FI89899B - SPECIELLT MED KLORHEXIDIN KOMPATIBEL KISELDIOXID FOER ANVAENDNING I TANDKRAEMSKOMPOSITIONER - Google Patents

Description

1 * 89899

Silica for use in Hamm & oakmake preference, specially compatible with chlorhexidine

The invention relates to silica, which is particularly suitable for toothpaste compositions, to a process for its preparation, as well as toothpaste compositions containing this silica.

It is known that silica is commonly used in the manufacture of toothpastes. Besides, it can have many functions in it.

First, it acts as an abrasive and, through its mechanical action, contributes to the removal of dental plaque.

It may also act as a thickening agent to impart to the toothpaste certain Theological properties as well as an optical agent to impart a desired color.

In addition, it is known that toothpastes contain various active ingredients, in particular for the prevention of tooth decay, to reduce the formation of dental plaque or for the formation of tartar. Among these substances, fluorides in particular can be mentioned. Other substances are also used, such as phosphates, pyrophosphates, polyphosphates, polyphosphonates, guanidines; especially bis-biguanidines, one of the most commonly used of which is chlorhexidine. Toothpaste formulations may also contain zinc, flavorings, perfumes, etc.

The presence of these active ingredients in toothpaste poses a problem of their compatibility with silica. Indeed, due to their adsorbent properties, silica may tend to react with these active ingredients so that they are no longer able to function therapeutically as described above.

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The object of the invention is therefore to find silicas which are compatible with the abovementioned active ingredients and in particular with guanidines and are therefore very suitable for the formulation of toothpastes.

Another object of the invention is to find a process which makes it possible to prepare such compatible silicas.

But with this in mind, it was realized that the compatibility properties sought depended above all on the surface chemistry of the silica used. Therefore, a number of conditions were established on the surface of the silica to make the silicas compatible.

The silica according to the invention is characterized in that it is compatible with guanidine-type products, and in particular chlorhexidine, at least 65% and more particularly at least 90%.

Furthermore, the silica according to the invention, which is compatible in particular with guanidine-type and in particular chlorhexidine, is also characterized in that its surface chemistry is such that its acid function Ho is at least 3.3.

In addition, according to a first variant, the silica production method of the type described above comprises reacting a silicate with an acid to obtain a silica suspension or gel, separating and drying the silica, and characterized in that the cake resulting from this separation is rinsed with water until the conductivity of the filtrate is at most 200 μS / cm.

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According to another variant, the process for preparing silica according to the invention comprises reacting a silicate with an acid to obtain a silica suspension or gel, separating and drying the silica, characterized in that the cake resulting from this separation is first rinsed with water followed by a second rinse or treatment with an acidic solution.

The invention therefore relates to toothpaste compositions containing silica of the type described above or silica prepared as mentioned above.

Other features and advantages of the invention will be best understood from the following description and the specific but non-limiting examples which follow.

As stated in the introduction, the essential features of the silicas according to the invention are located in their surface chemistry. More specifically, one of the notable aspects of this surface chemistry is acidity. In this respect, one of the characteristics of the silicas according to the invention is the strength of the acidic sites on their surface.

Here, acidity is understood as Lewis's notion, that is, it expresses the ability of a particular site to receive one pair of electrons from a base under the following equilibrium condition:

B: + A = BA

To characterize the silicas according to the invention, the term "acidity function" Ho, developed by Hammet, is used to measure the ability of an acid, in this case silica, to take up one electron pair from a base.

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The function Ho is defined by a known equation: pKa + log (B:) ---------- = Ho (B:> <A)

To determine the strength of the acidic sites of the silica according to the invention, the Hammett method uses the indicator method originally presented by Walling (J. Am. Chem. Soc. 1950, 72, 1164).

The intensity of the acidic sites is determined by color indicators for which the pKa of the transition between the acidic and basic forms under these conditions is known.

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

color

Indicator of the basic form of the acid form of pKa

Neutral red yellow red + 6.8

Methyl red yellow red + 4.8

Phenylazonaphthylamine yellow red +4.0 p-dimethylaminoazobenz yellow red + 3.3 mushene 2-amino-5-azotoluene yellow red + 2.0

Benzene azodiphenyl yellow red + 1.5 amine 4-dimethylamine azo-1-naphthalene yellow red + 1.2

Crystal purple blue yellow + 0.8 5 89899 p-nitro benzene iatβο- <ρ'-nitro] diphenylamine orange purple + 0.43

Disinfectant acetone yellow red - 3.0

Benealaetophenone colorless yellow - 5.6

Anthraquinone colorless yellow - 8.2

The color of the indicators adsorbed on a silica is a measure of the intensity of the acidic sites. If the color is the same as the color of the acid form of the indicator, the value of the Ho function of the surface is equal to or lower than the pKa of the indicator.

Low Ho values correspond to particularly strong acidic sites.

Thus, for example, silica which gives a red color with p-dimethylaminoazobenene and a yellow color with 2-amino-5-azotoluene will have an acidity function Ho between 3.3 and 2.

In the experiment, the dosing is carried out by placing 0.2 g of silica in a test tube with an indicator solution in a strength of 100 mg / l in cyclohexane.

. o

The silica is first dried at 190 ° C for 2 hours and stored protected from moisture in an eco-evaporator.

When mixed, any adsorption occurs within a few minutes and can be detected with the naked eye or by examining the adsorption spectra characteristic of any adsorbed color indicators in both their acidic and basic forms.

The first characteristic of the silicas according to the invention is that they have an acidity, as defined above, of at least 3.3.

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The intensity and nature of the acidic sites on the surface can also be measured by infrared spectrometry of pyridine adsorbed on silica.

It is known that the amount of pyridine adsorbed on a solid body makes it possible to determine in particular the nature of the acidic sites on the surface.

Pyridine is a relatively strong base (pKb = 9) and therefore does not react with weak sites in contrast to NH3 (pKb = 5).

+

In addition, the formation of the pyridinium ion (PyH>) allows the differentiation of Lewis-type and Bronsted-type sites.

Information on the acidity of the surface of a solid can also be obtained by examining pyridine absorption bands -1 -1 in the range 1700 cm 1400 cm

In addition, the band shift characteristic of pyridine and its ionized forms before and after adsorption allows the intensity of acidic sites to be quantified.

