IE63629B1 - Silica for dentifrice compositions particularly compatible with organic amino compounds - Google Patents

Abstract

Silica capable of being employed in particular in dentifrice compositions and compatible especially with organic amino compounds. The silica of the invention is characterised in that it results in an aqueous suspension whose pH varies according to defined equations, depending on its concentration and its electrical conductivity.

Description

The present invention relates to a silica particularly suitable for use in dentifrice compositions, its preparation process and dentifrice compositions incorporating it.

It is known that silica, which is widely used in the preparation of dentifrices, can serve several functions. Thus, it can act as an abrasive agent, when its mechanical action assists in eliminating dental plaque. It can also serve as-a thickening agent for giving the dentifrice specific rheological properties and as an optical agent for giving it the desired colouring.

Moreover, it is known that dentifrices generally contain a fluoride source, usually sodium fluoride or monofluorophosphate used as a caries prophylactic; a binder, e.g. an algal colloid such as carragheen, guar gum or xanthan gum; and a humectant, which can be a polyol, e.g. glycerine, sorbitol, xylitol or propylene glycol.

There are also optional constituents, e.g. surfactants, agents for reducing dental plaque or tartar deposits, taste correcting agents, colouring agents and pigments.

Among the different components of the dentifrice formulation are organic amino compounds, by which is meant compounds having an active molecule containing at least one nitrogen atom. More specific such compounds are fluorine-containing amines used as caries propylactics and in particular long-chain amino acid or amino addition products with hydrogen fluoride, such as cetylamine hydrofluoride, [bis-(hydroxyethyl)-aminopropyil -N-hydroxyethyl-octadecylamine dihydrofluoride, octadecylamine hydrofluoride and N,N’,N’-tri-(polyoxyethylene)-N-hexadecyl-propylenediamine dihydrofluoride; amine oxides used as nonionic surfactants resulting from the oxidation of tertiary aliphatic amines by hydrogen peroxide, especially alkylamine oxides of formula R(CH3)2 N—>0, in which R is a straight or branched-chain ^10-24 alkyl radical, and amine oxides of formula: R(CH2CH2CH)2 N—» 0; alkylamines, which can be primary, secondary, tertiary or quaternary amines used.as cationic surfactants, e.g. those of formula R-CHjNHj, dimethyl alkyl amines of formula R-N(CH3)2, and cetyl trimethyl ammonium bromide; and alkyl-betaines, which are N-alkyl derivatives of N,N-dimethylglycine and alkyl-amidoalkyl-betains designated hereinafter as alkyl betaines .

Examples of this class of amphoteric surfactants are: alkyl betains of formula: CH, R - N - CH2 - COO CH, and alkyl amidopropyl dimethyl betaines of formula: CH, r - co - nh2 - (ch2)3 - N - ch2 - COO CH, R being a straight or branched-chain ^|θ_2^ alkyl radical.

The presence of organic amino compounds causes the problem of compatibility with silica. Thus, particularly as a result of their absorbing capacities, silica tends to react with such compounds, so that they can no longer fulfil their function.

Therefore the object of the invention is to provide a novel silica more particularly compatible with the aforementioned organic amino compounds and in particular those of the class of fluorinecontaining amines and betaines and therefore usable in dentifrice formulations.

Another object of the invention is to supply a silica having a good compatibility with respect to the different cations present in dentifrice formulations, such as e.g. zinc, strontium, tin, etc.

Another object of the invention is to supply a silica which has maximum compatibility with products of the guanidine type and in particular bis-biguanides, whose most representative element is chlorhexidine.

Finally, another object of the invention is the preparation process for such compatible silicas.

The Applicnt has found in this connection that the sought compatibility properties were essentially dependent on the surface chemistry of the silica used. The Applicant has also established a certain number of conditions with respect to the surface of the silicas in order that they are compatible.

The characteristic of the silica of the present invention is that it leads to an aqueous suspension, whose pH varies as a function of its concentration in the area defined by the two inequations: - pH 7.5 - 0.7 and log (C) (la) - pH2-5.0 - 0.5 log (C) (lb) and whose pH varies as a function of its electrical conductivity in the area defined by the two inequations. - pH^8.5 - 0.4 log (D) (Ila) and - pHZ.7.0 - 0.6 log (D) (lib) in the inequations da) and (lb), (C) represents the weight concentration of the aqueous silica suspen sion expressed as a % of SiO2> in the inequations (Ila) and (lib), (D) represents the electrical conductivity of the aqueous silica suspension expressed in microsiemens cm Another characteristic of the silica according to the invention is that it has an acidity function Ho of at least 4.0.

Another characteristic of the silica according to the invention 2 is that it has a number of OH sites per nm equal to or below 12.

Another characteristic of the silica according to the invention is that it has a zero charge point (ZCP) of at least 4.

A feature of the silica according to the invention is that it has an at least 30% compatibility with organic amino compounds and more particularly at least 50% and preferably at least 80% with the organic amino compounds chosen from within the group formed by fluor ine-containing amines, amine oxides, alkyl amines and alkyl betaines Another feature of the silica according to the invention is that it has an at least 50% and more particularly at least 70% compatibility with metal cations.

Another feature of the silica according to the invention is 25 that it has a compatibility with guanidine-type products and in part icular chlorhexidine of at least 30% and more particularly at least 60%.

The present invention is also directed at one of the silica preparation processes, which is characterized in that it consists of reacting a silicate with an acid thus leading to a silica gel or suspension, carrying out a first aging at a pH equal to or above 6 and equal to or below 8.5, then a second aging at a pH equal to or below 6.0, carrying out a third aging at a pH equal to or below 5.0, separating the silica, washing it with water until it leads to an aqueous suspension, whose pH, measured on a 20% SiO2 suspension, complies with the following equation: - pH = d - e log (D) (III) in the equation (III) e is a constant equal to or above 0.6 and equal to or below 1.0, d is a constant equal to or above 7.0 and equal to or below 8.5, (D) represents the electrical conductivity of the aqueous silica suspension expressed in microsiemens.cm \ followed by the drying thereof.

Finally, the invention relates to dentifrice compositions characterized in that they contain silicas as described hereinbefore or prepared in accordance with the process defined hereinbefore.

Other features and advantages of the invention will be better understood from reading the following description and specific examples.

The silica according to the invention is characterized in that the pH of its aqueous suspension varies as a function of its concentration and its electrical conductivity, according to the equations given hereinbefore.

The procedure for measuring the pH as a function of the concentration of the aqueous silica suspension and its electrical conductivity is given hereinafter.

As stated hereinbefore, the essential characteristics of the silicas according to the invention are their surface chemistry.

More specifically, one of the aspects to be taken into account in said surface chemistry is the acidity. In this connection, one of the characteristics of. the silicas.according to the invention is the force of their surface acid sites. In this case the acidity is taken in the Lewis sense, i.e. it represents the tendency of a site to accept a pair of electrons of a base in accordance with the equilibrium: B : + A .---' BA For characterizing the silicas according to the invention, use is made of the notion of ’’acidity function" Ho developed by Hammett for measuring the tendency of the acid, the silica in the present case, to accept a pair of electrons from a base.

Therefore the function Ho is defined by the standard relation: (B :) pKa + log - = Ho (B :) (A) In order to determine the force of the said acid sites of a silica according to the invention using the Hannett method, use is made of indicators as initially described by Walling, J. Am. Cham. Soc., 1950, 72, p 1164. The force of the acid sites is determined by colour indicators, whose passage pKa between the acid and basic forms is known under the conditions of use.

Thus, the lower the pKa of the indicator undergoing the oolour change the higher the acidity of the site. The following table gives in exemplified manner a list of Hammett indicators usable for covering the value of Ho by determining in which form are adsorbed two successive indicators.

