Note: Descriptions are shown in the official language in which they were submitted.
PATENT
1 334458 Docket D 7898
PROCE88 FOR FORMING LOW-VI8CO8ITY ENUL8ION8 OF POLAR OIL8
IN WATER
Field of the Invention
This invention relates to a process for the production
of oil-in-water emulsions of polar oil components contain-
ing one or more ester functions in the molecule, or of mix-
tures of such polar oils with relatively small quantitiesof nonpolar hydrocarbons, under conditions which lead to
particularly stable low-viscosity emulsions.
Statement of Related Art
It is known that oil-in-water emulsions prepared and
stabilized with nonionic emulsifiers undergo phase inver-
sion on heating, i.e. the continuous or outer aqueous phase
can become the dispersed or inner phase at relatively high
temperatures. This process is generally reversible, i.e.
the original emulsion type is reformed again on cooling.
It is also known that the temperature of the phase
inversion is dependent on many factors, for example on the
type and phase volume fraction of the oil component and on
the hydrophilicity and chemical structure of the emulsifier
or mixtures of emulsifiers; cf. for example K. Shinoda and
H. Kunieda in Encyclopedia of Emulsion Technology, Vol. 1,
ed. P. Becher 1983 (M. Decker, N.Y.), pages 337 - 367. It
is also known that emulsions prepared at or just below the
phase inversion temperature are distinguished by particular
fineness and stability while those prepared above the phase
inversion temperature are less finely divided (cf. S.
Friberg, C. Solans, J. Colloid Interface Sci., 66, 367 -
368 (1978)).
F. Schambil, F. Jost and M. J. Schwuger report in
"Progress in Colloid & Polymer Science 73, (1987), 37 - 47
on the properties of cosmetic emulsions containing
aliphatic alcohols and aliphatic alcohol polyglycol ethers
1 33445`8
and also state that emulsions prepared above the phase
inversion temperature show relatively low viscosity and
high stability in storage.
However, the publications cited above are concerned
only with emulsions of which the oil phase consists com-
pletely or predominantly of nonpolar hydrocarbons. By con-
trast, corresponding emulsions in which the oil component
consists completely or predominantly of polar esters and
triglycerides do not show any phase inversion at temper-
atures below 100C, when emulsifiers or emulsifier
combinations known for such purposes in the prior art are
used.
Accordingly, an object of the present invention is to
provide an emulsifier system for completely or pre-
dominantly polar oil components which makes it possible to
produce emulsions which invert at temperatures below 100C
and which can thus be converted into particularly stable
low-viscosity emulsions.
Description of the Invention
The present invention comprises a process for the
production of low-viscosity oil-in-water emulsions of an
oil component (A) which consists of
(A.l) 50 to 100% by weight of mono- or di-ester
molecules that contain at least 10 carbon atoms
and that correspond to one of the formulae (I)
R1COOR2, (II) R2ooc-R3-cooR2~ and (III) R1Coo-R3-
OOCR1, in which each of R1 and R2 independently
represents a C122 alkyl group or C822 alkenyl
group, and R3 represents a C216 alkylene group;
and, optionally,
(A.2) 0 to 50% by weight of aliphatic acid
triglycerides of C8 22 aliphatic acids; and,
optionally,
(A.3) 0 to 25% by weight of hydrocarbon molecules,
characterized in that the oil component (A) and an amount
of water having a mass at least equal to the mass of the
oil component (A) are made into an emulsion with the aid
~ of 1 334458
0.1 to 0.5 part by weight - per part by weight of the
oil component - of a primary emulsifier component (B)
having an HLB value of 11 to 12 and consisting of
molecules selected from the group of;
(B.l) adducts of ethylene oxide with C1622
aliphatic alcohols and
(B.2) adducts of ethylene oxide with partial
esters of C36 polyols with C1422 aliphatic
acids;
and, preferably, also with the aid of 0.1 to 0.5 part
by weight - per part by weight of the oil component -
of a co-emulsifier component (C) consisting of
molecules selected from the group of:
(C.l) saturated C1622 aliphatic alcohols and
(C.2) partial esters of C36 polyols with saturated
C1422 aliphatic acids,
said emulsion being made at a temperature above the melting
point of the mixture of water, oil component (A),
emulsifier (B), and co-emulsifier (C) if used, and that the
emulsion is heated to, or is prepared at, a temperature
within or above the phase inversion temperature range of
the mixture, after which the emulsion is cooled to a
temperature below the phase inversion temperature range
and, optionally, further diluted with water.
Within the compositions defined above and under the
working conditions mentioned, emulsions of the polar oil
component selected from the monoesters and diesters men-
tioned show a phase inversion below 100C, so that particu-
larly stable, finely divided, and low-viscosity emulsions
can also be prepared with these polar oil components under
practical conditions by the described process.
Oil components selected from the monoesters and di-
esters of formulae I, II and III are known as cosmetic and
pharmaceutical ingredients and also as lubricant compon-
ents. Among the monoesters and diesters of this type,
those which are liquid at room temperature (20C) are the
1 334458
most important. Monoesters (I) suitable as oil components
are, for example, the methyl and isopropyl esters of C1222
aliphatic acids such as, for example, methyl laurate,
methyl stearate, methyl oleate, methyl erucate, isopropyl
palmitate, isopropyl myristate, isopropyl palmitate,
isopropyl stearate, isopropyl oleate. Other suitable
monoesters are, for example, n-butyl stearate, n-hexyl
laurate, n-decyl oleate, isooctyl stearate, isononyl
palmitate, isononyl isononanoate, 2-ethyl hexyl palmitate,
2-ethyl hexyl laurate, 2-hexyl decyl stearate, 2-octyl
dodecyl palmitate, oleyl oleate, oleyl erucate, erucyl
oleate, and also esters obtainable from technical aliphatic
alcohol mixtures and technical aliphatic carboxylic acids,
for example esters of saturated and unsaturated C1222
aliphatic alcohols and saturated and unsaturated C1222
aliphatic acids, of the type obtainable from animal and
vegetable fats. Naturally occurring monoester and wax
ester mixtures, of the type present for example in jojoba
oil or in sperm oil, are also suitable.
Suitable dicarboxylic acid esters (II) are, for
example, di-n-butyl adipate, di-n-butyl sebacate, di-(2-
ethylhexyl)-adipate, di-(2-hexyldecyl)-succinate and diiso-
tridecyl azelate. Suitable diol esters (III) are, for
example, ethylene glycol dioleate, ethylene glycol diiso-
tridecanoate, propylene glycol di-(2-ethylhexanoate), bu-
tanediol diisostearate and neopentyl glycol dicaprylate.
Suitable aliphatic acid triglycerides are natural
vegetable oils, for example olive oil, sunflower oil,
soybean oil, peanut oil, rapeseed oil, almond oil, palm
oil, and also the liquid fractions of coconut oil or palm
kernel oil, and also animal oils, such as for example
neat's foot oil, the liquid fractions of beef tallow, or
even synthetic triglycerides of the type obtained by
esterification of glycerol with C822 aliphatic acids, for
example triglycerides of caprylic acid/capric acid
mixtures, triglycerides of technical oleic acid or of
palmitic acid/oleic acid mixtures.
- ~ 334458
As stated above, monoesters and diesters and trigly-
cerides which are liquid at normal temperature (20C) are
preferable as oil components for the process according to
the invention, although higher-melting fats and esters
corresponding to the above formulae may also be used,
preferably in such quantities that the total mixed oil
component remains liquid at normal temperature.
The oil component may also contain hydrocarbon oils in
quantities of up to at most 25~ by weight, based on the
total oil component. Suitable hydrocarbons are,
especially, paraffin oils and synthetic hydrocarbons, for
example liquid polyolefins, or specific hydrocarbons, for
example alkyl cyclohexanes, such as for example 1,3-
diisooctyl cyclohexane.
Some nonionic ethylene oxide adducts with C1622
aliphatic alcohols suitable as primary emulsifiers (B) are
commercially available. The technical products are
mixtures of homologous poly(oxyethylene) ethers of the
starting aliphatic alcohols, in which the average degree of
ethoxylation corresponds to the molar quantity of ethylene
oxide added on per mole of starting alcohol. Other
suitable emulsifiers are ethylene oxide adducts with
partial esters of any C36 polyol and any C1422 aliphatic
acid. Products such as these may be obtained, for example,
by ethoxylation of glycerol monostearate, glycerol
monopalmitate or of mono- and di-aliphatic acid esters of
sorbitan, for example sorbitan monostearate or sorbitan
sesquioleate. Emulsifiers suitable for the process
according to the invention should have an HLB value of 11
to 12. The HLB (hydrophilic-lipophilic balance) is a value
which may be calculated in accordance with the following
equation: HLB = (100 - L)/5, in which L is the percent by
weight of lipophilic groups, i.e. the aliphatic alkyl or
aliphatic acyl groups, in the ethylene oxide adducts.
Preferred emulsifiers are adducts of 8 to 12 moles of
ethylene oxide with one mole of saturated C1622 aliphatic
alcohols. Adducts of 8 to 12 moles of ethylene oxide with
1 334458
a molar amount of saturated C20-C22 aliphatic alcohol are
particularly preferred as emulsifiers for the
emulsification in accordance with the invention of oil
components which contain no apolar hydrocarbon oils, i.e.
which consist of 50 to 100% by weight monoesters and
diesters of formulae I, II and III and O to 50% by weight
aliphatic acid triglycerides.
In many cases, a co-emulsifier (C) is preferably used
in addition to the primary emulsifier for preparing the
oil-in-water emulsions by the process according to the
invention. On account of its hydrophilicity, the co-
emulsifier is not suitable on its own for the preparation
of oil-in-water emulsions, even though particularly stable
and finely divided emulsions of the polar oil components
may be prepared in conjunction with the use of both types
of emulsifiers defined above. According to the invention,
suitable co-emulsifiers are those of the saturated C1622
aliphatic alcohol type, for example cetyl alcohol, stearyl
alcohol, arachidyl alcohol, behenyl alcohol, or mixtures of
these alcohols such as are obtained in the technical
hydrogenation of vegetable and animal C16-C22 aliphatic acids
or the corresponding aliphatic acid methyl esters. Other
suitable co-emulsifiers are partial esters of a C36 polyol
and saturated C1422 aliphatic acids. Partial esters such as
these are, for example, the monoglycerides of palmitic
and/or stearic acid, the sorbitan mono- and/or diesters of
myristic acid, palmitic acid, stearic acid, or of mixtures
of these aliphatic acids, the monoesters of tri-
methylolpropane, erythritol or pentaerythritol and satur-
ated C1422 aliphatic acids. Other suitable monoesters are
the technical monoesters which are obtained by
esterification of 1 mole of polyol with 1 mole of aliphatic
acid and which represent a mixture of monoester, diester,
and unesterified polyol.
Cetyl alcohol, stearyl alcohol, or a glycerol, sorbi-
tan, or trimethylolpropane monoester of a saturated C1422
aliphatic acid, or mixtures thereof, are preferred as co-
' 334458
`- emulsifiers for the process according to the invention.
To obtain particularly preferred low-viscosity
emulsions with the oil components (A), emulsifiers (B) and
co-emulsifiers (C) specified above by the process according
to the invention, these components have to be used in
relatively closely defined quantitative ratios. A ratio by
weight of A to B to C of 1 : 0.1 - 0.3 : 0.1 - 0.3 is
preferred, a ratio by weight of A to B to C of l : 0.2 :
0.15 being more preferred.
The process according to the invention may be carried
out after initially determining the phase inversion temper-
ature, by heating a sample of the emulsion prepared in the
usual way at or near room temperature, using a conductivity
measuring instrument and determining the temperature at
which there is a pronounced reduction in conductivity. The
specific conductivity of the oil-in-water emulsion
initially present normally decreases from initial values of
more than 1 millisiemens per cm (mS/cm) to values below 0.1
mS/cm over a temperature range of 2 to 8C. This
temperature range is referred to herein as the phase
inversion temperature range.
Once the phase inversion temperature range of the
mixture of components needed for a particular emulsion to
be made according to this invention is known, the process
according to the invention may be carried out either by
heating an emulsion initially prepared at a lower
temperature to a temperature lying within or above the
phase inversion temperature range or by preparing the
emulsion at a temperature lying within or above the phase
inversion temperature range. After exposure to a
temperature within or above the phase inversion temperature
range, the mixture is cooled below that temperature range
as part of the process of forming the final emulsion.
The oil-in-water emulsions prepared by the process
according to the invention are extremely finely divided and
stable. It is particularly noticeable that the emulsions
prepared in accordance with the invention have a consider-
`1 334458
ably lower viscosity than emulsions prepared by the conven-
tional process.
Accordingly, it is also possible by the process ac-
cording to the invention to produce emulsions of polar oil
components of low viscosity and distinctly increased sta-
bility which, hitherto, could only be produced from
nonpolar hydrocarbons.
Oil-in-water emulsions of the type obtained by the
process according to the invention are useful, for example,
as skin-care and body-care preparations, as cooling lubri-
cants, or as fabric and fiber finishes. The process ac-
cording to the invention is particularly useful for the
production of emulsion-like preparations for skin and hair
treatment purposes. The following Examples are intended to
illustrate the invention without limiting it in any way.
EXAMPLES
1. Preparation of the emulsions (general procedure)
The oil components, emulsifiers and co-emulsifiers
were mixed, heated to a temperature above the melting point
of the mixture, and homogenized. The melt was then emulsi-
fied while stirring in the water, which had been heated to
approximately the same temperature. The compositions of
the emulsions are shown in Table I.
2. Determination of the phase inversion temperature
Using a conductivity measuring bridge (of a type made
by the Radiometer company of Copenhagen), the electrical
conductivity of the emulsions was measured as a function of
temperature. To this end, each emulsion was initially
cooled to +20C. At this temperature, the emulsions showed
a conductivity of more than 1 millisiemens per cm (mS/cm),
indicating that they were present as oil-in-water emul-
sions. A conductivity chart was determined by slowly
heating, at a rate of approximately 0.5C/minute under the
control of a temperature programmer, a sample of the
emulsion contained in a thermally insulated vessel. The
temperature range in which the conductivity fell from a
value of at least 1 mS/cm to a value below 0.1 mS/cm
1 334458
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1 334458
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~ 334458
~- wasrecorded as the phase inversion temperature range.
With all the emulsions shown in Table I, this temperature
range was below 100C (See Table II, phase inversion
values).
3. Preparation of the emulsions in accordance with the
invention
The emulsions were prepared as described in 1. and
then briefly heated (for about 1 minute) to a temperature
in, or slightly above, the phase inversion temperature
range. (See Table II, production temperature values.)
The emulsions were then rapidly cooled with stirring to
room temperature at a cooling rate of approximately 2OC
per minute. After storage for 1 hour at 20C, the
viscosity was measured using a rotational viscosimeter
(Brookfield type LVT).
4. Comparison Tests
For comparison, the emulsions were prepared as des-
cribed in part 1, but were heated only to a temperature
below the phase inversion temperature range. (See Table
II, production temperature values). Cooling was carried
out under the same conditions as in part 3.
5. Result
The results of processing in accordance with the in-
vention and of the Comparison Tests are shown in Table II
for the formulations according to Table I. Processing in
accordance with the invention by the process described in
part 3 always gave stable, low-viscosity liquid oil-in-
water emulsions. By contrast, the Comparison Tests gave
oil-in-water emulsions of relatively high viscosity and,
in some cases, of relatively low stability.
The embodiments of the invention in which a
proprietary or exclusive right is claimed are:
