FI91387B - Especially with metallic cations compatible silica for toothpastes - Google Patents

Abstract

Silica compatible with metal ions such as zinc, tin or strontium, characterised by a surface OH<-> number expressed as OH<->/nm<2> lower than or equal to 10, a zero charge point (ZCP) of between 3 and 6.5 and resulting in an aqueous suspension whose pH varies as a function of its electrical conductivity according to the equation - pH = b - a log (D), in which a is a constant lower than or equal to 0.6, b is a constant lower than or equal to 8.5 and (D) represents the electrical conductivity of the aqueous suspension of silica, expressed in microsiemens cm<-><1>. Process for preparing the silica, consisting in reacting a silicate with an acid, thus resulting in a silica suspension or gel, in performing a first aging at a pH higher than or equal to 6 and lower than or equal to 8.5, then a second aging at a pH lower than or equal to 5.0, in separating off the silica, in subjecting it to washing with hot water until it produces an aqueous suspension whose pH measured on a suspension containing 20 % of SiO2 obeys the equation - pH = d - c log (D> in which c is a constant lower than or equal to 1.0, d is a constant lower than or equal to 8.5 and (D) denotes the electrical conductivity of the aqueous suspension of silica, expressed in microsiemens cm<-><1>; and finally in drying it. Dentifrice composition containing the silica described.

Description

91387

The present invention relates in particular to silica for use in toothpastes, to a process for its preparation and toothpastes containing said silica.

Silica is now known to be used in the manufacture of toothpastes. It can have several functions in a compound.

It acts as an abrasive, helping to mechanically remove dental plaque.

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

Toothpastes generally contain a source of fluorine, most commonly sodium fluoride or monofluorophosphate, which is used to prevent caries; a binder, for example an algal colloid such as carrageenan, guar gum or xanthan gum; a humectant which may be a polyalcohol, for example glycerin, sorbitol, xylitol and propylene glycol. In addition, optional constituents are used, such as surfactants, anti-plaque or anti-plaque agents, flavors and dyes, pigments, etc.

A certain amount of metal cations can be used in toothpastes. Examples which may be mentioned are alkaline earth cations, in particular calcium, strontium, barium, group 3a cations, aluminum, indium, group 4a germanium, tin, lead and group 8 manganese, iron, nickel, titanium, zirconium, palladium, etc.

These cations may be in the form of mineral salts, for example, chloride, fluoride, nitrate, phosphate, sulfate, or organic salts such as acetate, citrate, and the like.

More specific examples are zinc citrate, zinc sulphate, strontium chloride, tin fluoride as single (SnF2) or double salt (SnF2, KF), tin chlorofluoride (SnClF) and zinc fluoride (ZnFa).

The suitability of substances containing metal cations for use with silica poses problems. In fact, due to its adsorbent nature, it can react with these substances so that they are no longer able to perform their intended function.

French Patent No. 87/15276 describes silicas suitable for use with zinc. However, these silicas are incompatible with other metal cations such as tin, strontium, etc.

It is an object of the present invention to provide novel silicas suitable for use with zinc and the other metal cations mentioned above.

Another object of the invention is to provide silica which is also suitable for use with a fluoride anion. Improved compatibility with cations reduces compatibility with the fluoride anion. It is therefore important that the proposed silica remains suitable for use with the fluoro-dianion used in all toothpastes.

The invention further relates to a process for the preparation of such suitable silicas.

It has been found that the desired compatibility properties necessarily depend on the surface chemistry of the silica used. Thus, a number of silica surface conditions have been sought in which they are compatible.

91387 3 The silica according to the invention, which is used for this purpose in particular in toothpaste compounds, is characterized in that the number of OH * groups on its surface, expressed in OIT / nm2, is <10, its zero charge point (PZC) is between 3 and 6.5 and it is a conductor in aqueous suspension, whose pH varies as a function of electrical conductivity according to the following formula I:

pH = b - a log (D) I

where a is constant <0,6 b is constant <8,5 D is the conductivity of the aqueous silica suspension in με / οπι.

Another feature of the silica according to the invention is that its suitability for use with at least one divalent or higher divalent metal cation selected from Group 2a, 3a, 4a or 8 of the Periodic Table is at least 30%, in particular at least 50% and preferably at least 80%.

This invention also relates to a process for the preparation of silica according to the invention, characterized in that the silicate is reacted with a conductive acid, suspension or silica gel, first matured at pH> 6 and <8.5, followed by a second maturation at pH <5 , the silica is separated off, washed with hot water until an aqueous suspension is obtained whose pH in a suspension containing 20% of silica corresponds to the following equation

pH * d - c log (D) II

where c is constant <1.0 d is constant <8.5 (D) is the conductivity of the aqueous silica suspension in 4 units pS / cm, after which the silica is dried.

