Material Selection and Application Scenarios for Three-Side Sealed Food Bags

The performance of three-side-sealed bags depends largely on the combination of film materials selected. Different types of food impose varying requirements on packaging in terms of barrier properties, oil resistance, and low-temperature resistance; therefore, selecting the appropriate materials is essential to ensuring effective packaging.

I. Common Material Combinations and Functional Orientations

Three-side sealed bags typically feature a multi-layer composite structure that combines the properties of different materials:

Transparent combination: The outer layer is made of biaxially oriented polyester (BOPP) or biaxially oriented polypropylene (BOPP), providing stiffness and printability; the inner layer is made of cast polypropylene (CPP) or low-density polyethylene (LDPE), providing heat sealability and flexibility. This combination is suitable for displaying contents such as dry goods, candies, and small snacks

High-barrier combination: Building on the transparent type, this adds a metallized layer or aluminum foil layer, or incorporates an ethylene-vinyl alcohol copolymer intermediate layer, significantly enhancing barrier properties against oxygen, water vapor, and light. It is suitable for temperature-sensitive foods such as meat, sauces, and tea.

Low-Temperature Resistant Laminates: The outer layer uses low-temperature-resistant materials, while the inner layer features a specially formulated heat-seal layer, ensuring the bag remains flexible and resistant to tearing even in frozen environments. Suitable for frozen food packaging

II. Considerations for Selecting Heat-Seal Layer Materials

The heat-seal layer is the layer that comes into direct contact with food and forms the seal; its performance affects the user experience:

Heat-seal strength: Sufficient seal strength prevents leakage during transportation and storage. Different heat-seal materials offer varying levels of seal strength.

Contamination-resistant heat-sealing: For powdered or oily foods, the seal area may become contaminated with the contents. Selecting contamination-resistant heat-seal materials ensures a reliable seal even under certain levels of contamination.

Low-Temperature Heat-Sealability: High-speed packaging machines require a lower initial heat-seal temperature to increase production speed and reduce heat loss.

III. Printing and Information Storage

The outer surface of three-side-sealed pouches typically displays product information and brand imagery. There are two main printing methods:

Surface printing: Ink is printed directly onto the outer surface of the film, resulting in vibrant colors; however, friction or scratching may damage the design.

Inner printing: Ink is printed on the inner layer of the laminated film (between the two layers of film). The design is protected by the outer layer, offering better scratch resistance; this is the mainstream printing method for flexible packaging.

IV. Accessibility Design to Enhance Usability

To enhance the consumer experience, three-side sealed bags can be equipped with a variety of additional features:

Easy-tear design: An easy-tear notch is added to one side or the top of the bag, combined with laser marking or a pre-cut tear line, to make opening easier

Zipper closure: A reusable zipper is added to the opening, allowing for the secure storage of partially consumed food items.

Hanging hole design: A round hole is provided at the top of the bag, enabling it to be hung on display hooks on shelves for convenient retail display.

Snap fastener: Similar to a zipper closure but with a wider structure, this is suitable for repeated opening and closing of large packages or heavy items.

V. Bag Selection Recommendations for Different Types of Food

Selecting the appropriate three-side sealed pouch based on food characteristics can effectively extend shelf life and maintain food quality:

Dry solid foods (nuts, candies, cookies): Transparent standard barrier pouches are recommended, as they facilitate product display and offer moderate cost

Powders or fine granules (seasoning powders, coffee grounds): Pouches with a contamination-resistant heat-seal layer are required to prevent powder from getting trapped at the seal and causing poor sealing

Foods with high fat content (fried snacks, meat products): Choose inner materials with good oil resistance to prevent fat penetration, which can cause delamination or leakage

Foods requiring light-proof storage (tea, milk powder): Select metallized or aluminum foil composite bags to effectively block light and prevent oxidation

Frozen foods: Select a low-temperature-resistant composite structure to ensure the bag does not become brittle and crack under freezing conditions, while maintaining good flexibility at low temperatures

Selecting materials for three-side-sealed food bags is a comprehensive process that requires balancing packaging performance, cost, ease of use, and environmental requirements. Understanding the characteristics and suitable applications of different materials helps in making more informed packaging decisions.