Colour Indicator Basic form Acid form pKa Neutral red yellow red * 6.8 Methyl red yellow red * 4.8 Pheny lazenzphthy lamine yellow red * 4.0 p-dimethylaminoazobenzene yellow red ♦ 3.3 2-anino-5-azotoluene yellow red ♦ 2.0 Benzene azodlpheny lamine yellow red ♦ 1.5 4-dimethylaminoazo-l-naphthalene yellow red * 1.2 Crystal violet blue yellow ♦ 0.8 p-nitrobenzene azo-(p*-nitro) diphenylanine orange violet ♦ 0.43 Dicinnamalaoetcne yellow red - 3.0 Benz alacetcphenone colourless yellow - 5.6 Anthraquinone colourless yellow - 8.2 The colour of the indicators adsorbed cn a silica is a measure of the force of the acid sites. If the colour is that of the acid form of the indicator, then the value cf the Ho function of the surface is equal to or below the pKa of the Indicator. Lew Ho values correspond to high force acid sites. Thus, e.g. a silica giving a red colouring with p-dimethylaminoazobenzene and yellow with 2-amino-5-azotoluene will have an acidity function Ho between 3.3 and 2.

Experimentally, the assay takes place with 0.2 g of silica placed in a test tube in the presence of a 100 mg/1 indicator solution in cyclohexane. •fi The silica is previously dried at 190 *C far 2 hours and kept protected fran moisture in a desslcator. As a result of stirring, adsorption, if it takes place, occurs in a few minutes and the colour change visible with the naked eye is observed or possibly by studying the characteristic adsorption spectra of the adsorbed colour indicators, both in their acid farm and in their basic faun.

The first characteristic of the silicas according to the invention is that they have an acidity function, as determined hereinbefore, of at least 4.0.

The surface state of the silica according to the invention is such that o conditions regarding the number of acid surface sites are fulfilled. The number can be measured in the number of CH~ or silanol groups per rrm2.

This number is determined as follows. The number of CH- surface sites is likened to the quantity of water released by the silica between 190 and 900*. The ail ira samples are previously dried at 105°C for 2 hours. A silica mass PQ is placed in a thermobalance and heated to 190’C for 2 hours, so that Ρ^θ is the mass obtained. The silica is then heated to 900 *C for 2 hours and Ρ^θθ is the new mass obtained.

The number of CH~ sites is calculated by the following equation: N, CH 66922.2 χ 190 in which: N~._ is the number of CH sites/rm2 of surface, CH A is the specific surface of the solid measured by BET and expressed in In the present case, the silicas according to the invention advantageously have a CH~/nm2 number equal to or below 12 and more particularly at the noet 10 and more specifically between 6 and 10.

The nature of the CH* sites of the silicas according to the invention, which also constitutes a characterization of their surface chemistry, can also be evaluated by the zero charge point, which ia defined by the pH of a silica suspension for which the electric charge of the surface of the solid ia zero, no matter what the ionic force of the medium. Thia ZCP measures the real pH of the surface, provided that the latter is free from all ionic impurities.

The electric charge is determined by potentiometry. The principle of the method is based on the overall balance of the protons adsorbed or desorbed cn the surface of the silica at a given pH.

On the basis of equations describing the σ/erall balance of the operation, 10 it is easy to demonstrate that the electric charge c of the surface relative to a reference corresponding to a zero surface charge is given by the equation: F C - - (H ) - (CH ) AJ4 in which: A represents the specific surface of the solid in m /g, M is the solid quantity in the suspension in g, F is the Faraday, (H*) or (CH-) represents the variation per surface unit of the excess of H* or CH" ions respectively an the solid. 0 The experimental protocol for determining the ZCP is as follows. Use is made of the method described by Berube and de Bruyn, J. Colloid Interface Sc., 1968, 27, p 305. The silica is washed beforehand in high resistivity deionized water (10 megaohm.cm), dyed and then pregassed. In practice, a series of solutions at pHo - 8.5 is prepared by adding KCH or HNO^ and containing an indifferent electrolyte (WO,) at a concentration variable -5 -1 between 10 and 10 mole/1. To these solutions is added a given silica mass and the pH of the suspensions obtained is allowed to stabilize, acccnpanied by Btirring, at 25°C and under nitrogen for 24 hours, i.e. pH’o is its value.

Standard solutions are constituted by the supernatant obtained by centrifuging for 30 min at 1000 r.pjn. of part of said same suspensions, i.e. pH'o is the pH of these supernatants.

The pH of a given volume of these suspensions and the oarresponding standard solutions is then brought to pHo by adding the necessary KEH quantity and the suspensions and standard solutions are allowed to stabilise for 4 hours, VCH" ’ nunber be*® equivalents added to pass from pH'o to pHo a known volune (V) of suspension or standard solution.

The potentiometric assay of the suspensions and standard solutions is carried out cn the basis of the pHo by adding nitric acid to pHf - 2.0. Preferably, the procedure involves the addition of an acid increment corresponding to a pH variation of 0.2 pH unit. Following each addition, the pH is stabilized for 1 min, i.e. V^+ . N^+ represents the nunber of acid equivalents to arrive at pHf.

Starting iron pHo, the term (VH+ . N^* ~ Vch ’ nch") plotted as a function of the incremented pH values for all the suspensions (at least 3 ionic forces) and for all the corresponding standard solutions.

For each pH value (0.2 unit step), the difference is then farmed between the ccnsurption of H* or CH for the suspension and for the corresponding standard solution. This operation is repeated for all the ionic forces, which gives the term (H*) - (CH ) corresponding to the proton oonsurption of the surface. The surface charge is calculated by the equation given hereinbefore. The surface charge curves are then plotted as a function of the pH for all the considered ionic forces. The ZCP is defined by the intersection of the curves. The silica concentration is adjusted as a function of its specific surface. For example, 2% suspensions are used for 2 m /g silicas with 3 ionic forces (0.1; 0.01 and 0.001 mole/1). The assay is performed cn 100 ml of suspension using 0.1 M potassium hydroxide.

In practice, it is preferable fear the ZCP value to be at least 4 and in particular between 4 and 6. In the case of a better compatibility with the metal cations, it is at the most 6.5. Poor a good compatibility with fluorine, the ZCP is preferably at the most 7.

Still with a view to inproving the ccnpetibility, particularly with respect to fluorine, it is of interest that the ocntent of divalent and high valency cations contained in the silica is at the most equal to 1000 ppm. It is desirable for the aluminium content of the silicas according to the inven* 5 tion to be at the most 500 ppm. The iron ocntent of the silicas according to the invention is advantageously at the most 200 ppm. Moreover, in preferred manner, the calcium content is at the most 500 ppm and more particularly at the most 300 ppm. The silicas according to the invention preferably also have a carbon ocntent of at the most 50 ppm and more 1 0 particularly at the most 10 ppm.

The silicas according to the invention, which are ccnpatible with organic auino ccnpounda are also ccnpatible with the different metal cations used in dentifrice caipoeiticns. Thus, the latter can inter alia contain metal cations with a valency higher than 1 supplied by active molecules. For example, reference is made to divalent and higher valency metal cations chosen from groups 2a, 3a, 4a and 8 of the periodic classification. More specifically, reference is made to cations of group 2a, namely calcium, strontium and barium, cations of group 3a, namely aluminium and indium, of group 4a, namely germanium, tin end lead end group 8, nonely manganese, iron, nickel, zinc, titanium, zirconium, palladium, etc.

The said cations can be in the foam of mineral salts, e.g. chloride, fluoride, nitrate, phosphate or sulphate, or in the form of organic salts, namely acetate, citrate, etc. More specific exanples are zinc citrate, zinc sulphate, strontium chloride, tin fluoride in the form of the single salt (SnF2) or in the form of the double salt (9iF2, KF), stannous chlorofluoride SnCIF and zinc fluoride (ZnF2).

