Method of exfoliating skin

Details Method of exfoliating skin Method of exfoliating skin

1996-05-24

2001-09-25

Page, Thurman K. (Department: 1615)

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Cosmetic, antiperspirant, dentifrice

C510S109000, C510S130000, C510S139000

Reexamination Certificate

active

06294179

ABSTRACT:

TECHNICAL FIELD
The present invention relates to exfoliant compositions.
BACKGROUND TO THE INVENTION
The skin of the human body periodically requires deep cleansing in order to remove therefrom sebaceous secretions, soil deposits and dead skin resulting from desquamation of the epidermal tissue. Exfoliation can be accomplished by the use of a rough cleaning rag, a natural sponge or an exfoliant composition.
Known exfoliant compositions comprise an abrasive component to facilitate removal of the above-mentioned substances and debris. While such compositions are generally applied to the skin for cosmetic purposes, their use as paint removers (for use, for instance, after decorating) and in methods of medical treatment, such as treatment of acne, has also been proposed. It has been suggested that exfoliative cleaning promotes regeneration of the epidermal tissues such that the skin regains suppleness. It has also been proposed that the penetration of cosmetic or dermo-pharmaceutical products is facilitated by exfoliation.
Known exfoliant abrasives include hydrogenated fats, inorganic salts such as sodium citrate or relatively low-molecular weight organics, such as sugars (U.S. Pat. No. 4,048,123); synthetic polymers such as polyethylene powders and granulated particles (JP 60-152407) or organo-polysiloxane (EP 295886); vegetable matter such as the endocarp of apricot, peach and walnut seeds, almond flesh, and wood flour (U.S. Pat. No. 4,508,634). Traditionally, birch powder or coconut pulp have been suggested as exfoliants. Other proposals have related to the use of animal matter such as pearl dust (JP 56-131512) or powdered crab shell and finely ground minerals such as, silica or 10 micron glacial limestone of a highly specific type (EP 257458). A general review of scrub cosmetics can be found in ‘Cosmetics and Toiletries’, volume 101, July 1986.
Mineral exfoliants also include those listed in the patent of Saperstein (U.S. Pat. No. 3,092,111) wherein the use of aluminium oxide, synthetic alumina, corundum, volcanic ash, diatomaceous earth, bentonite, feldspar and silica is suggested. Known exfoliant compositions are provided as thick pastes for topical administration to small regions of the body such as the face or feet.
BRIEF DESCRIPTION OF THE INVENTION
We have now devised a viscous, liquid, skin washing composition comprising water, at least one surface active agent, suspended, abrasive particles and a viscosifier, CHARACTERISED IN THAT the viscosity of the composition is in the range 4000-8000 mpa.s measured at a shear rate of 10 s
−1
the particles have a mean diameter of 40-400 microns and the particles have a specific gravity in the range 1-4.
The above-mentioned, characteristic viscosity measurements may be determined exactly (as in the case of the non-zero shear viscosities) or may be obtained from an extrapolation according to the Cross model (as in the case of the zero shear viscosity).
In the specification, measurements of viscosity were made at 25° C. using a Haake RV20 Rotoviscometer using ether an SV1 or an NV cup and bob.
In general, the compositions will exhibit an extrapolated Newtonian viscosity at a low shear rate of at least 10,000 Pa.s, preferably greater than 40,000 Pa.s, most preferably greater than 100,000 Pas.
DETAILED DESCRIPTION OF THE INVENTION
Abrasive
The presence of abrasive particles have a mean diameter of 40-400 microns and a specific gravity in the range 1-4 is an essential element of the present invention.
We have determined that water-insoluble mineral particles are particularly well-suited for use in exfoliant compositions according to the present invention.
In particular, minerals are free of bacterial and/or fungal contamination and have a reduced tendency to generate immunochemical responses at the skin surface. It is known that materials which are potentially contaminated with bacteria and other pathogens can be sterilised by the use of gamma radiation but this pretreatment of raw materials is expensive and has been found to be unacceptable to some groups of consumers.
Preferred minerals have a Moh hardness of 1-6 so as to avoid excessive abrasion of and damage to the skin.
Particularly preferred minerals have a Moh hardness in the range 2.5-4.0.
Calcite (3 Moh) particles are most particularly preferred.
Calcite particles of a size range of 50-400 microns and a mean particle size of 130 microns are available as ‘DURCAL 130’ [RTM] from Croxton & Garry. Preferred products comprise 5-15% wt. of mineral particles, more preferably around 10% wt.
Preferred particle sizes are such that the bulk of the particles have a mean size in the range 40-250 microns. The preferred particle size distribution is such that 80-95% wt of the particles have a mean size of less than 250 microns, 55-75% wt of the particles have a mean size of less than 150 microns and less than 10% wt have a mean size of less than 10 microns, i.e over 50% wt of the particles have a mean size in the range 40-250 microns.
The relatively large size of the particles is important in establishing the correct ‘in-use feel’ of the products.
As is shown below by way of example, when smaller particles are used the products did not score as well in comparative human studies.
Viscosity Modifiers
A viscosity in the range 4000-8000 mPas measured at a shear rate of 10 s
−1
, is an essential element of the present invention.
Whereas known exfoliant compositions have viscosities very much higher than that of embodiments of the present invention, the embodiments of the present invention have viscosities which are similar to ‘shower-gel’ compositions.
Shower-gels themselves typically have a viscosity which is higher than that of other liquid washing products such some facial cleaners and shampoo compositions. This relatively high viscosity of shower gel compositions is normally achieved by the formation of rod-micelles which do not suspend particles. For example a typical embodiment of the present invention has a viscosity a 1 Hz shear of around 12320 mPa.s. The viscosity of a hair shampoo (TIMOTEI [RTM]) measured under the same conditions is lower, around 3587 mPa.s and would not support calcite. Similarly, at 10 Hz, the viscosity of a typical embodiment of the invention is 4800 mPa.s whereas the shampoo composition has a viscosity of 3164 mPa.s. For pasty compositions, such as DOVE [RTM] facial wash, the viscosities at 1 and 10 Hz are 84360 mPa.s and 11980 mPa.s respectively, much higher than the composition of the invention.
It will be noted from the above-mentioned figures that the embodiments of the present invention generally have a ratio of viscosity at 1 Hz:10 Hz between 2 and 5, i.e. shear thinning occurs over this range.
Compositions according to the present invention comprise a viscosifier, preferably a swelling clay, more preferably a synthetic hectorite (laponite) clay.
In a particularly preferred embodiment of the invention the composition comprises a hectorite clay and further comprises an electrolyte salt capable of causing the clay to thicken so as to suspend the exfoliant particles.
Preferred levels of clay range from 1-2% wt, with an electrolyte level of 0.1-2.0%, 1.0-2.0% being preferred.
Suitable electrolytes include alkaline and alkaline earth salts such as halides, ammonium salts and sulphates.
It should be noted that, with commercial hectorites, some minor experimentation is required to determine the exact level of electrolyte needed to reach a particular viscosity: this arises from variations in the properties of hectorite as received and from variations in either the level of or the electrolyte content of surfactant raw materials.
As an alternative a thickening polymer can be employed, either alone or in combination with other viscosifiers such as swelling clays. Preferred polymers are the natural gums including alginates, guar, xanthan and polysaccharide derivatives including carboxy methyl cellulose and hydroxypropyl guar. Xanthan gums are particularly preferred. Xanthan gums have the advantageous feature of shear thinning, wh

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