-1

Pyridinium ion gives a band at 1540 cm, while hydrogen-bonded pyridine or coordinated pyridine gives belts in the band 1440-1465 cm. In addition, it can be seen that the pyridine band at 1583 cm shifts as the pyridine adsorbs. This belt indicates the existence of Lewis-type acidic sites. The acidity of the latter is proportional to the displacement of the belt.

In summary, it is possible to use the bands at -11540, 1640 and 1485 cm for the determination of Bronsted-type acidity and the bands at 1440-1465 cm for the determination of Lewi-type acidity.

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Experimental measurements are performed with a carbon tetrachloride suspension of silica in the presence of pyridine.

o

First, the silica is dried at 190 ° C for 2 hours and stored protected from moisture. After cooling, it is dispersed using magnetic stirring, followed by an ultrasonic dispersion (10 min), 1 g of silica 50 any CCl 4.

0.8 g of pyridine per square meter of silica added is added. Heat to reflux with cooling and stirring for 1 hour.

Following the same procedure, prepare a reference solution of the same pyridine concentration but without silica and a reference suspension of the same silica concentration but without pyridine.

The adsorption spectrum of pyridine is obtained by infrared spectroscopy from a suspension, a pyridine solution without silica and a silica suspension without pyridine.

Subtract from the spectrum obtained from the starting spectrum the spectrum corresponding to the reference solution and the spectrum corresponding to the reference suspension.

Silica is determined by the location of the remaining bands and the displacement of the pyridine and pyridinium ion absorption bands relative to the location of the non-adsorbed forms of the bands.

In general, the spectrum obtained should not have a pyridinium peak (belt at 1540 cm), since the absence of this peak indicates an acid function Ho with a silica of at least 3.3.

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The significance of the displacement of the pyridine bands as well as the adsorbed pyridine makes it possible to evaluate the higher or lower acidity of the acidic sites on the surface. In general, for a belt of 1440 cm, this displacement <) should be at most 10 cm, more particularly at most 5 cm

According to a most preferred embodiment of the invention, this () is zero.

Silica as defined above is highly compatible with chlorhexidine, the compatibility measured by the test described below being at least 65X, especially at least 80X and most preferably at least 90X.

According to a particular embodiment of the invention, the silicas may be additionally compatible with fluorine. In this case, they have an anion content of the type SOA, Cl, 3- 2- -3 NOg, PO2, CO3 up to 5.10 moles / 100 g of silica.

The lower the concentration, the higher the compatibility. According to the preferred variants, it is at most -3 -3 1.10 moles and in particular 0.2.10 moles / 100 g of silica.

When sulfuric acid is used as the starting silica, this anion content is most conveniently expressed as SO 2 and by weight. In this case, this concentration is not more than 0.5 X.

According to a most preferred embodiment of the invention, this concentration is at most 0.1 X and preferably at most 0.02 X.

This compatibility can be further improved, especially for certain substances such as zinc, by observing the conditions for the number of acidic sites on the surface. This number can be measured as the number of 2 OH groups or silanols / nm.

9 89899 This chapter is determined as follows:

The number of OH sites on the surface is assimilated to the amount of water released between 190 ° C and 900 ° C.

o

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

Silicon oakeaeea Po is placed in a thermostat and kept at o 190 ° C for 2 hours; the mass obtained is denoted P190. The silica is then maintained at 900 ° C for 2 hours, at which time the new mass obtained is designated P900.

The number of OH sites is obtained from the following equation: 66922.2 P190-P900 NOH = _ x _ A P 190 2 where NOH is the number of OH sites per nm of surface; :: 2 A is the specific surface area of the solid body <BET> in m / g. In this case, the silicas according to the invention preferably have an OH / nm number of 15 or less, preferably at most 12 and in particular between 3 and 12.

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

This zero charge point (PZC) is determined by the pH of a silica suspension at which the electrical charge on the surface of the solid body is zero and remains so regardless of the ionic strength of the environment. This PZC measures the true pH of a surface based on how free it is from all ionic impurities.

ίο 3 9 8 99 The electric charge is determined by potentiometry. The principle of the method is based on the total balance of protons adsorbed on or desorbed from the surface of silica at a given pH.

As a starting point, it is easy to show the equations describing the overall balance of the operation that the electric charge C of the surface, taken in relation to the comparison corresponding to the zero surface charge, is obtained from the equation:

F

C = -------- (H - OH)

a.m

where: A is the specific surface area of the solid in m / g, M is the amount of solid in the suspension in grams, F is the Faraday constant, + - H resp. OH are H, resp. Excess OH ions on the surface of the solid per unit area.

The experiment for the determination of PZC is as follows: The method described by Perube and de Bruyn (J. Colloid Interface Sc. 1968, 27, 305) is used.

The silica is first rinsed in deposited water of high resistivity (10 Mega.Ohm.cm), dried and dry distilled.

In practice, KHH or HNOg is prepared by adding a series of solutions with a pH of 8.5 and containing an inert electrolytic electrolyte (KNOg) in the range of 10 to 10 mol / l in varying concentrations.

I: 11 8 9 899 To these solutions a certain mass of silica is added and the suspensions obtained are allowed to equilibrate with stirring, at 25 DEG C. and under a nitrogen atmosphere for 24 hours; let its value be pH'o.

The reference solutions consist of the supernatant obtained by centrifugation at 1000 l / min for 30 minutes of a portion of these same suspensions; let the pH of these supernatants be pH'o.

The pH of a certain volume of these suspensions and the corresponding reference solutions are then adjusted to pHo by adding the required amount of KOH and the suspensions and reference solutions are allowed to equilibrate for 4 hours.

Let Voh.Noh be the number of counter-values of the added base as it moves from pH'o to pHo of the suspension or reference solution in a given volume (V).

Potentiometric dosing of the suspensions and reference solutions is carried out as a starting point for pHo by adding nitric acid until pHf = 2.0.

Most preferably, the process is performed by making an acid addition corresponding to a pH change of 0.2 pH units. After each addition, the pH is allowed to equilibrate for 1 minute.

Let Vh.Nh be the number of acid equivalents to reach pHf.

As a starting point, the pHo is formulated according to the added pH values of the term <Vh.Nh-Voh.Noh) for all suspensions (at least 3 io levels) and for all corresponding reference solutions.

+

For each pH value (not 0.2) the difference in consumption of H or OH for both the suspension and the corresponding reference solution is then calculated. This procedure is repeated for all ionic strengths.

12 39899 This results in the term, <H-OH>, which corresponds to the proton consumption of the surface. The surface charge is calculated by the above equation.