The si 1 leas according to the invention are ccnpatible with the different metal cations. The ccnpetibility of said silicas with the cations defined according to the tests described hereinafter is at least approximately 50%, - 30 preferably at least 70% and in more preferred manner at least 80%.

The silicas according to the invention can consequently be used with advantage in dentifrice cenpoeitions containing divalent and higher valency 2 cations and more particularly In ocnpoeitions incorporating at least one at the following components: zinc citrate, zinc sulphate, strontium chloride and tin fluoride.

According to a special embodiment of the Invention, the Inventive silicas 5 can also be oonpatible with guanidines and In particular chlorhexldlne.

The compatibility measured by the tests described hereinafter is at least approximately 30%. It can be inproved and can be at least 60% and preferably at least 90%. 2In this case, the silica has a content of anions of the type 90. , Cl , 3- 2- -3 * NO?-, PO^ , OD? of at least 5.10 mole/100 g of silica. The lower this content, the higher will be this compatibility. According to preferred variants it is at the most 1.10-^ moles and more particularly 0.2»10*^ moles/100 g of silica.

In the case of silicas prepared from sulphuric acid, said anion content is 1 5 more appropriately expressed by a content in 90^ and by weight. In this case, the content Is at the most 0.1%. According to a preferred variant of the invention said content Is at the most 0.05% and more particularly at the most 0.01%.

Thus, the silicas according to the invention are particularly well suited 20 for use in dentifrice ccnpoeiticns containing guanidines aid bisguanides.

Reference can be made to those described in US patents 3 934 002 and 4 110 083.

The pH of the silicas according to the invention measured according to standard NFT 45-007 is generally at the most 8 and more particularly between 6.0 and 7.5.

The above characteristics make it possible to have a silica compatible with the aforementioned organic amino compounds, metal cations and, according to the case, also with fluorides and guanidines and in parHaGar chlorhexidine. 3 Apart from the surfaoe chemistry characteristics described hereinbefore and which condition the corpatibilities, the silicas according to the invention can also have physical characteristics making them suitable for use in dentifrices. These structural characteristics will be described hereinafter.

Generally the BET surface of allleas according to the invention is between 2 40 and 600 m /g, more particularly between 40 and 350 m /g. Their CTAB surface normally varies between 40 and 400 m /g and more specifically 2 between 40 and 200 m /g. The BET surface is determined according to the 1 0 BRUNAUER-EM4ET-TELLER method described in the Journal of the American Chemical Society, vol. 60, p 309, February 1938 and standard NF XII-622 (3.3).

The CTAB surface is the external surface determined according to standard ASTM D3765, but whilst carrying out the adsorption of hexadecyl trimethyl ammonium bremide (CTAB) at pH 9 and taking 35 a as the projected area of the CTAB molecule.

The silicas according to the invention can obviously correspond to the three types normally distinguished in the field of the dentifrice. Thue, the silicas according to the invention can be of the abrasive type. They then 2 have a BET surface between 40 and 300 m /g. In this case the CTAB surface 0 is between 40 aid 100 m2/g.

The silicas according to the invention can also be of the thickening type.

They then have a BET surface between 120 oxi 450 m2/g and more particularly 2 between 120 and 200 m /g. They could then have a CTAB surface between 120 2 and 400 m /g and more particularly between 120 and 200 m /g.

Finally, according to a third type, the silicas according to the invention can be bifunctional and then have a BET surface between 80 and 200 m/g, the CTAB surface then being between 80 and 200 m /g.

The silicas according to the invention can also have an oil absorption between 80 and 500 an3/100 g determined according to standard NFT 30-022 4 (March 53) using dibutyl phthalate. More specifically, eaid oil absorption is between 100 and 140 am3/100 g for abrasive silicas, 200 and 400 far thickening silicas and 100 and 300 for bifunctionals.

Moreover and still with a view to use in dentifrices, the silicas preferably hove a particle size between 1 and 10 pm. This mean particle size (d^) ia measured by the Coulter counter.

The apparent density will generally vary between 0.01 and 0.3. According to a special embodiment of the invention the silicas are precipitation silicas. Finally, the silicas according to the invention have a refractive index which 1s generally between U40 and 1465.

The process for the preparation of the silicas according to the invention will new be described in greater detail. As stated hereinbefore, this process is of the type involving reacting a silicate with an acid, which gives rise to the formation of a suspension or a silica gel. it should be noted that it is possible to use any known operating procedure to arrive at said suspension or gel (addition of acid to a silicate sediment, simultaneous total or partial addition of acid and silicate to a water sediment or silicate solution, etc.), the choice essentially being a function of the physical characteristics of the silica which it is wished; to obtain.

A preferred embodiment of the invention consists of preparing the suspension or silica gel by simultaneously adding the silicate and the acid to a sediment, which can be water, a colloidal silica dispersion containing 0 to 150 g/1 of silica expressed as SiO^, a silicate or a mineral or organic salt, preferably alkali metal, such as e.g. sodium sulphate or sodium acetate. The two reagents are added simultaneously in such a way that the pH is kept constant between 4 and 10, preferably between 8.5 and 9.5. The tenperature is advantageously between 60 and 95*C.

Cne procedure for preparing the colloidal silica dispersion preferably having a concentration between 20 and 150 g/1 ocnsiata of heating an aqueous silicate solution, e.g. to between 60 and 95‘C and adding the acid to said aqueous solution until a pH between 8 and 10 and preferably around 9.5 is obtained. The concentration of the aqueous Urate solution expressed as SiDj is preferably between 20 and 150 g/1. Use can be made of a dilute or concentrated acid and its normality can vary between 0.5 and 36 N, preferably between 1 and 2 N.

Hereinbefore, the term silicate has been advantageously understood to mean an alkali metal silicate and preferably a sodiun silicate with a SiO^/Na^O weight ratio between 2 and 4 and preferably equal to 3.5. The acid can be gaseous, such as carbonic acid, or liquid, preferably sulphuric acid.

In another stage of the inventive process, the suspension or gel undergoes ageing operations.

A first ageing is carried out at a pH of at the most 8.5 and which is e.g. between 6 and 8.5, preferably at 8. Ageing preferably takes place hot, e.g. at a temperature between 60 and 100 *C and preferably at 95 °C for a time between 10 minutes and 2 hours.

Another variant of the invention consists of preparing a suspension or a Hoa gel by progressively adding the acid to a sediment containing the 0 «·ί i inate until the desired ageing pH is obtained. This operation is performed at a temperature preferably between 60 and 95’C. The ageing of the suspension or silica gel takes place under the conditions described hereinbefore.

This is followed ty a second ageing at a pH below 6, preferably between 5 2 5 and 6 and more particularly equal to 5.5. The temperature and time conditions are the same as for the first ageing. For this purpose, the pH is brought to the desired ageing pH by adding acid. Use is e.g. made of a mineral acid, such as nitric, hydrochloric, sulphuric or phosphoric acid, or a carbonic acid formed by carbon dioxide gas bubbling.

A third ageing is carried out at a pH below 5, preferably between 3 and 5 6 aid even more preferably at around 4.

The terrperature and time ocnditicne are the same as far the two other ageing opera tiers. The desired ageing pH is obtained by acid addition. Thia la followed by the separation of the silica from the reaction medlun using any known means, such as e.g. a vacuun filter or a filter press. Thus, a silica cake is collected.

The process according to the invention can then be performed according to two main variants.

The first variant relates to the preparation of aiHr/w ccrrpatible with tbs organic amino ccrrpcunds and the divalent and higher valency metal caticns.

