The Complete Manufacturing Process of Plastic Bags-1

Plastic Bags are made from resins such as polyethylene through processes including raw material preparation, film blowing, bag making, and quality inspection. Through melting, shaping, cooling, and setting processes, polymer materials are transformed into flexible and sealable films, which then undergo cutting, sealing, and other treatments to finally form practical packaging products suitable for various scenarios.

1. Raw Material Preparation: Laying the Foundation for Quality

The first step in Plastic Bag Production is raw material preparation, with polyethylene (PE) as the core raw material, among which high-density polyethylene (HDPE) and low-density polyethylene (LDPE) are most widely used. Raw materials undergo strict screening to remove impurities before entering the pretreatment stage. First, solid resin particles are mixed with necessary additives in proportion. Additives include antioxidants, lubricants, and colorants. Antioxidants delay material aging, lubricants ensure smooth processing, and colorants give plastic bags specific colors. The mixed raw materials are dried to remove moisture, preventing bubbles caused by water evaporation during molding. Pretreated raw material particles must pass quality testing to ensure purity, melt index, and other indicators meet production standards, providing a stable material basis for subsequent processing.

2. Film Blowing: Shaping the Film Form

Film blowing is a key step in plastic bag formation, converting pretreated raw materials into continuous plastic films. Raw material particles are fed into an extruder, where they are gradually heated to a molten state by heating devices in the barrel, with temperatures controlled between 150 - 200℃. Specific temperature parameters are matched for different types of polyethylene. The molten plastic melt is extruded through an annular die to form a tubular film blank. Meanwhile, compressed air is introduced from the center of the die, using air pressure to inflate the tubular blank, expanding its diameter several times. The inflated film moves upward under the action of traction rollers and is quickly cooled and set by cold air from a cooling air ring, forming a uniform plastic film. Film thickness is precisely controlled by adjusting extrusion speed, inflation ratio, and traction speed to ensure thickness deviation is within the allowable range.

3. Bag Making Processing: Achieving Functional Transformation

After cooling and setting, the plastic film enters the bag making process to complete the transformation from film to finished bags. First, a slitting machine cuts wide-width films into rolls of required width, ensuring neat edges without burrs. The rolls are then fed into a bag making machine for processing according to different bag type requirements. For vest bags, the bag making machine uses heat-sealing devices to seal specific positions of the film, forming sealed bottom and sides, while punching out handle shapes. Flat Bags mainly undergo heat-sealing treatment on sides and bottom. During bag making, heat-sealing temperature and pressure must be precisely controlled to ensure firm sealing without leaks. Some plastic bags also undergo printing at this stage, using gravure or flexographic printing technology to print patterns, text, and other information on the bag surface, enhancing product recognition.

4. Quality Inspection: Ensuring Product Qualification

Finished plastic bags must go through multiple quality inspection procedures to meet usage requirements. First, appearance inspection is conducted to check for defects such as bubbles, impurities, and scratches on the bag body, whether printed patterns are clear and complete, and whether seals are flat. Then physical performance tests are carried out, including tensile strength testing using a tensile testing machine to detect the film's tensile resistance; sealability testing by inflating the bag and immersing it in water to check for air leaks; and load-bearing testing by placing standard weight items in the bag to check the load-bearing performance of handles and seals. For plastic bags in contact with food, hygiene index testing is also required to detect heavy metal content, volatile organic compounds, etc., to ensure compliance with food safety standards. All qualified products are counted, packaged, and then stored for sale, ensuring reliable quality of plastic bags entering the market.