The surface charge curves are then plotted according to pH for all ionic strengths considered. The intersection of the curves determines the PZC.

The silica concentration is adjusted according to the specific surface area of the silica.

2 For example, a 2% suspension is used for 50 m / g silicas with three ionic strengths <0.1; 0.01 and 0.001 mol / l).

Dosing is done with 100 ml of suspension using 0.1 M potassium hydroxide.

In practice, it is preferred that the value of this PZC is at least 3 and more preferably between 4-6. To be most compatible with zinc, it is at most 6.5. To be compatible with fluorine, it is most preferred for PZC to be at most 7.

In order to further improve the compatibility, in particular with fluorine, it is preferred that the silicas according to the invention have an aluminum content of at most 500 ppm.

On the other hand, the iron content of the silicas according to the invention can preferably be at most 200 ppm.

In addition, it is preferred that the calcium content is at most 500 ppm and preferably at most 300 ppm.

It is also preferred that the silicas according to the invention have a carbon content of at most 50 ppm and preferably at most 10 ppm.

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

The above properties make it possible for silica which is compatible at least with guanidines and in particular chlorhexidine and, where appropriate, also with fluorides, phosphates and their derivatives and in particular zinc.

In addition to the surface chemistry properties described above, which set the conditions for compatibility, the silicas of the invention also have physical properties that make them well suited for use in toothpastes. These structure type characteristics are described below.

In general, the surface area BET of the silicas according to the invention is between 40 and 600 m / g, more particularly between 40 and 350 m / g. Their surface CTAB usually varies between 40 and 400 m / g, more particularly between 40 and 200 m / g. / g.

The surface BET is determined according to the Brunauer-Emmet-Teller method as described in the Journal of the American Chemical Society vol. 60, page 309, February 1938 and according to standard NF-X11-622 (3.3).

Surface CTAB is an outer surface determined, however, according to ASTM D3765 using adsorption of hexadecyltrimethylammonium bromide at pH 9 and assuming a CTAB molecule in o2.

projected area 35 A

The silicas according to the invention can, of course, correspond to three types which are customarily distinguishable in toothpastes.

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The silicas according to the invention can thus be abrasive in blast. In this case, their surface BET is between 40-300 m / g. In this case, the surface CTAB is between 40 and 100 m / g.

The silicas according to the invention can also be of a thickening type. In this case, their surface BET is between 120-450 m / g 2, more particularly between 120-200 m / g. In this case, their surface area 2 CTAB can be between 120-400 m / g and even more particularly co-2

It has 120-200 m / g.

Finally, according to the third type, the silicas according to the invention can be bifunctional. Then their surface BET is 2 2 between Θ0-200 m / g. The surface CTAB, on the other hand, is between 80-200 m / g.

The silicas according to the invention can also have an oil uptake capacity of 80-500 cm / 100 g, determined according to standard NFT-30-022 (March 53), by carrying out dibutyl phthalate.

3 More specifically, this oil uptake capacity is between 100 and 140 cm / 100 g in the case of abrasive silicas, between 200 and 400 for thickening silicas and between 100 and 300 for double-acting silicas.

In addition, still contemplated for use in toothpaste, the particle size of the silica is most preferably in the range of 1-10 μm.

This average particle size is measured by the Counter-Coulter method.

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

The silicas of the invention generally have a refractive index between 1.440 and 1.465.

15 2 9 8 99

The process for the preparation of the silicas according to the invention will now be described in more detail.

As mentioned above, this method is of the type which involves the reaction of a silicate with an acid, resulting in the formation of a silica suspension or gel.

It should be noted that any known mode of action can be used to access this suspension or gel (addition of acid to the silicate mixture base, simultaneous, complete or partial addition of acid and silicate to the aqueous or silicate solution base, etc.); the choice is determined above all by the physical properties of the silica to be obtained. It will be appreciated that it may be advantageous to bring the pH of the suspension or gel obtained up to a maximum of 6 and more particularly between 4 and 6.

The separation of the silica from the reaction medium is then carried out by any known method, for example by suction filtration or filtration.

This is how the silica cake is collected.

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

The first variant relates in particular to the preparation of guanidines and, in particular, chlorhexidine-compatible silicas.

In this case, the method comprises one rinse of the cake. This rinsing takes place with water, usually deionized water, until a rinsing filtrate with a conductivity of at most 200 μS / cm is obtained.

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If the conductivity of the silicas obtained by the process is to be further improved, rinsing is continued.

In particular, according to the most preferred embodiment of the invention, the rinsing is continued until the conductivity is at most 100 μS / cm.

After the silica cake has been rinsed as just described, it is dried or, if it has broken up, its suspension using any known method. In particular, drying can be done by spraying. If necessary, the dried product is ground to achieve the desired granular composition.

Another variant of the process concerns the preparation of not only guanidines but also silicas compatible with other substances such as fluorine, zinc and phosphates.

Again, the method includes rinsing with water; usually with deionized water, as in the first-sack variant. However, this rinsing does not have to be as intense. For example, it can be carried out to obtain a filtrate having a conductivity of up to 2000 μS / cm.

After this first rinsing with water, in a second variant, a second rinsing or treatment of the cake with an acidic solution or acidic water is performed. The purpose of this second rinsing or treatment is to obtain from the process silica having a pH of at most 8 and more particularly between 6.0-7.5 and in addition a PZC of at least 3 and even more particularly between 4-6.

The rinsing or treatment can be done by pouring the acidic solution onto the cake or by adding the solution to the resulting suspension after the cake has broken down.

il 17 09899 This acid rinsing and treatment is carried out under conditions such that, in order to obtain the silica having the pH indicated in the preceding paragraph, the pH of the suspension or the environment before drying must be between 4-8, in particular 5-8 and even more particularly 6-7.

This acidic solution may be, for example, a solution of a mineral acid such as nitric acid.

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

Examples of such acids are acetic acid and, as complexing acids, tartaric acid, malic acid, glycerol acid, gluconic acid and citric acid.

It may be advantageous, especially when using a solution of a mineral acid, to perform a final rinse with deposited water.

After rinsing or treatment according to the second variant, the drying is performed in the same way as described above for the first variant.

According to another specific variant of the invention, after the reaction of the acid and the silicate, the maturation of the suspension or gel is carried out just before the separation of the silica. This cooking usually takes place at a pH of at most 6 and, for example, between 4-6.

