FI91386B - For silicone compositions intended for silica, especially compatible with organic amine 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

91386

The present invention relates to silica, which can be used in particular in toothpaste mixtures, to a process for its preparation and toothpaste mixtures containing this silica.

It is known that silica is commonly used in toothpaste compositions. In addition, it may have several functions in them.

First of all, it acts as an abrasive that mechanically helps to remove dental plaque.

It can also act as a thickener to impart certain rheological properties to the toothpaste, as well as an optical agent to impart the desired color to it.

In addition, it is known that toothpastes generally contain a source of fluoride, most often sodium fluoride or monofluorophosphate, which is used as an anti-caries agent; a binder, for example an algae colloid such as carrageenan, guar gum or xanthan gum; a humectant which may be a polyalcohol, for example glycerin, sorbitol, xylitol and propylene glycol. They also have optional ingredients, for example pin-. . active substances, dental plaque or tartar reducing agents, flavor enhancers, colorants and pigments, etc.

Organic amine compounds are found among the various ingredients in toothpaste compositions. By "organic amine compound" is meant any active molecule contained in toothpaste compositions containing at least one nitrogen atom. In particular, the following compounds may be mentioned: fluorinated amines used as anti-caries agents, in particular adducts of amines and long-chain amino acids and hydrogen fluoride, such as ketylamine hydrogen fluoride, bis- (hydroxyethyl) aminopropyl dihydrogen fluoride, N-hydroxyethyloctadecylamine, ', N'-tri- (polyoxyethylene) -N-hexadecylpropylenediamine dihydrofluoride; - amine oxides used as non-ionic surfactants, obtained by oxidation of tertiary aliphatic amines with oxygen-saturated water. Particular mention may be made of alkylamine oxides of the formula: R (ch3) 2 N -> O, in which R is a linear or branched alkyl radical containing from about 10 to 24 carbon atoms.

Mention should also be made of amine oxides of the formula: R (CH 2 CH 2 OH) 2 N-> O; - alkylamines, which may be primary, secondary, tertiary or quaternary aliphatic amines, used as cationic surfactants. Examples which may be mentioned are alkylamines of the formula R-CH2NH2 or dimethylalkylamines of the formula R-N (CH3) 2, ketyltrimethylammonium bromide; alkyl betaines, which are N-alkyl derivatives of N-dimethylglycine, and alkylamide alkyl betaines, hereinafter also referred to as "alkyl betaines".

Examples of amphoteric surfactants in this class are: - alkyl betaines of the formula: CH3 R - N + - ch2 - cocr CH3 91386 3 - alkylamidopropyldimethylbetaines of the formula: CH3 R - CO - NH2 - (CH2) 3 - N + - CH2 to COO "CH3 wherein R is a linear or branched alkyl radical containing from 10 to 24 carbon atoms.

The use of organic amine compounds raises problems with regard to their compatibility with silica. In particular, because of their adsorption properties, silica may tend to react with said compounds, thereby no longer being able to fulfill their intended function.

It is therefore an object of the present invention to provide a novel silica which is particularly compatible with the abovementioned organic amine compounds, in particular with compounds belonging to the class of fluorinated amines and betaines, and which is therefore fully usable in toothpaste mixtures.

Another object of the invention is to provide silica which is well compatible with various cations present in toothpaste mixtures, such as zinc, strontium, tin, etc.

It is also an object of the invention to provide silica which is also highly compatible with guanidine-type products, in particular bis-biguanides, the most representative component of which is chlorhexidine.

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

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But in this context, the Applicant has found that the desired compatibility properties depend essentially on the surface chemistry of the silica used. The applicant has therefore defined a number of conditions that the surface of the silica must meet in order to be compatible.

The silica of the present invention is characterized in that it results in an aqueous suspension whose pH varies according to its concentration in a range defined by two inequalities: - pH i 7.5 to 0.7 log (C) (Ia) and - pH 1 5.0 - 0,5 log (C) (Ib) and the pH of which varies according to its electrical conductivity in the range defined by two inequalities: - pH _ <8,5 to 0,4 log (D) (Ha), and - pH 2 7,0 to 0, 6 log (D) (IIb) in which the inequalities (Ia) and (Ib) to (C) represent the weight concentration of the aqueous silica suspension expressed in% SiO 2, and in the inequalities (IIa) and (Hb) - (D) represents the aqueous silica suspension electrical conductivity expressed in microsiemens.cm-1s

Another feature of the silica according to the invention is that it has an acid function Ho of at least 4.0.

Another characteristic of the silica according to the invention 91386 5 is that the number of OH "positions per nm 2 is less than or equal to 12.

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

One feature of the silica of the invention is that it is at least 30% compatible with organic amine compounds and more particularly at least 50% and preferably at least 80% compatible with organic amine compounds selected from the group consisting of fluorinated amines, amine oxides, alkylamines. and alkyl betaines.

Another feature of the silica according to the invention is that it is at least 50% and, in particular, at least 70% compatible with metal cations.

Another feature of the silica according to the invention according to one embodiment is that it is compatible with guanidine-type products, in particular chlorhexidine, at least 30% and more particularly at least 60%.

The present invention relates to a process for the preparation of silica according to the invention, characterized in that a silicate is reacted with an acid to form a silica suspension or gel, the first maturation being carried out at a pH of greater than or equal to 6 and less than or equal to 8.5, then a second ripening at a pH of more than or equal to 6.0, a third ripening at a pH of less than or equal to 5.0, the silica is separated off, washed with water until an aqueous suspension is obtained, which The pH value measured from a suspension containing 20% SiO 2 corresponds to the following equation: 6 - pH - d - e log (D) (lii) where in equation (III): - e is a constant greater than or equal to 0.6 and less than or equal to 1.0, - d is a constant greater than or equal to 7.0 and less than or equal to 8.5, - (D) represents the electrical conductivity of an aqueous silica suspension expressed in microsiemens.cm - ^ »and finally dried.

Finally, the invention further relates to toothpaste compositions which are characterized in that they contain the silicas described above or prepared according to the above-mentioned process.

Other features and advantages of the invention will become more apparent from the following description and concrete examples, which do not limit the scope of the invention.

The silica of the present invention is characterized in that the pH of its aqueous suspension varies according to its concentration and its electrical conductivity according to the above equations.

The procedure for measuring the pH according to the concentration of the aqueous silica suspension and its electrical conductivity is given below.

As mentioned in the introduction, the main features of the silicas according to the invention are in their surface chemistry. More specifically, one factor to consider in this surface chemistry is acidity. In this connection, one of the characteristics of the silicas according to the invention is the strength of the acid ions on their surface.

Here, the acidity is treated according to Lewis acid-base theory, i.e., the tendency of an ion to receive a base electron pair according to the following equation: B: + A <> BA.

To characterize the silicas of the invention, the term "acidity function" Ho, developed by Hammett to measure the tendency of an acid, in this case silica, to accept an electron pair of a base, is used herein.

The function Ho is thus defined by the classical expression: (B :) pKa + log - * Ho.

(B :) (A)

To determine the strength of the acid sites of the silica according to the invention, the indicator method of Walling (J. Am. Chem. Soc. 1950, 72, 1164) was originally used.

The strength of acid ions is determined by color indicators for which the transition pKa between the acid and base forms under the conditions of use is known.

Thus, the lower the pKa of the indicator of color change, the stronger the acidity of the molecule. The table below summarizes, by way of example, a non-limiting list of Hammett indicators that can be used to delimit the Ho value by determining the form in which two consecutive indicators are adsorbed.

