CA1307646C - Silicas - Google Patents
SilicasInfo
- Publication number
- CA1307646C CA1307646C CA000530368A CA530368A CA1307646C CA 1307646 C CA1307646 C CA 1307646C CA 000530368 A CA000530368 A CA 000530368A CA 530368 A CA530368 A CA 530368A CA 1307646 C CA1307646 C CA 1307646C
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- Canada
- Prior art keywords
- silica
- range
- surface area
- weight
- microns
- Prior art date
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Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61Q—SPECIFIC USE OF COSMETICS OR SIMILAR TOILETRY PREPARATIONS
- A61Q11/00—Preparations for care of the teeth, of the oral cavity or of dentures; Dentifrices, e.g. toothpastes; Mouth rinses
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61K—PREPARATIONS FOR MEDICAL, DENTAL OR TOILETRY PURPOSES
- A61K8/00—Cosmetics or similar toiletry preparations
- A61K8/18—Cosmetics or similar toiletry preparations characterised by the composition
- A61K8/19—Cosmetics or similar toiletry preparations characterised by the composition containing inorganic ingredients
- A61K8/25—Silicon; Compounds thereof
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/113—Silicon oxides; Hydrates thereof
- C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
- C01B33/18—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof
- C01B33/187—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof by acidic treatment of silicates
- C01B33/193—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof by acidic treatment of silicates of aqueous solutions of silicates
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/02—Amorphous compounds
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/10—Solid density
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/12—Surface area
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/19—Oil-absorption capacity, e.g. DBP values
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
- C01P2006/82—Compositional purity water content
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/90—Other properties not specified above
Abstract
R.3016 ABSTRACT
An amorphous silica, especially precipitated silica, suitable for use in toothpastes, has a high abrasivity represented by a perspex abrasion value in the range from about 23 to about 35.
An amorphous silica, especially precipitated silica, suitable for use in toothpastes, has a high abrasivity represented by a perspex abrasion value in the range from about 23 to about 35.
Description
`
1 ~07646 - 1 - R.3016 Title: SILICAS
Field of the invention This invention relates to synthetic amorphous silicas, especially precipitated silicas, of use, for example, as abrasive agents in toothpaste compositions.
Background to the invention Toothpaste compositions are well characterised in the literature and many compositions are disclosed in patent specifications and other literature. Toothpaste compositions contain a number of specific components for example abrasive agents,; fluoride sources, binders, ~- preservatives, humectants, anti~ plaque agents, colouring agents, water, flavour and other optional ingredients. Of these components the abrasive agent is required to provide the appropriate cleaning and plaque removal without subjecting the tooth itself to excessive abrasion.
Typically a toothpaste compositian will contain from about ':
~ ` 1 307646 - 2 - R.3016 5~ to about 50% preferably up to about 30% by weight of abrasive. Commonly used abrasives are aluminas, calcium carbonates and calcium phosphates. More recently synthetic silicas have been adopted because of their efficient cleaning, compatibility with other ingredients and their physical properties.
General de_ ription of the invention The silicas of the invention provide a novel range of properties, combining remarkedly high levels of abrasivity coupled with low surface areas and an unusually high degree of openness of structure as defined by porosity measurements. In particular, such high levels of abrasivity have not been found previously from a precipitate route.
The silicas of the invention are capable of providing high levels of abrasion even at relatively low particle sizes i.e. 3 to ~ micron range and/or levels of moisture from about 1% to about 35~. Abrasive materials can also be obtained at particle sizes beyond the stated upper limit but they are not suitable for use in toothpastes because of the unacceptable mouth feel of the coarser particles.
In general, characterisation of the pore structure of siIicàs containing higher levels of openness and wider pores by nitrogen adsorption techniques is not meaningful because this technique is useful only for pores up to about 30 nm diameter. To measure the full range of porosity present in such materials it is necessary to employ alternative procedures, for example oil absorption or mercury porosimetry. Since the products of this invention have considerable pore structure in excess of 30 .
1 ~07646 - 1 - R.3016 Title: SILICAS
Field of the invention This invention relates to synthetic amorphous silicas, especially precipitated silicas, of use, for example, as abrasive agents in toothpaste compositions.
Background to the invention Toothpaste compositions are well characterised in the literature and many compositions are disclosed in patent specifications and other literature. Toothpaste compositions contain a number of specific components for example abrasive agents,; fluoride sources, binders, ~- preservatives, humectants, anti~ plaque agents, colouring agents, water, flavour and other optional ingredients. Of these components the abrasive agent is required to provide the appropriate cleaning and plaque removal without subjecting the tooth itself to excessive abrasion.
Typically a toothpaste compositian will contain from about ':
~ ` 1 307646 - 2 - R.3016 5~ to about 50% preferably up to about 30% by weight of abrasive. Commonly used abrasives are aluminas, calcium carbonates and calcium phosphates. More recently synthetic silicas have been adopted because of their efficient cleaning, compatibility with other ingredients and their physical properties.
