GB2165467A - Cosmetic emulsion - Google Patents

Abstract

An oil-in-water emulsion suitable for topical application to human skin includes, in addition to water, a vegetable oil and an emulsifier derived from soap which has been partially acidified with mineral acid to provide a mixture of soap and acidified soap (as fatty acid). The oil and emulsifier together form a fatty component whose composition falls within the area designated ABCDEFG on the diagram. <IMAGE>

Description

SPECIFICATION Cosmetic emulsion Field ofinvention The invention relates to cosmetic emulsions such as creams and lotions and to a process preparing such emulsions.

Cosmetic emulsions are traditionally prepared by vigorously mixing together an oil phase containing an oil and emulsifier and an aqueous phase comprising water.

Soaps are the oldest and best known emulsifiers. Sodium and potassium soaps together with the soaps of amino bases such as ethanolamines have been used to prepare oil-in-water emulsions. Traditionally such soaps are generally formed in situ, free fatty acid in the oil phase being added to the alkali or organic base in the aqueous phase. Usually, the fatty acid is only partly neutralised so that the excess remains part of the oil phase.

Prior art As an example of this traditional art, WA Poucher in "Perfumes, Cosmetics & Soaps" (1929) in Volume II at page 436 et seq describes the preparation of vanishing creams as consisting of stearic acid partly saponified with alkali, the bulk of the fatty acid being emulsified by the soap thus formed, the main constituent of such creams being water. The author emphasises that the stearic acid employed should be of the finest quality and the amount employed should be from 10 to 25% by weight of the cream, 20% by weight giving a satisfactory stable cream.

Poucher also stipulates that the amount of fatty acid to be saponified during the preparation of vanishing cream should not exceed 30% for best results, while very often less than this amount will be found to be quite satisfactory.

Background to the invention While appreciating that the cost today of pure fatty acids, such as stearic acid, "of the finest quality" is too high to enable simple oil-in-water creams to be prepared economically in large quantities for a mass market, we have made a study of the possibilities of employing an inexpensive soap as an emulsifier in such creams, while using an approach which is in direct juxtaposition from that reported by Poucher. Indeed, in some parts of the world, high quality stearic acid is in any case not readily available, and therefore it is necessary to employ alternative locally available and preferably cheaper raw materials to provide the basis for an emulsifying system when manufacturing creams and lotions. Soap derived from the detergent industry can for example fulfill this need.

This totally new approach, which is the reverse of that advocated by Poucher, includes the step of treating soap with a mineral acid to yield a mixture of soap, free fatty acids derived from the soap, hereinafter referred to as "acidified soap"; and the corresponding inorganic salt derived from the acid employed. Using this new approach, we have however discovered that it is only possible to obtain stable emulsions which are completely acceptable cosmetically if the ratio of the soap to acidified soap falls well outside the corresponding ratio which Poucher states is essential. To reiterate this point, Poucher states that the amount of free fatty acid to be saponified with alkali should not exceed 30%, thus indicating that at least 70% of the soap/fatty acid mixture should remain as free fatty acid.In contrast we have found that if soap/acidified soap mixtures are prepared by acidification of soap with a mineral acid, then the amount of acidified soap produced should be from 35 to 65% of this mixture, if an emulsion is to be obtained which is stable at a high temperature, such as can be experienced in tropical countries, and has a pH value that is acceptable for cosmetic products that are intended to be left on the skin surface.

The oil selected forthe manufacture of creams and lotions is usually a mineral oil in view of its known ability to resist oxidative changes which might otherwise adversely affect the stability and consumer acceptability of such products.

In some parts of the world, mineral oils are impossible to obtain or are prohibitively expensive, and it is then necessary to seek an alternative type of oil when contemplating the manufacture of creams and lotions.

Surprisingly, it has been found that vegetable oils, particularly indigenous vegetable oils, can be used for this purpose at relatively high levels in the product, in spite of their known tendency to autoxidise. Although conventional anti-oxidants will in part contribute to reducing this tendency to autoxidation, it has been found that creams and lotions manufactured from vegetable oils using the partially acidified soap as the emulsifying system, as described above, show resistance to autoxidative deterioration.

Definition ofthe invention Accordingly, the invention provides an oil-in-water emulsion suitable for topical application to human skin which comprises by weight of the emulsion: (i) from 5 to 40% of a vegetable oil; (ii) from 0.7 to 12% of an emulsifier comprising a mixture of: (a) from 0.35 to 8% of soap, and (b) from 0.35 to 6% of acidified soap; (iii) the balance of the emulsion in addition to water comprising emulsion adjuncts; the oil and the emulsifier together forming a fatty component whose composition falls with the area designated ABCDEFG on the accompanying diagram.

