Antiperspirant salts, and methods of their preparation

Details Antiperspirant salts, and methods of their preparation Antiperspirant salts, and methods of their preparation

2000-05-25

2002-08-13

Dees, Jose′ G. (Department: 1616)

Drug, bio-affecting and body treating compositions

Anti-perspirants or perspiration deodorants

Aluminum compound containing

C423S462000, C423S495000, C424S065000, C424S401000

Reexamination Certificate

active

06432392

ABSTRACT:

This invention relates to novel basic aluminium antiperspirant salts having improved properties, and to methods of their preparation.
Many conventional forms of antiperspirant active salt are aluminium chlorhydrates (ACH), and have the general formula Al
2
(OH)
6−a
X
a
, where X is a halogen and preferably chlorine, and a is between about 0.5 and 5. Such salts have generally been used in topical antiperspirant products for many years, and have found widespread consumer acceptance.
It is known to attempt to increase the efficacy of such active salts by a number of routes. A popular route has been to vary the processing parameters used in the production of the salt, to attempt to modify the polymer form of the salt, and hence to affect amongst other things the salt's efficacy in topical antiperspirant compositions.
A further route for modification of such salts is to modify them chemically. An example of this approach is to be found in EP 337,464, in which a solution of basic aluminium chloride is modified by the addition to it of a predetermined amount of monosilicic acid. Such treatment is said to result in an increase in efficacy of the basic aluminium chloride. However, the synthetic routes described in this application are complicated, and as such may not be straightforward to commercialise or carry out on a large scale.
In general, whilst activated aluminium chlorhydrate (AACH) compounds made by prior methods have produced antiperspirant actives which have a generally relatively high efficacy in topical products, it is desirable that antiperspirant actives continue to be made of a relatively high efficacy, certainly compared to aluminium chlorhydrate, whilst being made at the same time as cheaply as possible. In particular, many of the processes which are known for making AACHs utilise heating regimes which last for many hours, for example for 24 hours or more, and may require temperatures in excess of 100° C. Clearly such heating regimes require much energy, and are therefore expensive, and may cause the resulting salts to be expensive to produce.
We have surprisingly found after much investigation that it is possible to provide novel antiperspirant actives from conventional aluminium chlorhydrate antiperspirant salts by treating them with an effective amount of a phosphorus containing compound. The resulting salts have good antiperspirant efficacy compared with conventional unmodified aluminium chlorhydrate salts, and further it is possible to manufacture such salts at relatively low temperatures, thus providing activated aluminium chlorhydrate salts by means of an energetically less demanding, and consequently cheaper process.
Thus, according to a first aspect of the invention, there is provided an antiperspirant salt made by treating an aluminium salt of general formula:
Al
2
(OH)
6−a
X
a
wherein X is Cl, Br or I, and a is 0.3 to 4, preferably 0.6 to 4.0, with an effective amount of a phosphorus containing material, and ageing the salt.
According to a further aspect of the invention, there is provided a method of improving the antiperspirant efficacy of an aluminium compound having the empirical formula:
Al
2
(OH)
6−a
X
a
wherein X is Cl, Br or I, and a is between 0.3 and 4.0, preferably 0.6 to 4.0, comprising treating a solution (preferably an aqueous solution) of the aluminium compound with an effective amount of a phosphorus containing compound, and ageing the resultant solution.
According to yet a further aspect of the invention, there is provided a method of manufacturing a modified aluminium chlorhydrate composition comprising treating a solution (preferably an aqueous solution) of an aluminium compound having the empirical formula:
Al
2
(OH)
6−a
X
a
wherein X is Cl, Br or I, and a is between 0.3 and 4.0, preferably 0.6 to 4.0, with an effective amount of a phosphorus containing compound, and ageing the resultant solution.
The conditions under which the reaction may be carried out are not critical, but may conveniently be carried out by dissolving an aqueous solution of a phosphorus containing material, such as dilute phosphoric acid, in a solution of aluminium chlorhydrate. Ageing may conveniently be carried out at room temperature, but may also be carried out either at elevated or reduced temperatures (in the latter case should it be necessary to cool the reaction mixture).
With regard to the resulting product, it is preferred that the resulting aluminium salt has an Al/X ratio of between 1.5:1 and 2.5:1, and that the aluminium concentration in the solution resulting after treatment with the phosphorus source is between 0.1 and 10 wt %, more preferably 0.5 and 5.0 wt %, and even more preferably 1.0-4.0 wt %. In a highly preferred embodiment, the resultant solution is dried to provide a salt which has a water content of less than 12 wt %.
In aspects of the invention involving a solution of a phosphorus containing material, the phosphorus concentration in the resultant aged solution is preferably in the region 0.01 to 10 wt %, more preferably 0.5 to 8 wt %, more preferably 1 to 5 wt % , even more preferably 1.0 to 4.0% by weight.
In all aspects of the invention, it is preferred that the concentration of any sulphate and/or sulphuric acid present is less than 0.05 mole per mole of aluminium present. It is also preferred that the molar concentration of such sulphur containing materials is less than half the molar concentration of phosphorus containing compounds present. More preferably, such sulphur containing materials are not present.
In this specification, reference to aluminium and phosphorus concentrations refer to the concentrations of any aluminium or phosphorus containing species present; examples of the former including aluminium chlorhydrate and examples of the latter including phosphoric acid.
The combination of parameters described herein has been found to result in an activated salt which is preferred, and which provides a good level of antiperspirant efficacy when incorporated into a topical antiperspirant composition, in particular when compared to unmodified aluminium chlorhydrate.
Preferably, the anion in the polymeric aluminium compound is chloride. Conveniently, a may be between 0.8 and 2.1; preferably a is between 0.8 and 1.5, and most preferably is about 1.0.
Preferably, the ratio of Al/X in the final product is in the region 1.6:1 to 2.3:1, and is conveniently in the region 1.7:1 to 2.0:1.
Conveniently, solutions of salts made according to the invention can be left for periods of 2 hours to thirty days to age. Ageing need not be carried out at elevated temperatures, and indeed can be carried out at room temperature.
Conveniently, the water content in the resulting (dried) antiperspirant active salt is no lower than about 2%, is preferably at least about 4%, is more preferably at least 6%, and is even more preferably at least 8% by weight of the composition. Preferably, the water content of the salt is less than 12%, more preferably less than 10% by weight of the salt. It has been found that reducing the water content of the salt is desirable for the long term stability of the salt. With regard to the minimum water content, it is believed that whilst too little water is in itself not harmful to the stability of the salt, the drying regimes to which the salt needs to be subjected to get the water content to particularly low levels may be deleterious to the more active polymer species in the salt. Water content may conveniently be measured using a moisture balance, for example a Sartorius MA30 moisture balance, used on an “auto” programme with a set point of 100° C.
Dried activated aluminium actives according to the invention can conveniently be isolated on an industrial scale by freeze drying or spray drying. Freeze drying is generally considered to be a less harsh drying technique, and hence may be considered to be a preferred drying method in certain circumstances, though spray drying may be considered to be a preferred technique in other circumstances, since it tends to result in a dried salt with a more consiste

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