NO137773B - PROCEDURES FOR THE MANUFACTURE OF DENTAL CONTAINERS CONTAINING VISIBLE GAS BUBBLES - Google Patents

Description

The invention relates to a method for the production of dental care agents, in particular dental care agents which are essentially clear and which contain visible gas bubbles.

Although most dentifrices sold are opaque or opaque, i.e. cloudy, it has generally been found, due to their content of insoluble and cloudy polishing agents, that some users strongly prefer clear translucent or transparent dentifrices. When a number of clear liquid dentifrices were marketed several years ago, they suffered from the disadvantage that they did not contain a suitable polishing agent, and teeth that were brushed with such dentifrices got deposits of tartar, film coating and stains despite the fact that the dentifrices contained excellent cleaning agents. This disadvantage has recently been overcome by the introduction of polishing agents which can be incorporated into dental care agents and which make it possible to produce clear dental care agents even if a significant amount of polishing agent is present. Such polishes are themselves transparent and have refractive indices in the same range as the refractive index of the carrier and the rest of the dentifrice. There occurs ^e_-"or no disturbance of the light's path through the partials of pc 1 is 1 new about Leide'i ,

and to an observer the toothpaste gel appears clear.

It has been shown that despite the fact that they seem attractive

according to several observers, there are also several users who are dismissive of the toothpaste's properties. For some users, a transparent product does not give the impression of being an effective cleaning agent. Nevertheless, some of these users and others prefer a clear product that is broken by other materials in it. These materials give the product more "character", make it easier to distinguish from other dental care products and give it a more attractive appearance.

Most materials that can be suspended in a dentifrice are palpable, insoluble or gritty and may be unacceptable to the user. On the other hand, it is not unfortunate to have portions of dispersions of differently colored dentifrice parts or of gases in the main part of the dentifrice. Although the colors of dispersed, solid materials or gels may flow out, the gases preserve a distinct appearance of their own in the dental care product and for an unlimited time in the products manufactured according to the invention. They also offer other advantages in that it is possible to regulate the specific gravity of the product and the ratio of solids in an extruded length of the dental care agent by introducing different proportional amounts of gas into the mixture.

In the manufacture of dental care agents and other thick products in which solid materials are dispersed in a liquid medium, air can occasionally dissolve in the medium or be trapped in the product. Such air is not desirable in dentifrices, especially not in clear dentifrices, as this is visible to the user and can make the product unattractive. This is because the air is often unevenly distributed, has such a particle size that the product appears cloudy or that it is distributed with uneven shapes that are less attractive than perfect spheres.

Such a dispersed gas can therefore be deliberately removed from dental care products. However, the invention relates to a method by which evenly distributed bubbles of the desired shape and size are produced so that the presence of these particularly improves the appearance of clear gel-like dental care products.

From US patent document no. 3011950, which relates to transparent cosmetic preparations, it is known that these preparations can contain gas bubbles. The cosmetic preparations according to the US patent are pourable liquids in which air bubbles have been suspended due to a sufficient thickening of the liquids to counteract the bubbles' otherwise natural tendency to rise and collect at the top of the container for the preparations. These should usually be poured out of a bottle with a relatively wide opening as a laminar stream without having to make a strong deformation of the container as when a tube of toothpaste is squeezed, and the use of known preparations under the normal conditions for these would not be taken as a indication that a dentifrice gel could be used while retaining the air bubbles therein. As the preparations according to the US patent are not observed after they have been emptied (they are normally poured into the hand and applied to the hair or they are applied directly to the hair), it does not matter if the bubbles in the preparations leave the liquid after it has been emptied . In the present method, however, it is important for the appearance of the toothpaste produced by the method that the bubbles are retained in this with a desired uniform shape and that they retain their place in the toothpaste after it has been squeezed out on a toothbrush. The presence of the gas bubbles in the dentifrice produced by the present method allows an evaporation of flavoring substances in the gas and therefore a more effective release of flavor in the mouth. Moreover, with the present method, a regulation of the dentifrice's specific gravity, which is often of importance when packaging the dentifrice, can be obtained by regulating the size and number of bubbles per volume- . unit in the toothpaste produced by the present method.

In the present method, a dental care agent containing gas bubbles is produced, and the method is characterized by the fact that a gas-free or substantially gas-free, viscous, extrudable dental care agent is produced in the form of a paste or gel containing a polishing agent, a gelling agent and a carrier,

and gas bubbles with a diameter of 0.1-4 mm of an equivalent sphere are mixed with the dental care agent so that 2-100 such bubbles are obtained per cm^ of the dentifrice which is prepared with a sufficient viscosity to keep the bubbles suspended in it.

