KR20000016390A - Silica capable of being used in toothpaste compositions - Google Patents

Abstract

PURPOSE: A precipitation silica for polishing having an average diameter of particle over 10 micrometers and good particle cohesion factor and a manufacturing method thereof are provided. CONSTITUTION: The invention discloses an abrasive precipitation silica useable in toothpaste compositions, said silica having a BET specific surface ranging from 15 to 300 m2/g, a DOP oil absorption ranging from 40 to 160 ml/g, a median particle diameter of at least 10 micrometers, generally ranging from 12 to 30 micrometers, a particle cohesion factor of at least 85 % about for a median particle diameter ranging from 12 to 20 micrometers. Method for preparing silica by reacting an alkaline metal silicate with an acidifying agent, to form a silica slurry, separating and optionally drying the recuperated silica suspension, the operation for forming the slurry being effected according to the following steps:a first step consisting in using one initial heel solution constituted of water, an electrolyte salt of the alkaline or alkaline-earth metal group; a second step consisting in introducing the silicate and the acidifying agent, the reaction medium pH remaining constant from 4 to 7 and particularly from 5.8 to 6.7; and a third optional step, consisting in acidifying the reaction medium until a silica slurry with a pH of less than 6 and particularly of 4 is obtained. The silica is useful in toothpaste compositions. Toothpaste compositions containing the said silica are also disclosed.

Description

Silicas That Can Be Used in Toothpaste Compositions

The present invention relates to abrasive precipitated silica having a median diameter of 10 μm or more and good particle cohesion, which can be used in dentifrice compositions, in particular anti-tartar compositions, and methods of making such silicas; The present invention also relates to a dentifrice composition containing the silica.

Abrasives (particularly silica) used in dentifrice compositions usually have a median particle diameter of 10 μm or less, and less than 1.5% of the weight of the particles is more than 44 μm in diameter.

Certain formulations, especially those with anti-tartar effect, require the use of large abrasives.

The so-called "crunchy" effect, ie granulation, and complete brushing in the mouth may be required by the consumer. This effect can only be achieved if the abrasive has sufficient particle cohesion during brushing.

The problem can be solved with silica gel (continuous three-dimensional rigid structure) which typically has a BET specific surface of more than 300 m ² / g. However, the method for preparing the gel requires long-term and expensive washing and filtration steps.

Precipitated silica (agglomerates composed of discrete particulates bonded together by weak bonds) is obtained by a simpler method of execution, but does not have a sufficient degree of particle cohesion for the intended use.

Applicants have found that polishing silica having a median diameter of 10 μm or more and sufficient particle cohesion can be obtained by a simple method, for example, a method of producing silica by precipitation.

A first subject matter of the invention is abrasive precipitated silica that can be used in dentifrice compositions, wherein the silica is

A BET specific surface of about 15 to 300 m ² / g, preferably about 20 to 250 m ² / g,

About 40 to 160 ml / g of DOP oil absorption, preferably about 50 to 140 ml / g,

At least 10 μm median particle diameter, usually about 12-30 μm,

A particle agglomeration of at least about 85% for a median particle diameter of about 12 μm to 20 μm.

The silica also has a CTAB specific surface of about 10 to 120 m ² / g, preferably about 15 to 100 m ² / g.

The BET specific surface is described in the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society" (No. 60, page 309, February 1938) and corresponding to ISO standard 5794/1 (Annex D). It is measured according to the Brunauer-Emmet-Teller method.

DOP oil absorption is measured according to ISO standard 787/5 using dioctyl phthalate.

Silica particle cohesion is quantified using a specific test of cohesion by ultrasound; The test is evaluated by measuring the particle size before and after sonication by varying the median diameter d ₅₀ of the silica suspension.

In the above test, the Vibracell Bioblock Sony categorizer equipped with a probe, a timer and a converter having a diameter of 19 mm (by laser scattering using a Laser Sympatec particlemeter) was subjected to the following operation. Vibracell Bioblock sonicator)

Run on silica suspension sonicated using (600 W power ratio):

Preparation of silica suspensions

Preparing a homogeneous suspension of 15 g of silica in 135 g of water using a Rayyneri propeller-disperser; Then 70 g of the suspension are transferred to a 50 ml glass flask.

-Ultrasonic treatment

A pre-adjusted probe is placed in the flask to a depth of 4 cm without contact with the glass wall; The timer is programmed into a wave for a period of 2000 seconds, yielding an active ultrasonic cycle of 600 seconds.

After the flask is sealed, the ultrasonic cycle is started.

