Different materials (such as cement, chemical powder, and food) have special requirements for packaging bags and bag-making processes.

Bag manufacturing is never a one-size-fits-all industry. Anyone who has worked on the front lines of packaging production knows that cement bags, chemical powder bags, and food bags, although all bags, are completely different worlds in terms of design concepts, material selection, and even the parameter settings of the entire production line. Trying to use cement bag manufacturing processes to fill coffee powder bags, or applying food bag hygiene standards to cement packaging, isn't just a misstep; it's a joke.

Today, let's break down the three types of materials—cement, chemical powder, and food—and see what special requirements they place on packaging bags and bag-making processes.

I. Cement Packaging Bags: Dustproof and Environmentally Friendly are the Top Priorities

Cement is a typical heavy, bulk material, with each bag weighing 50 kilograms. The packaging process generates a lot of dust, and the repair costs after the bags are damaged are extremely high. Therefore, the two most crucial indicators for cement bags are high strength and minimal cement leakage.

Cement packaging bags are mainly divided into laminated woven plastic bags and paper-plastic composite bags, with a maximum weight of 50kg. In terms of physical performance requirements, laminated woven plastic bags and composite bags, after heat treatment, must withstand at least 8 drops without breaking; the requirements for paper bags are relatively lenient, at least 6 drops. Simultaneously, there are strict standards for moisture resistance; after curing in an environment with 80% humidity, the compressive strength after 3 days must be no less than 85%.

At the technological level, the biggest change in cement bags in recent years is that the national standard GB/T 9774-2020 has standardized the bag-making process to square-bottom valve bags using adhesive bonding and heat sealing, completely eliminating traditional sewn-bottom bags. At the same time, the requirements for bag-making materials have been increased for woven plastic fabric and film, with the lamination quality required to be greater than 18g/m². The core technology of square-bottom valve bags is heat sealing. The valve bag manufacturing process involves several steps: cutting the tubular fabric, opening and folding the bottom corners, hot air welding, and attaching reinforcing paper to the bottom. The key is that after folding the top and bottom, high-temperature hot air is used to weld the sealing strip of the lamination layer to the bag body film layer, eliminating the need for glue. This is both environmentally friendly and reduces adhesive pollution, while also avoiding the problem of insufficient cleanliness of the bonding surface due to dust pollution, leading to poor adhesion—adhesive bonding processes require high cleanliness of the bonding surface, and the adhesion is greatly reduced once dust adheres to the bag surface, while hot air welding is not affected by dust, and the welding coefficient can reach 90%. The valve bag surface also uses ultra-micro-perforation technology to create micro-ventilation holes, resulting in a completely pinhole-free bag body. This allows for both air ventilation and prevents ash leakage. After filling, the bag has a square shape, ensuring stable stacking, high storage utilization, and a smoother and more aesthetically pleasing appearance compared to sewn-bottom bags. Of course, making cement bags is not simply a matter of welding equipment. The entire square-bottom valve bag production line involves many processes and long film travel distances, requiring high precision in the tension of the main film, the adhesion of the bottom gusseted material, and the bonding accuracy of the bottom paper. Even slight deviations can lead to insecure bottom sealing or bottom opening and curling.

By the way, don't be fooled by the fact that some factories in the industry are still making old-style sewn-bottom bags for cement plants—those are outdated product lines. After the new standards are implemented, except for some customized bags for special scenarios, the mainstream cement packaging has basically shifted to square-bottom valve bags.

Tip: In cement bag production, the gap of the heat-sealing knife is generally controlled between 1.0-1.5mm. If it's too thin, the sealing melts insufficiently; if it's too thick, it's prone to thermal stress concentration and cracking. The bottom eight layers are stacked together, and fewer than two heat-sealing passes won't achieve a complete weld. However, there are trade-offs; the center of the bottom is prone to weld penetration after multiple heat-sealing passes. Therefore, the number of heat-sealing passes must be just right—neither too few nor too many. Cooling is done with 20°C tap water or circulating water; even a slight deviation in this parameter can cause the weld to shrink and wrinkle.

