Improvements in or relating to abrasive compositions for incorporation in a toothpaste and methods for their production

This invention relate» to novel polymer aggregates optionally containing pigments, to processes for the production of such aggregates and to paints containing such aggregates.

The term polymer aggregates as used herein, means 5 polymeric particles formed by aggregation of a plurality of smaller particles. On microscopic examination of materials produced by particular embodiments of the process, one may β

distinguish between Primary Particles which are the units from which the aggregates appear to be formed, first stage aggregates, which appear to consist of a number of primary particles fused together, and second stage aggregates which appear to be agglomerates consisting of a number of first stage aggregates.

The first stage aggregates may bp very extensively fused together, frequently to the point at which the primary particles cannot be differentiated therein. The second stage aggregates are usually seen to be less extensively fused and the first stage aggregates of which they appear to be composed can more readily be recognised.

It is well known to those skilled in the art how to produce small discrete polymer particles, not aggregates, by polymerisation of alpha-bete-ethylen ically unsaturated monomers or monomer solutions of unsaturated polyester resins in suspension in an aqueous phase, the reaction being initiated by a catalyst soluble in the polymerisable material.

This process, known a& suspension polymerisation, produei spheroidal particles of sizes essentially determined by the size of the particles produced in tho su.jpansi.01· before

6113 tubes for sale on the commercial market. It is usually preferred to use aluminium tubes but it has been discovered that when such toothpaste compositions contain a therapeutic fluoride compound, a reaction with the interior of the unlined aluminium tube takes place so that staining and other corrosive action occurs apparently because of some reaction or incompatibility between the bare aluminium surface and one or more of the materials in the toothpaste. This incompatibility appears in the form of gas production, swelling of the tube, corrosion, and black stains on the inside surface of unlined aluminium container. Accordingly, the standard practice in the marketing of therapeutic toothpastes today has been to line the aluminium tube with a plastic, lacquer or other material, which therefore substantially adds to the cost of packaging and marketing the toothpaste.

Many prior art attempts have been made to solve this problem because unlined aluminium tubes are much more economical to use and are generally lighter in weight than the lined tubes. For e,-ample, J.S. Patents Nos. 3,662,060 and 3,624,199 disclose compositions which are said to overcome this problem. Further, U.S. Patent No. 3,678,155 discloses that monofluorophosphate ions prevent corrosion of unlacquered aluminium tubes when the toothpaste contains milled alpha-alumina trihydrates as an abrasive. Also U.S. Patent No. 3,864,471 discloses a dentrifice composition containing a monofluorophosphate and a polishing agent containing alkaline earth metal carbonate and insoluble alkali metal phosphate, alumina or mixture thereof, to minim’2e corrosion in unlined aluminium containers.

It is an object of this invention to provide a novel abrasive for use in toothpaste compositions which will not stain or otherwise corrode unlined tubes, and provide a method for the production of such compositions. A further object of the invention is to provide a therapeutic dentifrice composition containing an abrasive composition.

- 3 46112

Other objects and advantages of the present invention will become apparent as the description thereof proceeds.

According to one aspect of the present invention an abrasive composition useful for incorporation into a therapeutic toothpaste composition and for preventing fluoride-caused corrosion and staining of an unlined aluminium tube containing said toothpaste composition consists essentially of a silica which has been treated with a water soluble salt, oxide or hydroxide of an alkaline earth metal so as to have present therein from 158-7000 ppm of the alkaline earth metal, said silica being suitable for use in a toothpaste composition having an RDA value of between 200 and 400 functioning as a carrier for the alkaline earth metal. Preferably, said silica is selected from amorphous precipitated silica, sodium aluminosilicates, silica xerogels and mixtures thereof; said abrasive composition being prepared, when amorphous precipitated silica is selected as the silica, by preparation of an amorphous silicon dioxide by precipitation through acidulation of an alkali metal silicate solution with a mineral acid in the presence of an alkali metal sulfate, isolating a wet cake of said precipitated product, and treating said wet cake with the salt of said alkaline earth metal.

According to a second aspect of the invention, a method for the production of an abrasive composition for incorporation in a toothpaste which will prevent corrosion of an unlined aluminium tube when an amorphous precipitated silica is selected as the silica comprises forming an aqueous solution of an alkali metal silicate having an Si0₂ to X₂0 mole ratio of 2.0 to 2.7 and of an alkali metal sulfate at a reaction temperature in the range of 66 to 83°C., wherein X represents the alkali metal; acidulating said aqueous solution with a mineral acid with continuous agitation until precipitation of silicon dioxide is substantially complete at a pH of 8.0 to 10.4; continuing the mineral acid addition until the pH is 6.0 or less; digesting at a temperature that is

- 4 4 6112

10-30C. higher than the reaction temperature for a period of 10 to 30 minutes; filtering the resulting slurry and washing the solid product with fresh water; reslurrying the resulting wet cake in water, and under agitation conditions, adding thereto at ambient temperature a water soluble salt, oxide or hydroxide of an alkaline earth metal in an amount sufficient to add to said wet cake from 168-7000 ppm of the alkaline earth metal based on the dry recoverable product; agitating the resulting mixture to provide adherence of the effective level of said metal on the surface of said silicon dioxide; and drying and recovering said abrasive composition.

