactor wherein the hot air flame is subjected to the surface of silica. The heating is performed at an adiabatic temperature in between 600 to 1500 °C in less than one second to seconds in the flame reactor, preferably at a temperature between 700 °C - 1400 °C, more preferably between 800 °C - 1300 °C and the average residence time ofthe silica in the reactor is in a range from 0.1 to 10 seconds, preferably from 0.1 to 1 .5 seconds.

[0067] According to the present invention, the process for obtaining thermally treated precipitated silica is followed as below; the silica containing solution (silica slurry) is sprayed into flame reactor and hot air flame is sprayed on the silica surface by means of a flame spray wherein the flame has an adiabatic combustion temperature in a range of 600-1500 °C, and the average residence time ofthe silica in the flame reactor is in a range from 0.1 to 10 seconds.

[0068] The heating may be performed at reduced pressure to facilitate removal of gases evolving from the dehydroxylation (i.e. H2O).

[0069] Method of Measurements

[0070] BET and CTAB Surface Area Measurement and Pore Volume Measurement

[0071] The BET surface areas and the pore volumes (total mercury intrusion pore volumes) disclosed herein were determined on a Micromeritics TriStar II 3020 V1 .03 using, respectively, the BET nitrogen adsorption method of Brunaur et al., J. Am. Chem. Soc., 60, 309 (1938), and BJH Adsorption / Desorption isotherms with a Halsey Faas Correction, Halsey, G.D., J. Chem. Phys. (1948), 16, pp. 931 , and such techniques are well known to those skilled in the art.

[0072] CTAB surface areas disclosed herein were determined by absorption of CTAB (cetyltrimethylammonium bromide) on the silica surface, the excess separated by centrifugation and the quantity determined by titration with sodium lauryl sulfate using a surfactant electrode. Specifically, about 0.5 grams of the silica and / or silicate particles were placed in a 250-mL beaker with 100 mL CTAB solution (5.5 g / L), mixed on an electric stir plate for 1 hour, then centrifuged for 30 min at 10,000 RPM. One mL of 10% Triton X-100 was added to 5 mL of the clear supernatant in a 100-mL beaker. The pH was adjusted to 3-3.5 with 0.1 N HCI and the specimen was titrated with 0.01 M sodium lauryl sulfate using a surfactant electrode (Brinkmann SUR1501-DL) to determine the endpoint.

[0073] According to the present invention, no significant decrease have been observed on surface area that will negatively affect the thickening performance when being used in an oral care composition. The spray calcined precipitated silicas have a BET surface area from 20 m2 / g to 250 m2 / g after spray calcination treatment. The precipitated silicas have a CTAB surface area from 20 m2 / g to 250 m2 / g after spray calcination treatment.

[0074] According to the present invention, the spray calcined silica particles have a pore volume of at least about 0.5-1 .5 cm3 / g.

[0075] Loss of Ignition (LOI) Measurement:

[0076] According to the present invention, the extent of thermal de hydroxylation can be measured by determining the loss on ignition (LOI) for the silica. As referred to in this application, the LOI is determined by the % weight loss of the calcined sample compared to the weight of the non-treated sample.

[0077] Loss on Ignition (LOI) was determined by a thermogravimetric analysis (TGA) method. The appropriate quantity of sample was placed in a TA Instruments Model SDT Q60 TGA / DAC from TA Instruments, New Castle, DE, USA. It was heated for 2 hours under a gentle flow of nitrogen at 105 °C, followed by heating to 1000 °C at 20 °C / min. The LOI was the loss in weight between the temperatures of 105 and 1000 °C.

[0078] Sears Number Measurement:

[0079] The reduction in -OH density can be observed with a reduction in the Sears number of the silica particles. SEARS number measurement is being used to determine the number of silanol groups on the surface of silica based on titration. The specific consumption of sodium hydroxide solution depends primarily on the surface area and the silanol groups.

[0080] SEARS number was determined with a Titrando 809 from Metrohm.

[0081] 1.5g of sample is placed in a titration vessel and 150ml of sodium chloride (pH 3) solution is added, stirring and tempering the solution at 25°C. The starting pH can adjusted with diluted HCI to pH 4. The solution is titrated with O.l mol / L NaOH to pH 9. The titrator interpolates the consumption volume of sodium hydroxide solution at pH 4 and the end value at pH 9 and calculates the exact consumption from the difference.

[0082] According to the present invention, the sears number of the calcined precipitated silica is in the range of 11 ml / 1 ,5g to 1 ml / 1 ,5g

[0083] Acorn SA (the number of -OH groups on silica surface) Measurement: Acorn SA, which is an NMR technique to determine surface area of solid particles in a slurry, uses differences in the relaxation times of a protic solvent (e.g. water or ethanol, etc.) that is associated with a particle surface compared to that of the bulk solvent. With the silica particles, the strength of the interaction of the water with the silica surface is dependent on the -OH density of the silica surface. Since the interaction is weaker as the number of -OH groups is reduced, the measured surface area value decreases accordingly.