Description of the invention The oil The oil-in-water emulsion of the invention accordingly contains a vegetable oil, preferred examples of which include: coconut oil hardened coconut oil palmkernel oil hardened palmkernel oil palm oil hardened and fractionated palm oil, and blended oils used in margarine manufacture The preference here is dictated by relatively low cost, availability and suitability for cosmetic purposes.

Many other vegetable oils can be employed if costs are not prohibitive. Examples include: avocado pear oil babassu kernel oil almond kernel oil apricot kernel oil corn kernel oil olive oil sesame oil cotton seed oil grape seed oil safflower oil sunflower seed oil rape seed oil hemp seed oil linseed oil soya bean oil castor oil cacao butter shea butter Carthamus tinctorius seed oil It is to be understood that the above selection of oils is non-limiting, and that other vegetable oils can be employed in the emulsions according to the invention.

Mixture of two or more different vegetable oils can be employed.

The amount of vegetable oil to be employed will be from 5 to 40%, preferably from 10 to 30% by weight of the emulsion, the actual amount chosen depending on whether it is intended to prepare a cream or a lotion.

The emulsifier The oil-in-water emulsions of the invention will also contain an emulsifier comprising soap and acidified soap.

It is to be understood that the soap employed can be that derived, for example from traditional soap manufacture by the saponification of any cosmetically acceptable oil or fat or by treatment of one or more free fatty acids with an alkali such as sodium hydroxide, potassium hydroxide or an alkanolamine.

The acidified soap component of the emulsifying system is preferably that which is derived from the soap by partial acidification with a mineral acid. Itisto be understood howeverthattheemulsifying system can alternatively consist of a mixture of soap and acidified soap derived from a different source.

The amount of the emulsifier comprising soap and acidified soap to be employed in the emulsions of the invention should form from 0.7 to 12%, preferably from 2 to 10% by weight of the emulsion. The amount of soap present in the emulsifier should form from 0.35 to 8%, preferably from 1 to 7% by weight of the emulsion and likewise the amount of acidified soap should also form from 0.35 to 6%, preferably from 1 to 5% by weight of the emulsion.

It is important to ensure that the relative amounts of soap and acidified soap which comprise the emulsifier fall within the limits as defined above, otherwise the emulsion can possess poor cosmetic properties, poor stability at high storage temperatures (for example, up to 50"C) or a pH value which is unacceptable for cosmetic products which are normally left on the skin surface and not deliberately removed, for example by washing, soon after application, (i.e. "leave on" products).

Water The emulsion will also contain water and optionally other emulsion adjuncts as necessary.

The amount of water present can accordingly form the balance of the composition of the emulsion which amounts to up to 94.3% where no emulsion adjuncts are present. Usually, however, the amount of water present in the emulsion will form from 30 to 85%, preferably from 40 to 85% and most preferably from 50 to 80% of the emulsion.

The fatty component of the emulsion The stability and cosmetic acceptability of the emulsion according to the invention is also governed by the composition of the fatty component of the emulsion consisting of vegetable oil, and the soap and acidified soap which together form the emulsifier. The fatty component should accordingly comprise: (a) from 65 to 97%, preferably from 67 to 95% by weight of the vegetable oil; (b) from 0.5 to 23%, preferably from 2 to 22% by weight of the soap; and (c) from 2 to 12%, preferably from 3 to 12% by weight of the acidified soap.

It is apparent however that not all possible combinations of these three ingredients will provide acceptable emulsions, and it is accordingly necessary to definefurthertheir respective interrelated limits. These are illustrated in the accompanying diagram.

The accompanying diagram The accompanying diagram shows the composition of the fatty component of the emulsion. The fatty component accordingly consists essentially of three ingredients namely (a) vegetable oil; (b) soap (remaining unchanged after acidification); and (c) fatty acid (derived from soap by acidification).

The sum of a + b + c will accordingly account for 100% of the fatty phase of the emulsion, or very nearly 100% if other oil soluble minor ingredients such as antioxidants, preservatives and perfumes are also present in the emulsion.

The shaded areas within the diagram define the compositions of the fatty phase of emulsions which are stable at high (tropical) temperatures, which have acceptable cosmetic properties and whose pH is not too high for normal cosmetic use. The captions on the diagram indicate by way of explanation why emulsions whose compositions fall outside the shaded areas are unsuitable for cosmetic use.