The invention therefore relates to toothpastes which are characterized in that they contain silicas as described above or prepared by a process to be mentioned later.

Other features and advantages of the invention will be better understood from the description and the following non-limiting examples.

As already mentioned in the introduction, the essential properties of the silicas of the invention are due to their surface chemistry. More specifically, one of the aspects to be considered in surface chemistry is acidity. Thus, one of the features of the silicas of the invention is the number of acid groups on the surface.

This amount is measured in ΟίΓ groups or silicon compounds at nm2. In practice, the measurement is made by comparing the number of 0H ~ groups with the amount of water released by silica at 190-900 ° C.

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

The mass of Po silica is placed in a thermobalance and kept at 190 ° C for 2 hours, the mass obtained being P 1 SO · The silica is then kept at 900 ° C for 2 h, the new mass obtained being P®oo.

The number of OtT groups is calculated from the following equation: 66922.2 Pi9o “P®oo

Hdh ~ = X

A Px® o 91387 5 where

The number of Noh "on OH" groups at 2 nm A is the specific surface area of the solid as measured by BET and expressed in m2 / g.

In this case, the amount of OH "/ nm2 of the silicas of the invention is <10 and more specifically between 4-10.

The number of OH "groups of the silicas according to the invention, which is also a means of characterizing their surface chemistry, can also be estimated by means of a zero charge point.

The zero charge point (PZC) is determined from the pH of a silica suspension whose zero surface electrical load is zero regardless of the ionic strength of the environment.

PZC measures the true pH of a surface when it is free of all ionic impurities.

The electrical load is determined by potentiometry. The method is based on the global balance of protons adsorbed or desorbed by the silica surface at a given pH.

Starting from the equations describing the global balance, it is easy to show that the electric charge c of the surface with respect to the zero-charge reference surface is

F

c = - (H *) - (OH ")

A * M

where A is a certain solid surface, m2 / g M is the amount of solid in the suspension, g F is the variation of the excess H * or OH "ion per unit area of the Farady (H * ·) or (OH ~) solid PZC is determined experimentally as follows.

Use the method described by Berube and Bruyn (J.

Colloid Interface Sc. 1968, 27, 305).

6

The silica is pre-washed in deionized water of high resistivity (10 MQcm), dried and dry distilled.

Prepare a series of solutions with pHo = 8.5 with the addition of KOH or HNOα, containing an indifferent electrolyte (KNQ *) and with a concentration ranging from 10 “®-10“ 1 mol / l.

To these solutions is added a given mass of silica and the pH of the resulting suspensions is allowed to stabilize with stirring at 25 ° C for 24 h.

The reference solutions consist of surface solutions obtained by centrifuging some of the same suspensions for 30 min at 1000 rpm.

The pH of a known volume of these suspensions and reference solutions is then adjusted by adding the required amount of KOH and allowed to stabilize the suspensions and reference solutions for 4 h.

That is, the amount of Voh "-Ndh" base equivalents added to adjust the suspension of the known volume V or the reference solution to pH'o pH.

Potentiometric addition of the suspensions and reference solutions is carried out starting from pHo by adding nitric acid until pHf = 2.0.

The acid is preferably added in an amount corresponding to a change in pH of 0.2. After each addition, the pH is allowed to stabilize for 1 min.

That is, the number of acid equivalents to give the pHf.

Starting from the pH, the term (VH * JiH * -ν0Η - Ι ^> Η_) is searched for as a function of the pH increase for all suspensions 91387 7 (at least 3 ionic forces) and for all corresponding reference solutions.

At all pH values (every 0.2 units) the difference between the H * or OH 'consumption of the suspension and that of the reference suspension is examined. This is repeated with all ionic forces.

This gives the term (H *) - (OH-), which corresponds to the proton consumption of the surface. The surface charge is calculated from the above equation.

The surface charge curve as a function of pH is then determined for all ionic forces used. PZC is determined from the intersection of the curves.

The silica concentration is adjusted as a function of this particular surface.

For example, 2% suspensions are used for 50 m 2 / g silica with an ionic strength of 3 (0.1; 0.01 and 0.001 mol / l).

The addition is made to 100 ml of suspension using 0.1 M potassium hydroxide.

For the silicas of the invention, the PZC must be between 3 and 6.5.

In addition, in order to improve the compatibility of the silicas according to the invention with other elements, in particular fluorine, it is interesting that the content of divalent and higher cations in the silica is at most 1000 ppm. It is particularly desirable that the aluminum content of the silicas according to the invention be at most 500 ppm.

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

In addition, the calcium content may preferably be δ up to 500 ppm and more specifically up to 300 ppm.