[0084] Acorn surface area was measured on an Acorn Surface Area Analyzer from XiGo Nanotools, Bethlehem, Pennsylvania, USA. Samples were run at 10.5% solids with a bulk relaxation time of 2100 ms and the ka value was determined by the procedure outlined in the operating instructions. The T2 relaxation time was initially set to 100 and was adjusted appropriately during the sample measurement process.

[0085] Compatibility Measurement (Stannous and Fluoride Compatibility):

[0086] Stannous compatibility (%) was determined as follows.

[0087] A stock solution containing 431.11 g of 70% sorbitol, 63.62 g of de-oxygenated deionized water, 2.27 g of stannous chloride dihydrate, and 3 g of sodium gluconcate was prepared. 34 g of the stock solution was added to a 50 mL centrifuge tube containing 6 g of the silica sample to be tested. The centrifuge tube was placed on a rotating wheel at 5 RPM and was aged for 1 week at 40 °C. After aging, the centrifuge tube was centrifuged at 12,000 RPM for 10 minutes, and the stannous concentration in the supernatant was determined by ICP-OES (inductively coupled plasma optical emission spectrometer). The stannous compatibility was determined by expressing the stannous concentration of the sample as a percentage of the stannous concentration of a solution prepared by the same procedure, but with no silica added.

[0088] Fluoride compatibility (%) was determined as follows.

[0089] 3.5g of silica was added to a 50mL centrifuge tube containing 12.00g of stannous fluoride stock solution, which was previously prepared by combining 0.34g of stannous fluoride, 0.48g of sodium gluconate and 74.30 g of deionized water. The solution was rotated in an oven at 60 °C for 2 hours. After heating, it was centrifuged for 15 minutes at 15,000RPM to obtain a clear supernatant. 2.0g of supernatant was added to 18.00 g of EDTA / THAM buffer solution and the fluoride concentration was determined by fluoride ion selective electrode. The fluoride compatibility was determined by dividing the values for the test sample by a control sample where no silica has been added.

[0090] The compatibility of the silica with a particular therapeutic agent can be measured by comparing the availability or concentration of the therapeutic agent in a mixture at a reference pH before and after contact with the silica. The compatibility of the silica may be expressed as the percentage ratio of concentration of the agent in the mixture after contact with the silica to the concentration of the agent in the mixture before silica addition. The pH of the silica-containing mixture is preferably adjusted to the reference pH on addition of the silica. The concentration after contact with silica is preferably measured after separation of the silica from the mixture. The method of determining the concentration of the therapeutic agent may be any conventional method suitable for the particular agent (e.g. ultraviolet light absorption).

[0091] The improvement in compatibility would simply involve comparison of the compatibility values for the untreated and treated silicas. The compatibility test may be applied to all spray calcined silicas and any degree of improvement in compatibility would be encompassed by the invention, preferably the spray calcination treatment of the invention results in at least about 5% improvement in compatibility in comparison with the untreated silica.

[0092] According to the present invention, the spray calcined precipitated silicas comprises a stannous compatibility of greater than 40%.

[0093] According to the present invention, the spray calcined precipitated silicas comprises a fluoride ion compatibility of greater than 60%, preferably greater than 63%.

[0094] Quartz Measurement:

[0095] Calcined silica samples were evaluated on a D2 phaser powder x-ray diffractometer from Bruker Corporation, Billerica, MA, USA. 3.00g samples of spray calcined silica were heated with 25 mL of 85% orphophosphoric acid to dissolve any non-crystalline silica material. After cooling, the sides of the beaker containing the orthophosphoric acid were washed with 100 mL of hot deionized water, followed by 10mL of fluoroboric acid, followed by an additional rinse with 25 mL of deionized water. After allowing to stand for 60 minutes at room temperature, 5% Aerosol OT (American Cyanamid) was then added and the solution was exposed to ultrasound for 15 minutes. The solids were separated by filtration and dried at 105 °C they were then analyzed by powder x-ray diffraction. Peaks at 26.66° 20 were for quartz and 21 .93° 20 were for the presence of cristobalite. The peak intensities were then compared with calibration curves prepared with quartz and cristobalite standards (NIST SRM 1878a- alpha quartz and NIST 1879- cristobalite) at different concentrations to determine the quantity of crystalline material present. The crystalline material was then expressed as a percentage based on the original 3.00g sample weight to determine the amount of crystalline silica that was present in the silica sample.