It has been discovered that the problem of corrosion of unlined aluminium tubes when filled with a therapeutic dentifrice composition can be overcome by incorporation within the toothpaste composition of a controlled amount of an alkaline earth metal. The alkaline earth metal may be calcium, magnesium, strontium or mixtures thereof. Calcium is preferred because of its ready availability, inexpensiveness and ease of incorporation into the dentifrice.

The metal may be incorporated into the dentifrice or toothpaste mixture in any substantially water soluble form such as the nitrate, oxide, hydroxide or chloride. The most preferred materials for incorporation into the therapeutic dentifrice compositions of this invention include calcium nitrate, calcium oxide, calcium hydroxide, and calcium chloride. It should also be noted however, that organic salts such as calcium acetate, calcium formate may also be used. Corresponding strontium and magnesium salts may also be used.

The only limitations to be placed on the alkaline earth metal salt, oxide or hydroxide are that it be substantially soluble, not cause any problems of safety in the compositions and remain available to combat corrosion.

There are of course dentifrice and other toothpaste compositions known in the art which contain calcium salts in substantial amounts, as taught for example in U.S. Patent No. 3,864,471 which contains 40-50% o^£ calcium carbonate, a 46112 and U.S. Patent No. 3,624,199 which contains 20-75% calcium carbonate.

However, calcium carbonate is generally insoluble, and is not effective to inhibit corrosion of the tube. Therefore an important aspect of the present invention resides in the carefully controlled amount of water5 soluble alkaline earth ion which is incorporated into the toothpaste composition. According to the present invention, the controlled amount of alkaline earth metal ion which is present must be sufficient to be effective and available to prevent corrosion but yet insufficient to stoichiometrically interfere with fluoride availability in the toothpaste.

The specified amount of the alkaline earth metal 0.005 to 0.20 wt. % is considered essential to prevent corrosion and yet avoid interference with fluoride availability.

The precipitated silicon dioxides of the present invention are prepared by charging a 3-15 weight percent aqueous solution of alkali metal sulfate,· preferably sodium sulfate, to a reactor and adding a solution of an alkali metal silicate solution, preferably a sodium silicate solution, to the reactor to achieve a pH of 8-10.4. This results in prepolymerization of the alkali metal silicate. The aqueous sodium silicate solution should have a silicate concentration range of 10-25 weight percent and more preferably

18 to 22 weight percent, and a composition of Na₂0 2.6 Si0_z for best results.

The aqueous solution is then raised to a temperature of 66° to 83°C (150 to 180°F) and with continuous agitation the solution is acidulated by the addition of an aqueous solution of a mineral acid having a concentration of 10-25 weight percent at a substantially constant pH in the range of 8.0 to

10.4. Preferably the mineral acid and alkali metal silicate are added simultaneously as described in my U.S. Patent No. 3,960,586. The mineral acid is preferably sulfuric acid as sulfuric acid provides best results but as known in the art as in my prior U.S. Patent No. 3,960,586, other acidulation agents such as nitric acid, phosphoric acid, hydrochloric acid, carbonic acid

- 6 46112 and the 11!« -.iay also hs employed. The time , erio·.' over which tie alkali metal silicate and/or sulfuric acid are added to the reactor can ne predeterr.iitied and is generally bused on tie volume- of tie reactor and the difficulties in control or. fie wlw» of the reactor at.t the difficulties in control of tie taa.israture and agitation. After completion of the* additions, the acidelation acid is continued to be added until the ρΐϊ of the slurry falls below about and preferably in the range of 4.3-5.0. The resulting slurry is the precipitated silicon dioxide contained in the reaction medium.

After the pH of below 5.3 is obtained, the slurry is then heated for a 10 digestion period of 10 to 30 .einutes at a tenperature of 10° to 30°C. above the reaction tenperature and the reaction pH again adjusted as necessary.

The resulting slurry is then filtered and washed with additional water to remove any reaction by-product such as sodium sulfate which may be contained in the silicon dioxide product.

In the process of the present invention, at the point of filtration and

•./ashing of the silicon dioxide './et cake, the material is then subjected to treatment with alkaline earth metal ions to produce the new abrasive products of the present invention. In accordance with the process of the present invention, the wet wash filter cake is then reslurried in its own water or with the addition of fresh water at ambient tenperature with agitation.

