EP0759737A1

EP0759737A1 - Micro-emulsions

Info

Publication number: EP0759737A1
Application number: EP95921741A
Authority: EP
Inventors: Thomas Förster; Marcus Claas; Werner Seipel; Bernhard Guckenbiehl; Armin Wadle
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 1994-05-19
Filing date: 1995-05-10
Publication date: 1997-03-05
Also published as: WO1995031957A1; DE4417476A1

Abstract

Micro-emulsions of a liquid oil phase (A) consisting to the extent of over 70 wt.% of preferably only hydrocarbons or dialkyl ethers with at least 10 C atoms, can be produced, preferably using an emulsifier combination (B) of (B1) an alkyl glycoside of the formula R1O(G))x in which R1 is a linear alkyl group with 8 to 14 C atoms, G is a glycoside radical and x is its mean degree of oligomerisation and a number from 1 to 3, and (B2) a fatty acid polyol partial ester with an HLB value of under 11, of a fatty acid with 10-18 C atoms and a polyol with 2-8 hydroxyl groups. The preferred oligoglucosides are of the given formula in which R1 is a C¿8?-C12 alkyl group and (G)x is an oligoglucoside radical with a mean degree of oligomerisation x of 1 to 2. Suitable fatty acid polyol partial esters are technical glycerine or sorbitan monoesters of lauric acid, myristic acid and technical C8?-C14-cocoa butter fatty acid sections.

Description

"Microemulsions"

The invention relates to microemulsions and a process for their preparation, in which a combination of an alkyl glycoside and a fatty acid polyol ester is used as the emulsifier.

Microemulsions are optically isotropic, thermodynamically stable systems which contain a water-insoluble oil component, emulsifiers and water. The clear or transparent appearance of the microemulsions is a consequence of the small particle size of the dispersed emulsion droplets, which is essentially below 300 nm, fine particles in the range between 100 and 300 nm, brown-red in the view and bluish shimmer in the reflected light, and in the range optically clear microemulsions occur below 100 nm. The droplet size of macroemulsions is essentially over 300 nm.

Microemulsions are frequently described in the literature, but their targeted production is associated with great difficulties, since the areas of existence of the microemulsion in the oil component, water The three-phase diagram formed by this and the emulators are usually very small and the location of these areas of existence is greatly influenced by structural features of all components and all other constituents of such systems.

Because of their greater stability than macroemulsions, finer distribution of the inner phase, mostly higher effectiveness and better transdermal penetration of the active ingredients incorporated therein, microemulsions are of considerable importance in the formulation of cosmetic and pharmaceutical preparations. There is therefore a need for reliable methods of producing microemulsions.

DE-A-40 33 928 describes oil-in-water emulsions of water-insoluble oil components which contain an alkyl glucoside as emulsifier. Microemulsions of hydrocarbons are not disclosed there.

From Langmuir 9 (1993), No. 11, pages 2921-2925, the area of existence for a microemulsion of cyclohexane using alkyl glucoside as an emulsifier component and at very low emulsifier concentrations is known.

It has now been found that higher molecular weight hydrocarbons and dialkyl ethers having at least 10 carbon atoms can be converted into microemulsions with a wide range of existence if the combination of a short-chain alkyl glycoside and a fatty acid-polyol partial ester with an HLB value is used as the emulsifier below 11.

The invention accordingly relates to a microemulsion of a water-insoluble oil phase (A) in water (C), the oil phase (A) being liquid at 20 ° C. and preferably excluding more than 70% by weight. lent, consists of hydrocarbons or dialkyl ethers, each with at least 10 carbon atoms or mixtures thereof, and a combination of as emulsifier (B)

(B1 ⁾ an alkyl glycoside of the formula R ^ GJJx, in which R ^{1 is} a linear alkyl group having 8 to 14 carbon atoms, G is a glycoside residue and x whose average degree of oligomerization is a number from 1 to 3, and

(B2) a fatty acid-polyol partial ester with an HLB value below 11 consisting of a fatty acid with 10 to 18 carbon atoms and a polyol with 2-8 hydroxyl groups

is included.