[0096] Spray calcination conducted by flame spray in less than seconds does not enable crystalline forms and accordingly the silicas are available for oral care formulations. The inventive silica should not induce crystallinity, but must be enough to cause a reduction in the -OH density of the silica. According to the present invention, the spray calcined precipitated silica comprises Quartz of lower than 0.1 %.

[0097] The silica treated in accordance with the invention may be any silica conventionally used in dentifrices or other oral care compositions. Preferably, the silica is an amorphous silica gel or an amorphous precipitated silica. Amorphous silica gels and precipitated silicas are typically used in dentifrices or other oral care compositions as abrasives / cleaners and / or thickeners.

[0098] The treatments of the invention provide improved compatibility of the silica with therapeutic agents in general at pH values commonly used in dentifrice and other oral care compositions (e.g. a pH of about 6- 7). The treatments within the present invention also result in improved compatibility at more acidic or basic pH levels. Measurement:

[0099] For tamped density (packed density), 20 grams of the sample was placed into a 250 mL graduated cylinder with a flat rubber bottom. The initial volume was recorded. The cylinder was then placed onto a tap density machine where it was rotated on a cam at 60 RPM. The cam is designed to raise and drop the cylinder a distance of 5.715 cm once per second, until the sample volume is constant, typically for 15 min. This final volume is recorded and used to calculate the packed density by dividing it into the weight of sample used. The pH values disclosed herein (5% pH) were determined in an aqueous system containing 5 wt. % solids in deionized water using a pH meter.

[0100] Dioctyadipate (DOA) absorption measurements were made on a Brabender Torque Rehometer from C.W. Brabender Instruments, Inc., South Hackensack, NJ, USA. Samples were run according to ASTM 2414.

[0101] Oral Care Compositions

[0102] The treated 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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, ACEMATT 400, all available from Evonik Corporation.

[0109] Abrasive or cleaning silicas; for utilization within a toothpaste composition, for example, include, as a nonlimiting example, ZEODENT 103, 113, 120, 124, 116 all available from Evonik Corporation.

[0110] 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 discussed herein or 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.

[0111] 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. %.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] EXPERIMENTAL PART

[0118] The invention is further illustrated in detail hereinafter with reference to inventive examples and comparative examples, without any intention to limit the scope of the present invention.

[0119] The thermal treated precipitated silica is being calcined as defined in claims 1 to 3, by use of flame spray pyrolysis within the given adiabatic temperature and resilience time in the reactor.

[0120] As already disclosed in US 2021 / 0163304 A1 reference from Evonik itself, the term “flame spray pyrolysis” is well known to the person skilled in the art and relates to a process for thermal oxidative conversion of a liquid raw material finely distributed in the gas stream by spraying or of a suspension in a flame generated by combustion of a fuel in the presence of oxygen.

[0121] Examples of fuels used in the process according to the invention include hydrogen, methane, ethane, propane, butane, natural gas and mixtures thereof. These are preferably supplied in a gaseous state to the reactor suitable for the performance of calcination.

[0122] The oxygen can be fed in in the form of any oxygenous gas. Preference is given to using air. The adiabatic combustion temperature is a standard parameter, as also described in the given US prior art, in the specialist field for characterization of the combustion process of at least one fuel and an oxidant, the state of which is known prior to commencement of the combustion. Accordingly, the adiabatic combustion temperature, for example in a corresponding reactor, can be calculated in a manner known to the person skilled in the art from the known process parameters such as preheating temperatures, mass flow rates et al. Accordingly, the applicant hereby refers to the mentioned US 2021 / 0163304 A1 reference regarding the details and technical interpretations of calcination process by means of a flame spray hydrolysis.

[0123] The temperature of the flame itself and also what the SiO2 particles are directly be subjected to might be higher, such as from 600 to 2200° C. Therefore the adiabatic combustion temperature during the process according to the invention can be measured within a range from 600 to 2200 °C. The adiabatic combustion temperature is especially preferably within a range from 600 to 1500 °C. , more preferably within a range from 700 to 1400 °C and more preferably within a range from 800 to 1300 °C According to the site of measurement thereof, the temperature actually generated in the flame varies within a relatively wide range. For instance, according to the invention, the temperature measured 1 .5 m beneath the ignition site may be at least 100 °C.; preferably, the temperature 1 .5 m below the ignition site is within a range from 100 to 850 °C, preferably between 300 to 750 °C..

[0124] The average residence time of the silica solution in the reactor for the performance may be from 1 ms to 100 s. Preferably, the average residence time is within a range from 0.1 to 10 s; more preferably within a range from 0.5 to 5 s.

[0125] The calculation of the abovementioned average residence time in the reactor (t, [s]) is conducted using the total volume of gas fed to the reactor per unit time (Vt, [m3 / s (STP)]) and reactor volume (VR, [m3]). t=VR / VT

[0126] The abovementioned temperatures and the average residence time in the reactor according to the invention are preferably selected such that the oxidative breakdown of the organic template takes place in this step, but the product obtained is not damaged by high temperatures. Thus, if a relatively high flame temperature which, could lead to irreversible changes in the pore structure and also compatibility within formulations , it is advantageous to choose a relatively short residence time in the flame.