Particle size contrast

After manual homogenization of the sealed flask, 2 ml of the homogeneous suspension is pipetted off, and then the suspension is poured into a particle size cuvette and, if necessary, the amount of water is adjusted to obtain an optical concentration of 20% ± 3%.

After ultrasonic dispersion of the suspension in the cuvette for 30 seconds, the median diameter d ₅₀ is measured using a 100 mm focusing device.

Then the aggregation rate of the test silica is calculated; The higher the cohesive force of silica, the higher the cohesion rate.

-Coagulation rate

The initial median particle diameter d _50i is measured on a homogeneous silica suspension before sonication.

The final median diameter d _50f is measured on a homogeneous silica suspension after sonication.

The coagulation rate CF is calculated as (%) according to the following equation:

CF = (d _50f / d _50i ) × 100

The CF value 100 corresponds to the maximum cohesion value.

The CTAB specific surface is the outer surface area measured according to standard NFT 45007 (November 1987).

A second subject matter of the present invention is to react alkali metal M silicates having a SiO ₂ / M ₂ O ratio of about 2 to 4, preferably about 3 to 3.8, with an acidifying agent, optionally aged and recovered silica mash formed. A process for preparing abrasive silica having good particle cohesive force that can be used in a dentifrice composition by separating and optionally drying the separated silica suspension, and optionally grinding, wherein the process is carried out according to the following steps for forming a silica mesh. Shall be:

Electrolytic salts, water and any acidobasic from alkali or alkaline earth metals, wherein the amount of electrolyte present is about 0.1 to 1 mole of alkali metal electrolytic salt or about 10 to 100 mmol of alkaline earth metal electrolytic salt per liter of stock solution a first step consisting of using an initial stock consisting of an agent) at a temperature of about 70 to 98 ° C., preferably about 80 to 95 ° C .;

Conditions where the pH of the reaction medium maintained at a temperature of about 70 to 98 ° C., preferably about 80 to 95 ° C. is somewhat constant at values of about 4 to 7, preferably about 5.5 to 7, and especially about 5.8 to 6.7 Under a second step consisting of introducing alkali metal silicate and acidifying agent as aqueous solution into the stock solution until a target silica concentration is obtained in the medium;

And, after any aging, any third step consisting in acidifying the reaction medium until a silica mash of less than pH 6, preferably less than 5, most particularly about 4 is obtained.

The choice of silicates and acidifiers to carry out the process of the invention is chosen by methods well known per se.

Alkali metal silicates are advantageously sodium silicate or potassium silicate. Most particularly mention may be made of sodium silicate.

The silicate is used in the form of an aqueous solution having a concentration of about 150 to 400 g / l, preferably about 200 to 400 g / l, expressed in SiO ₂ .

Commonly used acidifying agents are strong inorganic acids such as sulfuric acid, nitric acid or hydrochloric acid, or organic acids such as acetic acid, formic acid or carbonic acid. Preferably, sulfuric acid. The acid can be used in dilute or concentrated form, preferably in the form of an aqueous solution at a concentration of about 60 to 400 g / l.

Mention may be made in particular of the metal salts and acidifying agents of the starting silicates, ie preferably sodium sulfate, in the electrolyte.

In order to confirm that the pH of the stock solution is similar to that selected in the second step of the process, an acidifying agent can be used in the initial stock solution and it is possible to adjust the pH with a strong acid or strong base. Particularly mentionable acidifiers are alkali metal hydrogen phosphates.

The stock solution may also contain silicates; The amount of any silicate ions expressed in SiO ₂ is less than 10 g per liter of stock solution. Preferably, the stock solution does not contain silicate ions.

The obtained stock solution is brought to a temperature of about 70 to 98 ° C., preferably about 80 to 95 ° C., and stirring is continued.

The second step adds the silicate solution and the acidifier simultaneously to the stock solution maintained under vigorous stirring.

The amount of each of the alkali metal silicate and the acidifying agent is selected to maintain the pH of the reaction medium at a somewhat constant value of about 4 to 7, preferably about 5.5 to 7, most particularly about 5.8 to 6.7 throughout the introduction of the two reagents.

The two solutions are introduced while maintaining the medium at a temperature of about 70 to 98 ° C, preferably about 80 to 95 ° C.

The introduction of the silicate solution is stopped when the target amount of silica formed is obtained. The amount is at least about 65 g, usually about 65 to 120 g, preferably about 70 to 100 g per liter of reaction medium.

Under the same temperature conditions any third step is below pH 6, preferably below 5 and most particularly about 4, the addition of acidifying agent to the reaction medium with stirring is carried out to improve the filtration and washing operations.