Color

Indicator Base form Acid form pKa

Neutral Red Yellow Red + 6.8

Methyl1 red Yellow Red + 4.8

Phenylazonaphthylamine Yellow Red + 4.0 8 p-Dimethylaminoazobenzene Yellow Red + 3.3 2-Amino-5-azotoluene Yellow Red + 2.0

Benzeniazodiphenylamine Yellow Red + 1.5 4-Dimethylaminoazo-1-naphthalene Yellow Red + 1.2

Crystal Purple Blue Yellow + 0.8 p-Ni Trobenzeneazo (p'-nitro) diphenylamine Orange Purple + 0.43

Disinnamalacetone Yellow Red - 3.0

Benzacetophenone Colorless Yellow - 5.6

Anthraquinone Colorless Yellow - 8.2

The color of the indicators adsorbed on silica is one measure of the intensity of acid sites. If the color is the color of the acid form of the indicator, then the value of the surface function Ho is less than or equal to the pKa of the indicator. Low Ho values correspond to strong acid sites.

Thus, for example, silica, which turns red p-dimethylaminoazobenzene red and yellow 2-amino-5-azotoluene, has an acidity function Ho of 3.3-2.

Experimentally, the measurement is carried out by placing 0,2 g of silica in a test tube containing 100 mg of indicator dissolved in a liter of cyclohexane.

The silica is pre-dried at 190 ° C for 2 hours and stored in a desiccator protected from moisture.

When the tube is mixed, adsorption, if any, occurs within minutes and the color change is detected with the naked eye or possibly by examining the adsorption spectra characteristic of the adsorbed color indicators in both their acid and base forms.

91386 9

The first characteristic of the silicas according to the invention is that their acid function, as described above, is at least 4.0.

The surface state of the silica according to the invention is such that the conditions concerning the number of acid sites on the surface are met. The number can be measured as the number of OH ~ groups or silanols / nm ^.

This number is determined as follows: the number of OH ~ sites on the surface is assimilated to the amount of water released by the silica at 190-900 ° C.

The silica samples are pre-dried at 105 ° C for 2 hours.

The silica mass Pg is placed in a heat equalizer and heated at 190 ° C for 2 hours: a Pigo mass is obtained.

The silica is then heated at 900 ° C for 2 hours to give a new mass. The number of Pggg »OH“ sites is calculated by the following equation: 66922.2 p190 “p900 N0h- - - x - A P190 where: - N0H- is the number of OH ~ sites number per nm nm of surface - A is the specific surface area of the solid measured in BET and expressed in m ^ / g.

In the present case, the silicas according to the invention have an OH number / nm of less than or equal to 12, in particular not more than 10 and in particular 6 to 10.

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The quality of the OH 'sites of the silicas according to the invention, which is also a characteristic feature of their surface chemistry, can also be determined by the zero charge point.

This zero charge point (PZC) is determined at the pH of the silica suspension, where the electrical charge on the surface of the solid is zero and thus regardless of the ionic strength of the medium. This PZC measures the true pH of a surface if it is free of all ionic impurities.

The electric charge is determined potentiometrically. The principle of the method is based on the total balance of protons adsorbed on or desorbed from a given pH surface of silica.

From the equations describing the total balance of the measure, it is easy to show that the electrical charge c of the surface compared to the reference value corresponding to the zero charge of the surface is obtained from the equation:

F

c - - (H +) - (OH ") A.M.

where: - A represents the specific surface area of the solid, m2 / g - M is the amount of solid in the suspension, g - F is the Faraday constant - (H +) or (OH ”) represents the variation of the excess of H + or OH” ions per unit area in the solid, respectively .

The procedure for the experimental determination of PZC is as follows: The method described by Berube and de Bruyn (J. Colloid Interface Sc. 1966, 27, 305) is used.

The silica is washed beforehand with highly resistive deionized water (10 megohms.cm), dried and dewatered 91386 11.

It is convenient to prepare a series of solutions with a pH of 8.5 by adding KOH and HNO 3 and containing any electrolyte (KNO3) at a concentration ranging from 10-5-10 moles / l.

To this solution is added a given mass of silica and the pH of the resulting suspensions is allowed to stabilize by stirring at 25 ° C and nitrogen for 24 hours to give a pH of 0 °.

The reference solutions consist of the supernatant obtained by centrifuging 30 parts of these suspensions for 30 minutes at 1000 rpm; that is, pH'o is the pH of these rising parts.

The pH of these suspensions and the corresponding reference solutions is then restored to pHo by adding the required amount of KOH and the suspensions and reference solutions are allowed to stabilize for 4 hours.

In this case, Vqh ~ · Noh ”is the number of base equivalents added to bring the pH'o of the known volume (V) of the suspension or reference solution to pHo.

Potentiometric measurement of the suspensions and reference solutions is carried out starting from pHo by adding nitric acid until a pHf <2,0 is obtained.

Preferably, an acid addition corresponding to a pH change of 0.2 pH units is performed. After each addition, the pH is allowed to stabilize for 1 minute.

Then Vh * · Nh + is the number of acid equivalents at which pHf is reached.

12 Starting from pH, the expression (Vh + · Ny * - Vqh ”· n0h") is obtained as a function of the added pH values for all suspensions (3 ionic strengths at least) and for all corresponding reference solutions.

For each pH value (0.2 unit increments), the difference in consumption of H + or 0H® ions for the suspension and the corresponding reference solution is then calculated. This procedure is repeated for all ionic strengths1 la.

This gives the expression (H +) - (OH-), which corresponds to the consumption of surface protons. The surface charge is calculated from the above expression.

Surface charge curves are then plotted as a function of pH for all possible ionic strengths. The PZC is determined by the intersection of the curves.

Adjust the silica concentration according to its specific surface area.

For example, 2% suspensions are used in the case of silicas with a specific surface area of 50 m 2 / g, 3 ionic strength 11a (0.1, 0.01 and 0.001 mol / l / l).

The measurement is performed on 100 ml of suspension using 0.1 M potassium hydroxide.

In practice, it is desirable that this PZC value be at least 4, more specifically 4-6. For better compatibility with metal cations, it is up to 6.5. For good fluoride compatibility, the PZC is preferably up to 7.

In order to further improve the compatibility, especially with regard to fluorine, it is advantageous that the content of the double-cation i cations contained in the silica does not exceed 91386 13 1000 ppm. In particular, it is desirable that the silicas according to the invention have an aluminum content of at most 500 ppm.

On the other hand, the silicas according to the invention may preferably have an iron content of at most 200 ppm.

In addition, the calcium content is preferably at most 500 ppm and more particularly at most 300 ppm.

The silicas according to the invention also preferably contain no more than 500 ppm of carbon and more particularly no more than 10 ppm.

The silicas according to the invention, which are compatible with organic amine compounds, are also compatible with the various metal cations contained in toothpaste mixtures.

Namely, they may contain metal cations carried by active molecules with a valence higher than 1. Examples are divalent and higher metal ions belonging to classes 2a, 3a, 4a and 8 of the Periodic Table. More specifically, the cations of group 2a are: calcium , strontium, barium, group 3a cations: Aluminum, indium, group 4a cations: germanium, tin, lead and group 8 cations: manganese, iron, nickel, zinc, titanium, zirconium, palladium, etc.

Said cations may be in inorganic salts, for example, chloride, fluoride, nitrate, phosphate, sulfate, or organic salts, acetate, citrate, etc.

More specific examples are zinc citrate, zinc sulphate, strontium chloride, tin fluoride in the form of a single salt (SnF2) or in the form of a double salt 14 (SnF2 / KF), tin (IV) chlorofluoride SnClF, zinc fluoride (ZnF2).

