Due to its light weight, small size, fast heat conduction, short sterilization time, and better retention of the color and aroma of the contents, the retort bag gradually replaces some iron cans and glass jars. The impact of the process is large, so there is a potential risk of bag breakage.
Common retort bag making materials include PET, aluminum foil, BOPA, PE and CPP, etc. These materials have mechanical properties (tensile strength, peel strength and impact resistance, etc.), physical properties (moisture resistance, oxygen resistance and cold resistance and heat resistance. etc.) have their own advantages and disadvantages, so in production, two-layer, three-layer or multi-layer composite structures will be used according to the type and requirements of the content to obtain the best performance. The retort pouch has thin walls and good thermal conductivity, which can reach the sterilization standard in a short time, thus saving energy. In addition, the cooking bag occupies less space, is easy to carry, and has low transportation and storage costs, so it is deeply loved by enterprises and consumers.
However, in practical applications, because the many properties of its packaging materials are greatly affected by processes such as bag making and sterilization, retort bags have certain defects, of which “broken bags” is the most troublesome problem. In order to deeply analyze the reasons for the broken bags of cooking bags, we must first start with the production process. Conventional retort bags are usually used in the following production processes: raw material acceptance → processing → bagging → hot melt sealing → inspection → heat sterilization → cooling → dry packaging, in which the bag breakage phenomenon mostly occurs in heat sterilization and cooling.
1. Substrate problem:
The retort bag is heated together with the product, which determines that the surface material of the retort bag has very good stability after cooking, especially the dimensional stability after cooking and cooling. If the thermal stability of the substrate is not good, it is easy to appear After cooking, cooling and shrinking, the delamination will lead to bag breakage.
Countermeasures: Retort bags are generally made of PET, NY, AL, RCPP and other substrates with better high temperature resistance. Pay attention to the shelf life of various substrates, especially the shelf life of RCPP, because RCPP is used as the inner layer material for high temperature cooking. , plays a central role in the performance of the cooking bag. If the quality of RCPP is relatively poor or has passed the shelf life, it will be brittle and rupture to a large extent when it is compressed after cooking and cooling.
2. The influence of bag making process:
The temperature, pressure and machine speed of the heat sealing knife are the three major elements of the retort bag making process. In order to make a good sealing bag, a reasonable match of the three is required.
Countermeasures: Due to the high requirements of the use environment, the retort bag is generally required to have strong heat sealing strength. When making retort bags, special attention should be paid to the point sealing of the junction between the bottom and the bag body, because under the cooking conditions, as the material shrinks, the junction will become the focus of moisture and heat attack. The number of heat seals affects the heat seal strength to a large extent. Reasonable setting of the number of horizontal seals and vertical seals during bag making can well ensure that each edge has a good heat seal strength. At the same time, attention should be paid to the cooling after heat sealing. During cooling, under a certain pressure, use a lower temperature to shape the position just melted and heat sealed to eliminate stress concentration.