[0127] Below given example set 1 and set 2 refers different types of silicas being used in oral care formulations. Examples set 1 refers to thickening silicas, and example set 2 refers to cleaning silicas.

[0128] Example Sets:

[0129] Example Set 1 (Thickening silica)

[0130] ZEODENT® 168 is an commercial Evonik precipitated silica grade, that is used as one of the example. No heat treatment according to the invention is applied on the surface of precipitated silica.

[0131] ACEMATT® HK400 is an commercial Evonik precipitated silica grade, that is used as one of the comparative example. No heat treatment according to the invention is applied on the surface of precipitated silica.

[0132] Preparation of Inventive Examples 2A, 2B, 3A, 3B and Comparative Example 2C

[0133] Example 2A - (ACEMATT® HK400)- Spray Calcination with Flame

[0134] 10 kg / h of a solution containing 10 wt% silica in water (silica slurry) was sprayed into a tubular reactor with 15 Nm3 / h Nitrogen through a two-phase nozzle with internal diameter 2 mm and gap 1 mm forming an aerosol. The hydrogen / air flame was operated with 8.5 Nm3 / h of hydrogen and 27 Nm3 / h of primary air. 25 N m3 / h of a secondary air was added to prevent plugging at the reactor wall. The temperature measured 1 .5 m below the ignition site was adjusted to 500 °C. by slight variation of the hydrogen. The residence time of the silica in the reactor was 1-1 .5 seconds. The calculated adiabatic flame temperature, inside the flame reactor, considering all gases, is 804 °C.

[0135] The off gases, including calcined silica, were guided through a water-cooled cooling zone (coolant temperature: 25 °C) having a diameter of 100 mm and a length of 6 m and then collected at filter candles at max. 250 °C. By sequential cleaning of the filter candles, it was possible to collect the ready-calcined product owing to the high ignition loss, and compatible when being used in toothpaste formulation.

[0136] Example 2B - (ACEMATT® HK400) - Spray Calcination with Flame

[0137] 10 kg / h of a solution containing 10wt% silica in water (silica slurry) was sprayed into a tubular reactor with 15 Nm3 / h Nitrogen through a two-phase nozzle with internal diameter 2 mm and gap 1 mm forming an aerosol. The hydrogen / air flame was operated with 11.7 Nm3 / h of hydrogen and 27 Nm3 / h of primary air. 25 N m3 / h of a secondary air was added to prevent plugging at the reactor wall. The temperature measured 1 .5 m below the ignition site was adjusted to 700 °C. by slight variation of the hydrogen. The residence time of the silica in the reactor was 1-1 .5 seconds. The calculated adiabatic flame temperature, inside the flame reactor, considering all gases, is 1044 °C.

[0138] The off gases, including calcined silica, were guided through a water-cooled cooling zone (coolant temperature: 25 °C) having a diameter of 100 mm and a length of 6 m and then collected at filter candles at max. 250 °C. By sequential cleaning of the filter candles, it was possible to collect the ready-calcined product owing to the high ignition loss, and compatible when being used in toothpaste formulation.

[0139] Example 2C - (ACEMATT® HK400) - Spray Calcination with Flame at higher temperatures

[0140] 10 kg / h of a solution containing 10 wt% silica in water (silica slurry) was sprayed into a tubular reactor with 15 Nm3 / h Nitrogen through a two-phase nozzle with internal diameter 2 mm and gap 1 mm forming an aerosol. The hydrogen / air flame was operated with 16.2 Nm3 / h of hydrogen and 27 Nm3 / h of primary air. 25 N m3 / h of a secondary air was added to prevent plugging at the reactor wall. The temperature measured 1 .5 m below the ignition site was adjusted to 900° C. by slight variation of the hydrogen. The residence time of the silica in the reactor was 1-1 .5 seconds. The calculated adiabatic flame temperature, inside the flame reactor, considering all gases, is 1366 °C.

[0141] The off gases, including calcined silica, were guided through a water-cooled cooling zone (coolant temperature: 25 °C) having a diameter of 100 mm and a length of 6 m and then collected at filter candles at max. 250 °C. By sequential cleaning of the filter candles, it was possible to collect the ready-calcined product owing to the high ignition loss, and compatible when being used in toothpaste formulation.