General de_ ription of the invention The silicas of the invention provide a novel range of properties, combining remarkedly high levels of abrasivity coupled with low surface areas and an unusually high degree of openness of structure as defined by porosity measurements. In particular, such high levels of abrasivity have not been found previously from a precipitate route.
The silicas of the invention are capable of providing high levels of abrasion even at relatively low particle sizes i.e. 3 to ~ micron range and/or levels of moisture from about 1% to about 35~. Abrasive materials can also be obtained at particle sizes beyond the stated upper limit but they are not suitable for use in toothpastes because of the unacceptable mouth feel of the coarser particles.
In general, characterisation of the pore structure of siIicàs containing higher levels of openness and wider pores by nitrogen adsorption techniques is not meaningful because this technique is useful only for pores up to about 30 nm diameter. To measure the full range of porosity present in such materials it is necessary to employ alternative procedures, for example oil absorption or mercury porosimetry. Since the products of this invention have considerable pore structure in excess of 30 .
- 3 - R.3016 nm it is necessary to define them by means of such techniques.
The invention provides an amorphous silica, preferably a precipitated silica, having i) a surface area in the range from about 10, preferably from about 50, to about 450m2/g, usually about 200 to about 400m2/g, ii) a weight mean particle size in the range 3 microns to 20 microns, preferably above 5 micron and below 15 microns, iii) a perspex abrasion value in the range from about 23 to about 35, and, optionally for precipitated silicas, iv) an oil absorption in the range from about 60 to about llOcc/lOOg, preferably up to about 95cc/lOOg. These perspex abrasion values correspond to Radioactive Dentine Abrasion values of 150 to 300.
The invention extends to a method of reacting a silicate solution and acid solution in the presence of electrolyte to provide precipitated silicas according to the invention.
The invention includes a method of preparing an amorphous precipitated silica, suitable for use as a toothpaste abrasive, and having i) a surface area in the range from about 10 to about ~50 mZ/g, ii) a weight mean particle size in the range from about 3 to about 20 microns, iii) a perspex abrasion value in the range from about 23 to about 35, and optionally, iv) an oil absorption in the range from about 60 to ; about 110 ccilOOg which is produced by the ;~ reaction of sodlum silicate, having a , :
``" 1 307646 - 4 - R.3016 silica:Na20 ratio ln the range from 1.8 to 3.5:1, with mineral acid, with the concentration and volume of the reactants controlled to give a reaction in the pH range from about 10 to about 10.5, in the presence of a water soluble electrolyte comprising a cation selected from the group comprising aluminium, magnesium, calcium, sodium and potassium with an associated anion selected from the group comprising bromide, carbonate, chloride, nitrate, acetate and sulphate wherein the electrolyte:silica weight ratio is from about 0.1 to 1 to about 2 to 1, the precipitation reaction being performed in the temperature range of àbout 95C to about 100C.
Optionally the reaction medium ls subjected to a hydrothermal ageing step during the final acid addition step to provide materials with lower surface areas. ?
Standard Procedures The silicas of the invention are defined,in terms of their physical and che~ical properties. The standard test metnods used for these properties are:-i) Surface Area:
Surface area is determined using standard nitrogen adsorption methods of Brunauer, Emmett and Teller ~BET), ` using a single poin~t method with a Sorpty 1750 apparatus supplied by Carlo Erba company of Italy. The sample was outgassed under vacuum at 270C for 1 hour before measurement.
`
.
The invention provides an amorphous silica, preferably a precipitated silica, having i) a surface area in the range from about 10, preferably from about 50, to about 450m2/g, usually about 200 to about 400m2/g, ii) a weight mean particle size in the range 3 microns to 20 microns, preferably above 5 micron and below 15 microns, iii) a perspex abrasion value in the range from about 23 to about 35, and, optionally for precipitated silicas, iv) an oil absorption in the range from about 60 to about llOcc/lOOg, preferably up to about 95cc/lOOg. These perspex abrasion values correspond to Radioactive Dentine Abrasion values of 150 to 300.
The invention extends to a method of reacting a silicate solution and acid solution in the presence of electrolyte to provide precipitated silicas according to the invention.
