Innovative Technology for Antiperspirants and Deodorants Dow Corning Silicone Elastomers by Anne Buckingham Mike Starch and Heidi Van Dort Dow Corning Corporation  ABSTRACT An increasing number of co
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Innovative Technology for Antiperspirants and Deodorants Dow Corning Silicone Elastomers by Anne Buckingham Mike Starch and Heidi Van Dort Dow Corning Corporation ABSTRACT An increasing number of co

Todays global formulators depend on these innovative silicones to provide superior aesthetics uniform delivery of actives improved product stability and efficient rheology control in a wide range of product forms In response to these needs raw mater

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Innovative Technology for Antiperspirants and Deodorants Dow Corning Silicone Elastomers by Anne Buckingham Mike Starch and Heidi Van Dort Dow Corning Corporation ABSTRACT An increasing number of co

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Innovative Technology for Antiperspirants and Deodorants: Dow Corning Silicone Elastomers by Anne Buckingham, Mike Starch and Heidi Van Dort Dow Corning Corporation
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ABSTRACT An increasing number of consumer product companies have discovered the unique benefits of Dow Corning brand silicone elastomers that can be used to create new generations of improved antiperspirants and deodorants. Today’s global formulators depend on these innovative silicones to provide superior aesthetics, uniform delivery of actives, improved product stability and efficient rheology

control in a wide range of product forms. In response to these needs, raw material suppliers have continued to develop new elastomers based on unique patented technology. This paper highlights the wide range of silicone elastomers cited in public literature and the history of their use in antiperspirants and deodorants.
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Why Use a Silicone Elastomer in an Antiperspirant or Deodorant? Market research confirms it: The global market for antiperspirants and deodorants continues to grow based on the ability of consumer products to safely and effectively reduce odor. To meet consumer

demands for products around the globe, formulators must provide multiple benefits in a wide range of product forms including aerosols, sticks, creams and gels. These product forms will require silicones that are skin friendly, have good aesthetics, are non-staining on clothing and reduce whiteness on skin. Based on the targeted benefits, a number of silicones are essential to formulating antiperspirant products. For example, volatile cyclomethicones have become an indispensable com- ponent of antiperspirant products since their introduction in the late 1970s. Although the use of cyclomethicone

to deliver antiperspirant salts represented a breakthrough in product aesthetics, cyclomethicone presented formulators with a major technical challenge. Antiperspirant salts are not soluble in cyclomethicone and in the absence of an effective thickener, the salt particles fall rapidly to the bottom of the container because of the inherently low viscosity of cyclomethicone. Products that have historically been used to suspend the salt in cyclomethi- cone such as clays, silicas and silicone gums each have inherent problems. More recently, silicone elastomers were introduced to this category

based on their unique ability to thicken the anhydrous-based formulations and to provide good aesthetics. What Is a Silicone Elastomer? Crosslinked siloxanes have been produced and used commercially for almost as long as the silicone industry has been in existence. Historically, Table 1. Terms for crosslinked polymers Rubber Technical definition – A natural or synthetic polymer with elastic properties that demonstrates recovery after vulcanization. Common usage – A common term to describe crosslinked polymers with elastic behavior. Sealant Technical definition/Common usage – A polymer

that is soft enough to pour yet hardens after application to form a barrier to gases and liquids. These properties are derived from a reaction that takes place between a reactive fluid, filler and catalyst upon application. Elastomer Technical definition – A polymer that can be stretched under low stress to twice its length and recover to its original length. Common usage – This term is used widely in polymer chemistry to generically describe rubber. In personal care, silicone elastomers are described as lightly crosslinked polymers that swell in the presence of solvents. Product forms in

the personal care industry include: crumb rubbers, pastes, powders, and solutions (of varying viscosities). Latex Technical definition – A colloidal suspension of natural rubber in water. Common usage – Elastomer or rubber particles suspended in water. Gel Technical definition – A non-flowable crosslinked material, or a two-phase system that behaves more as a solid than a liquid. Common usage – In personal care, this term is most often used to describe a viscous solution or a water-in-oil emulsion. Resin Technical definition – A solid or semisolid that has no definite melting point.