While under agitation, this slurry is then treated with sufficient alkaline earth raetal ions and preferably calcium ions, in the form of substantially soluble salt, oxide or hydroxide to provide sufficient alkaline earth ratal ions corresponding to provide about 30 to 2003 parts per million, intimately associated with the silicon dioxide, this amount being based on 100 parts of dentifrice. The amount of alkaline earth metal ions added is based on the total weight of the dry product contained in the wet cake form, tret is

- 7 recoverable solid. Since the amount of abrasive may vary in dentifrice compositions, the amount of alkaline earth metal salt, oxide or hydroxide will also be varied.

The calcium ions may be incorporated into the silicon dioxide at this stage 5 in any substantially water soluble form such as the nitrate, oxide, hydroxide, or chloride, but lime or calcium hydroxide is preferred. Food grade salts should be used. 3y soluble salt, oxide or hydroxide is meant that any reasonably soluble salt of calcium may be used since it is only necessary to provide extremely small amounts of the calcium ions to the mixture. Also, organic salts such as calcium acetate, or calcium formate, may also be used.

The corresponding strontium and magnesium salts of the alkaline earth class may also be used. The only limitations to be placed on the alkaline earth metal salt, oxide or hydroxide to be added are that it be sufficiently water soluble to provide the ions, not present any problems of safety in the resulting toothpaste compositions, and be effective to provide the necessary fluoride compatibility.

After treatment with the alkaline earth metal ion, the cake slurry is then agitated vigorously for 10-20 minutes, preferably 15 minutes, to provide the effective level of alkaline earth metal for treatment on the surface of the silicon dioxide abrasive. The resulting product is then filtered, spray dried, preferably at an inlet temperature of 483°C. (900°F.) and outlet temperature of 122°C. (250°F.) as known in the art, and subsequently milled to the desired degree of fineness.

The precipitated amorphous silicas which are preferably used in this embodiment may be characterised by the following combinations of properties:

Oil Absorption-Rub-Out Method (cc/100 mg) = 30-120

3ET Surface Area (m^Z/g) = 75-325

- 3 can be utilised when alkaline earth metal nstal ions, as described 'ISA Average Aggregate Size (nicrons) = 1-10

Bulk OaiSit;/ (lbs./cu.ft.) = 10 - 30

As has been referred to above, the invention includes other types of silica polishing agents including Xerogels as described in U.5. Patent Ίο. 3,533,230. Commercially available Xerogels such as Syloid 53 (Registered Trade Mark) manufactured by Davison Division of 0. Grace ’ Co., incorporated with controlled amounts of calcium ion or ions or pretreated with calcium ion or alkaline earth < _ .

herein. It is also to be understood that sodium aluminosilicate nolishing , ι

agents can be formulated in therapeutic compositions according to this \ invention ’/hen the sodium aluminosilicate materials are combined vrith the critical amounts of alkaline earth metal as described herein.

I

As known in the ar·, a dentifrice may contain; e.g., humectant materials and J binders to give the dentifrice a smooth texture and good flowability. The specific formulations of toothpastes are wall knoi-:n in the art and are disclosed for example in U.S. Patents has. 2,994,642 and 2,533,239 and numerous publications. A further detailed disclosure of dentifrice formulations is given in IJ.S. Patent o. 3,72G,9G1.

Most dental cream formulations use one of several conventional phosphate J materials as the polishing agent. Examples of the phosphate polishing agents are dicalcium phosphate, anhydrous dicalciu/π phosphate, tricalcium phosphate, thermally converted dicalcium phosphate, and insoluble sodium metaphosphate.

The amount of phosphate materials added to the dental formulations will range {

between 3 percent and 50 percent by ’./eight.

The most widely used humectants in toothpaste are glycerine and sorbitol. ί

Propylene glycol is also used in small amounts and to a very limited extent. '

The primary function of humectant as part of the liquid phase is to retain ’ moisture which provides good texture and maintains an attractive glossy appearance when the paste is exposed to air.

A binder can be employed in the toothpaste composition to prevent separation of the liquid and solid phases. The most conventionally used binders are the seaweed colloids and synthetic derivatives of cellulose, specifically Carrageenan and sodium carboxymethyl cellulose. Others such as gums have been used. Combinations of these binders have also been employed.

Since the natural and synthetic water dispersions of organic binders are subjected to microbial or mold attack, a relatively small amount of preservatives is added to the paste. Examples of preservatives used in the industry are the esters of parahydroxyl benzoates.

The function of the detergents within the dental formulation is to provide greater cleansing action due to the lowering of the surface tension and the sudsing action in the mouth. Among detergents used are sodium il-lauryl snrcosinate, sodium lauryl sulfate, sulfoculaurate, sodium alkyl sulfoacetate, and sodium dioctyl sulfosuccinate.

Since toothpaste flavouring probably represents the greatest single factor in consumer acceptance, great care has been employed in selecting balanced blends of different essential oils. These are rarely, if ever, used alone.

Combinations Of principal flavours are Wintergreen, peppermint, and sassafras, and are used with secondary oils such as pimento, clove and anise.