According to a preferred embodiment of the present method, a dental care agent is produced in the form of a clear gel. The introduction of the evenly distributed gas bubbles will particularly improve the appearance of such clear dentifrice gels. It is therefore important to preserve the clarity of the dentifrice that the polarizing agent has a refractive index like the rest of the dentifrice, is insoluble in the dentifrice and exists in the form of particles with a diameter of less than 100 pm, and that the gelling agent is an organic or inorganic rubber or thickening agent which gives a clear gel in the described mixtures, and the carrier comprises a polyhydric alcohol with a refractive index equal to the polishing agent, and where a cleaning agent or foaming agent is also present to provide a particularly good cleaning effect. According to this preferred embodiment of the present method, the gas bubbles that are mixed in the dentifrice are formed by blowing gas bubbles through a channel with an outlet diameter of 0.1-4 mm into the mass of the degassed dentifrice which is moved relative to the channel outlet so that the bubbles are broken after that they have been drained from the channel and that they are prevented from agglomerating.

The organic or inorganic rubber gelling agents used are easily gelled together with the polyhydric alcohol.

According to a further preferred embodiment of the present method, a complex aluminum silicate is used,

a silicon dioxide dxerol gel or a mixture thereof as a polishing;

medium. These polishing agent ingredients have a refractive index of 1.4-1.5, which is essentially the same as the refractive index of 1.44-1.48 for a polyhydric alkanol with 3-6 hydroxyl groups per molecule, such as glycerol and sorbitol, and which according to the further preferred embodiment is used as a carrier in the dental care product. For such a dentifrice which additionally contains a natural or synthetic organic rubber, a synthetic inorganic silicate clay or a silicon dioxide aerogel or pyrogenically produced silicon dioxide as a gelling agent and an anionic or non-ionic synthetic organic washing-active compound as a cleaning agent, the further preferred embodiment of the present method is characterized by the fact that gas bubbles are mixed into the dentifrice which contain a large amount of nitrogen and have a diameter of 1-4 mm, that the dentifrice is produced so that it has a viscosity of over 100,000 centipoise at 25°C, and that the gas bubbles are distributed in a mass of the dentifrice at a temperature of 30-60°C by passing the gas at a linear gas velocity of at least 0.1 m/s into the dentifrice which is kept in motion with a linear velocity component at right angles to the discharge direction of the gas at the place where the gas is discharged, and which is at least 2 times the speed of the gas at this point place.

According to another preferred embodiment of the present method, the polishing agent used is sodium aluminum silicate, the gelling agent Irish moss, sodium carboxymethylcellulose or a synthetic, inorganic silicate clay with the formula

[Si8M<c>?5,l<Li>0.6<H>7.6°24<]>°'<6> Na<+>0.6'

the carrier is sorbitol and/or glycerol and water, and the foaming agent or cleaning agent is sodium lauryl sulfate, and this embodiment of the present method is characterized by introducing 2-40 gas bubbles per cm^ which is distributed throughout the dentifrice by passing air or nitrogen through

spreader channels or channels in a porous material with several passages into the heated dentifrice while this is being mixed using a stirrer, the dentifrice having a viscosity above 5000 centipoise upon the addition of the gas bubbles.

The more detailed justification for why the above-mentioned three preferred embodiments offer special advantages is set out in more detail below, and in particular the process features distinctive for the various embodiments.

The polishing agents for clear dentifrices are usually finely divided, water-insoluble, powdery materials of such a particle size that they pass a 140 mesh sieve (U.S. standard sieve series). The particles preferably have a diameter below 1G0 or 65 µm, are substantially spherical or of the same length and width, are transparent and have a refractive index similar to the refractive index of the rest of the dentifrice medium. The particles preferably have a diameter of 1-40 pm, and preferably 2-20 pm, and the particle size distribution will be normal within the described or narrower ranges. Of the most applicable polishing agents that satisfy these conditions, mention can be made of complex aluminum silicates, such as sodium aluminum silicate, and silica xerogels which are often partial, e.g. 20%, hydrated. Such materials have refractive indices of 1.4-1.5, preferably 1.44-1.48, and usually 1.46 or 1.47. The silica xerogel or other colloidal or amorphous silicon dioxides or silicon hydrides often have a surface area of 200-1000 m 2 /g, usually 200-500 m 2 /g. Such surface areas per unit weight are desirable for the polishing agents used. The colloidal silicon dioxides described above are commercially available under the name "Syloid". These "Syloid" xerogels and hydrogels are designated by numbers, and

it has been found that "Syloid" 63, 72 and 74 are useful in the same way as related materials sold under the name "Santocel", e.g. "Santocel" 100. The bulk density of such compounds is usually 0.05-0.4 g/cm 3 and it has been shown that they can be easily and evenly suspended in dentifrice gels. Of other excellent polishing agents that can be used, mention may be made of synthetic, amorphous, complex metal aluminum silicate salts, especially alkali metal salts such as the sodium salts, and alkaline earth metal salts such as the calcium salt. Such materials contain up to 20% by weight of moisture and up to 10% by weight of an alkali metal or alkaline earth

metal oxide. They are sold under the brand name "DeGussa", e.g.