The silicas according to the invention are compatible with various metal cations. The compatibility of said silicas with cations, as determined by the experiments described below, is at least about 50%, preferably at least 70% and even more preferably at least 80%.

Thus, the silicas according to the invention can be used advantageously in toothpaste mixtures containing divalent or higher cations, and in particular in mixtures containing at least one of the following components: zinc citrate, zinc sulphate, strontium chloride, tin fluoride.

According to an embodiment of the invention, the silicas according to the invention can furthermore be used in combination with guanidines and in particular chlorhexidine. The compatibility determined by the experiment described below is at least about 30%. It can be improved and can be at least 60% and preferably at least 90%.

In this case, the silica contains anions of the type SO42-, cl-, NO3-, PO43-, CO32- at most 5.10- ^ moles per 100 g of silica. This compatibility is better the lower the concentration of such anions. According to proven variations, it is at most 1.10-3 moles, and more specifically 0.2.10 “3 moles per 100 g of silica.

In the case of silicas prepared from sulfuric acid, this anion content is most conveniently expressed by the concentration expressed as SO2- and by weight. In this case, this content is at most 0.1 According to an embodiment of the invention, this content is at most 0.05% and, in particular, at most 0.01%.

91386 15

The silicas according to the invention are therefore particularly suitable for use in toothpaste compositions containing guanidines, bisguanidines. Mention may be made of those described in US-3934002 or US-4110083, the contents of which are incorporated herein by reference.

The pH of the silicas according to the invention, measured according to the standard NFT 45-007, is generally at most 8. More specifically, it is 6.0-7.5.

The above-mentioned properties make it possible to prepare a silica which is compatible with said organic amine compounds, metal cations and, where appropriate, in addition to fluorides and guanidines, in particular chlorhexidine.

In addition to the surface chemistry properties described above that retain compatibility, the silicas of the invention also have physical properties that make them fully suitable for toothpastes. These structural type features are described below.

In general, the BET surface area of the silicas according to the invention is 40-600 m 2 / gf, in particular 40-350 m 2 / g. Their CTAB surface usually ranges from 40 to 400 m2 / g, more specifically from 40 to 200 m2 / g.

The BET surface is determined according to the method of Brun & uer-Emmet-Te1ler described in the Journal of the American Chemical Society, Vol. 60, page 309, February 1938, and in accordance with standard NF X11-622 (3.3).

The CTAB surface is an outer surface determined according to ASTM D3765, but using the adsorption of hexadecyltrimethylammonium bromide (CTAB) at pH 9 and taking the CTAB molecule as the projected area 35 A2.

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The silicas according to the invention can, of course, be of three types, which are usually separated in toothpastes.

Thus, the silicas of the invention may be of the abrasive type. Their BET surface is then 40-300 m2 / g. In this case, the CTAB surface is 40-100 m2 / g.

The silicas according to the invention can also be of the thickening type. Their BET surface area is then 120-450 m2 / g, more specifically 120-200 m2 / g. Their CTAB surface can then be 120-400 m2 / g, more specifically 120-200 m2 / g.

Finally, according to a third type, the silicas according to the invention can be of dual action. In this case, their BET surface area is 80-200 m2 / g. The CTAB surface is then 80-200 m2 / g.

The oil solidification value of the silicas according to the invention may also be 80-500 cm 3/100 g determined according to NFT 30-022 (March 53) using dibutyl phthalate.

More specifically, this oil solidification value is 100-140 cm3 / 100 g for abrasive silicas, 200-400 cm3 / 100 g for thickening silicas and 100-300 cm3 / 100 g for bifunctional silicas.

In addition, still for a toothpaste application, the particle size of the silicas is preferably 1 to 10.

This mean particle size (d5Q) was measured by the Counter-Coul-ter method.

The apparent density usually ranges from 0.01 to 0.3. According to a particular embodiment of the invention, the silicas are precipitating silicas.

Finally, the refractive index of the silicas according to the invention is generally 1.440 to 1.465.

91386 17

The process for the preparation of the silicas according to the invention is described in more detail below.

As mentioned above, this method is of the type in which a silicate is reacted with an acid to form a silica suspension or gel.

It should be noted that any known procedure can be used to reach this suspension or gel (acid can be added to the silica mixture, acid and silicate added in whole or in part simultaneously to the base of water or silica solution, etc.), depending mainly on the physical properties. silica is desired to be prepared.

In a preferred embodiment of the invention, a silica suspension or gel is prepared by simultaneously adding a silicate and an acid to a mother liquor, which may be water, a colloidal silica solution containing 0-150 g / l of silica, expressed as SiO 2, a silicate or preferably an inorganic metal. an organic salt such as sodium sulfate, sodium acetate.

Both reagents are added simultaneously so that the pH remains at 4-10, preferably at 8.5-9.5. The temperature is preferably 60-95 ° C.

In one method of preparing a colloidal silica solution having a concentration of preferably 20 to 150 g / l, the aqueous silicate solution is heated to 60-50 ° C and acid is added to said aqueous solution until the pH is 8.0-10.0, preferably about 9. 5.

The concentration of the Si 1 licate water 1 solution, expressed as SiO 2, is preferably 20-150 g / l. A dilute or 18 concentrated acid may be used: its normality may vary from 0.5 N to 36 N, preferably 1-2 N.

By the foregoing, silicate preferably means an early metal silicate and preferably sodium silicate having a weight ratio of SiO 2 / Na 2 O of 2-4, more preferably 3.5. The acid, in turn, may be gaseous, such as carbon dioxide or liquefied petroleum gas, preferably sulfuric acid.

In the second step of the process according to the invention, the suspension or gel is subjected to ripening operations.

The first ripening is carried out at a pH of at most 8.5 and 6-8.5, for example preferably 8.0. The ripening is preferably carried out under the influence of heat, for example at a temperature of 60 to 100 ° C, preferably at 95 ° C, and for a time which can vary from 10 minutes to 2 hours.

In another embodiment of the invention, a silica suspension or gel is prepared by gradually adding an acid to a mother liquor containing silicate until the desired ripening pH is obtained. This operation is carried out at a temperature of preferably 60-95 ° C.

Maturation of the silica suspension or gel is then performed under the conditions described above.

A second maturation is then carried out at a pH of less than 6, preferably 5-6 and even more preferably 5.5.

The temperature and duration are the same as in the first maturation.

To this end, the pH is adjusted to the desired ripening pH by adding acid.

For example, an inorganic acid such as nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, or a carbonic acid formed by blowing carbon dioxide can be used.

The third maturation is carried out at a pH of less than 5.0, preferably 3-5 and even more preferably about 4.0.

The temperature and duration conditions are the same as for other cooking. The desired ripening pH is obtained by adding acid.

The silica is then separated from the reaction medium in a known manner, for example by vacuum filtration or by spray filtration.

The silica cake thus obtained is recovered.

The method according to the invention can then be carried out with two main variations.

The first variant relates to the preparation of silicas which are compatible with organic amine compounds and divalent or higher metal cations.

In this case, the method involves washing the cake under conditions such that the pH of the suspension or medium before drying corresponds to the following equation: - pH - d - e log (D) (III) where in equation (III): - e is a constant greater than or equal to 0.6 and less than or equal to 1.0, - d is a constant greater than or equal to 7.0 and less than or equal to 8.5, - (D) represents the electrical conductivity of the aqueous silica suspension expressed in terms of microsiemens.cn ~ ^ * 20 For this purpose, the cake can be washed with water, usually deionized water, and / or an acid solution having a pH of 2-7.

This acid solution may be, for example, a solution of an inorganic acid such as nitric acid.