Saccharin and sodium cyclamate are widely used to improve taste and enhance the flavour qualities of the toothpaste. The synthetic sweeteners nay be used in combination to obtain optimum sweetness and absence of after-taste.

Their desirable properties are obtained at very low concentrations and consequently they have negligible influence on the toothpaste consistency.

- 10 4δί12

Since water is such a common element, it is important in obtaining stable toothpaste formulations to employ substantially pure water therein. It is common practice to demineralize the water that is employed.

The invention is operable with respect to any of the therapeutic agents now being used in therapeutic dentifrice compositions including the alkali metal fluorides such as sodium fluoride, sodium monofluorophosphate, or stannous fluoride, all of which are well known.

In general, such dentifrice compositions will normally contain 5-503 of polishing agent, up to 1 wt. % of fluoride-containing therapeutic agent,

30-40 wt. % deionized water, and the remainder being liquid phase carrier materials such as glycerine or sorbitol. As indicated above, according to the present invention, the composition will also contain 0.005 up to 0.20 parts of alkaline earth metal, preferably calcium ion, based on the toothpaste composition. It has been found that this amount of alkaline earth metal is sufficient <.0 overcome problems with staining and corrosion of unlined aluminium tubes, but is insufficient to interfere with the fluoride availability in the paste and thus not interfere with the therapeutic action of the dentifrice composition.

With respect to incorporation of the controlled amount of alkaline earth metal in the composition of the present invention, it is to be noted that in Degussa Technical Bulletin No. 9, there is a disclosure of an Aerosil 200 (Registered Trade Mark) polishing agent for use in chalk toothpastes, and it is pointed out on page 8 of this Bulletin that in toothpastes containing the cheaper polishing agent, chalk, the use of Aerosil 200 is worthwhile to the extent that the less expensive unlacquered aluminium tubes can be used since corrosion protection for unlacquered aluminium tubes is by formation of minute quantities of insoluble calcium silicate from this composition. A minimum of 1% of Aerosil 200 is required. However at page 8 of the same Bulletin, it is stated that even with the use of Aerosil, it is not possible to attain

- 11 4S11S effective corrosion protection for nontreated aluminium tubes when the toothpaste compositions contain fluorine in the form of monofluorosodium phosphate. However, this reference does teach on page 8, that when

3-5 weight percent of Light Hydrated Alumina W-16 is incorporated into the fluoride-containing toothpaste, corrosion protection can be obtained.

Contrary to the teachings of this Technical Bulletin, it has been discovered according to the present invention that fluorine-containing toothpastes can be placed in unlined aluminium tubes if there is placed therein a controlled amount of alkaline earth metal ion.

Silica abrasives are preferably used at loadings of about 15-30 wt. % in the dentifrice. The contain a minimum of 158 ppm calcium at 30 wt. % and 336 ppm at 15 wt. % to provide minimum amounts of calcium. However they can also contain up to 7000 ppm.

The following specific examples are further illustrative of the nature of the present invention, but it is to be understood that the invention is not limited thereto. The compositions are prepared in the conventional manner and all amounts of the various ingredients are by weight unless otherwise specified. In the following examples and throughout the specification parts are by weight unless otherwise indicated.

EXAMPLES

In the following examples the toothpaste compositions v/ere prepared and compared v/ith commercial products or controls. In evaluating the toothpaste compositions, a chart v/as used to rate the interior tube wall to determine the presence or absence of staining and corrosion. As basis for the chart, each composition was prepared and then aged at 49°C. for nine weeks. The percentage of soluble fluoride ion and tube compatibility data v/ere determined periodically during the nine-week storage stability period. In this examination, each three weeks under the aging conditions (49°C.) corresponds to

- 12 4 6112 about one year aging at room temperature. During the studies, the uniined tubes containing the compositions were opened periodically and examined for any staining/corrosion on the tube interior wall. The following legend was used for rating the tube properties of the compositions:

Rating Tube Interior Wall

- 9

- 7

- 5

- 3

No air

No air

Air on

Air on

Air on

Air on on wall, no discolouration on wall on wall, light gray stain on wall wall, light gray stain on wall wall, gray stain on wall wall, dark gray stain on wall wall, black stain with pitting of wall

In all of the following examples, the alkaline earth metal was calcium and was added as soluble calcium nitrate to provide the amount of calcium in each composition.

EXAMPLES 1-4.

Dentifrice Compositions in which Calcium was added to the Toothpaste

The following dentifrice compositions were prepared with a low structure silica polishing agent and a known level of calcium was added to the composition to provide tube compatability properties.