In one embodiment, after the introduction of the silicate solution is stopped, the medium obtained at the end of the second step is aged to stand for at least about 10 minutes, preferably 10 minutes to 2 hours, under the same temperature conditions, and then the acidifying agent is Reintroduce to execute any third step.

At the end of the third step, the addition of the acidifying agent is stopped, and the reaction medium is aged by optionally leaving under the same temperature conditions. Any of the above aged operations may be maintained for about 10 minutes to 2 hours.

After this operation, a silica mesh is obtained and then separated (liquid-solid separation); The operation usually consists of filtration (eg using a rotary filter under vacuum) followed by washing with water.

The recovered silica suspension (filter cake) contains at least about 35% solid mass. Then, for example, reflux dryers (spray, spin-flash,

Drying optionally using a tunnel oven, etc.) or a conductive dryer (rotary oven, screw dryer, decalcifier, drum dryer, etc.).

Silica in suspension or dry form has a particle agglomeration of at least about 85%, for median particle diameters of about 12 μm to 20 μm.

The silica may optionally be ground until a desired median particle diameter d ₅₀ , usually about 10 to 40 μm, preferably about 12 to 30 μm, is obtained.

Silica of good particle cohesion, obtained according to the method of forming the subject matter of the present invention or the subject matter of the present invention, is particularly suitable for use as an abrasive in dentifrice compositions.

When the silica is in the form of a suspension, the suspension can be stabilized by any known means, in particular using hydrocolloids, in particular polysaccharides such as xanthan gum, guar gum, water soluble cellulose ethers and the like.

The subject matter of the present invention is also the use of silicas which form the subject matter of the invention or obtained according to the process of the invention as abrasives in toothpaste compositions, as well as toothpaste compositions containing said silica. The silica may be present in the dentifrice composition at a rate of about 5-50% of the weight of the composition.

The composition may also contain other common ingredients, in particular other inorganic, water soluble abrasives, thickeners, wetting agents and the like.

As other abrasives, mention may be made of standard silica particle sizes (less than 10 μm) of abrasive silica, calcium carbonate, hydrated alumina, bentonite, aluminum silicate, zirconium silicate, and metaphosphate and sodium phosphate, potassium, calcium and magnesium. The total amount of abrasive powder comprises about 5-50% of the weight of the dental composition.

Among the thickeners, mention is made of thickened silica, xanthan gum, guar gum, carrageenans, cellulose derivatives and alginates, most particularly in amounts of about 1 to 15% by weight of the thickened silica, which may be up to 5% by weight of the composition. can do.

Among the humectants, mention may be made of glycerol, sorbitol, polyethylene glycol, polypropylene glycol and xylitol in an amount of about 2 to 85%, preferably about 3 to 55%, by weight of the dentifrice composition, for example, expressed as a solid.

The toothpaste compositions also contain surfactants, detergents, dyes, antibacterial agents, fluoro derivatives, opacifiers, flavors, sweeteners, tartar removers, antiplaque agents, bleaches, sodium bicarbonate, preservatives, enzymes, natural extracts (camo) Millet, timus, and the like).

The following examples are provided for illustrative purposes.

Comparative Example 1

The following is introduced into a 25 liter reactor:

1110 g of aqueous sodium silicate containing SiO ₂ / Na ₂ O ratio 3.4, containing 236 g / l SiO ₂ ,

-1.8 liters of water,

Sodium sulfate 58.6 g.

The temperature is brought to 90 ° C. with vigorous stirring.

Then, at 80 g / l, 856 g of sulfuric acid is added to bring the pH to 9.2.

With an SiO ₂ / Na ₂ O ratio of 3.4, an aqueous sodium silicate solution containing 236 g / l SiO ₂ , and an aqueous sulfuric acid solution at 80 g / l were then introduced simultaneously at a constant pH 9.2 to obtain 76 g of SiO ₂ per liter of suspension. Achieve concentration.

Acid addition is continued until pH 4 is obtained.

The product is then dried by filtration, washing and spraying.

Comparative Example 2

Three liters of water are introduced into a 25 liter reactor.

The temperature is brought to 80 ° C. with vigorous stirring.

Aqueous sodium silicate solution containing 230 g / l SiO ₂ and an aqueous sulfuric acid solution at 80 g / l at a constant pH 6 for 80 minutes at a SiO ₂ / Na ₂ O ratio of 3.5, 84 g of SiO ₂ per liter of suspension To achieve a concentration.

Acid addition is continued until pH 4 is obtained.