A more specific definition for silicones – Silicone resins are highly branched polymers. Branching is achieved primarily from the inclusion of T (MeSiO 3/2 ) and Q (SiO 4/2 ) substituents. these materials were produced using a number of cure systems and fillers to create products with a wide range of physical properties and performance. The crosslinked siloxanes manufac- tured today are broadly described in literature using terms such as rubbers, sealants, elastomers, latex, gels and resins. Table 1 provides simple defini- tions of these terms from both a tech- nical and commonly used

perspective. Because of numerous possibilities, crosslinked silicones have been used in applications ranging from high- performance engine gaskets to medical tubing to such familiar consumer products as bathtub caulk. To under- stand the technical differences, it is helpful to consider how these materials vary based on the chemistry, the process used to produce the material and the resulting three-dimensional structure. Many references are available on both the chemistry and the analysis of silicones. In general, silicone rubbers, resins and non- flowable gels have more rigid net- works that

can be characterized using properties such as hardness, tensile strength, elongation and modulus. In contrast, silicone latex and crumb rubbers produced from emulsion polymerization are described based on the functionality of the polymers, the size of each particle and the hardness or compatibility of the final elastomer. Silicone elastomer blends that are used to modify the rheology and aesthetics of cyclomethicone consist of entangled networks that are swollen in the presence of a carrier solvent. As a result, these materials are more
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Figure 1: The Hydrosilylation Reaction

Pt Catalyst SiH + CH =CH-R Si-CH -CH -R difficult to evaluate by traditional techniques. In general, these elastomers are typically described based on the functionality of the polymers, the relative differences in the density of the network, the carrier fluids, the process conditions and more importantly, their viscoelastic proper- ties. A summary of the structural differences and potential applications for the range in crosslinked silicones is shown in Table 2. Silicone Elastomers in Personal Care Applications The Basic Chemistry In the late 1980s, patents disclosing various crosslinked

siloxanes, methods of manufacture and applications in personal care began to appear based on the ability of these materials to absorb low molecular weight non-polar materials such as cyclomethicone. Silicone elastomers that are effective thickeners for cyclomethicone gener- ally consist of polydimethylsiloxane (PDMS) that is crosslinked through the use of reactive sites along the polymer chain. The most popular crosslinking scheme utilizes the sili- cone hydrosilylation reaction in which silicone hydride adds across a vinyl group to form a silicon-carbon bond. This reaction is shown in Figure

1. The reaction is initiated by the addition of a platinum catalyst. The crosslinker can be selected from a wide variety of materials containing the two or more vinyl groups necessary for the crosslinker to form a bridge between the modified PDMS chains and thereby form the extended network structure that characterizes an elastomer. The exact chemistry and process used to produce each elasto- mer determine the viscoelastic proper- ties of that material. These same properties have a significant impact on the performance of the siloxane elastomer in the final application. The remainder of this

paper will focus on differences in the various elastomers and the relevance of those differences in the numerous public documents available today. The Utility of Silicone Elastomers in Personal Care Applications To understand the differences in the various silicone elastomers utilized in personal care and the history of their development, it is important to care- fully study the public disclosures describing the various products on the market today. The first public disclosure of an elastomer composition utilized for personal care applications was described in the late 1980s in numer- ous

patents and product literature provided by Dow Corning Toray Silicones. The original patents included the elastomeric (or rubber) Table 2: Structural Differences of Crosslinked Siloxanes Siloxane Type Elastomers/ Latex/Crumb Rubbers Hard Rubber Sealants Resins Typical Applications Personal Care, Electronics Numerous Caulks, Gaskets, Adhesives, Molds, Encapsulants Paints and Coatings, Electronics, Water Repellents, Personal Care Distinctive Characteristics Produced using a wide range of cure systems and intermediates based on desired final properties. In general, increasing the polymer chain

length increases the elongation. Incorporation of fillers or increased crosslinker will result in higher tensile strength. Prepared by milling silicone polymers, fillers, plasticizers, vulcanizing agents and other additives. This stock is then molded into a final form and cured. Formulated from PDMS, cross- linkers, plasticizers, catalysts and fillers. Typically less flexible than unfilled silicone elastomers. 3D structures are produced based on various silane structures that are further reacted to create prod- ucts that range from rubbery to rigid structures delivered in a range of carriers.

