Intellectual Property Trends in Color Cosmetics
Recent patent activity in color cosmetics is summarized in this article. Trends toward natural-looking makeup, iridescence and transfer-resistance are evident.
Robert Y. Lochhead and Laura Anderson
The Institute for Formulation Science and The School of Polymers & High Performance Materials
The University of Southern Mississippi
There is a pronounced effort to devise new ways to develop “no makeup” makeup; that is, makeup that hides blemishes but leaves skin looking natural. There is also a noticeable trend to produce and manipulate color formed by iridescence. Attempts continue to improve transfer resistance and effective gelling with lower polymer concentrations.
A great deal of recent patent activity has focused on “no makeup” makeup. These products attempt to hide imperfections while enhancing natural beauty rather than covering it with thick coats of matte makeup containing high contents of pigments such as iron oxides. The latter approach covered blemishes but did not disguise the fact that a woman’s skin may have had a dull, drab appearance. Reducing pigment loads and adding moisturizers provide a more natural appearance but these systems do not address the issue of “natural” facial color. Soft focus particles and fractal particles of inorganic pigments obscure skin imperfections.
Recently there has been a flurry of activity to diffract, refract and reflect light to disguise skin imperfections. Much of this effort has been focused on composite particles, which are designed to overcome the challenge posed by packed inorganic pigment particles on the skin surface that become visible and look unnatural. Physical blends of elastomer particles and pigment have been proposed1,2 but, according to P. Maitra et. al., they can phase-separate on the skin and the pigment particles tend to collect in pores and wrinkles. Unfortunately, particle concentration in blemishes emphasizes the flaws that the user is trying to hide. Adding nacres to conventional pigmented systems can produce shadows that enhance, rather than hide, the wrinkles. Nacres are platelets that are covered with closely packed particulate pigments. For example, Timiron nacres from Merck are mica coated with titanium dioxide, iron oxide or bismuth oxychloride.
Hiding Wrinkles and Blemishes
Avon researchers have tackled this challenge by embedding sub-micron pigment particles on silicone elastomer gels.3 This can be achieved, for example, by applying substantial shear and compression to cyclopentasiloxane (and) C30-45 alkyl cetearyl dimethicone copolymer (Velvisil 125 Silicone Copolymer Network from Momentive) and alkyl silane-treated TiO2 using a Hosakawa Micron Merchanofusion System. The refractive index of the embedded particles is greater than that of the elastomer gels and when the composite gels are applied over skin imperfections, the light falling on the gel is scattered backward and forward to effectively conceal the blemish.
|Natural-looking makeup is always in fashion.
Blemishes can be rendered translucent by glass beads coated with a polyamide or nylon layer.5 Glass plate- lets coated with silver (Metashine from Nippon Sheet Glass) improve the luminance of particle-containing cosmetics, but these advantages can be negated by a yellowing of the bright pigment because short wavelength light has lower reflectance than long wavelength light. This yellowing effect can be suppressed by alloying the silver with minor amounts of noble metals selected from gold, palladium and platinum.6
Hollow glass particles less than 25 microns in diameter refract light to produce blemish-hiding skin treatments that look soft and confer a texture more like natural skin.7 Similarly, glass beads as large as 180 microns have been coated with colored polymer layers to achieve hiding effects but such large particles are clearly visible and this would likely detract from their utility.8 Ciba, recently acquired by BASF, introduced the reverse of this concept by micro-encapsulating colored pigments with polystyrene or poly(methyl methacrylate) to provide camouflaging opacity.9 A variation of this theme is to coat small glass-bead lenses with polyurethane having refractive indices in the range 1.25 to 1.75.10 The coating provides a double convex lens that effectively conceals visual signs of aging, wrinkles and other imperfections, and the polyurethane coating provides wearable comfort to the user. The refractive indices of the glass and the polymer do not need to differ much.
An alternative approach is to coat pigment particles with networks of smaller particles that have significantly higher refractive indices.11 These composite pigments hide wrinkles and large pores and they have a transparency that makes the skin look natural.
Alternatively, base-coat/topcoat systems can be utilized to diffract or reflect light away from wrinkles.12 This is manifested in systems that comprise a basecoat with a higher refractive index than the topcoat. Alternatively, the basecoat can be pigmented and diffusers, such as nylon particles, can be included in the topcoat.
|The right chemistry can help women’s skin appear flawless.