The total shaded area indicates in general terms the acceptable compositions of the fatty component of emulsions, the amounts of (a) vegetable oil, (b) soap, and (c) fatty acid falling within the area designated ABCDEFG.

The two shaded sub-areas indicate the acceptable compositions of the fatty component of emulsion containing either a low level of emulsifier (i.e. soap plus fatty acid) or a higher level of the emulsifier.

It is accordingly apparent that emulsions whose fatty component comprises from 0.7 to 2% by weight of the emulsifier consisting of both soap and acidified soap will preferably have compositions falling within the area designated DEFH on the accompanying diagram. Such emulsions will usually, but not always, be fluids, i.e. lotions ratherthan solids, such as creams.

It is also apparent that emulsions whose fatty component comprises from 2 to 12% by weight of the emulsifier consisting of both soap and acidified soap will preferably have compositions falling with the area designated ABCDHFG on the accompanying diagram. Such emulsions will usually, but not always, be solids, i.e. creams, rather than fluids such as lotions.

It should be explained that compositions of the emulsion which fall outside the area ABCDEFG so defined are excluded from the scope of the invention as being unsuitable or inferior compositions. For example, compositions falling to the left of the line ABC will have a pH which is too high for "leave on" cosmetic use; compositions falling below the designated area will generally have poor cosmetic properties; compositions falling to the right of the line CDEFG will have poor storage characteristics, especially at tropical ambient temperatures of up to 50"C; and compositions falling above the designated area (i.e. above the line AG) will contain insufficient emulsifier to produce a stable emulsion.

Optional emulsion adjuncts The emulsion according to the invention can also optionally contain emulsion adjuncts, that is ingredients other than oil, emulsifier and water which are conventionally employed in emulsions.

Examples of emulsion adjuncts include thickeners, such as Xanthan gum, sodium carboxymethyl cellulose, guar gum and bentonite clays; humectants, such as sorbitol and glycerol; antioxidants, such as butylated hydroxytoluene and butylated hydroxyanisole; chelating agents, such as ethylene diamine tetraacetic acid; preservatives such as formalin, para-hydroxy benzoate esters, 2-bromo-2-nitropropane-1 ,3diol (e.g. BRONOPOL), emollients, colourants and perfumes.

When a thickener is incorporated into the emulsion, the amount employed should preferably form from 0.2 to 1% by weight of the emulsion.

Emulsion product forms and packaging The emulsion of the invention can be formulated as a fluid, for example a product such as a lotion for use in conjunction with an applicator such as a roll-ball applicator, or a container fitted with a pump to dispense the emulsion, or simply for storage in a non-deformable bottle or a squeeze container. Alternatively, the emulsion of the invention can be solid or semi-solid, for example a cream or gel, for use in conjunction with a suitable applicator, or simply for storage in a tube or lidded jar.

The invention accordingly also provides a closed container containing a cosmetically acceptable emulsion as herein defined.

Process for preparing the emulsion The invention also provides a process for preparing an emulsion of the type defined herein, which comprises the steps of: i) preparing a dispersion comprising soap, water and mineral acid at a temperature of from 60 to 100C, the amount of acid being sufficient to acidify only part of the soap; ii) adding oil to this dispersion comprising soap and acidified soap, with mixing, while maintaining the temperature at a value of from 60 to 100 C, to form an emulsion; iii) cooling the emulsion and filling it into containers.

A preferred process for preparing an emulsion of the type defined herein which incorporates additional but optional ingredients, includes the steps of: i) preparing a dispersion comprising soap, humectant, chelating agent and water by mixing at a temperature of from 80 to 90"C until all ingredients are in solution; ii) dispersing in the solution so formed a thickening agent dispersed in a small portion of the oil while maintaining the temperature at a value of from 80 to 90 C; iii) adding to the dispersion so obtained the mineral acid in an amount sufficient to acidify only part of the soap, together with the remainder of the oil and with anti-oxidant; iv) mixing at a temperature of from 80 to 90"C with sufficient shear to form an emulsion;; v) cooling the emulsion to a temperature of not more than 50"C, preferably not more than 45"C, and adding preservative and perfume ingredients; and vi) finally filling the finished emulsion into containers.

In the process according to the invention, other mineral acids, such as sulphuric acid, can be used in addition to or in place of hydrochloric acid.

Examples The invention is further illustrated by the following examples. The composition of the fatty component in each example is shown on the accompanying diagram.