Examples 1 - 4

Composition

<td></td><td> 1</td><td> 2</td><td> 3</td><td> 4</td>

<td> Sodium monofluorophosphate</td><td> 0.76</td><td> 0.76</td><td> 0.76</td><td> 0.76</td>

<td> Low Structure silica</td><td> 30.00*</td><td colspan="2"> 29.97 0 29.941</td><td> 29.587</td>

<td> Calcium as water soluble Ca(NO₃)₂ . 4H₂0**</td><td> 0.00</td><td> 0.0295</td><td> 0.059</td><td> 0.413</td>

<td> Glycerine</td><td> 23.00</td><td> 23.00</td><td> 23.00</td><td> 23.00</td>

<td> Sodium carboxymethylcellulose</td><td> 1.30</td><td> 1.30</td><td> 1.30</td><td> 1.30</td>

- 13 003

<td> Hydrated alumina</td><td> 1.00</td><td> 1.00</td><td> 1.00</td><td> 1.00</td>

<td> Sodium lauryl sulfate</td><td> 2.00</td><td> 2.00</td><td> 2.00</td><td> 2.00</td>

<td> Sodium benzoate</td><td> 0.50</td><td> 0.50</td><td> 0.50</td><td> 0.50</td>

<td> Sodium Saccharin</td><td> 0.20</td><td> 0.20</td><td> 0.20</td><td> 0.20</td>

<td> Elavour</td><td> 0.90</td><td> 0.90</td><td> 0.90</td><td> 0.90</td>

<td> Water (deionized)</td><td> Balance</td><td> Balance</td><td> Balance</td><td> Balance</td>

<td> Total</td><td> 100.00</td><td> 100.00</td><td> 100.00</td><td> 100.00</td>

* low structure silica containing 5 ppm calcium ** The conversion factor for calcium nitrate 4H₂0 to calcium is 5.9. The molecular weight of Ca(NO₃)₂ . 4H₂0 is 236. The Atomic weight of calcium is

40. Therefore 236 parts of calcium nitrate . 4H_z0 provide 40 parts of calcium ion, or 236/40 or 5.9 parts of calcium nitrate . 4H₂0, which corresponds to one part of calcium.

in compositions 2, 3, and 4, calcium nitrate . 4H₂0 was added in the dentifrice composition which corresponds to calcium level of 0.0295/5.9 or 50 ppm (0.005%) : 100 ppm (0.01%) and 700 ppm (0.07%), respectively. The tube compatibility data for these Examples are set forth in following Table 1.

TABLE 1

Rating of Tube Properties - 49°C Aging Study

Weeks

<td> Composition</td><td> 0</td><td> 1</td><td> 3</td><td> 6 9</td>

<td> 1</td><td> 10</td><td> 4</td><td> 3</td><td> 3 1</td>

<td> 2</td><td> 10</td><td> 10</td><td> 10</td><td> 10 10</td>

<td> 3</td><td> 10</td><td> 10</td><td> 10</td><td> 10 10</td>

<td> 4</td><td> 10</td><td> 10</td><td> 10</td><td> 10 10</td>

<td colspan="3"> It is clear from above data that composition '</td><td colspan="2"> 1 was unacceptable in tube</td>

compatibility properties because it did not contain the minimum critical level of calcium in the therapeutic dentifrice composition.

- 14 46112

EXAMPLES 5 - 8.

The following dentifrice compositions were prepared wherein the content of sodium monofluorophosphate in each is equivalent to 0.1% of fluoride ion.

Composition

Sodium monofluorophosphate Low Structure silica Glycerine

Sodium carboxymethyl cellulose Hydrated alumina Sodium lauryl sulfate Sodium benzoate

Sodium saccharin

Flavour

Water (deionized)

Total

<td> 0.76</td><td> Parts 0.76</td>

<td> 36.00(A)</td><td> 30.00(B)</td>

<td> 23.00</td><td> 23.00</td>

<td> 1.30</td><td> 1.30</td>

<td> 1.00</td><td> 1.00</td>

<td> 2.00</td><td> 2.00</td>

<td> 0.50</td><td> 0.50</td>

<td> 0.20</td><td> 0.20</td>

<td> 0.90</td><td> 0.90</td>

<td> 40.34</td><td> 40.34</td>

<td> 100.00</td><td> 100.00</td>

<td> 0.76</td><td> 0.76</td>

<td> 30.00(C)</td><td> 30.00(D)</td>

<td> 23.00</td><td> 23.00</td>

<td> 1.30</td><td> 1.30</td>

<td> 1.00</td><td> 1.00</td>

<td> 2.00</td><td> 2.00</td>

<td> 0.50</td><td> 0.50</td>

<td> 0.20</td><td> 0.20</td>

<td> 0.90</td><td> 0,.90</td>

<td> 40.34</td><td> 40.34</td>

<td> 100.00</td><td> 100.00</td>

(A) low structure silica of composition S contained 5 ppm calcium (B) low structure silica of composition 6 contained 168 ppm calcium (C) low structure silica of composition 7 contained 406 ppm calcium (D) low structure silica of composition 8 contained 688 ppm calcium

The low structure silicas employed in Examples 5, 6, 7 and 8 were characterised by the following combination of properties:

Oil Absorption - Rub-Out Method (cc/100 mg) = 80 - 120 BET Surface Area (m*/g) = 75 - 325 MSA Average Aggregate Size (microns) = 1 - 10