It is also possible to carry out the maturation during the reaction, for example at a pH of 6-8. These ripenings are most preferably carried out in the hot, for example at a temperature of 80 to 8 9 899 ° C, in a time which can vary from 15 minutes to two hours.

It was found that it was possible to further improve the compatibility of the products according to the invention with another additional treatment.

The treatment involves the use of some alkaline earth. This substance can be added either to the silica suspension or gel or, most preferably, to the cake, especially when it has decomposed, for example in the form of a salt or hydroxide.

An organic salt is used which is complexed with an alkaline earth alkali, usually a barium salt, for example barium acetate.

The invention also relates to toothpaste compositions containing silicas of the type described above or obtained by the above process.

The amount of silica according to the invention when using the toothpaste composition can vary widely, generally between 5-35%.

The silicas according to the invention are particularly well suited for toothpaste compositions which contain at least one substance from the following group: fluorides, phosphates and guanidines, to which chlorhexidine belongs. Indeed, according to the tests that follow, these silicas may be at least 90% compatible with all of these substances.

The silicas according to the invention are furthermore compatible with copolymers of maleic acid and vinylethyl ether and can therefore be combined with i-containing copolymers.

^ 39899 for toothpaste compositions. They may be at least 50%, most preferably at least 80% compatible with the zinc people.

As for the fluorine compounds, their amount in the composition most preferably corresponds to a fluorine concentration of 0.01 to 1 * by weight, and more particularly 0.1 to 0.5 X. The fluorine compounds are in particular salts of monofluorophosphoric acid and especially sodium, potassium, lithium , calcium, aluminum and ammonium salts, mono- and difluorophosphates as well as various fluorides containing, in the form of a bound ion, in particular basic fluorides such as sodium, lithium, potassium fluoride, arammonium fluoride, tin-containing fluoride, manganese fluoride , zirconium fluoride, aluminum fluoride as well as adducts of these fluorides with each other or in combination with other fluorides such as potassium, sodium or manganese fluorides.

Other fluorides may also be used in this invention, such as zinc fluoride, germanium fluoride, palladium fluoride, titanium fluoride, basic fluorozirconates, various sodium and calcium zirconate, and tin fluorosulphate and fibroborate.

Organofluoro compounds can also be used, most preferably those known as long chain amine or amino acid adducts, together with hydrogen fluoride, cetylamine fluoride, bis- (hydroxyethyl> aminopropyl-N-hydroxyethyl-octadecylamine N-fluorine, dihydrofluoramide, octadecylamine, octadecyl N'-tri- (polyoxyethylene) -N-hexadecyl-propenediamine with dihydrofluoride enters the zinc, is especially present in the citrate or ®U1fate form.

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As the elements to be used as plaque agents, which are of the type polyfoefates or polyfoefonates, guanidines, bie-biguanidines, those mentioned in U.S. Pat. No. 3,934,002 or 4,110,083, the knowledge of which is incorporated herein by reference, may be mentioned.

In addition, the toothpaste compositions may contain a binder. The main binders used are selected in particular from the following: cellulose-containing derivatives: methylcellulose, hydroxyethylcellulose, sodium carboxylmethylcellulose; vegetable glues: carrageenates, alginates, agar-agar and gelatins; gums: gum arabic and tragacanth, xanthan gum, karaya gum; carboxyl vinyl and acrylic polymers; polyoxyethylene resins.

In addition to the silicas of the invention, the toothpaste compositions may also contain one or more other leveling abrasives selected in particular from: doped calcium carbonate, magnesium carbonate, di- and tricalcium-containing, potassium phosphates, insoluble sodium metaphane, phosphatophosphate, calcium sicides, aluminas and silicon aluminates, zinc and tin oxides, talc, kaolin.

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Toothpaste compositions may also contain detergents, humectants, flavors, sweeteners, and colorants and preservatives.

The main detergents used are selected in particular from sodium lauryl sulfate, lauryl ether sulfate and sodium lauryl sulfoacetate, sodium dioctyl sulfosuccinate, sodium lauryl sarcosinate, sodium risinosilate, sulfated monoglycerides.

The main wetting agents used are selected in particular from polyalcohols: glycerol, sorbitol, usually 70 X in solution in water, glycol propylene.

The main flavorings (fragrance) are selected in particular from the following: anise, star anise, mint, juniper berry, cinnamon, cloves and rose oils.

The main sweeteners are selected in particular from orthosulfobenzoimides and cyclamates.

The main dyes used are selected according to the desired color in particular: red and pink: amaranth, azorubine, ka-teku, new coxin (PONCEAU-4-R>, cochineal, erythrosine; green color: chlorophyll and chlorophyllin; yellow color: sun yellow) -S) as well as quinoline-yellow.

22 89 899 The main preservatives used are: parahydroxybenzoates, formol and its derivatives, hexstidine, quaternary ammonium, hexachlorophene, bromophen and hexamedamine.

Finally, toothpaste compositions contain therapeutically active substances, the most important of which are selected in particular from antiseptic and antibiotic substances, enzymes, trace elements and the above-mentioned fluorine compounds.

Hereinafter, concrete but non-limiting examples of the invention will be provided.

First, theses made to measure compatibility between silica and various substances are presented.

Measurement of compatibility with chlorhexidine 4 g of silica are dispersed in 16 g of an aqueous solution of chlorhexidine having a chlorhexidine digluconate concentration of 1 X. The suspension is stirred for 24 hours at 37 ° C.

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

Then separate 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.

The reference solution is made in the same way but without silica. An aqueous solution of chlorhexidine digluconate at 1X is stirred for 24 hours at 37 ° C, then centrifuged at 2000 rpm and the supernatant 23 89899 is filtered through a Millipore 0.2 filter. Dilute 0.5 ml of the solution thus obtained to 100 ml with water in a graduated flask.

The absorbance of each of the 254 solutions is then measured using a spectrometer (Uvikon 810/820).

Amount of free chlorhexidine expressed as% Compatibility is determined by the ratio:

Absorption of test solution% Compatibility = _____x 100

Absorption of the reference solution

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

The reference solution is made in the same way but without silica.

Compatibility with fluorides is determined by the amount of free fluoride X measured with a fluoride selective electrode (Orion). It is determined using the equation below.

