Comparing Triethoxycaprylylsilane and Methicone Coated Black Iron Oxides for Sunscreen Dispersion
Question
I am formulating a sunscreen containing ZnO + TiO2 (O/W emulsion, Phase A water-based + Phase B oil-based, 1 kg batch size, pH 6-6.5, Halal standard). I plan to incorporate black iron oxide color into Phase B (oil phase) at a temperature not exceeding 75°C, using Polyhydroxystearic Acid as a dispersant in non-polar oils such as Coco-Caprylate/Caprate, Cetiol CC, or Squalane.
What are the differences between these two grades of black iron oxide, and which is more suitable for this specific formulation context?
Iron Oxides Black (Triethoxycaprylylsilane Coated)Iron Oxides Black (Ultra-fine, Methicone-Coated)
Answer
The two grades of black iron oxide differ primarily in their coating material and, consequently, their dispersibility in your oil phase (Phase B).
Here is a comparison and recommendation for your sunscreen formulation (ZnO + TiO2, O/W, color in Phase B with Polyhydroxystearic Acid in Cetiol CC/Squalane):
Comparison of the Two Grades
| Feature | 1. Iron Oxides Black (Triethoxycaprylylsilane Coated) (ID 31885) | 2. Iron Oxides Black (Ultra-fine, Methicone-Coated) (ID 298) |
|---|---|---|
| Coating | Triethoxycaprylylsilane (a type of Silane) | Methicone (a type of Silicone) |
| Dispersibility | Easy to spread/disperse. The Silane coating promotes excellent compatibility and wetting in oil/silicone bases, making the dispersion process much simpler. | Difficult to spread/disperse. This grade is highly concentrated and requires a high-speed blender (high shear) to ensure even dispersion and prevent agglomeration. |
| Particle Size | Small particles, soft (standard fine grade). | Ultra-fine (average 0.5 microns). This size offers excellent color payoff and a smoother feel. |
| Water Resistance | Excellent adhesion and waterproof properties. | Good waterproof performance. |
Recommendation for Your Formula
We recommend using Iron Oxides Black (Triethoxycaprylylsilane Coated) (ID 31885).
Reasons:
- Superior Dispersibility: Given that you are dispersing the color in the oil phase (Phase B) using Polyhydroxystearic Acid in non-polar oils (Cetiol CC or Squalane), the Triethoxycaprylylsilane-coated pigment is the most suitable. Its coating is designed for easy wetting and spreading in oil/silicone systems, which will help you achieve a uniform, streak-free color in your small 1kg batch without requiring a high-shear homogenizer.
- Compatibility: The Silane coating is highly compatible with the non-polar dispersant (Polyhydroxystearic Acid) and the oil base you plan to use, ensuring stable dispersion.
- Halal Standard: Both types of Iron Oxides are mineral pigments and are generally suitable for Halal formulations, but the Triethoxycaprylylsilane coating is a synthetic compound that should be confirmed with your Halal certifier if necessary (though it is widely accepted).
Note on Methicone-Coated (ID 298): While the ultra-fine particle size is desirable, the difficulty in dispersion means that if you do not have access to a high-speed blender or ball mill, you risk having color specks or streaks in your final sunscreen. For easy manufacturing, the Silane-coated version is the safer and more efficient choice.
Technical Tips for Dispersion
To ensure the best result for your 1kg batch:
- Pre-Disperse: Mix the Iron Oxide Black with your dispersant (Polyhydroxystearic Acid) and a portion of your oil phase (Cetiol CC/Squalane) before heating Phase B.
- Heat and Shear: Heat the dispersion to your target temperature (not exceeding 75°C). Use a high-speed mixer (if available) or a homogenizer to ensure the pigment is fully wetted and de-agglomerated. Even with the easy-to-disperse grade, proper shear is essential for a perfect color.
- Check for Agglomerates: Before combining Phase A and B, check the color dispersion under a microscope or by drawing a thin film on a glass slide to ensure no visible color specks remain. This is crucial for a quality sunscreen.