1. Light and cool: 70 > L* > 55 and 55° >h> 40°;
2. Light and warm: 70 > L* > 55 and 70° >h>55°;
3. Dark and cool: 55>L*>35 and 55° >h> 40; and
4. Dark and warm: 55>L*>35 and 70° >h>55°.
The potential inventors introduce a natural non-makeup that lies outside these conventional ranges. For example, for “light and cool” non-makeup, the color space of the product in the bottle occupies a color space defined by 75> L*> 55 and hue < 25°. A non-makeup that lowers the spectral reflectance at about 550nm meets these requirements for a healthy skin look. Such a product can be made using polysaccharide beads (Unispheres from Induchem) loaded with 40% pigment comprising titanium dioxide and red iron oxide. The beads are encapsulated by an acrylate copolymer and a nonionic alkoxylate.
Pressed Cake Products
Pressed cake powders must have weak structures to permit adequate pay-out during application, but the resulting inherent fragility can cause these products to flake, crumble or crack upon impact. Conventionally, the structures are strengthened by the application of wet and dry binders. The wet binders are ester oils, but when these interact with skin oils, they can “glaze” which can reduce the transfer of product to the skin. The structure may be strengthened by melting and re-solidying wax in the pressed cake.14
Flaky extender pigments such as talc, mica and sericite are commonly added to pressed powder cosmetics to confer luster, softness and ease of payout from the pressed cake. However, these natural products contain impurities such as iron, which tend to cause darkening in the presence of cosmetic oils. On the other hand, synthetic substitutes such as synthetic mica and flaky silica can be made iron-free but these materials are rather brittle and tend to be crushed during normal processing. This reduces the aspect ratios of the particles, which in turn detracts from the desired luster and mechanical properties of the pressed powders. Moreover, the manufacturing process for these materials can result in extender pigments that are too glossy and this also detracts from the desired luster when applied to the skin.
Irregularly-shaped silica gel can be used as an extender pigment, but this is a porous material which tends to absorb moisture from the skin and then aggregates, which results in poor spreadability and rough skin. Nippon Sheet Glass Company has attempted to address this challenge by making glass flakes from E-glass or boron-free E glass.15 E-glass is the high-tensile strength material that forms the reinforcing component of “fiberglass” composites. Glass flakes with high aspect ratios can be made from E-glass and these survive processing better than synthetic mica or flaky silica. These tough, smooth, transparent E-glass flakes adhere well on skin to give a “natural” finish.
Diffraction and Iridescence
Glass can also be coated with rutile (titanium dioxide) to give pigments that iridesce with a blue, green, yellow or silvery sheen. These diffractive effects arise from the same phenomenon that produces the brilliant colors of peacock feathers, namely from interference effects of light as it interacts with lattice “gratings” formed by regular arrays of feathers in the peacocks’ tails. Iridescent effects are also responsible for the pearlescence inside the shells of mollusks and such effects can be produced synthetically in nacres.
Goniochromatic coloring agents change color depending upon the angle from which they are viewed. These are interference multilayer pigments exemplified by Sicopearl from BASF, Xirona from Merck (Darmstadt), or Infinite Colors from Shiseido.
Goniochromatic effects can also be obtained from multilayered polymer films, such as Color Glitter from 3M or Micro Glitter Pearl from Venture Chemical. If the refractive indices of the polymer layers are adjusted to cause total internal reflection, reflective pigments can be formed; for example, layers of 2,6-poly(ethylene naphthalate)and poly(methyl methacrylate) available from 3M as Mirror Glitter. Goniophotometric pigments can be used in nail polishes to give interesting optical effects in air-cured, transparent nail polishes. They may even alleviate the solvent odor and longer wear properties than conventional nail varnishes.16
Diffracting pigments comprising an ordered lattice of monodisperse particles can produce opalescence. Spectra- flair pigments from JDS Uniphase Corporation are examples of such pigments. Colloidal crystals are well-ordered arrays of monodisperse particles. If the particle sizes and interparticle spacing are in the correct range, these arrays can become “photonic crystals” that produce interference colors by interaction with visible light. In this respect, L’Oréal scientists have recently disclosed their attempts to achieve such iridescent colors on keratin by depositing ordered lattices of monodisperse particles.17 The keratin is first coated with a film-forming polymer, exemplified by an acrylate/ammo- nium acrylate copolymer called Ultrasol 2075 from Ganz Chemical, and then the monodisperse particle layer is applied on top of the film-forming polymer to produce a photonic crystal layer with improved color.