[0142] Example 3A - (ZEODENT® 168)- Spray Calcination with Flame

[0143] 10 kg / h of a solution containing 10 w% silica in water (silica slurry) was sprayed into a tubular reactor with 15 Nm3 / h Nitrogen through a two-phase nozzle with internal diameter 2 mm and gap 1 mm forming an aerosol. The hydrogen / air flame was operated with 9 Nm3 / h of hydrogen and 27 Nm3 / h of primary air. 25 N m3 / h of a secondary air was added to prevent plugging at the reactor wall. The temperature measured 1 .5 m below the ignition site was adjusted to 700 °C. by slight variation of the hydrogen. The residence time of the silica in the reactor was 1-1 .5 seconds. The calculated adiabatic flame temperature, inside the flame reactor, considering all gases, is 843 °C.

[0144] The off gases, including calcined silica, were guided through a water-cooled cooling zone (coolant temperature: 25 °C ) having a diameter of 100 mm and a length of 6 m and then collected at filter candles at max. 250 °C. By sequential cleaning of the filter candles, it was possible to collect the ready-calcined product owing to the high ignition loss, and compatible when being used in toothpaste formulation.

[0145] Example 3B - (ZEODENT® 168) - Spray Calcination with Flame

[0146] 10 kg / h of a solution containing 10 wt% silica in water (silica slurry) was sprayed into a tubular reactor with 15 Nm3 / h Nitrogen through a two-phase nozzle with internal diameter 2 mm and gap 1 mm forming an aerosol. The hydrogen / air flame was operated with 12.3 Nm3 / h of hydrogen and 27 Nm3 / h of primary air. 25 N m3 / h of a secondary air was added to prevent plugging at the reactor wall. The temperature measured 1 .5 m below the ignition site was adjusted to 700 °C. by slight variation of the hydrogen. The residence time of the silica in the reactor was 1-1 .5 seconds. The calculated adiabatic flame temperature, inside the flame reactor, considering all gases, is 1088 °C.

[0147] The off gases, including calcined silica, were guided through a water-cooled cooling zone (coolant temperature: 25 °C) having a diameter of 100 mm and a length of 6 m and then collected at filter candles at max. 250° C. By sequential cleaning of the filter candles, it was possible to collect the ready-calcined product owing to the high ignition loss, and compatible when being used in toothpaste formulation.

[0148] Table 1 : Physical Properties of Precipitated Silica Examples

[0149] Table 2: Chemical Properties of Precipitated Silicas

[0150] Table 1 and Table 2 provide the chemical and physical properties of precipitated silicas of the comparative and inventive examples. Several interesting improved effects observed from the spray calcination of the silica particles. Without applying any pre-treatment (such as simple drying) or providing high temperatures for a long time, the particles were exposed to a zone of hot air (heat-treatment with flame) sufficient to increase the degree of polymerization of the silica particles, which means that the silica material has been heated sufficiently to have a dehydroxylated surface (reduced SEARS number). This increased degree of polymerization results in a decrease in the loss on ignition (LOI) of the silica particles. The lower LOI should result in a higher particle hardness, resulting in higher cleaning values and a low -OH density on the silica surface. The lower -OH density, if it is stable to rehydration when exposed to an aqueous environment, should result in a more inert silica particle that is more compatible with ingredients that typically interact with -OH groups. Acorn SA value also indicates the loss of -OH density on the surface of silica particles.

[0151] The reduction in -OH density can be observed with a reduction in the Sears number of the silica particles. When the silica is being treated according to the present invention, such as after spray calcination, the ACEMATT® HK400 (inventive example 2B) sears number dropped from 14.88 ml / 1 .5g to 6.40 ml / 1 .5g, indicating a reduction in the -OH density on the silica surface.

[0152] Acorn SA, which is an NMR technique to determine surface area of solid particles in a slurry, uses differences in the relaxation times of a protic solvent (e.g. water or ethanol, etc.) that is associated with a particle surface compared to that of the bulk solvent. With the silica particles, the strength of the interaction of the water with the silica surface is dependent on the -OH density of the silica surface. Since the interaction is weaker as the number of -OH groups is reduced, the measured surface area value decreases accordingly. It was observed that the Acorn SA of the ACEMATT® HK400 (inventive example 2B) decreased from 13.6 to 4.2 m2 / g after spray calcination, indicating a loss in -OH density on the silica surface. This loss in -OH density can also be observed with a decrease in CTAB SA values, but not to the extent that as with the Acorn SA values. Similar outcome regarding Sears number and Acorn SA together with LOI should be expected for Example 2A as well.

[0153] Figures 1 to 6 provide SEM images of the comparative (1A-B) and inventive examples (2A-B and 3A-B). The lack of fusing in the primary structure is obvious from Figures 2, 3 5 and 6, wherein spray calcination is applied on precipitated silica surface.