However, according to a particular embodiment of the invention, this acid solution can also be a solution of an organic acid, in particular a solution of an organic complexing acid. This acid may be selected from the group consisting of carboxylic acids, dicarboxylic acids, hydroxycarboxylic acids and aminocarboxylic acids.

Examples of such acids include acetic acid and complexing acids such as tartaric acid, maleic acid, glyceric acid, gluconic acid and citric acid.

It may be advantageous, especially when a solution of an inorganic acid is used, to carry out the final wash with deionized water.

Another variation relates to the preparation of silicas that are compatible with guanidines and especially chlorhexidine.

In such a case, a more thorough wash is performed. Washing is continued until a washing filtrate with an electrical conductivity of not more than 200 microsiemens.cm-1, preferably less than 100 microsiemens.cm ~ 1 is obtained. · As mentioned above, it is important that the anion concentration does not exceed 5.10 ”3 moles / 100 g of silica.

Depending on the case, one or more washes can be carried out, generally two washes with water, preferably deionized water and / or an aqueous solution of an organic acid, especially those mentioned above.

91386 21 From a practical point of view, the washing operations can be carried out by pouring the washing solution onto the cake or by passing it into the resulting suspension after breaking the cake.

Namely, the filter cake is broken down before drying and can be carried out in any known manner, for example by means of a high-speed rotary mixer.

Thus, the silica cake is decomposed before or after washing and then dried in any known manner. Drying can be performed, for example, in a tunnel or muffle furnace or by spraying it into a hot air stream having an inlet temperature ranging from about 200 to 500 ° C and an outlet temperature of about 80 to 100 ° C; the oven time is from 10 seconds to 5 minutes.

The dried product can then be ground, if necessary, to obtain the desired grain size. The operation is carried out in a conventional apparatus: a blade grinder or an air-jet grinder.

The invention also relates to toothpaste compositions comprising silicas of the type described above or prepared by the process discussed above.

The amount of silica according to the invention used in the tooth paste mixture can vary within wide limits: it is usually 5-35%.

The silicas according to the invention are particularly well suited for toothpaste mixtures containing at least one component selected from the group consisting of fluorides, phosphates, guanidines, including chlorhexidine. Their compatibility, as determined by the experiments described below, may be at least 90% for each ingredient.

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They are also well suited for Hamm & stach blends containing at least one ingredient selected from the group consisting of organic amine components and components that provide a divalent or higher metal cation. Their compatibility can also be as high as 80% for each ingredient, as determined by the experiments described below.

The silicas according to the invention are particularly well suited for toothpaste mixtures which simultaneously contain at least one component selected from the group consisting of simple inorganic fluorides and organic fluorides, at least one component selected from the group consisting of alkyl betaines and at least one component selected from the group consisting of guanidines. especially chlorhexidine.

More specifically, mention may be made of mixtures comprising sodium fluoride and / or tin fluoride and / or a fluorinated amine, in particular ketylamine hydrofluoride, bis (hydroxyethyl) aminopropyl-N-hydroxyethyl-octadecylamine dihydrofluoride and an alkyl chloride.

The silicas according to the invention are furthermore compatible with m & leic acid-vinyl ethyl ether copolymers and can thus be incorporated into toothpaste mixtures containing these copolymers.

The amount of fluorinated compounds, in turn, preferably corresponds to a fluorine concentration in the mixture of 0.01 to 1% by weight * and more particularly 0.1 to 0.5% by weight *. Fluorinated compounds include, in particular, salts of monofluorophosphoric acid, and in particular its sodium, potassium, lithium, calcium, aluminum and ammonium salts, mono- and difluorophosphates, and various fluorides containing fluorine in the form of a bound ion, especially time fluorides such as sodium, lithium, potassium fluorides, ammonium fluoride, stannous fluoride, 91386 23 manganese fluoride, zirconium fluoride, aluminum fluoride and adducts of these fluorides with each other or with other fluorides such as potassium fluoride or sodium fluoride or manganese fluoride.

Other fluorides may be used in this invention, such as zinc fluoride, germanium fluoride, palladium fluoride, titanium fluoride, temporal fluorozirconates, for example sodium or potassium fluorozirconates, tin (II) fluorozirconate, fluoroborate or sodium and potassium fluoride.

The organofluorine compounds mentioned at the beginning of the description can also be used, preferably ketylamine fluoride and bis (hydroxyethyl) aminopropyl-N-hydroxyethyl-octadecylamine dihydrofluoride.

Of the ingredients that introduce divalent or higher value metal cations, and those mentioned above in this specification, the most common are zinc citrate, zinc sulfate, strontium chloride and tin fluoride.

Ingredients which can be used as anti-plaque agents of the polyphosphate, polyphosphonate, guanidine, bis-guanidine type can be mentioned in U.S. Pat. No. 3,934,002 or U.S. Pat. No. 4,110,183, the contents of which are incorporated herein by reference.

Toothpaste compositions may additionally contain a binder.

The main binders used are, in particular: - cellulose derivatives: methylcellulose, hydroxyethylcellulose, sodium carboxymethylcellulose, - mucilages: carrageenans, alginates, agar-agar and gelling agents, - gums, gum arabic, gum arabic, gum tragacanth carboxyvinyl and acrylic polymers, polyoxyethylene resins.

In addition to the silicas according to the invention, the toothpaste compositions may also contain one or more other abrasive and wetting agents, in particular: - doped calcium carbonate - magnesium carbonate - calcium, dicalcium and tricalcium phosphates - and silico aluminates - zinc and tin oxides - talc - kaolin.

Toothpaste compositions may also contain surfactants, wetting agents, perfumes, sweeteners, and coloring and preservative agents.

The main surfactants used are: sodium lauryl sulphate - sodium lauryl ether sulphate and lauryl sulphoacetate - sodium dioctyl sulphosuccinate - sodium lauryl sarcosinate - sodium ricinoleate - sulphated monoglycerides.

The wetting agents used are mainly polyalcohols, such as: - glycerol - sorbitol, usually as a 70% aqueous solution - propylene glycol.

91386 25 The main fragrances are in particular: anise, star anise, mint, juniper berry, cinnamon, spice carnation and rose essences.

The main sweeteners are orthosulfobenzoic acid imides and cyclamates.

The dyes used are mainly depending on the color desired: - red and pink color: amaranth, azorubine, tannin extracted from catechuase, new carmine (Ponceau 4 R), cochineal, erythrosine - green color: chlorophyll and chlorophyllin - yellow color: sun yellow and yellow quinolein yellow.

The most commonly used main preservatives are: parahydroxybenzoates, formaldehyde and its release products, hexetidine, quaternary ammonium, hexachlorophene, bromophen and hexamedine.

Finally, the toothpaste compositions contain therapeutic substances, the most important of which are in particular: - antiseptics and antibiotics - enzymes - oligogens and fluorinated compounds described above.

The following are concrete examples that illustrate but do not limit the invention.

Before that, a procedure for measuring pH as a function of electrical conductivity and concentration is described, as well as experiments for measuring the compatibility of silica with various components.

26

Procedure for measuring pH as a function of silica concentration and electrical conductivity

Silica suspensions with a concentration ranging from 0 to 25% by weight are formed by dispersing a mass of silica m pre-dried at 120 ° C for 2 hours in a mass of deionized and degassed water of 100 m (Mi 11ipore grade). The suspensions are stirred for 24 hours at 25 ° C.

The pH of suspensions and solutions obtained by centrifuging a portion of the suspension at 8000 rpm for 40 minutes and filtering through a 0.22 μm Mi 11ipore filter is measured at 25 ° C under a nitrogen atmosphere with a Titroprocessor Metrohm 672 type sieve measuring system.