F-concentration of the test solution (ppm) X Compatibility = __________— x * 00

F concentration of the reference solution (ppm)

Measurement of compatibility with zinc 4 g of silica are dispersed in 100 ml of a solution with a ZnSO 4, 7H 2 O concentration of 0.06 X. A suspension is obtained whose pH is stabilized at 7 for 15 minutes by adding NaOH or H 2 SO 4. The suspension is then stirred for 24 hours at 24 8 9 899 ° C and then centrifuged at 20,000 rpm for 30 minutes.

The eupernatant filtered through a Millipore 0.2 filter forms a test solution.

The reference solution is made in the same way but without silica.

The concentration of free zinc in each solution is determined by atomic absorption (<214 nm).

Compatibility is determined by the equation below:

Zn concentration of the test solution (ppm) X Compatibility = _ x 100

Zn concentration of the reference solution <ppm>

Measurement of compatibility of sodium and potassium prophosphates Kang-SA

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

The supernatant is filtered through a Millipore 0.2 filter.

A solution of 0.2 g in a graduated flask diluted in 100 ml of water forms a test solution.

The reference solution is made in the same way but without silica.

The concentration of free pyrophosphate ion <P2 ° 7> in each solution is determined by ion chromatography with an integrator (DIONEX-2000i system).

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The compatibility is determined from the ratio of the areas of the peaks obtained in the chromatograms, which peaks correspond to the retention time of the pyrophosphate in both the test and reference solutions.

peak area of the test solution * Compatibility = 100 x _______ peak area of the reference solution

Example 1 This example relates to the preparation of a compatible abrasive type silica.

6 l of deionized water are introduced into a reactor vessel equipped with a heat and pH control system and a turbine mixing system.

After stirring (<300 l / min), the mixture base thus obtained is heated to 85 ° C.

When the temperature has been reached, 8.5 l of sodium silicate with a silicate concentration of 120 g / l, a SiO2 / NaCl4 ratio of 3.5 and a flow rate of 0.34 l / min and 13.5 l of sulfuric acid with a concentration of 80 g / l are added simultaneously. The acid flow is adjusted so that the pH of the environment is constantly 8.0.

After the addition is continued for 40 minutes, the addition of silicate is stopped and the addition of acid is continued until the pH of the reaction mixture stabilizes at 4.

Maturation is then carried out for 15 minutes at this pH.

O

value and Θ5 C: eea.

The mixture is then filtered and the moist cake is rinsed with deionized water until the conductivity of the filtrate is less than 100 / US.

26 3 98 99 One cake rinse is then carried out with water adjusted to pH 4 by the addition of acetic acid.

The final rinse is performed with deionized water.

The product is then dried by melting and ground in a Forplex-type mill to give a 10 micron granular composition.

The physico-chemical properties of the silica thus obtained are as follows: 2

Surface BET 100 m / g 5

Surface CTAB 55 m / g 3 Absorption capacity 120 cm / 100 g pH 6.5

The chemical analyzes of silica are grouped in the following table.

ions S04 AI Fe Ca C

ppM 100 250 130 300 10

Surface chemistry is quantified by the following parameters:

Ho higher than 3.3 PZC = 4 -1 AV = 2 5 cm OH / nm number: 9.

The table below shows the compatibility of silica with the various ingredients of a toothpaste composition.

li 27 8 9 8 99

Ingredients Fluoride Pyrophosphate Chlorhexidine- Zinc NaF Na / K digluconate ZnSO 4% Total 95 98 75 70 Compatibility

Example 2

Follow Example 1 until a silica cake is rinsed once with water adjusted to pH 4 by the addition of acetic acid.

The cake thus obtained is decomposed in a disperser to obtain a liquid suspension.

0.2 g of barium acetate are added with stirring.

The silica is then dried by melting and ground to give an average particle size of 10.

The physico-chemical properties of the silica thus obtained are as follows: 2

Surface BET 100 m / g 2

Surface CTAB 60 m / g 3 01 absorption 110 cm / 100 g pH 6.5

The chemical analyzes of silica are grouped in the following table.

ions SO ^ AI Fe Ca C

ppM 100 250 130 400 40 28 89 899

Surface chemistry is quantified by the following parameters:

Ho higher than 3.3 PZC = 4.5 AV = 2 cm 2 OH / nm number = 8

Ingredients Fluoride Pyrophosphate Chlorhexidine Zinc NaF Na / K digluconate ZnSO 4 X compatibility 95 98 90 70 compatibility

Example 3 This example relates to the preparation of a gel containing a thickening silica.

A reactor vessel equipped with a heat and pH control system and a turbine mixing system is charged with 14 l of Na-sorlate with a silica concentration of 86 g / l and a SiO2 / Na2O ratio of 3.5.

When stirring is started <100 l / min), 1.45 l of 28% ammonia are added over 2 minutes.

0.8 l of sulfuric acid with a concentration of 200 g / l is then added at a flow rate of 0.2 l / min.

In this state, the mixture is allowed to react for 5 minutes at a controlled temperature of 20 ° C.

5.2 l of sulfuric acid at a concentration of 200 g / l are then added at a flow rate of 0.2 l / min, li 29; 9899

When the gel appears (visibly or by measuring the turbidity of the water), the mixture is allowed to mature for 10 minutes.

The gel is then dispersed by stirring the mixture at 400 rpm for 30 minutes.

The pH of the medium is then lowered to 3.5 by adding sulfuric acid (200 g / l) at a flow rate of 0.2 l / min.

The reaction mixture is allowed to equilibrate for 1 hour at 0 ° C.

The preparation of the gel is terminated by filtering this mixture and rinsing the resulting cake twice in 20 l of deionized water at a temperature of 60 ° C and in 20 l of water with a pH of 3.

The treatment according to the invention is then carried out by rinsing with deionized water at 20 ° C until a conductivity of 200 μS / cm is reached.

The resulting cake is decomposed to obtain a homogeneous silica suspension with a concentration of 10%, which concentration is adjusted by adding water.

The silica is dried by killing with an Anhydro-type eumutifier. The silica is then micronized with a JET Powder Mill to obtain a 1.5 micron grain composition.

The physico-chemical properties of the silica thus obtained are as follows: 2

Surface BET 450 m / g 2

Surface CTAB 350 m / g 3 01bsorption 300 cm / 100 g pH 6, Θ

Mean density 0.270

Refractive index 1,445 30 89899

The chemical analyzes of the silica are grouped in the table below.

ions SO4 AI Fe Ca C

ppM 500 200 120 300 10

Surface chemistry is quantified by the following parameters:

Ho higher than 3.3 PZC = 3.6

No pyridine adsorption bands Compatibilities

Ingredients Fluoride Pyro Foephate Chlorhexidine- Zinc

NaF NaK digluconate ZnSO 4 * compatible with 90 95 65 50

Example 4 This example relates to thickening silica.