Suitable oil components are preferably liquid hydrocarbons or dialkyl ethers with 10-32 carbon atoms. However, higher molecular or solid paraffins can also be used in a mixture with these as long as the mixture remains liquid at 20 ° C. Suitable hydrocarbons are e.g. n-decane, n-dodecane, n-tetradecane, n-hexadecane, isohexadecane, l, 3-di- (2-ethylhexyl) cyclohexane, triisobutene, pentapropylene and other liquid oligo-olefins and their hydration products, paraffin oils and squalane .

Suitable dialkyl ethers are e.g. Lauryl butyl ether, myristyl methyl ether, cetyl hexyl ether, di-n-octyl ether, di-n-decyl ether, decyl octyl ether, di-n-lauryl ether. The aliphatic dialkyl ethers * with 6-10 C atoms per alkyl group are particularly suitable.

Other oils, in particular those used in cosmetics, for example esters, triglycerides or fatty alcohols, can also be used as oil components. However, their proportion should not exceed 25% by weight of the water-insoluble oil phase. Alkyl glycosides (B1), their preparation and use as surface-active substances are known, for example, from DE 19 43 689 or from DE 3827 543. They are produced by reacting glucose or oligosaccharides with primary alcohols with 8 to 14 carbon atoms or by acetalizing starch with, for example, lower alcohols and re-acetalizing it with the Cβ-C ^ fatty alcohol.

With regard to the glycoside residue, both monoglycosides in which a cyclic sugar residue is glycosidically linked to the fatty alcohol and oligomeric glycosides with a degree of oligomerization of up to about 3 are suitable. Suitable alkyl glycosides for the preparation of the microemulsion according to the invention are those of the general formula R * 0 - (G) _x , in which R ^{1 is} an aliphatic radical of a primary fatty alcohol having 8 to 14 C atoms and (G) _{x is} an oligoglucoside radical with a medium one Degree of oligomerization x is from 1 to 3. Oligoglucosides of the aforementioned general formula are particularly preferred, in which R * denotes a linear alkyl group with 8 to 12 C atoms and (G) _x denotes an oligoglucoside residue with an average degree of oligomerization x of 1 to 2. It can also be technical mixtures with small amounts of C _j ö-alkyl glycosides. The average degree of oligomerization results from the molar proportions of the individual oligomers by dividing the sum of the structural units by the sum of the molecules (cf. Principles of Polymer Chemistry, Paul J. Flory, Cornell University Press, Ithaca, New York 1953, page 35-36).

Fatty acid-polyol partial esters (B2) suitable as lipophilic co-emulsifiers are preferably the monoesters or the technical mixtures of monoesters, diesters and free polyol obtained by esterifying the polyols with 1-2 moles of fatty acid or by transesterifying the polyols with 1-2 moles of fatty acid methyl ester suitable. Examples of suitable polyols are propylene glycol, glycerol, erythritol, triethylolpropane, pentaerythritol, sorbitol, diglycerol, aldoses such as glucose or mannose, ketoses such as fructose or disaccharides such as sucrose, maltose or lactose or alkylglycosides, for example methylglucoside, butylglucoside or laurylglucoside, with an average degree of oligomerization of 1-2. Suitable fatty acid polyol partial esters are, for example, the technical ones Glycerol or sorbitan monoesters of lauric acid, myristic acid or of technical coconut fatty acid C8-Ci4 cuts. Sorbitan monolaurate and lauric acid onoglyceride are preferably used. Other suitable fatty acid-polyol partial esters are, for example, triglycerol diisostearate, methylgucoside sesquistearate, laurylglucoside monolaurate.

The HLB value of such fatty acid-polyol partial esters can be calculated using the formula

HLB = ____________

where L is the proportion of alkyl or acyl groups in% by weight of the molecular weight.

The emulsifier combination (B) is preferably used in an amount of 0.2-0.5 parts by weight per part by weight of the oil phase (A). For microemulsions which are said to be highly dilutable without changing the particle size, higher amounts of up to 1.5 parts by weight per part by weight of the oil component may be required.