In this case, the process involves washing the cake under conditions such that the pH of the suspension or the medium before drying mist comply with the following equation; - pH - d - e log (D) (III) in which; e is a constant equal to or higher than 0.6 and equal to or lower than 1.0, d is a constant equal to or higher than 7.0 and equal to or lower than 8.5, (D) represents the electrical conductivity of the aqueous suspension expressed in microsiemens, cm \ To this end, it is possible to envisage washing with water, generally deionized water and/or washing with the aid of an acid solution with a pH between 2 and 7. this acid solution can e.g. be a solution of a mineral acid such as nitric acid.

However, according to a special embodiment of the invention said acid solution can also be a solution of an organic acid, particularly si organic complexing acid. This acid can be chosen from among carboxylic, dicarbcocylic, hydroxy carboxylic and aminocarbaxylic acids. Examples of such acids are acetic acid and exanples of complexing acids are tartaric, maleic, glyceric, gluccnic and citric acids. Particularly when using a solution of a mineral acid, it can be advantageous to carry out a final washing with deionized water.

The second variant relates to the preparation of silicas, which are also ccnpatible with guanidines and in particular chlorhexidine.

In l*r cases, a more pronounced washing is carried out. It must be continued until a washing filtrate is obtained, whose conductivity is at the mo6t 200 microsiemens.cm and preferably below 100 microsiemens.ot’\ As stated hereinbefore, it is important that the anion concentration is at the most 5.10~3 mole/100 g of silica.

As a function of the particular case, it is possible to carry out one or more washing operations, generally two such operations in water and preferably deionized water and/or with the aid of an aqueous solution of an organic acid, particularly those referred to hereinbefore.

From a practical standpoint, the washing operations can take place by passing the washing solution onto the cake or by introducing the latter into the suspension obtained, following the crumbling of the cake. Thus, the filter cake, prior to the drying operation, undergoes crumbling using any known means, e.g. a high speed rotary stirrer.

The silica cake, before or after washing, is consequently crumbled and 2q dried using any known means. Drying can e.g. take place in a tunnel or muffle furnace or by atomizing in a hot air flow, whose intake terperature can be between approximately 200 and 500’C and whose outlet temperature is between approximately 80 and 100*C. The residence time is between 10 seconds and 5 minutes. If necessary, the dried product can be ground to obtain the desired grain size. The operation is carried cut in a conventional apparatus, such as an impeller mill or an air Jet grinder.

The invention also relates to dentifrice compositions containing silicas of the type described hereinbefore or obtained by the process in question. The silica quantity according to the invention used in the dentifrice 3Q compositions can vary within wide limits and is normal ly between 5 and 351 The silicas according to the invention can be particularly appropriately used in dentifrice compositions containing at least one fluoride, phosphate and/or guanidine (in particular chlorhexidine). Thus, they can have a compatibility, according to the tests described below, of at least 904 for each of these materials.

They are also suitable for dentifrice compositions containing at least one organic amino component and/or components supplying a metal cation of valency 2 or more. They can then have a compatibility, according to the tests described below, of up to 804 for each element.

The silicas according to the invention are particularly suitable for dentifrice formulations simultaneously having at least one single mineral fluoride and/or organic fluoride, at least one alkyl betaine and at least one guanidine, in particular chlorhexidine.

More specific formulations incorporate a sodium fluoride and/or a tin fluoride and/or a fluorine-containing amine, more specifically cetylamine hydrofluoride and/or [bis-(hydroxyethyl)-aminopropyl ]-Nhydroxyethyl-octadecylamine dihydrofluoride, an alkyl betaine and chlorhexidine.

The silicas according to the invention are also compatible with copolymers of maleic acid and vinyl ethyl ether and can therefore be incorporated into dentifrice compositions comprising such copolymers. The quantity of the fluorine-containing compounds preferably corresponds to a fluorine concentration in the composition between 0.01 and 14 by weight, more specifically between 0.1 and 0.54. The fluorine-containing compounds are in particular monofluorophosphoric acid salts and more specifically those of sodium, potassium, lithium, calcium, aluminium, ammonium, monofluorophosphates and di fluorophosphates, as well as various fluorides, containing fluorine in bonded ion form and in particular alkali metal fluorides, like those of sodium, lithium and potassium, ammonium fluoride, stannous fluoride, manganese fluoride, zirconium fluoride, and aluminium fluoride, together with addition products of these fluorides with one another or with other fluorides, such as potassium, sodium or manganese fluorides. Other fluorides are also usable for the present invention, e.g. zinc fluoride, germanium fluoride, palladium fluoride, titanium fluoride, alkali metal fluozirconates, e.g. those of sodium and potassium, stannous fluozirconate and sodium or potassium fluosulphates or fluoborate.

The organic fluorine-compounds referred to at the start of the description can also be used, preferably cetylamine hydrofluoride and (bis-(hydroxyethyl)-aminopropyl]-N-hydroxyethyl-octadecylamine dihydrofluoride.

The most frequently encountered components supplying metal cations of valency 2 or more are zinc citrate, zinc sulphate, strontium chloride and tin fluoride.

Suitable elements usable as plaque prophylactics of the polyphosphate, polyphosphonate, guanidine and bis-biguanide types are disclosed in US patents 3 934 002 or 4 110 083The dentifrice compositions can also contain a binder, e.g. cellulose derivatives: methyl cellulose, hydroxyethyl cellulose, and sodium carboxymethyl cellulose; mucilages: carragenates, alginates, agar-agar and geloses; gums: gum arabic and tragacanth, xanthan gum and karaya gum; carboxyvinyl and acrylic polymers; and polyoxyethylene resins.

Apart from the silicas according to the invention, the dentifrice compositions can also contain one or more polishing abrasive agents, e.g. precipitated calcium carbonate, magnesium carbonate, calcium, dicalcium and tricalcium phosphates, insoluble sodium metaphosphate, calcium pyrophosphate, titanium dioxide (whitening agent), silicates, aluminas, aluminosilicates, zinc and tin oxides, talc and kaolin.

The dentifrice compositions can also incorporate surfactants, hunectanta, aromatizing agents, sweeteners, colouring agents and preservatives.

The moat widely used surfactants are sodhm laxryl sulphate, sodium lauryl sulphoacetate and lauryl ether sulphate, sodium dioctyl sulphoeuocinate, sodium Lauryl earcoeinate, sod ion ricinoleate and sulphated mcnoglyceridee.

The most widely used humectants are chosen from among the polyalcohols, such as glycerol, sorbitol, generally in 701 solution in water and propylene glycol.

The train aromatizing agents (perfumes) are chosen from among aniseed, etar anise, mint, juniper, cinnamon, clove and rose oils.

The main sweetening agents are chosen from among orthosulphobenzoic imides and cyclamatea.

The main colouring agents are chosen as a function of the desired colour, namely: red and pink colouring: amaranth, azorubin, catechi, new coccin (PCNCEMJ 4 R), cochineal and ery throe in? green colouring: chlorophyll and chlorophyllin; yellow colouring: sun yellow (Orange S) and qinoline yellow. 2Q The most widely used preservatives are parahydroxybenzoates, formol ard products giving off the same, hex et id ine, quaternary ammoniums, hexachlorophene, brcmcphene and hexamed ine.

Finally, the dentifrice compositions contain therapeutic agents, the meet i important being antiseptics, antibiotics, enzymes, oligo-elements and fluorine-containing compounds described hereinbefore.

Specific examples of the invention will now be given.

However, before this the measuring protocol for the pH, as a function of 1 the conductivity and concentration, aa well aa testa for.measuring the compatibility of ail lea with different elements will be described.

PFOIOOOL FOR MEASURING THE pH AS A FUNCTION OF THE SILICA (XNCzNTFATICN AND THE CONDUCTIVITY si 1 Ιγλ suspensions with a rising concentration varying between 0 and 25¾ by weight are formed by dispersing a mass m of silica previously dried at 120*0 for 2 hours in a mass 100-m of deionized, degassed water (Hillipore quality. The suspensions are stirred for 24 hours at 25’C.