[0154] It is also critical to note that spray calcining at a very high temperature (e.g: Comparative example 2C) will result in the formation of quartz in with the silica sample. Quartz, with its crystalline nature, can be harmful and is not used in consumer products. Values for quartz must remain at baseline levels during the spray calcination process. Spray calcination temperatures must be kept low enough to not induce crystallinity, but must be high enough to cause a reduction in the -OH density of the silica surface to increase stannous ion compatibility. Example 2C; ACEMATT® HK400 is an comparative example of a silica with levels of crystallinity too high to be used in toothpaste formulations.

[0155] Below Table 3 provides the summary of nitrogen physisorption data for comparative and inventive examples.

[0156] Table 3: Summary of nitrogen physisorption data

[0157] Figure 7 provides a chart showing the nitrogen physisorption and BJH pore size distribution for ACEMATT® HK400 comparative example 1 B and spray calcined ACEMATT® HK400, example 2B. From there, it can be observed that BET surface area drops slightly during the heating process as shown in the nitrogen physisorption data plotted in Figure 7. There is a slight decrease observed in the pore volume of the silica upon heating, as indicated in the isotherm and BJH desorption pore diameter distribution, but there did not seem to be a meaningful shift in pore size or pore size distribution.

[0158] Figure 8 also provides a chart showing nitrogen physisorption and BJH pore size distribution for ZEODENT® 168 comparative example 1A, spray calcined ZEODENT® 168 example 3A and example 3B. A pore volume reduction was also observed with ZEODENT® 168. The drop in pore volume increased with increasing spray calcination temperature, and there was no shift in the pore size or pore size distribution with ZEODENT® 168 as well.

[0159] Oral Care Testing:

[0160] The silica samples are also formulated into toothpaste to compare the compatibility with stannous ions and fluoride ions as shown in below Table 4.

[0161] Toothpaste formulation shown in Table 5 is used, as the inventive treated thickening silica (2B) is formulated into a toothpaste formulation shown in Table 5, containing 18% ZEODENT® 113 as the cleaning silica.

[0162] Table 4: Ion Compatibility Results

[0163] Calcination from 800 to 1300 °C sufficient to create a stable surface (stable Si-O-Si bonds) with a lower -OH density. It is obvious from Table 4 that compatibility with stannous ions increased upon spray calcination for ACEMATT® HK400 from 31 to 62%. The highest increase is observed when the silica is calcined at 1044 °C. Fluoride values also increased from 58 to 67% as a result of the spray calcination step at 1044 °C. The refractive index did not shift, however, the transmittance did decrease from 62.5 to 34.1%.

[0164] The silica samples are formulated into toothpaste also to determine the viscosity change and confirm that the toothpaste viscosity is not negatively impacted as a function of spray calcination. In the below formulation shown in Table 5, the treated thickening silicas are formulated into a toothpaste formulation containing 18% ZEODENT® 113 as the cleaning silica.

[0165] Table 5: Example of a Toothpaste Formulations containing Spray Calcined Thickening Silicas Figure 9 provides a chart showing the Toothpaste viscosity comparison of ZEODENT® 165 ,ACEMATT® HK 400 control and spray calcined ACEMATT® HK 400 (2B), and ZEODENT® 168 control and spray calcined ZEODENT® 168 (3A) and (3B). It is observed that spray calcination of silica particles did not negatively impact their ability to deliver a viscosity build in toothpaste at the same level or higher than the ZEODENT® 165 control. ZEODENT® 165 is being used as the control silica since it is a well-known oral care thickening silica that has is commonly used in toothpaste formulations.

[0166] Table 6: Viscosity Measurements of the Toothpaste Formulations

[0167] According to the result table provided above, it is observed that the viscosity for all tested samples are suitable for use in toothpaste products. All spray calcined ACEMATT HK400 and ZEODENT® 168 prototypes showed increased viscosity performance that is a proof of allowability to be used in toothpaste formulations.

[0168] This method can be additionally employed to, lower pore volume, cleaning silicas to improve their cleaning efficacy, as well as, improve their compatibility with various actives at these relatively moderate temperature conditions.

[0169] Example Set 2 (Cleaning Silica):

[0170] Comparative Example 4A (ZEODENT® 113)

[0171] ZEODENT® 113 is an commercial Evonik precipitated silica grade, that is used as one of the comparative example. No treatment applied on the surface of precipitated silica.

[0172] Comparative Example 4B (ZEODENT® 113)

[0173] ZEODENT® 113 is an commercial Evonik precipitated silica grade, that is used as one of the comparative example. Standard calcination treatment, at 700 °C for 2 hours, was applied on the surface of precipitated silica.