"DeGussa" P820. The complex aluminosilicate salts which appear to contain silicon dioxide and aluminum oxide bound together by Al-O-Si bonds are described by Tamele in "Chemistry of the Surface and Activity of the Aluminium-Silica Cracking Catalysts" printed in Discussions of the Faraday Society, No. 8, pp. 270-279 (1950), especially on page 273, and in an article by Milliken et al entitled "The Chemical Characteristics and Structure of Cracking Catalysts" on pages 279-290 of the same publication, especially in the section connecting pages 284 and 285.

Other clear polishes or polishes that become clear in a special medium can also be used. The main requirement is that the refractive index must be similar to the refractive index of the other components and that the materials must have a suitable hardness and particle size similar to those stated above in order to achieve a good polishing effect without scratching.

Although the present method is particularly suitable for the production of clear, gel-like dentifrices containing bubbles, it can also be used to uniformly introduce bubbles into cloudy dentifrices in order to thereby regulate density, and in such cases the various polishing agents used in such preparations may be present . The various polishes are described in standard handbooks, such as Cosmetics: Science and Technology, by Sagarin, second edition, 1963, published by Interscience Publishers, Inc.

The gelling agents that can be used to gel or thicken the present dental care agents are known in the art.

The gelling agents used can be gelled together with polyhydric alkanols, such as glycerol and sorbitol, and with water and lower alkanols. The gels are usually formed when at least some water is present. The liquid part of the mixture may comprise water, lower alkanol and polyhydric alkanol. Although propylene glycol can be used, it is generally preferred that the main liquid component is polyhydric alcohols, such as glycerol, sorbitol or a mixture of glycerol and sorbitol together with some water. Such carrier fluids have refractive indices of 1.44-1.48 and are therefore excellent for use with polishing agents of silica xerogels or complex aluminum silicates.

Although it is not absolutely necessary, it is generally desirable that organic surface-active agents are present in the dental care products because of their properties as cleaning or foaming agents. The cationic cleaning agents can be used, but are usually avoided in favor of anionic, non-ionic or amphoteric surfactants. Of these, the anionic ones are the most preferred.

Different additives can be used in the present dental care products. Perhaps the most important of these are the flavourings. Solvents may occasionally be present to dissolve the flavoring agents and to give a desirable effect in the preparations according to the invention whereby trapped gases are first removed from the product before a controlled addition of gas bubbles is made. In most cases, the solvents should have a boiling point at atmospheric pressure of 80°C or below to achieve the best gas removal. A preferred range is 40 or 50-70°C.

Other useful additives are buffers, preservatives and fluorine-containing compounds, which protect the teeth from decay. For most additives, the relative amounts of insoluble materials with refractive indices that are different from the refractive indices of the rest of the dentifrice will of course be kept sufficiently low that they will not influence the clarity of the product.

The gas used to form the bubbles in the dentifrice can be any of a number of suitable gases, the main requirement being that it should not be so soluble in the dentifrice that the bubbles will disappear in the dentifrice because they dissolve in it. This does not imply that a certain solubility cannot be accepted and that it cannot be desirable in certain 1 traps. If e.g. the solubility of the gas is sufficiently low so that part of it dissolves in the dental care agent, the bubbles can be given a desirable smaller size, and it may be possible to utilize bubble equipment that does not need to be regulated as precisely as if microbubbles had been introduced. Such use of larger bubbles is acceptable because their size is reduced after they have been distributed in the dentifrice. However, it is generally preferred to use gases which are soluble to an extent of less than 10% in the dentifrice, and those which have a solubility of less than 5% seem to give the best results. Among the gases that can be used are nitrogen, argon and air. Of these, nitrogen is preferred, but due to its easier availability and because it gives almost the same results, air is often used. Besides these gases, other gases, such as the aerosol propellants which are halogenated hydrocarbons, can be used on the condition that they are not too soluble. In this connection, it can be mentioned that carbon dioxide can occasionally be used and contribute to the toothpaste giving a fizzy or sharp effect.