General Properties Structures are analyzed using IR, NMR and GPC. Products are characterized by visco- elastic, mechanical, electrical and adhesive properties. Structures are analyzed using IR, NMR, and GPC. Prod- ucts are characterized by their mechanical properties. Structures are analyzed using IR, GC-MS, GPC, XRF and functionality. Structures are analyzed using IR, 29 Si NMR and GPC. Products are characterized by flexibility, heat and chemical resistance.
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powders produced by suspension polymerization in which a silicone polymer and a crosslinker were emulsified in water

and reacted to produce spherical elastomer particles that were recovered as a dry powder. The resulting elastomer was supplied to the industry with the INCI nomen- clature of Dimethicone/ Vinyldimethi- cone Crosspolymer. Shin-Etsu patents later published in 1987 also described additional inventions made through suspension polymerization. Subsequent patents published by several manufacturers disclose various methods to produce silicone elastomers using bulk polymerization. In bulk polymerization, the crosslinking reac- tion is done in the presence of a solvent (diluent). These inventions are

based on the differences in siloxane back- bones or SiH-containing polymer, the crosslinker, diluents and the finishing methods used to produce the final products. For example, Shin-Etsu patents published in 1990 described the use of SiH-containing polymer and an unsaturated polyorganosiloxane polymerized in the presence of low- viscosity siloxane fluids. In 1997, Dow Corning disclosed an invention to produce an elastomer based on a SiH polymer and an organic diene to make a non-emulsifying elastomer described as a cyclomethicone and dimethicone crosspolymer. General Electric has patents that

claim a silicone elastomer that is the hydrosilylation addition product of a linear alkenyl-functional- ized polyorganosiloxane, an MQ resin containing SiH functionality and a low molecular weight siloxane fluid. For clarity, the differences in the elasto- mers described by these patents are included in Table 3. Not All Elastomers are the Same Next, the reader must consider the variation in compositions and properties within a defined invention. Dow Corning can create a series of elastomers with different viscoelastic properties based on our bulk Table 3: Description of Personal Care Dimethyl

Silicone Elastomers Pr oducer Si-H Reactant Cr osslinker Carrier Fluid INCI Name Dow Corning 9040 Intermediate Organic diene Organic or silicone Cyclomethicone (and) Dimethicone Crosspolymer Bulk Polymerization MW Si-H polymer Dow Corning 9506 Low MW Si-H V inyl Si-polymer Silicone or water Dimethicone/Vinyldimethicone Crosspolymer Suspension polymer Polymerization Shin-Etsu Bulk Low MW Si-H Vinyl Si-polymer Organic or silicone Dimethicone/Vinyldimethicone Crosspolymer Polymerization polymer General Electric Si-H functional High MW Vinyl Silicone Cyclomethicone and Viny ldimethicone/Methicone

Bulk Polymerization MQ resin Si-polymer Crosspolymer Figure 2A 20 40 60 80 100 120 0 2040 6080100 % St r a i n G" G' Figure 2B 1000 2000 3000 4000 5000 6000 7000 8000 050100150 % St r a i n G' G" polymerization process used to manufacture Dow Corning 9040 Elastomer Blend. Key variables for this technology include the siloxane backbone, the carrier fluid and the process conditions used to manufacture each material. For silicone elastomers made using bulk polymerization, processing conditions have a large effect on rheological performance. An example is shown in Figure 2. Figures 2A and 2B show

