In the production process of high-temperature cooking bags, many common problems will occur. Due to the relatively high cost, it will bring significant economic losses to the printing enterprises. Common failures include layering of high-temperature sterilization white ink, delamination of printing substrate and composite substrate, and surface wrinkling after high-temperature sterilization. In combination with the actual situation, we will analyze the phenomenon of surface wrinkling after high temperature boiling.

1、 Wrinkle form of high-temperature cooking bag after sterilization

No matter any composite bag, it is required to have good flatness, true color and excellent opening. High temperature cooking bag is no exception.

There are three types of wrinkling:

1. The printing substrate has longitudinal, transverse or irregular wrinkles.

2. The surface of the base material and the composite base material is wrinkled and cracked together, and the flatness is poor.

3. The printing substrate shrinks. The shrinkage part is separated from the composite substrate, and there is air in the middle. It is in strip form, and the peel strength is often poor.

2、 Common substrates and structure classification of high-temperature cooking bags

When most enterprises on the market are printing high-temperature cooking bags, most of the printing substrates are PET and NY, most of the middle layer is aluminum foil, and the inner heat seal layer is salivating CPP or boiling resistant PE film. Among them, PET is well shaped, with excellent frost resistance and heat resistance; N Y has poor moisture resistance and is easy to absorb moisture. Aluminum foil is an important substrate film in the soft plastic packaging industry. It is rolled at high temperature and has silver white luster. The aluminum foil used on flexible plastic packaging is 9 – 15 μ M, It is not suitable to use too much tension for unwinding and winding, because the tension is large and easy to tear. The aluminum foil does not pass through too many guide rollers directly, which is easy to crack due to folding, affecting the good barrier property. The aluminum foil has good thermal conductivity and conductivity, making it widely used in soft packaging. In high-temperature cooking bags, using aluminum foil as the intermediate layer material can improve the heat transfer speed, so that the food temperature in the cooking bag is uniform. Aluminum foil has good barrier property, and the surface should be free of oil stain. Good pretreatment before printing or laminating can make the surface tension meet the required requirements, which can significantly improve the printing fastness and the composite fastness of aluminum foil. The extruded salivation CPP reinforcement film is often used as the inner layer. The salivation CPP has good barrier property, high temperature resistance, boiling resistance, and good alkali and acid resistance. The heat shrinks, and the heat sealing strength is better. It can reach 121 ℃ for 30 minutes for sterilization. When it is 30 minutes at 100 ℃, LDPE | LLDPE EVA, mPE and other heat sealing materials can be used.

3、 Factors of Surface Wrinkle of High Temperature Cooking Bag after Sterilization

The wrinkling phenomenon found on the surface shall be carefully observed and accurately analyzed. If the printing substrate has longitudinal, transverse or irregular wrinkles.

It is mainly analyzed from three aspects:

1. During printing, the drying road temperature is too high, the constant tension of winding and unwinding is inconsistent, and the unwinding tension is too large to cause PET film or deformation.

2. The paper core of the coiling roll is not smooth. As the volume of the finished product continues to increase, the bottom of the coiling roll will be wrinkled longitudinally or transversely, making the original flat printing substrate uneven. This wrinkling phenomenon is not easy to eliminate in the composite process.

3. The printing traction roller has foreign matters or is too dirty. When the printing substrate passes through the foreign matters, it will slide laterally. When the sliding substrate passes through the imprinting rubber roller, it will be wrinkled. This kind of wrinkle is regular. One section has no one section.

4、 Influence of composite process

1. When printing compound, the ambient air must be kept dry. The lower the prominent relative humidity, the better, should not exceed 85%, otherwise the printing compound fastness will be affected.

2. Ink and adhesive: When cooking film printing, add less or no alcohol solvent to the ink thinner.