II. Chemical Powder Packaging Bags: Safety and Isolation Above All Else

The complexity of chemical powders far exceeds that of cement. Today's chemical powders may be non-explosive polypropylene particles or pharmaceutical excipients with high barrier properties, but tomorrow they may be oxidants that can be fatal even with a tiny leak, flammable materials that are easily ignited when wet, or even nano-metal powders that can ignite with the slightest friction.

Therefore, the first principle for selecting chemical packaging bags is to consider the hazard level of the material: Type A ton bags are completely non-conductive and cannot be used to pack any flammable solid powders; for flammable and explosive hazardous chemicals, the packaging design must incorporate protective structures such as double seals, pressure balancing valves, and anti-static grounding terminals. More importantly, the structural design and composite process of the packaging bag material must be sufficiently robust—multi-layer structures are a common solution, with an outer moisture-proof inner film, and, if necessary, anti-static and UV-resistant coatings, along with vacuum aluminum foil packaging for external sealing, and inner packaging within metal drums, among other structures.

Fine chemicals require extremely high corrosion resistance. Certain organic acids or strong oxidizing agents can corrode ordinary packaging, necessitating the use of PTFE or HDPE as the inner lining. Photosensitive materials require the addition of UV absorbers to the outer layer, and materials that are flammable when wet may even require a three-layer moisture-proof sealing structure.

From a technological perspective, the production challenges of chemical bags lie in several aspects: First, high sealing requirements are essential. Many chemical powders are extremely sensitive to humidity and oxygen. Even a slight micropore at the seal or incomplete sealing during bag making can lead to material deterioration or even a reaction. Therefore, many chemical powder packaging materials employ vacuum sealing combined with degassing. Before filling, a vacuum pump and microporous tube are used to automatically degas the bag, minimizing the gas content. This degassing process places high demands on the bag's resistance to negative pressure. Second, antistatic treatment is crucial. The base fabric of antistatic ton bags typically incorporates conductive fibers or undergoes a coating treatment within the polypropylene woven layer, requiring a surface resistivity controlled between 10^6 and 10^9 Ω. Third, chemical compatibility is critical. For bags containing corrosive materials, the inner lining material must be tested and confirmed to have no corrosive reaction with the material. Compatibility testing must be conducted before mass production; otherwise, discovering inner lining swelling only upon shipment is too late.

There are also some more "tricky" chemical materials, such as lithium battery powder, coal powder and other flammable and explosive powders. Not only must the packaging materials themselves have anti-static properties, but the equipment on the entire filling line must also be explosion-proof. Bag making and filling must be considered simultaneously to ensure production safety.

Tip: Newcomers to the industry often overlook the "vent valve" design. Some chemical powders experience pressure differences due to temperature and humidity changes during handling and transportation. Ordinary sealed packaging will either bulge and rupture or absorb moisture and become damp—a multi-layered aluminum foil packaging equipped with a one-way vent valve can solve this problem. Also, anti-static ton bags cannot be simply slipped on; the lifting straps must be grounded to form a complete static discharge path, otherwise, it's useless.

III. Food Packaging Bags: The Red Lines of Hygiene Regulations Must Not Be Crossed

Food bags may look thinner than cement bags and lighter than chemical bags, but they have the most difficult entry requirements of the three categories—not because the equipment is complex, but because the regulations and standards system are very restrictive.

The most important benchmark is GB 4806.13-2023, "National Food Safety Standard for Composite Materials and Products for Food Contact," which has been in effect since September 2024. This standard incorporates the entire material system of food contact composite bags into its control, with clear restrictions on everything from the outer printing ink to the additives in the inner adhesive and coating, unlike the old standard which only measured the total migration amount. For exports, the EU has even stricter PPWR regulations—food contact packaging must meet the limits for heavy metals and PFAS; a total PFAS content exceeding 50 mg/kg is considered non-compliant, and packaging without a compliance declaration after August 12, 2026, will be directly detained.

