Using Acrylates Copolymer for Water Resistance in Sunscreen: Disperser vs. Film Former
Question
I am developing a sunscreen formulation and need to achieve water and sweat resistance. I am currently reviewing Ammonium Acrylates Copolymer (a pigment disperser for water-based formulas).
How should Acrylates Copolymer be correctly used in a sunscreen formulation to create a robust water and sweat-resistant film? Should I use this specific grade, and what are the recommended usage rates and mixing methods for achieving water resistance claims?
Answer
The specific product you are reviewing, Ammonium Acrylates Copolymer (ID 9096), is primarily marketed as a pigment disperser for water-based formulas, with a recommended usage rate of 0.1-3%. While it belongs to the Acrylates Copolymer family, this grade is optimized for pigment stabilization, not robust film-forming for water resistance.
To create a strong water and sweat-resistant film in a sunscreen, you generally need a specialized film-forming polymer (often another grade of Acrylates Copolymer or similar polymer) used at a higher concentration.
How to Use Acrylates Copolymer for Water Resistance:
- Select the Correct Grade: Use a grade explicitly designed as a film former for sunscreens (e.g., Acrylates/C12-22 Alkyl Methacrylate Copolymer or similar specialized polymers).
- Usage Rate: The concentration must be significantly higher than a disperser. Dedicated film formers are typically used ranging from 5% to 15% of the raw material (depending on the active polymer content and the desired water resistance level, e.g., 40 or 80 minutes).
- Mixing: Incorporate the polymer dispersion directly into the water phase of your emulsion.
- Mechanism: The polymer forms a continuous, water-insoluble film on the skin as the product dries, which locks the UV filters in place and prevents wash-off by water or sweat. This is the key to achieving water resistance claims.