The product is then dried by filtration, washing and spraying.

Example 3

3 liters of water and 156 g of sodium sulfate are introduced into a 25 liter reactor.

The temperature is brought to 80 ° C. with vigorous stirring.

Aqueous sodium silicate solution containing 230 g / l SiO ₂ and an aqueous sulfuric acid solution at 80 g / l at a constant pH 6 for 80 minutes at a SiO ₂ / Na ₂ O ratio of 3.5, 84 g of SiO ₂ per liter of suspension To achieve a concentration.

Acid addition is continued until pH 4 is obtained.

The product is then dried by filtration, washing and spraying.

Example 4

3 liters of water and 156 g of sodium sulfate are introduced into a 25 liter reactor.

The temperature is brought to 70 ° C. with vigorous stirring.

Aqueous sodium silicate solution containing 230 g / l SiO ₂ and an aqueous sulfuric acid solution at 80 g / l at a constant pH 6 for 80 minutes at a SiO ₂ / Na ₂ O ratio of 3.5, 84 g of SiO ₂ per liter of suspension To achieve a concentration.

Acid addition is continued until pH 4 is obtained.

The product is then dried by filtration, washing and spraying.

Example 5

3 liters of water and 156 g of sodium sulfate are introduced into a 25 liter reactor.

The temperature is brought to 90 ° C. with vigorous stirring.

Aqueous sodium silicate solution containing 230 g / l SiO ₂ and an aqueous sulfuric acid solution at 80 g / l at a constant pH 6 for 80 minutes at a SiO ₂ / Na ₂ O ratio of 3.5, 84 g of SiO ₂ per liter of suspension To achieve a concentration.

Acid addition is continued until pH 4 is obtained.

The product is then dried by filtration, washing and spraying.

Example 6

3 liters of water and 156 g of sodium sulfate are introduced into a 25 liter reactor.

The temperature is brought to 85 ° C. with vigorous stirring.

Aqueous sodium silicate solution containing 230 g / l SiO ₂ and an aqueous sulfuric acid solution at 80 g / l at a constant pH 6 for 80 minutes at a SiO ₂ / Na ₂ O ratio of 3.5, 84 g of SiO ₂ per liter of suspension To achieve a concentration.

Acid addition is continued until pH 4 is obtained.

The product is then dried by filtration, washing and spraying.

Examples 7 and 8

3 liters of water, 96 g of sodium sulfate and 24 g of sodium hydrogen phosphate are introduced into a 25 liter reactor. The pH of the medium is 8.5.

The temperature is brought to 85 ° C. with vigorous stirring.

The pH of the medium is brought to 6.2 by the addition of sulfuric acid.

At an SiO ₂ / Na ₂ O ratio of 3.5, an aqueous sodium silicate solution containing 230 g / l of SiO ₂ , and an aqueous sulfuric acid solution at 80 g / l were added simultaneously for 80 minutes at a constant pH 6.2 to obtain 84 g of SiO ₂ per liter of suspension. To achieve a concentration.

Acid addition is continued until pH 4 is obtained.

The product is then filtered off and washed.

A suspension containing 49% solids is obtained ( Example 7 ).

The suspension is then dried by spraying ( Example 8 ).

The characteristics of the silicas obtained in Examples 1-8 are shown in Table 1 below.

Example BET (m ² / g) CTAB (m ² / g) DOP Absorption (ml / g) d _50i μm d _50f μm CF% One 40 25 70 14.7 11.2 76 2 222 - 87 14.5 11.8 81 3 80 51 80 15.1 14.3 95 4 250 89 132 16.3 14.8 90 5 40 26 70 15.4 15.4 100 6 60 39 81 17.2 16 93 7 (suspension) - - - 14.9 13.26 89 8 71 44 76 14.6 13 89

It was observed that the product prepared according to the process of the invention, having a d _50i value of about 15 μm, had a cohesion rate of at least 85% CF.

Example 9

The silica obtained in any of Examples 3 to 6 or 8 is used to obtain the following toothpaste composition.

Sorbitol (50% solution) 47%

Silica 19% of Examples 3-6 or 8

Thickened silica 3%

Sodium pyrophosphate 1%

Pyrophosphate tetrapotassium 4%

Titanium Dioxide 0.5%

Xanthan gum 0.8%

Sodium Saccharate 0.2%

Sodium benzoate 0.3%

Sodium fluoride 0.22%

Sodium lauryl sulfate 1.4%

Flavor 1%

Deionized water 100%

Claims (18)

Abrasive precipitated silica with A BET specific surface of about 15 to 300 m ² / g, preferably about 20 to 250 m ² / g, About 40 to 160 ml / g of DOP oil absorption, preferably about 50 to 140 ml / g, At least 10 μm median particle diameter, usually about 12-30 μm, At least about 85% particle agglomeration for a median particle diameter of about 12 μm to 20 μm. The silica according to claim 1, wherein the CTAB specific surface is about 10 to 120 m ² / g, preferably about 15 to 100 m ² / g. An alkali metal M silicate having an SiO ₂ / M ₂ O ratio of about 2 to 4, preferably about 3 to 3.8, is reacted with an acidifying agent, optionally aged the formed silica mash, and the recovered silica suspension is separated and optionally A method for producing silica by dry grinding after drying, wherein the forming of the silica mesh is carried out according to the following steps: Electrolytic salts, water and any acidobasic from alkali or alkaline earth metals, wherein the amount of electrolyte present is about 0.1 to 1 mole of alkali metal electrolytic salt or about 10 to 100 mmol of alkaline earth metal electrolytic salt per liter of stock solution a first step consisting of using an initial stock consisting of an agent) at a temperature of about 70 to 98 ° C., preferably about 80 to 95 ° C .; Conditions where the pH of the reaction medium maintained at a temperature of about 70 to 98 ° C., preferably about 80 to 95 ° C. is somewhat constant at values of about 4 to 7, preferably about 5.5 to 7, and especially about 5.8 to 6.7 Under a second step consisting of introducing alkali metal silicate and acidifying agent as aqueous solution into the stock solution until a target silica concentration is obtained in the medium; And, after any aging, any third step consisting in acidifying the reaction medium until a silica mash of less than pH 6, preferably less than 5, most particularly about 4 is obtained. 4. The process of claim 3 wherein the alkali metal silicate is sodium silicate or potassium silicate. The method according to claim 3 or 4, characterized in that the alkali metal silicate is sodium silicate used in the form of an aqueous solution of about 150 to 400 g / l, preferably about 200 to 400 g / l, represented by SiO ₂ . How to. The method according to any one of claims 3 to 5, wherein the acidifying agent is an inorganic or organic acid. The method according to claim 6, wherein the acidifying agent is sulfuric acid, nitric acid, hydrochloric acid, acetic acid, formic acid or carbonic acid. 8. The method of claim 7, wherein the acidifying agent is sulfuric acid used in the form of an aqueous solution having a concentration of about 60 to 400 g / l. The process according to claim 3, wherein the electrolyte is a metal salt of the starting silicate and the acidifying agent, preferably sodium sulfate. 10. The process according to any one of claims 3 to 9, wherein the acidifier is an alkali metal hydrogen phosphate. The pH of the reaction medium according to any one of claims 3 to 10, wherein the silicate solution and the acidifying agent are added to the stock solution in which the second step is maintained under stirring to adjust the pH of the reaction medium to about 4 to 7, preferably about 5.5 to 7, most particularly, in each amount being added simultaneously and simultaneously so as to be maintained at a rather constant value of about 5.8 to 6.7. 12. The process according to any one of claims 3 to 11, wherein the third step is carried out by adding an acidifying agent to the reaction medium with stirring until a pH of less than 6, preferably less than 5 and most particularly about 4 is obtained. How to. 13. The medium according to any one of claims 3 to 12, wherein the medium obtained at the end of the second stage is left to mature after leaving the introduction of the silicate solution for at least about 10 minutes, preferably 10 minutes to 2 hours. How to. The process according to claim 3, wherein at the end of the third step, after stopping the addition of the acidifying agent, the reaction medium is left to mature for about 10 minutes to 2 hours. 15. The process according to any one of claims 3 to 14, wherein the forming of the silica mesh is carried out at a temperature of about 70 to 98 ° C, preferably about 80 to 95 ° C. Use of a silica obtained in a dentifrice composition according to the method of forming the subject of claim 1 or 2 or of the subject of any one of claims 3 to 15. A dentifrice composition containing about 5-50% of the weight of silica obtained according to the method of forming the subject of claim 1 or 2 or of the subject of any one of claims 3 to 15. 18. The composition of claim 17 wherein the toothpaste composition comprises other abrasives, thickeners, wetting agents, surfactants, detergents, dyes, antimicrobials, fluoro derivatives, opaques, flavors, sweeteners, tartar removers, antiplaques, bleaches, sodium bicarbonates, preservatives. Toothpaste composition, characterized in that it also contains at least one common ingredient selected from enzymes and natural extracts.