a dynamic strain sweep, performed on a parallel plate viscometer, for Dow Corning 9040- type elastomers with the same siloxane backbone, elastomer concentration and carrier fluid. The only difference in these materials involves a variable in the reaction conditions; yet, these elastomers have substantially dif ferent Figure 2: Stress/Strain Curves for Dow Corning 9040-type Elastomers Made with Different Processing Conditions Figure 2A Figure 2B dyne/cm Strain, percent dyne/cm Strain, percent
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dynamic viscosities. The elastomer in Figure 2A behaves more fluid-like than the

elastomer in Figure 2B. The Impact of the Elastomer Type on Performance One of the principal performance attri- butes of silicone elastomers in anti- perspirants is the effect on formula rheology. One illustration that demonstrates the impact that changes in bulk polymer- ization have on the silicone elastomer and final product is shown in Figures 3 and 4. These graphs depict the rheo- logical profiles of a series of simple anhydrous antiperspirant formulations containing Dow Corning 9040 Elastomer Blends synthesized with different diluents. Based on the diluent, the yield stress for these

formulations varies by over 20 fold. Dow Corning has also completed a number of studies that examine the impact of the type of polymerization process on the performance of the elastomer in simple anhydrous formulas. For example, Figure 5 shows the effect of using a silicone elastomer made by suspension polymerization versus a silicone elastomer made by bulk polymerization. A formula based on a non-crosslinked silicone polymer (silicone gum) was also included for comparison. All of the rheology modifiers were used at the same concentration (4%). The rheology of the three formulas was measured

using a controlled-stress rheometer. From the forgoing examples, it is clear that the performance of silicone elastomers is very sensitive to changes in processing even when the basic chemistry is the same. 10 100 1,000 10,000 100,000 1,000,000 10,000,000 10 100 1000 1000 Viscosity [Poise] Silicone Elastomer Crosslinked in 1 cSt Dimethicone Silicone Elastomer Crosslinked in 1.5 cSt Dimethicone Silicone Elastomer Crosslinked in 5 cSt Dimethicone Figure 3: Stress Ramps for Anhydrous Roll-ons Made with Silicone Elastomer Crosslinked in Diluents with Different Viscosities Silicone Elastomer

Crosslinked in Different Solvents 10 100 1,000 10,000 100,000 1,000,000 10,000,000 10 100 1000 Viscosity [Poise] Silicone Elastomer Crosslinked in Cyclomethicone Silicone Elastomer Crosslinked in Hydrocarbon Solvent Figure 4: Stress Ramps for Anhydrous Roll-ons Made with Silicone Elastomer Crosslinked in Different Diluents The Utility of Silicone Elastomers in Antiperspirants and Deodorants The subsequent use of elastomers in antiperspirants and deodorants is evident by the growing number of patents. These patents provide a serious challenge to any formulator because it is often difficult to

interpret whether these patents impact the ability to incorporate elastomers in an antiperspirant or deodorant. To assist readers in their search, Dow Corning has provided a brief summary of the most important patents, the scope of the inventions and the known INCI nomenclature referenced in each public document. From a supplier perspective, there are numerous examples where the result- ing application patents have been issued based on the differences in the elastomer structure or performance. For example, Dow Corning Toray Silicones was issued a patent in 1986 that focused on cosmetic

compositions containing silicone elastomeric pow- ders made with different cure systems. Stress, dyne/cm Viscosity, poise Stress, dyne/cm Viscosity, poise
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10 100 1,000 10,000 100,000 1,000,000 10,000,000 100 1000 10000 Viscosity [Poise] Silicone Elastomer made by Bulk Poly mer iz ation Silicone Elastomer made by Suspension Poly mer iz ation Silicone Gum An additional Dow Corning patent issued in 1996 included claims for an antiperspirant using elastomeric pow- der made by suspension polymeriza- tion. Dow Corning was also granted a subsequent patent, published in 1997, that

included antiperspirant claims based on silicone latex elastomers produced through other emulsion polymerization techniques. Consider another example related to Dow Corning 9040 Elastomer Blend. In January 1997, two Unilever patents were published that describe the use of elastomers in antiperspirant sticks, fluids, aerosols and creams. The pre- ferred elastomer in those patents was described as the hydrosilylation product of vinyl silicone fluids with hydrosilox- anes or MQ hydride fluids. Although these patents were in the public domain, Dow Corning filed a patent issued in August 1997 (US