The pH of the suspensions and solutions obtained after centrifuging part of the suspension at 8000 r.pun. for 40 min and filtering cn a 0.22 ym Millipore filter are measured at 25 *C under a nitrogen atmosphere with a Metrofrn 672 Titroprocessor measuring system.

In the same way, measurement takes place of the conductivity of the suspensions and solutions obtained at 25*C using a Radiometer conductivity meter (CDM83), equipped with a CDC3O4 cell with a cell constant equal to 1 The conductivity is expressed in pSianens/cm.

The suspension effect (SE) is defined by the pH differer.ee between the pH of a 20% silica suspension and the pH of its supernatant solution separated by centrifuging. 2Q Measuring the compatibility with bis-(hydroocyethyl)-amincpropyl-Nhydroxy ethyl-octadecyl amine dihydrofluoride 1) An aqueous solution (1) containing 1.65% of fluorine-containing amine is farmed by adding 5 g of 33% fluorine-containing amine to propane diol in 95 g of bidistilled water. 2) 4 g of silica are dispersed in 16 g of solution obtained in 1). The thus obtained suspension is stirred for 4 weeks at 37*C. 3) The suspension is then centrifuged at 8000 r.pjn. for 30 min and the supernatant obtained in (3) is filtered cn a 0.22 ym Millipore filter. 4) The free fluorine-containing amine concentration ie determined by nitrogen microanalyeie in the solution obtained in 1) and in the supernatant obtained in 3).

) The compatibility is determined by the following relation j , corpatibility . N «««««to to. «jgMnattnt (3) x 100 N concentration insolutier (1) Hereinafter, I fluorine-containing amine compatibility is designated AF.

Measuring the compatibility with cetyl amine hydrofluoride 1) An aqueous solution (1) containing 1.721 of fluorine -containing amine is formed by dissolving 1.72 g of cetyl amine hydrofluoride in 98.28 g of o bidlstilied water. 2) 4 g of silica are dispersed in 16 g of solution obtained in 1).

The thus obtained suspension is stirred far 4 weeks at 37 ’C. 3) The suspension is then centrifuged at 8000 r.p.m. for 30 min and the supernatant obtained in (3) is filtered cn the 0.22 urn Millipore filter. 4) The free fluorine-containing amine concentration is determined by nitrogen microanalysis in the solution obtained in 1) and in the supernatant obtained in 3).

) The compatibility is determined by the following relation: compatibility - N concentration in supernatant (3) x 100 20 N concentration in solution (1) Hereinafter, I floor ine-containing amine compatibility is designated AT.

Measuring the ccnpatibillty with an alkyl betaine The alkyl betaine used is a product marketed by AKSO under the trademark 3 ARCTERIC LB. 1) An aqueous solution (1) containing 2% alkyl betaine is formed by dissolving 6.67 g of 301 alkyl betaine in 93.33 g of bidiatniad water. 2) 4 g of silica are dispersed in 16 g of solution obtained in 1). The thus obtained suspension is stirred for 4 weeks at 37*C. 3) The suspension is then centrifuged at 8000 r.pum. for 30 min and the supernatant obtained in (3) is filtered on a 0.22 jjm Min ipnrp filter. 4) The free alkyl betaine concentration is determined by organic carton fpirT-Qan^ lysis in the solution obtained in 1) and the supernatant obtained in 3).

) The compatibility is determined by the following relation: » ccnpatibility - c p) x 100 C concentration in solution (1) Hereinafter, I alkyl betaine compatibility is designated aBeta.

Measuring the compatibility with an alkylamidoalkyl betaine 1) An aqueous solution (1) containing 2.01 alkylanido alkyl betaine is formed by dissolving 6.67 g of 30% alkylamidoalkyl betaine in 93.33 g of bid is tilled water. 2) 4 g of silica are dispersed in 16 g of solution obtained in 1). The thus obtained suspension is stirred for 4 weeks at 37 ’C. 3) The suspension is then centrifuged at 8000 r.p.m. for 30 min and the supernatant obtained in (3) is filtered an a 0.22 un Millipore filter. 4) the free alkylamidoalkyl betaine concentration is determined by organic carton microanalysis in the solution obtained in 1) and the supernatant obtained in 3).

) The ccnpatibility ie determined by the following relation: « OTpatlhUity . C In supernatant (3, x 100 C concentration in solution (1) Hereinafter, I alkylamidoalkyl betaine ccnpatibility is designated by beta.

Measuring the ccnpatibility with chlorhexidine 4 g of silica are dispersed in 16 g of an aqueous chlorhexidine solution with a II concentration in chlorhexidine digluocnate. The suspension is stirred for 24 hours at 37’C. The suspension 1s then centrifuged at 20000 r.pjri. for 30 min and the supernatant obtained is filtered cn a 0.2 ym Millipore filter. 0.5 ml of the thus filtered solution is saTpled and diluted in 100 ml of water in a graduated flask. This solution forma the test solution.

A reference solution is farmed using the same protocol, but without wilier, A It chlorhexidine digluocnate aqueous solution is stirred for 24 hours at 37*C, centrifuged at 20000 r.pun. and the supernatant filtered an a 0.2 Millipore filter. 0.5 ml of the thus obtained solution is diluted in 100 ml of water in a graduated flask.

The absorptivity of the two solutions is then measured at 254 rm using a spectrophotometer (Uvikcn 810/820).

The free chlorhexidine quantity, designated % ccnpatibility is determined 20 by the relation: % ccnpatibility Test absorptivity x 100 Reference absorptivity Measuring the ccnpatibility with fluorides g of silica are dispersed in 16 g of 0.3% sodium fluoride solution (NaF). The suspension is stirred far 24 hours at 37*C. After centrifuging the suspension at 20000 r.p.m. for 30 min, the supernatant ia filtered an the 0.2 urn Millipore filter. The thus obtained solution forms the teat solution. A reference solution is formed using the same protocol, but without **rj, The compatibility with fluorides is determined by the percentage free fluoride measured by the selective fluoride electrode (Orion). It ia determined by the following relation: , ccnpatibUity - <=°n«ntratlcnof test Ifpr,) x 100 F concentration of reference (ppm) Measuring the ccnpatlblllty with zinc g of silica are dispersed in 100 ml of 0.06¾ 7H2O solution. A suspension is obtained, whose pH is stabilized at 7 for 15 minutes by aridIng NaCH or H-SO^. susPer-s^cn i·3 then stirred for 24 hours at 37*C and centrifuged at 20000 r.p.m. for 30 min. The supernatant filtered cn the 0.2 ym Millipore filter forms the test solution. A reference solution is formed by following the same protocol, but without silica. The free zinc concentration of the two solutions is determined by atomic absorption (214 nm).

The compatibility is determined by the following relation: » ccnpacihility__test (ppn) x 100 Zn concentration of reference (ppm) Measuring the compatibility with sodium and potassltm pyrophosphates 4 g of silica are dispersed in 16 g of 1.5% sodium or potassium pyrophosphate suspension. The suspension is stirred for 24 hours at 37’C and then centrifuged at 20000 r.p.m. for 30 min. The supernatant is filtered cn the 0.2 ym Millipore filter. 0.2 g of the solution diluted in 100 ml of water in a graduated flask forms the test solution. A reference solution is formed by following the same protocol, but without silica.