In addition, the silicas according to the invention have a carbon content of at most 50 ppm and, in particular, at most 10 ppm.

In addition, the pH of the silicas according to the invention, measured in accordance with NFT 45-007, is usually at most 7. It is in particular between 6-7.

Said properties give silica suitable for use with divalent and higher metal cations, in particular zinc, strontium and tin. This compatibility, as measured by the test to be described later, is at least 30%, more specifically at least 50% and preferably at least 80%.

In addition, the silicas of the invention may have good compatibility with the fluoroanion, at least about 80% and preferably at least 90%.

In addition to their surface chemical and compatibility-regulating properties, which will be described later, the silicas according to the invention also have physical properties which make them perfectly suitable for use in toothpastes. These structural properties are described below.

Generally, the BET surface area of the silicas of the invention is between 40 and 600 mA / g. Their CTAB surface usually ranges from 40 to 400 m2 / g.

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

The CTAB surface is an outer surface determined according to ASTM D3765, but using bromide hexadecyltrimethylammonium adsorption (CTAB) at pH 9 and 91387 9, taking the CTAB molecule as a projection surface of 35 Å2.

The silicas according to the invention can, of course, correspond to three types commonly used in toothpastes.

The silicas according to the invention can be of the abrasive type. In this case, their BET surface area is between 40-300 m2 / g. In this case, the CTAB surface is between 40 and 100 m2 / g.

The silicas of the invention may also be of the thickening type. In this case, their BET surface area is between 120-450 m2 / g and more precisely between 120-200 m2 / g. In this case, their CTAB surfaces can be between 120-400 m2 / g and more specifically between 120-200 m2 / g.

Based on the third type, the silicas according to the invention can have a dual function. In this case, their BET surface area is between 80-200 m2 / g. The CTAB surface is then between 80-200 m2 / g.

The silicas of the invention can also bind oil between 80-500 cm 3/100 g as determined according to NFT 30-022 (March 53) using dibutyl phthalate.

More specifically, this oil is between 100 and 140 cm 3/100 g for abrasive silicas, between 200 and 400 cm 3/100 g for thickening silicas and between 100 and 300 cm 3/100 g for dichotomous activities.

In addition, in terms of suitability for toothpastes, the particle size of the silicas is between 1 and 10 .mu.m.

The apparent density ranges from 0.01 to 0.3.

According to a particular embodiment of the invention, the silicas are precipitated silicas.

10

In addition, the refractive indices of the silicas according to the invention are between 1.440 and 1.465.

The following is a more detailed description of the production method of the silicas of the invention.

As already mentioned, in the process, the silicate reacts with an acid to form a silica suspension or gel.

It should be noted that all known methods can be used to obtain this suspension or gel (addition of acid to silicate, simultaneous addition of oxygen and silicate to all or part of water or silicate solution, etc.) depending on the desired physical properties of the silica.

In a preferred embodiment of the invention, the silica suspension or gel is prepared by simultaneously adding silicate and acid to water, 0-150 g / l SiO 2 expressed as silica to a colloidal dispersion of silica, a mineral or organic silicate or salt, preferably an alkali metal sulfate, for example an alkali metal, for example.

The addition of the two reagents takes place simultaneously so that the pH is kept constant between 4 and 10 and preferably between 8.5 and 9.5. In addition, the temperature is between 60-95 ° C.

In a preferred process for the preparation of a silica colloid dispersion, preferably at a concentration of between 20 and 150 g / l, the aqueous silicate solution is heated, for example between 60 and 95 ° C, and acid is added to the solution until a pH of between 8 and 10 and preferably about 9.5 is obtained.

The concentration of the aqueous silicate solution, expressed as SiO 2, is preferably between 20 and 150 g / l. Diluted 91387 11 or concentrated acid can be used, its normality can vary between 0.5-36 N and preferably between 1-2 N.

Hereinafter, silicate also means alkali metal silicate and preferably sodium silicate with a weight ratio of SiO 2 / Na 2 O of between 2 and 4 and preferably 3.5. The acid, in turn, may be gaseous, such as carbonic acid, or liquid, such as sulfuric acid.

In the second step of the process according to the invention, the suspension or gel is matured twice.

The first maturation takes place at a pH of at most 8.5 and between 6-8.5, for example preferably 8.0. The ripening is preferably carried out in heat, for example at a temperature between 60-100 ° C, preferably 95 ° C, for a time which can vary between 10 minutes and 2 hours.

In one variation of the invention, the silica suspension or gel is prepared by continuously adding acid to the silicate until the desired cure pH is obtained. This operation takes place at a temperature which is preferably between 60 and 95 ° C.

The silica suspension or gel is then matured under the above conditions.

