M. Heldermann, K. Burch* Maximizing the Performance of Color Cosmetics by Multifunctional Ingredients Introduction Consumers have many demands concerning color cosmetic products that they wish to see fulfilled. When picking a mascara factors like thickening, lengthening, smudge- proof, long-lasting, maybe waterproof, graceful curl effect, color intensity, volumizing or non-clumping are considered. Additionally it should be easy to remove and an important feature is also the price. Developing a perfect foundation / cover stick / concealer can be tricky too, as there are even more parameters that play a major role. Besides activity like anti-ag- ing, moisturization or anti-acne there are lots of expectations concerning long lasting effect, smudge-proof, and no masklike effect. Additionally consumers have different requirements for coverage. Lipsticks and lip glosses are a big part of the color cosmetic market and also for these products consumers would like to Abstract This article introduces several approaches to solve performance issues of color cosmetics: Castor Oil was for many years the main oil used in lipsticks. The main disadvantage when using Castor Oil is its inherent oxidative instability. Without combining it with high amounts of antioxidants the odor and taste becomes offensive as the material oxidizes and finally becomes rancid. Innovative and modern lipstick formulations require an oxidative stable replacement. Tests were performed to show that Polyester-4 is more resistant against oxidative degradation and is efficient as Castor Oil in dispersing pigments. Therefore the oil stability index of several raw materials was measured by an Omnion OSI (oxidative stability instrument) and the results were compared. Additionally the wetting efficiency was checked. The lower the viscosity of a pigment slurry in similar viscosity oils, the better the wetting. Another important topic is transfer resistance, which is a desired attribute in color cosmetics as it improves long wear and helps reducing rub-off. Studies were conducted in order to evaluate if it is possible to extend wear resistance by film formers. Amongst other tests like water resistance a chromameter was used to measure the lightness of transferred color cosmetics. The results indicate that Polyester-4 is an oxidatively stable alternative to Castor Oil for color cosmetics. In addition it is as efficient as Castor Oil in dispersing pigment. Its performance and ease of use make Polyester-4 the logical choice for formulating innovative and luxurious color cosmetics. Furthermore it could be proven that Inolex s patented polyester polymer technology have a big impact in improving color cosmetic formulations for transfer resistance, water-proofing, and pleasant film forming. 34 SOFW-Journal 138 3-2012
COSMETICS experience many different benefits. During application the product must be smooth, but not greasy; it should adhere well to the skin of the lips and, during wear, the color should remain the same and not smear or run. It should remain on the lips as long as possible and not transfer from the lips to other surfaces. Lipsticks should not break when force is applied like during application. However, a too hard texture would be difficult to apply. The stick should be free of blemishes and pinholes, which can be caused by too much air in molten mass when sticks are poured. This phenomenon is most commonly found in sticks with pearlescent pigments. The properties of the stick should remain consistent and it is important that particles of wax or oil should not form on the surface, a phenomenon called 'sweating'. This can occur due to ingredient incompatibility and insufficient solubilization or can be caused by not having enough powder fill the powder fill sits between wax matrix keeping liquids bound. Lip products have been used since ancient times to enhance the appearance of the lips by imparting color and gloss, and by re-defining the outline of the lips. The three most common products used to achieve this are lipsticks, lip glosses and lip liners, of which lipsticks are the most common. Many women wear lipstick even when they use no other makeup. The biggest market share for color cosmetics formulations are mass market products. Developers have to find reasonably priced and multi-functional ingredients to cover most of the listed aspects. So, how to maximize performance for color cosmetics aesthetics? The most effective way is to take care of a light skin feel with a good spreadability. Additionally the transfer resistance should be improved and if desired shine / gloss can be enhanced. For lipstick formulations it is crucial to use raw materials with no taste and to avoid oxidation that could lead to odor / taste problems. Polyester-4 An Oxidatively Stable Alternative to Castor Oil Castor Oil has been the preferred base oil in lipsticks for decades. Castor Oil has some unique properties among natural oils that make it a favorable choice for lipstick manufacture. Its hydroxyl functionality makes it polar in nature, which allows for the dissolving of organic dyes and easy dispersion of pigments. Castor Oil is also relatively viscous, which helps to keep pigments suspended during manufacture at elevated temperature. Modern manufacturing techniques such as using monochromatic bases and pro- SOFW-Journal 138 3-2012 35