The concentration of free pyrcphoephate ion (P^) of 80^ticn» 6 is determined by Icn chrcmatogrzphy (DICNEX 20001 system) equipped with «η integrator. The compatibility is determined by the ratio of the areas of the peaks obtained on the chromatograms and corresponding to the pyrcphoephate retention time of both the test and the reference. c peak area of test x 100 5 I compatibility · —k2=--peak area of reference EXAMPLE 1 Into a reactor equipped with a tenperature and pH regulating system and a propeller stirring systan (Mixel), are introduced 8.32 litres of sodium silicate with a 130 g/1 silica concentration and a SiO^/Naj0 ratio o of 3.5 and 8.33 litres of soft water with a conductivity of 1 pS/αη. After putting stirring into operation (350 r.pjn.), the thus farmed sediment Is tea ted at 90*C. When the sought temperature is reached, sulphuric acid with a concentration of 80 g/1 1s added with a ocnatant flow rats of 0.40 1/min in order to bring the pH to 9.5.

Thin is followed by the simultaneous addition of 45.25 1 of sodium silicate with a silica concentration of 130 g/1, a SiQ^/Na^O molar ratio of 3.5 and a flow rate of 0.754 1/min and 29.64 1 of 80 g/1 sulphuric acid. The sulphuric acid rate is adjusted so as to maintain the pH of the reaction medium at a constant value of 9.5.

After adding for 60 min, sodium silicate addition is stopped and sulphuric acid addition continued at a rate of 0.494 1/min until the pH of the reaction mixture is stabilized at 8. During this phase, the temperature of the medium is raised to 95 *C. This is followed by ageing for 30 min at said pH and at 95*C. During ageing, the pH is maintained at 8 by adding acid.

At the end of ageing, the pH is brought to 5.5 by adding sulphuric acid at a flow rate of 0.494 1/min and this is followed by ageing for 30 min at eaid pfi and at 95*C. At the end of ageing, the pH is brought to 3.5 by adding sulphuric acid and is maintained at this level for 30 min. 7 After stepping the heating, the mixture is filtered and the cake obtained washed with deionized water until a filtrate with a conductivity at 2000 pS/cm is obtained. The cake obtained after washing is dispersed in the presence of deionized water to form a suspension with a silica concentration of 10%. The pH of the suspension is adjusted to 6 by adding acetic acid.

This is followed ty a second filtration, and then by water washing, so as to adjust the conductivity to 500 pS/am and water washing with a pH adjusted to 5 by acetic acid, so as to adjust the pH to 5.5. A check is then made to establish that the following relation is fulfilled: pH 8.20 - 0.91 log (D).

The cake is then cnmbled and the silica dried by atomization. This is followed by grinding of the silica obtained cn on impeller mi 11 in order to obtain a powder, whose average agglomerate diameter measured cn the COULTER counter is 8 pm.

The physicochemical characteristics of the thus obtained silica appear in the following table: EET surface m /g 65 CTAB surface m2/g 60 DOP oil absorption ml/100 g of nil ioa 125 Pore volume Hg cm^/g 1.90 pH (5% water) 6.2 Refractive index 1.450 Translucency % 90 Na* ppm 60 SO. ppm 100 Al^* ppm 200 ppm 120 Ca2+ ppm 30 Cl ppm 20 C ppm 5 Table I gives the surface chemistry characteristics of the silica according 8 to the invention, as well aa the results of the ccnpatibility with the organic amino ocnpounda. Table II gives the ccnpatibility results with the ocnventicnal ccnpcnents of dentifrice femulations, namely chlorhexidine, fluoride, zinc and pyrephoephate.

EXAMPLE 2 - Into a reactor equipped with a tenperature and pH regulating system and a propeller stirring systen (Hixel) are introduced 530 1 of sodium silicate with a silica concentration of 135 g/1 and a SiO^/Na^O molar ratio of 3..5 and 15 1 of soft water with a conductivity of 1 pS/ση. After starting up the stirring system (350 r.pun.), the thus fanned sediment is heated to 90*C. When this terrperature is reached, sulphuric acid with a concentration of 80 g/1 is added with a constant flow rate of 0.38 1/min to bring the pH to 9.5.

This is followed by the simultaneous addition of 44.70 1 of sodium silicate 15 with a 135 g/1 silica concentration, a SiO^/Na^O molar ratio of 3.5 and a flow rate of 0.745 1/min and 25.30 1 of 80 g/1 sulphuric acid. The sulphuric acid rate ia adjusted so as to maintain the pH of the reaction medium at a constant value of 9.5.

After 60 min addition, sodium silicate addition is stepped and sulphuric acid addition is continued at a rate of 0.350 1/min until the pH of the reaction mixture is stabilized at 8. During this phase, the tenperature of the medium is raised to 95’C. This is followed by ageing for 30 min at this pH and at 95’C. During ageing the pH is kept at 8 ty acid addition.

At the end of ageing the pH is brought to 5 by adding sulphuric acid at a rate of 0.400 1/min and subsequently ageing takes place for 30 min at said pH and at 95’C. At the end of ageing the pH is brought to 3.5 by adding sulphuric acid and said pH is maintained at 3.5 for 30 min.

After stepping heating, the mixture is filtered and the cake obtained washed with deionized water until a filtrate is obtained with a conductivity of 0 2000 fis/αη. The cake is then crumbled in the presence of water to form a % silica suspension and the pH is adjusted to 5.1 so as to ensure that Π 100 eilica 200 3.35 6.5 1.455 95 0.5 0.25 350 120 the following relation ia proved I pH < 8.20 - 0.91 log (D).

The 81,1 Ina ia dried by atomization end ground cn an impeller mill to obtain a powder, whose mean agglomerate diameter ia 8 pi.

The physicochemical characteristics of the thus obtained «11 Ira appear below: BET surface m2/g CTAB surface m2/g DOP oil absorption ml/100 g Pore volume Hg an3/g pH (5% water) Refractive index Translncency I 904* % Na* % Al3* ppm > Fe ppm „ 2+ Ca ppm Cl ppm C ppm Table I gives the surface chemistry characteristics of the silica according to the invention, as well as the ccrrpatibility results with the organic amino ccnpounds. Table II gives the corpatibility results with the conventional components of dentifrice fcumulations, namely chlorhexidine, fluoride, zinc and pyrophosphate.

EXAMPLE 3 Into a reactor equipped with a toiperature and pH regulating system and a propeller stirring system (Mixel) are introduced 5.601 of sodium silicate with a silica concentration of 135 g/1 and a SiO2/Na20 molar ratio of 3.5.

After starting up the stirring system (350 r.p.m.), the thus formed sediment is heated to 85*C. When the tenperature ia reached, sulphuric acid with a concentration of 85 g/1 and preheated to 70*C is added at a constant flew rate of 0.50 1/min in order to bring the pH to 9.7.

This is followed by the simultaneous addition of 52.64 1 of sodium silicate with a 135 g/1 silica concentration, a molar ratio SiOj/Na^O of 3.5 and at a rate of 0.745 1/min and 30 1 of 85 g/1 sulphuric acid. The sulphuric acid rate is adjusted so as to maintain the pH of the reaction medium at a constant value of 9.7. The simultaneous addition takes place at 85’C using reagents preheated to 70*C.

After adding for 45 min, sodiun silicate addition is stopped and sulphuric acid addition continued at a rate of 0.450 1/min until the pH of the reaction mixture is stabilized at 8. Curing this phase, the terperature of the medium is raised to 95*C. This is followed by ageing for 10 min at said pH and 95*C. Curing ageing, the pH is kept at 8 by adding acid. At the end of ageing the pH is brought to 5 by adding sulphuric acid at a rate of 0.750 1/min and this is followed by ageing for 15 min at said pil and 95’C. At the end of ageing the pH is brought to 3.7 by adding sulphuric acid and said pH level is maintained for 60 min. 2Q Cn stopping heating, the mixture is filtered and the cake obtained washed with deionized water until a filtrate with a conductivity of 2500 yiS/αη is obtained. The cake is then crumbled in the presence of water to form a 20% κΉ ioa suspension and the pH is adjusted to 5.5 to ensure that the following relation is proved: pH ί 7.5 - 0.70 log (D).