The invention includes a method of preparing an amorphous precipitated silica, suitable for use as a toothpaste abrasive, and having i) a surface area in the range from about 10 to about ~50 mZ/g, ii) a weight mean particle size in the range from about 3 to about 20 microns, iii) a perspex abrasion value in the range from about 23 to about 35, and optionally, iv) an oil absorption in the range from about 60 to ; about 110 ccilOOg which is produced by the ;~ reaction of sodlum silicate, having a , :
``" 1 307646 - 4 - R.3016 silica:Na20 ratio ln the range from 1.8 to 3.5:1, with mineral acid, with the concentration and volume of the reactants controlled to give a reaction in the pH range from about 10 to about 10.5, in the presence of a water soluble electrolyte comprising a cation selected from the group comprising aluminium, magnesium, calcium, sodium and potassium with an associated anion selected from the group comprising bromide, carbonate, chloride, nitrate, acetate and sulphate wherein the electrolyte:silica weight ratio is from about 0.1 to 1 to about 2 to 1, the precipitation reaction being performed in the temperature range of àbout 95C to about 100C.
Optionally the reaction medium ls subjected to a hydrothermal ageing step during the final acid addition step to provide materials with lower surface areas. ?
Standard Procedures The silicas of the invention are defined,in terms of their physical and che~ical properties. The standard test metnods used for these properties are:-i) Surface Area:
Surface area is determined using standard nitrogen adsorption methods of Brunauer, Emmett and Teller ~BET), ` using a single poin~t method with a Sorpty 1750 apparatus supplied by Carlo Erba company of Italy. The sample was outgassed under vacuum at 270C for 1 hour before measurement.
`
.
- 5 - R.3016 ii) Oil Absorption:
The oil absorption is determined by the ASTM spatula rub-out method (American Society of Test Material Standards D, 281).
The test is based upon the principle of mixing linseed oil with a silica by rubbing with a spatula on a smooth surface until a stiff putty-like paste is formed which will not break or separate when it is cut with the spatula. The volume of oil used is then put into the following equation:-Oil absorption = cm3 oil absorption x 100 wt. of silica sample in gms = cm3 oil/lOOg silica iii) Weight Mean Particle Size:
The weight mean particle size of the silicas wasdetermined with the aid of a Malvern Particlesizer, Model 3600 E. This instrument, made by Malvern Instruments, Malvern, Worcestershire uses the principle of Fraunh~ffer diffraction utilising a low power He/Ne laser. Before measurement the sample was dispersed ultrasonically in water for a period of 7 minutes to form an aqueous suspension.
iv) Perspex Abrasion Value:
This test is based upon a toothbrush head brushing a perspex plate in contact with a suspension of the silica ~ in a sorbitol/glycerol mixture. Normally the slurry composition is as ~ollows:
:
': , -` 1 3n7646 - 6 - R.3016 Silica 2.5 grams Glycerol 10.0 grams Sorbitol Syrup* 23.0 grams * Syrup contains 70~ sorbitol/30% water.
All components are weiyhed into a beaker and dispersed for 2 minutes at 1500 rpm using a simple stirrer. A llOmm x 55mm x 3mm sheet of standard clear Perspex is used for the test, supplied by Imperial Chemical Industries Plc under code 000.
The test is carried out using a modified Wet Paint Scrub Tester produced by Research Equipment Limited, Wellington Road, Hampton Hill, Middlesex. The modification is to change the holder so that a toothbrush can be used instead of a paint brush. In addition a weight of 14 ozs is attached to the brush to force the brush onto the perspex plate.
A Galvanometer is calibrated using a 45 Plaspec gloss head detector and a standard (50~ gloss) reflecting plate. The Galvanometer reading is adjusted to a value of 50 under these conditions. The reading of the fresh perspex plate is then carried out using the same reflectance arrangement.
The fresh piece of perspex is then fitted into a holder. Two mls of the dispersed silica, sufficient to lubricate fully the brushing stroke, is placed on the plate and the brush head lowered onto the plate. The machine is switched on and the plate subjected to three hundred strokes of the weighted brush head. The plate is removed from the holder and all the suspension is washed off. It is then dried and re-measured for its gloss value. The abrasion value is the difference between the unabraded value and the value after abrasion.
.
. .
.
The oil absorption is determined by the ASTM spatula rub-out method (American Society of Test Material Standards D, 281).
The test is based upon the principle of mixing linseed oil with a silica by rubbing with a spatula on a smooth surface until a stiff putty-like paste is formed which will not break or separate when it is cut with the spatula. The volume of oil used is then put into the following equation:-Oil absorption = cm3 oil absorption x 100 wt. of silica sample in gms = cm3 oil/lOOg silica iii) Weight Mean Particle Size:
The weight mean particle size of the silicas wasdetermined with the aid of a Malvern Particlesizer, Model 3600 E. This instrument, made by Malvern Instruments, Malvern, Worcestershire uses the principle of Fraunh~ffer diffraction utilising a low power He/Ne laser. Before measurement the sample was dispersed ultrasonically in water for a period of 7 minutes to form an aqueous suspension.
iv) Perspex Abrasion Value:
This test is based upon a toothbrush head brushing a perspex plate in contact with a suspension of the silica ~ in a sorbitol/glycerol mixture. Normally the slurry composition is as ~ollows:
:
': , -` 1 3n7646 - 6 - R.3016 Silica 2.5 grams Glycerol 10.0 grams Sorbitol Syrup* 23.0 grams * Syrup contains 70~ sorbitol/30% water.