This is followed by a second maturation at a pH of less than 5 and preferably between 3-5 and most preferably between 3.5-4.0.

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

The pH is adjusted to the desired ripening pH by adding acid.

12

For example, a mineral acid such as nitric, hydrochloric, sulfuric or phosphoric acid or carbonic acid prepared by bubbling carbon dioxide can be used.

The silica is then separated from the reaction mixture by known methods, for example by vacuum or pressure filtration.

Silica cake is obtained.

The silica cake obtained in the next step is washed. The washing takes place under conditions in which the pH of the suspension or the reaction mixture before drying corresponds to the following equation:

pH = d - e log (D) II

where c is constant <1.0 d is constant £ 8.5 (D) is the electrical conductivity of the aqueous silica suspension in pS / cm.

The washing is carried out with water, the temperature of which is preferably between 40 and 80 ° C. Depending on the case, one or more washes, usually two, may preferably be performed with deionized water and / or an acid solution having a pH between 2-7.

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

According to one embodiment of the invention, this acid can also be a solution of an organic acid, in particular a complexing organic acid. The acid may be selected from carboxylic acids, dicarboxylic acids, hydrocarboxylic acids and aminocarboxylic acids.

91387 13 Examples of these acids are acetic acid and the complexing acids are tartaric acid, maleic acid, glyceric acid, gluconic acid and citric acid.

Especially when using a mineral acid solution, it may be useful to perform a final wash with deionized water.

Washing can take place by passing the washing liquid through the cake or by forming a suspension after breaking the cake.

The filter cake is broken before drying, which can be done by any known method, for example by using a rapidly rotating mixer.

The silica cake, before or after washing, is broken and dried by any known method. The drying can take place, for example, in a tunnel or sleeve oven or by hot air spraying with an inlet temperature of about 200-500 ° C and an outlet temperature of about 80-100 ° C; the residence time is between 10 s and 5 min.

If necessary, the dried product can be ground to obtain the desired grain size. Grinding takes place in classic equipment: a knife mill or an air-jet grinder.

The invention also relates to toothpastes of the type described or containing silica obtained by the process described.

The amount of silica according to the invention in toothpastes can vary widely; usually between 5-35%.

The silicas according to the invention are particularly well suited for toothpastes which contain at least one of the following substances: florides, phosphates, metal cations.

The amount of fluorine compounds in the mixture preferably corresponds to 14 fluorine concentrations between 0.01-1% by weight and more specifically 0.1-0.5%. Fluorine compounds are, in particular, salts of monofluorophosphoric acid and, more specifically, potassium, sodium, lithium, calcium, aluminum and ammonium salts, mono- and difluorophosphate, and several fluorine-bound ion-containing fluorides, in particular alkali fluorides such as potassium, lithium, sodium , ammonium, tin, manganese, zirconium or aluminum fluoride and addition products of these or other fluorides, such as sodium, potassium or manganese fluorides.

Other fluorides may be used in the invention, such as zinc, germanium, palladium and titanium fluoride, alkaline fluorozirconates such as potassium, sodium and tin fluorosirconate, fluoroborate or potassium and sodium fluorosulphates.

Organic fluorine compounds can also be used, preferably known addition products of long-chain amines or amino acids and hydrogen fluoride, such as cetylamine hydrofluoride, bis- (hydroxyethyl) aminopropyldihydrofluoride, N-hydroxyethyloctadecylamine, octene-diolecylamine-octylidene-trioxyl -Roxif chloride.

Compounds containing a divalent metal cation, and in particular those most frequently mentioned above, are zinc citrate, zinc sulphate, strontium chloride and tin fluoride.

Among the polyphosphates or polyphosphonates, guanides or bis-biguanides of the type used as anti-plaque agents, mention may be made of those disclosed in U.S. Pat. No. 3,934,002.

In addition, toothpastes may contain a binder.

The binders used mainly are selected from: - cellulose derivatives: methyl, hydroxyethyl, 91387 15 sodium carboxyethylcellulose - mucilages: carrageenans, alginates, agar-agar and geloses - gums: gum arabic and adragant, xanthan and karayin gum - acacia and karaya gum polyoksietyleenihartsit.

In addition to the silicas of the invention, the toothpastes may contain one or more other polishing abrasives, generally selected from: precipitated calcium carbonate - magnesium carbonate - calcium, di- and tricalcium phosphates - insoluble sodium metaphosphate - aluminum titanium - calcium pyrite phosphate - - zinc and tin oxides - talc - kaolin.

Toothpastes may also contain surfactants, moisturizers, aromatics, sweeteners, colorants and preservatives.

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

The main wetting agents used are selected in particular from polyalcohols, such as: - glycerol - sorbitol, usually in 70% aqueous solution 16 - propylene glycol.

