The effect of printing ink on the safety of liquid food cartons
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Liquid food carton packaging is favored by liquid food manufacturers and consumers for its convenience, environmental protection, long shelf life of liquid food at room temperature, and the production and consumption of various liquid food cartons in China. Each year, there are tens of billions of packs, including milk, tea, juice, alcohol and so on. Liquid food cartons have a common characteristic - high barrier properties regardless of their shape and production process. The raw material for production is based on food-grade base paper, and the PE film layer or the aluminum foil layer is covered on the front and back sides of the base paper by a laminating process to form a clean and hygienic high barrier material. The high barrier material is generally called PE coated paper. Or aluminum foil coated paper, which can be used in various subsequent printing methods to process a variety of liquid food cartons. Since each liquid food carton is filled in different ways, the requirements for the carton sheet are different. It is divided into two types: a coil and a single carton. The coil must be printed by flexo or gravure. For processing, a single carton is suitable for various printing methods such as flexo, gravure and offset printing. In different printing methods, the influence of printing ink on the food safety of the liquid food carton is not the same.
The first is flexographic printing. Flexo printing is a relatively environmentally friendly and hygienic printing method currently recognized internationally. Printing inks are generally made of water-based inks. The diluents are water and ethanol, non-toxic solvents, high safety factor, and the largest sales volume in the world. The proportion of Tetra Pak's Tetra Pak is based on this type of printing. However, the acrylic resin in the main components of the traditional water-based ink still contains trace amounts of toluene and other organic solvent components. In the process of printing and laminating process, the printing ink is sealed on the paper by the PE layer. Toluene and other organic solvents will remain in each carton. The coiled material must be immersed in hydrogen peroxide before being packaged in liquid food. The hydrogen peroxide will be immersed from the side of the carton into the ink layer to form a wetting channel. If the subsequent sealing strip is not heat-sealed, there is micro-porosity, packaging. After the box is formed, the liquid food is also immersed in the ink layer, so that part of the ink is released into the liquid food to form a contamination.
Gravure printing is the most commonly used packaging production method for many second- and third-line liquid food (beverage) carton manufacturers in China in recent years. Due to the rapid development of the domestic ink production industry in recent years, a series of non-phenyl alcohol soluble gravure inks have been developed, which can be applied to printing and processing liquid food cartons. However, like water-based inks, there are also trace amounts of toluene and other organic solvents in the non-phenyl alcohol-soluble gravure ink. The printed matter also has traces of toluene and other organic solvents remaining, although it is covered by a coating, if it is edge-sealed during packaging. The sealing strip is not heat-sealed, and liquid foods may also come into contact with the printing ink to form a contamination.
The offset printing method is mainly applied to the production of roofing carton. As the name suggests, the roofing bag is a roof-shaped liquid food packaging carton, which is divided into three types: non-porous roof, aluminum foil hole roof and plastic roof. It is produced in a single carton and has low production efficiency. It is mainly used in semi-automatic packaging of liquid foods with small batches.
At present, offset printing inks are generally made of synthetic pigments without heavy metals, organic solvents and synthetic resins, and have a good safety factor. However, in the printing production, because the surface of the printed matter needs to be dusted to prevent sticking, the printing powder (the main component is starch and additives) will adhere to the back side of the printed matter, that is, the side in contact with the liquid food, if before the liquid food is packaged. If the dusting is not sufficiently removed, the powder may dissolve in the liquid food to form certain contaminants. The bonding of the roof bag does not need to be heat-sealed with a sealing strip, but directly folds the bonding edge of the roof bag, and heat-sealing and bonding with the PE layer of the sheet, thereby effectively preventing the printing ink and the liquid food. Direct contact to prevent secondary pollution.
In summary, liquid food cartons are processed in any printing mode. Due to the limitations of current production processes and ink properties, there is a certain risk of contaminating liquid foods. The fundamental method for controlling pollution may be strict control. The production process, improve the testing system, minimize the possibility of pollution, so as to ensure the safety of liquid food and protect the personal safety of consumers.