In the same way, the electrical conductivity of the suspensions and the solutions prepared as described above is measured at 25 ° C by an electrical conductivity radio meter 1a (CDM83) equipped with a type CDC304 cell with a cell constant of 1 cm ~ 1. Electrical conductivity is expressed in microsiemens.cm.

The potency (SE) of the suspension is determined by the difference between the pH of the suspension containing 20% silica and the pH of the supernatant solution separated by centrifugation.

Measurement of compatibility with bis (hydroxyethyl) aminopropyl-N-hydroxyethyl-octadecylamine dihydrofluoride 1) Form an aqueous solution (1) containing 1.65% of a fluorinated amine by adding 5 g of a solution containing 33 l of a fluorinated amine in propanediol, 95 g of doubly distilled water.

2) Disperse 4 g of silica in 16 g of the solution prepared in 1).

The suspension thus obtained is stirred for 4 weeks at 37 ° C.

91386 27 3) The suspension is then centrifuged at 8000 rpm for 30 minutes and the resulting surface solution (3) is filtered through a 0.22 μm Mi 11 ipore filter.

4) The content of free fluorinated amine in the solution obtained in 1) and in the supernatant solution obtained in 3) is determined by microanalysis of nitrogen.

5) Compatibility is determined using the equation belowa: N concentration in the supranatant (3) ♦ compatibility ---—- x 100 N concentration in solution (1)

In the following, compatibility - * with a fluorinated amine is denoted by AF.

Measurement of Compatibility with Ketylamine Hydrofluoride 1) An aqueous solution (1) containing 1.72% of a fluorinated amine is formed by dissolving 1.72 g of ketylamine hydrofluoride in 98.28 g of doubly distilled water.

2) Disperse 4 g of silica in the solution attenuated in 1).

The suspension thus obtained is stirred for 4 weeks at 37 ° C.

3} The suspension is then centrifuged at 8000 rpm for 30 minutes and the resulting supranatant (3) is filtered through a 0.22 μm Mi 11ipore filter.

4) The content of free fluorinated amine in the solution obtained in 1) and in the supranatant obtained in 3) is determined by microanalysis of nitrogen.

5) Compatibility is determined using the equation below: 28 N content in the supranatant (3)% compatibility - -——- x 100 N content in solution (1)

The following% compatibility with the fluorinated amine is denoted AFC.

Measurement of compatibility with alkyl betaine The alkyl betaine used is a product sold by AKSO under the trade name Armoteric LB.

1) An aqueous solution (1) containing 2.0% of alkyl betaine is formed by dissolving 6.67 g of alkyl betaine at 30% in 93.33 g of doubly distilled water.

2) Disperse 4 g of silica in 16 g of the solution prepared in 1).

The suspension thus obtained is stirred for 4 weeks at 37 ° C.

3) The suspension is then centrifuged at 8000 rpm for 30 minutes and the supernatant (3) obtained is filtered through a 0.22 μm Mi 11ipore filter.

4) The content of free alkyl betaine in the solution obtained in 1) and in the supranatant obtained in 3) is determined by microanalysis of organic carbon.

5) Compatibility is determined using the equation below: C concentration in the supranatant (3) * compatibility - x 100 C concentration in solution (1)

In the following, the% compatibility with alkyl betaine is denoted by ABeta.

91386 29

Measurement of compatibility with alkylamidoalkyl betaine 1) An aqueous solution (1) containing 2.0% alkylamidoalkyl betaine is formed by dissolving 6.67 g of alkylamidoalkyl betaine at 30% in 93.33 g of doubly distilled water.

2) Disperse 4 g of silica in 16 g of the solution prepared in 1).

The suspension thus obtained is stirred for 4 weeks at 37 ° C.

3) The suspension is then centrifuged at 8000 rpm for 30 minutes and the supernatant (3) obtained is filtered through a 0.22 μm Mi 11ipore filter.

4) The content of free alkylamidoalkyl betaine in the solution obtained in 1) and in the supranatant obtained in 3) is determined by microanalysis of organic carbon.

5) Compatibility is determined using the equation below: C content in the supranatant (3)% compatibility ---- 100 C concentration in solution (1)

In the following, the% compatibility with alkylamidoalkyl betaine is denoted by Beta.

Measurement of chlorhexidine compatibility 4 g of silica are dispersed in 16 g of an aqueous solution of chlorhexidine at a concentration of 1% of chlorhexidine di-gluconate.

The suspension is stirred for 24 hours at 37 ° C.

30

The suspension is then centrifuged at 20,000 rpm for 30 minutes and the resulting supranatant is filtered through a 0.2 μm Millipore filter.

Then take 0,5 ml of the solution thus filtered and dilute to 100 ml with water in a graduated flask. This solution forms a test solution.

Prepare the reference solution by the same procedure but without silica. The aqueous solution containing 1 * chlorhexidine digluconate is stirred for 24 hours at 37 ° C, then centrifuged at 20,000 rpm and the supernatant is filtered through a 0.2 μια: η Mi 11 ipore filter. Dilute 0.5 ml of the solution thus obtained to 100 ml of water in a graduated flask.

The absorbance of the two solutions is then measured at 254 nm with a spectrophotometer (Uvikon 810/820).

Once the amount of free chlorhexidine has been determined, the% compatibility is determined by the equation:% absorbance of the test solution% compatibility - x 100 absorbance of the reference solution

Measurement of compatibility with fluorides 4 g of silica are dispersed in 16 g of a solution of 0.3% sodium fluoride (NaF). The suspension is stirred for 24 hours at 37 ° C. After centrifugation of the suspension at 20,000 rpm for 30 minutes, the supranatant is filtered through a 0.2 μm Mi 11ipore filter. The solution thus obtained forms a test solution.

Prepare the reference solution using the same procedure but without silica.

91386 31

Compatibility with fluorides is determined by the percentage of free fluorine at the fluoride-selective electrode (Orion). It is determined according to the equation below.

F concentration in the test solution (ppm) Compatibility% x 100 F concentration in the test solution (ppm)

Measurement of compatibility with zinc 4 g of silica are dispersed in 100 g of a solution containing 0.06% ZnSO4, 7Η2θ. A suspension is obtained, the pH of which stabilizes at 7 within 15 minutes by the addition of NaOH or ^ 2 ^ 4 4 * The suspension is then stirred for 24 hours at 37 ° C and then centrifuged at 20,000 rpm for 30 minutes.

When the supranatant is filtered through a 0.2 μm Mi 11ipore filter, it forms a test solution.

Prepare the reference solution using the same procedure but without silica.

The free zinc concentration of these two solutions is determined by atomic absorption (214 nm).

Compatibility is determined by the equation below:

Zn concentration in the test solution (ppm)

Compatibility ä - x 100

Zn content in the vertical solution (ppm)

Measurement of compatibility with sodium and potassium pyrophosphates 4 g of silica are dispersed in 16 g of a 1.5% suspension of sodium or potassium pyrophosphate. The suspension is stirred for 24 hours at 37 ° C, then centrifuged at 20,000 rpm for 30 minutes.

32

The supranatant is filtered through a 0.2 micron porous filter. 0.2 g of the solution diluted in 100 ml of water in a graduated flask forms a test solution.

Prepare the reference solution using the same procedure but without silica.

The free pyrophosphate ion content (P2O7--) of both solutions is determined with an ion chromatograph equipped with an integrator (DIONEX 2000i system).

The compatibility is determined by the ratio of the areas of the peaks in the chromatogram obtained with the test solution and those of the reference solution which correspond to the retention time of the pyrophosphate.