The quantitative ratio of emulsifier (alkyl glycoside) to co-emulsifier (fatty acid-polyol partial ester) can be (B1): (B2) = 1: (0.3 - 3).

The water content of the microemulsions according to the invention is preferably 0.5 to 2 parts by weight of H2O per part by weight of the oil phase. se. However, the microemulsions according to the invention can be diluted with water without changing the particle size.

The area of existence of the microemulsions according to the invention can also be expanded by dissolving electrolyte salts in the water phase, which makes microemulsions with a particularly high water content accessible. Suitable electrolyte salts are, in particular, the ammonium, alkali and alkaline earth halides and the ammonium, alkali and magnesium sulfates and hydrogen sulfates, preferably in an amount of 0.02 to 2% by weight of the water phase. Suitable electrolytes are e.g. Sodium chloride, sodium sulfate, magnesium chloride, ammonium chloride and ammonium sulfate.

Ionic surfactants can also be incorporated into the microemulsions according to the invention without the transparency and the particle size being impaired. Water-soluble ionic surfactants in an amount of up to about 0.2 part by weight, based on 1 part by weight of the oil phase, are preferably suitable for this. Suitable anionic surfactants are e.g. Cio-Ciö fatty alcohol sulfate salts, fatty alcohol polyglycol ether sulfate salts, acyl isethionate salts, acyl acid salts, sulfosuccinic acid monoester salts, soaps, fatty acid oligopeptide condensates (amide soaps) and fatty acid monoglyceride surfactants, sulfate compatible and other skin compatible sulfate anionics preferably in the form of their water-soluble ammonium, alkanolammonium, alkali or magnesium salts. In addition, amphoteric, zwitterionic and cationic surfactants are also suitable.

The microemulsions according to the invention are suitable as carriers for a large number of cosmetic or pharmaceutical active ingredients, but, owing to the clearly solubilized oil component, also as skin care lotion or make-up removal lotion. By incorporating the high-foaming, anionic surfactants, the microemulsions according to the invention are converted into cosmetic cleaning agents which are of interest from an application point of view, for example of the type of foam bath and shower bath preparations, liquid soaps and body cleaning solutions which, owing to the stable and clearly solubilized oil components, have a particularly good skin and have mucosal compatibility.

The microemulsions according to the invention are prepared by mixing the components and simply stirring, e.g. using conventional emulsifying and homogenizing devices. The water-soluble components, e.g. the alkylglycoside (B1) as a concentrated solution in part of the water and the oil-soluble components, e.g. the fatty acid-polyol partial glyceride (B2) dissolved in the oil phase and the phases mixed in the usual way. Ionic surfactants and the remaining amount of water are then added with stirring. The use of heat is not necessary here, at most heat must be added to accelerate the dissolution of solid components.

In addition to the constituents mentioned, the microemulsions according to the invention can contain customary auxiliaries and additives, e.g. Contain dyes, preservatives, fragrances and buffer substances for pH adjustment without the microemulsion form being disturbed.

In the following examples, the transparency (optical transmission) was determined using a Mettler photometer, model 662.

The mean particle size was determined on the principle of quasi-elastic light scattering using a Zetasizer 3 (from Malvern). Examples

Nonionic microemulsions

Table I

n-decane 45 n-dodecane - 45 45 45 - n-tetradecane - - - - - n-hexadecane - - - - 45

Plantaren 1200 (1) 6 5 6 5 5

Sorbitan monolaurate 4 5 - - 5

Glycerol monolaurate - - 4 5 -

Water (+ citric acid up to pH = 6 45 45 45 45 45

Transparency (% at 650 nm) 66 36 56 70 23 Table II

8 10 11 12

1,3-di (2-ethylhexyl) cyclohexane

»45 35 32.3 45.9 16.72 19.0 23.7

Plantaren 1200 (1) 5 10 5.7 3.2 8.36 2.85 2.96 sorbitan monolaurate 5 10 10.9 5.6 12.0 - - glycerol onolaurate - - - - - 5.75 7.10 fatty alcohol ether sulfate (3) - - 1.9 0.8 2.79 3.50 4.44 water (+ citric acid to pH = 6 45 45 - - - 68.9 61.8 water + 1% by weight NaCl - - 48 .8 44.0 60.13 - -