The main flavorings are selected in particular from the following: anise, mint, juniper berry, cinnamon, cloves and rose essence.

The main sweeteners are selected in particular from orthosulfobenzene imides and cyclamates.

The main dyes used are selected according to the desired color, in particular: - red and pink colors amaranth, azorubine, cachou color, coccine nouvelle color (PONCEAU 4 R), cochineal, erythrosine - green colors chlorophyll and chlorophyllin - yellow colors yellow-yellow and quinoline yellow.

The most commonly used preservatives are; parahydroxybenzoates, formol and its release products, hexetidine, quaternary ammonium compounds, hexachloroprene, bromophen and hexamediene.

In addition, toothpastes contain therapeutic substances, the most important of which are selected in particular from: - antiseptics and antibiotics - enzymes - oligoelements and the fluorine compounds described.

The following are concrete, non-limiting examples.

The text describes the measurement of pH as a function of conductivity and concentration, as well as tests to measure the compatibility of silica and various elements.

A series of silica suspensions are prepared with an increasing concentration between 0-25% by weight by dispersing the pulp m 2 hours in silica at 100 ° C in 100 m of degassed deionized water (Millipore grade). The suspensions are stirred for 24 h at 25 ° C.

Centrifuge a portion of the suspension at 8000 rpm for 40 min and filter through a Millipore 0.22 filter, after which the pH of the resulting solutions and suspensions is measured at 25 ° C under nitrogen with a Titroprocessor Metrohm 672.

Similarly, the conductivity of the suspensions and solutions obtained by the method described above is measured at 25 ° C with a Radiometer (CDM83) conductivity meter equipped with a CDC304 chamber with a chamber constant of 1 cm-1. The unit of conductivity is pS / cm.

The suspension effect (SE) is determined as the difference between the pH of the 20% silica pension and the solution separated on its surface by centrifugation.

Measurement of zinc compatibility: 4 g of silica are dispersed in 100 ml of a 0.06% solution of ZnSO4 * 7H2O. A suspension is obtained, the pH of which is allowed to stabilize at 7 for 15 min by adding NaOH or H2SO4. The suspension is stirred for 24 h at 37 ° C and centrifuged at 20,000 rpm for 30 min.

The solution filtered through a Millipore 0.2 filter is a test solution.

The reference liquid is prepared in the same way but without silica.

The free zinc content of the solutions is determined by atomic absorption (214 nm).

compatibility is determined by the following relationship:

Compatibility% Zn concentration of the sample (ppm) = - x 100

Zn concentration of the reference sample (ppm)

Hereinafter, the zinc compatibility% is denoted "Zn".

Measurement of tin fluoride compatibility (SnF2).

1) An aqueous solution 1 containing 0.40% SnF2 and 20% glycerin is prepared by dissolving 0.40 g SnZ2 and 20 g glycerin in 79.60 g of doubly distilled water.

2) Dissolve 4 g of silica in 16 g of the solution obtained in 1). the pH of the suspensions is adjusted to 5 by adding 0.1 N NaOH.

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

3) The suspension is centrifuged at 8000 rpm for 30 min and the surface solution 3 is filtered through a Millipore 0.22 μm filter.

4) The free tin concentration of the solution obtained in 1) and the surface solution obtained in 3) is determined by atomic absorption.

5) Compatibility is determined from the following ratio: Compatibility%

3 Sn concentration of the surface solution = - x 100

Concentration of 1 Sn in solution

Hereinafter, tin compatibility is denoted as “Sn”.

Measurement of strontium chloride compatibility (SrCl2 * 6H2O): 1) An aqueous solution 1 containing 1% SrCl2 * 6HaO is prepared by dissolving 1 g of SrCl2 * 6HaO in 99 g of doubly distilled water. The pH of the suspensions is adjusted to 7.0 by adding 0.1 N NaOH.

91387 19 2) Dissolve 4 g of silica in 16 g of the solution obtained in 1).

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

3) The suspension is centrifuged at 8000 rpm for 30 min and the surface solution 3 is filtered through a Millipore 0.22 μm filter.

4) The concentration of free strontium in the solution obtained in 1) and the supernatant solution obtained in 3) is determined by atomic absorption.

5) Compatibility is determined from the following ratio: Compatibility%

3 Sr concentration of the surface solution = - x 100

1 Sr concentration of the solution

Hereinafter, strontium compatibility is denoted as "Sr".

Measurement of fluoride compatibility: Dissolve 4 g of silica in 16 g of 0,3% sodium fluoride solution (NaF). The suspension is stirred for 24 h at 37 ° C. The suspension is centrifuged at 20,000 rpm for 30 min and the supernatant is filtered through a Millipore 0.2 μm filter.

Prepare the reference solution in the same way but without silica.