Peak area of the test solution

Compatibility ä --——- x 100

Peak area of the reference solution

Example 1

A reactor equipped with a temperature and pH control system and a coil mixing system (Mixel) is charged with 8.32 l of sodium silicate with a silica content of 130 g / l and a molar ratio of SiO 2 / Na 2 O to 3.5, and 8.33 l of softened water with an electrical conductivity of 1 pS / cm.

After stirring (350 rpm), the mother liquor thus prepared is heated to 90 ° C.

When this temperature is reached, sulfuric acid at a concentration of 80 g / l is added at a constant rate of 0.40 l / min to adjust the pH to 9.5.

Then 45.25 l of sodium silicate with a silica concentration of 130 g / l and a molar ratio of SiO 2 / Na 2 O of 3.5 are added simultaneously at a rate of 0.754 l / min and 29.64 l of sulfuric acid with a concentration of 80 g / l. The rate of addition of sulfuric acid is adjusted so that the pH of the reaction medium remains constant at 9.5.

After the addition has continued for 60 minutes, the addition of sodium silicate is stopped and the addition of sulfuric acid is continued at a rate of 0.494 l / min until the pH of the reaction mixture stabilizes at 8.0. During this step, the temperature of the medium is raised to 95 ° C. Maturation is then carried out for 30 minutes at this pH and at 95 ° C. During ripening, the pH is maintained at 8 by the addition of acid.

At the end of the maturation, the pH is adjusted to 5.5 by adding sulfuric acid at a rate of 0.494 l / min and then maturing for 30 minutes at this pH and at 95 ° C.

At the end of ripening, the pH is adjusted to 3.5 by adding sulfuric acid. This pH of 3.5 is maintained for 30 minutes.

When the heating is stopped, the mixture is filtered and the cake obtained is washed with deionized water until a filtrate with a conductivity of 2000 pS / cm is obtained. The cake obtained after washing is dispersed in the presence of deionized water to give a suspension with a silica content of 10 *. The pH of the suspension is adjusted to 6 by adding acetic acid.

A second filtration is performed, followed by washing with water to adjust the electrical conductivity to 500 pS / cm and washing with water adjusted to pH 5 with acetic acid to adjust the pH to 5.5.

The validity of the following equation is then checked: pH <8.20 to 0.91 log (D).

The cake is then broken up and the silica is spray dried. The silica obtained is finally ground in a blade mill to give a powder with an average diameter of the agglomerates of 8 μm as measured by Counter-Coulteri.

34 The physicochemical properties of the silica thus obtained are summarized in the table below: BET surface m ^ / g 65 CTAB surface m ^ / g 60 Solidification DOP ml / 100 g silica 125 Pore volume Hg cm ^ / g 1.90 pH (5 % water) 6.2

Refractive index 1,450 Transparency% 90 SC> 4 “ppm 100

Na + ppm 60

Al 2 + ppm 200

Fe 2+ ppm 120

Ca 2+ ppm 30

Cl- ppm 20 C ppm 5

Table 1 summarizes the surface chemistry properties of the silica of the invention and Table 1 gives results for compatibility with organic amine compounds and Table 2 for results with compatibility with the classic ingredients of toothpaste mixtures: chlorhexidine, fluoride, zinc and pyrophosphate.

Es i merkk i 2

A reactor equipped with a temperature and pH control system and a coil mixing system (Mixel) is charged with 5.30 l of sodium silicate with a silica content of 135 g / l and a molar ratio of SiO 2 / Na 2 O - 3.5 and 15.00 l of softened water. with an electrical conductivity of 1 pS / cm.

After stirring (350 rpm), the mother liquor thus prepared is heated to 90 ° C.

91386 35

When this temperature is reached, sulfuric acid at a concentration of 80 g / l is added at a constant rate of 0.38 l / min to adjust the pH to 9.5.

Then, 44.70 l of sodium silicate with a silica concentration of 135 g / l and a molar ratio of SiO 2 / Na 2 O of 3.5 are added simultaneously at a rate of 0.754 l / min and 25.30 l of sulfuric acid with a concentration of 80 g / l. The rate of addition of sulfuric acid is adjusted so that the pH of the reaction medium remains constant at 9.5.

After the addition has continued for 60 minutes, the addition of sodium silicate is stopped and the addition of sulfuric acid is continued at a rate of 0.350 l / min until the pH of the reaction mixture stabilizes at 8.0. During this step, the temperature of the medium is raised to 95 ° C. Maturation is then carried out for 30 minutes at this pH and at 95 ° C. During ripening, the pH is maintained at 8 by the addition of acid.

At the end of the maturation, the pH is adjusted to 5.0 by adding sulfuric acid at a rate of 0.400 l / min and then maturing for 30 minutes at this pH and at 95 ° C.

At the end of ripening, the pH is adjusted to 3.5 by adding sulfuric acid. This pH of 3.5 is maintained for 30 minutes.

When the heating is stopped, the mixture is filtered and the cake obtained is washed with deionized water until a filtrate with an electrical conductivity of 2000 pS / cm is obtained.

The cake is then decomposed in the presence of water to give a suspension with a silica content of 20% and the pH is adjusted to 5.1 so that the following equation is true: pH <8.20 to 0.91 log (D).

The silica is dried by annealing and ground in a blade mill to give a powder with an average diameter of the agglomerates of 8.

36 The physicochemical properties of the silica thus obtained are summarized in the table below: BET surface m2 / g 100 CTAB surface m ^ / g 80 Solidification DOP ml / 100 g silica 200 Pore volume Hg cm ^ / g 3.35 pH (5 % water) 6.5

Refractive index 1.455 Transparency% 95 SO4 * ppm 0.5

Na + ppm 0.25

Al 2 + ppm 350

Fe 2+ ppm 120

Ca 2+ ppm 50

Cl "ppm 20 C ppm 5

Table 1 summarizes the surface chemistry properties of the silica of the invention and Table 1 gives the results for compatibility with organic amine compounds and Table 2 the results for compatibility with the classic ingredients of toothpaste mixtures: chlorhexidine, fluoride, zinc and pyrophosphate.

Example 3

5.60 l of sodium silicate with a silica content of 135 g / l and a molar ratio of SiO2 / Na2O of 3.5 are charged to a reactor equipped with a temperature and pH control system and a helical mixing system (Mixel).

After stirring (350 rpm), the mother liquor thus prepared is heated to 85 ° C.

When this temperature is reached, sulfuric acid preheated to 70 ° C at a concentration of 91386 37 85 g / l is added at a constant rate of 0,50 l / min to adjust the pH to 9,7.

52.64 l of sodium silicate with a silica concentration of 135 g / l and a molar ratio of SiO2 / Na2O of 3.5 are then added simultaneously at a rate of 0.745 l / min and 30.00 l of sulfuric acid with a concentration of 85 g / l. The rate of addition of sulfuric acid is adjusted so that the pH of the reaction medium remains constant at 9.7. Simultaneous addition is performed at 85 ° C using reagents preheated to 70 ° C.

After the addition has continued for 45 minutes, the addition of sodium silicate is stopped and the addition of sulfuric acid is continued at a rate of 0.450 l / min until the pH of the reaction mixture stabilizes at 8.0. During this step, the temperature of the medium is raised to 95 ° C. Maturation is then carried out for 10 minutes at this pH and at 95 ° C. During ripening, the pH is maintained at 8 by the addition of acid.

At the end of the maturation, the pH is adjusted to 5.0 by adding sulfuric acid at a rate of 0.750 l / min and then maturing for 15 minutes at this pH and at 95 ° C.