[0174] Preparation of Inventive Examples 5A, 5B

[0175] Example 5A - ZEODENT® 113 -Spray Calcination with Flame

[0176] 10 kg / h of a solution containing 35wt% silica in water (silica slurry) was sprayed into a tubular reactor with 15 Nm3 / h Nitrogen through a two-phase nozzle with internal diameter 2 mm and gap 1 mm forming an aerosol. The hydrogen / air flame was operated with 7.7 Nm3 / h of hydrogen and 27 Nm3 / h of primary air. 25 N m3 / h of a secondary air was added to prevent plugging at the reactor wall. The temperature measured 1 .5 m below the ignition site was adjusted to 700 °C. by slight variation of the hydrogen. The residence time of the silica in the reactor was 1-1 .5 seconds. The calculated adiabatic flame temperature, inside the flame reactor, considering all gases, is 742 °C.

[0177] The off gases, including calcined silica, were guided through a water-cooled cooling zone (coolant temperature: 25 °C 25 N m3 / h ) having a diameter of 100 mm and a length of 6 m and then collected at filter candles at max. 250° C. By sequential cleaning of the filter candles, it was possible to collect the ready-calcined product owing to the high ignition loss, and compatible when being used in toothpaste formulation.

[0178] Example 5B - ZEODENT® 113 -Spray Calcination with Flame

[0179] 10 kg / h of a solution containing 35wt% silica in water (silica slurry) was sprayed into a tubular reactor with 15 Nm3 / h Nitrogen through a two-phase nozzle with internal diameter 2 mm and gap 1 mm forming an aerosol. The hydrogen / air flame was operated with 11.3 Nm3 / h of hydrogen and 27 Nm3 / h of primary air. 25 N m3 / h of a secondary air was added to prevent plugging at the reactor wall. The temperature measured 1 .5 m below the ignition site was adjusted to 700 °C. by slight variation of the hydrogen. The residence time of the silica in the reactor was 1-1 .5 seconds. The calculated adiabatic flame temperature, inside the flame reactor, considering all gases, is 1015 °C.

[0180] The off gases, including calcined silica, were guided through a water-cooled cooling zone (coolant temperature: 25 °C25 N m3 / h ) having a diameter of 100 mm and a length of 6 m and then collected at filter candles at max. 250 °C. By sequential cleaning of the filter candles, it was possible to collect the ready-calcined product owing to the high ignition loss, and compatible when being used in toothpaste formulation.

[0181] Table 7: Physical Properties of Precipitated Silica Examples

[0182] Table 8: Chemical Properties of Precipitated Silica Examples

[0183] Above Table 7 and Table 8 provide the chemical and physical properties of precipitated silicas according to the comparative and inventive examples.

[0184] The same characterization tests applied for the Example Set 2 as applied in Example Set 1 . Accordingly the same technical comments can be applied hereby such as reducing -OH density without decreasing the absorption abilities but improving the cleaning performance.

[0185] The spray calcination of the ZEODENT® 113 cleaning silica also resulted in downward trends in Sears number and Acorn surface area, indicating a similar reduction in -OH density as was observed with the thickening silicas. The Sears number of this material was observed to decrease further with increasing temperature (13.16 ml / 1.5g control to 6.74 ml / 1 .5g (5A) to 1 .93 ml / 1 .5g (5B)), which was also seen in the Acorn surface area trend (19.2 m2 / g control to 8.6 m2 / g (5A) to 4.2 m2 / g (5B)). These trends also correspond with a further reduction in LOI (3.87% control to 2.50% (5A) to 1 .42% (5B)), which provided a higher particle hardness and a further increase in cleaning performance once milled to an appropriate size. It is also obvious from the tables that the Quartz value is not changed with the treatment which is suitable to be used in consumer products.

[0186] As the temperature is increased there is a reduction in both the BET and CTAB surface areas of this material, which resulted from an overall reduction in pore volume and some degree of sintering. It should also be noted that under these conditions no meaningful shift in the pore size or pore size distribution was observed. Figure 13 provides a chart showing the nitrogen physisorption and BJH pore size distribution for comparative and inventive examples. Hgl Isotherm and pore size distribution for comparative and inventive examples are also shown in Figure 14.

[0187] These trends can be seen in the nitrogen physisorption isotherms and BJH desorption pore size distributions and where also confirmed by mercury intrusion analysis, all of which are included in below Table 9 which provides the summary of nitrogen physisorption data for comparative and inventive examples.

[0188] Figures 10 to 12 also provide SEM images of the comparative 4A and inventive examples (5A-5B). The lack of fusing in the primary structure is obvious from Figures 1 1 and 12, wherein spray calcination is applied on precipitated silica surface.

[0189] Table 9: Summary of nitrogen physisorption and mercury intrusion of spray calcined silicas

[0190] Oral Care Testing:

[0191] Table 10: Summary of oral care test values regarding fluoride compatibility for spray dried and spray calcined silicas.

[0192] As seen from Table 10 an increase in the Fluoride compatibility values was observed going from 55% to 66% as the applied adiabatic temperature increased to 1015 °C. This is a benefit difference observed in using this technique over a standard calcination type process (static furnace or rotary) at these temperatures.