All components are weiyhed into a beaker and dispersed for 2 minutes at 1500 rpm using a simple stirrer. A llOmm x 55mm x 3mm sheet of standard clear Perspex is used for the test, supplied by Imperial Chemical Industries Plc under code 000.
The test is carried out using a modified Wet Paint Scrub Tester produced by Research Equipment Limited, Wellington Road, Hampton Hill, Middlesex. The modification is to change the holder so that a toothbrush can be used instead of a paint brush. In addition a weight of 14 ozs is attached to the brush to force the brush onto the perspex plate.
A Galvanometer is calibrated using a 45 Plaspec gloss head detector and a standard (50~ gloss) reflecting plate. The Galvanometer reading is adjusted to a value of 50 under these conditions. The reading of the fresh perspex plate is then carried out using the same reflectance arrangement.
The fresh piece of perspex is then fitted into a holder. Two mls of the dispersed silica, sufficient to lubricate fully the brushing stroke, is placed on the plate and the brush head lowered onto the plate. The machine is switched on and the plate subjected to three hundred strokes of the weighted brush head. The plate is removed from the holder and all the suspension is washed off. It is then dried and re-measured for its gloss value. The abrasion value is the difference between the unabraded value and the value after abrasion.
.
. .
.
- 7 - R.3016 This test procedure, when applied to known abrasives, gave the following values:
Perspex abrasion value Calcium carbonate (15 micron) ...................... 32 Silica xerogel (10 micron) prepared 10 by UK 1264292 method .~............................. 25 Alumina trihydrate (Gibbsite) (15 micron~ .... 16 Calcium pyrophosphate (10 micron) .~................ 14 Dicalcium phosphate dihydrate (15 micron) .......... 7 v) Loose Bulk Density:
Loose bulk density is determined by weighing approximately 180 ml of silica into a dry 250 ml measuring cylinder, inverting the cylinder ten times to remove air pockets and reading the final settled volumeO
Loose bulk density = Weight x 1000 g/l Volume : vi) : Electrolyte Levels:
: ~ Sulphate:is determined gravimetrically by hot water extrac~ion of the silica, followed by precipitation as , :
: barium sulphate. Chloride is determined by hot water extraction of the silica, followed by titration with standard silver nitrate solution:using potassium chromate as indicator (Mohr's method).
~: ,,, :
~ ,.
.,.. ~ ~ , .
Perspex abrasion value Calcium carbonate (15 micron) ...................... 32 Silica xerogel (10 micron) prepared 10 by UK 1264292 method .~............................. 25 Alumina trihydrate (Gibbsite) (15 micron~ .... 16 Calcium pyrophosphate (10 micron) .~................ 14 Dicalcium phosphate dihydrate (15 micron) .......... 7 v) Loose Bulk Density:
Loose bulk density is determined by weighing approximately 180 ml of silica into a dry 250 ml measuring cylinder, inverting the cylinder ten times to remove air pockets and reading the final settled volumeO
Loose bulk density = Weight x 1000 g/l Volume : vi) : Electrolyte Levels:
: ~ Sulphate:is determined gravimetrically by hot water extrac~ion of the silica, followed by precipitation as , :
: barium sulphate. Chloride is determined by hot water extraction of the silica, followed by titration with standard silver nitrate solution:using potassium chromate as indicator (Mohr's method).
~: ,,, :
~ ,.
.,.. ~ ~ , .
- 8 - R.3016 vii) Moisture Loss at 105C:
Moisture loss is determined by the loss in weight of a silica when dried to constant weight in an electric oven at 105C.
viii)Ignitlon Loss at 1000C:
Ignition loss is determined by the loss in weight of a silica when ignited- in a furnace at 1000C to constant weight.
ix) pH:
This measurement is carried out on a 5~ w/w suspension of the silica in boiled demineralised water (C2 free).
x) Filter Cake Ignition Loss:
Filter cake ignition loss is determined by the loss in weight of a silica filter cake when ignited in a furnace at 1000C to constant weight.
xi) Radioactive Dentine Abrasion Test (RDA):
The procedure follows the method for assessment of dentifrice abrasivity recommended by the American Dental Association (Journal of Dental Research 55 (4) 563, 1976).
In this procedure extracted human teeth are irradiated with a neutron flux and subjected to a standard brushing regime. The radioactive phosphorous 32 removed from the dentin in the roots is used as the index of the abrasion of the dentifrice tested. A reference slurry containing 3S lOg of calcium pyrophosphate in 15 ml of 0.5~ aqueous solution of sodium carboxymethyl cellulose is also . , . . .
