Process for producing small droplet emulsions at low pressure

Abstract

The present invention relates to novel process for making oil-in-water nanoemulsions. The oil phase contains oil selected from the group consisting of triglyceride oil and/or petrolatum and a C.sub.8 to C.sub.16 fatty acid just be added during preparation; and the aqueous phase contains specific N-acyl derivatives of carboxylic amino acid as primary emulsifier.

Claims

1. A process for making a nanoemulsion composition comprising: a) an internal phase comprising (i) 55 to 75% by wt. of total nanoemulsion composition of oils selected from the group consisting of triglyceride, petrolatum and mixtures thereof, wherein the melting point of the petrolatum is 30 to 60° C.; and (ii) 1.1 to 8% by wt. nanoemulsion of a C.sub.8 to C.sub.18 fatty acid; and b) an external aqueous phase comprising 2 to 15% by wt. of total nanoemulsion composition of a surfactant or surfactants which are N-acyl derivatives of amino acid salt; wherein the surfactant of (b) comprises 50% or greater of all surfactant present in said external aqueous phase; wherein the volume average diameter of droplets of (a) is 20 to 600 nanometers, wherein said process comprises: 1) adding the C.sub.8 to C.sub.18 fatty acid of component (a)(ii) to oil of (a)(i); 2) heating oil phase (a) to a sufficient temperature so that all compounds are molten; and 3) Heating the aqueous phase to a temperature range of 45 to 75° C.; and 4) Simultaneously pumping the heated aqueous and oil phases via a sonolator or a conventional homogenizer using process pressure of 500 pounds per square inch (psi) or less.

2. The process according to claim 1, wherein said surfactant or surfactants are selected from the group consisting of (i) salt of N-acyl derivatives of dicarboxylic amino acid, wherein greater than 65% to 100% of the acyl group has chain length of C.sub.14 or less; and (ii) salt of N-acyl derivatives of monocarboxylic amino acid, wherein 65% to 100% of the acyl group has chain length C.sub.14 or less; and (iii) mixtures thereof.

3. The process according to claim 2, wherein the N-acyl derivative of dicarboxylic amino acid is a salt of acylglutamic acid, salt of acylaspartic acid or mixture thereof.

4. The process according to claim 2, wherein the salt of N-acyl derivative of monocarboxylic amino acid is a salt of acylglycinate, salt of acylalaninate or mixture thereof.

5. The process according to claim 1, wherein volume average diameter of the droplets is 100 to 500 nm.

6. The process according to claim 1, wherein volume average diameter of droplets is 70 to 400 nm.

7. The process according to claim 1, wherein the oil is a triglyceride oil and said triglyceride oil is selected from the group consisting of soybean oil, sunflower seed oil, coconut oil, rapeseed oil, palm oil, palm kernel oil, grape seed oil, fish oil and mixtures thereof.

8. The process according to claim 1, wherein the oil is petrolatum and the melting point of the petrolatum is 30 to 60° C.

9. The process according to claim 1, wherein the oil mixture is a mixture of triglyceride oil and petrolatum.

10. The process according to claim 1, wherein the fatty acid having a chain length C.sub.8-C.sub.18, is selected from the group consisting of lauric acid, myristic acid, coconut fatty acid and their mixtures, most preferably, lauric acid.

11. The process according to claim 1, wherein the fatty acid is at least 1.5 to 8% by wt. of total nanoemulsion.

12. The process according to claim 1, wherein the salts of acylglutamate acylaspartate, acylglycinate, and acylalaninate are sodium and/or potassium salts.

13. The process according to claim 1, wherein the nanoemulsion is prepared at pressure from a homogenizer or sonolator and said pressure is 150 to 450 psi.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) Except in the examples, or where otherwise explicitly indicated, all numbers in this description indicating amounts of material or conditions of reaction, physical properties of materials and/or use are to be understood as modified by the word “about.” All amounts are by weight of the final composition, unless otherwise specified.

(2) It should be noted that in specifying any range of concentration or amount, any particular upper concentration can be associated with any particular lower concentration or amount.

(3) For the avoidance of doubt, the word “comprising” is intended to mean “including” but not necessarily “consisting of” or “composed of.” In other words, the listed steps or options need not be exhaustive.

(4) The disclosure of the invention as found herein is to be considered to cover all embodiments as found in the claims as being multiply dependent upon each other irrespective of the fact that claims may be found without multiple dependency or redundancy.

(5) The present invention provides a novel process for making nanoemulsions containing a specific selection of oils and surfactants. The nanoemulsions can be prepared using processing pressure of 500 psi or less. The novel nanoemulsions are ideally suited for use in liquid cleansing compositions, for example, structured (e.g., micellar or lamellar structured) liquid cleansing compositions.

(6) The nanoemulsions of the invention are defined with more particularity below.

Oil Phase

(7) Oils in the oil phase of the nanoemulsions may be triglyceride oil or oils (animal and/or vegetable oils); petrolatum; or mixtures of one or more triglyceride oil.

(8) Examples of triglyceride oils which may be used include soybean oil, sunflower seed oil, coconut oil, rapeseed oil, palm oil, palm kernel oil, grape seed oil and fish oil. Soybean and sunflower seed oils are preferred triglycerides.

(9) The oil in the oil phase may also be petrolatum. The petrolatum preferably has a melting point ranging from 30° to about 60° C. Examples of such petrolatum oils include Vaseline® Petrolatum Jelly from Unilever, WHITE PETROLATUM USP from Calumet Penreco, Petrolatum G2212 and White Protopet® 1S from Sonneborn.

(10) The oils can range from 40% to 75% by wt. of the total nanoemulsion composition. The preferred volume average diameter of the triglyceride oil or petrolatum droplets is 100 to 600 nm, preferably 50 to 575 nm, more preferably 20 to 400 nm. Lower limit can be 20 or 50 or 100 or 125 or 150 nm; and upper limit can be 250 or 300 or 400 or 500 or 575 or 600 nm.

(11) The choice of triglyceride oils and petrolatum helps impart emolliency and occlusivity to skin when the triglyceride oils and/or petrolatum deposit onto skin after the skin is washed with fully formulated cleansing compositions into which the nanoemulsions of this invention have been incorporated.

(12) In addition to the triglyceride oil (or oils) and/or petrolatum, the oil phase may comprise oil soluble skin beneficial actives such as, for example, Vitamin A, Vitamin E, sun screen, fragrances, retinol palmitate, 12-hydroxy stearic acid, conjugated linoleic acid; antibacterial agents; mosquito repellents etc. at level of 0.01 to 5%.

(13) Another ingredient which might be found in the oil phase is an oil phase stabilizer. For example, small amounts (0.01 to 2%, preferably 0.1-1% by wt. nanoemulsion) of antioxidant may be used. When the oil used is triglyceride, a preferred antioxidant which may be used is butylated hydroxytoluene (BHT). This is often used as a food grade antioxidant.

(14) Greater than 1.0% to 8%, preferably 1.1 to 8%, more preferably 1.2 to 6% by wt. total nanoemulsion is comprised of C.sub.8 to C.sub.18, preferably C.sub.10 to C.sub.14 fatty acid. Examples of fatty acid are lauric acid, myristic acid, coconut fatty acid and their mixtures. This co-emulsifier is required to ensure low pressure can be used and still produce drops of 600 nm or less. For example, oil phase may contain petrolatum ranging from 40 to 70% by wt. of nanoemulsion and lauric acid 1.1 to 8% by wt. of nanoemulsion.

(15) The fatty acid preferably is present at level of 1.2% by wt. of nanoemulsion, or 1.3% or 1.5% or 2.0% or 2.5 or 3.0% or 3.5% or 4.0%; preferred range is 1.5 to 5.0% or 2.0 to 4.0% or 2.5 to 4.0%.

Aqueous Phase

(16) The aqueous phase contain salts of N-acyl derivatives of amino acids as primary emulsifier (50% or greater, preferably 60% or greater of all surfactant present in the aqueous phase of the nanoemulsion). Preferred emulsifiers are acylglutamate, acylaspartate, acylglycinate and acylalaninate surfactants. Preferably, these are potassium and/or sodium salts of acylglutamate or acyl aspartate or acylglycinate or acylalaninate, wherein greater than 65% of the acyl chains has chain length C.sub.14 or less, e.g., C.sub.8 to C.sub.14 (e.g., derived from coconut fatty acid). The acyl chains preferably have greater than 75%, more preferably greater than 80% C.sub.14 or less chain length. Preferably, greater than 75%, most preferably greater than 80% of the chain length are C.sub.12, C.sub.14 or mixtures thereof. These predominantly short chain acyl groups (relative to longer chain C.sub.16 and C.sub.18, for example) ensure that, when nanoemulsions of the invention are incorporated into fully formulated liquid cleansing compositions (especially structured liquid cleansing compositions), they help maintain or enhance foaming capacity.

(17) There are two formats of amino acid surfactants commercially available. One is powder or flake format, which is typically more expensive and high in purity. Examples of solid dicarboxylic amino acid surfactants include: sodium N-cocoyl-L-glutamate (e.g., Amisoft® CS-11 by Ajinomoto) sodium N-lauroyl-L-glutamate (e.g., Amisoft® LS-11 by Ajinomoto) sodium N-myristoyl-L-glutamate (Amisoft® MS-11 by Ajinomoto) potassium N-cocoacyl_I-Glutamate (e.g., Amisoft® CK-11 by Ajinomoto) potassium N-myristoyl-L-glutamate (Amisoft® MK-11 by Ajinomoto) potassium N-lauroyl-L-glutamate (Amisoft® LK-11 by Ajinomoto) Sodium Lauroyl Aspartate (AminoFoamer™ FLMS-P1 by Asahi Kasei Chemical Corporation) Sodium Lauroyl Glutamate (Aminosurfact™ ALMS-P1/S1 by Asahi Kasei Chemical Corporation) Sodium Myristoyl Glutamate (Aminosurfact™ AMMS-P1/S1 by Asahi Kasei Chemical Corporation)

(18) Examples of solid monocarboxylic amino acid surfactants include: sodium cocoyl glycinate (e.g., Amilite® GCS-11 by Ajinomoto) potassium cocoyl glycinate (e.g., Amisoft® GCK-11 by Ajinomoto)

(19) In addition to the amino acid surfactants noted above (which are in powder form and are not convenient to handle in plant production), using fatty acid as co-emulsifier permits use of amino acid surfactants in liquid form, which is typically less expensive but high in pH and inorganic salt. The use of a fatty acid as co-emulsifier, especially lauric acid, in conjunction with the industrial liquid amino acid surfactant resulted in the formation of stable emulsions and the efficient formation of smaller oil droplets to form a highly superior nanoemulsion. Oil droplet sizes below 600 nm were produced using process pressure of 500 psi or less.

(20) Liquid amino acid surfactants typically contains 20˜35% surfactant active, high in pH and inorganic salt (e.g. 3 to 6% NaCl). Examples include: AMISOFT® ECS-22SB: Disodium Cocoyl Glutamate (30% Aqueous Solution) AMISOFT® CS-22: Disodium Cocoyl Glutamate sodium Cocoyl Glutamate (25% Aqueous Solution) AMISOFT® CK-22: Potassium Cocoyl Glutamate (30% Aqueous Solution) AMISOFT® LT-12: TEA-Lauroyl Glutamate (30% Aqueous Solution) AMISOFT® CT-12 TEA-Cocoyl Glutamate (30% Aqueous Solution) AMILITE® ACT-12: TEA-Cocoyl Alaninate (30% Aqueous Solution) AMILITE® ACS-12: Sodium Cocoyl Alaninate (30% Aqueous Solution) AMILITE® GCK-12/GCK-12K: Potassium Cocoyl Glycinate (30% Aqueous Solution) Aminosurfact™ ACDS-L: Sodium Cocoyl Glutamate (25% Aqueous Solution) Aminosurfact™ ACDP-L: Potassium Cocoyl Glutamate (22%)+Sodium Cocoyl Glutamate(7%) Aminosurfact™ ACMT-L: TEA-Cocoyl Glutamate (30% Aqueous Solution) AminoFoamer™ FLDS-L: Sodium Lauroyl Aspartate (25% Aqueous Solution) In addition to Amisoft and Amilite series from Ajinomoto, Aminosurfact™ and AminoFoamer™ from Asahi Kasei Chemical Corporation), other suppliers of liquid amino acid surfactants include Clariant (e.g. Hostapon SG Sodium cocoyl glycinate), Solvay (e.g. Geropon® PCG Potassium Cocoyl Glutamate aqueous solution; Gerapon® LG 3S sodium lauryl glycinate with glycerin), Galaxy (Galsoft® KCGL Potassium Cocoyl Glutamate aqueous solution; GalSoft® SCG plus sodium cocoyl glycinate, 20% active) and Sino Lion (Eversoft® USK-30K Potassium Cocoyl Glutamate aqueous solution; Eversoft® YCS-305 sodium cocoyl glyciinate).

(21) Additionally, other mild cleansing surfactants can be used in the aqueous phase. Anionic surfactants which may be used include sodium cocoyl isethionate, sodium lauroyl isethionate, and other amino acid based surfactants, such as sodium lauroyl sarcosinate, sodium cocoyl sarcosinate. Amphoterics such as coco betaine, cocamidopropyl betaine, sodium lauroamphoacetate, Lauramidopropyl hydroxysultaine and Cocamidopropyl hydroxysultaine can also be used. These co-surfactants are typically present at a level of 50% or less, preferably 40% or less, preferably 30% or less of total surfactants in the aqueous phase of the nanoemulsion.

(22) Overall surfactants in aqueous phase comprise 1 to 15% preferably 4 to 12% by wt. of total nanoemulsion. As indicated, the salts of N-acyl derivatives of amino acid, preferably acylglutamate, acylaspartate, acyl acylglycinate, acylalaninate or mixtures thereof are the principal surfactant of the nanoemulsion. They constitute 50% or greater, preferably 60% or greater of all surfactant in the aqueous phase. Preferably they constitute greater than 70% or greater, more preferably 75% or greater. They may of course be the only surfactant present.

(23) Preferably, the aqueous phase may contain a preservative or preservatives. Typically, they are present at a level of 0.01 to 1.0%, preferably 0.1 to 0.5% by wt.

(24) Nanoemulsions of the invention, have volume average diameter (also used interchangeably in and with terms “volume mean diameter” or “volume average size”) of 600 nm or less, preferably 50 nm to 575 nm, more preferably 100 to 400 nm. Lower and upper limit may be as previously defined.

(25) Nanoemulsions with droplet sizes of these ranges are obtained in the subject invention using low pressure (500 psi or less) flow in a homogenizer or sonolator. Specifically, pressure per square inch (psi) can be an upper range of 500 or 450 or 400 psi and lower range of 250 or 300 or 350 psi. A preferred range is 300 to 400 psi.

Preparation of Nanoemulsion

(26) Nanoemulsions are formed as noted below.

(27) First, it is critical to ensure that fatty acid (e.g., 1.1 to 5% by wt. of nanoemulsion) is added to oil. The oil phase and aqueous phase were heated up to 75° C. separately such that it was clear and uniform; then simultaneously pumping the aqueous and oil phases via a sonolator or a homogenizer at pressures no higher than 500 psi. Pressures higher than 500 psi are not required for nanoemulsion formation in this invention. The emulsion may be created by using a homogenizer operating at low pressure (500 psi or less). One example is the standard Sonolator device produced by Sonic Corporation of Connecticut, for example, these standard sonolators are normally operated at pressures of 200-500 psi to form the emulsion.

(28) In the examples, the following terms are defined as noted below:

(29) D[4, 3]: volume average diameter or volume mean diameter or volume average size The average diameters are determined by a Malvern Mastersizer.

(30) Comparative A and Examples 1-6: 50-55% Petrolatum was used to form nanoemulsions, with either potassium cocoyl Glutamate or Sodium cocoyl glycinate in the liquid form as primary emulsifier, ranging 4 to 8.2% in active and lauric acid as co-emulsifier ranging 1 to 4%. The emulsion was prepared by a low pressure sonolator at a pressure up to 450 psi, where the molten oil phase and aqueous phase at 60˜75 C were simultaneously pumped through the orifice of low pressure sonolator and thus formed the emulsion.

(31) As seen from Examples 1-6

(32) TABLE-US-00001 Comparative A Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Ingredient Wt. % Wt. % Wt. % Wt. % Wt. % Wt. % Wt. % Oil Phase Petrolatum 55% 55% 55% 55% 55% 55% G2212 Whiter 50% petrolatum Lauric acid  1%  2%  2%  4%  4%  4%  4% Aqueous Phase Potassium 27.3% 27.3% 13.3% 13.3% 20% 27.3% Cpocoyl (8.2% (8.2% (4% (4% (6% (8.2% Glutamate active) active) active) active) active) active) (Galaxy, Galsoft KCGL, Active 30%) Sodium cocoyl 40% glycinate (8%) (Galsoft SCG Plus Active 20%) Deionized Q.S. Q.S. Q.S. Q.S. Q.S. Q.S. Q.S. water DMDM 0.158%   0.158%   0.158%   0.158%   0.158%   0.158%   0.4%  Hydantoin (and) Iodopropynyl Butylcarbamate (Glydant ™ PIus ™ Liquid) D.sub.[4,3], nm 855 514 560 350 279 285 334 (@450 psi) (350 psi) (350 psi)

(33) As seen from Examples 1-6, use of greater than 1.0% C.sub.8 to C.sub.18 fatty acid (e.g., lauric) allow low pressure process to be used while yielding droplet size under 600 nm.

(34) Efficient production of small droplets is not believed to be just function of total surfactant amount, but rather of type and interaction of surfactants. This is seen comparing Example 1 to Example 4. Although there is almost equal overall surfactant active in Example 1 (10.2% vs. 10% in Example 4), because of interaction of anionic glutamate and greater amounts of fatty acid, the droplet size for petrolatum of Example 4 is 279 nm versus 514 nm for Example 1.