Fluorine compatibility is determined from the percentage of free fluorine measured with a fluoroselective electrode (Orion). Compatibility is determined from the following relationship:

Compatibility% F concentration of the sample (ppm) = - x 100

F concentration of the reference solution (ppm) 20

Measurement of sodium and potassium pyrophosphate compatibility: Dissolve 4 g of silica in 16 g of a 1.5% suspension of sodium or potassium pyrophosphate. The suspension is stirred for 24 h at 37 ° C and centrifuged at 20,000 rpm for 30 min.

The supernatant solution is filtered through a Millipore 0.2 filter. Dissolve 0.2 g of this solution in 100 ml of water in a graduated flask to form a test solution.

Prepare the reference solution in the same way but without silica.

The concentration of free pyrophosphate ions (P2O7) is determined by ion chromatography with an integrator (DIONEX 2000i system).

The compatibility is determined from the ratio of the area of the peaks corresponding to the retention time of the pyrophosphate obtained from the chromatograms of the test and reference solutions.

Compatibility% Sample peak area = - x 100

Peak area of the reference solution

Example 1 A reactor equipped with temperature control, pH measuring and mixing equipment (Mixel) is charged with 8.32 l of sodium silicate having a silicate concentration of 130 g / l and a molar ratio of SiO 2 / Na 2 O = 3.5 and 8.33 l of deionized water, with a conductivity of 1 pS / cm.

After starting the stirring (350 rpm), the mixture is heated to 90 ° C.

When the temperature is reached, sulfuric acid with a concentration of 80 g / l is added at a rate of 0.40 l / min until the pH is 9.5.

91387 21

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

After 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 is 8.0. The temperature is raised to 95 ° C. The mixture is allowed to mature for 30 minutes at this pH and 95 ° C. During cooking, the pH is maintained at 8 by the addition of acid.

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

After the heating is stopped, the mixture is filtered and the resulting cake is washed with 20 l of deionized water heated to 80 ° C. The cake obtained after washing is dispersed in the presence of deionized water to form a suspension with a silica concentration of 10%.

Perform a second filtration and wash with water to give a conductivity of 500 / iS / cm and wash with water adjusted to pH 5 by adding citric acid so that the pH is below 6. Perform a final wash with deionized water.

Check that the pH of the aqueous suspension of the broken cake with a SiO 2 content of 20% corresponds to the equation pH 8.20 to 0.91 log (D).

The silica is spray dried. The silica obtained is ground to give a powder with an average grain diameter of 8 μχα measured with a COUNTER-COULTER.

The physico-chemical properties of the silica thus obtained are summarized in the table below: BET surface m2 / g 65 CTAB surface m2 / g 60 DOP consumption ml / 100 g silica 125

Pore volume by the Hg method cm3 / g 2.1 pH (5% water) 6.2 refractive index 1,450 translucency% 90 SO * - ppm 100

Na * ppm 60

Ai3 * ppm 150

Fe3 * ppm 100

Ca2 * ppm 10

Cl "ppm 20 C ppm ppm

Table I summarizes the surface chemical properties of the silica according to the invention and Table II gives the results of compatibility with the metal cations zinc, tin, strontium and with the fluoride and pyrophosphate used in classical toothpastes.

Example 2 A reactor equipped with temperature control, pH measuring and mixing equipment (Mixel) is charged with 5.30 l of sodium silicate having a silicate concentration of 135 g / l and a molar ratio of SiO 2 / Na 2 O = 3.5 and 15.00 l of deionized water, with a conductivity of 1 pS / cm.

After starting the stirring (350 rpm), the mixture is heated to 90 ° C.

When the temperature is reached, sulfuric acid with a concentration of 80 g / l is added at a rate of 0.38 l / min until the pH is 9.5.

Next, 44.70 l of sodium silicate with a silica concentration of 135 g / l 91387 23 and a molar ratio of SiO2 / Na2 O = 3.5 are added simultaneously at a rate of 0.745 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 mixture remains constant at 9.5.

After 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 is 7.0. The temperature is raised to 95 ° C. The mixture is allowed to mature for 30 minutes at this pH and 95 ° C. During cooking, the pH is maintained at 7 by the addition of acid.

At the end of ripening, the pH is adjusted to 4.0 by adding acid. This pH 4.0 is maintained for 30 min.

After heating, the mixture is filtered and the resulting cake is washed with deionized water until a filtrate with a conductivity of 2000 μδ / cm is obtained.

Next, the cake is broken in the presence of water to obtain a suspension with a silica concentration of 20%.

Carry out a final wash with water so that the pH of the aqueous suspension of the broken cake with a SiO2 content of 20% corresponds to the equation pH = 8.20 to 0.91 log (D).

