How Can CPP Film Meet Performance Requirements of Different Packaging Scenarios?

Why CPP Film Becomes a Common Material in the Packaging Field

In scenarios such as food packaging, daily necessities encapsulation, and industrial product wrapping, CPP film has emerged as a widely used packaging material due to its unique physical properties. Its core advantage lies in balanced comprehensive performance: CPP film (cast polypropylene film) boasts excellent heat-sealing properties with a wide temperature range (120-160℃), making it compatible with various sealing equipment. It also features high heat-sealing strength, ensuring packages are less likely to crack after encapsulation. With outstanding chemical stability, it resists acids, alkalis, and oils, avoiding reactions with components in food or daily necessities and thus safeguarding the safety of contents. Boasting a transparency of over 85%, it clearly displays products inside while offering a certain glossiness that enhances packaging aesthetics. Compared to PE film, CPP film has higher stiffness, maintaining a more stable shape after packaging and resisting wrinkles; compared to PET film, it exhibits better flexibility and excellent puncture resistance, making it suitable for packaging items with edges and corners. Additionally, CPP film can be functionalized by adding different additives—for example, antistatic CPP film is ideal for electronic component packaging, and anti-fog CPP film suits refrigerated food packaging. Such diverse characteristics enable it to meet packaging needs in various scenarios, establishing itself as an ideal choice in the packaging field.

Key Points for Controlling Heat-Sealing Temperature in CPP Film Food Packaging

When CPP film is used for food packaging, precise control of heat-sealing temperature directly affects the sealing performance and shelf life of contents. Excessively low heat-sealing temperatures result in weak seals, leading to leakage or false sealing—particularly problematic when packaging liquid or powdered foods. Conversely, excessively high temperatures cause excessive melting of film edges, resulting in scorching, embrittlement, reduced heat-sealing strength, and potential release of harmful substances that contaminate food. In practice, temperature must be adjusted according to film thickness: for 20-30μm thick CPP film, heat-sealing temperature should be controlled between 120-140℃; for 30-50μm thick film, the temperature needs to be increased to 140-160℃. Heat-sealing pressure and time also require coordinated adjustment—thin films suit 0.2-0.3MPa pressure with 0.5-1 second sealing time, while thick films need 0.3-0.4MPa pressure and 1-1.5 seconds to ensure the inner layer fully melts and bonds. Before heat-sealing, the sealing knife surface must be cleaned of impurities to prevent uneven sealing caused by local contamination. During continuous operation, heat-sealing strength should be checked hourly (using a tensile testing machine, with a passing standard of ≥3N/15mm) to prevent equipment temperature drift from affecting packaging quality.

Lamination Process and Tension Adjustment for CPP Film and PET Film

Laminating CPP film with PET film (forming PET/CPP composite film) combines their advantages—the high strength of PET and the heat-sealing property of CPP—making it widely used in high-end packaging. Tension adjustment during the lamination process is crucial for ensuring lamination quality. Both films require pretreatment before lamination: CPP film needs corona treatment (surface tension ≥38dyn/cm) to enhance adhesion with adhesives; PET film should be preheated to 40-50℃ to remove surface moisture and avoid bubbles after lamination. During lamination, tension control must follow the “gradient reduction” principle: in the unwinding stage, PET film tension is set to 20-30N, while CPP film tension is slightly lower (15-25N) to prevent stretching deformation.Tension at the lamination roller needs to be synchronized reduced by 5-10N to avoid curling caused by internal stress in the laminated roll. Adhesive coating amount should be adjusted according to film application—2.5-3.5g/m² for food packaging composite films to ensure peel strength ≥3N/15mm, and 4-5g/m² for heavy-duty packaging. Laminated rolls must be cured at 40-50℃ for 24-48 hours to fully cure the adhesive, with the rolls kept flat during curing to prevent tension imbalance due to gravity.

Impact Resistance Testing of CPP Film in Low-Temperature Environments

When CPP film is used for packaging refrigerated or frozen foods, it must possess good low-temperature impact resistance, and testing methods should simulate actual usage conditions. A commonly used test is the “low-temperature dart impact test”: CPP film samples are placed at -18℃ (simulating frozen environments) for 2 hours, then immediately fixed on the testing device. A dart head weighing 500g is dropped freely from a 1-meter height to impact the center of the film, and whether the film breaks is observed. The passing standard is that no more than 1 out of 5 consecutive samples breaks; if too many break, cold-resistant CPP film with toughening agents (usually containing 5%-10% ethylene-propylene copolymer) should be used. Another test is the “low-temperature puncture resistance test”: at -5℃, a steel needle with a diameter of 1mm punctures the film at a speed of 50mm/min, and the puncture force is recorded. Cold-resistant CPP film should have a puncture force ≥3N, while ordinary CPP film may have a puncture force below 2N due to low-temperature embrittlement. After testing, the film’s fracture surface should be inspected—smooth, brittle fracture indicates insufficient low-temperature resistance, while fibrous stretching marks on the fracture surface indicate good toughness, suitable for low-temperature environments.

Surface Treatment and Parameter Settings for CPP Film Before Printing

CPP film has a smooth surface and low polarity, requiring surface treatment before printing to enhance ink adhesion, with corona treatment being the most commonly used method. Key parameters for corona treatment include discharge power, processing speed, and electrode distance: discharge power must be adjusted according to film thickness—1.5-2kW for 20-30μm CPP film and 2-3kW for 30-50μm film. Insufficient power results in low surface tension (below 36dyn/cm) and easy ink peeling, while excessive power causes over-oxidation of the film surface, leading to aging and yellowing. Processing speed should match the production line speed, typically 30-50m/min—too fast causes insufficient treatment, while too slow affects production efficiency. Electrode distance (distance between electrode and film surface) must be maintained at 1-2mm—too large reduces discharge intensity, while too small may scratch the film surface. Printing should be completed within 24 hours after treatment to avoid surface tension attenuation over time. Before printing, surface tension must be tested (using a tension test pen) to ensure it reaches the optimal printing range of 38-42dyn/cm, guaranteeing uniform ink layer adhesion that resists peeling even after friction or boiling.

Relationship Between Oxygen Transmission Rate and Shelf Life of CPP Film for Cooked Food Packaging

When CPP film is used to package cooked foods (such as meat and bean products), oxygen transmission rate (OTR) is a key factor affecting shelf life, requiring OTR control according to food characteristics. Excessively high OTR causes food oxidation and spoilage (such as meat browning and fat rancidity), while excessively low OTR may trigger spoilage due to anaerobic bacteria growth. Ordinary CPP film has an OTR of 300-500cm³/(m²·24h·0.1MPa), suitable for packaging cooked foods with short shelf lives (1-3 days). High-barrier CPP film, made by adding barrier resins (such as EVOH), can reduce OTR to below 50cm³, extending shelf life to 7-10 days. In practical applications, OTR must be adjusted according to storage temperature: at 25℃ room temperature storage, OTR should be controlled at 100-200cm³ to balance oxidation and anaerobic environments; at 0-4℃ refrigeration, OTR can be relaxed to 200-300cm³ as low temperatures slow oxidation and bacterial reproduction. Packaging should be combined with vacuuming or nitrogen flushing (oxygen content ≤5%) to reduce initial oxygen content in packages, creating a synergistic effect with CPP film’s OTR to ensure cooked foods maintain color, flavor, and safety within their shelf life.