At the end of ripening, the pH is adjusted to 3.7 by adding sulfuric acid. This pH of 3.7 is maintained for 60 minutes.

When the heating is stopped, the mixture is filtered and the cake obtained is washed with deionized water until a filtrate with an electrical conductivity of 2500 pS / cm is obtained.

The cake is decomposed in the presence of water to give a suspension with a silica content of 20% and the pH is adjusted to 5.5 by adding to verify the following equation: pH <7.5 - 0.70 log (D).

38

The silica is spray dried and ground in a blade mill to give a powder with an average diameter of the agglomerates of 8.

The physicochemical properties of the silica thus obtained are summarized in the table below: BET surface n »2 / g 200 CTAB surface n» 2 / g 55 Solidification DOP ml / 100 g silica 110

Pore volume Hg cm3 / g 2.65 pH (5 * water) 7.0

Refractive index 1,460 Transparency% 85 S04 “% 200

Na +% 60

Al3 + ppm 150

Fe3 + ppm 120

Ca 2+ ppm 50

Cl- ppm 2 0 C ppm 5

The following Table 1 summarizes the surface chemistry properties of the silicas of the invention described in Examples 1-3.

Table 1 gives the results concerning the compatibility of the silicas according to the invention with organic amine compounds.

Table 2 below gives the results for compatibility with the classic ingredients of toothpaste mixtures: chlorhexidine, fluoride, zinc and pyrophosphate.

By way of comparison, Tables 1 and 2 show the properties and different compatibility of commercial silicas, for which the list below constitutes a representative collection of classical silicas.

S81: Syloblanc 81 (GRACE) Z113: Zeodent 113 {HUBER)

Sid12: Sident 12 (DEGUSSA)

Sy115: Sylox 15 (GRACE) T73: Tixosil 73 (RHONE-POULENC) T83: Tixosil 83 (RHONE-POULENC).

table 1

Physicochemical properties and compatibility with organic amine compounds of the silicas and classical silicas according to the invention

Physicochemical Properties of Silicas Compatibility

Silica * oxide pH / log (C) pH / log (D) SE Ho PZC AF Beta CHx S81 4.7-0.75x 7.0-0.62z -0.17 <2 2.2,000 Z113 8, 1-0.94x 10-1, Oz -0.70 <3 2.5,000

Sid12 7.6-0.55x 8.5-0.60z -0.20 <3 2.8,000

Sy115 8.1-0.70x 9.2-0.74z -0.94 <3 2.5,000 T73 8.6-0.81x 10-0.87z -0.20 <3 3.0,000 T83 7 , 5-0.60x 8.6-0.60z -0.18 <_3 2.5 0 0 0

Eg 1 7.5-0.30x 8.0-0.50z -0.00 _> 4 4.3 85 60 95

Example 2 6.5-0.80x 8.2-0.90z -0.10> 4 4.5 85 50 30

Example 3 7.0-0.40x 7.4-0.60z -0.06> 4 4.0 80 50 90

The meanings of the symbols used in the table above are as follows: - pH / log (C) represents the equation pH * ba.log (C), where a and b 40 are two constants and C represents the weight percentage of silica in the suspension - pH / log (D) represents the equation pH b'-a'log (D), where b 'and a' are two constants and 0 is the electrical conductivity of the silica suspension expressed in pSiemens / cm - SE represents the efficiency of the suspension measured by the equation SE «suspension pH - pH of the supranatant defined on the other hand - Ho is the Hammett constant - PZC is the pH at which the surface charge of silica is zero - AF, AFc, Beta, ABeta and CHx represent percent compatibility with fluorinated amines, alkylbetaines and chlorhexidine, respectively. These quantities are defined elsewhere.

The percentages of compatibility obtained with the fluorinated amine AFc and the alkyl betaine ABeta are the same as those obtained with AF and Beta, respectively.

Table 2

Compatibility of silicas with active molecules

Compatibility Jr

Silicon, oxide P207 "Zn ++ F- AF Beta CHx S81 80 0 90 0 0 0 Z113 90 0 95 0 0 0

Sid12 80 10 90 0 0 0

Sy115 80 0 90 0 0 0 T73 90 20 90 0 0 0 T83 95 10 95 0 0 0

Eg 1 95 80 95 85 60 95

Eg 2 90 75 95 85 50 30

Eg 3 95 80 95 80 50 90 91386 41

The results in Table 1 above show that the silicas of the invention, which are compatible especially with organic amine compounds, clearly differ from the classical silicas in the following equations: pH <. 8.5-0.40 log (D) and pH ± 7.0-0.60 log (D) pH A 7.5-0.70 log (C) and pH 2 5.0-0.50 log ( C).

Claims (57)