[0193] During standard calcination comparative example 4B trial (as shown in table 10), it was observed that Fluoride compatibility of ZEODENT® 113 was significantly reduced at temperatures up to about 700 °C with residence times of 2 hours. This is another key differentiator of the present inventive method vs. standard calcination approaches (bed calcination at higher temperatures with extended resilience times) as it allows this negative impact on Fluoride compatibility to be overcome at these milder treatment temperatures.

[0194] Another attribute of silicas with higher degrees of polymerization, is an increase in particle hardness / rigidity. Typically, as the hardness of the silica particles increase, so does their cleaning performance. These silicas were formulated as shown below and PCR and RDA tests were conducted at Indiana University following the standard methods.

[0195] Relative Dentin Abrasion (RDA)

[0196] The RDA values of dentifrice compositions of cleaning silica examples 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.

[0197] Pellicle Cleaning Ratio (PCR)

[0198] The cleaning properties of dentifrice compositions of cleaning silica examples 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 cleaning silica in the toothpaste formulation.

[0199] Table 12: Example of a Toothpaste Formulations containing Spray Calcined Cleaning Silicas

[0200] It can be seen from Table 12 that all spray calcined cleaning silica samples increased in both cleaning and abrasion. The Examples 5A and 5B increased in PCR by about 25% and about 32%, respectively. In addition, it was seen that the thickening example 2B (when compared to Comparative example 1 B) could provide a significant increase in cleaning with minimal increase in abrasion when used in conjunction with a traditional cleaning silica.

Claims

CLAIMS1 . A process for obtaining thermally treated precipitated silica by calcination of the silica characterized by the following steps; the silica containing solution (silica slurry) is sprayed into flame reactor and hot air flame is sprayed on the silica surface by means of a flame spray wherein the flame has an adiabatic combustion temperature in a range of 600-1500 °C, and the average residence time of the silica in the flame reactor is in a range from 0.1 to 10 seconds.

2. The process for obtaining thermally treated precipitated silica according to claim 1 , wherein the flame has an adiabatic combustion temperature in a range of 700 °C - 1400 °C, preferably of 800 °C - 1400 °C, and the average residence time of the silica in the reactor is in a range from 0.1 to 1 .5 seconds.

3. The process for obtaining thermally treated precipitated silica according to claim 1 or 2, wherein the calcination temperature is measured 1 .5 m below the ignition site which is between 100 to 850 °C, preferably between 300 to 750 °C.

4. A thermally treated precipitated silica obtained according to any one of the preceding claims,, wherein said thermally treated precipitated silica particle has;LOI less than 3 %, measured in accordance with thermogravimetric analysis, and Sears number less than 11 to 1 ml / 1 .5 g, measured in accordance with titration method.

5. The thermally treated precipitated silica according to claim 4, wherein the treated precipitated silica has a LOI equal or less than 2.5 %.

6. The thermally treated precipitated silica according to claims 4 or 5, wherein the treated precipitated silica has a quartz content of less than 0.1 %, measured in accordance with x-ray diffractometry.

7. The thermally treated precipitated silica according to claims 4 to 6, wherein the treated precipitated silica has a pore volume of between 0.5-1 .5 cm3 / g, measured in accordance with mercury intrusion method.

8. The thermally treated precipitated silica according to claims 4 to 7, wherein the treated precipitated silica has an Acorn SA in the range of from 9.5 to 4 m2 / g, measured in accordance with an NMR technique by determining surface area of solid particles in a slurry with Acorn Surface Area Analyzer.

9. The thermally treated precipitated silica according to claims 4 to 8, wherein the treated precipitated silica has median particle size from 1 to 100 pm.

10. The thermally treated precipitated silica according to claims 4 to 9, wherein the treated precipitated silica has a BET surface area from 20 to 250 m2 / g, measured in accordance with BJH adsorption and desorption method.11 . The thermally treated precipitated silica according to claims 4 to 10, wherein the treated precipitated silica has a CTAB surface area from 20 to 250 m2 / g, measured in accordance with absorption of CTAB on the silica surface.

12. The thermally treated precipitated silica according to claims 4 to 11 , wherein the treated precipitated silica has a stannous compatibility greater than 40 % and a fluoride compatibility greater than 63 %, preferably in the range of 65 to 73 %.

13. Use of thermally treated precipitated silica according to any preceding claims, in oral care compositions, wherein the oral care composition is a toothpaste formulation comprising at least one therapeutic agent.

14. An oral care composition comprising the thermally treated precipitated silica according to preceding claims, from 3 to 35% by total weight of the composition.

15. An oral care composition according to claim 14, wherein the oral care composition is a toothpaste formulation further comprising a peroxide source, a fumed silica thickener, and / or a fluoride source.

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