The most troublesome issue in the manufacturing process is odor control. Food products like seasonings and coffee powder easily absorb solvent residues. If the residual organic matter in the ink and adhesive exceeds the standard, an unpleasant odor will waft out as soon as the bag is opened, and the entire batch must be rejected. Therefore, in the production of food bags, the selection of adhesives, the control of drying temperature, and the aging and ventilation time are all very important. Oven temperature and dwell time are two interdependent variables—too low a temperature will not allow the solvent to evaporate completely, while too high a temperature and too fast a drying time will also be problematic. The optimal baking curve is different for each composite material.

Besides odor issues, there are also challenges in packaging coordination. Most food packaging uses multi-layered composite bags—PE composite BOPP, nylon composite PE, aluminized film composite PE, etc.—the outer layer is responsible for printing stiffness, while the inner layer is responsible for heat sealing and barrier properties. Different materials have different heat-sealing temperature windows, and the temperature and pressure of the heat-sealing blade in the bag-making equipment must be precise for each layer. Many food bags now incorporate resealable zippers; uneven pressure during ultrasonic welding of the zipper can easily cause it to warp or burn through. There's also vacuum degassing packaging. Ultrafine powders like milk powder and coffee powder easily trap air during filling, requiring vacuum degassing to reduce the air content inside the bag, placing higher demands on the bag's resistance to negative pressure and its seal integrity.

In addition, microorganisms are another unavoidable hurdle. GB 4806.13 clearly stipulates that for any composite material that comes into direct contact with food and is not disinfected or cleaned before use, it must be negative for E. coli and Salmonella. This means that the cleanliness of the bag-making workshop and the packaging process of the finished product must be strictly controlled. No matter how fast your bag-making machine runs, if the air purification in the workshop does not meet the standards, the bags produced will still be unacceptable.

Tip: The biggest concern in food bag manufacturing is unclear raw material traceability. The total migration and heavy metal content of the final food packaging bag are determined based on the directly contact layers—each layer's material must be thoroughly labeled. If a layer of cheap material of unknown origin is sandwiched in between, there's no way to trace which layer's indicators exceed the limits during testing. Additionally, when using bio-based biodegradable materials like PLA to make food bags, they must be processed separately from recycled materials—firstly, the temperature control process differs significantly from traditional plastics, and secondly, it avoids cross-contamination of ordinary plastic production lines by biodegradable resins, which could lead to substandard recycled materials.

IV. General Industry Trends: Green Environmental Protection and Performance Testing

Whether in the cement, chemical, or food industries, the green transformation of packaging bags is a common trend. In the cement industry, the government's "abandon sewn bottom bags and switch to glued bottom bags" policy is forcing the entire industry to eliminate sewn bottom bags and reduce dust emissions during the packaging process. The EU's PPWR regulation requires the full implementation of recyclable packaging, recycled material content targets, and packaging minimization. In the future, exported food-grade packaging bags must comply with these regulations; otherwise, they will not even pass customs.

In performance testing, drop tests, stacking tests, and anti-aging tests are mandatory for all types of bags. The drop test standard for cement bags is eight consecutive drops without breakage, while FIBCs (Flexible Intermediate Bulk Containers) require additional tests such as top-lifting tests and cyclic lifting tests. Food contact materials exported to the EU also need to undergo specific screening for total heavy metal content and PFAS (Potentially Perceived Natural Gases). Only with these rigorous tests can packaging bags reliably reach their destination.

In general, why are there such big differences between bags, even though they are all the same type? The reason is simple: cement bags prioritize leaks, chemical bags prioritize safety, and food bags prioritize hygiene. The production logic behind each type of item is different, and the bag-making processes vary greatly. Bag making is sometimes a battle of structural mechanics, sometimes a battle of electrical and material compatibility, and sometimes a combined game of chemistry and microorganisms.

The longer you work in this field, the more you understand: good packaging is not just about containing things, but about ensuring that every particle, every gram of powder, and every gram of food inside is worthy of its contents from the moment it leaves the factory.