The relative amounts of the various components used in the dental care agent are such that a satisfactory extrudable gel or a similar product is obtained which will essentially retain its shape after it has been removed from a dispensing container. The product will contain a sufficient amount of polishing agent so that the teeth will be cleaned well, but it will not contain so much that it gives a sandy feeling or that it will affect the smoothness of the gel. Similarly, the liquid carrier present will be compatible with the other ingredients and act as a medium in which they are dissolved or dispersed. The liquid carrier should not be present in such a large amount that the product will be too liquid or in such a small amount that the dentifrice will lose its smooth, attractive appearance. The cleaning agent or foaming agent is used in a small amount that is sufficient to give a satisfactory foaming effect to facilitate the cleaning of the teeth and not in such a large amount that the product will become tarnished or opaque. Similarly, the gelling agent present will thicken the dentifrice sufficiently that it will retain its shape and hold the gas bubbles in place at room temperature, but there will not be so much gelling agent present that the dentifrice will become rubbery, lumpy or opaque. It is desirable to use such a relative quantity of the gelling agent that the viscosity of the dental care agent will increase to over 100,000 centipoise at 25°C, preferably over 200,000 or 1,000,000 centipoise.

For materials that have non-Nev/tonic properties, viscosity measurement may not give an accurate indication of the thickness or force required to hold the bubbles in place. In such cases, the product should be sufficiently firm so that, even if it can be extruded at room temperature (25°C), it holds the bubbles in place and does not enable them to accumulate towards the upper part of the dentifrice in the container. For Newtonian fluids, the specified centipoise numbers are measures for such a satisfactory property. As described below, the dentifrice's viscosity, thickness or firmness should be lower at higher temperatures, so that spherical gas bubbles can form at such temperatures even if the initially introduced bubbles in the dentifrice are not completely round.

The generally proportionate amounts of materials used

for achieving the above-described properties, can vary within a wide range, but experience has shown that certain areas are the most desirable for the production of the best products. Thus, as a rule, 5-50% polishing agent, 0.5-5% gelling agent or thickening agent 1 , 30-85% polyhydric alcohol, 5-30% water and 0.5-5% cleaning agent or foaming agent are used. The preferred amounts are 5-10% polishing agent, 0.5-3% gelling agent, 50-75% polyhydric alkanol or polyhydric alkanols, 10-20% water and 1-3% detergent. For unclear dentifrices, the amount can be, if desired

of polishing agent be higher, 20-75%, the amount of water be higher, 5- h- 0%, and the amount of polyhydric alkanol be lower,,

usually 10-35$. Other materials and additives may be present to give additional undesirable properties in the manufacture or for the end use. Thus, flavoring agents and coloring agents make the dental care agent more attractive to the user, and solvents can facilitate the temporary removal of gas. As a rule, no more than 10% of each of such materials is used, and in most cases the amount used is usually 0.1-5%- > preferably 0.1-3%, and the total amount of such materials under 20%.

Within the quantity ranges described above, excellent dentifrices with sufficient ability to hold the bubbles can be produced. By the present method, bubble-containing dentifrices can be produced which will remain essentially clear despite the fact that the dentifrices are broken by both the gaseous and solid materials in these. The shape of the bubbles does not change in an unfortunate way when the bubbles hit the solid materials, and there is no irregular appearance due to changes in the path of the light through the product.

Although bubbles have been formed purely by chance in earlier dentifrices, they have been considered disadvantageous and attempts have been made to remove them. This is because they had one. tellingly, uneven shape, that they were unevenly distributed and that they were likely to cause density variations in the dentifrice. Even in clear dentifrices, bubbles can cause a tarnished appearance. By using the present method, these disadvantages are avoided, and a desirable clear dentifrice with attractive and evenly distributed bubbles therein can be produced.

As a first step in the production of such a product, a dentifrice is produced which is essentially free of trapped gases and which is preferably also free of dissolved

LO t I l o 10

gases. Such removal of gas can be carried out by means of any known technique, and it is usually carried out using a vacuum during the mixing of the various components in the dentifrice or after the dentifrice has been produced.

The vacuum used will usually be 500-730 mmHg, corresponding to an absolute pressure of 30-260 mmHg, but a higher vacuum of up to . 759 or 760 mmHg can also be used to achieve faster gas removal. If the finished dentifrice is to be degassed and prior treatments are not carried out under vacuum, it can take up to 2-3 hours to satisfactorily remove trapped and dissolved gases from the product. Such removal can be easily carried out using such devices as Dopp, Unimix and Versator mixers in which thin films, e.g. with a thickness below

6.2 cm, of dental care products are exposed to low pressure. It is possible to achieve faster gas removal by subjecting the various components or premixes of the dental care agent to vacuum before and/or during mixing. Gas removal is facilitated by the use of hot or volatile solvents in an amount of usually 1-10%, preferably 1-5%, or a volatile flavoring agent to dilute the preparations and to promote a coalescence of the gas bubbles and their removal. According to a particularly preferred method used for the preparation of clear gel dentifrices, heat is used, with or without the described vacuum, to remove gas or air from a mixture of polyalkanol and surfactant, i.e. a cleaning or foaming agent, and this is mixed under vacuum together with the rest of the previously degassed preparation. The degassed intermediate product is produced by subjecting a mixture of gelling agent and liquid carrier to a vacuum, after which a polishing agent is mixed in and gas is removed during or after the addition. By following this method, which can be modified by the addition of solvents or flavoring agents which are volatile and have a boiling point of ^0-70°C, it is possible to produce an essentially gas-free dentifrice.