5,654,362) that included claims and examples for an antiperspirant based on non- emulsifying elastomers produced from an SiH intermediate and an organic diene. Example III and Claims 13 and 14 include AP and DEO compositions containing the elastomer, salt, diluent, emollients and fragrance. Benefits cited included stability, dry aesthetics, payout, spreadability, ease of prepara- tion, thickening, low residue and delivery of the AP salt or fragrance. Other cosmetic compositions were patented or published based on Dow Corning 9040 Elastomer Blend. In November 1997, Colgate published a world

patent application that claimed a cosmetic cream based on a gelling agent that can include antiperspirant or deodorant actives. It is important to note that this patent makes a general claim with a crosslinked siloxane but subsequent claims define the structures made by the reaction of a vinyl- terminated siloxane and a hydride crosslinking agent. These examples reinforce the importance of under- standing the elastomer structure and the polymerization conditions for freedom-to-practice considerations. In addition to the elastomer structure, the reader must also carefully consider the patents

issued in the country of interest, the current active status of many patents and the details within the claims. Dow Corning literature research uncovered significant Figure 5: Stress Ramps for Anhydrous Creams Made with Silicone Elastomers differences in the information that was considered as prior art from case to case. Moreover, the description of the elastomers included in some inventions actually conflicts with the descriptions used in the silicone composition patents, making analysis of the patents more confusing. Because of these issues, it is critical that readers make their own

decision on their right to practice based on a thorough analysis of their formulation. The Future Silicone elastomers have been used since the late 1980s to provide improved aesthetics, rheology and stability to antiperspirant and deodor- ant formulations. Many patents disclose unique inventions to produce elastomers that have application in personal care. Since the original introduction of dimethyl elastomers, silicone manufacturers have also developed crosslinked systems that incorporate other chemistry or functionality in the polymers. These elastomers provide additional benefits based on

their ability to emulsify or often compatibilize other ingredients that are common in the personal care industry today. Because of the range of properties available within the various inventions, silicone manufacturers and consumer product companies will continue to innovate new products that provide multiple benefits. To determine the ability to practice within the market, readers must carefully study the patents applicable to the countries, the product formulations and the elastomer structures of interest. For more informa- tion on this topic, please contact a Dow Corning representative to

discuss your formulation needs and their match with our specialty silicones. Stress, dyne/cm Viscosity, poise
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WARRANTY INFORMATION The information contained herein is offered in good faith and is believed to be accurate. However, because conditions and methods of use of our products are beyond our control, this information should not be used in substitution for customer’s tests to ensure that Dow Corning’s products are safe, effective, and fully satisfactory for the intended end use. Dow Corning’s sole warranty is that the product will meet the Dow Corning sales

specifications in effect at the time of shipment. Your exclusive remedy for breach of such warranty is limited to refund of purchase price or replacement of any product shown to be other than as warranted. Dow Corning specifically disclaims any other express or implied warranty of fitness for a particular purpose or merchantability, unless Dow Corning provides you with a specific, duly signed endorsement of fitness for use. Dow Corning disclaims liability for any incidental or consequential damages. Suggestions of use shall not be taken as inducements to infringe any patent. Dow Corning is a

registered trademark of Dow Corning Corporation. WE HELP YOU INVENT THE FUTURE is a trademark of Dow Corning Corporation. ©2000 Dow Corning Corporation. All rights reserved. Printed in USA AGP5354 Form No. 27-050-01 WE HELP YOU INVENT THE FUTURE.