Bulk Density (pounds/cu.ft.) = 10 - 30

4S112

The calcium treated Tow structure silicas of compositions 5, 6, 7 and 8 were prepared by the following procedure:

Dry sodium sulfate was added to 10.0 gallons of water in a 200 gallon reactor so that the sodium sulfate concentration in the reaction medium was 10%. The pH of the reaction medium was then adjusted to 9.0 by the addition of sodium silicate. The reaction temperature v/as 65°C. (150°F.). The sodium silicate solution had an SiO₂ . Na₂0 mole ratio of 2.5 and a concentration of 2.0 pounds per gallon. Sodium silicate v/as added to the reaction medium for a minutes.

At this point the sodium silicate addition v/as stopped and sulfuric acid of

11.4% concentration was added to the reaction medium until the pH of 9.0 was reached. At this point the sodium silicate solution and the sulfuric acid solution v/as added simultaneously for a period of 35 minutes. At the end of the 35 minute period of silicate addition, the silicate v/as discontinued and the acid addition v/as continued until a slurry pH of 5.5 v/as obtained. The,batch was digested at 77°C. (170°F.) for 20 minutes and the resulting wet cake recovered and washed.

The wet cake was then divided into four separate portions and treated by the following procedure.

Each batch of wet wash filter cake was then reslurried without water addition at ambient temperature v/ith agitation. While under agitation, the slurry v/as treated v/ith sufficient Codex grade (U.S. purity food grade) hydrated lime (calcium hydroxide) to provide the amount of calcium ion treatment described in compositions 5, 6, 7 and 8. The amount of calcium hydroxide v/as based on the weight of dry recoverable solid product in the wet cake form. After treatment v/ith the calcium ion, the cake slurry v/as agitated vigorously for 15 minutes to provide the effective level of calcium ion treatment on the surface of the silicon dioxide abrasive. Each resulting product is then spray dried at an inlet temperature of 483°C. and outlet temperature of 122°θ· milled and character· ised.

- 16 46112

Compositions 5, 6, 7 and 8 were aged at 49°C. for nine weeks and tube compatibility data were determined periodically during the nine-week storage stability period. The results for tube compatibility properties are listed below in Table 2.

TABLE 2.

Rising of Tube Properties - 49° Aging Study

Weeks

<td></td><td> Composition 5</td><td> 0 10</td><td> 1 4</td><td> 3 3</td><td> 6 3</td><td> 9 1</td>

<td> 10</td><td> 6</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td>

<td></td><td> 7</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td>

<td></td><td> 8</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td><td> |0</td>

It will be noted from Table 2 that dentifrice composition 5 caused a severe degree of black stain and pitting on the tube wall after nine weeks of aging study. Compositions 6, 7 and 8 were stable and showed excellent tube compatibility properties. Thus, it is very clear that when a silica polishing agent contains a minimum critical level of calcium, it does not corrode the unlined aluminium tubes.

EXAMPLES 9-11.

Stabilization of Xerogel Therapeutic Dentifrices with Calcium

Therapeutic dentifrices were prepared with xerogel polishing agents. All compositions contained a known level of calcium ions (aoded as water soluble calcium nitrate) except composition 9. The compositions were prepared in the conventional manner and packaged in unlined aluminium tubes. All amounts of the various ingredients were by weight unless otherwise specified.

The following dentifrice compositions were prepared. The content of sodium monofluorophosphate in each was equivalent to 0.1% fluoride ion.

- 17 Composition Parts

<td> Glycerine (99.5% solution)</td><td> 9 22.00</td><td> 10 22.00</td><td> 11 22.00</td>

<td> Sodium benzoate</td><td> 0.50</td><td> 0.50</td><td> 0.50</td>

<td> Sodium saccharin</td><td> 0.20</td><td> 0.20</td><td> 0.20</td>

<td> CMC - 7 MF</td><td> 1.00</td><td> 1.00</td><td> 1.00</td>

<td> Sodium monofluorophosphate</td><td> 0.76</td><td> 0.76</td><td> 0.76</td>

<td> Water (deionized)</td><td> 36.54</td><td> 36.54</td><td> 36.54</td>

<td> Xerogel (Syloid 53)</td><td> 35.00</td><td> 34.82</td><td> 34.70</td>

<td> Hydrated alumina</td><td> 1.00</td><td> 1.00</td><td> 1.00</td>

<td> TiO₂</td><td> 0.50</td><td> 0.50</td><td> 0.50</td>

<td> Sodium lauryl sulfate</td><td> 1.50</td><td> 1.50</td><td> 1.50</td>

<td> Calcium nitrate . 4H₂0*</td><td> 0.00</td><td> 0.18</td><td> 0.30</td>

<td> Flavour</td><td> 1.00</td><td> 1.00</td><td> 1.00</td>

<td colspan="2"> * 0.18% and 0.30% calcium nitrate .</td><td colspan="2"> 4H₂0 in compositions 10 and 11 correspond</td>

to 0.18/5.9 or 0.03% calcium (300 ppm calcium) and 0.30/5.9 or 0.05% calcium (500 ppm calcium).

