Additives to Improve Antifog Performance （添加剂改善Antifog性能）.pdf

Additives to Improve Antifog Performance Background The formation of “fog” on plastic film or sheet is the result of the condensation of water vapor on the surface of transparent sheet or film. The physical condition that causes this may be the result of a number of things: • The temperature of the film surface on the inside falls below the dew-point temperature of the air and water vapor that is within the headspace of the article • Air near the film’s surface cools to a temperature at which it can’t retain all the water vapor; as a result, excess water condenses on the film’s surface. This effect is based on the relationship between the temperature of enclosed air, the relative humidity of the air, and dew point temperature • The difference between the surface tension of the condensed water and the critical wetting tension of the film’s surface In packaging applications, food that is being wrapped or stored in a plastic article usually has high moisture content. When this packaged item is stored in a cool environment, the moisture condenses on the surface causing fog to occur. Depending upon the application, this fog is typically not considered aesthetically pleasing and may impact food spoilage. There are two routes the packaging industry uses to minimize the formation of fog on sheet, film, or thermoformed articles: internal additives or external topical coatings. Internal Additives Internal antifog additives are generally non-ionic surfactants. These additives are added at the film producers mainly in form of concentrates or master batches. These additives usually have a certain level of incompatibility with the polymer matrix they are blended into, and as a result, migrate to the surface. The internal agents have a level of durability over time with regards to maintaining the antifog performance since there is a source of the agent