The silica is dried by atomization and ground cn an impeller mill to obtain a powder having a mean agglomerate diameter of 8 urn.

The physicochemical characteristics of the thus obtained silica appear in the following table: 1 BET surface m2/g 200 CTAB surface m2/g 55 DOP oil absorption ml/100 g of silica 110 Pore volume Hg am3/g 2.65 pH (5% water) 7.0 Refractive index 1.460 Translucency I 85 SO* % Na* % Al3* ppm Fe3* ppm Ca2* ppm Cl" ppm C ppm 200 150 120 The following table I gives the surface chemistry characteristics of the silicas of the invention described in examples 1 to 3. It also gives the compatibility results of the silicas according to the invention with organic amino compounds.

Table II gives the compatibility results with the ccnventional corpcnents used in dentifrice formulations, namely chlorhexidine, fluoride, zinc and py rophosphate.

For ccnpariscn purposes, tables I and II gives the characteristics and different compatibilities of commercially available silicas, the following 1 ist constituting a representative range thereof: S81 : Syloblanc 81 (GRACE) 2113 : Zecdent 113 (HUBER) Sidl2 : Sident 12 (DBGUSSA) Syll5 : Sylox 15 (GRACE) T73 : Tixosil 73 (FHCNE-POULENC) 0 T83 : Tixosil 83 (FHCNE-PCULENC) 2 TABLE 1 physicochemical characteristics and compatibility with organic amino carpcunds of silicas according to the invention and conventional silicas.

Physicochemical characteristics of silicas I compatibility silica pH/log(C) pH/log(D) SE Ho ZPC AF Beta CHx s81 4.7-0.75x 7.0-0.62z - 0.17 i 2 2.2 0 0 0 Z113 8.1-0.94x 10-1.Oz - 0.70 <, 3 2.5 0 0 0 Sidl2 7.6-O.55x 8.5-0.60Z - 0.20 <. 3 2.8 0 0 0 Syll5 8.1-O.7OX 9.2-0.74Z - 0.94 s 3 2.5 0 0 0 T73 8.6-0.8 lx 10-0.87z - 0.20 < 3 3.0 0 0 0 T83 7.5-0.60x 8.6-0.60Z - 0.18 i 3 2.5 0 a· 0 Ex 1 7.5-O.3OX 8.0-O.SOz - 0X)0 > 4 4.2 85 60 95 2x 2 6.5-O.8Ox 8.2-O.9OZ - 0.10 ' 4 4.5 85 50 30 Ex 3 7.0-0.40X 7.4-0.60z - 0.06 a 4 4.0 80 50 90 The symbols used in the above table have the fn.1 lowing meanings: p«/log(C) represents the equation pH - b-a .log(C), in ’ which a and b are two constants and C is the weight percentage of silica in the suspension; pH/log(D) represents the equation pH - b'-a'log(D), in which b' and a' are two constants and D is the conductivity of the silica suspension in pSiemens/om; SE represents the suspension effect measured by the relation SE >= pH suspen sicn - pH supernatant defined elsewhere; Ho is the Hammett constant; 2C? represents the pH for which the surface charge of the silica is zero; AF, AFc, Beta, aBeta and CHx represent the compatibility percentages of fluorine-containing amines, alkyl betaine and chlorhex id ine respectively, said quantities being defined elsewhere.

The compatibility percentages obtained with the fluorine-containing amine 3 0 AFc ard the alkyl betaine aBeta are similar to thoee obtained respectively for AF and Beta. 3 TABLE II Compatibility of silicas with the active molecules: % Compatibility Silica P207 Zh** f AF Beta CHx s81 80 0 90 0 0 0 Z113 90 0 95 0 0 0 Sid 12 80 10 90 0 0 0 Syll5 80 0 90 0 0 0 T73 90 20 90 0 0 0 T83 95 10 95 0 0 0 Ex 1 95 80 95 85 60 95 EX 2 90 75 95 85 50 X Ex 3 95 80 95 80 50 90 The results of the table show that the silicas according to the inven- tier and more particularly compatible with organic amino compounds, differ markedly ccnpared with the standard a 115 through the following relations: pH s 8.5-0.40 log (D) and pH 7.0-0.60 log (D) pH < 7.5-0.70 log (C) and pH > 5.0-0.50 log (C) .3 4

Claims (5)

Claims

1. Silica; characterized in that it leads to an aqueous suspension, whose pH varies as a function of its concentration in the area defined by the two inequations: pH 7.5 - 0.7 log (C) (Ia) and pH >5.0 - 0.5 log (C) (lb) and whose pH varies as a function of its electrical conductivity in the area defined by the two inequations: pH 8.5 - 0.4 log (D) (Ila) and pH 7.0 - 0.6 log (D) (lib) in the inequations (Ia) and (lb), (C) represents the weight concentration of the aqueous silica suspension as a percent of Si0 2 , in the inequations (Ila) and (lib), (D) represents the electrical conductivity of the aqueous silica suspension in tnicrosiemens.cm 2. 2 450 m /g and more particularly between 120 and 200 m /g. 26. Silica according to claim 25, characterized in that it has a CTAB surface between 120 and 400 m /g. 27. Silica according to one of the claims 1 to 22 of the bifunctional type, characterized in that it has a BET surface between 80 and 200 2, m /g. 28. Silica according to claim 27, characterized in that it has a CTAB surface between 80 and 200 m /g. 29. Silica according to one of the claims 1 to 28, characterized in that it has an oil absorption between 80 and 500 cm /100g. 30. Silica according to one of the claims 1 to 29, characterized in that it has an average particle size between 1 and 10 pm. 31. Silica according to one of the claims 1 to 30, characterized in that it has an apparent density between 0.01 and 0.3. 2- -3 4 j j COg of at the most 5.10 moles per 100 g of silica. 15. Silica according to claim 14, characterized in that it has a content of the above anions of at the most 1.10 , more particularly _3 at the most 0.2.10 moles per lOOg of silica. 16. Silica according to one of the claims 1 to 13, characterized 2in that it has a sulphate content, expressed as S0^ of at the most 0.1%, preferably at the most 0.05% and more particularly at the most 0.01%. 17. Silica according to one of the claims 1 to 16, characterized in that it has a content of divalent and higher metal cations of at the most 1000 ppm. 18. Silica according to claim 17, characterized in that the aluminium content is at the most 500 ppm, the iron content at the most 200 ppm, the calcium content at the most 500 ppm and more particularly at the most 300 ppm. 19. Silica according to one of the claims 1 to 18, characterized in that it has a carbon content of at the most 50 ppm and more particularly at the most 10 ppm. 20. Silica according to one of the claims 1 to 19, characterized in that it has a pH of at the most 8 and more particularly between 6.0 and 7.5.