6 l of water are introduced into a reactor vessel equipped with a heat and pH control system and 150 g of sodium sulphate are then added with stirring.

o

The mixture is heated to 60 ° C. Then 10 l of sodium silicate (Rm = 3.5 and S1O2 = 220 g / l) and sulfuric acid at a concentration of 80 g / l are added simultaneously in 40 minutes.

3i 89899

The sulfuric acid flow rate is adjusted so that the pH of the reaction medium remains constant at 7.8.

The pH of the environment is stabilized at 4.0 by the rapid addition of sulfuric acid. Allow to cook for 15 minutes at 60 ° C.

o

The reaction mixture is filtered at 60 ° C and the silica cake is rinsed with deionized water to give a conductivity of 900 μS / cm. The cake is then rinsed with water to pH 4, which is adjusted by the addition of acetic acid, and one final rinse is performed with deionized water.

The silica cake thus obtained is decomposed and then 2 g of calcium acetate is added thereto with stirring.

The silica is dried by melting and micronized with a Jet Pulverizer to give a silica particle size of 1.5.

The physico-chemical properties of the silica thus obtained are as follows: 2

Surface BET 320 m / g 2

Surface CTAB 120 m / g 3 Absorption capacity 250 cm / 100 g pH 6.5

The chemical analyzes of silica are grouped in the following table.

ions SO ^ AI Fe Ca C

ppM 100 200 120 300 20 32 89 899

Surface chemistry is quantified by the following parameters:

Ho higher than 3.3 PZC = 4 2 OH / nm = 11 No pyridine adsorption bands

compatibilities

Ingredients Fluoride Pyrophosphate Chlorhexide ini- Zinc

NaF Na / K digluconate ZnSO 4% combined 90 95 90 80 compatible

Example 5 This example relates to the preparation of abrasive silica.

6 l of deionized water are introduced into a reactor vessel equipped with a heat and pH control system and a turbine mixing system.

After stirring (300 l / min), the mixture base thus obtained is heated to 85 ° C.

When the temperature is reached, 8.5 l of sodium silicate with a silica concentration of 120 g / l, a SiO2 / Na2O ratio of 3.5 and a flow rate of 0.34 l / min and 13.5 l of sulfuric acid with a concentration of 80 g / l are added simultaneously. The acid flow is adjusted so that the ambient pH is constantly 8.0.

After the addition is continued for 40 minutes, the addition of silicate is stopped and the mixture is allowed to mature for 15 minutes at 85 ° C at pH 8.

33 8 98 99

Continue the acid slurry until the pH of the reaction mixture stabilizes at 4.

The mixture is then allowed to mature for 15 minutes at this pH and Θ5 ° C.

The mixture is then filtered and the moist cake is rinsed with deposited water until the conductivity of the filtrate is 100 μS / cm.

The cake is then rinsed twice with water adjusted to pH 4 by the addition of acetic acid.

The final rinse is performed with deionized water.

The material is then dried by melting and ground in a forplex-type mill to give a granular composition of 9.0 microns.

The physico-chemical properties of the silica thus obtained are as follows: 2

Surface BET 60 m / g 2

Surface CTAB 50 m / g 30 g absorption 120 cm / 100 g pH 6.0

Chemical analyzes of silica are given as follows:

Ionite SO 4 AI Fe Ca C

ppM 100 250 100 200 10

Surface chemistry is quantified by the following parameters: 34 8 9 899

Ho greater than 3.3 PZC = 4.5

No pyridine adsorption belts Compatibility

Ingredients Fluoride Pyrophosphate Chlorhexaidine Zinc NaF Na / K digluconate ZnSO 4 X combined 95 9Θ 70 80 suitable

Example 6 This example relates to the preparation of thickening silica in a reactor vessel equipped with a turbine mixing system, into which 5.07 l of sodium silicate with a silica concentration of 120 g / l and a SiO 2 / Na 2 O ratio of 3.5 and 3.8 l of deionized water are introduced.

After stirring (300 l / min), the mixture base thus obtained is heated to 68 ° C.

When the temperature has been reached, 2.64 l of sulfuric acid with a concentration of 80.5 g / l are added. The acid flow is 0.120 rpm.

After the addition is continued for 22 minutes, the addition of acid is stopped and the mixture is allowed to mature for 10 minutes (a sudden increase in turbidity is observed).

4.2 l of sulfuric acid are then added over a period of 35 minutes.

o The temperature is then raised to 87 ° C and at the same time sodium silicate is added at a flow rate of 30 ml / min and sulfuric acid at a flow rate of 52 ml / min for 30 minutes, 35 8 9 899 o The temperature is brought to 95 ° C and 0.523 l of sulfuric acid is added in 10 minutes.

The mixture is then allowed to cook for 10 minutes.

The pH of the medium is then adjusted to 4 by the addition of acid.

The mixture is filtered and the moist cake is rinsed with deionized water until the conductivity of the filtrate is 100 μS / cm.

One cake rinse is then performed with water adjusted to pH 4 by the addition of acetic acid.

The final rinse is performed with deionized water.

The product is then spray dried and micronized with a Jet Pulverizer type mill to give a 1.2 micron granule composition.

The physical and chemical properties of the silica thus obtained are as follows: 2

Surface BET 180 m / g 2

Surface CTAB 170 m / g 3 Absorption capacity 350 cm / 100 g pH 6.8

The chemical analyzes of silica are grouped in the following table.

ions SO4 AI Fe Ca C

ppM 500 200 120 300 10! 36 89899

Surface chemistry is quantified by the following parameters:

Ho higher than 3.3 PZC = 3.6

No pyridine adsorption butter Compatibility

Ingredients Fluoride Pyrophosphate Chlorhexidine- Zinc

NaF Na / K digluconate ZnSO 4% combined 90 95 70 60 suitable

Saimexkfci 7 This example describes the preparation of the silica cake which is the basic product for the silicas of Examples Θ-12.

A 30 l reaction vessel equipped with a heat and pH control system and a Mixel-type stirring system is charged with 1.4 l of sodium silicate with a SiO 2 / Na 2 O ratio of 3.45 ° and a SiO 2 concentration of 135 g / l, preheated to 75 ° C. After stirring (300 l / min), the eeo base thus obtained is heated to 85 ° C.