It will be noted that the composition of Example 9 did not contain any calcium. The tube properties were then determined when the dentifrices were aged at 49°C. for nine weeks and were rated at intervals of 1, 3, 6 and 9 weeks. The following Table 3 shows the degree of corrosion or staining of the unlined aluminium tubes.

TABLE 3.

Tube Compatibility Properties - 49°C aging Study

Weeks

<td> Composition</td><td> 0</td><td> 1</td><td> 3</td><td> 6</td><td> 9</td>

<td> 9</td><td> 10</td><td> 7</td><td> 6</td><td> 6</td><td> 5</td>

<td> 10</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td>

<td> 11</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td>

<td></td><td> - 18 -</td><td></td><td></td><td></td><td></td>

From the data in Table 3 it is clear that the compositions of Examples 10 and 11 exhibit excellent tube compatibility properties. Note that rating of 10 means no discolouration of the unlined tube container. Since composition 9 did not contain the critical level of calcium, the tube compatibility properties were found to be unacceptable after nine weeks storage at 49°C.

According to the suppliers bulletin, the Xerogel, Syloid 63, has the following properties:

Loss on ignition 6.5

5% slurry pH 4.1 %SiO₂ ignited basis 99.5

Particle size, microns 9.0

Surface area, m /g 625

Oil absorption, #100 lb 60

Bulk density, pounds/cu. ft. 29

In addition to above properties, Syloid 63 has the following chemical composition (from supplier's bulletin):

Chemical Analysis (dry basis) %

Aluminium as Al₂0₃ 0.04

Titanium as Ti0₂ 0.03

Calcium as CaO 0.01

Sodium as Na₂0 0.02

Zirconium as Zr0₂ 0.01

Trace element (oxides) 0.02

EXAMPLE 12.

Effect of Calcium on Commcerial Toothpastes

Aim (Registered Trade Mark) clear-gel therapeutic toothpaste is packaged in a lined container to prevent corrosion and staining of tube interior wall.

- 19 4 6 1 3. 2

Colgate Dental Cream (Registered Trade Mark) (CDC) is also packaged in a lined container to avoid the corrosion and staining of the tube interior wall.

To check the effectiveness of calcium addition in solving the tube compatibility problem, both Aim and CDC were purchased from the supermarket and each paste was divided into three parts.

Aim toothpaste was divided in parts A, B, and C. Part A was packaged in an unlined aluminium tube without any addition of calcium to the toothpaste. Parts B and C were mixed with a known level of calcium and then packaged in unlined aluminium tubes.

CDC (Colgate Dental Cream) was also divided into three parts D, E, and F.

Part D was packaged in an unlined aluminium tube without the addition of any calcium. To parts E and F, a known level of calcium was added. The data obtained with Aim and CDC compositions packaged in unlined containers, are listed in Table 6 and the compositions for each are as follows:

EXAMPLE 12.

<td> Composition</td><td> (3 I % Calcium ¹ '</td><td> Commercial % Dentifrice</td>

<td> A</td><td> 0.00</td><td> 100.00 (1)</td>

<td> B</td><td> 0.10</td><td> 99.41 (1)</td>

<td> C</td><td> 0.16</td><td> 99.16 (1)</td>

<td> D</td><td> 0.00</td><td> 100.00 (2)</td>

<td> E</td><td> 0.10</td><td> 99.41 (2)</td>

<td> F</td><td> 0.15</td><td> 99.16 (2)</td>

(1) Aim toothpaste, purchased from supermarket (2) Colgate Dental Cream, purchased from supermarket (3) Added as Ca(NO₃)₂.4 H₂0

- 20 46112

TABLE 4.

Tube Compatibility Properties - 49°C Aging Study

Weeks

<td> Composition</td><td> 1</td><td> 3</td><td> 6</td><td> 9</td>

<td> A</td><td> 5</td><td> 4</td><td> 3</td><td> 1</td>

<td> B</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td>

<td> C</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td>

<td> D</td><td> 5</td><td> 5</td><td> 4</td><td> 2</td>

<td> E</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td>

<td> F</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td>

Compositions B, C, E and F have excellent tube compatibility properties when

<td colspan="2"> compared with compositions A and 0. The addition</td><td colspan="3"> of che calcium thus helped</td>

<td> stabilize these therapeutic</td><td colspan="2"> dentifrice compositions.</td><td></td><td></td>

<td> EXAMPLES 13 - 17.</td><td></td><td></td><td></td><td></td>

<td colspan="4"> The following dentifrice compositions were prepared to illustrate che</td><td> ί use of</td>

<td colspan="2"> sodium aluminosilicates (SAS) as polishing agents.</td><td colspan="2"> The composition</td><td> of</td>

