Sunscreen Products Auxiliary Ingredient: Film-Forming Agent

The function of the film-forming agent

Any polymer that can form a continuous film can be called a film-forming agent.

Film formation is a crucial step for sunscreen cosmetics to play their role in sun protection. If it does not form a film, it will be like a sieve and unable to block the damage of ultraviolet rays.

Make the sunscreen spread evenly

The filming agent can carry the sunscreen together to form a uniform, stable and flexible film on the skin surface, ensuring that the sunscreen is evenly distributed on the skin surface without leaving loopholes. Otherwise, if the sunscreen ingredients are not continuous in some places, the product will lose its protective effect.

Waterproof, sweatproof, anti-friction, prolong the protection time

Good film formation can also improve the durability of the sunscreen effect, prevent the effects of water, sweat and various friction. The film layer formed by the film agent has excellent adhesion and waterproof properties, which can prolong the protection time of sunscreen products.

The principle of film forming and auxiliary sun protection

Form a continuous film

Film-forming agents are called film-forming agents because they form a continuous film on the surface of an object by physical or chemical means.

The core principle of film-forming agent is to form a network structure between polymer chains through solvent volatilization, hydrogen bond, van der Waals force, surface tension or chemical cross-linking, and finally become a stable film. Film-forming agent is widely used in coatings, cosmetics, adhesives, pesticides and other fields.

In sunscreen products, different types of film agents have slightly different film forming mechanisms.

Solvent volatilization

When the film-forming agent dissolves in a volatile solvent such as water, the surface solvent evaporates first. As this happens, the concentration of the polymer on the surface gradually increases, forming a dense and taut film. Meanwhile, the lower layer components evaporate more slowly. Through molecular movement and diffusion, these components gradually spread evenly across the skin, ultimately creating a relatively uniform film.

Emulsion coagulation

When the film-forming agent is dissolved in the oil phase with relatively poor volatility, with the volatilization of water in the external phase, the surface tension (or capillary phenomenon) between the oil phase tends to make the gap smaller, pulling the oil phase particles together and spreading evenly, finally forming a uniform film on the skin surface including the sunscreen ingredients.

Common types and components of film forming agents

Ethylpyrrolidone derivatives:

Examples: VP/HEXADECENE COPOLYMER (SLM-V216)

It has good film-forming performance and skin affinity. After film formation, the film has good flexibility and good water resistance to prevent powder aggregation in the formula and keep the product free flow.

Silicone organosiloxanes:

Examples: TRIMETHYLSILOXYSILICATE

With exceptional water resistance, breathability, and smooth texture, this product creates a film that delivers a silky, dry feel and softness to the skin. It forms a continuous waterproof barrier with excellent powder dispersion properties. The high molecular weight enhances the film's mesh structure, providing superior long-lasting water resistance and compatibility. Its compatibility significantly improves SPF protection.

Acrylic polymer:

For example:

ACRYLATES/DIMETHICONE COPOLYMER

ACRYLATES/OCTYLACRYLAMIDE COPOLYMER

ACRYLATES/C12-22 ALKYL METHACRYLATE COPOLYMER

ACRYLATES/VINYL ISODECANOATE CROSSPOLYMER

STYRENE/ACRYLATES COPOLYMER

The film can be formed quickly, the hardness and wear resistance of the film are good, and the film forming performance can be changed by adjusting the polymer structure.

Polyurethanes :

For example: polyurethane-35

The film is tough and resistant to friction, has a good adhesion to the skin, and can adjust the flexibility and hardness of the film. 

Polyester:

For example: polyester-5

The film forming performance is stable, the compatibility with other components is good, and a uniform and continuous film can be formed on the skin surface.

While film-forming agents play a crucial role in enhancing sun protection effectiveness, their performance as polymers can be compromised when formulated improperly. Poor ingredient selection or improper formulation may result in suboptimal auxiliary effects, potentially causing skin irritation or even the undesirable "mud-scrubbing" phenomenon. Therefore, careful consideration of ingredient compatibility and strategic formulation selection is essential when applying film-forming agents.