When the temperature has been reached, the same sodium silicate is added simultaneously at a flow rate of 0.28 l / min and sulfuric acid preheated to 75 ° C at a concentration of 80 g / l at a flow rate of 0.16 l / min.

The average pH of the medium during the simultaneous addition is 9.8.

After the co-addition has been continued for 47 minutes, stop the addition of silicate and continue the acid addition with the same flow until a pH of 8 is reached. In this state, 37 39899 ° C is brought to 95 ° C in 10 minutes while continuing to add acid to the reaction mixture. to 4.2 at this same time.

The mixture is then allowed to mature for 15 minutes at this pH and 95 ° C.

The mixture is then filtered and the moist cake is rinsed with deposited water until the conductivity of the filtrate is 2000 μS / cm.

The cake obtained in this state is used as a starting point for the preparation of surface chemically controlled silicas according to Examples Θ-12.

Example 8

Take the cake obtained in Example 7.

This cake is dispersed in deionized water to form a suspension containing 100 g / l of silica and the suspension is then filtered. The procedure is repeated until the conductivity of the filtrate is 100 μS / cm.

The cake is then redispersed in suspension form at a concentration of 150 g / l in deionized water, the pH of which is adjusted to 6 by adding acetic acid.

After filtration, one final rinse with Deio-treated water is performed.

The product is then dried by melting and ground in a forplex-type mill to give a grain composition of 9.0 .mu.m.

38 39899

Example 9

The cake obtained by proceeding according to Example 7 is rinsed with deposited water until the conductivity of the filtrate is 500 / US / cm.

The cake is then rinsed with 10 l of water adjusted to pH 4 by the addition of gluconic acid.

One final rinse with deionized water is then performed.

The cake is broken down to obtain a homogeneous suspension and 8.5 g of barium acetate <Ba (C2H2O2, H2O) are added with stirring.

The mixture is allowed to cook for 30 minutes.

The product is then spray-dried and ground in a forplex-type mill to give a grain composition of 9.0.

Example 10

The cake obtained by operating according to Example 7 is rinsed with deionized water until a conductivity of the filtrate of 500 μS / cm is obtained.

The cake is then redispersed in a euepension formulation at a concentration of 150 g / l in deposited water and the pH of the water is adjusted to 6 by adding acetic acid.

25 g of barium hydroxide (Ba <OH> 2, 8H2O) are added with stirring and the mixture is allowed to cool for 30 minutes.

The suspension is then filtered and rinsed with 5 l of water.

The product is then spray dried and milled with forplex type 1 Mynyna to give a grain composition of 9.0 microns.

39 S 9 899

Example 11

The cake obtained by proceeding according to Example 7 is rinsed with deionized water until the conductivity of the filtrate is 100 μS / cm.

The cake is then redispersed in suspension at a concentration of 150 g / l in deionized water and the pH of the water is adjusted to 6.3 by adding acetic acid.

One final rinse with deposited water is then performed.

0.1 g of barium acetate (BaCC2H2O2) is added with stirring and the mixture is allowed to mature for 30 minutes.

The product is then dried by melting and ground in a forplex-type mill to give a grain composition of 9.0 microns.

Example 12

Take the cake of Example 7. This cake is dispersed in deionized water to form a suspension having a silica concentration of 100 g / l and the suspension is then filtered. The procedure is repeated until the conductivity of the filtrate is 200 yuS / cm.

The product is then dried by melting and ground in a forplex-type mill to give a grain composition of 9.0 microns.

The characteristics of the silicas of Examples 8-12 are given in the following tables: 40 89899

Example Surfaces pH Oil intake- PZC Ho Refill- BET CTAB tolerance factor 2 OH / nm 2 m / g 8 250 50 6.9 12 102 4.5> 3.3 1.460 9 250 45 6.8 10 110 4> 3.3 1.457 10 250 60 7.2 12 105 3.8> 3.3 1.458 11 260 55 7.0 10 105 6> 3.3 1.457 12 250 55 7.5 12 100 3.6> 3.3 1.446

Chemical Analysis of Ions (ppM)

Examples SO 4 Al Fe Ca C

8 70 300 150 300 20 9 150 350 200 350 20 10 200 400 200 350 50 11 50 230 120 120 20 12 200 415 200 355 20

compatibilities

Examples Fluoride Pyrophosphate Chlorhexidine-Zinc NaF Na / K digluconate ZnSO 4 90 90 75 70 9 95 98 80 85 10 96 95 70 65 11 95 96 98 80 12 95 95 70 60 4i 89899

Comparative Example 13

For comparison, the following table provides compatibility assays for commonly used commercial silicas with toothpaste compositions as well as their physicochemical properties.

The assays have been performed according to the tests presented elsewhere.

2 2

Silicas Surface m / g Ho OH / nm SO 2% Compatibility

Brand CTAB BET% CHx F Zn PYR

Manufacturer by weight

Zeodent 113 50 100 43 30 0.65 1 95 0 95

Hubert Z113 70 175 <3 17 0.50 1 96 0 95

Zeof inn

Syloblanc Θ1 240 400 43 17 1.56 0 90 40 95

Grace

Syloid 244 400 ^ 3 17 0.7 4 90 2 90

Grace

Sipernat 22S 180 190 43 16 1.0 0 90 20 90

Degussa

Tixosil 53 50 250 <^ 3 30 0.8 0 60 0 90

Rhone Poulenc CHx = chlorhexidine, F = fluorine, Zn = zinc, Pyr = pyrophosphate.

It is found that for all products mentioned in the table, the PZC is less than 3.

Example 14 This example relates to the formulation of a gel-like, translucent toothpaste containing the silicas of the invention.

42 39899

The formula is:

Sorbitol (70 X water): 65 (oo

Glycerol o, 00 CMC 7mFD q 0q

Sodium acarinate 0.20

Sodium fluoride 0.24

Sodium benzoate. 0.08

Flavoring 2.00

Abrasive silica, Example 2: 15.00

Thickening silica, Example 6 8.00

Chlorhexidine digluconate 1.00

Distilled water f qq

Toothpaste offers good Theological properties and extracts suitably from the beginning and after storage <2 months).

An expert opinion based on the appearance of the toothpaste ensures that the extrudate has a firm firmness and is in the form of a translucent gel.

