How to Make Supermarket Shopping Bags

From Raw Materials to Finished Products: An Analysis of the Precise Manufacturing Process of Supermarket Shopping Bags

In the daily operations of the modern retail industry, supermarket shopping bags play an indispensable role. They are not only tools for carrying and transporting goods but also carriers of brand image and environmental responsibility. Producing a qualified supermarket shopping bag is far more complex than simple "plastic bag production"; it involves a rigorous and precise industrial production system. This article provides an in-depth analysis of the entire production process of supermarket shopping bags, presenting each key step from polymer resin to finished packaging from a professional perspective.

Chapter 1: Preliminary Planning and Materials Science

Before the machines start, scientific planning and material selection form the foundation for ensuring product quality.

1.1 Demand Analysis and Design Specifications

First, the positioning and requirements of the shopping bag must be clearly defined:

Load-bearing standards: Determine the load-bearing capacity based on the intended use (e.g., lightweight vest bags, sturdy shopping bags), typically ranging from 5 kg to 20 kg.

Dimensions: Precisely design the length, width, side gusset width (for gusseted bags), and handle length.

Printing plan: Decide whether to use monochrome, multi-color, or full-color printing, design the graphics and text, and consider the potential impact on the material's mechanical properties.

Environmental regulations: Strictly comply with national and local "plastic restriction" policies, such as ensuring a thickness of at least 0.025 mm or directly opting for biodegradable materials.

1.2 Core Raw Material: Selection of Polyethylene (PE)

The main raw material for supermarket shopping bags is polyethylene, and its specific choice directly affects the performance of the final product.

High-Density Polyethylene (HDPE): Commonly used for making vest bags. Its highly linear molecular structure results in bags that are stiff to the touch, with high tensile strength, good surface gloss, and excellent moisture resistance. HDPE bags produce a crisp sound when crumpled.

Low-Density Polyethylene (LDPE): Often used for making flat-mouth handle bags. Its branched molecular structure gives the bags excellent flexibility, tear resistance, and transparency. LDPE bags feel soft and have good noise-reducing properties.

Linear Low-Density Polyethylene (LLDPE): Often blended with LDPE or HDPE. It combines high impact resistance, puncture resistance, and tear resistance, significantly enhancing the bag's durability and achieving a "thin yet strong" effect.

Biodegradable Plastics: Such as Polylactic Acid (PLA) and PBAT, used for producing eco-friendly shopping bags. These materials require specific composting conditions to fully degrade, and production must ensure compliance with relevant international (e.g., EN13432) or national standards.

Chapter 2: Core Production Processes

The production of shopping bags is a continuous, highly automated process, primarily divided into three main steps: film blowing, printing, and bag making.

2.1 Blow Molding: From Pellets to Film

This is the critical step of transforming plastic pellets into a tubular film.

Feeding and Melting: PE plastic pellets are fed into an extruder via a vacuum feeder. Inside the extruder, the pellets are heated and melted into a viscous melt through electric heating and screw shear.

Filtration and Extrusion: The melt passes through a multi-layer screen pack to filter out impurities and unmelted particles, ensuring film quality. The purified melt is then forced through a circular die.

Inflation and Cooling: Compressed air is introduced into the center of the tubular melt exiting the die, inflating it like a balloon to form a bubble. Simultaneously, the bubble is rapidly shaped into a film of the required thickness and width by the pulling action of the nip rolls and cooling from the air ring below. Thickness uniformity is a key control indicator in this step, ensured by the precision of the die, cooling air volume, and haul-off speed.

2.2 Printing Process: The Carrier of Brand and Information

The rolled film is printed according to design requirements.

Gravure Printing: This is the most mainstream printing method. The graphics and text are engraved onto a copper cylinder, creating recessed cells. The cylinder picks up ink from an ink pan, and a doctor blade scrapes off the excess surface ink, leaving ink only in the cells. When the film passes between the impression roller and the plate cylinder, the ink in the cells is transferred to the film. Gravure printing offers rich colors, good gradation, wear resistance, and is suitable for large-volume production.

Flexographic Printing: Uses flexible photopolymer plates and is a type of relief printing. It is more environmentally friendly (often using water-based inks) and has lower plate-making costs, but is slightly inferior to gravure printing in terms of color saturation and fine detail.

Key Quality Control Points: The printing process requires strict control of ink adhesion, color difference, registration accuracy, and ensuring the ink is completely dry to avoid blocking in subsequent processes.

2.3 Bag Making and Cutting: Forming and Function Realization

This is the final step of converting the printed film roll into individual bags.

Folding and Heat Sealing: The film is precisely folded into the desired double-layer structure through guide rollers. The bottom and sides of the film are heated and pressurized by heat sealing jaws, causing them to fuse and seal, forming the bag body. Heat seal temperature, pressure, and time are critical parameters determining seal strength.

Punching Handles: For vest bags, precision dies are used to punch handle holes on both sides of the bag opening. The punching process must be clean, without burrs or stringing, to ensure handle comfort and load-bearing strength. For handled bags, additional plastic strips (handles) are heat-sealed onto the bag.

Cutting and Counting: Continuous bag tubing is cut into individual shopping bags of set lengths using rotary knives or hot knives. The finished bags are stacked and packaged in predetermined quantities via automatic counting devices.

Chapter 3: Strict Quality Control System

To ensure every batch of shopping bags meets standards, a comprehensive quality control system must be established throughout the process.

Raw Material Inspection: Testing incoming PE raw materials for indicators such as Melt Flow Index (MFI) and density.

Online Inspection: Using online thickness gauges, vision inspection systems, etc., during film blowing and printing to monitor film thickness and printing defects in real-time.

Finished Product Testing:

Physical Performance Tests: Including tensile strength, elongation at break, and dart drop impact strength tests to verify load-bearing and puncture resistance.

Seal Strength Test: Ensuring the heat seal does not split under load.

Dimension and Weight Inspection: Checking finished product dimensions, thickness, and batch weight to ensure compliance with specifications.

Chapter 4: Industry Trends and Future Outlook

The manufacturing technology for supermarket shopping bags is continuously evolving with environmental trends and societal demands.

Lightweighting and High Performance: By using high-quality LLDPE raw materials and optimizing processes, the weight per bag is continuously reduced while maintaining load-bearing capacity, reducing plastic consumption at the source.

Popularization of Biodegradable Materials: With global efforts to manage "white pollution," the production technology for biodegradable shopping bags is maturing, costs are gradually decreasing, and their market share is expanding.

Reuse and Design Innovation: Encouraging the design of more durable, reusable shopping bags and exploring the integration of shopping bags into recycling systems for closed-loop cycles.

Intelligent Manufacturing: Introducing Industrial Internet of Things and big data to enable real-time optimization of production parameters and predictive maintenance, further enhancing production efficiency and product consistency.

Conclusion

Producing a seemingly simple supermarket shopping bag is actually a systems engineering project that integrates polymer materials science, precision mechanical design, and automation control technology. From subtle adjustments in raw material formulation to precise control of the film blowing process, and finally to strict inspection of the finished product, every step embodies professionalism and rigor. In an era that emphasizes both environmental protection and efficiency, the manufacturing of supermarket shopping bags is no longer just about fulfilling functional needs; it is also a profound reflection of corporate social responsibility and sustainable development idea. Only by upholding a professional spirit can we achieve a perfect balance of technology, environment, and commerce in this small object.