Silica, characterized in that it results in an aqueous suspension whose pH varies as a function of its concentration in the range defined by the following two inequalities: - pH <7,5 to 0,7 log (C) (Ia) - pH 2 5,0 - 0.5 log (C) (Ib) and whose pH varies according to its electrical conductivity in the range defined by two inequalities: - pH _ <8.5 - 0.4 log (D) (Ha) and - pH _> 7.0 - 0 , 6 log (D) (IIb) in which inequalities (Ia) and (Ib) to (C) represent the weight concentration of the aqueous silica suspension expressed in * S1O2, and in inequalities (IIa) and (IIb) to (D) represent the electrical conductivity of the aqueous silica suspension expressed in microsiemens.cm ~ 1. Silica according to Claim 1, characterized in that its surface chemistry is such that its acidity function Ho is at least 4.0. Silica according to Claim 1 or 2, characterized in that its surface chemistry is such that the number of OH ~ ions, expressed in OH ~ / nm 2, is less than or equal to 12, preferably 6 to 10. 91386 Silica according to one of Claims 1 to 3, characterized in that it has a zero charge point (PZC) of at least 4, preferably 4 to 6. Silica according to one of Claims 1 to 4, characterized in that it is at least 30% compatible with organic amine compounds. Silica according to Claim 5, characterized in that it has a compatibility with the organic amine compounds of at least 50%, in particular at least 80%. Silica according to Claim 5 or 6, characterized in that it is compatible with organic amine compounds selected from the group consisting of fluorinated amines, amine oxides, alkylamines and alkylbetaines. Silica according to Claim 7, characterized in that the organic amine compound is ketylamine hydrofluoride, bis (hydroxyethyl) aminopropyl-N-hydroxyethyl-octadecylamine dihydrofluoride, an amine oxide of the formula R (CH 3) 2 N -> O, any alkyl betaine of the formula R-N + (CH3) 2-CH2-COO '' an alkylamidoalkyl betaine of the formula R-CO-NH2- (CH2) 3-N + (CH3) 2-CH2-COO '· wherein R represents a linear or branched alkyl group containing 10 to 24 carbon atoms. Silica according to Claim 1, characterized in that its compatibility with divalent or higher-value metal cations selected from groups 2a, 3a, 4a and 8 of the Periodic Table is at least 50%, in particular at least 70%. Silica according to Claim 9, characterized in that the metal cation is calcium, strontium, barium, aluminum, indium, germanium, tin, lead, manganese, iron, nickel, zinc, titanium, zirconium or palladium. Silica according to Claim 9 or 10, characterized in that the metal cation is in the form of a mineral salt, chloride, fluoride, nitrate, phosphate, sulphate or organic salt, acetate or citrate. Silica according to Claim 11, characterized in that the metal cation is in the form of zinc citrate, zinc sulphate, strontium chloride and tin fluoride. Silica according to Claim 1, characterized in that it is at least 30% and, in particular, at least 60% compatible with guanidine-type products, in particular chlorhexidine. Silica according to one of Claims 1 to 13, characterized in that it contains anions of the type SO 2, Cl, NO 3, PO 4, CO 3, not more than 5.10 m 3/100 g of silica. Silica according to Claim 14, characterized in that it contains up to 1.10 μmol, in particular 0.2.10 μmol / 100 g of silica. Silica according to one of the preceding claims, characterized in that it has a sulphate content, expressed as SO 1, of at most 0.1%, preferably at most 0.05% and even more preferably at most 0.01 k. Silica according to one of Claims 1 to 16, characterized in that it has a content of divalent or higher values of metal cations of at most 1000 ppm. Silica according to Claim 17, characterized in that the aluminum content is at most 500 ppm, the iron content is at most 200 ppm, the calcium content is at most 500 ppm and, in particular, at most 300 ppm. Silica according to one of Claims 1 to 18, characterized in that it has a carbon content of at most 50 ppm and, in particular, at most 10 ppm. Silica according to one of Claims 1 to 19, characterized in that it has a pH of at most 8 and, in particular, 6.0 to 7.5. Silica according to one of Claims 1 to 20, characterized in that it has a BET surface area of 40 to 600 m 2 / g. Silica according to one of Claims 1 to 21, characterized in that it has a CTAB surface area of 40 to 400 m 2 / g. Abrasive silica according to one of Claims 1 to 22, characterized in that it has a BET surface area of 40 to 300 m 2 / g. Silica according to Claim 23, characterized in that it has a CTAB surface area of 40 to 100 m 2 / g. Thickening type silica according to one of Claims 1 to 22, characterized in that it has a BET surface area of from 120 to 450 m 2 / g, in particular from 120 to 200 m 2 / g. Silica according to Claim 25, characterized in that it has a CTAB surface area of 120 to 400 m 2 / g. Dual-acting silica according to one of Claims 1 to 22, characterized in that it has a BET surface area of 80 to 200 m 2 / g. Silica according to Claim 27, characterized in that it has a CTAB surface area of 80 to 200 m 2 / g. Silica according to one of Claims 1 to 28, characterized in that it has an oil solidification value of 80 to 500 m 2/100 g. Silica according to one of Claims 1 to 29, characterized in that it has an average particle size of 1 to 10 μm. Silica according to one of Claims 1 to 30, characterized in that it has a bulk density of 0.01 to 0.3. Silica according to one of Claims 1 to 31, characterized in that it is a precipitation oxide. Process for the preparation of silica according to one of Claims 1 to 32, characterized in that a silicate is reacted with an acid to obtain a silica suspension or gel, the first maturation being carried out at a pH of greater than or equal to 6 and less than or equal to 8.5, then a second ripening at a pH of less than or equal to 6.0, a third ripening at a pH of less than or equal to 5.0, the silica is separated off, washed with water until an aqueous suspension is obtained, which The pH, measured from a suspension containing 20% Siesta, corresponds to the following equation: - pH - d - e log (D) (III) 91386 where in Equation (III): - e is a constant greater than or equal to 0,6 and less than or equal to 1.0, - d is a constant greater than or equal to 7.0 and less than or equal to 8.5, - (D) represents the electrical conductivity of the aqueous silica suspension expressed in microsiemens.cm-1 'and finally dried. Process according to Claim 33, characterized in that the silica suspension or gel is prepared by simultaneously adding a silicate and an acid to a base, which may be water, a colloidal suspension of silica containing 0 to 150 g / l of silica, expressed as fungi, silicate or inorganic or organic a salt, preferably an early metal salt. Process according to Claim 34, characterized in that both reagents are added simultaneously so that the pH remains constant at 4 to 10, preferably 8.5 to 9.5. Process according to Claim 34 or 35, characterized in that the temperature is 60 to 95 ° C. Process according to Claim 34, characterized in that a colloidal silica dispersion containing 20 to 150 g / l of silica is prepared by heating an aqueous silica solution at a temperature of 60 to 95 ° C and adding acid to said aqueous solution until the pH is 8. , 0-10.0, preferably 9.5. Process according to Claim 33, characterized in that a silica suspension or gel is prepared by gradually adding the acid to a base containing silicate until the desired ripening pH is obtained at a temperature of 60 to 95 ° C. Process according to one of Claims 33 to 36, characterized in that the silica suspension or gel is subjected to a first maturation at a pH of 6 to 8.5, preferably 8.0, 60 to 100 ° C, more preferably 95 ° C. temperatures in the evening. Process according to one of Claims 33 to 39, characterized in that the silica suspension or gel is subjected to a second maturation at a pH of 5 to 6, preferably 5.5, at a temperature of 60 to 100 ° C, more preferably 95 ° C. Process according to one of Claims 33 to 40, characterized in that the silica suspension or gel is subjected to a third maturation at a pH of 3 to 5, preferably 4, at a temperature of 60 to 100 ° C, more preferably 95 ° C. Process according to Claim 33, characterized in that the washing is carried out with water or an acidic solution. A method according to claim 33, characterized in that the washing is performed, which is continued until the electrical conductivity of the washing filtrate is at most 200 micro-seeds.cm ~ 1 * A method according to claim 43, characterized in that the washing is performed with water or an acidic solution. Process according to Claim 42 or 44, characterized in that said acid solution is a solution of an organic acid, in particular a co-acid. A process according to claim 45, characterized in that the organic acid is selected from the group consisting of carboxylic acids, dicarboxylic acids, aminocarboxylic acids, hydroxycarboxylic acids. Process according to Claim 45 or 45, characterized in that the organic acid is selected from the group consisting of acetic acid, gluconic acid, tartaric acid, citric acid, maleic acid and glyceric acid. Toothpaste mixture, characterized in that it contains silica according to one of Claims 1 to 32 or silica prepared by a process according to one of Claims 33 to 47. A toothpaste mixture according to claim 48, characterized in that it further comprises at least one ingredient selected from the group consisting of fluorine, phosphates and guanidines. The toothpaste composition of claim 48, further comprising at least one ingredient selected from the group consisting of organic amine compounds and divalent and higher cations. A toothpaste mixture according to claim 48, characterized in that it comprises at least one organic amine compound selected from the group consisting of fluorinated amines, amine oxides, alkylamines and alkylbetaines. Toothpaste composition according to Claim 51, characterized in that the organic amine compound is ketylamine hydrofluoride, bis (hydroxyethyl) aminopropyl-N-hydroxyethyl-octadecylamine dihydrofluoride, an amine oxide of the formula R (CH 3) 2 N-> O, an alkyl of the formula R-N + (CH3) 2-CH2-COO-, an alkylamidoalkyl betaine of the formula R-CO-NH2- (CH2) 3 ~ N + (CH3) 2 ~ CH2-COO ", in which R represents a linear or a branched alkyl group containing 10 to 24 carbon atoms. A toothpaste mixture according to claim 48, characterized in that it contains at least one divalent or higher metal cation selected from groups 2a, 3a, 4a and 8 of the Periodic Table. Toothpaste mixture according to Claim 53, characterized in that the metal cation is calcium, strontium, barium, aluminum, indium, germanium, tin, lead, manganese, iron, nickel, zinc, titanium, zirconium or palladium. Toothpaste mixture according to Claim 53 or 54, characterized in that the metal cation is in the form of a mineral salt, chloride, fluoride, nitrate, phosphate, sulphate or organic salt, acetate or citrate. Toothpaste mixture according to one of Claims 53 to 55, characterized in that the metal cation is in the form of zinc citrate, zinc sulphate, strontium chloride and tin fluoride. Toothpaste mixture according to Claim 48, characterized in that it contains chlorhexidine. 91386