A. Skin creams Example 1 Ingredients % wlw Hardened Palm Oil 25.00 Soap (Tallow: Palm Kernel -85:15) 5.00 Hydrochloric acid (7.3% wlw) 3.60* Sorbitol solution (70%) 6.00 Butylated hydroxy toluene (BHT) 0.05 Xanthan Gum 0.50 EDTA (Na4) 0.05 Formalin 0.10 Perfume 1.00 Water 58.70 *sufficient to acidify 40% of soap Composition of fatty component % wlw Oil 83.5 Soap 10.0 Fatty acid 6.5 Method Soap, sorbitol, EDTA and water are mixed together at 80 to 900C until dissolved. Xanthan gum is dispersed in a portion of palm oil (5% of the total emulsion) and added to the aqueous phase at 80"C with mixing.

To the above mixture is added: (a) hydrochloric acid; (b) the remainder of the palm oil containing BHT.

Mixing is continued using a medium shear mixer at 80"C, and then the emulsion so formed is cooled slowly to 450C. Formalin and perfume are then added with further mixing.

Example 2 Ingredients %wlw Margarine Oil 20.00 Soap (Tallow: Palm Kernel -85:15) 10.00 Hydrochloric acid (7.3% w/w) 6.50* Sorbitol (70%) 6.00 Butylated hydroxytoluene 0.05 Xanthan Gum 0.50 EDTA (NA4) 0.05 Formalin 0.10 Perfume 1.00 Water 55.80 *sufficient to acidify 35% of soap Composition of fatty component % wlw Oil 67.0 Soap 21.5 Fatty acid 11.5 Method Soap, sorbitol, EDTA and water are mixed together at 80 to 90"C until dissolved. Xanthan gum is dispersed in a portion of the margarine oil (5% of total emulsion) and added to the aqueous phase at 80"C with mixing.

To the above mixture is added: (a) hydrochloric acid; (b) the remainder of the margarine oil containing the BHT.

Continue mixing for 10 minutes using a medium shear mixer at 80"C, and then slowly cool to 45"C.

Formalin and perfume are then added with further mixing.

B. Skin lotions Example 3 Ingredients % wlw Palm Oil 5.0 Palm Stearin 10.00 Soap (Palm Kernel:Palm Stearin:Palm oil -30:30:40 2.00 Hydrochloric acid (7.3%) 1.78* Sorbitol (70%) 6.00 Xanthan Gum 0.50 Butylated hydroxytoluene 0.05 EDTA (Na4) 0.05 Methyl p-hydroxy benzoate 0.20 Propyl p-hydroxy benzoate 0.10 2 Bromo-2-nitro propane 1 .3.diol 0.01 Perfume 1.00 Water 73.31 *sufficient to acidify 50% of soap Composition of fatty component %wlw Oil 88.5 Soap 5.7 Fatty acid 5.8 Method Sorbitol, EDTA, soap, methyl p-hydroxy benzoate and two thirds of the water are heated with mixing at 80-90"C until dissolved. Xanthan gum is dispersed in the remainder of the water and added to the above solution. Hydrochloric acid is then added to this mixture.

The vegetable oils, propyl p-hydroxy benzoate and BHT are melted together and added to the aqueous phase. Mixing is continued at 70-800C for 15 minutes. The emulsion so formed is cooled slowly to 450C and Bronopol and perfume are added.

Example 4 Ingredients % wlw Shea Butter 10.00 Soap (Tallow: Palm Kernel -85:15) 2.00 Hydrochloric acid (7.3%) 1.60* Sorbitol (70%) 6.00 Guar Gum 0.50 Butylated hydroxytoluene 0.05 EDTA (Na4) 0.05 Formalin 0.10 Perfume 1.00 Water 78.70 *sufficient to acidify 45% of soap Composition of fatty component %wlw Oil 83.5 Soap 9.0 Fatty acid 7.5 Method Sorbitol, EDTA, soap in two thirds of the water are heated with mixing at 80-90"C until dissolved. Guar gum is dispersed in the remainder of the water and is then added to the above solution. Hydrochloric acid is then added to this mixture.

Shea Butter and BHT are then melted together and then added to the aqueous phase. Mixing is continued at 70-80"C for 15 minutes, after which the emulsion is cooled slowly to 45"C and formaline and perfume are finally added to provide the finished emulsion.

