The number of layers and structure of composite plastic bags have great flexibility according to the requirements of different applications. Generally speaking, they are composed of 2 to 7 layers or more, and each layer plays a specific function to ensure that the material has the required performance.
1. Outer layer (printing layer/protective layer)
Material: Common materials include BOPP (biaxially oriented polypropylene), PET (polyethylene terephthalate), etc.
Function: The outer layer is responsible for the appearance of the bag and also plays a protective role. It not only supports high-definition printing to make the packaging visually attractive, but also provides wear resistance to prevent damage due to friction or other external factors. The outer layer also protects the printed content inside from scratches or humid environments.
Application: Food, daily necessities and consumer product packaging usually need to have a beautiful appearance, so the outer layer material usually has good transparency and printing adaptability.
2. Adhesive layer
Material: Use special adhesives such as polyurethane glue or other environmentally friendly adhesives.
Function: The main function of this layer is to tightly combine different functional layers. Since composite materials are usually composed of a variety of different materials, the adhesive layer ensures a strong connection between these layers and prevents the materials from delaminating or peeling during use.
Application: In composite multilayer packaging, the adhesive layer is an indispensable part, especially in the bond between the barrier layer and the outer layer.
3. Barrier layer
Material: Common materials include aluminum foil, EVOH (ethylene-vinyl alcohol copolymer), PVDC (polyvinylidene chloride), etc.
Function: This layer is one of the most important functional layers in the composite material. It mainly provides barrier properties to prevent the penetration of air, oxygen, water vapor and light, thereby extending the shelf life of the product. For example, the aluminum foil layer can almost completely block light and gas, while EVOH has excellent oxygen barrier properties.
Application: This type of material is widely used in food packaging (such as coffee bags, milk powder bags) to ensure that the food inside the package does not deteriorate due to contact with air and moisture.
4. Middle layer
Material: Usually PA (polyamide, commonly known as nylon), EVOH and other materials are used.
Function: The middle layer provides strength and toughness in the composite material, improving the tear and puncture resistance of the bag, especially when storing sharp or heavy objects. PA materials are known for their excellent mechanical properties. They are not only wear-resistant and have high tensile strength, but also maintain good flexibility.
Application: Commonly used in packaging that needs to withstand high pressure or heavy objects, such as frozen food bags or industrial product packaging.
5. Moisture barrier
Material: PE (polyethylene), PP (polypropylene), etc.
Function: The main function of this layer is to prevent moisture or humidity from penetrating and ensure that the items inside the package remain dry. Especially in food packaging, the existence of a moisture barrier is crucial. PE materials are both moisture-proof and have good heat-sealing properties. They are often used in the packaging of products that need to be moisture-proof, such as food and medicine.
Application: Used for packaging items that are sensitive to moisture, such as dry goods, biscuits, and medicine packaging.
6. Heat sealing layer
Material: PE, CPP (cast polypropylene), etc.
Function: The heat sealing layer is usually the innermost layer and is used to seal the bag. This layer is sealed by hot pressing technology to ensure that the bag has excellent sealing performance and is not easy to crack. Both PE and CPP have low melting points and can be easily sealed by heat sealing machines.
Application: Commonly used in packaging products that require heat sealing, such as food packaging bags and ziplock bags, to ensure packaging sealing and ease of use.
7. Special functional layer (optional)
Material: Antistatic layer, anti-ultraviolet layer, oil-resistant layer, etc. can be selected.
Function: According to specific uses, composite materials can also add some special functional layers. For example, for the packaging of electronic products, an antistatic layer is necessary; and for the packaging of oily foods, an oil-resistant layer can prevent grease penetration.
Application: Special functional layers are mostly used in product packaging with special needs, such as packaging of electronic components and packaging of outdoor products.
The multi-layer design of composite plastic roll bags can be adjusted and optimized according to specific uses. Common composite materials include two layers (such as PE+PA) or three layers (such as PET+AL+PE). When enhanced protection or higher barrier properties are required, more functional layers will be added, such as five-layer and six-layer structures. Multilayer composite bags are widely used in food, medicine, chemical industry and other fields due to their high barrier properties, durability, moisture resistance, gas resistance and light resistance. At the same time, with the development of technology, composite materials can also achieve more functions, such as environmental protection, biodegradability, high temperature resistance, etc., to meet the needs of different customers.