longed storage of pigment dispersions have created a need for more oxidatively stable base oils. While Castor Oil is one of the more oxidatively stable natural oils, it still has significant potential to become rancid and develop off tastes and odors. In addition, there have been reports of dermatitis associated with some compound found in Castor Oil and its derivatives. A logical solution to these issues is to use more stable, synthetic ester oils in place of Castor Oil. Higher viscosity synthetic esters were developed, such as Pentaerythrityl Tetraisostearate, which provide the viscosity needed for effective pigment suspension. However, they are too low in polarity and they do not contain the hydroxyl functionality required to be a suitable replacement for Castor Oil. Due to this deficiency, two other approaches have been investigated. The first concept is an ester based on polyglycerol, such as Polyglyceryl-2 Triisostearate. The second concept is an ester based on hydroxy acids, such as Diisostearyl Malate. Although both approaches demonstrate improved pigment wetting, they do not provide a significant improvement in oxidative stability compared to Castor Oil. Inolex Chemical Company has researched available materials on the market and compared them to new patent pending complex polyester (Polyester-4). Inolex employed two approaches to determine whether Polyester-4 is an effective alternative to Castor Oil: The Oil Stability Index Ingredients The Oil Stability Index (OSI) is an evaluation of the oxidative stability of fats, oils and esters. The OSI instrument accelerates the development of oxidative rancidity so that the useful life of an oil containing material may be determined. The test material is heated to 110 C. Air is then bubbled through the sample and into a sample of water. The water sample is monitored with a conductivity probe to detect the generation of volatile oxidation by-products (rancidity). The longer the period of time to generate oxidation by-products, the more resistant is the material to rancidity. Standard lipstick formulations were prepared utilizing the four base oils being tested. The formulas were then analyzed for oxidative stability using the OSI instrument (Table 1 and Fig. 1). % w/w Base Oil 40.00 Red No. 7 Calcium Lake 5.60 Dipentaerythrityl Hexa C5-9 Acid Esters 1 8.40 Propylene Glycol Dibenzoate 1 11.00 Neopentyl Glycol Diheptanoate 1 15.00 Candelilla Wax 2 9.00 Ozokerite Wax 2 3.00 Microcrystalline Wax 2 3.00 Colorona Bordeaux 3 1.50 Colorona Glitter Bordeaux 3 1.50 Colorona Aborigine Amber 3 1.00 Tocopheryl Acetate 4 0.50 Caprylyl Glycol 1 0.50 1 Inolex Chemical Company 2 Strahl and Pitsch 3 EMD Chemicals Rona 4 BASF Table 1 Lipstick formulas Oil Stability Index All oils and fats have a resistance to oxidation. Oxidation is slow until this resistance is overcome, at which point oxidation accelerates and becomes very rapid. The length of time before this rapid acceleration of oxidation occurs is the measure of the resistance to oxidation and is commonly referred to as the»induction period«, or Oxidative Stability Index. Dispersion Viscosity Comparison The viscosity of pigment dispersions is related to the ability of the base material to wet out pigment. Dispersions of Red No. 7 Calcium Lake were compared at various pigment loadings to evaluate the relative pigment wetting ability of several base materials. Fig. 1 Oxidative stability comparison of lipsticks formulated with various base oils. Induction time measured in hours at 110ºC. Lipstick A (40.0% Polyester-4 (LexFeel 7001) Lipstick B (40.0% Polyglyceryl-2 Triisostearate) Lipstick C (40.0% Diisostearyl Malate) Lipstick D (40.0% Ricinus (Castor Oil) Communis) 36 SOFW-Journal 138 3-2012
