How can food packaging bags achieve zero defects? Try this!

High-temperature retort pouches are a common type of food packaging bag. They are made from plastic films, metal foils, or composite materials to create airtight and light-blocking bags. After melt sealing, they are sterilized by heating under pressure and used to contain processed foods. Because of their long shelf life, easy opening, and convenient post-processing, they are very popular with customers. Below, Shunxingyuan Packaging, a professional flexible packaging manufacturer, analyzes the processing applications and technical requirements of high-temperature retort pouches, and how food packaging bags can achieve zero defects.

1. Basic Processing Structure of High-Temperature Retort Pouches

According to user-specified requirements, the type of contents, and the form of circulation, the product structure of high-temperature retort pouches is generally divided into three categories: two-layer film, three-layer film, and four-layer film structures. Two-layer films are generally BOPA/CPP, PET/CPP; three-layer film structures are PET/AL/CPP, BOPA/AL/CPP; four-layer film structures are PET/BOPA/AL/CPP, PET/AL/BOPA/CPP.

2. Performance Requirements of High-Temperature Retort Pouches

High-temperature retort pouches are usually stored at room temperature and require a long shelf life, generally exceeding one year. Therefore, higher requirements are placed on the quality of the composite packaging:

1. The appearance is smooth and flat, without wrinkles, bubbles, or foreign matter.

2. Non-toxic, odorless, residual solvent measurement less than 5mg/m2.

3. Completely sealed, water vapor permeability is close to zero, for three-layer and four-layer structures, it is no more than 0.5g/m2·24h.

4. Light-blocking and gas-impermeable. Ordinary PET/CPP bags have slightly lower requirements, with oxygen permeability no more than 3000px3/m2·24h·atm, and three-layer and four-layer structures 12.5px3/m2·24h·atm.

5. No leakage, excellent oil resistance, oil absorption rate no more than 1%.

6. Excellent heat and pressure resistance, no deformation or delamination after high-temperature sterilization at 121℃ for 40 minutes.

3. Processing Requirements for High-Temperature Retort Pouches

Many companies, although strictly controlling the personnel, materials, and equipment aspects in the processing of high-temperature retort pouches, the products produced are still unsatisfactory, and they frequently receive customer complaints due to pouch expansion and delamination of composite bags. The following aspects should be noted in actual production:

1. Selection of printing inks. Specific high-temperature retort inks are used, which do not turn yellow or black after sterilization at 121℃ for 40 minutes. Two-component polyurethane inks are mostly selected.

2. Selection of composite adhesives. Generally, two-component polyurethane adhesives that meet the sterilization requirements are selected.

3. The choice of structure is also important. Appropriate structures should be selected according to customer requirements.

4. The coating amount, coating mesh roller, adhesive processing viscosity, and oven temperature must be strictly controlled. The coating amount should be maintained at around 4-5g/m2, the coating roller is generally selected at around 80 lines/inch, and the cleanliness of the coating roller should be checked before compounding to ensure the coating amount and coating state. The oven requires good ventilation and a clean environment (one point is one source of damage).

5. Sufficient curing. To ensure the complete main curing reaction of the retort adhesive and guarantee the compounding quality, a curing period of 40℃-55℃ for 3-5 days is required.

6. Retort compounding also has high requirements for aluminum foil. Aluminum foil with a thickness of 7μm-15μm should be used. For 135℃, 9μm or more should be selected. In addition, attention should be paid to the pinhole diameter and number of pinholes. There should be no dense, continuous, or periodic pinholes.

7. Storage requirements for AL and NY. Aluminum foil product cores should have a certain strength. Each roll of product should be tightly wrapped with a layer of clean and hygienic neutral or weakly acidic moisture-proof paper or wrapped with a layer of clean plastic film, and the joints should be sealed with adhesive tape. Rolls should be separated by soft pads and tightly pressed together without gaps to ensure that the end faces are not damaged. During transportation, moisture and high temperatures must be prevented, and the shelf life is one year. NY film storage requirements: Due to the high hygroscopicity of NY, it must be wrapped with aluminum foil.

8. Selection of ethyl ester. For ethyl esters used in composite retort pouches, the water and alcohol content must be more strictly controlled.

9. The inner layer uses a high-temperature-resistant retort-grade CPP film, which has high temperature resistance, good strength, and heat sealability. The CPP surface tension is required to be >40dyn/cm (for 121℃, the CPP surface tension >39dyn/cm is sufficient).

10. Random corona treatment will achieve better compounding effects and make the compounded retort pouch materials more stable. Random corona treatment is used when compounding retort pouches with aluminum foil structures.

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