Gray mailing bags have become one of the most common packaging options in modern e-commerce and logistics. They are not only waterproof, tear-resistant, and tamper-evident, but also offer excellent privacy protection. These premium features are achieved through a rigorous and scientifically rigorous film blowing and bag-making process.
I. Film Blowing Process: The Evolution from Particles to Film
Entering the production workshop, the first thing that catches your eye is the neatly arranged film blowing machines. The raw materials used to produce gray mailing bags are primarily LDPE, LLDPE, and a moderate amount of recycled PE granules. Gray masterbatch is then added to ensure uniform color and strong light-blocking properties, depending on customer requirements.
Loading and Melting:
The raw materials are fed into the extruder hopper via an automatic loading system. The screw then heats, extrudes, and melts the material at high temperatures. Precise temperature control in each heating zone ensures uniform plastic melt flow.
Extrusion and Film Forming:
The molten plastic is extruded through the die, where it is cooled by a powerful air ring to form a bubble-like film. Workers carefully adjust the air pressure and pulling speed to ensure a stable film thickness and smooth surface.
Cooling and Winding:
After the bubbles are stretched and formed, they are flattened by guide rollers, forming a double-layer film roll. An automatic thickness gauge monitors the film thickness in real time, ensuring it remains within a ±3% tolerance. The film is then wound into smooth gray rolls, ready for the next bag-making process.
2. Bag-Making Process: Precision Manufacturing from Film to Finished Product
The gray film rolls, after blown film, are delivered to the bag-making workshop for the molding process of mailing bags.
Printing:
According to customer requirements, a company logo, warning message, or environmental label can be printed using a flexographic printing machine. The printed colors are accurate, the adhesion is strong, and it resists rubbing and fading.
Laminating and Flanging:
Some express bags feature a double-layer design, with a black inner layer and a gray outer layer, providing both light-blocking and aesthetically pleasing results. The bag-making machine precisely aligns the two layers of film, folds the edges, and heat-seals them to ensure a neat bag shape.
Heat Sealing and Bag Cutting:
Under the high-temperature pressure of a heat-sealing knife, the bag opening, bottom, and sides are securely sealed. The equipment, equipped with a photoelectric tracking system, automatically cuts bags based on printed markings, ensuring consistent size and smooth edges for each bag.
Strip Application:
Mailer bags are typically sealed with a disposable adhesive strip. This design ensures that the sealed bag cannot be opened again, preventing tampering during transport and protecting user privacy.
Inspection and Packaging:
Each batch of finished bags undergoes multiple inspections for appearance, size, thickness, and adhesive strip adhesion. Once qualified, they are neatly packaged and packed into boxes for shipment.
3. Lean Production and Quality Assurance
From film blowing to bag making, every process is carried out in a constant temperature and clean production environment.
Fully automated equipment ensures production efficiency;
Experienced operators monitor quality in real time;
Samples are retained for testing of each batch, complying with ISO9001 and ISO14001 quality management system standards. It's this meticulous approach to craftsmanship that ensures each gray mailing bag is:
thick and durable, waterproof and tear-resistant, light-blocking and privacy-enhancing, and safe and environmentally friendly.