2. Silica according to claim 1, characterized in that it has a surface chemistry such that its acidity function Ho is at least 4. 3. 832. Silica according to one of the claims 1 to 31, characterized in that it is a precipitation silica. 33. Process for the preparation of a silica as described in one of the claims 1 to 32, characterized in that it consists of reacting a silicate with an acid thus leading to a suspension or silica gel, carrying out a first aging at a pH equal to or above 6 and equal to or below 8.5, then a second aging at a pH equal to or below 6.0, a third aging at pH equal to or below 5.0, separating the silica, washing it with water until an aqueous suspension is obtained, whose pH, measured on a 20% Si0 2 suspension, complies with the following equation: pH = d - e log (D) (III) in the equation (III) e is a constant equal to or above 0.6 and equal to or below 1.0, d is a constant equal to or above 7.0 and equal to or below 8.5, (D) represents the electrical conductivity of the aqueous silica -1 suspension in microsiemens·cm , followed by the washing thereof. 34. Process according to claim 33, characterized in that it consists of preparing the suspension or silica gel by simultaneously adding the silicate and acid to a sediment, which can be water, a colloidal dispersion of silica containing 0 to 150 g/1 of silica expressed as Si0 2 » a silicate or a mineral or organic salt, preferably alkali metal salt. 35. Process according to claim 34, characterized in that the addition of two reagents takes place in simultaneous manner, so that the pH is kept constant at between 4 and 10 and preferably between 8.5 and 9.5. 36. Process according to one of the claims 34 and 35, characterized in that the temperature is between 60 and 95°C. 37. Process according to claim 34, characterized in that the colloidal silica dispersion containing 20 to 150 g/1 of silica is prepared by heating an aqueous silicate solution at between 60 and 95°C and adding acid to said aqueous solution until a pH is obtained which is between 8.0 and 10.0 and preferably is 9.5. 38. Process according to claim 33, characterized in that it consists of preparing a silica gel or suspension by progressively adding the acid to a sediment containing the silicate until the desired aging pH is obtained at a temperature between 60 and 95°C. 39. Process according to one of the claims 33 to 36, characterized in that the silica gel or suspension undergoes a first aging at a pH between 6 and 8.5 and preferably at 8 at a temperature between 60 and 100°C and preferably 95°C. 40. Process according to one of the claims 33 to 39, characterized in that the silica gel or suspension undergoes a second aging at a pH between 5 and 6 and preferably at 5.5 and at a temperature between 60 and 100°C and preferably at 95°C. 41. Process according to one of the claims 33 to 40, characterized in that a third aging of the silica gel or suspension is carried out at a pH between 3 and 5 and preferably at 4 and at a temperature between 60 and 100°C and preferably at 95°C. 42. Process according to claim 33, characterized in that washing takes place with water or using an acid solution. 43. Process according to claim 33, characterized in that a washing is carried out until the conductivity of the washing filtrate is at the most 200 microsiemens · cm 44. Process according to claim 43, characterized in that washing takes place with water or using an acid solution. 45. Process according to one of the claims 42 and 44, characterized in that the aforementioned acid solution is a solution of an organic acid, particularly a complexing acid. 46. Process according to claim 45, characterized in that the aforementioned organic acid is chosen from among carboxylic acids, dicarboxy lie acids, amino carboxylic acids and hydrocarboxylic acids. 47. Process according to one of the claims 45 and 46, characterized in that the organic acid is chosen from within the group including acetic, gluconic, tartaric, citric, maleic and glyceric acid. 48. Dentifrice composition, characterized in that it contains a silica according to one of the claims 1 to 32 or a silica prepared by the process according to one of the claims 33 to 47. 49. Dentifrice composition according to claim 48, characterized in that it comprises at least one element chosen from within the group including fluorine, phosphates and guanadines. 50. Dentifrice composition according to claim 48, characterized in that it comprises at least one element chosen from the group including organic amino compounds and divalent and higher cations. 51. Dentifrice composition according to claim 48, characterized in that it comprises at least one organic amino compound chosen from within the group formed by fluorine-containing amines, amine oxides, alkyl amines and alkyl betaines. 52. Dentifrice composition according to claim 51, characterized in that the organic amino compound is cetyl amine hydrofluoride, bis-(hydroxyethyl)-aminopropyl-N-hydroxyethyl-octadecyl amine dihydrofluoride, an amine oxide of formula RiCH^^-N—»0, an alkyl betaine of formula R-N+iCH^^-CI^-COO , an alkylamidoalkylbetaine of formula ^-^0-^2-(0112) 3 ~N (CH^^-Q^-COO - , in which R represents a straight or branched-chain alkyl radical with 10 to 24 carbon atoms. 53. Dentifrice composition according to claim 48, characterized in that it comprises at least one divalent and higher metal cation chosen from within the group 2a,3a,4a and 8 of the periodic classi5 fication. 54. Dentifrice composition according to claim 53, characterized in that the metal cation is calcium, strontium, barium, aluminium, indium, germanium, tin, lead, manganese, iron, nickel, zinc, titanium, zirconium and palladium. 10 55. Dentifrice composition according to one of the claims 53 and 54, characterized in that the metal cation is in the form of metal salts, chloride, fluoride, nitrate, phosphate, sulphate or in the form of organic salts acetate and citrate. 56. Dentifrice composition according to one of the claims 53 to 15 55, characterized in that the metal cation is in the form of zinc citrate, zinc sulphate, strontium chloride and tin fluoride. 57. Dentifrice composition according to claim 48, characterized in that it comprises chlorhexidine. 58. Silica according to claim 1, substantially as hereinbefore > 0 described and exemplified. 59. A process for the preparation of a silica according to claim 1, substantially as hereinbefore described and exemplified. 60. A silica according to claim 1, whenever prepared by a process claimed in a preceding claim. 3 7 21. Silica according to one of the claims 1 to 20, characterized in that it has a BET surface between 40 and 600 m /g. 22. Silica according to one of the claims 1 to 21, characterized in that it has a CTAB surface between 40 and 400 m /g. 23. Silica according to one of the claims 1 to 22 of _the abrasive type, characterized in that it has a BET surface between 40 and 300 m 2 /g. 24. Silica according to claim 23, characterized in that it has a CTAB surface between 40 and 100 m /g. 25. Silica according to one of the claims 1 to 22 of the thickening type, characterized in that it has a BET surface between 120 and 3 6 or tin fluoride. 13. Silica according to claim 1, characterized in that it also has a compatibility with guanadine-type products and in particular chlorhexidine of at least 30% and more particularly at least 60%. 14. Silica according to one of the claims 1 to 13, characterized in that it has a content of anions of type SO, , Cl , N0« , Ρ0~ 3 5 6. Silica according to claim 5, characterized in that it has a compatibility with the organic amino compounds of at least 50% and more particularly at least 80%. 7. Silica according to either of the claims 5 and 6, characterized in that it has a compatibility with the organic amino compounds chosen from within the group formed by fluorine-containing amines, amine oxides, alkyl amines and alkyl betaines. 8. Silica according to claim 7, characterized in that the organic ami no compound is cetylamine hydrofluoride, bis-(hydroxyethyl)-amino propyl-N-hydroxyethyl octadecylamine dihydrofluoride, an amine oxide of formula RCCH^^N—>0, an alkyl betaine of formula R-N + (CH3)2-CH2COO , an alkyl amido alkyl betaine of formula R-CO-NH2~(CH2)3-N + (CH3) 2 -CH 2 -COO , in said formulas R representing a straight or branched-chain alkyl radical with 10 to 24 carbon atoms. 9. Silica according to claim 1, characterized in that it has a compatibility with the divalent and higher metal cations chosen from within groups 2a,3a,4a and 8 of the periodic classification of at least 50% and more particularly at least 70%. 10. Silica according to claim 9, characterized in that the metal cation is calcium, strontium, barium, aluminium, indium, germanium, tin, lead, manganese, iron, nickel, zinc, titanium, zirconium and palladium. 11. Silica according to either of the claims 9 and 10, characterized in that the metal cation is in the form of mineral salts, chloride, fluoride, nitrate, phosphate, sulphate or in the form of organic salts acetate and citrate. 12. Silica according to claim 11, characterized in that the metal cation is in the form zinc citrate, zinc sulphate, strontium chloride

3. Silica according to either of the claims 1 and 2, characterized in that it has a surface chemistry such that the OH number expressed in OH /nm is equal to or below 12 and preferably between 6 and 10.

4. Silica according to one of the claims 1 to 3, characterized in that it has a zero charge point (ZCP) of at least 4 and preferably between 4 and 6. 5. Silica according to one of the claims 1 to 4, characterized in that it has a compatibility with the organic am-i pn compounds of at least 30%.

5. >5 61. A dentifrice composition according to claim 48, substantially as hereinbefore described.