This toothpaste also offers the following properties: pH solution 10 *: 6.8

Grinding ability with copper standard LNE (mg): 5.6

Plastic viscosity (Pa.s): 0.5

Anti-bacterial activity detectable.

EgimerKki 1? This example relates to the formulation of a paste-like, opaque toothpaste.

The formula is as follows:

Glycerol 22.00 CMC 7mFD 1.0 43 39899

Sodium acarinate 0.20

Sodium monofluorophosphate 0.76

Sodium fluoride 0.10

Sodium lauryl sulphate (30% water) 4.67

Sodium benzoate 0.10

Flavoring agent: 0.90

Titanium oxide 1.00

Abrasive silica, Example 5 31.50

ZnSO 4, 7 H 2 O 0.48

Distilled water 37.29

Of course, the invention is in no way limited to the described embodiments, which are given by way of example only. It covers, in particular, all methods which are the technical equivalent of the methods described, as well as combinations thereof, provided that they are implemented within the framework of the required protection.

Claims (40)

1. Silica, characterized in that it is compatible with guanidine-type products and especially chlorhexidine at least 65% and especially at least 90%. Silica according to claim 1, characterized in that it is compatible with zinc at least 50%, preferably 80%. 3. Silica compatible with, in particular, guanidine-type products and especially chlorhexidine, characterized in that it exhibits such surface chemistry that its acidity function Ho exceeds 3.3. Silica according to claim 3, characterized in that it exhibits an infrared spectrum for the adsorption of pyridine which, in comparison with the pyridine spectrum, exhibits only a displacement of not more than 10 cm -1, especially not more than 5 cm 1. Silica according to claim 4, characterized in that the aforementioned displacement is zero. Silica according to any of the preceding claims, characterized in that it has an anion content of type SO42 ', ·. Cl ', NO3', PO43 ', CO32' not more than 10'3 mol / 100 g silica. Silica according to claim 6, characterized in that it has a content of the above-mentioned anions which is not more than 1 10'3, especially not more than 0.2 · 10'3 mol / 100 g silica. Silica according to claim 6 or 7, characterized in that it has a sulfate content, expressed as SO4, of not more than 0.5%; preferably at most 0.1% and especially at most 0.02%. Silica according to any of the preceding claims, characterized in that it has such a surface chemistry that the OH-number, expressed as OH / nm2, is at most 15 and especially at most 12. Silica according to any of the preceding claims, characterized in that it has a zero charge point (PZC) of at least 3, especially between 4 and 6. Silica according to any of the preceding claims, characterized in that it has an aluminum content of not more than 500 ppm. Silica according to any of the preceding claims, characterized in that it has an iron content of not more than 200 ppm. Silica according to any of the preceding claims, characterized in that it has a calcium content of not more than 500 ppm, especially not more than 300 ppm. Silica according to any of the preceding claims, characterized in that it has a carbon content of not more than 50 ppm and especially not more than 10 ppm. Silica according to any of the preceding claims, characterized in that it has a pH of not more than 8 and especially between 6.0 and 7.5. 16- Silica according to any of the preceding claims, characterized in that it has a surface BET between 40 and 600 m2 / g. Silica according to any of the preceding claims, characterized in that its CTAB surface is between 40 and 400 m2 / g. Silica according to any of the preceding claims, characterized in that its BET surface area is between 40 and 300 m2 / g. Silica according to claim 18, characterized in that its CTAB surface area is between 4 and 100 m2 / g. 52 '3 9 8 99 Silica according to any one of claims 1 to 17, characterized in that its BET surface is between 120 and 450 m2 / g, especially 120 and 200 m2 / g. Silica according to claim 20, characterized in that its CTAB surface is between 120 and 400 m2 / g. Silica according to any of claims 1-17, characterized in that its BET surface area is between 80 and 200 m2 / g. Silica according to claim 22, characterized in that its CTAB surface is between 80 and 200 m2 / g. Silica according to any of the preceding claims, characterized in that its oil absorption capacity is between 80 and 500 cm3 / g. Silica according to any of the preceding claims, characterized in that its average particle size is between 1 and 10 μιη. Silica according to any of the preceding claims, characterized in that its mean density is between 0.01 and 0.3. . Silica according to any of the preceding claims, characterized in that it is the question of precipitated silica. A process for preparing a silica compatible with guanidines, especially chlorhexidine, according to any of the preceding claims of the type comprising a reaction of a silicate with an acid to obtain a silica suspension or gel, a separation and a drying of the silica, characterized in that after the separation of the silica, a separation of the cake resulting from this separation is carried out with water until the conductivity of the filtrate is at most 200 μ3 / αη. 53 89899 Process according to Claim 28, characterized in that the above-mentioned cake is rinsed with water until the conductivity of the filtrate is at most 100 μΞ / cm. A process for preparing a silica compatible with guanidines, especially chlorhexidine, according to any of the preceding claims of the type comprising a reaction of a silicate with an acid to obtain a silica suspension or gel, characterized in that a first rinsing of the cake resulting from this separation is performed with water and then a second rinsing or treatment with an acidic solution. Process according to claim 30, characterized in that the first rinsing is carried out until the conductivity of the filtrate is at most 2000 μβ / αη. The process according to claim 30 or 31, characterized in that said acidic solution is a solution of an organic acid, in particular a seed pie forming acid. Process according to claim 32, characterized in that the above organic acid is selected from carboxylic acids, dicarboxylic acids, amino carboxylic acids, hydroxycarboxylic acids. 34. A process according to claim 32 or 33, characterized in that the organic acid is selected from the group consisting of; - contains acetic, glucon, wine, lemon, maleic and glycerol acids. Process according to any one of claims 28-34, characterized in that the suspension or gel of the precipitated silica was allowed to mature before the separation. Process according to any of claims 28-35, characterized in that, after the reaction of the silicate with an acid, the pH of the suspension or gel is adjusted to a value of not more than 6, especially between 4 and 6. 54 39899 37. A process according to any of claims 28-36, characterized in that an alkaline earth salt is added to either the suspension or gel or then the cake possibly after its decomposition. 38. A method according to claim 37, characterized in that an organic site is used, which in particular forms complexes with soil alkali. 39. Toothpaste composition, characterized in that it contains a silica according to any one of claims 1-27 or a silica produced using a process according to any of claims 28-38. 40. Toothpaste composition according to claim 39, characterized in that it contains at least one element selected from the group containing fluorine, phosphates, guanidines, zinc, copolymers of maleic acid and vinyl ethyl ether. IN: