Patent Application
20080014168
The invention relates to cleansing compositions providing enhanced post wash hydration or moisturization. According to the invention, specific amphiphiles (defined as molecules having both hydrophilic and hydrophobic groups, e.g., surfactants, emulsifiers) of defined HLB are mixed with moisturization additive or additives, also of specific HLB, to form compositions having a combined surfactant/additive HLB also of a defined range. The addition of additive forms a particle dispersion of the additive having a “milky” appearance when the additive(s) is mixed in. This particle dispersion is believed in turn responsible for the surprising moisturization effect when the specific parameters are met. In a co-pending application, applicants also claim a method of determining/measuring what the hydration value is (e.g., to see whether the value is enhanced or not), as well as a method of selecting compositions of enhanced hydration value based on measured values and defined levels of significance.
More particularly, hydrophilic-lipophilic balance (HLB) is based on the relative percentage of hydrophilic to hydrophobic groups in a surfactant molecule(s). Generally, surfactants of low HLB tend to form water-in-oil (W/O) emulsions, whereas those of high HLB form oil-in-water (O/W) emulsions.
A summary of HLB ranges typically required for various purposes is given by I. Becker in “Encyclopedia of Emulsion Technology”, Marcel Bekker, Inc. (1983); Amphiphiles with HLB of about 3 to 6 are typically W/O emulsifier; amphiphiles of HLB about 7 to 9 are typically wetting agents; and amphiphiles with HLB about 8 to 18 are typically O/W emulsifier. Amphiphiles with HLB greater than 13 are typically detergents or solubilizers.
Davies (Proceedings of the Second International Congress on Surface Activity, Vol. 1 London, Butterworths, 1957, p. 440) has devised a method for calculating the HLB values for surfactants directly from their chemical formulas, introducing so-called group numbers, that is HLB numbers which correspond not to the molecule as a whole entity, but to the constituting groups (molecular structural units). Once the group numbers gi are known, one can calculate the HLB number from the chemical formula of a surfactant using the equation:
For hydrophilic groups, gi>0; while for lipophilic groups, gi<0. The letter “i” defines the number of groups.
In the case of a mixture of amphiphiles in water, the combined HLB is defined as follows:
where cj and HLBj are the weight concentration and the HLB value, calculated according to [1], of the amphiphile “j”, respectively. All the HLB values are calculated at room temperature (about 25° C.).
It is well known that to increase the detergency of ionic surfactants or the lather stability, low HLB co-surfactants are used in conjunction with the HLB ionic surfactants. For example, typical low HLB co-surfactant are fatty acid, fatty alcohol or poly(oxyethylene)glycol alky ether. In that case, the mixing ratio of co-surfactant and ionic surfactant is chosen in order to form optimum mixed interfacial monolayer with lower surface tension. The low HLB amphiphile concentration is such that it forms co-micelles with the HLB surfactants and does not deposit readily on skin. By contrast, in the present invention it is believed that the low HLB amphiphile forms a dispersed phase, which deposits and has a head group which has strong affinity with water.
“Moisturization effect” refers to an increase of hydration of skin or hair with respect to a baseline value, which can be measured for example using conductivity.
In one embodiment, the invention relates to a method of measuring what amount of moisture retention is attributable to an additive used to provide moisturization (e.g., in reality any given compositional element which can provide moisture) to the skin. The method factors out other values which are present and affect or provide moisturization (evaporation, environmental conditions) to focus on that amount attributable to the component. Using such method, it is possible to determine what precisely are the optimal moisturizer additives which can be used.
This method comprises:
The HEV value is then averaged across all subjects.
It is noted that 5 and 20 minutes are not criticalities. The lower limit, for example, is simply what is enough to have statistical meaning. In theory there is no upper limit.
This embodiment of the invention further comprises a method for selecting a composition having enhanced post wash hydration which comprises measuring the HEV according to steps (1)-(6) noted above, and selecting those compositions having a defined “significant” value for hydration enhancement. While applicants have defined on HEV value of greater than about 27 as significant, it should be understood that any value might in theory be considered significant depending on what is considered “sufficient” hydration for the defined audience. Thus, hydration values greater than about 15 (e.g., control with no additive has HEV of 15), preferably greater than about 20 and more preferably greater than about 27 might be used.
The selected skin site for testing is typically an area on the arm such as the forearm, although in theory it can be applied to any skin. The control and non-control sites should ideally be in the same proximate area in order to ensure minimal if any variation in testing. If two areas tested are immediately adjacent to one another (see
The base line value (before applying control or non-control) is established by multiple readings (only one is needed although typically, about 10 to 20 values are taken) of the skin hydration in the tested area. The hydration value can be measured, for example, using electrical capacitance and conductance of the skin as indicators of the hydration. These in turn can be measured using equipment such as Skicone® 200 hygrometers. Other equipment to measure hydration may include Corneometer® CM420 hydrometer and Servo Med EPI® evaporimeters. Besides conventional corneometry, additional methods for measuring hydration may include nuclear magnetic resonance spectroscopy (NMR-5) and transient thermal transfer (TTT). In any event, methods for obtaining hydration values are well known and well understood by those skilled in the art.
After obtaining baseline measurements, control compositions and non-control compositions are applied to selected measured area and standard wash protocol are applied.
The compositions preferably are surfactant containing compositions (containing at least one surfactant) although, the method can be used for any composition. Typically tested compositions comprised a blend of anionic and/or nonionic surfactants and water.
After rinsing and drying (typically although not necessarily by drying with paper towel), skin hydration values are then recorded as a function of time (e.g., 1 reading/second for a period of time basically 15 minutes to an hour).
Post wash hydration values are then obtained by substracting a measured average basis on conductivity (or whatever value used) prior to wash from the measured value after rinse and drying.
Final values of enhanced hydration are obtained by calculating mean change from baseline difference between the applied product and the control product averaged across all subject (including all areas on each subject and all time points.
A typical measurement is as follows:
Results are then recorded as per steps (4)-(6) of the method noted earlier.
In a second embodiment, the subject of the present invention, the invention relates to a specific composition or cleansing system for enhancing post hydration. The compositions comprise:
In addition, the amphiphile mix (1) and additive(s) of (2) have combined HLB greater than 6 and less than 16, preferably between 8 and 14. By “milky dispersion is meant a dispersion of particles of size 0.05 to 1.0, preferably 0.1 and 0.4 microns, and which form spontaneously under mixing conditions. For the dispersion, the particles do not coalesce, flocculate or agglomerate over some period of time (e.g., at least 2 weeks) due to thermal agitation (e.g., Brownian motion).
While not wishing to be bound by theory, the noted conditions appear to allow formation of a hydrophobic film while, because of the hydrophilic moiety of the low HLB additive, water can be retained.
Suitable anionic or amphoteric amphophiles of (1) with HLB>20 are disclosed, for example, in Laughlin, R. G., “The Aqueous Phase Behavior of Surfactants”, Academic Press, New York (1994). Non-limiting examples of suitable high HLB amphiphiles include anionics such as alkyl sulfates (including acyl isethionates), alkyl ether sulfates, alkyl sulfonates, alkyl carboxylates, alkyl ether carboxylates, alkyl aminocarboxylates, taurates, sulfosuccinates, sarcosinates and monoalkyl phosphates.
It should be noted that HLB of surfactants with pH dependent functional groups (e.g., carboxylates which may be in form of soap or fatty acid; glycinates—glycinic acid; phosphates, phosphoric acid, etc.) is in fact dependent on pH since there will be a combination of anionic species and uncharged species at intermediate pH values. For such surfactants, the effective HLB will correspond to the mixture of corresponding acids and anionic species.
Typical co-surfactants which can be used include fatty acids or long chain alcohols.
The moisturizing additive 2 should have an HLB value between 2 and 13 and preferably have a hydrophilic head group forming multiple hydrogen bonds with water. Typical water-in-oil emulsifier include fatty acid esters of sugar derivatives (fatty acid esters of anhydrosorbitols, fatty acid esters of glycerol). Other examples are and also alkoxylated triglyceride oils. Other examples include water/oil emulsifiers such as cetylpolyethyleneglycol/polypropyleneglycol dimethicone.
The solvent is a polar solvent, including water, polyols and may contain other ingredients such as buffers and/or stabilizers. Preferably the weight concentration is greater than 50%, more preferably greater than 70%.
Control and non-control compositions are applied as described above. Typically, 2 milliliters of system is applied to cloth and a clinician produces lather for a few seconds. The test site(s) are than moistened with warm water (about 40° C.) for specified time (5 to 60 seconds). Test site(s) are washed for about 5 to 30 seconds and product remains on the site (for 60 to 120 seconds). The test site is than rinsed and dried.
Skin hydration values are recorded and a post wash hydration value is determined by subtracting measured average baseline skin conductivity measured prior to wash, from measured value of conductivity after the wash. Hydration enhancement values can than be calculated.
The Examples below set forth various compositions which are prepared and applied to skin according to the invention. In each case, the final compositions (shown) were measured and compared to composition without moisturizing additive.
As can be seen from results summarized in Table 1 after all the examples and from
Effect of enhanced hydration based on particle size can be seen from Table 2 and