The gas-free dentifrice preferably has an elevated temperature or is controlled in some other way so that it has a sufficiently low viscosity so that it becomes possible for the gases intentionally dispersed therein to assume a spherical shape. At this stage, the toothpaste will have a lower viscosity than when it is finally packaged and when it is at room temperature. However, it will have a sufficient viscosity that the bubbles dispersed in it will not easily come into contact with other bubbles and will not be removed from the dentifrice or moved to an area thereof. They will stick to-

widely dispersed for a sufficiently long time that the dental care

the agent can be packed and quenched or subjected to another curing mechanism to produce an extrudable but dimensionally stable final product. It is generally preferred to use heat as the thinning precaution and to cool the product so that it thickens, but other techniques, such as the use of dissolution

agents and time-dependent curing agents can also be used.

After the production of the essentially gas-free dentifrice which preferably contains less gas than the amount necessary for the production of a bubble with a diameter of 2 mm per

cm^, i.e. below 0.5 volume$, and preferably below one bubble with a diameter of 1 mm per cm^, the dentifrice's temperature or another variable is regulated to make the dentifrice thin enough that spherical gas bubbles can form when gas bubbles are injected into it. For Newtonian fluids, this preferably corresponds to a viscosity of 25,000 centipoise or less, as a rule above 1,000 eenti-poise, and preferably above 5,000 centipoise. At such viscosities, bubbles of gas to be dispersed in the toothpaste can be added in a controlled manner, and they are distributed throughout the toothpaste as the addition of bubbles continues until the desired concentration has been reached, and the toothpaste is then filled in an end-use container, such as toothpaste tubes, and cooled in the container to bind the gas bubbles in the toothpaste. The added gas bubbles have an equivalent spherical diameter of 0.1-^t- mm, preferably 1-h mm, and preferably 2-3 mm. They are added until 2-100 such bubbles occur per cm^ dentifrice, preferably 2- hO or 2-20 per cm^.

Various methods for the precise formation of bubbles of the aforementioned sizes and for their distribution throughout the dentifrice can be used, but the method which is considered to be simple, yet the most effective, is to add bubbles through passages which approximately have the desired final diameter for the bubbles . The linear speed with which the bubbles are added, although it is usually 1-50 cm/s, preferably above 0.1 m/s, can be varied within a wide range, provided that the gas bubbles are broken at the correct length so that spheres with the desired diameter are formed. It is therefore generally preferred that the passages through which the gas enters the dentifrice mass should have a distance of at least 1 or 2 diameters, and the dentifrice should be kept in motion by stirring or other agitation in such a way that a velocity component at right angles to to the gas inlet path is at least 2 times the gas velocity at the inlet location. Thus, the bubbles will be divided into a length with approximately the desired diameter and agglomeration is prevented. By regulating the gas flows, changing the pressure and varying the toothpaste speed and by changing the mixing apparatus or the agitator speeds, bubbles of the desired size and i. the desired concentration can be formed. Various types of mixers can be used, but common propeller, paddle, pump and circulation mixers are satisfactory. Of course, as a general rule, mixers with high shear force or thin film mixing should be avoided. To achieve a good production capacity, the linear gas velocity is at least 0.1 m/s, and the gas pressure is regulated, even if it is low,

to achieve the correct speed. The passages through which the gas is added to the dentifrice may consist of separate fine tubes or may be in a single part, such as a porous plate or spreader. Mechanical separation equipment can also be used to form the bubbles, but this can be less accurate than the passage method described.

At the viscosities or thicknesses that the toothpaste has to which the gas is added at an elevated temperature, e.g. 30-60°C,

the bubbles will not run together and they are not adversely affected by the dispersed, insoluble polishing agent. The polishing agent particles with a diameter below 100 µm, preferably 1-65 µm, and most preferably 1-20 µm, do not weaken the bubbles nor form sites where the bubbles can bind to other bubbles, contrary to what might have been expected. Larger particles of polishing agents are considered undesirable for this reason and also because they are undesirably flabble. Due to the initially low gas content in the dentifrice, few bubbles are formed with a size outside the desired range, and because the gas is preferably added at an elevated temperature, there is little tendency for bubbles to form on cooling, as cold gases are generally more soluble than warm ones. It is an advantage of the existing dental care agents that gas bubbles of volatile materials are present in them which can enhance the taste and smell, at least in connection with such flavoring agents which mainly provide odor-

effect.

After production, the bubbly dentifrice is packed into the container as soon as possible, usually within an hour, and preferably within 10 minutes. It is cooled to room temperature over the course of a further 5 hours, preferably over the course of 2 hours, and is then ready for transport.

Although the described method for producing the gaseous, gel-like dentifrices is strongly preferred, other methods can also be used. In some cases, bubbles can thus be dispersed mechanically using a mixing device or they can be formed chemically. It may be preferred to fill the product cold in the end-use containers, and under the condition that the bubbles are spherical when filling and that the equipment can be used for filling a thickened product, good dental care agents can be produced by such a method. The dentifrice can also be vacuum packed either by using a vacuum during filling or by filling the dentifrice hot and by lowering the pressure due to volume reduction on cooling. In some cases, uneven bubbles can be formed on purpose, and in such cases it may be undesirable that the dental care agent, when the gas is added, is sufficiently mobile that gas balls will form. The clear dentifrices can be produced by the method below

the invention during the anticipated

ning that the gas bubbles have a diameter of 1-k mm and are distributed throughout the toothpaste so that 2-20 bubbles occur per cmJ " in dentifrice, preferably uniformly distributed, in clear dentifrices containing an insoluble polishing agent, a gelling agent' and a liquid carrier. In such products the dispersed' comprises

gas preferably a mainly nitrogen quantity, and it consists

preferably of nitrogen although air is also satisfactory. It is strongly preferred to pack such dental care products in clear. plastic, e.g. in transparent, flexible tubes of polyvinyl chloride or polypropylene, that they have a final viscosity above 2C'.-000 centipoise and that ±3

contains 5-10 spherical bubbles with a diameter of 2-3 mm per cm „ Especially in such preparations in which the polishing agent is sodium aiumiriium silicate with a diameter of 1-20 lira. and a refractive index of 1 ?'+8, the gelling agent is a synthetic. inorganic silicate l^ira of the "Laponite" type, d~:i liquid carrier ;r .jr_ aqueous solution. of glycerol and sorbitol with a glycerol:sorbitol molar ratio of 1:5-5:1, and the relative amounts of the components are 5-50% polishing agents, 0.5-5% gelling agent, 30-85% polyhydric alkanol, 5 -30% water and 0.5-5$ foaming agent, excellent products are obtained.

In the following examples, all parts are based on weight and all temperatures are in °C unless otherwise stated.

Example 1

The sodium aluminum silicate used was a complex salt with

a refractive index of 1.7, a moisture content of approx. 10$ and an aluminum oxide content of 8$ and contained 78$ silicon dioxide and 10$ sodium oxide. The particle sizes ranged from 1 to 20 µm.

The "Laponite" SP, flavoring agent, sooting agent and coloring agent used were mixed with approx. 1/3 of the glycerol and 1/3 of the sorbitol plus 1/2 of the water, and a vacuum of 700 mm Hg was applied for 10 minutes. Then 1/3 of the glycerol and 1/3 of the sorbitol were used along with 1/2 of the water to disperse the sodium aluminum silicate and sodium monofluorophosphate, and a similar vacuum was used at the same time to remove any entrapped air. The sodium N-lauroyl sarcoside was then mixed with the rest of the glycerol and sorbitol. The material was heated to 50°C and held at this temperature for 5 hours without the application of vacuum or for 10 minutes using the same vacuum as indicated above. Then, the portion of the polyhydric alkanol and gelling agent was mixed with the portion of liquid carrier-polishing agent-fluoride at a temperature of h0°C and using a vacuum of 700 mmHg for 5 minutes, after which the surfactant mixture was mixed using the same vacuum and with a holding time of approx. 10 minutes. The mixing was carried out in a mixing device of the Unimix type which was equipped with "Teflon" scraper blades which kept the walls clean of the mixture up to a thickness of 0.2 mm so that only a very thin film of dentifrice remained on the walls. The product produced was essentially gas-free and contained less than 0.1 volume$ of trapped air. The toothpaste's pH was approx. 8. This was well within the range for pH that the existing dental care products should have, which is 5-9. The product produced was a clear, gel-like dentifrice with an attractive appearance.

