Colloid systems and wetting agents; subcombinations thereof; pro – Continuous liquid or supercritical phase: colloid systems;... – Aqueous continuous liquid phase and discontinuous phase...
Reexamination Certificate
2001-07-20
2003-07-01
Lovering, Richard D. (Department: 1712)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous liquid or supercritical phase: colloid systems;...
Aqueous continuous liquid phase and discontinuous phase...
C424S070190, C424S070210, C516S027000, C516S028000, C516S029000, C516S070000, C516S925000
Reexamination Certificate
active
06586479
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to fine emulsions comprising sorbitol esters, and to a process for the preparation of such fine emulsions.
DESCRIPTION OF THE RELATED ART
Fine emulsions or microemulsions are low-viscosity, optically transparent dispersions of two immiscible liquids which are stabilized by at least one ionic or nonionic surfactant. In the case of fine emulsions, the particle diameters are in the range from about 0.1 to 10 micrometers. The interfacial tension between the two phases is extremely low.
The viscosity of many fine emulsions of the O/W type is comparable with that of water.
In contrast to fine emulsions, “macroemulsions” have high viscosities and their particle diameter is in the range from about 10 to 100 micrometers. Macroemulsions are milky white in color and, upon heating, tend toward phase separation or toward sedimentation of the dispersed substances.
Sprayable emulsions call for low viscosities (about 100 mPas), as are realizable in the case of fine emulsions even at room temperature.
With regard to cosmetic and pharmaceutical applications, spray emulsions have decisive advantages over the classic emulsions formulated as lotions, creams or ointments. For example, spray emulsions impart a pleasant feel to the skin, can be readily dosed and are protected against contamination.
According to the prior art, fine emulsions can be prepared by the “hot/hot process”. In the “hot/hot process”, the fatty phase is heated to about 75° C., melted completely and combined with the water phase, likewise at about 75° C., using an extremely high input of mechanical energy in order to ensure rapid dispersion and to achieve high fineness of the system. This process requires high thermal and mechanical energy expenditure.
A second process, the “phase inversion temperature (PIT) process” makes it possible to dispense with intensive mechanical dispersion operations. The “phase inversion temperature process” is based on the fact that the O/W character of a hydrophilic, nonionic surfactant decreases with increasing temperature and converts to the W/O type at a certain conversion temperature. Upon cooling, conversion back to the O/W type takes place. The conversion temperature is referred to as the “phase inversion temperature (PIT)”. In the preparation of the emulsion, the procedure involves dissolving the actually hydrophilic emulsifier above its PIT in a preferably polar oil phase and emulsifying it with the water phase. Upon cooling, a transparent microemulsion is firstly traversed, then highly disperse, low-viscosity formulations form without a homogenization step.
A disadvantage of the PIT process is that it is limited to ethoxylated surfactants which display a sufficiently high temperature dependency of their hydrophilic/lipophilic properties.
The use of ethoxylated surfactants for cosmetic and pharmaceutical uses is, however, problematic since they are suspected of making the skin permeable to harmful substances and of forming undefined, possibly harmful substances under the action of UV.
Accordingly, it was an object of the invention to develop fine emulsions which can be prepared without the use of ethoxylated products and without high thermal and/or mechanical energy expenditure.
SUMMARY OF THE INVENTION
Surprisingly, it has been found that fine emulsions comprising at least one W/O emulsifier and at least one hydrophilic component can be prepared without the use of ethoxylated products and without high thermal and/or mechanical energy expenditure.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention thus provides fine emulsions comprising at least one W/O emulsifier and at least one hydrophilic component.
The particle size of the fine emulsions according to the invention is preferably in the range from 0.1 to 10 micrometers.
The fine emulsions preferably comprise 0.01 to 10% by weight, particularly preferably 0.1 to 8% by weight and especially preferably 0.2 to 4% by weight, of W/O emulsifiers.
The fine emulsions preferably comprise 0.01 to 10% by weight, particularly preferably 0.1 to 7% by weight and especially preferably 0.3 to 5% by weight, of hydrophilic components.
The nonaqueous fraction of the fine emulsions, which is largely composed of the W/O emulsifiers and the oily substance, is preferably 0.1 to 95% by weight and particularly preferably 0.5 to 45% by weight.
The fine emulsions are preferably those obtainable by converting a W/O preemulsion comprising at least one W/O emulsifier into an O/W fine emulsion by adding at least one hydrophilic component and, where appropriate, changing the temperature.
The conversion of the W/O preemulsion into the O/W fine emulsion preferably takes place without increasing the temperature.
As W/O emulsifiers, preference is given to using sorbitol esters, polyglycerol esters, sorbitan esters, fatty acid esters and/or dimethicone copolyols. Particularly preferred W/O emulsifiers are the sorbitol esters.
Preference is giving to using sorbitol esters obtainable by transesterifying sorbitol, optionally alkoxylated sorbitol, with fatty acid methyl esters or fatty acid triglycerides, the reaction products obtained by transesterification then optionally being alkoxylated. In the case of alkoxylated sorbitol as reaction product, this is preferably ethoxylated sorbitol. The content of ethoxylate groups is preferably 1 to 90 —CH
2
CH
2
O— groups per molecule of sorbitol. The alkoxylation of the sorbitol can be carried out by processes known to the person skilled in the art.
However, during the transesterification of sorbitol with fatty acid methyl esters, the procedure preferably involves firstly carrying out the transesterification with sorbitol and then alkoxylating the reaction product by known processes. The fatty acid radicals of fatty acid methyl esters and fatty acid triglycerides are preferably (C
8
-C
22
) radicals which are straight-chain and/or branched and saturated and/or unsaturated. Examples thereof are palmitic acid, stearic acid, lauric acid, linoleic acid, linolenic acid, isostearic acid or oleic acid. Examples of suitable fatty acid triglycerides are native animal or vegetable oils, fats and waxes, such as, for example, rapeseed oil, olive oil, palm kernel oil, sunflower oil, coconut oil, linseed oil, castor oil, soybean oil, optionally also in refined or hydrogenated form. Since the natural fats, oils and waxes normally comprise mixtures of fatty acid radicals of varying chain length, this applies correspondingly also to the sorbitol esters prepared therefrom.
For cosmetic and pharmaceutical applications, sorbitol esters based on rapeseed oil are particularly suitable.
The preparation of the sorbitol esters from fatty acid methyl esters or fatty acid triglycerides can be carried out according to DE 197 27 950 and EP-A-1029586.
The reaction of sorbitol with the fatty acid triglycerides or methyl esters is preferably carried out in a one-pot process without solvents at temperatures of, preferably, 120-140° C. in the presence of an alkaline catalyst. The molar ratio of sorbitol to fatty acid methyl ester is preferably 1:1 to 1:2. If fatty acid triglycerides are used, the molar ratio of sorbitol to fatty acid triglyceride is 1:3.5 to 1:4.5. The reaction time is preferably 12 to 13 hours.
If fatty acid methyl esters are used, the methanol which forms during the reaction is distilled off. Since sorbitol is usually commercially available as an aqueous solution, the water is advantageously removed prior to use by distillation at a maximum 120° C. under reduced pressure.
As well as containing residual amounts of unreacted sorbitol, the reaction product of this transesterification reaction essentially consists of the sorbitol monofatty acid esters and the sorbitol difatty acid esters. The corresponding triesters are formed only in minor amounts. If fatty acid triglycerides are used as starting material, the reaction product also comprises mono- and difatty acid glyceride and unreacted triglyceride, depending on the molar ratio of the starting compounds chosen in each case.
The hydrophobic/hydrophil
Henning Torsten
Johannpeter Wiebke
Miller Dennis
Wiener Eva-Maria
Clariant GmbH
Lovering Richard D.
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