--` 1 307646 - 9 - R.3016 measured and the RDA of this mixture is arbitrarily taken as 100. The precipitated silica to be tested is prepared as a suspension at the same concentration as the pyrophosphate and submitted to the same brushing regime.
The RDA's obtained are quoted for a number of the examples of silicas prepared within the present invention.
By examining a range of silicas, including those described in the present invention, it has been found there is a correlation between plastics abrasion value and RDA over fifteen samples with a correlation coefficient of 0.91 (confidence 99%).
xii) Mercury intrusion volume:
Mercury intrusion volumes are determined (in cc/g) by standard mercury intrusion procedures using a Micromeritics Autopore 9220 mercury porosimeter. The pore radius is calculated from the Washburn equation using values of surface tension for mercury of 485 dynes/cm and contact angle of 140.
Prior to measurement the sample was outgassed at room temperature to a pressure of S0 microns of mercury. The mercury intrusion volume recorded is that occurring over the range of calculated pore diameters of 0.05 to 1.0 mlcron.
xiii) Refractive index (RI)/transmission:
; ~ The sample silica was dispersed in a range of water/sorbitol ~70~ syrup) mixtures. The RI for each dispersion was measured together with the percentage transmission using illumination of 589 nm and water as a blank. The RI of the silica is taken to correspond to the maximum transmiss~on and presentation of the transmission ., ,~, .
~ " 1 307646 - 10 - R.301~
against RI graphically allows the transmission over a range of RI to be readily demonstrated.
Specific description of the invention Examples of the preparation of precipitated silicas will now be given to illustrate but not limit the invention. Example ll is included as a comparison to show the criticality of the reaction temperature on the abrasivity of the resulting silica.
A heated stirred reaction vessel was used for the silicate/acid reaction.
The solutions used in the process were as follows:-i) Sodium silicate solutions having a SiO2:Na20 ratio in the range of 1.9 to 3.4:1.
ii) A sulphuric acid solution of specific gravity 1.11 ( 16.1% W/W solution) to 1.185 (25.9% W/W
solution).
iii) An electrolyte solution as defined in each example.
The following procedure was adopted in the preparation of the precipitated silicas. Values of reactant concentrations and volumes, and reaction temperatures are given in Table 1.
(A) litres of water were placed in the vessel together with (B) litres of electrolyte solution and (C) litres of the sodium silicate solution. This mixt~re was then stirred and heated to (E)C.
~ ~:9 ' - 1 3076a6 - 11 - R.3016 The sodium sllicate ((D) litres) and sulphuric acid ((F) litres) solutions were then added simultaneously over a period of about 20 minutes with stirring while maintaining the temperature at (E)C. The flow rates of the silicate and acid solutions were uniform throughout the addition period to ensure that a constant pH was maintained in the vessel. (G) litres of electrolyte solution was then added over a period of (H) minutes with continued mixing at (E)C. Sulphuric acid solution was then added over a period of 10 minutes with continued mixing to reduce the pH of the liquid to the range of 3.0 to 3.5. During this addition of acid the temperature was maintained. Optionally a hydrothermal ageing step can be introduced during the acid addition if materials with lower surface areas are required. This is illustrated by Examples 5, 13, 14, 15, 16, 17 and 18. The resultant slurry was then filtered and washed with water to remove excess electrolyte. Typically, for a toothpaste application, the residual electrolyte would be less than 2~ on a dry weight basis.
A~ter washing, the filter cake, which had a moisture content of (J)%, was dried and comminuted to the desired particle size range. Alternatively the filter cake can be ~5 hot air milled, without drying to the desired particle size range and this procedure was used in E~amples 3, 4 and 5.
The precipitated silica obtained had the properties, expressed on a dry weight basls, as listed in Table II.
The precipitated silicas prepared as described provided satisfactory cleaning properties for the toothpastes in which they were incorporated. The toothpastes had commercially suitable properties for stability and usage. The major outlet for the use of ~.
.
---` 1 307646 - 12 - ~.301 these silicas is in opaque dentrifices since the percentage transmission (589 nm) of the silicas of the invention has a maximum vlaue of about 35% over the refractive index range of 1.433 to 1.445. Typical formulations using the silicas of this invention are listed below.
;
. i~
,..,; . . .
"` 1 3076~
Moisture loss is determined by the loss in weight of a silica when dried to constant weight in an electric oven at 105C.
viii)Ignitlon Loss at 1000C:
Ignition loss is determined by the loss in weight of a silica when ignited- in a furnace at 1000C to constant weight.
ix) pH:
This measurement is carried out on a 5~ w/w suspension of the silica in boiled demineralised water (C2 free).
x) Filter Cake Ignition Loss:
Filter cake ignition loss is determined by the loss in weight of a silica filter cake when ignited in a furnace at 1000C to constant weight.
xi) Radioactive Dentine Abrasion Test (RDA):
The procedure follows the method for assessment of dentifrice abrasivity recommended by the American Dental Association (Journal of Dental Research 55 (4) 563, 1976).