Similar clear gas-free gel dentifrices were prepared by increasing the amount of sorbitol to 70% of the polyhydric alkanol content, replacing "Laponite" SP with 1 part sodium carboxymethylcellulose (sorbitol being added to replace the other part of the omitted "Laponite") by replacing the sodium aluminum silicate with silica xerogel ("Syloid" 63), by replacing the sarcoside with sodium lauryl sulfate and by replacing the sodium monofluorophosphate with 0.2 part sodium fluoride, water being used for the additional 0.6 part . Such a composition and the one previously described were degassed, under a vacuum of 7^0 mmHg for h hours while the mixture was carried out in a Dopp type mixer which was provided with a scraper to keep the inner walls of the mixer clean. All the products described, whether they were prepared by the stepwise application of vacuum, occasionally with the application of heat as in the deaeration of the cleaning agent mixture, or in the final deaeration of the entire dentifrice, were clear gels. In some cases, the deaeration was intentionally ended before the production was finished so that the product contained a comparatively smaller amount of air or nitrogen bubbles, e.g. a relatively smaller amount of preferably less than 20% of the final content of bubbles in the dentifrice.

The described dentifrices were heated to ^O<*>^ and had

at this temperature a viscosity of 5,000-25,000 centipoise or was similarly thickened so that gas bubbles added to the dentifrices assumed spherical shape. Then air was blown through e.r: diffusers with several passages mol diameter of 2 mm and an im-

a distance of 1 cm is placed through the bottom of paddle mixers containing the various degassed dental care agents. The linear flow velocity of the air (nitrogen was used in some of the experiments) was 10 cm/s and the speed of the mixer so that the average tangential velocity of the toothpaste in relation to the air channel on the spot where the air came out of it, 50 cm/s. Air was added for approx. 1 minute until it occurred approx. 10 bubbles per cm-1 toothpaste, as each bubble had a diameter of approx. 2 mm.

In the course of 5 minutes after the addition of the air, the dentifrice was filled into transparent polyvinyl chloride tubes and 2 hours later cooled to 25°C, and the dentifrice had at this temperature a viscosity of approx. 500,000 centipoise.

The products were packed and transported, and even after a longer storage time, e.g. 6 months - 1 year, they were still attractive and useful dentifrices that were sparkling clear and contained evenly distributed air bubbles in the same places as when they were manufactured.

These trials were varied by using Irish moss instead of sodium carboxymethylcellulose and by replacing 1A of the foaming agent with "Igepal" CA-630 (nonylphenoxypolyethoxyethanol).

A product with similar properties to the dental care products described above was obtained. When a silica airgel or pyrogen-made silicon dioxide was used as a partial replacement for the gelling agent, usually in an amount of $50, the prepared dentifrice was also satisfactorily clear, and the bubbles were also clearly visible therein. However, when the polishing agent was replaced with a polishing agent having a refractive index outside the range of 1.^-1.5 or having particles larger than 100 µm, this became visible in the dentifrice and its clarity was lost. It is sometimes considered desirable that a smaller percentage of the polishing agent should have a size greater than 100 y. m or a refractive index outside the described permissible range for the polishing agent to be visible, but in no case should the amount of this be greater than 20%

of the total amount of polishing agent present. Even if the liquid carrier can consist exclusively of sorbitol or glycerol together with some water and even if the water can in some cases be omitted completely without this affecting the clarity of the product and the retention of the well-dispersed gas bubbles therein, the best results are obtained with mixtures of sorbitol, glycerol and water, as smaller amounts of polypropylene glycol may also occasionally be present. Instead of air and nitrogen, argon and various propellant gases of the "Freon" type (chlorofluorinated lower alkanes) can be used, and good, clear dental care products are also obtained.

Example 2

A substantially clear, gel dentifrice was prepared according to the recipe below, and any entrapped air was removed by applying a vacuum of 700 mmHg for 2 hours using 2% of a solvent (ethanol, chloroform or acetone). to facilitate the removal of the trapped air bubbles - The composition used was as follows:

The sodium aluminum silicate used was a complex salt with a refractive index of 1,*+5? 10% moisture, 8% aluminum oxide, approx.

70$ silicon dioxide, 7% sodium oxide, a particle diameter of 98$

-30 jLtm and a space weight in the unpacked state of Ojll1* g/cm . The same apparatus was used as described in example 1, with separated passage tubes with a diameter of 1 mm and a mutual distance of J mm, and air was blown into the dentifrice until there was approx. 20 bubbles per cmJ •3 with a diameter of approx. 1 mm. The bubbles were spherical, and in the course of the times indicated in example 1, the toothpaste was filled into tubes,

and the tubes were cooled and sent to storage.