The silica is dried at 120 ° C for 24 h, after which it is ground to give a powder with an average grain diameter of 8 μπι.

The physico-chemical properties of the silica thus obtained are summarized in the table below: BET surface m2 / g 85 CTAB surface m2 / g 80 DOP consumption ml / 100 g silica 150

Pore volume by the Hg method cm3 / g 3.20 24 pH (5% water) 6.5 refractive index 1.455 translucency% 70 SQ «”% 0.5

Na *% 0.05

Ai3 * ppm 250

Fe3 * ppm 120

Ca2 * ppm 50

Cl ~ ppm 20 C ppm 5

Table I summarizes the surface chemical properties of the silicas of the invention described in Examples 1 and 2.

Table II gives the results of the compatibility of the silicas according to the invention with the zinc, tin, strontium metal cations and the fluoride and pyrophosphate used in classical toothpastes.

For comparison, Tables I and II provide the characteristics and compatibility information of the following commercial silicas, which form a comprehensive group of classical silicas.

S 81: Syloblanc 81 (GRACE) Z113: Zeodent 113 (HUBER)

Sidl2: Sident 12 (DEGUSSA)

Syli5: Sylox 15 (GRACE) T73: Tioxil 73 (RHONE-POULENC) T33: Tioxil 83 (RHONE-POULENC) 91387 25

table 1

Physico-chemical properties of the and classical silicas according to the invention

Physico-chemical properties of silicas

Silicon pH / log (D) SE Ho PZC

oxide s81 7.0-0.62z - 0.17 <22 ^ 2 Z113 10-1.0z - 0.70 <3 2.5

Sidl2 8.5-0.60z - 0.20 <3 2.8

Syll5 9.2-0.74z - 0.94 <3 2.5 T73 10-0.87z - 0.20 <3 3.0 T83 8.6-0.60z - 0.18 <3 2.5

Example 1 8.0-0.50z - 0.00 <4 4.2

Example 2 7.4-0.30z - 0.03 <4 4.0

The meaning of the symbols used in the table is as follows: - pH / log (D) means the equation pH = b - a log (D), where b and a are constants and D is the conductivity of the silica suspension in pS / cm.

- SE is the suspension effect measured by the equation SE = pH of the liquid remaining on the pH surface of the suspension

- Ho is Hammet's constant - PZC is the pH at which the surface charge of silica is zero.

Table II

Compatibility of silicas with active molecules

Compatibility%

Silicon Zn Sn Sr F P sO 7 oxide s81 0 25 20 90 80 Z113 0 15 10 95 90

Sidl2 10 25 20 90 80

Syll5 0 10 10 90 80 T73 20 15 10 90 90 T83 10 10 10 95 95

Eg 1 80 60 90 95 95

Eg 2 85 75 95 95 90 ______ 26

The silicas according to the invention differ from classical silicas in their physicochemical properties and their better compatibility with zinc, tin and strontium.

Claims (41)