If the particles have sufficient magnetic susceptibility, the optical patterning effects can be changed by aligning them by imposition of a magnetic field.18
Dye-polymer complexes with outstanding stable coloration have been described in a recent Ciba patent application.19 The complexes are formed from cationic polymers with a range of anionic dyes. It is interesting that claim one specifically excludes the cationic polymers polyvinylamine hydrochloride and polyquatrnium-6. The polymer-dye complexes are exemplified as colorants for a broad range of products, including shampoos, styling spray, moisturizing cream, nail lacquers, eyeshadow, face powder, O/W foundation, lipstick and sunscreen.
“Dry water” cosmetics are powdery compositions in which hydrophobic particles trap an aqueous phase. These preparations have the appearance of a powder but when applied, the water is released by rubbing and the product spreads like a lotion to produce a cool, fresh sensation. These products are difficult to make in a stable form. One approach to confer stability has been to include gelling agents to contain the aqueous phase but such compositions tend to cake and streak. Kosé researchers reportedly found a “dry water” powder that is stable, does not streak and confers a cool fresh sensation when applied to the skin.20 This is achieved by combining specific hydrophobic particles with specific plate like particles in the composition. The hydrophobic particle can be hydrophobized silicic anhydride, spherical poly(methyl methacrylate), silicone-treated titanium dioxide, fluorine-treated talc, or metallic soap treated sericite, or silicone-treated Red No 226.
In this instance, plate-like particles were exemplified as plate-like poly(methyl methacrylate), plate-like polystyrene powder, silicone-treated mica, or silicone treated plate-like polystyrene powder. “Dry-water” powder foundation and eyeshadow were prepared from these blends of particles and plate-like particles.
Transfer-resistance, inspired in the 1990s by Revlon’s Colorstay products, remains a preferred attribute. Color-stay achieved transfer resistance by including silicone resins in the formulations. Recent attempts have been made to achieve transfer resistance by including film-forming polymers in color cosmetics. In this application, the physical demands on the polymer are considerable. For example, the polymer must adhere to the substrate and be capable of massive extensions that are experienced from a smile, a yawn and the significant compression from a “pucker.” Moreover, the polymers must resist food oils and liquids ranging from water to alcohol to hot beverages to sweat and sebum. Now, improvements are claimed by applying a film comprising a silicone resin and a polyamide-silicone copolymer over the color layer on the keratin.21 The system is provided as a “kit” that includes the coloring composition, the film-former and may even contain a remover component. These films reportedly resist several washing cycles.
The advent of living free radical polymerization has initiated the exploration of block copolymers for these film-forming purposes because such polymers can be designed to simultaneously possess the conflicting properties desired.22 Recently, gradient copolymers have been billed as improvements that offer advantages in rheological properties while being easily employed from cosmetic oils.23 The preferred gradient polymers comprise two monomers chosen from isobornyl or isobutyl acrylate or methacrylate and 2-ethylhexylacrylate.
Ethylenediamine/stearyl dimer dilinoleate and tallate copolymers have been used for several years as oil-phase gellants. The advantage of these polymers is the clarity they confer on the gels. The clear gels convey more intense and brighter colors than the traditional wax gellants. Arizona Chemical has introduced variants to this chemistry by linking internal polyether blocks and internal fatty blocks into the polyamides.24 The new polymers have higher molecular weights and are effective as gellants at lower concentrations than previous polymers. They are viscoelastic thickeners in some solvents and soft or hard gels can be tailored by judicious selection of solvents. The higher molecular weights favor the formation of better films upon evaporation of the solvents and the new polymers do produce tough flexible films.
Oligoesters of glycerin, behenic acid, eicosane diacid (Nomcortt HK-G from Nisshin OilliO) are also useful wetting agents for W/O lipglosses.25
In summary, the following trends were identified:
• The development of a wide range of composite particles that hide skin blemishes by diffracting, reflecting or scattering light.
• The production of colors by iridescence from photonic crystals.
• Continuing efforts to improve transfer resistance and effective gelling with ever lower concentrations of polymer.
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