The products produced were excellent clear dentifrices with visible bubbles. The bubbles were evenly dispersed and had a diameter of approx. 1 mm. In a variation of this experiment, channels with a diameter of 0.5 mm and 3.0 mm were used instead of the channels with a diameter of 1 mm and approx. Twice as many of the smaller channels. Using this technique, a dentifrice was obtained containing a mixture of bubbles with a diameter of 0.5 mm and 3.0 mm. In some cases, such mixtures are preferred under the condition that the bubbles are spherical and that the distribution of the bubbles with the two different sizes is uniform.

This attempt was repeated several times, but instead

air to use argon, and the gels were stained with different colors and different flavors were added. In some cases, 1% chloroform was added to the product due to its flavoring effect. All these products were clear gels with excellently dispersed argon bubbles.

Example 3

The sodium aluminum silicate was a complex salt with a refractive index of 1.^6, a moisture content of approx. 6$, an aluminum oxide content of 8.2$, a silicon dioxide content of 72$, a sodium oxide content of 7$, an average particle size of approx. 20 ^m and a space weight in the sieve, unpackaged state of approx. 0.07 g/cm^.

The manufactured product was after degassing with those in example 1

and 2 detailed methods and after the introduction of air bubbles with a diameter of 0.5-^ mm by means of a spreader for the introduction of air and by otherwise applying the method according to examples 1 and 2, an acceptable clear dentifrice.

Example h

The sodium aluminum silicate used was the same as in example 2. The product was prepared using the method according to example 1 and was a clear gel-like dentifrice containing bubbles and with an appealing appearance.

Example 5

A clear gel dentifrice was prepared using the method of Example 1 and proved to be an excellent tooth cleanser with a pleasing appearance and taste and with good foaming power and excellent storage stability. The bubbles were evenly distributed in this and remained in place during storage for 6 months in a transparent, flexible dispensing tube. polyvinyl chloride.

Claims (4)

1. Method for the production of a dental care agent containing gas bubbles, characterized in that a gas-free or essentially gas-free, viscous, extrudable dental care agent is produced in the form of a paste or gel containing a polishing agent, a gelling agent and a carrier, and gas bubbles with a diameter of 0.1-4 mm of an equivalent ball is mixed with the dental care agent so that 2-100 such bubbles are obtained per cm 3 of the dentifrice which is produced with a sufficient viscosity to keep the bubbles suspended in it. 2. Method according to claim 1, where the used dentifrice is a clear gel, the polishing agent has a refractive index like the rest of the dentifrice, is insoluble in the dentifrice and is in the form of particles with a diameter of less than 100 µm, and the gelling agent is an organic or inorganic rubber or thickening agent that gives a clear gel in the described mixtures, and the carrier comprises a polyhydric alcohol with a refractive index equal to that of the polishing agent, and where a cleaning agent or foaming agent is also present, characterized in that the gas bubbles that are mixed in the dental care agent are formed by blowing gas bubbles through a channel with an outlet diameter of 0.1-4 mm into the mass of degassed dentifrice which is moved in relation to the channel outlet so that the bubbles are broken after they have been emptied from the channel and they are prevented from agglomerating. Method according to claim 1 or 2, where the dental care agent used comprises a polishing agent which is a complex aluminum silicate, a silicon dioxycixerogen or a mixture thereof, with a particle size of 1-65 pm and a refractive index of 1.4-1.5 , the gelling agent is a natural or synthetic organic rubber, a synthetic inorganic silicate clay or a silicon dioxide airgel or pyrogenically produced silicon dioxide, the carrier comprises a polyhydric alkanol with 3-6 hydroxyl groups per molecule, and the cleaning agent is an anion-active or non-ionic, synthetic, organic detergent-active compound, characterized in that the gas bubbles that are mixed in the dental care agent contain a substantial amount of nitrogen and have a diameter of 1-4 mm, that the dental care agent is manufactured so that it has a viscosity above 100,000 centipoise at 25 pC, and that the gas bubbles are distributed through a mass of the dentifrice at a temperature of 30-60°C by passing the gas with a linear gas velocity of at least 0.1 m/s into the dentifrice which is kept in motion by a linear velocity component which is at right angles to the gas discharge direction at the point where the gas is discharged, and which is at least 2 times the gas velocity at this point. 4. Method according to claims 1-3, where the polishing agent used is sodium aluminum silicate, the gelling agent is Irish moss, sodium carboxymethylcellulose or a synthetic, inorganic silicate clay with the formula the carrier is sorbitol and/or glycerol and water, and the foaming agent or cleaning agent is sodium lauryl sulfate, characterized by introducing 2-40 gas bubbles per cm<3 >which is distributed throughout the dentifrice by passing air or nitrogen through diffuser channels or channels in a porous material with several passages into the heated dentifrice while this is mixed using a stirrer, the dentifrice having a viscosity above 5000 centipoise.