In this procedure extracted human teeth are irradiated with a neutron flux and subjected to a standard brushing regime. The radioactive phosphorous 32 removed from the dentin in the roots is used as the index of the abrasion of the dentifrice tested. A reference slurry containing 3S lOg of calcium pyrophosphate in 15 ml of 0.5~ aqueous solution of sodium carboxymethyl cellulose is also . , . . .
--` 1 307646 - 9 - R.3016 measured and the RDA of this mixture is arbitrarily taken as 100. The precipitated silica to be tested is prepared as a suspension at the same concentration as the pyrophosphate and submitted to the same brushing regime.
The RDA's obtained are quoted for a number of the examples of silicas prepared within the present invention.
By examining a range of silicas, including those described in the present invention, it has been found there is a correlation between plastics abrasion value and RDA over fifteen samples with a correlation coefficient of 0.91 (confidence 99%).
xii) Mercury intrusion volume:
Mercury intrusion volumes are determined (in cc/g) by standard mercury intrusion procedures using a Micromeritics Autopore 9220 mercury porosimeter. The pore radius is calculated from the Washburn equation using values of surface tension for mercury of 485 dynes/cm and contact angle of 140.
Prior to measurement the sample was outgassed at room temperature to a pressure of S0 microns of mercury. The mercury intrusion volume recorded is that occurring over the range of calculated pore diameters of 0.05 to 1.0 mlcron.
xiii) Refractive index (RI)/transmission:
; ~ The sample silica was dispersed in a range of water/sorbitol ~70~ syrup) mixtures. The RI for each dispersion was measured together with the percentage transmission using illumination of 589 nm and water as a blank. The RI of the silica is taken to correspond to the maximum transmiss~on and presentation of the transmission ., ,~, .
~ " 1 307646 - 10 - R.301~
against RI graphically allows the transmission over a range of RI to be readily demonstrated.
Specific description of the invention Examples of the preparation of precipitated silicas will now be given to illustrate but not limit the invention. Example ll is included as a comparison to show the criticality of the reaction temperature on the abrasivity of the resulting silica.
A heated stirred reaction vessel was used for the silicate/acid reaction.
The solutions used in the process were as follows:-i) Sodium silicate solutions having a SiO2:Na20 ratio in the range of 1.9 to 3.4:1.
ii) A sulphuric acid solution of specific gravity 1.11 ( 16.1% W/W solution) to 1.185 (25.9% W/W
solution).
iii) An electrolyte solution as defined in each example.
The following procedure was adopted in the preparation of the precipitated silicas. Values of reactant concentrations and volumes, and reaction temperatures are given in Table 1.
(A) litres of water were placed in the vessel together with (B) litres of electrolyte solution and (C) litres of the sodium silicate solution. This mixt~re was then stirred and heated to (E)C.
~ ~:9 ' - 1 3076a6 - 11 - R.3016 The sodium sllicate ((D) litres) and sulphuric acid ((F) litres) solutions were then added simultaneously over a period of about 20 minutes with stirring while maintaining the temperature at (E)C. The flow rates of the silicate and acid solutions were uniform throughout the addition period to ensure that a constant pH was maintained in the vessel. (G) litres of electrolyte solution was then added over a period of (H) minutes with continued mixing at (E)C. Sulphuric acid solution was then added over a period of 10 minutes with continued mixing to reduce the pH of the liquid to the range of 3.0 to 3.5. During this addition of acid the temperature was maintained. Optionally a hydrothermal ageing step can be introduced during the acid addition if materials with lower surface areas are required. This is illustrated by Examples 5, 13, 14, 15, 16, 17 and 18. The resultant slurry was then filtered and washed with water to remove excess electrolyte. Typically, for a toothpaste application, the residual electrolyte would be less than 2~ on a dry weight basis.
A~ter washing, the filter cake, which had a moisture content of (J)%, was dried and comminuted to the desired particle size range. Alternatively the filter cake can be ~5 hot air milled, without drying to the desired particle size range and this procedure was used in E~amples 3, 4 and 5.
The precipitated silica obtained had the properties, expressed on a dry weight basls, as listed in Table II.
The precipitated silicas prepared as described provided satisfactory cleaning properties for the toothpastes in which they were incorporated. The toothpastes had commercially suitable properties for stability and usage. The major outlet for the use of ~.
.
---` 1 307646 - 12 - ~.301 these silicas is in opaque dentrifices since the percentage transmission (589 nm) of the silicas of the invention has a maximum vlaue of about 35% over the refractive index range of 1.433 to 1.445. Typical formulations using the silicas of this invention are listed below.
;
. i~
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- 13 - R.3016 OPAQUE WHITE DENTAL_CREAMS .
