Antiperspirant compositions

Details Antiperspirant compositions Antiperspirant compositions

2003-01-17

2003-11-25

Dodson, Shelley A. (Department: 1616)

Drug, bio-affecting and body treating compositions

Anti-perspirants or perspiration deodorants

C424S400000, C424S401000

Reexamination Certificate

active

06652843

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to antiperspirant compositions for application to human skin, and to the preparation and use of such compositions.
BACKGROUND OF THE INVENTION AND SUMMARY OF PRIOR ART
A wide variety of cosmetic compositions for application to human skin make use of a structured liquid carrier to deliver an active material to the surface of the skin, including in particular antiperspirant or deodorant compositions which are widely used in order to enable their users to avoid or minimise wet patches on their skin, especially in axillary regions or to control or prevent the emission of malodours, which could otherwise arise when the user perspires.
Antiperspirant or deodorant formulations have been provided with a range of different product forms. One of these is a so-called “stick” which is usually a bar of an apparently firm solid material held within a dispensing container and which retains its structural integrity and shape whilst being applied. When a portion of the stick is drawn across the skin surface, a film of the stick composition is transferred to the skin surface. Although the stick has the appearance of a solid article capable of retaining its own shape for a period of time, the material often has a structured liquid phase so that a film of the composition is readily transferred from the stick to another surface upon contact.
Although structuring is a term that has often been employed in respect of materials which structure a carrier liquid, various other terms have been employed alternatively, including solidifying and gelling.
Antiperspirant sticks can be divided into three categories. Suspension sticks contain a particulate antiperspirant active material suspended in a structured carrier liquid phase which often is anhydrous and/or in many instances may be water-immiscible. Emulsion sticks normally have a hydrophilic phase, commonly containing the antiperspirant active in solution, this phase forming an emulsion with a second, more hydrophobic, liquid phase. The continuous phase of the emulsion is structured. Solution sticks typically have the antiperspirant active dissolved in a structured liquid phase which is polar and may comprise a polar organic solvent, which is often water-miscible, and the polar phase can contain water.
There is substantial literature on structuring of antiperspirant or deodorant compositions.
Conventionally, many suspension sticks have been structured using naturally-occurring or synthetic waxy materials, in which term we include materials which resemble beeswax, in that they soften progressively with increase in temperature until they are fluid, generally by about 95° C. Examples of wax-structured sticks are described in an article in Cosmetics and Toiletries, 1990, Vol 105, P75-78, in U.S. Pat. Nos. 5,169,626 and 4,725,432 and in many other publications, in some of which such materials are called solidifying agents.
More specifically, it has been common practice for suspension sticks to be structured or solidified by incorporating fatty alcohol into the composition, often accompanied by a smaller amount of castor wax. Sticks which are structured with fatty alcohol tend to leave visible white deposits on application to human skin; moreover the deposits can also transfer onto clothing when it comes into contact with the skin and the wearer can, for example, find white marks at the armhole of the sleeveless garment. Fatty alcohols are often regarded as coming within the general category of waxy materials, but we have observed that they are a more significant source of white deposits than various other waxy materials. Consumer tests have identified that such white marks are disliked by some consumers and indeed, at least in some countries a market has developed for antiperspirant products which leave little or no such apparent marks on application to the skin.
Patent literature has also proposed the preparation of a suspension composition that not only does not leave visible marks upon skin application, but additionally is clear. Thus, for example Vu et al in U.S. Pat. No. 5,384,117 disclose anhydrous antiperspirant compositions in which a particulate antiperspirant is suspended in a liquid carrier having a matched refractive index to within about 0.02 such that the resultant composition has a relative turbidity of less than 800 FTU. The text exemplified the use of a polyethylene-vinyl acetate copolymer (AC-400 from Allied Corp) as gelling agent to solidify compositions containing various aluminium chlorohydrates antiperspirants, but did not exemplify any other structurants. Even a polyethylene homopolymer that was mentioned as an alternative was not exemplified, though the inventor was under a duty to disclose the best mode of operating the invention. It will be recognised that the text provides no teaching to the skilled man as to how to identify an alternative to the polyethylene-vinyl acetate copolymer.
It would be desirable to find an alternative structurant to the polymers exemplified by Vu for several reasons. First, the polymer exemplified by Vu is not a particularly effective structurant for water-immiscible liquids. The instant inventors found that gels produced using 20 parts by weight of AC-400A to 80 parts by weight of water-immiscible liquid containing a significant fraction of silicone oils were rather soft rather than firm at ambient temperature, even though that is a high weight ratio of structurant to carrier liquid. Moreover the gels produced appeared to be opaque when the refractive indexes of the carrier liquids were similar to those in Vu's Examples. Vu also discloses potential processing difficulties with polymer gellants, including the need to prevent the carrier fluid/gellant mixture exceeding its cloud point.
The difficulty of creating a clear suspension stick which employs a non-polymeric material can be seen from the fact that many readily available non-polymeric gellants render a water-immiscible liquid carrier opaque when it is solidified by them. Such agents include many of the waxes and similar materials to which reference has been made hereinabove.
The difficulty of obtaining clear solidified compositions is further compounded by the fact that antiperspirant actives tend to have a refractive index that is significantly higher than conventional silicone oils, including particularly volatile silicone oils, such as cyclomethicones that have a refractive index just below 1.4, or even those commercially available non-volatile polyphenylmethylsiloxane liquids such as Dow Corning DC-556 which have an intermediate refractive index of around 1.45. Such a low refractive index renders it difficult to obtain sufficiently close refractive index matching to permit the resultant suspension to be clear without some additional carrier being employed. This becomes a greater problem as the refractive index of the antiperspirant increases, for example when employing an activated aluminium chlorohydrate instead of an aluminium chlorohydrate. Moreover, the overall difficulty of selecting a liquid carrier is exacerbated at least in part because antiperspirant compositions are left in place on the skin for long periods between washing, often all day, so that the other properties of a prospective liquid carrier must be kept in mind as well.
The problem of refractive index matching of active and carrier is at its worst for aluminium-zirconium antiperspirants which have the highest refractive index of conventional aluminium-containing antiperspirant actives, if the producer wishes to avoid alkoxycinnamate compounds such as octylmethoxy cinnamate, that have known disadvantage characteristics for leave on skin product (such as an antiperspirant) of colour, irritancy and possible toxicity. The skilled man would be prejudiced against employing the compositions of Vu's Examples 1 to 12 on account of the presence of at least 13.5% up to 72.3% by weight of an alkoxy cinnamate therein. The skilled man can also recognise that Vu's polymer would cause a suspension of aluminium-zirconium anti

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