<td colspan="5"> Example 13 was used as a control in which no calcium was added. Known amounts</td>

<td> of calcium were added to the</td><td colspan="2"> compositions of Examples 13, 15</td><td> , 16 ana</td><td> 17.</td>

<td colspan="2"> The compositions were as follows:</td><td></td><td></td><td></td>

<td></td><td> Parts</td><td></td><td></td><td></td>

<td> Composition</td><td> 13 14</td><td> 15</td><td> 16</td><td> 17</td>

<td> Glycerine (99.5%)</td><td> 22.00 22.00</td><td> 26.00</td><td> 25.00</td><td> 30.00</td>

<td> Sodium benzoate</td><td> 0.50 0.50</td><td> 0.50</td><td> 0.50</td><td> 0.50</td>

<td> Sodium saccharin</td><td> 0.20 0.20</td><td> 0.20</td><td> 0.20</td><td> 0.20</td>

<td> CMC - 7 MF</td><td> 1.00 1.00</td><td> 1.00</td><td> 1.00</td><td> 1.00</td>

<td> Sodium monofluorophosphate</td><td> 0.76 0.76</td><td> 0.76</td><td> 0.76</td><td> 0.76</td>

<td> Calcium nitrate . 4H₂0*</td><td> 0.00 0.20</td><td> 0.20</td><td> 0.20</td><td> 0.24</td>

<td> Deionized water</td><td> 36.54 36.34</td><td> 39.54</td><td> 38.54</td><td> 43.30</td>

<td> SAS Polishing agent</td><td> 35.00(A) 35.00(A)</td><td> 27.80(B)</td><td> 29.80(C)</td><td> 20.00(D)</td>

<td></td><td> - 21 -</td><td></td><td></td><td></td>

as

<td> Hydrated alumina</td><td> 1.00</td><td> 1.00</td><td> 1.00</td><td> 1.00</td><td> 1.00</td>

<td> Ti0₂</td><td> 0.50</td><td> 0.50</td><td> 0.50</td><td> 0.50</td><td> 0.50</td>

<td> Sodium lauryl sulfate</td><td> 1.50</td><td> 1.50</td><td> 1.50</td><td> 1.50</td><td> 1.50</td>

<td> Flavour</td><td> 1.00</td><td> 1.00</td><td> 1.00</td><td> 1.00</td><td> 1.00</td>

* Note that in compositions 14, 15 and 16, 0.2% Ca(N0₃)₂.

4H_a0 corresponds to 0.03% calcium ion and 0.24% Ca(N0₃)₂.

4H₂0 in composition 17 corresponds to 0.04% calcium ion.

(A) The SAS product used in compositions 13 and 14 has a Si0₂/Al₂0₃ ratio of 11.0.

(B) The SAS product used in composition 15 has a SiO₂/Al₂O₃ ratio of 2.5.

(C) The SAS product used in composition 16 has a SiO₂/Al₂O₃ ratio of 130.

(D) The SAS product used in composition 17 has a Si0₂/Al₂O₃ ratio of 400.

The preferred sodium aluminosilicates (SAS) have the following molar chemical composition:

x Na₂O . y Al₂0₃ . z SiO₂ . w H₂0 wherein x denotes the moles of Na₂O y denotes the moles of Al₂0₃z denotes the moles of SiO₂w denotes the moles of water

When y is fixed at 1, the value of z corresponds to the silica/alumina molar ratio of SAS. The low structure SAS abrasives and polishing agents have a silica/alumino ratio or z values of 2.5 to 400.

The properties of SAS polishing agents are:

Oil Absorption, Rub-Out Method (cc/100g) = 75 - 125 BET Surface Area (m²/g) = 50 - 300 MSA Average Aggregate Size (microns) = 1-10 Bulk Density (pounds/cu. ft.) = 12 - 35

- 22 46112

Compositions 13 through 17 were aged at 49°C. for nine weeks and the tube compatibility properties were evaluated at intervals of 1, 3, 6 and 9 weeks and the results are shown in the following Table 5.

TABLE 5.

Tube Compatibility Properties, 49°C,

Weeks

<td> Composition</td><td> 1</td><td> 3</td><td> 6</td><td> 9</td>

<td> 13</td><td> 1</td><td> 1</td><td> 1</td><td> 1</td>

<td> 14</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td>

<td> 15</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td>

<td> 16</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td>

<td> 17</td><td> 10</td><td> 10</td><td> 10</td><td> 10</td>

Note that compositions 14 through 17 have excellent tube compatibility properties.

In Patent Specification No. 45111 there is described and claimed an article of manufacture comprising an unlined aluminium tube containing a toothpaste composition and to a method of preventing the corrosion and staining by toothpaste of an unlined aluminium tube, and no claim is made to such articles of manufacture and methods of preventing the corrosion and staining by toothpaste of an unlined aluminium tube herein.