FORMULATION 1 % FORMULATION 2 %
Sorbosil TC1012.0 Sorbosil TC10 8.0 Silica of invention 8.0 Silica of invention 14.0 Xanthan Gu~ 1.0 Sodium Carboxymethyl Cellulose 0.9 Sorbitol, 70~ non- Sorbitol, 70% non-crystallisable40.0 crystallisable40.0 Sodium Lauryl Polyethylene Glycol Sulphate 1.5 1500 5.0 Sodium Monofluro- Sodium Lauryl phosphate 0.8 Sulphate 1.5 20 Flavour 1.0 Sodium Monofluorophosphate 0.8 Saccharin 0.2 Flavour 1.0 25 Titanium Dioxide 1.0 Saccharin 0.2 Titanium Dioxide 1.0 Water and Minor Water and Minor Ingredients to 100 Ingredients to 100 Properties - Initial Properties - Initial Density @ 25C 1.36 gml Density @ 25C 1.33 gml Sorbosil TC10 is a thickening silica obtainable from Crosfield Chemicals of Warrington, England.
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FORMULATION 1 % FORMULATION 2 %
Sorbosil TC1012.0 Sorbosil TC10 8.0 Silica of invention 8.0 Silica of invention 14.0 Xanthan Gu~ 1.0 Sodium Carboxymethyl Cellulose 0.9 Sorbitol, 70~ non- Sorbitol, 70% non-crystallisable40.0 crystallisable40.0 Sodium Lauryl Polyethylene Glycol Sulphate 1.5 1500 5.0 Sodium Monofluro- Sodium Lauryl phosphate 0.8 Sulphate 1.5 20 Flavour 1.0 Sodium Monofluorophosphate 0.8 Saccharin 0.2 Flavour 1.0 25 Titanium Dioxide 1.0 Saccharin 0.2 Titanium Dioxide 1.0 Water and Minor Water and Minor Ingredients to 100 Ingredients to 100 Properties - Initial Properties - Initial Density @ 25C 1.36 gml Density @ 25C 1.33 gml Sorbosil TC10 is a thickening silica obtainable from Crosfield Chemicals of Warrington, England.
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Claims (12)
1. An amorphous precipitated silica having i) a surface area in the range from 10 to 450m2/g, ii) a weight mean particle size in the range from 3 to 20 microns, and iii) a perspex abrasion value in the range from 23 to 35.
2. A silica according to claim 1 wherein the silica has an oil absorption in the range from 60 to 110 cc/100g.
3. A silica according to claim 1 wherein the surface area is at least 50 m2/g.
4. A silica according to claim 3 wherein the surface area is at least 200 m2/g.
5. A silica according to any one of claims 1 to 3 wherein the surface area is not more than 400 m2/g.
6. A silica according to any one of claims 1 to 3 with a moisture content from 1% to 35%.
7. A silica according to any one of claim 1 to 3 wherein the weight mean particle size is at least 5 microns.
8. A silica according to any one of claims 1 to 3 wherein the weight mean particle size is not more than 15 microns.
9. A silica according to any one of claims 1 to 3 wherein the oil absorption is up to 95 cc/100g.
10. A toothpaste composition containing from 5% to 50% by weight of an amorphous silica defined in any one of claims 1 to 3.
11. A method of preparing an amorphous precipitated silica, suitable for use as a toothpaste abrasive, and having i) a surface area in the range from 10 to 450 m2/g, ii) a weight mean particle size in the range from 3 to 20 microns, and iii) a perspex abrasion value in the range from 23 to 35, iv) which is produced by the reaction of sodium silicate, having a silica:Na2O ratio in the range from 1.8 to 3.5:1, with mineral acid, with the concentration and volume of the reactants controlled to give a reaction in the pH range from 10 to 10.5, in the presence of a water soluble electrolyte comprising a cation selected from the group comprising aluminium, magnesium, calcium, sodium and potassium with an associated anion selected from the group comprising bromide, carbonate, chloride, nitrate, acetate and sulphate wherein the electrolyte:silica weight ratio is from 0.1 to 1 to 2 to 1, the precipitation reaction being performed in the temperature range of 95°C to 100°C.