1. Silica, characterized in that the amount of OH ~ groups on its surface expressed in unit OIT / nm2 is SLO, its zero charge point (PZC) is 3-6.5 and it is a conductor in a water suspension which The pH varies as a function of the electrical conductivity of the following formula (I): pH = b - a log (D) (I) in which a is constant, s 0.6 b is constant, s 8.5 D is the electrical conductivity of an aqueous suspension of silica in the unit μβ / αη. Silica according to claim 1, characterized in that the amount of OIT groups on its surface expressed as the unit ΟΙΓ / nm2 is 4-10. Silica according to claim 1 or 2, characterized in that its PZC is 3-6.5. Silica according to any of the preceding claims, characterized in that its compatibility with at least one bivalent or polyvalent metal cation selected in the group 2a, 3a, 4a or 8 of the periodic system is at least 30%, preferably at least 50% and more preferably at least 80%. Silica according to claim 4, characterized in that the metal cation is calcium, strontium, barium, aluminum, indium, germanium, tin, lead, manganese, iron, nickel, titanium, zirconium or palladium. Silica according to claim 4 or 5, characterized in that the metal cation has the mineral salts found, for example chloride, fluoride, nitrate, phosphate, sulphate or organic salts, scisome acetate or citrate. Silica according to claim 5, characterized in that the metal cation is zinc citrate, zinc sulphate, strontium chloride or tin fluoride. Silica according to claim 1, characterized in that its compatibility with fluorine anion is at least 80% and preferably at least 90%. Silica according to any of claims 1-8, characterized in that the content of divalent or polyvalent metal cations is not more than 1000 ppm. Silicon dioxide according to claim 9, characterized in that the aluminum content is at most 500 ppm, the iron content at most 200 ppm, the calcium content at most 500 ppm and more specifically at most 300 ppm. Silicon dioxide according to any of claims 1-10, characterized in that its carbon content is at most 50 ppm and more specifically at most 10 ppm. Silica according to any of claims 1 to 11, characterized in that its pH is at most 7 and especially 6-7. Silica according to any of claims 1-12, characterized in that its BET surface area is 40-600 m2 / g. Silica according to any of claims 1-13, characterized in that its CTAB surface area is 40-400 m2 / g. Silica according to any of claims 1-14, characterized in that its BET surface area is 40-300 m2 / g. Silica according to any of Claim 15, biscuits characterized in that its CTAB surface is 40-100 mVg. 17. Thickening type silica according to any one of claims 1-14, biscuits characterized in that its BET surface is 120-450 m2 / g and more specifically 120-200 m2 / g. Silica according to claim 17, biscuit characterized in that its CTAB surface is 120-400 mVg. 19. Bifunctional silica according to any one of claims 1 to 14, biscuits characterized in that its BET surface area is 80-200 m2 / g. Silica according to claim 19, biscuit characterized in that its CTAB surface area is 80-200 m2 / g. 21. Silica according to claims 1-20, biscuits characterized in that it binds oil 80-500 cm3 / 100 g. Silica according to any one of claims 1-21, biscuits characterized in that its average particle size is 1-10 µπι. Silicon dioxide according to any of claims 1-12, biscuits characterized in that its apparent density varies between 0.01 and 0.3. Silica according to any one of claims 1-23, biscuits characterized in that it is a thickening silica. A process for producing silica according to any one of claims 1-24, which is bisculated by reacting silicate with an electrically conductive acid, suspension or silica gel, is allowed to mature a first batch at a pH * 6 and s8. After the second ripe, a second batch at pH 5, silica is separated, washed in hot water until a water suspension is obtained, the pH of a suspension containing 20% silica corresponds to the following equation: pH = d - c log (D) II in which c is constant s 1.0 d is constant s 8.5 (D) is the electrical conductivity of the aqueous suspension of silica in the unit με / cm after which it is dried. Process according to claim 25, characterized in that the silica suspension or gel is prepared by simultaneously adding silicate and acid in water, expressed as 0-150 g / l SiO 2 in a colloidal dispersion of silica-containing silica, mineral or organic silicate. or salt, which is preferably alkali metal. Process according to Claim 25, characterized in that the addition of two reagents takes place simultaneously, so that the pH is constantly poured between 4-10 and preferably between 8.5-9.5. 28. A method according to claim 25 or 26, characterized in that the temperature is 60-95 ° C. Process according to claim 25, characterized in that a silica colloid dispersion is prepared containing 20-150 g / l silicate, the aqueous silicate solution is heated to 60-95 ° C and acid is added in the solution to a pH of 8-10 and preferably c. 9.5 is achieved. Preparation process according to any of claims 25-29, characterized in that the silica suspension or gel first matures at a pH between 6-8.5 and preferably 8.0 and at a temperature between 60-100 ° C, preferably 95 ° C. . 31. Process according to claim 25, characterized in that the silica suspension or gel is prepared by continuous addition of acid to the silicate until the desired ripening pH is obtained at a temperature between 60-95 ° C. Process according to claim 25, characterized in that washing is carried out with water or acid solution whose temperature is 40-80 ° C and preferably 60-80 ° C. The process according to claim 32, characterized in that said acid solution is a solution of an organic, particularly complex-forming organic acid. The process according to claim 33, characterized in that said organic acid is selected from the following: carboxylic acids, dicarboxylic acids, hydrocarboxylic acids and amino carboxylic acids. 35. A process according to claims 33 and 34, characterized in that the organic acid is selected from the following: acetic acid, gluconic acid, tartaric acid, citric acid, maleic acid and glycerol acid. 36. Toothpaste, characterized in that it contains silica according to any of claims 1-24, or silica made according to any of claims 25-35. 37. Toothpaste according to claim 36, characterized in that it contains at least one substance selected from the following: fluorine, phosphates. A toothpaste according to claim 36, characterized in that it contains at least one divalent metal cation selected in groups 2a, 3a, 4a and 8 of the periodic system. 39. A toothpaste according to claim 36, characterized in that the metal cation is calcium, strontium, barium, aluminum, aluminum, germanium, tin, lead, manganese, iron, nickel, zinc, titanium, zirconium or palladium. A toothpaste according to any of claims 36-37, characterized in that the metal cation is in the form of mineral salt, chloride, fluoride, nitrate, phosphate, sulphate or salt, acetate, or citrate of organic acid. The toothpaste according to any of claims 36-40, characterized in that the metal cat ion is zinc citrate, zinc sulphate, strontium chloride or tin fluoride.