Testing Methods for BOPP Film

Testing the properties of BOPP film is a crucial step in ensuring it meets the requirements of specific applications. In accordance with standards such as the "Quality Management Guidelines for BOPP Plastic Film Manufacturers," the testing process typically follows prescribed inspection methods and rules. Taking BOPP cigarette packaging film-which has stringent technical requirements-as an example, key quality control parameters include tensile strength and elongation, elastic modulus, thickness, oxygen transmission rate, water vapor barrier properties, heat seal strength, coefficient of friction, and thermal shrinkage.

BOPP cigarette film requires adequate tensile strength to minimize package breakage during the packaging process; generally, the tensile strength must exceed 140 N/mm² in the machine direction (MD) and 220 N/mm² in the transverse direction (TD). Elongation at break must be controlled to below 200% in the MD and below 80% in the TD. The elastic modulus is generally required to be above 2000 N/mm².

Uneven thickness in BOPP cigarette film can affect tensile strength, barrier properties, and subsequent processing; therefore, thickness control is a critical aspect of production. Given the film's thinness (typically around 20–22 μm), high-precision thickness gauges are required for measurement.

To prevent cigarettes from becoming damp or moldy, the film must possess high water vapor barrier properties; industry standards generally require a water vapor transmission rate of less than 10 g/m²·day (with an ideal value of less than 5 g/m²·day). Oxygen transmission rate must also be controlled to ensure the shelf life and quality of the cigarettes.

To accommodate high-speed packaging machines, BOPP cigarette film requires high heat seal strength and a broad heat-sealing temperature range; heat seal strength is generally required to exceed 1.5 N/15 mm. The coefficient of friction-particularly the hot slip coefficient of friction at 60°C-must be strictly controlled to ensure the film's ability to slide smoothly at high speeds under heated conditions.

Thermal shrinkage performance is another key indicator that requires testing and control.