Example5 Ingredients % wlw Hardened cotton seed oil 10.00 Soap (Tallow:Coconut 80:20) 2.00 Hydrochloric acid (7.3%)* 1.98 Glycerol 4.00 Xanthan gum 0.50 Butylated hydroxytoluene 0.05 EDTA (Na4) 0.05 Methyl p-hydroxy benzoate 0.20 Propyl p-hydroxy benzoate 0.10 2-bromo-2-nitro propane 1.3 diol 0.01 Perfume 1.00 Water 80.11 *sufficient to acidify 55% of soap Composition of fatty component % wlw Oil 83.33 Soap 7.50 Fatty acid 9.17 Method Glycerol, EDTA, soap, methyl p-hdroxy benzoate and two thirds of the water are heated with mixing at 80-90"C until dissolved. Xanthan gum is dispersed in the remainder of the water and added to the above solution. Hydrochloric acid is then added to this mixture.

The vegetable oils, propyl p-hydroxy benzoate and BHT are melted together and added to the aqueous phase. Mixing is continued at 70-80"C for 15 minutes. The emulsion so formed is cooled slowly to 45"C and Bronopol and perfume are added.

C. Hair cream Example 6 Ingredients % wlw Coconut oil 15.00 Hardened Palm Oil 15.00 Soap (Palm:Coconut65:35) 7.50 Hydrochloric acid (7.3%) 5.40* Butylated hydroxytoluene 0.05 EDTA (Na4) 0.05 Sodium carboxy methyl cellulose (SCMC) 1.00 Formalin 0.20 Perfume 0.45 Water 55.35 *sufficient to acidify 40% of soap Composition of fatty component % wiz Oil 80.0 Soap 12.0 Fatty acid 8.0 Method Soap, sorbitol, EDTA and water are mixed together at 80-90"C until dissolved. SCMC is dispersed in portion of the vegetable oil (5% of total emulsion) and this dispersion is then added to the aqueous phase at 80"C with mixing.

To the above mixture is added: (a) hydrochloric acid; (b) the remainder of the vegetable oils with the BHT melted together.

Mixing is continued for 10 minutes using a medium shear mixer at a temperatue of 80"C. The emulsion so formed is cooled slowly to a temperature of 450and formalin and perfume are mixed in to provide the finished emulsion.

Claims (7)

1. An oil-in-water emulsion suitable for topical application to human skin which comprises by weight of the emulsion: (i) from 5 to 40% of a vegetable oil; (ii) from 0.7 to 12% of an emulsifier comprising a mixture of: (a) from 0.35 to 8% of soap, and (b) from 0.35 to 6% of acidified soap; (iii) the balance of the emulsion in addition to water comprising emulsion adjuncts; the oil and the emulsifier together forming a fatty component whose composition falls within the area designed ABCDEFG on the accompanying diagram.

2. An oil-in-water emulsion according to claim 1, comprising from 0.7 to 2% by weight of the emulsifier mixture, the composition of the fatty component then falling within the area designated DEFH on the accompanying diagram.

3. An oil-in-water emulsion according to claim 1, comprising from 2 to 12% by weight of the emulsifier mixture, the composition of the fatty component then falling within the area designated ABCDHFG on the accompanying diagram.

4. An oil-in-water emulsion according to claim 1,2 or3, in which the vegetable oil forms from 10 to 30% by weight of the emulsion.

5. An oil-in-water emulsion according to any preceding claim, in which the emulsifier forms from 1 to 7% byweightofthe emulsion.

6. A process for preparing an emulsion of the type defined in any preceding claim which comprises the steps of: (i) preparing a dispersion comprising soap, water and mineral acid at a temperature of from 60 to 1 00 C, the amount of acid being sufficient to acidify only part of the soap; (ii) adding oil to this dispersion comprising soap and acidified soap, with mixing, while maintaining the temperature at a value of from 60 to 100C, to form an emulsion; (iii) cooling the emulsion and filling it into containers.

7. A process for preparing an emulsion of the type defined in any of claims 1 to 5, which comprises the steps of: (i) preparing a dispersion comprising soap, humectant, chelating agent and water by mixing at a temperature of from 80 to 90"C until all ingredients are in solution; (ii) dispersing in the solution so formed a thickening agent dispersed in a small portion of the oil while maintaining the temperature at a value of from 80 to 90"C; (iii) adding to the dispersion so obtained the mineral acid in an amount sufficient to acidify only part of the soap, together with the remainder of the oil and with anti-oxidant; (iv) mixing at a temperature of from 80 to 90"C with sufficient shear to form an emulsion; ; (v) cooling the emulsion to a temperature of not more than 50"C, preferably not more than 45"C, and adding preservative and perfume ingredients; and (vi) finally filling the finished emulsion into containers.