The automatic biaxial stretching film production line produces high-strength and high transparency films through unique technology, which are widely used in fields such as food, medicine, and electronics. The future development trend is towards high performance, environmental friendliness, intelligence, and diversification.

Technical principle of biaxial stretching film production line

The basic principle of plastic film processing technology is to use high polymer raw materials (such as polypropylene, polyethylene, polyester, etc.) to be heated, melted and extruded into thick sheets through an extruder. Then, in an appropriate temperature range above the glass transition temperature and below the melting point (i.e. high elasticity state), they are stretched by a certain multiple along the longitudinal and transverse directions under external force through a longitudinal and transverse drawing machine. During this process, the molecular chains or crystal planes are oriented in a direction parallel to the plane of the film and arranged in an orderly manner. Then, they are heat set under tension to fix the oriented macromolecular structure. Finally, after cooling, cutting, winding and other processes, a biaxially oriented film with excellent performance is produced.

Process flow of biaxial stretching film production line

The process flow of a biaxially oriented film production line can be roughly divided into steps such as raw material preparation, extrusion casting, longitudinal stretching, transverse stretching, heat setting, cooling, edge cutting, winding, and subsequent processing.

1. Raw material preparation:

The selection of high quality polypropylene, polyethylene or polyester polymer materials, after drying, mixing and other pretreatment, to ensure the purity and uniformity of raw materials.

2: Preheat

Before stretching, the film material first needs to be preheated. This process is usually carried out under the action of a heating roller or an infrared heater, and the purpose is to bring the film to a certain temperature, thereby reducing its viscosity and increasing its stretchability. By heating, the activity of the molecular chain structure of the film is enhanced, which lays the foundation for the subsequent stretching.

3. Extrusion casting:

The pre-treated raw material is fed into the extruder, heated and melted in the extruder, and then extruded into thick sheets through the die head. During the extrusion process, the temperature, pressure and extrusion speed need to be precisely controlled to ensure the uniformity and quality of the thick sheet.

4. Stretch lengthwise

After the preheating is completed, the film enters the longitudinal stretching stage. The process is usually carried out by a specialized longitudinal drawing device between two rolls of unequal speed. The film is sandwiched between rollers and then moved quickly on one side while the other side moves relatively slowly, causing the film to stretch along its longitudinal direction. During this process, the thickness of the film decreases while the length increases. Longitudinal stretching usually increases the strength and toughness of the film significantly.

5 Cool

After the longitudinal stretching is complete, the film passes through a cooling zone to ensure that the film retains its new shape and solidifies its molecular structure after stretching. This cooling process helps lock in the directional state of the molecular chain, preventing the film from shrinking during subsequent processing.

4. Lateral stretching:

The cooled film will enter the transverse stretching stage. The purpose of this stage is to further enhance the mechanical properties and dimensional stability of the film. Similar to longitudinal stretching, transverse stretching usually uses two sets of rollers of different speeds to stretch the film in the lateral direction. In the process of transverse stretching, the width of the film increases and the thickness decreases, which also improves its strength and transparency.

5. Heat setting:

After transverse stretching, the film is thermally set. This often relies on the combination of heating rollers and cooling rollers to maintain the orientation of the film by heating, and further improve the thermal stability, dimensional accuracy and surface properties of the film. This step is essential to ensure the subsequent processing and performance of the film.

6. Cooling and trimming:

The film after heat setting needs to be cooled quickly to fix its shape and properties. Then, the irregular part of the edge is removed by the edge cutter.

7. Roll up

The focus of this process is to roll the stretched film neatly, ensuring that there are no wrinkles and bubbles. The winding method and speed should be consistent to prevent the film from deformation or damage during the winding process.

8. Quality inspection

After winding, the quality inspection of the film is an indispensable step. Visual inspection, thickness measurement, tensile strength testing and other methods are usually used to ensure that the film meets the specified technical standards.

The drawing process of biaxial stretched film involves many links such as preheating, longitudinal drawing, cooling, transverse drawing, heat setting, winding and quality testing. Each step has a profound impact on the performance of the final product, and careful and precise execution of the stretching process is the key to ensuring the quality of the biaxial stretched film.

Product characteristics of biaxially oriented film production line

The film products produced by the biaxially oriented film production line have many excellent characteristics, which make them widely used in multiple fields.

1. High strength and toughness: Through biaxial stretching, the molecular structure of the film is uniformly and densely stretched in both longitudinal and transverse directions, thereby improving the tensile performance and tear resistance of the film. This enables biaxially oriented films to withstand significant tensile and tearing forces during use, demonstrating excellent durability.
2. High transparency: The biaxial stretching process makes the molecular arrangement of the film more uniform and orderly, thereby improving the transparency of the film. This enables biaxially oriented films to exhibit better appearance effects in the packaging industry, increasing the attractiveness and competitiveness of products.
3. Good heat sealing and printing performance: Bidirectional stretch films can maintain good heat sealing performance during heat sealing molding, while also having good printing adaptability. This makes the printed patterns on the surface of the film clearer and more durable, meeting the high requirements of the packaging and printing industry for film performance.
4. Excellent moisture resistance and temperature resistance: The biaxial stretching process makes the molecular structure of the film more dense and compact, thereby improving the moisture resistance and impermeability of the film. At the same time, the finished film also has certain temperature resistance, which can maintain stability and performance at higher or lower temperatures.

Application fields of biaxially oriented thin films

Biaxially oriented films are widely used in multiple fields due to their excellent properties.

1. Food packaging: Biaxially oriented polypropylene film (BOPP) has become the preferred material in the food packaging field due to its excellent transparency and barrier properties. It is widely used in the packaging of biscuits, candies, chocolates and other foods, effectively protecting the freshness and taste of the food.
2. Pharmaceutical packaging: Biaxially oriented polyester film (BOPET) is widely used in the field of pharmaceutical packaging due to its high strength, high transparency, and excellent barrier properties. It is commonly used as packaging material for drugs, such as aluminum foil composite film and blister packaging, effectively protecting the quality and safety of drugs.
3. Electronic product packaging: Biaxially oriented films are widely used in the field of electronic product packaging due to their excellent insulation and moisture resistance properties. It is commonly used as an inner packaging material for electronic products, such as protective films and cushioning materials for mobile phones, tablets, and other electronic products, effectively protecting electronic products from environmental factors such as static electricity and moisture.
4. Building materials: Biaxially oriented films are also widely used in the field of building materials. It is commonly used in the manufacturing of building films, such as sunshade films, insulation films, etc., effectively regulating indoor temperature and light, improving the comfort and energy efficiency of buildings.
5. Agricultural coverage: Biaxially oriented films are also widely used in the agricultural field. It is commonly used as a covering material for greenhouses, such as vegetable greenhouses, flower greenhouses, etc., effectively protecting crops from adverse weather conditions and improving crop yield and quality.

In addition, biaxially oriented films are widely used in fields such as labels, advertising, optical films, and household appliance casings, providing high-quality material support for these areas.