Antiperspirant salts are well known in the personal care industry. Examples of such salts include the halogen, nitrate and sulfate salts of base metals, such as aluminum and zirconium. Well known and widely used antiperspirant salts include aluminum chlorohydrate, and mixtures of aluminum and zirconium chlorohydrate, in both inactivated and activated forms. Lesser known varieties of antiperspirant salts include zirconium chlorohydrate, aluminum and zirconium bromohydrates, iodohydrates, fluorohydrates, nitrohydrates, sulfohydrates and mixtures thereof, in both inactivated and activated forms.
For years, these materials have been prepared according to a process referred to herein as the "standard" antiperspirant salt preparation process. In the standard process, the base metal, such as aluminum, is first oxidized and then hydrolyzed with an acid, such as HCl, in order to make a solution of aluminum chlorohydrate. This process typically takes five or more days to complete depending on the surface area of the aluminum and the concentration. Although the materials obtained according to the standard process provide a measure of protection against perspiration, more recent research in the personal care industry has been directed at improving the materials for use as antiperspirant salts.
Recent research has made it known in the art that antiperspirants salts are polymeric in nature. The ability for the salts to polymerize in water is due to the base metal components (aluminum and zirconium) being polyvalent. In general polyvalent elements, in particular, aluminum and zirconium which have rich hydrolysis chemistry, are capable of forming compounds having a polymeric structure in water. In fact, compounds of aluminum and zirconium in water normally exist in a polymeric state, except when exposed to highly acidic environments.
In a typical sample of an antiperspirant salt composition, a mixture of salt species will be found, with the species being based on the various polymeric states in which the salt exists. Differences in the size, molecular weight and molecular structure of the polymers readily enable one to distinguish the various antiperspirant polymer species. The molecular size, weight and structure of the various species and the relative amounts of the various species present in the antiperspirant salt composition are dependent on the methods and conditions used in processing the antiperspirant salt. It has been found that the concentration of raw materials, pH and temperature of the processing system may all impact the types and relative proportions of the various species formed by the process.
Certain antiperspirant salt species are more useful and desirable than others in the antiperspirant salt compositions. It is recognized in the industry that when these species are present in the antiperspirant salt composition in sufficient quantities, the antiperspirant salt composition is referred to as an "activated antiperspirant salt", "enhanced antiperspirant salt", "super antiperspirant salt", or as preferred by the inventors, an "activated salt". The preferred species has been theorized as having the structure {AlO.sub.4 Al.sub.12 (OH).sub.24 (H.sub.2 O).sub.12 }.sup.+7 and is sometimes referred to as Al.sub.13, Band III or a "peak 3" material. The "peak 3" terminology come from the fact that it is typically the 3rd peak or 3rd material to be eluted when using High Performance Liquid Chromotography, HPLC, to characterized aluminum chlorohydrate salts (according to the method taught in EP Patent No. 0,256,831). Inactivated salts are typically those that have more of "peak 2" material (theorized as being solublized Al(OH).sub.3 entities held together by H bonding and adjunct Cl ions) than "peak 3" material.
Experimentation has lead to the discovery that antiperspirant salt processing techniques can be practiced which favor the formation of the highly useful species, in particular Al.sub.13. The resulting activated salts containing these useful and desired species are generally recognized as having a high commercial value.
U.S. Pat. No. 4,359,456 to Gosling et al. describes a process for making an aluminum chlorohydrate salt having a high concentration of the useful species. The process taught by Gosling et al. comprises heating an aqueous solution of Al.sub.2 (OH).sub.6-a X.sub.a, wherein X represents a halide selected from Cl, Br and I, and a ranges from 0.3 to 4, at a temperature of from 50.degree. to 140.degree. C. for a period of time ranging from one half hour to thirty days. The resulting salt solution is allowed to cool to room temperature and is then spray dried to obtain an activated antiperspirant salt powder.
Several techniques are known in the art and regarded as industry standards for determining whether basic requirements for classifying materials as activated salts have been met. One highly regarded method, referred to generally herein as the "Inward Size Exclusion Chromatography Test", (or "Inward SEC") is disclosed in detail in European Patent Application 0,256,831, which is incorporated herein by reference. In the calculations for determining activation of the salts, according to the Inward SEC method, the area of chromatography peak 3 is compared to that of the total area of all peaks eluted by the sample. A test used by the present inventor generally utilizes the methods, equipment and techniques of the Inward SEC test, but compares the area of chromatography peak 3 to that of peak 2. This version of the Inward SEC test is known as the "p3:p2 SEC" test. Typical activated salts that are commercially available today have a ratio of the area of peak 3 to peak 2 ranging from 0.2 to 1.2.
Other testing methods include the NMR spectral analysis of .sup.27 Al, as described in "Multinuclear Magnetic Resonance Studies of the Hydrolysis of Aluminum (III). Part 8. Base Hydrolysis monitored at Very High Magnetic Field" J. W. Akitt and J. M. Elders, J. Chem. Soc., Dalton Trans. 1988, 1347- 1355, wherein activated salts exhibit an intense resonance at 63.1 ppm. Yet another test for determining activation involves determining the conductivity of solutions of antiperspirant salt materials. Conductivity increases with increased activation of the salt material. Typically a conductivity value over 3.0 mmhos.sup.-1 /cm represents an activated salt.
In general, a salt classified as being an activated salt according to only one of the above tests will also meet the requirements to be classified as activated by the other tests. Overall, an activated salt is one having higher efficacy when used in antiperspirant formulations.
It is an object of this invention to provide a process for the preparation of novel activated antiperspirant salts using a standard acid-base neutralization reaction.
It is further an object of this invention wherein the process comprises the reaction between a hydroxide of a base metal and a strong acid to produce the activated antiperspirant salt.
It is further an object of this invention wherein the process comprises the reaction between a hydroxide of a base metal, a strong acid and ZrO(OH)X or ZrOX.sub.2, where X is selected from Cl, Br and I, to produce an activated aluminum- zirconium salts.
It is further an object of this invention wherein the process comprises a method for making activated aluminum- zirconium-amino acid salts.