The Effect of Printing Ink on the Safety of Liquid Food Cartons

Liquid food carton packs are favored by liquid food manufacturers and consumers for their convenience, environmental protection, and longevity of liquid foods at room temperature. A variety of liquid food cartons, including Tetra Pak, Combibloc, Roof packs and so on, in China's production volume and consumption amounted to tens of billions of packs per year, the types of milk, tea, juice, alcohol and so on. The liquid food cartons have a common characteristic of high barrier properties regardless of their shape and production process. The production raw materials are based on food-grade raw paper. After the lamination process, PE film or aluminum foil is coated on the front and back sides of the paper to form a clean, hygienic high-barrier material. This high-barrier material is commonly referred to as PE coated paper. Or aluminum foil coated paper, can be used for a variety of subsequent printing methods into a variety of liquid food cartons. Due to the different filling methods of each liquid food cartons, the requirements for the carton sheets are also different. They are divided into two kinds: coils and individual cartons. The Tetra Pak is a roll and the roof pack is a single sheet. Boxes and coils must be printed by flexo printing or gravure printing. A single carton is suitable for flexo, gravure, offset, and other printing methods. Different printing methods are used to print ink to liquid food paper. The effect of the food safety of the box is not the same.

The first is flexo printing. Flexo printing is a relatively environmentally friendly and hygienic printing method that is currently recognized internationally. Printing inks generally use water-based inks. Their diluents are water and ethanol, and are non-toxic solvents. They have a high safety factor and account for the largest sales in the world. The proportion of Tetra Pak's Tetra Pak uses 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. During printing and subsequent laminating, the printing ink is sealed on the paper surface by the PE layer. Toluene and other organic solvents still remain in each tray. Tetra Pak must be immersed in hydrogen peroxide solution before packaging liquid foods. Hydrogen peroxide can be immersed into the ink layer from the side of the carton to form a wetting channel. If the subsequent edge seals are not heat-sealed, they have micropores. 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 cause contamination.

Gravure printing is the most commonly used packaging production method for many second and third-tier liquid food (beverage) carton manufacturers in China in recent years. Due to the monopolized production of Tetra Pak in China, the unit price of the sheets in Tetra Pak remained high, while the manufacturers of liquid food (beverage) in the second and third tiers used the Tetra Pak produced by the genuine Tetra Pak due to fierce market competition. The products produced by product packaging are basically in a state of loss in market sales. In order to reduce the production cost, they can only use the Tetra Pak substitute packaging of the domestic second and third line liquid food (beverage) cartons manufacturers. Instead of packaging, gravure printing is mostly used for printing processes using solvent inks. Due to the rapid development of domestic ink production industry in recent years, a series of non-benzene-soluble gravure printing inks have been developed and can be applied to the printing and processing of liquid food cartons. However, like water-based inks, there are also traces of toluene and other organic solvents in non-benzene-soluble gravure inks. Traces of toluene and other organic solvents remain in the prints, although they are covered by laminating film. The heat sealing of the sealing strip is not secure, and the liquid food also comes in contact with the printing ink to form a contamination.

The offset printing method is mainly applied to the production of roof wrap boxes. As its name implies, the roof wrapper is a roof-shaped liquid food packaging carton, divided into non-porous roofs, roofs with aluminum foil holes and roofs with plastic roofs. When filling, The use of a single tray for production, lower production efficiency, mainly used in semi-automatic liquid food packaging of small batches.
At present, offset inks are generally made of synthetic pigments and synthetic resins that are free of heavy metals, organic solvents, and have a good safety factor. However, in the printing production, due to the need to dust the print surface to prevent dirt, printing and dusting (the main ingredient is starch and additives) will be attached to the back of the print, that is, the side in contact with the liquid food, if the liquid food before packaging Without adequate removal of dust, powders may dissolve in liquid foods to form certain contaminants. Unlike the Tetra Pak package, the roof package does not need to be heat-sealed with a seal, but directly folds back the adhesive edge of the roof package, using the PE layer of the sheet for heat-seal bonding, thus effectively preventing Direct contact between printing ink and liquid food to prevent secondary pollution.

In summary, no matter which type of printing method the liquid food cartons are used for processing, due to the limitations of the current production process and ink performance, there will be a certain risk of contaminating liquid foods. The fundamental method for controlling the occurrence of pollution is strict control. Production process, improve the detection system, to minimize the possibility of pollution, thus ensuring the safety of liquid foods, to protect the personal safety of consumers.