Transparency (% at 650 nm) 42 42 81 14 59 12 12

Table III

13 14 15 16

1,3-di- (2-ethylhexyl) cyclohexane 35 11.6 7 3.5 3.5

»

Plantaren 1200 (1) 10 3.3 2 1.0 1.0 Sorbitan ono1aurat 10 3.3 2 1.0 1.0 Cχ2_i4 fatty alcohol + 2.5 E0 (narrow ranks ethoxylate) _ _ _ _ 1.8 fatty alcohol ether sulfate (3) - - - - 9.0 water (+ citric acid to pH - 6 45 81.7 89 94.5 83.7

Transparency (% at 650 n) 42 63

average particle size (nm) 271 255 226 158 79

Table VI

17 18 19 20 21 22 23

n-hexadecane 45 l, 3-di- (2-ethylhexyl) cyclohexane 35

Di-n-octyl ether 32 30 35 35 35 n-decyl oleate 5

Perfume oil 3

Plantaren 1200 10 10

Sorbitan monolaurate 10 10

Glycerol monolaurate 10 10 10 10

Lauryl glucoside monolaurate zwitterionic surfactant (4) cationic surfactant (5)

Water 45 45 45 45 45 45 45

Transparency (% at 650 nm) 85 45 40 35.6 40 84.3 83.6

Preparation of the microemulsions

Oil components and nonionic emulsifiers (alkyl glycoside, fatty acid polyol esters) were mixed at 40 ° C. Water, citric acid (up to pH = 6) and possibly table salt and possibly ionic surfactant were also mixed. The phases were heated to 40 ° C., then the oil phase was emulsified into the aqueous phase with stirring. Homogeneous, optically isotropic microemulsions were formed. Small proportions of coarser emulsion particles (100 - 300 nm) can cause a sharp decrease in transparency (measured as transmission at 650 nm).

Emulsions No. 13-15 were obtained by diluting emulsion No. 7 with water, emulsion No. 16 by diluting emulsion No. 7 with a shampoo.

The following raw materials were used:

(1) Plantaren 1200: alkyl (Ci2-i6) oligo (1,4) glucoside

(2) Plantaren 2000: alkyl (C8_i6) oligo (1,4) glucoside

(3) Fatty alcohol ether sulfate: alkyl (Ci2_i4) poly (2) glycol ether sulfate, sodium salt

(4) zwitterionic surfactant: N-Cβ-iβ-cocosamidopropyl-dimethyl-ammonium-acetobetaine

(5) Cationic surfactant: cetyl trimethyl ammonium chloride

The figures in the tables relate to% by weight of water-free active substance.

Claims

1. Microemulsion of a water-insoluble oil phase (A) in water (C), characterized in that the oil phase (A) is liquid at 20 ° C and more than 70 wt .-%, preferably exclusively, from hydrocarbons or dialkyl ethers each consists of at least 10 carbon atoms or mixtures thereof and a combination of as emulsifier (B)

(B1) an alkyl glycoside of the formula R10 (G)) _x , in which R is a linear alkyl group having 8 to 14 carbon atoms, G is a glycoside residue and x whose average degree of oligomerization is a number from 1 to 3, and

is included.

2. Microemulsion according to claim 1, characterized in that the water phase is a dissolved electrolyte salt from the group of ammonium, alkali and alkaline earth metal halides and ammonium, alkali and magnesium sulfates and hydrogen sulfates in an amount of 0.02 - Contains 2% by weight of the water phase.

3. Microemulsion according to claim 1 or 2, characterized in that a water-soluble ionic surfactant is additionally present in an amount of up to 0.2 part by weight, based on 1 part by weight of the oil phase.

4. A process for the 'preparation of a microemulsion according to any one of claims 1-3, characterized in that the water-soluble components, e.g. the alkyl glycoside (B1) in water, the oil-soluble components, e.g. the fatty acid-polyol partial glyceride (B2) dissolves in the oil phase and the phases are mixed intensively.