12. A method according to claim 11 wherein the reaction medium is subjected to a hydrothermal ageing step during the final acid addition.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8604985 | 1986-02-28 | ||
| GB868604985A GB8604985D0 (en) | 1986-02-28 | 1986-02-28 | Precipitated silicas |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1307646C true CA1307646C (en) | 1992-09-22 |
Family
ID=10593833
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000530368A Expired - Lifetime CA1307646C (en) | 1986-02-28 | 1987-02-23 | Silicas |
Country Status (10)
| Country | Link |
|---|---|
| US (2) | US4956167A (en) |
| EP (1) | EP0236070B1 (en) |
| JP (1) | JPS62223014A (en) |
| AT (1) | ATE73110T1 (en) |
| AU (1) | AU600256B2 (en) |
| CA (1) | CA1307646C (en) |
| DE (1) | DE3776922D1 (en) |
| ES (1) | ES2030057T3 (en) |
| GB (1) | GB8604985D0 (en) |
| ZA (1) | ZA871440B (en) |
Families Citing this family (64)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB8610118D0 (en) * | 1986-04-25 | 1986-05-29 | Unilever Plc | Manufacture of silica gels |
| GB8707526D0 (en) * | 1987-03-30 | 1987-05-07 | Unilever Plc | Amorphous silicas |
| GB8721644D0 (en) * | 1987-09-15 | 1987-10-21 | Unilever Plc | Silicas |
| US5614177A (en) * | 1987-11-04 | 1997-03-25 | Rhone-Poulenc Chimie | Dentifrice-compatible silica particulates |
| FR2622565B1 (en) * | 1987-11-04 | 1990-11-09 | Rhone Poulenc Chimie | SILICA FOR TOOTHPASTE COMPOSITIONS COMPATIBLE IN PARTICULAR WITH ZINC |
| FR2622439B1 (en) * | 1987-11-04 | 1991-07-12 | Rhone Poulenc Chimie | SILICA FOR TOOTHPASTE COMPOSITIONS COMPATIBLE IN PARTICULAR WITH CHLORHEXIDINE |
| US5286478A (en) * | 1987-11-04 | 1994-02-15 | Rhone-Poulenc Chimie | Dentifrice-compatible silica particulates |
| FR2625676B1 (en) * | 1988-01-07 | 1994-03-04 | Pharmascience Laboratoires | TOOTHPASTE WITH GOOD RATIO / ABRASIVE POWER |
| FR2632185B1 (en) * | 1988-06-01 | 1992-05-22 | Rhone Poulenc Chimie | SILICA FOR TOOTHPASTE COMPOSITIONS COMPATIBLE IN PARTICULAR WITH ZINC |
| FR2649089B1 (en) * | 1989-07-03 | 1991-12-13 | Rhone Poulenc Chimie | CONTROLLED POROSITY SILICA AND PROCESS FOR OBTAINING SAME |
| US5234673A (en) * | 1990-02-20 | 1993-08-10 | J. M. Huber Corporation | Low temperature-very high structure silica and methods |
| US5094829A (en) * | 1990-06-21 | 1992-03-10 | Ppg Industries, Inc. | Reinforced precipitated silica |
| US5108734A (en) * | 1991-07-01 | 1992-04-28 | Colgate-Palmolive Company | Prophy mouthfeel dentifrice having low RDA value |
| KR960010781B1 (en) * | 1991-10-02 | 1996-08-08 | 유니레버 엔브이 | Silicas |
| DE69304546T3 (en) * | 1992-10-28 | 2002-11-21 | Crosfield Joseph & Sons | SILICA |
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-
1986
- 1986-02-28 GB GB868604985A patent/GB8604985D0/en active Pending
-
1987
- 1987-02-23 CA CA000530368A patent/CA1307646C/en not_active Expired - Lifetime
- 1987-02-24 AU AU69200/87A patent/AU600256B2/en not_active Ceased
- 1987-02-26 ES ES198787301689T patent/ES2030057T3/en not_active Expired - Lifetime
- 1987-02-26 EP EP19870301689 patent/EP0236070B1/en not_active Expired - Lifetime
- 1987-02-26 DE DE8787301689T patent/DE3776922D1/en not_active Expired - Lifetime
- 1987-02-26 AT AT87301689T patent/ATE73110T1/en not_active IP Right Cessation
- 1987-02-27 ZA ZA871440A patent/ZA871440B/en unknown
- 1987-02-27 JP JP62045112A patent/JPS62223014A/en active Granted
-
1989
- 1989-03-22 US US07/327,392 patent/US4956167A/en not_active Expired - Lifetime
-
1993
- 1993-11-29 US US08/158,818 patent/US5447704A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| ATE73110T1 (en) | 1992-03-15 |
| US5447704A (en) | 1995-09-05 |
| JPH0522644B2 (en) | 1993-03-30 |
| EP0236070A2 (en) | 1987-09-09 |
| ZA871440B (en) | 1988-10-26 |
| ES2030057T3 (en) | 1992-10-16 |
| US4956167A (en) | 1990-09-11 |
| AU600256B2 (en) | 1990-08-09 |
| EP0236070A3 (en) | 1988-05-04 |
| DE3776922D1 (en) | 1992-04-09 |
| EP0236070B1 (en) | 1992-03-04 |
| JPS62223014A (en) | 1987-10-01 |
| GB8604985D0 (en) | 1986-04-09 |
| AU6920087A (en) | 1987-09-03 |
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