260 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Production of sub-micron pigments by treatment and high solids dispersion DAVID SCHLOSSMAN and GLEN FINEMAN, KOBO Products, Inc., South Plainfield, NJ 07080. INTRODUCTION Titanium dioxide, zinc oxide, and iron oxides are essential ingredients in formulating cosmetics and toiletries. They provide color and may offer other benefits such as UV absorption, skin protection, or antibacterial properties. Pigments are known to give the maximum scattering of light of a particular wavelength, giving the best brightness and hiding power when their particles have diameters equal to half that wavelength. Sub- micron pigments approaching the primary size are produced by treating particles and subsequently dispersing the treated particles in a suitable vehicle (Table I). High solids dispersion of treated pigments produce optimum color and strength, trans- parency, UV absorption, or other activity corresponding with the pigments' primary particle size. Novel finished products and improvements such as consistency, smooth- ness, and product stability can be expected. Finished products houses will also benefit from reduced processing times in a dust-free environment. BACKGROUND Pigments are prone to agglomerate trapping air and surface water between particles. Mechanical grinding such as jet milling or hammer milling may reduce agglomerates, but non-treated pigments are likely to re-agglomerate upon dispersion in a liquid system. In order to produce sub-micron pigments, the particles must be treated. Lipophilic, hydrophobic, lipophobic, or hydrophilic treatments may be employed (Table II). Lipophilic, hydrophobic, and lipophobic treatments similarly form covalent bonds with hydroxyl groups on the surface of pigment particles. The surface-modified particles should be pulverized after treatment to reduce agglomerates created during drying. The pulverized treated pigments are ready to be dispersed in an organic vehicle as high solids. This could not be achieved with untreated pigments, because air voids and water of hydration would impair proper wetting, limiting the solids' percentage. Hydrophilic treatments are required if the dispersion system is aqueous. We have developed a Table I Production of Sub-Micron Pigments 1. Select pigment with small primary particle size 15-50 nanometers 2. Treat pigment: Hydrophobic, Hydrophilic, Lipophobic, Lipophilic 3. Match treatment with suitable vehicle 4. Premix pigment in vehicle 5. Grind high solids dispersion

PREPRINTS OF THE 1996 ANNUAL SCIENTIFIC MEETING 261 Table 11 Surface Treatments for Pigments Lipophilic Hydrophobic Lipophobic Hydrophilic Metal soap Methicone C9-15 Fluoroalcohol Isopropyl titanium triisostearate Triethoxycaprylyl silane phosphates Lecithin Dimethicone Polyionic Table III Vehicles Suitable for High Solids Dispersion Isonoyl isononanoate Caprylic-capric triglyceride Cyclomethicone Phenyl trimethicone C12-15 Alkyl benzoate Butylene glycol Tridecyl neopentanoate Octyldodecyl neopentanoate Water Table IV Micronized Pigment Dispersions (Figures 1 & 2) Refractive Primary size Surface Pigments index (nanometers) treatment % Solids Vehicle A. TiO2--rutile 2.71 15 A1 stearate 60 B. TiO2--rutile 2.71 15 A1 stearate 42 C. TiO2--rutile 2.71 35 Methicone 50 D. ZnO 1.99 15-35 ITT* 70 E. ZnO 1.99 15-35 Methicone 50 F. TiO2--anatase 2.52 50 ITT* 50 Isononyl isononanoate Phenyl trimethicone Isonoyl isononanoate Octyldodecyl neopentanoate Isonoyl isononanoate Octyl palmitate * Isopropyl titanium triisostearate (Patent #4,877,604) Figure 1. Transmittance curves. polyionic system where an ionic polymer swells the water layer separating pigment particles and is subsequently cross-linked. Charged pigment particles are electrostati- cally repulsed from each other. The treated pigments must be matched with a vehicle to optimize percent solids.