Viscosity Dispersion Comparison In color cosmetics, pigments and fillers represent an additional phase that influences the integrity and performance of the final formulation. Wetting and dispersion are necessary steps in the manufacture of all pigmented products. Wetting is the spreading of a liquid over the surface of a solid, displacing air, and is influenced by the physical properties of both solid and liquid. As supplied, most pigments are highly agglomerated, requiring high shear agitation to become adequately dispersed. A simple method to compare wetting efficiency of liquids of similar viscosity is to measure viscosity of slurries made from the liquids of interest. The lower the viscosity of a pigment slurry in similar viscosity oils, the better the wetting. Various loadings of Red No. 7 Calcium Lake were dispersed into samples of each base oil. The pigment was gently mixed into each base oil with a glass stir rod. Once dispersed, the mixture was homogenized for 10 minutes at 5000 rpm using a Ross HSM-100LC Homogenizer. The dispersions were then allowed to cool to ambient temperature (20 C). A viscosity measurement was then taken using a Brookfield RVT viscometer with helipath spindles. The results of these studies (Fig. 2) indicate that Polyester-4 is very resistant against oxidative degradation and additionally is efficient as Castor Oil in dispersing pigments. The new patent pending chemistry of Polyester-4 outperforms any current Castor Oil replacement chemistry on the market today. It is now possible to create oil-free, fragrance-free, and antioxidant-free formulas without compromising product performance. Odorless, colorless, and tasteless, Polyester-4 allows formulators limitless flexibility in shade and flavor/ fragrance development. Based on this, Polyester-4 allows formulating the richest, creamiest, smoothest lip products. It creates a revolutionary thixotropic formula that delivers the shine of a gloss and the comfort of a lipstick with a buttery-soft, luxuriously smooth feel. Extending Wear Resistance of Color Cosmetic Formulations with Film Formers Film formers are used in color cosmetics to perform a wide range of functions, including transfer resistance, improved gloss, water-proofing and moisturization through occlusivity. Transfer resistance is a desired attribute in color cosmetics as it improves long wear and helps to reduce rub-off. Lexorez 100, INCI: Adipic Acid/Diglycol Crosspolymer (ADC) and Lexorez 200, INCI: Trimethylpentanediol/Adipic Acid/ Glycerin Crosspolymer (TAGC) are polyester polymers and 100% active, polar, and viscous liquids. They are dispersible Fig. 2 Viscosity comparison of Red No. 7 Calcium Lake at 50% loading in oils and esters and are used in sun care and color cosmetics for to provide water proofing and water/ transfer resistance. Besides wetting activity for effect pigments and UV-filters they also show low odor, minor taste, and little color. The best way to make something waterproof is to exclude water from it totally and use ingredients that are insoluble in water. Waterproof mascaras are therefore usually solvent-based systems. The basic solvent has to be volatile to give a quick-drying formulation. Using high-melting-point waxes can result in a stiff and sometimes brittle film, incorporating low-melting-point waxes such as beeswax can lead to smudging as the resultant film can become soft and therefore is easily disturbed. Therefore it is much better to use film formers that are compatible with the solvent system, do not lead to a sticky skin feel and form a breathable, flexible but complete film. First a water resistance study was performed with 5 people according to the FDA methodology (whirl pool study). ADC demonstrated to be very water resistant at a use level of 3%. Mascara s perfomance is usually judged by application, appearance, wear, and ease of removal. It is also critical to use a proper brush. Generally, mascaras and eyeliners consist of high amount of film formers to feature resistance against various stress factors. Therefore a second test was conducted with following procedure: Three mascara formulations were applied with a light even coverage to a blank plate that was weighted five times before and after application. Then the treated plated were placed in a shallow dish of water and agitated for three minutes. Afterwards the plates were removed carefully and patted dry with paper towel without rubbing the surface. Each plate was weighted and product loss was calculated (Fig. 3). Traditionally there are different film forming technologies that are known to offer some of the desired properties which are Polyisobutene and products based on Polyvinylpyrrolidone (VP/Eicosene Copolymer, VP/Hexadecane Copolymer) or carboxylated resins (Acrylate Copolymer, Acrylate/ Acrylamide Copolymer). Therefore a comparative evaluation was conducted. Lip gloss formulations utilized in evalu- 38 SOFW-Journal 138 3-2012
COSMETICS ating ADC as substantivity, application, and shine aid. The test protocol was based on a survey of 10 participants who where given each of the formulas and directed to answer the questions immediately after application as directed by the study leader. One sample was tested each day, so as not to influence the final results (Table 1). The volunteers clearly judged that ADC features superior results compared to Polyisobutene and PVP Hexadecane copolymer in relation to drag on application, adherence, film forming, lip feel, shine on lips, and water resistance. Fig. 3 Evaluation of water resistance of mascaras with and without film former Control Lexorez 100 Polyisobutene PVP Hexadecane Copolymer %w/w % w/w % w/w % w/w Castor Oil 76.75 71.98 71.98 71.98 Candelilla Wax 8.23 8.23 8.23 8.23 Carnauba Wax 2.07 2.07 2.07 2.07 Microcrystalline Wax 4.19 4.19 4.19 4.19 Beeswax 1.08 1.08 1.08 1.08 Glyceryl stearate (and) PEG-100 Stearate 1.09 1.09 1.09 1.09 Lanolin Alcohol (and) Petrolatum 2.01 2.01 2.01 2.01 Caprylic/Capric Triglyceride 1.08 1.08 1.08 1.08 Ethylhexyl Stearate 2.06 2.06 2.06 2.06 Propylene Glycol Diethylhexanoate 1.06 1.06 1.06 1.06 Silica 0.13 0.13 0.13 0.13 Lexorez 100 4.77 Polyisobutene 4.77 PVP/Hexadecene Copolymer 4.77 Table 1 Lipstick formulas It is very important for many decorative cosmetic products that a long wear is guaranteed and the foundation, the eye shadow, the cream blush or the mascara stays in place. A waterproof formulation helps against sweating, humidity or is perfect for the use during sport, tanning or at the beach. But for the normal user it is sufficient when the product shows after hours still excellent performance at the spot where it is supposed to be. Therefore several formulations for transfer resistance were tested. The results for lip gloss and lipstick formulations are shown in Fig. 4. The study was conducted with following procedure: 0.035 0.050 g of lip gloss was applied to inner arm and spread over 1 inch diameter cir- Fig. 4 Transfer resistance of lip gloss formulations SOFW-Journal 138 3-2012 39
cle. This was repeated three times per formula. The lip gloss was allowed to dry for 5 minutes. Blotting paper was weighted. The lip gloss on the arm was blotted, and then the paper was weighted again to determine quantity transferred. It was repeated for each test site. The results of the study of Lightness indicate that Lexorez 100 provides the most transfer resistance properties to a standard lip gloss formula. A quantitative comparison of color transfer was evaluated using a chromameter. Lightness indicates a lack of color on the white blotting paper. A greater L value corresponds to less lip gloss transferred which can be interpreted as less lost color intensity (Fig. 5). Moreover the transfer resistance of two lipsticks was evaluated. The formulations were designed with different concepts, one was Castor Oil based, and the other one was based on polyester technology (Polyester-4). In both formulations ADC and TAGC reduced in both scenarios the transfer of the lipstick (Fig. 6). Fig. 5 Lightness of transferred lip gloss Conclusion Polymers are often used as texture enhancers, but Adipic Acid/Diglycol Crosspolymer and Trimethylpentanediol/Adipic Acid/Glycerin Crosspolymer offer much more benefits for decorative cosmetic formulations. They are are so-called oilfree polyester polymers that are able to extend wear resistance and lead to long lasting color cosmetic formulations. Due to their ability to improve film continuity and adhesion, an outstanding performance together with a comfortable wear comfort is guaranteed. They are both not mattifying but do not add to much additional shine so they are also suitable for foundations and compact make-ups. They also impart uniformity of color coverage and a powdery velvety finish. Thanks to its chemical structure TAGC additionally allows clear oil-based (water-free) formulations so even transparent lip gloss products are possible. ADC and TAGC have an excellent toxicological profile which permits problem-free the use in products for sensitive or mixed skin types. Fig. 6 Transfer resistance of two different lipsticks Literature (1) H. Butler (editor), P. Riley: Decorative Cosmetics. Poucher s Perfumes; Cosmetics and Soaps, 10 th Edition, 2000; Kluwer Academic Publishers, Pages 167-216 (2) N. Morante, Sweating in Lipsticks, June 2007; www.specialchem4cosmetics.com (3) J. Parker, A. Caragiulo, Complex Polyesters, the Castor Oil Alternative; Technical Report, Inolex Chemical Company, May 2005 (4) Z. D. Draelos, L. A. Thaman (editors), Cutaneous Formulation Issues - Lips. Formulation of Skin Care Products; Cosmetic, Science and Technologies Series; Vol. 30, 2006; Taylor & Francis Group, Pages 10-13 (5) M. R. Rosen (editor): Delivery System Handbook for Personal Care and Cosmetic Products. 2005; William Andrew Publishing (6) A. O. Barel, M. Paye, H. I. Maibach (editors), M. L. Schlossman: Decorative Products. Handbook of Cosmetic Science and Technology; 2001; Marcel Dekker, Inc., Pages 645-683 (7) K. Burch: Transfer Resistance of Film Formers; Technical Report, Inolex Chemical Company, August 2011 * Authors address: Martina Heldermann Kimberly Burch Inolex GmbH Unter den Linden 21 10117 Berlin Germany Email: k.burch@inolex.com 40 SOFW-Journal 138 3-2012